MEMS and Nanotechnology
The following discussion of micro-electro-mechanical systems (MEMS) and nanotechnology is provided courtesy of Dr. Michael Huff of the MEMS and Nanotechnology Exchange (See: http://mems-exchange.org) at the Corporation for National Research Initiatives.
MEMS is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through microfabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS), 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 mechanical and electromechanical devices (see Figure 5.1).
FIGURE 5.1 MEMS structure. (Courtesy of the MEMS and Nanotechnology Exchange.)
MEMS promises to revolutionize nearly every product category by bringing together silicon-based microelectronics with micromachining technology, making possible the realization of complete systems-on-a-chip. MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of microsensors and microactuators, and expanding the space of possible designs and applications.
Microelectronic integrated circuits can be thought of as the “brains” of a system and MEMS augments this decision-making capability with “eyes” and “arms,” to allow microsystems to sense and control the environment. Sensors gather information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The electronics then 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. Because MEMS devices are manufactured using batch fabrication techniques similar to those used for integrated circuits, unprecedented levels of functionality, reliability, and sophistication can be placed on a small silicon chip at a relatively low cost.
There are numerous possible applications for MEMS and nanotechnology. As a breakthrough technology, allowing unparalleled synergy between previously unrelated fields such as biology and microelectronics, many new MEMS and nanotechnology applications will emerge, expanding beyond that which is currently identified or known. Following are a few applications of interest to neuroscience.
MEMS and nanotechnology have enabled new discoveries in science and engineering such as polymerase chain reaction (PCR) microsystems for DNA amplification and identification, micromachined scanning tunneling microscopes (STMs), biochips for the detection of hazardous chemical and biological agents, and microsystems for high-throughput drug screening and selection.
MEMS accelerometers are quickly replacing conventional accelerometers for crash air-bag deployment systems in automobiles, and they are also used in some helmet sensors. 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; this approach costs over $50 per automobile. MEMS and nanotechnology have made it possible to integrate the accelerometer and electronics into a single silicon chip between $5 and $10. These MEMS accelerometers are much smaller, more functional, lighter, more reliable, and are produced for a fraction of the cost of the conventional macroscale accelerometer elements.
MEMS and nano devices are extremely small. For example, MEMS and nanotechnology have made possible electrically driven motors smaller than the diameter of a human hair (see Figure 5.2) but MEMS and nanotechnology are not primarily about size. MEMS and nanotechnology are also not about making things out of silicon, even though silicon possesses excellent material properties, which make it an attractive choice for many high-performance mechanical applications; for example, the strength-to-weight ratio for silicon is higher than many other engineering materials, which allows very high-bandwidth mechanical devices to be realized. Instead, the deep insight of MEMS and nano is as a new manufacturing technology, a way of making complex electromechanical systems using batch fabrication techniques similar to those used for integrated circuits, and uniting these electromechanical elements together with electronics.
FIGURE 5.2 MEMS electrically-driven motor. (Courtesy of the MEMS and Nanotechnology Exchange.)