With the new arena of smart and Internet of things (IoT) enabled devices, a terahertz frequency-based network like 6G with high speed and low latency is required. Solid-state devices show good response till 5 GHz. However, at higher frequencies, the electromagnetic responses of these devices start to degrade. On the other hand, RF MEMS technology is matured, and devices until 30 GHz have been demonstrated. The present paper shows the advancement of RF MEMS to a new terahertz MEMS switch for 6G communication applications. The terahertz switch has an actuation voltage of 20 V with a mechanical frequency of 138.9 kHz. MEMS terahertz switch’s most important factor is its high-frequency linearity. A single switch can handle all the communication bands like 2G, 3G, 4G, 5G and 6G to 150 GHz frequency. Insertion loss is less than − 0.18 dB, and isolation is more than − 20 dB from DC to 150 GHz frequency. The return loss of the switch is also better than − 23 dB for the same band.

On the 4H-SiC substrate, C-face and Si-face oxide layers have been grown by thermal oxidation process and sputtering. The thermal oxidation temperature dependence of 4H-silicon carbide (SiC) is systematically investigated using capacitance-voltage (C–V) measurements. The oxidation quality and thickness vary according to the temperature and time duration of the thermal oxidation. The layers’ thicknesses are determined by atomic force microscopy (AFM), and the temperature range is between 800°C and 1110 °C. The primary reason to fabricate the Metal-Oxide-Silicon (MOS) capacitor is to know the thermal oxidation process and a working principle. In this paper, we optimize a thermal oxidation process and fabricate the MOS structure. Then we determine the various parameters such as flat band voltage (V f b ), Inversion threshold voltage (V t ), Surface depletion capacitance (C dep ), Oxide capacitance (C ox ), the total capacitance of the device (C o ), doping concentration (N d ), Depletion width (X d ), Maximum depletion width (X dt ) and Interface trap density (D it ). Finally, we analyze and discuss the MOS capacitance.

This article presents the analytical modeling, design, and performance analysis of an electrostatic micromirror for space-based Multiobject Spectroscopy (MOS). The micromirror under investigation is a double-bridge design with hidden cantilevers architecture in which the deflection is achieved by a combination of bending and twisting cantilevers. A simple closed-form solution of pull-in voltage and deflection is obtained using the parallel-plate capacitor model that assumes micromirror deflection dominated by bending cantilevers due to electrostatic actuation. The design optimization is done to achieve a micromirror of size $200\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$ , deflection $2.5~\mu \text{m}$ , pull-in voltage smaller than 25 V, and a shock survival capacity of at least 10 000 g. The static and dynamic behavior of the optimized design is obtained using the analytical model and compared with the finite-element method (FEM) and characterization results and found to be in close agreement. The micromirror exhibits an analytical pull-in voltage near the FEM and measured pull-in voltage with a deviation of 5% and 0.9%, respectively. The analytical resonance frequency is also closer to simulation and measurement results with a deviation of 4.66% and 2.58%, respectively. The analytical switching time is also very close to the FEM results, with a deviation of 28%. The analytical model and the simple approach of design optimization using tuning parameters presented in the article can be used to design the micromirror according to desired specifications.

The technology for radio frequency micro-electro-mechanical system (RF MEMS) is well established. In the next phase of miniaturization, RF MEMS transforming into RF nano-electro-mechanical system (NEMS) requires scaling laws. For MEMS devices, vertical scaling laws are available in the literature. However, existing scaling laws are isotropic and not valid for the majority of the MEMS devices. Like VLSI technology, the scaling in the MEMS is asymmetric and needs optimization in each direction. In the MEMS, depending upon the working principle, the scaling laws vary from device to device. In the present work, spring constant scaling laws for the electrostatic RF MEMS devices are derived given the device performance. The scaling laws are derived in such a way that existing limitations of the MEMS technology like low switching speed, high pull-in voltage, stiction, etc., are minimized and the response of the switch is improved.

RF MEMS switches are well known to exhibit performance superior to solid-state devices. However, electromechanical issues, such as repeatability and higher pull-in voltage, are a matter of concern. MEMS switches generally consist of metallic beams which curl up or down based on stresses in the structure. Stress-induced curling-up phenomenon, in such structures, increases the gap between the actuating electrode and the freely suspended metallic structure which in turn increases the pull-in voltage. This article focuses on simulations and curve fitting to analyze the effect of stress on pull-in voltage. The pull-in voltage of the switch is proportional to stress, and accordingly, its dependence on in-built stress and Young's modulus is analyzed. In addition to mechanical analysis, RF response of the single pole double throw (SPDT) switch is discussed as a case study. Measured stress and pull-in voltage of the SPDT switch is 50 MPa and 16 V. In the presence of stress, the curled-up cantilever switch shows measured isolation better than 31 dB for dc to 10-GHz range.

This article presents the design, development, and characterization of a double-bridge electrostatically actuated micromirror for multiobject spectroscopy (MOS). The proposed structure is an improvement over single-bridge micromirrors in terms of aperture size, pull-in voltage, degrees of freedom, and fill factor. The two-axis symmetric rotation mechanism of the proposed micromirror is achieved by bending and twisting action of the suspended cantilevers which is contrary to the twisting cantilevers of a conventional one-axis torsional micromirror. The placement of anchor and cantilevers under the mirror plate results in a high fill factor when arranged in a 2-D array. The analytical modeling, design optimization, and static and dynamic analysis are done using finite-element method (FEM) in Coventorware. An optimized design is fabricated using a simple approach of surface micromachining and electroplating. For a micromirror of size $200\,\,\mu \text{m}\,\,\times 200\,\,\mu \text{m}$ and the actuation gap of $2.5~\mu \text{m}$ , the device exhibits a tilt angle of 1.5° at a pull-in voltage of 23.1 V, a switching time of $38~\mu \text{s}$ , and the resonance frequency of 35.23 kHz. A ${3} \times {3}$ array of the micromirror is demonstrated with a fill factor of more than 95%. The deflection range can be increased by simply increasing the thickness of the sacrificial layer and without any major process modification.

Recently, microstructured PDMS based pressure sensors are explored as a potential candidate in bio-signal monitoring and electronic-skin applications. Here, we have fabricated capacitive pressure sensors with micro-pyramidal PDMS dielectric thin films, and studied the influence of surface coverage and arrangement of these structures on the sensitivity of pressure sensor devices. Pressure sensor with periodically arranged pyramids (surface coverage: 36.7%) exhibited sensitivity of 0.16 kPa(-1) in <1 kPa and 0.04 kPa(-1) in 0.75-2.5 kPa pressure range, whereas the pressure sensor with diagonally arranged pyramids (surface coverage: 45.2%) exhibited sensitivity of 0.1 kPa(-1) in <1 kPa and 0.05 kPa(-1) in 0.75-2.5 kPa pressure range respectively. Despite having large surface coverage, pressure sensor with the diagonally arranged pyramids exhibited high sensitivity (0.05 kPa(-1)) in 1-2.5 kPa pressure range than the periodically arranged pyramids owing to the large displacement and increase in effective permittivity of diagonally arranged pyramids. Simulation studies on the developed pressure sensor structures using Ansys and Opera also confirmed the relatively large displacement and Delta C/Co in diagonally arranged pyramids compared to periodically arranged pyramids having slightly low surface coverage. Experimental results and simulations demonstrate that the sensitivity of these kinds of pressure sensors can also be tuned by arrangement of pyramids. Also, the developed flexible capacitive pressure sensor is demonstrated for in-vivo, real-time pulse wave form recording. (C) 2020 Elsevier B.V. All rights reserved.

This paper presents a novel structure of capacitance shunt type RF switch for 5G applications. The proposed RF MEMS switch is having Cantilever type designed with optimized dimensions to operate in V-band applications. The electromechanical analysis is done by using the COMSOL tool. The actuation voltage of the proposed switch is 10.5 V with the air gap of 1 µm and gold as a beam material. The proposed switch with the meanders and perforations show the scattering parameters in HFSS software such as insertion loss (S 12 ) of − 0.033 dB and return loss (S 11 ) less than − 48 dB and the isolation (S 21 ) calculated in off-state as − 62 dB at 50 GHz.

The mechanical actuation of suspended structures in microelectromechanical system (MEMS) switches plays an important role in obtaining an open or short circuit in radio-frequency (RF) transmission lines. These micromachined switches have moving parts which are realized by a sacrificial layer. Several sacrificial materials have been utilized in the fabrication of MEMS structures. The traditional method of using metal such as copper or nickel as a sacrificial layer is difficult due to metal etchant compatibility issues. A photoresist is the best choice for this process. Generally, the HiPR photoresist has been found to be suitable␣for the role of sacrificial layer. However, the HiPR is no longer available in the commercial market. As an alternative to the HiPR, the AZ4620 photoresist can be used. In this paper, a unit process optimization technique is described featuring an AZ4620 photoresist as a sacrificial layer for the microfabrication of a suspended structure. The AZ4620 meets all the requirements for the development of RF MEMS switches. Hence, the recipe and fabrication technique are optimized according to the required thickness. Preliminary measurements of the fabricated switch beam indicate that the required gap has been achieved. This optimized process is compatible with standard MEMS technology.

Surface micromachined devices are known to have residual stress-induced deformation. This paper presents the effects of residual stress on the flatness of an electrothermally actuated large aperture MEMS bilayer platform. The platform consists of a SiO2-Al composite plate of area 500 x 500 mu m(2) suspended over a cavity through bimorph actuators. The bilayer platform consists of 0.95 mu m thick aluminum film on a thermally grown 0.75 mu m thick silicon dioxide on a silicon substrate. Bimorph actuators also consist of laminated layers of silicon dioxide and aluminum of thicknesses the same as on the platform. The ensuing compressive stress in silicon dioxide (240 MPa) & tensile stress in aluminum (35 MPa) manifests itself in significant post-release curling of the bilayer platform. Finite Element Simulation is done in Coventorwaree to analyze the room temperature post-release deformation behavior of the platform. In order to correct the platform curvature, two methods of stress counterbalancing i.e. (i) metal reinforcement framing, and (ii) deposition of a stress compensation layer are proposed and their effectiveness is investigated using FEM simulations. The simulation results show that a 1 mu m thick gold reinforcement frame results in a 13 mu m peak-to-valley height difference between center and corner of the platform, which improves to 6 mu m for a gold reinforcement thickness of 3 mu m. The maximum height difference reduces to 1 mu m for silicon dioxide of thickness 0.75 mu m. According to FEM results, the presence of a stress compensation layer at the top is more effective in curvature correction compared to metal reinforcement framing; however, the post-release elevation of the stress-compensated platform is 5 mu m below the post-release elevation of the reinforced platform and 25 mu m below the zero reference plane. To verify the simulation results, the platform is fabricated with a deposition of 1 mu m thick silicon dioxide layer at the top. The fabricated platform exhibit significant improvement in post-release deformation with a stress compensation layer compared to an unbalanced platform.

This paper reports a novel capacitive RF-MEMS switch. The presented device has frequency reconfigurable characteristics and thus can be used in multi-band wireless systems. The switch is realized through two non-uniform cantilevers with dissimilar shape. The structure of the cantilevers is kept dissimilar to achieve the different value of inductance in the down-state of the device and hence the different electrical resonant frequency. Further, the proposed device has also overcome issue of shift in the isolation response caused by residual stress in switching structure and micro-roughness in the deposited SiO2 layer. The device forms a M-I-M capacitor at the central conductor of the transmission line to resolve the above cited problem and also allows the use of cantilever structures for the implementation of capacitive switches in place of conventional bridge type structures. The measured isolation response shows three optimum values of 25.40 dB, 20.44 dB, and 30.80 dB at 9.4 GHz, 11.6 GHz, and 25.2 GHz respectively. The measured insertion loss is also better than 0.41 dB up to 30 GHz. Under, mechanical characterization, cantilever with two narrow beams shows resonant frequency of 3.90 kHz and cantilever with single narrow beam shows resonant frequency of 4.66 kHz. Furthermore, the device has measured pull-in voltage which is less than 16 V.

Radio frequency micro-electro-mechanical system (RF MEMS) switch is basic component for transponders used in communication system. Switch “OFF/ON” capacitance ratio plays major role in controlling signal to noise ratio. Theoretically, with high dielectric constant material or floating metal concept, capacitance ratio can be improved up to 2000 or even more. Whereas, in most of the practical cases, measured ratio is less than 200. In present paper, RF MEMS capacitive switch LCR parameters are extracted considering parasitic capacitance to explain the mismatch of measured results. Parasitic capacitance is independent from device overlap area. Parasitic capacitance is function of switch geometry and directly proportional to dielectric constant of the substrate material.

In this paper, TiN film has been deposited and optimized at room temperature for high power radio-frequency microelectromechanical system (RF-MEMS) applications. Being hard, titanium nitride is used in the contact area. The contact material should have low resistance and high hardness. TiN thin films were deposited by DC magnetron reactive sputtering using a four inch high purity titanium target in a nitrogen (N-2) environment. X-ray diffraction (XRD) analysis is used to confirm crystal structure and purity of TiN film. The effect of various N-2 pressure on resistivity and hardness of TiN thin film is investigated. The resistivity of the film decreases and hardness increases with N-2 pressure.

RF MEMS ohmic switches are prone to stiction and contact degradation. In literature, bumps are made at the contact area to reduce stiction with additional fabrication steps. In this article, ohmic switch based on cantilever configuration is developed without using any additional step. The switch structure is modified to improve its mechanical parameters, such as pull-in voltage and switching speed. The measured switching time of the switch is 1.8 mu s. A footprint of the developed single pole single throw (SPST) switch is 0.9 mm(2). The insertion loss and isolation of the SPST switch are better than 0.8 and 20 dB, respectively. The switch has a wide bandwidth of 10 GHz (dc to 10 GHz). The switch has completed 725 million hot cycles at 1-dBm power.

This paper presents the design and fabrication of MEMS based electro-thermally actuated square membrane/plate with gold and silicon dioxide bimorph beams. The main objective of this work is to generate a suspended bimorph structure for tunable cavity filters and resonators. A surface micromachining process has been employed in which bimorph structure is suspended by removing underneath sacrificial layer of photoresist through dry and wet etching. A major fabrication challenge is the release of square plate bimorph structure. Increase in temperature during subsequent processing steps cause excessive baking of photoresist. The possible reason of the hard sacrificial resist is baking beyond its thermal budget. Active layer of silicon dioxide utilized as a reinforcing layer during release. In the proposed process, over etched silicon dioxide and presence of sacrificial resist leads to process failure. Controlled thermal budget of sacrificial resist is essential for fully suspended structure.

Here, we report on the experimental and theoretical understanding of seamless junction Au mesh network flexible transparent heaters. Three Au mesh transparent conductors (TCs) are fabricated using the photolithography-etching process to compare the influence of metal surface coverage on their electrical and thermal performance. The fabricated mesh networks are quite transparent (T similar to 80%) in the 400-900 nm spectral region and exhibit small variation in sheet resistance (Delta R-max similar to 0.12, 0.05, and 0.22 Omega square(-1)) under different bending radii (minimum radii of similar to 7.5 mm). The Au mesh with large surface coverage (i.e. similar to 4.8%) exhibited the highest figure of merit (1035), and the Au mesh with small surface coverage (i.e. similar to 2.5%), which eventually tested as a heater, exhibited the highest thermal efficiency (i.e. 249 degrees C/(W/cm(2))) and temperature of 150 degrees C at the lowest input power (0.5 W cm(-2)). A 1D analytical heat transfer model is developed for quick estimation of temperature of heater samples. The thermal simulation of heaters is carried out using an ANSYS tool. The experimental, simulation and 1D analytical results are compared and validated, revealing that the simulation results are more aligned with experimental results. The flexible TCs with short response time and high thermal resistance are very useful in various flexible heating applications.

Packaging is one of the most critical tasks for MEMS devices. Unlike solid state devices, MEMS structures involves moving structures which needs to be protected from outer environment ensuring free movement of the structure. In the present paper, inverted silicon cavity is used for capping the MEMS devices. However, in case of RF MEMS, silicon cavity would add parasitics and affects its electrical performance. Enclosing the MEMS structure, its mechanical response will also alter. The electrical as well as mechanical characteristics of the RF MEMS switch are analyzed using finite element method simulations. The electrical response of the fabricated switch after packaging is compared with unpackaged device.

Fifth generation (5G) communication system enables the pathway for a higher data transfer rate. The frequency bands used for 5G communication system are distributed from lower frequency range (600 MHz) to a higher frequency range (60 GHz). So it is necessary that a single switch should be able to cover the complete range of 5G frequency bands. The ohmic radio frequency-micro electromechanical system (RF-MEMS) switch has offered high isolation at lower frequencies (> 40 dB up to 2.5 GHz). However, 5G requires a higher frequency range which is covered by capacitive switch. The capacitive switch has limitations of limited bandwidth and large size. In this paper, a hybrid technique is used for the designing of a compact, high isolation and the enhanced bandwidth SPDT RF MEMS switch for 5G applications. The size of the proposed switch is half from the conventional capacitive RF MEMS switch and offer greater than 40 dB isolation over a wide frequency range (> 40 dB over 22.10 GHz bandwidth) with less than 0.30 dB insertion loss over the entire band.

Pyroelectric infrared sensors utilize interfacial polymer bonding, thick porous silica layer and Si3N4 thin film as conventional methods of reducing heat sinking with substrate. The thick polymer and porous silica layers cause additional enhancement in thermal time constant (τ D ) as well thermal mass (C th ) of pyroelectric sensor which reduces the rate of temperature change (dT/dt) and limits responsivity at lower frequencies. The SiO2 thin layer posses lower heat conductivity than Si3N4 thin films and often used in Si bulk micromachining as etch barrier. This paper proposes use of micromachined SiO2 thin membrane as thermal insulation layer in bulk micromachined pyroelectric infrared sensor. The study is supported by the comparative radiation heat transfer, finite element analysis and the practical thermal measurements on fabricated pyroelectric infrared sensor using non destructive thermal imaging method.

RF MEMS switches have moving microstructures which are realized either by dry release method or by wet releasing process. In dry release process, suspended bridges gets curled up due to high process temperature while in wet release method, surface of the released devices is get contaminated which affects the final performance of the device. In this paper, a mixed release process of wet and dry is presented to release the stiction free suspended microstructures. Contamination from the devices is removed by plasma cleaning. Isolation of the device under test has been improved to 22 from 15 dB after plasma exposure.