Showing papers in "IEEE\/ASME Journal of Microelectromechanical Systems in 2011"
TL;DR: In this paper, a piezoelectric MEMS energy harvesting cantilever with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized, where the whole chip was assembled onto a metal carrier with a limited spacer such that the operation frequency bandwidth can be widened to 17 Hz at the input acceleration of 1.0 g during frequency upsweep.
Abstract: A piezoelectric MEMS energy harvester (EH) with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized. The MEMS piezoelectric energy harvesting cantilever consists of a silicon beam integrated with piezoelectric thin film (PZT) elements parallel-arranged on top and a silicon proof mass resulting in a low resonant frequency of 36 Hz. The whole chip was assembled onto a metal carrier with a limited spacer such that the operation frequency bandwidth can be widened to 17 Hz at the input acceleration of 1.0 g during frequency up-sweep. Load voltage and power generation for different numbers of PZT elements in series and in parallel connections were compared and discussed based on experimental and simulation results. Moreover, the EH device has a wideband and steadily increased power generation from 19.4 nW to 51.3 nW within the operation frequency bandwidth ranging from 30 Hz to 47 Hz at 1.0 g. Based on theoretical estimation, a potential output power of 0.53 μW could be harvested from low and irregular frequency vibrations by adjusting the PZT pattern and spacer thickness to achieve an optimal design.
332 citations
TL;DR: The Parametric Frequency-Increased Generator (PFIG) as mentioned in this paper utilizes three magnetically coupled mechanical structures to initiate high-frequency mechanical oscillations in an electromechanical transducer.
Abstract: This paper presents a new inertial power generator for scavenging low-frequency nonperiodic vibrations called the Parametric Frequency-Increased Generator (PFIG). The PFIG utilizes three magnetically coupled mechanical structures to initiate high-frequency mechanical oscillations in an electromechanical transducer. The fixed internal displacement and dynamics of the PFIG allow it to operate more effectively than resonant generators when the ambient vibration amplitude is higher than the internal displacement limit of the device. The design, fabrication, and testing of an electromagnetic PFIG are discussed. The developed PFIG can generate a peak power of 163 μW and an average power of 13.6 μW from an input acceleration of 9.8 m/s2 at 10 Hz, and it can operate at frequencies up to 65 Hz, giving it an unprecedented operating bandwidth and versatility. The internal volume of the generator is 2.12 cm3 (3.75 cm3 including the casing). The harvester has a volume figure of merit of 0.068% and a bandwidth figure of merit of 0.375%. These values, although seemingly low, are the highest reported in the literature for a device of this size and operating in the difficult frequency range of ≤ 20 Hz.
169 citations
TL;DR: In this paper, the authors presented the successful fabrication of capacitive micromachined ultrasonic transducers (CMUTs) with an improved insulation layer structure, which is based on consecutive thermal oxidation steps, on local oxidation of silicon (LOCOS), and on direct wafer bonding.
Abstract: We present the successful fabrication of capacitive micromachined ultrasonic transducers (CMUTs) with an improved insulation layer structure. The goal is to improve device reliability (electrical breakdown) and device performance (reduced parasitic capacitance). The fabrication is based on consecutive thermal oxidation steps, on local oxidation of silicon (LOCOS), and on direct wafer bonding. No chemical-mechanical polishing step is required during the device fabrication. Aside from the advantages associated with direct wafer bonding for CMUT fabrication (simple fabrication, cell shape flexibility, wide gap height range, good uniformity, well-known material properties of single-crystal materials, and low intrinsic stress), the main vertical dimension (electrode separation) is determined by thermal oxidation only, which provides excellent vertical tolerance control ( <;10 nm) and unprecedented uniformity across the wafer. Thus, we successfully fabricated CMUTs with gap heights as small as 40 nm with a uniformity of ±2 nm over the entire wafer. This paper demonstrates that reliable parallel-plate electrostatic actuators and sensors with gap heights in the tens of nanometer range can be realized via consecutive thermal oxidation steps, LOCOS, and direct wafer bonding without chemical-mechanical polishing steps.
115 citations
TL;DR: In this paper, the authors investigate the usefulness of softening springs in a microelectromechanical system electrostatic energy harvester under colored noise vibrations and show that the nonlinear harvesters has performance benefits when the vibration's center frequency varies in the frequency range of its softening response.
Abstract: We experimentally investigate the usefulness of softening springs in a microelectromechanical systems electrostatic energy harvester under colored noise vibrations. It is shown that the nonlinear harvester has performance benefits when the vibration's center frequency varies in the frequency range of its softening response. With a vibration 3-dB bandwidth of 50 Hz, less than 3-dB variation in output power can be obtained over a 85-Hz wide range of vibration center frequencies. Compared to a simulated linear-spring device, the nonlinear device gives more output power for a wide range of vibration bandwidths. The nonlinear device shows less than 1-dB variation in output power when the vibration bandwidth varies from 12 to 120 Hz and is centered on the resonant frequency.
115 citations
TL;DR: In this article, an analytical expression for the electrostatic force generated between the combs of the rotor and the stator is derived and takes into account both the transverse and longitudinal capacitances present.
Abstract: This paper studies analytically and numerically the spring softening and hardening phenomena that occur in electrostatically actuated microelectromechanical systems comb drive resonators utilizing folded suspension beams. An analytical expression for the electrostatic force generated between the combs of the rotor and the stator is derived and takes into account both the transverse and longitudinal capacitances present. After formulating the problem, the resulting stiff differential equations are solved analytically using the method of multiple scales, and a closed-form solution is obtained. Furthermore, the nonlinear boundary value problem that describes the dynamics of inextensional spring beams is solved using straightforward perturbation to obtain the linear and nonlinear spring constants of the beam. The analytical solution is verified numerically using a Matlab/Simulink environment, and the results from both analyses exhibit excellent agreement. Stability analysis based on phase plane trajectory is also presented and fully explains previously reported empirical results that lacked sufficient theoretical description. Finally, the proposed solutions are, once again, verified with previously published measurement results. The closed-form solutions provided are easy to apply and enable predicting the actual behavior of resonators and gyroscopes with similar structures.
112 citations
TL;DR: In this article, a polymer-based flat heat pipe (PFHPs) with a thickness on the order of 1 mm have been successfully developed and tested, and a copper micropillar/woven mesh hybrid wicking structure was designed and fabricated to promote evaporation/condensation heat transfer and the liquid supply to the evaporator.
Abstract: In this paper, polymer-based flat heat pipes (PFHPs) with a thickness on the order of 1 mm have been successfully developed and tested. Liquid-crystal polymer (LCP) films with copper-filled thermal vias are employed as the case material. A copper micropillar/woven mesh hybrid wicking structure was designed and fabricated to promote evaporation/condensation heat transfer and the liquid supply to the evaporator of the PFHP. Water was selected as the working fluid because of its superior thermophysical properties. An experimental study was conducted to examine the PFHP performance. The test data demonstrated that the PFHP can operate with a heat flux of 11.94 W/cm2 and results in effective thermal conductivity ranging from 650 to 830 W/m · K, with the value varying with the input heat flux and the tilt angle. With the employment of flexible LCP as casing material, the PFHP could potentially be directly integrated into a printed circuit board or flexible circuits for thermal management of heat-generating components.
98 citations
TL;DR: In this article, a microelectromechanical system (MEMS) device for simultaneous electrical and mechanical characterization of individual nanowires is presented, which is capable of acquiring all measurement data (force and displacement) electronically without relying on electron microscopy imaging.
Abstract: This paper presents a microelectromechanical systems (MEMS) device for simultaneous electrical and mechanical characterization of individual nanowires. The device consists of an electrostatic actuator and two capacitive sensors, capable of acquiring all measurement data (force and displacement) electronically without relying on electron microscopy imaging. This capability avoids the effect of electron beam (e-beam) irradiation during nanomaterial testing. The bulk-microfabricated devices perform electrical characterization at different mechanical strain levels. To integrate individual nanowires to the MEMS device for testing, a nanomanipulation procedure is developed to transfer individual nanowires from their growth substrate to the device inside a scanning electron microscope. Silicon nanowires are characterized using the MEMS device for their piezoresistive as well as mechanical properties. It is also experimentally verified that e-beam irradiation can significantly alter the characterization results and must be avoided during testing.
96 citations
TL;DR: A review of the wafer-to-wafer alignment used for 3D integration can be found in this article, where a comprehensive review of current research activities over wafer to wafer alignment, including alignment methods, accuracy requirements, and possible misalignments and fundamental issues are discussed.
Abstract: This paper presents a review of the wafer-to-wafer alignment used for 3-D integration. This technology is an important manufacturing technique for advanced microelectronics and microelectromechanical systems, including 3-D integrated circuits, advanced wafer-level packaging, and microfluidics. Commercially available alignment tools provide prebonding wafer-to-wafer misalignment tolerances on the order of 0.25 μm. However, better alignment accuracy is required for increasing demands for higher density of through-strata vias and bonded interstrata vias, whereas issues with wafer-level alignment uniformity and reliability still remain. Three-dimensional processes also affect the alignment accuracy, although the misalignment could be reduced to certain extent by process control. This paper provides a comprehensive review of current research activities over wafer-to-wafer alignment, including alignment methods, accuracy requirements, and possible misalignments and fundamental issues. Current misalignment concerns of the major bonding approaches are discussed with detailed alignment results. The fundamental issues associated with wafer alignment are addressed, such as alignment mechanisms, uniformity, reproducibility, thermal mismatch, and materials. Alternative alignment approaches are discussed, and perspectives for wafer-to-wafer alignment are given.
84 citations
TL;DR: In this article, a new way to design MEMS (microelectromechanical system) metal contact switches for RF applications using miniature MEMS cantilevers was presented, and a single 25 × 25 μm switch was first demonstrated with a Au-to-Ru contact, Cu = 5 fF and Ron = 7 Ω at an actuation voltage of 55 V. The measured switching time is 2.2 μs and the release time is <;1 μs.
Abstract: This paper presents a new way to design MEMS (microelectromechanical system) metal contact switches for RF applications using miniature MEMS cantilevers. A single 25 × 25 μm switch is first demonstrated with a Au-to-Ru contact, Cu = 5 fF and Ron = 7 Ω at an actuation voltage of 55 V. The measured switching time is 2.2 μs and the release time is <;1 μs. The switch is robust to stress effects (residual and stress gradients) which increases its yield on large wafers. To reduce the effective switch resistance, 10-20 miniature RF MEMS switches have been placed in parallel and result in equal current division between the switches, an up-state capacitance of 30-65 fF and a down-state resistance of 1.4-1.5 Ω. Furthermore, 10-20 element back-to-back switch arrays are developed and result in a marked improvement in the reliability of the overall switching device. A series-shunt design is also demonstrated with greatly improved isolation. The device has a figure-of-merit of fc = 1/(2πRonCu) = 3.8 THz (RonCu = 42 fs).
79 citations
TL;DR: In this paper, a novel high-density CMOS-based silicon microprobe array for intracortical recording applications is presented. But instead of performing a mechanical translation of the probe shaft relative to the brain tissue to optimize the distance between electrodes and neurons, the electrode position is adjusted by electronically switching between the different electrodes along the shaft.
Abstract: This paper reports on a novel high-density CMOS-based silicon microprobe array for intracortical recording applications. In contrast to existing systems, CMOS multiplexing units are integrated directly on the slender, needle-like probe shafts. Single-shaft probes and four-shaft combs have been realized with 188 and 752 electrodes, respectively, with a pitch of 40 μm arranged in two columns along 4-mm-long probe shafts. Rather than performing a mechanical translation of the probe shaft relative to the brain tissue to optimize the distance between electrodes and neurons, the electrode position is adjusted by electronically switching between the different electrodes along the shaft. The paper presents the probe concept, the CMOS circuitry design, the applied post-CMOS fabrication process, and the assembled probe systems.
78 citations
TL;DR: In this article, a blow molding method based on thermoplastic forming of bulk metallic glasses (BMGs) is used to fabricate 3D microshells, which are attached to the Si wafer through mechanical locking, which is achieved in the same processing step.
Abstract: A blow molding method based on thermoplastic forming of bulk metallic glasses (BMGs) is used to fabricate 3-D microshells. The 3-D microshells are attached to the Si wafer through mechanical locking, which is achieved in the same processing step. Versatile sizes and shapes of the 3-D shells can be precisely controlled. High strength ( >; 1 GPa), elasticity (~ 2%), and controlled surface roughness (<; 2 nm), which are achievable for BMGs, suggest their potential use in devices, including resonators, microlenses, microfluidic, and packaging.
TL;DR: An entirely passive and wireless microsystem for recording neuropotential signals and results were wireless recovery of neuropotentials as low as approximately 500 microvolts peak-to-peak (μVpp) and with 128 epoch signal averaging of repetitive signals.
Abstract: The ability to safely monitor neuropotentials is essential in establishing methods to study the brain. Current research focuses on the wireless telemetry aspect of implantable sensors in order to make these devices ubiquitous and safe. Chronic implants necessitate superior reliability and durability of the integrated electronics. The power consumption of implanted electronics must also be limited to within several milliwatts to microwatts to minimize heat trauma in the human body. In order to address these severe requirements, we developed an entirely passive and wireless microsystem for recording neuropotentials. An external interrogator supplies a fundamental microwave carrier to the microsystem. The microsystem comprises varactors that perform nonlinear mixing of neuropotential and fundamental carrier signals. The varactors generate third-order mixing products that are wirelessly backscattered to the external interrogator where the original neuropotential signals are recovered. Performance of the neurorecording microsystem was demonstrated by wireless recording of emulated and in vivo neuropotentials. The obtained results were wireless recovery of neuropotentials as low as approximately 500 microvolts peak-to-peak (μVpp) with a bandwidth of 10 Hz to 3 kHz (for emulated signals) and with 128 epoch signal averaging of repetitive signals (for in vivo signals).
TL;DR: In this paper, the authors used pressure and surface tension driven plastic deformation (glassblowing) on a wafer scale as a mechanism for creating inherently smooth and symmetric 3D resonant structures.
Abstract: This paper introduces a new paradigm for design and batch fabrication of isotropic 3-D spherical shell resonators. The approach uses pressure and surface tension driven plastic deformation (glassblowing) on a wafer scale as a mechanism for creating inherently smooth and symmetric 3-D resonant structures. The feasibility of the new approach was demonstrated by fabrication and characterization of Pyrex glass spherical shell resonators with millimeter-scale diameter and average thickness of 10 μm . Metal electrodes cofabricated along with the shell were used to actuate the two dynamically balanced four- and six-node vibratory modes. For 1-MHz glass-blown resonators, the relative frequency mismatch Δf/f between the two degenerate four-node wineglass modes was measured as 0.63% without any trimming or tuning. For the higher order six-node wineglass modes, the relative frequency mismatch was only 0.2%, demonstrating the potential for precision manufacturing. The intrinsic manufacturing symmetry enabled by the technology may inspire new classes of high-performance 3-D MEMS for communication and inertial navigation.
TL;DR: In this article, a complementary metal-oxide-semiconductor compatible fabrication technique for ultrathin silicon chips of arbitrary shape is reported, which combines deep reactive ion etching and wafer grinding to define the in-plane geometry and thickness of the chips, respectively.
Abstract: A complementary-metal-oxide-semiconductor-compatible fabrication technique for ultrathin silicon chips of arbitrary shape is reported. It combines deep reactive ion etching and wafer grinding to define the in-plane geometry and thickness of the chips, respectively. Neural probes with shaft lengths up to 12 mm and thicknesses down to 25 μm were fabricated.
TL;DR: In this article, a microelectromechanical system (MEMS) Lorentz force navigation magnetometer whose fabrication is fully compatible with existing foundry processes used to manufacture MEMS inertial sensors was presented.
Abstract: This paper describes a microelectromechanical systems (MEMS) Lorentz force navigation magnetometer whose fabrication is fully compatible with existing foundry processes used to manufacture MEMS inertial sensors. Operating at 1 atm, the magnetometer is shown to have a Brownian-noise-limited field resolution of 87 nT/√Hz and a corresponding angular resolution of 0.7°/√Hz. To achieve Brownian-noise-limited performance at 1 atm, parametric amplification was performed which amplifies the Lorentz force 40% more than the Brownian noise force and increases the field sensitivity of the device up to 82.5 folds. Here, the parametric signal is also used to perform electromechanical amplitude modulation to mitigate capacitive feedthrough of the drive signal to the sensing electronics.
TL;DR: In this article, a 4H-SiC micronuclear battery with a Schottky barrier diode was used for carrier separation and a theoretical model was derived to predict the output electrical power.
Abstract: Based on the betavoltaic and alphavoltaic effects, a 4H-SiC micronuclear battery was demonstrated. A Schottky barrier diode, in place of the previously used p-n junction diode, was utilized for carrier separation. A theoretical model was derived to predict the output electrical power. Using beta radioisotope 63Ni and alpha radioisotope 241Am as the radiation sources, the micro nuclear battery was tested and proved to be effective to transfer decay energy into electrical power. The experimental results show that the theoretical model can basically predict the performance of the micronuclear battery. Although the energy conversion efficiencies under illumination of 63Ni and 241Am are only 0.5% and 0.1% at current status, an improvement by an order of magnitude can be expected if the doping concentration of the epilayer can be decreased to the optimal value.
TL;DR: In this paper, the authors describe the fabrication, characterization, and modeling of complementary metal-oxide-semiconductor (CMOS)-compatible capacitive micromachined ultrasound transducers (CMUTs).
Abstract: This paper describes the fabrication, characterization, and modeling of complementary metal-oxide-semiconductor (CMOS)-compatible capacitive micromachined ultrasound transducers (CMUTs). The transducers are fabricated using the interconnect and dielectric layers from a standard CMOS fabrication process. Unlike previous efforts toward integrating CMUTs with CMOS electronics, this process adds no microelectromechanical systems-related steps to the CMOS process and requires no critical lithography steps after the CMOS process is complete. Efficient computational models of the transducers were produced through the combined use of finite-element analysis and lumped-element modeling. A method for improved computation of the electrostatic coupling and environmental loading is presented without the need for multiple finite-element computations. Through the use of laser Doppler velocimetry, transient impulse response and steady-state frequency sweep tests were performed. These measurements are compared to the results predicted by the models. The performance characteristics were compared experimentally through changes in the applied bias voltage, device diameter, and medium properties (air, vacuum, oil, and water). Sparse clusters of up to 33 elements were tested in transmit mode in a water tank, achieving a center frequency of 3.5 MHz, a fractional bandwidth of 32%-44%, and pressure amplitudes of 181-184 dB re 1 μParms at 15 mm from the transducer on axis.
TL;DR: In this article, the authors presented the design, fabrication, and characterization of thermal infrared imaging arrays operating at room temperature which are based on Y-cut-quartz bulk acoustic wave resonators.
Abstract: This paper presents the design, fabrication, and characterization of thermal infrared (IR) imaging arrays operating at room temperature which are based on Y-cut-quartz bulk acoustic wave resonators. A novel method of tracking the resonance frequency based upon the measurement of impedance is presented. High-frequency (240-MHz) micromachined resonators from Y-cut-quartz crystal cuts were fabricated using heterogeneous integration techniques on a silicon wafer. A temperature sensitivity of 22.16 kHz/°C was experimentally measured. IR measurements on the resonator pixel resulted in a noise equivalent power of 3.90 nW/Hz1/2, a detectivity D* of 1 × 105 cm · Hz1/2/W, and a noise equivalent temperature difference of 4 mK in the 8- to 14-μm wavelength range. The thermal frequency response of the resonator was determined to be faster than 33 Hz, demonstrating its applicability in video-rate uncooled IR imaging. This work represents the first comprehensive thermal characterization of micromachined F-cut-quartz resonators and their IR sensing response.
TL;DR: In this paper, the authors experimentally demonstrate stable operation of these oscillators far beyond the critical vibration amplitude, and demonstrate that open-loop resonators can operate far beyond this amplitude.
Abstract: In microelectromechanical systems resonators, nonlinear operation is feasible, but instabilities can arise if open-loop resonators operate above the critical vibration amplitude. This fact has led to a reluctance to operate resonator-based oscillators above this amplitude. This study experimentally demonstrates stable operation of these oscillators far beyond the critical vibration amplitude.
TL;DR: In this article, a high quality-factor (Q) film bulk acoustic resonator (FBAR) operating in liquid environments is reported, which can achieve a Q of up to 150 with direct liquid contacting.
Abstract: We report a high-quality-factor (Q) film bulk acoustic resonator (FBAR) operating in liquid environments. By integrating a microfluidic channel to a longitudinal-mode FBAR, a Q of up to 150 is achieved with direct liquid contacting. A transmission line model is used to theoretically predict the Q behavior of the FBAR. The model suggests an oscillatory pattern of Q as a function of the channel thickness and the acoustic wavelength in the liquid, which is experimentally verified by precisely controlling the channel thickness. This FBAR biosensor is characterized in liquids for the real-time in situ monitoring of the competitive adsorption/exchange of proteins, the Vroman effect. The FBAR offers a minimum detectable mass of 1.35 ng/cm2 and is successfully implemented in a Pierce oscillator as a portable sensing module.
TL;DR: In this paper, a piezoelectric shunt control is used to control the damping of an AFM microcantilever to improve the scan rate and image resolution.
Abstract: The scan rate and image resolution of the atomic force microscope (AFM) operating in tapping-mode may be im proved by modifying the quality (Q) factor of the AFM micro cantilever according to the sample type and imaging environment. Piezoelectric shunt control is a new method of controlling the Q factor of a piezoelectric self-actuating AFM microcantilever. The mechanical damping of the microcantilever is controlled by an electrical impedance placed in series with the tip oscillation circuit. A synthetic impedance was designed to allow easy modification of the control parameters which may vary with environmental conditions. The proposed techniques are experimentally demonstrated to reduce the Q factor of an AFM microcantilever from 297.6 to 35.5. AFM images obtained using this method show significant improvement in both scan rate and image quality.
TL;DR: In this article, the authors report the development of piezoresistive accelerometers based on an asymmetrically gapped cantilever which is composed of a bottom mechanical layer and a top piezoreistive layer separated by a gap.
Abstract: This paper reports the development of piezoresistive accelerometers based on an asymmetrically gapped cantilever which is composed of a bottom mechanical layer and a top piezoresistive layer separated by a gap. The asymmetrically gapped cantilever helps to increase the sensitivity and enables the majority of mechanical energy to be effectively used to strain the piezoresistive layer. An analytic model of the asymmetrically gapped cantilever was developed and verified using finite-element simulation. Design optimization was discussed based on the analytical model. A figure of merit was defined as the product of the signal-to-noise ratio and resonant frequency. It was demonstrated that the energy efficiency is a critical criterion of design optimization. The prototypes of the piezoresistive accelerometer were successfully fabricated using deep reactive-ion etching from both the front and back sides of silicon-on-insulator wafers. The fabricated devices were preliminarily characterized. A sensitivity of 0.36 mV/V/g and a fundamental resonant frequency of 4060 Hz were obtained. The noise of the fabricated device was also measured and analyzed.
TL;DR: In this paper, a floating-element-based capacitively sensed direct wall-shear-stress sensor was developed for measurements in a turbulent boundary layer. The design principle is presented, followed by details of the fabrication, packaging, and characterization process.
Abstract: This paper presents the development of a floating-element-based capacitively sensed direct wall-shear-stress sensor intended for measurements in a turbulent boundary layer. The design principle is presented, followed by details of the fabrication, packaging, and characterization process. The sensor is designed with an asymmetric comb finger structure and metalized electrodes. The fabrication process uses deep reactive ion etching on a silicon-on-insulator wafer, resulting in a simple two-mask fabrication process. The sensor is dynamically characterized with acoustically generated Stokes layer excitation. At a bias voltage of 10 V, the sensor exhibits a linear dynamic sensitivity of 7.66 mV/Pa up to the testing limit of 1.9 Pa, a flat frequency response with resonance at 6.2 kHz, and a pressure rejection of 64 dB. The sensor has a noise floor of 14.9 μPa/√(Hz) at 1 kHz and a dynamic range >;102 dB. The sensor outperforms previous sensors by nearly two orders of magnitude in noise floor and an order of magnitude in dynamic range.
TL;DR: In this paper, a planar rotating probe was developed for residual stress analysis to split the stress into the following two components: 1) the gradient residual stress (σ1) related to the film defects and 2) the uniform stress (λ 0) related with the substrate.
Abstract: SiC is a candidate material for microelectromechanical and nanoelectromechanical systems, but the high residual stress created during the film grow limits the development of the material for these applications. To understand the stress relaxation mechanism in hetero-epitaxial 3C-SiC films, different micromachined free-standing structures have been realized. In this paper, assisted by finite-element method (FEM), a micromachined planar rotating probe was developed for residual stress analysis to split the stress into the following two components: 1) the gradient residual stress (σ1) related to the film defects and 2) the uniform stress (σ0) related to the substrate. Transmission electron microscopy characterization studies about the defect formation and the defect evolution as a function of thickness on 3C-SiC on the Si substrate revealed the problems due to the incorrect linear stress approximation in a heteroepitaxial thin film. With FEM, an exponential approximation of the stress relationship was studied, yielding a better fit with the experimental data. This paper shows that the new approximation of the total residual stress function reduces the actual disagreement between experimental and simulation data.
TL;DR: In this paper, a lead zirconate titanate (PZT) microelectromechanical systems (MEMS) digital switch was designed as a low-power low-frequency control system intended to create energy-efficient microcontrollers, control higher voltage systems, and provide integrated control over other MEMS platforms.
Abstract: A lead zirconate titanate (PZT) microelectromechanical systems (MEMS) digital switch was designed as a low-power low-frequency control system intended to create energy-efficient microcontrollers, control higher voltage systems, and provide integrated control over other MEMS platforms. In addition, the technology is inherently insensitive to high energy radiation and has been shown to operate over a wide range of temperatures. Initial devices were fabricated with three design variables of interest-actuator length, width, and contact metallurgy (Au/Pt, Au/Ru, and Au/Au). To assess the impact of each variable on device performance, device wafers were measured using a SUSS semiautomated probe station and associated control hardware and software. Devices were evaluated based on contact resistance, actuation voltage, minimum actuation voltage using a voltage bias, propagation delay, dynamic power, and static power consumption. The measurements were then analyzed to determine the optimal switch geometry and contact material combination for digital applications. With the data collected, a software model was developed for accurate simulation of higher complexity circuits composed of these switches.
TL;DR: In this article, a compositional, structural, and electrical characterization of the TaN and Ta2O5 films is preliminarily performed, demonstrating that they are valid alternatives to the conventional materials used in III-V technology for RF MEMS switches.
Abstract: In this paper, shunt capacitive RF microelectromechanical systems (MEMS) switches are developed in III-V technology using tantalum nitride (TaN) and tantalum pentoxide (Ta2O5) for the actuation lines and the dielectric layers, respectively. A compositional, structural, and electrical characterization of the TaN and Ta2O5 films is preliminarily performed, demonstrating that they are valid alternatives to the conventional materials used in III-V technology for RF MEMS switches. Specifically, it is found that the TaN film resistivity can be tuned from 0.01 to 30 Ω · cm by changing the deposition parameters. On the other hand, dielectric Ta2O5 films show a low leakage current density of few nanoamperes per square centimeter for E ~ 1 MV/cm, a high breakdown field of 4 MV/cm, and a high dielectric constant of 32. The realized switches show good actuation voltages, in the range of 15-20 V, an insertion loss better than -0.8 dB up to 30 GHz, and an isolation of ~-40 dB at the resonant frequency, which is, according to bridge length, between 15 and 30 GHz. A comparison between the measured S-parameter values and the results of a circuit simulation is also presented and discussed, providing useful information on the operation of the fabricated switches.
TL;DR: In this article, the authors demonstrate the first high-resolution spatial-light-modulator chip with 1 million tilting micromirrors made of monocrystalline silicon on analog highvoltage complementary metal-oxide-semiconductor driving electronics.
Abstract: In this paper, we demonstrate the first high-resolution spatial-light-modulator chip with 1 million tilting micromirrors made of monocrystalline silicon on analog high-voltage complementary metal-oxide-semiconductor driving electronics. This device, as result of a feasibility study, shows good optical and excellent mechanical properties. The micromirrors exhibit excellent surface properties, with a surface roughness below 1-nm root mean square. Actuated micromirrors show no imprinting behavior and operate drift free. Very large-scale heterogeneous integration was used to fabricate the micromirror arrays. The detailed fabrication process is presented in this paper, together with a characterization of the SLM devices. Large arrays of individually controllable micromirrors are the enabling component in high-perfomance mask-writing systems and promising for high throughput deep-ultraviolet maskless lithography systems. The adoption of new materials with enhanced characteristics is critical in meeting the challenging demands with regard to surface quality and operation stability in the future. Very large-scale heterogeneous integration may enable virtually any solid-state material to be integrated together with CMOS electronics.
TL;DR: In this paper, the authors used two recently developed high-throughput MEMS tensile test techniques to estimate strength distribution tails by testing approximately 1500 tensile bars and found that the micromachined polycrystalline silicon that was tested in this paper has a lower bound to its tensile strength.
Abstract: Designing reliable MEMS structures presents numerous challenges. Polycrystalline silicon fractures in a brittle manner with considerable variability in measured strength. Furthermore, it is not clear how to use measured tensile strength data to predict the strength of a complex MEMS structure. To address such issues, two recently developed high-throughput MEMS tensile test techniques have been used to estimate strength distribution tails by testing approximately 1500 tensile bars. There is strong evidence that the micromachined polycrystalline silicon that was tested in this paper has a lower bound to its tensile strength (i.e., a strength threshold). Process-induced sidewall flaws appear to be the main source of the variability in tensile strength. Variations in as-fabricated dimensions, stress inhomogeneity within a polycrystal, and variations in the apparent fracture toughness do not appear to be dominant contributors to tensile strength variability. The existence of a strength threshold implies that there is maximum flaw size, which consequently enables a linear elastic fracture mechanics flaw-tolerance analysis. This approach was used to estimate a lower bound for the strength of a double edge-notched specimen that compared favorably with our measured values.
TL;DR: The half-power bandwidth formula used for measurement of quality factor Q does not apply for nonlinear systems that have jump discontinuities in their frequency responses, since one of the half power amplitudes is not observable as mentioned in this paper.
Abstract: The convenient half-power bandwidth formula used for measurement of quality factor Q does not apply for nonlinear systems that have jump discontinuities in their frequency responses, since one of the half-power amplitudes is not observable. This paper shows alternatives to the half-power formula that do apply to such nonlinear systems, while preserving all of the convenience of the method. Their practical use is illustrated by experimental Q measurements for a microelectromechanical systems scanning mirror.
TL;DR: In this article, a capacitive-type CMOS microelectromechanical system tactile sensor containing a capacitance-sensing gap filled with polymer is reported, which can be modulated by the polymer fill-in, so as to further tune its sensing range.
Abstract: This paper reports a capacitive-type CMOSmicroelectromechanical system tactile sensor containing a capacitance-sensing gap filled with polymer. Thus, the equivalent stiffness of the tactile sensor can be modulated by the polymer fill-in, so as to further tune its sensing range. Moreover, the polymer fill-in has a higher dielectric constant to increase the sensitivity of the tactile sensor. In short, the sensing range and sensitivity of the proposed tactile sensor can be easily changed by using the polymer fill-in. In application, the tactile sensor and sensing circuits have been designed and implemented using the 1) TSMC 0.35 μm 2P4M CMOS process and the 2) in-house post-CMOS releasing and polymer-filling processes. The polydimethylsiloxane (PDMS) material with different curing agent ratios has been exploited as the fill-in polymers. The experiment results demonstrate that the equivalent stiffness of tactile sensors can be adjusted from 16.85 to 124.43 kN/m. Thus, the sensitivity of the tactile sensor increases from 1.5 to 42.7 mV/mN by varying the PDMS filling. Moreover, the maximum sensing load is also improved.