Monolithic CMOS microhotplate-based gas-sensor system

Silicon technologies have been the foundation building blocks of integrated digital and analog electronic circuits for almost four decades. Complementary Metal Oxide Semiconductor (CMOS) is an important silicon technology that is being used to create MicroElectroMechanical systems (MEMS) devices for different sensor applications. The work presented in this dissertation combines the traditional CMOS and emerging MEMS technology to formulate a gas sensor system on a single chip.; In this dissertation, a description of a CMOS gas-sensor system design and implementation is presented. This document describes the design and implementation of integrated microhotplates in CMOS technology, electro-thermal and infrared characterization of microhotplates, realization of an on-chip operational amplifier for measurement and signal conditioning, and an on-chip digital decoder and driver circuit for multiplexing gas-sensor-array signals and heater activation.; This work makes several contributions in the development of metal-oxide microhotplate-based gas sensing systems. It describes the development of a method to implement gold sensing electrodes over the active area of the microhotplate suspended membrane as a post-processing step on a standard commercial CMOS chip. It details the design and implementation of an efficient interface circuit design topology to measure the conductance of sensing films from each of the gas-sensor elements of an array. It also describes the investigation and characterization of the transient thermal behavior of the microhotplate device structures using a high-speed infrared imaging system. Finally, the operation of a 4-by-1 gas-sensor-array with on-board interface electronics is demonstrated using several gases with different concentrations. The gas sensor is shown to have excellent sensitivity, and gas concentrations as low as 100 ppb are easily detected.