Relative-Air Humidity Sensing Element Based on Heat Transfer of a Single Micromachined Floating Polysilicon Resistor

Abstract

An air-humidity sensing element based on heat transfer mechanisms (conduction and convection) is presented. The sensing element is a single floating resistor of doped polysilicon, which operates in two phases: thermal actuation and thermal sensing. As thermal actuation, a convenient biasing current is applied to the resistor leading its self-heating by Joule Effect. As thermal sensing, the resistor biasing current is reduced and its Thermal Time Constant (τ) during the cool-down process is measured. Characterization results show that τ is closely related to the air relative humidity (%RH). This sensor presents a maximum power consumption of 5 mW.