Highly Sensitive CO Sensor Based on Thickness-Selective ZnO Thin Film: Device Fabrication and Packaging

In this report, the thickness‐dependent carbon monooxide (CO)‐sensing characteristics of sputtered zinc oxide (ZnO) films are investigated, followed by their morphological and electrical characterizations. ZnO films, ≈21 nm, show repeatable and high change in their resistances on exposure to CO and the observed maximum response is ≈52.2%, whereas ≈219 nm films fail to show reproducibility in sensing performance. Response and recovery time of ≈21 nm films are ≈28 and 250 s, which are faster than the time observed in case of ≈219 nm films. An ≈21 nm film is able to resolve 100 parts‐per‐billions (ppb) CO concentration in air. Later, on‐chip integration of ≈21 nm film is successfully implemented on specifically designed Micro‐Electro‐Mechanical‐System (MEMS) platform, inbuilt with microheater and utilizes power of ≈23.7 Milliwatts (mW) (375 °C). The packaged sensor chip is further tested and qualified for indoor and outdoor detection of CO gas in the atmosphere.