Micro-Electro-Mechanical Systems (MEMS)
The microfabrication technology, which has been the key to the success of microchips and microelectronics, is now revolutionizing the microsystems field involving both microelectronics and micro-mechanical components. The basis for this revolution is the excellent mechanical properties of silicon and other microfabrication-compatible materials and their suitability for batch-processing. Well-established processing techniques for microelectronics devices and a few additional processes are today referred to as micromachining. Etching out portions of silicon or any other material to realize the miniaturized mechanical structure is one of the several micromachining techniques. Miniature systems involving one or more micromachined devices are generally referred to as MEMS, which stands for Micro-Electro-Mechanical systems or simply the microsystems.
Many of today's microsystems devices are sensors; some are actuators, and the remaining few are integrated systems. Micromachined sensors have been enormously successful in the market place. Inertial sensors such as accelerometers and gyroscope, pressure sensors, bio-sensors, etc., are some examples. Microactuators are useful in some microsensors. Most others are used to move a mechanical element that serves a specific purpose. Examples are micro-mirror in optical display or projection applications, switches and relays, pumps and valves, etc. Examples of microsystems are inkjet print-heads, portable point-of-care blood-analyzers, hand-help projectors, etc. Additionally, miniaturization of sensors and actuators makes them useful for biomedical applications which need to be invasive. These include applications such as pressure sensors for intracranial pressure monitoring on patients with head injury or tumor in the brain, and for monitoring blood pressure just at or near the heart, and acceleration sensors for pacemaker applications.
While sensors respond to physical phenomena and give electrical signal output, the actuators do the converse and convert electrical signal into physical phenomena such as force and displacement. A very good example of a microactuator is the micropump which can be used when there is requirement for delivering fluids in very small quantities in the range of microliters per minute. Some of the applications of micropump are transdermal insulin delivery, blood transportation and injection of glucose for diabetes patients. Research work is in progress to realize drug delivery and drug dosage systems using microsystems involving micropump, micro-valve, micro-needle arrays, etc.
Miniaturization is required for realizing filters and resonating circuits for operation in the GHz frequency range, because the inductors and capacitors in those frequencies tend to perform poorly due the power loss especially to the substrate and to the surrounding space by radiation Efforts to realize RF filters using microsystems with MEMS components for application in trans-receiver systems such as in cell phone are in progress to minimize power consumption and weight and size. These include resonating beams and RF switches which can operate at low power level.
Microstructures such as the micro-tip and micro-needle find wide applications in Atomic force microscopy (AFM), in biomedical applications for drug delivery. Considerable research effort is being focused on micro-tip array for application in vacuum tube electronics (VTE) to replace the filament with the field emission array (FEA) using micro-tips to serve as a source of electrons. This has attracted attention mainly because the FEA is more reliable over long periods of operation and allows modulation of signal at the electron source itself, where as when the heated filament is used source of electron the emission loss affects the performance over a period of time and also additional modulation of electron beam is required along the path of its travel thus making the high power high frequency vacuum tube such as the traveling wave Tube (TWT) very bulky.
Thus, the microsystems technology is enabling technology for integration of almost any physical, chemical and biological phenomena that includes motion, light, sound, chemistry, biochemistry, RF signals and computation, probably all in a single chip. Simpler systems, such as hearing aids, have already been implemented. In the future, one can expect the emergence of extraordinary bio-systems in which MEMS will add the eyes, nose, ears, tactile feel, and other sensory input while the on-chip electronics circuit will serve as ‘brain’ to condition signals, organize data , analyze and integrate input and output. In the automobile industry, most of the modern cars have the micro-accelerometer which triggers and deploys an air balloon and protects the passengers from injury during a sudden deceleration or acceleration. Microsystems based on pressure sensors find wide range of applications in all walks of life including defense, aerospace, automobile and home appliances. Microsystems using micro-accelerometers and micro-gyroscopes are most important in the inertial navigation systems for tracking position and to maintain stability of the system.
Thus, the microsystem is a fascinating area which has been progressing with rapid strides. There is scope for research and product development in this field for researchers and entrepreneurs in all the areas of science, engineering and technology.