Silicon Piezoresistive Sensor Research Articles

Design of flexible sensor for wind pressure monitoring of stay cables

Strong winds can make a bridge’s cable-stayed cables produce violent vibrations, leading to fatigue of the cable-stayed cables and damaging the cable-stayed bridge’s structure. Accurately and effectively obtaining data on the wind loads applied to the cable-stayed cables is important for assessing the cable-stayed cables’ health. The existing sensing elements for detection include diffusion silicon piezoresistive sensor, strain gauge, and other rigid sensors. However, most of them present such disadvantages as rigidity, difficult to fit the curved surface, high cost and low sensitivity. And it cannot be directly installed on the surface of the cable. In this paper, a conductive hydrogel flexible pressure sensor based on TA/CB@PDMS was developed, using carbon black (CB) as the main conductive medium, with good electrical conductivity, high sensitivity (0.65 kPa−1) and excellent tensile properties (210% tensile breakage). Meanwhile, a salt permeation method (Soak the sensor in LiBr solution) was used to effectively inhibit the sensor’s water from being evaporated and frozen. Its substrate incorporates tannic acid to increase the sensor’s adhesion so that it adheres well to the diagonal cable’s surface. In this paper, the wind speed variation around the diagonal cable and the force distribution on the surface with considering the fluid-structure coupling effect are analyzed by ANSYS WORKBECH finite element simulation. Wind tunnel experiments simulate the sensor’s force response when the inclined cable is subjected to different wind speeds, and the detection accuracy reaches 96.17%. The results show the sensor developed in this paper can realize accurate wind pressure detection of the inclined cable. This study provides a new method for wind pressure detection and health inspection of diagonal cables.

Focus on test, measurement, quantum metrology, and analytical equipment

Focus on test, measurement, quantum metrology, and analytical equipment

A numerical modeling approach to estimate the piezoresistance of diffused resistors with experimental validation

Silicon piezoresistive sensors have been widely used for many applications in recent decades. Monocrystalline silicon resistors are realized using an ion-implantation or a thermal diffusion process with a Gaussian or complementary error function profile. However, over the years, most researchers have neglected the doping concentration profile of the piezoresistor in the modeling stages resulting in erroneous responses that are far removed from experimental results of fabricated resistive sensors. In the present work, we propose a simulation approach to accurately estimate the piezoresistance of thermally diffused resistors with a non-uniform doping profile. We have modeled the diffused resistor as a parallel combination of several small slices, each having a unique piezoresistive coefficient. Three different slicing strategies were investigated to evaluate the impact of the piezoresistive coefficients, the electrical resistivity of the resistor slices, and the stress profile across the thickness of the resistor embedded in an accelerometer device. The cumulative impact of these parameters on the sensor’s overall sensitivity is evaluated. Further, we have also studied the influence of the accelerometer’s flexure thickness on the sensor’s sensitivity. It is observed from the simulation results that one of the slicing strategies with more slices at the surface of the resistor results in less than 1% error compared to the experimental results of an accelerometer device with a 60 µm flexure thickness.

Comparison between the portable pressure measuring device and PicoPress® for garment pressure measurement on hypertrophic burn scar during compression therapy

PurposeThe current standard treatment for hypertrophic scars following burn injury is pressure garment therapy. The experimenters developed the novel portable pressure measuring device using silicon piezoresistive sensors. As PicoPress® is the most accurate (i.e., lowest variation and error) manometric sensor for pressure measurement, we sought to compare and examine the accuracy of the novel device regarding in vitro pressure measurements at the hypertrophic scar–pressure garment interface. MethodsThe novel device was designed to operate in non-corrosive media, such as air. The device can use up to six pressure sensing points and was developed to adjust the number of pressure sensors according to the size of the scar. Pressure measurements were acquired through a readout circuit consisting of an analog-to-digital converter, a microprocessor, and a Bluetooth transmission module for wireless data transmission to an external device. All signals were converted into mean pressure expressed in millimeters of mercury (mmHg). The mean pressure values measured by the sensors were compared to those obtained from PicoPress®. 55 garment pressures recordings were obtained from the sensors over this study conducted in 2018–February 2020. We then analyzed the test–retest reliability using the intraclass correlation coefficients (ICC). PicoPress® was also employed in the same pressure garments for obtaining similar measurements. A two way random effects model ICC with 95% confidence intervals was used to compare the mean pressure values obtained from the silicon piezoresistive sensors to the PicoPress® measurements. ResultsThe test–retest reliability of the pressure sensors was close to the acceptable level for clinical use regarding stationary interface pressure measurement (ICC = 0.99, 95% CI 0.990−0.997). The mean pressure obtained from the silicon piezoresistive pressure sensors showed an accordance with the measurements from PicoPress® (ICC = 0.97, 95% CI 0.947−0.985). ConclusionThe novel device may present a viable alternative to PicoPress® for garment pressure measurements. In addition, the novel device improves adaptability to the hypertrophic scar shape and size. Complementary characteristics such as wireless transmission to an external device may allow burn patients to continuously wear the device for real-time measurements during pressure garment therapy, thus improving existing devices including PicoPress®.

Field Test of Excess Pore Water Pressure at Pile-Soil Interface Caused by PHC Pipe Pile Penetration Based on Silicon Piezoresistive Sensor.

Prestressed high-strength concrete (PHC) pipe pile with the static press-in method has been widely used in recent years. The generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking have an important influence on the pile’s mechanical characteristics and bearing capacity. In addition, this can cause uncontrolled concrete damage. Monitoring the change in excess pore water pressure at the pile–soil interface during pile jacking is a plan that many researchers hope to implement. In this paper, field tests of two full-footjacked piles were carried out in a viscous soil foundation, the laws of generation and dissipation of excess pore water pressure at the pile–soil interface during pile jacking were monitored in real time, and the laws of variation in excess pore water pressure at the pile–soil interface with the burial depth and time were analyzed. As can be seen from the test results, the excess pore water pressure at the pile–soil interface increased to the peak and then began to decline, but the excess pore water pressure after the decline was still relatively large. Test pile S1 decreased from 201.4 to 86.3 kPa, while test pile S2 decreased from 374.1 to 114.3 kPa after pile jacking. The excess pore water pressure at the pile–soil interface rose first at the initial stage of consolidation and dissipated only after the hydraulic gradient between the pile–soil interface and the soil surrounding the pile disappeared. The dissipation degree of excess pore water pressure reached about 75–85%. The excess pore water pressure at the pile–soil interface increased with the increase in buried depth and finally tended to stabilize.

A Model Test for the Influence of Lateral Pressure on Vertical Bearing Characteristics in Pile Jacking Process Based on Optical Sensors.

Photoelectric integrated testing technology was used to study precast piles during pile jacking at the pile–soil interface considering the influence of the earth and pore water pressures on its vertical bearing performance. The low temperature sensitive fiber Bragg grating (FBG) strain sensors and miniature silicon piezoresistive sensors were implanted in the model pile to test the changes of earth pressure, pore water pressure and pile axial force of the jacked pile at the pile–soil interface, and the influence of lateral pressure on pile axial force was studied. The test results showed that the nylon rod is feasible as a model pile. The FBG strain sensor had a stable performance and monitored changes in the axial force of the model pile in real time. The miniature earth and pore water pressure sensors were small enough to avoid size effects and accurately measured changes in the earth and pore water pressures during the pile jacking process. During pile jacking, the lateral earth pressure increased gradually in depth, and the lateral earth pressure at the same depth tended to decrease at greater depths. Lateral pressures caused the axial force of the pile to increases by a factor of 1–2, where the maximum was 2.7. Therefore, the influence of the lateral pressure must be considered when studying the residual pile stress.

Effect of Roughness on Shear Characteristics of the Interface between Silty Clay and Concrete

In order to study the effect of roughness on the mechanical parameters of silty clay‐concrete interface, and to explore the applicability of silicon piezoresistive sensor to test the interface pressure, a large‐scale direct shear test system was used to carry out experimental research on the shear characteristics of silty clay‐concrete interface under different roughness conditions. Based on silicon piezoresistive sensor, the shear characteristics of silty clay‐concrete interface are analyzed. The results show that the silicon piezoresistive sensor has excellent performance in measuring the interface pressure and can accurately obtain the shear characteristics of the silty clay‐concrete interface. The roughness has a significant influence on the shear strength, shear stiffness, and other mechanical properties of the prefabricated pile‐soil interface. With the increase of roughness, interface shear strength, interface friction angle, shear stiffness coefficient, and interface residual shear stress all show an increasing trend, with the maximum increase of 37.0%. The interface adhesion decreased first and then increased with the increase of roughness, with an increase of 23.7%. The test results can provide reference for the engineering practice of jacked pile.

Temperature characteristic and compensation algorithm for a marine high accuracy piezoresistive pressure sensor

Pressure sensor used in marine hydrographic survey is an important device for the deep sea detection, the tsunami forecast and the marine engineering. Owing to its mature technology process and low production cost, silicon piezoresistive sensor is widely applied in the field of industrial pressure measurement. However, its temperature effect can result in non-negligible dynamic error, which cannot meet requirement of deep sea environment. The silicon-on-sapphire pressure sensor based on stress cup structure is presented. The output voltage values show a high deviation in the range of −6∼50°C due to temperature drift. In order to minimise this temperature effect, a temperature compensation algorithm is proposed to realise 0.03% accuracy in the full scale 60 MPa range. Compared with a reference commercial sensor in deep sea experiment, the test pressure sensors exhibit minor error, excellent similarity and coherence. This numerical method provides a new research direction for environmental self-adaptive sensor. It can be emphasised that this sensor will have a good application prospect in unattended long-term ocean observation system.

High-Gauge Factor Strain Sensor Based on Piezoelectric Aluminum Nitride Coupled to MOSFET

The development of high-sensitive and economical strain sensors is crucial for precise and efficient measurement of ultra-small strain in industrial applications. This paper reports a microfabricated strain sensor based on aluminum nitride (AlN) combined with a metal-oxide-semiconductor field effect transistor (MOSFET). A high-quality AlN thin film works as a sensing element, which is connected electrically to the gate electrode of the MOSFET for the amplification of piezoelectric response of the AlN thin film. The pseudo gauge factor (GF) of the MOSFET is evaluated from the source-drain resistance change under the application of stress to the piezoelectric AlN thin film. A GF of as high as 1340 is obtained, which is seven times larger than the best GF demonstrated for the state-of-the-art silicon piezoresistive strain sensor. The exponential change of drain-source current with gate voltage in subthreshold region of the MOSFET offers a large enhancement of the sensitivity of such sensors. The developed strain sensor has various applications in strain and stress measurements in an ultra-small strain range.

A chip-level oven-controlled system used to improve accuracy of silicon piezoresistive pressure sensor

High precision is an important indicator for the silicon piezoresistive pressure sensor, which is deeply affected by the ambient temperature. This paper presented a chip-level oven-controlled system to operate the silicon piezoresistive pressure sensor at a constant temperature. However, the changes in ambient temperature still affect the temperature of the silicon piezoresistive pressure sensor due to the non-coplanar temperature control and the direct heat transfer between the piezoresistance on the surface of the pressure sensor and the environment. In order to decrease the effects and further improve the accuracy of the silicon piezoresistive sensor, a compensation function was introduced in the designed system. In addition, the oven-controlled structure fabricated by the MEMS process and the silicon piezoresistive pressure sensor were implemented at the chip level, which further reduced power consumption. The feasibility of the design was verified by the results of the thermodynamic model and COMSOL Multiphysics simulation analysis. Test results showed that when the pressure ranged from 100 hPa to 1100 hPa, the designed system performed a maximum measurement error no more than ±0.2 hPa from −45 °C to 45 °C. After compensation, the accuracy, sensitivity temperature coefficient, offset temperature coefficient of the silicon piezoresistive pressure sensor can reach 0.02% FS, 1.081 × 10−5/°C, 2.22 × 10−4% FS/°C respectively.

Piezoresistive temperature sensors fabricated by a surface micromachining CMOS MEMS process

This paper presents a micromachined monocrystalline silicon piezoresistive temperature sensor fabricated by a surface micromachining CMOS (Complementary Metal Oxide Semiconductor) MEMS (Micro-Electro-Mechanical System) process. The design of the temperature sensor is based on the structure of the multi-layer cantilever beam and the bimetallic effect. The temperature change of the cantilever beam is translated into the change of the piezoresistance’s value. The test results show that the sensitivities of the sensors are 27.9 mV/°C with 100 Ω/▯ piezoresistance between −40 °C to 60 °C and 7.4 mV/°C with 400 Ω/▯ piezoresistance between −90 °C to 60 °C. The temperature sensor proposed in this paper can be used in radiosondes for its low operating temperature (as low as −90 °C), small size (below 1 mm2) and low heat capacity.

A Monolithic Approach to Downscaling Silicon Piezoresistive Sensors

Multi-scale integration remains the primary challenge in the fabrication of miniature piezoresistive sensors, as the co-fabrication of a silicon nanowire along with a microscale shuttle is the main architecture facilitating high-sensitivity transduction. The efforts in this field are marred by the lack of batch techniques compatible with semiconductor manufacturing. A technology is introduced here that leads to the fabrication of a piezoresistive silicon nanowire sharing the same single-crystalline device layer of a thick silicon-on-insulator wafer as the microscale component. The approach is based on a combination of high-resolution lithography with a two-stage etching process. The demonstration is carried out by spanning an electrostatic comb-drive actuator and a micromechanical amplifier by a single nanowire. A gage factor range of 135-145 is obtained, corresponding to an almost 20% resistance change for a nanowire strain of 1.26 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The technique is shown to generate a two-order-of-magnitude scale difference within the same silicon crystal. It also provides ease of electrical access to the nanowire, as the nanowire does not remain buried underneath the thick micromechanical system. With the associated lack of high-temperature processes and its CMOS-compatibility, the technique is a promising enabler for future miniaturized piezoresistive sensors.

Numerical study on the influence of buried oxide layer of SOI wafers on the terminal characteristics of a micro/nano cantilever biosensor with an integrated piezoresistor

Piezoresistive micro/nano cantilever sensors have been extensively utilized in the detection and quantification of miniscule forces generated due to the physical interaction of biomolecules. Due to the ultra-sensitive nature of piezoresistive cantilever sensors, they have found numerous applications, especially in the development of point-of-care testing systems for healthcare applications. Over the years, silicon-on-insulator (SOI) wafers have been widely utilized to realize silicon based piezoresistive cantilever sensors due to their performance and fabrication related advantages. Treatise encompasses examples where researchers have retained the buried oxide (BOX) layer of SOI wafers to realize piezoresistive cantilever devices. In this paper, we investigate the impact of BOX layer of SOI wafers on the performance of composite piezoresistive cantilever biosensors. Typically, the response of piezoresistive cantilever sensors is evaluated by considering only the electro-mechanical response. However, the design of such sensors is a multi-variant problem due to (i) their composite structure and (ii) interdependent nature of the electrical, mechanical and thermal characteristics. Therefore, in the present study, we devise a new figure of merit (FoM) defined as the product of sensitivity ratio and the square of resonant frequency of the sensor. The sensitivity ratio represents the ratio of the electrical sensitivity due to surface stress and thermal sensitivity of the sensor. The proposed FoM takes into account the interplay between the electrical, mechanical and thermal response of the sensor. Finite element method based numerical simulations are performed to model and investigate the influence of BOX layer on the thermo-electro-mechanical response of a square shaped silicon piezoresistive cantilever sensor. Simulation results show that the presence of the supporting BOX layer enhances the mechanical stability i.e. spring constant and resonant frequency of the sensor. In addition, it is found that the BOX layer reduces the zero bias deflection of the cantilever due to difference in TCE of the constituent layer materials. Furthermore, it is shown that by dimensional optimization of the thicknesses of the constituent layers, sensitivity ratio of the sensor with BOX layer can be improved up to 2.96.

Double-meander spring silicon piezoresistive sensors as microforce calibration standards

A transferable force calibration standard based on a silicon microelectromechanical sensor has been designed, fabricated, and characterized for micrometrology applications. Two essential elements of double-meander springs and full piezoresistive etched p-silicon-on-insulator Wheatstone bridges (WBs) are integrated to the sensor for enhancing the device’s sensitivity and eliminating the current leakage during an active sensing operation, respectively. The design process is supported by three-dimensional finite element modeling to select the optimal proposed sensors as well as simulating their mechanical and electrical properties in the desired force range (≤1000 μN). To fabricate the microforce sensors, a bulk micromachining technology is used by frequently involving an inductively coupled plasma deep reactive ion etching at cryogenic temperature. Several optical and electrical characterization techniques have been utilized to ensure the quality of the fabricated WBs, where their measured offset voltage can be down to 0.03±0.071 mV/V. In terms of its linearity, the fabricated device exhibits a small nonlinearity of <3%, which leads this sensor to be appropriate for precise microforce standard.

4H-SiC Piezoresistive Pressure Sensors at 800 °C With Observed Sensitivity Recovery

Uncooled MEMS-based 4H-SiC Wheatstone bridge configured piezoresistive pressure sensors were demonstrated from 23 °C to 800 °C. The full-scale output (FSO) voltage exhibited gradual decrease with increasing temperature from 23 °C to 400 °C, then swung upward as temperature increased further to where the values measured at 800 °C were nearly equal to or higher than the room temperature values. This newly observed FSO behavior in 4H-SiC contrasts sharply with the FSO behavior of silicon piezoresistive sensors that decrease continuously with increasing temperature. The increase in the sensor output sensitivity at 800 °C implies higher signal to noise ratio and improved fidelity, thereby offering promise of further insertion into >600 °C environments without the need for cooling and complex signal conditioning.

Piezoresistive sensors for force mapping of hip-prostheses

The success of artificial prosthetic replacements depends on the fixation of the artificial prosthetic component after being implanted in the thighbone. This work shows a smart prosthesis based on highly sensitive silicon thin-film piezoresistive sensors attached to a hip prosthesis. The performance of the sensors for this application is studied and compared to commercial strain gauge sensors. Mechanical stress–strain experiments were performed in compressive mode, during 10,000 cycles and data was acquired at mechanical vibration frequencies of 0.5Hz, 1Hz and 5Hz, and sent to a computer by means of a wireless link. The results show that there is a decrease in sensitivity of the thin-film silicon piezoresistive (n-type nanocrystalline Si) sensors when they are attached to the prosthesis, however this decrease does not compromise its monitoring performance. The sensitivity, compared to that of commercial strain gauges, is much larger due to their higher gauge factor (−23.5), when compared to the gage factor of commercial sensors (2).

An Ultra-Thin Piezoresistive Stress Sensor for Measurement of Tooth Orthodontic Force in Invisible Aligners

A silicon piezoresistive stress sensor is developed to measure the three components of the orthodontic forces of a tooth in invisible aligners. The stress sensor chip consists of multiple piezoresistor rosettes, and is fixed on the tooth surface to measure the orthodontic force induced stresses. An inverse problem algorithm is established to reconstruct the orthodontic forces of the tooth from the measured stresses. A key thinning process is developed using chemical-mechanical polishing to thin the sensor chip from 650 to 100 , such that it can be accommodated to the limited space between the aligner and the tooth, without much influence on the orthodontic force. The ultra-thin thickness enables the sensor chip to be compliance with tooth deformation, and improves the stress measurement sensitivity as much as 40 times, making it capable of measuring small orthodontic force. The sensor design, fabrication, orthodontic stress measurement, and force reconstruction are given in details, and the experimental results demonstrate the feasibility of using miniaturized and ultra-thin sensors to determine the in vitro orthodontic forces.

Research Based on Barycenter Identification about Array Haptic System Pressure and Temperature Information

Robot touch sensation is an important feeling pattern for robots to gain environment information in non-vision sensor domain, in this thesis, the writer uses silicon piezoresistive sensor to form Array haptic system, and form gray level image from collected pressure and temperature information, and judge the slippage condition of objects through image preprocessing, region segmentation, centroid identification, and show the result picturesquely by using image. The experimental result shows that this method can fastly and effectively judge the slippage condition of objects, and it can intuitionally shows the condition of distribution of object temperature.

Piezoresistive Cantilever Beam for Force Sensingin Two Dimensions

A novel two-dimensional piezoresistive nano-Newton resolution force sensing cantilever is presented. The silicon cantilever is fabricated using bulk micromachining. Two 500-nm-thick p-doped epitaxial silicon piezoresistive sensors are located on both sides of the cantilever. This structure detects both the lateral and vertical applied forces by electronic switching between two configurations of a Wheatstone bridge. A force sensitivity is measured up to 100 and 540 V/N for lateral and vertical configurations, respectively. The corresponding force resolution is estimated at 21 and 4 nN, respectively. This force-sensing cantilever can be used for measuring the contact force between manipulating tools and small objects in, e.g., living cell handling, minimally invasive surgery, and microassembly

Hydrogel-based piezoresistive pH sensors: Design, simulation and output characteristics

The paper summarizes a detailed design study of silicon piezoresistive pH sensors, whose operation relies on the pH sensitive swelling of a polymer hydrogel. It is based on an analytical model of the hyperelastic–viscous behaviour of hydrogel. The pH sensor behaviour was investigated by simulating and measuring the silicon membrane deflection and the stress inside the membrane. Simulation was performed using finite element method (ANSYS). A technology to manufacture such hydrogel-based sensors was developed. We found satisfying agreement between simulation and measured results for the sensor output characteristics.