Integrated CMOS sensor microsystems for biochemical monitoring
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Complementary metal-oxide semiconductor (CMOS) based sensor systems play an important role in various medical, biotechnological, industrial, food and beverage, security and defense, and environmental applications. This is primarily because standard CMOS fabrication processes allow us to produce low cost, low power, and miniaturized systems which can be easily mass-produced. This dissertation deals with the development of integrated CMOS optical based and CMOS solid-state based sensor microsystems for monitoring various analytes including oxygen (O 2 ), glucose, solvents, and pH. The optical sensors developed as part of this dissertation are based on phase fluorometric measurement techniques and use sol-gel derived xerogel based sensing elements to encapsulate analyte specific fluorophores in nanoscopic porous structures. The majority of the research efforts have concentrated on the development of ultrahigh sensitivity photodetectors and the subsequent conversion of the current signals into voltage signals for easy processing. Finally, these contributions have led to the first demonstration of a single-chip CMOS integrated circuit with monolithically integrating detectors and signal processing for phase fluorometric sensor systems. The solid-state sensors developed as part of this dissertation are based on CMOS ion-sensing field effect transistors (ISFET). We concentrated on the development of the ISFET readout circuitry and ISFET layout architecture which would improve the performance and the reliability of the pH-sensitive microsystems for various biomedical applications. We proposed a novel differential read-out architecture which uses a pseudo-reference electrode (gold wire) and overcomes the requirement of an ideal reference electrode (Ag/AgCl or calomel electrodes) for applications where measuring changes in pH is sufficient. Finally, using this architecture enables the CMOS ISFET microsystem to be fabricated using a standard CMOS process without any post-fabrication processing. In the future, based on the principles described here, the integration of CMOS devices with various emerging sensing elements such as surface activated nanoparticles, porous materials, and imprinted sensing layers can lead to the development of novel sense and response systems with high sensitivity, selectivity and dynamic range.