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.

Morphological Engineering of Sensing Materials for Flexible Pressure Sensors and Artificial Intelligence Applications

As an indispensable branch of wearable electronics,flexible pressure sensors are gaining tremendous attention due to their extensive applications in health monitoring,human-machine interaction,artificial intelligence,the internet of things,and other fields.In recent years,highly flexible and wearable pressure sensors have been developed using various materials/structures and transduction mechanisms.Morphological engineering of sensing materials at the nanometer and micrometer scales is crucial to obtaining superior sensor performance.This review focuses on the rapid development of morphological engineering technologies for flexible pressure sensors.We discuss different architectures and morphological designs of sensing materials to achieve high performance,including high sensitivity,broad working range,stable sensing,low hysteresis,high transparency,and directional or selective sensing.Additionally,the general fabrication techniques are summarized,including self-assembly,patterning,and auxiliary synthesis methods.Furthermore,we present the emerging applications of high-performing microengineered pressure sensors in healthcare,smart homes,digital sports,security monitoring,and machine learning-enabled computational sensing platform.Finally,the potential challenges and prospects for the future developments of pressure sensors are discussed comprehensively.

A Flexible Pressure Sensor Based on Poly(dimethylsiloxane) Nanostructures Film

This paper proposed a flexible pressure sensor based on poly(dimethylsiloxane) nanostructures film and report an efficient,simple,and low-cost fabrication strategy via soft nanoimprint lithography.The pressure sensor can convert external pressure or mechanical deformation into electrical signal to detect pressure and strain changes based on the coupling of triboelectrification and electrostatic induction.To enhance the performance of the pressure sensor,it consists of sub-500 nm resolution on the surface of elastic poly(dimethylsiloxane) sensitive layer and an indium tin oxide electrode thin film.When the pressure applied on the nanostructures layer,triboelectrostatic charges are induced.In the experiment,it measures up to sensitivity of 0.8 V/kPa at frequency of 5 Hz.This study results in potential applications such as wearable smart devices and skin-attachable diagnostics sensing systems.

Advancing the pressure sensing performance of conductive CNT/PDMS composite film by constructing a hierarchical-structured surface

Flexible pressure sensors have attracted wide attention due to their applications to electronic skin,health monitoring,and human-machine interaction.However,the tradeoff between their high sensitivity and wide response range remains a challenge.Inspired by human skin,we select commercial silicon carbide sandpaper as a template to fabricate carbon nanotube(CNT)/polydimethylsiloxane(PDMS)composite film with a hierarchical structured surface(h-CNT/PDMS)through solution blending and blade coating and then assemble the h-CNT/PDMS composite film with interdigitated electrodes and polyurethane(PU)scotch tape to obtain an h-CNT/PDMS-based flexible pressure sensor.Based on in-situ optical images and finite element analysis,the significant compressive contact effect between the hierarchical structured surface of h-CNT/PDMS and the interdigitated electrode leads to enhanced pressure sensitivity and a wider response range(0.1661 kPa^(-1),0.4574 kPa^(-1)and 0.0989 kPa^(-1)in the pressure range of 0–18 kPa,18–133 kPa and 133–300 kPa)compared with planar CNT/PDMS composite film(0.0066 kPa^(-1)in the pressure range of 0–240 kPa).The prepared pressure sensor displays rapid response/recovery time,excellent stability,durability,and stable response to different loading modes(bending and torsion).In addition,our pressure sensor can be utilized to accurately monitor and discriminate various stimuli ranging from human motions to pressure magnitude and spatial distribution.This study supplies important guidance for the fabrication of flexible pressure sensors with superior sensing performance in next-generation wearable electronic devices.

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.

Highly Sensitive Pseudocapacitive Iontronic Pressure Sensor with Broad Sensing Range

Flexible pressure sensors are unprecedentedly studied on monitoring human physical activities and robotics.Simultaneously,improving the response sensitivity and sensing range of flexible pressure sensors is a great challenge,which hinders the devices’practical application.Targeting this obstacle,we developed a Ti_(3)C_(2)T_(x)-derived iontronic pressure sensor(TIPS)by taking the advantages of the high intercalation pseudocapacitance under high pressure and rationally designed structural configuration.TIPS achieved an ultrahigh sen-sitivity(S_(min)>200 kPa^(−1),S_(max)>45,000 kPa^(−1))in a broad sensing range of over 1.4 MPa and low limit of detection of 20 Pa as well as stable long-term working durability for 10,000 cycles.The practical application of TIPS in physical activity monitoring and flexible robot manifested its versatile potential.This study provides a demonstration for exploring pseudocapacitive materials for building flexible iontronic sensors with ultrahigh sensitivity and sensing range to advance the development of high-performance wearable electronics.

Lithographic printing inspired in-situ transfer of MXene-based films with localized topo-electro tunability for high-performance flexible pressure sensors

MXene-based films have been intensively explored for construction of piezoresistive flexible pressure sensors owing to their excellent mechanical and electrical properties.High pressure sensitivity relies on pre-molding a flexible substrate,or regulating the micromorphology of MXene sheets,to obtain a micro-structured surface.However,the two avenues usually require complicated and time-consuming microfabrication or wet chemical processing,and are limited to non-adjustable topographicelectrical(topo-electro)properties.Herein,we propose a lithographic printing inspired in-situ transfer(LIPIT)strategy to fabricate MXene-ink films(MIFs).In LIPIT,MIFs not only inherit ridge-and-valley microstructure from paper substrate,but also achieve localized topo-electro tunability by programming ink-writing patterns and cycles.The MIF-based flexible pressure sensor with periodical topo-electro gradient exhibits remarkably boosted sensitivity in a wide sensing range(low detection limit of 0.29 Pa and working range of 100 kPa).The MIF sensor demonstrates versatile applicability in both subtle and vigorous pressuresensing fields,ranging from pulse wave extraction and machine learning-assisted surface texture recognition to piano-training glove(PT-glove)for piano learning.The LIPIT is quick,low-cost,and compatible with free ink/substrate combinations,which promises a versatile toolbox for designing functional MXene films with tailored morphological-mechanical-electrical properties for extended application scenarios.

Advancing pressure sensors performance through a flexible MXene embedded interlocking structure in a microlens array

Piezoresistive composite elastomers have shown great potentials for wearable and flexible electronic applications due to their high sensitivity,excellent frequency response,and easy signal detection.A composition membrane sensor with an interlocked structure has been developed and demonstrated outstanding pressure sensitivity,fast response time,and low temperature drift features.Compared with a flexible MXene-based flat sensor(Ti_(3)C_(2)),the interlocked sensor exhibits a significantly improved pressure sensitivity of two magnitudes higher(21.04 kPa^(-1)),a fast reaction speed of 31 ms,and an excellent cycle life of 5000 test runs.The viability of sensor in responding to various external stimuli with high deformation capacity has been confirmed by calculating the force distribution of a polydimethylsiloxane(PDMS)film model with a microlens structure using the solid mechanics module in COMSOL.Unlike conventional process,we utilized three-dimensional(3D)laser-direct writing lithography equipment to directly transform high-precision 3D data into a micro-nano structure morphology through variable exposure doses,which reduces the hot melting step.Moreover,the flexible pressure device is capable of detecting and distinguishing signals ranging from finger movements to human pulses,even for speech recognition.This simple,convenient,and large-format lithographic method offers new opportunities for developing novel human-computer interaction devices.

Soft-template synthesis of hierarchically porous structured polydimethylsiloxane toward flexible capacitive pressure sensor

Flexible pressure sensors play an important role in the field of monitoring, owing to their inherent safety and the fact that they are embedded at the material level. Capacitive pressure sensors have been proven to be quite versatile, with the ability to change the sensitivity and monitoring range by modifying the pore structure of the dielectric layer(elastic modulus). In this paper, capacitive pressure sensors are devised, comprising hierarchical porous polydimethylsiloxane. Due to the inherent hollow and hierarchical micropore structure, the capacitive pressure sensor allows operation at a wider pressure range(~1000 kPa) while maintaining sensitivity(6.33 MPa-1) in the range of 0–300 k Pa. Subsequently, the capacitance output model of the sensor is optimized, which provides an overall approximation of the experimental values for the sensor performance. Additionally, the signal response of the“break up the whole into parts”(by analysis of the whole sensor in parts) is simulated and outputted by the finite element analysis. The simplified analysis model provides a good understanding of the relationship between the local pressure and the signal response of the pressure sensor. For practical applications, seal monitoring and rubber wheel pressure array system are tested, and the proposed sensor shows sufficient potential for application in large deformation elastomer products.

CMC/PAM/LiCl复合离子导电水凝胶及传感性能

柔性力敏传感器能够将外界的机械刺激转换为相应的电信号,在可穿戴电子设备、电子皮肤、智能机器人等领域得到了广泛的应用。为满足以上应用需求,材料需要具有可变形、拉伸、回弹、导电等性能、较高的灵敏度及较好的重现性。因此,基于双网络结构,以羧甲基纤维素(CMC)与聚丙烯酰胺(PAM)为原料,设计并制备了一种离子水凝胶,并且,探究了交联剂及无机盐含量对水凝胶力学性能及导电性能的影响。结果表明,二者之间的内在相互作用赋予了水凝胶较好的力学强度(150 kPa)及拉伸/回弹性(可压缩/拉伸循环1 000次以上),同时具有较高的透明度,其值为69.1%。将其用作组装压力传感器,具有较高的灵敏度(S=7.13 kPa-1)及较好的重现性(1 000次);将其用作组装应变传感,其仍可以表现出及时的响应(50/60 ms)及较好的稳定性(1 000次)。因此,水凝胶有望应用于人体及智能机器人的活动监测及人机界面等领域。

ZnO@PAN柔性复合纳米纤维膜的制备及压电特性

采用静电纺丝技术,通过两步低温水热法制备了ZnO@聚丙烯腈(PAN)柔性复合纳米纤维膜。研究了静电纺丝电压和滚筒转速对ZnO@PAN柔性复合纳米纤维膜压电和铁电性能的影响。研究结果表明,当静电纺丝电压为20 kV、滚筒速度为1000 r/min时,ZnO@PAN柔性复合纳米纤维膜的输出性能达到最佳,输出开路电压可达到5.5 V,短路电流可达到0.61μA,剩余极化强度可达到0.43μC/cm^(2)。在外部负载电阻为13 MΩ时,柔性复合纳米纤维膜达到最大输出功率0.63μW。经过5000次循环敲击测试,所制备的ZnO@PAN柔性复合纳米纤维膜输出性能保持稳定。通过ZnO@PAN柔性复合纳米纤维膜可实时监测握力器微握、半握、全握三种不同的状态,在自供电柔性压力传感器领域有着广阔的应用前景。

作物茎秆膨胀收缩监测柔性可穿戴传感器研制与试验

作物茎秆膨胀和收缩变化与其水分状态密切相关,实时监测茎秆的膨胀和收缩变化能够及时掌握作物水分状态,对指导灌溉、提高农业水资源利用率具有重要意义。目前,对于作物茎秆膨胀和收缩变化的监测主要采用基于线性微位移测量原理的传感器,通过测量茎秆的膨胀和收缩引起的位移变化来反映水分状态,存在体积大、价格高、安装不便等问题。为此,该研究提出了一种基于压阻效应的柔性可穿戴传感器,采用柔性压力电极作为传感元件,贴附在作物茎秆表面,通过监测茎秆膨胀和收缩引起的压力变化来反映作物的水分状态,压力检测电路和数据采集电路将作物茎秆的压力信号转换成电信号进行输出和存储。首先在实验室环境下对传感器性能进行测试和标定,然后在温室环境下将传感器安装在番茄茎秆上观测番茄茎秆的压力变化,并与线性微位移传感器观测结果进行比较,最后在充分灌溉和水分亏缺2种条件下观测番茄茎秆的膨胀和收缩变化。结果表明,柔性压力传感器稳定性测试的平均相对变化率为0.109%;弯折前后引起的输出变化非常小,可以忽略不计;标定结果的决定系数大于0.99,最合适的工作压力范围为2~100 kPa;实验室环境下,柔性压力传感器与线性微位移传感器输出值之间的决定系数为0.9551;温室环境下,充分灌溉组中柔性压力传感器与线性微位移传感器输出值变化趋势一致,两者之间的决定系数为0.7672,亏缺灌溉组中两类传感器输出值均因水分亏缺而呈现下降趋势,输出值之间的决定系数为0.8519。本文所设计的柔性可穿戴压力传感器不仅能够实时监测番茄茎秆的膨胀和收缩变化,还可以对番茄亏水胁迫进行诊断,为实现高效节水灌溉提供重要的技术支撑。

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.

Recent advances in flexible pressure/strain sensors using carbon nanotubes

In the context of the information society,wearable devices show broad prospects in the fields of vital signs monitoring,plant health monitoring,artificial electronic skin.As an inseparable part of wearable devices,flexible pressure/strain sensors have attracted wide attention.Structures and active materials are core factors affecting sensing performance.For the past few years,the introduction of carbon materials,especially carbon nanotubes,has provided more possibilities for improving performance.Great efforts have been devoted to researching pressure/strain sensors based on carbon nanotubes with excellent performance or unique features.Herein,the process in recent years in novel flexible pressure/strain sensors based on carbon nanotubes is reviewed.Fabrication strategies are discussed because it suggests sensing performance with significant differences and gives additional features like biodegradability and corrosion resistance to sensors.Furthermore,the scope of application has been extended to plant monitor,except for common human movement monitor.This review can help the researchers compare the influence of different fabrication strategies on the sensing performance and provide references for fabricating sensors in different applications.

智能可穿戴柔性压力传感器的研究进展

柔性压力传感器可以附着在人体皮肤感知外界压力信号,且具有传感范围广、响应时间短、灵敏度和耐久性高等特点,因此被广泛应用于电子皮肤和人机交互等领域。柔性压力传感器通常由柔性基底、活性材料、导电电极组成。其中,一种或多种活性材料通过与柔性基底复合形成传感材料,其受外界刺激产生的变形会引起阻值等变化,进而实现传感功能。此外,通过引入微结构可增加传感材料的可压缩性以及对微小压力的敏感度,提升传感性能。本文围绕薄膜和织物两类基底,综述了在其中掺杂碳基、金属基与黑磷基等活性材料的柔性压力传感器的研究,重点论述了不同传感器的制备方法、机电性能与应用场景,总结了各类传感器的优缺点。在此基础上,对未来智能可穿戴柔性压力传感器如何实现宽范围压力检测、商业化以及制作流程无毒化与长时期生物相容性实验等方面的研究做出了展望。

全纳米纤维离电式柔性压力传感器的制备及性能研究

为解决传统的电容式压力传感器灵敏度低的问题,基于聚丁二酸丁二醇酯对苯二甲酸丁二醇酯(PBST)和离子液体(ILs),采用静电纺丝技术制备离子介电层(ILs/PBST),并利用离电式压力传感机制开发了一种灵敏、透气的全纳米纤维离电式柔性压力传感器。该器件具有超高灵敏度(902.4 kPa-1,0~6 kPa)和快速响应/恢复时间(147 ms/147 ms),能够快速稳定地监测多种人体运动及生理信号。此外,三维多孔纳米纤维网络赋予其良好的透气性,确保其长期佩戴的舒适性,该器件有望应用在智能医疗领域。

具有多孔双微结构层的柔性电容式压力传感器

电极和介电层的材料性能和表面结构是决定柔性电容式压力传感器性能的关键因素。将碳纳米管(CNT)与硅橡胶结合制备出拉伸性能优良的斜线型微结构电极层。以聚二甲基硅氧烷(PDMS)/BaTiO_(3)/SrTiO_(3)复合材料制备多孔砂纸微结构介电层。电极与介电层交界面构成双重微结构以提升电荷携带能力。场发射扫描电子显微镜与光学显微镜观测结果验证了上述微结构的存在。基于电容模型的分析表明,传感器灵敏度主要取决于多孔介电层的形变量。所制备的多孔双微结构层柔性电容式压力传感器最高灵敏度为2.681 kPa^(-1),在3~5 kPa的压力区间仍具有0.412 kPa^(-1)的灵敏度,响应时间和释放时间分别约为39和61 ms。该传感器能够检测出吞咽时咽部运动的微小压力,实验中测得的最小电容变化率为0.13%,能够识别0.53 Pa的微小压力,具有较低的检测限。进行6000次以上的压缩循环测试后,传感器加载-卸载曲线重合性好,同时对不同频率压力的响应良好,验证了传感器良好的可重复性。总之,所提出的传感器具有良好的压力感知性能,在生理信号监测、人机交互等领域具有广阔的应用前景。

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。