With the fast development of the fifth-generation cellular network technology (5G), the future sensors and microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) are presenting a more and more critical role to provide information in our daily life. This review paper introduces the development trends and perspectives of the future sensors and MEMS/NEMS. Starting from the issues of the MEMS fabrication, we introduced typical MEMS sensors for their applications in the Internet of Things (IoTs), such as MEMS physical sensor, MEMS acoustic sensor, and MEMS gas sensor. Toward the trends in intelligence and less power consumption, MEMS components including MEMS/NEMS switch, piezoelectric micromachined ultrasonic transducer (PMUT), and MEMS energy harvesting were investigated to assist the future sensors, such as event-based or almost zero-power. Furthermore, MEMS rigid substrate toward NEMS flexible-based for flexibility and interface was discussed as another important development trend for next-generation wearable or multi-functional sensors. Around the issues about the big data and human-machine realization for human beings’ manipulation, artificial intelligence (AI) and virtual reality (VR) technologies were finally realized using sensor nodes and its wave identification as future trends for various scenarios.

Development Trends and Perspectives of Future Sensors and MEMS/NEMS.

Inductor–capacitor ( $LC$ ) passive wireless sensors use a transformer with loose coupling between an external readout coil and an inductor that receives power through this inductive coupling. Changes in the sensor are wirelessly and remotely detected by the readout coil, which makes them highly useful in applications that require the sensor to be powered remotely and to occupy a small volume, such as harsh and sealed environments, where physical access to the sensor is difficult. Although the sensor to accomplish this function dates from the 1960’s, its rapid extension over the past decades has benefited from microelectromechanical systems. This paper provides an overview of the status and challenges in the $LC$ passive wireless sensor toward a wireless sensing platform. The basic sensing principles are first categorized into detecting changes of the sensor in response to the capacitance, resistance, inductance, or coupling distance due to the parameter of interest through monitoring the impedance magnitude and phase spectrum. The present state of the art in sensor applications for pressure, strain, temperature, humidity, biochemical, gas, and so on is then reviewed and compared. For emerging applications from many Internet of Things scenarios, geometrical constraints, such as small and non-invasive coils, reduce the magnetic coupling between the sensor and the readout coil, resulting in a limited interrogation distance. Furthermore, an increasing number of applications also require the simultaneous measurement of multiple parameters. Recent efforts to increase the interrogation distance and to extend the measurement of single parameter to multiple parameters are finally outlined. [2016-0093]

LC Passive Wireless Sensors Toward a Wireless Sensing Platform: Status, Prospects, and Challenges

This article presents a broad review on optical, radio-frequency (RF), microwave (MW), millimeter wave (mmW) and terahertz (THz) biosensors. Biomatter-wave interaction modalities are considered over a wide range of frequencies and applications such as detection of cancer biomarkers, biotin, neurotransmitters and heart rate are presented in detail. By treating biological tissue as a dielectric substance, having a unique dielectric signature, it can be characterized by frequency dependent parameters such as permittivity and conductivity. By observing the unique permittivity spectrum, cancerous cells can be distinguished from healthy ones or by measuring the changes in permittivity, concentration of medically relevant biomolecules such as glucose, neurotransmitters, vitamins and proteins, ailments and abnormalities can be detected. In case of optical biosensors, any change in permittivity is transduced to a change in optical properties such as photoluminescence, interference pattern, reflection intensity and reflection angle through techniques like quantum dots, interferometry, surface enhanced raman scattering or surface plasmon resonance. Conversely, in case of RF, MW, mmW and THz biosensors, capacitive sensing is most commonly employed where changes in permittivity are reflected as changes in capacitance, through components like interdigitated electrodes, resonators and microstrip structures. In this paper, interactions of EM waves with biomatter are considered, with an emphasis on a clear demarcation of various modalities, their underlying principles and applications.

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EM-Wave Biosensors: A Review of RF, Microwave, mm-Wave and Optical Sensing.

This paper describes the development of aluminum nitride (AlN) resonant accelerometers that can be integrated directly over foundry CMOS circuitry. Acceleration is measured by a change in resonant frequency of AlN double-ended tuning-fork (DETF) resonators. The DETF resonators and an attached proof mass are composed of a 1-mum-thick piezoelectric AlN layer. Utilizing piezoelectric coupling for the resonator drive and sense, DETFs at 890 kHz have been realized with quality factors (Q) of 5090 and a maximum power handling of 1 muW. The linear drive of the piezoelectric coupling reduces upconversion of 1/f amplifier noise into 1/f 3 phase noise close to the oscillator carrier. This results in lower oscillator phase noise, -96 dBc/Hz at 100-Hz offset from the carrier, and improved sensor resolution when the DETF resonators are oscillated by the readout electronics. Attached to a 110-ng proof mass, the accelerometer microsystem has a measured sensitivity of 3.4 Hz/G and a resolution of 0.9 mG/radicHz from 10 to 200 Hz, where the accelerometer bandwidth is limited by the measurement setup. Theoretical calculations predict an upper limit on the accelerometer bandwidth of 1.4 kHz.

Post-CMOS Compatible Aluminum Nitride Resonant MEMS Accelerometers.

Radio frequency identification (RFID) technology has enabled a new class of low cost, wireless zero-power sensors, which open up applications in highly pervasive and distributed RFID-enabled sensing, which were previously not feasible with wired or battery powered wireless sensor nodes. This paper provides a review of RFID sensing techniques utilizing chip-based and chipless RFID principles, and presents a variety of implementations of RFID-based sensors, which can be used to detect strain, temperature, water quality, touch, and gas.

RFID-Based Sensors for Zero-Power Autonomous Wireless Sensor Networks

This paper reports the performance of a wireless MEMS bimorph temperature sensor integrated on a bearing for component health monitoring applications. The sensor consists of a robust array of bimorphs consisting of gold and thermally-grown oxide operable to at least 300°C. Fabrication details are included, as well as the hermetic packaging information. Speed of actuation results from a high-speed camera is included showing the actuation time is less than 600 µs. Reliability testing of the bimorph array up to 400 million thermal cycles is also shown, after which the bimorphs still yield consistent behavior. Finally, dynamic testing is performed showing actual bearing temperature values at different speeds on a real-world helicopter bearing

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Wireless temperature microsensors integrated on bearings for health monitoring applications

An automotive vehicle molding (10) for enhancing the appearance of a vehicle includes a thermoplastic elastomer main body (14) and an ionomeric show surface (32). A plastic or metal core member (12) can be embedded in the main body (14) to provide additional stiffness and support. The ionomeric show surface (32) is extruded onto a belt line seal portion or other visible section of the molding (10). The ionomeric show surface (32) provides a tough, scratch resistant exterior that can easily be colored provided with a glossy surface to improve the aesthetics of the molding (10) and more closely match its appearance with the painted exterior of the vehicle.

Extrusion having thermoplastic elastomer co-extruded on core with additional ionomeric show surface

In this paper we present a new slot antenna with an embedded temperature sensor for remote sensing in harsh environment applications. When the antenna is illuminated with a plane wave it returns a signal. The returned signal's frequency is modulated by the loaded capacitance formed by an array of MEMS bimorph (metal-dielectric) cantilevers. The MEMS cantilevers deflect downwards when the temperature is changed from 20°C to 300°C. As a result, the resonant frequency of the slot is linearly tuned from 19.45 to 19.30 GHz. The design yields a totally passive and integrated antenna/sensor. The MEMS fabrication is inherently robust, does not suffer from the creep or fatigue problems of traditional bimorph temperature sensors, and has a very high manufacturing yield, even in an academic clean room environment.

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A capacitively-loaded MEMS Slot element for wireless temperature sensing of up to 300°C

Presented is an inherently-robust wireless capacitive MEMS temperature sensor capable of operating to 300°C. The heart of the sensor is an array of bimorph (metal-dielectric) cantilevers whose deflections are sensed by an array of appropriatelyplaced electrodes. The key advantages of this configuration are the following. First, its dielectric layer is SiO 2 thermally-grown at 1,100°C as opposed to conventional low-temperature PECVD or sputtered films. Second, the lack of a sensing surface directly beneath the movable structures renders stiction nearly impossible. Third, the fringing-field sensing results in constant sensitivity throughout the entire temperature range. Fourth, the employed passive approach is immune to high-temperature reliability issues faced by active devices. Furthermore, the fabrication yield is over 99%, even in an academic cleanroom (Birck Nanotechnology Center at Purdue University). When configured with an inductor and wirelessly interrogated, the measured resonant frequency has a linear shift from 206 MHz at room temperature to 199 MHz at 300°C.

An inherently-robust 300°C MEMS temperature sensor for wireless health monitoring of ball and rolling element bearings

An acoustically coupled frequency selective radio frequency (RF) device is provided. The device includes a piezoelectric substrate overlain by a plurality of electrodes. The device further includes a pair of RF input terminals at least one of which is electrically connected to at least one of the electrodes, and a pair of output RF terminals, at least one of which is electrically connected to at least one other of the electrodes. At least one of the electrodes is electromechanically reconfigurable between a state in which it is closer to a face of the piezoelectric substrate and at least one state in which it is farther from the face of the piezoelectric substrate.

Sean Scott

Papers

Wireless temperature microsensors integrated on bearings for health monitoring applications

Extrusion having thermoplastic elastomer co-extruded on core with additional ionomeric show surface

A capacitively-loaded MEMS Slot element for wireless temperature sensing of up to 300°C

An inherently-robust 300°C MEMS temperature sensor for wireless health monitoring of ball and rolling element bearings

Programmable electroacoustic filter apparatus and method for its manufacture