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Note for Micro-Electro-Mechanical Systems - MEMS by Upesh Patel

  • Micro-Electro-Mechanical Systems - MEMS
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  • Rashtra Santh Tukduji Maharaj Nagpur University - RTMNU
  • Electrical and Electronics Engineering
  • B.Tech
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MEMS & SOC, NOTES JUNCTION, MH-34, Upesh Patel SUBJECT: MICRO ELECTROMECHANICAL SYSTEMS and SOC 8th Semester Electronics Engineering, PCE Nagpur. RTM Nagpur University Syllabus UNIT 1: Introduction to MEMS (06 Marks) Benefits of Miniaturization, Types of MEMS: Optical MEMS, Bio- MEMS, RF- MEMS, Micro-fluidics, Success Stories, Pressure sensor, Accelerometer, Micro-mirror TV Projector. Q.1) Define of MEMS and short introductory description of MEMS. Answer: Micro Electromechanical systems is the promising technology that considers micro manufacturing of microscale transducers, actuators, probes, capacitors, inductors, valves, gears, pumps, gyroscope, mirrors, switches, and other required microdevices. Mems are the advanced product and equipment design concept. These are small and integrated devices, which combines electronics, electrical as well as mechanical elements to meet the control related functional requirements. Mems is the technology that can manufacture capacitor and inductor as well as mechanical elements such as springs, gears, beams, diaphragms, and other mechanical components wherever needed and depending upon requirements.Not all the Mems devices need compulsorily electrical or mechanical components but advance design approaches related to particular Mems device. MEMS sensors combine electrical and mechanical components into or on top of a single chip - i.e. they are electro-mechanical sensors. In this way, MEMS sensors represent a continuum bridging electronic sensors at one end of the spectrum, and mechanical sensors at the other. The key criterion of a MEMS sensor however, is that there are typically some elements with mechanical functionality - i.e. an element that is able to stretch, deflect, spin, rotate, or vibrate. Micro Electro Mechanical Systems (MEMS) describes both a type of device or sensor, and a manufacturing process. MEMS sensors incorporate tiny devices with miniaturized mechanical structures typically ranging from 1100 µm (about the thickness of a human hair), whilst MEMS manufacturing processes provide an alternative to conventional macro-scale machining and assembly techniques. Also known as 'Microsystems' in Europe, and 'Micromachines' in Japan, MEMS devices have come to the fore in recent years with the wide-scale adoption of MEMS motion sensors by the automotive industry, and the growing use of accelerometers and gyroscopes in consumer electronics. Perhaps the most well known consumer electronics incorporating MEMS motion sensors include a number of the leading smart phones, and Gamingconsoles/controllers. MEMS development stems from the microelectronics industry, and combines and extends the conventional techniques developed for integrated circuit (IC) processing with MEMS-specific processes, to produce small mechanical structures measuring in the micrometer scale (one millionth of a meter). As with IC fabrication, the majority of MEMS 1|Page

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MEMS & SOC, NOTES JUNCTION, MH-34, Upesh Patel sensors are manufactured using a Silicon (Si) wafer, whereby thin layers of materials are deposited onto a Si base, and then selectively etched away to leave microscopic 3D structures such as beams, diaphragms, gears, levers, or springs. This process, known as 'bulk micromachining', was commercialized during the late 1970s and early 1980s, but a number of other etching and micromachining concepts and techniques have since been developed. The first Micromachined pressure sensors - or 'diffused' sensor as they were originally known - were designed and manufactured by Kulite Semiconductor in the mid-1960s. Known as a 'piezoresistive' pressure sensor, or 'silicon cell', a pressure sensor consists of a micromachined silicon diaphragm with piezoresistive strain gauges diffused into it, fused to a silicon or glass back plate. The top-side of the diaphragm is exposed to the environment through a port, and deforms in reaction to a pressure differential across it. The extent of the diaphragm deformation is then converted to a representative electrical signal, which appears at the sensor output. Mems combines physics, microelectronics, micromechanics, material science and computer aided design (CAD) logics to achieve the target Mems devices. Application areas of Mems: ➢ Automotive Industry ➢ Aircraft Industry ➢ Consumer products ➢ Medical Field ➢ Electronics ➢ Communications ➢ Defence applications ➢ Optical field ➢ RF field It’s a developing field so lots of research is being carried around the globe. Methodology and design prospects of Miniaturization of product needs ➢ Fundamental physics ➢ Material science ➢ Computing methods ➢ Ultra precision engineering ➢ Fabrication technology Micromachining based upon the principles, characteristics, modelling, simulation and state of art technology. 2|Page

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MEMS & SOC, NOTES JUNCTION, MH-34, Upesh Patel Q.2) Write different application sector of MEMS. Answer: MEMS technology has very wide scope in various sectors. MEMS devices can be used in many sectors of industry as given in below table: Q.3) Write in short about Mems packaging and design considerations? Answer: Like an IC package Mems devices must have the ability to meet some important criterion such as: 1. There should be good isolation between the non-sensing and sensing areas of the device. 2. There must not be any hindrance to the driving actions such as tilting, twisting, rotating, sliding or vibrating. 3. Efficient coupling at the links, junction anchor areas is must. 4. Unreliability issues due to the reasons such as contamination, fusing, sticking, clamping, static overload, delamination, creep, fatigue. Q.4) Write benefits of Miniaturization. Answer: ➢ Microdevices can measure or sense minute changes that cannot be achieved by the large sensing devices. ➢ Micro instrumentation equipment is essential useful where higher sensitivity, resolution, selectivity, fidelity and repeatability are desired. ➢ Miniaturization improves portability and speed of operation. 3|Page

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MEMS & SOC, NOTES JUNCTION, MH-34, Upesh Patel ➢ Miniaturization can help the engineer to measure and analyse the physical, chemical and biological parameters of an application where space and weight are limited factors. ➢ Micro instruments can be applied in nuclear reactors, space shuttle spectrography, surface analysis, tribology study, micro tomography imaging and so on. ➢ Micro instrumentation equipment includes micropositionning stage, Micro spectrometer, Micro gripper, surface plasma resonance immunator micro radar. Q.4) Write short notes on different micromachining techniques. Answer: ➢ Bulk micromachining - whereby the bulk of the Si substrate is etched away to leave behind the desired micromechanical elements ➢ Wafer bonding - permits an Si substrate (aka 'wafer') to be attached to another substrate, typically Si or glass, to construct more complex 3D microstructures such as microvalves and micropumps. ➢ Surface micromachining - where the structures are built on top of the substrate and not inside of it, enabling fabrication of multi-component, integrated micromechanical structures not possible using bulk micromachining ➢ Micro molding - a process using molds to define the deposition of the structural layer, and enabling the manufacture of high aspect ratio 3D microstructures in a variety of materials such as ceramics, glasses, metals, and polymers ➢ LIGA - a micro molding process that combines extremely thick-film resists (>1 mm thick) and high-energy x-ray lithography, to enable the manufacture of high-aspect-ratio 3D microstructures in a wide variety of materials ➢ High aspect ratio micromachining (HAR) - combines aspects of both surface and bulk micromachining to allow for silicon structures with extremely high aspect ratios through thick layers of silicon (hundreds of nanometers, up to hundreds of micrometers) Q.5) Short description about MEMS Actuator with Greater Force and Range of Motion. Answer: There are a variety of force actuation methods that can be used in Micro Electromechanical Systems (MEMS) to move structures. The most common is electrostatic actuation where the application of an electrical potential induces an attractive force between surfaces. However, current micro actuators are subject to stroke-dependence 4|Page

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