Resonant Pressure Sensor Research Articles

A composite structure pressure sensor based on quartz DETF resonator

Resonant pressure sensors are widely used in petrochemical, aerospace, biomedical and other fields due to their advantages of high resolution, precision and anti-interference ability. In this paper, we report a composite structure pressure sensor based on a quartz resonator. The sensor consists of a silicon film and a quartz tuning fork, forming a membrane-island-beam structure. The sensitivity factor of our sensor is 35.6 mHz/Pa in the operating range of 0–240 kPa at room temperature. The bias stability of the sensor is 72 ppb at 0.1 s. The nominal theoretical resolution of our sensor was 66 mPa. Testing results show a nonlinearity of 0.83% FS, a hysteresis of 0.79% FS, and a repeatability of 0.76% FS. The temperature coefficient of the sensor is 93.6 Hz/℃, and the sensitivity factor of the pressure sensor after temperature compensation is 44.96 mHz/Pa.

Design and simulation of an aluminum nitride piezoelectric resonant pressure sensor

In this paper, a novel aluminum nitride (AlN) resonant pressure sensor with piezoelectric-excitation and piezoelectric-detection is presented. The key structure of this resonator is an AlN flexible beam. Parallel electrodes are designed on the beam to excite the resonance structure in-plane. All layers of this AlN resonant structure are grown on a silicon-on-insulator (SOI) wafer by the deposition process. Anchor islands are fabricated in the top silicon layer of the SOI. The structure is designed and optimized by finite element simulation software, and the performance of this pressure sensor is simulated. The resonance frequency is 60.04 kHz, and the sensitivity is 13.6 Hz/kPa under a pressure range of 0–120 kPa. This AlN sensor is advantageous in that its structure and fabrication processes are simple, and it is a new choice for resonant pressure sensors.

A Resonant Differential Pressure Microsensor With Stress Isolation and Au-Au Bonding in Packaging

Resonant differential pressure (DP) sensors are prone to environmental disturbances [e.g., temperatures ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}$ </tex-math></inline-formula> ) and static pressure (SP)] due to poor packaging. In order to address this issue, this article presents a resonant DP microsensor where the core pressure-sensitive element was assembled with the packaging house using stress isolation and Au–Au bonding. The stress isolation was used to reduce the effect of packaging house on the core-sensitive element when the environmental disturbances of temperature and SP varied, and the Au–Au bonding was used to improve the structural stability to reduce the frequency drift over time. Numerical simulation was conducted to confirm the positive effect of including the stress isolation structure and fabrication processes were developed to realize Au–Au bonding in packaging. Experimental characterization was conducted, reporting reductions of three times in temperature disturbance, 25 times in SP disturbance, and 35 times in frequency drift in comparison with the counterpart without stress isolation and Au–Au bonding. Based on these improvements, the accuracy of the developed resonant DP microsensor was quantified as 0.03%FS within the DP of 0–100 kPa, the temperature of −10 °C to 60 °C, and the SP of 110–200 kPa.

Research Progress of Graphene Nano-Electromechanical Resonant Sensors-A Review.

Graphene nano-electromechanical resonant sensors have wide application in areas such as seawater desalination, new energy, biotechnology, and aerospace due to their small size, light weight, and high sensitivity and resolution. This review first introduces the physical and chemical properties of graphene and the research progress of four preparation processes of graphene. Next, the principle prototype of graphene resonators is analyzed, and three main methods for analyzing the vibration characteristics of a graphene resonant sheet are described: molecular structural mechanics, non-local elastic theory and molecular dynamics. Then, this paper reviews research on graphene resonator preparation, discussing the working mechanism and research status of the development of graphene resonant mass sensors, pressure sensors and inertial sensors. Finally, the difficulties in developing graphene nano-electromechanical resonant sensors are outlined and the future trend of these sensors is described.

A Quartz Resonant Ultra-High Pressure Sensor With High Precision and High Stability

A quartz resonant pressure sensor for ultra-high pressure measurement has been designed and verified. The pressure conversion unit of the sensor is composed of a pressure cylinder and a flexible lever, which can accurately and efficiently meet the role of converting and passing the ultra-high pressure to the resonant unit. The resonant unit of the sensor uses quartz DETF resonators and forms a differential output structure to meets the requirements of high precision and stability. The theory of the overall sensor design scheme is consistent with the simulation results, which verifies the feasibility of the design scheme. The experimental results show that in the pressure range of 120 Mpa, the sensitivity of the ultra-high pressure sensor is 27.3 Hz/Mpa, the linearity reaches 0.0112%, and the total accuracy is 0.0365%. The sensor can be used for high-precision and high-stability detection of ultra-high pressure, which is necessary in special fields such as deep-sea exploration.

An Innovative LC-C Resonant Pressure Sensor Based on Capacitive Feedthroughs

LC resonant wireless passive pressure sensor has been receiving increased attention nowadays. In this paper, an innovative LC-C resonant wireless passive pressure sensor based on dual capacitors was designed and manufactured to replace the traditional LC device. In addition to the inductor and capacitor structure required by the traditional LC device, this paper innovatively designs the fixed capacitor as the inter-layer interconnection structure. The key structural dimensions of the sensor were determined through the numerical analysis of the planar inductor theory and the electromechanical coupling simulation of the dual capacitors model in the previous stage, and the processing of the sensor was carried out through MEMS technology. The final test results showed that within the pressure range of 5kPa to 100kPa, the sensor’s average sensitivity was greater than 69.0 kHz/kPa, while the maximum linear fitting error was smaller than 4.18%. The temperature drift in atmospheric environment was 2.7kHz/°C, and the sensitivity temperature drift was 0.0062kHz/(kPa·°C).

Design and experiment of a cantilever beam pressure sensor using an optical microring resonator

Recently miniaturization, integration and high sensitivity are becoming the mainstream of the development of pressure sensing technology. This paper proposes a pressure sensor realized with the microring resonator on a cantilever beam. The performance of the pressure sensor is theoretical analyzed and then simulated using finite element modeling. It shows that the cantilever beam substrate can greatly improve the sensitivity compared with a simple supported beam. The fabricated microring resonator pressure sensor has 3 dB bandwidth of about 0.1488 nm and a Q-factor of 10511. The experimental results demonstrate that the resonant wavelength shift of the microring pressure sensor has an almost linear relationship with the displacement of pressure testing device.

Temperature-insensitive silicon resonant pressure sensor by thermal stress control

A temperature-insensitive silicon resonant pressure sensor is developed with an extremely low temperature coefficient of frequency (TCF). A novel self-compensation method is proposed to counteract the effect of the elastic modulus temperature coefficient (TCE) of silicon on the TCF by the thermal stress generated by vacuum packaging layers. On this basis, a positive TCFS shift is introduced by thermal tensile stress, and a negative TCFE shift is introduced by the TCE of silicon. The TCFS shifts can be adjusted as close as possible to the value of −TCFE by adjusting the thickness of the diaphragm and resonator, sharply decreasing the total TCF. The resonant pressure-sensing chip is fabricated using micromachining technology. Experimental results show that the maximum TCF value of the proposed resonant pressure sensor is 7.3 ppm/°C (that is, 0.46 Hz/°C). Moreover, its nonlinearity after polynomial compensation is better than 0.01% FS at the temperature ranging from −10 ℃ to +60 ℃.

High-accuracy differential resonant pressure sensor with linear fitting method

A high-accuracy differential resonant pressure sensor with two similar resonators is proposed using the linear fitting method to guarantee its output linearity without polynomial compensation. Results reveal that the nonlinearity of the differential resonant pressure sensor is largely dependent on the tensile/compressive sensor pressure–stress ratio c when two similar resonators are used separately as compressive and tensile elements. Nonlinearity decreases sharply with an appropriate ratio c. A theoretical model is proposed to obtain minimal nonlinearity and shows satisfactory agreement with the simulation results. The impact factors of ratio c are analyzed to facilitate adjustments with the designed value. Moreover, micromachining methods are used to fabricate sensing chips. Experiment results show that the nonlinearity and measurement sensitivity of the proposed differential resonant pressure sensor are ±0.02% FS and 35.5 Hz kPa−1 with the linear fitting method in a pressure range of 0–200 kPaA and temperature range of −40 °C to +40 °C. The differential linear fitting method largely decreases compensation complexity without polynomial fitting for high-precision pressure measurement.

A High-Sensitivity Resonant Differential Pressure Microsensor Based on Bulk Micromachining

This paper presents a high-sensitivity micromachined resonant differential pressure sensor based on bulk silicon. The sensor includes a sensing unit made of a SOI wafer, which is vacuum packaged by a glass-on-silicon (GOS) wafer. More specifically, two resonators located in the SOI device layer were coupled to the GOS glass layer and deployed on the central and side areas of the pressure-sensitive diaphragm respectively, enabling differential outputs. According to the relevant theory of elasticity, the differential pressure sensitivity is high, where the conversion efficiency of the differential pressure to resonators stress is improved by the special cap design, large pressure-sensitive diaphragm and narrow resonators. The developed differential pressure microsensors were manufactured leveraging well-established microfabrication steps including lithography, etching and boning. Characterization of the micromachined sensors was conducted, reporting averaged differential pressure sensitivities of 1) -143.17 Hz/kPa (~2051 ppm/kPa) and a linear correlation coefficient of 0.999992 under a static pressure of 110 kPa and a temperature range from -°C to 40°C; 2) -143.36 Hz/kPa (~2051 ppm/kPa) and a linear correlation coefficient of 0.999997 under a static pressure range from 110 kPa to 250 kPa and a temperature of 25°C. Compared to previous study, the high differential pressure sensitivity of the sensor can pave ways for the subsequent high-precision measurement of differential pressures, which can be used to measure micro differential pressure in the field of nuclear power.

Free vibration for a micro resonant pressure sensor with cross-type resonator

In this paper, a cross resonator pressure sensor is proposed to improve the detection accuracy of capacitor-detecting sensor. Considering electrostatic force and molecular force, the multi-field coupled dynamic equation of the sensor is established. By solving the dynamic equation, the equations for the mode function and the natural frequencies of the resonator are obtained. Using these equations, the natural frequency and mode function of the sensor are given. Changes of natural frequency of sensor with main parameters are studied. Influence of molecular force on the natural frequency is analyzed. Results show that within a considerable range of pressure, the natural frequencies increase approximately linearly with pressure. Under small pressure, small initial distance between resonator and base, and lower order modes, effects of the Van der Waals force on the natural frequencies are quite obvious.

Novel resonant pressure sensor based on piezoresistive detection and symmetrical in-plane mode vibration

In this paper, a novel resonant pressure sensor is developed based on electrostatic excitation and piezoresistive detection. The measured pressure applied to the diaphragm will cause the resonant frequency shift of the resonator. The working mode stress–frequency theory of a double-ended tuning fork with an enhanced coupling beam is proposed, which is compatible with the simulation and experiment. A unique piezoresistive detection method based on small axially deformed beams with a resonant status is proposed, and other adjacent mode outputs are easily shielded. According to the structure design, high-vacuum wafer-level packaging with different doping in the anodic bonding interface is fabricated to ensure the high quality of the resonator. The pressure sensor chip is fabricated by dry/wet etching, high-temperature silicon bonding, ion implantation, and wafer-level anodic bonding. The results show that the fabricated sensor has a measuring sensitivity of ~19 Hz/kPa and a nonlinearity of 0.02% full scale in the pressure range of 0–200 kPa at a full temperature range of −40 to 80 °C. The sensor also shows a good quality factor >25,000, which demonstrates the good vacuum performance. Thus, the feasibility of the design is a commendable solution for high-accuracy pressure measurements.

Development of CMOS Micromachined Capacitive Squeeze-Film Pressure Sensors

Squeeze-film damping due to compressed thin-film gas comprises both the viscous and elastic effects. Based on the latter, this work reports two capacitively-transduced resonant pressure sensors implemented in a complementary metal oxide semiconductor (CMOS) process to provide sensor miniaturization, integration and sensitivity enhancement. Post-CMOS fabrication is simplified as a sealed membrane in conventional pressure sensors is not required. The squeeze-film elastic effect enhanced by the narrow sub- $\mu \text{m}$ gap leads to improved sensitivity and reduced sensor size. The two designs have resonant plates of $200\times200$ and $100\times 100\,\,\mu \text{m}^{2}$ , and demonstrate sensitivities of 0.77 and 5.34 Hz/Pa, respectively.

A Resonant Pressure Sensor based on Magnetostrictive/Piezoelectric Magnetoelectric Effect

This study proposed a resonant pressure sensor based on magnetoelectric effect induced in magnetostrictive/piezoelectric materials. Due to the magnetoelectric effect, the resonant frequency of the sensor varies as the external applied pressure changes. By studying the nonlinear constitutive parameters of the magnetostrictive material and adopting the equivalent circuit method, the sensor is theoretically analysed and the relationship between the resonant frequency and applied pressure is determined. The prototype of the sensor is optimized based on theoretical model. Optimal parameters of the sensor are determined to ensure high sensitivity. The measurement range of the sensor is 0-360 kPa and experimental studies show that the sensitivity reaches to 11.63 Hz/kPa. The experimental result is in good agreement with theoretical analysis. It can be concluded that the pressure measurement method based on magnetostrictive/piezoelectric magnetoelectric effect is of robustness and accuracy. Analysis shows the proposed mechanism also has the potential in mass measurement.

A resonant pressure MEMS sensor based on levitation force excitation detection

This paper proposes a MEMS resonant pressure sensor through implementing an out-of-plane repulsive (levitation) force to enhance the sensor detection threshold and consequently widen its sensing range. 2D and 3D finite-element simulations are conducted and compared to some available experimental data. The simulated results show an increase in the generated levitation force as outstanding merit owing to the added side upper electrodes. The levitation force is then further increased by lateral spacing optimization in association with the assumed applied voltage, which decreases the overall size (footprint) as well. The dynamical behavior around the static equilibrium is first numerically solved using the so-called shooting technique and then compared with an available online simulation tool: the “Matcont” package. The simulated results prove the capability of the online simulator to capture the dynamic response of the resonant micro-sensor when approaching its respective bifurcation points where the stable and unstable branches collide, when in contrary, the shooting technique failed to get the dynamic responses when passing by these bifurcations. Thanks to the fast converging outcomes of the “Matcont” online simulation equipped with simultaneous stability analysis, a comprehensive analysis of the micro-sensor dynamical response is conducted. Three sensing mechanisms as: measurements of frequency shift, amplitude alternation, and amplitude rise/fall near a bifurcation region are evaluated and characterized. Along with enumerating the strengths of the proposed sensor over the conventional capacitive pressure sensors, the advantage of measuring the amplitude rise/fall near the corresponding bifurcation region comparing to the two other sensing mechanisms is detailed, and its possible failure for performance repeatability is resolved by means of the slow-varying frequency sweep. Unlike the traditional parallel-plate configuration in which only one-side frequency shift is observed, in this proposed design, two-sides frequency shift is detected, and accordingly, the reinitialization is categorized based on that. As compared to the conventional MEMS pressure sensor, this revisited design equipped with the suggested sensing mechanism offers wider tunability and sensing range, resolution power enhancement, and simplification of the signal processing circuit.

A Micromachined Resonant Differential Pressure Sensor

This article presents a new micromachined resonant differential pressure sensor, which is mainly composed of an SOI wafer as the sensing element and a glass-on-silicon (GOS) cap for vacuum packaging. More specifically, two resonators were deployed on the central and side areas of the pressure-sensitive diaphragm in the SOI handle layer and coupled to the pressure-sensitive diaphragm in the GOS glass layer, enabling differential outputs. The proposed differential pressure sensor was fabricated based on conventional microfabrication processes (e.g., photolithography, deep reactive ion etching, and anodic boning) and characterized in both open- and closed-loop manners, producing quality factors of the resonators higher than 18 000. Furthermore, averaged differential pressure sensitivities were quantified as -4.4664 Hz/kPa (~64 ppm/kPa) with a linear correlation coefficient of 0.9992 (a static pressure of 110 kPa and a temperature from -30 °C to 80 °C) and -4.4516 Hz/kPa (~64 ppm/kPa) with a linear correlation coefficient of 0.9992 (static pressure from 110 to 310 kPa and temperature of 25 °C). In addition, averaged temperature sensitivities and averaged static pressure sensitivities were quantified as -1.2932 Hz/°C (~18 ppm/°C) and 0.0989 Hz/kPa (~1 ppm/kPa), which further validated the proposed differential pressure sensor.

Conceptual Design of a Resonant Pirani Gauge Toward Wide-Range Pressure Sensing

This letter reports a CMOS-microelectromechanical system (MEMS) pressure sensor comprising a double-ended tuning fork capacitive resonant transducer and a Pirani gauge thermal transducer in a single device configuration, which demonstrates a wide-range pressure sensing capability, small form factor, and sensor fusion. The device integrated with an interfaced circuit was fabricated through a 0.35- μ m CMOS foundry process, together with an in-house release process. Thanks to the resonant transducer which is sensitive to pressure due to squeezed-film damping effect, the high pressure sensing range is achieved by measuring resonant frequency shift, whereas the medium pressure region is sensed by quality factor ( Q ) change of the resonator. As a result, a full-scale range of 10–760 torr is realized by the proposed CMOS-MEMS pressure sensor using its resonant transducer. To further extend the measurement range to the lower pressure range, an embedded thermal transducer of the device is used to serve as Pirani gauge that is capable of detecting pressure from 0.02 to 10 torr by the use of thermal resistance $(R_{{\rm{th}}})$ change. Through a simple algorithm combining variations of Q , resonant frequency $f_{o}$ , and thermal resistance $R_{{\rm{th}}}$ , the proposed resonant Pirani gauge pressure sensor features a very wide-range pressure sensing capability from 0.02 to 760 torr.

Highly sensitive and wide-range resonant pressure sensor based on the veering phenomenon

We report a highly sensitive wide-range resonant pressure sensor. The concept is based on tracking multiple modes of vibration of an electrothermally heated initially curved micro-beam experiencing the veering phenomenon between its first and third vibration modes. For low values of pressure, the third resonance frequency is very sensitive, and thus its variation with pressure is monitored and recorded. As increasing pressure, the resonance frequency of the third mode decreases until reaching the veering phenomenon. At that point, the first mode exchanges role with the third mode, becoming very sensitive, and hence its frequency is tracked afterward as varying pressure. We show that using this concept, the sensitivity of the resonant pressure micro-sensor is significantly enhanced. Finite element method (FEM) simulations and experimental data show that the proposed micro-sensor becomes highly sensitive for wide-range of pressure from 38 mTorr to 200 Torr. The effect of various parameters on the performance of the proposed pressure sensor is investigated including the thickness of the micro-beam, the vacuum chamber size, and the thermal actuation load.

A Temperature-Insensitive Resonant Pressure Micro Sensor Based on Silicon-on-Glass Vacuum Packaging.

This paper presents a temperature-insensitive resonant pressure sensor, which is mainly composed of a silicon-on-insulator (SOI) wafer for pressure measurements and a silicon-on-glass (SOG) cap for vacuum packaging. The variations of pressure under measurement bend the pressure sensitive diaphragm and regulate the intrinsic frequencies of the resonators in the device layer. While, variations of temperature cannot significantly change the intrinsic frequencies of the resonators, due to the SOG cap to offset generated thermal stress. Numerical simulations, based on finite element analysis, were conducted to calculate the residual thermal stress and optimize the sensing structures. Experimental results show that the Q-factors of the resonators are higher than 16,000, with a differential pressure sensitivity of 11.89 Hz/kPa, a nonlinearity of 0.01% F.S and a low fitting error of 0.01% F.S with the pressure varying from 100 kPa to 1000 kPa. In particular, a temperature sensitivity of ~1 Hz/°C was obtained in the range of −45 °C to 65 °C, which is one order of magnitude lower than the previously reported counterparts.

A Resonant Pressure Sensor Based upon Electrostatically Comb Driven and Piezoresistively Sensed Lateral Resonators.

This study proposes a microfabricated resonant pressure sensor in which a pair of double-ended tuning forks were utilized as resonators where comb electrodes and single-crystal silicon-based piezoresistors were used for electrostatic excitation and piezoresistive detection, respectively. In operations, pressures under measurements deform the pressure-sensitive diaphragm to cause stress variations of two resonators distributed on the central and side positions of the pressure-sensitive diaphragm, where the corresponding changes of the intrinsic resonant frequencies are then captured piezoresistively. The developed resonant pressure sensors were fabricated based on MEMS with open-loop and closed-loop characterizations conducted. Key sensing parameters including quality factors, differential pressure/temperature sensitivities and fitting errors were quantified as higher than 17,000, 48.24 Hz/kPa, 0.15 Hz/°C and better than 0.01% F.S. (140 kpa), respectively. In comparison to previously reported resonant pressure sensors driven by parallel-plate electrodes, the developed sensor in this study is featured with a lower temperature sensitivity and a higher stability.