Purpose: Pressure, being one of the key variables investigated in scientific and engineering research, requires critical and accurate measurement techniques. With the advancements in materials and machining technologies, there is a large leap in the measurement techniques including the development of micro electromechanical systems (MEMS) sensors. These sensors are one to two orders smaller in magnitude than traditional sensors and combine electrical and mechanical components that are fabricated using integrated circuit batch-processing technologies. MEMS are finding enormous applications in many industrial fields ranging from medical to automotive, communication to electronics, chemical to aviation and many more with a potential market of billions of dollars. MEMS pressure sensors are now widely used devices owing to their intrinsic properties of small size, light weight, low cost, ease of batch fabrication and integration with an electronic circuit. This paper aims to identify and analyze the common pressure sensing techniques and discuss their uses and advantages. As per our understanding, usage of MEMS pressure sensors in the aerospace industry is quite limited due to cost constraints and indirect measurement approaches owing to the inability to locate sensors in harsh environments. The purpose of this study is to summarize the published literature for application of MEMS pressure sensors in the said field. Five broad application areas have been investigated including: propulsion/turbomachinery applications, turbulent flow diagnosis, experimentalaerodynamics, micro-flow control and unmanned aerial vehicle (UAV)/micro aerial vehicle (MAV) applications. Design/methodology/approach: The first part of the paper deals with an introduction to MEMS pressure sensors and mathematical relations for its fabrication. The second part covers pressure sensing principles followed by the application of MEMS pressure sensors in five major fields of aerospace industry. Findings: In this paper, various pressure sensing principles in MEMS and applications of MEMS technology in the aerospace industry have been reviewed. Five application fields have been investigated including: Propulsion/Turbomachinery applications, turbulent flow diagnosis, experimental aerodynamics, micro-flow control and UAV/MAV applications. Applications of MEMS sensors in the aerospace industry are quite limited due to requirements of very high accuracy, high reliability and harsh environment survivability. However, the potential for growth of this technology is foreseen due to inherent features of MEMS sensors’ being light weight, low cost, ease of batch fabrication and capability of integration with electric circuits. All these advantages are very relevant to the aerospace industry. This work is an endeavor to present a comprehensive review of such MEMS pressure sensors, which are used in the aerospace industry and have been reported in recent literature. Originality/value: As per the author’s understanding, usage of MEMS pressure sensors in the aerospace industry is quite limited due to cost constraints and indirect measurement approaches owing to the inability to locate sensors in harsh environments. Present work is a prime effort in summarizing the published literature for application of MEMS pressure sensors in the said field. Five broad application areas have been investigated including: propulsion/turbomachinery applications, turbulent flow diagnosis, experimental aerodynamics, micro-flow control and UAV/MAV applications.

An SOI CMOS multi-sensor MEMS chip, which can simultaneously measure temperature, pressure and flow rate, has been reported. The multi-sensor chip has been designed keeping in view the requirements of researchers interested in experimental fluid dynamics. The chip contains ten thermodiodes (temperature sensors), a piezoresistive-type pressure sensor and nine hot film-based flow rate sensors fabricated within the oxide layer of the SOI wafers. The silicon dioxide layers with embedded sensors are relieved from the substrate as membranes with the help of a single DRIE step after chip fabrication from a commercial CMOS foundry. Very dense sensor packing per unit area of the chip has been enabled by using technologies/processes like SOI, CMOS and DRIE. Independent apparatuses were used for the characterization of each sensor. With a drive current of 10 µA–0.1 µA, the thermodiodes exhibited sensitivities of 1.41 mV/°C–1.79 mV/°C in the range 20–300 °C. The sensitivity of the pressure sensor was 0.0686 mV/(V_excit kPa) with a non-linearity of 0.25% between 0 and 69 kPa above ambient pressure. Packaged in a micro-channel, the flow rate sensor has a linearized sensitivity of 17.3 mV/(L/min)^−0.1 in the tested range of 0–4.7 L/min. The multi-sensor chip can be used for simultaneous measurement of fluid pressure, temperature and flow rate in fluidic experiments and aerospace/automotive/biomedical/process industries.

In this paper, we report for the first time an SOI CMOS multi-sensors MEMS chip, capable of sensing three key flow parameters i.e. pressure, temperature and flow rate simultaneously. The chip contains an array of ten silicon diode temperature sensors, a piezoresistive pressure sensor and an array of nine micro hot-film flow rate sensors. The chip has been fabricated through a commercial CMOS foundry. The sensors have been embedded in thin oxide membranes that were obtained through a single, post-CMOS DRIE (deep reactive ion etching) back-etch step at the foundry. Characterization of each type of sensor was carried out using independent calibration setups. Temperature sensors exhibited a sensitivity of 1.6 mV/ °C at 1μA constant current in forward bias mode. Pressure sensor showed a sensitivity of 0.4734 mV/V/psi whereas the flow rate sensors showed typical third order calibration curve once operated in constant current mode. The chip can be used in micro-channels for micro-fluidic applications as well as on real aerodynamic surfaces and wind tunnel models for experimental verification of CFD results.

A maskless etching technique for fabrication of 3D MEMS structures has been presented. The technique has been applied to micro structures embedded during a CMOS process in the dielectric membrane, which was realized by post-CMOS DRIE (deep reactive ion etching) back etch step. A comparison of the conventional etching technique with the developed maskless technique has been presented. The proposed technique takes advantage of the UV (ultra violet) transparent dielectric membrane supporting the CMOS-process based micro structures, where the UV light exposure of the photoresist on the top surface of the device is carried out from the reverse side through the UV-transparent membrane. The surrounding excess membrane is then etched away using suitable anisotropic etching technique such as RIE (reactive ion etching) to release 3D active structures in the CMOS MEMS device. The technique eliminates the requirement of a dedicated photo-mask as the CMOS metallization layer based micro structures are used to transfer the exact pattern on the device surface. Furthermore, expensive mask alignment equipment and skilled human resource is also not required. Thus the reported technique results in overall process simplification, fabrication process time and cost reduction and device yield enhancement. The proposed technique has also been successfully demonstrated to fabricate CMOS MEMS thermal wall shear stress sensors with significantly lower power consumption and stable performance.