An Oxide Electrothermal Filter in Standard CMOS

Abstract

Due to their relatively stable phase shift over temperature, electrothermal filters (ETFs) with an oxide heat path have been used as on-chip phase references, e.g. for thermal diffusivity (TD) temperature sensors. However, previous oxide ETFs were limited to SOI processes, whose deep-trench isolation could be used to create an oxide-dominated heat path. This paper describes, for the first time, an oxide ETF realized in a bulk CMOS process. It achieves a phase spread of 0.6 % (3 sigma, no trim) from -40 °C to 125 °C. When used as a reference for a TD temperature sensor, this translates into a temperature sensing spread of ±2.7 °C (3 sigma, no trim). This is 1.8 times less than the spread reported for SOI implementations, making the CMOS variant not only feasible, but also competitive.