Thin film amorphous semiconductor microwave switches

Abstract

Microwave switches operating in the X band were designed and fabricated using amorphous chalcogenide semiconductors of composition Ge_xTe_yAs_z. Threshold devices were shown to operate as microwave modulators at modulation frequencies of up to 100 MHz. No delay time was observed at the highest frequency although the modulation efficiency decreased above 10 MHz owing to the finite recovery time which was approximately 0.3 × 10^-8s. The devices can also be used as variolossers, the insertion loss being 0.5 dB in the OFF state and increasing on switching from 5 dB at 1 mA device current to 18 dB at 100 mA. The behaviour of the threshold switches can be explained in terms of the formation of a conducting filament in the ON state with a constant current density of 2 × 10⁴Acm^-2 that is shunted by the device capacitance. The OFF state conductivity s varies as ω ⁿ (0.5 < n < 1) which is characteristic of hopping in localized states. However, there was evidence of a decrease in n or a saturation of the conductivity at high frequencies. As a result of phase separation memory switches require no holding current in the ON state and may be used as novel latching semiconductor phase-shifters.