JPS6117150B2 - - Google Patents
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- Publication number
- JPS6117150B2 JPS6117150B2 JP55054001A JP5400180A JPS6117150B2 JP S6117150 B2 JPS6117150 B2 JP S6117150B2 JP 55054001 A JP55054001 A JP 55054001A JP 5400180 A JP5400180 A JP 5400180A JP S6117150 B2 JPS6117150 B2 JP S6117150B2
- Authority
- JP
- Japan
- Prior art keywords
- region
- transistor
- imaging device
- semiconductor substrate
- impurity density
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- 239000004065 semiconductor Substances 0.000 claims description 38
- 239000000758 substrate Substances 0.000 claims description 35
- 239000012535 impurity Substances 0.000 claims description 29
- 238000003384 imaging method Methods 0.000 claims description 16
- 238000007667 floating Methods 0.000 claims description 14
- 230000007274 generation of a signal involved in cell-cell signaling Effects 0.000 claims description 2
- 238000001444 catalytic combustion detection Methods 0.000 description 54
- 230000003287 optical effect Effects 0.000 description 37
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 25
- 229920005591 polysilicon Polymers 0.000 description 25
- 239000000969 carrier Substances 0.000 description 24
- 230000035945 sensitivity Effects 0.000 description 24
- 238000012546 transfer Methods 0.000 description 20
- 108091006146 Channels Proteins 0.000 description 19
- 239000010408 film Substances 0.000 description 19
- 230000003071 parasitic effect Effects 0.000 description 18
- 239000003990 capacitor Substances 0.000 description 13
- 238000000034 method Methods 0.000 description 13
- 238000009792 diffusion process Methods 0.000 description 12
- 238000005286 illumination Methods 0.000 description 12
- 238000003860 storage Methods 0.000 description 12
- 229910052721 tungsten Inorganic materials 0.000 description 11
- 238000010586 diagram Methods 0.000 description 10
- 230000001066 destructive effect Effects 0.000 description 9
- 230000010354 integration Effects 0.000 description 8
- 230000002829 reductive effect Effects 0.000 description 8
- 238000005070 sampling Methods 0.000 description 8
- 229910021332 silicide Inorganic materials 0.000 description 8
- 230000002123 temporal effect Effects 0.000 description 8
- 230000008878 coupling Effects 0.000 description 7
- 238000010168 coupling process Methods 0.000 description 7
- 238000005859 coupling reaction Methods 0.000 description 7
- 229910052750 molybdenum Inorganic materials 0.000 description 7
- 238000009825 accumulation Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 230000005684 electric field Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- FVBUAEGBCNSCDD-UHFFFAOYSA-N silicide(4-) Chemical compound [Si-4] FVBUAEGBCNSCDD-UHFFFAOYSA-N 0.000 description 6
- 229910004298 SiO 2 Inorganic materials 0.000 description 5
- 238000009826 distribution Methods 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 5
- 238000011156 evaluation Methods 0.000 description 5
- 239000012212 insulator Substances 0.000 description 5
- 238000002844 melting Methods 0.000 description 5
- 230000008018 melting Effects 0.000 description 5
- 230000002093 peripheral effect Effects 0.000 description 5
- 238000001514 detection method Methods 0.000 description 4
- 230000004044 response Effects 0.000 description 4
- 230000002441 reversible effect Effects 0.000 description 4
- 229920006395 saturated elastomer Polymers 0.000 description 4
- 229910006404 SnO 2 Inorganic materials 0.000 description 3
- 238000003491 array Methods 0.000 description 3
- 238000010276 construction Methods 0.000 description 3
- 230000006870 function Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 238000005468 ion implantation Methods 0.000 description 3
- 230000035515 penetration Effects 0.000 description 3
- 229910052697 platinum Inorganic materials 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 229910052710 silicon Inorganic materials 0.000 description 3
- 229910052715 tantalum Inorganic materials 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 239000008186 active pharmaceutical agent Substances 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
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- 229910052745 lead Inorganic materials 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 229910000661 Mercury cadmium telluride Inorganic materials 0.000 description 1
- 229910016006 MoSi Inorganic materials 0.000 description 1
- 102000004129 N-Type Calcium Channels Human genes 0.000 description 1
- 108090000699 N-Type Calcium Channels Proteins 0.000 description 1
- 206010034960 Photophobia Diseases 0.000 description 1
- 239000004642 Polyimide Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 229910008484 TiSi Inorganic materials 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- -1 etc. Inorganic materials 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 208000013469 light sensitivity Diseases 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 229920001721 polyimide Polymers 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000011514 reflex Effects 0.000 description 1
- WDZCUPBHRAEYDL-GZAUEHORSA-N rifapentine Chemical compound O([C@](C1=O)(C)O/C=C/[C@@H]([C@H]([C@@H](OC(C)=O)[C@H](C)[C@H](O)[C@H](C)[C@@H](O)[C@@H](C)\C=C\C=C(C)/C(=O)NC=2C(O)=C3C(O)=C4C)C)OC)C4=C1C3=C(O)C=2\C=N\N(CC1)CCN1C1CCCC1 WDZCUPBHRAEYDL-GZAUEHORSA-N 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000011282 treatment Methods 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14679—Junction field effect transistor [JFET] imagers; static induction transistor [SIT] imagers
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Electromagnetism (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Solid State Image Pick-Up Elements (AREA)
- Transforming Light Signals Into Electric Signals (AREA)
Description
ãçºæã®è©³çŽ°ãªèª¬æã
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å ±ãéç Žå£ã«èªã¿åºãããã€ã
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眮ã«é¢ãããDETAILED DESCRIPTION OF THE INVENTION The present invention provides a solid-state imaging device that can nondestructively read out optical information, has a wide dynamic range, has improved sensitivity, is resistant to noise, and has excellent spatial and temporal resolution. Regarding equipment.
åŸæ¥ã€ã¡ãŒãžã»ã³ãµãç¹ã«åºäœããã€ã¹ã«ãã
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ååšãããããããïŒã€ã®è£œé æè¡ã䌌ããã€ãŠ
ããã«ãããããããMOSåãCCDåäž¡è
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ã¡ãŒãžã»ã³ãµãšããŠã®ç¹æ§ã¯ãå
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ä¿¡å·é»è·ã®èªã¿åºãæ¹æ³ã®éããããç°ãªã€ãã
ã®ãšãªã€ãŠãããCCDåã€ã¡ãŒãžã»ã³ãµã§ã¯ã
MOSãã€ãã·ã¿é»æ¥µã®äžåŽåå°äœé åã«çãã
ããã³ã·ã€ã«äºæžã®äžã«ä¿¡å·é»è·ã¯èç©ãããäž
æ¹èªã¿åºãã¯ãã¢ã¬ã€ç¶ã«äžŠãã é»çã«ãã€ãŠç
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ãããã«ãMOSåã€ã¡ãŒãžã»ã³ãµã«ãããŠã¯ã
ä¿¡å·é»è·ã¯æ¡æ£ãããã¯ã€ãªã³æ³šå
¥çã§è£œé ãã
ããããã€ãªãŒãã«ãã€ãŠéããããèªã¿åºãã¯
ãã®ãããã€ãªãŒãããé£æ¥ããMOSFETãé
ããŠãããªåºååè·¯ãžãšå°ããå®äºãããïŒç¬¬ïŒ
å³åã³ç¬¬ïŒå³ïŒã Conventional image sensors, especially those based on solid-state devices, can be roughly divided into two types: CCD type and MOS type. Although the two manufacturing technologies are similar, the characteristics of the MOS type and CCD type image sensors are different due to differences in the method of receiving light and the method of reading signal charges. . In CCD type image sensor,
Signal charges are accumulated in potential wells created in the lower semiconductor region of the MOS capacitor electrode, and readout is performed by sequentially transferring them through the potential wells created by an electric field arranged in an array. This is done by leading it to the output circuit.
However, in MOS image sensors,
The signal charge is collected by a photodiode manufactured by diffusion or ion implantation, and readout is completed by leading from the photodiode through an adjacent MOSFET to the video output circuit. (1st
(Fig. and Fig. 2).
第ïŒå³åã³ç¬¬ïŒå³ã¯åŸæ¥ã®MOSååã³CCDå
ã®ã€ã¡ãŒãžã»ã³ãµã®åç説æã®ããã®å³é¢ã§ã
ãã 1 and 2 are drawings for explaining the principles of conventional MOS type and CCD type image sensors.
第ïŒå³ã¯ãMOSåã€ã¡ãŒãžã»ã³ãµã®åç説æ
å³ã§ããã FIG. 1 is a diagram explaining the principle of a MOS image sensor.
MOSFETïŒïŒïŒãšãããã€ãªãŒãïŒïŒïŒãã
æãã¢ã¬ã€ããããMOSFETïŒïŒïŒã®ã²ãŒãéš
ã«ã·ããã¬ãžã¹ã¿ã¯ããã¯ïŒïŒïŒãé»æºïŒïŒïŒã
é
眮ãããMOSã¹ãã€ã³ã·ããã¬ãžã¹ã¿ïŒïŒïŒ
ãæ¥ç¶ãããŠããããããã®ã€ã¡ãŒãžã»ã³ãµã¢ã¬
ã€åã³åšèŸºåè·¯ããæãåºæ¿ïŒïŒïŒäžã«æ§æãã
ãã€ã¡ãŒãžã·ã¹ãã ã«ã€ã¡ãŒãžïŒå
å
¥åïŒïŒïŒïŒ
ãç
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å ±ããããã€ãªãŒãã¢ã¬ã€ïŒ
ïŒïŒã§èãããåšèŸºã®èµ°æ»åè·¯ïŒïŒïŒã®åäœã§ã
ããªåºåéšïŒïŒïŒã«åãåºããããããªåçã«ãª
ã€ãŠããã There is an array consisting of a MOSFET 108 and a photodiode 101, and a MOS scan shift register 104 has a shift register clock 103 and a power supply 105 arranged at the gate of the MOSFET 108.
are connected, and an image (light input) 102 is sent to an image system configured on a substrate 107 consisting of these image sensor arrays and peripheral circuits.
is irradiated and the information is transmitted to photodiode array 1.
The principle is that the data is stored in the video output section 106 by the operation of the peripheral scanning circuit 104.
äžæ¹ãCCDåã€ã¡ãŒãžã»ã³ãµã¯ã第ïŒå³ã«ç€º
ãããããã«åºæ¿ïŒïŒïŒäžã«æ§æããããã€ãŒãž
æ€åºåšã®ã·ã¹ãã ïŒïŒïŒãå³ã¡ãããã§ã¯ã¯ãã
ã¯ÏïŒïŒïŒïŒãåã³ã¯ããã¯ÏïŒïŒïŒïŒã®ïŒçžã¯
ããã¯ã§åäœããCCDã®ã·ã¹ãã ãäžããããŠ
ãããã€ã¡ãŒãžïŒå
¥åå
ïŒïŒïŒïŒã®æ
å ±ã¯MOS
é»æ¥µäžã®ããã³ã·ã€ã«ãŠãšã«å
ã«èããããäºçž
ã¯ããã¯ÏïŒïŒïŒïŒãåã³ÏïŒïŒïŒïŒã«ãã次ã
ãšè»¢éãããããªåºåéšïŒïŒïŒã«ãããªåºåä¿¡å·
ïŒïŒïŒãšããŠåãåºãããããã«ãªã€ãŠããã On the other hand, the CCD image sensor operates with a charge detector system 110 constructed on a substrate 112 as shown in FIG. A CCD system is given, and the information of the image (input light) 109 is MOS
The signal is stored in a potential well under the electrode, and is transferred one after another by two-phase clocks Ï 1 113 and Ï 2 114, and taken out as a video output signal 111 to a video output section 115.
第ïŒå³ã«ã¯ã¯ããã¯ä¿¡å·åã³åºåä¿¡å·ã®ã¿ã€ã
ãã€ãŒããç°¡åã«å
¥ã€ãŠããã FIG. 2 also briefly includes a time chart of the clock signal and output signal.
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匷床ã®é«ãå Žåãåã³äœãå Ž
åããŸã解å床ïŒimage clarityïŒçã®ç¹ã§å€§ã
ãªå·®ãšãªã€ãŠãããå
匷床ã®äœãå Žåã«ã¯ã€ã¡ãŒ
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解åããããæå°åŒ·åºŠã®å
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ããã Differences in structure, construction method, and readout method between these two devices result in large differences, particularly in the case of high and low light intensity, and in terms of resolution (image clarity) and the like. When the light intensity is low, the minimum intensity light input value that can be resolved by the image sensor has a large effect on the image sensor's light receiving ability, or in other words, the efficiency of how much irradiated light it can capture. dependent. Similarly, the minimum intensity light input value that can be resolved by an image sensor at low light intensities is also affected by noise generated by the sensor body and its associated circuitry.
MOSåã€ã¡ãŒãžã»ã³ãµã¯CCDåã«æ¯ã¹å
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å·ãžã®å€æå¹çããããããã¯ããã€ã¹è¡šé¢ãã
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ãèç©ãããäœçœ®ã®éãã«ãããã®ã§ããã MOS image sensors are more efficient at converting light into signals than CCD types. This is due to differences in the amount of light reflected from the device surface and the location where the signal load generated by the light is accumulated.
éåžžãã¢ããªã·ãã¯éç©åãããã€ã¡ãŒãžã»ã³
ãµã«ãããŠã¯åå°äœåºæ¿ãç
§å°ããæ¹æ³ã«ã¯è¡šé¢
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§å°ïŒfront illuminationïŒååã³è£é¢ç
§å°
ïŒback illuminationïŒåã®ïŒéãååšããïŒç¬¬ïŒ
å³ïŒã Normally, in monolithically integrated image sensors, there are two methods of illuminating a semiconductor substrate: front illumination type and back illumination type.
figure).
第ïŒå³ã¯åŸæ¥ã®è¡šé¢ç
§å°åïŒfront
illuminatedïŒCCDåã³è£é¢ç
§å°åïŒback
illuminatedïŒCCDã®ïŒã€ã®ã¿ã€ãã®CCDåã€ã¡
ãŒãžã»ã³ãµã®æé¢æ§é å³ã§ããã Figure 3 shows the conventional front-illuminated type (front illumination type).
illuminated) CCD and back-illuminated (back
FIG. 2 is a cross-sectional structure diagram of two types of CCD image sensors (illuminated) CCD.
第ïŒå³ïœã«ã¯ãïœåSiåºæ¿ïŒïŒïŒäžã«åœ¢æãã
ãã·ãªã³ã³çµ¶çžå±€ïŒïŒïŒïŒéæïŒãAlé»æ¥µïŒïŒïŒ
åã³éæãã€ãã·ã¿é»æ¥µïŒïŒïŒããæãïŒçž
CCDã瀺ãããŠãããè¡šé¢ããç
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ããã€ãŒãžïŒå°æ°ãã€ãªã¢ïŒïŒïŒïŒãããã³ã·ã€
ã«ãŠãšã«ïŒïŒïŒå
ã«èç©ãããåèšAlé»æ¥µïŒïŒ
ïŒåã³éæãã€ãã·ã¿é»æ¥µïŒïŒïŒã®ïŒçžã¯ããã¯
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ããã FIG. 3a shows a silicon insulating layer 119 (transparent) formed on an n-type Si substrate 121 and an Al electrode 118.
and a transparent capacitor electrode 117.
CCD is shown. A charge (minority carrier) 120 generated by the light as information corresponding to the light input 116 irradiated from the surface is accumulated in the potential well 122, and the Al electrode 11
8 and the two-phase clock voltage of the transparent capacitor electrode 117, the signals are sequentially transferred within the well.
äžæ¹ã第ïŒå³ïœã¯è£é¢ç
§å°åïŒback
illuminatedïŒCCDã®æé¢æ§é ã瀺ããå
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ååºæ¿ïŒïŒïŒå
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ãã絶çžå±€ïŒïŒïŒãä»ããŠæ§æãããïŒçžCCD
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å§é¢ä¿ã«ãã€ãŠçããããã³ã·ã€ã«ãŠãšã«ïŒïŒïŒ
å
ã«èç©ãããã On the other hand, Fig. 3b shows a back-illuminated type (back illumination type).
(illuminated) shows the cross-sectional structure of the CCD. Input light 1
23 is irradiated from the n-type substrate 126 side, and
Minority carriers 125 generated in the mold substrate 126
is a two-phase CCD configured through an insulating layer 127.
Potential well 124 created by the voltage relationship on overlapping electrodes 128 and 129 of
accumulated within.
CCDåæãã¯MOSåã§ã©ã¡ãã®æ¹æ³ã䜿çšå¯
èœã§ããããCCDåã®å Žåãè¡šé¢ã«äžéæãªé»
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å°ïŒfront illuminationïŒåã§ã¯äžéœåãªããšã
å€ãã Either the CCD type or the MOS type can be used, but in the case of the CCD type, opaque electrodes are lined up on the surface, which reduces the light capture area, which is often inconvenient for the front illumination type.
ãŸãäžå¹žãªããšã«è£é¢ç
§å°ïŒback
illuminationïŒåã®å Žåã補é äžã®åé¡åã³åäœ
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illuminationïŒåã®å Žåãå
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çãšãªã€ãŠããããã®çŽ åééã«å¯Ÿããå¶éæ¡ä»¶
ã¯å€§å®¹éã®ã€ã¡ãŒãžã»ã³ãµãå®çŸããããšããå Ž
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For the illumination type, there are manufacturing problems and operating characteristic limitations. Backside illumination
In the case of the illumination type, the carriers generated by the input of light (usually generated within about 5 ÎŒm from the light input surface for visible light in the case of Si) are effectively collected, and the carriers generated by the input of light are effectively collected and In order for it to accumulate in the underlying empty layer, the thickness of the substrate needs to be reduced. The thinnest semiconductor substrate that can be manufactured is approximately
It is about 25 ÎŒm, which means that the device
The problem is that it cannot be arranged in a space of 25 ÎŒm or less; in other words, carriers generated within the substrate in the back illumination type spread out by diffusion, so when considering spatial resolution, the thicker the substrate becomes, the more difficult it becomes. The MOS capacitor electrodes on the surface must be spaced apart from each other. This limits the resolution of back-illuminated CCDs. This restriction on the element spacing requires a larger Si substrate area when attempting to realize a large-capacity image sensor, and is a major obstacle to realizing an image sensor consisting of a large number of pixels.
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These noise pulses are all of the same height,
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This is because in the case of a CCD, the surface is in a non-equilibrium state, which causes thermal instability.
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ãªãã However, in CCD image sensors, there is transfer loss noise that affects operation more than fixed pattern noise. This type of noise, which occurs as a result of the charge left behind after the transfer operation, appears on the sensed screen as a white smear to one side of the sensed white spot. This appears most conspicuously as a high-intensity spot when the amount of charge being transferred is large. For example, if a 512 pixel array (1024 transfers as a two-phase clock device) is operated with a transfer loss of 10 -5 per transfer (99.999% effective), the total transfer loss is 10 -2 . In the case of a three-phase clock, the total transfer loss charge increases even more with the same transfer efficiency. Transfer loss noise also reduces the exposure range that the CCD has and therefore essentially reduces the contrast that the sensor can detect. One method for reducing transfer loss noise is to bury a transfer channel to a depth of about 1 ÎŒm from the surface by ion implantation or the like. The charge transferred in the buried channel is not affected by surface trap noise, the non-transfer of charge caused by surface traps present at the semiconductor-oxide interface.
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Figures 4a and 4b show the circuitry of the output section of a conventional image sensor, particularly the operational amplifier section.
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䌎ãJohnsonéé³æºïŒïŒïŒãäžããããŠããã Figure 4a shows an example in which an ordinary low-noise, high-gain operational amplifier 136 is connected to the image sensor 130, and Figure 4b shows what is called a charge amplifier, and the capacitance C 1 146 in Figure 4b is minimized. By doing so, the Johnson noise 145 associated with the reset resistor R 1 144 can be reduced. Figure 4a
In the end, the output of the image sensor 130 is represented by a capacitance C 1 indicated by a source impedance 131, and in parallel therewith a reset resistor R 1 132 in series with the power supply E 1 and an accompanying Johnson noise source 133 are represented. has been done. The noise sources of operational amplifier 136 itself are shown at 135 and 134.
R 2 138 is the feedback resistance from output 137. In contrast to the operational amplifier shown in FIG. 4a, FIG. 4b shows a charge amplifier that minimizes the Johnson noise source 145. Also in FIG. 4b, the output of the image sensor 139 is shown as a capacitance indicated by a source impedance 140. An equivalent operational amplifier noise source 141 and an operational amplifier noise source 142 in series with the power supply E 1 are provided on the input side of the operational amplifier 143 itself, and the feedback amount from the operational amplifier output 147 is a reset resistor R 1 144, a capacitor C 1 146, and R A Johnson noise source 145 associated with 1 144 is given.
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§å°æéã¯ãã¬ãŒã æéãšãªã€ãŠããã Yet another noise source is the noise present in reset resistor R1 as shown in FIG. 4a. This resistor generates an equivalent noise charge (called Johnson noise) of magnitude qnoise=KTC 1 on the video signal. That is, the larger the capacitance in parallel with the reset resistor, the larger the equivalent noise charge. Fortunately, a charge amplifier such as that shown in FIG. 4b can be used to reduce the effect of this fundamental noise source by making capacitance C 1 very small. Exposure saturation, a parameter that describes high input light intensity levels, is generally a function of the maximum amount of charge that can be stored in a sense pixel on a photoarray during a light exposure period. The light irradiation period is the time during which charges representing the irradiated image are collected. Usually, the light irradiation period is a frame time.
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åããã In a MOS image sensor, the maximum signal charge that can be accumulated depends on the bias voltage applied to the photodiode. In a CCD image sensor, it depends on the accumulated surface potential.
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ãªå€ã«ãããŸã€ãŠããã The pixels of both CCD and MOS image sensors have similar geometric dimensions and storage potential levels, so the saturation exposure level is similar for both devices. .
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ãããã§ããã The allowable value of the maximum incident light intensity level of both sensors can be maximized by increasing the storage capacity of the pixel and masking areas other than the pixel from the incident light. This monolithic construction increases the light receiving capacity of the line scan array while keeping noise in the covered area low. Monolithically integrated area sense arrays do not offer much advantage in this configuration. This is because a loss of spatial resolution occurs as a result of creating larger pixels to achieve increased capacity.
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æéãå¢å€§ããã MOS image sensors benefit greatly from this approach. Because M.O.S.
This is because in the type, the pn junction serves as an optical pixel and is read out immediately. On the other hand, in CCD,
By configuring a photoarray of adjacent capacitors, the size of the optical pixel can be increased, but at the same time, the time required to transfer signal charges from the adjacent optical capacitors to the analog CCD shift register increases.
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ããã In CCDs with low transfer efficiency, there is a phenomenon in which charges left behind during transfer between electrodes appear as a blurred image at the output terminal of the device. Unfortunately, the transfer losses that cause blur in CCDs increase not only with increasing number of transfers, but also with low light intensity levels. However, with a MOS image sensor, the image is transferred only once, so there is no blurring associated with the transfer. In other words, the signal reaches the output only through one analog switch.
以äžã§å è¡æè¡ã®èª¬æãçµãã This concludes the explanation of the prior art.
æ¬çºæã®ç®çãåæãããšä»¥äžã®ããã«ãªãã The objects of the present invention are listed below.
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ãè©äŸ¡ããïŒã€ã®èŠçŽ ã(1)ãã€ãããã¯ã¬ã³ãžã
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ãµãæäŸããããšã«ããã The purpose of the present invention is to evaluate four elements for evaluating the operating characteristics of a solid-state image sensor: (1) dynamic range;
(2) Sensitivity, (3) Noise, (4) Resolution (image clarity) It compensates for the shortcomings of conventional CCD type and MOS type image sensors, and also protects them in principle. Our goal is to provide a new image sensor.
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ãã The basic idea was already "semiconductor device" published in 1983.
No. 124259 (published September 25, 1980), IEEE
Transactions on Electron Devices, Vol.EDâ
26, No. 12, December 1979 âStatic Induction
Transistor Image Sensorsâ.
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ãµãæäŸããããšã§ããã Specifically, one of the objects of the present invention is MOS type,
The object of the present invention is to provide an image sensor whose dynamic range is improved by at least one order of magnitude compared to a CCD type when operated using conventional technology.
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ãªã€ãã€ã¡ãŒãžã»ã³ãµãæäŸããããšã§ããã Another object is to provide an image sensor in which the impedance to light is matched, the light input surface is made flat, and almost the entire area hit by light becomes an optical pixel.
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ããã Furthermore, one of the objects of the present invention is that the input surface on which the light is irradiated is flat, has an impedance matching for the light, and has a lens-shaped area for concentrating the light. It is an object of the present invention to provide an image sensor in which the accumulation effect of the carriers thus generated is activated and the resolution and sensitivity are improved.
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There is a problem with thinning the substrate, which is a conventional problem with illumination type image sensors.
The object of the present invention is to essentially improve this and provide an image sensor that does not require a structurally very thin substrate, and therefore has an improved spatial resolution and an improved degree of integration.
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ã¡ãŒãžã»ã³ãµãæäŸããããšã§ãããã Therefore, one of the objects of the present invention is to achieve the second half of the above.
Conventional CCD, MOS
Another object of the present invention is to provide an image sensor with improved sensitivity compared to both image sensors.
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ãžã»ã³ãµãæäŸããããšã§ããã Furthermore, one of the objects of the present invention is the MOS type and
It is an object of the present invention to provide an image sensor in which thermal excitation noise accompanying a thermally excited carrier, which cannot be avoided in both CCD types, is extremely reduced, and dark current is extremely reduced.
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ããã Furthermore, one of the other objects of the present invention is the MOS type,
Parasitic capacitive noise, fixed pattern noise (FPN), etc., which exist to the same extent as conventional image sensors such as CCD type, are removed using a low pass filter (low pass filter).
The objective of the present invention is to provide an image sensor system using a high-gain, low-noise operational amplifier.
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ã¡ãŒãžã»ã³ãµãæäŸããããšã«ããã Furthermore, one of the major objects of the present invention is that in conventional MOS type, CCD type, etc. image sensors, once the light information accumulated during the light irradiation period (light integration time) is read out, Whereas it was a destructive readout in which the data disappears, it is possible to perform a non-destructive readout operation with improved temporal resolution and can be read out any number of times until the refresh transistor operates once it has been read out. The purpose is to provide sensors.
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äŸããããšãæ¬çºæã®ç®çã®äžã€ã§ããã Furthermore, in the non-destructive read operation mentioned above,
Since it is a non-destructive operation during the light irradiation period, it can be read out any number of times, and even once read out, the previous history remains, so the light irradiation time can be divided using sampling pulses. However, it is possible to sample, integrate and read light information that changes moment by moment during the light irradiation period, and one of the objects of the present invention is to provide an image sensor equipped with such a readout function. It is.
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ãµãæäŸããããšãæ¬çºæã®ç®çã®äžã€ã§ããã Furthermore, there are various methods of sampling during the above-mentioned light irradiation period; one example is sampling on a logarithmic scale, for example, 10 msec.
integration time 100nsec, 1ÎŒsec 10ÎŒsec,
Another object of the present invention is to provide an image sensor that samples logarithmically at 100 ÎŒsec, 1 msec, and 10 msec, stores each output voltage in a separate memory unit, and outputs the same.
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ãã®ã€ã¡ãŒãžã»ã³ãµãæäŸãããã®ã§ããã The present invention evaluates all four elements for evaluating the operating characteristics of solid-state image sensors: (1) dynamics range, (2) sensitivity, (3) noise, and (4) image clarity. It compensates for the shortcomings of conventional solid-state image sensors in all aspects and provides a completely new image sensor in principle.
The present invention provides an image sensor in which information does not disappear no matter how many times the readout operation is performed within an integration time, that is, non-destructive readout.
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FIG. 5 shows a light sensing region using a hook structure, which is one of the embodiments of the present invention, and a SIT (of the opposite conductivity type) Q 1 and a refresh transistor (P channel SIT) Q 2 connected thereto. This is an example of a SIT image sensor consisting of:
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ãã€ã¢ã¹ãããããšã«ãªãã To explain the operation, a constant bias voltage V s
The light input that penetrates through the transparent electrode 4 to which (+) is applied (this is formed of SnO 2 or In 2 O 3 or doped polysilicon, etc.) is n + 8.
Electron-hole pairs are generated particularly in the high resistance layer 6 near the n + layer 5 of the hook structure consisting of p + 7i6n + 5.
The entire region of the high resistance region 6 is completely depleted by the applied voltage Vs , and an electric field is applied to most of the region so that carriers travel at a saturation speed. All the generated electrons are pulled by the V s (+) bias and absorbed into the n + layer 5, but the pairs of holes generated accumulate in the p + region 7. This is because the i-region 6 is almost depleted by the bias voltage V s (+), and the setting is such that a strong electric field is applied over the entire thickness of the i-layer. p +
When holes accumulate in layer 7, p + layer 7 becomes positively charged. In other words, the barrier potential of n + region 8 to electrons decreases. As a result, electrons in the n + region 8 of the n + 8p + 7 junction in a floating state flow over the thin p + region 7 to the substrate side. In other words, when light of a constant intensity hits the i-layer of the hook structure n + p + in + with a constant bias for a time t, the potential V of the n + region 8 forming a capacitor with the ground point (t) becomes positively charged as electrons flow out, and when the p + region 7 is extremely thin, as a one-dimensional model, approximately V(t)ãSCq/Cft per unit light-receiving area...(1) Given. Here, S: photon density of optical input signal, C: speed of light, q: unit charge, Cf: capacitance of floating p + region, t: light irradiation time. This formula is based on the paper IEEE published by the inventors.
Transactions on Electron Devices, Vol.EDâ
26, No. 12, December 1979, PPã»1970â1977
Published in, p. 1976. Equation (1) means that voltage V(t) can be obtained with almost completely linear characteristics with respect to optical input. That is, the potential of the n + region 8 increases linearly in proportion to the light intensity and the light irradiation time. Therefore, the n + region 8 in FIG. 5a is positively biased to the potential V(t) shown by equation (1).
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ãã«ãªãã Each part of FIG. 5a will be explained. A bit line 1 is connected to the electrode (polysilicon or polysilicon and high melting point metal such as Mo, W, Pt, etc., or silicide) of the n + source region 12 of SITQ 1 . Reference numeral 2 denotes a word line, which is made up of a diffusion line of the p + gate 2' of SITQ 1 or a line partially made of polysilicon or a high melting point metal to lower the resistance. 2'' is an electrode made of polysilicon or a combination of polysilicon and a high melting point metal (MO, W, Pt, etc.) or silicide. 3 is a refresh line, which is a diffusion line or a partial diffusion line of the n + gate 3' of SITQ 3 . It consists of a line made of metal or polysilicon to lower the resistance. 3" is made of polysilicon or polysilicon and a high melting point metal (Mo, W, Pt).
etc.) and silicide. 4 is a transparent electrode (SnO 2 or
In 2 O 3 etc.) and is connected to the power supply V s (+). 5 is the n + diffusion region and the impurity density is 10 19 to 10 21 cm
It is doped to about -3 . If the impurity density is made too high, the forbidden band width becomes narrow, and input light on the shorter wavelength side is intensively absorbed in this region, resulting in a drawback that it becomes difficult for short wavelength light to reach the photoelectric detection region. Therefore, the impurity density of n + region 5 should not be too high. It is also desirable that the thickness is thinner than the penetration depth of visible light. wavelength 5000
The penetration depth of light of Ã
is about 1 ÎŒm, and for light of 4400 Ã
, the penetration depth is about 0.5 ÎŒm. Therefore, to make the sensitivity to blue and violet light sufficiently high, n +
The region is preferably thinner than about 0.5 ÎŒm. Furthermore, in order to improve the sensitivity of blue and violet, n +
It is sufficient that the region 5 is not provided and the transparent electrode is formed by a shot junction. In this case, holes locally excited on the surface of the high resistance region also flow into the accumulation region 7.
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ãã The image sensor of the present invention can be made into an infrared image sensor having a peak of relative sensitivity characteristics in the infrared region while maintaining the same operating principle.
As a means to achieve this, a material with a narrower bandgap than Si is formed epitaxially, CVD, or vapor deposited on the n + region portion 5 and the transparent electrode portion 4 in FIG. Sensitivity can be improved. For example, by providing HgCdTe on Si and controlling the composition of Hg and Cd, it is possible to create an image sensor with a very wide wavelength range.
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ã§äžããããããšãå®éšçã«ããã€ãŠããã On the other hand, as a means for operating the image sensor of the present invention as an image sensor having a peak of relative sensitivity characteristics on the short wavelength side of visible light, FIG.
A material such as GaP or InGaP, which is an indirect transition type and has a wide forbidden band width, may be formed in the an + region 5 and the transparent electrode portion 4 by epitaxial, CVD, vapor deposition, or the like. 6 is a high resistance region, which may be a p - or n - region of about 1Ã10 13 to 1Ã10 14 cm â3 or a region with an impurity density lower than that;
The relationship between V s (+) and the thickness l requires that almost the entire region be depleted. Reference numeral 7 denotes a p + diffusion or ion implantation region, which serves as a region where holes are accumulated with an n + p + in + hook structure, and at the same time serves as a source region of the P channel SITQ 2 .
The thickness of P + region 7 is desirably as thin as possible in order for holes to accumulate and electrons to efficiently flow from n + region 8 to high resistance region 6 . For example, it is about 0.2 ÎŒm to 3 ÎŒm. 8 is an n + region adjacent to p + region 7 and is separated from the ground point by a capacitor Cs, and when SITQ 1 and Q 2 are non-conducting, both n + region 8 and p + region 7 are completely closed. It is becoming floating. In response to light irradiation, this n + region 8 is charged to V(t) as approximately expressed by equation (1). The numerator term Scqt on the right side of equation (1) is the total charge amount of holes excited in the photodetection region when the incident light photon density S is the light irradiation period t. Equation (1) states that the potential change in the n + storage region 8 is given by the total amount of charges excited by light divided by the capacitance Cf of the p + region 7. n + area 8
No matter how large the storage capacitance Cs is, the potential of the n + region 8 is determined almost regardless of the value of Cs. This continues until the potential of the n + region 8 reaches a certain balance with the potential of the p + region 7.
This is due to the fact that electrons continue to flow out. Therefore, even if the n + region 8 has a large storage capacitance Cs, the sensitivity can be sufficiently increased by reducing the capacitance Cf of the p + region 7. In conventional MOS image sensors, optically excited carriers are accumulated directly in the accumulation region, so the potential of the accumulation region is
It will be given as Scqt/Cs. In the photodetection of the present invention having a hook structure and the photodetection of a conventional image sensor, this photodetection section already has Cs/Cf.
The sensitivity is different by a factor of two. The main part of Cf is n +
Since this is the junction capacitance between region 8 and p + region 7, if this junction area is kept small to a certain extent, Cs/Cf can be reduced.
It can be easily increased by 10 to 100 times. 8' is an electrode of this n + region 8, which is made of polysilicon or the like;
It is formed over almost the entire surface of the cell to increase Cs. 9 is an oxide film, Si 3 N 4 film, Ta 2 O 5 film, or a composite film thereof formed on 8' to a thickness of about 1000 Ã
(or 200 Ã
to 1000 Ã
), and 10 is an Al film forming a ground electrode. Alternatively, it is formed of polysilicon or the like. This 8'-9
-10 forms a storage capacitor Cs, which is preferably as large as possible in order to increase the sensitivity of the image sensor. If the parasitic capacitance of the bit line is C B , then
At the moment SITQ 1 is turned on, an electron current flows from the bit line to the selected cell, and the voltage rise on the bit line at this time is such that node A becomes V(t) =
If Scq/Cfã»t, then approximately per unit light-receiving surface area (Equation (1)) It is experimentally known that it is given by
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+ n for the capacitance Cf of area 7 + significant capacitance of area 8
The goal is to make the ratio of Cs as large as possible. 1
Reference numeral 1 denotes an isolation region, which is usually made of SiO 2 and, depending on the case, is further filled with an insulating material such as polyimide. 12 is the source n + region of SITQ 1 , 1
3 is the channel p -region of SITQ 1 , and SITQ 1
is a device with channels of opposite conductivity type. This structure is such that SITQ 2 is a P-channel SIT, and the manufacturing process of the p - layers 13 and 14 is performed at the same time. Furthermore, when the 13 regions are set to p - , compared to n - , SITQ 1 's
Source 1 of SITQ 1 with reliable characteristics when OFF
Electrons leaking across the barrier in the channel from 2 can be controlled more easily than n - . of course
The SITQ 1 channel can operate even when formed with an n - layer of about 10 13 to 10 15 cm -3 . At this time, it is necessary to set the channel width between the p + gates to be relatively narrow. 15 is a drain region of the P channel SITQ 2 , which is connected to 10 and has a ground potential. Reference numeral 16 denotes a region in which an insulator such as an oxide or nitride film is formed on the opposing side surface regions in order to reduce the parasitic capacitance between the gate and drain of the P channel SITQ 2 . Similarly, 17 is a region in which an insulator is formed directly under the n + gate 3' and on the surface facing the source 7 in order to reduce the parasitic capacitance between the gate and source of SITQ 2 . This can be formed by ion-implanting O 2 , N 2 , etc. using a technique such as SIMOX. Regions 18 and 19 are also insulator regions formed for the same purpose. Such a process is best
When implementing this mode, it is especially necessary to reduce capacitive coupling noise in the image sensor. of course,
Insulating layer regions 16, 17, 18, and 19 may not be provided if the operating characteristics may be degraded to some extent. Noise reduction has been measured by introducing similar insulation layers into SITs such as peripheral circuits such as operational amplifiers, vertical and horizontal scanning circuits, and video output sections.
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FIG. 5b is a circuit diagram of the image sensor cell portion of FIG. 5a according to an embodiment of the present invention. The optical input is through two reversely connected diodes D 1 and D 2 with a hook structure.
It is mainly absorbed in the middle part of the body. p + midpoint A between parasitic capacitance Cf of floating region 7 and storage capacitance Cs
(n + region 8) is charged to V(t) in response to optical input, and when word line 2 is opened, SITQ 1 becomes conductive instantly and electron current In flows from the bit line. Then, the gate Ï w is turned off, and electrons in the n + region 8 flow to the n + region 5 on the back side of the substrate due to the hook operation by the carriers generated by light in the n + p + in + hook structure. When Q1 is turned off for a sufficiently long time compared to Ï: Equation (3)), and the gate is opened again to conduct, the voltage appearing on the bit line will be even higher than when it first became conductive. This is because holes excited by light irradiation continue to accumulate in the p + region 7, and the history of light irradiation after entering the light irradiation period after refreshing is Q 1 until the next refresh is performed. This is because it remains even if you open it. The holes accumulated in the p + floating region escape to the ground point by the refresh transistor Q 2 . Solid-state image sensors that operate in a non-destructive manner are
The principle is different from the CCD type and MOS type. Conventional CCD type and MOS type image sensors use destructive readout in which once the image information is read out, the optical information in the cell is cleared, whereas the image sensor of the present invention uses non-destructive readout. No matter how many times the optical information is read out within a given frame time, the optical information continues to be accumulated inside the cell in the form of an integrated optical information after refresh, and various operation modes are possible. Simple experimental results have already shown that it is possible to increase the refresh interval to 10 seconds or more. Of course, it is also possible to make it longer or to the same extent. Furthermore, compared to conventional image sensors, dark current is structurally suppressed to an extremely low level, and there are extremely few limitations due to dark current noise.
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å²ããããã®ãèããã An example of the operation mode based on the principle operation is shown in the fifth example.
Shown in Figure c. The output on the bit line, the pulse Ï w on the word line 2, and the pulse Ï R on the refresh line 3 are shown. First, Q 2 is turned on from to to within to + T R to perform a refresh, and the optical information integration time begins. Q1
is initially in the OFF state, but when Q1 is turned ON (pulse indicated by S1 ), an output is generated on bit line 1, which is the voltage at point A divided by the bit line capacitance during the period after refresh. Voltage D 1 is output. Furthermore, after a time ts that is sufficiently longer than the carrier travel time Ï has elapsed,
When the S 2 pulse is applied and Q 1 is turned ON, the integrated optical information from to+ TR to S 2 will appear in the output D 2 from now on. In this way, when the word line pulse Sn is input, the integrated value of optical information for almost the entire light irradiation period appears at the output Dn. Then refresh transistor Q2
When turned ON, the holes accumulated in the p + floating region escape to the ground point, and the refresh is completed.
The traveling time of the carrier is approximately 1 nsec when the carrier travels at the saturation speed, assuming a distance l = 100 ÎŒm.
For example, it is sufficient to operate with the period ts of the word line sampling pulse being approximately ts = 1 ÎŒsec. Of course, if the incident light intensity is very strong, ts may be shortened. In short, Ï
It is sufficient to set âªtsâªTs (Ts: light irradiation period). Therefore, the more Ï, which can be called the response time to optical input, can be made extremely small, the better the resolution of the image sensor of the present invention with respect to temporal optical input will be. As is clear from the above explanation of the operation mode, the response time Ï of the sensor cell to optical input is extremely fast, and if ts and Ts are appropriately selected, the optical input S(t) (Photon density) changes from moment to moment. word line Ï w
It can be considered that the temporal resolution increases by the sampling period ts. This means that a temporal change in the optical input S(t) that changes from moment to moment appears as an output voltage Di on the bit line in a temporal step width of the sampling period ts. In other words, it can be said that the image sensor of the present invention has extremely good not only spatial resolution but also temporal resolution. Data output (output on bit line) D(t)
Since is the integral value of the optical input S(t) that changes from moment to moment, it can be expressed as D(t)=Aâ« t p S(t)dt (:integral output) A: constant...(10). A more detailed explanation is as follows. Equation (1) is a constant photon density S for t seconds from O
This is an approximate expression when calculating the voltage accumulated in the n + region due to the hook operation of the n + p + in + structure when the optical input is input using a one-dimensional model. Here is the light irradiation period
Consider the data output D(t) when an arbitrary S(t) is irradiated for a period of Ts. (Fig. 5 d, e) Consider the waveform of S(t) divided into S 1 , S 2 ...S i , ...S o in steps of sampling period ts as shown in Fig. 5 e. .
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(t) dt (1 5) It can be seen that the image sensor of the present invention completely outputs the integrated output of optical input information as data.
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Instead of reading every sec, for example,
Reading can be performed at 1 ÎŒsec, 10 ÎŒsec, 100 ÎŒsec, and 1 msec. The light irradiation period of 1 ÎŒsec is 1/10 4 of the light irradiation period of 10 msec. 10 m for cells with very strong incident light intensity.
If it is read after sec, it is a blooming phenomenon,
Linearity is lost. In that case, for example,
When reading at 1 ÎŒsec or 10 ÎŒsec and outputting it as a video output, it is sufficient to multiply the standard 10 msec read output by 10 4 or 10 3 times. If the output at each readout is stored in a memory provided on the same chip or in each part, and multiplied by a predetermined multiple at the time of output, the dynamic range will be extremely wide. The blooming phenomenon caused by strong input light can be almost completely eliminated.
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FIG. 6 simply shows an example in which the embodiment of the present invention is assembled as a matrix area image sensor system. The cell 20 of the embodiment of the present invention shown in FIG. 6a is shown in FIG. 6b with Cij (i=1...m,
j=1...m). Reference numeral 21 denotes a refresh line, which is connected to the refresh signal generating circuit 30. 22 is the Vs (+) power line, 2
3 is a word line 2, and the word line and power line 2 are connected to the X direction word line driver and the scanning circuit 28.
It is connected with 9. 24 is bit line 25
A high sensitivity, low noise, high gain operational amplifier connected to each of the operational amplifier noise,
A designed circuit configuration is used to reduce Johnson noise and the like. 26 is an operational amplifier output and is a video output section. Reference numeral 27 indicates various clock pulse generation units for realizing the operation modes, 28 indicates an X-direction scanning circuit and a word line driver as described above, 30 indicates a refresh signal generation circuit, and 31 indicates a Y-direction scanning circuit as a whole.
It constitutes a directional scanning circuit.
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FIG. 7 and FIG. 8 show another embodiment of an image sensor for non-destructively reading optical information according to the present invention. Figure 7 shows an n-channel MOSSIT in which the readout transistor Q1 exhibits unsaturated current-voltage characteristics (a MOSFET with saturated current-voltage characteristics may also be used).
, which shows the cross-sectional structure and circuit representation of a cell portion of an image sensor in which the refresh transistor Q 2 is a P-channel J-SIT (of course, it may be a JFET). Figure 8 shows that the readout transistor Q1 is an n-channel MOSSIT.
2 shows a cross-sectional structure of a cell portion of an image sensor and its circuit representation when the refresh transistor Q 2 is a p-channel MOSSIT (which may also be a MOSFET). An explanation of each area is as follows. Reference numeral 57 denotes a light input (image information), which is irradiated from the back side as in the embodiment shown in FIG. Reference numeral 51 denotes a transparent electrode made of In 2 O 3 , SnO 2 , doped polysilicon, or the like, and is biased at Vs(+):52. Reference numeral 53 denotes an n + region to which electrodes are attached at 51, and is formed thinly to increase short wavelength light sensitivity. 54 is a high resistance region formed of i, n - , p -, and n + 60p + 55i54n + 53 from the p + floating region 55 and the n + accumulation region 60.
A hook structure is formed. The impurity density of the p + region 55 is preferably about 10 18 cm -3 or more, and the impurity density of the n + region 53 is preferably about 10 19 cm -3 or more. This is to reduce thermal noise associated with thermally excited minority carriers. The n + region 61 is the source of the read transistor Q 1 , and the gate (word line 63') on the gate insulating film 63 of Q 1 is preferably made of p + polysilicon in order to shorten the channel. If the resistance becomes too high with only p + polysilicon, a high melting point metal such as W, Mo, or Pt may be further provided. Also, TiSi 2 , TaSi 2 ,
Silicides such as MoSi 2 and WSi 2 may be used. The n + region 60 is an optical information storage region and at the same time serves as the drain of the transistor Q1 . area 59
is the channel of the read transistor Q1 and is of P type. This readout transistor
Q1 is formed using normal MOS technology, in which case it is an n-channel MOSFET, and need not be limited to a MOSSIT. 61' is the electrode of the source 61 of Q1 , which is made of polysilicon or W, Mo, Ta,
It is made of silicide such as Ti and Pb. Similarly, the p + floating region 55 is also formed as the source of the refresh transistor Q2 . The n + region 62 is the gate of the transistor Q 2 , the p â layer 58 is the channel, and the p + region 63 is the source. 62' is an electrode of the n + region 62, which is made of doped polysilicon, W, Mo,
It is formed from silicides such as Ta, Ti, and Pb, and serves as a reflex line. Reference numeral 60' denotes an electrode of the n + region 60, which is made of doped polysilicon or the like, and is connected to the thin insulating layer 64 (thin film of TaO 2 , Si 3 N 4 , SiO 2 , etc.) and the ground electrode 65 above it. A storage capacitor Cs is formed between them. This Cs is formed almost over the entire surface of the image sensor cell, and is designed to be several times larger than the floating capacitance Cf around the p + region 55. Furthermore, 56 and 5
Regions such as 6' are formed of an insulator.
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Each part of the figure will be explained. Figure 8 shows the read transistor Q1 and the refresh transistor.
This is the case where Q 2 is a FET (SIT) with a MOS gate structure. The part that receives the optical input 72 is set in advance.
n + 75p + 70 biased to Vs(+) 67
The hook structure made of i69n + 68 is similar to the embodiments shown in FIGS. 5 and 7 described above. The conductive part of the read transistor Q1 is the n + region 76 and the channel region (p:7
3), the drain n + region 75 is formed, and the gate portion is formed of a thin gate insulating film 78 and an electrode 78' formed of polysilicon or silicide such as W, Mo, Ta, Ti, Pd, etc. (at the same time, a word formed by lines). The conductive portion of the read transistor Q 2 is p + which has reached the p + floating region 70 by diffusion from the surface.
P + drain region 77 electroded with source region and n-type channel 74 and ground electrode 82
The gate part is formed with a thin gate insulating film 79 and an electrode 79' (which also serves as a refresh line) formed of doped polysilicon or silicide such as W or Mo on top of the gate insulating film 79. It is formed. The n + storage region 75 is electroded with doped polysilicon 75', and a thin insulating film 81 (TaO 2 ,
(formed of Si 3 N 4 , SiO 2 , etc.) and the ground electrode line 82 connected to the p + drain 77 of Q 2 form a storage capacitor Cs. Regions 71 and 80 are formed of an insulator such as SiO 2 . Transistors Q 1 and Q 2 can also be formed using normal MOS process technology. In that case
MOSFET, and the display in FIG. 8b is not limited to MOSSIT.
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Why is the sensitivity and resolution of image sensors different from conventional ones?
Explain whether it is superior to the CCD type or MOS type. FIG. 9 is an enlarged view of the n + p + in + portion of FIG. Here, consider the case where a hole group with a ÎŽ function-like distribution n 0 ÎŽ (x, y) is generated at in + junction interface coordinates (O, O). The high-resistance layer 6 is almost depleted by the bias voltage Vs (+), and the carriers running in the high-resistance layer 6 run almost at the saturation speed, so the hole at the coordinate (x, y) after t seconds The distribution of
t)âŠâŠ(2) is given. Here, n 0 is the total number of holes in the initial ÎŽ functional hole distribution, and Vs is the hole saturation velocity: approximately 1Ã10 7
cm/sec, and D is the diffusion coefficient of holes in the high resistance layer.
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ã³è§£å床ãåäžãããããšãã§ããã If the thickness of the high resistance layer 6 is l, then x of the high resistance layer 6
The transit time Ï in the direction is given by Ï=l/Vs âŠâŠâŠâŠâŠ(3), so the hole distribution at the p + i junction is n(x,y) = n 0 exp(â (x-VsÏ) 2 /4D-y 2 /4DÏ
)âŠâŠ(4) is given by. Therefore, the broadening of the electron distribution in the y direction at the p + i junction interface is due only to diffusion, so y
Together with the positive and negative directions of the axis is given by For example, the thickness l of the high resistance layer is 100
Even in terms of ÎŒm, the carrier spread given by equation (5) is approximately 4 ÎŒm when considered in terms of Si. This overcomes the resolution problem that limits the operating characteristics of back-illuminated conventional CCD and MOS image sensors. ,
Therefore, taking into consideration the fact that carriers generated within the substrate are diffused and spread, the limitation on element spacing that prohibits pixels from being arranged at a spacing of 25 ÎŒm or less is overcome. this is,
This is because the optically excited carriers are made to run almost at saturation speed to the storage region.
Therefore, the resolution can be dramatically improved by the image sensor shown in FIG. 5 of the present invention. The carrier spread given by equation (5) is l
becomes smaller as it becomes thinner. Furthermore, the high integration of the cell part does not reduce resolution.
Rather, it is possible to improve this, and an area image sensor with extremely large capacity and good resolution can be realized. Furthermore, as can be seen from the structure of FIG.
All areas are image-sensing areas, and the areas exposed to light are extremely flat. This is because in conventional front-illuminated image sensors, both MOS and CCD types, transparent electrodes, polysilicon, oxide films, etc. are arranged in a convex-concave manner in the area that is irradiated with light. In particular, the transparent electrode shown in FIG. 5a is manufactured to be extremely flat by designing its thickness in consideration of impedance matching to light. Also, to further prevent light reflection from surfaces, e.g.
It is also easy to provide a multilayer film in which SiO 2 films and Si 3 N 4 films are alternately arranged with a predetermined thickness. Therefore, in the image sensor of the present invention, the sensitivity to optical input is also significantly improved compared to the conventional image sensor. Furthermore, in order to absorb the light irradiated onto the high-resistance layer under the separation area into one of the adjacent cells, a transparent electrode material with a concave lens-like structure is added to the n + region or the transparent electrode part below the separation area. By manufacturing, the sensitivity and resolution of the cell can be further improved.
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å°ãªããšã10VçšåºŠä»¥äžã§ããã(b) Dynamic Lens The sensitivity and resolution of the image sensor of the present invention have been described above, and now an example of the present invention will be described regarding the dynamic range, which is another evaluation element of the image sensor. As is clear from the explanation of the prior art, the dynamic range is the upper limit to which the sensor element can operate linearly and without blooming with respect to the noise level.For example, the dynamic range of the conventional MOS type In image sensors, fixed pattern noise due to the spike nozzle associated with the MOS analog switch occurs in the range of 10 -3 to 0.5 x 10 -2 Volt, while the bias voltage of the photodiode adjacent to the MOSFET is about 5V, so the dynamic range is low. It is determined that the ratio is 100:1 or more. In CCDs as well, the depth of the potential well determines the maximum light receiving capacity of the sensor itself, which is also around 5V. The low output side of the dynamic range is determined by noise, which is an extremely important problem when the intensity of the input light is weak, as will be explained later, while the high output side of the dynamic range is determined by the light reception of the sensor body. It is determined by the ability, that is, how much strong light can be received when the intensity of the input light is strong. Noise, which is an important evaluation factor for image sensors, will be discussed later, but here we will discuss the case where the light input is strong, that is, the saturated output with respect to light. As mentioned above, in a MOS image sensor, the maximum optical input value is determined by the bias voltage of adjacent photodiodes and is approximately 5V. Similarly, in a CCD, the voltage is determined by the depth of the potential well, which is also about 5V. If more carriers accumulate, the accumulation region and its surroundings will be biased in the forward direction and will flow as a current. If an attempt is made to increase the bias voltage to raise the upper limit of the dynamic range, problems such as leakage current from the reverse bias diode will occur, leading to an increase in dark current and noise, so the bias voltage is set at around 5V. Another factor, especially in MOS image sensors, is that
The voltage range in which the voltage accumulated in the photodiode (capacitor) by the MOSFET can be read out with good linearity is about 5V. This is because in conventional J-FETs and MOSFETs, the current is limited due to the particularly high source resistance rs.
This is equivalent to obtaining I DS -V DS characteristics with saturation characteristics. Already published paper by the inventors: IEEE Transactions on Electron
Devices, Vol.EDâ26, No.12, December 1979
As published in 2016, simple experimental results show that when using an FET (in this case, a MOSFET) whose source resistance is already high and whose current-voltage characteristics exhibit saturation characteristics, the source resistance is set extremely low and the output current characteristics deteriorate. SIT designed to maintain good linearity over an extremely wide drain-source voltage range
The results show that the linearity of the output voltage through the device is an order of magnitude worse than that using the device. This is a point that has not been noticed much in the past, but when designing an image sensor combination of a simple photodiode and a switching device, considering the linearity and upper limit of the dynamic range, the characteristics of the switching device are important. It means to be an element. In other words, in order to extract the voltage accumulated in the photodiode to an external circuit with good linearity, the characteristics of the switching device must not be a device that exhibits saturation characteristics that limit the current, but rather a device that has a current proportional to the voltage accumulated in the photodiode. A flowing device is best. This is a conventional J-
Instead of devices such as FETs, BJTs, and MOSFETs, SITs that exhibit linear IV characteristics are suitable. Therefore, by using J-SIT or MOSSIT, etc., which are specially designed to reduce the parasitic capacitance between the gate and source and between the gate and drain, instead of the switching device in the conventional image sensor, the saturated output as an image sensor can be improved. can be increased by at least one order of magnitude. In other words, the upper limit of the dynamic range is improved by at least one order of magnitude. In the embodiment shown in FIG. 5, the entire thickness l of the high-resistance layer 6 is depleted, and the voltage Vs provides an electric field strength that causes carriers to run at a saturation speed over almost the entire area.
As for the value of (+), as l increases, Vs(+) also increases, and as mentioned above, the distance over which the carrier spreads in the lateral direction is extremely small compared to the thickness of l, and the limit on the thickness is limited by space. The value of Vs(+) is determined by the resolution and degree of integration, but the value of Vs(+) is at least about 10V or more.
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is the electric field at which the carrier reaches saturation velocity. Of course, if the resolution is acceptable to a certain extent, Vs may be smaller than this. The read transistor Q 1 of the present invention is a p-channel SIT with a reverse conductivity type channel, and electrons, which are minority carriers with respect to the channel, determine the drain-source current, and the drain-source current is 10 V or more. IDS with extremely good linearity with respect to voltage
It is designed to flow. That is, the channel region is completely depleted. Of course, the channel may be made into a high resistance n - region. Therefore, in the image sensor of the present invention, the upper limit of the dynamic range that conventionally causes problems such as blooming is at least one order of magnitude wider. This is a significant improvement in the noise level and can be said to be an improvement in the dynamic range of image sensor evaluation factors.
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Fixed pattern noise (FPN) associated with MOSFET analog switch spikes is 0.5Ã10 -2 Volt ~
It is at 10 -3 Volt, which is the lower limit of the dynamic range. Furthermore, dark current noise associated with thermally excited carriers becomes a problem especially when the light input level is 10 ÎŒW/cm 3 or less and the light irradiation period is 100 msec or more. In addition, there is operational amplifier noise and Johnson noise associated with the operational amplifier in the output section, but this is about one to two orders of magnitude smaller than that of FPN, making it possible to manufacture a high-gain, low-noise operational amplifier along with a low-pass filter on the same chip. Although it cannot be completely removed, it can be kept to a fairly small size. As already explained in the description of the prior art, the dark current of the CCD is larger than that of the MOS type.
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åŽã«åºããã In the embodiment of the present invention, the generation of dark current in the sensor body is reduced by one order of magnitude compared to conventional MOS type and CCD type.
The structure and impurity density are set to reduce the impurity density by two orders of magnitude or more. The region where light is sensed in FIG. 5a is the high resistance layer 6, and the dark current in this photodetection region is p + Determined by electrons in region 7 and holes in n + region 5. p +
The acceptor impurity density in region 7 is N A , n + region 5
Assuming that the donor impurity density in is N D and that it is almost ionized, the minority carriers in each region are n pp = ni 2 /N A âŠâŠ(6) P op = ni 2 /N D âŠâŠ(7) is given by However, ni is the density of thermally excited carriers in the intrinsic semiconductor. Considering room temperature operation with Si, ni=1.3Ã10 10 cm -3 or so,
For example, by setting N A and N D to about 10 20 cm -3 , n and p can each be kept to about 3 to 4. The saturation current of the reverse biased p + in + diode is approximately given by the following equation Js = (qDpPno/Lp + qD on pp /Ln) x (exp -qVg/kT -1) (8). Equation (8) is the diffusion length L of holes and electrons.
This formula can be applied when p and Lo are shorter than the thickness W o of the n region 5 and the thickness W p of the P region 7, respectively. If W o and W p are shorter than L p and Lo, L p and Lo in equation (8) are replaced by W o and W p . D p and D o are holes in the n region 5, respectively;
This is the electron diffusion coefficient in the p region 7. If the voltage V in equation (8) is large to some extent, equation (8) becomes Js=qDpPno/Lp+qD on pp /Ln...(8
)' Or, Js=qDpPno/Wn+qD on pp /Wp...(8
)â³.As is clear from equations (8)â² and (8)â³, P
If op and npp are small, the dark current Js will be small.
Normally, the impurity density of semiconductor substrates used for CCDs and MOSFETs is about 10 15 to 10 16 cm -3 . Therefore, either n pp or P op becomes a relatively large value. By the way, in the present invention,
The n + region 5 can be easily manufactured to a size of about 10 19 to 10 21 cm -3 , and the p + region 7 can also be easily manufactured to a size of about 10 18 to 10 19 cm -3 . Therefore, the dark current in the photodetection region of the present invention can be reduced by at least two orders of magnitude. The fact that the dark current is small means that the light irradiation period can be lengthened accordingly. The detection limit for weak light extends further to the weak light side.
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ããŠããããã§ããã As can be seen from the above explanation, in the present invention, MOS
The structure and impurity density are designed to reduce thermally generated carrier noise by more than two orders of magnitude compared to image sensors using conventional solid-state devices such as type and CCD types. In the conventional MOS type and CCD type, the substrate is rarely used as a high resistance layer, and therefore the generation of minority carriers is more common than in the present invention.On the contrary, in the present invention, the light incident area (substrate)
is a high-resistance layer, and is almost depleted in reverse bias, and in order to suppress the generation of minority carriers, p +
This is why the impurity density of region 7 and n + region 5 is set high.
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äœãæãã工倫ããªãããŠããã In the embodiment of the present invention, dark current noise is suppressed to an extremely low level compared to conventional image sensors, but the margin for the light irradiation period is also improved by at least two orders of magnitude. Noises that are as problematic as those of MOS image sensors include operational amplifier noise and Johnson noise associated with the operational amplifier in the output section, as well as spike noise associated with spike fluctuations of analog switches, and fixed pattern noise. Among these, efforts have been made to reduce noise due to capacitive coupling as much as possible. In other words, there are SITs manufactured in the same process in the sensor body, peripheral scanning circuit, and video output section, and in order to reduce the parasitic capacitance between the gate and source and between the gate and drain of these SITs as much as possible, the parasitic capacitance between the gate and source, Gate·
A structure is introduced in which an insulating layer is interposed between the opposing drains. This method of reducing parasitic capacitance is particularly useful for images with low light intensity levels, especially
It is most suitable for use when detecting images of 10 ÎŒW/cm 2 or less, and there is no need to introduce it for operations where the normal 0.5 Ã 10 -2 to 10 -3 Volt is the lower limit of the dynamic range. . However, with the introduction of the structure for reducing the parasitic capacitance described above, the lower limit of the dynamic range has been expanded by at least two orders of magnitude.
Furthermore, by manufacturing a high-gain, low-noise operational amplifier and low-pass filter on the same chip, efforts have been made to keep the capacitive coupling noise and fixed pattern noise of each part low.
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ãŠããããšããéç©åºŠãé«ãã As described above, while comparing the image sensor of the present invention with a conventional image sensor, the evaluation factors of the image sensor are (1) dynamic range (2) sensitivity (3) noise (4)
This was explained from the four points of resolution. Conventional MOS type,
Significant improvements have been made in all aspects compared to CCD-based image sensors. Furthermore, the image sensor of the present invention has a higher degree of integration than the MOS type, since the light receiving portion and the switching device are configured almost vertically.
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ãµã§ããããŸãã«é©æ°çãªçºæã§ããã As explained above, the present invention improves the performance of conventional image sensors in all four elements that evaluate the operating characteristics of solid-state image sensors: (1) dynamic range, (2) sensitivity, (3) noise, and (4) resolution. It compensates for the shortcomings of CCD and MOS image sensors, and because it uses non-destructive readout, it has much better temporal resolution, which was previously unthinkable in principle. It is an image sensor that has the ability to store information minutely and integrally output it, making it a truly innovative invention.
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šãåæ§ã«åäœããã Image sensor (semiconductor imaging device) of the present invention
However, it is needless to say that the present invention is not limited to the embodiments mentioned here. Even if the conductivity type is completely reversed, if the applied voltage is reversed, it will operate in exactly the same way.
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æ£ãããã°ããã Naturally, the image sensor of the present invention uses color filters corresponding to blue, green, red, etc. that are already used in current technology, and performs various treatments on the light incident surface. It is readily apparent that it is used as For example, you can mark three adjacent cells as blue, green,
It is arranged so that it responds only to the color red. If the detection sensitivities for blue, green, and red colors are different in the light detection section, a predetermined intensity correction may be performed for each color at the time of readout so as to return to a predetermined intensity relationship.
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Figure 1 is a diagram explaining the principle of a MOS image sensor, Figure 2 is a diagram explaining the principle of a CCD image sensor, and Figure 3 is a diagram explaining the principle of two types of CCD image sensors: front-illuminated and back-illuminated. , 4th
The figure shows the configuration of the output OP.Amp. of the image sensor, FIG. 5 shows an embodiment of the present invention, FIG. Figure 5c is a diagram showing an example of the operation mode.
Figure 5d is a diagram for explaining the relationship between optical input and data output in this operation mode, Figure 5e is a diagram for explaining sampling of optical input during light irradiation time,
6a and 6b show an example in which the embodiment of the present invention is assembled as a matrix area image sensor system, and FIGS. 7a and 7b show the cross-sectional structure and circuit structure of another embodiment of the image sensor cell portion of the present invention. Expression,
FIGS. 8a and 8b are cross-sectional structures and circuit representations of still another embodiment of the image sensor cell portion of the present invention,
FIG. 9 is a diagram for explaining to what extent the spread of carriers in the i-layer is suppressed when a drift electric field is applied.
Claims (1)
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ç¯å²ç¬¬ïŒïŒé èšèŒã®åå°äœæ®åè£ çœ®ã[Scope of Claims] 1. A readout transistor and a refresh transistor are provided adjacent to each other on a first main surface of a semiconductor substrate, a photodetector is provided on a second main surface of the semiconductor substrate, and a readout transistor and a refresh transistor are provided on a second main surface of the semiconductor substrate, and In a semiconductor imaging device having a plurality of cells each including a transistor and a photodetection section, the photodetection section is provided inside a semiconductor substrate adjacent to a high-resistance region that substantially detects light and the high-resistance region. and a high impurity density region of opposite conductivity type provided adjacent to the high impurity density region and used as a floating region, and the high impurity density region A semiconductor imaging device characterized in that: is a main electrode region of the refresh transistor, and the opposite conductivity type high impurity density region is a main electrode region of the read transistor. 2. A high impurity density region of a predetermined thickness is provided on the second main surface side of the semiconductor substrate in the high resistance region, and a transparent electrode is provided in electrical contact with the high impurity density region. Said claim 1
The semiconductor imaging device described in . 3. A transparent electrode is provided on the second main surface side of the semiconductor substrate in the high resistance region in electrical contact with the high resistance region, and the high resistance region and the transparent electrode are formed by a shot junction. A semiconductor imaging device according to claim 1. 4. The impurity density of the high impurity density region provided in the semiconductor substrate adjacent to the high resistance region is approximately 1Ã10 18 cm -3 or more. The semiconductor imaging device according to any one of items 1 to 3. 5. The thickness of the high impurity density region provided inside the semiconductor substrate adjacent to the high resistance region is approximately 3.
A semiconductor imaging device according to any one of claims 1 to 4, characterized in that the semiconductor imaging device is formed to be approximately ÎŒm or more. 6. According to any one of claims 1 to 5, wherein the light-receiving surface on the second main surface side of the semiconductor substrate, which becomes the photodetector, is substantially flat. The semiconductor imaging device described. 7. Claims characterized in that a semiconductor region having a predetermined thickness and having a forbidden band width different from that of the semiconductor substrate is provided on the second main surface side of the semiconductor substrate in the high resistance region. 2. The semiconductor imaging device according to item 1. 8. The thickness and impurities of the high resistance region are adjusted such that the high resistance region is depleted by the voltage applied to the transparent electrode and the optically excited carrier traveling in the high resistance region travels at approximately a saturation speed. The semiconductor imaging device according to claim 2 or 3, characterized in that the density is selected. 9 A readout transistor and a refresh transistor are provided adjacent to each other on a first main surface of a semiconductor substrate, a photodetector is provided on a second main surface of the semiconductor substrate, and the readout transistor, the refreshment transistor, and the photodetector are provided on a second main surface of the semiconductor substrate. In a semiconductor imaging device having a plurality of cells consisting of a portion, the photodetecting portion is a high resistance region that substantially detects light, and a floating region provided inside a semiconductor substrate adjacent to the high resistance region. It has a hook structure composed of a high impurity density region and a high impurity density region of an opposite conductivity type provided adjacent to the high impurity density region and used as a floating region, and the high impurity density region is connected to the refresh transistor. one main electrode region and the opposite conductivity type high impurity density region as one main electrode region of the read transistor;
A semiconductor imaging device characterized in that the gate of the read transistor is connected to a word line, the gate of the refresh transistor is connected to a refresh line, and the source of the read transistor is connected to a bit line. 10. The semiconductor imaging device according to claim 9, wherein the word line is connected to a scanning circuit, the refresh line is connected to a refresh signal generation circuit, and the bit line is connected to an operational amplifier. 11. The semiconductor imaging device according to claim 10, wherein the word line is connected to a scanning circuit that generates a plurality of read signals during one refresh signal period.
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP5400180A JPS56150878A (en) | 1980-04-22 | 1980-04-22 | Semiconductor image pickup device |
EP81301732A EP0038697B1 (en) | 1980-04-22 | 1981-04-21 | Semiconductor image sensor |
DE8181301732T DE3167682D1 (en) | 1980-04-22 | 1981-04-21 | Semiconductor image sensor |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP5400180A JPS56150878A (en) | 1980-04-22 | 1980-04-22 | Semiconductor image pickup device |
Publications (2)
Publication Number | Publication Date |
---|---|
JPS56150878A JPS56150878A (en) | 1981-11-21 |
JPS6117150B2 true JPS6117150B2 (en) | 1986-05-06 |
Family
ID=12958354
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP5400180A Granted JPS56150878A (en) | 1980-04-22 | 1980-04-22 | Semiconductor image pickup device |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPS56150878A (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5945781A (en) * | 1982-09-09 | 1984-03-14 | Fuji Photo Film Co Ltd | Semiconductor image pickup device |
US4686554A (en) | 1983-07-02 | 1987-08-11 | Canon Kabushiki Kaisha | Photoelectric converter |
US4731665A (en) * | 1984-12-28 | 1988-03-15 | Canon Kabushiki Kaisha | Image sensing apparatus with read-out of selected combinations of lines |
JPH0646655B2 (en) * | 1985-04-01 | 1994-06-15 | ãã€ãã³æ ªåŒäŒç€Ÿ | Solid-state imaging device |
EP1284021A4 (en) | 2000-04-20 | 2008-08-13 | Digirad Corp | Fabrication of low leakage-current backside illuminated photodiodes |
US20040164321A1 (en) * | 2003-02-26 | 2004-08-26 | Dialog Semiconductor | Vertical charge transfer active pixel sensor |
-
1980
- 1980-04-22 JP JP5400180A patent/JPS56150878A/en active Granted
Also Published As
Publication number | Publication date |
---|---|
JPS56150878A (en) | 1981-11-21 |
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