High Temperature Bipolar SiC Power Integrated Circuits

Sammanfattning: In the recent decade, integrated electronics implemented using wide bandgap semiconductor technologies such as Gallium Nitride (GaN) and Silicon Carbide (SiC) have been shown to be viable candidates in extreme environments (e.g high-temperature and high radiation). Such electronics have applications in down-hole drilling, automobile-, air- and space- industries. In this thesis, integrated circuits (ICs) in bipolar 4H-SiC for high-temperature power applications are explored. In particular, device modelling, circuit design, layout design, and measurements are discussed for a range of circuits including operational amplifiers, linear voltage regulators, drivers for power switches, and power converters with integrated control. All the circuits demonstrated in this thesis were designed for operation over a wide temperature range, and nearly all were tested from 25 °C up to 500 °C. Circuit design in bipolar SiC technology involves challenges such as the fabrication process’ uncertainties and incomplete models of the devices. Furthermore, high temperature modelling of the integrated devices is needed for circuit design and simulation. On the device side, the current gain (β) of the Bipolar Junction Transistors (BJTs) varies over temperature due to the dopants’ ionization. Moreover, the integrated resistors vary non-monotonically over temperature because of two opposing phenomena: increasing dopants’ ionization and decreasing minority carrier mobility. From the circuit design viewpoint, techniques such as negative-feedback, temperature-insensitive biasing, buffering and Darlington stages, and amplifiers with fewer gain stages, were shown to be useful for high-temperature IC design in bipolar SiC. In this thesis, several high-temperature ICs in bipolar SiC were demonstrated. It is shown that the linear voltage regulator can be improved by using a tailored high-current lateral Darlington power device in the same fabrication process. This results in a high temperature high current power supply solution. Moreover, the drivers can be improved by design in order to provide higher voltage levels and peak currents, in order to drive different types of power devices (bipolar and MOSFET based). In addition, a DC-DC converter with fully integrated hysteretic control is designed taking advantage of several sub-circuits such as operational amplifier, Schmitt trigger and driver for the power switch. This study is followed by preliminary experimental results for the converter and controller IC.