DE2336287A1 - Easy switch-off thyristor of integrated transistors - has partial vertical transistor of high current amplification and lateral low-amplifying one - Google Patents

Abstract

The two transistors form an integrated semiconductor chip with a thin, high-resistance film, with a low-resistance region of identical conductivity underneath. This region provides low flow resistance of the thyristor, with a low life of minority charge carriers. One part of the region, extending laterally over the vertical transistor emitter zone is of increased width and is provided with a switch-off contact. This wider part and the contact extend along the emitter edge of the vertical transistor and also across this direction in a manner sufficient for derivation of a high switching-off current flow across the base contact from the base current flowing internally in the semiconductor body towards the vertical transistor.

Description

Deutsche Bundespost 2038

Easily switchable thyristor

The invention relates to a thyristor which can be easily switched off and consists of a vertical sub-transistor with high current gain ß * and a lateral sub-tranaiBfcor relatively low current gain β 27, the thyristor type are built integrated in a common plate-shaped semiconductor body, the semiconductor body having a thin, relatively high-resistance surface layer, underneath which is a low-resistance area of the same conductivity type, which ensures low on-resistance of the thyristor and in which the life of the minority charge carriers is very short compared to that in the surface layer.

So-called "turn-off ^{thyristors 11} , consisting of two vertical sub-transistors, are known which can be switched from conduction to blocking state with a negative control pulse between cathode gate and cathode. With a suitable construction, such a thyristor can be switched to a certain degree - also from the load dependent - value of the forward current and switch off with a certain switch-off current gain, which is defined as the ratio of the through current to the minimum gate current required for the switch-off (Mindeet switch-off current).

- 2 - . 409886/1 U9

Deutsche Bundespost 2038

When switching off, apart from transporting away the base charge stored in the npn transistor, this internally incoming base current via the external base connection (cathode gate) can be derived to such an extent that everywhere the blocking state occurs quickly in the thyristor. To do this, the gate must have a negative potential in relation to the cathode (Emitter of the npn transistor), but here is a limit due to the breakdown voltage of the emitter-base junction set.

In such a thyristor, the cathode and cathode gate contact are very narrow, closely spaced strips formed and the p-base zone not too thin, so that the sheet resistance of the area between the gate contact and that of This most distant point of the base zone is as small as possible and at a certain voltage between Gate contact and cathode as large a cut-off current as possible can flow through the gate. Besides this, the Size of the switchable current through the switch-off current gain determined, which depends essentially on the ratio of the current gain factors of the two partial transistors. It is greater, the smaller the current gain of the pnp transistor (with a correspondingly large current gain of the npn transistor) and the less the collector current of the pnp transistor during the switch-off phase via its Value grows out in the duroscale state.

Because of the desired high current gain of the npn transistor the requirement of a large base thickness must be restricted and because of the requirement of a small forward voltage the transistors must drive each other into saturation. This in turn limits the value of the current gain factor of the npn transistor up and that of the pnp-Transietors down at the expense of the cut-off current gain. Also by the requirement of a sufficiently large maximum permissible disconnection voltage and with regard to the

409886 / 1U9

Deutsche Bundespost 2038

Doping the p-base zone gives rise to further contradictions. Due to the various conflicting demands as well as the complicated technology, it is difficult to obtain one Switch-off thyristor with satisfactory properties and reproducible to manufacture. The turn-off thyristors that have become known to date have the following disadvantages:

The breaking current gain is low, the breaking power required is high, especially since the breaking voltage required increases sharply with the current density in the thyristor. The forward voltage increases with the breaking current (resp. -Performance-) amplification strongly. The cut-off voltage reaches the permissible maximum value even with a relatively small forward current (breakdown of the emitter-base transition). During the switch-off phase, a particularly pronounced current constriction occurs due to the unfavorable interaction of the internal control with the base transverse resistance one, which also limits the current that can be switched off to a low value and the switch-off power loss as well as the deletion time increased. The current that can be switched off drops considerably when the operating voltage is increased. The polarity of the switch-off pulses is that of the ignition pulses on the contrary, which, given the size of the required breaking capacity, has a not insignificant effect on the control side Requires effort.

Likewise, the unilaterally constructed thyristors (mostly designed as thyristor tetrodes) known to date are also available with negative pulses via the cathode or positive pulses via the anode gate only with very small forward currents or very low switch-off current gain can be switched off.

From DAS No. 1 299 766 a unilaterally constructed thyristor is known which has a high-resistance epitaxial layer on a low-resistance subetrat plate and one

409B86 / 1U9

Deutsche Bundespost 2038

additional zone of the located between the base zone of the vertical and the emitter zone of the lateral transistor same type of conduction used to generate the minority charge carrier flow Interrupt in the base zone of the lateral transit gate to be able to. Because of this zone pushed into the base of the Lateraltran-Bistro and the extreme resulting from it however, a large base width is used, inter alia. the current gain this sub-transistor is greatly reduced. Since this additional zone that plays the role of when switching off the thyristor The collector zone of the lateral transistor takes over, although its collector zone is close to the emitter of the lateral transistor at the same time the base zone of the vertical transistor), however, is very far from the emitter, the switch-off gate current is d. H. the current that is discharged during shutdown via the connection of the additional zone (shutdown gate) must be much larger than the current driving the vertical transistor gate. As a result, forward resistance hang and cut-off current gain from each other in a particularly unfavorable way - if one disregards the fact that it is at all It is very difficult to achieve sufficient control of the to achieve a tolerably low forward resistance Achieve vertical transistor. The effort involved in production and the space required are compared to simple ones Unilateral thyristors enlarged by the required epitaxial structure and the additional zone.

The invention is based on the object of finding a turn-off thyristor which is simple to manufacture and which from a state of high current passage with low thermosetting voltage easy, d. H. in the case of a high absorption current gain by a gate switch-off pulse of low voltage, if possible but already by briefly establishing a shunt between a gate and the associated main connection can be switched to the blocking state without changing the polarity at the gate. The advantage of being able to be switched off duroh a shunt, generated by means of a simple, controlled

409886 / 1U9

Deutsche Bundespost 2038

ble switching elements, z. B. a bipolar transistor as a quenching transistor, which in turn has a high current · »and Has power gain, consists, among other things, in the fact that the cut-off current gain and even more so the cut-off power gain as a total stand-off current (or power B) gain increased by a large factor and switch-off pulses of both polarities can be used.

The solution to the problem is based on a unilaterally constructed thyristor with a vertical and a lateral sub-transistor limited, because in this case, in contrast to the one consisting of two vertical sub-transistors Thyristor, the aforementioned difficulties, as will be shown, bypassing. In particular, it is remarkable that such an easily disconnectable thyristor according to the invention is hardly more expensive to manufacture than a conventional one Thyristor with a unilateral structure is and has the advantage of good switch-off behavior and other advantages due to no disadvantages compared to the conventional unilateral thyristor must be bought as is to be shown. This possibility, which lies in the unilateral structure, remains the conventional types of this type unused.

The object is inventively achieved in that at least that portion of the laterally over the emitter region E. of Vertikaltraneistors T ₁ protruding portion of the base region B _1, between the emitter region E ₁ of the Vertikaltranslstors T ₁ and the emitter region E 'is the lateral transistor T ₂ , widened and provided with a contact G ₁ for disconnection, so that the overall widened part of this area as well as the contact G ₁ extend along the emitter edge of the vertical transistor T ₁ and transversely to this direction at least as far and the relatively high-resistance surface layer 1 is at least so thin that the vertical transistor T ₁ internally in the semiconductor body to-

409886/1149

Deutsche Bundespost 2038

flowing base current, for switching off a large forward current, via the Ba8i.s' (gate) connection G _{1 is} derived.

The good switch-off, which is also possible when deleting with a quenching transistor as a shunt up to forward currents of a multiple of the maximum permissible continuous direct current can be achieved is based on the favorable interaction of the required measures, which ensure that the internal in the semiconductor body the vertical transistor incoming base current slightly via its base connection (Gate) can be derived. This is given by the fact that the density of the inflowing base current in the part of the Base zone is strongest where the base terminal is, while it decreases in the direction in which the Railway resistance increases towards the base connection. How thin the high-resistance surface layer must be at least depends on various parameters, such as current gain and lateral base width of the lateral transistor, service life of the Minority charge carriers in the high-resistance surface layer, doping profile in the area of its lower interface, Thickness and specific conductivity of the base zone of the vertical transit door as well as its depth of penetration (from the surface the high-resistance layer from inside) and contact width. However, according to the present experimental result both the thickness of the high-resistance surface layer and the other parameters with regard to design and manufacture of the components are not particularly critical. The thickness of the high-resistance surface layer is reduced downwards the required reverse voltage of the thyristor is limited. The range of particularly favorable values should be between about 8 and 20 / um, if all other dimensions and Values approximately the same as the experimental example described below it is based on where with the thickness of 20 yum however, by no means has the upper limit with regard to the defined switch-off capability by means of a hole-in-transit gate been reached.

409886/1 U9

German Federal Post Office 2038

In the interest of a high current gain, the base zone of the vertical transistor can be relatively thin and high-resistance without losing the defined disconnection capability. Rather, if the current gain P * * of the vertical transistor is increased and the current gain ft> « & ^eB lateral transistor is increased, the switch-off current (or power) gain increases for this Pail.

The cut-off power loss is also when switching off currents that are a multiple of the maximum permissible continuous direct current due to the rapid current drop and the elimination of the pronounced current constriction effect described above As it occurs with the turn-off thyristor made up of two vertical transistors, it is very much small amount.

The somewhat larger distance between the n- and p-emitter zone caused by the special gate arrangement, compared to conventional unilateral thyristors, results in _{no increase in the forward resistance with a large fr .. and a small j ^ 2} >, because the low-ohmic area and the only thin, Eats located above this, high-resistance surface layer for a very low-resistance current path. The current gain fb ^ which can be achieved for the vertical transistor in spite of the special gate arrangement is also completely sufficient.

Area by the required measures, through the thin high-resistance surface layer and the low-resistance region, which also provides a low path resistance to the base terminal of the lateral transistor, and by the broadening of the lying between n- and p-type emitter Baeis, it is also possible, the thyristor in the specified way by means of a quenching transistor via the base connection of the Lateraltraneistore, but with less and less

-8-409886 / 1U9

Deutsche Bundespost 2038

Switch off current amplification. For this type of switch-off, the instruction for widening the area of the base zones between the two emitters does not necessarily refer to the base zone B ₁ , since no connection is required here, but to the total width of the base zones between the emitters.

When using a thyristor tetrode in the known operating mode, at which the emitter connection of the vertical transietore and the base connection of the lateral transistor instead of the emitter connections of the two sub-transistors as main connections serve and the load between the base connection of the lateral transistor and the associated operating voltage pole is (in a known manner additionally for a sufficient current flow over the emitter of the lateral transistor must be taken care of), if the hatreds according to the invention are observed, a particularly good one results as a tortelle Can be switched off in the specified manner (e.g. using Lösohtransistor) between the emitter and base connection of the Vertical transistor at very low forward voltage and small anode current. Compared to the conventional shutdown in this operating mode, there is a considerable Increase in the breaking current and, in particular, the breaking power gain achieved. The low Durohlaßspannung is achieved that the load current only over the Vertical transistor flows and the substrate has a low resistance. In this mode of operation, too, it is the case in accordance with the invention Measures possible, the thyristor in the specified way by means of Lösohtransistor between the emitter and Disconnect the base connection of the lateral transistor, but what also here to a reduction in the amplification of the cut-off current leads.

In principle, there are various options for the construction and manufacture of such a component, e.g. B. regarding the low-resistance area, the relatively high-resistance area

409886/1149

Deutsche Bundespost 2038

Surface layer, the conductivity type of the sub-transistors and the introduction of the different zones (base and emitter zone of the vertical transistor, emitter zone of the lateral transistor) on the surface of the semiconductor body.

Figure 1 shows a not to scale for the implementation by means of the silicon planar technology particularly advantageous embodiment with its most essential parts.

FIG. 2 shows the equivalent circuit diagram used for the description.

In the example according to FIG. 1, the low-resistance region is a heavily doped semiconductor substrate plate of the same conductivity type as the relatively high-resistance surface layer 1, which is an epitaxial layer grown on the substrate plate 2. The vertical sub-transistor T ₁ with the zones E ₁ , B ₁ , C ₁ is of the npn type and the lateral transistor T ₂ with the zones E ₂ , B ', O _{2 is} of the pnp type. The base zone B ₁ of T ₁ is at the same time the collector _{zone C 2} of T ₂ and all the remaining semiconductor area outside the named zones simultaneously forms the collector _{zone C 1} of T ₁ and the base zone B ₂ of T ₂ . The semiconductor body is firmly and conductively applied to a metallic base which also forms the base connection O ₂ (anode-side gate) of T ₂ . H ₁ and H ₂ are the main connections (cathode and anode) of the thyristor and G _{1 is} the gate on the cathode side (base connection of T ₁ ). The semiconductor zones and the contacts at the upper boundary surface I of the semiconductor body are shown in FIG. 1 in a possibly simple form, which, however, does not exclude other forms of design within the scope of the instructions given. Among other things, a symmetrical structure is conceivable that has a zone B ₁ = C ₂ with the associated emitter zone E ₁ and the contacts G ₁ and H _{1 on both sides of the emitter zone E 2} , or a symmetrical structure that has one zone

- 10 - 409886/1149

Deutsche Bundespost 2038

B ₁ s C ₂ , which is laterally contacted by the two long sides of the emitter zone E ₁ , and has an emitter zone E ₂ on both sides of this central zone, or a circular and ring-shaped structure or one with comb-shaped structures. The thyristor is shown as a tetrode, but can also be implemented as a triode (if G «is omitted, for example). The secondary connection resistors R ₂ and / or R ₁ between G ₂ and H ₂ and / or G ₁ and H ₁ can also be integrated components of the component.

Various possibilities for controlling a thyristor according to the invention are indicated in FIG. On the cathode side, positive pulses of very low power are used both for ignition (at G ₁ ) and for extinguishing (via T,), where T, has the puncture of a controllable shunt. On the other hand, on the anode side, negative impulses with somewhat greater power cause ignition (at G ₂ ) and extinguishing (via T ¹ ,). If the circuit shown in FIG. 2 is changed so that the npn quenching transistor is replaced by a pnp quenching transistor on the cathode side and a diode is connected in front of its base connection and in front of the cathode gate connection in a suitable manner, then one can use the Ignite the thyristor via one and the same control pole of the circuit with a positive pulse of very low power and switch off with a pulse that is negative compared to the cathode, also with very low power. The same applies again to the anode side, only that here again the amplification of the absolute current is correspondingly lower.

Thyristors of the type shown in FIG. 1, symmetrically in the form already mentioned with E ₂ as the central zone, were produced and investigated. It is a laboratory test sample produced with simple technological means, but it already clearly shows the advantages and versatility of the thyristor according to the invention, which is very simply constructed and can be produced:

409886 / 1U9

Deutsche Bundespost 2038

On a low-resistance η-conductive substrate (0.01 Ώ. Cm) there is an η-conductive epitaxial layer (4.3 Sicm) with a thickness of about 20 μm. The zones E ₁ and B 1 are 3.5 to 4 μm deep (with boron) and the emitter zones E ₁ 2 μm deep (with phosphorus). The distance between the p-conductive zones is approximately 20 / μm, the distance available _{for attaching the gate contact G 1} ^{between an n +} emitter zone E .. and the edge of the p-base zone facing the p-emitter zone Ep is 50 / μm . The zones have the following dimensions: p-emitter E ₂ 400 70 / um ² , p-base B ₁ each 440 χ 120 / um ² , n ⁺ emitter E ₁ each 400 χ 50 / um. The breakdown voltage of the thyristor is approximately 120 volts. With a continuous current of 500 mA, which corresponds approximately to the maximum permissible continuous direct current, the forward voltage is approx. 1.2 volts. The current gain of the vertical transistor is more than 10 times greater than that of the lateral transistor. The thyristor is designed as a tetrode and can be operated and controlled in various ways. For example, it can be easily controlled according to FIG

a) A transistor of the type 2N 2218 was used as the quenching transistor T to produce the shunt between G ₁ and H _1. The load resistance was 50 £ 1 , the shunt R ₂ between Gp and H ₂ 1 k Ώ-. A load current of 500 mA was switched on by positive ignition pulses of 4 mA at G ₁ with an ignition time of 300 ns and switched off by positive switch-off pulses of 3 mA at the base of the quenching transistor with a release time of 150 ns (within ignition and quenching time 90 i » the total change in the load current). The peak of the Absohalt-Gate current pulse reached a value of 100 mA. Since the current gain / ^ _{1 of} the npn transistor in this laboratory sample is very low, ie it is far below the values attainable with planar transistors of this type, the forward characteristic curve is no longer linear above 800 mA. By acquaintances

- 12 - A09886 / 1U9

Deutsche Bundespost 2038

Procedural measures (in addition to an optimized structure of the component) can _{significantly increase / ^ 1} and thus also the maximum flow rate which can be used for pulsed operation, which can also be switched off, to a multiple of the value of the maximum permissible continuous direct current. If the current gain / ^ _{2 of} the lateral transistor is increased at the same time, an increase in the maximum permissible pulse current is no longer achieved, but at the expense of the cut-off current gain.

b) The thyristor can also be _{shunted between G 2} and H ₂ (anode gate and anode), e.g. B. realized by a Lösohtransistor (T ¹ ,), switch off: A transistor of the type 2N 2904 was used for this. The load resistance was 50 Ώ. . A load current of 500 mA was switched off by switch-off pulses of 20 mA and a minimum duration of 1 / us at the base of the erase transistor with an erase time of 1.2 / us.

o) The thyristor can also be operated in the already mentioned, known catfish in such a way that H. and G ₂ instead of H. and H _? serve as main connections and the load is between Gp and the associated operating voltage pole. In this operating mode, too, the thyristor can be operated in the advantageous manner indicated, that is to say only by establishing a shunt between G ₁ . and H ₁ or G ₂ and H ₂ with the Lösohtransistor, turn off.

Despite the small values of the current amplifications ^ ₁ and with a !! test resistor R »« 50 Ώ, a load current Xj ₁ ^s 100 mA and anode electric current I. «7 mA, the voltage between the main connections was only 0.4 volts, and the load current could can be switched off by switching off pulses of 2 mA at the base of a Löeohtransistor (type 2N 2218) connected _{between G. and H 1 with a Löeoheeit of 100 ne.}

4 09886/1 U9

German Federal Post Office 2033

In the case of components that are specially manufactured for operating mode c), a large value can be aimed for both for β> ^ and for β ₂ . This results in much larger load currents which, with a low forward voltage, require only a small anode current without, as in operating mode a), reducing the switch-off _{current gain by increasing / ^ 2.}

The following should also be noted regarding the dynamic behavior of such a thyristor in operating cases a) and c) , the current to be discharged via the gate briefly exceeds the minimum gate current applicable for slow AMckaltem (I _n ^ ₁ " ^ ^ Q mA for I _n " 500 mA). -

Urmin "a

The somewhat reduced gate current gain can easily be accepted, especially in the event of a shutdown, for example with the help of a quenching transistor (ϊ *) .; do In. the total turn-off current gain nosh the high current gain of the quenching transistor enters. With this type of disconnection, the vertical transistor is in the blocking state after the end of the release and a current only flows due to the base charge of the lateral transistor, the value of which at this point in time (namely in operating mode a) due to the low current gain of the lateral transistor in operating mode c) due to the small anode current and the lower base charge) in the test case this is already less than 10 ^ of the forward current and which in turn amounts to about 10 i> in case a) about ibis 1.5 / us, in case c) about 500 ns to about 10 i> this value decreases.

The remaining duration of the switch-off pulse or the switch-off causing shunt, which is necessary so that the thyristor does not then re-ignite automatically in normal cases mainly due to the switch-off time of the

409886/1149 - H -

Deutsche Bundespost 2038

similarly sluggish lateral transit gate and is in test case a) about 2 / US, in test case c) about 300 na. It can be many / vlb in pell a) with a long carrier life in the base of the lateral transit gate. On the other hand, it can be reduced to values below 1 / μs by reducing the carrier plane duration (if the possibilities that remain to achieve the required current amplifications are used). By locally influencing the carrier plane duration (only in the base area of the lateral transeptore) through one of the known methods suitable for this, the minimum pulse duration can be reduced to a fraction of> us and at the same time a large ratio of the current amplification factors / if / ß 2 is ^achieved limits the area outside the collector barrier layer, a very high blocking resistance can be achieved in the forward direction at the same time.

Because of the special suitability of a unilateral thyristor In accordance with the structure of the invention as a thyristor that can be switched off, it makes sense to use such thyristors also for much larger ones Build currents than are usually used in unilateral thyristors.

The voltages that are switched with such thyristors can be made possible by the technologies that are coming into being achievable blocking voltages are limited, these being increased by known technological measures can. For example, in the case of silicon planar technology, it is precisely the special gate arrangement that enables the contacts to overlap over the entire line of intersection of the collector-base junction with the semiconductor surface, whereby the Collector blocking voltage of the partial transistors and thus the forward blocking voltage of the thyristor is increased.

- 15 -

409886/1149

German Federal Poet 2038

On the other hand, such a lockable thyristor can through Reduction of its dimensions, suitable doping and influencing its carrier life to a fast bistable switch, for example for fast digital applications, modified will.

The component is very well suited for integration in monolithic silicon technology, with the puncture of the low-resistance Substrate must be taken over by a low-resistance buried layer.

With regard to the state of the art, particular attention was paid to: DAS No. 1 299 766.

A09886 / 1U9

Claims (5)

German Federal Post Office 2058
Patent claims: Easily disconnectable thyristor consisting of a vertical sub-transistor (T ₁ ) with a high current gain and a lateral sub-transistor (T _? ) With a relatively low current gain, which are built in a common plate-shaped semiconductor body like a thyristor, the semiconductor body having a thin, relatively high-ohmic surface layer (1 ), under which there is a low-resistance area (2) of the same line type, which ensures low on-resistance of the thyristor and in which the life of the minority charge carriers is very short compared to that in the surface layer (1), characterized in that at least the part of the laterally over the emitter region (E.) of the vertical transistor (T ₁₎ protruding region of the base zone (B ₁₎ connected between the emitter zone (e ₁₎ of the vertical transistor (T ₁₎ and the emitter zone (e ') of the lateral (T «) is widened and is provided with a contact (G ₁ ) for switching off that the overall widened part of this area as well as the contact (G ₁ ) extend along the emitter edge of the vertical transistor (T ₁ ) and transversely to this direction at least as far and the relatively high-resistance surface layer (1) is at least so thin that the the vertical transistor (T ₁ ) flowing internally in the semiconductor body base current, for switching off a large forward current _{, is derived via the base (gate) terminal (G 1} ) (Figures 1 and 2). 2. Easily switchable thyristor according to claim 1, characterized in that the thin, relatively high-resistance surface layer (1) an epitaxial layer (1), which is on a low-resistance substrate plate (2), which is the low-resistance Area (2) forms, grew up 1st (Figure 1). - 17 - 409886 / 1U9 Deutsche Bundespost 2038 3. Easily peelable thyristor according to claim 1 or 2, characterized in that both the thickness of the thin, relatively high-resistance surface layer (1) and the distance between the base zone (B ₁ ) of the vertical _{transistor (T 1} ) and the emitter zone ( E ₂ ) of the lateral transistor (T ₂ ) are preferably between 8 and 30 μm (FIG. 1). 4. Easily switchable thyristor according to claim 1, 2 or 3, characterized in that the minority charge carrier life in the vicinity of the emitter zone (E ₂ ) of the lateral transistor (T ₂ ) is reduced. 5. Easily switched off thyristor according to one of the claims 1. to 4., characterized * that "with respect to at least one of its sub-transistors (T ₁ or T ₉ ) the base current flowing internally in the semiconductor body by (briefly) establishing a shunt (e.g. T, or T ') between base connection (G ₁ or β «) and smitter connection (H ₁ or H ₂ ), for switching off a large forward current, via the base (gate) connection (G ₁ or G ₂ ) is derived (Figure 1 and 2) " 409886 / 11A 9 Blank page