Overgrown PBT's: Calculations and Measurements

The device parameters of overgrown silicon permeable base transistors (PBT’s) have been systematically investigated by two dimensional drift diffusion simulations and analytical calculations. Hence some design rules arise for optimizing the high frequency performance of PBT’s. The calculations indicate the source-drain distance as the essential PBT parameter, which should be kept below 200 nm in order to expect unity current- gain frequencies fT over 50 GHz. In addition, PBT’s with buried monocrystalline CoSiz -gates have been fabricated by high dose cobalt ion implantation through a grid-like mask into MOS-compatible n -type Si(lO0). Measurements revealed a transconductance of 70 mS/mm and a fT value of 6 GHz. The comparison between measured and simulated output characteristics shows good agreement.