Wearable gas sensor microsystem for personal healthcare and environmental monitoring

Exposure to air pollutants is an ever present concern for human health in modern society. Most existing tools for monitoring air pollution are stationary and incapable of accurately measuring individual exposures that vary with personal lifestyles and environments. To study the health impacts of personal exposure, researchers need new monitoring tools that are suitable for long term personal use. This dissertation seeks to overcome the challenges of implementing an inexpensive, highly miniaturized, and rapidly responding gas sensor array system to measure air pollutants for personal health. By thoroughly studying the requirements of wearable gas sensing and the characteristics of prevailing gas sensing technologies, room-temperature-ionic-liquid (RTIL) electrochemical gas sensing technology is identified for the wearable microsystem development. To overcome the RTIL-based sensor's inherent slow response, a planar porous-electrode-on-permeable-membrane (PEoPM) structure is introduced, demonstrating a 180% faster response to SO 2 compared to a traditional structure. Microfabrication processes are utilized to miniaturize PEoPM sensors and construct a physically flexible sensing platform. To achieve a low-cost low-power sensory system, a new electrochemical instrumentation circuit topology is introduced. The new circuit uniquely utilizes the inherent nature of electrochemical sensor properties to significantly reduce circuit complexity compared to traditional architectures. Finally, this thesis presents the first ever single-chip CMOS electrochemical gas sensor that further miniaturizes the sensory microsystem. The monolithic CMOS-RTIL gas sensor occupies 0.48mm2 per sensing channel and demonstrates a limit of detection that is seven times better than a hybrid (multi-chip) solution. The results of this research lay a solid foundation for a personally wearable environmental monitor that could greatly improve human healthcare.