Silicon pνn avalanche transit-time diodes

Negative resistance characteristics have been observed in the range 3-12 GHz in silicon pvn diodes using avalanche transit-time operation (IMPATT diodes). The diodes, made by a single boron diffusion into epitaxial wafers, had breakdown voltages from 40 to 100 volts. A few hundred diodes all showed, quite reproducibly, microwave negative resistance. Measurement by swept-frequency reflection showed that the negative resistance was present over wide frequency ranges. Oscillation was observed when the diode was put in the coaxial and waveguide "cavities." The oscillation could be tuned over a wide frequency range. The maximum output observed is 30 mW at 11 GHz with 1.7 percent efficiency. Cooling experiments indicated that substantially larger output is possible by proper engineering of the heat disposal. The spectrum width of oscillation, when the diode is reasonably well tuned, ranged from 100 to slightly below 5 kHz. The load impedance into which the diode can oscillate changes from capacitive to inductive, going through a maximum as the oscillation frequency increases. The diodes were found to have so-called microplasmas.