Limits of Si/CoSi2/Si heterotransistors at high frequencies : measurement and estimation

We report on the characterization of Si/CoSi2/Si heterotransistors. Transistor action results from the current flow through pinholes in the CoSi2 base layer. By fabricating integrated transistor structures the high-frequency performance of Si/CoSi2/Si heterotransistors was accessed for the first time. The cutoff-frequency fα of a low-α device is higher than 20 GHz. Using a deduced model of the transistor we conclude that this result should be true for high-α devices as well. A maximum oscillation frequency of 45 GHz is calculated for an experimental device with improved contact resistance. The high-frequency performance of the devices is enhanced by increasing the emitter current. Considering the limits for high current operation we propose an advantageous configuration of pinholes and how to achieve this configuration.