In the past decade, there has been a growing interest for the development of olfactory machines and Electronic Nose systems in order to fulfill a variety of real-life applications. New development of nanomaterial/nanostructure based gas sensors has enable performance improvement, miniaturization and integration potential for olfactory system. However, the biggest challenge towards nanomaterial based gas senor developed into real product is the issue of process flow CMOS-compatibility as well as power consumption. In this thesis, CMOS-compatible process flow of sensor based on nanomaterial/nanostructure with potential of integration as well as low power consumption is explored.

First of all, a novel hierarchical morphology is fabricated, characterized and analyzed. As ultra-high...[ Read more ]

In the past decade, there has been a growing interest for the development of olfactory machines and Electronic Nose systems in order to fulfill a variety of real-life applications. New development of nanomaterial/nanostructure based gas sensors has enable performance improvement, miniaturization and integration potential for olfactory system. However, the biggest challenge towards nanomaterial based gas senor developed into real product is the issue of process flow CMOS-compatibility as well as power consumption. In this thesis, CMOS-compatible process flow of sensor based on nanomaterial/nanostructure with potential of integration as well as low power consumption is explored.

First of all, a novel hierarchical morphology is fabricated, characterized and analyzed. As ultra-high sensitivity is discovered experimentally, a simulation model of the internal electrical field is developed and the outcome gives a hint on the enhanced sensing performance and suggests that a negative “self-gate” is formed on the branches of hierarchical nanostructure, which affects the conduction path when exposed to NO₂ environment.

To fully use this novel nanomaterial, a fabrication recipe consisting of complementary-metal-oxide-semiconductor (CMOS)-compatible techniques is proposed. It is discovered that a room-temperature high response of 32(20ppm NO₂) within 72 seconds is achieved by the proposed sensor leading to high-sensitivity at room temperature, hence drastically reducing the power consumption. Combining the low-power room temperature operation with CMOS-compatible fabrication process, our work sheds light on the system level integration of the sensor with processing CMOS circuit for real-life applications.

The thesis explores further three dimensional nanostructure templates to be used for gas sensor application leveraging on highly reduced fabrication cost and mature fabrication technique. Specifically, photolithography-free programmable anodic aluminum oxide (AAO) growth method is demonstrated to provide diverse options in morphology, diameter, pitch and length. In addition, low-cost ultrasonic spray pyrolysis (USP) method is successfully applied in depositing high aspect ratio but conformal SMO film into AAO templates. Preliminary sensing characterization verifies that AAO substrate based sensors exhibit good responsivity to gases leading to great promise for future development of sensor array based olfactory systems.