A Miniaturized Temperature Controlled Capacitive MEMS Transducer for MOF based Gas Sensing Applications

Abstract

Sensors have been used in different forms and fields, where the sensors play important roles in identifying and quantifying different environmental conditions for various purposes used in mobile applications. Among these are the MOX and polymer based sensors. However, the MOX sensors have larger power consumption and poor selectivity. The main drawback of the polymer based gas sensor is the short lifetime and drift in measured signal over its lifetime. In this thesis work, aMetal Organic Frameworks (MOF) MEMS gas sensor is designed and fabricated. The sensor requires a micro-hotplate and an Interdigitated electrodes (IDC) capacitor where the IDC needs to have capacitance values in the pico-farad range. This is achieved by using modeling and FEM simulations to arrive at the final design. Before the final device first a proof of concept design is developed and fabricated. This has the purpose of proving the in-situMOF growth method for obtaining the sensing layer used as the dielectric of the IDC capacitor. The microhotplate is designed to be as low power as possible not exceeding 20mW. The design is derived from design rules and FEM simulations to arrive at the design parameters in order to achieve not only low power consumption but also high temperature uniformity. The membrane and micro-hotplate are designed to be efficient. The designed device is fabricated in the EKL and MEMS labs at the TU Delft while keeping the process flow as simple as possible. Both the design and the fabrication are developed to be a baseline for developing such gas sensors. The successful process developed during the project has produced >95% yield in final micro-hotplate and IDC devices. The devices show successful preliminary gas measurements for different concentration methanol.