CA1087756A - High voltage thyristor - Google Patents
High voltage thyristorInfo
- Publication number
- CA1087756A CA1087756A CA281,590A CA281590A CA1087756A CA 1087756 A CA1087756 A CA 1087756A CA 281590 A CA281590 A CA 281590A CA 1087756 A CA1087756 A CA 1087756A
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- Prior art keywords
- zone
- anode
- major surface
- disposed
- cathode
- 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
Links
- 230000000903 blocking effect Effects 0.000 claims abstract description 38
- 239000004065 semiconductor Substances 0.000 claims abstract description 17
- 230000005684 electric field Effects 0.000 claims abstract description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 8
- 239000000463 material Substances 0.000 claims description 5
- 229910021420 polycrystalline silicon Inorganic materials 0.000 claims description 4
- 235000012239 silicon dioxide Nutrition 0.000 claims description 4
- 239000000377 silicon dioxide Substances 0.000 claims description 4
- 230000002093 peripheral effect Effects 0.000 claims 1
- 230000015556 catabolic process Effects 0.000 abstract description 13
- 239000002674 ointment Substances 0.000 description 43
- 230000000875 corresponding effect Effects 0.000 description 3
- 238000000034 method Methods 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 230000003466 anti-cipated effect Effects 0.000 description 1
- 238000010420 art technique Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/402—Field plates
- H01L29/405—Resistive arrangements, e.g. resistive or semi-insulating field plates
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/74—Thyristor-type devices, e.g. having four-zone regenerative action
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/74—Thyristor-type devices, e.g. having four-zone regenerative action
- H01L29/7404—Thyristor-type devices, e.g. having four-zone regenerative action structurally associated with at least one other device
- H01L29/7408—Thyristor-type devices, e.g. having four-zone regenerative action structurally associated with at least one other device the device being a capacitor or a resistor
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- Ceramic Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Thyristors (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A thyristor structure is described which is capable of achieving the maximum theoretical breakdown voltage of both forward and reverse blocking junctions. An annular electrical field spreading member bridges the blocking junctions of the thyristor, both of which emerge on one major semiconductor surface of the device. The resistive layer spreads the electric field to a degree sufficient to raise the surface breakdown voltage up to the bulk breakdown capability.
A thyristor structure is described which is capable of achieving the maximum theoretical breakdown voltage of both forward and reverse blocking junctions. An annular electrical field spreading member bridges the blocking junctions of the thyristor, both of which emerge on one major semiconductor surface of the device. The resistive layer spreads the electric field to a degree sufficient to raise the surface breakdown voltage up to the bulk breakdown capability.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross sectional view of a thyristor device of the prior art;
Figure 2 is a cross sectional view of a prior art ,; diode employing a field spreader;
., ' Figure 3 is a cross sectional view o$ a thyristor ; device employing field spreaders;
Figure 4 is a cross sectional view of a thyristor device of the present invention; and Figure 5 is one possible plan view of the deYice of Figure 4.
BACKGROUND OF THE INVENTION
, Field of the Invention:
The present invention pertains to semiconductor devices and particularly to high voltage thyristors.
Descri~tion of the Prior Art:
There has been an effort in the prior art to produce PN ~unction semiconductor devices with high voltage blocking capabilityO It is known that the blocking oapability of a PN ~unction depends on both the bulk properties and the surface properties of the semiconductor body. Surface breakdown has been the principle voltage limiting factor in prior art devices. Thus, much effort in the prior art has been directed to increasing surface breakdown capability ~n order to bring surface breakdown voltage up to a level comparable with the theoretical bulk breakdown.
One such device is illustrated by prior art thyris-tor 10 in Figure lo Thyristor 10 comprises a body of semi-conductor material or wafer 12 on which there is disposed 45,544 1 0~ ~ 5~
electrodes 14, 16 and 18. The wafer 12 comprises four zones of alternate conductivity type: an N-type cathode emitter zone 20 disposed at the top ma~or surface 21 of the wafer 12, a P-type cathode base zone 22 disposed below zone 20, an N-type anode base zone 24 disposed below zone 22, and a P-type anode emitter zone 26 disposed below zone 24. Cathode electrode 14 is aI'rixed to top major surface ~1 contacting - zone 20. Anode electrodæ 18 is affixed to bottom ma~or surface 27 of the wafer 12 thereby contacting zone 26.
10The device 10 has a beveled edge 28 produced in a known manner for the purpose of increasing surface breakdown ; capability. As will be appreciated by those skilled in the art, beveled edge 28 increases the blocking capability of PN
junctions 31 and 33 which terminate on surface 28.
Thyristor device 10 operates as an electrical switch by blocking the flow of current until such time as the devlce is gated in the presence of a forward biasing voltage. Specifically, when a positive voltage potential is impressed on cathode electrode 14 with respect to anode electrode 18, PN junction 31 is reverse biased and the device 10 is said to be in the reverse blocking mode. When a positive voltage potential is impressed on anode electrode 18 with respect to cathode electrode 14, PN ~unction 33 is reverse biased and the device 10 is said to be in a forward blocking mode. The device 10 may be switched from the ~orward blocking mode to a ~orward conducting mode by impres-sing a positive voltage on gate electrode 16 with respect to cathode electrode 14. The voltage at gate electrode 16 causes emission to occur at PN junction 35, which causes the device to be switched from the forward blocklng mode to the 10~56 45'544 forward conducting mode in a manner known to those skllled ln the art. Note that PN ~unction 35 is not a high voltage blocklng ~unction and does not terminate on beveled surface 28, but rather on top ma~or surface 21.
The purpose of beveled edge 28 is to spread the electrlc fleld at the intersection of the blocking Junctions 31 and ~3 with the surrace Or wafer 12.
Referrln~ now to Flgure 2 there is illustrated a prior art diode 40 which achieves fleld spreading of the electric field around a single blocking PN ~unction at its intersection with a flat ma~or semiconductor surface. Diode 40 comprises a semiconductor wafer 42, a field spreading member 44, top electrode 46 and bottom electrode 48.
Disposed in the wafer 42 is an N-type zone 52 ad~acent to top ma~or surface 51, and a P-type zone 54 ad~acent to bottom ma~or surface 55. PN ~unction 57 interfaces N-type zone 52 and P-type zone 54. Electrode 48 is affixed to bottom ma~or surface 55 contacting zone 54. Zone 54 extends past zone 52 to the-outer periphery of ma~or surface 51, so 20 that PN ~unction 57 intersects top major surface 51. Field spreader 44 is disposed on major surface 51 covering PN
~unction 57.
The field spreader 44 preferably comprises a silicon dioxide layer 60, which is disposed on ma~or surface 51 bridging zones 52 and 54. Upon silicon dioxide layer 60 is disposed a resistive layer 62 of polycrystalline silicon.
Layers 60 and 62 are prepared in a known manner, layer 62 having a resistivity typically from about 106 ohm-cm to about 108 ohm-cm. Field spreader 44 further comprises two metallic contacts 64 and 66 which are deposited in a known 45,544 ;, manner. Inner contact 64 electrically connects resistive ,~ layer 62 to zone 52 as shown. Outer contact 66 electrically connects reslstive layer 62 to zone 54 as shown. Inner contact 64 is ~uxtaposed over PN ~unction 57 at its inter-section w1th ma~or surface 51.
It is prererred that wafer 42 be circular and that PN ~unction 57 form a circular ring at lts ~ntersection with ma~or surface 51. Similarly, field spreader 44 preferably takes the shape of an annular ring corresponding to the ring formed by PN junction 57 at surface 51. In the case where wafer 42 is in the shape Or a sQuare chip, it is preferred that zone 52 be generally square but having rounded corners.
The radius of curvature Or PN ~unction ~7 at the corners Or the square should be several times greater than the anti-cipated dimension Or the depletion layer at maximum blocking voltage.
Field spreaders as described above have also been used on one ~unction of a transistor as illustrated by French Patent No. 2,099,704, issued on March 17, 1972, in the name of Fairchild Camera & Instrument Corporation.
SUMMARY OF THE INVENTION
The present invention is a thyristor device in which both a forward blocking ~unction and a reverse block-ing ~unction emerge at a top ma~or surface of the wafer. An electric field spread~ng member is disposed on the top surface Or the wafer overlapping both bloc~ing ~unctions.
108775~
DESCRIPTION OF THE' P~EFERRED EMBODIMENTS
Presently, high power commercial thyristors employ a structure similar to that shown in Figure 1. Hlgh blocking voltages are achieved by using the well-known edge beveling technique as described abcve. However, it is known that PN
~unctions are capable of even higher blocking voltages, and that a field spreader as described above relative to the device of Figure 2 achieves blocking voltages at maximum bulk breakdown levels. It would thererore be desirable to produce a thyristor device with maximum forward and reverse blocking capability.
Figure 3 is a logical combination of the above-described prior art techniques. Figure 3 illustrates a thyristor device 100 comprising a body or wafer 102 of semiconductor material, metallic electrodes 104, 106 and 108 and electric field spreading members 110 and 112. The wafer 102 has four zones of alternate conductivity type separated by PN ~unctions. Cathode emitter zone 114 of N-type con-ductivity is disposed in body 102 at top ma~or surface 115.
A cathode base zone 116 of P-type conductivity ls disposed in body 102 beneath zone 114 and extending past zone 114 to ma~or surface 115. Anode base zone 118 of N-type conduc-tivity is disposed in body 102 beneath zone 116 and extend-108775~ 45,544 ing past zone 116 to an outer portion of ma~or surface 115.
An anode emitter zone 120 of P-type conductivity is disposed ln body 102 beneath zone 118 and ad~acent to bottom ma~or surface 121. N-type base zone 118 encompasses the periphery 1 of body 102 from top ma~or surface 115 to bottom ma~or surface 121. Cathode electrode 104 is affixed to top ma~or surface 115 in contact with N-type emitter zone 114. Gate electrode 106 is afrixed to top ma~or surface 115 in contact with P-type base zone 116. Anode electrode 10~ is affixed to bottom ma~or surface 121 in contact with P-type emitter zone 120. PN ~unction 123, which separates zones 114 and 116, intersects top ma~or surface 115 in a circle or closed loop. PN ~unction 125, which separates zones 116 and 118, intersects top major surface 115 in a circle or closed loop surrounding the loop of PN junction 123. PN ~unction 127, which separates zones 118 and 120, intersects bottom ma~or surface 121 in a circle or closed loop.
It will be apparent to those skilled in the art from a comparison of device 100 of Figure 3 with prior art device 40 of Figure 2 that field spreaders 110 and 112 increase the blocking capability of PN ~unctions 125 and 127. Since PN ~unction 123 is not a high voltage blocking ~unction, it is not necessary to cover it with a field spreader. Field spreaders 110 and 112 form annular rings on surfaces 115 and 121 overlying PN ~unctions 125 and 127 respectively. Field spreader 110 comprises an insulating layer 130 of silicon dioxide disposed on ma~or surface 115 bridging PN ~unction 125, a resistive layer 132 of poly-crystalline silicon disposed on layer 130, an inner metallic contact 134 disposed on zone 116 and overlapping the inner 45,544 . .
portion of layer 132 in ~uxtaposition over the intersection of PN ~unction 125 with ma~or surface 115, and an outer metallic contact 136 disposed on zone 118 and overlapping the outer portion of layer 132. Field spreader 110 provides a resistive path between N-type base zone 118 and P-type base zone 116, which increases the surface breakdown cap-ability of PN ~unction 125 in a known manner as described above. Similarly, field spreader 112 increases the surface blocking capability of PN ~unction 127, numerals 140, 142, 144 and 146 being analogous to numerals 130, 132, 134 and 136.
Thus, thyristor device 100 of Figure 3 is an example of a structure which is capable of achieving higher forward and reverse blocking voltages than can be achieved by a prior art thyristor such as device 10 shown in Figure 1. However, thyristor device 100 of Figure 3 is impractical for several reasons. Firstly, since wafer 102 is fragile and ls not supported at the periphery on either one of its ma~or surfaces, device 100 is subject to breakage. For example, both prior art devices 10 and 40 have metallic electrodes 18 and 48, which serve the dual purposes of mechanical support as well as electrical contacting. Secondly, device 100 has the impractical aspect of requiring com-plicated masking and deposition on both major surfaces to produce field spreaders 110 and 112.
Now referring to Figure 4, a thyristor device 200 illustrates a presently preferred embodiment of the inven-tion. The thyristor 200 comprises a body or wafer 202 of semiconductor material, metallic electrodes 204 and 208, and electric field spreading member 210. Cathode electrode 204 ~0877S6 45,544 ,,~
i8 dlsposed on top ma~or surface 215 of the wafer 202 in contact wlth cathode emitter zone 214 of N-type conductivity.
Cathode base zone 216 of P-type conductivity ls disposed beneath zone 214 and extending past zone 214 to share a portion of top ma~or surface 215 as shown. Anode base zone 218 of N-type conductivity is disposed beneath zone 216 and extends past zone 216 to top ma~or surface 215. Anode emitter zone 220 of P-type conductivity is disposed beneath zone 218 ad~acent to bottom ma~or surface 221 of the wafer 202 where contact is made with anode electrode 208. P-type anode emitter zone 220 also encompasses the entire periphery of the wafer 202 extending past zone 218 and terminating at the periphery of top ma~or surface 215. It will be recognized that the invention is equally applicable to a thyristor wherein zones 214, 216, 218 and 220 have the opposite con-ductivity shown in Figure 4.
Separating the four zones of alternate conductivity are three PN ~unctions, all of which emerge at top ma~or surface 125. Separating zones 214 and 216 is PN ~unction 223, separating zones 216 and 218 is PN ~unction 225, and separating zones 218 and 220 is PN ~unction 227. PN ~unc-tion 225 serves as the forward blocking ~unction and PN
~unction 227 serves as the reverse blocking ~unction of the thyristor device 200. Unlike PN ~unctions 225 and 227, PN
~unction 223 is not a high voltage blocking ~unction; rather, PN ~unction 223 serves to initiate conduction of the thy-ristor device 200.
As shown in Figure 4, field spreader 210 overlaps both high voltage blocking ~unctions 225 and 227. Field spreader 210 comprises an insulating layer 230 of silicon 1 O 8 ~ 5 6 45~544 dioxlde disposed on top ma~or surface 215, a resistive layer 232 o~ polycrystalline silicon disposed on and conforming to insulating layer 230, and metallic contacts 234 and 236 partially overlapping resistive layer 232 and the ad~acent portions of surface 215. The insulating layer 230 covers anode base zone 218 forming a closed loop on top ma~or surface 215. Inner contact 234 electrically connects resi-stlve layer 232 to zone 216, contact 234 being ~uxtaposed over PN ~unction 225 at its intersection with surface 215.
Outer contact 236 electrically connects resistive layer 232 to zone 220, contact 236 being ~uxtaposed over PN ~unction 227 at its intersection with surface 215. Note that it is not necessary to have a separate gate electrode, since electrode 234 can also perform the gating function.
Reslstive layer 232 provides a resistive path across N-type base zone 218. When the thyristor device 200 is operating in the forward blocking mode, PN ~unction 225 is reverse biased and PN junction 227 is forward biased. As known in the art, there exists a depletion layer around a blocking ~unction which spreads away from the ~unction as the blocking voltage ls increased. Therefore, when device 200 is operating in the forward blocking mode, the depletion layer around PN ~unction 225, along with its corresponding electrical field, spreads in the semiconductor body 202 and along ma~or surface 215 at the portion of surface 215 under ` the field spreading member 210. Resistive layer 232 and inner metallic contact 234 operate to spread the electrical field in a known manner to maximize the surface breakdown voltage of blocking ~unction 225. Likewise, when the device 200 is operating in a reverse blocking mode, PN ~unction 227 _9_ 45,544 ~0~'~75~
ls reverse blased and PN ~unction 225 ls forward blased.
Therefore, ln the reverse blocking mode, field spreader 210 slmllarly serves to maxlmize the surface breakdown voltage of PN ~unctlon 227, in which case outer metalllc contact 236 and resistive layer 232 operate to spread the electric field.
The present invention provides a novel thyristor device having a single field spreader which effectively serves to maximize the surface breakdown capability of both the forward and reverse blocking ~unctions. Furthermore, device 200 is easily manufactured with known techniques since only one ma~or surface requires a field spreader. In addition, device 200 has an anode electrode 208 which sup-ports the semiconductor wafer 202 at its fragile periphery, thereby providing a rigid commercially practlcal device.
It is presently preferred that the semiconductor wafer 202 be circular or disc-shaped and that the PN ~unctions intersect ma~or surface 215 in concentric circles. In such an embodiment, field spreader 210 will appear as an annular ring. It is possible, however, to conceive of a number of different shapes equally suitable to practicing the present lnvention.
For example, in Figure 5 there is shown a plan view of device 200 wherein the semiconductor wafer 202 is in the shape of a quadrangle. In such an embodlment field spreader 210 has straight edges and rounded corners cor-- responding to the intersections of the blocking PN ~unctions with ma~or surface 215. The straight edges are necessary to maximize the active surface area available to cathode elec-trode 204, and the rounded corners are necessary to prevent 108~5~ 45.544 high fleld concentrations. A suitable radlus of curvature at the corners would be about twice the maxlmum spread of the depletlon layer from the blocking ~unctions. In any event, whatever geometrical shape is chosen for device 200, it is only necessary that the field spreader 210 form a closed loop on the semiconductor surface correspondlng to the underlying closed loops delineated by the intersections of the blocking ~unctions with top ma~or surface 215.
Figure 1 is a cross sectional view of a thyristor device of the prior art;
Figure 2 is a cross sectional view of a prior art ,; diode employing a field spreader;
., ' Figure 3 is a cross sectional view o$ a thyristor ; device employing field spreaders;
Figure 4 is a cross sectional view of a thyristor device of the present invention; and Figure 5 is one possible plan view of the deYice of Figure 4.
BACKGROUND OF THE INVENTION
, Field of the Invention:
The present invention pertains to semiconductor devices and particularly to high voltage thyristors.
Descri~tion of the Prior Art:
There has been an effort in the prior art to produce PN ~unction semiconductor devices with high voltage blocking capabilityO It is known that the blocking oapability of a PN ~unction depends on both the bulk properties and the surface properties of the semiconductor body. Surface breakdown has been the principle voltage limiting factor in prior art devices. Thus, much effort in the prior art has been directed to increasing surface breakdown capability ~n order to bring surface breakdown voltage up to a level comparable with the theoretical bulk breakdown.
One such device is illustrated by prior art thyris-tor 10 in Figure lo Thyristor 10 comprises a body of semi-conductor material or wafer 12 on which there is disposed 45,544 1 0~ ~ 5~
electrodes 14, 16 and 18. The wafer 12 comprises four zones of alternate conductivity type: an N-type cathode emitter zone 20 disposed at the top ma~or surface 21 of the wafer 12, a P-type cathode base zone 22 disposed below zone 20, an N-type anode base zone 24 disposed below zone 22, and a P-type anode emitter zone 26 disposed below zone 24. Cathode electrode 14 is aI'rixed to top major surface ~1 contacting - zone 20. Anode electrodæ 18 is affixed to bottom ma~or surface 27 of the wafer 12 thereby contacting zone 26.
10The device 10 has a beveled edge 28 produced in a known manner for the purpose of increasing surface breakdown ; capability. As will be appreciated by those skilled in the art, beveled edge 28 increases the blocking capability of PN
junctions 31 and 33 which terminate on surface 28.
Thyristor device 10 operates as an electrical switch by blocking the flow of current until such time as the devlce is gated in the presence of a forward biasing voltage. Specifically, when a positive voltage potential is impressed on cathode electrode 14 with respect to anode electrode 18, PN junction 31 is reverse biased and the device 10 is said to be in the reverse blocking mode. When a positive voltage potential is impressed on anode electrode 18 with respect to cathode electrode 14, PN ~unction 33 is reverse biased and the device 10 is said to be in a forward blocking mode. The device 10 may be switched from the ~orward blocking mode to a ~orward conducting mode by impres-sing a positive voltage on gate electrode 16 with respect to cathode electrode 14. The voltage at gate electrode 16 causes emission to occur at PN junction 35, which causes the device to be switched from the forward blocklng mode to the 10~56 45'544 forward conducting mode in a manner known to those skllled ln the art. Note that PN ~unction 35 is not a high voltage blocklng ~unction and does not terminate on beveled surface 28, but rather on top ma~or surface 21.
The purpose of beveled edge 28 is to spread the electrlc fleld at the intersection of the blocking Junctions 31 and ~3 with the surrace Or wafer 12.
Referrln~ now to Flgure 2 there is illustrated a prior art diode 40 which achieves fleld spreading of the electric field around a single blocking PN ~unction at its intersection with a flat ma~or semiconductor surface. Diode 40 comprises a semiconductor wafer 42, a field spreading member 44, top electrode 46 and bottom electrode 48.
Disposed in the wafer 42 is an N-type zone 52 ad~acent to top ma~or surface 51, and a P-type zone 54 ad~acent to bottom ma~or surface 55. PN ~unction 57 interfaces N-type zone 52 and P-type zone 54. Electrode 48 is affixed to bottom ma~or surface 55 contacting zone 54. Zone 54 extends past zone 52 to the-outer periphery of ma~or surface 51, so 20 that PN ~unction 57 intersects top major surface 51. Field spreader 44 is disposed on major surface 51 covering PN
~unction 57.
The field spreader 44 preferably comprises a silicon dioxide layer 60, which is disposed on ma~or surface 51 bridging zones 52 and 54. Upon silicon dioxide layer 60 is disposed a resistive layer 62 of polycrystalline silicon.
Layers 60 and 62 are prepared in a known manner, layer 62 having a resistivity typically from about 106 ohm-cm to about 108 ohm-cm. Field spreader 44 further comprises two metallic contacts 64 and 66 which are deposited in a known 45,544 ;, manner. Inner contact 64 electrically connects resistive ,~ layer 62 to zone 52 as shown. Outer contact 66 electrically connects reslstive layer 62 to zone 54 as shown. Inner contact 64 is ~uxtaposed over PN ~unction 57 at its inter-section w1th ma~or surface 51.
It is prererred that wafer 42 be circular and that PN ~unction 57 form a circular ring at lts ~ntersection with ma~or surface 51. Similarly, field spreader 44 preferably takes the shape of an annular ring corresponding to the ring formed by PN junction 57 at surface 51. In the case where wafer 42 is in the shape Or a sQuare chip, it is preferred that zone 52 be generally square but having rounded corners.
The radius of curvature Or PN ~unction ~7 at the corners Or the square should be several times greater than the anti-cipated dimension Or the depletion layer at maximum blocking voltage.
Field spreaders as described above have also been used on one ~unction of a transistor as illustrated by French Patent No. 2,099,704, issued on March 17, 1972, in the name of Fairchild Camera & Instrument Corporation.
SUMMARY OF THE INVENTION
The present invention is a thyristor device in which both a forward blocking ~unction and a reverse block-ing ~unction emerge at a top ma~or surface of the wafer. An electric field spread~ng member is disposed on the top surface Or the wafer overlapping both bloc~ing ~unctions.
108775~
DESCRIPTION OF THE' P~EFERRED EMBODIMENTS
Presently, high power commercial thyristors employ a structure similar to that shown in Figure 1. Hlgh blocking voltages are achieved by using the well-known edge beveling technique as described abcve. However, it is known that PN
~unctions are capable of even higher blocking voltages, and that a field spreader as described above relative to the device of Figure 2 achieves blocking voltages at maximum bulk breakdown levels. It would thererore be desirable to produce a thyristor device with maximum forward and reverse blocking capability.
Figure 3 is a logical combination of the above-described prior art techniques. Figure 3 illustrates a thyristor device 100 comprising a body or wafer 102 of semiconductor material, metallic electrodes 104, 106 and 108 and electric field spreading members 110 and 112. The wafer 102 has four zones of alternate conductivity type separated by PN ~unctions. Cathode emitter zone 114 of N-type con-ductivity is disposed in body 102 at top ma~or surface 115.
A cathode base zone 116 of P-type conductivity ls disposed in body 102 beneath zone 114 and extending past zone 114 to ma~or surface 115. Anode base zone 118 of N-type conduc-tivity is disposed in body 102 beneath zone 116 and extend-108775~ 45,544 ing past zone 116 to an outer portion of ma~or surface 115.
An anode emitter zone 120 of P-type conductivity is disposed ln body 102 beneath zone 118 and ad~acent to bottom ma~or surface 121. N-type base zone 118 encompasses the periphery 1 of body 102 from top ma~or surface 115 to bottom ma~or surface 121. Cathode electrode 104 is affixed to top ma~or surface 115 in contact with N-type emitter zone 114. Gate electrode 106 is afrixed to top ma~or surface 115 in contact with P-type base zone 116. Anode electrode 10~ is affixed to bottom ma~or surface 121 in contact with P-type emitter zone 120. PN ~unction 123, which separates zones 114 and 116, intersects top ma~or surface 115 in a circle or closed loop. PN ~unction 125, which separates zones 116 and 118, intersects top major surface 115 in a circle or closed loop surrounding the loop of PN junction 123. PN ~unction 127, which separates zones 118 and 120, intersects bottom ma~or surface 121 in a circle or closed loop.
It will be apparent to those skilled in the art from a comparison of device 100 of Figure 3 with prior art device 40 of Figure 2 that field spreaders 110 and 112 increase the blocking capability of PN ~unctions 125 and 127. Since PN ~unction 123 is not a high voltage blocking ~unction, it is not necessary to cover it with a field spreader. Field spreaders 110 and 112 form annular rings on surfaces 115 and 121 overlying PN ~unctions 125 and 127 respectively. Field spreader 110 comprises an insulating layer 130 of silicon dioxide disposed on ma~or surface 115 bridging PN ~unction 125, a resistive layer 132 of poly-crystalline silicon disposed on layer 130, an inner metallic contact 134 disposed on zone 116 and overlapping the inner 45,544 . .
portion of layer 132 in ~uxtaposition over the intersection of PN ~unction 125 with ma~or surface 115, and an outer metallic contact 136 disposed on zone 118 and overlapping the outer portion of layer 132. Field spreader 110 provides a resistive path between N-type base zone 118 and P-type base zone 116, which increases the surface breakdown cap-ability of PN ~unction 125 in a known manner as described above. Similarly, field spreader 112 increases the surface blocking capability of PN ~unction 127, numerals 140, 142, 144 and 146 being analogous to numerals 130, 132, 134 and 136.
Thus, thyristor device 100 of Figure 3 is an example of a structure which is capable of achieving higher forward and reverse blocking voltages than can be achieved by a prior art thyristor such as device 10 shown in Figure 1. However, thyristor device 100 of Figure 3 is impractical for several reasons. Firstly, since wafer 102 is fragile and ls not supported at the periphery on either one of its ma~or surfaces, device 100 is subject to breakage. For example, both prior art devices 10 and 40 have metallic electrodes 18 and 48, which serve the dual purposes of mechanical support as well as electrical contacting. Secondly, device 100 has the impractical aspect of requiring com-plicated masking and deposition on both major surfaces to produce field spreaders 110 and 112.
Now referring to Figure 4, a thyristor device 200 illustrates a presently preferred embodiment of the inven-tion. The thyristor 200 comprises a body or wafer 202 of semiconductor material, metallic electrodes 204 and 208, and electric field spreading member 210. Cathode electrode 204 ~0877S6 45,544 ,,~
i8 dlsposed on top ma~or surface 215 of the wafer 202 in contact wlth cathode emitter zone 214 of N-type conductivity.
Cathode base zone 216 of P-type conductivity ls disposed beneath zone 214 and extending past zone 214 to share a portion of top ma~or surface 215 as shown. Anode base zone 218 of N-type conductivity is disposed beneath zone 216 and extends past zone 216 to top ma~or surface 215. Anode emitter zone 220 of P-type conductivity is disposed beneath zone 218 ad~acent to bottom ma~or surface 221 of the wafer 202 where contact is made with anode electrode 208. P-type anode emitter zone 220 also encompasses the entire periphery of the wafer 202 extending past zone 218 and terminating at the periphery of top ma~or surface 215. It will be recognized that the invention is equally applicable to a thyristor wherein zones 214, 216, 218 and 220 have the opposite con-ductivity shown in Figure 4.
Separating the four zones of alternate conductivity are three PN ~unctions, all of which emerge at top ma~or surface 125. Separating zones 214 and 216 is PN ~unction 223, separating zones 216 and 218 is PN ~unction 225, and separating zones 218 and 220 is PN ~unction 227. PN ~unc-tion 225 serves as the forward blocking ~unction and PN
~unction 227 serves as the reverse blocking ~unction of the thyristor device 200. Unlike PN ~unctions 225 and 227, PN
~unction 223 is not a high voltage blocking ~unction; rather, PN ~unction 223 serves to initiate conduction of the thy-ristor device 200.
As shown in Figure 4, field spreader 210 overlaps both high voltage blocking ~unctions 225 and 227. Field spreader 210 comprises an insulating layer 230 of silicon 1 O 8 ~ 5 6 45~544 dioxlde disposed on top ma~or surface 215, a resistive layer 232 o~ polycrystalline silicon disposed on and conforming to insulating layer 230, and metallic contacts 234 and 236 partially overlapping resistive layer 232 and the ad~acent portions of surface 215. The insulating layer 230 covers anode base zone 218 forming a closed loop on top ma~or surface 215. Inner contact 234 electrically connects resi-stlve layer 232 to zone 216, contact 234 being ~uxtaposed over PN ~unction 225 at its intersection with surface 215.
Outer contact 236 electrically connects resistive layer 232 to zone 220, contact 236 being ~uxtaposed over PN ~unction 227 at its intersection with surface 215. Note that it is not necessary to have a separate gate electrode, since electrode 234 can also perform the gating function.
Reslstive layer 232 provides a resistive path across N-type base zone 218. When the thyristor device 200 is operating in the forward blocking mode, PN ~unction 225 is reverse biased and PN junction 227 is forward biased. As known in the art, there exists a depletion layer around a blocking ~unction which spreads away from the ~unction as the blocking voltage ls increased. Therefore, when device 200 is operating in the forward blocking mode, the depletion layer around PN ~unction 225, along with its corresponding electrical field, spreads in the semiconductor body 202 and along ma~or surface 215 at the portion of surface 215 under ` the field spreading member 210. Resistive layer 232 and inner metallic contact 234 operate to spread the electrical field in a known manner to maximize the surface breakdown voltage of blocking ~unction 225. Likewise, when the device 200 is operating in a reverse blocking mode, PN ~unction 227 _9_ 45,544 ~0~'~75~
ls reverse blased and PN ~unction 225 ls forward blased.
Therefore, ln the reverse blocking mode, field spreader 210 slmllarly serves to maxlmize the surface breakdown voltage of PN ~unctlon 227, in which case outer metalllc contact 236 and resistive layer 232 operate to spread the electric field.
The present invention provides a novel thyristor device having a single field spreader which effectively serves to maximize the surface breakdown capability of both the forward and reverse blocking ~unctions. Furthermore, device 200 is easily manufactured with known techniques since only one ma~or surface requires a field spreader. In addition, device 200 has an anode electrode 208 which sup-ports the semiconductor wafer 202 at its fragile periphery, thereby providing a rigid commercially practlcal device.
It is presently preferred that the semiconductor wafer 202 be circular or disc-shaped and that the PN ~unctions intersect ma~or surface 215 in concentric circles. In such an embodiment, field spreader 210 will appear as an annular ring. It is possible, however, to conceive of a number of different shapes equally suitable to practicing the present lnvention.
For example, in Figure 5 there is shown a plan view of device 200 wherein the semiconductor wafer 202 is in the shape of a quadrangle. In such an embodlment field spreader 210 has straight edges and rounded corners cor-- responding to the intersections of the blocking PN ~unctions with ma~or surface 215. The straight edges are necessary to maximize the active surface area available to cathode elec-trode 204, and the rounded corners are necessary to prevent 108~5~ 45.544 high fleld concentrations. A suitable radlus of curvature at the corners would be about twice the maxlmum spread of the depletlon layer from the blocking ~unctions. In any event, whatever geometrical shape is chosen for device 200, it is only necessary that the field spreader 210 form a closed loop on the semiconductor surface correspondlng to the underlying closed loops delineated by the intersections of the blocking ~unctions with top ma~or surface 215.
Claims (7)
1. A thyristor device comprising:
a body of semiconductor material having first and second opposed major surfaces and comprising a cathode emitter zone of a first conductivity type disposed in said body along said first major surface of said body, a cathode base zone of a second conductivity type disposed in said body adjoining said cathode emitter zone to form a first PN junction therewith and extending past said cathode emitter zone to adjoin a portion of said first major surface, an anode base zone disposed in said body adjoining said cathode base zone to form a second PN
junction therewith and extending past said cathode base zone to adjoin a portion of said first major surface, and an anode emitter zone disposed in said body adjoining said anode base zone and extending past said anode base zone to adjoin a portion of said first major surface, and an anode emitter zone disposed in said body adjoining said anode base zone and extending past said anode base zone to adjoin a portion of said first major surface, said anode emitter zone disposed in said body adjoining said anode base zone to form a third PN junction therewith and adjoining said second major surface of said body;
means for making electrical connections to said body; and means cooperatively disposed adjacent said first major surface bridging said second and third PN junctions for spreading an electrical field in said body when said thyristor device is in a blocking mode.
a body of semiconductor material having first and second opposed major surfaces and comprising a cathode emitter zone of a first conductivity type disposed in said body along said first major surface of said body, a cathode base zone of a second conductivity type disposed in said body adjoining said cathode emitter zone to form a first PN junction therewith and extending past said cathode emitter zone to adjoin a portion of said first major surface, an anode base zone disposed in said body adjoining said cathode base zone to form a second PN
junction therewith and extending past said cathode base zone to adjoin a portion of said first major surface, and an anode emitter zone disposed in said body adjoining said anode base zone and extending past said anode base zone to adjoin a portion of said first major surface, and an anode emitter zone disposed in said body adjoining said anode base zone and extending past said anode base zone to adjoin a portion of said first major surface, said anode emitter zone disposed in said body adjoining said anode base zone to form a third PN junction therewith and adjoining said second major surface of said body;
means for making electrical connections to said body; and means cooperatively disposed adjacent said first major surface bridging said second and third PN junctions for spreading an electrical field in said body when said thyristor device is in a blocking mode.
2. The thyristor device of claim 1 wherein said field spreading means comprises an annular shaped member spanning said anode base zone at said first major surface to provide a resistive path between said cathode base zone and said anode emitter zone.
3. The thyristor device of claim 1 wherein said field spreading means comprises an insulating layer disposed on said first major surface covering said anode base zone and forming a closed loop on said first major surface, a resistive layer disposed on and conforming to the shape of said insulating layer, first conductive means electrically connecting the inner portion of said resistive layer to said cathode base zone, and second conductive means electrically connecting the outer portion of said resistive layer to said anode emitter zone.
4. The thyristor device of claim 3 wherein said insulating layer comprises silicon dioxide, and said resistive layer comprises polycrystalline silicon having a resistivity from about 106 ohm-cm to about 108 ohm-cm.
5. The thyristor device of claim 3 wherein said second PN junction adjoining said first major surface in a closed loop intersection therewith, said first PN junction adjoining said first major surface in a closed loop inter-section therewith, said first conductive means comprises an inner metallic contact disposed on said resistive layer in juxtaposition over said second PN junction, and said second conductive means comprises an outer metallic contact disposed on said resistive layer in juxtaposition over said just PN
junction.
junction.
6. The thyristor of claim 5 wherein said anode emitter zone encompasses the entire peripherial portion of said body of semiconductor material.
7. The thyristor device of claim 1 wherein said means for making electrical connections to said semiconductor body comprise a cathode electrode affixed to said cathode emitter zone at said first major surface of said body, and an anode electrode affixed to said anode emitter zone at said second major surface of said body, said anode electrode supporting the peripheral portion of said body.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US70635576A | 1976-07-19 | 1976-07-19 | |
| US706,355 | 1976-07-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1087756A true CA1087756A (en) | 1980-10-14 |
Family
ID=24837198
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA281,590A Expired CA1087756A (en) | 1976-07-19 | 1977-06-28 | High voltage thyristor |
Country Status (12)
| Country | Link |
|---|---|
| JP (1) | JPS5311586A (en) |
| AU (1) | AU514314B2 (en) |
| BE (1) | BE856827A (en) |
| CA (1) | CA1087756A (en) |
| DE (1) | DE2732360A1 (en) |
| FR (1) | FR2393431A1 (en) |
| GB (1) | GB1585790A (en) |
| IN (1) | IN148931B (en) |
| NL (1) | NL7706586A (en) |
| PL (1) | PL113044B1 (en) |
| SE (1) | SE7708242L (en) |
| ZA (1) | ZA773577B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56154525A (en) * | 1980-04-23 | 1981-11-30 | Mitsubishi Rayon Co | Production of special knot like processed yarn |
| JPS56154527A (en) * | 1980-04-28 | 1981-11-30 | Mitsubishi Rayon Co | Production of special knot like processed yarn |
| US4595941A (en) * | 1980-12-03 | 1986-06-17 | Rca Corporation | Protection circuit for integrated circuit devices |
| US10197999B2 (en) | 2015-10-16 | 2019-02-05 | Lemmings, Llc | Robotic golf caddy |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1539877A1 (en) * | 1965-11-19 | 1969-12-11 | Itt Ind Gmbh Deutsche | Switchable semiconductor component |
| US3432731A (en) * | 1966-10-31 | 1969-03-11 | Fairchild Camera Instr Co | Planar high voltage four layer structures |
| NL7114864A (en) * | 1970-10-30 | 1972-05-03 | ||
| JPS541431B2 (en) * | 1973-12-26 | 1979-01-24 |
-
1977
- 1977-06-14 ZA ZA00773577A patent/ZA773577B/en unknown
- 1977-06-15 NL NL7706586A patent/NL7706586A/en not_active Application Discontinuation
- 1977-06-21 IN IN926/CAL/77A patent/IN148931B/en unknown
- 1977-06-21 AU AU26273/77A patent/AU514314B2/en not_active Expired
- 1977-06-28 CA CA281,590A patent/CA1087756A/en not_active Expired
- 1977-07-13 JP JP8309977A patent/JPS5311586A/en active Pending
- 1977-07-14 BE BE179356A patent/BE856827A/en unknown
- 1977-07-15 SE SE7708242A patent/SE7708242L/en unknown
- 1977-07-18 GB GB30010/77A patent/GB1585790A/en not_active Expired
- 1977-07-18 DE DE19772732360 patent/DE2732360A1/en not_active Withdrawn
- 1977-07-19 PL PL1977199746A patent/PL113044B1/en unknown
- 1977-07-19 FR FR7722122A patent/FR2393431A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| ZA773577B (en) | 1978-05-30 |
| GB1585790A (en) | 1981-03-11 |
| DE2732360A1 (en) | 1978-01-26 |
| PL199746A1 (en) | 1978-03-28 |
| NL7706586A (en) | 1978-01-23 |
| PL113044B1 (en) | 1980-11-29 |
| AU2627377A (en) | 1979-01-04 |
| AU514314B2 (en) | 1981-02-05 |
| IN148931B (en) | 1981-07-25 |
| JPS5311586A (en) | 1978-02-02 |
| BE856827A (en) | 1978-01-16 |
| FR2393431A1 (en) | 1978-12-29 |
| SE7708242L (en) | 1978-01-20 |
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