Recent development of MEMS sensor technology

Citation

Du, H. and Chen, D. (2007), "Recent development of MEMS sensor technology", Sensor Review, Vol. 27 No. 1. https://doi.org/10.1108/sr.2007.08727aaa.002

Recent development of MEMS sensor technology

The ability of sensing plays a particularly important role in engineering and our daily life. This is generally accomplished by the units of sensors that are capable of obtaining and transforming the required information to electrical signals. Today's sensors development has been primarily motivated by the need of small size, low cost and high performance. As an emerging technology, microelectromechanical systems (MEMS) have revolutionized the development and market for sensors in recent years by providing tiny, fast- responding and highly reliable sensing devices at low cost. An ever-increasing demand has been seen for MEMS-based (or silicon-based) sensors due to the search for continuous improvement in the performance of products at reduced cost.

MEMS technology, although leveraging on many technologies from the integrated circuit industry, is considerably different in that MEMS more often deals with mechanical components/structures such as membranes, cantilever beams, gears, springs, mirrors, etc. This allows development of MEMS sensors of tiny size, low cost and high performance to replace the traditional sensors in biomedical, automotive, aeronautical sectors. Many types of such micro- sensors have been intensively studied and developed for various applications including inertial, electromagnetic, thermal, radiation, pressure sensors, etc. Recent research and development of MEMS sensors seem to be centered on the following few major themes.

Towards commercialization

The hunt for commercialization of MEMS technologies has never been ceased. It has been and will continue to be the fundamental drive for continuous research and improvements of MEMS technology. MEMS inertial sensors (accelerometers and gyroscopes) have been the most successful examples of commercialized MEMS technologies. The market for MEMS inertial sensors is set to grow to over $1360 million by 2009. Currently, the main applications are in the automotive industry. The physical mechanisms underlying MEMS accelerometers include capacitive, piezoresistive, electromagnetic, piezoelectric, ferroelectric, optical and tunneling. The most successful types are based on capacitive transduction, in that a linear output of capacitance versus displacement is presented. Other (partially) commercialized products include MEMS-based humidity sensors, temperature sensors, pressure sensors, etc.

Sensors-on-a-chip

Early MEMS sensor systems utilized a multi-chip approach with the sensing element (MEMS structure) on one chip, and the signal conditioning electronics on another. While this approach is simpler from the process standpoint, it has many disadvantages including large package size, low yields, chip- chip capacitive interference and high cost. To overcome these, modern MEMS sensors have been pursued to integrate the electronics and sensors onto one single silicon chip with advanced miniaturization and IC manufacturing technologies. These sensors-on-a-chip would have advantages of small size, high integration and low cost. However, such an integrated approach presents challenges such that many standard production steps for the mechanical structures may degrade the electronic components and vice versa. The lack of standard manufacturing practice influenced the market growth of the integrated sensors.

High ratio of performance to cost

The search for improved performance and reduced cost is the principal drive for the development of many MEMS-based sensors. The high ratio of performance to cost is one of the major advantages of MEMS sensors over the traditional macroscopic counterparts. For example, a three-axis low-g Analog accelerometer with high sensitivity and accuracy costs a few dollars only. This was achieved through the smart design and advanced manufacturing techniques.

BioMEMS sensors

As an emerging development trend, researchers have been exploring the applications of MEMS technology to the areas of biology, medicine, and biomedical engineering by developing MEMS-based biosensors or BioMEMS sensors. A BioMEMS sensor usually consists of a sensor array with microelectrodes or microcantilevers, which allows highly sensitive detection of micro-organism or toxins with highest selectivity using minimal sample quantity. The detection is generally performed using biological capture molecules (e.g. enzymes, antibodies, DNA, and RNA) as part of the transduction mechanism. Transduction signals might be in electrical, optical, thermal, chemical, or magnetic forms. BioMEMS sensors have aroused considerable interests from researchers due to their merits such as high sensitivity and selectivity, small sample requirement, low cost, quick response, etc.

Based on the MEMS technology and methodologies of traditional sensors, silicon-based sensors are replacing some of their macroscopic precursors and establishing new markets of their own. It is anticipated that the research and development in MEMS and microsensors will lead to more successful products of MEMS sensors in new areas of applications, particularly biological and biomedical applications. This will require a concerted and multi- disciplinary research effort from researchers in a wide variety of academic and industrial settings.

Hejun Du and Dafeng Chen School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore