What is MEMS/Microsystems?
Below we give an introduction MEMS/Microsystems.
Over the last fifty years, since the invention of the transistor, the electronics industry has virtually exploded. With the invention of the Integrated Circuit (IC) engineers were able to fit entire electronic systems onto a single small piece of mono-crystalline silicon. These can be mass-produced from large wafers on which each process step is performed on hundreds or thousands of circuits simultaneously. This parallel production usually refereed to as batch processing has enabled the big electronics companies, such as Intel and Motorola, to produce massive quantities of circuits at a low price. This same basic concept, which made microelectronics so successful, can be adopted to make low-cost, small, mechanical structures with high-performance. Such mechanical structures including crash detection sensors used in cars to detect a collision and inflate the airbag to protect the passengers.
The most notable area today is the automotive industry, where the new car models often have 20 or more sensors, many of which are already made in silicon. The number of sensors used in cars is expected to increase as car manufacturers continually add new features such as active suspension, roll over protection, in the interest of increasing performance, comfort and safety for passengers.
Silicon besides being a good microelectronics material with well-documented characteristics has many outstanding mechanical properties, such as a yield strength and elasticity, equal to that of steel. The single crystal silicon, used in the microelectronics industry, can also be micromachined to produce various types of semi three-dimensional structures. The etching and lithographic processes from the IC industry can be adopted to produce mechanical structures with tolerances in the micrometer scale. The applications to date include micro motors, micro pumps, pressure sensors and thermal flow sensors.
Single-crystal silicon has, like the single-crystal quartz material used in the time-base in watches, excellent mechanical resonance properties. This makes it possible to produce sensory structures where a change in the measured quantity (such as mass, pressure and mass-flow) gives a change in the mechanical resonance frequency of the sensor. The measured resonant frequency of a pressure sensor is then a measure of the measured quantity (in this case pressure). Frequency measurements are the simplest and most accurate we can make in the electrical domain, it is also the most resistant to external electrical disturbances.
This type of research requires access to advanced equipment, processes and clean-room facilities of the same type as used for the fabrication of microelectronics. The research group fabricates their silicon structures at KTH Semiconductor Laboratory (HLB) located in Kista, 12 km outside of Stockholm. The Semiconductor Laboratory comprises of 1000 square meters of clean-room area ranging from class 100 to class 10, 000. The facility is equipped for research and small scale production of special purpose structures and components in silicon, III-V semiconductor materials and silicon carbide (SiC).