The development of flexible electronic skins with high sensitivities and multimodal sensing capabilities is of great interest for applications ranging from human healthcare monitoring to robotic skins to prosthetic limbs. Although piezoresistive composite elastomers have shown great promise in this area of research, typically poor sensitivities and low response times, as well as signal drifts with temperature, have prevented further development of these materials in electronic skin applications. Here, we introduce and demonstrate a design of flexible electronic skins based on composite elastomer films that contain interlocked microdome arrays and display giant tunneling piezoresistance. Our design substantially increases the change in contact area upon loading and enables an extreme resistance-switching behavior (ROFF/RON of ∼105). This translates into high sensitivity to pressure (−15.1 kPa–1, ∼0.2 Pa minimum detection) and rapid response/relaxation times (∼0.04 s), with a minimal dependence on temperatu...

Giant Tunneling Piezoresistance of Composite Elastomers with Interlocked Microdome Arrays for Ultrasensitive and Multimodal Electronic Skins

Pull-in instability as an inherently nonlinear and crucial effect continues to become increasingly important for the design of electrostatic MEMS and NEMS devices and ever more interesting scientifically. This review reports not only the overview of the pull-in phenomenon in electrostatically actuated MEMS and NEMS devices, but also the physical principles that have enabled fundamental insights into the pull-in instability as well as pull-in induced failures. Pull-in governing equations and conditions to characterize and predict the static, dynamic and resonant pull-in behaviors are summarized. Specifically, we have described and discussed on various state-of-the-art approaches for extending the travel range, controlling the pull-in instability and further enhancing the performance of MEMS and NEMS devices with electrostatic actuation and sensing. A number of recent activities and achievements methods for control of torsional electrostatic micromirrors are introduced. The on-going development in pull-in applications that are being used to develop a fundamental understanding of pull-in instability from negative to positive influences is included and highlighted. Future research trends and challenges are further outlined.

Electrostatic pull-in instability in MEMS/NEMS: A review

Sensors based on the detection of small resistance variations are universally recognized as piezoresistive. Being one of the simplest, most common and most investigated classes of sensors, continuous efforts are focused on creating improved devices with higher performance that can be used in many commercial and non–commercial applications (e.g. evaluation of strain, pressure, acceleration, force etc.). Consequently, despite the fact that more than 150 years have passed since the discovery of the piezoresistive effect in some classes of metals and semiconductors, the development of such sensors remains interesting and topical. Moreover, with the advent of second–generation robotics, research on piezoresistive sensors has undergone a massive increase. This paper aims to be a short, self–consistent vademecum which would be useful to researchers and engineers, since it focuses on the fundamentals of theory, materials, and readout–circuit design pertinent to the most recent developments in the field of piezoresistive sensors.

Theory, technology and applications of piezoresistive sensors: A review

1 wileyonlinelibrary.com C o m m u n iC a io n and their possible applications. The ultimate form of active manipulation of EIT phenomenon will be when all three primary parameters are controlled independently. The independent control of individual resonators demands for the controllability at unit cell level, and conventional approaches such as optical pumping of photoconductive elements or thermally controlled superconductor are restricted to provide only global control. Recently, microelectromechanical systems (MEMS) based tunable metamaterials have been reported to achieve controllability at unit cell level, along with the added advantage of being electrically controlled, miniaturized size and enhanced electrooptic performance. The versatility of MEMS design has enabled active manipulation of numerous THz properties such as magnetic resonance,[19–22] electrical resonance,[23–25] anisotropy,[26] broadband response,[27] isotropic resonance switching[28] multiresonance switching,[29–31] and coupling strength between resonators.[32] The enhanced controllability and direct integration of MEMS actuators into metamaterial unit cell geometry is an ideal fit for the realization of selective control of coupled mode resonators. In this Communication, reconfigurable metamaterial with independently controlled bright and dark mode resonators is proposed for advanced manipulation of the classical analog of EIT and slow light effects in THz spectral region. The active control of bright mode resonator enables modulation of EIT intensity, while the tuning of dark mode resonance causes the EIT peak to tune in frequency. Furthermore, simultaneous switching of bright and dark mode resonators results in dynamic switching of the system between coupled and uncoupled states. The proposed approach of selective reconfiguration can be scaled for multiresonator systems, which can be coupled either through inductive, capacitive, or conductive means. The metamaterial consists of 80 × 80 periodic array of cut wire resonator (CWR) with closely placed split ring resonators (SRRs), as shown in Figure 1 and Figure 2. The periodicity of unit cell is 100 μm along both axial directions. The CWR has length, lC = 60 μm and width, wC = 5 μm, respectively. The SRRs have a base length, bS = 30 μm, side length, lS = 20 μm, and split gap, gS = 4 μm. The SRRs are placed at a distance of S = 2 μm from the CWR. When the polarization of the excitation field is along the CWR arm, the dipole mode resonance of the CWR will be the bright mode and the inductive-capacitive (LC) mode of SRR resonance acts as the dark mode. Thus for the incident THz polarization, the direct excitation of the bright mode induces image charges on the nearby SRRs through nearfield inductive coupling, thereby exciting the LC resonance of the SRRs. These bright-dark resonances have contrasting line widths with identical resonance frequencies and under a strong coupling regime they experience an EIT-type of interference that gives rise to a sharp transmission peak. Thus, through Active Control of Electromagnetically Induced Transparency Analog in Terahertz MEMS Metamaterial

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Active Control of Electromagnetically Induced Transparency Analog in Terahertz MEMS Metamaterial

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.

The linearity of a gate-all-around junctionless silicon nanowire (SiNW) FET has been analyzed. The SiNW FET shows a perfectly linear ID-VG relation and a nearly zero output conductance. The mechanism of its linear behaviors due to degenerate doping level has been also demonstrated. For RF applications, the proposed SiNW FET exhibits a much lower distortion for a whole range of load resistance, making it superior to modern short-channel MOSFET.

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A Junctionless Gate-All-Around Silicon Nanowire FET of High Linearity and Its Potential Applications

A pressure sensor with a 200 µm diaphragm using silicon nanowires (SiNWs) as a piezoresistive sensing element is developed and optimized. The SiNWs are embedded in a multilayered diaphragm structure comprising silicon nitride (SiNx) and silicon oxide (SiO2). Optimizations were performed on both SiNWs and the diaphragm structure. The diaphragm with a 1.2 µm SiNx layer is considered to be an optimized design in terms of small initial central deflection (0.1 µm), relatively high sensitivity (0.6% psi−1) and good linearity within our measurement range.

/pdf/optimization-of-nems-pressure-sensors-with-a-multilayered-3i2xrpk7z7.pdf

Optimization of NEMS pressure sensors with a multilayered diaphragm using silicon nanowires as piezoresistive sensing elements

A dual-silicon-nanowires based U-shape nanoelectromechanical switch with low pull-in voltage is fabricated using standard complementary metal-oxide-semiconductor compatible process on silicon-on-insulator wafer. The switch consists of a capacitive paddle with dimension of 2 μm by 4 μm supported by two silicon nanowires, suspended on top of the substrate with a gap of 145 nm. The nanowires are 5 μm long with cross-section of 90 nm by 90 nm. The average pull-in voltage is about 1.12 V and the ratio of the ON/OFF current is measured to be over 10 000. According to the preliminary results, this U-shape structure demonstrates great potential in lowering down the pull-in voltage.

https://www.ece.nus.edu.sg/stfpage/elelc/Publication/2012/93.%20APL_12V100_113102_A%20dual-silicon-nanowires%20based%20U-shape%20nanoelectromechanical%20switch%20with%20low%20pull-in%20voltage.pdf

A dual-silicon-nanowires based U-shape nanoelectromechanical switch with low pull-in voltage

We present nanoelectromechanical system based cantilever air flow sensor using silicon nanowires (SiNWs). The cantilever is fabricated in the complementary metal-oxide-semiconductor compatible process with dimension of 90 μm × 20 μm × 3 μm. SiNWs with the size of 2 μm × 90 nm × 90 nm (length × width × height) are embedded at the edge of the cantilever fixed end to experience the maximum air flow induced strain. Compared with recently reported air flow sensors, our device shows a better sensitivity of 198 Ω/m/s and a flow sensing range up to 65 m/s. In addition, improvements in terms of linearity, hysteresis, and lower power consumption are reported as well.

/pdf/piezoresistive-silicon-nanowire-based-nanoelectromechanical-4bvdo5pjj1.pdf

Piezoresistive silicon nanowire based nanoelectromechanical system cantilever air flow sensor

We present a nanoelectromechanical system piezoresistive pressure sensor with annular grooves on the circular diaphragm where silicon nanowires (SiNWs) are embedded as sensing elements around the edge. In comparison with our previous flat diaphragm pressure sensor, this new diaphragm structure enhances the device sensitivity by 2.5 times under pressure range of 0-120 mmHg. By leveraging SiNWs as piezoresistors, this improvement is even remarkable in contrast to other recently reported piezoresistive pressure sensing devices. In addition, with the miniaturized sensing diaphragm (radius of 100 µm), the sensor can be potentially used as implantable device for low-pressure sensing applications. (2013-0305)

Liang Lou

Papers

A Junctionless Gate-All-Around Silicon Nanowire FET of High Linearity and Its Potential Applications

Optimization of NEMS pressure sensors with a multilayered diaphragm using silicon nanowires as piezoresistive sensing elements

A dual-silicon-nanowires based U-shape nanoelectromechanical switch with low pull-in voltage

Piezoresistive silicon nanowire based nanoelectromechanical system cantilever air flow sensor

Annularly Grooved Diaphragm Pressure Sensor With Embedded Silicon Nanowires for Low Pressure Application