Comparison of Single-Event Transients in SiGe HBTs on Bulk and Thick-Film SOI

A comparison of heavy-ion-induced single-event transients (SETs) in silicon-germanium heterojunction bipolar transistors (SiGe HBTs) fabricated on both bulk and silicon-on-insulator (SOI) substrates is presented. Experimental heavy-ion data show a reduction of sensitive volume of $\approx 350\times $ for the SiGe HBTs fabricated on SOI compared to those on a bulk substrate. Furthermore, the results indicate that the sensitive volume of the SOI SiGe HBTs is confined to the intrinsic device. These results have been confirmed using pulsed laser data and TCAD simulations. Limiting the charge collection depth of SiGe HBTs by fabricating them on SOI facilitates correlation of ion and laser results. The improved ease of correlation is a result of suppressing diffusive charge collection mechanisms that are difficult to replicate with the charge deposition profile generated by two-photon absorption using a tightly focused laser beam. However, a potential issue with pulsed laser testing is determining the loss of the pulse energy through the buried oxide, which requires detailed knowledge of the semiconductor platform. Overall, the reduction of sensitive volume for the SOI SiGe HBTs compared to those on a bulk substrate is a clear advantage from a single-event upset vulnerability perspective.

I. Introduction

Silicon–Germanium heterojunction bipolar transistors (SiGe HBTs) have many characteristics that make them an attractive solution for both on-orbit and terrestrial extreme environments, particularly those requiring high-performance analog, high-frequency RF, and highly integrated digital circuitry on a single die for improved size, weight, power, and cost (SWaP-C) metrics. SiGe HBTs have a built-in tolerance to total ionizing dose (TID) up to multi-Mrad(SiO₂) levels [1], and their operation has been demonstrated from 70 mK to 573 K [2], [3]. In addition, these devices are seamlessly integrated with CMOS fabrication processes. However, these devices have been shown to be very susceptible to single-event effects (SEEs) [1]. Thus, research on mitigating SEEs in circuits and systems built with SiGe HBTs continues.