Thermal analysis and design for high power GaAs PCSS

Abstract

Compact configuration and repetitive operation are important for pulsed power. Photoconductive semiconductor switches (PCSS) have attracted increased attention due to their high power capacity, high repetition rates, low inductance, and low jitter; however, joule heating seriously degrades the electrical properties and deice lifetime. Thermal characteristics of PCSS vary with different photoconductive modes. The filament heat source is characteristic of the nonlinear mode, compared to a bulky heat source in the linear mode. This paper determines the critical frequency using finite difference time domain (FDTD) based upon the location, radius, number of filaments, dimensions of the PCSS chip, and temperature. We found that the critical frequency increases exponentially with radius or the number of current filaments, decreases exponentially with filament depth or chip thickness, and decreases linearly as environment temperature increases in a special range. When the PCSS temperature exceeds the critical temperature, the PCSS is runway in the first shot. To improve the critical frequency, a multi-current-filament discharge is introduced and its effectiveness demonstrated by simulation and experiment. Moreover, a silicon rectangular micro-channel cooler consisting of a main body structure and a cover joined by Si-Si bonding is designed and tested experimentally. The main body contains an array of micro-channels between the distributary groove and the conflux groove, and the cover is punched by semiconductor etching. The experimental results indicate that he cooler has a heat flux as high as 43 W/cm2. In experiments, the cooler satisfied a high power PCSS chip run at 1 KHz for half an hour of continuous operation. Lastly, the degradation mechanism of ohmic contact is analyzed. We propose that high temperature increases the interdiffusion of multi-ion doping, thermal fatigue is caused by the circular thermal stress of the metal electrode, the semiconductor material plays an important role on the detachment of the metal electrode, and thermal mismatch is the main factor of disengagement of silicon nitride protective layer in some PCSS chips.