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Study of cryogenic temperature effects in 250 nm bulk cmos technology using a charge-based mosfet model

Tzanetos Evangelos

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Summary

This thesis investigates the behavior of MOS transistors at cryogenic temperatures, specifically targeting the modeling of NMOS and PMOS devices. The research is motivated by the interest in cryogenic electronics, particularly for quantum computing and ultra-low-noise applications, in which room-temperature models fail to accurately describe device behavior.The experimental basis of this work came through the collaboration between Prof. M. Bucher and CERN, in which a 250nm Bulk CMOS technology was used. The modeling procedure was conducted utilizing the ICCAP software for the variation of different lengths (5μm, 1μm, 280nm) and temperatures (300 K, 150 K, 70 K, 20 K) of both NMOS and PMOS. This model was augmented so as to match the cryogenic behavior observed from the data acquired, using a full measurement set including transfer characteristics (ID − VG), (ID − VS), transconductance (gm), and transconductance efficiency ((gmUT )/ID −ID) curves. Long, intermediate and shortchannel devices were scaled, allowing the extraction of critical parameters such as threshold voltage (VT H), subthreshold slope factor (n), specific current (I0), velocity saturation effect (λc), and their temperature scaling behavior.The model was based on the simplified EKV (SEKV) model, with the necessary modifications to provide a concise yet physics-based model of the MOSFET operation in weak, moderate, and strong inversion regions covering the full temperature range. The purpose is to show the challenges caused by incomplete dopant activation, mobility enhancement, and deviations in short-channel behavior at deep-cryogenic conditions.

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