Electro-thermo-mechanical study of membrane devices for smart IC technologies

• Main Author: Ali, S. Z.
• Published: University of Cambridge 2008
• Subjects: 537.622
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595441

Silicon on Insulator membranes are increasingly finding applications in many semiconductor devices and circuits. This thesis studies thermal and mechanical behaviour of two very different membrane based devices: Smart Gas Sensors and Membrane Power Devices. Both the devices are CMOS compatible and can easily be integrated with circuitry in a smart IC. The same fabrication process has been used for both these devices – a standard SOI CMOS process, followed by Deep Reactive Ion Etching (DRIE). Gas sensors need to micro-hotplate to heat the sensing material for better sensitivity and faster response time. The use of a membrane greatly reduces the power consumption of the heater. In lateral SOI power devices the membrane can greatly enhance the breakdown voltage and switching time. However, this comes at the expense of higher temperatures within the device – which can significantly reduce the lifetime. While in gas sensors it is desirable to have a high temperature for a given amount of power, in power devices the aim is to have a low operating temperature. Novel tungsten based SOI micro-hotplates are presented. A thorough thermal analysis of the power consumption (via conduction, convection and radiation), transient time and temperature uniformity of the micro-hotplate is presented by extensive simulation and analytical analysis. Following the study, micro-hotplate devices were fabricated at a commercial foundry. The measured results were analysed and matched with the simulations. The devices have very low power consumption (14 mW at 600°C), fast response time (2 ms for 600°C), good mechanical stability and excellent uniformity within a wafer and from wafer to wafer.