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 3
µ
²
and 12
µ
²
, respectively, and a comparison is made with larger geometries fabricated on the same wafer. Ion implanted microemitter devices have f
T
= 4.8 GHz at currents as low as 100 µA and peak f
T
= 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 f
T
falloff with current density is lower for the microemitter than for larger geometries. This effect may make these devices also useful as microwave transistors.