The effect of base-Schottky geometry on Si PBT device performance

Experimental device results are compared with two-dimensional numerical simulations of etched-groove Si permeable base transistors (PBT´s). Both the simulations and experimental devices indicate that small variations in the metal-semiconductor contact area of the base fingers can lead to substantial (≥ 50-percent) deviations in key device parameters such as transconductance Gm, threshold voltage VT, and intrinsic input capacitance Cin. In spite of these variations, the maximum small-signal short-circuit unity-current-gain frequency fTdoes not change significantly because the maximum ratio of Gmto Cinremains nearly constant. In the experimental devices, fTis limited to about 40 percent of the predicted value due to parasitic capacitances (e.g., base pad capacitance).