Modeling, design and simulation of a monolithic synchronous buck converter with time-based control in SiC CMOS for high temperature environments

The demand for power management integrated circuits (ICs) capable of operating in extreme environments is rapidly increasing, driven by the requirements of ”New Space” exploration, deep-well drilling, and advanced automotive systems. Traditional Silicon (Si) electronics suffer from severe degradation above 200◦C due to exponential increases in intrinsic carrier concentration and leakage currents. This thesis presents the design and simulation-based validation of a monolithic synchronous DC-DC buck converter utilizing the Fraunhofer IISB 2µm 4H-SiC CMOS technology, specifically optimized for operation up to 500◦C. The research begins with an experimental characterization of the 4H-SiC technology node to extract temperature-dependent parameters. The findings reveal a significant mobility disparity and a negative threshold voltage (Vth) temperature coefficient, which pose challenges for conventional high-gain analog control loops. To mitigate these limitations a time-domain control architecture is adopted. This scheme utilizes a Voltage-Controlled Oscillator (VCO) to perform voltage-to-time conversion and act as a phase integrator, while a Phase Detector (PD) generates the implicit Pulse-Width Modulated (PWM) signal. The complete system, comprising the power half-bridge, cascaded gatedrivers, and non overlap circuits, was designed for a nominal 12V output and validated through circuit-level simulations in Cadence Spectre®. Results demonstrate robust stability and precise load regulation across the entire thermal profile from 25◦C to 500◦C. The system achieved a power-conversion efficiency of 86% at 25◦C, which improved to 87.4% at 400◦C for a nominal 100mA load, meeting the project’s target of > 80%. This work validates the feasibility of using time-based control to overcome the inherent material constraints of Silicon Carbide CMOS, paving the way for fully integrated, high-temperature power-on-chip solutions.