Cobalt oxide nanosheet humidity sensor integrated with circuit on chip

The work studies a micro humidity sensor integrated with a seven-stage ring oscillator circuit-on-a-chip fabricated by the commercial 0.35 mu m complementary metal oxide semiconductor (CMOS) process and a post-process. The structure of the humidity sensor consists of interdigitated electrodes and a sensing film. The sensing film is cobalt oxide nanosheet that is prepared by a precipitation-oxidation method. The sensor, which is a capacitive type, changes in capacitance when the sensing film adsorbs or desorbs water vapor. The ring oscillator circuit is employed to convert the capacitance of the sensor into the oscillation frequency output. The post-process of the sensor includes etching the sacrificial oxide layer and coating the sensing film on the interdigitated electrodes. (C) 2011 Elsevier B.V. All rights reserved.