The permeable base transistor and its application to logic circuits

The permeable base transistor (PBT), which has been fabricated and operated as a microwave device, is described. Numerical solutions of Poisson's equation and the continuity equation show that this transistor could be used as a very high speed switch in a logic gate. It is predicted that with this device in an inverter gate having a fan out of one, a gate delay of 2 ps and a power-delay product of 0.1 fJ are possible. The unique feature of this transistor is the use of a metal grating embedded in the single-crystal semiconductor. The voltage on this grating controls the current between the grating fingers. By proper choice of carrier concentration and grating dimensions, enhancement and depletion mode devices can be made which allow simple gate designs similar to those of nMOS to be used. The lithographic and metal grating fabrication technologies are already well advanced and appear capable of producing PBT integrated circuits. The crystal embedding techniques for placing the metal inside the crystal are new and need further development. In the design of gates and circuits the embedded metal layers will provide the advantage of an interconnect layer inside the crystal, which reduces the number of layers required on the top of the semiconductor surface.