The Sensitivity of Microwave Bipolar Transistors and Amplifiers To

© 1979 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. IEEE Transactions on Nuclear Science,Vol. NS-26,No. 3, June 1979 THE SENSITIVITY OF MICFWAVF,BIPOLAR TRANSISTORS ANDAMPLIFIERS n> IONIZING RADIATION I. Thmon, M.H. Gibson, M.B. Christensen and G.J.G. Janssens European Space Technology Centre, European Space Agency, Noordwijk, The Netherlands ABsm full design life of the sateljite without due care to radiation “hardening” design , It has been previously shown that small-signal micrawave transistors are sensitive to ionizing ra- Detailed component and amplifier characterisation diation 2 a3ndthat this can lead to application and analysis work referred to in References 2 and 3 limitations . This paper extends the work to a related to three types of small-signal transistors wider range of currently used transistor types and from a specific manufacturer and in linear amplifier amplifiers with applications ranging from low noise applications. Although similar effects had been obser- front-end to class C wer output amplifiers. TW ved on a wide range of transistor types frckn various types of degradation have been identified viz. manufacturers, not 11 these devices had been studied “permanent% Eand room-temperature current dependent in the same detail 3 . “recoverable”. Both types of degradation have been found throughout the range of transistor types and it MicrcxlJave bipolar transistors are used in a wide is shm that they can also be si..muilated by avalan- variety of applications from ICW noise linear receivers ching the emitter-base junctions. to high power class C transmitters and in view of the results of references 2 and 3 on small-signal linear Class A amplifier performance of all power levels applications, it is important to determine whether or can be directly affected by either type of degradation not similar problems can occur in other device types and a detailed example is given in the m3re ccqlex and other applications. This paper presents the results case of “recoverable” characteristics. Class C ampli- of a study of the sensitivity of a wide range of micro- fiers are not directly affected by cumulative ionizing wave bipolar transistor to cumulative ionizing radia- radiation doses of up to 1 Mrad (Si) or emitter-base tion effects. The problems of high dose rate irradia- avalanche although significant transistor degrada- tions such as those stilated in flash X-ray systems tion can occur in both cases. Gne example “F0 Em.icru4ave are not addressed in this paper. Supplementary work on performance degradation in a Class B/C amplifier is emitter-base avalanche stress is also discussed. Be- described to illustrate the only knm exception to sults are presented for two general groups of transis- this rule. tors : 1) small-signal, 2) mediumand high mr. The former group is always used in class A applications, 1. INTRCDUCI’ION whereas the latter operates at higher current densi- ties in class A through class C applications. Data Micrmave bipolar transistors are frequently already presented on small-signal devices is supplemen- found in applications where the radiation environment ted here with results on other manufacturer’s devices must be considered. One practical example of such an and detailed new results are presented on other device application is that of the space environment where types which exhibit current-dependent annealing. Indi- limitations due to the cumulative damaging effects of vidual transistor and amplifier degradation are dis- ionizing radiation on electronic components has led cussed in terms of their effect on applications per- to a large effort on charac:erization and “hardening” formance for both groups of devices. of lower frequency devices . The same effort has not been expended on micrcxlrave bipolar transistors despite 2. SENSITIVITY OF SMALL-SIGNAL the fact that they are nm cmnly used in amnunica- TRANSISTORSAND AMPLIFIERS tions spacecraft with 7 to 10 years design lives in geosynchronous orbits. There are also applications in The effects of cumulative ionizing radiation on small-signal tran istors have been described in sc~ scientific spacecraft which are intended to pass 9 through high radiation fields such as those in the vi- detail elsewhere and an expression has been derived cinity of Jupiter. for the degradation of hFE as a function of radiation dose, measured collector current, and starting value A recent study of small-signal microwave transis- of Since the hFE‘s of these cmnly used devices tors has shm that cmnly used devices can b sen- were% ound to be very sensitive to radiation, small- sitiv to the cumulative effects of ionizing radia- signal transistors frcm other manufacturers were stu- tion 5 . The hFE was shm to be the most radiation died to determine the generality of the problem. In sensitive parameter and significant permanent degrada- addition, amplifiers using these devices were also ir- tion occurred under normal operating conditions at radiated in instances where it was considered that this would add to the knowledge lready gained from previous dose levels expected in many space applications. This 2 d.c. degradation was shm to have an indirect but amplifier irradiation work . ‘IW types of paramater significant effect on the micrmave performance of degradation were found viz. “permanent” and “recovera- these devices due to the resulting hange in bias con- ble”: and the experimental results are ncrwpresented ditions in practical bias circuits 5 . Irradiation of separately in terms of these descriptions since they complete amplifier assemblies containing such transis- require different treatments. tors has confirrred that significant microwave performance degradation can cur at relatively mcderate 2.1 Permanent Parameter Degradation cumulative dose levels 9 . Estimates of equipment performance in geosynchronous orbits indicated that, Pement parameter degradation has been discussed with the present knclwledge of the expected radiation in detail for three different transistor types from the environrtent and the aforementioned ground-based tes- Nippon Electric Co. (NEC) which are denoted A, B and C ting results, specifications would not be met for the in Reference 2. The hFE degradation of transistors A, IPhnuscri~t received Novemlher17, 1978. B and C, whose commercial designations are 2SC1268, 2SC1336 (2N5650) and V222, respectively, obeyed the 4298 0018-9499/79/0600-4298$00.75@I 1979IEEE folkming relationship for the normalized hFE, H, the difference in sensitivity, the transistors (E h&$& : shum in Figure 1 ved in the same general manner and the degradation was permanent. No significant an- (l/m)-1 (l-e-BD) -1 nealing effects were measured at room temperature. 9-,FjJ c (Ic) 1 (1) is the pre-irradiation value of hF , I is the Since the micrmave S-parameter/collector-current ector current in Amps and D is the rzdiafion dose functions were found to be similar for all the above at chip level. For the transistor types discussed in devices, it was not necessary to irradiate amplifiers Referyce 2, the constants C, qand B were found to built with these devices to determine their applica- be 10 1.9 and 12 IQ-ads (Si) , respectively. In tions limitations. The results already obtained frcm order t; compare the previously studied devices with amplifiers built yith transistor types 2SC1268, new results, H is shmn in Figure 1 as a function of 2SC1336and V222 can be extended to given an estirra- for a dose of 500 Krads (Si) which ensures satu- te of the results for devices with lamer sensitivities. degradation. These results apply for a collector current value of 4 mA. This value of collector It is concluded that transistors can be chosen current has been chosen since results my be mre which have a relatively lm radiation sensitivity and easily ccmpared with devices described in the next the judicious choice of such devices is the first step section. in radiation hardening of the equipment in which they are used. EQ-uipmnt designers have not taken radiation sensitivity into account in the past and have normally designed around devices which have the best micrmave performance, but clearly these devices may be the mst radiation sensitive. It skmld be noted that a deter- mination of sensitivity alone my not be sufficient to predict overall9% equipment performme and the prace- dure for radiation hardening at equipmnt level described in Reference 3 is reccmrier&d for applications involving the aforementioned types of devices with per- i manent degradation. 04 I 2.2 Recoverable Parameter Degradation 2.2.1 General--------c- description---- 02 - I All the transistors described in the previous Section had similar gain and noise figure performance -’ I --l-J--.-! _I .--1 --IL-i.- characteristics in the frequency range up to 4 GHz. 20 40 60 80 100 120 140 I60 180 200 These performances have been exceeded recently by two hFEO types of transistors with high fT’s (8.5 and 12 GHz) and lmr noise figures (-1.7 dB at 2 GHz). Both device types are produced by NEK and are designated NE 645 and 644 referring to the 8.5 and 12 GHz fI,‘s respectively. Fquipnt level performance advantages in using Figure 1. A comparison of permanent these transistors in broad-band lm noise front end of srmll-signal transistors frcm dif receivers is such that they are being designed into turers for the same collector current (4 mA) and U.S. and European satellites. Both types of transistor irradiation dose (500 Krads (Si) ) . exhibited a different radiation sensitivity behaviour from that reported for the devices described in the previous Section and a more detailed description of Results of irradiating similar devices frcm other this behaviour is nm presented.

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