30 and 90 MHz oscillators operating through 450 and 470 °C for high temperature wireless sensors

This paper presents the first demonstration of oscillators operating above 400°C. The oscillators are fabricated with Cree SiC MESFETs and thin film, MIM capacitors and inductors on an alumina substrate. The tank circuit inductor is used to magnetically couple the oscillator signal to a coil placed 1 m from the circuit. The first oscillator is designed at 30 MHz, it operated at 27.8 MHz, and the second is designed to operate at 100 MHz, it operated at 90 MHz. The 30 MHz oscillator operated through 450°C and the 100 MHz oscillator operated through 470°C. The received power, frequency, and phase noise as a function of temperature is presented. In addition, the failure mechanism of the oscillator is discussed.