Optimization of pulsed GaAs IMPATT diodes for 200 GHz

Abstract

ABSTRACT RF power generation of IMPATT diodes at mm-wave frequencies is limited mainly by thermal effects. The challengeto obtain output power at 200 GHz and above can be met only by extremely high DC current densities to push thecharacteristic avalanche frequency near to the oscillation frequency. The active devices have to be optimised withregard to pure IMPATT mode operation, low break-down voltage and efficient heat dissipation. Since these threeconditions influence each other, a compromise is necessary. From theoretical simulations (Monte Carlo simulation anddrift-diffusion model) a double-drift Read IMPATT diode structure results which is capable to be operated at DCcurrent densities up to 225 kA/cm2 for short pulses of 50 ns with maximum device temperature below 500 K. The initialmaterial is grown by MBE technique taking special care to control the thickness and doping concentration of thedifferent GaAs layers. The individual devices are fabricated by standard photo-resist technology with an integrated goldcone on top which adjusts the encapsulation height in the used full height inductive post waveguide resonator. Thereby,a low loss device mounting in the resonator without parasitic elements and an optimum impedance matching of diodeand resonator can be realised. By means of different double-drift Read IMPATT structures the experimental results interms of RF output power, conversion efficiency and oscillation frequency are compared. The highest output power sofar is 1W at 176.5 GHz with 5.5 % conversion efficiency. At a frequency of 210 GHz 0.25 W output power and 1.8 %conversion efficiency were realised at a DC current density of 225 kAIcm2. The experimental results are in goodagreement with calculations applying a pulsed oscillator model.Keywords: GaAs IMPATT diodes, RF power generation, mm-waves, pulsed operation, waveguide resonator