Challenges in MEMS Technology

Advances in experimental mechanics are typically triggered by challenges posed by developing fields. The recently developed field of microelectromechanical systems (MEMS) poses some of the greatest challenges that are being addressed by experimental mechanics. According to available literature, MEMS is a revolutionary enabling/emerging technology (ET), which is based on manufacturing processes that have their roots in long-established photolithography used in microelectronics. This ET is effectively employed in development of complex machines with micron feature sizes. The MEMS machines are batch-fabricated with no piece-part assembly required, and are ready to use at the end of the fabrication process. Continued advances in MEMS technology have led to development of a multitude of new devices heretofore impossible. However, applications of these devices are hampered by challenges posed by their integration and packaging. Current trend in micro-/nanosystems is to produce ever smaller, lighter and more capable devices at a lower cost than ever before. In addition, the finished products have to operate at very low power and in very adverse conditions while assuring durable and reliable performance. Some of the new devices have been developed to function at high operational speeds (e.g. 1 000 000 rpm microengine), others to make accurate measurements of operating conditions of specific processes (e.g. MEMS pressure sensor). Regardless of their applications, the devices have to be packaged to facilitate their use. MEMS packaging, however, is application-specific and, usually, has to be developed on a case-by-case basis. To facilitate advances of MEMS, educational programmes have been introduced, addressing all aspects in their development. This editorial presents pertinent aspects in development of MEMS including, but not limited to, design, analysis, fabrication, characterisation, packaging and testing. Advances in MEMS technology allow monolithic integration of MEMS with driving, controlling and signal-processing electronics. This integration improves performance of micromechanical devices as well as reduces the cost of manufacturing, packaging and interconnecting these devices by combining them with a complementary electronic subsystem(s) in the same manufacturing and packaging process. This new multilevel polysilicon process enables fabrication of complex micromechanical systems with intricate coupling mechanisms. One of the systems that was made possible by the MEMS technology is a ‘micromirror system’ for optical applications. This microsystem is a part of a group of micro-optoelectromechanical systems (MOEMS). The MOEMS, fabricated using silicon and polysilicon micromachining processes, have widespread applications including, but not limited to, optical beam steering, scanners, adaptive optical arrays, flat panel displays, optical interconnects, Internet, HDTV, etc. Specific advantages that MOEMS have over their larger, conventional counterparts are lower mass, faster response speeds, lower operating power, compact design and the potential for large arrays of micro-optical elements. Contemporary microsystems are designed and analysed using highly specialised computer-aided designing (CAD) software packages that are able to account for pertinent fabrication steps. The CAD packages readily interface with multiphysics software that can perform high-fidelity computations with multiscale capabilities, which are essential to analyse micron-scale features of MEMS together with their millimetre-scale packages for specific applications. One approach to fabrication of microsystems is based on the use of surface micromachining (SMM) of multiple (structural) polysilicon films with intervening (sacrificial) oxide films. All structural films are typically made using low-pressure chemical vapour deposition (LPCVD) of polycrystalline silicon. The sacrificial oxide films are also deposited by LPCVD. Fabrication of the micromirror system, including the electrostatic comb drives, gears and the interconnecting linkages, requires four polysilicon layers. These microengines are being developed to function at high operational speeds: on the order of 1 000 000 rpm. Operational functionality of the micromirror system depends also on the quality and reliability of motions, especially of its hinged micromirror. Functional operation of a pressure sensor depends on deformations of a thin diaphragm, which is fabricated using