CA1114522A - Thyristor with voltage breakover current control and method - Google Patents
Thyristor with voltage breakover current control and methodInfo
- Publication number
- CA1114522A CA1114522A CA332,272A CA332272A CA1114522A CA 1114522 A CA1114522 A CA 1114522A CA 332272 A CA332272 A CA 332272A CA 1114522 A CA1114522 A CA 1114522A
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- zone
- emitter
- breakover
- thyristor device
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- 238000013021 overheating Methods 0.000 description 2
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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
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
- H01L29/861—Diodes
- H01L29/87—Thyristor diodes, e.g. Shockley diodes, break-over diodes
-
- 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
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/10—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode not carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
- H01L29/1012—Base regions of thyristors
- H01L29/1016—Anode base regions of thyristors
-
- 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
- H01L29/7424—Thyristor-type devices, e.g. having four-zone regenerative action having a built-in localised breakdown/breakover region, e.g. self-protected against destructive spontaneous, e.g. voltage breakover, firing
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Ceramic Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Thyristors (AREA)
Abstract
TO ALL WHOM IT MAY CONCERN:
BE IT KNOWN that I, VICTOR A. K. TEMPLE, a citizen of Canada, residing in the city of Clifton Park, county of Saratoga, state of New York, have invented certain new and useful improve-ments in a THYRISTOR WITH VOLTAGE BREAKOVER
CURRENT CONTROL AND METHOD
of which the following is the specification.
Abstract of the Disclosure A thyristor of the type having a localized voltage break-over region is provided with current limiting means for control-ling the current through the device during initial voltage break-over. The thyristor base zone is divided into two at least par-tially separated base portions, one of which is in the vicinity of the localized breakover region. The other base portion is in the main current-carrying part of the thyristor in contact with the main emitter. The two base portions are electrically con-nected by current limiting means. When breakover occurs by way of a forward anode-cathode voltage which exceeds the thyristor forward breakover voltage, the rise in current is limited by the current limiting means.
BE IT KNOWN that I, VICTOR A. K. TEMPLE, a citizen of Canada, residing in the city of Clifton Park, county of Saratoga, state of New York, have invented certain new and useful improve-ments in a THYRISTOR WITH VOLTAGE BREAKOVER
CURRENT CONTROL AND METHOD
of which the following is the specification.
Abstract of the Disclosure A thyristor of the type having a localized voltage break-over region is provided with current limiting means for control-ling the current through the device during initial voltage break-over. The thyristor base zone is divided into two at least par-tially separated base portions, one of which is in the vicinity of the localized breakover region. The other base portion is in the main current-carrying part of the thyristor in contact with the main emitter. The two base portions are electrically con-nected by current limiting means. When breakover occurs by way of a forward anode-cathode voltage which exceeds the thyristor forward breakover voltage, the rise in current is limited by the current limiting means.
Description
1~1452Z
~, Background of the Invention The invention relates generally to thyristors, and more particularly to thyristors of the type having a localized reg-ion within the semiconductor body at which voltage breakover - -initiates when the forward anode-cathode voltage exceeds the ;
forward breakover voltage.
, Switching a thyristor into conduction by exceeding the ¦ forward breakover voltage can result in damage to the device.
One cause of damage is the small size of the voltage breakover region which is initially turned on. If the current rises rap-idly to large values before a sufficient portion of the main ¦ current carrying part of the device turns on, significant power I dissipation occurs. As a result of local overheating in the initial breakover region, the device fails. -Techniques have been developed for localizing the init-ial breakover region within a thyristor. One method is to prod- -uce a localized region of lower resistivity in the N- substrate.
A region of lower resistivity can be produced by passing a beam of neutrons through the semiconductor material. By the well --~
known process of neutron transmutation, the silicon is partially `
converted to phosphorus, which raises the level of N-type doping within the irradiated area. The result is a localized reduction in resistivity, which creates a localized initial breakover reg-ion at the adjacent pn junction, The position of the breakover region can be advantageously located within the thyristor body.
For example, it is known that positioning the voltage breakover region beneath a centrally located gate electxode i~ known to produce more rapid thyristor turn-on.
Localizing and positioning the voltage breakovex region in a thyristor does not solve the problem of large power dissi-' ~' 1~14SZ2 pation during initial ~reakcYer, ho~ever, m e large currents ~hich occur at breakover must still initially pass through a small junction area.
Unless external circuit conditions control the initial currentr overheating and destruction of the ~reakover Junction will lead to premature failure of the device. .
C~jects and Surnary of the In~ention ~ :.
It is a general object of the present invention to proriae a thyristor device which includes ~eans for controllin~ the current through the device when the forward ~reah~ver voltage is ex oeeded~
la Another o~ject of the present invention is to provide a methcd of :~
forming a thyristor device which includes a current-oontrolling inpedance for oontrolling power dissipation during voltage ~reakover.
Ac ding to one ~road aspect of the invention there is provided a thyristor de~ice for oontrolling current flo~ ~etween a pair of terminals :
;~ and which switches into forward conduction ~y means of a gate electrode and gate current or frcm a blocking ~ode when the terminal voltage ~etween said terminals exceeds a ~reakoYer voltage, said thyristor device com~
: prising: a semioonductor kody ~aving at least four zones of alternate .:
oonductivity type extending between said terminals~ incllding an enitter zone having a first emitter in contact with one said terminal~ a hase -~
zone adjaoent said emitter zone~ a ~lockin~ pn junction defining the houndary hetw~en said ~ase zone and a third said zone adjaoe nt said ~ase zone, means in said body far locaIizing a ~reakover portion of said block-ing pn junction where forward ~reakover initiates ~hen said terminal voltage exceeds said Ereakover voltage, said ~ase zone including a first hase ~-pcrtion disposed adjacent said ~reakover portion of said klocking pn :-~
junction and a seoond ~ase portion in contact with said first emitter, said gate electrode ~eing disposed on said second kase portion and forming a gate turn-on channel region for said gate current in said : . - 3 -A
~11452Z
second base portion bet~een said gate electrode and said emitter zone, and current limiting ~eans for limiting current flow in :~
said base zone ~et~een said first and second ~ase portions, said current limiting means electrically inter-connecting and provid- .
ing an impedance fietween said first and second base portions.
According to anot~er aspect of t~e invention t~ere is provided a thyrister device for controlling current flow fietween a pair of terminals and which switches into forward conduction by :j means of a gate electrode and gate current or from a blocking . ~.
mode when the terminal voltage ~etween saia terminals exceeds a :
~reakover voltage, said thyristor device comprising: a semi- ;
i conductor body ~aYi.ng a top surface and having at least four zones ; of alternate conductivity type extending between said terminals, ~
.~j including an emitter zone extending to said top surface having a - ~`
first emitter contacting one said terminal, a base zone adjacent ~: said emitter zone and also e~tending to said top surface, a ~lock-ing pn ~unction defining the fioundary ~etween said ~ase zone and a third said zone adjacent said base zone, means in said body for .`
localizing a breakover portion of said ~locking pn junction where forward breakover initiates when said terminal voltage exceeds said ~reakover Yoltage, an etch. formed on said top surface extend ing into said ~ase zone to at least partially divide said baæe ~ ~
zone into a first ~ase portion adjacent saia breakover portion .
of said pn junction and a second base portion in contact wit~
said first emitter, said gate electrode ~eing disposed on said ~ ;
second ~ase portion and formin~ a gate turn-on channel region for . ~ said gate current in said secona base portion between said gate electrode and said emitter zone, and current limiting means for limiting current flow in said ~ase:zone between said first and 3Q second ~ase portions, said current limiting means electrically interconnectLng and providing an impedance ~etween said first and second ~ase portions.
A
The method of forming a thyrister from the semiconductor body described above includes the step of etching into the semi- `~
conductor body to divide and at least partially separate the base zone into the two base portions. The method also includes pro-viding current limiting means to interconnect the first and second base portions to control the current across the breakover portion of the ~locking pn junction when the breakover voltage is exceedea. ,, Brief Description of the Drawings lQ Figures 1-5 are perspective views in partial cross-section showing the method of forming a thyrister according to the present invention.
Figure 6 is a partial top view of the thyrister of Figure S.
Figure 7 is a cross-sectional view of the thyrister of Figure 6 taken along the line 7-7.
Figure 8 is a cross sectional view as in Figure 7 show- ;
ing another embodiment of a thyrister according to the ;nvention.
Figure 9 is a cross-sectional view as in Figure 7 show-ing another embodiment of a thyrister according to the invention.
Figure 10 is a cross-sectional view as in Figure 7 show-ing another embodiment of a thyrister according to the invention, Figure 11 is a cross-sectional view a~ in Figure 7 show-ing another embodiment of a thyrister according to the invention.
Figure 12 is a cross-sect;onal view as in Figure 7 show-ing another embodiment of a thyrister accord;ng to the invention.
Figure 13 is a cross-sectional view as in Figure 7 show-ing another embodiment of a thyrister according to the invention.
Figure 14 is a cross-sectional view as in Figure 7 show-3Q ing -4a~
.~ , 111452Z ~ ~
another embodiment of a thyristor according to the invention.
Fig. 15 is a cross-sectional view as in Fig. 7 showing another embodiment of a thyristor according to the invention.
Description of the Preferred Embodiment -, 5 A thyristor device according to the present invention is formed beginning with a foundation semiconductor body 20 hav-'~ ing opposed top and bottom surfaces 22 and 2~ respectively.
Body 20 is typically formed of monocrystalline silicon processed to provide a PNP structure having intermediate pn junctions substantially parallel with surfaces 22 and 24. A suitable method of forming body 20 begins with an ~J-type silicon chip into which impurities are subseauently diffused through the top and bottom surfaces. One or more of the conductivity zones may , alternatively be formed by epitaxial growth, ion implantation or another suitable method. The resultant three layers comprise -~
a bottom layer 26 of P conductivity type, an intermediate layer ; 28 of N conductivity type, and an upper layer 30 of P conductiv-ity type. Body 20 preferably includes a localizecl region of j lower resistivity in N-type intermediate layer 28, to provide a region of lower breakover voltage centrally disposed in the body.
! Formation of such a localized region in body 20 can be achieved by suitable manufacturing techniques well known in the art. For example, a beam of neutrons can be passed through body 20 in ¦ the direction of arrows 31. The neutron beam causes a localized 29 region 32 in the body to be partially converted to phosphorus by the process of neutron transmutation. The phosphorus enhances `
the level of N-type dopant in zone 28 to produce a small area having lower resistivity. ~egion 32 produces a localized volt-age breakover region centrally disposed in body 20. ~ ;' :
- S
,, , ,, ,,, .; , ~ -, ,, , - 1 " - , -1~14S22 - ~
i, .
The method of forming a first embodiment of a thyris-tor according to the invention from body 20 is illustrated in Figs. 2-S. An additional zone 35 is first added to body 20 to provide the typical thyristor structure having at least four zones of alternate conductivity type, 26, 28, 30 and 35, as -~
: ` `
shown in Fig. 2. Top zone 35 is formed by any suitable method `~
such as diffusion, epitaxial growth or ion implantation. The resultant thyristor body has an NPNP structure with layer 35 forming the emitter zone and adjacent layer 30 forming the base ~ -zone. The third zone of the body is intermediate zone 28. A ;~`
pn junction 36 defines the boundary between base 30 and third zone 28. In Fig. 2 zones 35 and 28 arè respectively designated N+ and N- to reflect the relatively higher level of N-type im-, purity doping in zone 35. ~;
15~ ~ Following formation of the four-zone structure, the top surface of body 20 is covered with a masking layer 38. A
suitable photoresist mask can be used. Mask 38 initially coverC
the entire top surface 22. Portions are then removed by conven-tional photolithographic techniques to pro~uce a masking pattern as shown in Fig. 2. The pattern lncludes a large central open-in~ 40. Additional smaller openings 42 are formed outside open- , ing 40 to provide emitter shorts.
Following formation of the masking pattern of Fig. 2, - ;~
conventional etching echniques are employed to etch into the upper surface 22 of body 20. An etching solution is used which attacks the silicon of the body but not the masking layer 38.
Etching is allowed to proceed to a depth sufficient to penetrate ;~
emitter zone 35 and expose a portion of base zone 30 within open~
ings 40 and 42.
:
The configuration resulting after mask 38 is removed is shown in Fig. 3. Emitter zone 35 has been removed from within mask opening 40. The portion of emitter 35 which remains forms the first or main emitter of the thyristor. Base zone 30 ex-tends to top surface 22 within mask opening 40. The inner edgeof the emitter-base pn junction forms the turn-on line 46 of the thyristor. Openings 47 in the emitter correspond to open- ~
ings 42 in mask 38. ~ -Another etching step is then performed on the body.
This etching step produces a deep etch 48 in base zone 30 ex-tending from top surface 22, as shown in Fig. 4. Etch 48 is substantially ring-shaped and encircles a central portion of the . .
base zone overlying voltage breakover region 32. To produce ~--etch 48, a suitable etch-impervious mask layer such as silicon ,~
lS dioxide is first grown or otherwise formed on top surface 22.
A ring-shaped opening corresponding to the width of etch 48 is -: .
then formed in the mask layer by conventional photolithographic and etching techniques. The exposed ring-shaped portion of sur-face 22 is then subjected to an etching solution of the type ~:
which etches into the semiconductor body but does not attack .
the mask of silicon dioxide. In the first embodiment, etching is allowed to proceed to a predetermined depth in base zone 30.
The resultant etch 48 forms a closed ring cutting deep into base zone 30, dividing the base into a first base portion 50 centrally disposed over region 32 of the body, encircled by a second base :
portion 52 extending outwardly from the etch. The two base por- ~ r tions are only partially separated, being interconnected by a ~ -broad and relatively thin unremoved connecting portion 53 of the base zone.
-~ ;:
` 11145Z2 Connecting portion 53 provides the current control mech-anism of the first embodiment of the invention~ Portion 53 has a much higher resistivity than the adjacent unetched base por-tion, The specific resistance R in the base zone between the inner first base portion 50 and second base portion 52 is given by R = 2~- ln rUt where ~ is the sheet res1stance of the ;
thinned connecting portion 53, and rOut and ri are the outer ~ -and inner radii of the deep etch (see Fig. 7). The value of R
is controlled both by the depth of the etch and the values of rOut and rin. A wide leeway is available in the value of R, -;
allowing the thyristor to be tailored to specific circuit requirements. A typical value for the resistance R of connectins portion 53 would be, for example, 500 ohms.
, Following removal of the maskina layer employed in forming etch 48, top surface 22 is~coated by conventional means~ `
; with a layer of suitable conductive metal, such as aluminum. ~ ~
Portions of the metal layer are then removed by conventional -photolithographic and etching techniques to provide a metaliza-tion pattern as shown in Fig. 5. The metal in contact with first emitter 35 outside turn-on line 46 forms an emitter electrode S5.
Electrode 55 extends into openings 47 to contact base 30 and provide a line of emitter shorts. Another metal electrode 58 remains within turn-on line 46, encircling first base portion S0.
Electrode 58 extends around etch 48 in contact with second base portion 52, forming the gate electrode of the thyristor. It is also desirable to leave a metalized area S9 on the top surface of first base portion S0. Electrode S9, which is referred to herein as the first base electrode, serves to more evenly distri-bute the current through first base portion S0 during voltage -- 8 ~
1~452Z
". , breakover. The completed thyristor also includes a metalized electrode 62 on bottom surface 24 in contact with bottom layer 26, forming the thyristor anode electrode, Andoe 62 is applied -either simultaneously with the top surface metalization, or at ; ~-another time. A pair of terminals provide for external connec-tions to the anode and sathode metalizations. Terminal 64 is connected to anode 62 and terminal 66 contacts first emitter 35 -by way of emitter electrode 55. The four zones of the device extend between terminals 6a and 66. -The resultant thyristor serves as a switching device for controlling current flow between terminals 64 and 66. When in a forward blocking mode with anode terminal 64 forward biased relative to cathode terminal 66, only a small leakage current passes through the device due to carrier depletion in the vic~
inity of junction 36. Junction 36 thus serves as a forward blocking pn junction. Application of a small positive voltage to gate electrode 58 causes electrons to flow in large numbers across the emitter-base junction starting at turn-on line 46.
The resultant infusion of electrons into base 30 turns on the thyristor, allowing a large forward current to flow. Turn-on is substantially uniform along turn-on line 46 because the encircl-ing emitter 35 is spaced an equal minimum distance from the gate at all points. Such gate-triggered turn-on allows a relatively ~ : -small gate current to control a much larger current between ter-minals 64 and 66. The forward blocking state is restored by momentarily reversing the bias on terminals 64 and 66, as is ~ -well known in the art~ ~
- ~:
The thyristor can also be switched into forward con- ~`~
duction from a blocking mode by raising the terminal voltage between terminals 64 and 66 above the forward breakover voltage.
.
9 ~ ::
lllq522 To simplify the forward breakover turn-on process, as the for-ward bias of the anode increases, the leakage current through the device begins to rise. When the terminal voltage across the device reaches the forward breakover voltage, the leakage cur-rent produces avalanche breakdown at the blocking pn junction. ;`
Avalanche breakdown generates large numbers of carriers in the ~-base zone. Electrons are drawn toward the anode and holes pass through the base toward emitter shorts 47. The hole current in the base turns on the thyristor at the emitter-base junction.
Turn-on via voltage breakover requires no external gate current. ~ -The blocking mode is restored after momentary reversal of the ~ .:
:~ terminal voltage.
The region of lower resistivity 32 in the N- substrate ;;
28 provides means for localizing a breakover portion 70 of junc- -~15~ tion 36 at which forward voltage breakover will initiate. Ereak-over occurs first at portion 70 because the higher doping in ~- -region 32 of adjacent zone 28 reduces the width of the depletion `-layer, lowering the breakover voltage. The higher breakover : , , ~
voltage along the remainder of junction 36 prevents initial `
~20 breakover outside breakover portion 70.
In the first embodiment thyristor, when turn-on is by forward voltage breakover, current between terminals 64 and 66 will initially pass through connective base portion 53. This is because most of junction 36 remains blocking and only portion 70 is conducting. Arrows 72 in Fig. 7 illustrate paths of init-ial forward voltage breakover current flow through the thyristor.
Connecting portion 53 of base 30 has a si~nificantly higher sheet resistance than the remainder of the base zone because of etch 48. The initial current between terminals 64 and 66 is ;
therefore limited by the higher resistivity of etched portion 53.
~:
,' , . , . ,; ~ . . - -Portion 53 introduces a series resistance between the anode and cathode during breakover which prevents localized burnout along .
junction 36. As the current flows through breakover region 70 and into first base portion 50, metalized area 59 helps to more evenly distribute the charge. The current passing through the base zone will rapidly switch the main current carrying part of the thyristor into forward conduction after voltage breakover.
A substantially free flow of current between terminals 64 and 66 will therefore be established. Once the thyristor is turned on, breakover portion 70 is bypassed by the low resistance path through the remainder of the device. ~
The present invention provides for current control in ~ -the voltage breakover region of a thyristor. Power dissipation in the voltage breakover region is greatly reduced. The built-~15 in impedance provided by etch 48 significantly limits the for-ward voltage breakover current through the thyristor device. -Precise control of the size of the impedance and hence the cur-rent limiting ability is achieved by controlling the width and ~ -depth of etch 48. Performance of the gate-triggered portion of ~ ~r the thyristor outside etch 48 is not impaired by the partial isolation of a small portion of the base zone.
The size and depth of deep etch 48 can be varied to ~ ~-accommodate design requirements. E'or example, where relatively ~
high breakover currents are anticipated, there will be a poten- - ~-tial problem with ohmic heating of base connecting portion 53.
To compensate for possible excessive temperatures, the volume of portion 53 should be enlarged by making etch 48 broader, but less -deep. Alternatively, portion 53 could be enlarged by increasing the total length of the etch, enlarging the diameter of central base portion 50. The shape and size of etch 48 as shown in the ~
. :
figures lS suggestive only, and alternative deep etch configur- ~
ations can be employed~ -An alternative embodiment of the invention, employing an external current limiting circuit impedance element, is shown in Fig. 8. The method of forming this embodiment begins with :. .:
the same fabrication steps shown in Flgs. 1-3 for the first em-bodiment. A semiconductor body 20 having at least four zones of ~ ;
alternate conductivity type is provided. The semiconductor body has a centrally-disposed region of lo~er resistivity 32 in the N- substrate. Consequently, the ad~acent pn junction 36 includes the localized breakover portion 70 of the first embodiment. The top surface emitter pattern is the same as in the first embodi-ment. The second etching step producing etch 48 is prolonged ~ -~
~ .
slightly in this embodiment to etch the semiconductor body to a greater deptk. The resultant etch 78 extenas through base zone 30 to third zone 28, dividing and fully separating the base zone ~
into first and second base portions 80 and 82, respectively. ~;
~ The electrodes in the alternative embodiment include ~ ;
a first base electrode 59 in contact with the central first base portion 80. First base electrode 59 is essentially the same as in the first embodiment. A gate electrode 58 and emitter elec- ;~
trode 55 are also provided, as in the first embodiment. Forma-tion of the electrodes of this embodiment is accomplished by first metalizing the entire top surface 22 of the semiconductor body and then removing selected portions of the metalization by ;
conventional photolithographic and etching techniques to leave electrodes 55, 58 and 59.
Fabrication of this alternative embodiment includes the additional step of connecting an impedance element between gate 58 and electrode 59. In the embodiment of Fig. 8, such `.~
~`' ';
.. ; . . , . , ~ ... . . .
11:1~22 '~
impedance preferably includes one or more resistors 86. Resis-tors 86 serve to interconnect the separated base portions 80 and 82, in the same manner as connecting portion 53 of the first embodiment.
The embodi~ent of Fig. 8 functions in essentially the same way as the first embodiment thyristor. If the terminal voltage between terminals 64 and 66 exceeds the forward break-over voltage, forward breakover initiates at breakover portion 70. The initial current path between the cathode and anode passes through resistors 86. The resistors reduce the initial breakover current to a level which prevents excessive power `
dissipation at junction 36. The remainder of the device is sub-sequently turned on by the breakover current passing through the base zone.
,: .
As in the first e~bodiment, once the thyristor is ;
fully turned on, the additional impedance of resistors 86 is ef- ~ '~
fectively removed from the circuit. The larae area of junction 36 outside base portion 80 provides an essentially open path for current flow between the *erminals. The performance of the thy-ristor under normal gate-tri~ered turn-on is unimpaired by resistors 86, The external circuit element realization of the invention can provide larger resistance values than the partial etch of the first embodiment. The difficulty of precise depth ; -control of the etch is also eliminated. ;
Another embodiment having an external impedance elem-ent is shown in Fig. 9. This embodiment has exactly the same -semiconductor body and method of formation as for the embodiment of Fig. 8. ~tch 78 extends through base zone 30 to third zone 28, dividins the base and fully separating first and second base portions 80 and 82, respectively. A first base electrode 59 is --1114S2~
,., :, provided on portion 80. In the embodiment of Fig. 9, an induc-tive element 90 is connected between gate 58 and electrode 59.
Inductive element 90 interconnects the two base portions to pro-vide an alternative type of current limiting means in the break- -;
over region.
Operation of the embodiment of Fig. 9 i5 exactly the same as for the embcdiment of Fig. 8. When the terminal voltage between terminals 64 and 66 exceeds the forward breakover volt- 5 age of the thyristor, forward breakover initiates at breakover portion 70 of junction 36, The forward volta~e breakover current ~ ~
between the terminals passes through inductive elements 90. The inductive elements serve as current limiting means durins init-ial turn-on when the current gradient is high. Excessive power ;
dissipation in the breakover region 70 is thereby averted. As ~ -~- . ., 15~in the previous embodiments, current through the base zone sub--sequently turns on the remainder of the device, effectively re-moving inductive elements 90 from the circuit. Normal gate-` ~ triggered turn-on is not impaired.
The embodiment of Fig. 9 provides current limiting ;
impedance of a type not readily realizable without the use of an external circuit element. Other external impedance elements could also be used, either singly or in combination. The thy- ;
ristor can thus be tailored to specific circuit conditions.
Another embodiment of a thyristor according to the -invention is shown in Fig. 10. In this embodiment, the built-in impedance feature of the present invention is applied to an amplifying-gate thyristor. In the method of forming the thyris-tor of Fig. 10, an additional ring-shaped portion of first mask ;
38, within circle 40, is left unremoved. In the subsequent etching step, the emitter zone is divided into a first emitter ' ~, -1~14522 :
35 and a separate amplifying sta~e emitter 94 on top surface 22.
.
As in the first embQdiment, the deep etching step produces an etch 48 which divides base zone 30 and partially separates first and second base portions 50 and 52, respectively~ Both emitters 35 and 94 are left in contact with second base portion 52. In the metalization step, a cathode electrode 55, cate electrode 58, and first base electxode 59 are provided as before. An amp-lifying gate electrode 96 is also provided on top surface 22, in contact with both amplifying stage emitter 94 and second por-tion 52 of base 30. Anode and cathode electrodes 62 and 55 are -;
provided as in the first e~bodiment, To turn on the thyristor of Fig. 10 by gate trigger-ing, a positive gate current is supplied to electrode 58. Ii~ith ; the anode forward biased relative to the cathode, electrons flow ~lS out of amplifying stage emitter 94 and across the base, turning on the amplifyin~ stage. As a result ! amplifying stage electrode ;~
96 becomes positive, turning on the main thyristor at the junc-, , .
tion between first emitter 92 and the base.
If the terminal voltage between the anode and cathode ~20 exceeds the breakover voltage of the thyristor, avalanche break-down initiates at breakover portion 70 of junction 36. Because , ~
breakover portion 70 is adjacent first base portion 50 and par-tially separated from the remainder of the base, a resistive current path is provided-through connecting base portion 53.
~25 The high resistivity of connecting base portion 53 serves as ; means for limiting the initial breakover current. As in the previous embodiments, the rest of the thyristor is subse~uently ; -~
turned on by current flow in the base, effectively removing impedance 53 from the circuit. `
. .
.. . . ...... ... ..
1114S2Z ~ ~-The embodiment of Fig~ 10 illustrates that the present invention can be readily employed in amplifying-gate thyristor configurations. The built-in impedance does not impair the func-tionins of the gate-triggered portion of the thyristGr. It is readily apparent that the external circuit element realizations -of the invention shown in Figs. 8 and 9 could also be provided ;
with amplifying stages as shown in Fig. 10.
Another embodiment of the invention is shown in Fig. ;;
11, In this embodiment, a semiconductor body is used having at least four zones of alternate conductivity type as shown in Figs.
-:
~, Background of the Invention The invention relates generally to thyristors, and more particularly to thyristors of the type having a localized reg-ion within the semiconductor body at which voltage breakover - -initiates when the forward anode-cathode voltage exceeds the ;
forward breakover voltage.
, Switching a thyristor into conduction by exceeding the ¦ forward breakover voltage can result in damage to the device.
One cause of damage is the small size of the voltage breakover region which is initially turned on. If the current rises rap-idly to large values before a sufficient portion of the main ¦ current carrying part of the device turns on, significant power I dissipation occurs. As a result of local overheating in the initial breakover region, the device fails. -Techniques have been developed for localizing the init-ial breakover region within a thyristor. One method is to prod- -uce a localized region of lower resistivity in the N- substrate.
A region of lower resistivity can be produced by passing a beam of neutrons through the semiconductor material. By the well --~
known process of neutron transmutation, the silicon is partially `
converted to phosphorus, which raises the level of N-type doping within the irradiated area. The result is a localized reduction in resistivity, which creates a localized initial breakover reg-ion at the adjacent pn junction, The position of the breakover region can be advantageously located within the thyristor body.
For example, it is known that positioning the voltage breakover region beneath a centrally located gate electxode i~ known to produce more rapid thyristor turn-on.
Localizing and positioning the voltage breakovex region in a thyristor does not solve the problem of large power dissi-' ~' 1~14SZ2 pation during initial ~reakcYer, ho~ever, m e large currents ~hich occur at breakover must still initially pass through a small junction area.
Unless external circuit conditions control the initial currentr overheating and destruction of the ~reakover Junction will lead to premature failure of the device. .
C~jects and Surnary of the In~ention ~ :.
It is a general object of the present invention to proriae a thyristor device which includes ~eans for controllin~ the current through the device when the forward ~reah~ver voltage is ex oeeded~
la Another o~ject of the present invention is to provide a methcd of :~
forming a thyristor device which includes a current-oontrolling inpedance for oontrolling power dissipation during voltage ~reakover.
Ac ding to one ~road aspect of the invention there is provided a thyristor de~ice for oontrolling current flo~ ~etween a pair of terminals :
;~ and which switches into forward conduction ~y means of a gate electrode and gate current or frcm a blocking ~ode when the terminal voltage ~etween said terminals exceeds a ~reakoYer voltage, said thyristor device com~
: prising: a semioonductor kody ~aving at least four zones of alternate .:
oonductivity type extending between said terminals~ incllding an enitter zone having a first emitter in contact with one said terminal~ a hase -~
zone adjaoent said emitter zone~ a ~lockin~ pn junction defining the houndary hetw~en said ~ase zone and a third said zone adjaoe nt said ~ase zone, means in said body far locaIizing a ~reakover portion of said block-ing pn junction where forward ~reakover initiates ~hen said terminal voltage exceeds said Ereakover voltage, said ~ase zone including a first hase ~-pcrtion disposed adjacent said ~reakover portion of said klocking pn :-~
junction and a seoond ~ase portion in contact with said first emitter, said gate electrode ~eing disposed on said second kase portion and forming a gate turn-on channel region for said gate current in said : . - 3 -A
~11452Z
second base portion bet~een said gate electrode and said emitter zone, and current limiting ~eans for limiting current flow in :~
said base zone ~et~een said first and second ~ase portions, said current limiting means electrically inter-connecting and provid- .
ing an impedance fietween said first and second base portions.
According to anot~er aspect of t~e invention t~ere is provided a thyrister device for controlling current flow fietween a pair of terminals and which switches into forward conduction by :j means of a gate electrode and gate current or from a blocking . ~.
mode when the terminal voltage ~etween saia terminals exceeds a :
~reakover voltage, said thyristor device comprising: a semi- ;
i conductor body ~aYi.ng a top surface and having at least four zones ; of alternate conductivity type extending between said terminals, ~
.~j including an emitter zone extending to said top surface having a - ~`
first emitter contacting one said terminal, a base zone adjacent ~: said emitter zone and also e~tending to said top surface, a ~lock-ing pn ~unction defining the fioundary ~etween said ~ase zone and a third said zone adjacent said base zone, means in said body for .`
localizing a breakover portion of said ~locking pn junction where forward breakover initiates when said terminal voltage exceeds said ~reakover Yoltage, an etch. formed on said top surface extend ing into said ~ase zone to at least partially divide said baæe ~ ~
zone into a first ~ase portion adjacent saia breakover portion .
of said pn junction and a second base portion in contact wit~
said first emitter, said gate electrode ~eing disposed on said ~ ;
second ~ase portion and formin~ a gate turn-on channel region for . ~ said gate current in said secona base portion between said gate electrode and said emitter zone, and current limiting means for limiting current flow in said ~ase:zone between said first and 3Q second ~ase portions, said current limiting means electrically interconnectLng and providing an impedance ~etween said first and second ~ase portions.
A
The method of forming a thyrister from the semiconductor body described above includes the step of etching into the semi- `~
conductor body to divide and at least partially separate the base zone into the two base portions. The method also includes pro-viding current limiting means to interconnect the first and second base portions to control the current across the breakover portion of the ~locking pn junction when the breakover voltage is exceedea. ,, Brief Description of the Drawings lQ Figures 1-5 are perspective views in partial cross-section showing the method of forming a thyrister according to the present invention.
Figure 6 is a partial top view of the thyrister of Figure S.
Figure 7 is a cross-sectional view of the thyrister of Figure 6 taken along the line 7-7.
Figure 8 is a cross sectional view as in Figure 7 show- ;
ing another embodiment of a thyrister according to the ;nvention.
Figure 9 is a cross-sectional view as in Figure 7 show-ing another embodiment of a thyrister according to the invention.
Figure 10 is a cross-sectional view as in Figure 7 show-ing another embodiment of a thyrister according to the invention, Figure 11 is a cross-sectional view a~ in Figure 7 show-ing another embodiment of a thyrister according to the invention.
Figure 12 is a cross-sect;onal view as in Figure 7 show-ing another embodiment of a thyrister accord;ng to the invention.
Figure 13 is a cross-sectional view as in Figure 7 show-ing another embodiment of a thyrister according to the invention.
Figure 14 is a cross-sectional view as in Figure 7 show-3Q ing -4a~
.~ , 111452Z ~ ~
another embodiment of a thyristor according to the invention.
Fig. 15 is a cross-sectional view as in Fig. 7 showing another embodiment of a thyristor according to the invention.
Description of the Preferred Embodiment -, 5 A thyristor device according to the present invention is formed beginning with a foundation semiconductor body 20 hav-'~ ing opposed top and bottom surfaces 22 and 2~ respectively.
Body 20 is typically formed of monocrystalline silicon processed to provide a PNP structure having intermediate pn junctions substantially parallel with surfaces 22 and 24. A suitable method of forming body 20 begins with an ~J-type silicon chip into which impurities are subseauently diffused through the top and bottom surfaces. One or more of the conductivity zones may , alternatively be formed by epitaxial growth, ion implantation or another suitable method. The resultant three layers comprise -~
a bottom layer 26 of P conductivity type, an intermediate layer ; 28 of N conductivity type, and an upper layer 30 of P conductiv-ity type. Body 20 preferably includes a localizecl region of j lower resistivity in N-type intermediate layer 28, to provide a region of lower breakover voltage centrally disposed in the body.
! Formation of such a localized region in body 20 can be achieved by suitable manufacturing techniques well known in the art. For example, a beam of neutrons can be passed through body 20 in ¦ the direction of arrows 31. The neutron beam causes a localized 29 region 32 in the body to be partially converted to phosphorus by the process of neutron transmutation. The phosphorus enhances `
the level of N-type dopant in zone 28 to produce a small area having lower resistivity. ~egion 32 produces a localized volt-age breakover region centrally disposed in body 20. ~ ;' :
- S
,, , ,, ,,, .; , ~ -, ,, , - 1 " - , -1~14S22 - ~
i, .
The method of forming a first embodiment of a thyris-tor according to the invention from body 20 is illustrated in Figs. 2-S. An additional zone 35 is first added to body 20 to provide the typical thyristor structure having at least four zones of alternate conductivity type, 26, 28, 30 and 35, as -~
: ` `
shown in Fig. 2. Top zone 35 is formed by any suitable method `~
such as diffusion, epitaxial growth or ion implantation. The resultant thyristor body has an NPNP structure with layer 35 forming the emitter zone and adjacent layer 30 forming the base ~ -zone. The third zone of the body is intermediate zone 28. A ;~`
pn junction 36 defines the boundary between base 30 and third zone 28. In Fig. 2 zones 35 and 28 arè respectively designated N+ and N- to reflect the relatively higher level of N-type im-, purity doping in zone 35. ~;
15~ ~ Following formation of the four-zone structure, the top surface of body 20 is covered with a masking layer 38. A
suitable photoresist mask can be used. Mask 38 initially coverC
the entire top surface 22. Portions are then removed by conven-tional photolithographic techniques to pro~uce a masking pattern as shown in Fig. 2. The pattern lncludes a large central open-in~ 40. Additional smaller openings 42 are formed outside open- , ing 40 to provide emitter shorts.
Following formation of the masking pattern of Fig. 2, - ;~
conventional etching echniques are employed to etch into the upper surface 22 of body 20. An etching solution is used which attacks the silicon of the body but not the masking layer 38.
Etching is allowed to proceed to a depth sufficient to penetrate ;~
emitter zone 35 and expose a portion of base zone 30 within open~
ings 40 and 42.
:
The configuration resulting after mask 38 is removed is shown in Fig. 3. Emitter zone 35 has been removed from within mask opening 40. The portion of emitter 35 which remains forms the first or main emitter of the thyristor. Base zone 30 ex-tends to top surface 22 within mask opening 40. The inner edgeof the emitter-base pn junction forms the turn-on line 46 of the thyristor. Openings 47 in the emitter correspond to open- ~
ings 42 in mask 38. ~ -Another etching step is then performed on the body.
This etching step produces a deep etch 48 in base zone 30 ex-tending from top surface 22, as shown in Fig. 4. Etch 48 is substantially ring-shaped and encircles a central portion of the . .
base zone overlying voltage breakover region 32. To produce ~--etch 48, a suitable etch-impervious mask layer such as silicon ,~
lS dioxide is first grown or otherwise formed on top surface 22.
A ring-shaped opening corresponding to the width of etch 48 is -: .
then formed in the mask layer by conventional photolithographic and etching techniques. The exposed ring-shaped portion of sur-face 22 is then subjected to an etching solution of the type ~:
which etches into the semiconductor body but does not attack .
the mask of silicon dioxide. In the first embodiment, etching is allowed to proceed to a predetermined depth in base zone 30.
The resultant etch 48 forms a closed ring cutting deep into base zone 30, dividing the base into a first base portion 50 centrally disposed over region 32 of the body, encircled by a second base :
portion 52 extending outwardly from the etch. The two base por- ~ r tions are only partially separated, being interconnected by a ~ -broad and relatively thin unremoved connecting portion 53 of the base zone.
-~ ;:
` 11145Z2 Connecting portion 53 provides the current control mech-anism of the first embodiment of the invention~ Portion 53 has a much higher resistivity than the adjacent unetched base por-tion, The specific resistance R in the base zone between the inner first base portion 50 and second base portion 52 is given by R = 2~- ln rUt where ~ is the sheet res1stance of the ;
thinned connecting portion 53, and rOut and ri are the outer ~ -and inner radii of the deep etch (see Fig. 7). The value of R
is controlled both by the depth of the etch and the values of rOut and rin. A wide leeway is available in the value of R, -;
allowing the thyristor to be tailored to specific circuit requirements. A typical value for the resistance R of connectins portion 53 would be, for example, 500 ohms.
, Following removal of the maskina layer employed in forming etch 48, top surface 22 is~coated by conventional means~ `
; with a layer of suitable conductive metal, such as aluminum. ~ ~
Portions of the metal layer are then removed by conventional -photolithographic and etching techniques to provide a metaliza-tion pattern as shown in Fig. 5. The metal in contact with first emitter 35 outside turn-on line 46 forms an emitter electrode S5.
Electrode 55 extends into openings 47 to contact base 30 and provide a line of emitter shorts. Another metal electrode 58 remains within turn-on line 46, encircling first base portion S0.
Electrode 58 extends around etch 48 in contact with second base portion 52, forming the gate electrode of the thyristor. It is also desirable to leave a metalized area S9 on the top surface of first base portion S0. Electrode S9, which is referred to herein as the first base electrode, serves to more evenly distri-bute the current through first base portion S0 during voltage -- 8 ~
1~452Z
". , breakover. The completed thyristor also includes a metalized electrode 62 on bottom surface 24 in contact with bottom layer 26, forming the thyristor anode electrode, Andoe 62 is applied -either simultaneously with the top surface metalization, or at ; ~-another time. A pair of terminals provide for external connec-tions to the anode and sathode metalizations. Terminal 64 is connected to anode 62 and terminal 66 contacts first emitter 35 -by way of emitter electrode 55. The four zones of the device extend between terminals 6a and 66. -The resultant thyristor serves as a switching device for controlling current flow between terminals 64 and 66. When in a forward blocking mode with anode terminal 64 forward biased relative to cathode terminal 66, only a small leakage current passes through the device due to carrier depletion in the vic~
inity of junction 36. Junction 36 thus serves as a forward blocking pn junction. Application of a small positive voltage to gate electrode 58 causes electrons to flow in large numbers across the emitter-base junction starting at turn-on line 46.
The resultant infusion of electrons into base 30 turns on the thyristor, allowing a large forward current to flow. Turn-on is substantially uniform along turn-on line 46 because the encircl-ing emitter 35 is spaced an equal minimum distance from the gate at all points. Such gate-triggered turn-on allows a relatively ~ : -small gate current to control a much larger current between ter-minals 64 and 66. The forward blocking state is restored by momentarily reversing the bias on terminals 64 and 66, as is ~ -well known in the art~ ~
- ~:
The thyristor can also be switched into forward con- ~`~
duction from a blocking mode by raising the terminal voltage between terminals 64 and 66 above the forward breakover voltage.
.
9 ~ ::
lllq522 To simplify the forward breakover turn-on process, as the for-ward bias of the anode increases, the leakage current through the device begins to rise. When the terminal voltage across the device reaches the forward breakover voltage, the leakage cur-rent produces avalanche breakdown at the blocking pn junction. ;`
Avalanche breakdown generates large numbers of carriers in the ~-base zone. Electrons are drawn toward the anode and holes pass through the base toward emitter shorts 47. The hole current in the base turns on the thyristor at the emitter-base junction.
Turn-on via voltage breakover requires no external gate current. ~ -The blocking mode is restored after momentary reversal of the ~ .:
:~ terminal voltage.
The region of lower resistivity 32 in the N- substrate ;;
28 provides means for localizing a breakover portion 70 of junc- -~15~ tion 36 at which forward voltage breakover will initiate. Ereak-over occurs first at portion 70 because the higher doping in ~- -region 32 of adjacent zone 28 reduces the width of the depletion `-layer, lowering the breakover voltage. The higher breakover : , , ~
voltage along the remainder of junction 36 prevents initial `
~20 breakover outside breakover portion 70.
In the first embodiment thyristor, when turn-on is by forward voltage breakover, current between terminals 64 and 66 will initially pass through connective base portion 53. This is because most of junction 36 remains blocking and only portion 70 is conducting. Arrows 72 in Fig. 7 illustrate paths of init-ial forward voltage breakover current flow through the thyristor.
Connecting portion 53 of base 30 has a si~nificantly higher sheet resistance than the remainder of the base zone because of etch 48. The initial current between terminals 64 and 66 is ;
therefore limited by the higher resistivity of etched portion 53.
~:
,' , . , . ,; ~ . . - -Portion 53 introduces a series resistance between the anode and cathode during breakover which prevents localized burnout along .
junction 36. As the current flows through breakover region 70 and into first base portion 50, metalized area 59 helps to more evenly distribute the charge. The current passing through the base zone will rapidly switch the main current carrying part of the thyristor into forward conduction after voltage breakover.
A substantially free flow of current between terminals 64 and 66 will therefore be established. Once the thyristor is turned on, breakover portion 70 is bypassed by the low resistance path through the remainder of the device. ~
The present invention provides for current control in ~ -the voltage breakover region of a thyristor. Power dissipation in the voltage breakover region is greatly reduced. The built-~15 in impedance provided by etch 48 significantly limits the for-ward voltage breakover current through the thyristor device. -Precise control of the size of the impedance and hence the cur-rent limiting ability is achieved by controlling the width and ~ -depth of etch 48. Performance of the gate-triggered portion of ~ ~r the thyristor outside etch 48 is not impaired by the partial isolation of a small portion of the base zone.
The size and depth of deep etch 48 can be varied to ~ ~-accommodate design requirements. E'or example, where relatively ~
high breakover currents are anticipated, there will be a poten- - ~-tial problem with ohmic heating of base connecting portion 53.
To compensate for possible excessive temperatures, the volume of portion 53 should be enlarged by making etch 48 broader, but less -deep. Alternatively, portion 53 could be enlarged by increasing the total length of the etch, enlarging the diameter of central base portion 50. The shape and size of etch 48 as shown in the ~
. :
figures lS suggestive only, and alternative deep etch configur- ~
ations can be employed~ -An alternative embodiment of the invention, employing an external current limiting circuit impedance element, is shown in Fig. 8. The method of forming this embodiment begins with :. .:
the same fabrication steps shown in Flgs. 1-3 for the first em-bodiment. A semiconductor body 20 having at least four zones of ~ ;
alternate conductivity type is provided. The semiconductor body has a centrally-disposed region of lo~er resistivity 32 in the N- substrate. Consequently, the ad~acent pn junction 36 includes the localized breakover portion 70 of the first embodiment. The top surface emitter pattern is the same as in the first embodi-ment. The second etching step producing etch 48 is prolonged ~ -~
~ .
slightly in this embodiment to etch the semiconductor body to a greater deptk. The resultant etch 78 extenas through base zone 30 to third zone 28, dividing and fully separating the base zone ~
into first and second base portions 80 and 82, respectively. ~;
~ The electrodes in the alternative embodiment include ~ ;
a first base electrode 59 in contact with the central first base portion 80. First base electrode 59 is essentially the same as in the first embodiment. A gate electrode 58 and emitter elec- ;~
trode 55 are also provided, as in the first embodiment. Forma-tion of the electrodes of this embodiment is accomplished by first metalizing the entire top surface 22 of the semiconductor body and then removing selected portions of the metalization by ;
conventional photolithographic and etching techniques to leave electrodes 55, 58 and 59.
Fabrication of this alternative embodiment includes the additional step of connecting an impedance element between gate 58 and electrode 59. In the embodiment of Fig. 8, such `.~
~`' ';
.. ; . . , . , ~ ... . . .
11:1~22 '~
impedance preferably includes one or more resistors 86. Resis-tors 86 serve to interconnect the separated base portions 80 and 82, in the same manner as connecting portion 53 of the first embodiment.
The embodi~ent of Fig. 8 functions in essentially the same way as the first embodiment thyristor. If the terminal voltage between terminals 64 and 66 exceeds the forward break-over voltage, forward breakover initiates at breakover portion 70. The initial current path between the cathode and anode passes through resistors 86. The resistors reduce the initial breakover current to a level which prevents excessive power `
dissipation at junction 36. The remainder of the device is sub-sequently turned on by the breakover current passing through the base zone.
,: .
As in the first e~bodiment, once the thyristor is ;
fully turned on, the additional impedance of resistors 86 is ef- ~ '~
fectively removed from the circuit. The larae area of junction 36 outside base portion 80 provides an essentially open path for current flow between the *erminals. The performance of the thy-ristor under normal gate-tri~ered turn-on is unimpaired by resistors 86, The external circuit element realization of the invention can provide larger resistance values than the partial etch of the first embodiment. The difficulty of precise depth ; -control of the etch is also eliminated. ;
Another embodiment having an external impedance elem-ent is shown in Fig. 9. This embodiment has exactly the same -semiconductor body and method of formation as for the embodiment of Fig. 8. ~tch 78 extends through base zone 30 to third zone 28, dividins the base and fully separating first and second base portions 80 and 82, respectively. A first base electrode 59 is --1114S2~
,., :, provided on portion 80. In the embodiment of Fig. 9, an induc-tive element 90 is connected between gate 58 and electrode 59.
Inductive element 90 interconnects the two base portions to pro-vide an alternative type of current limiting means in the break- -;
over region.
Operation of the embodiment of Fig. 9 i5 exactly the same as for the embcdiment of Fig. 8. When the terminal voltage between terminals 64 and 66 exceeds the forward breakover volt- 5 age of the thyristor, forward breakover initiates at breakover portion 70 of junction 36, The forward volta~e breakover current ~ ~
between the terminals passes through inductive elements 90. The inductive elements serve as current limiting means durins init-ial turn-on when the current gradient is high. Excessive power ;
dissipation in the breakover region 70 is thereby averted. As ~ -~- . ., 15~in the previous embodiments, current through the base zone sub--sequently turns on the remainder of the device, effectively re-moving inductive elements 90 from the circuit. Normal gate-` ~ triggered turn-on is not impaired.
The embodiment of Fig. 9 provides current limiting ;
impedance of a type not readily realizable without the use of an external circuit element. Other external impedance elements could also be used, either singly or in combination. The thy- ;
ristor can thus be tailored to specific circuit conditions.
Another embodiment of a thyristor according to the -invention is shown in Fig. 10. In this embodiment, the built-in impedance feature of the present invention is applied to an amplifying-gate thyristor. In the method of forming the thyris-tor of Fig. 10, an additional ring-shaped portion of first mask ;
38, within circle 40, is left unremoved. In the subsequent etching step, the emitter zone is divided into a first emitter ' ~, -1~14522 :
35 and a separate amplifying sta~e emitter 94 on top surface 22.
.
As in the first embQdiment, the deep etching step produces an etch 48 which divides base zone 30 and partially separates first and second base portions 50 and 52, respectively~ Both emitters 35 and 94 are left in contact with second base portion 52. In the metalization step, a cathode electrode 55, cate electrode 58, and first base electxode 59 are provided as before. An amp-lifying gate electrode 96 is also provided on top surface 22, in contact with both amplifying stage emitter 94 and second por-tion 52 of base 30. Anode and cathode electrodes 62 and 55 are -;
provided as in the first e~bodiment, To turn on the thyristor of Fig. 10 by gate trigger-ing, a positive gate current is supplied to electrode 58. Ii~ith ; the anode forward biased relative to the cathode, electrons flow ~lS out of amplifying stage emitter 94 and across the base, turning on the amplifyin~ stage. As a result ! amplifying stage electrode ;~
96 becomes positive, turning on the main thyristor at the junc-, , .
tion between first emitter 92 and the base.
If the terminal voltage between the anode and cathode ~20 exceeds the breakover voltage of the thyristor, avalanche break-down initiates at breakover portion 70 of junction 36. Because , ~
breakover portion 70 is adjacent first base portion 50 and par-tially separated from the remainder of the base, a resistive current path is provided-through connecting base portion 53.
~25 The high resistivity of connecting base portion 53 serves as ; means for limiting the initial breakover current. As in the previous embodiments, the rest of the thyristor is subse~uently ; -~
turned on by current flow in the base, effectively removing impedance 53 from the circuit. `
. .
.. . . ...... ... ..
1114S2Z ~ ~-The embodiment of Fig~ 10 illustrates that the present invention can be readily employed in amplifying-gate thyristor configurations. The built-in impedance does not impair the func-tionins of the gate-triggered portion of the thyristGr. It is readily apparent that the external circuit element realizations -of the invention shown in Figs. 8 and 9 could also be provided ;
with amplifying stages as shown in Fig. 10.
Another embodiment of the invention is shown in Fig. ;;
11, In this embodiment, a semiconductor body is used having at least four zones of alternate conductivity type as shown in Figs.
-:
2-4, As in the first embodiment, the body includes a centrally disposed initial breakover region 32 defining a localized break-over portion 70 of pn junction 36. ;-In the first masking and etching steps, e~uivalent to ~; 15 Figs. 2 and 3 of the first embodiment, the N+ emitter zone is ~-etched to provide an encircling first emitter 100. I~ithin cir- -cular turn-on line 102 is an exposed portion of base zone 30 ex-tending to top surface 22. The second etching step e~uivalent to Fi~. 4 of the first embodiment provides a ring-shaped etch 106 extending into base zone 30 from the top surface. Etch 106 divides the base, partially separating first base portion 108, centrally disposed on the body, and second base portion 110, which extends xadially outwardly from etch 106. The two base -~
portiQns are joined by connecting portion 112 which provides a region of high resistivity in the base. As in the first embodi-ment, the first base portion is disposed adjacent breakover por-tion 70 of junction 36 and first emitter 100 is in contact with -~
the second base portion 110. -The metalization formin~ emitter electrode 114 and gate 116 is applied in the conventional manner. In the embodi-1~14~2Z
ment of Fig, 11, the gate electrode is disposed on top surface 22 in contact with first base portion 108. ~s before, an anode ~ contact 62 is provided on bottom surface 24. Anode and cathode j terminals 64 and 118, respectively, permit external circuit connections.
portiQns are joined by connecting portion 112 which provides a region of high resistivity in the base. As in the first embodi-ment, the first base portion is disposed adjacent breakover por-tion 70 of junction 36 and first emitter 100 is in contact with -~
the second base portion 110. -The metalization formin~ emitter electrode 114 and gate 116 is applied in the conventional manner. In the embodi-1~14~2Z
ment of Fig, 11, the gate electrode is disposed on top surface 22 in contact with first base portion 108. ~s before, an anode ~ contact 62 is provided on bottom surface 24. Anode and cathode j terminals 64 and 118, respectively, permit external circuit connections.
3 In operation~ the embodiment of Fig. 11 can be turned on when anode terminal 64 is forward biased relative to cathode terminal 118. Gate triggerinS is accomplished by supplying a positive gate current to gate electrode 116. The gate current causes turn-on along the emitter-base junction beginning at turn-on line 102. Turn-on via voltage breakover occurs when the terminal voltage between terminals 64 and 118 exceeds the for~
ward breakover voltage. Forward breakover initiates at breakover portion 70 of junction 36. As ln the previous embodiments, the , 15~ initial current path between the anode and cathode terminals at breakover passes through the current limiting resistance 112 in-corporated into base zone 30.
The resistive impedance provided by connecting portion :
112 serves to reduce the initial breakover current thereby prev-~20 enting excessive power dissipation at the localized breakover region. As is apparent to those skilled in the art, external ~ circuit realizations could be provided for impedance 112 in the ~ ;
¦ form of external resistive, inductive, or other impedance ele- ` ~-ments. Etch 106 would simply be deepened to divide the base into fully separate portions 108 and 110, and an additional met-alized electrode would be provided outside the etch. As in the embodiments of Figs. 8 and 9, an external circuit element would F
then be installed between the two base portions. `
The embodiment of Fig. 11 provides an additional im~
, 30 pedance not only during voltage breakover but also in the gate ; ``
.
:~
1$14S2Z
circuit. As such, this embodiment is only desirable where a realtively large triggering gate voltage is available.
Another embodiment of a thyristor according to the `;~
invention is shown in Fig. 12. This embodiment incorporates essentially the same thyristor structure and method of fabrica-tion as the first embodiment shown in Figs. 1-7. The only dif-ference is the inclusion of an additional N+ region extending to top surface 22 in contact with the centrally disposed first base portion S0. This N+ region forms a second emit.er 125 extending to top surface 22, and is easily provided during the fabrication process outlined for the first embodiment. To form the embodi- -;-;
ment of Fig. 12, the masking layer 38 shown in Fig. 2 is modi-fied to include an additional circular mask portion centrally disposed over the voltage breakover region 32. ~hen the emitter zone is etched in the subsequent etching step, second emitter ~: ' I' -125 is formed, separated from first emitter 35. After deep etch 48 is formed, second emitter 125 is left in contact with first - ;
. .
base portion 50. The metalization steps of the first embodiment are used in the formation of the embodiment of Fig. 12. The ; -centrally-disposed first base electrode 126 is equivalent to electrode 59 of the first embodiment, but contacts both first base portion SO and second emitter 125. ~lectrode 126 serves a current-distributing function similar to electrode 59 of the first embodiment.
The resultant thyristor of this embodiment provides for a four-layer thyristor structure in the voltage breakover region. The significance of second emitter 125 during initial voltage breakover is illustrated in Fig. 12. As in the first -embodiment, the thyristor can be switched into forward conduc-tion from a blocking mode by raising the terminal voltage : :
1~14~2iZ
..
between terminals 64 and 66 above the forward breakover volt-age. ~hen the terminal voltage exceeds the forward breakover -~
voltage, current begins to flow across the localized breakover portion 70 of blocking pn junction 36. The path of positive .
hole current is shown generally by arrows 127. The pn junction 128 extending between second emitter 125 and first base portion ~ -50 becomes forward biased when the initial voltage breakover current increases sufficiently. This induces electrons to cross junction 128, as sho~n by arrow 130. The result is localized thyristor action producing a momentary low-resistance current path through the breakover region. The voltage drop across breakover junction 70 is significantly reduced by the injection -:~ ;",. ,,: .
of carriers from second emitter 125, lessening the possibility ~
of localized burnout. ;~-",~-, -l~S~ The improved conductivity produced during breakover by the presence of second emitter 125 is only momentary. Immedi~
ately after breakover initiates, the breakover current is lim-, , ited by the above-described current limiting means, which in the embodiment of Fig. 12 is the higher resistance of connecting ~20 portion 53 in the base zone. As in the first embodiment, the main current-carrying portion of the device is eventually turned on by the positive hole current through base zone 30. The mom-entary reduction in the voltage drop produced by second emitter 125 is intended to further reduce the likelihood of locali7ed ~;25 junction burnout, whlch is already significantly reduced by the presence of the current limiting means of the present invention.
Another embodiment of the invention is shown in Fig.
13. This embodiment is essentially the same as the embodiment shown in Fig. 8, but also includes the second emitter 125 and -first base electrode 126 of the embodiment of Fig. 12. It will -- 1 9 -- : : . :
;, be readily appreciated that the fabrication of the embodiment of Fig. 13 is essentially the same as the fabrication of the ~ embodiment of Fig, 8, except that an additional N+ emitter is v'l left in contact with first base portion 80.
The operation of the embodiment of Fig. 13 is essen~
j tially the same as the embodiment of Fig. 8. The only differ-l ence in operation occurs during initial voltage breakover when ;~ -i~ the momentary thyristor action described with respect to the embodiment of Fig. 12 is produced. The result is a momentary reduction in the voltage drop along breakover portion 70 which serves to further reduce the likelihood of localized junction burnout.
Although the embodiment of Fig. 13 is shown having i, external impedance elements 86 which are resistors as in Fig. 8, , ~15 inductive impedance elements such as shown in Fig. 9 could also ~;
be provided. -Another embodiment of the invention is shown in Fig.
, 14. This embodiment is essentially the same as the embodiment ¦ shown in Fig. 10, but also includes the second emitter 125 and first base electrode 126 of the embodiment of Fig. 12. The fab- --rication of the embodiment of Fig. 14 is essentially the same as the fabrication of the embodiment of Fig. 10, except that an ;~ --additional Nt emitter is left in contact with first base portion 50.
The operation of the embodiment of Fig. 14 is essen-tially the same as the embodiment of Fig. 10. The only differ-ence in operation occurs during initial voltage breakover when the momentary thyristor action described with respect to the embodiment of Fig. 12 is produced. The result is a momentary ; 30 reduction in the voltage drop along breakover portion 70 which ~ .
':
' ': , .
: ` :
1~1452~
serves to further reduce the likelihood of localized junction .
burnout.
Another embodiment of the invention is shown in Fig. ~ -15. This embodiment is essentially the same as the embodiment ~ ~5 shown in Fig. 11, but also includes the second emitter 125 of 3 ~: the embodiment of Fig. 12. An electrode 132 serves as a gate '-;~ electrode disposed on top surface 22 in contact with first base portion 108 and second emitter 125. Gate electrode 130 operates ; in exactly the same manner as gate electrode 116 in the embodi-ment of Fig. 11. The fabrication of the embodiment of Fig. 15 ;~ is essentially the same as the fabrication of the embodiment of Fig. 11, except that an additional N~ emitter is left in contact ` ;
with first base portion 108. .~
; The operation of the embodiment of Fig. 15 is essen- -tially the same as the embodiment of ~ig. 11. The only differ- !;;'; .~: .
; ence in operation occurs during initial voltage breakover when ; . . .
the momentary thyristor action described with respect to the embodiment of Fig. 12 is produced. The result is a momentary ! ~ reduction in the voltage drop along breakover portion 70 which l20 serves to further reduce the likelihood of localized junction ! burnout.
The present invention provides a thyristor device which effectively controls the net power dissipation in the voltage ~ breakover region. Several simple steps performed on the semi-12~5 conductor body of the thyristor device effectively limit the for-~ard voltage breakover current through the thyristor. Dividing ;~
the base zone of the semiconductor body serves to separate the portion of the base adjacent the breakover region from the re-mainder of the base which is in the main current-carrying part ~30 of the device. Current limiting means are then provided between ~;
111452Z .
,~ .
the separated base portions. Since the initial forward voltage breakover current is constrained to enter the base zone through `~ the breakover region, and then must pass into the main portion of the device, the breakover current will pass through the cur-~,l 5 rent limiting means. In e~ch of the above embodiments, whether employing an etch extending partially or entirely through the ~, base zone, the current limiting impedance will be in series with `I the anode and cathode during initial breakover. Because after ; turn-on the current is no longer constrained to pass through the , 10 voltage breakover region, the current limiting means is bypassed during all operations other than initial voltage breakover.
Effective reduction in voltage breakover current is therefore '~-provided without undesirable impairment of other thyristor per-formance parameters. Embodiments are provided which control either the level of initial breakover current or the current gradient. Effective protection is thus provided asainst thyris-tor failure during thyristor turn-on by voltage breakover.
Alternative embodiments are possible within the scope of the invention. Different external impedance elements could , 20 be installed, for example. Combined resistive and inductive impedances could be used. Eoth the internal connecting base portion and an external impedance could be employed in a single thyristor. ~he external impedances need not necessarily be wire- -mounted but could be in the form of a ring which bridges the deep etch. Alternate means could also be provided for dividing the base portion to isolate the portion adjacent the voltage breakover region. One such alternative technique, shown in U.S. ~;
Patent 4,047,219, involves the formation of a deep region of op-~ posite conductivity type in the base zone which effectively lim-; 30 its lateral current flow. The invention could also be used in . , , .
` non-radial-emitter configurations. It is only necessary that the base be divided to separate the initial voltage breakover . j .
region from the remainder of the thyristor to permit installation ;~
of an intervening impedance~ The base zone could initially be ~5 formed into separated portlons, thus eliminating the need for the deep etch. Additional amplifying stages could be provided in any of the described embodiments. -~
`~' A thyristor is provided which includes means for con-' trolling the current through the device when the forward break-,10 over voltage is exceeded. The invention additionally provides ~ a method of forming a thyristor device which includes a current-:,.
1~ controlling impedance for controlling power dissipation during voltage breakover. ~;
il: ' -' ``
.! ,, , ~
~ ';
1' ;
:1 ',`':
. .
.
.,~ : .
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.
~ .
ward breakover voltage. Forward breakover initiates at breakover portion 70 of junction 36. As ln the previous embodiments, the , 15~ initial current path between the anode and cathode terminals at breakover passes through the current limiting resistance 112 in-corporated into base zone 30.
The resistive impedance provided by connecting portion :
112 serves to reduce the initial breakover current thereby prev-~20 enting excessive power dissipation at the localized breakover region. As is apparent to those skilled in the art, external ~ circuit realizations could be provided for impedance 112 in the ~ ;
¦ form of external resistive, inductive, or other impedance ele- ` ~-ments. Etch 106 would simply be deepened to divide the base into fully separate portions 108 and 110, and an additional met-alized electrode would be provided outside the etch. As in the embodiments of Figs. 8 and 9, an external circuit element would F
then be installed between the two base portions. `
The embodiment of Fig. 11 provides an additional im~
, 30 pedance not only during voltage breakover but also in the gate ; ``
.
:~
1$14S2Z
circuit. As such, this embodiment is only desirable where a realtively large triggering gate voltage is available.
Another embodiment of a thyristor according to the `;~
invention is shown in Fig. 12. This embodiment incorporates essentially the same thyristor structure and method of fabrica-tion as the first embodiment shown in Figs. 1-7. The only dif-ference is the inclusion of an additional N+ region extending to top surface 22 in contact with the centrally disposed first base portion S0. This N+ region forms a second emit.er 125 extending to top surface 22, and is easily provided during the fabrication process outlined for the first embodiment. To form the embodi- -;-;
ment of Fig. 12, the masking layer 38 shown in Fig. 2 is modi-fied to include an additional circular mask portion centrally disposed over the voltage breakover region 32. ~hen the emitter zone is etched in the subsequent etching step, second emitter ~: ' I' -125 is formed, separated from first emitter 35. After deep etch 48 is formed, second emitter 125 is left in contact with first - ;
. .
base portion 50. The metalization steps of the first embodiment are used in the formation of the embodiment of Fig. 12. The ; -centrally-disposed first base electrode 126 is equivalent to electrode 59 of the first embodiment, but contacts both first base portion SO and second emitter 125. ~lectrode 126 serves a current-distributing function similar to electrode 59 of the first embodiment.
The resultant thyristor of this embodiment provides for a four-layer thyristor structure in the voltage breakover region. The significance of second emitter 125 during initial voltage breakover is illustrated in Fig. 12. As in the first -embodiment, the thyristor can be switched into forward conduc-tion from a blocking mode by raising the terminal voltage : :
1~14~2iZ
..
between terminals 64 and 66 above the forward breakover volt-age. ~hen the terminal voltage exceeds the forward breakover -~
voltage, current begins to flow across the localized breakover portion 70 of blocking pn junction 36. The path of positive .
hole current is shown generally by arrows 127. The pn junction 128 extending between second emitter 125 and first base portion ~ -50 becomes forward biased when the initial voltage breakover current increases sufficiently. This induces electrons to cross junction 128, as sho~n by arrow 130. The result is localized thyristor action producing a momentary low-resistance current path through the breakover region. The voltage drop across breakover junction 70 is significantly reduced by the injection -:~ ;",. ,,: .
of carriers from second emitter 125, lessening the possibility ~
of localized burnout. ;~-",~-, -l~S~ The improved conductivity produced during breakover by the presence of second emitter 125 is only momentary. Immedi~
ately after breakover initiates, the breakover current is lim-, , ited by the above-described current limiting means, which in the embodiment of Fig. 12 is the higher resistance of connecting ~20 portion 53 in the base zone. As in the first embodiment, the main current-carrying portion of the device is eventually turned on by the positive hole current through base zone 30. The mom-entary reduction in the voltage drop produced by second emitter 125 is intended to further reduce the likelihood of locali7ed ~;25 junction burnout, whlch is already significantly reduced by the presence of the current limiting means of the present invention.
Another embodiment of the invention is shown in Fig.
13. This embodiment is essentially the same as the embodiment shown in Fig. 8, but also includes the second emitter 125 and -first base electrode 126 of the embodiment of Fig. 12. It will -- 1 9 -- : : . :
;, be readily appreciated that the fabrication of the embodiment of Fig. 13 is essentially the same as the fabrication of the ~ embodiment of Fig, 8, except that an additional N+ emitter is v'l left in contact with first base portion 80.
The operation of the embodiment of Fig. 13 is essen~
j tially the same as the embodiment of Fig. 8. The only differ-l ence in operation occurs during initial voltage breakover when ;~ -i~ the momentary thyristor action described with respect to the embodiment of Fig. 12 is produced. The result is a momentary reduction in the voltage drop along breakover portion 70 which serves to further reduce the likelihood of localized junction burnout.
Although the embodiment of Fig. 13 is shown having i, external impedance elements 86 which are resistors as in Fig. 8, , ~15 inductive impedance elements such as shown in Fig. 9 could also ~;
be provided. -Another embodiment of the invention is shown in Fig.
, 14. This embodiment is essentially the same as the embodiment ¦ shown in Fig. 10, but also includes the second emitter 125 and first base electrode 126 of the embodiment of Fig. 12. The fab- --rication of the embodiment of Fig. 14 is essentially the same as the fabrication of the embodiment of Fig. 10, except that an ;~ --additional Nt emitter is left in contact with first base portion 50.
The operation of the embodiment of Fig. 14 is essen-tially the same as the embodiment of Fig. 10. The only differ-ence in operation occurs during initial voltage breakover when the momentary thyristor action described with respect to the embodiment of Fig. 12 is produced. The result is a momentary ; 30 reduction in the voltage drop along breakover portion 70 which ~ .
':
' ': , .
: ` :
1~1452~
serves to further reduce the likelihood of localized junction .
burnout.
Another embodiment of the invention is shown in Fig. ~ -15. This embodiment is essentially the same as the embodiment ~ ~5 shown in Fig. 11, but also includes the second emitter 125 of 3 ~: the embodiment of Fig. 12. An electrode 132 serves as a gate '-;~ electrode disposed on top surface 22 in contact with first base portion 108 and second emitter 125. Gate electrode 130 operates ; in exactly the same manner as gate electrode 116 in the embodi-ment of Fig. 11. The fabrication of the embodiment of Fig. 15 ;~ is essentially the same as the fabrication of the embodiment of Fig. 11, except that an additional N~ emitter is left in contact ` ;
with first base portion 108. .~
; The operation of the embodiment of Fig. 15 is essen- -tially the same as the embodiment of ~ig. 11. The only differ- !;;'; .~: .
; ence in operation occurs during initial voltage breakover when ; . . .
the momentary thyristor action described with respect to the embodiment of Fig. 12 is produced. The result is a momentary ! ~ reduction in the voltage drop along breakover portion 70 which l20 serves to further reduce the likelihood of localized junction ! burnout.
The present invention provides a thyristor device which effectively controls the net power dissipation in the voltage ~ breakover region. Several simple steps performed on the semi-12~5 conductor body of the thyristor device effectively limit the for-~ard voltage breakover current through the thyristor. Dividing ;~
the base zone of the semiconductor body serves to separate the portion of the base adjacent the breakover region from the re-mainder of the base which is in the main current-carrying part ~30 of the device. Current limiting means are then provided between ~;
111452Z .
,~ .
the separated base portions. Since the initial forward voltage breakover current is constrained to enter the base zone through `~ the breakover region, and then must pass into the main portion of the device, the breakover current will pass through the cur-~,l 5 rent limiting means. In e~ch of the above embodiments, whether employing an etch extending partially or entirely through the ~, base zone, the current limiting impedance will be in series with `I the anode and cathode during initial breakover. Because after ; turn-on the current is no longer constrained to pass through the , 10 voltage breakover region, the current limiting means is bypassed during all operations other than initial voltage breakover.
Effective reduction in voltage breakover current is therefore '~-provided without undesirable impairment of other thyristor per-formance parameters. Embodiments are provided which control either the level of initial breakover current or the current gradient. Effective protection is thus provided asainst thyris-tor failure during thyristor turn-on by voltage breakover.
Alternative embodiments are possible within the scope of the invention. Different external impedance elements could , 20 be installed, for example. Combined resistive and inductive impedances could be used. Eoth the internal connecting base portion and an external impedance could be employed in a single thyristor. ~he external impedances need not necessarily be wire- -mounted but could be in the form of a ring which bridges the deep etch. Alternate means could also be provided for dividing the base portion to isolate the portion adjacent the voltage breakover region. One such alternative technique, shown in U.S. ~;
Patent 4,047,219, involves the formation of a deep region of op-~ posite conductivity type in the base zone which effectively lim-; 30 its lateral current flow. The invention could also be used in . , , .
` non-radial-emitter configurations. It is only necessary that the base be divided to separate the initial voltage breakover . j .
region from the remainder of the thyristor to permit installation ;~
of an intervening impedance~ The base zone could initially be ~5 formed into separated portlons, thus eliminating the need for the deep etch. Additional amplifying stages could be provided in any of the described embodiments. -~
`~' A thyristor is provided which includes means for con-' trolling the current through the device when the forward break-,10 over voltage is exceeded. The invention additionally provides ~ a method of forming a thyristor device which includes a current-:,.
1~ controlling impedance for controlling power dissipation during voltage breakover. ~;
il: ' -' ``
.! ,, , ~
~ ';
1' ;
:1 ',`':
. .
.
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~ ' .
' -. , .
.
~ .
Claims (23)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A thyristor device for controlling current flow between a pair of terminals and which switches into forward conduction by means of a gate electrode and gate current or from a blocking mode when the terminal voltage between said terminals exceeds a breakover voltage, said thyristor device comprising: a semi-conductor body having at least four zones of alternate conduct-ivity type extending between said terminals, including an emitter zone having a first emitter in contact with one said terminal, a base zone adjacent said emitter zone, a blocking pn junction de-fining the boundary between said base zone and a third said zone adjacent said base zone, means in said body for localizing a breakover portion of said blocking pn junction where forward breakover initiates when said terminal voltage exceeds said breakover voltage, said base zone including a first base portion disposed adjacent said breakover portion of said blocking pn junction and a second base portion in contact with said first emitter, said gate electrode being disposed on said second base portion and forming a gate turn-on channel region for said gate current in said second base portion between said gate electrode and said emitter zone, and current limiting means for limiting current flow in said base zone between said first and second base portions, said current limiting means electrically inter-connecting and providing an impedance between said first and second base portions.
2. A thyristor device as in claim 1 in which said current limiting means includes a connecting portion of said base zone extending between said first and second base portions, said con-necting portion having a higher resistivity than the remainder of said base zone.
3. A thyristor device as in claim 2 including an etch extend-ing into said base zone to divide said base zone and partially separate said first and second base portions, said connecting portion being the portion of said base zone unremoved by said etch and extending between said first and second base portions.
4. A thyristor device as in claim 1 in which said first and second base portions are separated from one another and said current limiting means includes a resistor connected between said first and second base portions.
5. A thyristor device as in claim 1 in which said emitter zone includes a first emitter contacting one said terminal and said second base portion, and a second emitter separated from said first emitter and contacting said first base portion.
6. A thyristor device for controlling current flow between a pair of terminals and which switches into forward conduction by means of a gate electrode and gate current or from a blocking mode when the terminal voltage between said terminals exceeds a breakover voltage, said thyristor device comprising: a semi-conductor body having a top surface and having at least four zones of alternate conductivity type extending between said terminals, including an emitter zone extending to said top surface having a first emitter contacting one said terminal, a base zone adjacent said emitter zone and also extending to said top surface, a block-ing pn junction defining the boundary between said base zone and a third said zone adjacent said base zone, means in said body for localizing a breakover portion of said blocking pn junction where forward breakover initiates when said terminal voltage exceeds said breakover voltage, an etch formed on said top surface extend-ing into said base zone to at least partially divide said base zone into a first base portion adjacent said breakover portion of said pn junction and a second base portion in contact with said first emitter, said gate electrode being disposed on said second base portion and forming a gate turn-on channel region for said gate current in said second base portion between said gate electrode and said emitter zone, and current limiting means for limiting current flow in said base zone between said first and second base portions, said current limiting means electrically interconnecting and providing an impedance between said first and second base portions.
7. A thyristor device as in claim 6 in which said etch ex-tends partially into said base zone to divide said base zone and partially separate said first and second base portions, said cur-rent limiting means including the unremoved portion of said base zone beneath said etch extending between said first and second base portions.
8. A thyristor device as in claim 6 in which said etch ex-tends through said base zone to said third zone to divide said base zone and fully separate said first and second base portions, said current limiting means including a resistor connected be-tween said first and second base portions.
9. A thyristor device as in claim 6 said gate electrode being disposed on said top surface in contact with said second base portion.
10. A thyristor device as in claim 9 including a first base electrode on said top surface in contact with said first base portion.
11, A thyristor device as in claim 10 in which said etch extends through said base zone to said third zone to divide said base zone and fully separate said first and second base portions, said current limiting means being connected between said gate electrode and said first base electrode.
12. A thyristor device as in claim 6 in which said emitter zone includes said first emitter in contact with one said terminal and a separate amplifying stage emitter, both said emitters ex-tending to said top surface and both contacting said second base portion, a gate electrode for switching said thyristor device into forward conduction by means of gate current, said gate elecrode being disposed on said top surface in contact with said second base portion, and an amplifying stage electrode on said top surface in contact with said amplifying stage emitter and said second base portion.
13. A thyristor device as in claim 6 in which said breakover portion of said blocking pn junction and said first base portion are centrally disposed in said semiconductor body, said etch forming a closed ring on said top surface encircling said first base portion, said second base portion extending outwardly from said etch.
14. A thyristor device as in claim 13 including a gate elec-trode for switching said thyristor device into forward conduction by means of gate current, said gate electrode forming a ring on said top surface in contact with said second base portion and en-circling said first base portion.
15. A thyristor device as in claim 14 in which said emitter zone encircles said gate electrode, being an equal minimum dis-tance from said gate electrode at all points.
16. A thyristor device as in claim 6 in which said emitter zone includes a first emitter contacting one said terminal and said second base portion, and a second emitter separated from said first emitter and contacting said first base portion.
17. A thyristor device as in claim 16 in which said etch extends partially into said base zone to divide said base zone and partially separate said first and second base portions, said current limiting means including the removed portion of said base zone beneath said etch extending between said first and second base portions, and including a first base electrode on said top surface in contact with said first base portion and said second emitter.
18. A thyristor device as in claim 17 including a gate elec-trode for switching said thyristor device into forward conduction by means of gate current, said gate electrode being disposed on said top surface in contact with said second base portion.
19. A thyristor device as in claim 16 in which said etch ex-tends through said base zone to said third zone to divide said base zone and fully separate said first and second base portions, said current limiting means including an external impedance ele-ment connected between said first and second base portions.
20. A thyristor device as in claim 19 including a gate elec-trode for switching said thyristor device into forward conduction by means of gate current, said gate electrode being disposed on said top surface in contact with said second base portion, and including a first base electrode on said top surface in contact with said first base portion and said second emitter, said ex-ternal impedance element being connected between said gate elec-trode and said first base electrode.
21. A thyristor device as in claim 16 in which said emitter zone further includes a separate amplifying stage emitter extend-ing to said top surface in contact with said second base portion, a gate electrode for switching said thyristor device into forward conduction by means of gate current, said gate electrode being disposed on said top surface in contact with said second base portion, an amplifying stage electrode on said top surface in contact with said amplifying stage emitter and said second base portion, and a first base electrode on said top surface in con-tact with said first base portion and said second emitter.
22. A thyristor device as in claim 16 including a gate elec-trode for switching said thyristor device into forward conduction by means of gate current, said gate electrode being disposed on said top surface in contact with said first base portion and said second emitter.
23. A thyristor device as in claim 1 or 6 where said impedance has a resistance value at least an order of magnitude greater than the resistance of said channel region.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US92656478A | 1978-07-20 | 1978-07-20 | |
| US926,564 | 1978-07-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114522A true CA1114522A (en) | 1981-12-15 |
Family
ID=25453381
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA332,272A Expired CA1114522A (en) | 1978-07-20 | 1979-07-20 | Thyristor with voltage breakover current control and method |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS6040192B2 (en) |
| CA (1) | CA1114522A (en) |
| DE (1) | DE2928685A1 (en) |
| SE (1) | SE449538B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4261000A (en) * | 1980-05-23 | 1981-04-07 | General Electric Company | High voltage semiconductor device having an improved dv/dt capability |
| IE54111B1 (en) * | 1982-03-11 | 1989-06-21 | Westinghouse Electric Corp | Laser treatment of thyristor to provide overvoltage self-protection |
| US4555845A (en) * | 1982-10-13 | 1985-12-03 | Westinghouse Electric Corp. | Temperature stable self-protected thyristor and method of producing |
| US4514898A (en) * | 1983-02-18 | 1985-05-07 | Westinghouse Electric Corp. | Method of making a self protected thyristor |
| US4516315A (en) * | 1983-05-09 | 1985-05-14 | Westinghouse Electric Corp. | Method of making a self-protected thyristor |
| IT1212767B (en) * | 1983-07-29 | 1989-11-30 | Ates Componenti Elettron | SEMICONDUCTOR OVERVOLTAGE SUPPRESSOR WITH PREDETINABLE IGNITION VOLTAGE WITH PRECISION. |
| CA1272811A (en) * | 1985-04-24 | 1990-08-14 | Hitachi, Ltd. | Semiconductor device of overvoltage self-protection type |
-
1979
- 1979-07-16 DE DE19792928685 patent/DE2928685A1/en not_active Withdrawn
- 1979-07-19 SE SE7906202A patent/SE449538B/en not_active IP Right Cessation
- 1979-07-20 JP JP9249379A patent/JPS6040192B2/en not_active Expired
- 1979-07-20 CA CA332,272A patent/CA1114522A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6040192B2 (en) | 1985-09-10 |
| SE7906202L (en) | 1980-01-21 |
| DE2928685A1 (en) | 1980-01-31 |
| JPS5515300A (en) | 1980-02-02 |
| SE449538B (en) | 1987-05-04 |
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