A fast-response/recovery ZnO hierarchical nanostructure based gas sensor with ultra-high room-temperature output response

In this paper, a ZnO hierarchical nanostructure based gas sensor is presented. The proposed implementation features short response/recovery time and ultra-high output response at room temperature (RT). In order to take the advantages of complementary-metal-oxide-semiconductor (CMOS) process in terms of miniaturization and cost-effectiveness, a novel fabrication recipe, consisting of CMOS-compatible techniques, is proposed to form a patterned triple-layer metal, which functions as both interconnection electrodes and catalyst for our reported ZnO hierarchical nanostructure. This enables rapid and local growth of ZnO hierarchical nanostructure directly on a single silicon chip. Reported peak RT output response of 32 (20 ppm NO₂) provides a significant 28-fold improvement over the traditional widely adopted nanowire-based gas sensor. Meanwhile, a time efficient gas sensor is also validated by the presented temporal performance with a response and recovery time of 72 s and 69 s, respectively. In addition, compared with the previously demonstrated gas sensors operating at 200-300 °C, the proposed RT sensing completely removes the power-hungry heater and eliminates the related thermal reliability issues. Moreover, the demonstrated process flow well addresses the challenging issues of the traditional mainstream "drop-cast" method, including poor yield, non-uniformity of device performance and low efficiency caused by inevitable manual microscope inspection.