Wheatstone Bridge Structure Research Articles

Angular Position Sensor Based on Anisotropic Magnetoresistive and Anomalous Nernst Effect

Magnetic position sensors have extensive applications in various industrial sectors and consumer products. However, measuring angles in the full range of 0–360° in a wide field range using a single magnetic sensor remains a challenge. Here, we propose a magnetic position sensor based on a single Wheatstone bridge structure made from a single ferromagnetic layer. By measuring the anisotropic magnetoresistance (AMR) signals from the bridge and two sets of anomalous Nernst effect (ANE) signals from the transverse ports on two perpendicular Wheatstone bridge arms concurrently, we show that it is possible to achieve 0–360° angle detection using a single bridge sensor. The combined use of AMR and ANE signals allows a mean angle error in the range of 0.51–1.05° within a field range of 100 Oe–10,000 Oe to be achieved.

Implementation of a full Wheatstone-bridge GMR sensor by utilizing spin–orbit torque induced magnetization switching in synthetic antiferromagnetic layer

A giant magnetoresistance (GMR) sensor with a Wheatstone bridge structure and an out-of-plane linear response was developed. The spin-valve structure consists of a synthetic antiferromagnetic [(Co/Pt)n/Ru/(Pt/Co)n] reference layer with perpendicular magnetic anisotropy, a Cu spacer layer, and a Co-free layer with in-plane easy magnetization. By utilizing the spin–orbit torque induced magnetization switching in the synthetic antiferromagnetic layer, the magnetization of the reference layers in the adjacent bridge arms is set to the opposite direction, achieving a GMR sensor with a full Wheatstone bridge structure. The sensor exhibits linear response to the out-of-plane magnetic field with adjustable dynamic ranges from hundreds to thousands of Oe, depending on the thickness of the Co-free layer. A similar Wheatstone bridge sensor consisting of magnetic tunnel junctions was also proposed. The sensor with out-of-plane linear response may have promising applications in three-dimensional magnetic field detection and current sensing field.

Research on high temperature performance of pressure sensor

This work proposes a molybdenum (Mo) based pressure sensor capable of operating at temperatures higher than 300 °C. The sensor utilizes a 30 μm thick rectangular pressure-sensitive film and 2 μm thick gate Mo resistors to form a Wheatstone bridge structure to enhance pressure sensing. Finite element analysis (FEA) has been performed to design the sensor and analyze the pressure and temperature effect. The developed sensor with the excitation of 1 V voltage exhibits excellent performance characteristics at room temperature (25 °C), including a sensitivity of 0.05689 mV V−1 kPa−1, 0.15% full scale (FS) accuracy, a nonlinearity of 0.79% FS, and 0.02% FS repeatability. The thermal zero shift of −0.13% FS/°C is obtained in the 25 °C to 300 °C temperature range. The simulation findings illustrate that the thermal mismatch weakens the thermal zero shift by +0.012‰ FS/°C, while the deviation of the temperature coefficient of resistance (TCR) and initial resistivity () aggravate the thermal zero shift by −0.139% FS/°C. Among both, the deviation of and TCR is the major contributor to thermal zero shift. Moreover, it was found that the Seebeck effect caused by the on-chip temperature gradient also affects the accuracy of the sensor. A temperature difference of 5.4 °C produces a thermoelectric potential of 37.95 μV equivalent to a pressure of 670 Pa loading on the chip. Besides, the response characteristics of the sensor at different temperature rates were investigated.

A temperature-stable Pd nanofilm hydrogen sensor with a Wheatstone bridge structure

A temperature-stable Pd nanofilm hydrogen sensor with a Wheatstone bridge structure

A Model to Design Giant Magnetoresistive Sensor

Giant magnetoresistive (GMR) sensor has developed rapidly in automobile, consumer electronics and current sensing areas due to its high sensitivity and low power consumption. In this work, we suggest a method to design GMR sensor based on Stoner-Wohlfarth coherent rotation model. We have investigated the influence of width of GMR sensor to its performance with the model and verified with experiments. And different pinning direction GMR elements are also researched to study Wheatstone bridge structure. The experimental results matched well with the simulation results which proved that the model is efficient in designing GMR sensor.

The accurate measurement of spin orbit torque by utilizing the harmonic longitudinal voltage with Wheatstone bridge structure

The microscopic mechanism for the current-induced spin–orbit torque (SOT) in magnetic heterostructures is still under debate. The accurate measurement of SOT effective fields and their thickness dependence is the basis for understanding this issue. In this work, we measured the SOT effective fields for Pt/NiFe bilayers by utilizing the harmonic longitudinal voltage (HLV) method with a Wheatstone bridge structure. Benefiting from the elimination of the linear resistance in the bridge structure and the large magnetoresistance difference resulting from the large length–width ratio of the bridge element, we achieved very high measurement accuracy for both field-like and damping-like effective fields in the Pt/NiFe bilayers. On this basis, we demonstrated the possibility of the SOT measurement with a relatively low current density (∼109 A/m2) by utilizing the HLV method with a Wheatstone bridge structure and found that the method we proposed is also applicable to the Pt/CoFeB system with a low anisotropic magnetoresistance ratio.

High-Precision Acceleration Measurement System Based on Tunnel Magneto-Resistance Effect.

A high-precision acceleration measurement system based on an ultra-sensitive tunnel magneto-resistance (TMR) sensor is presented in this paper. A “force–magnetic–electric” coupling structure that converts an input acceleration into a change in magnetic field around the TMR sensor is designed. In such a structure, a micro-cantilever is integrated with a magnetic field source on its tip. Under an acceleration, the mechanical displacement of the cantilever causes a change in the spatial magnetic field sensed by the TMR sensor. The TMR sensor is constructed with a Wheatstone bridge structure to achieve an enhanced sensitivity. Meanwhile, a low-noise differential circuit is developed for the proposed system to further improve the precision of the measured acceleration. The experimental results show that the micro-system achieves a measurement resolution of 19 μg/√Hz at 1 Hz, a scale factor of 191 mV/g within a range of ± 2 g, and a bias instability of 38 μg (Allan variance). The noise sources of the proposed system are thoroughly investigated, which shows that low-frequency 1/f noise is the dominant noise source. We propose to use a high-frequency modulation technique to suppress the 1/f noise effectively. Measurement results show that the 1/f noise is suppressed about 8.6-fold at 1 Hz and the proposed system resolution can be improved to 2.2 μg/√Hz theoretically with this high-frequency modulation technique.

High performance AlGaN/GaN pressure sensor with a Wheatstone bridge circuit

In this work, by taking into account the isotropic piezoelectric property of III-nitrides and the stress distribution in the circular diaphragm, AlGaN/GaN pressure sensor with a specially designed Wheatstone bridge structure is demonstrated. Two pairs of gateless HEMTs are placed at the tensile (near to the edge) and compressive (in the center) stress regions of the circular diaphragm, respectively, to maximize the pressure sensor's responsivity and stability. As a result, the 2DEG resistors located diagonally featured completely opposite piezoelectric polarization effects, which translated to a linear response of the fabricated AlGaN/GaN pressure sensor with a high sensitivity of 72 μV/kPa/V. The device also showed a large output capability of 64.8 mV/V, suggesting a potentially low power consumption in the practical applications.

Low Concentration Response Hydrogen Sensors Based on Wheatstone Bridge.

The PdNi film hydrogen sensors with Wheatstone bridge structure were designed and fabricated with the micro-electro-mechanical system (MEMS) technology. The integrated sensors consisted of four PdNi alloy film resistors. The internal two were shielded with silicon nitride film and used as reference resistors, while the others were used for hydrogen sensing. The PdNi alloy films and SiN films were deposited by magnetron sputtering. The morphology and microstructure of the PdNi films were characterized with X-ray diffraction (XRD). For efficient data acquisition, the output signal was converted from resistance to voltage. Hydrogen (H2) sensing properties of PdNi film hydrogen sensors with Wheatstone bridge structure were investigated under different temperatures (30 °C, 50 °C and 70 °C) and H2 concentrations (from 10 ppm to 0.4%). The hydrogen sensor demonstrated distinct response at different hydrogen concentrations and high repeatability in cycle testing under 0.4% H2 concentration. Towards 10 ppm hydrogen, the PdNi film hydrogen sensor had evident and collectable output voltage of 600 μV.

AlGaN/GaN pressure sensor with a Wheatstone bridge structure

In this work, a Wheatstone bridge-type pressure sensor based on AlGaN/GaN heterostructure was fabricated for the first time. The pressure sensor consisted of four gateless high electron mobility transistors (HEMTs) on a 585 μm depth circular membrane, in which 15-μm-thick silicon substrate was left. Direct voltage readout was realized in the AlGaN/GaN pressure sensor, which exhibited a non-linearity of 0.6% with a sensitivity of 1.25 μV/kPa/V over a wide pressure range from 0.1 MPa to 5 MPa. Because of the in-plane isotropic properties, the working mechanism in the AlGaN/GaN pressure sensor is found to be quite different from the silicon-based sensor. Although the resistances of the four gateless HEMTs all increased with enlarging pressure, the changes of neighboring resistors varied with alignments under the piezoelectric effects. Finally, voltage linear readout was realized by the differential operation of Wheatstone bridge circuit.

Direct-readout pressure sensor based on AlGaN/GaN heterostructure

Based on the excellent piezoelectricity of AlGaN/GaN heterostructures, a pressure sensor was fabricated combined with micro machining technology. Direct readout was realized by adopting Wheatstone bridge structure and the sensor showed favourable pressure responses. At the operation voltage of 5 V, the fabricated AlGaN/GaN pressure sensor exhibited a sensitivity of 7 μV/kPa with low non-linearity of 0.8% over a wide pressure range (from 0.1 to 5 MPa). As far as we know, this is a recorded responsive sensitivity in the reported direct-readout AlGaN/GaN pressure sensor.

Investigation and Optimization of Pirani Vacuum Gauges With Monocrystal Silicon Heaters and Heat Sinks

This paper presents micro-Pirani vacuum gauges using low-resistivity monocrystal silicon for the heaters and the heat sinks. We designed a new Pirani gauge with an embedded Wheatstone bridge made by thick-silicon resistors that allows an improvement in resolution and sensitivity. With the optimized Wheatstone bridge structure, the temperature coefficient of the gauges pressure measure decreases from 2.5%/°C to 0.74%/°C, and the resolution was optimized from 0.071 to 0.008 Torr at 1 Torr. In addition, the gauges were packaged into non-hermetic cavities by wafer-level AlGe eutectic bonding to undergo the wafer-dicing process, with sensitivity improved from 1.65 to 17.1 V/Torr at 1 Torr.

A CMOS Compatible MEMS Pirani Vacuum Gauge with Monocrystal Silicon Heaters and Heat Sinks**Supported by the National High Technology Research and Development Program of China under Grant No 2015AA042602.

We present a micro-Pirani vacuum gauge using the low-resistivity monocrystal silicon as the heaters and heat sinks fabricated by the post complementary metal oxide semiconductor (CMOS) microelectromechanical system (MEMS) process. The metal interconnection of the device is fabricated by a 0.5 μm standard CMOS process on 8-inch silicon wafer. Then, a –Si low-temperature fusion bonding is developed to bond the CMOS wafer and the MEMS wafer, with the electrical connection realized by the tungsten through silicon via process. Wafer-level AlGe eutectic bonding is adopted to package the Pirani gauge in a non-hermetic cavity to protect the gauge from being damaged or contaminated in the dicing and assembling process, and to make it suitable for actual applications. To increase the accuracy of the test and restrain negative influence of temperature drift, the Wheatstone bridge structure is introduced. The test results show that before capping, the gauge has an average sensitivity of 1.04 × K· in dynamic range of 0.01–20 Torr. After capping, the sensitivity of the gauge does not decrease but increases to 1.12 × K· .

Measurement and study of low-frequency noise in TMR magnetic field sensor

The magnetic field sensor based on tunnel magnetoresistance (TMR) effect has potential applications in various fields due to its very high field sensitivity and low power comsuption. However, the resolution of magnetic sensor depends on not only field sensitivity, but also intrinsic noise level. The intrinsic noise of an electronic device is normally frequency-dependent and increases in low frequency range. In a magnetic tunneling system, thermal magnetization fluctuation in the magnetic layer can couple to the resistance through the spin-dependent tunneling effect and create low-frequency magnetic noise. In addition, the charge trapping effect in the oxide barrier may also contribute to the external low-frequency noise. Therefore, the depression of the noise in TMR magnetic field sensor, especially the low-frequency noise, is extremely important for the application with high resolution requirement. In this work, a low-frequency noise measurement system for TMR magnetic sensor is built by using a highaccuracy data acquisition card and a low noise preamplifier. After subtracting the circuit noise from the measured noise, the noise spectral patterns of TMR magnetic field sensor with a full Wheatstone bridge structure are obtained under various bias currents and external magnetic fields. It is found that the noise spectra of the TMR sensor exhibit a clear 1/f character in the low frequency region and the noise power spectral intensity is proportional to the square of the bias current. By fitting the power spectral density of the noise versus frequency in the TMR sensor, the Hooge parameters are obtained, which remain unchanged in the measurement. The noise intensity increases abruptly in the magnetization switching region of the free layer in magnetic tunnel junction, suggesting that the 1/f noise mostly comes from the magnetic noise. In a magnetic hysteresis loop, this noise power is strongly field-dependent, which is due to thermal magnetization fluctuations in magnetic layers. We attribute this magnetic fluctuation to thermally excited hopping of the magnetic domain wall between the pinning sites. Finally, according to the R-H transfer curves and the measured noise spectra of the TMR sensor, the detectable minimum magnetic fields of the sensor are 9 nT and 1.3 nT at 100 Hz and 4 kHz with 1 V input voltage, respectively. These results pave a way for optimizing the noise properties of TMR magnetic sensors.

Design of a MEMS piezoresistive differential pressure sensor with small thermal hysteresis for air data modules.

The design, fabrication, and evaluation results of a MEMS piezoresistive differential pressure sensor fabricated by the dry etching process are described in this paper. The proposed sensor is designed to have optimal performances in mid-pressure range from 0 psi to 20 psi suitable for a precision air data module. The piezoresistors with a Wheatstone bridge structure are implanted where the thermal effects are minimized subject to sustainment of the sensitivity. The rectangular-shaped silicon diaphragm is adopted and its dimension is analyzed for improving pressure sensitivity and linearity. The bridge resistors are driven by constant current to compensate temperature effects on sensitivity. The designed differential pressure sensor is fabricated by using MEMS dry etching techniques, and the fabricated sensing element is attached and packaged in a Kovar package in consideration of leakage and temperature hysteresis. The implemented sensors are tested and evaluated as well. The evaluation results show the static RSS (root sum square) accuracy including nonlinearity, non-repeatability, and pressure hysteresis before temperature compensation is about 0.09%, and the total error band which includes the RSS accuracy, the thermal hysteresis, and other thermal effects is about 0.11%, which confirm the validity of the proposed design process.

基于纳米多晶硅薄膜压力传感器胎压监测系统

本文给出纳米多晶硅薄膜压力传感器，由方形硅膜和四个纳米多晶硅薄膜电阻构成惠斯通电桥结构组成，采用MEMS技术在 硅片实现传感器芯片制作。当工作电压VDD = 5.0 V时，传感器灵敏度为0.15 mV/kPa，准确度为0.39 %F.S.，可实现轮胎胎压测量。根据胎压传感器特性和NRF24L01无线通信技术，实现胎压监测系统设计。通过无线模块实现实时数据传输，该系统可实现对轮胎胎压的实时监测，保证车辆安全。 This paper presents the nano-polysilicon thin film pressure sensor, which consists of four nano- polysilicon thin film resistances fabricated on the silicon membrane of C-type silicon cup, and the resistances make up the Wheatstone bridge structure. The chip of sensor is fabricated by micro electromechanical system (MEMS) technology on a silicon wafer. When supply voltage VDD = 5.0 V, the sensitivity is 0.15 mV/kPa, and the accuracy is 0.39 %F.S.; tire pressure measurement can be realized. According to the characteristics of tire pressure sensors and the NRF24L01 wireless communication technology, the Tire Pressure Monitoring System (TPMS) is designed. By transmitting data timely through the wireless module, this system can realize the wireless and real-time monitoring, so as to ensure the safety of the vehicle.

A Compact Behavioral Simulation Model for CMOS Vertical Hall-Effect Devices

A compact behavioral simulation model for CMOS five-contact vertical Hall devices is presented. In term of the internal current flow geometry, the vertical Hall device is modeled based on an asymmetric Wheatstone bridge structure, including four current-controlled Hall voltage sources and four asymmetric lumped resistors. The lumped resistors on the Wheatstone bridge are calculated preliminarily by conformal mapping method. More importantly, the model takes into account the lateral diffusion effect and junction field effect which further improves the simulation accuracy. The behavioral model has been written in Verilog-A language with ten more physical and process parameters. The behavioral model simulation has been successfully performed in the Cadence Spectre environment with 0.8 μm high voltage CMOS technology parameters. The model’s simulation results are in good agreement with the reported experimental results.

Piezoresistive bridge microcantilevers biosensor based on SOI wafer for glucose detecting

To measure glucose accurately, a high sensitivity piezoresistive four-set Wheatstone bridge structure microcantilevers glucose biosensor was developed. The microcantilevers with a piezoresistor were fabricated using a series of bulk silicon processes based on a silicon-on-insulator wafer. An improved Wheatstone bridge readout circuit with voltage closed-loop auto-zero and high-gain magnified functions is proposed. The sensing microcantilever gold-coated surface was functionalised by immobilising a self-assembled monolayer of 4-mercaptophenylboronic acid, the reference cantilever was not functionalised. The relationship between a piezoresistive bridgeout caused by the microcantilevers bending and glucose solution concentration was obtained at 5 and 15 mM. Experimental results demonstrated that the output voltage induced by microcantilevers bending is proportional to the glucose concentrations and the sensitivity is up to 0.1 V/mM.

Structure Design, Fabrication and Characteristics of Polysilicon Nano-Thin Films Resistances Pressure Sensor Based on MEMS Technology

A polysilicon nano-thin films pressure sensor was designed and fabricated on single crystal silicon substrate by MEMS technology in this paper, and the sensor is composed by Wheatstone bridge structure with four polysilicon nano-thin films resistances fabricated on squared silicon membrane. The experiment result shows that, under constant current power supply of 0.875mA , full scale output is 24.05 mV at room temperature, sensitivity is 0.15 mV/kPa, when the temperatures are from -20 to 80°C, the coefficient of zero temperature and sensitivity temperature is –960 ppm/°C and –820 ppm /°C respectively.

Point-of-care temperature and respiration monitoring sensors for smart fabricapplications

Advances in smart sensors, miniaturization, and related technologies leading to theemergence of smart fabrics are prerequisites to the construction of a point-of-care (POC)system for continuous health monitoring and illness prevention. Low manufacturing cost,light weight, portability and flexibility are among the requirements for smartsensors when embedded into smart fabrics. Organic semiconductor technologyhas recently been envisioned to meet these requirements, and to encourage thedevelopment of organic semiconductor based sensors because of its low processtemperature and potential for very low cost manufacturing. In this paper, wepresent flexible sensors based on an organic semiconductor capable of measuringphysiological parameters such as strain and temperature, adopting pentacene thin filmtransistors (TFTs) and Wheatstone bridge structures. It is expected that these sensors,integrated into textile structures, will enable real time POC monitoring of a patient’srespiration rate, skin temperature, body heat flow and body temperature at an earlystage.