MEMS-based gas flow sensors

Abstract

Micro-electro-mechanical system (MEMS) devices integrate various mechanical elements, sensors, actuators, and electronics on a single silicon substrate in order to accomplish a multitude of different tasks in a diverse range of fields. The potential for device miniaturization made possible by MEMS micro-fabrication techniques has facilitated the development of many new applications, such as highly compact, non-invasive pressure sensors, accelerometers, gas sensors, etc. Besides their small physical footprint, such devices possess many other advantages compared to their macro-scale counterparts, including greater precision, lower power consumption, more rapid response, and the potential for low-cost batch production. One area in which MEMS technology has attracted particular attention is that of flow measurement. Broadly speaking, existing micro-flow sensors can be categorized as either thermal or non-thermal, depending upon their mode of operation. This paper commences by providing a high level overview of the MEMS field and then describes some of the fundamental thermal and nonthermal micro-flow sensors presented in the literature over the past 30 years or so.Keywords Cantilever type flow sensor Á Differential pressure flow sensor Á Lift force flow sensor Á Micro-electro-mechanical systems Á Resonating flow sensor Á Thermal flow sensor Origin and applications of MEMS technologyThe concept of micro-electro-mechanical systems (MEMS) dates back to the early 1960s, but only became an achievable reality when the tools and techniques originally developed for integrated circuit (IC) manufacturing became sufficiently advanced. Whereas electronic semiconductor devices are fabricated using IC process sequences, MEMS devices are produced by selectively etching away parts of the underlying silicon wafer or adding and patterning additional metallic and polymer layers to form the required mechanical and electromechanical devices. Typical MEMs micro-fabrication techniques include deposition [e.g. electroplating, sputtering, chemical vapor deposition (CVD), etc.], photolithography, and etching (e.g. wet etching, reactive ion etching (RIE), etc.]. Although still an emerging technology, MEMS devices are being increasingly deployed for mainstream commercial and industrial applications such as pressure sensors, accelerometers, gas sensors, RF switches, micro-mirrors, etc. (Löfdahl and Gadel-Hak 1999). In addition to the obvious advantages accruing from their diminutive scale (including a greater portability, a more discrete implementation and a reduced power consumption), MEMS devices permit the bulk

Design Issues for Low Power Integrated Thermal Flow Sensors with Ultra-Wide Dynamic Range and Low Insertion Loss

“…The introduction of MEMS (Micro-Electro-Mechanical Systems) technology allowed the fabrication of miniaturized flow sensors with unprecedented performance in terms of spatial resolution, response times, sensitivities, measurement range and power consumption. Integrated flow sensors have been largely investigated in last decades and literature reviews can be found in [1][2][3][4][5][6]. The wide majority of the proposed devices are based on a thermal principle.…”

“…Although differential temperature flow sensors have been widely investigated [1][2][3][4][5][6], very few works have been devoted to find the impact of the sensor structure and dimensions on the key figures of merit of the devices [14][15][16][17][18][19][20]. Fluid dynamic simulations provide useful indications on particular aspects of the sensor operation, but are unable to embrace the whole transduction process, involving different physical domains that altogether contribute to the sensor performance.…”

Micromachined Thermal Flow Sensors—A Review

“…These sensors complement technologies such as microfluidic channels, valves, pumps, and heaters that are assembled together to create so-called lab on a chip (LOC) devices or micro total analysis systems (µTAS). As such, there has been great interest in their development in the microelectromechanical systems (MEMS) community since the first micromachined thermal flow sensor in 1974 [8][9][10].…”

Micromachined Flow Sensors in Biomedical Applications

“…They are also divided in subgroups. In an exhaustive and recent review, Wang et al [2] classified non-thermal flow sensors depending on the principle of measurement used: resonating, differential pressure-based, lift-force-based, and cantilever type flow sensors. A brief description of these working principles and a more detailed description of laser Doppler anemometry (LDA) will be provided.…”

“…Although often associated to silicon, because of its frequent use, its economical characteristics and its desirable mechanical properties, micromachining has been performed on several materials including metals, polymers and glasses. The concept of micro-electro-mechanical systems (MEMSs) is still considered to be an emerging technology, but it was born in the early sixties [2], and almost fourteen years (1974) passed until a milestone study appeared, describing the first integrated silicon-based sensor for gas flow measurement [3]. A high growth of research works in the field of MEMS and micromachined flow sensors took place in the eighties and about a decade was needed to develop the integration of many microfluidic devices into a single chip (e.g., micro pumps, valves and flow sensors).…”