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arXiv · 2302.14210

Investigation of Cryogenic Current-Voltage Anomalies in SiGe HBTs: Role of Base-Emitter Junction Inhomogeneities

Nachiket R. Naik·Bekari Gabritchidze·Justin H. Chen·Jacob Kooi·Kieran A. Cleary·Austin J. Minnich
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Abstract

The deviations of cryogenic collector current-voltage characteristics of SiGe heterojunction bipolar transistors (HBTs) from ideal drift-diffusion theory have been a topic of investigation for many years. Recent work indicates that direct tunneling across the base contributes to the non-ideal current in highly-scaled devices. However, cryogenic discrepancies have been observed even in older-generation devices for which direct tunneling is negligible, suggesting another mechanism may also contribute. Although similar non-ideal current-voltage characteristics have been observed in Schottky junctions and were attributed to spatial inhomogeneities in the base-emitter junction potential, this explanation has not been considered for SiGe HBTs. Here, we experimentally investigate this hypothesis by characterizing the collector current ideality factor and built-in potential of a SiGe HBT versus temperature using a cryogenic probe station. The temperature-dependence of the ideality factor and the relation between the built-in potential as measured by capacitance-voltage and current-voltage characteristics are in good qualitative agreement with the predictions of a theory of electrical transport across a junction with a Gaussian distribution of potential barrier heights. These observations suggest that lateral inhomogeneities in the base-emitter junction potential may contribute to the cryogenic non-idealities. This work helps to identify the physical mechanisms limiting the cryogenic microwave noise performance of SiGe HBTs.

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Nachiket R. Naik, Bekari Gabritchidze, Justin H. Chen, Jacob Kooi, Kieran A. Cleary, Austin J. Minnich. 2023-02-28. Investigation of Cryogenic Current-Voltage Anomalies in SiGe HBTs: Role of Base-Emitter Junction Inhomogeneities. https://arxiv.org/abs/2302.14210

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