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

Abstract

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 G <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> , threshold voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> , and intrinsic input capacitance C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</inf> . In spite of these variations, the maximum small-signal short-circuit unity-current-gain frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> does not change significantly because the maximum ratio of G <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> to C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</inf> remains nearly constant. In the experimental devices, f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> is limited to about 40 percent of the predicted value due to parasitic capacitances (e.g., base pad capacitance).