B.S.T.J. Briefs: A 1/4- Watt Si PvN X-Band IMPATT (IMPact Avalanche Transit Time) Diode

An output of 250 mW CW at 12 GHz with an efficiency of 2.8 percent was obtained from an Si P»N diode. Previously 1 we discussed characteristics of Si PvN I M P A T T (IMPact Avalanche Transit Time) diodes. In that study the emphasis was primarily in understanding device properties rather than extending their output power. In those diodes, the input power had to be kept less than 2 watts to avoid device burnout. The average microwave power output was about 10 mW with the efficiency seldom exceeding 1 percent. However, by immersing the diode holder in liquid nitrogen, and thus increasing heat flow, it was shown that the diodes were capable of CW output on the order of 100 mW in the X-band (8.2 to 12.4 GHz). The main deterrent to increased output power was the fairly large thermal impedance from junction to package. To relieve the heating limitations, we recently mounted similar diodes with junction side down 2 which allowed us to apply input powers as large as 10 watts without lowering the ambient temperature. Fig. 1 shows the output and efficiency vs input plot for the best diode. The oscillation was measured in the 50 mil high waveguide circuit used by De Loach and Johnston. 3 The breakdown voltage was 54 volts. At the highest input the current density is about 2,000 A/cm 2 . The efficiency is still increasing. This is a feature of the pi-n structure in contrast to the Read structure which shows efficiency saturation at lower current density. 4 The oscillation frequency at the highest input current was 12.04 GHz; as the input current was decreased the frequency decreased by 0.2 GHz.