What is MEMS ?

Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through the utilization of microfabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes), 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. MEMS promises to revolutionize nearly every product category by bringing together silicon-based microelectronics with micromachining technology, thereby, making possible the realization of complete systems-on-a-chip. MEMS is truly an enabling technology allowing the development of smart products by augmenting the computational ability of microelectronics with the perception and control capabilities of microsensors and microactuators. MEMS is also an extremely diverse and fertile technology, both in the applications it is expected to be used, as well as in how the devices are designed and manufactured. MEMS technology makes possible the integration of microelectronics with active perception and control functions, thereby, greatly expanding the design and application space.



Microelectronic integrated circuits (ICs) can be thought of as the "brains" of systems and MEMS augments this decision-making capability with "eyes" and "arms", to allow microsystems to sense and control the environment. In its most basic form, the sensors gather information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena; the electronics process the information derived from the sensors and through some decision making capability direct the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby, controlling the environment for some desired outcome or purpose. Since MEMS devices are manufactured using batch fabrication techniques, similar to ICs, unprecedented levels of functionality, reliability, and sophistication can be placed on a small silicon chip at a relatively low cost. MEMS technology is enabling new discoveries in science and engineering such as the Polymerase Chain Reaction (PCR) microsystems for DNA amplification and identification, the micromachined Scanning Tunneling Microscopes (STMs), biochips for detection of hazardous chemical and biological agents, and microsystems for high-throughput drug screening and selection. In the industrial sector, MEMS devices are emerging as product performance differentiators in numerous markets with a projected market growth of over 50% per year. As a breakthrough technology, allowing unparalleled synergy between hitherto unrelated fields of endeavor such as biology and microelectronics, many new MEMS applications will emerge, expanding beyond that which is currently identified or known.



Although MEMS devices are extremely small (e.g. MEMS has enabled electrically-driven motors smaller than the diameter of a human hair to be realized), MEMS technology is not about size. Furthermore, MEMS is not about making things out of silicon, even though silicon possesses excellent materials properties making it a attractive choice for many high-performance mechanical applications (e.g. the strength-to-weight ratio for silicon is higher than many other engineering materials allowing very high bandwidth mechanical devices to be realized). Instead, MEMS is a manufacturing technology; a new way of making complex electromechanical systems using batch fabrication techniques similar to the way integrated circuits are made and making these electromechanical elements along with electronics.

This new manufacturing technology has several distinct advantages. First, MEMS is an extremely diverse technology that potentially could significantly impact every category of commercial and military products. Already, MEMS is used for everything ranging from in-dwelling blood pressure monitoring to active suspension systems for automobiles. The nature of MEMS technology and its diversity of useful applications makes it potentially a far more pervasive technology than even integrated circuit microchips. Second, MEMS blurs the distinction between complex mechanical systems and integrated circuit electronics. Historically, sensors and actuators are the most costly and unreliable part of a macroscale sensory-actuator-electronics system. In comparison, MEMS technology allows these complex electromechanical systems to be manufactured using batch fabrication techniques allowing the cost and reliability of the sensors and actuators to be put into parity with that of integrated circuits. Interestingly, even though the performance of MEMS devices and systems is expected to be superior to macroscale components and systems, the price is predicted to be much lower.

As a recent example of the advantages of MEMS technology, consider the MEMS accelerometers which are quickly replacing conventional accelerometers for crash air-bag deployment systems in automobiles. The conventional approach uses several bulky accelerometers made of discrete components mounted in the front of the car with separate electronics near the air-bag and costs over $50. MEMS has made it possible to integrate onto a single silicon chip the accelerometer and electronics at a cost under $5 to $10. These MEMS accelerometers are much smaller, more functional, lighter, more reliable, and are sold for a fraction of the cost of the conventional macroscale accelerometer elements. Within the next few years, MEMS accelerometers are expected to completely displace the conventional devices in all foreign and domestic model cars. The dramatically lower component costs of MEMS accelerometers allow manufactures to consider placing air-bag deployment systems for protection of passengers against side impacts. Continued improvements in the MEMS accelerometer technologies over the next few years may allow the sensor to determine the size and weight of an auto passenger and calculate the optimal response of the system to reduce the possibly of air-bag deployment induced injuries.
 

Current R&D investments

Federal funding for MEMS research and development has been growing at a rapid pace. This growth is accompanied by increasing levels of investment in MEMS R&D from U.S. industry. In the mid-to-late 1980s, Federal support for MEMS R&D came primarily from the National Science Foundation (NSF) and reached a total of approximately $2 to $3 million in 1991. By 1995, the Federal government investment in MEMS R&D grew to around $35 million, with about $30 million of that support coming from the U.S. Department of Defense (DOD), principally the Electronics Technology Office (ETO) at the Defense Advanced Research Project Agency (DARPA).

In addition to the U.S. Government funding, U.S. industry investments in MEMS research, development and production capability are currently estimated to be over $100 million per year. Most of the industrial R&D investments are directed toward applications of replacing conventional technology (e.g., data storage, fluid regulation, optical switches, etc.) with a comparable MEMS device in order to reduce cost, increase functionality, and/or improve reliability.

The United States is not alone in recognizing the potential impact of MEMS technology; The Japanese and European Governments have increased their support of MEMS R&D to a combined level of over $70 to $100 million a year. The Japanese Government sponsored effort is primarily funded through the Ministry of International Trade and Industry (MITI) and began in 1991 under the Micromachines Project.. MITI's approach is unique in that its emphasis has been on miniaturizing conventional electromechanical elements and systems, as opposed to the U.S. and European MEMS efforts which are based on microelectronics technologies. The investments by European Governments, primarily Germany, Switzerland, Netherlands, and France, are coordinated through the European Community to reducing duplication and promoting collaboration across borders and has resulted in some significant developments including: deep reactive-ion etching for silicon; bonding aligners; and LIGA technologies. The combined European and Japanese industrial annual investments in MEMS R&D were estimated to be over $200 million and growing.

Despite the size and scale of MEMS research and development investments, they are small compared to the R&D expenditures made by the integrated circuit industry. However, the size of the MEMS industrial base is still very small and unable to sustain larger R&D expenditures. Since its inception, MEMS technology has been able to leverage heavily from the developments in the integrated circuit technologies. However, the magnitude of this leveraging has begun to lessen due to the speed of progress and change in the integrated circuit fabrication arena.
 

Source www.memsnet.org

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