Early effect modeling of silicon-on-insulator SiGe heterojunction bipolar transistors

Abstract

Silicon germanium (SiGe) heterojunction bipolar transistor (HBT) on thin silicon-on-insulator (SOI) has recently been demonstrated and integrated into the latest SOI BiCMOS technology. The Early effect of the SOI SiGe HBT is analysed considering vertical and horizontal collector depletion, which is different from that of a bulk counterpart. A new compact formula of the Early voltage is presented and validated by an ISE TCAD simulation. The Early voltage shows a kink with the increase of the reverse base-collector bias. Large differences are observed between SOI devices and their bulk counterparts. The presented Early effect model can be employed for a fast evaluation of the Early voltage and is useful to the design, the simulation and the fabrication of high performance SOI SiGe devices and circuits.

An Analytical Avalanche Multiplication Model for Partially Depleted Silicon-on-Insulator SiGe Heterojunction Bipolar Transistors

“…The vertical and horizontal electric fields and depletion widths for each case can be obtained from Eqs. ( 2), ( 4), ( 5) and ( 3), ( 6), (7), respectively,…”

“…Experiment [7] Model calibrated Physical simulation The smaller avalanche multiplication in SOI HBTs explains the inherent higher emitter-to-collector breakdown voltage BV CE0 than that found in bulk HBTs, as the breakdown voltage can be derived from avalanche multiplication when β × (M − 1) = 1, where β is the current gain. Since there is a trade-off between transit frequency f T and breakdown voltage, higher f T × BV CE0 products are reached and hence there is a higher transit frequency for the same breakdown voltage.…”