CHARACTERIZATION AND COMPACT MODELING OF SILICON-GERMANIUM HETEROJUNCTION BIPOLAR TRANSISTORS FROM ROOM TO CRYOGENIC TEMPERATURES

Silicon-Germanium Heterojunction Bipolar Transistors (SiGe HBTs) are
preferred for quantum computing (QC) readout circuits due to their
high gain and speed as well as the integration with complementary
metal-oxide-semiconductor (CMOS) technology. The device physics of
SiGe HBTs at cryogenic temperatures (CT), like carrier scattering, carrier
transport, high-injection effects were not systematically and physically
investigated. Thus, a physical compact model for circuit simulation did
not exist at the start of this thesis work.
In this work, the measurement setup has been built for obtaining directcurrent
(DC) and small-signal characteristics from medium to high
frequencies over a wide temperature range. The radio frequency (RF)
power of network analyzer and integration time of source monitor units
have been investigated to ensure the accuracy of the DC and smallsignal
measurement. The key electrical parameters of SiGe HBTs have
been characterized. The temperature trend of the transfer current, base
current, sheet resistance, depletion capacitance, and built-in voltage,
zero-bias hole charge have been extensively demonstrated and physically
analyzed.
Based on the comprehensive investigation on the electrical parameters
over a wide range of temperatures, the following work consists of
two parts: (1) the existing analytical formulations for various electrical
components have been compared for their validation, and (2) in case of
evident discrepancies the physical origin has been analyzed and valid
compact formulations have been derived.