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Noise in space-charge-limited solid-state devices
Solid-State Electronics Pergamon
NOISE
IN
Press 1967. Vol. 10, pp. 129-13.5.
Printed in Great Britain
SPACE-CHARGE-LIMITED
SOLID-STATE
DEVICES* S. T. HSU, A. VAN Department
DER ZIEL and E. R. CHENETTE
of Electrical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A.
(Received 26 August 1966; in revisedform 29 September 1966) Abstract-Measurements on noise in space-charge-limited solid-state diodes and triodes show that the limiting noise of these devices is thermal noise. The equivalent noise resistance R, of the diodes is equal to the d.c. resistance v,/1, of the device. The equivalent noise resistance R, of the triodes is of the order of 2/g, ,where g, is the transconductance. At high frequencies there is induced grid noise and a grid conductance g,, in the triode which vary both as wa in a wide frequency range. The equivalent noise temperature of the grid conductance is equal to room temperature. The induced grid noise is practically uncorrelated with the anode noise. Present devices show large amounts of excess noise which may extend well into the MC range. Rhsumb-Des mesures du bruit dans les diodes et triodes B charge d’espace limitee en &at solide dCmontrent que le bruit limiteur de ces dispositifs est le bruit thermique. La resistance equivalente de bruit R, des diodes est Bgale in la resistance du dispositif a courant continue V,/I,. La rdsistance equivalente de bruit des triodes est de l’ordre de 2/g,, oh g, est la transconductance. Aux hautes frkquences, il existe un bruit de grille et une transconductance de grille g,, dam la triode qui varient en fonction de ws le long d’une gamme de frkquences &endue. La temperature Bquivalente de bruit de la conductance de grille est pratiquement indtpendante du bruite de plaque. Les dispositifs actuels produisent de grandes quantitCs de bruit excbdent qui peuvent s’&endre dans la gamxne des MHz. Zusammenfassung-Messungen des Rauschens in raumladungsbegrenzten FestkGrper-Dioden und -Trioden zeigen, dass die untere Grenze fiir das Rauschen in diesen Bauelementen durch thermisches Rauschen gegeben ist. Der Iiquivalente Rauschwiderstand R, der Dioden entspricht dem Gleichstromwiderstand V,/L des betreffenden Bauelementes. Der iiquivalente Rauschwiderstand R, der Trioden ist von der GrGssenordnung 2/g,, wo g, die Steilheit bedeutet. Bei hohen Frequenzen entsteht in den Trioden eine Gitterleitfghigkeit g,, und ein Gitterrauschen, die beide in einem weiten Frequenzbereich proportional zu wa sind. Die lquivalente Rauschtemperatur der GitterleitfAigkeit ist gleich der Raumtemperatur. Das Gitterrauschen ist mit dem Anodenrauschen praktisch unkorreliert. Die untersuchten Bauelement zeigen in betriichtlichem Ausmass zus%tzliches Rauschen, das sich weit in den MH-Bereich hinein erstrecken kann. 1. INTRODUCTION
ACCORDINGto VAN DER ZIEL(~) the thermal noise in an open-circuited space-charge-limited solidstate diode is given by e2 = 4kTR,Af
= 4kT(V,JI,)Af.
(1)
Here V, is the anode voltage and 1, the anode current. In other words the open circuit noise e.m.f. corresponds to the thermal noise of the d.c. *Supported contract. 4
by
Army
Research
Office
resistance Va/Ia, and the equivalent noise resistance R, of the device equals Va/Ia. We measured the equivalent saturated diode current I,, of a GaAs diode, of a silicon n-i-n diode and of two silicon space-charge-limited triodes. I,, measures the short-circuit noise current of the device. If the device has a low-frequency conductance g,, then i2 = 2qI,,Af
(Durham)
or 129
= e2 *go2,
(4
130
S. T. HSU,
If the device
A.
VAN
ZIEL
DER
has a characteristic I,
=
then got=ldIa/dVa (2) mayLbeLwritten
and E. R. CHENETTE
the bulk material. At higher frequencies one would expect thermal noise of the CR series combination
cv,n,
= nIa/Va, so that
2kT lea = n*--go. 4
equation
(2a)
i2 = 4kTAf
W?l?R 1+ m2C2R2
= 4kTg,,Af
(6)
where g,, = m2C2R/(1 +u2C2R2) is the h.f. input conductance seen at the grid. This is analogous to the induced grid noise in a vacuum tube.
In the silicon n-i-n diode the characteristic was linear at low anode voltages and became quadratic at higher anode voltages. Hence n gradually changes from 1 to 2 when the anode voltage is increased. As a consequence I,, should shift from the value (2kT/q)go to the value (4kT/q)g, for increasing anode voltage. The solid-state space-charge-limited silicon triode, developed by Zuleeg, consisted of a P-type grid imbedded in n-type material provided with an ohmic emitter contact serving as cathode and a collector contact serving as anode. The current flow in the triode can be described by replacing the grid by a solid electrode at an equivalent potential v,
= c(V,+
VlJP)
(3)
where Vg is the grid voltage, V, the anode voltage, p the amplification factor and 0 a factor somewhat smaller than unity that takes account of the grid structure. The characteristic of the device is then 1, = CVen, the conductance g,, of the equivalent diode is g,, = dIJdV, = nI,/V, and the transconductance of the triode is g,
%Z =
= ~
aV&?
aI, av, * __ av, av,
= g,,o.
(4)
In the triode one would thus expect an equivalent saturated diode current equal to that of the equivalent diode, or 2kT (5) This is completely equivalent to the noise theory of a vacuum triode. Since the grid current is zero for normal operation, one would expect no grid noise for relatively low frequencies. Since the “grid wires” are surrounded by a space-charge sheath, the grid couples capacitively to the resistance R of
V IN VOLE-
FIG. 1. GaAs diode d.c. characteristics. Sinceg,, varies as w2 over a wide frequency range, the noise figure will become progressively worse at the higher frequencies. The measurements were performed in the range 100 kc < f < 100 MC by standard techniques. 2. MEASUREMENTS Figure 1 shows the characteristic of the GaAs diode. It is of the form I, = CVan with n = 2.6. Figure 2 shows the noise of this diode at 0.1, 0.5 and 1 mA, together with the theoretical value of the thermal noise deduced from equation (2a). It is seen that the device shows considerable amounts of excess noise at the lower frequencies but that it approaches the thermal noise limit, set
NOISE
IN
SPACE-CHARGE-LIMITED
- -
-
SOLID-STATE
THERMAL
FREQUENCY IN
FIG. 2. GaAs diode I,,
FIG. 3. D.C. characteristics
NOISE LEVEL
MHz-
vs. frequency.
of silicon device Si-1.
DEVICES
131
132
S. T. HSU,
A.
VAN
DER
ZIEL
FREQIJEWY
FIG. 4. Si-1 I,,
vs.
by equation (2a) at higher frequencies. Apparently then, the limiting noise of the device is thermal noise. Figure 3 shows the characteristic of the n-i-n silicon diode Si-1. It has a linear characteristic I ,
V,j IN VOLTS-
FIG. 5. (la, Ya) characteristics z19-9.
of triodes 211-4
and
iN
and E. R. CHENETTE
M!+
--I--
frequency at various I,. at low voltages and a quadratic characteristic at large voltages. Figure 4 shows the noise of this device between 0.1 and O-5 mA. It is seen that there is a large amount of excess noise at low frequencies. Also shown is the thermal noise iimit LJ = (4~~/!&0* It is seen that at 1, = 0.5 mA the noise approaches this limit at 100 MC, whereas at lower currents the limiting noise seems to lie more and more below it if the current is decreased. This is what would be expected theoretically, for at the lowest currents one would expect I,, = (Z~~/~)g~ rather than I,, = (4kZ’,$)g,. The results of Fig. 4 are compatible with this, Figure 5 shows the characteristics of two solidstate space-charge-limited triodes 211-4 and 219-9 at V, = 0 V. The current varies as Va3/2*, rather than as Va2. This most probably can be attributed to the fact that the mobility is fielddependent. A mobility p = po(E,/E)1’2 would give the v;13’2 characteristic. Figures 6 and 7 show (I,,), at the drain and (I&, at the grid as a function of frequency for devices 211-4 and * This corresponds to Child’s law for vacuum tubes, The cause is, of course, a different one.
NOISE
IN SPACE-CHARGE-LIMITED
DE VICES
NI 3SION31vo omaNI
-vd
4-W
-r-d
SOLID-STATE
Nl XION
NI 3SlON XV0
NIWW
033flONl
asl EE
. s r.u -V’”
NI 3SlON NlWtfCI
133
134
S. T.
HSU,
A.
VAN
DER
ZIEL
Z19-9, respectively. It is seen that the devices show a considerable amount of excess noise at low frequencies, but that the noise approaches the limiting value (4kT/q)g, very closely at 100 MC. This means, since n = 3/Z for these devices, that n/a z 2 or (T N 0.75. This is a reagives sonable value. Putting i2 = 4kTR,Afg,2 for the noise resistance of the device R,
= 2/g,,,
=
The results are shown in Tables
tg)
1 and 2. We see
Table 1. 21 l-4 induced gate noise -v”p
Vd
Ia
(V)
(V)
(mA)
&)
0.6
11.4
223
11.4
296
10.7
296
0.2 0.4 0.6 0.8 1.0
R. CHENETTE
that T, corresponds to normal room temperature within the limit of accuracy (2: 100/h) of the experiment. Table 2. 219-9
SCL
triode
0 0 0 0
5 10 15 20
0.58 2.5 3.5 4.9
22.8 18.1 18.1 18.2
424 339 336 333
15.1 14.6 13.8 13.7
312 310 303 317
0.2 0.4 0.6 0.8 1.0
15 15 15 15 15
3.0 2.4 2.08 1.67 1.37
15.9 14.1 12.5 11.9 11.2
308 258 249 230 224
12.8 12.2 12.0 11.7 11.3
295 317 292 300 290
A measurement of the correlation between the drain noise and the induced gate noise, obtained by detuning the input circuit,(4) indicated that such a correlation, if present, is quite small. For all practical purposes the induced gate noise and the drain noise may thus be considered independent. A comparison of various triodes is given in Table 3.
4kTngnAf;
Tn = WWe,/g,,)~
2
E.
(7)
comparable with the value obtained for vacuum triodes and field-effect transistors. The induced gate noise varies as f 2 at low frequencies, but levels off at the higher frequencies. This effect is especially pronounced in device 211-4. If one applies equation (6), determines C and calculates R from the lower frequency value g,, = w2C2R one obtains a leveling off at too high a frequency. Apparently then, the simple lumped-circuit CR series approximation is too simple at the higher frequencies. Not enough is known about the device to make a better approximation, however. By measuring the equivalent saturated diode current I,, of the gate noise the input conductance g,, and the input capacitance C,, at 30 MC, one can calculate the equivalent noise temperature T, of g,, from the relation ig2 = 2qI,,Af
and
(p%o)
Table 3. Comparison of vacuum triodes, FET’s and space-charge-limited triodes (T, = cathode temperature, T = room temperature) R,,
T, of i,=
Correlation between i, and ia
vacuum triodec4’
zz ii
2 1.4 T,
rather small
2;)
4
2.16
10.4
202
6 8
3.8 5.7
10.7 10.2
201 202
10.4 10.2
309 291
junction FET(“)
N ‘2
N 1.2 T
rather small
10 12
7.0 8.7
9.9 9.5
193 193
10.0 9.8
297 286
MOS FET*
N 02 grill
N 1.3 T
rather small
12 12 12 12 12
5.3 4.7 4.1 3.6 3.1
8.6 7.6 6.4 6.7 5.4
161 138 123.5 122.5 103.5
311 311 301 317 303
SCL triode
‘2:- 2
rT
quite small
9.8 9.5 9.23 8.87 8.67
.&Tm
_ * The data for the MOS FET are theoretical estimates.@’ The values measured of R, are up to about 5 times larger.
NOISE
IN
SPACE-CHARGE-LIMITED
3. CONCLUSIONS
Earlier unpublished measurements on a CdS diode seemed to indicatec2) that the noise could be extremely low. This led to the development of the earlier space-charge-suppression theory by VAN DER ZIEL,(~) which was developed independ(3) Subsequent measurements ently by SERGIESCU. on this device failed to substantiate these effects, however. ‘Measurements on other devices all seem to agree with the result reported in this paper, viz. that the limiting noise of these devices is thermal noise. This would make the triode rather useful, especially if the h.f. grid noise and the 1.f. excess noise can be reduced. ZULEEG(~) has reported a considerable reduction of gI, in the newer units; this would make the induced grid noae, ig2, smaller and improve the noise figure of the device. The exact cause of the excess noise is at present
SOLID-STATE
DEVICES
not fully understood. We intend data about this effect elsewhere.
135
to give further
Acknowledgments-The authors are indebted to American Electronics Laboratory, Colmar, Pa., for providing the GaAs diodes. They are indebted to Dr. R. W. SOSHEA, h.p. Associates, Palo Alto, California, for providing the n-i-n silicon diodes. They are indebted to Mr. R. ZULEEG, Solid State Research Center, Hughes Aircraft Company, Newport Beach, California for providing the silicon solid state triodes.
REFERENCES 1. 2. 3. 4.
A. A. V. A.
VAN DER ZIEL, Solid-St. Electron. 9, 899 (1966). VAN DER ZIEL, Solid-St. Electron. 9, 123 (1966). SERGIESCU,BY. J. appl. Phys. 16, 1435 (1965). VAN DER ZIEL, Noise, Chap. 5-6. Prentice-Hall, Englewood Cliffs, New Jersey (1954). 5. W. C. BRUNCKE and A. VANDER ZIEL, IEEE Trans. electron Devices 13, 323 (1966). 6. M. SHOJI, IEEE Trans. electron Devices 13, 520 (1966). 7. R. ZULEEG, Proc. IEEE 54, 1197 (1966).
NOISE
IN
Press 1967. Vol. 10, pp. 129-13.5.
Printed in Great Britain
SPACE-CHARGE-LIMITED
SOLID-STATE
DEVICES* S. T. HSU, A. VAN Department
DER ZIEL and E. R. CHENETTE
of Electrical Engineering, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A.
(Received 26 August 1966; in revisedform 29 September 1966) Abstract-Measurements on noise in space-charge-limited solid-state diodes and triodes show that the limiting noise of these devices is thermal noise. The equivalent noise resistance R, of the diodes is equal to the d.c. resistance v,/1, of the device. The equivalent noise resistance R, of the triodes is of the order of 2/g, ,where g, is the transconductance. At high frequencies there is induced grid noise and a grid conductance g,, in the triode which vary both as wa in a wide frequency range. The equivalent noise temperature of the grid conductance is equal to room temperature. The induced grid noise is practically uncorrelated with the anode noise. Present devices show large amounts of excess noise which may extend well into the MC range. Rhsumb-Des mesures du bruit dans les diodes et triodes B charge d’espace limitee en &at solide dCmontrent que le bruit limiteur de ces dispositifs est le bruit thermique. La resistance equivalente de bruit R, des diodes est Bgale in la resistance du dispositif a courant continue V,/I,. La rdsistance equivalente de bruit des triodes est de l’ordre de 2/g,, oh g, est la transconductance. Aux hautes frkquences, il existe un bruit de grille et une transconductance de grille g,, dam la triode qui varient en fonction de ws le long d’une gamme de frkquences &endue. La temperature Bquivalente de bruit de la conductance de grille est pratiquement indtpendante du bruite de plaque. Les dispositifs actuels produisent de grandes quantitCs de bruit excbdent qui peuvent s’&endre dans la gamxne des MHz. Zusammenfassung-Messungen des Rauschens in raumladungsbegrenzten FestkGrper-Dioden und -Trioden zeigen, dass die untere Grenze fiir das Rauschen in diesen Bauelementen durch thermisches Rauschen gegeben ist. Der Iiquivalente Rauschwiderstand R, der Dioden entspricht dem Gleichstromwiderstand V,/L des betreffenden Bauelementes. Der iiquivalente Rauschwiderstand R, der Trioden ist von der GrGssenordnung 2/g,, wo g, die Steilheit bedeutet. Bei hohen Frequenzen entsteht in den Trioden eine Gitterleitfghigkeit g,, und ein Gitterrauschen, die beide in einem weiten Frequenzbereich proportional zu wa sind. Die lquivalente Rauschtemperatur der GitterleitfAigkeit ist gleich der Raumtemperatur. Das Gitterrauschen ist mit dem Anodenrauschen praktisch unkorreliert. Die untersuchten Bauelement zeigen in betriichtlichem Ausmass zus%tzliches Rauschen, das sich weit in den MH-Bereich hinein erstrecken kann. 1. INTRODUCTION
ACCORDINGto VAN DER ZIEL(~) the thermal noise in an open-circuited space-charge-limited solidstate diode is given by e2 = 4kTR,Af
= 4kT(V,JI,)Af.
(1)
Here V, is the anode voltage and 1, the anode current. In other words the open circuit noise e.m.f. corresponds to the thermal noise of the d.c. *Supported contract. 4
by
Army
Research
Office
resistance Va/Ia, and the equivalent noise resistance R, of the device equals Va/Ia. We measured the equivalent saturated diode current I,, of a GaAs diode, of a silicon n-i-n diode and of two silicon space-charge-limited triodes. I,, measures the short-circuit noise current of the device. If the device has a low-frequency conductance g,, then i2 = 2qI,,Af
(Durham)
or 129
= e2 *go2,
(4
130
S. T. HSU,
If the device
A.
VAN
ZIEL
DER
has a characteristic I,
=
then got=ldIa/dVa (2) mayLbeLwritten
and E. R. CHENETTE
the bulk material. At higher frequencies one would expect thermal noise of the CR series combination
cv,n,
= nIa/Va, so that
2kT lea = n*--go. 4
equation
(2a)
i2 = 4kTAf
W?l?R 1+ m2C2R2
= 4kTg,,Af
(6)
where g,, = m2C2R/(1 +u2C2R2) is the h.f. input conductance seen at the grid. This is analogous to the induced grid noise in a vacuum tube.
In the silicon n-i-n diode the characteristic was linear at low anode voltages and became quadratic at higher anode voltages. Hence n gradually changes from 1 to 2 when the anode voltage is increased. As a consequence I,, should shift from the value (2kT/q)go to the value (4kT/q)g, for increasing anode voltage. The solid-state space-charge-limited silicon triode, developed by Zuleeg, consisted of a P-type grid imbedded in n-type material provided with an ohmic emitter contact serving as cathode and a collector contact serving as anode. The current flow in the triode can be described by replacing the grid by a solid electrode at an equivalent potential v,
= c(V,+
VlJP)
(3)
where Vg is the grid voltage, V, the anode voltage, p the amplification factor and 0 a factor somewhat smaller than unity that takes account of the grid structure. The characteristic of the device is then 1, = CVen, the conductance g,, of the equivalent diode is g,, = dIJdV, = nI,/V, and the transconductance of the triode is g,
%Z =
= ~
aV&?
aI, av, * __ av, av,
= g,,o.
(4)
In the triode one would thus expect an equivalent saturated diode current equal to that of the equivalent diode, or 2kT (5) This is completely equivalent to the noise theory of a vacuum triode. Since the grid current is zero for normal operation, one would expect no grid noise for relatively low frequencies. Since the “grid wires” are surrounded by a space-charge sheath, the grid couples capacitively to the resistance R of
V IN VOLE-
FIG. 1. GaAs diode d.c. characteristics. Sinceg,, varies as w2 over a wide frequency range, the noise figure will become progressively worse at the higher frequencies. The measurements were performed in the range 100 kc < f < 100 MC by standard techniques. 2. MEASUREMENTS Figure 1 shows the characteristic of the GaAs diode. It is of the form I, = CVan with n = 2.6. Figure 2 shows the noise of this diode at 0.1, 0.5 and 1 mA, together with the theoretical value of the thermal noise deduced from equation (2a). It is seen that the device shows considerable amounts of excess noise at the lower frequencies but that it approaches the thermal noise limit, set
NOISE
IN
SPACE-CHARGE-LIMITED
- -
-
SOLID-STATE
THERMAL
FREQUENCY IN
FIG. 2. GaAs diode I,,
FIG. 3. D.C. characteristics
NOISE LEVEL
MHz-
vs. frequency.
of silicon device Si-1.
DEVICES
131
132
S. T. HSU,
A.
VAN
DER
ZIEL
FREQIJEWY
FIG. 4. Si-1 I,,
vs.
by equation (2a) at higher frequencies. Apparently then, the limiting noise of the device is thermal noise. Figure 3 shows the characteristic of the n-i-n silicon diode Si-1. It has a linear characteristic I ,
V,j IN VOLTS-
FIG. 5. (la, Ya) characteristics z19-9.
of triodes 211-4
and
iN
and E. R. CHENETTE
M!+
--I--
frequency at various I,. at low voltages and a quadratic characteristic at large voltages. Figure 4 shows the noise of this device between 0.1 and O-5 mA. It is seen that there is a large amount of excess noise at low frequencies. Also shown is the thermal noise iimit LJ = (4~~/!&0* It is seen that at 1, = 0.5 mA the noise approaches this limit at 100 MC, whereas at lower currents the limiting noise seems to lie more and more below it if the current is decreased. This is what would be expected theoretically, for at the lowest currents one would expect I,, = (Z~~/~)g~ rather than I,, = (4kZ’,$)g,. The results of Fig. 4 are compatible with this, Figure 5 shows the characteristics of two solidstate space-charge-limited triodes 211-4 and 219-9 at V, = 0 V. The current varies as Va3/2*, rather than as Va2. This most probably can be attributed to the fact that the mobility is fielddependent. A mobility p = po(E,/E)1’2 would give the v;13’2 characteristic. Figures 6 and 7 show (I,,), at the drain and (I&, at the grid as a function of frequency for devices 211-4 and * This corresponds to Child’s law for vacuum tubes, The cause is, of course, a different one.
NOISE
IN SPACE-CHARGE-LIMITED
DE VICES
NI 3SION31vo omaNI
-vd
4-W
-r-d
SOLID-STATE
Nl XION
NI 3SlON XV0
NIWW
033flONl
asl EE
. s r.u -V’”
NI 3SlON NlWtfCI
133
134
S. T.
HSU,
A.
VAN
DER
ZIEL
Z19-9, respectively. It is seen that the devices show a considerable amount of excess noise at low frequencies, but that the noise approaches the limiting value (4kT/q)g, very closely at 100 MC. This means, since n = 3/Z for these devices, that n/a z 2 or (T N 0.75. This is a reagives sonable value. Putting i2 = 4kTR,Afg,2 for the noise resistance of the device R,
= 2/g,,,
=
The results are shown in Tables
tg)
1 and 2. We see
Table 1. 21 l-4 induced gate noise -v”p
Vd
Ia
(V)
(V)
(mA)
&)
0.6
11.4
223
11.4
296
10.7
296
0.2 0.4 0.6 0.8 1.0
R. CHENETTE
that T, corresponds to normal room temperature within the limit of accuracy (2: 100/h) of the experiment. Table 2. 219-9
SCL
triode
0 0 0 0
5 10 15 20
0.58 2.5 3.5 4.9
22.8 18.1 18.1 18.2
424 339 336 333
15.1 14.6 13.8 13.7
312 310 303 317
0.2 0.4 0.6 0.8 1.0
15 15 15 15 15
3.0 2.4 2.08 1.67 1.37
15.9 14.1 12.5 11.9 11.2
308 258 249 230 224
12.8 12.2 12.0 11.7 11.3
295 317 292 300 290
A measurement of the correlation between the drain noise and the induced gate noise, obtained by detuning the input circuit,(4) indicated that such a correlation, if present, is quite small. For all practical purposes the induced gate noise and the drain noise may thus be considered independent. A comparison of various triodes is given in Table 3.
4kTngnAf;
Tn = WWe,/g,,)~
2
E.
(7)
comparable with the value obtained for vacuum triodes and field-effect transistors. The induced gate noise varies as f 2 at low frequencies, but levels off at the higher frequencies. This effect is especially pronounced in device 211-4. If one applies equation (6), determines C and calculates R from the lower frequency value g,, = w2C2R one obtains a leveling off at too high a frequency. Apparently then, the simple lumped-circuit CR series approximation is too simple at the higher frequencies. Not enough is known about the device to make a better approximation, however. By measuring the equivalent saturated diode current I,, of the gate noise the input conductance g,, and the input capacitance C,, at 30 MC, one can calculate the equivalent noise temperature T, of g,, from the relation ig2 = 2qI,,Af
and
(p%o)
Table 3. Comparison of vacuum triodes, FET’s and space-charge-limited triodes (T, = cathode temperature, T = room temperature) R,,
T, of i,=
Correlation between i, and ia
vacuum triodec4’
zz ii
2 1.4 T,
rather small
2;)
4
2.16
10.4
202
6 8
3.8 5.7
10.7 10.2
201 202
10.4 10.2
309 291
junction FET(“)
N ‘2
N 1.2 T
rather small
10 12
7.0 8.7
9.9 9.5
193 193
10.0 9.8
297 286
MOS FET*
N 02 grill
N 1.3 T
rather small
12 12 12 12 12
5.3 4.7 4.1 3.6 3.1
8.6 7.6 6.4 6.7 5.4
161 138 123.5 122.5 103.5
311 311 301 317 303
SCL triode
‘2:- 2
rT
quite small
9.8 9.5 9.23 8.87 8.67
.&Tm
_ * The data for the MOS FET are theoretical estimates.@’ The values measured of R, are up to about 5 times larger.
NOISE
IN
SPACE-CHARGE-LIMITED
3. CONCLUSIONS
Earlier unpublished measurements on a CdS diode seemed to indicatec2) that the noise could be extremely low. This led to the development of the earlier space-charge-suppression theory by VAN DER ZIEL,(~) which was developed independ(3) Subsequent measurements ently by SERGIESCU. on this device failed to substantiate these effects, however. ‘Measurements on other devices all seem to agree with the result reported in this paper, viz. that the limiting noise of these devices is thermal noise. This would make the triode rather useful, especially if the h.f. grid noise and the 1.f. excess noise can be reduced. ZULEEG(~) has reported a considerable reduction of gI, in the newer units; this would make the induced grid noae, ig2, smaller and improve the noise figure of the device. The exact cause of the excess noise is at present
SOLID-STATE
DEVICES
not fully understood. We intend data about this effect elsewhere.
135
to give further
Acknowledgments-The authors are indebted to American Electronics Laboratory, Colmar, Pa., for providing the GaAs diodes. They are indebted to Dr. R. W. SOSHEA, h.p. Associates, Palo Alto, California, for providing the n-i-n silicon diodes. They are indebted to Mr. R. ZULEEG, Solid State Research Center, Hughes Aircraft Company, Newport Beach, California for providing the silicon solid state triodes.
REFERENCES 1. 2. 3. 4.
A. A. V. A.
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