Temperature dependence of vacuum encapsulated resonators for humidity measurement

This paper demonstrates the effect of temperature on humidity measurements using a charge-biased microshell encapsulated single-anchored double-ended tuning fork resonator (DETF). The resonator is electrically connected to a metal bond pad on the external surface silicon dioxide. Changes in the ambient humidity alter the charge decay characteristics of the resonator by modifying the surface resistance of the oxide. This change is monitored by measuring the shift in resonant frequency due to electrostatic spring softening. Varying the temperature from 12°C to 32°C and the relative humidity (RH) from 0 to 60%, the temperature dependence of time decay ranged from −0.05/°C to −0.03/°C and the relative humidity dependence of time decay ranged from 0/RH to −15/RH.