AC characteristics of Cr/p/sup +/a-Si:H/V analog switching devices

Experimental results on the ac characteristics of electro-formed Cr/p/sup +/ hydrogenated amorphous silicon (a-Si:H)/V thin film memory devices are presented. The impedance spectrum of the memory switching device has been measured over a wide frequency range from 1 Hz-32 MHz while keeping the ac voltage amplitude below 0.02 V. Simulation of the measured impedance spectrum using an equivalent circuit indicates that the capacitance associated with a conducting filament tends to increase as the memory resistance decreases. This is explained on the basis of an activated tunnelling mechanism. Charge transport is dominated by electron tunnelling via metallic particles in the filament, and hence small changes in interparticle spacing influences the tunnelling process considerately, leading to changes in both memory resistance and effective dielectric constant.