Temperature Compensated Zener Diode

Abstract

This is a temperature compensated zener diode wherein the compensation is provided by having a transistor structure with two base emitter junctions, one operating in forward bias and the other (zener) being reversed biased. This device has a number of these transistor structures cascaded to give the desired zener voltage and temperature compensation. The negative voltage variation with respect to temperature of a forward biased emitter base junction compensates for the positive voltage variation of the zener diode.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a temperature compensated Zener diode in the form of a semiconductor solid state or integrated circuit consisting of several nonlinear and, if necessary, linear individual elements arranged in a common semiconductor body of the one conductivity type and connected among each other with the aid of applied metal coatings, and which is provided with two external connecting terminals.

It is well-known that the breakdown voltage of Zener diodes is not only current-dependent, but also temperature-dependent. This is because Zener diodes with a breakdown voltage below approximately 5 volts have a negative, and above this value a positive temperature coefficient. Moreover, it is known to compensate the positive temperature coefficient of Zener diodes having a breakdown voltage of more than 5 volts, in that one or more semiconductor diodes operated in the forward direction, are connected in series with the Zener diode (as regards the above reference is made to "Elektronische Rundschau," Dec. 1957, page 376, right-hand column).

This kind of temperature compensation can only be carried out with a reasonable expenditure for breakdown voltage of slightly more than 5 volts. Since the breakdown voltage variation with respect to temperature increases as the breakdown voltage increases, and since, on the other hand, the breakdown voltage variation which is due to temperature, of a silicon semiconductor diode which is operated in the forward direction, amounts to about -2 millivolts/.degree.C., (mv./.degree.C.) there is required with respect to higher breakdown voltages, in particular for such ones lying above approximately 8 to 10 volts, such a great number of forward diodes that this kind of temperature compensation with the aid of discrete components becomes uneconomical. Thus, for example, a Zener diode having a breakdown voltage of 15 volts requires seven forward diodes.

There are also commercially available temperature compensated Zener diodes having breakdown voltages around 8 volts in which, inside a casing, there is arranged a separate Zener diode as well as the number of semiconductor diodes which are driven in the forward direction, and which are required for effecting the temperature compensation, see e.g. the INTERMETAL-Z-diode combination BZY 25 (INTERMETALL-data book transistors-diodes 1965/66, pp. 484 and 485).

This Zener diode combination, however, on account of its construction consisting of discrete individual semiconductor components accommodated inside a housing, still has dimensions which are considerably larger than the ones of an individual Zener diode of comparable power loss. Thus, for example, the aforementioned temperature compensated Zener diode BZY 25 requires a space of about 2.8 cm..sup.3 at an admissible power loss of 200 mw., whereas the comparable, noncompensated Zener diode Z 8 only requires a space of about 0.02 cm..sup.3. In addition thereto the differential resistance increases to an unfavorably high extent as the breakdown voltage increases.

Efforts are now made, on one hand, with a view to reduce the size of the temperature compensated component and, on the otherhand, for still further improving also the temperature compensation quality, as well as the differential resistance.

For the purpose of reducing the dimensions, there is offered the well known technique of the monolithic integrated semiconductor solid state circuits. Thus, for example, there is known from the U.S. Pat. No. 3,244,949 a voltage stabilizing circuit in the form of a semiconductor solid state or integrated circuit in which a Zener diode disposed between the base and the collector of a transistor, and this transistor as well are arranged within a common semiconductor body.

In this circuit there is only contained one single Zener diode and only one single forward diode, so that the circuit, as already mentioned above, has a breakdown voltage of merely somewhat more than 7 volts.

Whenever it is the problem to manufacture components with substantially higher breakdown voltages, several such components may be connected in series. If such a series connection is supposed to be constructed or built up in the form of a semiconductor solid state of integrated circuit, then this, however, can only be realized in that each individual component is accommodated in a separate insulation island on a common substrate. This, however, implies a substantial complication of the manufacturing process, because for the formation of the insulation islands there is required a further step of process.

Furthermore, from the U.S. Pat. No. 3,140,438 it is known to manufacture both the Zener diode and the forward diode, for the purpose of effecting a temperature compensation, as one single component which, in its construction, corresponds to the construction of a transistor with a zone sequence of alternating conductivity types, the mode of operation of which, however, differs from the mode of operation of a transistor on account of the doping conditions of the individual zones which differ in kind from those of an ordinary transistor.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a temperature compensated Zener diode having in particular a high breakdown voltage, with the dimensions of the diode not being substantially greater than of the individual Zener diode of the type known hitherto.

It is a further object of the present invention to improve the temperature compensation properties of the well-known temperature compensated Zener diodes consisting of discrete components, just as the differential resistance thereof. Moreover, the o above-mentioned expenditure caused by the additional step of process, shall be reduced if possible.

According to the invention more than two transistor structures are used as individual elements, the semiconductor body representing the common collector zone of all transistor structures and the base-emitter PN junctions of the transistor structures with respect to the direction of the total current flowing during operation are connected in such a way in series that a part of the base-emitter PN junctions in the backward direction up into the breakdown region are operated as Zener diodes, and that the remaining ones in the forward direction, are operated as forward diodes, that for the purpose of reducing the dynamic internal resistance, there is used the transistor effect of at least a part of the transistor structures operated as forward diodes, and that the semiconductor body is connected to the first outer connecting terminal and either the base of the last Zener diode or the emitter of the last forward diode is connected to the second outer connecting terminal.

General principles relating to the construction of semiconductor solid state or integrated circuits are described in "Scientia electrica," 1963, pp. 67 to 91, in particular on pages 79, 85 and 88, where it is stated that for diodes and Zener diodes either the base-collector or the base-emitter PN junctions of transistor structures can be used. These statements, however, refer to semiconductor IC's for amplifier or switch applications, so-called linear or digital semiconductor IC's, in which the intended function already a priority requires transistor structures. Additionally required diodes or Zener diodes are then realized in such semiconductor IC's in the manner stated hereinbefore.

With respect to a pure two-terminal network, as is represented by the inventive type of temperature compensated Zener diode, this kind of realization of Zener diodes and semiconductor diodes is not obvious, because the use of transistor structures for diodes is more expensive when looked at from the standpoint of conventional circuitry engineering. From the inventive type of construction of the temperature compensated Zener diode there also result advantageous effects which are not to be considered as a self-suggesting matter of fact, and which are still to be explained in detail hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the usual construction of a semiconductor IC comprising a transistor structure and a diode structure;

FIG. 2 shows diodes connected in series in the same sense, and which are located in a common collector zone;

FIG. 3a shows the electrical equivalent circuit diagram relating to two series connected Zener diodes, arranged according to FIG. 2;

FIG. 3b shows the electrical equivalent circuit diagram relating to series connected forward diodes positioned in a common collector zone and which are likewise arranged according to FIG. 2;

FIG. 4 shows FIG. 3b in a redrawn manner the forward diode chain;

FIG. 5 shows the equivalent circuit diagram of FIG. 4 amended by the emitter resistances;

FIG. 6a shows series connected Zener diodes and forward diodes in a common collector zone;

FIG. 6b shows the electrical equivalent circuit diagram of the arrangement according to FIG. 6a;

FIG. 7 shows an advantageous modification of the arrangement according to FIGS. 6a and 6b;

FIG. 8 shows another advantageous modification of the arrangement according to FIGS. 6a and 6b;

FIG. 9, at an enlarged scale, shows a part of FIG. 6a;

FIG. 10a shows an advantageous further embodiment of the inventive type of Zener diode constructed by using the partial arrangement according to FIG. 9;

FIG. 10b shows the electrical equivalent circuit diagram relating to the arrangement according to FIG. 10a;

FIG. 11 shows another advantageous embodiment of the inventive type of Zener diode;

FIG. 12 shows a further embodiment of the arrangement according to FIG. 11;

FIG. 13 shows a still further embodiment of the arrangement according to FIG. 11;

FIG. 14 shows a transistor structure and circuit for adjusting the voltage variation of the collector to emitter;

FIG. 15 shows another embodiment of the invention in which the current source shown in FIG. 14 is connected to the embodiment shown in FIG. 13;

FIG. 16, in a plan elevation, shows a section of the semiconductor body of the temperature compensated Zener diode containing the inventive further transistor structure, as well as the ohmic resistors;

FIG. 17, in a schematic representation, shows another arrangement of the additional ohmic resistors;

FIG. 18, in a schematic representation, shows an arrangement of the ohmic resistors differing from that of FIG. 17; and

FIG. 19, in a schematic representation, shows a further possibility of arranging the ohmic resistors.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the well-known construction of a semiconductor IC which, for the sake of simplicity, merely contains one transistor structure and one diode structure. As the diode structure there is likewise used a transistor structure, in which case the collector terminal C is connected to the base terminal B, so that the collector base PN junction is short circuited. The collector region n.sub.C, via the contacting zone n.sub.E which has resulted simultaneaously with the emitter zone n.sub.E, and the contact coating A1, is connected to the collector terminal C.

In the same way both the base zone p.sub.B and the emitter zone n.sub.E are connected to their respective outer connecting terminal B or E respectively, via the contact coating A1. Owing to the insulation diffusion p.sub.J extending from the one surface through the n.sub.C zone to the substrate p.sub.S, there are produced individual collector zones n.sub.C which are insulated from one another by PN junctions. The surface, with the exception of the contact areas, are coated with a passivating protective layer S s.

The diodes may be operated either as forward or as backward diodes, for example, as Zener diodes in the conventional way in voltage stabilizing circuits. Decisive for the breakdown voltage of these components operated as reference signal sources, are each time substantially the forward or breakdown properties of the PN junction forming the diode.

Since in semiconductor integrated circuits, above all the breakdown voltage of the PN junctions can only be chosen within narrow limits, it is often required to connect several Zener diodes in series, in order to obtain the desired breakdown voltage.

As already mentioned hereinbefore, the Zener diodes, in the conventional way, can be connected in series with forward diodes in order to compensate the positive temperature coefficient of the breakdown voltage by the negative temperature coefficient of the forward voltage. All of these circuit arrangements are also possible in this case, as long as the voltages between the collector areas of the individual diodes and the substrate area are reliably below the collector substrate breakdown voltage, as the substrate is the most negative or the most positive point of the circuit, depending on the type of conductivity of the substrate.

In FIG. 2 and 3a there is shown a number of transistor structures connected in series and as Zener diodes. The maximum number n.sub.max of the series connected Zener diodes is dependent upon the connection of the substrate or on the basic material of the collector zone n.sub.C respectively.

The following possibilities of connections are conceivable which, in FIGS. 2 and 3a are indicated by the corresponding small letters:

a. The substrate is not connected. Since the substrate is electrically not assigned to any circuit potential, this mode of operation is unfavorable. With respect to n.sub.max, the following relationship can be stated;

wherein V.sub.EB symbolizes the breakdown voltage of the emitter base diodes, and V .sub.CE symbolizes the breakdown voltage of the collector emitter path of the transistor structures, in particular the collector emitter breakdown voltage of the transistor structure 1.

b. The substrate is connected to the first outer connecting terminal I, hence to the plus pole of an external source of voltage. This results in the most reliable and inventive mode of operation. The maximum number of Zener diodes capable of being connected in series, is as follows:

c. The substrate is connected to the p.sub.B region of the first Zener diode in the chain. This connecting possibility, just as that of case a above, is unfavorable.

d., e. These connecting possibilities have proved unsuitable and, therefore, are to be considered as being prohibitive.

With the possibility according to b it is possible to obtain breakdown voltages of the entire arrangement within the area between the breakdown voltage V.sub.EB of the base emitter PN junction and the breakdown voltage V.sub.CB of the base collector PN junction as integer multiples of the base emitter breakdown voltage V.sub.EB.

The remaining properties of the arrangement do not distinguish substantially over the properties of conventional Zener diodes. This also applies to the dynamic resistance which increases as the number n increases, just as in the case of conventional Zener diodes the dynamic resistance increases as the breakdown voltage increases.

In the equivalent circuit diagram of FIG. 3a only the two first ones and the two last ones of the n transistor structures are shown, which are effective as Zener diodes, and are indicated by the references 1, 2, (n-1) and n respectively. The emitter of the transistor structure 1 is applied to the first outer connecting terminal I. The base of the transistor structure 1 is connected to the emitter of the next following transistor structure 2, likewise the base of this transistor structure is connected to the emitter of the next following one, and so on, up to the emitter of the last transistor structure The base of this last transistor structure is applied to the second outer connecting terminal II, which is connected to the minus pole of an external source of current.

FIG. 3b shows the transistor structures 1' to m corresponding to those of FIGS. 2 and 3a, but now operated in the forward direction. The maximum number m.sub.max of the series connected forward diodes is dependent upon the connection of the substrate, or upon the connection of the basic material of the collector zone n.sub.C, n.sub.C, respectively. The following possibilities for the connection are conceivable:

a. The substrate or wafer is not connected. This case is unfavorable for the same reasons as case a of the Zener diode chain. There applies the following relationship:

wherein V.sub.CE indicates the collector emitter breakdown voltage of the last transistor structure m, and V'.sub.BE indicates the emitter base forward voltage of the transistor structures.

e. The substrate or wafer is connected to the plus pole of an external source of voltage. There applies the following relationship:

This results in the most reliable and inventive mode of operation.

d. The substrate or wafer is connected to the emitter of the last transistor structure m. This way of connecting is similarly as unfavorable as the one referred to under a above.

b. and c. These connections have proved unsuitable and, therefore, are to be considered as prohibitive.

In this way it is possible to obtain forward voltages for the entire arrangement from the integer multiples of the forward voltage of one single base emitter PN junction. The remaining properties of the arrangement, however, partly differ considerably from the properties of series connected discrete forward diodes. The same applies above all to the dynamic resistance.

In the equivalent circuit diagram of FIG. 3b, there are shown the two first ones and the two last ones of the m transistor structures acting as forward diodes, which are indicated by the references 1', 2', m-1 and m. The emitter of the first transistor structure 1' is connected to the first outer connecting terminal which is applied to the minus pole of an external source of current. The base of this transistor structure is connected to the emitter of the next following transistor structure 2', whose base is again connected to the emitter of the next following transistor structure, and so on, up to the emitter of the last transistor structure m. The base of this last transistor structure is applied to the second outer connecting terminal II which is to be connected to the plus pole of the external source of voltage.

In FIG. 4 the equivalent circuit diagram of FIG. 3b is shown in a redrawn fashion. When connecting the collector zone n.sub.C to the outer connecting terminal II which is applied to plus, then the chain of forward diodes represents an m-fold DARLINGTON amplifier. The respective base currents of the m transistor structures are indicated by the references J.sub.2 to J.sub.m+1. The base current of the m-1st transistor structure is equal to the emitter current of the mth transistor structure.

The dynamic resistance r of this arrangement is substantially determined by the properties of the transistor structure 1', for r is approximately inversely in proportion to the transconductance S.sub.1 of the transistor structure 1', because almost the entire current J flowing through the arrangement, is led via the collector of the transistor structure 1', so that the latter acts as a transistor, i.e., in a current amplifying way. The collector current J.sub.C1 of the transistor structure 1' is equal to the total current J reduced by the emitter current J.sub.2 of the transistor structure 2'. J.sub.2, however, is smaller by the current amplification factor B.sub.1 of the transistor structure 1', so that J.sub.C1 is approximately equal to J.

With the aid of a suitable geometric embodiment of the transistor structure 1' care may be taken that also in the case of very high currents, the favorable properties are maintained.

The DARLINGTON amplifier is controlled by the potential of the outer connecting terminal I. As the forward voltage of the arrangement, as already described hereinbefore, there is available the sum of the forward voltages of the base emitter PN junctions. Accordingly, there is utilized the transistor effect of the transistor structures 1' to m.

With respect to the further reduction of the dynamic resistance r, the circuit according to FIG. 4 can be improved and further embodied by increasing the base currents diminishing as the ordinal number increases, of the transistor structures 2' to m acting as emitter followers, so that also the further transistor structures will obtain an operating point at which there appears the current amplifying transistor effect. The collector of the transistor structure 1' almost conducts the entire current J. With respect to the emitter currents J.sub.Em it applies, by way of approximation in the case of sufficiently large current amplification factors B.sub.m, that the mth emitter current is equal to the total current J divided by the product of the m current amplification factors B.sub.m. In this way, however, also the forward voltage V.sub.m of the forward diodes decreases as the ordinal number m increases, because V.sub.m is in proportion to the natural logarithm of the quotient from the mth emitter current and the associated leakage emitter current. Moreover, as the emitter current becomes smaller, there increases the amount of the relative and absolute temperature coefficient, and the current amplification factor B.sub.m likewise drops off.

The emitter currents J.sub.Em can be freely selected within certain limits when advantageously inserting ohmic resistances in the arrangement according to FIG. 4, in the course of further embodying the invention, as is shown in FIG. 5.

In the emitter lead-in of each of the transistor structures 2' to m there is each time inserted an ohmic resistor R'.sub.2 to R.sub.m whose end not facing the emitter is connected to the second outer connecting terminal II. The emitter of the transistor structure 1' conducts the current J', whereas the base current of the transistor structure m is indicated by the reference J.sub.m+1.

The ohmic resistors may be included as well in the semiconductor integrated circuit, and may be formed, for example, by the p.sub.B diffusion, and may be embedded in the n.sub.C base material representing the common collector of the forward diodes 1' to m. Since the base collector PN junctions of these ohmic resistors are always biased in the backward direction there results the very substantial advantage with respect to the simplicity of the semiconductor IC, that there are not required any further insulation islands. The ohmic resistors, however, may also be deposited on the semiconductor body in the form of resistance layers. A further substantial advantage of the insertion of the ohmic resistors is to be seen in the fact that the temperature coefficient of the forward voltage of the arrangement can be freely selected within limits, because it is current dependent and can be precisely adjusted by the resistance value.

FIGS. 6a and 6b now show the series connection of the chain of Zener diodes and the chain of forward diodes as already considered separately hereinbefore. A number of n Zener diodes and m forward diodes with the associated emitter resistors R'.sub.2 to R.sub.m are led into the common collector zone n.sub.C. The ohmic resistor R.sub.n which is required for adjusting the current flowing through the chain of Zener diodes is advantageously likewise arranged in the common collector zone.

The common collector zone may again be connected in different ways. Of the three possibilities a, b, c as shown in the drawings, the connection according to b is to be preferred, because in this case, according to the arrangement in FIG. 4, again the greatest portion of the total current flows through the transistor structure 1'. The connections a and c, however, are more unfavorable.

The dynamic resistance r of this arrangement and in the case of the connection b, is approximately inversely in proportion to the transconductance S.sub.1 of the transistor structure 1'; this value, however, is small with respect to the dynamic resistance of conventional types of Zener diodes.

The number of forward diodes is chosen thus that the temperature coefficient of the base-emitter forward voltage will just compensate the temperature coefficient of the breakdown voltage of the n Zener diodes.

A fine adjustment of the compensation is achieved, in further embodying the invention, by correspondingly selecting the emitter currents of the forward diodes with the aid of the value of the ohmic resistors R'.sub.2 to R.sub.m.

Appropriately, the current flowing through the Zener diodes is chosen with the aid of R.sub.n, in such a way that the noise of the Zener diodes will become as small as possible.

It is not necessary for the Zener diodes and the forward diodes to be each time connected in series in associated groups. For example, according to FIG. 7 one part of the forward diodes can be connected in front, and one part behind the Zener diodes, which may offer some production-technical advantages.

In the example according to FIG. 7 the ohmic resistor R'.sub.2 is determinative of the current flowing through the transistor structure 2', the ohmic resistor R.sub.4 is determinative of the current flowing through the transistor structure 4, and the ohmic resistor R".sub.2 is determinative of the current flowing through the Zener diodes 1, 2 and through the transistor structure 3. In doing so, all of the ohmic resistors are relatively low-resistive, hence are particularly favorable for being accommodated within the collector zone without requiring any considerable space.

FIG. 8 shows a further advantageous construction of a temperature compensated Zener diode. By a distribution or subdivision of the ohmic resistors differing from that of the arrangement according to FIG. 7, the latter obtains still more favorable, i.e. lower resistance values with respect to semiconductor integrated circuits, Instead of connecting the end of each individual emitter resistance not facing the emitter, to the second outer connecting terminal II, the emitter resistances are connected in such a way that the end not facing the emitter, is connected to the emitter of the preceding transistor structure, in the course of further embodying the invention. Thus, for example, the ohmic resistor R'.sub.2 which is associated with the forward diode of the transistor structure 2', is connected to the emitter of the preceding transistor structure 1'.

The ohmic resistor R'.sub.n represents the series resistance for the Zener diodes of the transistor structure 1 to n; it is positioned between the emitter and the base of the last transistor structure m of the chain of forward diodes. The resistor R'.sub.n can be advantageously replaced by the ohmic resistor R.sub.n connecting the base of the last forward diode m directly to the outer connecting terminal II. Accordingly, the transverse current of the Zener diodes which, under certain circumstances, may be high, will not flow through the chain of emitter resistances, which may thus result in favorable properties.

In the arrangement according to FIG. 6b the base lead-in conductors of the transistor structures n and m are connected to one another. For this reason the two associated emitter zones may be inserted in one common base zone, as is shown in FIG. 6a.

In FIG. 9 this arrangement is shown on an enlarged scale. The thus formed double diode represents a lateral NPN type transistor, because the right-hand NP diode is operated in the forward direction, hence with injection, whereas the left-hand PN diode is operated in the backward direction and within the breakdown area.

Such types of lateral transistors and their properties are well-known from "Proceedings of the IEEE", Dec. 1964, pp. 1491 to 1495, and from "Solid State Electronics", 1967, pp. 225 to 234. The employment with the inventive type of temperature compensated Zener diode, however, insofar produces a surprising effect as the properties of the Zener diode, by selecting the current amplification factor, which can be influenced appropriately and in an advantageous manner. Thus, for example, the breakdown voltage decreases as the base width X.sub.B becomes smaller. In cases where this effect is unwanted, X.sub.B is made large, and in the conventional planar structures values of X.sub.B greater than 30 to 50 .mu.m are sufficient to this end. Owing to the current amplification factor, the dynamic internal resistance, the quality of the temperature compensation, and the noise properties of the temperature compensated Zener diode can be influenced. The use of double structures is of a particular advantage with the temperature compensated Zener diode according to the invention, because the noise is substantially reduced on account of the one PN function which is operated with injection. Moreover, the positive temperature coefficient of the breakdown voltage of the Zener diode can be further reduced independently of the temperature compensation as given by the forward diodes. Likewise, the dynamic resistance is reduced and made adjustable, so that also the dynamic resistance of the total arrangement is reduce.

FIGS. 10a and 10b show the construction of a particularly favorable further embodiment of the inventive type of Zener diode. In this case all transistor structures which are intended for acting as Zener diodes, are each combined with a transistor structure acting as a forward diode to form, accordingly, a double structure consisting of two transistor structures, so that there will result the double structures 1" to p. These double structures are in such a way connected among each other that the emitter of the partial structure of the double structure 1" acting as the Zener diode, is connected to the outer connecting terminal I, hence to the plus pole of an external source of voltage, whereas the emitter of the partial structure of the double structure 1" acting as the forward diode, is connected to the emitter of the next double structure 2" forming part of the Zener diode. The emitter of the forward diode of 2" then again leads to the emitter of the Zener diode of the next double structure, and so forth, up to the double structure p. The forward diode emitter of the double structure p, if necessary, may be connected to the first base of an additional chain of forward diodes, corresponding to the connecting terminal II according to the arrangement shown in FIG. 3; of this chain of forward diodes the first transistor structure 1' is shown in FIGS. 10a and 10b.

Owing to the ohmic resistors R.sub.B1, to R.sub.Bp which are likewise capable of being brought into the collector zone n.sub.C, and which are connected to the base of the associated double structure, it is possible to select the currents flowing in the Zener diodes. With the aid of the ohmic resistors R.sub.E1, to R.sub.Ep which are likewise capable of being brought into the collector zone n.sub.C leading to the emitters belonging to the respective forward diode of the double structures, it is possible to adjust the emitter currents of the partial structures of the double structures acting as forward diodes.

Accordingly, the ohmic resistors R.sub.B1, to R.sub.Bp and R.sub.E1, to R.sub.Ep are likewise let into the common collector zone n.sub.C which is in accordance with the present invention, so that there are not required any other insulated n.sub.C zones.

By utilizing the principles explained with reference to FIGS. 10a and 10b, and by applying the considerations mentioned with respect to the explanation of FIGS. 5, 7 and 8, the arrangement according to FIGS. 10a and 10b can still be further advantageously modified and simplified. This is shown in FIG. 11.

The emitters of the double structures 1" to p are connected to one another in the way as stated in the course of explaining FIG. 10a. The emitter of the partial structure of the double structure p acting as the forward diode, is still followed by the chain of forward diodes 1" to m, of which there are shown the two transistor structures 1' and m. The ohmic resistors R.sub.B'1 to R.sub.B'p constitute a series connection, with the beginning thereof, namely the one end of R.sub.B'1 being connected to the base of the double structure 1", whereas its end is applied to the second outer connecting terminal II.

To each connecting point 22 to pp of two successively following ohmic resistors of the chain R.sub.B'1 to R.sub.B'p there is connected the base of the corresponding next double structure. Hence, for example, to the connecting point 22 between R.sub.B'1 and R.sub.B'2 there is connected the base of the double structure 2". Moreover, from these connecting points there extends each time one ohmic resistor R.sub.E'1 to R.sub.E'p-1 to the emitters of the partial structures of the associated double structures, acting as forward diodes. Thus, for example, the ohmic resistor R.sub.E'1 is lying between the forward diode emitter of the double structure 1" and the connecting point 22 of R.sub.B'1 and R.sub.B'2, hence also to the base of the double structure 2". The last ohmic resistor R.sub.E'p of the R.sub.E' series, unlike thereto, extends from the forward diode emitter of the double structure p which is also connected to the base of the forward diode of the transistor structures m, to the emitter of the transistor structure m and to the base of the next lower forward diode transistor structure, hence in this case to the base of transistor structure 1'. Between the base of the next lower transistor structure and the emitter thereof there is arranged the resistor R".sub.m.

FIGS. 12 and 13 show further possibilities as to how the double emitter structures can be connected in series. This will result in a saving of ohmic resistors.

Thus, FIG. 12 shows an arrangement in which the effective resistors R.sub.E'1 to R.sub.E'p-1 connecting the base to the forward diode emitter of the preceding double emitter structure, are omitted. Furthermore, the ohmic resistor R.sub.Ep of the forward diode emitter forming part of the last double emitter structure, is connected to the second outer connecting terminal II. In the same way the resistor R.sub.m, which is inserted in the emitter lead of the last one of the successively following chain of forward diodes, is applied to the outer connecting terminal II. The emitter resistors of further forward diodes may also be connected to the outer connecting terminal II, as has already been shown in FIG. 5.

Another further embodiment of the arrangement according to FIG. 11 will result in cases where, the series connection of the ohmic resistors R.sub.B'1 . . . R.sub.B'p is eliminated by omitting the leads or deposited leads by which these ohmic resistors are connected among each other. Also in this case it is again possible for forward diodes to be added to the emitter of the Zener diode of the last double structure p which, however, has not been shown in FIG. 13 for the sake of clarity.

The possibilities of arranging the individual ohmic resistors as shown in the accompanying drawings are still further capable of being modified and can be adapted to the respectively required quality of the temperature compensated Zener diode.

In FIG. 14, the additional transistor structure T is shown together with the voltage divider consisting of the ohmic resistors R.sub.1 and R.sub.2, as an electrical equivalent circuit diagram. The ohmic resistor R.sub.2 is positioned between the base and the collector electrode of the transistor structure T, and consists of the partial resistors R.sub.21 ; R.sub.22, R.sub.23, R.sub.2n. The ohmic resistor R.sub.1 is positioned between the base and the emitter electrode of the transistor structure T. In a good approximation, the following two relationships apply to this circuit arrangement:

wherein V.sub.CE indicates the collector emitter voltage, and V.sub.EB the base emitter voltage of the transistor structure T. By .DELTA.V.sub.CE and .DELTA.V.sub.EB there are indicated the voltage variations of the collector emitter voltage or of the base emitter voltage respectively, as caused by a temperature variation indicated by .DELTA..tau.. Since now the voltage variation with respect and due to temperature, of the base emitter voltage V.sub.EB amounts to about -2mv./.degree. C., it is possible to adjust the voltage variation with respect and due to temperature, of the collector emitter voltage V.sub.CE by varying the resistance values of the ohmic resistors R.sub.1 and R.sub.2. The aforementioned subject matter is known per se, i.e. from the "Consumer Application Note: 15 Watt Audio Amplifier with Short Circuit Protection" by Don Smith as published by Fairchild Semiconductors, Mountain View, California, on Nov. 24, 1965.

In FIG. 15 the circuit part as shown in FIG. 14, is connected together with an arrangement acting as a temperature compensated Zener diode. The complete arrangement substantially corresponds to the arrangements shown in the upper part of FIG. 7 and in FIG. 13. The emitter of the transistor structure T is connected at the most positive point of the arrangement according to FIG. 13. This offers the advantage that also the transistor structure T can be integrated in the common collector zone n.sub.C of the temperature compensated Zener diode, otherwise there is required an insulating island for the transistor structure.

FIG. 16 shows a portion of the semiconductor body of the temperature compensated Zener diode according to the invention, i.e. in a plane plan elevation, that particular portion containing the transistor structure T and the ohmic resistors R.sub.1 and R.sub.2. The resistance areas as produced in the semiconductor body forming the common collector zone n.sub.C, are indicated by the dash lines. Both the emitter and the base zone are not shown, whereas the squares and rectangles indicated by the dash lines, are to be considered as openings provided in a layer of insulating material covering the semiconductor body, with these openings exposing the zones lying beneath. In these openings, and on the respective zones, there is applied a metal coating serving the contacting of the zones. In the drawing there are shown the following zones with the corresponding openings in the layer of insulating material and the contacts attached thereto; the ohmic resistor R.sub.1 with the openings 1 a and 1b provided at the ends thereof, further the ohmic resistor R.sub.2 consisting of the series connected partial resistors R.sub. 21, R.sub.22, R.sub.23, R.sub.24. The series connection of these resistors comprises the contacting openings 2a, 2b, 2c, 2d, 2e. Over the three zones of the transistor structure T there are provided the contacting openings B for the base, C for the collector, and E for the emitter, and in these openings there is likewise deposited a contact coating.

With the exception of the contacting coatings produced in the openings, the surface of the semiconductor body is covered with a further layer of insulating material. On this layer of insulating material the areas indicated by the dot-and-dash lines, are provided with a metal coating enlarging the surface of the contacts lying underneath. One portion of these enlarged contact coatings also establishes the electrically conducting connections between the individual contact coatings lying underneath. In detail there are provided the following larger contact coatings: the contact coating 31 connecting the emitter contact E and the one end 1a of the ohmic resistor R.sub.1 to one another; further the contact coating 32 connecting the base contact B, the other end 1 b of the ohmic resistor R.sub.1 and the one end 2 a of the ohmic resistor R.sub.2 to one another; moreover the contact coating 33 which enlarges the surface of the contact coating 2 d; furthermore the contact coatings 34 and 35 each of which serving to enlarge the contact surface of the contact coatings 2b and 2c; finally the contact coating 36 connecting the other end 2e of the ohmic resistor R.sub.2 to the collector contact C.

The arrangement of the enlarging contact coatings 31 to 36, in an advantageous manner and in further embodying the invention, is now chosen thus that each contact coating extends up into the proximity of the other one. This, for example, may be taken from the geometrical arrangement of the contact coating 31 whose part 31a connecting the contact coatings E and 1a, via the part 31b, extends to the part 31c, so that the contact coating 31 extends up to almost the contact coating 36. The contact coatings 33 to 35, in their surfaces, are chosen so large that only a small distance remains between them. Each time two edges of these contact coatings extend parallel in relation to one another. Likewise also the contact coatings 31, 32 and 36 are so designed that each time two edges extend parallel in relation to one another.

The course of the ohmic resistor R.sub.2 and the arrangement of the contacting openings 21 to 25 are chosen thus that the larger contact coatings 33 to 35 can be arranged next to each other. In FIG. 16 this is accomplished by the approximately U-shaped course of the ohmic resistor R.sub.2.

Owing to the described arrangement of the enlarged contact coatings 31 to 36, and owing to the described arrangement of the ohmic resistor R.sub.2 it is now possible that either parts of the ohmic resistor R.sub.2 or the entire transistor structure including the ohmic resistors R.sub.1 and R.sub.2 are short circuited. This means to imply when the temperature dependent voltage variation .DELTA. V.sub.CE of the collector emitter voltage can be selected in dependence upon the resistance value of the ohmic resister R.sub.2. In this way, however, the entire component of the temperature compensated Zener diode can be balanced to an optimum temperature coefficient. With the aid of only one additional metal coating, the described arrangement of the ohmic resistor R.sub.2 and of the contact coatings 31 to 36 permits to let one, two, three or four partial resistors remain effective, or to short circuit the entire arrangement. There exist the following short circuit connections which may consist of a correspondingly applied metal layer, with the surface thereof being indicated in FIG. 16 by the solid line rectangles: The short circuit coating I serving the shorting of three partial resistors, namely of the partial resistors R.sub.21, R.sub.22, and R.sub.23 ; furthermore the short circuit coating II shorting the partial resistor R.sub.22 ; the short circuit coating III shorting the partial resistor R.sub.22 and the partial resistor R.sub.23 ; the short circuit coating IV shorting the entire ohmic resistor R.sub.2; finally, the short circuit coating V shorting the collector emitter path of the transistor structure T.

The ohmic resistors R.sub.1 and R.sub.2 with the corresponding partial resistors can be produced, as is described with reference to the example of embodiment of FIG. 16, in the form of zones having a conductivity type which is in opposition to the conductivity type of the semiconductor body, and diffused into the common collector zone. According to another embodiment of the invention, however, it is also possible to produce the ohmic resistors in the form of resistance layers applied to the semiconductor body.

The short circuiting of the partial resistors or of the collector emitter path of the transistor structure T is advantageously effected with the aid of evaporated metal layers, which are evaporated through corresponding masks. According to another type of embodiment the short circuiting, however, can also be effected with the aid of thin wires which, by employing one of the conventional types of bonding methods, are mounted to the enlarged contact coatings. The arrangement according to FIG. 16 permits a stepwise balancing of the temperature coefficient, with the steps being determined by the resistance value of the partial resistors R.sub.21 to R.sub.24. This possibility is in many cases sufficient for effecting the desired adjustment of the temperature coefficient. There might be some cases, however, in which there is required a refined and improved possibility of adjustment. In these cases the ohmic resistors R.sub.1 and R.sub.2 must be arranged differently. One such different arrangement is shown schematically in FIG. 17. The ohmic resistors R.sub.1 and R.sub.2 are split up into the partial resistors R.sub.11 to R.sub.16 or R.sub.21 to R.sub.26 respectively. The resistance value of the partial resistors is determined by the respective length of the zone either diffused in or deposited. In the example of embodiment shown in FIG. 17 this length differs from partial resistor to partial resistor, so that the partial resistors are likewise differently dimensioned.

The partial resistors R.sub.11 to R.sub.16 are chosen thus that their resistance value decreases from resistor to resistor, whereas the resistance value of the partial resistors R.sub.21 to R.sub.26 increases from resistor to resistor. The ohmic resistor R.sub.1 comprises the final contacts 11 and 17, whereas the ohmic resistor R.sub.2 comprises the final contacts 21 and 27. The contacts 12 to 16 serve to connect the partial resistors R.sub.11 to R.sub.16 to one another; in the same way the contacts 22 to 26 serve to connect the partial resistors R.sub.21 to R.sub.26. The arrangement of the final contacts and of the connecting contacts 11 to 17 and 21 to 27 is made in such a way that they, on one hand, are arranged next to each other in one row and that, on the other hand, corresponding contacts of the partial resistors are each time arranged opposite each other. In this way the contacts 11 to 17 are arranged in one row, likewise the contacts 21 to 27, and the contacts 11 and 21, 12 and 22 etc. up to 17 and 27 are arranged opposite each other. Between the oppositely arranged contacts there is deposited a strip-shaped contact lead 28 which is connected to the base contact of the transistor structure T. With the aid of one single contact bridge VI which, in FIG. 17, connects the contacts 14 and 24 to one another and to the contact lead 28, it is possible to perform a finely graduated adjustment within wide limits.

FIG. 18, in a schematical representation, shows another possibility regarding the arrangement of the low ohmic resistors R.sub.1 and R.sub.2. The ohmic resistor R.sub.1, just like in the example of embodiment of FIG. 16, has a fixed value, whereas the ohmic resistor R.sub.2, according to the example of embodiment of FIG. 17, consists of partial resistors R.sub.21 to R.sub.25. In this exemplified embodiment an adjustment is achieved in that several short circuit coatings, hence in this particular example, the short-circuit coatings VII and VII, serve to short circuit individual partial resistors. Thus, in FIG. 18, the partial resistors R.sub.22 and R.sub.24 are short circuited. By employing several short-circuiting contact coatings it is possible to perform a refined and finely graduated adjustment of the temperature coefficient.

FIG. 19 shows a further possibility as to how, by varying the resistance value of the ohmic resistor R.sub.2, the temperature coefficient can be adjusted. In this particular example of embodiment the resistor R.sub.2 consists of a zone which, with respect to the ohmic resistor R.sub.1, is substantially broader and is diffused into the semiconductor body, or alternatively a layer of higher resistive material is deposited. By way of sandblasting or etching at the point indicated by the arrow, there is removed so much of the applied resistive material of the ohmic resistor R.sub.2, that there is achieved an optimum adjustment of the temperature coefficient. This adjusting method has the advantage over the one described hereinbefore, that the resistance value of R.sub.2 can be varied continuously.

Claims

We claim:

1. A temperature compensating Zener diode in the form of a body of a semiconductor integrated circuit having a first and second outer connecting terminal, consisting of several individual elements placed in a common semiconductor body of one conductivity type, said elements being connected to each other with deposited metallized coatings, wherein current flows from said first outer connecting terminal through said Zener diode to said second outer connecting terminal when an appropriate positive signal is applied to said first outer connecting terminal with respect to said second outer connecting terminal, comprising:

A plurality of transistor structures used as individual elements, each element having an emitter base and collector terminal;

said body representing a common collector zone for all said transistor structures;

each of said transistor structures having its base-emitter diode connected in series with the base-emitter diode of the next succeeding transistor structure to establish a chain of base-emitter diodes from said plurality of transistor structures, at least one base-emitter diode being interconnected within said chain so as to be forward-biased upon the application of said positive signal to said first outer connecting terminal with respect to said second outer connecting terminal, and at least another base-emitter diode being interconnected within said chain so as to be reversed biased beyond its Zener breakdown voltage upon the application of said appropriate positive signal to said first outer connecting terminal with respect to said second outer connecting terminal;

said body being connected to said first outer connecting terminal; and

one of the base and emitter terminals of the first transistor of said chain being connected to said first outer connecting terminal, and one of the base and emitter terminals of the last transistor of said chain being connected to said second outer connecting terminal.

2. A temperature compensated Zener diode according to claim 1, wherein ohmic resistors are provided to adjust the current flowing across individual PN junctions.

3. A temperature compensated Zener diode according to claim 1, wherein one end of an ohmic resistor is connected to the emitter lead of each forward diode of said series chain except the last forward diode, and the other end of each said resistor is connected to said second outer connecting terminal so as to further reduce said dynamic internal resistance.

4. A temperature compensated Zener diode according to claim 1, wherein one end of an ohmic resistor is connected to the emitter lead of each forward diode of said series chain, and the other end of each said resistor is connected to the emitter of the preceding forward diode, and the emitter of the first forward diode of said chain is directly connected to the second of said outer connecting terminals.

5. A temperature compensated Zener diode according to claim 1, wherein each transistor structure acting as Zener diode and each transistor structure acting as forward diode are combined to form a double emitter configuration and are arranged in a common base zone, said base zone having a type of conductivity which is in opposition to the type of conductivity of said semiconductor body, with each emitter of the same said one conductivity type as said body.

6. A temperature compensated Zener diode according to claim 5, wherein a number of said double emitter configurations and, according to requirements, further single emitter transistor structures acting as forward diodes are connected in series so that the emitter of the first of said double emitter configuration forming part of said Zener diode, is connected to said first outer connecting terminal, while the emitter of said first double emitter configuration forming part of the forward diode, is connected to said Zener diode emitter of the next said double emitter configuration, and so forth, up to the last said double emitter configuration, with said forward diode emitter of the last said double emitter configuration being coupled either to the second of said outer connecting terminals, or to the base of the last single emitter transistor structure of the chain of forward diodes.

7. A temperature compensated Zener diode according to claim 6, wherein the base of each successive double emitter configurations are coupled to each other by means of an ohmic resistor and one end of ohmic resistors are arranged in the emitter lead-in conductors of the subsequently following single emitter transistor structures, the other end of said resistors being directly connected to the second one of said outer connecting terminals.

8. A term temperature compensated Zener diode according to claim 6, wherein both the base and the forward diode emitter of each said double emitter configuration is coupled to each other by means of an ohmic resistor.

9. A temperature compensated Zener diode according to claim 6, wherein the base of each successive double emitter configuration is coupled to each other by means of an ohmic resistor and the base of the first of said double emitter configurations is coupled to the second of said outer connecting terminals by means of another ohmic resistor, each forward diode emitter of each double emitter configuration being coupled to the base of the preceding double emitter transistor by means of a further ohmic resistor, the forward diode emitter of said last double emitter configuration being coupled to the emitter of the last of said single emitter transistors by means of a still further ohmic resistor, and base and emitter of the first of said single emitter transistors is coupled to each other by means of another still further ohmic resistor.

10. A temperature compensated Zener diode according to claim 1, wherein the emitter base diode of the first transistor of said chain is reversed biased beyond its Zener breakdown voltage upon the application of said positive signal to said first outer connecting terminal with respect to said second outer connecting terminal, the emitter terminal of the first transistor being connected to said first outer connecting terminal, and the emitter base diode of the last transistor of said chain is forward biased upon the application of said positive signal to said first outer connecting terminal with respect to said second outer connecting terminal, the emitter terminal of the last transistor being connected to said second outer connecting terminal.

11. A temperature compensated Zener diode according to claim 1, wherein the emitter base diodes of the respective first and last transistors of said chain are forward biased upon the application of said positive signal to said first outer connecting terminal with respect to said second outer connecting terminal, the base terminal of the first transistor being connected to said first outer connecting terminal, and the emitter terminal of the last transistor of said chain being connected to said second outer connecting terminal.