Nanomaterials such as carbon nanotubes (CNTs) show remarkable material properties, which can be utilized in various sensing applications by integrating them in a microsystem. The doctoral thesis presents the developed process of fabricating microheaters on electronic chips to grow CNTs at locally generated high temperatures (~650 – 800 ˚C) for realizing gas and pressure sensors. To the author’s knowledge, this is the first demonstration report for sensing applications using locally synthesized CNTs on the polysilicon layers of a commercial low-cost bulk Complementary Metal Oxide Semiconductor (CMOS) technology. It has also been verified that the microheaters have high thermal isolation around them, hence, the on-chip electronics retained their functionality during the high temperature heater operation needed for the growth of CNTs.
CNT-based sensors can offer room-temperature operation and the option for their surface modifications with metal or metal oxide nanoparticles to deliver enhanced sensitivity, selectivity, fast response along with the promises of a wireless, low-cost, power efficient system upon CMOS integration. There is a high demand for gas sensors of such qualities to utilize them in various domestic and industrial applications such as monitoring air quality of indoor (e.g., CO2, H2, odor) and outdoor (SO2, NO2, CO2) for health and environmental concerns, detecting quality of perishable food, breath analysis through volatile organic compounds for medical diagnosis, and detecting pesticides and pathogens in agricultural production.
Although CNTs show excellent potential as a sensing material, there is currently no inexpensive commercial CNT-based sensors available in the market. The main hindrance is the lack of a suitable and standard method to integrate CNTs in a matured and low-cost Si technology, such as CMOS that provides required signal processing for the smart sensors through the on-chip integrated circuits (ICs). The developed process in this PhD work for heterogenous integration of CMOS-CNT shows the promise of wafer-level manufacturing of CNT-based sensors by incorporating additional steps in an already existing foundry CMOS process.