U.S. patent number 3,567,965 [Application Number 04/781,358] was granted by the patent office on 1971-03-02 for temperature compensated zener diode.
This patent grant is currently assigned to International Standard Electric Corporation. Invention is credited to Hartmut Bleher, Hans Weinerth.
United States Patent |
3,567,965 |
Weinerth , et al. |
March 2, 1971 |
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.
Inventors: |
Weinerth; Hans
(Eindhoven-Woensel, NL), Bleher; Hartmut (Fishkill,
NY) |
Assignee: |
International Standard Electric
Corporation (New York, NY)
|
Family
ID: |
27509903 |
Appl.
No.: |
04/781,358 |
Filed: |
December 5, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Dec 9, 1967 [DT] |
|
|
1,589,707 |
|
Current U.S.
Class: |
327/513; 257/469;
257/552; 257/603; 327/565; 327/575; 327/577; 327/580 |
Current CPC
Class: |
H01L
27/0211 (20130101); G05F 3/18 (20130101); H01L
27/00 (20130101); G05F 3/225 (20130101); H01L
29/00 (20130101) |
Current International
Class: |
H01L
27/02 (20060101); H01L 27/00 (20060101); H01L
29/00 (20060101); G05F 3/18 (20060101); G05F
3/22 (20060101); G05F 3/08 (20060101); H01l
017/00 () |
Field of
Search: |
;317/23522,23522.1,23529.D,23530,2347 ;307/310,318 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Electronics, "Logic Principles for Multi-emitter Transistors" by
Thompson, Sept. 1963, pages 25--29.
|
Primary Examiner: Craig; Jerry D.
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.
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.
* * * * *