Porous Alumina Based Capacitive MEMS RH Sensor

TL;DR

This paper presents a novel porous alumina capacitive MEMS humidity sensor with high sensitivity, integrated heating, and CMOS compatibility, suitable for wireless sensor networks.

Contribution

It introduces a new porous alumina sensing layer and a post-CMOS process for fabricating a highly sensitive, low-power humidity sensor.

Findings

Sensitivity of approx. 15 pF/RH%, over an order of magnitude higher than previous sensors.

Integrated resistive heating enables drift reduction and temperature compensation.

The sensor is compatible with CMOS-MEMS processes for potential wireless applications.

Abstract

The aim of a joint research and development project at the BME and HWU is to produce a cheap, reliable, low-power and CMOS-MEMS process compatible capacitive type relative humidity (RH) sensor that can be incorporated into a state-of-the-art, wireless sensor network. In this paper we discuss the preparation of our new capacitive structure based on post-CMOS MEMS processes and the methods which were used to characterize the thin film porous alumina sensing layer. The average sensitivity is approx. 15 pF/RH% which is more than a magnitude higher than the values found in the literature. The sensor is equipped with integrated resistive heating, which can be used for maintenance to reduce drift, or for keeping the sensing layer at elevated temperature, as an alternative method for temperature-dependence cancellation.