Towards Ultra Low Thermo-Mechanical Sensitive Capacitors in CMOS

Fully integrated capacitors in CMOS with a low sensitivity to temperature and externally applied mechanical forces are crucial for highly stable, fully integrated frequency references. Thermal changes and external forces alter the physical structure of capacitors, affecting their capacitance. This paper presents measurements of the temperature dependency and mechanical stress sensitivity of several custom back-end capacitors, with a front-end capacitor for benchmarking. Onwafer and in-package measurements were conducted to (try to) separate thermal and stress effects. We show that both measured sensitivities are hardly (cor)related for backend capacitors. Thermal effects appear to be mainly related to inter-terminal oxide material whereas external force sensitivity shows a dependency on the capacitance direction and the distance from the top of the backend.