WO2018206606A1 - Detector for fast-gated detection of electromagnetic radiation - Google Patents
Detector for fast-gated detection of electromagnetic radiation Download PDFInfo
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- WO2018206606A1 WO2018206606A1 PCT/EP2018/061928 EP2018061928W WO2018206606A1 WO 2018206606 A1 WO2018206606 A1 WO 2018206606A1 EP 2018061928 W EP2018061928 W EP 2018061928W WO 2018206606 A1 WO2018206606 A1 WO 2018206606A1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/10—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
- H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
- H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
- H01L31/103—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PN homojunction type
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- 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
- H01L27/14601—Structural or functional details thereof
- H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
Definitions
- the present invention relates to the field of detection of electromagnetic radiation that generates minority carriers in a semiconductor substrate, such as for instance, but not limited thereto, detection of visible and infrared light. More particularly, the present invention relates to gated detection of electromagnetic radiation, mainly in the visible and NIR light. Background of the invention
- EP1513202B1 describes semiconductor detectors that apply a majority carrier current to generate a drift field for demodulation of incoming light.
- IEEE sensors journal Vol 7, NO. 3, pp317-318 "Photonic demodulator with sensitivity control" describes a drain tap that is able to drop demodulation sensitivity to 1% when applying a biasing to the tap of 3.3V.
- the above objective is accomplished by a detector device for detection of electromagnetic radiation impinging on a substrate, whereby the impinging radiation generates pairs of majority and minority charge carriers in the substrate.
- the detector device comprises at least one minority charge detection structure for detecting minority charge carriers generated in the substrate and for, in a first mode, injecting a majority current so as to create an electric field for directing minority charge carriers towards the at least one minority charge detection structure; two or more minority charge removal structures associated to each minority charge detection structure, e.g.
- fast-gated detection may be achieved. This fast-gated detection is achieved by changing a majority current flow between contacts, so that the corresponding minority charge carriers are either directed towards the minority charge detection structure or directed away from the minority charge detection structure and towards the minority charge removal structures, that can be optimized for fast removal because they only need to remove minority carriers and not detect them.
- the at least one minority charge detection structure may comprise a doped region of a first conductivity type (e.g. p-type), a doped region of a second conductivity type (e.g. n-type) different from the first conductivity type, the doped region of the second conductivity type being close to the doped region of the first conductivity type, and forming a pn junction with the substrate, the doped region of the first conductivity type being electrically contacted by a majority charge contact for injecting or extracting majority currents (e.g. generated by majority charge carriers) in or from the substrate, so as to create an electric field for directing the minority charge carriers towards the doped region of the second conductivity type for readout of detected charge carriers.
- a majority charge contact for injecting or extracting majority currents (e.g. generated by majority charge carriers) in or from the substrate, so as to create an electric field for directing the minority charge carriers towards the doped region of the second conductivity type for readout of detected charge carriers.
- the minority charge removal structures comprise a doped region of a first conductivity type (e.g. p-type), a doped region of a second conductivity type (e.g. n-type) different from the first conductivity type, the doped region of the second conductivity type being close to the doped region of the first conductivity type, and forming a pn junction with the substrate and a common terminal short-circuiting the formed pn junction.
- the common terminal may comprise a common contact to the doped region of the first conductivity type and to the doped region of the second conductivity type.
- a terminal is an electrical connection to the outside of the detector.
- the common terminal as in embodiments of the present invention makes the detector device a very compact one.
- the at least one substrate majority charge current sink may comprise a conductive structure surrounding the at least one minority charge detection structure and the two or more minority charge removal structures, for example a ring-shaped conductive structure, e.g. a single conductive ring.
- the at least one minority charge detection structure and the two or more minority charge removal structures are provided at the top surface of the detector device.
- the at least one substrate majority charge current sink may comprise a conductive structure at the bottom of the detector device, on a surface opposite to the top surface.
- a detector device may comprise a plurality of minority charge detection structures and a plurality of minority charge removal structures. In embodiments of the present invention, at least two of the plurality of minority charge detection structures may share at least one of the minority charge removal structures.
- Figure 1A shows a top view and a cross-section of a known minority charge detection structure, which may be used in a fast-gated detector according to embodiments of the present invention.
- Figure IB shows a cross-section of known minority charge detection structure based on a pinned pn-junction, which may be used in a fast-gated detector according to embodiments of the present invention.
- Figure 2A shows a minority charge removal structure according to embodiments of the present invention, which may be used in a fast-gated detector according to embodiments of the present invention
- Figure 2B shows a particular embodiment of a minority charge removal structure of the present invention, which may be used in a fast-gated detector according to embodiments of the present invention.
- Figures 3A and 3B show a fast-gated detector in a state wherein photo-generated minority charge carriers get removed, and Figures 3C and 3D show the same in a state wherein they get detected according to the findings of the present invention.
- Figures 3B and 3D are cross sections through line ⁇ - ⁇ and 11— 11' of Figs 3A and 3C, respectively.
- Figures 4A, and 4B show cross-sections of similar structures as in Figures 3B and 3D, with an additional substrate majority current sink at the bottom of the detector.
- Figures 5A and 5B show different substrate set-ups and light incidence sides for the structures according to embodiments of the present invention.
- Figures 6A, 6B, and 6C show three use cases using multiple minority charge detection structures according to embodiments of the present invention.
- Figures 7A and 7B show how incident light signals can be sampled using the fast- gated detectors according to embodiments of the present invention.
- a device A coupled to a device B should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means.
- p-diffusion or n-diffusion refers to a volume where there has been applied a specific change in doping level and/or doping type compared to the original substrate.
- the way that this has been achieved, e.g. in a CMOS foundry, is not critical for the present invention. It can have been done by diffusion, but also by implant, or by epitaxial layer growth, or whatever technique may be used to get this result.
- first conductivity type that is p
- second conductivity type that is n
- first conductivity type n and second conductivity type p the opposite configuration
- Electrons have a higher mobility than holes, making the detector intrinsically faster.
- a person skilled-in-the-art can easily implement the findings of the present disclosure by using the opposite configuration. However, for the clarity and understanding in the specification further only the fastest option is described.
- minority charge detection structure and “minority charge detector structure” are interchangeable.
- the fast-gated detectors of embodiments of the present invention have several parts.
- each fast-gated detector there is at least one minority charge detection structure 111, 112, for instance as disclosed with respect to Figure 1A or Figure IB, supported by two or more minority charge removal structures 210, 211, and at least one substrate majority current sink 305 altogether embedded in a lowly doped substrate 105.
- the constituting elements of the fast-gated detector must follow certain topology rules.
- At least two minority charge removal structures 210, 211 can be functionally linked or associated to one minority detection structure 111, 112.
- “functionally linked” or “associated” is meant that the structures can interact directly with each other, e.g. they can be biased so that electric field lines can be generated between them, and charge carriers can travel between these structures.
- the minority charge removal structures 210, 211 may be distributed on the substrate around a minority charge detection structure 111, 112, forming discrete islands.
- each minority charge detection structure 111, 112 may have at least two minority charge removal structures 210, 211 nearby, for example neighboring it, for example being separated only by portions of the substrate 307.
- the distribution of structures on the substrate can be tailored to improve the speed of ON/OFF transitions.
- charge removal is associated with charge detection; the removal structures remove charge that may otherwise be detected. Every charge detection structure has at least two charge removal structures associated to it, speeding up the charge removal and facilitating complete removal.
- the discrete minority charge removal structures 210, 211 may be placed in between the minority detection structure 111, 112 and a substrate majority current sink 305, for example a single ring-shaped structure serving as substrate majority current sink 305, surrounding the detection and removal structures. This further contributes to speed increase.
- Figure 1A and Figure IB describe two minority charge detection structures 111, 112 that are known in the state of the art.
- Figure 1A shows a minority charge detection structure 111 that is particularly well-suited for being used in a fast-gated detector according to embodiments of the present invention.
- the top part of Figure 1A shows a top view of the minority charge detection structure 111, while the bottom part of Figure 1A illustrates a cross-section according to line V-V.
- the minority charge detection structure 111 comprises a substrate 105 with thickness 106. It has a p-doped region, e.g. a p-diffusion 100, forming a closed structure with a hole, e.g.
- a central hole such as for example, however not being limited thereto, a structure having an annular shape, or a squared donut shape.
- the p-doped region e.g. p-diffusion 100
- the p-doped region is contacted by one or more majority charge contact(s) 104.
- n-doped region e.g. an n-diffusion 101
- the p-doped region e.g.
- p-diffusion 100 is in the p -substrate 105 and has a higher doping level than the substrate.
- Majority carriers in this case holes, can freely flow from the p-doped region, e.g. p-diffusion 100, to the p -substrate 105 and vice versa because both regions are of the same p-conductivity type.
- the n-doped region, e.g. n-diffusion 101 is contacted by minority charge contact 103.
- the p-doped region, e.g. p-diffusion 100, n-doped region, e.g. n-diffusion 101 can have a source, drain, p-well or n-well doping profile inherited from a standard CMOS or BICMOS process, or can be specifically tuned to the designer's preference.
- the majority charge contact 104 can be used for injecting or extracting majority charge carriers in or from the substrate 105, so as to create a majority current. This majority current creates an electric field in the substrate 105.
- majority charge contact(s) 104 injection of a majority current into the substrate 105 is possible through the p-doped region, e.g. p-diffusion 100, thereby creating an electric field in the p -substrate 105 that attracts minority charge carriers 115 (electrons in this case) in the p -substrate 105 towards the p-doped region, e.g. p-diffusion 100, from where these minority charge carriers diffuse towards the depletion layer 102.
- the n-doped region e.g.
- the minority charge carriers 115 can originate from thermal generation, photo-generation, or any other mechanism that provides minority carriers in the substrate 105.
- majority charge contact(s) 104 extraction of majority charge carriers from the substrate 105 is possible through the p-doped region, e.g. p-diffusion 100, thereby creating an opposite electric field in the p -substrate 105 that repels minority charge carriers 115 in the p -substrate 105 away from the p-doped region, e.g. p-diffusion 100, and also away from the depletion layer 102, due to which the minority charge carriers 115 are not reaching the n-doped region, e.g. n-diffusion 101, and are not getting detected over the pn- junction between n-doped region, e.g.
- n-diffusion 101 and p -substrate 105 n-diffusion 101 and p -substrate 105.
- Minority charge contact 103 contacts n-doped region, e.g. n-diffusion 101, to allow read-out circuitry (not shown) to be subsequently connected.
- read-out circuitry There are several read-out circuits possible, including the well-known 3T-transistor circuit, transimpedance amplifier etc...
- Figure IB shows a cross-sectional view of an alternative minority charge detection structure 112, of the pinned-type, which may be used in an alternative fast-gated detector according to embodiments of the present invention.
- the minority charge detection structure 112 comprises a substrate 105 with thickness 106. It has also majority charge contact(s) 104 connected to a first p-doped region, e.g. p-diffusion 110, a nearby n-doped region, e.g. n- diffusion 109, that forms a pn-junction with the second p-doped region, e.g. p + -diffusion 108, on top, with the first p-doped region, e.g.
- the gate 107 on top of oxide 111 forms a transistor which can be the first transistor in a classical four transistor (4T) read-out structure in a CMOS image sensor as known by a person skilled-in-the-art.
- 4T four transistor
- the removal of the detected charge carriers in the n- doped region, e.g. n-diffusion 109 will now happen through a channel that can be formed under the gate 107 connecting the n-diffusion 109 with the contact 113 by applying a high voltage on gate 107.
- the rest of a read-out circuit (not illustrated in Figure IB) can be attached to contact 113.
- the detection can be enabled (ON-state) or disabled (OFF-state) depending on the direction of the majority current through the majority charge contact(s) 104.
- minority charge carriers that are wandering around may arrive at the n-diffusion 101, 109 and be detected. This is in-between ON and OFF, say the neutral state. It can be achieved by leaving majority charge contact(s) 104 floating or by biasing the voltage such that the majority current becomes zero. This can e.g. be used when the minority charge detection structure is not in use.
- Figure 2A and Figure 2B describe two minority charge removal structures 210, 211 according to embodiments of the present invention.
- the aim of the minority charge removal structures 210, 211 is to drain away minority charge carriers 115 in the underlying p -substrate 105, when enabled, in a very quick and very efficient way.
- the drained minority charge carriers 115 do not have to be quantified.
- the minority charge carriers 115 are not removed.
- the minority charge removal structure 210 of Figure 2A includes a terminal providing electrical contact to the outside of the detector.
- it includes a common terminal 205, providing the same electrical connection of different contacts 203, 204 to the exterior of the detector, short-circuiting said contacts; contacts, being a vertical conduction path (a vertical low resistivity path) between the semiconductor material and the first metalization layer of the chip.
- the minority charge removal structure 211 of Figure 2B includes a horizontal conduction path (a horizontal low resistivity path).
- the horizontal conduction path may comprise a conductive layer 209 providing the same electrical connection between different doped regions 207, 208 and a single, common contact 206 serving as a single common terminal.
- the doped regions are preferably short-circuited to a source of common modulated or variable potential, rather than to a fixed potential, thus allowing different biasing.
- Figure 2A illustrates a first minority charge removal structure 210 according to embodiments of the present invention, which may be used in a fast-gated detector according to embodiments of the present invention.
- the top part of Figure 2A shows a top view of the minority charge removal structure 210, while the bottom part of Figure 2A illustrates a cross- section according to line VI-VI'.
- the minority charge detection structure 210 comprises a substrate 105 with thickness 106.
- Majority charge contacts 204 are connected to a p-doped region, e.g. p-diffusion 200, forming a closed structure with a hole, e.g. a central hole, such as for example, however not being limited thereto, a structure having an annular shape, or a squared donut shape.
- an n-doped region e.g. n-diffusion 201, that is contacted by minority charge contact 203. It may be a centrally placed n-doped region.
- the n-doped region, e.g. n-diffusion 201 forms a diode with the p-doped region, e.g. p-diffusion 200, and with p " -substrate 105, giving a depletion layer 202.
- the diode is short-circuited by short-circuit means, e.g. a common terminal 205, that connects majority charge contact(s) 204 with minority charge contact 203.
- Figure 2B illustrates a second minority charge removal structure 211 according to embodiments of the present invention, which may be used in a fast-gated detector according to embodiments of the present invention.
- the top part of Figure 2B shows a top view of the minority charge removal structure 211, while the bottom part of Figure 2B illustrates a cross- section according to line VII-VII'.
- the minority charge detection structure 211 comprises a substrate 105 with thickness 106.
- a p-doped region e.g. p-diffusion 207, forming a closed structure with a hole, e.g.
- a central hole such as for example, however not being limited thereto, a structure having an annular shape, or a squared donut shape, is abutted to the inner n-doped region, e.g. n-diffusion 208.
- the function of the p-diffusion 207 and n- diffusion 208 of Figure 2B are analogous to the p-diffusion 200 and the n-diffusion 201 of Figure 2A.
- a first option is to have a conductive layer 209 on top that makes contact to both p and n-doped regions, e.g.
- diffusions e.g. a common silicide layer 209 that is very metallic and conducting.
- Another option is that through the high doping levels of both types of doped regions, e.g. p and n-diffusions, there is a high level of tunneling and breakdown between them, in fact destroying normal diode behavior. Any (combination) of the different ways for short-circuiting is possible. Below the n-doped region, e.g. n- diffusion 208, there will nevertheless remain a depletion layer 202 with built-in diode voltage, which still has the capacity to attract and remove minority charge carriers 115 from the substrate 105.
- a common contact 206 can be placed that connects to both the diffusions 207, 208, this way making the minority charge removal structure 211 a very small one.
- the fact that both diffusions 207, 208 do not require a separate contact enables very compact charge removal structures, which is a very advantageous feature.
- a majority current in the p - substrate 105 will flow, generating a drift field that attracts minority charge carriers 115, and that will end-up in the shorted pn diode that is formed by n-diffusion 201, 208, resp., with the p-diffusion 200, 207, resp., and with p " -substrate 105. Due to the short-circuiting these charge carriers get effectively removed and are no longer available for detection elsewhere. Conversely, by extracting a majority current from the common terminal 205, e.g.
- the smaller minority charge removal structure 211 as illustrated in Figure 2B has a much faster and more efficient response time than minority charge removal structure 210 illustrated in Figure 2A, due to the shorter distance that the minority charge carriers 115 have to travel from doped regions, e.g. diffusions, 207 to 208 compared to the distance between doped regions 200 and 201.
- abutted pn-junctions such as the one of Figure 2B allow a p doping width much smaller than with non-abutted junctions.
- the short-circuiting is achieved by using an abutted pn-junction resulting in a p doping width that is smaller than the width of non- abutted junctions.
- This narrow width has the advantage of providing a correspondingly short minority carrier travel time along the width.
- the charge removal structure construction method enables both a very compact minority charge removal structure 211 and a very narrow p doped region, shortening the charge travel time along this region. This increases the speed of the sensor.
- Figure 3A and 3C show the top views, and Figure 3B and 3D cross-sectional views according to lines ⁇ - ⁇ and ⁇ - ⁇ , respectively, of fast-gated detectors 304 according to embodiments of the present invention.
- the detectors 304 are implemented in a substrate 307 with thickness 308.
- the squares 300 symbolize a minority charge detection structure as for instance minority charge detection structures 111, 112 as illustrated in Figure 1A or Figure IB.
- the 8 squares 301 symbolize 8 minority charge removal structures as for instance minority charge removal structures 210, 211 as illustrated in Figure 2A or Figure 2B.
- the minority charge detection structure 300 and the minority charge removal structures 301 are implemented in a top surface of the substrate 307.
- There is a ring contact 305 e.g.
- the ring contact 305 may be at a surface of the detector device, for instance at the surface where the charge detection and charge removal devices 300, 301 are provided.
- this sink 305 will extract a remainder of the inserted but not yet extracted majority currents. Its location determines the field line behavior and consequently determines where the detective volume will be located.
- Figure 3A and 3B show the condition whereby the photo-generated minority charge carriers in the substrate 307 get disposed of.
- majority current is injected into the common terminal 205, e.g. common contact 206 (see Figure 2A or 2B) of the 8 minority charge removal structures 301, and majority current gets extracted at the majority charge contact(s) 104 (see Figure 1A or IB) of the minority charge detection structure 300.
- the injected majority currents 302, 303 flow through the substrate 105 partly towards the substrate's majority sink 305 (currents 302), accepting (extracting, removing or sinking) these currents, and partly (currents 303) to the minority charge detection structure 300.
- the minority charge carriers will flow in the opposite direction and will get removed at the 8 minority charge removal structures 301.
- the majority current situation can be changed quickly, and evenly quick, detection can be promoted ( Figures 3C and 3D).
- majority current is extracted from the common terminal 205, e.g. common contact 206 (see Figure 2A or 2B) of the 8 minority charge removal structures 301, and majority current inserted at the majority charge contact(s) 104 of the minority charge detection structure 300.
- These latter majority currents 302, 306 flow through the substrate 307 partly towards the substrate majority current sink 305 (currents 302), accepting (extracting, removing or sinking) these currents, and partly to the 8 minority charge removal structures 301 (currents 306).
- Minority charge carriers will all flow in the opposite direction of the majority charge flow and will substantially all get detected and become available at the pn-junction of the minority charge detection structure 300 for later or immediate read-out.
- Figure 4A and 4B show a topology of a fast-gated detector 404 that is similar to the fast-gated detector 304 of Figure 3.
- the minority charge detection structure 300 and minority charge removal structures 301 are provided in a top surface of the substrate, but additional to a first substrate majority current sink 305 there is also a second substrate majority current sink 405, located at the bottom of the detector, e.g. at the surface of the substrate 307 opposite to the top surface, where the lowly doped substrate 307 stops (which may be surrounded by oxide, metal, air, material of different doping concentration, etc.).
- the majority current through the substrate can now end at substrate majority current sink 305 as well filling the detector volume with field lines 406 filling in a more homogeneous way.
- Figure 4A gives the OFF-state of the detection
- figure 4B gives the ON-state (sampling-state) of the detector.
- the second substrate majority current sink 405 may be any conductive surface at the bottom of the detector, for instance it may have the shape of a plane.
- Substrate majority current sink 305 is optional when a substrate majority current sink 405 is present at the bottom.
- the two minority charge removal structures 301 may be located at opposite sides of the minority detector structure 300. If more than two minority charge removal structures 301 are provided per minority detector structure 300, they may be substantially evenly spread around the minority detector structure 300.
- the at least two minority charge removal structures 301 should further be located nearby the minority detector structure 300. What is "nearby” depends on the distance to the closest part of the substrate majority current sink 305, 405. To reach acceptable speed, the at least two minority charge removal structures 301 should always be located closer to the minority detector structure 300, than to any part of the used substrate majority sink(s) 305, 405.
- each minority charge detector structure 300 needs to have at least two minority charge removal structures 301 nearby.
- each minority charge detector structure 300 may have two neighboring minority charge removal structures 301 surrounding it, or being separated only by a portion of the area of the top surface of the substrate 307, 510, without any intermediate structure between the minority charge removal structures 301 and its functionally linked minority detector structure 300.
- a minority charge removal structure 301 may be functionally linked, for example neighboring, one or more minority charge detection structures 300, but each minority charge detection structure 300 should be functionally linked to at least two minority charge removal structures 301. Thus, a single minority charge removal structure 301 may be shared by two minority charge detection structures 300.
- the minority charge removal structures 301 are placed as discrete islands between the minority charge detection structure 300 and the majority current sink 305, 405. This improves also speed, because charge carriers do not need to travel through the whole substrate towards the sink.
- a single ring-shaped majority current sink 305 may surround the one or more minority charge detection structures and the two or more minority charge removal structures.
- Figure 5A shows how the detector 304 is supporting front side illumination (FSI) and back-side illumination (BSI).
- FSI front side illumination
- BSI back-side illumination
- the detection volume in the p -substrate 307 where the majority currents are flowing, can be illuminated with light incident from the top 501 or from the bottom 502 side. Photo-generated minority carriers will in both cases effectively be detected during a gating period.
- the p -substrate 307, 510 will in most situations be, however, quite thin, having a thickness 512 between a few microns and 30 micron, and may need mechanical support.
- a good FSI set-up is shown in Figure 5B, whereby the p -substrate 510 can be on top of a thicker supporting substrate 511, having a thickness 513 sufficient to provide structural stability and strength. That thicker substrate 511 can for example be highly p-doped, as such also serving as a possible substrate majority current sink.
- This is an industrial set-up whereby production is started from a wafer with relative high conductivity of 20 Q.cm, on which an e.g. an EPI layer of 15 micron is deposited having a low to very low conductivity of 800-2000 Q.cm.
- Other options, including ones for BSI, using a stacked CMOS wafer can be considered by the person skilled in the art.
- Figure 6A shows that within a single rectangle-shaped substrate majority current sink 305 four pixels 600, 601, 602, 603 can be grouped, each covering a quadrant Ql, Q2, Q3, Q4 of the space enclosed by the rectangle-shaped substrate majority current sink 305, thereby quadrupling the effective resolution of pixels of fast-gated detectors.
- Minority charge detection structures 604, 605, 606 and 607 each attract mainly the photo-generated minority charge carriers from their respective quadrant Ql, Q2, Q3, Q4 with little crosstalk.
- the curves 610...614 in the right hand part of Figure 6A show how the voltages are applied to sample during the same time window.
- a high level is e.g.
- the curve 610...613 are the applied voltages to the four minority charge detection structures, 614 is the voltage applied to the 8 minority charge removal structures 301. The voltage on the minority charge removal structures can also be held constant.
- Figure 6B has a very similar set-up; however, it is considered a single detection volume 620, whereby four minority charge detection structures 621, 622, 623 and 624 each attract mainly the photo generated minority charge carriers in different time windows. This is demonstrated by the applied voltages (and hitherto currents) 630, 631, 632 and 633 that gate at different consecutive periods in time. These periods can be overlapping, or non- overlapping. Curve 634 is the voltage applied to the 8 minority charge removal structures 301. The voltage on the minority charge removal structures can also be held constant.
- Figure 6C shows a mixture of the principles explained in Figures 6A and 6B.
- Four minority charge detection structures 642, 643, 644 and 645 are provided, spread over two detection volumes 640, 641. Resolution doubles, and two separate time periods get sampled for each of the detectors 640 and 641.
- Minority charge detection structures 642, 643, 644 and 645 each attract mainly the photo-generated minority charge carriers from their respective halve HI, H2 with little crosstalk.
- the curves 650, 651, 652, 653 in the right hand part of Figure 6C show how the voltages are applied to sample during the same time window.
- a high level is e.g. 3.3V
- low level is 0V
- the voltage at the rectangle-shaped substrate majority current sink 305 can be permanently at e.g. -5V.
- the curves 650, 651, 652, 653 are the applied voltages to the four minority charge detection structures, 654 is the voltage applied to the 8 minority charge removal structures 301.
- Figure 7A shows how from an incident light signal 700 during a period defined by curve 701 the detection function can be turned ON, and the photo generated minority carriers can be integrated 702.
- Figure 7B shows how different slices of the incident light signal 700 can be integrated over the four minority charge detection structures 621, 622, 623 and 624 of detector 620 from Figure 6B, in this way using four times more signal of the incident light and improving the signal to noise ratio by the same factor.
- the light signal 700 can originate from different origins, e.g. from a fluorophore that has just been stimulated by a short light pulse.
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