MICRO- ELECTRO-MECHANICAL STSTEM

Author 1- Abhishek MahajanLine 1 – Electronics and Communication Line 2 – Shreejee Institute of Technology and ManagementLine 3 – KhargoneLine 4 – Abhishekmahajan6991@gmail.com

I Introduction

Micro-electro-mechanical system, also written as MEMS is the technology of very small devices; it merges at the Nano-scale into nanoelectromechnical system (NEMS) and nanotechnology. MEMS are separate and distinct from the hypothetical vision of molecular nanotechnology or molecular electronics. MEMS are made up of components between 1 to 100 micro meters in size and MEMS devices generally range in size from 20 micrometers to a millimeter. They usually consist of a central unit that processes data (the microprocessor) and several components that interact with the surroundings such as micro sensors. At these size scales, the standard constructs of classical physics are not always useful. Because of the large surface area to volume ratio of MEMS, surface effects such as electrostatics and wetting dominate over volume effects such as inertia or thermal mass. MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. These include molding and plating, wet etching and dry etching, electro discharge machining (EDM), and other technologies capable of manufacturing small devices. An early example of a MEMS device is the resonistor – an electromechanical monolithic resonator.

II History of MEMS:-

The physicist Richard Feynman delivered a talk at Caltech in December 1959 with the title “There’s Plenty of Room at the Bottom.” “What I want to talk about,” said Feynman “is the problem of manipulating and controlling things on a small scale.”In one sense, a real sense Feynman laid the roots for today’s MEMS industry.From those very early days and origins, MEMS has enjoyed classic hockey stick growth: i.e. dramatic increases in sales revenue or unit

shipment growth over time that started at a normal, linear pace from the 1960s through to the 1990s, hit an inflection point and took off in the 2000s and sustained its considerable momentum into the 2010s, fueled by such MEMS-enabled killer apps as the Nintendo Wii, the Apple iPhone, Bosch airbag systems, Epson ink jet print heads, microphones from Knowles Electronics, and blood pressure sensors from Acuity, Merit sensor, and others.

III Material used for MEMS manufacturing:-

The fabrication of MEMS evolved from the process technology in semiconductor device fabrication, i.e. the basic techniques are deposition of material layers, pattering by photolithography and etching to produce the required shapes.

a) Silicon: - Silicon is the material used to create most integrated circuits used in consumer electronics in the modern industry. The economics of scale ready availability of inexpensive high-quality materials, and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is fixed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetime in the range of billions to trillions of cycle without breaking.

b) Polymers: - Even though the electronics industry provides an economy of scale for the silicon industry, crystalline silicon is still a complex and relatively expensive material to be

produced. Polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. MEMS devices can be made from polymers by processes such as injection molding, embossing or stereo lithography and are especially well suited to microfluidic applications such as disposable blood testing cartridges.

c) Metals: - Metals can also be used to create MEMS elements. While metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability. Metals can be deposited by electroplating, evaporation, and sputtering processes. Commonly used metals include gold, nickel, aluminum, copper, chromium, titanium, tungsten, platinum, and silver.

d) Ceramic: - The nitrides of silicon, aluminum and titanium as well as silicon carbide and other ceramics are increasingly applied in MEMS fabrication due to advantageous combinations of material properties. AiN crystallizes in the wurtzite structure and thus shows pyroelectric and piezoelectric properties enabling sensors, for instance, with sensitivity to normal and shear forces. TiN, on the other hand, exhibits a high electrical conductivities and large elastic modulas allowing realizing electrostatic MEMS actuation schemes with ultrathin membranes. Moreover, the high resistance of TiN against bio corrosion qualifies the material for applications in biogenic environments and in biosensors.

IV MEMS basic processes:-

a) Deposition processes: - One of the basic building blocks in MEMS processing is the ability to deposit thin films of material with a thickness anywhere between a few nanometers to about 100 micrometers. There are two types of deposition processes, as follows

i) Physical deposition: - Physical vapor deposition ("PVD") consists of a process in which a material is removed from a target, and deposited on a surface. Techniques to do this include the process of sputtering, in which an ion beam liberates atoms from a target, allowing them to move through the intervening space and deposit on the desired substrate, and evaporation, in which a material is evaporated from a target using either heat (thermal evaporation) or an electron beam (e-beam evaporation) in a vacuum system.

ii) Chemical deposition: - Chemical deposition techniques include chemical vapor deposition ("CVD"), in which a stream of source gas reacts on the substrate to grow the material desired. This can be further divided into categories depending on the details of the technique, for example, LPCVD (Low Pressure chemical vapor deposition) and PECVD (Plasma Enhanced chemical vapor deposition).Oxide films can also be grown by the technique of thermal oxidation, in which the (typically silicon) wafer is exposed to oxygen and/or steam, to grow a thin surface layer of silicon dioxide.b) Patterning: - Patterning in MEMS is the transfer of a pattern into a material.i) Lithographyii) Electron beam lithographyiii) Ion beam lithographyiv) Ion track technologyv) X-ray lithographyvi) Diamond patterning

c) Die preparation: - After preparing a large number of MEMS devices on a silicon wafer, individual dies have to be separated, which is called die preparation in semiconductor technology. For some applications, the separation is preceded by wafer back grinding in order to reduce the wafer thickness. Wafer dicing may then be performed either by sawing using a cooling liquid or a dry laser process called stealth dicing.

V Applications:-

Some common commercial applications of MEMS include: Inkjet printers, which use piezoelectric or

thermal bubble ejection to deposit ink on paper.

Accelerometers in modern cars for a large number of purposes including airbag deployment and electronic stability control.

Accelerometers and MEMS gyroscopes in remote controlled, or autonomous, helicopters, planes and multirotors (also known as drones), used for automatically

sensing and balancing flying characteristics of roll, pitch and yaw.

Accelerometers in consumer electronics devices such as game controllers (Nintendo Wii), personal media players / cell phones (Apple iPhone, various Nokia mobile) phone models, various HTC PDA models and a number of Digital Cameras (various Canon Digital IXUS models). Also used in PCs to park the hard disk head when free-fall is detected, to prevent damage and data loss.

MEMS gyroscopes used in modern cars and other applications to detect yaw; e.g., to deploy a roll over bar or trigger electronic stability control

MEMS microphones in portable devices, e.g., mobile phones, head sets and laptops.

Silicon pressure sensors e.g., car tire pressure sensors, and disposable blood pressure sensors

Displays e.g., the digital micro mirror device (DMD) chip in a projector based on DLP technology, which has a surface with several hundred thousand micro mirrors or single micro-scanning-mirrors also called micro scanners

Optical switching technology, which is used for switching technology and alignment for data communications

Bio-MEMS applications in medical and health related technologies from Lab-On-Chip to MicroTotalAnalysis (biosensor, chemo sensor), or embedded in medical devices e.g. stents.

Interferometric modulator display (IMOD) applications in consumer electronics (primarily displays for mobile devices), used to create interferometric modulation − reflective display technology as found in mirasol displays

Fluid acceleration such as for micro-cooling

Micro-scale energy harvesting including piezoelectric, electrostatic and electromagnetic micro harvesters.

Micro machined ultrasound transducers.

VI Current Challenges:-

Some of the obstacles facing organizations in the development of MEMS and Nanotechnology devices include

a) Access to fabrication: - Most organizations who wish to explore the potential of MEMS and Nanotechnology have little or no internal resources for designing, prototyping, or manufacturing devices, as well as little to no expertise among their staff in developing these technologies. Few organizations will build their own fabrication facilities or establish technical development teams because of the prohibitive cost. Therefore, these organizations will benefit greatly from the availability of MNX’s fabrication services, which offers its customers affordable access to the best MEMS and Nano fabrication technologies available.

b) Packaging:- MEMS packaging is more challenging than IC packaging due to the diversity of MEMS devices and the requirement that many of these devices need to be simultaneously in contact with their environment as well as protected from the environment. Frequently, many MEMS and Nano device development efforts must develop a new and specialized package for the device to meet the application requirements. As a result, packaging can often be one of the single most expensive and time consuming tasks in an overall product development program. The MNX staffs are experts in packaging solutions for devices for any application.

c) Fabrication Knowledge Required: - MEMS device developers must have a high level of fabrication knowledge and practical experience coupled with a significant amount of innovative engineering skill in order to create and implement successful device designs. Often the development of even the most mundane MEMS device requires very specialized skills. Without this expertise and knowledge, at best device development projects can cost far more and take much longer. At worst, they can result in failure. The MNX has more expertise and knowledge in device design and fabrication than anyone in the world. 

VII Future of the MEMS:-

The future of MEMS is rich with commercial possibilities, including the trillions of MEMS sensors envisioned to be used as the eyes and ears of the Internet of Things (IoT); the future of MEMS also includes local MEMS-based environmental monitoring devices; deployments in the MEMS-enabled quantified self movement and in personalized medicine applications; MEMS-containing wearables; and MEMS-reliant drones and other small personal robots.