Realization of CMOS compatible micromachined chemical sensors
Demirci, Tuğba (2002) Realization of CMOS compatible micromachined chemical sensors. [Thesis]
The chemical sensors are fabricated using IC manufacturing technologies, providing a smaller size and lower weight, lower power consumption, and lower cost due to the automated and batch production. During the last two decades, largely two-dimensional Integrated Circuit (IC) fabrication technology has been extended into the third dimension by micromachining technologies . Micromachining has been used to produce a growing variety of micromechanical structures, including automotive pressure sensors, airbag deployment accelerometers and many others [2-4]. Given the similarities in IC fabrication and micromachining, microelectronics and micromechanics may be integrated on a single chip, allowing an on-chip monitoring and control of the mechanical/chemical functions. This has led to the term microelectromechanical systems (MEMS) to describe this technology. The use of MEMS technology could provide a number of opportunities for gas sensors: the sensing elementscan be miniaturized (reducing power consumption), multiple elements can be integrated into array con_gurations with each element optimized to sense a di_erent gas, improved selectivity/ sensitivity and the integration of sensing and signal processing/control devices on the same substrate. In addition, due to the small mass of micromachined-sensor element, rapid thermal programming can be employed to introduce a level of kinetic selectivity into the operation of the sensor. In this thesis, realization of Complementary Metal Oxide Semiconductor (CMOS) compatible chemical sensors using micromachining technology will be explained. During this realization 3x2 sensor array is designed to improve the selectivity and sensitivity of the sensor system. To address the needs of convenient and batch processes CMOS compatibility is incorporated inside the fabrication ow because CMOS compatibility o_ers convenient merging with read-out circuitry which comprises of operational transconductance ampliers (OTAs). OTAs are preferred in this design because they assist the detection of the resistance changes at the sensor output.
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