A transistor design for high fTat low currents

A design and processing technique allowing fabrication of devices with very small junction capacitances is presented. Emitter and base areas of the smallest device, called a microemitter, are reduced to about 3µ²and 12µ², respectively, and a comparison is made with larger geometries fabricated on the same wafer. Ion implanted microemitter devices have fT= 4.8 GHz at currents as low as 100 µA and peak fT= 7.0 GHz and should allow a great improvement in the speed-power product of ECL circuits. Emitter injection appears to approach the behavior of a point source, and it is observed that the rate of fTfalloff with current density is lower for the microemitter than for larger geometries. This effect may make these devices also useful as microwave transistors.