Bioinspired flexible piezoresistive sensor for high-sensitivity detection of broad pressure range

The human skin has the ability to sense tactile touch and a great range of pressures.Therefore,in prosthetic or robotic systems,it is necessary to prepare pressure sensors with high sensitivity in a wide measurement range to provide human-like tactile sensation.Herein,we developed a flexible piezoresistive pressure sensor that is highly sensitive in a broad pressure range by using lotus leaf micropatterned polydimethylsiloxane and multilayer superposition.By superposing four layers of micropatterned constructive substrates,the multilayer piezoresistive pressure sensor achieves a broad pressure range of 312 kPa,a high sensitivity of 2.525 kPa^(−1),a low limit of detection(LOD)of<12 Pa,and a fast response time of 45 ms.Compared with the traditional flexible pressure sensor,the pressure range of this sensor can be increased by at least an order of magnitude.The flexible piezoresistive pressure sensor also shows high robustness:after testing for at least 1000 cycles,it shows no sign of fatigue.More importantly,these sensors can be potentially applied in various human motion detection scenarios,including tiny pulse monitoring,throat vibration detection,and large under-feet pressure sensing.The proposed fabrication strategy may guide the design of other kinds of multifunctional sensors to improve the detection performance.

MXene-based flexible pressure sensor with piezoresistive properties significantly enhanced by atomic layer infiltration

The flexible pressure sensor has been credited for leading performance including higher sensitivity,faster response/recovery,wider detection range and higher mechanical durability,thus driving the development of novel sensing materials enabled by new processing technologies.Using atomic layer infiltration,Pt nanocrystals with dimensions on the order of a few nanometers can be infiltrated into the compressible lamellar structure of Ti3C2Tx MXene,allowing a modulation of its interlayer spacing,electrical conductivity and piezoresistive property.The flexible piezoresistive sensor is further developed from the Pt-infiltrated MXene on a paper substrate.It is demonstrated that Pt infiltration leads to a significant enhancement of the pressure-sensing performance of the sensor,including increase of sensitivity from 0.08 kPa^(-1)to 0.5 kPa^(-1),extension of detection limit from 5 kPa to 9 kPa,decrease of response time from 200 ms to 20 ms,and reduction of recovery time from 230 ms to 50 ms.The mechanical durability of the flexible sensor is also improved,with the piezoresistive performance stable over 1000 cycles of flexure fatigue.The atomic layer infiltration process offers new possibilities for the structure modification of MXene for advanced sensor applications.

The Effect of Temperature and Doping Level on the Characteristics of Piezoresistive Pressure Sensor

Piezoresistive pressure sensors based on silicon have a large thermal drift because of their high sensitivity to temperature. The study of the effect of the temperature and doping level on characteristics of these sensors is essential to define the parameters that cause the output characteristics drift. In this study, we adopted the model of Kanda to determine the effect of the temperature and of doping level on the piezoresistivity of the Silicon monocrystal. This is to represent P(N,T) and for p-type silicon as functions of impurity concentration for different temperatures. This allows us to see the effect of temperature and doping concentration on the output characteristics of the sensor. Finally, we study the geometric influence parameters and doping on these characteristics to optimize the sensor performance. This study allows us to predict the sensor behavior against temperature and to minimize this effect by optimizing the doping concentration.

Enhancing Accuracy of Flexible Piezoresistive Pressure Sensors by Suppressing Seebeck Effect

Flexible piezoresistive pressure sensors can offer convenient detection of mechanical deformations for wearable electronics.Previous studies of flexible piezoresistive pressure sensors focus on the sensitivity but the low-cost and self-powered sensors remain a challenge due to the deviation of resistance signal acquisition caused by thermoelectric voltage.Here,piezoresistive pressure sensors with ultralow Seebeck coefficient of-0.72μV/K based on carbon nanotubes(CNTs)/polyethyleneimine(PEI)/melamine(CPM)sponge are reported.Due to the diminished Seebeck effect,the CPM sponge pressure sensors successfully reduce the deviation to 18.75%and can keep stable sensitivity and resistance change under a very low working voltage and change temperature environment.The stable properties of the sensors make them successful to work for real-time sensing in self-powered wearable electronics.

Laser direct writing and characterizations of flexible piezoresistive sensors with microstructures

Functional materials with high viscosity and solid materials have received more and more attentions in flexible pressure sensors,which are inadequate in the most used molding method.Herein,laser direct writing(LDW)method is proposed to fabricate flexible piezoresistive sensors with microstructures on PDMS/MWCNTs composites with an 8%MWCNTs mass fraction.By controlling laser energy,microstructures with different geometries can be obtained,which significantly impacts the performances of the sensors.Subsequently,curved microcones with excellent performance are fabricated under parameters of f=40 kHz and v=150 mm·s^(-1).The sensor exhibits continuous multi-linear sensitivity,ultrahigh original sensitivity of 21.80%kPa^(-1),wide detection range of over 20 kPa,response/recovery time of~100 ms and good cycle stability for more than 1000 times.Besides,obvious resistance variation can be observed when tiny pressure(a peanut of 30 Pa)is applied.Finally,the flexible piezoresistive sensor can be applied for LED brightness controlling,pulse detection and voice recognition.

State-of-the-art and recent developments in micro/nanoscale pressure sensors for smart wearable devices and health monitoring systems

Small-sized,low-cost,and high-sensitivity sensors are required for pressure-sensing applications because of their critical role in consumer electronics,automotive applications,and industrial environments.Thus,micro/nanoscale pressure sensors based on micro/nanofabrication and micro/nanoelectromechanical system technologies have emerged as a promising class of pressure sensors on account of their remarkable miniaturization and performance.These sensors have recently been developed to feature multifunctionality and applicability to novel scenarios,such as smart wearable devices and health monitoring systems.In this review,we summarize the major sensing principles used in micro/nanoscale pressure sensors and discuss recent progress in the development of four major categories of these sensors,namely,novel material-based,flexible,implantable,and selfpowered pressure sensors.

Carbon nanotube cuprous oxide composite based pressure sensors

In this paper, we present the design, the fabrication, and the experimental results of carbon nanotube （CNT） and Cu20 composite based pressure sensors. The pressed tablets of the CNT Cu20 composite are fabricated at a pressure of 353 MPa. The diameters of the multiwalled nanotubes （MWNTs） are between 10 nm and 30 nm. The sizes of the Cu20 micro particles are in the range of 3-4 μm. The average diameter and the average thickness of the pressed tablets are 10 mm and 4.0 mm, respectively. In order to make low resistance electric contacts, the two sides of the pressed tablet are covered by silver pastes. The direct current resistance of the pressure sensor decreases by 3.3 times as the pressure increases up to 37 kN/m^2. The simulation result of the resistance-pressure relationship is in good agreement with the experimental result within a variation of ±2%.

Highly sensitive and fast response strain sensor based on evanescently coupled micro/nanofibers

Flexible strain sensors play an important role in electronic skins,wearable medical devices,and advanced robots.Herein,a highly sensitive and fast response optical strain sensor with two evanescently coupled optical micro/nanofibers(MNFs)embedded in a polydimethylsiloxane(PDMS)film is proposed.The strain sensor exhibits a gauge factor as high as 64.5 for strain≤0.5%and a strain resolution of 0.0012%which corresponds to elongation of 120 nm on a 1 cm long device.As a proof-of-concept,highly sensitive fingertip pulse measurement is realized.The properties of fast temporal frequency response up to 30 kHz and a pressure sensitivity of 102 kPa^(−1) enable the sensor for sound detection.Such versatile sensor could be of great use in physiological signal monitoring,voice recognition and micro-displacement detection.

Pressure and Arc Voltage Measurement in a 252 kV SF_6 Puffer Circuit Breaker

The pressure distribution in an arcing chamber is critically important for the SF6 puffer circuit breaker design. In this paper, the pressure variation of four locations in the nozzle was measured by piezoresistive and fiber optical pressure sensors at two current levels of 10 kA and 50 kA. An arc voltage measurement was also taken. The results demonstrate that using either type of sensor with a connecting tube is able to detect the fast pressure variation in circuit breakers, however the possible distortion and delay to the pressure transient caused by the tube need further study.

Ultrasensitive skin‐like wearable optical sensors based on glass micro/nanofibers

Electronic skin,a class of wearable electronic sensors that mimic the functionalities of human skin,has made remarkable success in applications including health monitoring,human-machine interaction and electronic-biological interfaces.While electronic skin continues to achieve higher sensitivity and faster response,its ultimate performance is fundamentally limited by the nature of low-frequency AC currents.Herein,highly sensitive skin-like wearable optical sensors are demonstrated by embedding glass micro/nanofibers(MNFs)in thin layers of polydimethylsiloxane(PDMS).Enabled by the transition from guided modes into radiation modes of the waveguiding MNFs upon external stimuli,the skin-like optical sensors show ultrahigh sensitivity(1870 k·Pa^-1),low detection limit(7 mPa)and fast response(10μs)for pressure sensing,significantly exceeding the performance metrics of state-of-the-art electronic skins.Electromagnetic interference(EMI)-free detection of high-frequency vibrations,wrist pulse and human voice are realized.Moreover,a five-sensor optical data glove and a 2×2-MNF tactile sensor are demonstrated.These initial results pave the way toward a new category of optical devices ranging from ultrasensitive wearable sensors to optical skins.

Progress in achieving high-performance piezoresistive and capacitiveflexible pressure sensors: A review

Electronic skin(e-skin) and flexible wearable devices are currently being developed with broad application prospects. Transforming electronic skin(e-skin) into true ¨skin¨is the ultimate goal. Tactile sensing is a fundamental function of skin and the development of high-performance flexible pressure sensors is necessary to realize thus. Many reports on flexible pressure sensors have been published in recent years,including numerous studies on improving sensor performance, and in particular, sensitivity. In addition,a number of studies have investigated self-healing materials, multifunctional sensing, and so on. Here,we review recent developments in flexible pressure sensors. First, working principles of flexible pressure sensors, including piezoresistivity, capacitance, and piezoelectricity, are introduced, as well as working mechanisms such as triboelectricity. Then studies on improving the performance of piezoresistive and capacitive flexible pressure sensors are discussed, in addition to other important aspects of this intriguing research field. Finally, we summarize future challenges in developing novel flexible pressure sensors.

Highly sensitive piezoresistive pressure sensors based on laser-induced graphene with molybdenum disulfide nanoparticles

Wearable pressure sensors have drawn significant attention because of their extensive applications in motion detection, tactile sensing, and health monitoring. However, the complex manufacturing process and high cost of active materials make low-cost,large-scale production elusive. In this work, we report a flexible piezoresistive pressure sensor assembled with two 3D laserinduced graphene(LIG) foam electrodes on a polyimide thin film from a simple laser scribing process in the ambient environment. The design of the air gap between the two foam electrodes allows the sensor to showcase a low limit of detection of 0.274 Pa, which provides favorable sensing performance in motion detection and wrist pulse monitoring. The addition of spherical MoS2 nanoparticles between the two foam electrodes further enhances the sensitivity to 88 k Pa-1 and increases the sensing range to significantly outperform the previous literature reports. The demonstrated LIG pressure sensors also exhibit fast response/recovery rates and excellent durability/repeatability.

High-performance Multilayer Flexible Piezoresistive Pressure Sensor with Bionic Hierarchical and Anisotropic Structure

Flexible pressure sensor that enables detection of multimodal signals has greater advantages in human–computer interaction,medical/health care,and other applications.To make a versatile flexible pressure sensor,hierarchical and anisotropy structure are key features to improve sensing performance and realize multi-signal detection.However,traditional flexible sensors usually have narrow linear range and single signal detection capability.Herein,a highly sensitive flexible piezoresistive pressure sensor which has broad linear range of pressure is developed by replicating one dimensional microstructures from reed leaf and using multilayer superposition of micropatterned polydimethylsiloxane(m-PDMS).Through superposing 4 layers of parallel micropatterned constructive substrates,the multilayer piezoresistive pressure sensor exhibits a high sensitivity of 2.54 kPa?1,a fast response time of 30 ms,and a broad linear range of 107 kPa.The flexible piezoresistive pressure sensor is also highly robust:there is no fatigue after testing for at least 1000 cycles.Due to the specific anisotropy of the micro-structure,the sensor can measure the tangential force in different directions.It permits multimode signal detection,including pressure,tangential force,and deformation.The versatile flexible pressure sensor enables effective monitoring of multisignals,it reveals great potential for medical and health care,flexible human–computer interaction,and intelligent robot.

基于纳米孔的宽量程石墨烯压力传感器

针对传统微机电系统(MEMS)压力传感器性能难以提升且结构复杂等问题,制备了一种基于纳米孔的宽量程石墨烯压力传感器结构。在Si_(3)N_(4)薄膜上刻蚀了阵列纳米孔作为压力腔,使用单层石墨烯夹在氮化硼薄膜间作为敏感结构,平铺于纳米孔阵列上,由金布线层导出信号。测试表明,在0~20 MPa压力范围内,该压力传感器的灵敏度为9.35×10^(-5) MPa^(-1),重复性误差为满量程输出(FSO)的5.70%,迟滞为1.91%FSO,线性度为2.43%FSO,其重复性与线性度良好且迟滞较小。设计的宽量程石墨烯压力传感器能够实现0~20 MPa以内的压力测量,且器件加工一致性高、测量误差小、制备方法相对简单,有助于降低生产成本和提高生产效率,在压力测试领域展现出良好的应用前景。

基于微气压传感器的室内行人高度估计方法

针对当前气压传感器解算高度存在误差随时间累积的问题,提出了一种基于微气压传感器的室内行人高度估计新方法。该方法结合微气压传感器的输出高度值,对多个相邻时间内的高度值进行合理性判断,并结合室内行人运动状态对高度变化进行约束,使得解算的高度符合室内行人运动规律。通过电脑采集MS5611微气压传感器数据进行仿真验证,结果表明:该方法能够有效地对高度误差进行修正,相较于微气压传感器直接解算的高度,该算法解算的高度更贴合实际情况,解算轨迹也更接近真实轨迹,轨迹的平均闭环误差从1.9%D下降至0.07%D。该算法有效地提高了室内行人高度估计的定位精度,在室内行人三维定位领域具有一定的工程应用价值。

MEMS正装传感器复合钝化层高温可靠性的研究

绝缘体上硅(SOI)所制备的压阻式正装压力传感器可在高温下良好工作,但高温环境下电阻条和金属引线长期暴露在环境中易受到氧化和腐蚀,对传感器的输出造成影响,使电学性能发生变化甚至失效,为避免这种情况,通常在表面进行钝化处理。文中采用SiO_(2)-Si_(3)N_(4)复合钝化层对SOI正装传感器芯片进行钝化,并且对钝化层进行高温老化考核,模拟高温和恶劣环境,验证其高温可靠性。实验结果表明:按照SiO_(2)厚度为200 nm、Si_(3)N_(4)厚度为300 nm的SiO_(2)-Si_(3)N_(4)复合钝化层能在350℃高温下对正装传感器进行有效保护且电学性能完好,满足芯片在高温下可靠性的要求。

多层结构柔性压力传感织物的设计与性能

智能可穿戴技术因其能够实时交互穿戴者与环境之间的信息而具有巨大发展潜力,在柔性可穿戴设备中,柔性压力传感器是用于压力检测的关键器件。使用导电材料MWCNTs与PEDOT:PSS制备3种不同的传感器敏感层,以镍铜织物作为传感器的上下电极,制备一种具有多层结构的柔性压阻式压力传感器,并对传感器性能进行测试。结果表明,PEDOT:PSS敏感层在0~5 kPa压强范围内,灵敏度高达0.168 12 kPa-1,具有较快的响应时间与恢复时间,以及较好的可重复性。该传感器性能良好,可以应用在柔性可穿戴设备中。

硅基MEMS梁-复合膜-岛压阻式压力传感器设计研究

针对微机电系统(MEMS)压力传感器灵敏度与非线性度难以兼顾的问题,提出了一种梁-复合膜-岛压力传感结构,运用有限元仿真软件优化整体结构尺寸以得到最大纵横应力差、挠度,并设计压阻条压敏电阻掺杂类型、掺杂浓度、结构尺寸及分布位置。将梁-复合膜-岛结构与传统结构的输出进行仿真对比,由仿真结果可知,梁-复合膜-岛结构在0~60 kPa压力范围内灵敏度较相关结构提升7%以上,较E型结构提升2倍,非线性度为0.029%FSS,满足MEMS微压压力传感器的高灵敏度、高线性度等要求,可支撑医疗领域相关应用研究。

基于共晶焊技术的高温压力传感器无引线封装技术研究

针对MEMS高温压力传感器在高温特种环境下存在引线电学失效的不可靠性因素,制备了基于共晶焊技术的无引线封装SOI高温压阻式压力传感器。利用金锗合金焊料共晶焊接技术完成芯片与陶瓷基板的焊盘之间的连接。推力测试结果表明:其焊接强度最大值可达28.30 MPa,均值约为26.47 MPa。完成300℃环境下的老化后,其300℃高温环境下零点漂移为0.216%,时漂约为7.64μV/h。老化后常温静态压力测试线性度为0.126%,迟滞为0.136%,重复性为0.197%,均小于2‰,基本误差为0.433%。研究结果验证了金锗焊料共晶焊接制备无引线封装压力传感器的技术路线可行性。

压敏结构对柔性传感器性能增强的仿真分析

在压阻层引入压敏结构是提高压阻传感器灵敏度的有效方法,但是压敏结构的形变在实际实验中难以直接观察,使得微结构的形变、电阻变化等机制尚不明确。为此,采用有限元仿真分析软件,模拟不同载荷大小和不同敏感结构对石墨烯基柔性传感器压敏结构的作用机制,揭示了压敏结构对传感器形变、电阻变化的影响。结果显示,方柱和圆柱压敏结构的传感器形变程度小,但电阻和应力变化区域大,而金字塔和半圆球压敏结构的传感器形变程度较大,但电阻和应力变化区域较小。