Enablement and Optimization of SiGe HBTs for Extreme Environment Electronics

Abstract

One of the remarkable characteristics of SiGe HBT is the ability to operate over a wide temperature range, from as low as sub 1K [1], to as high as over 400 K. This, together with excellent total dose radiation tolerance, makes it very attractive for implementing space electronics that can operate over a wide temperature range in presence of radiation as found in space missions [2].To enable such extreme designs, we have been recently developing SiGe HBT compact model as well as TCAD models that can function from 43 to 393K. Our compact model is based on Mextram. Completely new temperature scaling equations of many model parameters are developed with as much physics basis as possible to fit temperature dependence of transistor dc and ac characteristics. For example, carrier freezeout is now modeled accouting for latest research on Mott transition, leading to successful modeling of resistance temperature dependences for all resistances [3]. Temperature dependence of high-injection parameters are inherently more difficult to model at lower temperatures due to increased significance of self-heating. A 20K increase is more significant at 43K than at 300K, making "isothermal" parameter extraction impractical. Physics guided "guesses" are used in formulating their temperature dependences. The model is coded with Verilog-A and compiled for circuit simualtion. An example of the I C − V BE and I B − V BE modeling results is shown in Fig. 1.A more difficult set of challenges exist for extending TCAD physics models such as bandgap narrowing (BGN) to lower temperatures, as one has much less freedom in "empirical fitting" with device simulation. For instance, a change of BGN affects I C , I B , and f T simultaneously in TCAD, while in compact models, such coupling is much less. Sentaurus device, formerly Dessis, is used for implementing new physics models through its Physical Model Interface (PMI). The level of model access, however, is much more restricted compared to Verilog-A for compact modeling.Using a reasonably "calibrated" TCAD deck, we optimized the SiGe profile design of a first-generation SiGe HBT for improved high injection performance at lower temperatures. Fig. 2 shows experimental results of the optmization. The optimized HBT is able to operate at much higher J C at 43 K.The combination of 3-D TCAD with a compact model is then used to investigate temperature dependence of single-event upset. Interestingly, SEU immunity is found to improve with cooling, clearly good news as no additional SEU hardening is required for low temperature operation. References[1] L. Najafizadeh, et al., EDL, vol. 30, pp. 508-510, 2009.[2] J. D. Cressler, Proc. of the IEEE, vol. 93, No. 9, pp. 1559-1582, 2005 [3] L. Luo, et al., TED, vol. 56, pp. 2169-2177.[4] Z. Xu, et al., BCTM, pp. 81-84, 2008.

Sensitivity investigation of 100-MeV proton irradiation to SiGe HBT single event effect

“…Moreover, it can be concluded that when the incidence is from the emitter center, the device is particularly susceptible to SEE. This phenomenon can be attributed to the fact that when an incident occurs from the emitter center, the incident track passes not only through the larger collector/substrate (CS) junction, which is the most sensitive position of the device, [20,21] but also through all electrode areas of the device. As a result, a significant potential collapse occurs, causing the electron-hole pairs to be quickly collected by drift under the action of the electric field to form a large transient current peak as shown in Figs.…”