Tutorial T4: MEMS: Design, Fabrication, and their Applications as Chemical and Biosensors

The microfabrication technology has had a chequered history of over 50 years in the field of microelectronics. Aggressive miniaturization of microelectronic devices has resulted in faster logic circuits and it has also reduced their power requirements. MOSFET device dimensions have already entered the sub-100 nanometer regime. The same principles of microfabrication were applied to make miniaturized 3-dimensional mechanical structures. This helped in the advent of micro electro-mechanical systems or MEMS. Initially, i.e. in early nineties, the MEMS field was dominated by mechanical applications. However, now MEMS refers to all miniaturized systems including silicon based mechanical drivers, chemical and biological sensors and actuators, and miniature devices made from plastics or ceramics. The half-day tutorial would begin with a synoptic overview of the area, highlight some of the challenges and outline the scope of the tutorial. It would be followed with an introduction to the design of microsensors, such as the pressure sensor and the accelerometer that began the MEMS revolution. Micromachined Electro-Mechanical Systems (MEMS), also called Microfabricated Systems (MS), have evoked great interest in the scientific and engineering communities. This is primarily due to several substantive advantages that MEMS offer: orders of magnitude smaller size, better performance than other solutions, possibilities for batch fabrication and cost-effective integration with electronics, virtually zero dc power consumption and potentially large reduction in power consumption, etc. The application domains cover microsensors and actuators for physical quantities (MEMS), of which MEMS for automobile & consumer electronics forms a large segment; microfabricated subsystems for communications and computer systems (RF-MEMS & MOMS); and microfabricated systems for chemical assay (microTAS) and for biochemical and biomedical assay (bioMEMS and DNA chips). This tutorial would give an introduction to these exciting developments and the technology and design approaches for the realization of these integrated systems. We will also introduce the importance of material selection by understanding the impact of material properties, even at the micron scale. We will discuss polymeric materials such as SU-8 and also compare them with traditional materials such as Silicon. We will also discuss about the possibility of integrating MEMS with VLSI electronics. Simulators provide an excellent way to design, optimize and understand micromechanical systems. Particularly so because such systems are not of isolated, stand alone type; instead, they are based on the interplay of several domains. For example, in a microcantilever based biosensing system the different domains are: materials, mechanical, biological, electrical and chemical. Recently developed software packages such as Coventorware, Intellisuite etc. have the ability to simulate a system in different domains. One can, for example, use a thermoelectromechanical solver (i.e. study a system in the domains of temperature, mechanics and electricity). We will discuss basic philosophy of using MEMS simulation tools for simple devices. Unit processes for bulk and surface micromachining of silicon and integration of processes for fabricating silicon microsensors will be presented. Smart cell phones and wireless enabled devices are poised to become commercial engines for the next generation of MEMS, since MEMS provide not only better functionality with smaller chip area, but also alternative transceiver fabrication, characterization etc) include printerheads for inkjet printers, Digital Micromirror Devices and pressure sensors. We will discuss applications of microcantilevers & microheaters in detecting volatile organic compounds, and show that these devices can detect in particles in the order of a few parts per billion. We shall have a lecture on bioMEMS to highlight the immense possibilities that exist for MEMS in the life sciences & medicine. The idea of integrating microfluidics and biological or biomimetic material with electronic systems is alien to electronic systems designers and there are problems with integrating wet systems with electronics. We give a synopsis of the types of structures required and approaches for the design and test of such systems. Finally, we shall discuss the issues involved with embedding MEMS in complete systems, including issues related to design tools, simulation, test and parameter extraction & de-embedding. Ofcourse, we will present the future of MEMS (and NEMS); and they role they would play in smartwatches, mobiles, diagnostics; and thereby impact our lives.