The arguable history of MEMS began back on April 1, 1954, when C.S smith from Bell Telephone Lab published in a physical review journal describing the basics of MEMS for the first time which related to the certain stress–strain effects in the silicon and germanium called the piezoresistance. Scientists believe that the MEMS revolution is going to be the second revolution in micromanufacturing after the semiconductor microfabrication revolution. MEMS along with the combination of silicon-based microelectronics and micromachining technology has dramatically revolutionized both the industry technologies and consumer products from high-technology machines to tiny elements in smartphones. In addition, MEMS is one of the most promising technologies of the twenty-first century it has the potential to significantly alter all aspects of our lives and the way we live in the future. In simple words, the sensing process can be defined as energy transduction that provides us with understanding signals or recognition of unknown actions, whereas the actuation process can be classified as the energy conversion that produces mechanical actions. In fact, the output in the actuators is always in the mechanical form of energy. There are various actuators such as pneumatic actuators where their input is air, as well as piezoelectric actuators where their inputs are current or voltage, the micro-valves for controlling the gas and liquid flows, as well as the micro-pumps for fluids pressures that have been used in medical devices and many more. On the other hand, the actuator transducer is the part of the system that helps to achieve physical/mechanical movement after receiving energy in the form of electrical or other forms of energy. In particular, the sensors are the devices that detect and monitor events or changes in the environment such as gas, chemical, pressure, temperature, vibration, and flow. For instance, the sensors can convert a measured physical signal into an electrical signal, whereas the actuators can convert the electrical signals into mechanical signals just to move themselves or any other components from one position into another state inside the system. The well-addressed components of the MEMS devices are the microsensors and microactuators, also known as “transducers,” which are defined as the elements that perform the task of converting the energy or power from one domain to other domains. MEMS devices have been designed in several structural varying from simple structural with an element that does not perform any movement to extremely complex electromechanical system that contained multiple elements that performed sophisticated action and movement under the control of integrated microelectronic circuits. In addition, MEMS can be defined as miniaturized mechanical and electromechanical elements that are made through microfabrication techniques with dimensions varying from below one micron in the smallest elements all the way to several millimeters. However, MEMS devices are capable to perform these tasks despite their small sizes. Undoubtedly, the task of gathering and transforming information is usually performed by sophisticated technical systems. The main purpose and function of the MEMS are to collect physical and chemical information such as pressure, temperature, chemical and gases molecules from the surrounding environment and deliver this information in a more suitable form to human senses. Microelectromechanical systems (MEMS) originally referred to the integration of the mechanical and electrical components at the microscale and nanoscale dimensions. In this work, the various types of gas sensors based on piezoelectricity are investigated extensively including their operating principle, besides their material parameters as well as the critical design parameters, the device structures, and their sensing materials including the polymers, carbon, metal–organic framework, and graphene. The development of the piezoelectric MEMS gas sensors is investigated for the application of low-level concentration gas molecules detection. This paper presents the piezo-MEMS gas sensors’ characteristics such as their miniaturized structure, the capability of integration with readout circuit, and fabrication feasibility using multiuser technologies. Piezoelectric microelectromechanical system (piezo-MEMS)-based mass sensors including the piezoelectric microcantilevers, surface acoustic waves (SAW), quartz crystal microbalance (QCM), piezoelectric micromachined ultrasonic transducer (PMUT), and film bulk acoustic wave resonators (FBAR) are highlighted as suitable candidates for highly sensitive gas detection application.
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