Micromachining of Multilayer Thin Films for High-Speed Humidity Sensor Fabrication

Abstract

This paper reports the microfabrication and characteristics of a novel high-speed polyimide-based humidity sensor using an etch process based on a combination of isotropic and anisotropic etching steps with inductively coupled plasma (ICP) and a localized curing of polyimide films on microhotplate. The polyimide capacitive humidity sensors showed a sensitivity of 0.77 pF/percent relative humidity (%RH), a linearity of 0.9995, and a hysteresis of 0.62%RH, a response time of 3 s. In comparison, the sensors with a conventional structure exhibited a time response of 7s. High speed is achieved because a device has many holes and moisture is thus absorbed into the top and side surfaces of polyimide. (C) 2009 The Japan Society of Applied Physics