Wide Linear Range Fabric Pressure Sensors Based on Multiscale Inorganic Structures

Flexible piezo-resistive pressure sensor based on conducting PANI on paper substrate

Porous reduced graphene oxide@multi-walled carbon nanotubes/polydimethylsiloxane piezoresistive pressure sensor for human motion detection

This paper presents the design and simulation of MEMS based piezoresistive pressure sensor for microfluidic applications. Geometrical parameters are very much considerable when designing microstructure of the pressure sensor. Hence, an analysis is carried out by changing the dimensional parameters of three different diaphragm geometries namely square shaped diaphragm, circular shaped diaphragm and cross sectional beam shaped diaphragm respectively. This is performed in three dimensional mesh plots using Matlab. The Finite Element Method (FEM) analyses are performed in COMSOL and by comparing the results, the square type diaphragm is chosen as best diaphragm geometry for the microfluidic applications. In addition, modal analysis is carried out by using Ansys to identify the natural frequency of the best diaphragm geometry. Also Piezoresistive sensing elements are designed and simulated by performing coupled field analysis using COMSOL Multiphysics. Simulation results reveal that piezo resistive square type pressure sensors have high sensitivity in a wide range of pressures.

Pressure measurement is a key part of many commercial and industrial systems. Piezoresistive pressure sensors are simpler to integrate with electronics, they are inherently shielded from RF noise and their response is more linear while compared to capacitive pressure sensors. And piezoresistive devices have always dominated the pressure sensor market. The analyticals that are typically used to model the diaphragm of the pressure sensor have been analysed by many researchers. To optimize the pressure sensor for parameters like linearity and sensitivity, the Finite Element Method (FEM) is incorporated. The selection of appropriate parameters of piezoresistors such as the shape and the position of the piezoresistor on the pressure sensor diaphragm, thickness of diaphragm are important. This study shows the scope of using analytical solutions and design techniques for a piezoresistive pressure sensor.

Wearable devices have developed significantly due to the use and development of various materials such as organic materials and carbon nanotubes, and the demand for wearables is also growing. The piezoresistive pressure sensor has been developed using conductive fabric coated with a simple solution coating process. The fabric has an open structure with the interconnected top and lower layers that can be utilized as pressure sensors and can detect physical movements. The piezoresistive pressure sensor has excellent resistance linearity in the low pressure to 10kPa range, as well as consistent resistance to strain up to 20% when stretched. The pressure sensor array can detect pressure-induced local deformation and will be expected to contribute considerably to the development of wearable devices with a simplified process.

At present, the silicon piezoresistive pressure sensor is a mature technology in the industry, and its measurement accuracy is more rigorous in many advanced applications. Micro piezoresistive pressure sensor is fabricated by a MEMS process, and its main operational principle is that the external pressure loading causes the deflection, strain, and stress which occur on the silicon membrane. The environmental temperature, the humidity, and the pressure will reduce its performance. Moreover, the drifts of output voltage in the same temperature caused by the residual stress on the aluminum trace under thermal cycle loading also influence the performance of the piezoresistive pressure sensor. This is called the thermal hysteresis phenomenon, and the variation of output voltage is called the thermal hysteresis voltage. Among the critical issues of silicon piezoresistive pressure sensor, the hysteresis phenomenon should be deeply paid attention to obtain better sensor accuracy. For this reason, this research would like to investigate the effect of the external loading on the output voltage of a pressure sensor. Based on the process of pressure sensors, this research adopts the concept of pseudo temperature combined with a finite element method (FEM) to obtain the thermal hysteresis voltage. After several numerical analysis of thermal hysteresis voltage, the experiment is then performed to validate the simulation results. After being validated with the experimental results, the variation of thermal hysteresis voltage under a different trace layout is analyzed. Based on simulation results of a different trace layout, it is found that the trace line layout plays an important role in the thermal hysteresis performance of a pressure sensor, which indicates that the longer aluminum trace increases the hysteresis voltage. The uniform and symmetrical layout of aluminum trace can reduce the variation of resistance change and decrease the hysteresis voltage. Furthermore, the trace layout which is far away from the silicon membrane and piezoresistance is suggested to reduce the hysteresis voltage.

Pressure sensors are a key component in electronic skin (e-skin) sensing systems. Most reported resistive pressure sensors have a high sensitivity at low pressures (<5 kPa) to enable ultra-sensitive detection. However, the sensitivity drops significantly at high pressures (>5 kPa), which is inadequate for practical applications. For example, actions like a gentle touch and object manipulation have pressures below 10 kPa, and 10–100 kPa, respectively. Maintaining a high sensitivity in a wide pressure range is in great demand. Here, a flexible, wide range and ultra-sensitive resistive pressure sensor with a foam-like structure based on laser-scribed graphene (LSG) is demonstrated. Benefitting from the large spacing between graphene layers and the unique v-shaped microstructure of the LSG, the sensitivity of the pressure sensor is as high as 0.96 kPa−1 in a wide pressure range (0 ~ 50 kPa). Considering both sensitivity and pressure sensing range, the pressure sensor developed in this work is the best among all reported pressure sensors to date. A model of the LSG pressure sensor is also established, which agrees well with the experimental results. This work indicates that laser scribed flexible graphene pressure sensors could be widely used for artificial e-skin, medical-sensing, bio-sensing and many other areas.

Optimising polyurethane/CNTs piezoresistive pressure sensors by varying the modulus of the polymer matrix

Flexible piezoresistive pressure sensors may exhibit excellent sensing performances to be applied in wearable electronics, medical diagnosis, and electronic skin. Herein, we report a multi-layer and phased-responsive reduced graphene oxide/MXene-based piezoresistive pressure sensor with hierarchical microspines constructed by sandpaper as the template. Thanks to the multi-level and multi-layer structure, the obtained sensor realized phased response and showed wide detection range (up to 70 kPa), fast response (response/recovery time of 40/80 ms), and excellent working stability (1000 fatigue cycles). Furthermore, the sensor was successfully applied for detecting various human motions including pulse beats, cheek bulging, nodding, finger bending, speech recognition, handwriting, and other pressure signals. Besides, a 6 × 6 sensing matrix integrated by the sensors was able to sensitively perceive the distribution of plane pressure. The findings in this work conceivably stand out as a new strategy to fabricate high-performance piezoresistive pressure sensors in the fields of intelligent healthcare and medical diagnosis, wearable electronic devices, electronic skin, and human-machine interaction.

Flexible piezoresistive sensors have huge potential for health monitoring, human-machine interfaces, prosthetic limbs, and intelligent robotics. A variety of nanomaterials and structural schemes have been proposed for realizing ultrasensitive flexible piezoresistive sensors. However, despite the success of recent efforts, high sensitivity within narrower pressure ranges and/or the challenging adhesion and stability issues still potentially limit their broad applications. Herein, we introduce a biomaterial-based scheme for the development of flexible pressure sensors that are ultrasensitive (resistance change by 5 orders) over a broad pressure range of 0.1-100 kPa, promptly responsive (20 ms), and yet highly stable. We show that employing biomaterial-incorporated conductive networks of single-walled carbon nanotubes as interfacial layers of contact-based resistive pressure sensors significantly enhances piezoresistive response via effective modulation of the interlayer resistance and provides stable interfaces for the pressure sensors. The developed flexible sensor is capable of real-time monitoring of wrist pulse waves under external medium pressure levels and providing pressure profiles applied by a thumb and a forefinger during object manipulation at a low voltage (1 V) and power consumption (<12 μW). This work provides a new insight into the material candidates and approaches for the development of wearable health-monitoring and human-machine interfaces.

A nickel–chromium (Ni–Cr) piezoresistive pressure sensor is presented, which has the advantages of low-cost and easy fabrication processes. In the designed sensor, Ni–Cr alloy (80:20 wt%), which can be fabricated using simple processes, is used as the strain-detecting material with a smaller but acceptable gauge factor. Eutectic-bonding technology, based on silver–tin (Ag–Sn) alloy, which contains 3.5 wt% Ag and has 20 µm thickness, is used as an alternative and easy bonding choice to complete the vacuum package. Normally, Ag–Sn alloy is mostly obtained by the electrochemical deposition method. However, here the Ag–Sn solder film is directly used as a bonding material. It reduces the fabrication difficulty of eutectic bonding of the proposed pressure sensor. By studying the processes of annealing of Ni–Cr fabrication and eutectic bonding with Ag–Sn, the authors complete the alloy piezoresistive atmosphere pressure sensor. Bonding quality is evaluated by inspection through the deflection of a diaphragm of silicon with more than 95% of the area successfully bonded. The pressure–voltage characteristic test results suggest a precision within 0.3% in square fitting. The temperature coefficient offset is 620 ppm/(°C free space optic (FSO)).

Sensitivity analysis of packaging effect of silicon-based piezoresistive pressure sensor

High reliability of piezoresistive pressure sensors by wafer to wafer direct bonding at room temperature

Surface micromachining is becoming increasingly popular for microelectromechanical systems (MEMS) and a new application for this process technology is pressure sensors. Uncompensated surface micromachined piezoresistive pressure sensors were fabricated by Sandia National Labs (SNL). Motorola packaged and tested the sensors over pressure, temperature and in a typical circuit application for noise characteristics. A brief overview of surface micromachining related to pressure sensors is described in the report along with the packaging and testing techniques used. The electrical data found is presented in a comparative manner between the surface micromachined SNL piezoresistive polysilicon pressure sensor and a bulk micromachined Motorola piezoresistive single crystal silicon pressure sensor.

Piezoresistive pressure sensors based on sponge are widely concerned because of their wide strain range, convenient signal acquisition, and good compressibility, yet it is still a challenge to acquire sponge‐based pressure sensors with low cost and excellent sensing performance. Herein, low‐priced FeCl3.6H2O and pyrrole (Py) are dispersed in deionized water to form FeCl3.6H2O/Py solution. Commercial latex sponge is impregnated into this solution to prepare conductive polypyrrole/latex (PPy/latex) sponge through low‐temperature interfacial polymerization. The surface of latex sponge is covered by the micro‐wrinkled PPy, which endows the PPy/latex sponge with a certain electrical conductivity. The specific porous structure and high elasticity of the latex sponge are the basic conditions for PPy/latex sponge excellent piezoresistive behaviors. PPy/latex sponge based piezoresistive pressure sensor shows high sensitivity (0.084 kPa−1 at below 3.12 kPa), wider sensing range (0–85.0%) and long durability over 3800 s (1800 cycles). At the same time, the ability of the PPy/latex sponge based piezoresistive pressure sensor to monitor human movement has been successfully evaluated in some application scenarios, such as bending fingers, grabbing objects, tiptoe rising, and crouching.