Silicon Permeable Base Transistors for Low-Phase-Noise Oscillator Applications up to 20 GHz

摘要

Silicon permeable base transistors have been fabricated that exhibit a small-signal short-circuit current gain frequency exceeding 20 GHz and a maximum frequency of oscillation near 30 GHz. This transistor has been used to realize voltage-controlled oscillators at C, X, and Ku band that have provided low phase noise. There has been considerable interest in developing novel transistor structures and geometries which provide high frequency performance. One such device is the permeable base transistor (PBT). The important feature of the PBT is a thin Schottky-barrier base which is patterned into a submicrometer-periodicity grating. As shown in Figure 1, the active region of the Si PBT is formed from an array of 320-nm-period grooves etched in an n-type Si region. The Schottky-barrier base grid consists of a thin Pt-Si film in the groove bottoms. Although the Si device differs in structural detail from the GaAs version in which the Schottky barrier base grid is entirely encapsulated by GaAs, the principle of operation remains the same. The electron current flows vertically through the openings between the grid-like base fingers. The device can be viewed essentially as a vertical FET, with a very short gate length, which accounts for its high frequency capability.