CMOS Alcohol Sensor Employing ZnO Nanowire Sensing Films

摘要

This paper reports on the utilization of zinc oxide nanowires (ZnO NWs) on a silicon on insulator (SOI) CMOS micro-hotplate for use as an alcohol sensor. The device was designed in Cadence and fabricated in a 1.0 um SOI CMOS process at XFAB (Germany). The basic resistive gas sensor comprises of a metal micro-heater (made of aluminum) embedded in an ultra-thin membrane. Gold plated aluminum electrodes, formed of the top metal, are used for contacting with the sensing material. This design allows high operating temperatures with low power consumption. The membrane was formed by using deep reactive ion etching. ZnO NWs were grown on SOI CMOS substrates by a simple and low-cost hydrothermal method. A few nanometer of ZnO seed layer was first sputtered on the chips, using a metal mask, and then the chips were dipped in a zinc nitrate hexahydrate and hexamethylenetramine solution at 90°C to grow ZnO NWs. The chemical sensitivity of the on-chip NWs were studied in the presence of ethanol (C2H5OH) vapour (with 10% relative humidity) at two different temperatures: 200 and 250°C (the corresponding power consumptions are only 18 and 22 mW). The concentrations of ethanol vapour were varied from 175 – 1484 ppm (pers per million) and the maximum response was observed 40% (change in resistance in %) at 786 ppm at 250°C. These preliminary measurements showed that the on-chip deposited ZnO NWs could be a promising material for a CMOS based ethanol sensor.