MEMS Technology

Microelectromechanical systems (MEMS) are small integrated devices or systems that combine electrical and mechanical components. They range in size from micron (thousandth of a millimeter) to millimeter level, and a complete system could contain a few or thousands of such components. MEMS extend the fabrication techniques developed for the integrated circuit industry to add mechanical elements such as beams, diaphragms, springs and, even motors, gear drives and other similar moving structures.

Examples of MEMS device applications include inkjet-printer cartridges, accelerometers, miniature robots, micro-engines, locks, inertial sensors, micro-transmissions, micro-mirrors, micro-actuators, optical scanners, fluid pumps, transducers, and chemical, pressure and flow sensors. New applications are emerging as the existing technology is applied to the miniaturization and integration of conventional devices.

These systems can sense, control, and activate mechanical processes on the micro scale, and function individually or in arrays to generate effects on the macro scale. The micro fabrication technology enables fabrication of large arrays of devices, which individually perform simple tasks, but in combination can accomplish complicated functions.

MEMS is not limited to a single fabrication process or a few materials, which enables the development of numerous and diverse devices and applications, by selecting the appropriate fabrication process and material. The MEMS industry has reached $7B in 2007 and is expected to grow at a 10-20% annual growth rate, reaching $12B in 2012.

MEMS Fabrication typically combines innovations and techniques that fall into the following categories:

• IC Fabrication: The traditional techniques of film growth, doping, lithography, etching, dicing, and packaging are used extensively in the MEMS industry.
• Bulk Micromachining and Wafer Bonding: Bulk micromachining is an extension of IC technology for the fabrication of 3D structures. Bulk micromachining of Si uses wet- and dry-etching techniques in conjunction with etch masks and etch stops to create micromechanical devices from the Si substrate.
• Surface Micromachining: Surface micromachining enables the fabrication of complex multicomponent integrated micromechanical structures that would not be possible with traditional bulk micromachining. This technique utilizes layers of sacrificial material during the fabrication process. Using the substrate wafer as mechanical support, multiple layers are deposited and patterned to create the desired micro-structures. Subsequent chemical etching dissolves the sacrificial layers and forms the final structures. One of the most widely used technique, is polysilicon surface micromachining, in which polysilicon is the structural material.
• LIGA Process: LIGA is a German acronym standing for "Lithographie, Galvanoformung und Abformung" (Lithography, Electroplating, and Molding). This process can be used for the manufacture of high-aspect-ratio 3D microstructures in a wide variety of materials, such as metals, polymers, ceramics, and glasses. In difference to the bulk and surface micromachining, this technique uses a selective deposition process, typically a plating process, to deposit the material at predetermined locations.

The above mentioned applications range from fairly simple, commodity-type MEMS devices, such as accelerometers, or inkjet-printer cartridges to very sophisticated, complex devices, such as the ones offered by Block (ChemPen™ and ChemBox™). For such devices, a unique Surface Micromachining process is used, called Ultra-planar, Multi-level MEMS Technology 5 (SUMMiT V™), developed by Sandia National Labs (http://mems.sandia.gov/tech-info/summit-v.html). The process allows the formation of five layers and has led to some very impressive devices with both moving and stationary components.