There is a varicap effect on reverse bias PN junctions that reduces Cavg with Vdd so lowering the supply might offset the RdsOn which moves in the opposite direction of Cavg for Gate , Drain or Miller capacitance. I would expect series Rs and shunt Cavg to be the main factors of a ring oscillator and temperature sensitivity might be self-correcting this way with a current source rather than a voltage source for VVDD. I know that RdsOn rises with temperature, I forget how PN junction capacitance changes with temp.
(so much for my hand waving theory, maybe you can examine deeper.)
IDK but GPT says this...
The capacitance of a PN junction, often referred to as junction capacitance, typically decreases with an increase in temperature. This phenomenon can be attributed to several factors:
- Doping concentration: The doping concentration of impurities in the semiconductor material affects the width of the depletion region and, consequently, the junction capacitance. At higher temperatures, the number of charge carriers increases due to thermal excitation, which results in a reduction in the width of the depletion region and a decrease in junction capacitance.
- Carrier mobility: At elevated temperatures, the mobility of charge carriers in the semiconductor material typically increases. This increased mobility leads to a more rapid recombination of minority carriers in the depletion region, reducing the effective width of the depletion region and thus lowering the junction capacitance.
- Dielectric constant: The dielectric constant (also known as relative permittivity) of the semiconductor material decreases with increasing temperature. Since junction capacitance is inversely proportional to the dielectric constant of the material, an increase in temperature leads to a decrease in junction capacitance.
- Leakage current: At higher temperatures, the leakage current across the PN junction increases due to increased carrier generation and recombination processes. This increased leakage current can further reduce the effective width of the depletion region and thus decrease the junction capacitance.