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This work proposes a matching data science approach for the laser ablation quality, reb, the study of Si3N4 film based on supervised machine learning classifiers in the CMOS-MEMS process. The study demonstrates that there exists an energy threshold, Eth, for laser ablation. If the laser energy surpasses this threshold, increasing the interval time will not contribute significantly to the recovery of pulse laser energy. Thus, reb enhancement is limited. When the energy is greater than 0.258 mJ, there exists a critical value of interval time at which the reb value is relatively low for each energy level, respectively. In addition, the variation of reb, Δreb, is independent of the interval time at the invariant point of energy between 0.32 mJ and 0.36 mJ. Energy and interval time exhibit a Pearson correlation of 0.82 and 0.53 with reb, respectively. To maintain Δreb below 0.15, green laser ablation of Si3N4 at operating energies of 0.258–0.378 mJ can adopt a baseline interval time of the initial baseline multiplied by 1/∜2. Additionally, for operating energies of 0.288–0.378 mJ during Si3N4 laser ablation, Δreb can be kept below 0.1. With the forced partition methods, namely, the k-means method and percentile method, the XGBoost (v 2.0.3) classifier maintains a competitive accuracy across test sizes of 0.20–0.40, outperforming the machine learning algorithms Random Forest and Logistic Regression, with the highest accuracy of 0.78 at a test size of 0.20. [ABSTRACT FROM AUTHOR]

This work consists of a proposal of a micromotor with a linearly displaced shaft, driven by electrostatic forces designed for CMOS-MEMS technology. Four springs and a set of mobile electrodes make up the body of the micromotor; in turn, a plate whose function is to sense the position is attached to the main body, making the system a closed loop instance. A floating gate MOS transistor (FGMOS) is connected to the sensor plate of the micromotor's body to form the sensing system. The main body is made of a structural layer of aluminum, while a layer of polysilicon is used for the floating gate of the transistor which can operate as the shaft's position sensor. The proposed electronics and microsystem are monolithic, and the substrate is a single silicon wafer. Multiphysics simulations of the micromotor were performed considering a quasi-static case, since it is the one that best suits the behavior of the proposed micromotor, the results of the simulations show good agreement with the theoretical model. [ABSTRACT FROM AUTHOR]

The rational integration of many microfluidic chips and micropumps remains challenging. Due to the integration of the control system and sensors in active micropumps, they have unique advantages over passive micropumps when integrated into microfluidic chips. An active phase-change micropump based on complementary metal–oxide–semiconductor–microelectromechanical system (CMOS-MEMS) technology was fabricated and studied theoretically and experimentally. The micropump structure is simple and consists of a microchannel, a series of heater elements along the microchannel, an on-chip control system, and sensors. A simplified model was established to analyze the pumping effect of the traveling phase transition in the microchannel. The relationship between pumping conditions and flow rate was examined. Based on the experimental results, the maximum flow rate of the active phase-change micropump at room temperature is 22 µL/min, and long-term stable operation can be achieved by optimizing heating conditions. [ABSTRACT FROM AUTHOR]

This work reports the design, modelling, and simulation of a novel polymer MEMS gas sensor platform called a ring–flexure–membrane (RFM) suspended gate field effect transistor (SGFET). The sensor consists of a suspended polymer (SU-8) MEMS based RFM structure holding the gate of the SGFET with the gas sensing layer on top of the outer ring. During gas adsorption, the polymer ring–flexure–membrane architecture ensures a constant gate capacitance change throughout the gate area of the SGFET. This leads to efficient transduction of the gas adsorption-induced nanomechanical motion input to the change in the output current of the SGFET, thus improving the sensitivity. The sensor performance has been evaluated for sensing hydrogen gas using the finite element method (FEM) and TCAD simulation tools. The MEMS design and simulation of the RFM structure is carried out using CoventorWare 10.3, and the design, modelling, and simulation of the SGFET array is carried out using the Synopsis Sentaurus TCAD. A differential amplifier circuit using RFM-SGFET is designed and simulated in Cadence Virtuoso using the lookup table (LUT) of the RFM-SGFET. The differential amplifier exhibits a sensitivity of 2.8 mV/MPa for a gate bias of 3 V and a maximum detection range of up to 1% hydrogen gas concentration. This work also presents a detailed fabrication process integration plan to realize the RFM-SGFET sensor using a tailored self-aligned CMOS process adopting the surface micromachining process. [ABSTRACT FROM AUTHOR]

This work proposes a matching data science approach for the laser ablation quality, reb, the study of Si3N4 film based on supervised machine learning classifiers in the CMOS-MEMS process. The study demonstrates that there exists an energy threshold, Eth, for laser ablation. If the laser energy surpasses this threshold, increasing the interval time will not contribute significantly to the recovery of pulse laser energy. Thus, reb enhancement is limited. When the energy is greater than 0.258 mJ, there exists a critical value of interval time at which the reb value is relatively low for each energy level, respectively. In addition, the variation of reb, Δreb, is independent of the interval time at the invariant point of energy between 0.32 mJ and 0.36 mJ. Energy and interval time exhibit a Pearson correlation of 0.82 and 0.53 with reb, respectively. To maintain Δreb below 0.15, green laser ablation of Si3N4 at operating energies of 0.258–0.378 mJ can adopt a baseline interval time of the initial baseline multiplied by 1/∜2. Additionally, for operating energies of 0.288–0.378 mJ during Si3N4 laser ablation, Δreb can be kept below 0.1. With the forced partition methods, namely, the k-means method and percentile method, the XGBoost (v 2.0.3) classifier maintains a competitive accuracy across test sizes of 0.20–0.40, outperforming the machine learning algorithms Random Forest and Logistic Regression, with the highest accuracy of 0.78 at a test size of 0.20.

Lead (Pb) ion detection poses a critical problem, particularly in environmental monitoring, industrial operations, and public health, especially for young children and expecting women. Determining lead levels in blood early on is essential to minimizing the long-term consequences of lead exposure. Several sophisticated detection instruments, such as mass spectrometers which perform with high sensitivity, specificity and accuracy, but require a lab-based setting, multi-step sample preparation, expensive payment and professional operation. It is evident that a highly sensitive, portable, low-cost, quick sample-to-result, blood lead detection device that can be tested at the point-of-care is necessary. Consequently, we developed a unique ZnO/PEDOT:PSS nanocomposite layer integrated with a CMOS MEMS-based bridge-like membrane-type (BM) nanomechanical sensor for detecting lead levels in blood. PEDOT:PSS was combined with ZnO nanorods to increase lead ion binding. The sensor responds seven times better to lead ions using nanorods in the detecting layer. A linear resistance change rate response was found from 0.005 to 10 ppm, with the limit of detection (LOD) of 0.12 ppb. Similarly, our BM nanomechanical sensor can correctly assess Pb2+ in human serum with recovery rates of 86.25–150 %. Measurements of human blood samples from patients with varying lead ion concentrations validated by the standard AAS show a good linear connection with the BM nanomechanical sensors' concentration, with a regression coefficient of 0.92. This describes the first micromachined nanoachanical sensing system for detection of Pb2+ in only 5 μL of human serum sample. The device achieves a time-to-result of less than 10 min. The system is designed to be very sensitive and offers affordable, disposable sensing chips together with a portable signal acquisition platform. [Display omitted] • BM nanomechanical sensing chips were prepared by utilizing commercial CMOS MEMS standard process. • ZnO-nanorod/PEDOT:PSS nanocomposite as the sensing layer enhances the sensitivity. • The sensor was successfully implemented in the detection of toxic blood lead levels. • Low threshold detection and higher sensitivity. • Point of care devices candidate for the evaluation of toxic metal ions in serum samples. [ABSTRACT FROM AUTHOR]

CMOS-MEMS-based vibro-impact devices that utilize impact-induced nonlinear dynamics have been shown to yield unique and unprecedented functionalities with on-chip integration capability. For example, a 0.35-µm CMOS-based capacitively transduced comb-driven folded-beam resonant switch has been integrated with backend circuits to demonstrate a zero-quiescent power wireless receiver operating at the low-frequency (LF) band. In addition, CMOS-MEMS vibro-impact resonators have been used as AFM-alike surface condition monitoring for detecting chemical coating on structural sidewalls and clock generators with controllable duty cycles by manipulating the actuation conditions. This article will review these achievements and discuss the limitations and challenges in developing the vibro-impact devices using the CMOS-MEMS technology.

Microelectromechanical systems (MEMS) are in widespread commercial use due to their compact size, high performance, and low cost. MEMS resonators have emerged as front runners for sensing (accelerometers, gyroscopes, and particulate matter) and frequency (RF front-end, filters, timing, and frequency source) applications. The excellent stability, resolution, and accuracy of resonators lead them an ideal candidate for sensor implementation. The CMOS-MEMS technology allows for rapid, large-scale, and low-cost manufacturing. Thermal–piezoresistive resonators (TPRs) are promising candidates due to their favorable potential with scaling and robust performance in the ambient environment. A detailed finite element method (FEM) simulation flow is presented along with a mathematical model for device optimization. The devices were fabricated with the commercial CMOS technology utilizing the front-end-of-line (FEOL) polysilicon and back-end-of-line (BEOL) materials like silicon dioxide and interconnect metal. The flexibility of selective material placement in layout and complex routing using multi-metal interconnect is employed to develop a balanced TPR design at 2 MHz. A 5-MHz bulk mode TPR was designed for mass sensing application. The fabricated devices were characterized, and their performance is compared with other state-of-the-art works. Finally, the developed devices were used in real-world applications for mass sensing and pressure sensing. The device achieved 20 kHz/ng. The TPR devices combine principles of Pirani gauge and resonant sensors for improving the sensing range from 2 to 760 Torr (1 atm).

The rational integration of many microfluidic chips and micropumps remains challenging. Due to the integration of the control system and sensors in active micropumps, they have unique advantages over passive micropumps when integrated into microfluidic chips. An active phase-change micropump based on complementary metal–oxide–semiconductor–microelectromechanical system (CMOS-MEMS) technology was fabricated and studied theoretically and experimentally. The micropump structure is simple and consists of a microchannel, a series of heater elements along the microchannel, an on-chip control system, and sensors. A simplified model was established to analyze the pumping effect of the traveling phase transition in the microchannel. The relationship between pumping conditions and flow rate was examined. Based on the experimental results, the maximum flow rate of the active phase-change micropump at room temperature is 22 µL/min, and long-term stable operation can be achieved by optimizing heating conditions.

We present, for the first time, a single-layer plate resonator with specific folded anchors capable of reducing the temperature coefficient of frequency (TCF) by two orders of magnitude compared to straight beams. Folded anchors provide differential strain through either compressive or tensile thermal stress depending on the anchor design and, in turn, allow for positive and negative temperature-induced frequency change components. With a nominal 2 MHz frequency, we experimentally report a frequency shift of 2500 ppm over a temperature span from 0ºC to 90ºC using an optimal anchor folding aspect ratio. The frequency-temperature curve exhibits a turnover point at 27ºC granting a unique opportunity to, in a future application, complement this passive strategy with an active micro-oven for negligible TCF. The proposed approach main advantage relies on its mechanical design-level implementation exploiting a geometrical engineering strategy than can be directly extended to other topologies. This technique reveals as particularly suited for ultra-sensitive mass sensing applications based on microelectromechanical systems (MEMS) resonators where single-layer resonators are optimal thanks to their minimum footprint, attaining minimum mass structures. Results demonstrate that adoption of the proposed folded anchors strategy decreases effectively the thermally induced frequency fluctuations within the system intrinsic noise level. [Display omitted] • Geometrical engineering technique of the resonator anchor design to improve frequency stability with temperature. • Experimental results demonstrating the reduction of the TCF by two orders of magnitude are presented for the first time. • Particularly suited for ultra-sensitive mass sensors based on single-layer resonators to attain minimum mass structures. • Fully compatible with further sophisticated active compensation strategies for finer tuning. [ABSTRACT FROM AUTHOR]

This work reports the design, modelling, and simulation of a novel polymer MEMS gas sensor platform called a ring–flexure–membrane (RFM) suspended gate field effect transistor (SGFET). The sensor consists of a suspended polymer (SU-8) MEMS based RFM structure holding the gate of the SGFET with the gas sensing layer on top of the outer ring. During gas adsorption, the polymer ring–flexure–membrane architecture ensures a constant gate capacitance change throughout the gate area of the SGFET. This leads to efficient transduction of the gas adsorption-induced nanomechanical motion input to the change in the output current of the SGFET, thus improving the sensitivity. The sensor performance has been evaluated for sensing hydrogen gas using the finite element method (FEM) and TCAD simulation tools. The MEMS design and simulation of the RFM structure is carried out using CoventorWare 10.3, and the design, modelling, and simulation of the SGFET array is carried out using the Synopsis Sentaurus TCAD. A differential amplifier circuit using RFM-SGFET is designed and simulated in Cadence Virtuoso using the lookup table (LUT) of the RFM-SGFET. The differential amplifier exhibits a sensitivity of 2.8 mV/MPa for a gate bias of 3 V and a maximum detection range of up to 1% hydrogen gas concentration. This work also presents a detailed fabrication process integration plan to realize the RFM-SGFET sensor using a tailored self-aligned CMOS process adopting the surface micromachining process.

In this paper we present a comprehensive report on the issues found during the manufacturing of high-yield CMOS-MEMS sensors based on vapor-phase hydrogen fluoride (vapor- $HF$ ) oxide etching. During the study we have identified the main issues affecting CMOS-MEMS high-yield manufacturing regarding the silicon oxide as a sacrificial material, the passivation as a release mask, the BEOL as structural material for MEMS design and the aluminum-sputtering as a sealing layer for the MEMS cavity. This study has been carried out by systematically analyzing over 100 full wafers in 10 different runs on four different foundries using ${\mathrm {0.5~ \mu m }}$ , ${\mathrm {0.18~ \mu m }}$ and ${\mathrm {0.15~ \mu m }}$ CMOS processes, containing both test structures and full-sensor designs.

Over the past two decades, the advancement in microelectromechanical systems (MEMS) has been making headway in the development of miniaturized mechanical structures with integrated electronics. By adopting the existing layer in the complementary metal–oxide–semiconductor (CMOS) fabrication platform, the so-called “CMOS-MEMS” technology offers an intrinsic circuit-MEMS integration scheme, paving the way to realize monolithic micromechanical oscillators for frequency control and sensing applications. To enhance the functionality of the oscillator, it is cardinal to understand the secrets behind the resonator and circuit design techniques to generate high spectral purity signals. As the oscillator characteristics heavily depend on the resonator’s motional parameters, the circuit configuration is determined in accordance with the post-CMOS processing technology and the mode shape of the resonator. In this mini-review, we attempt to summarize and appraise studies related to the design and optimization of CMOS-MEMS oscillators and to give directions for future researchers in terms of phase noise.

MEMS accelerometers have been widely used in various applications with a wide range of signal levels and bandwidth. Therefore it is desired to have a sensor whose characteristics such as sensitivity and bandwidth can be reconfigured/tuned depending on specific applications. This paper presents a reconfigurable/tunable z-axis accelerometer whose mechanical resonant frequency, sensitivity and sensing bandwidth can be tuned by the electrostatic spring softening effect. The proposed accelerometer was designed using a commercial 0.35 μm CMOS foundry service. The tuning electrodes were implemented in the metal and polysilicon layers in the standard CMOS process. An on-chip chopper stabilized readout circuit was designed to convert the capacitance signal to a voltage readout. The sensing structure was released by post-CMOS wet metal etching. Measurement results showed the proposed accelerometer had a sensitivity of 12 mV/g in the range of 0–5 g. The sensitivity and bandwidth tuning ranges are 50% and 18%, respectively, for an applied tuning voltage of 25 V. The demonstrated device is the first reconfigurable/tunable CMOS-MEMS accelerometer in the literature to our best knowledge.

Environmental sensing units such as gas sensors, humidity sensors, pressure sensors, PM 2.5 sensors, or temperature sensors are widely used in our daily lives. In this study, CMOS-MEMS technology is exploited to fabricate and monolithically integrate the photo-sensors, temperature sensor, and mechanical structures for an optical gas sensing chip. An LED is bonded (heterogeneous integration) on the CMOS-MEMS chip as an excitation light source, and fluorescence quenching technology is employed for the presented optical gas sensor. Finally, the light emitted from the LED is reflected and redirected onto the CMOS-MEMS chip by using an encapsulated optical reflector to increase the sensitivity and reduce the power consumption for the presented sensor. In applications, the sensing materials are, respectively, mixed with C30H24Cl2N6Ru·6H2O and C16H7Na3O10S3 for O2 and CO2 detection. Moreover, the Si-based (by micromachining) and polymer-based (by 3D printing) optical reflectors are used to encapsulate the sensing chip to demonstrate the presented concept. Measurements show that the LED driving currents for gas sensors with reflectors are significantly reduced. Measurements also indicate that the sensitivities of gas sensors for sensing chips without optical reflectors are, respectively, 0.023 μA/% (O2/N2) and 0.12 μA/% (CO2/N2); for sensing chips with hemispherical shell optical reflectors are, respectively, 0.12 μA/% (O2/N2) and 0.19 μA/% (CO2/N2); and for sensing chips with flat plate optical reflectors are, respectively, 0.24 μA/% (O2/N2) and 0.32 μA/% (CO2/N2). The sensitivity of the temperature sensor is 0.07%/°C.

Monitoring of fabrication processes and the measurement of the electrical and mechanical properties of materials and devices at the silicon-wafer level are of vital importance on integrated system technologies. In this work, a test integrated circuit (IC) for the development of an IntraCMOS-MEMS fabrication process is presented. The test devices contained in the test IC are designed in such a way that 1) they can be used in CMOS-MEMS fabrication technologies using different materials, 2) take into account the capabilities of the manufacturing infrastructure, and 3) consider the selected integrated fabrication scheme; thus, any monolithic CMOS-MEMS process can be evaluated before, during and after the fabrication. The acquired data from the test devices will be useful to identify possible electrical and/or mechanical variations, in the properties of the materials used and in the performance characteristics of the devices, due to the fabrication process. The information acquired will help to adjust the simulation routines and the analytical modeling expressions. Finally, using the infrastructure of the MEMS Innovation Laboratory (LIMEMS-INAOE Mexico) preliminary experimental results are presented. [ABSTRACT FROM AUTHOR]

This article presents a fully integrated ultrasound system based on a single piezoelectric micromachined ultrasonic transducer (PMUT) monolithically fabricated with a 0.13 μm complementary metal oxide semiconductor (CMOS) process analog front-end circuitry. The PMUT consists of an aluminum nitride, AlN, squared device with 80 μm side that resonates at 2.4 MHz in liquid environment. The monolithic integration of the PMUT with the CMOS circuitry allows a reduction of the parasitic capacitance, a reduction of the electronic noise contribution and a clear improvement in the Signal-to Noise ratio (SNR ~ 27 dB better) compared to a non-integrated equivalent system. A pulse-echo experiment with the single PMUTon-CMOS for transmitting and sensing simultaneously is demonstrated, ensuring a 17.3 dB SNR, higher than the minimal necessary for accurate fingerprint images, paving the way towards a pixel sized imaging system with no need of multiple simultaneous PMUTs transmitters. Consuming only 0.3 mW and getting an input-referred noise of 3.26 mPa/√Hz at 2.4 MHz, the proposed pulse-echo system achieves a competitive noise efficient factor in comparison with the state-of-the-art.

In this work, a study case is presented in which the design of the layout for a CMOS sensor cell is partially automated by implementing a metaheuristic algorithm to find the best tradeoff between two conflicting objectives (two quantitative opposite and not totally independent yet desired performance or design qualities) among the set of feasible layout and electronic device configurations within a constricted search space. The feasibility of a solution (a particular configuration) and its capability to fulfill every requested objective, is determined by its compliance to the CMOS-MEMS design rules and fabrication process. Any given solution besides showing optimal or very near-to-the-optimal characteristics, must be suitable to be fabricated in the CMOS conventional process which for this case is a 0.5 μ m , 3-metal 2-poly N-well fabrication, beside this, since monolithic inertial sensors generally contains embedded movable electromechanical parts a surface micromachining must be considered. Simulation data and behavior of the bio-inspired metaheuristic algorithm used during the design process are presented, as well as electromechanical simulation results based the automatic-generated solutions. [ABSTRACT FROM AUTHOR]

A state of the art review on Radio Frequency Micro-Electromechanical Systems (RF MEMS) capacitive switches is reported by considering two key aspects: (1) materials selection approaches for improving performance, and (2) fabrication methods used in capacitive MEMS switches. The beam and dielectric materials used in capacitive MEMS switches and the performance achieved through them are reviewed and reported by a rigorous literature survey. Further, materials selection approaches for the beam membrane and the dielectric layer are discussed using Ashby's methodology, and other associated methods based on it, which uses material indices to evaluate the performance of a switch. Performance indicators for the beam materials selection are the pull-in voltage, RF loss, thermal residual stress, contact resistance, thermal conductivity, and maximum displacement, whereas the hold-down voltage, dielectric charging, leakage current, heat dissipation, capacitance ratio, and stability are performance indicators in dielectric materials selection. MEMS switch fabrication can be achieved through bulk micromachining processes and surface micromachining processes, but the surface micromachining process has been preferred over the last few decades. The fabricated MEMS switch components can be integrated using a monolithic complementary metal oxide semiconductor–micro-electromechanical systems (CMOS-MEMS) process for the realization of applications in sensors, resonators, amplifiers, phase shifters, and MEMS satellite vehicles for space applications. CMOS-MEMS monolithic fabrication is discussed further with the help of fabrication process involved and the process technology. The TSMC-CMOS 0.35 μ m technology is one of the leading technologies in CMOS-MEMS fabrication and is mainly used. [ABSTRACT FROM AUTHOR]

There have always been demands for the development of microscale sensors with integrated miniature electronics circuitry. Requirement of external amplification for the conventional MEMS accelerometer poses limitation on scaling, design, fabrication and on-chip Integrated Circuit (IC) compatibility. These limitations could be surpassed by the implementation of integrated CMOS-MEMS architectures for sensors and actuators. Here a novel U-channel suspended gate silicon on insulator field effect transistor (USG-SOIFET) is proposed to circumvent the pseudo short channel effects (P-SCE) present in the suspended gate field effect transistor (SGFET). In the proposed USG-SOIFET, the source and drain are separated by an air-gap and thereby ensuring effective screening of drain electric field penetration into source region. The gate length (L) of USG-SOIFET is 4 times lower than the conventional planar channel SGFET for the same performance of the device. Since the same performance is achieved with a smaller length, this results in a smaller device. Finite Element Modeling (FEM) of USG-SOIFET z-axis accelerometer using CoventerMP1.3 and TCAD process, device modeling and simulation of the USG-SOIFET using Synopsys Sentaurus are presented here. The sensitivity of the accelerometer is 4.185 μA/g with a non-linearity of 4.96% for ± 5 g detection range. The bandwidth of the accelerometer is 100 Hz and the cross-axis sensitivity is found to be 3.52%. A fabrication process integration scheme for realizing USG-SOIFET has also been discussed along with process simulation to demonstrate the feasibility of realizing this new device architecture. This device platform is a potential candidate for monolithic integration with CMOS. [ABSTRACT FROM AUTHOR]

This study presents the design and implementation of a MEMS capacitive tactile force sensor with polydimethylsiloxane (PDMS) filler for in-process and in-use modulation of the sensing range and sensitivity performance. The presented MEMS tactile force sensor consists of a loading unit with driving electrodes, PDMS filler, and a sensing unit. By varying input voltages on the driving electrodes (either in curing process or in-use), the stiffness of the PDMS filler as well as the loading unit can be modulated. Thus, the sensitivity and sensing range of the presented tactile force sensor was modulated accordingly. Since each sensor has its own driving electrodes and electrical routings, different input voltages can be applied to modulate the PDMS for each individual sensor. As a result, tactile sensors of different sensitivities and sensing ranges can be simultaneously fabricated and monolithically integrated on the same chip using the presented approach. The tactile sensors were implemented using TSMC $0.18~\mu \text{m}$ 1P6M standard CMOS process together with the in-house post-CMOS releasing and the polymer filling processes. Experiments demonstrate the capabilities of implementing various tactile sensors with different sensing ranges and sensitivities on a single chip by the in-process and in-use modulation techniques. Through the in-process and in-use modulation, the presented CMOS-MEMS tactile sensors show the sensing window: (1) for sensitivity modulation: 8.6 fF/N to 219.1 fF/N, and (2) for sensing range modulation: 30 mN to 270 mN. [ABSTRACT FROM AUTHOR]

In this work, we report a novel fully balanced drive and sense thermal-piezoresistive resonator (TPR) in 2P-4M $0.35~\mu \text{m}$ CMOS technology with maskless post-release process. Through the use of the Wheatstone bridge arrangement for both the thermal drive heater resistors and sense piezoresistors, the proposed design greatly simplifies the overall system by removing the need for bias-tee or noisy and power consuming current sink/source. This ensures that the differential terminals of drive and sense ports are at the same DC potential, thus allowing the use of standard differential amplifiers as interface circuits. In addition, this design utilizes bimorph like actuation which enables in-plane motion. An in-plane clamped-clamped beam (CCB) TPR was fabricated, demonstrating a quality factor (${Q}{)}$ of 1,600 at 2 MHz with transconductance (${g}_{m}{)}$ of $46.8~\mu \text{S}$ for a dc-power of 1.7 mW in a vacuum (1 mTorr). To go one step further, a double-ended tuning fork (DETF) TPR was designed, featuring a transconductance of 62.7 $\mu \text{S}$ with ${Q}$ of 4,400 at 1.9 MHz under the same conditions as CCB. The CCB thermal-piezoresistive oscillator (TPO) implemented using a discrete interface circuit had phase noise of −89 dBc/Hz and −100 dBc/Hz at 1 kHz and 1 MHz respectively while that for DETF TPO was −100 dBc/Hz at 1 kHz and −100 dBc/Hz at 1 MHz in air. Frequency stability was found to be 180 ppb and 125 ppb for CCB and DETF TPOs respectively in air. [ABSTRACT FROM AUTHOR]

This study demonstrates the integration of thermoelectric type MEMS infrared (IR) sensor with plasmonic metamaterial absorber (PMA) through a standard CMOS process platform to improve the responsivity of MEMS IR sensor in a specific range of wavelength. Based on an existing thermoelectric IR sensor with the serpentine film structure, the proposed device further combines with a Metal-Insulator-Metal (MIM) type PMA. The absorber consists of a top antenna layer, a middle dielectric spacer, and a bottom reflector, and the metal and dielectric films in the standard CMOS process are exploited in this study to implement the MIM design. The advantage of narrow linewidth in CMOS process can meet the need of critical dimensions for MIM antennas. The absorption wavelength can be adjusted by varying the pattern and dimension of antennas. The MIM PMAs are designed in the coupling regime, and hence the shifting of absorbed wavelength caused by the variation of antenna dimensions from fabrication can be prevented. The feasibility of the presented MIM PMA is demonstrated by simulations and experiments. The absorption spectra measured by FTIR show the capability of proposed MIM PMAs in extending the absorption range of far-infrared. Measurement results also indicate that under the same sensor footprint and the equal number of thermocouples, the device integrated with the proposed MIM PMA has a 20 percent improvement in responsivity as well as detectivity. [ABSTRACT FROM AUTHOR]

The infrared absorption efficiency (IAE) enhancement of the complementary-metal-oxide-semiconductorCMOS compatible thermopile with special subwavelength hole arrays in an active area was numerically investigated by the finite-difference time-domain method. It was found that the absorption efficiency of that thermopile was enhanced when the subwavelength rectangular-hole array added extra rectangular-columnar or ellipse-columnar structures in the hole array. The simulation results show that the IAEs of the better cases for the three types of rectangular columns and three ellipse columns were increased by 14.4% and 15.2%, respectively. Such special subwavelength hole arrays can be improved by the IAE of the CMOS compatible thermopile. [ABSTRACT FROM AUTHOR]

We present a thermally driven piezoresistively sensed resonator primarily consisting of backend of line (BEOL) CMOS material for mass sensing applications. A detailed analysis of the operation mechanism has been performed to develop a mathematical and an electrical equivalent model. The thermal-piezoresistive resonator (TPR) is composed predominantly of low loss materials like silicon dioxide (SiO2) and polysilicon for drive and sense. A differential configuration with drive and sense isolation was employed to significantly reduce the feedthrough level. Theoretical and simulated values are validated with experimental data. The proposed design has a resonance frequency of 5.13 MHz with a transconductance (gm) of 7.8 μS in the vacuum (<10−3 torr) for 1.2-mW bias while gm of 5 μS in the atmospheric pressure for 2.7-mW bias power at 5.09 MHz. One of the highest reported quality factors (Q) of 2600 for CMOS-MEMS was achieved in air, while the same in the vacuum was >10 000. The thermal-piezoresistive oscillator (TPO) has Allan Deviation of 80 ppb and 20 ppm in ambient pressure using a lock-in amplifier with a phase-locked loop (PLL) and interface circuit using commercial amplifiers on printed circuit board (PCB), respectively. Using silver nanoparticles, the mass sensitivity of 24.96 kHz/ng was measured. The extracted mass resolution in air was 16.3 fg, thus having great potential to serve as an aerosol sensor. [ABSTRACT FROM AUTHOR]

Besides the application of the photonic crystal for the photodetector in the visible range, the infrared devices proposed with subwavelength structure are numerically and experimentally investigated thoroughly for infrared radiation sensing in this research. Several complementary metal oxide semiconductor (CMOS) compatible thermopiles with subwavelength structure (SWS) are proposed and simulated by the FDTD method. The proposed thermopiles are fabricated by the 0.35 μm 2P4M CMOS-MEMS process in TSMC (Taiwan Semiconductor Manufacturing Company). The measurement and simulation results show that the response of these devices with SWS is higher than for those without SWS. The trend of the measurement results is consistent with that of the simulation results. Obviously, the absorption efficiency of the CMOS compatible thermopile can be enhanced when the subwavelength structure exists. [ABSTRACT FROM AUTHOR]

This work presents a monolithically integrated CMOS-MEMS three-axis capacitive accelerometer with an effective and practical method to compensate the sensor offset. By using correlated double sampling (CDS) and an automatic sensor offset compensated mechanism in the interface circuit, the purposes of low noise and low zero-gravity(zero-g) offset accelerometer are achieved. The zero-g offset compensated circuit calibrates the sensor offset in each axis. All of the calibrated procedure is executed automatically by a micro-control-unit (MCU). After calibration, the worst zero-g offset is reduced to ±50 mg and background calibration is no longer needed. The three-axis accelerometer was fabricated by using a 0.18-μm CMOS-MEMS process and the chip area containing the sensors and the integrated circuit is 2 × 2 mm2. It achieved a ±6 g sensing range and the noise was 350 μg/rtHz for the X- and Y-axes and Z-axes was 1.5 mg/rtHz with a total current consumption of 120 μA under 1.8 V. [ABSTRACT FROM AUTHOR]

CMOS-MEMS resonators have become a promising solution thanks to their miniaturization and on-chip integration capabilities. However, using a CMOS technology to fabricate microelectromechanical system (MEMS) devices limits the electromechanical performance otherwise achieved by specific technologies, requiring a challenging readout circuitry. This paper presents a transimpedance amplifier (TIA) fabricated using a commercial 0.35-µm CMOS technology specifically oriented to drive and sense monolithically integrated CMOS-MEMS resonators up to 50 MHz with a tunable transimpedance gain ranging from 112 dB to 121 dB. The output voltage noise is as low as 225 nV/Hz1/2—input-referred current noise of 192 fA/Hz1/2—at 10 MHz, and the power consumption is kept below 1-mW. In addition, the TIA amplifier exhibits an open-loop gain independent of the parasitic input capacitance—mostly associated with the MEMS layout—representing an advantage in MEMS testing compared to other alternatives such as Pierce oscillator schemes. The work presented includes the characterization of three types of MEMS resonators that have been fabricated and experimentally characterized both in open-loop and self-sustained configurations using the integrated TIA amplifier. The experimental characterization includes an accurate extraction of the electromechanical parameters for the three fabricated structures that enables an accurate MEMS-CMOS circuitry co-design.

A thermopile device with sub-wavelength hole array (SHA) is numerically and experimentally investigated. The infrared absorbance (IRA) effect of SHAs in active area of the thermopile device is clearly analyzed by the finite-difference time-domain (FDTD) method. The prototypes are manufactured by the 0.35 μm 2P4M complementary metal-oxide-semiconductor micro-electro-mechanical-systems (CMOS-MEMS) process in Taiwan semiconductor manufacturing company (TSMC). The measurement results of those prototypes are similar to their simulation results. Based on the simulation technology, more sub-wavelength hole structural effects for IRA of such thermopile device are discussed. It is found from simulation results that the results of SHAs arranged in a hexagonal shape are significantly better than the results of SHAs arranged in a square and the infrared absorption efficiencies (IAEs) of specific asymmetric rectangle and elliptical hole structure arrays are higher than the relatively symmetric square and circular hole structure arrays. The overall best results are respectively up to 3.532 and 3.573 times higher than that without sub-wavelength structure at the target temperature of 60 °C when the minimum structure line width limit of the process is ignored. Obviously, the IRA can be enhanced when the SHAs are considered in active area of the thermopile device and the structural optimization of the SHAs is absolutely necessary.

Based on experimental data, this paper thoroughly investigates the impact of a gas fluid flow on the behavior of a MEMS resonator specifically oriented to gas sensing. It is demonstrated that the gas stream action itself modifies the device resonance frequency in a way that depends on the resonator clamp shape with a corresponding non-negligible impact on the gravimetric sensor resolution. Results indicate that such an effect must be accounted when designing MEMS resonators with potential applications in the detection of volatile organic compounds (VOCs). In addition, the impact of thermal perturbations was also investigated. Two types of four-anchored CMOS-MEMS plate resonators were designed and fabricated: one with straight anchors, while the other was sustained through folded flexure clamps. The mechanical structures were monolithically integrated together with an embedded readout amplifier to operate as a self-sustained fully integrated oscillator on a commercial CMOS technology, featuring low-cost batch production and easy integration. The folded flexure anchor resonator provided a flow impact reduction of 5× compared to the straight anchor resonator, while the temperature sensitivity was enhanced to −115 ppm/°C, an outstanding result compared to the −2403 ppm/°C measured for the straight anchored structure.

In this research, a new application of reduced graphene oxide (rGO) for a complementary metal-oxide-semiconductor (CMOS)-MEMS infrared (IR) sensor and emitter is proposed. Thorough investigations of IR properties including absorption and emission were proceeded with careful calibration and measurement with a CMOS thermoelectric sensor. The thermocouples of the sensor consist of aluminum and n-polysilicon layers which are fabricated with the TSMC 0.35 μm CMOS process and MEMS post-process. In order to improve the adhesion of rGO, a sensing area at the center of the membrane is formed with an array of holes, which is easy for the drop-coating of rGO material upon the sensing region. To evaluate the performance of the IR sensor with rGO, different conditions of the IR thermal radiation experiments were arranged. The results show that the responsivity of our proposed CMOS-MEMS IR sensor with rGO increases by about 77% compared with the sensor without rGO. For different IR absorption incident angles, the measurement of field of view shows that the CMOS-MEMS IR sensor with rGO has a smaller view angle, which can be applied for the application of long-distance measuring. In addition, characteristics of the proposed thermopile are estimated and analyzed with comparisons to the available commercial sensors by the experiments.

The enhanced infrared absorbance (IRA) of the complementary metal-oxide-semiconductor (CMOS) compatible thermopile with the subwavelength rectangular-hole arrays in active area is investigated. The finite-difference time-domain (FDTD) method considered and analyzed the matrix arrangement (MA) and staggered arrangement (SA) of subwavelength rectangular-hole arrays (SRHA). For the better cases of MA-SRHA and SA-SRHA, the geometric parameters are the same and the infrared absorption efficiency (IAE) of the SA type is better than that of the MA type by about 19.4% at target temperature of 60 °C. Three proposed thermopiles with SA-SRHA are manufactured based on the 0.35 μm 2P4M CMOS-MEMS process. The measurement results are similar to the simulation results. The IAE of the best simulation case of SA-SRHA is up to 3.3 times higher than that without structure at the target temperature of 60 °C. Obviously, the staggered rectangular-hole arrays with more appropriate geometric conditions obtained from FDTD simulation can excellently enhance the IRA of the CMOS compatible thermopile.

The infrared absorption efficiency (IAE) enhancement of the complementary-metal-oxide-semiconductorCMOS compatible thermopile with special subwavelength hole arrays in an active area was numerically investigated by the finite-difference time-domain method. It was found that the absorption efficiency of that thermopile was enhanced when the subwavelength rectangular-hole array added extra rectangular-columnar or ellipse-columnar structures in the hole array. The simulation results show that the IAEs of the better cases for the three types of rectangular columns and three ellipse columns were increased by 14.4% and 15.2%, respectively. Such special subwavelength hole arrays can be improved by the IAE of the CMOS compatible thermopile.

The study investigates the design and fabrication of a micromachined radio frequency (RF) capacitive switch using the complementary metal oxide semiconductor-microelectromechanical system (CMOS-MEMS) technology. The structure of the micromachined switch is composed of a membrane, eight springs, four inductors, and coplanar waveguide (CPW) lines. In order to reduce the actuation voltage of the switch, the springs are designed as low stiffness. The finite element method (FEM) software CoventorWare is used to simulate the actuation voltage and displacement of the switch. The micromachined switch needs a post-CMOS process to release the springs and membrane. A wet etching is employed to etch the sacrificial silicon dioxide layer, and to release the membrane and springs of the switch. Experiments show that the pull-in voltage of the switch is 12 V. The switch has an insertion loss of 0.8 dB at 36 GHz and an isolation of 19 dB at 36 GHz.

Magnetic field sensors are becoming an essential part of everyday life due to the improvements in their sensitivities and resolutions, while at the same time they have become compact, smaller in size and economical. In the work presented herein a Lorentz force based CMOS-MEMS magnetic field sensor is designed, fabricated and optically characterized. The sensor is fabricated by using CMOS thin layers and dry post micromachining is used to release the device structure and finally the sensor chip is packaged in DIP. The sensor consists of a shuttle which is designed to resonate in the lateral direction (first mode of resonance). In the presence of an external magnetic field, the Lorentz force actuates the shuttle in the lateral direction and the amplitude of resonance is measured using an optical method. The differential change in the amplitude of the resonating shuttle shows the strength of the external magnetic field. The resonance frequency of the shuttle is determined to be 8164 Hz experimentally and from the resonance curve, the quality factor and damping ratio are obtained. In an open environment, the quality factor and damping ratio are found to be 51.34 and 0.00973 respectively. The sensitivity of the sensor is determined in static mode to be 0.034 µm/mT when a current of 10 mA passes through the shuttle, while it is found to be higher at resonance with a value of 1.35 µm/mT at 8 mA current. Finally, the resolution of the sensor is found to be 370.37 µT.

A new class of tri-axial miniature magnetometer consisting of a planar fluxgate structure with an orthogonal ferromagnetic fluxguide centrally situated over the magnetic cores is presented. The magnetic sensor possesses a cruciform ferromagnetic core placed diagonally upon the square excitation coil under which two pairs of pick-up coils for in-plane field detection are allocated. Effective principles and analysis of the magnetometer for 3-D field vectors are described and verified by numerically electromagnetic simulation for the excitation and magnetization of the ferromagnetic cores. The sensor is operated by applying the second-harmonic detection technique that can verify V-B relationship and device responsivity. Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum. As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well. The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency. Compared with the previous tri-axis fluxgate devices, this planar magnetic sensor with an orthogonal fluxguide provides beneficial enhancement in both sensory functionality and manufacturing simplicity. More importantly, this novel device concept is considered highly suitable for the extension to a silicon sensor made by the current CMOS-MEMS technologies, thus emphasizing its emerging applications of field detection in portable industrial electronics.

The design and fabrication of an ethanol microsensor integrated with a readout circuit on-a-chip using the complementary metal oxide semiconductor (CMOS)-microelectro -mechanical system (MEMS) technique are investigated. The ethanol sensor is made up of a heater, a sensitive film and interdigitated electrodes. The sensitive film is tin dioxide that is prepared by the sol-gel method. The heater is located under the interdigitated electrodes, and the sensitive film is coated on the interdigitated electrodes. The sensitive film needs a working temperature of 220 °C. The heater is employed to provide the working temperature of sensitive film. The sensor generates a change in capacitance when the sensitive film senses ethanol gas. A readout circuit is used to convert the capacitance variation of the sensor into the output frequency. Experiments show that the sensitivity of the ethanol sensor is 0.9 MHz/ppm.

We analyzed experimentally the noise characteristics of fully integrated CMOS-MEMS resonators to determine the overall thermomechanical noise and its impact on the limit of detection at the system level. Measurements from four MEMS resonator geometries designed for ultrasensitive detection operating between 2-MHz and 8-MHz monolithically integrated with a low-noise CMOS capacitive readout circuit were analyzed and used to determine the resolution achieved in terms of displacement and capacitance variation. The CMOS-MEMS system provides unprecedented detection resolution of 11 yF.Hz-1/2 equivalent to a minimum detectable displacement (MDD) of 13 fm.Hz-1/2, enabling noise characterization that is experimentally demonstrated by thermomechanical noise detection and compared to theoretical model values. [ABSTRACT FROM AUTHOR]

In this paper,we share our practical experience gained during the development ofCMOS-MEMS (ComplementaryMetal-Oxide Semiconductor Micro Electro Mechanical Systems) devices in IHP SG25 technology. The experimental prototyping process is illustrated with examples of three CMOS-MEMS chips and starts from rough process exploration and characterization, followed by the definition of the useful MEMS design space to finally reach CMOS-MEMS devices with inertial mass up to 4.3 μg and resonance frequency down to 4.35 kHz. Furthermore, the presented design techniques help to avoid several structural and reliability issues such as layer delamination, device stiction, passivation fracture or device cracking due to stress. [ABSTRACT FROM AUTHOR]

Featured Application: The thermoelectric microgenerators converted waste heat to electrical power and thus have a potential for application in electronic devices and microsensors. Manufacturing and testing of a TMG (thermoelectric microgenerator) with CNCs (carbon nanocapsules) film fabricated utilizing a CMOS (complementary metal oxide semiconductor) technology are investigated. The microgenerator includes a CNCs layer, thermopiles, and thermometers. CNCs, a heat absorbing material, are coated on the microgenerator, so that the TD (temperature difference) of HP (hot part) and CP (cold part) in the thermopiles increases, resulting in an enhancement of the microgenerator OP (output power). Thermometers fabricated in the microgenerator are employed to detect the HP and CP temperature in thermopiles. In order to enhance thermopiles’ TD, the HP in thermopiles was manufactured as suspension structures isolating heat dissipation, and the CP in thermopiles was made on a silicon substrate to increase the heat sink. Experiments showed that the microgenerator OV (output voltage) was 3.3 mV and its output power was 125 pW at TD 3 K. Voltage and power factors of TMG were 0.71 mV/K/mm2 and 9.04 pW/K2/mm2, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a behavioral modeling technique for CMOS microelectromechanical systems (MEMS) microresonators that enables simulation of an MEMS resonator model in Analog Hardware Description Language format within a system-level circuit simulation. A 100-kHz CMOS-MEMS resonant pressure sensor has been modeled into Verilog-A code and successfully simulated within Cadence framework. Analysis has shown that simulation results of the reported model are in agreement with the device characterization results. As an application of the proposed methodology, simulation and results of the model together with an integrated monolithic low-noise amplifier is exemplified for detecting the position change of the resonator. [ABSTRACT FROM PUBLISHER]

In this paper, we summarize research activities and technological progress in the field of current CMOS-MEMS resonators and oscillators for portable sensor node and timing applications. By employing CMOS-based fabrication technologies, we can monolithically integrate MEMS devices and their associated application-specific integrated circuits (ASICs), thereby enhancing their overall performance as compared with their stand-alone counterparts. Owing to the diversity of post-CMOS processing techniques, in this review, we mainly focus on the devices achieved by so-called foundry-orientated CMOS-MEMS platforms. On the basis of how the mechanical structure is achieved, in the paper we focus on two major strategies: (i) additive back-end-of-line (BEOL) compatible layers and (ii) machining of standard CMOS layers for device fabrication. Given their superior CMOS integration capability, the circuitry design concepts, testing results, and potential merits of state-of-the-art CMOS-MEMS oscillators are also presented. [ABSTRACT FROM AUTHOR]

This paper presents a proof of concept of a differential sensor based on the phase-difference of two injection-locked MEMS resonators, strongly coupled through their actuation voltages by a digital mixer. For the first time the feasibility of a fully monolithically co-integrated CMOS-MEMS differential resonant sensor, exploiting the capabilities of the injection-locked synchronization is proved. The principle of the system is first presented, from which optimal design guidelines are derived. The design of the different blocks of the system is then addressed. Our experimental results demonstrate the sensitivity enhancement of the proposed solution, as predicted by theory, and partial thermal drift rejection in a 70 °C range. The simulated and experimental results highlight the critical points of the system design, on which the emphasis of this article is placed. [ABSTRACT FROM AUTHOR]

In the past decade, micro-electromechanical systems (MEMS)-based thermoelectric infrared (IR) sensors have received considerable attention because of the advances in micromachining technology. This paper presents a review of MEMS-based thermoelectric IR sensors. The first part describes the physics of the device and discusses the figures of merit. The second part discusses the sensing materials, thermal isolation microstructures, absorber designs, and packaging methods for these sensors and provides examples. Moreover, the status of sensor implementation technology is examined from a historical perspective by presenting findings from the early years to the most recent findings. [ABSTRACT FROM AUTHOR]

This paper presents a novel class of miniature fluxgate magnetometers fabricated on a print circuit board (PCB) substrate and electrically connected to each other similar to the current “flip chip” concept in semiconductor package. This sensor is soldered together by reversely flipping a 5 cm × 3 cm PCB substrate to the other identical one which includes dual magnetic cores, planar pick-up coils, and 3-D excitation coils constructed by planar Cu interconnections patterned on PCB substrates. Principles and analysis of the fluxgate sensor are introduced first, and followed by FEA electromagnetic modeling and simulation for the proposed sensor. Comprehensive characteristic experiments of the miniature fluxgate device exhibit favorable results in terms of sensitivity (or “responsivity” for magnetometers) and field noise spectrum. The sensor is driven and characterized by employing the improved second-harmonic detection technique that enables linear V-B correlation and responsivity verification. In addition, the double magnitude of responsivity measured under very low frequency (1 Hz) magnetic fields is experimentally demonstrated. As a result, the maximum responsivity of 593 V/T occurs at 50 kHz of excitation frequency with the second harmonic wave of excitation; however, the minimum magnetic field noise is found to be 0.05 nT/Hz1/2 at 1 Hz under the same excitation. In comparison with other miniature planar fluxgates published to date, the fluxgate magnetic sensor with flip chip configuration offers advances in both device functionality and fabrication simplicity. More importantly, the novel design can be further extended to a silicon-based micro-fluxgate chip manufactured by emerging CMOS-MEMS technologies, thus enriching its potential range of applications in modern engineering and the consumer electronics market.

This paper presents the design, fabrication, and characterization of an inductive complementary metal oxide semiconductor micro-electromechanical systems (CMOS-MEMS) accelerometer with on-chip digital output based on LC oscillators. While most MEMS accelerometers employ capacitive detection schemes, the proposed inductive detection scheme is less susceptible to the stress-induced structural curling and deformation that are commonly seen in CMOS-MEMS devices. Oscillator-based frequency readout does not need analog to digital conversion and thus can simplify the overall system design. In this paper, a high-Q CMOS inductor was connected in series with the low-Q MEMS sensing inductor to improve its quality factor. Measurement results showed the proposed device had an offset frequency of 85.5 MHz, sensitivity of 41.6 kHz/g, noise floor of 8.2 mg/√Hz, bias instability of 0.94 kHz (11 ppm) at an average time of 2.16 s, and nonlinearity of 1.5% full-scale.

Superior to the traditional infrared temperature sensing architecture including infrared sensor and thermistor, we propose a novel sensing approach based on a single thermopile sensor with dual modes modulation. A switching and sensing circuit is proposed and realized with a chopper amplifier AD8551 and p-channel MOSFET (PMOS) for switching between detection of thermal radiation and the target and the ambient temperature for compensation. The error of target temperature after temperature compensation is estimated at less than 0.14 °C.

This study implements the metal-oxide-semiconductor (MOS) type gas sensor using the TSMC 0.35 μm 2P4M process. The gas concentration is detected based on the resistance change measured by the proposed sensor. This design has three merits: (1) low-cost post-CMOS process using metal/oxide wet etching, (2) composite sensing material based on ZnO-SnO2 coating on the CMOS-MEMS structure, (3) vertical integration of heater and ZnO-SnO2 gas-sensing films using CMOS-MEMS and drop casting technologies. Proposed design significantly increase the sensitivity at the high operating temperature. In summary, the sensitivity of presented sensor increased from 0.04%/% (O2/N2) at near room operating temperature to 0.2%/%(O2/N2) at near 140 °C for the range of 5–50% oxygen concentration.

This paper presents the enhancement in frequency shift per Celsius for high-temperature sensitive applications of microresonators. Using materials with different coefficients of thermal expansion in a substrate and beam, larger axial load on fixed ends are demonstrated. This results in a larger frequency shift with the increase in the ambient temperature. An analytical model is presented that closely matches simulation and measurement results. The 120- \mu \textm CMOS-MEMS fixed–fixed beam resonators, consisting of multiple metal, dielectric layers, and polysilicon layer, were designed and measured with a center frequency around 640 kHz. A sensitivity up to −2983 Hz/°C is achieved without sacrificing stiffness constant. [ABSTRACT FROM PUBLISHER]