CA1055165A - Thyristor fired by overvoltage - Google Patents
Thyristor fired by overvoltageInfo
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- CA1055165A CA1055165A CA267,466A CA267466A CA1055165A CA 1055165 A CA1055165 A CA 1055165A CA 267466 A CA267466 A CA 267466A CA 1055165 A CA1055165 A CA 1055165A
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- auxiliary
- extra
- emitter region
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Abstract
IMPROVED THYRISTOR FIRED BY OVERVOLTAGE
ABSTRACT OF THE DISCLOSURE
A thyristor having an auxiliary cathode emitter region disposed in the central portion of the device in PN
junction relationship with a cathode base region is dis-closed. An extra impurity region of the same conductivity type as the cathode base region is disposed in the cathode base region in the central portion of the device inwardly of the outer boundary of the auxiliary cathode emitter. The extra impurity region has a higher impurity density gradient adjacent the common PN junction formed by the cathode and anode base regions than the remainder of such junction.
ABSTRACT OF THE DISCLOSURE
A thyristor having an auxiliary cathode emitter region disposed in the central portion of the device in PN
junction relationship with a cathode base region is dis-closed. An extra impurity region of the same conductivity type as the cathode base region is disposed in the cathode base region in the central portion of the device inwardly of the outer boundary of the auxiliary cathode emitter. The extra impurity region has a higher impurity density gradient adjacent the common PN junction formed by the cathode and anode base regions than the remainder of such junction.
Description
BACKGROUND O~ THE INVENTION
Field of the Invention:
The present invention relates to the firing of thyristors by a forward overvoltage.
Description of the Prior Art:
A thyristor is a solid state four layer PNPN
semiconductor device which supports a high voltage without significant conduction of current when in its high impedance blocking or "off" statej and conducts current when in its low impedance conducting or "on" state. Thyristors are capable of being turned on or fired by causing a threshold emitter current to flow. This cathode emitter current is primarily made up of electrons that are in~ected into the cathode or P-base region. These in;ected electrons induce anode-to-cathode current to flow and the thyrlstor flres by regenerative actlon. Thyristors may be either of the two termlnal or three termlnal types. In the three termlnal -1- ~
', ', ' ''' ' ' "''"' "''. " ,,. ' , '' ' ' '-, ' ' '' ', ' '' " ' ' , ' ' ' , , ' ' , ,, ' ~
46,244 1~)55165 type of thyristor, the cathode emitter current that causes the thyristor to fire is generated by applying a forward voltage between its cathode electrode connected to its cathode emitter layer or region and its gate electrode con-nected to its cathode base region. In two termlnal thyris-tors, this cathode emitter current flows through the anode emitter. Thus, the difference between the two terminal and three terminal types of thyristor is primarily a matter of the manner in which the cathode emitter current which causes the thyristor to fire, ls generated. In the case of the two termlnal type, thls cathode emltter current is generated by elther of two means. The current can be created by increas-ing the anode-to-cathode voltage to the polnt at which the blocking PN ~unctlon (l.e., the ~unction between the cathode base and the anode base) loses lts blocklng ablllty (over-voltage) and starts to permlt current flow. Thls usually occurs at the avalanche voltage of the blocking PN ~unctlon.
Or, the emltter cathode current that flres the devlce can be generated by means of a rapidly lncreasing anode to cathode voltage that causes a displacement current to flow as the depletlon layer capacitance of the ~unction between the cathode base and anode base changes its charge.
Commerclally avallable two termlnal thyristors are somewhat deficlent ln that they turn on at some randomly located non-predetermlned polnt, the location of which depends on uncontrolled nonunlformities ln the device. Such nonuniformitles can make the performance of the device nonreproducible and cause it to be sub~ect to unnecessary swltchlng losses; and also sub~ect to failure. The unneces-sary swltchlng losses are related to the fact that the area
Field of the Invention:
The present invention relates to the firing of thyristors by a forward overvoltage.
Description of the Prior Art:
A thyristor is a solid state four layer PNPN
semiconductor device which supports a high voltage without significant conduction of current when in its high impedance blocking or "off" statej and conducts current when in its low impedance conducting or "on" state. Thyristors are capable of being turned on or fired by causing a threshold emitter current to flow. This cathode emitter current is primarily made up of electrons that are in~ected into the cathode or P-base region. These in;ected electrons induce anode-to-cathode current to flow and the thyrlstor flres by regenerative actlon. Thyristors may be either of the two termlnal or three termlnal types. In the three termlnal -1- ~
', ', ' ''' ' ' "''"' "''. " ,,. ' , '' ' ' '-, ' ' '' ', ' '' " ' ' , ' ' ' , , ' ' , ,, ' ~
46,244 1~)55165 type of thyristor, the cathode emitter current that causes the thyristor to fire is generated by applying a forward voltage between its cathode electrode connected to its cathode emitter layer or region and its gate electrode con-nected to its cathode base region. In two termlnal thyris-tors, this cathode emitter current flows through the anode emitter. Thus, the difference between the two terminal and three terminal types of thyristor is primarily a matter of the manner in which the cathode emitter current which causes the thyristor to fire, ls generated. In the case of the two termlnal type, thls cathode emltter current is generated by elther of two means. The current can be created by increas-ing the anode-to-cathode voltage to the polnt at which the blocking PN ~unctlon (l.e., the ~unction between the cathode base and the anode base) loses lts blocklng ablllty (over-voltage) and starts to permlt current flow. Thls usually occurs at the avalanche voltage of the blocking PN ~unctlon.
Or, the emltter cathode current that flres the devlce can be generated by means of a rapidly lncreasing anode to cathode voltage that causes a displacement current to flow as the depletlon layer capacitance of the ~unction between the cathode base and anode base changes its charge.
Commerclally avallable two termlnal thyristors are somewhat deficlent ln that they turn on at some randomly located non-predetermlned polnt, the location of which depends on uncontrolled nonunlformities ln the device. Such nonuniformitles can make the performance of the device nonreproducible and cause it to be sub~ect to unnecessary swltchlng losses; and also sub~ect to failure. The unneces-sary swltchlng losses are related to the fact that the area
-2-,. . .
.
46,244 of the initial turn-on nf the device is uncontrolled and larger than necessary. Thus, the build-up of current and charge denslty is slower than necessary. It ls understood that switching losses are decreased by increasing the speed of turn-on of any thyristor.
In three terminal thyristors, it is known that the switching speed and losses are improved by building a small pilot thyristor within the area of the thyristor device. A
glven gate drive current, in this case, fires the small area pilot thyristor rapidly; and this, in turn, provides from the anode circuik, a large drive current that, in turn, flres the main thyristor rapidly and efficlently. However, - -` even three terminal devices may be fired, intentionally or unintentiona11y, by the application of an overvoltage be-tween its anode and cathode elec~rodes in the same manner as the two terminal deviçe.
Thus, it has been proposed that a pilot thyristor may be utilized in a two terminal device to provide for more rapid flring or turn-on. In addition, various structures have been proposed to insure that the pilot thyristor fires prior to the firing of the main thyristor in response to an overvoltage.
For example, in U.S. Patent 3,766,450 there ls shown a three terminal thyrlstor with an auxlllary thyristor portion centrally located in the device where the portion of the anode base underlying the central portion of the cathode base to which the gate electrode is connected i~ formed with a higher lmpurity concentration than that of the anode base ; portlon lylng outwardly of ~uch area. In thi~ manner, the patent 3,766,450 teache~ that the application of a voltage , " . : . . . .
46,244 applied across the main anode to cathode terminals of the thyristor which exceeds the forward breakdown voltage ln-sures that the auxiliary emitter is triggered ahead of the main emitter of the device. Also, U.S. Patent No. 3,774,085 shows a three terminal thyristor, without an auxiliary thy-rlstor portlon, the anode or N-base whlch has an area of higher impurity concentration below the cathode and gate electrodes than that concentratlon of the N-base sltuated outwardly of the selected area ln order that the thyristor i9 gated or triggered within an area encompassed by the electrodes when a breakover voltage i5 applied to the anode electrode. Although such proposed devlces provlded advan-tages in the operation of a thyristor in response to an overvoltage, it is realized that they are difficult to manufacture, ln that the region of hlgher lmpurlty concen-tratlon had to be present in the starting slice. Thls is dlfflcult to produce. In the prlor art the higher impurity --concentration region ~s the result of natural area nonuni-formities that occur when the ingot is grown. These are difficult to control.
In U.S. Patent No. 3,906,545, there is shown a three terminal thyristor devlce that utilizes a higher impu-rity reglon within the cathode base of the devlce of the same conductlvlty type. In this prior art devlce, the hlgher doped P base reglon extends in the form of a plura-llty of narrow paths which emanate ~rom the gate electrode and spread over the entire cross-sectional area of the gate zone. The apparent ob~ective of that lnvention is to decrea e lateral reslstance in the cathode base, and would not effect the breakdown voltage of the ~unction between the .
46,244 1~55165 cathode and anode bases.
Thus, it is desirable to provide a thyristor that may be either of the two terminal or three terminal type;
and may be fired either intentionally or unintentionally, by overvoltage, with low swltching losses, and in a predlctable manner, and without danger of degrading or failure of the devlce. At the same time, it ls desirable that such devlce be practlcal to manufacture and slmple ln its deslgn.
In accordance wlth the present lnventlon, and ln 10 contrast to the known prior art, a two termlnal thyrlstor devlce has a centrally located auxlllary emltter portlon with an extra P type diffusion in the cathode base reglon, located wlthin the outer boundarles of such auxlllary emltter , portion which locally decreases the avalanche voltage i somewhat; and serves the purpose of insuring that in res-ponse to a high forward voltage, the avalanche will occur in the area of the extra diffusion. Further, in keeping with the invention, either a two or a three terminal device may include an additlonal P type diffusion layer in the cathode 20 base ln the central portion of the device and slightly ! overlap the lnner boundarles of the auxiliary emitter. Thls extra diffusion layer has a higher dopant density gradlent, - -~
ad~acent lts ~unction with the anode base, than the regular P type diffusion layer that is outslde of the extra dif-fusion region. Thls also insures that the avalanche wlll occur along the lnner edge of the auxlliary emltter in an area where lts electrlc field is highe~t ln depletion layer at the ~unction between lts cathode and anode bases. This J provldes for a further advantage ln that addltional carrlers
.
46,244 of the initial turn-on nf the device is uncontrolled and larger than necessary. Thus, the build-up of current and charge denslty is slower than necessary. It ls understood that switching losses are decreased by increasing the speed of turn-on of any thyristor.
In three terminal thyristors, it is known that the switching speed and losses are improved by building a small pilot thyristor within the area of the thyristor device. A
glven gate drive current, in this case, fires the small area pilot thyristor rapidly; and this, in turn, provides from the anode circuik, a large drive current that, in turn, flres the main thyristor rapidly and efficlently. However, - -` even three terminal devices may be fired, intentionally or unintentiona11y, by the application of an overvoltage be-tween its anode and cathode elec~rodes in the same manner as the two terminal deviçe.
Thus, it has been proposed that a pilot thyristor may be utilized in a two terminal device to provide for more rapid flring or turn-on. In addition, various structures have been proposed to insure that the pilot thyristor fires prior to the firing of the main thyristor in response to an overvoltage.
For example, in U.S. Patent 3,766,450 there ls shown a three terminal thyrlstor with an auxlllary thyristor portion centrally located in the device where the portion of the anode base underlying the central portion of the cathode base to which the gate electrode is connected i~ formed with a higher lmpurity concentration than that of the anode base ; portlon lylng outwardly of ~uch area. In thi~ manner, the patent 3,766,450 teache~ that the application of a voltage , " . : . . . .
46,244 applied across the main anode to cathode terminals of the thyristor which exceeds the forward breakdown voltage ln-sures that the auxiliary emitter is triggered ahead of the main emitter of the device. Also, U.S. Patent No. 3,774,085 shows a three terminal thyristor, without an auxiliary thy-rlstor portlon, the anode or N-base whlch has an area of higher impurity concentration below the cathode and gate electrodes than that concentratlon of the N-base sltuated outwardly of the selected area ln order that the thyristor i9 gated or triggered within an area encompassed by the electrodes when a breakover voltage i5 applied to the anode electrode. Although such proposed devlces provlded advan-tages in the operation of a thyristor in response to an overvoltage, it is realized that they are difficult to manufacture, ln that the region of hlgher lmpurlty concen-tratlon had to be present in the starting slice. Thls is dlfflcult to produce. In the prlor art the higher impurity --concentration region ~s the result of natural area nonuni-formities that occur when the ingot is grown. These are difficult to control.
In U.S. Patent No. 3,906,545, there is shown a three terminal thyristor devlce that utilizes a higher impu-rity reglon within the cathode base of the devlce of the same conductlvlty type. In this prior art devlce, the hlgher doped P base reglon extends in the form of a plura-llty of narrow paths which emanate ~rom the gate electrode and spread over the entire cross-sectional area of the gate zone. The apparent ob~ective of that lnvention is to decrea e lateral reslstance in the cathode base, and would not effect the breakdown voltage of the ~unction between the .
46,244 1~55165 cathode and anode bases.
Thus, it is desirable to provide a thyristor that may be either of the two terminal or three terminal type;
and may be fired either intentionally or unintentionally, by overvoltage, with low swltching losses, and in a predlctable manner, and without danger of degrading or failure of the devlce. At the same time, it ls desirable that such devlce be practlcal to manufacture and slmple ln its deslgn.
In accordance wlth the present lnventlon, and ln 10 contrast to the known prior art, a two termlnal thyrlstor devlce has a centrally located auxlllary emltter portlon with an extra P type diffusion in the cathode base reglon, located wlthin the outer boundarles of such auxlllary emltter , portion which locally decreases the avalanche voltage i somewhat; and serves the purpose of insuring that in res-ponse to a high forward voltage, the avalanche will occur in the area of the extra diffusion. Further, in keeping with the invention, either a two or a three terminal device may include an additlonal P type diffusion layer in the cathode 20 base ln the central portion of the device and slightly ! overlap the lnner boundarles of the auxiliary emitter. Thls extra diffusion layer has a higher dopant density gradlent, - -~
ad~acent lts ~unction with the anode base, than the regular P type diffusion layer that is outslde of the extra dif-fusion region. Thls also insures that the avalanche wlll occur along the lnner edge of the auxlliary emltter in an area where lts electrlc field is highe~t ln depletion layer at the ~unction between lts cathode and anode bases. This J provldes for a further advantage ln that addltional carrlers
3~ can be generated by carrler multipllcation.
, . .. .
, .. . . . .
46,244 ~OS5165 In contrast to the prior art, by maklng the diffused forward blocking PN ~unction more abrupt, rather than changing the dopant density in the anode base, the reduction in breakdown voltage is more easily kept small and reproducible. In princlple, one should decrease the break-down voltage only enough to bring lt below the lowest break-down voltage that would occur without the bene~it of the present invention. A decrease in breakdown voltage beyond that nece~sary to lnsure that the deslgnated region has the lowest breakdown voltage, needlessly degrades the perform-ance o~ the thyrlstor. Because most o~ the breakdown voltage ls supported ln the depletlon layer ln the anode .
base region, changes ln the cathode base produce only small, albeit adequate, decre~ses in the breakdown voltage. Hence, large process varlatlons produce small changes ln the break-down voltage, and thls lncreases the manufacturability of the devlce. ~ -; SUMMARY OF THE INV~NTION
Broadly, the present invention relates to a thyristor that may be fired in response to a predetermined forward voltage such that its performance ls reproducible and operates with low switching loss and without being -sub~ected to failure because o~ uncontrolled turn-on. The devlce lncludes a body of semlconductor material that has first and second outer surfaces with four lmpurity regions of alternate conductivity type disposed in PN ~unction relatlonship. The reglons lnclude a cathode emltter and a cathode base. Each cathode emltter region and the cathode ba8e reglon has a surface formlng a portlon of the flr~t outer surface of the bod~. The reglons also include an ,, , ~ , , / ,,.: ................................. . . .
,",, , . ,, , " , " , ~..... .. . .. .
46,244 1~55165 anode base region and an anode emitter region. The anodeemitter region has a surface forming at least a portion of the second outer surface of the body. The cathode emitter region includes an inner and outer portion. The surface of the inner portion forms the central portlon of the first outer surface, and has an outer boundary of a predetermined dimension. The outer portion is radially spaced from the outer boundary of the inner portion to form another portion of the first outer surface with at least a portion of the cathode base regions forming the outer surface of the body between the inner and outer cathode emitter regions. An ; extra impurity region of the same conductivity type as the cathode base region is disposed in the cathode base region centrally of the outer boundary of the inner cathode emitter region portion. The extra impurity region has a higher lmpurity density gradient, ad~acent the PN ~unction formed by the cathode and anode base regions, than the gradlent of said PN ~unction radially spaced from the extra impurity region.
A metallic electrode is in contact with the first outer surface and is disposed overlying the PN ~unction formed at the outer boundary of the inner cathode emitter portion and the cathode base region. Also, a metallic cathode electrode is in ohmic contact with the first outer surface formed by the outer cathode emitter region; and a metallic anode electrode is in ohmic contact with the second Outer ~urface formed by the anode emitter region.
Thus, a predetermined overvoltage applied to the anode electrode causes the device to avalanche inltially in the area of the extra P type region of the cathode base 46,244 region.
Speclfically, in one embodlment where the inner cathode emitter region is annular in conflguratlon, the outer boundary of the extra P type diffuslon in the cathode base region is so dimensioned that it intersects the lnner cathode emitter region intermediate its inner and outer boundarles. Preferably, the inner boundary of the extra impurity region is close to, but out of alignment with, the inner boundary of the inner cathode emitter region.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan vlew of a thyristor according to one embodiment of the invention with metallic electrodes cut away to show the diffusion pattern;
Fig. 2 is an elevation of Fig. 1 taken on llne 22 of Fig. l;
Fig. 3 is an elevation of another embodiment of the lnventlon having a rlng shaped auxlllary emltter; ~
Flg. 4 is stlll another embodiment of the inven- -tlon lllustrating an alternate pattern for the extra P type --~
20 dlffuslon; and, Fig. 5 is yet another embodiment of the invention illustrating the extra diffusion pattern in a ring shaped conflguratlon with a gate electrode for u~e as a three ter- ;~ -i mlnal device.
` DESCRIPTION OF THE PREFERRED EMBODIMENTS
t Referring to Figures 1 and 2, a semlconductor body j lO 18 provlded for forming the thyristor adapted to ~lre in response to overvoltage in accordance wlth one embodiment of the present lnventlon. The semlconductor body 10 ls typi-30 cally a commercially avallable~ single crystal sllicon wafer .1, ,, . , ~ ~ , . .
., ,, , `,, : :
46,244 of circular shape having a thickness typlcally o~ about 10 to 20 mils, and having first and second opposed outer surfaces 11 and 12, respectively. Provided in the seml-conductor body 10 are suitable impurities, to form impurity reglons 13, 14, 15, and 18 of alternate type conductivity.
The impurity region 13 is an anode emitter region, a surface of which forms the outer surface 12. The impurity region 14 is disposed in the body 10 ad~acent the anode emitter region 13 at ~unction 16 to form an anode base reglon. The impur-ity region 15 ad~oins the anode base region 14 at ~unctlon17 to form a cathode base region. The cathode emitter region 18 includes an inner or auxiliary cathode emitter portion 20, and an outer or main cathode emitter portion 21.
The maln cathode emitter portion 21 has an inner boundary 22 and forms a portion of the first outer surface 11 radially spaced from the auxiliary cathode emitter portion 20 with a portion of the cathode base region forming the first outer surface of the body between the inner edge 22 of the main cathode emitter and an outer edge 23 of the auxiliary cath-ode emitter. The outer main P base 15 has portions 19 thatextend to the first outer surface 11 to provide an emitter shunt configuration. In the embodiment of Figures 1 and 2, the auxiliary cathode emitter region 20 is disc shaped and forms the central portion of the outer surface 11 of the body 10. A ring shaped or annularly configurated cathode electrode 24 overlies and is in ohmic contact with the outer or maln cathode emitter reglon 21 and the portions 19 of the cathode base 15j and to which a suitable cathode terminal represented at 25 is connected. An inner ring shaped metal-llc electrode 26 overlies and is in ohmic contact with a PN
_g_ . .
46,244 lOS5165 ~unctlon formed by the outer boundary 23 of the auxlliary cathode emitter 20 and the contlguous portion of the cathode base 15. The metallic electrode 26 is so dimensioned that its outer boundary is spaced radially inward from the inner boundary 22 of the main cathode emltter region 21. The metalllc electrode 26 provides a path for current from an anode electrode 27 through the auxlllary cathode emltter 20 to the main cathode electrode 25. The anode electrode 27 is in ohmic contact with the anode emitter region 13 and has a suitable anode terminal referred to at 28.
Symmetrically located ad~acent the center o~ the body lO and the auxiliary cathode emitter 20 is an extra P
type diffusion reglon 30 that is cyllndrical in configura-tion and extends from the upper surface ll of the body lO to - the PN ~unction 17 between the cathode base region 15 and the anode base reglon 14. This extra diffusion portlon 30 ls formed to have a higher impurity density gradient withln , .- .
an outer boundary 31 at the central or forward blocking PN
~unction 17, than exists at the central or forward blocklng ~unction 17 outside of the extra diffusion 30. It is well known that a higher impurlty density gradient decreases the -~
. avalanche breakdown voltage. This decreased avalanche breakdown voltage provides the means for insuring that the :-, thyristor will avalanche first in this central predetermined j locatlon deflned by the extra dif~usion reglon 30. The ~ -central dlffusion layer 30, which of course ls of the same lmpurity type as the cathode base reglon, ls created by an additlonal masked dlffuslon with a species such as boron that ha~ a hlgh solld solubillty so that it can have a hlgher 8urface concentration than the P type dlffu~lon 46,244 l~SS165 surrounding the extra dlffusion region 30 over the remaining portion of the device. Typically, the surface density of the central diffusion layer 30 might be 102 boron atoms/cc, while that of the P type diffusion layer 15 outslde of the region 30 would be typically 1 to 10 x 1017 atoms/cc. The depth of the central diffusion layer is roughly the same (within 5 microns) as that o~ the main P type diPfusion layer. If the central layer 30 is too shallow, lt ls not effective for decreasing the breakdown voltage. If it is too deep, it decreases the breakdown voltage unnecessarily beyond that needed to insure that the initial area to break down is in this central region occupied by the extra P type diffusion layer 30. The diameter of this central diffusion layer 30 is roughly 10 to 20 mils.
Referring to the embodiment of Figure 3, the body 10 ls similar to the body 10 of Figure 2 and bears simllar reference numerals for identical parts thereof. However, in the embodiment of Figure 3, an auxiliary emitter portion 35 is annular in configuration instead of being circular or disc shaped such as the auxiliary cathode emitter 20 of Figure 2. The auxiliary cathode emitter 35 surrounds the extra P layer 30 in the cathode base region 15. The extra P
` diffusion 30 in the embodiment of Figure 3 has its outer boundary spaced from an inner boundary 36 of the auxillary emitter 35 and extends from ad~acent the PN ~unction 17 to the first other surface 11 without intersecting the aux-: illary cathode emitter 35.
Both the auxiliary cathode emitter 20 of Figure 2 and the auxlliary cathode emltter 35 of Fi~ure 3 can be made smaller than the auxlliary cathode commonly used in three , ` 46,244 lOS5~65 terminal devices since there is no need to contact this central region surrounded by the cathode emitter 35 with a gate electrode. By making the auxiliary emitter smaller, more area is left on the device ~or the main current carry-ing cathode emitter 24. In the event it is desired to construct a device which may include a gate electrode in contact with the P base region 15 centrally of the auxiliary cathode emitter 35, the outer diameter o~ the cathode emit-ter ~5 may be 140 mils, and the inner diameter of the cath-ode emitter 35 may be 100 mils, for example. This gives room for a central contact that can easily be fabricated within the package with an economical alignment method. In the event that the device is designed so that no contact ls needed, the aforesaid inner and outer diameters of the auxiliary cathode emitter 35 may be made much smaller. In -fact, the diameter of the inner boundary o~ the auxlliary cathode emitter may be only a ~ew mils larger than the diameter of the central dif~used region 30. The outer diameter of the auxiliary cathode emitter 35 should then be about 30 to 60% larger than the inner diameter. This provides for a resistance in the cathode base under the small auxiliary cathode emitter 35 that allows for e~ficient operation of the auxiliary cathode. With reference to Figure 2, where the auxiliary cathode emitter is disc shaped, the diameter could be in the neighborhood of 40 to 100 mils. For this embodiment, the outer diameter of the auxlllary cathode emitter 20 could be larger to yield a somewhat hlgher resistance to compensate for the ~act that at a given current density, the current galn might be de-creased by the hlgher dopant denslty o~ the cathode base 15.
.
46,244 . ., If desired, this decreased current gain may be avolded by diffusing the auxillary cathode emitter region 20 deeper than that of the main cathode emitter region 21.
With reference to the embodiment illustrated in Figure 4, the body 10 is slmilar to that described ln con-nection wlth Figures 1, 2 and 3 and bears slmllar reference numerals for llke parts of the devlce. However, ln thls embodlment, an extra lmpurlty reglon 40 whlch has a hlgher impurity denslty gradient ad~acent to PN ~unction 17 formed by the cathode and anode base regions 15 and 14, respec-tively, is circular or disc shaped and has an outer peri-pheral boundary 41 that intersects the auxlliary cathode i emitter 35 close to lts lnner boundary or ~unctlon 36.
Thus, the lnner boundary 36 of region 35 ls located entlrely wlthin the extra impurlty reglon 40. Thls has the advantage in that the in~ection of electrons from the auxlliary cathode emitter 35 occurs ln the area of the devlce in whlch the electric fields in the central blocking ~unctlon 17 are the hlghest. To assure thls, the area of overlap between ~ -the diffused cathode emitter region 35 and the extra im-purity region 40 in the cathode base 15 should be kept small. However, the additional P type impurity reglon 40 should not have lts perlphery allgned exactly wlth the inner boundary 36 of the auxiliary cathode emitter 35 because ln this case not all of the emitted electrons will flow in the region in whlch this electrlc field is highest.
Referring to Figure 5, the body 10 is slmllar to the device de~cribed in connection with the previously des-cribed figureg with like parts bearing similar reference nu-merals. However, thls embodlment i8 included to illustrate 46,244 the disposition of a gate electrode 45 such that the device can be used as a three terminal device if desired with the region of hlgher impurity in the cathode or P base 15 pro-viding protection agalnst overvoltage. Although the gate electrode 45 could be used with the extra impurlty region 40 whlch is circular in configuration, this embodlment illus-trates an annularly configured higher impurity region 46 which has an inner boundary 47 and an outer boundary 48. In this embodiment, the outer boundary 48 should be kept as closely as possible to the inner boundary 36 of the auxi-liary cathode emitter 35 for the same reason discussed in the disposition of a gate electrode 45 such that the device can be used as a three terminal device if desired with the region of higher impurity ln the cathode or P base 15 pro- :
viding protection against overvoltage. Although the gate electrode 45 could be used with the extra impurity reglon 40 which is circular in configuration, this embodiment illus-trates an annularly configured higher impurity region 46 which has an inner boundary 47 and an outer boundary 48. In this embodiment, the outer boundary 48 should be kept as closely as possible to the inner boundary 36 of the auxi-: liary cathode emitter 35 for the same reason discussed in connection with Figure 4. It is also understood, that the - annular region 46 may be utilized without the gate electrode 45.
Thus, it is seen that I have provlded an improved thyristor which may be utilized in applications where the devlce ls flred by a predetermlned high anode to cathode voltage or in applications where it is desired to protect 3o the device against inadvertent firing by a high anode to : -14-. .
,: ' ' ' ' 46,244 cathode voltage; which device has a low switching loss and ls capable of belng used in a series of two and three terminal silicon switches and thereby decreasing the amount of gate drive circuitry needed. Since the central region used to locally decrease the breakdown voltage ls a dlf-fusion layer that is added near the end of the fabrication processing sequence instead of being present in the starting material, there is a much sharper boundary to the higher doped region in the finished device. Also, it is much simpler to add one or more extra dlffuslons through the external surface than to construct the device wlth a hlgher dopant denslty localized wlthin the starting slice. Fur-ther, because the region is formed by a masked diffusion, it is much easier to align such region properly with the auxiliary cathode emitter.
While the invention has been specifically des-cribed in connection with several preferred embodlments, lt is distinctly understood that the lnvention may be otherwise variously embodled with alternate configurations of the metallic electrode 26 and the metallic electrode 24, such as provlding radially extending fingers ln the electrode 26 with corresponding recesses in the electrode 24 to provide for lnterdigitation, for example; or the electrode 26 in the embodlment of Flgures 1 through 4 may be disc shaped. Also, varlou~ other cathode shunt or shorted emltter configura-tlons may be utllized, and the relative dimenslonæ and conflguratlons wlth respect to the extra dlffusion of higher P type impurltles relatlve to the dlameter o~ the auxlllary cathode emltter may be varled in accordance wlth the teach-lngs of the pre~ent lnventlon and s¢ope of the appended ¢lalm~.
, . .. .
, .. . . . .
46,244 ~OS5165 In contrast to the prior art, by maklng the diffused forward blocking PN ~unction more abrupt, rather than changing the dopant density in the anode base, the reduction in breakdown voltage is more easily kept small and reproducible. In princlple, one should decrease the break-down voltage only enough to bring lt below the lowest break-down voltage that would occur without the bene~it of the present invention. A decrease in breakdown voltage beyond that nece~sary to lnsure that the deslgnated region has the lowest breakdown voltage, needlessly degrades the perform-ance o~ the thyrlstor. Because most o~ the breakdown voltage ls supported ln the depletlon layer ln the anode .
base region, changes ln the cathode base produce only small, albeit adequate, decre~ses in the breakdown voltage. Hence, large process varlatlons produce small changes ln the break-down voltage, and thls lncreases the manufacturability of the devlce. ~ -; SUMMARY OF THE INV~NTION
Broadly, the present invention relates to a thyristor that may be fired in response to a predetermined forward voltage such that its performance ls reproducible and operates with low switching loss and without being -sub~ected to failure because o~ uncontrolled turn-on. The devlce lncludes a body of semlconductor material that has first and second outer surfaces with four lmpurity regions of alternate conductivity type disposed in PN ~unction relatlonship. The reglons lnclude a cathode emltter and a cathode base. Each cathode emltter region and the cathode ba8e reglon has a surface formlng a portlon of the flr~t outer surface of the bod~. The reglons also include an ,, , ~ , , / ,,.: ................................. . . .
,",, , . ,, , " , " , ~..... .. . .. .
46,244 1~55165 anode base region and an anode emitter region. The anodeemitter region has a surface forming at least a portion of the second outer surface of the body. The cathode emitter region includes an inner and outer portion. The surface of the inner portion forms the central portlon of the first outer surface, and has an outer boundary of a predetermined dimension. The outer portion is radially spaced from the outer boundary of the inner portion to form another portion of the first outer surface with at least a portion of the cathode base regions forming the outer surface of the body between the inner and outer cathode emitter regions. An ; extra impurity region of the same conductivity type as the cathode base region is disposed in the cathode base region centrally of the outer boundary of the inner cathode emitter region portion. The extra impurity region has a higher lmpurity density gradient, ad~acent the PN ~unction formed by the cathode and anode base regions, than the gradlent of said PN ~unction radially spaced from the extra impurity region.
A metallic electrode is in contact with the first outer surface and is disposed overlying the PN ~unction formed at the outer boundary of the inner cathode emitter portion and the cathode base region. Also, a metallic cathode electrode is in ohmic contact with the first outer surface formed by the outer cathode emitter region; and a metallic anode electrode is in ohmic contact with the second Outer ~urface formed by the anode emitter region.
Thus, a predetermined overvoltage applied to the anode electrode causes the device to avalanche inltially in the area of the extra P type region of the cathode base 46,244 region.
Speclfically, in one embodlment where the inner cathode emitter region is annular in conflguratlon, the outer boundary of the extra P type diffuslon in the cathode base region is so dimensioned that it intersects the lnner cathode emitter region intermediate its inner and outer boundarles. Preferably, the inner boundary of the extra impurity region is close to, but out of alignment with, the inner boundary of the inner cathode emitter region.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan vlew of a thyristor according to one embodiment of the invention with metallic electrodes cut away to show the diffusion pattern;
Fig. 2 is an elevation of Fig. 1 taken on llne 22 of Fig. l;
Fig. 3 is an elevation of another embodiment of the lnventlon having a rlng shaped auxlllary emltter; ~
Flg. 4 is stlll another embodiment of the inven- -tlon lllustrating an alternate pattern for the extra P type --~
20 dlffuslon; and, Fig. 5 is yet another embodiment of the invention illustrating the extra diffusion pattern in a ring shaped conflguratlon with a gate electrode for u~e as a three ter- ;~ -i mlnal device.
` DESCRIPTION OF THE PREFERRED EMBODIMENTS
t Referring to Figures 1 and 2, a semlconductor body j lO 18 provlded for forming the thyristor adapted to ~lre in response to overvoltage in accordance wlth one embodiment of the present lnventlon. The semlconductor body 10 ls typi-30 cally a commercially avallable~ single crystal sllicon wafer .1, ,, . , ~ ~ , . .
., ,, , `,, : :
46,244 of circular shape having a thickness typlcally o~ about 10 to 20 mils, and having first and second opposed outer surfaces 11 and 12, respectively. Provided in the seml-conductor body 10 are suitable impurities, to form impurity reglons 13, 14, 15, and 18 of alternate type conductivity.
The impurity region 13 is an anode emitter region, a surface of which forms the outer surface 12. The impurity region 14 is disposed in the body 10 ad~acent the anode emitter region 13 at ~unction 16 to form an anode base reglon. The impur-ity region 15 ad~oins the anode base region 14 at ~unctlon17 to form a cathode base region. The cathode emitter region 18 includes an inner or auxiliary cathode emitter portion 20, and an outer or main cathode emitter portion 21.
The maln cathode emitter portion 21 has an inner boundary 22 and forms a portion of the first outer surface 11 radially spaced from the auxiliary cathode emitter portion 20 with a portion of the cathode base region forming the first outer surface of the body between the inner edge 22 of the main cathode emitter and an outer edge 23 of the auxiliary cath-ode emitter. The outer main P base 15 has portions 19 thatextend to the first outer surface 11 to provide an emitter shunt configuration. In the embodiment of Figures 1 and 2, the auxiliary cathode emitter region 20 is disc shaped and forms the central portion of the outer surface 11 of the body 10. A ring shaped or annularly configurated cathode electrode 24 overlies and is in ohmic contact with the outer or maln cathode emitter reglon 21 and the portions 19 of the cathode base 15j and to which a suitable cathode terminal represented at 25 is connected. An inner ring shaped metal-llc electrode 26 overlies and is in ohmic contact with a PN
_g_ . .
46,244 lOS5165 ~unctlon formed by the outer boundary 23 of the auxlliary cathode emitter 20 and the contlguous portion of the cathode base 15. The metallic electrode 26 is so dimensioned that its outer boundary is spaced radially inward from the inner boundary 22 of the main cathode emltter region 21. The metalllc electrode 26 provides a path for current from an anode electrode 27 through the auxlllary cathode emltter 20 to the main cathode electrode 25. The anode electrode 27 is in ohmic contact with the anode emitter region 13 and has a suitable anode terminal referred to at 28.
Symmetrically located ad~acent the center o~ the body lO and the auxiliary cathode emitter 20 is an extra P
type diffusion reglon 30 that is cyllndrical in configura-tion and extends from the upper surface ll of the body lO to - the PN ~unction 17 between the cathode base region 15 and the anode base reglon 14. This extra diffusion portlon 30 ls formed to have a higher impurity density gradient withln , .- .
an outer boundary 31 at the central or forward blocking PN
~unction 17, than exists at the central or forward blocklng ~unction 17 outside of the extra diffusion 30. It is well known that a higher impurlty density gradient decreases the -~
. avalanche breakdown voltage. This decreased avalanche breakdown voltage provides the means for insuring that the :-, thyristor will avalanche first in this central predetermined j locatlon deflned by the extra dif~usion reglon 30. The ~ -central dlffusion layer 30, which of course ls of the same lmpurity type as the cathode base reglon, ls created by an additlonal masked dlffuslon with a species such as boron that ha~ a hlgh solld solubillty so that it can have a hlgher 8urface concentration than the P type dlffu~lon 46,244 l~SS165 surrounding the extra dlffusion region 30 over the remaining portion of the device. Typically, the surface density of the central diffusion layer 30 might be 102 boron atoms/cc, while that of the P type diffusion layer 15 outslde of the region 30 would be typically 1 to 10 x 1017 atoms/cc. The depth of the central diffusion layer is roughly the same (within 5 microns) as that o~ the main P type diPfusion layer. If the central layer 30 is too shallow, lt ls not effective for decreasing the breakdown voltage. If it is too deep, it decreases the breakdown voltage unnecessarily beyond that needed to insure that the initial area to break down is in this central region occupied by the extra P type diffusion layer 30. The diameter of this central diffusion layer 30 is roughly 10 to 20 mils.
Referring to the embodiment of Figure 3, the body 10 ls similar to the body 10 of Figure 2 and bears simllar reference numerals for identical parts thereof. However, in the embodiment of Figure 3, an auxiliary emitter portion 35 is annular in configuration instead of being circular or disc shaped such as the auxiliary cathode emitter 20 of Figure 2. The auxiliary cathode emitter 35 surrounds the extra P layer 30 in the cathode base region 15. The extra P
` diffusion 30 in the embodiment of Figure 3 has its outer boundary spaced from an inner boundary 36 of the auxillary emitter 35 and extends from ad~acent the PN ~unction 17 to the first other surface 11 without intersecting the aux-: illary cathode emitter 35.
Both the auxiliary cathode emitter 20 of Figure 2 and the auxlliary cathode emltter 35 of Fi~ure 3 can be made smaller than the auxlliary cathode commonly used in three , ` 46,244 lOS5~65 terminal devices since there is no need to contact this central region surrounded by the cathode emitter 35 with a gate electrode. By making the auxiliary emitter smaller, more area is left on the device ~or the main current carry-ing cathode emitter 24. In the event it is desired to construct a device which may include a gate electrode in contact with the P base region 15 centrally of the auxiliary cathode emitter 35, the outer diameter o~ the cathode emit-ter ~5 may be 140 mils, and the inner diameter of the cath-ode emitter 35 may be 100 mils, for example. This gives room for a central contact that can easily be fabricated within the package with an economical alignment method. In the event that the device is designed so that no contact ls needed, the aforesaid inner and outer diameters of the auxiliary cathode emitter 35 may be made much smaller. In -fact, the diameter of the inner boundary o~ the auxlliary cathode emitter may be only a ~ew mils larger than the diameter of the central dif~used region 30. The outer diameter of the auxiliary cathode emitter 35 should then be about 30 to 60% larger than the inner diameter. This provides for a resistance in the cathode base under the small auxiliary cathode emitter 35 that allows for e~ficient operation of the auxiliary cathode. With reference to Figure 2, where the auxiliary cathode emitter is disc shaped, the diameter could be in the neighborhood of 40 to 100 mils. For this embodiment, the outer diameter of the auxlllary cathode emitter 20 could be larger to yield a somewhat hlgher resistance to compensate for the ~act that at a given current density, the current galn might be de-creased by the hlgher dopant denslty o~ the cathode base 15.
.
46,244 . ., If desired, this decreased current gain may be avolded by diffusing the auxillary cathode emitter region 20 deeper than that of the main cathode emitter region 21.
With reference to the embodiment illustrated in Figure 4, the body 10 is slmilar to that described ln con-nection wlth Figures 1, 2 and 3 and bears slmllar reference numerals for llke parts of the devlce. However, ln thls embodlment, an extra lmpurlty reglon 40 whlch has a hlgher impurity denslty gradient ad~acent to PN ~unction 17 formed by the cathode and anode base regions 15 and 14, respec-tively, is circular or disc shaped and has an outer peri-pheral boundary 41 that intersects the auxlliary cathode i emitter 35 close to lts lnner boundary or ~unctlon 36.
Thus, the lnner boundary 36 of region 35 ls located entlrely wlthin the extra impurlty reglon 40. Thls has the advantage in that the in~ection of electrons from the auxlliary cathode emitter 35 occurs ln the area of the devlce in whlch the electric fields in the central blocking ~unctlon 17 are the hlghest. To assure thls, the area of overlap between ~ -the diffused cathode emitter region 35 and the extra im-purity region 40 in the cathode base 15 should be kept small. However, the additional P type impurity reglon 40 should not have lts perlphery allgned exactly wlth the inner boundary 36 of the auxiliary cathode emitter 35 because ln this case not all of the emitted electrons will flow in the region in whlch this electrlc field is highest.
Referring to Figure 5, the body 10 is slmllar to the device de~cribed in connection with the previously des-cribed figureg with like parts bearing similar reference nu-merals. However, thls embodlment i8 included to illustrate 46,244 the disposition of a gate electrode 45 such that the device can be used as a three terminal device if desired with the region of hlgher impurity in the cathode or P base 15 pro-viding protection agalnst overvoltage. Although the gate electrode 45 could be used with the extra impurlty region 40 whlch is circular in configuration, this embodlment illus-trates an annularly configured higher impurity region 46 which has an inner boundary 47 and an outer boundary 48. In this embodiment, the outer boundary 48 should be kept as closely as possible to the inner boundary 36 of the auxi-liary cathode emitter 35 for the same reason discussed in the disposition of a gate electrode 45 such that the device can be used as a three terminal device if desired with the region of higher impurity ln the cathode or P base 15 pro- :
viding protection against overvoltage. Although the gate electrode 45 could be used with the extra impurity reglon 40 which is circular in configuration, this embodiment illus-trates an annularly configured higher impurity region 46 which has an inner boundary 47 and an outer boundary 48. In this embodiment, the outer boundary 48 should be kept as closely as possible to the inner boundary 36 of the auxi-: liary cathode emitter 35 for the same reason discussed in connection with Figure 4. It is also understood, that the - annular region 46 may be utilized without the gate electrode 45.
Thus, it is seen that I have provlded an improved thyristor which may be utilized in applications where the devlce ls flred by a predetermlned high anode to cathode voltage or in applications where it is desired to protect 3o the device against inadvertent firing by a high anode to : -14-. .
,: ' ' ' ' 46,244 cathode voltage; which device has a low switching loss and ls capable of belng used in a series of two and three terminal silicon switches and thereby decreasing the amount of gate drive circuitry needed. Since the central region used to locally decrease the breakdown voltage ls a dlf-fusion layer that is added near the end of the fabrication processing sequence instead of being present in the starting material, there is a much sharper boundary to the higher doped region in the finished device. Also, it is much simpler to add one or more extra dlffuslons through the external surface than to construct the device wlth a hlgher dopant denslty localized wlthin the starting slice. Fur-ther, because the region is formed by a masked diffusion, it is much easier to align such region properly with the auxiliary cathode emitter.
While the invention has been specifically des-cribed in connection with several preferred embodlments, lt is distinctly understood that the lnvention may be otherwise variously embodled with alternate configurations of the metallic electrode 26 and the metallic electrode 24, such as provlding radially extending fingers ln the electrode 26 with corresponding recesses in the electrode 24 to provide for lnterdigitation, for example; or the electrode 26 in the embodlment of Flgures 1 through 4 may be disc shaped. Also, varlou~ other cathode shunt or shorted emltter configura-tlons may be utllized, and the relative dimenslonæ and conflguratlons wlth respect to the extra dlffusion of higher P type impurltles relatlve to the dlameter o~ the auxlllary cathode emltter may be varled in accordance wlth the teach-lngs of the pre~ent lnventlon and s¢ope of the appended ¢lalm~.
Claims (7)
1. A thyristor adapted to fire in response to a predetermined forward overvoltage, comprising:
a body of semiconductor material having first and second outer surfaces with four impurity regions of alter-nate type conductivity disposed in PN junction relationship said regions being a cathode emitter region and a cathode base region, each having surfaces forming a portion of the first outer surface of the body, an anode base region and an anode emitter region, said anode emitter region having a surface forming at least a portion of the second outer surface of the body;
said cathode emitter region including an inner auxiliary and an outer main portion, said auxiliary portion being disposed to form the central portion of the first outer surface and having an outer boundary of predetermined dimension said main portion being radially spaced from the inner portion with at least a portion of the cathode base region forming the first outer surface of the body between the auxiliary and main cathode emitter regions;
an extra impurity region of the same conductivity type as the cathode base region disposed in the cathode base region centrally of the outer boundary of the auxiliary cathode emitter region portion;
said extra impurity region having a higher impu-rity density gradient adjacent the PN junction formed by the cathode and anode base regions than the density gradient of the PN junction radially spaced from said extra region;
a metallic electrode in ohmic contact with the first outer surface disposed overlying the PN junction formed at the outer boundary of the auxiliary cathode emit-ter region and the cathode base region;
a metallic cathode electrode in ohmic contact with the first outer surface formed by the main cathode emitter region portion; and a metallic anode electrode in ohmic contact with the second outer surface formed by the anode emitter region, whereby a predetermined overvoltage applied to the anode electrode causes the device to avalanche initially in the area of the said extra region of the cathode base region.
a body of semiconductor material having first and second outer surfaces with four impurity regions of alter-nate type conductivity disposed in PN junction relationship said regions being a cathode emitter region and a cathode base region, each having surfaces forming a portion of the first outer surface of the body, an anode base region and an anode emitter region, said anode emitter region having a surface forming at least a portion of the second outer surface of the body;
said cathode emitter region including an inner auxiliary and an outer main portion, said auxiliary portion being disposed to form the central portion of the first outer surface and having an outer boundary of predetermined dimension said main portion being radially spaced from the inner portion with at least a portion of the cathode base region forming the first outer surface of the body between the auxiliary and main cathode emitter regions;
an extra impurity region of the same conductivity type as the cathode base region disposed in the cathode base region centrally of the outer boundary of the auxiliary cathode emitter region portion;
said extra impurity region having a higher impu-rity density gradient adjacent the PN junction formed by the cathode and anode base regions than the density gradient of the PN junction radially spaced from said extra region;
a metallic electrode in ohmic contact with the first outer surface disposed overlying the PN junction formed at the outer boundary of the auxiliary cathode emit-ter region and the cathode base region;
a metallic cathode electrode in ohmic contact with the first outer surface formed by the main cathode emitter region portion; and a metallic anode electrode in ohmic contact with the second outer surface formed by the anode emitter region, whereby a predetermined overvoltage applied to the anode electrode causes the device to avalanche initially in the area of the said extra region of the cathode base region.
2. A thyristor according to claim 1 wherein the auxiliary portion of the cathode emitter region is annularly configured to surround the extra region with the centermost boundary of the inner cathode emitter region being radially spaced from the outer boundary of said extra region.
3. A thyristor according to claim 1 wherein the auxiliary portion of the cathode emitter region forms the central portion of the first outer surface, and the extra region is disposed to intersect the auxiliary cathode emit-ter region centrally in said inner cathode emitter region.
4. A thyristor according to claim 1 wherein the auxiliary portion of the cathode emitter region is of annu-lar configuration, and the extra region is dimensioned such that it intersects the inner cathode emitter region inter-mediate its inner and outer boundaries.
5. A thyristor according to claim 4 wherein the intersection of the auxiliary cathode emitter region and the extra region is close to and larger than the inner boundary of the auxiliary cathode emitter region.
6. A thyristor according to claim 1 further including a gate electrode in ohmic contact with the first outer surface and so dimensioned that its outer boundary is radially spaced inwardly from the inner boundary of the auxiliary cathode emitter region portion.
7. A thyristor according to claim 4 wherein the extra region is annularly configured and has an inner boundary radially spaced inwardly from the inner boundary of the auxiliary cathode emitter region.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US64782476A | 1976-01-09 | 1976-01-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1055165A true CA1055165A (en) | 1979-05-22 |
Family
ID=24598417
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA267,466A Expired CA1055165A (en) | 1976-01-09 | 1976-12-08 | Thyristor fired by overvoltage |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5286089A (en) |
| CA (1) | CA1055165A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4502071A (en) * | 1981-03-31 | 1985-02-26 | Siemens Aktiengesellschaft | FET Controlled thyristor |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS508315B1 (en) * | 1970-02-20 | 1975-04-03 | ||
| US3914781A (en) * | 1971-04-13 | 1975-10-21 | Sony Corp | Gate controlled rectifier |
| JPS5321274B2 (en) * | 1972-07-28 | 1978-07-01 | ||
| JPS5342394B2 (en) * | 1973-03-26 | 1978-11-10 |
-
1976
- 1976-12-08 CA CA267,466A patent/CA1055165A/en not_active Expired
-
1977
- 1977-01-10 JP JP89277A patent/JPS5286089A/en active Granted
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4502071A (en) * | 1981-03-31 | 1985-02-26 | Siemens Aktiengesellschaft | FET Controlled thyristor |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5643662B2 (en) | 1981-10-14 |
| JPS5286089A (en) | 1977-07-16 |
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