- Email: [email protected]
Some basic logic circuits employing Gunn-effect devices
568
NOTES
maps of the same emitter base junction with 0 and 6.4 V bias respectively. It is apparent from these and other micrographs that there is a localized region of breakdown associated with the linear faults in this case. Figures l(g) and l(h) show a similar array at a higher magnification. From our studies we can conclude that the linear faults, which we interpret as diffusion induced dislocations, are a main cause of localized breakdown at the emitter base junction. This result is consistent with observations made on silicon planar avalanche diodes.(5) With regard to the other prevalent fault (i.e. the iron rich regions) the position is less definite and is best stated as follows. This type of fault is probably a further main cause of localized breakdown in its own right but, as the bulk of the regions examined occurred in regions where diffusion induced dislocations existed, some ambiguity existed. If thii type of fault is not a primary cause it at least increases the probability of localized breakdown occurring in dislocated areas and so merits further attention. Bearing in mind the size of the two defects described (l-5 p in most cases) relative to the base width (0.5 CL>it is probable that the distortion of the emitter-base and base-collector junctions causes the junctions to come together in the manner shown in Fig. l(d). This distortion would lead to the emitter-collector ‘short’ and would leave the emitter-base characteristic ‘hard’, with the most likely region for localized breakdown occurring in the vicinity of the ‘shorting channel’. For the defects to cause the necessary bending of the two junctions towards each other, each must be a region of increased n-type dopant. This is known to be true for both defects as iron gives two deep, donor levels in silicon@) and the diffusion induced dislocations are formed to take up the misfit associated with the high density of dopant used to form the n+ emitter region. Further results on transistors made with a lower concentration of dopant in the emitter, in which diffusion-induced dislocations were not present, confirmed that the breakdown was caused by the iron inclusions.
Acknowledgment-The authors wish to thank Dr. D. W. F. JAMES for help with the X-ray microanalysis.
School of Engineering Science U.C.N. W., Bangor Caerns., U.K.
D. V. SULWAY P. R. THORNTON
Ferranti Ltd. Manchester, U.K.
M. J. TURNER
REFERENCES 1. H. J. QUEISSER,J. appl. Phys. 32, 1776 (1961). 2. S. PRUSSIN, J. appl. Pkys. 32, 1876 (1961). 3. W. CZAJA and J. R. PATEL, J. appl. Phys. 36, 1476 (1965). 4. I. G. DAVIES, I<. A. HUGHES, D. V. SULWAY and P. R. THORNTON, Solid-St. Electron. 9, 275 (1966). 5. P. R. THORNTON, D. V. SULWAY and N.-F. B.‘N&, Proc. IEEE. 9th Annual Svrnposium on Electron. Ion and La&r Beam TechLoI&y, Berkeley, May; (1967). 6. E. M. CON~ELL, Proc. Int. Radio Engrs 46, 1281 (1958).
Solid-State Electronics pp. 568-572.
Pergamon Press 1968. Vol. 11, Printed in Great Britain
Some basic logic circuits employing Gunneffect devices (Received
26 October
1967)
RECENTLY, a new logicGunn-effect device, namely a comparator, was suggested(l) and experimentally verified.c2’ It enables the development of essentially. all basic logic circuits with the extremely high: ?pe_ed of operation of Gunn-effect pulse app 1.lcatlons, as will be shown in this communica‘. tion. As the time constants involved are of the order of 100 psec, these new circuits will have to be built in strip-line technique, with perhaps semi-insulating GaAs as dielectric, so that a short delay line of about 8.5 mm length produces 100 psec delay. Figure 1 shows an adder. All Gunn-effect elements are biased below threshold for domain nucleation, but high enough for a domain to be sustained once it has been produced by an external pulse. ‘?he biasing voltage V, is applied from a voltage source with an internal resistance, which has to be several times the value of the low-field Gunn-device resistance, so that the input pulse is not shorted via the voltage supply. The input pulse will originate from another Gunn-effect
NOTES
569 + and
I Ri
FIG. 1. Gum-effect adder. (Co = comparator, Q = delay line, c = cathode, a = anode, D = ordinary Gunn diode as pulse invertor, R, = internal d.c.-supply resistance of high value, RI = load resistance, R, = input-terminal resistance of ‘and’.)
pulse circuit. If only one negative input pulse is applied, a domain forms in the negatively biased comparator, which will produce a positive pulse at the input of the following Gunn-effect device, which is biased positively so that a domain can be nucleated by the positive pulse of the first comparator. The output signal of the adder will finally be a positive pulse. The polarity of a pulse can easily be changed by passing the pulse via an ordinary Gunn diode D. The ‘and’ elements consist of a Gunn-effect diode, where the input pulses are applied via two separate resistors, so that the applied voltage will only be high enough for domain nucleation if two pulses are applied simultaneously. The two ‘and’ elements of Fig. 1 deal with the carry signals, which are subsequently delayed by the time of a domain transit. The Gunn diodes D of the circuit in front of the second comparator has the purpose of changing the pulse polarity, as a comparator can only operate with negative input pulses. The time consumption for
the addition of two one-digit numbers is about twice the domain-transit time across one Gunn element. An important device is the transformer of logicalinto-digital information. A first approach has been made with the DOFIC,‘3’ which does not yet produce digital information, but only a succession of pulses which still have to be added up. A more convenient transformer is shown in Fig. 2, which produces the digital information directly. It can therefore be used also as an ultrafast pulse-code modulator. The analogue signal is travelling along a succession of delay lines, and is attenuated simultaneously by fixed amounts. At the end of each delay line, are placed Gunn-effect diodes which have a third domain-triggering electrode near the cathode. They will produce a domain if a triggering signal arrives at the additional electrode, (as reported inc4)), and if the applied analogue voltage is high enough. For a given amplitude of the analogue voltage, only the first triggered Gunneffect diodes will produce domains, the remaining
570
NOTES
Dlgitol output pdS.f3
FIG. 2. Gunn-effect pulse code modulator. (S = triggering signal; its repetition time has to be n times domain-transit time, where ns is the number of digitized quanta for the maximum analogue-signal value, number of delay lines is n-2 and the number of attenuator steps is n-l, Dt = Gunn-effect diode with third (capacitive or ohmic) electrode along its domain trajectory for domain triggering by external signal (i.e. a logic ‘and’, where the input signal for one electrode can have a voltage of any amplitude.) Q = delay line.
NOTES
571
FIG. 3. Gunn-effect memory device, I = ‘read-in’ negative pulses, R = triggering pulse for a read-out output, Q = delay line.
ones do not respond in spite of the triggering signal. This system operates in the same way as the DOFIC, but here the delay between pulses can be controlled more easily and the output pulses have a larger amplitude. The individual output pulses have to be added up, where, however, only
terminal for pulse at the
simplified adders are required. The digital signal will be produced continuously as with any classical pulse code modulator, i.e., the time constant for an output pulse is the transit time of a domain, and the time constant for one set of n digits is n times the transit time. This is, therefore, a very fast
FIG. 4. M = memory device of Fig. 3, I = input to register, I,, la etc. = input to individual memory device, R = triggering pulse for read-out at output, 0 = output of each memory device.
NOTES
572
transformer and will be of advantage, particularly in pulse code modulation, e.g. television circuitry for outer-space applications. A further logic circuit is a Gunn-effect memory device, as shown in Fig. 3. The comparator enables one to switch the ring between ‘on’ and ‘off’. If a negative pulse is applied at 1, a signal will travel continuously round the loop formed by the comparator and the Gunn-effect diode D. It can be read off without being erased from the memory device, if a positive ‘read-out’ pulse is applied at the second input terminal R formed by a Gunneffect ‘and’. The stored signal can be erased by applying a second negative pulse at the ‘read-in’ terminal I. Instead of an ordinary Gunn diode, a second comparator can be employed if a separate terminal is required for the ‘erase’ signal. Such devices as shift registers can be built as shown in Fig. 4, where the basic unit is the memory device of Fig. 3. Finally, it should be mentioned that many Gunn-effect applications are possible for pulse modulation. For example a pulse-phase modulator can be obtained with a Gunn-effect diode having as a cathode a large electrode and as an anode a small electrode. The field will always be larger near the anode. The transit-time of a domain depends, therefore, on the applied voltage as it controls the place of domain nucleation.
Solid-State
Electronics
pp. 572-574.
Pergamon Press 1968. Vol. 11, Printed in Great Britam
Noise parameters of a silicon space-chargelimited triode* (Received 3 August
1967; in revisedform
3 November
1967)
IN A PREVIOUS paper Hsu, et al.(l) determined some of the noise parameters of a silicon SCL triode at 30 MHz. The device had a large amount of l/f noise that extended even beyond 30 MHz. This made the determination of the noise parameters somewhat uncertain. Recently a better SCL triode of the same type became available and hence it was decided to determine all the significant noise parameters of this device at 30 MHz, in order to obtain more accurate information about the noise behavior of such devices.7 This note gives the results. Figure 1 shows the equivalent saturated diode
Acknowledgements-The author is grateful to his colleagues, Mr. S. H. IZADPANAH and Dr. S. MAHROUS for useful discussions.
H.
HARTNAGEI.
Department of Elecironic and Electrical Engineering University of Sheffield England References 1. H. L. HARTNAGEL, &x. IEEE 55, 1236 (1967). 2. S. H. IZADPANAH, H. HARTNAGEL, Proc. IEEE 55, 1748 (1967). 3. C. P. SANDBANK, Solid-St. 10, 369 Eleciron. (1967). 4. J. A. COPELAND, T. HAYASHI, M. UENOHARA, Proc. IEEE 55, 584 (1967).
d IO”
3
5
I
,ol
1
5 ’ 1:’
FHEQJENCY (MHz!-
FIG. 1. Si SCL triode drain noise spectrum; v,, = ov.
Id = 3 m.4,
current of the output noise for short-circuited input as a function of frequency; we see that the noise is flat beyond 20 MHz. Figure 2 shows the equivalent circuit of the device. Here i, is the output noise for short-circuited input and i, the input noise for short-circuited output; i, consists of a part i,’ fully correlated with i, and a part i,” * Supported by AR0 contract. -1 Courtesy R. ZULEEG, Hughes Aircraft New Port Beach, California, U.S..4.
Company,
NOTES
maps of the same emitter base junction with 0 and 6.4 V bias respectively. It is apparent from these and other micrographs that there is a localized region of breakdown associated with the linear faults in this case. Figures l(g) and l(h) show a similar array at a higher magnification. From our studies we can conclude that the linear faults, which we interpret as diffusion induced dislocations, are a main cause of localized breakdown at the emitter base junction. This result is consistent with observations made on silicon planar avalanche diodes.(5) With regard to the other prevalent fault (i.e. the iron rich regions) the position is less definite and is best stated as follows. This type of fault is probably a further main cause of localized breakdown in its own right but, as the bulk of the regions examined occurred in regions where diffusion induced dislocations existed, some ambiguity existed. If thii type of fault is not a primary cause it at least increases the probability of localized breakdown occurring in dislocated areas and so merits further attention. Bearing in mind the size of the two defects described (l-5 p in most cases) relative to the base width (0.5 CL>it is probable that the distortion of the emitter-base and base-collector junctions causes the junctions to come together in the manner shown in Fig. l(d). This distortion would lead to the emitter-collector ‘short’ and would leave the emitter-base characteristic ‘hard’, with the most likely region for localized breakdown occurring in the vicinity of the ‘shorting channel’. For the defects to cause the necessary bending of the two junctions towards each other, each must be a region of increased n-type dopant. This is known to be true for both defects as iron gives two deep, donor levels in silicon@) and the diffusion induced dislocations are formed to take up the misfit associated with the high density of dopant used to form the n+ emitter region. Further results on transistors made with a lower concentration of dopant in the emitter, in which diffusion-induced dislocations were not present, confirmed that the breakdown was caused by the iron inclusions.
Acknowledgment-The authors wish to thank Dr. D. W. F. JAMES for help with the X-ray microanalysis.
School of Engineering Science U.C.N. W., Bangor Caerns., U.K.
D. V. SULWAY P. R. THORNTON
Ferranti Ltd. Manchester, U.K.
M. J. TURNER
REFERENCES 1. H. J. QUEISSER,J. appl. Phys. 32, 1776 (1961). 2. S. PRUSSIN, J. appl. Pkys. 32, 1876 (1961). 3. W. CZAJA and J. R. PATEL, J. appl. Phys. 36, 1476 (1965). 4. I. G. DAVIES, I<. A. HUGHES, D. V. SULWAY and P. R. THORNTON, Solid-St. Electron. 9, 275 (1966). 5. P. R. THORNTON, D. V. SULWAY and N.-F. B.‘N&, Proc. IEEE. 9th Annual Svrnposium on Electron. Ion and La&r Beam TechLoI&y, Berkeley, May; (1967). 6. E. M. CON~ELL, Proc. Int. Radio Engrs 46, 1281 (1958).
Solid-State Electronics pp. 568-572.
Pergamon Press 1968. Vol. 11, Printed in Great Britain
Some basic logic circuits employing Gunneffect devices (Received
26 October
1967)
RECENTLY, a new logicGunn-effect device, namely a comparator, was suggested(l) and experimentally verified.c2’ It enables the development of essentially. all basic logic circuits with the extremely high: ?pe_ed of operation of Gunn-effect pulse app 1.lcatlons, as will be shown in this communica‘. tion. As the time constants involved are of the order of 100 psec, these new circuits will have to be built in strip-line technique, with perhaps semi-insulating GaAs as dielectric, so that a short delay line of about 8.5 mm length produces 100 psec delay. Figure 1 shows an adder. All Gunn-effect elements are biased below threshold for domain nucleation, but high enough for a domain to be sustained once it has been produced by an external pulse. ‘?he biasing voltage V, is applied from a voltage source with an internal resistance, which has to be several times the value of the low-field Gunn-device resistance, so that the input pulse is not shorted via the voltage supply. The input pulse will originate from another Gunn-effect
NOTES
569 + and
I Ri
FIG. 1. Gum-effect adder. (Co = comparator, Q = delay line, c = cathode, a = anode, D = ordinary Gunn diode as pulse invertor, R, = internal d.c.-supply resistance of high value, RI = load resistance, R, = input-terminal resistance of ‘and’.)
pulse circuit. If only one negative input pulse is applied, a domain forms in the negatively biased comparator, which will produce a positive pulse at the input of the following Gunn-effect device, which is biased positively so that a domain can be nucleated by the positive pulse of the first comparator. The output signal of the adder will finally be a positive pulse. The polarity of a pulse can easily be changed by passing the pulse via an ordinary Gunn diode D. The ‘and’ elements consist of a Gunn-effect diode, where the input pulses are applied via two separate resistors, so that the applied voltage will only be high enough for domain nucleation if two pulses are applied simultaneously. The two ‘and’ elements of Fig. 1 deal with the carry signals, which are subsequently delayed by the time of a domain transit. The Gunn diodes D of the circuit in front of the second comparator has the purpose of changing the pulse polarity, as a comparator can only operate with negative input pulses. The time consumption for
the addition of two one-digit numbers is about twice the domain-transit time across one Gunn element. An important device is the transformer of logicalinto-digital information. A first approach has been made with the DOFIC,‘3’ which does not yet produce digital information, but only a succession of pulses which still have to be added up. A more convenient transformer is shown in Fig. 2, which produces the digital information directly. It can therefore be used also as an ultrafast pulse-code modulator. The analogue signal is travelling along a succession of delay lines, and is attenuated simultaneously by fixed amounts. At the end of each delay line, are placed Gunn-effect diodes which have a third domain-triggering electrode near the cathode. They will produce a domain if a triggering signal arrives at the additional electrode, (as reported inc4)), and if the applied analogue voltage is high enough. For a given amplitude of the analogue voltage, only the first triggered Gunneffect diodes will produce domains, the remaining
570
NOTES
Dlgitol output pdS.f3
FIG. 2. Gunn-effect pulse code modulator. (S = triggering signal; its repetition time has to be n times domain-transit time, where ns is the number of digitized quanta for the maximum analogue-signal value, number of delay lines is n-2 and the number of attenuator steps is n-l, Dt = Gunn-effect diode with third (capacitive or ohmic) electrode along its domain trajectory for domain triggering by external signal (i.e. a logic ‘and’, where the input signal for one electrode can have a voltage of any amplitude.) Q = delay line.
NOTES
571
FIG. 3. Gunn-effect memory device, I = ‘read-in’ negative pulses, R = triggering pulse for a read-out output, Q = delay line.
ones do not respond in spite of the triggering signal. This system operates in the same way as the DOFIC, but here the delay between pulses can be controlled more easily and the output pulses have a larger amplitude. The individual output pulses have to be added up, where, however, only
terminal for pulse at the
simplified adders are required. The digital signal will be produced continuously as with any classical pulse code modulator, i.e., the time constant for an output pulse is the transit time of a domain, and the time constant for one set of n digits is n times the transit time. This is, therefore, a very fast
FIG. 4. M = memory device of Fig. 3, I = input to register, I,, la etc. = input to individual memory device, R = triggering pulse for read-out at output, 0 = output of each memory device.
NOTES
572
transformer and will be of advantage, particularly in pulse code modulation, e.g. television circuitry for outer-space applications. A further logic circuit is a Gunn-effect memory device, as shown in Fig. 3. The comparator enables one to switch the ring between ‘on’ and ‘off’. If a negative pulse is applied at 1, a signal will travel continuously round the loop formed by the comparator and the Gunn-effect diode D. It can be read off without being erased from the memory device, if a positive ‘read-out’ pulse is applied at the second input terminal R formed by a Gunneffect ‘and’. The stored signal can be erased by applying a second negative pulse at the ‘read-in’ terminal I. Instead of an ordinary Gunn diode, a second comparator can be employed if a separate terminal is required for the ‘erase’ signal. Such devices as shift registers can be built as shown in Fig. 4, where the basic unit is the memory device of Fig. 3. Finally, it should be mentioned that many Gunn-effect applications are possible for pulse modulation. For example a pulse-phase modulator can be obtained with a Gunn-effect diode having as a cathode a large electrode and as an anode a small electrode. The field will always be larger near the anode. The transit-time of a domain depends, therefore, on the applied voltage as it controls the place of domain nucleation.
Solid-State
Electronics
pp. 572-574.
Pergamon Press 1968. Vol. 11, Printed in Great Britam
Noise parameters of a silicon space-chargelimited triode* (Received 3 August
1967; in revisedform
3 November
1967)
IN A PREVIOUS paper Hsu, et al.(l) determined some of the noise parameters of a silicon SCL triode at 30 MHz. The device had a large amount of l/f noise that extended even beyond 30 MHz. This made the determination of the noise parameters somewhat uncertain. Recently a better SCL triode of the same type became available and hence it was decided to determine all the significant noise parameters of this device at 30 MHz, in order to obtain more accurate information about the noise behavior of such devices.7 This note gives the results. Figure 1 shows the equivalent saturated diode
Acknowledgements-The author is grateful to his colleagues, Mr. S. H. IZADPANAH and Dr. S. MAHROUS for useful discussions.
H.
HARTNAGEI.
Department of Elecironic and Electrical Engineering University of Sheffield England References 1. H. L. HARTNAGEL, &x. IEEE 55, 1236 (1967). 2. S. H. IZADPANAH, H. HARTNAGEL, Proc. IEEE 55, 1748 (1967). 3. C. P. SANDBANK, Solid-St. 10, 369 Eleciron. (1967). 4. J. A. COPELAND, T. HAYASHI, M. UENOHARA, Proc. IEEE 55, 584 (1967).
d IO”
3
5
I
,ol
1
5 ’ 1:’
FHEQJENCY (MHz!-
FIG. 1. Si SCL triode drain noise spectrum; v,, = ov.
Id = 3 m.4,
current of the output noise for short-circuited input as a function of frequency; we see that the noise is flat beyond 20 MHz. Figure 2 shows the equivalent circuit of the device. Here i, is the output noise for short-circuited input and i, the input noise for short-circuited output; i, consists of a part i,’ fully correlated with i, and a part i,” * Supported by AR0 contract. -1 Courtesy R. ZULEEG, Hughes Aircraft New Port Beach, California, U.S..4.
Company,