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Microelectromechanical systems (MEMS) An Introduction Shivam Vishwanath Centre For Nanotechnology Central University of Jharkhand shivamvishwanath174@gmail .com
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Microelectromechanical systems(MEMS)
An Introduction
Shivam Vishwanath Centre For Nanotechnology
Central University of [email protected]
What are MEMS?(Micro-electromechanical Systems)
miniaturized mechanical and electro-mechanical elements.
fabricated using micromachining technology.
usually integrated with electronic circuitry for control and/or information processing.
Microsensors • Converts a measured mechanical signal into an electrical signal.• every possible sensing modality including pressure , inertial
forces , temperature , magnetic field , radiation , etc.•micromachined version of pressure transducer outperforms a
pressure sensor made using the most precise macroscale level machining techniques. • stellar device performance.• relatively low cost level.
Microactuators•Microscopic mechanism that supplies and transmits a
measured amount of energy for the operation system of another system.• A number of microactuators includes: microvalves for control of gas and liquid fluids. micropumps to develop positive fluid pressures. microflaps to modulate airstreams on airfoils.
Microelectronic•miniaturized sensors, actuators, and structures merged onto
a common silicon substrate.
• the micromechanical components are fabricated using compatible "micromachining" processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
Vision of MEMS•microsensors, microactuators and microelectronics and other
technologies, can be integrated onto a single microchip.• sensors gather information from the environment.• electronics then process the information derived from the
sensors.• decision making capability direct the actuators to respond. • MEMS is revolutionizing many
product categories by enabling complete systems-on-a-chip.
Bulk Micromachining
• selective removal of the substrate material in order to realize miniaturized mechanical components. A widely used bulk micromachining technique is chemical wet etching.
Two types of chemical wet etching in bulk micromachining a) isotropic wet etching - the etch rate is independent of the crystallographic orientation of the substrate. b) anisotropic wet etching - the etch rate is dependent of the crystallographic orientation of the substrate.
[email protected] of shape of the etch profiles of a <100> oriented silicon substrate after immersion in an anisotropic wet etchant solution.
SEMS of a <100> oriented silicon substrate after immersion in an anisotropic wet etchant.
Surface Micromachining• Steps of surface micromachining a) temporary mechanical layer. b) structural layer. c) removal of the temporary layer. d) release of mechanical structure layer from constraint.
• It provides for precise dimensional control in the vertical direction.• used to fabricate the Analog Devices integrated MEMS
accelerometer device used for crash airbag deployment.
Polysilicon resonator structure fabricated using a surface micromachining process.
[email protected] micromotor fabricated using a surface micromachining process.
LIGA• Non-silicon based technology.• use of synchrotron generated x-ray radiation. The basic process are 1.cast of an x-ray radiation sensitive PMMA onto a suitable substrate. 2.mask is used for the selective exposure of the PMMA layer. 3.PMMA is then developed, with extremely smooth and vertical wall. 4. the patterned PMMA acts as a polymer mold and plated into bath.
5. Nickel is plated into the open areas of the PMMA. 6. PMMA is then removed. 7. leaving the metallic microstructure.• LIGA is relatively expensive.• The dimensional control of this process is quite good.
An illustration of the steps involved in the LIGA process to fabricate high aspect ratio MEMS devices.
Hot EmbossingThe basic process of hot embossing process are:
1. A mold insert is made using an appropriate fabrication method having the inverse pattern.2. The mold insert is placed into a hot embossing system.3. The substrate and polymer are heated to above the glass transition temperature Tg.4. The polymer material and the mold insert is pressed into the polymer substrate.5. The substrates are cooled and force is applied to de-emboss the substrates.
• This process can make imprints into a polymer hundreds of microns deep with very good dimensional control.• The advantage of this process is that the cost of the individu
al polymer parts is very low.• Producing microfluidic components for medical application.
Illustration of the hot embossing process to create microdevices. (Courtesy of the MNX at CNRI).
SEM of a variety of small test structures made in a plastic substrate using hot embossing technology at the MNX. The height of the plastic microstructures is nearly 300 um and the smallest features have a diameter of about 25 um. (Courtesy of the MNX at CNRI).
Applications• Biotechnology: discoveries such as Polymerase Chain Reaction (PCR)
microsystems for DNA amplification and identification, enzyme linked immunosorbent assay (ELISA), biochips for detection of hazardous chemical and biological agents.• Medicine: MEMS pressure sensor is widely used a) disposable sensor used to monitor blood pressure. b) monitor the patient’s breathing. c) analysis of concentrations of O2, CO2, glucose in blood. d) kidney dialysis to monitor the inlet and outlet pressures of blood.
• Communications: High frequency circuits and mechanical switches are much advanced RF-MEMS technology. Another successful application of RF-MEMS is in resonators as mechanical filters for communication circuits.• Inertial Sensing : MEMS inertial sensors, specifically
accelerometers and gyroscopes, are completely accepted. MEMS accelerometers is used for crash air-bag deployment systems in automobiles. MEMS gyroscopes (i.e., rate sensor) have been developed for both automobile and consumer electronics applications.
Challenges
•Access to Fabrication: Only few organizations build their own facilities.•Packaging:
Many of these devices need to be simultaneously in contact with their environment as well as protected from the environment.• Fabrication Knowledge Required: Without expertise and
knowledge, at best device development projects can cost far and take much longer. At worst, they can result in failure.
Biblography• Marc Madou, Fundamentals of Microfabrication, CRC Press 1997, ISBN 0-8493-9451-1
• Julian W. Gardner, Microsensors: Principles and Applications, Wiley 1994, ISBN 0-47194135-2
• Gregory Kovacs, Micromachined Transducers Sourcebook, McGraw-Hill 1998, ISBN 0-07290722-3
• Héctor J. De Los Santos, Introduction to Microelectromechanical (MEM) Microwave Systems, Artech House 1999, ISBN 0-8900-6282-x
• Sergey Edward Lyshevski, Nano- and Microelectromechanical Systems, CRC Press 2000, ISBN 0-8493-0916-6
• Mohamed Gad-el-Hak, ed., The MEMS Handbook, CRC Press 2011, ISBN 0-8493-0077-0
• P. Rai-Choudhury, ed., MEMS and MOEMS: Technology and Applications, SPIE Press Monograph 2000, ISBN 0-8194-3716-6
• Julian W. Gardner, and Vijay K. Varadan, and Osama O. Awadelkarim, Microsensors, MEMS and Smart Devices, Wiley 2001, ISBN 0-4718-6109-X
• Nadim Maluf, An Introduction to Microelectromechanical Systems Engineering, Artech House 1999, ISBN 0-8900-6581-0
• Randy Frank, Understanding Smart Sensors, 2nd ed., Artech House 2010, ISBN 0-89006311-7
• Ljubisa Ristic, ed., Sensor Technology and Devices, Artech House 1994, ISBN 0-89006532-2
• Vijay Varadan, Xiaoning Jiang, and Vasundara Varadan, Microstereolithography and other Fabrication Techniques for 3D MEMS, Wiley 2001, ISBN 0-4715-2185-X
• Tai-Ran Hsu, MEMS and Microsystems: Design and Manufacture, McGraw-Hill 2011, ISBN 0-0723-9391-2
• Gabriel M. Rebeiz, RF MEMS: Theory, Design, and Technology, 2001
