Emerging Technologies of Flexible Pressure Sensors: Materials,Modeling, Devices,and Manufacturing

As an important branch of wearable electronics, flexible pressure sensors have attracted extensive research owing to their wide range of applications, such as human–machine interfaces and health monitoring. To fulfill the requirements for different applications, new material design and device fabrication strategies have been developed in order to manipulate the mechanical and electrical properties and enhance device performance. In this paper, the important progresses in flexible pressure sensor development over recent years are selectively reviewed from a material and application perspective. First, an overview of the fundamental working mechanism and the systematic design approach is presented. Particularly, how the theoretical modeling has been used as an auxiliary tool to achieve better sensing performance is discussed. A number of applications, including human–machine interfaces, electronic skin and health monitoring, and certain application‐driven functions, e.g., pressure distribution visualization and direction‐sensitive force detection, are highlighted. Lastly, various advanced manufacturing methods used for realizing large‐scale fabrication are introduced.     

Microengineering Pressure Sensor Active Layers for Improved Performance

Pressure sensors play an integral role in a wide range of applications, such as soft robotics and health monitoring. In order to meet this demand, many groups microengineer the active layer—the layer that deforms under pressure and dictates changes in the output signal—of capacitive, resistive/piezoresistive, piezoelectric, and triboelectric pressure sensors in order to improve sensor performance. Geometric microengineering of the active layer has been shown to improve performance parameters such as sensitivity, dynamic range, limit of detection, and response and relaxation times. There are a wide range of implemented designs, including microdomes, micropyramids, lines or microridges, papillae, microspheres, micropores, and microcylinders, each offering different advantages for a particular application. It is important to compare the techniques by which the microengineered active layers are designed and fabricated as they may provide additional insights on compatibility and sensing range limits. To evaluate each fabrication method, it is critical to take into account the active layer uniformity, ease of fabrication, shape and size versatility and tunability, and scalability of both the device and the fabrication process. By better understanding how microengineering techniques and design compares, pressure sensors can be targetedly designed and implemented.     

MEMS F-P 干涉型压力传感器

为了满足工业、航天、国防等领域对微型化压力传感器的需求,提出了基于微机电系统（MEMS,Micro electromechanical System）技术制作的非本征型光纤法布里-珀罗（F-P）压力传感器,该传感器传感头由全玻璃材料构成。主要研究了MEMS 技术制作全玻璃结构式压力传感器工艺,结合溅射、光刻、腐蚀等工艺在7 740 wafer 基底上制作出F-P 腔体,利用低压化学气相沉积（LPCVD）的方法在基底上沉积一层40 nm 的非晶硅作为中间层。通过阳极键合技术在温度400℃下完成玻璃与玻璃的键合,并搭建了该传感器的压力测量平台。实验结果表明:在压力线性范围0~400 kPa 内传感器具有很高的重复性,达到0.3%。灵敏度达到1.764 nm/kPa;在传感器使用范围0~80℃内,热敏感系数为 0.15 nm/℃。该传感器的研究对设计制作改善了该类传感器的热膨胀失配问题,对低温漂型压力传感器的研究有一定参考价值。     

基于光学Tamm态的磁流体磁场传感器研究

磁场的传感测量在相关领域具有重要应用.利用磁流体的磁光效应,提出了一种基于光学Tamm态的磁场传感结构.该结构由加载了金属层和电介质层的一维磁流体光子晶体构成.数值研究了该结构的结构参数对传感性能的影响.结果 表明,磁流体层越厚,探测灵敏度就越高.金属层和电介质层的厚度均存在一个最佳值,使得传感器具有较高的探测精度.结...     

Modelling and fabrication of wide temperature range Al0.24Ga0.76As/GaAs Hall magnetic sensors

Silicon Hall-effect sensors have been widely used in industry and research fields due to their straightforward fabrication process and CMOS compatibility. However, as their material property limitations, technicians usually implement complex CMOS circuits to improve the sensors’ performance including temperature drift and offset compensation for fitting tough situation, but it is no doubt that it increases the design complexity and the sensor area. Gallium arsenide (GaAs) is a superior material of Hall-effect device because of its large mobility and stable temperature characteristics. Concerning there is no specified modelling of GaAs Hall-effect device, this paper investigated its modelling by using finite element method (FEM) software Silvaco TCAD^® to help and guide GaAs Hall-effect device fabrication. The modeled sensor has been fabricated and its experimental results are in agreement with the simulation results. Comparing to our previous silicon Hall-effect sensor, the GaAs Hall-effect sensor demonstrates potential and reliable benchmark for the future Hall magnetic sensor developments.     

湿度传感器封装的研究进展

湿敏芯片的关键元件是湿度传感器，为了延长湿敏元件的使用寿命，提高湿度传感器的性能，必须对湿敏芯片进行封装。本文主要介绍了湿度传感器封装的研究现状和发展趋势，详细描述了TO、SIP、SOP、LCC等几种湿度传感器封装形式的结构、工艺以及特点，指出了各种封装形式的优缺点。并且对湿度传感器封装的发展趋势作了一定的探讨，指出了SOP，LCC等封装方法将是未来湿度传感器的主流封装方法。     

A Fabrication Strategy for Reconfigurable Millimeter-Scale Metamaterials

Rather than depending on material composition to primarily dictate performance metrics, metamaterials can leverage geometry to achieve specific properties of interest. For example, reconfigurable metamaterials have enabled programmable shape transformations, tunable mechanical properties, and energy absorption. While several methods exist to fabricate such structures, they often place severe restrictions on manufacturing materials, or require significant manual assembly. Moreover, these arrays are typically composed of unit cells that are either macro-scale or micro-scale in dimension. Here, the fabrication gap is bridged, and laminate manufacturing is used to develop a method for designing reconfigurable metamaterials at the millimeter-scale, that is compatible with a wide range of materials, and that requires minimal manual assembly. In addition to showing the versatility of this fabrication method, how the use of laminate manufacturing affects the behavior of these multi-component arrays is also characterized. To this end, a numerical model that captures the deformations exhibited by the structures is developed, and an analytic model that predicts the strain of the structure under compressive stress is built. Overall, this approach can be leveraged to develop millimeter-scale metamaterials for applications that require reconfigurable materials, such as in the design of tunable acoustics, photonic waveguides, and electromagnetic devices.     

A wearable and highly sensitive capacitive pressure sensor integrated a dual-layer dielectric layer of PDMS microcylinder array and PVDF electrospun fiber

Recently, high-performance flexible pressure sensors have received considerable attention because of their potential application in fitness tracking, human–machine interfaces, and artificial intelligence. Sensitivity is a key parameter that directly affects a sensor's performance; therefore, improving the sensitivity of sensors is a vital research topic. This study developed a dual-layer dielectric structure comprising a layer of electrospun fiber and an array of microcylinders and used it to fabricate a novel high-sensitivity capacitive pressure sensor. A simple, rapid, low-cost, and controllable microstructured method that did not require complex and expensive equipment was adopted. The proposed sensor can efficiently detect capacitance changes by analyzing changes in the fiber and microcylinder structure when compressed. It has high sensitivity of 0.6 kPa⁻¹, rapid response time of 25 ms, ultralow limit of detection of 0.065 Pa, and high durability and high reliability without any signal attenuation up to 10,000 load/unload cycles and up to 5000 bending/unbending cycles. Moreover, it yielded favorable results in real-time tests, such as pulse monitoring, acoustic tests, breathe monitoring, and body motion monitoring. Furthermore, experiments were conducted using a robotic arm, and the obtained results verify that the sensor has different capacitance responses to objects with different shapes, which is crucial for its future applications in smart machinery. Finally, the sensors were arranged as a 6 × 6 matrix, and they successfully displayed the pressure distribution in a plane. Thus, the contributions of the capacitance pressure sensor with a dual-layer dielectric structure in the field of high-performance pressure sensors were verified.     

Lightweight,Superelastic Boron Nitride/Polydimethylsiloxane Foam as Air Dielectric Substitute for Multifunctional Capacitive Sensor Applications

Porous polymeric foams as dielectric layer for highly sensitive capacitive based pressure sensors have been extensively explored owing to their excellent flexibility and elasticity. Despite intensive efforts, most of previously reported porous polymer foams still suffer from difficulty in further lowering the attainable density limit of ≈0.1 g cm^?3 while retaining high sensitivity and compressibility due to the limitations on existing fabrication techniques and materials. Herein, utilizing 3D interconnected networks of few‐layer hexagonal boron nitride foams (h‐BNFs) as supporting frameworks, lightweight and highly porous BN/polydimethylsiloxane composite foams (BNF@PDMS) with densities reaching as low as 15 mg cm^?3 and permittivity close to that of air are fabricated. This is the lightest PDMS‐based foam reported to date. Owing to the synergistic effects between BN and PDMS, these lightweight composite foams possess excellent mechanical resilience, extremely high compressibility (up to 95% strain), good cyclic performance, and superelasticity. Being electrically nonconductive, the potential application of BNF@PDMS as a dielectric layer for capacitive sensors is further demonstrated. Remarkably, the as‐fabricated device can perform multiple sensing functions such as noncontact touch sensor, environmental monitoring sensor, and high sensitivity pressure sensor that can detect extremely low pressures of below 1 Pa.     

探空集成传感器设计

微型化、集成化可以使得传感系统减少体积、重量 ,降低成本 ,提高系统的可靠性 ,具有重要的科学意义。本文设计了一个用于测量大气湿度、温度和气压检测微型集成传感器。考虑到MEMS加工工艺兼容性 ,分别采用空气导热检测法、铂电阻法和电容法对湿度、温度、压力进行检测 ,并且进行了理论计算 ,设计了加工工艺步骤 ,制作出雏形器件     

Dielectric films for Si solar cell applications

Thin films of many dielectric materials have been used in the past for fabrication of solar cells and as a part of their device structure. However, current efforts to reduce solar cell costs in commercial production have led to simplification of cell design and fabrication. Use of self-aligning techniques has obviated the need for photolithography and conventional masking with dielectric films for cell fabrication. Currently, the most favored dielectric material in Si solar cell production is SiN:H, deposited by the plasma-enhanced chemical vapor deposition (PECVD) process. The SiN:H layer and its processing play multiple roles of serving as an antireflection coating, a surface passivating layer, a buffer layer through which metal is fired, and a means of transporting hydrogen into the bulk of the solar cell. In order to optimize the solar cell performance, the SiN:H layer must meet some conflicting demands. The various applications of the SiN:H layer in solar cell fabrication are described here.     

Enhanced Sensitivity of Capacitive Pressure and Strain Sensor Based on CaCu3Ti4O12 Wrapped Hybrid Sponge for Wearable Applications

Pressure sensors with highly sensitive and flexible characteristics have extensive applications in wearable electronics, soft robotics, human–machine interface, and more. Herein, an effective strategy is explored to enhance the sensitivity of the capacitive pressure sensor by fabricating a dielectric hybrid sponge consisting of calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO), a giant dielectric permittivity material, in polyurethane (PU). An ultrasoft CCTO@PU hybrid sponge is fabricated via dip‐coating the PU sponge into surface‐modified CCTO nanoparticles using 3‐aminopropyl triethoxysilane. The overall results show that the –NH₂ functionalized CCTO attributes proper adhesion of CCTO with the –OCN group of the PU to enhance interfacial polarization leading to a high dielectric permittivity (167.05) and low loss tangent (0.71) beneficial for flexible pressure sensing applications. Moreover, the as‐prepared CCTO@PU hybrid sponge at 30 wt% CCTO concentration exhibits excellent electromechanical properties with an ultralow compression modulus of 27.83 kPa and a high sensitivity of 0.73 kPa^?1 in a low‐pressure regime (<1.6 kPa). Finally, pressure and strain sensing performance is demonstrated for the detection of human activities by mounting the sensor on various parts of the human body. The work reveals a new opportunity for the facile fabrication of high performance CCTO‐based capacitive sensors with multifunctional properties.     

激光微纳制造在传感领域中的应用

物联网和可穿戴器件的快速发展对传感器的制备和性能提出了更高的要求。由于加工速度快、精度高、可控性强、易集成、与材料兼容性高等优点,激光微纳制造已逐渐成为一种流行的材料制备和器件加工技术。通过激光诱导加热、反应和分离这三种激光加工方式实现了对不同材料的激光处理,这为传感器的制备奠定了基础。近年来,研究人员利用激光微纳加工技术制备了应用于紫外线、气体、湿度、温度、应变/应力、生物、环境等信号监测的不同传感器。总结和归纳了目前存在的问题,展望了激光微纳制造在传感领域中的发展方向。希望文中对激光微纳制造应用于传感领域的介绍和总结能够为未来的研究和发展提供思路和参考。     

非侵入式无线无源MEMS眼压传感器

连续监测眼压对于辅助诊断与治疗青光眼疾病具有重要作用,现有的眼压传感器存在相对灵敏度较低、中心谐振频率较高、制作工艺难度大等问题。为了解决上述问题,该文提出一种基于MEMS的非侵入式无线无源型眼压传感器。该传感器为5层堆叠结构,采用Parylene作为柔性衬底层、铜作为电极层、PDMS作为介电层,其中电极层和介电层构成两个电感和两个电容,形成C-L-C-L串联谐振电路。通过MEMS平面工艺和热塑形方法制作成能够与眼球紧密贴合的曲面形状,这种设计方案能有效地解决传感器的制作工艺难度大等问题。实验结果表明：该眼压传感器的中心谐振频率降低到了40 MHz,相对灵敏度达到1028.57 ppm/kPa,能够分辨出最小50 Pa(0.375 mmHg)的眼压值变化,为实现长期、连续性地监测眼压提供了技术支持。     

Microporous Polypyrrole‐Coated Graphene Foam for High‐Performance Multifunctional Sensors and Flexible Supercapacitors

This study reports on the fabrication of pressure/temperature/strain sensors and all‐solid‐state flexible supercapacitors using only polydimethylsiloxane coated microporous polypyrrole/graphene foam composite (PDMS/PPy/GF) as a common material. A dual‐mode sensor is designed with PDMS/PPy/GF, which measures pressure and temperature with the changes of current and voltage, respectively, without interference to each other. The fabricated dual‐mode sensor shows high sensitivity, fast response/recovery, and high durability during 10 000 cycles of pressure loading. The pressure is estimated using the thermoelectric voltage induced by simultaneous increase in temperature caused by a finger touch on the sensor. Additionally, a resistor‐type strain sensor fabricated using the same PDMS/PPy/GF could detect the strain up to 50%. Flexible, high performance supercapacitor used as a power supply is fabricated with electrodes of PPy/GF for its high surface area and pseudocapacitance. Furthermore, an integrated system of such fabricated multifunctional sensors and a supercapacitor on a skin‐attachable flexible substrate using liquid–metal interconnections operates well, whereas sensors are driven by the power of the supercapacitor. This study clearly demonstrates that the appropriate choice of a single functional material enables fabrication of active multifunctional sensors for pressure, temperature, and strain, as well as the supercapacitor, that could be used in wirelessly powered wearable devices.     

A Double‐Layer Mechanochromic Hydrogel with Multidirectional Force Sensing and Encryption Capability

Hydrogel‐based soft mechanochromic materials that display colorimetric changes upon mechanical stimuli have attracted wide interest in sensors and display device applications. A common strategy to produce mechanochromic hydrogels is through photonic structures, in which mechanochromism is obtained by strain‐dependent diffraction of light. Here, a distinct concept and simple fabrication strategy is presented to produce luminescent mechanochromic hydrogels based on a double‐layer design. The two layers contain different luminescent species—carbon dots and lanthanide ions—with overlapped excitation spectra and distinct emission spectra. The mechanochromism is rendered by strain‐dependent transmittance of the top‐layer, which regulates light emission from the bottom‐layer to control the overall hydrogel luminescence. An analytical model is developed to predict the initial luminescence color and color changes as a function of uniaxial strain. Finally, this study demonstrates proof‐of‐concept applications of the mechanochromic hydrogel for pressure and contact force sensors as well as for encryption devices.     

巨磁阻生物传感器阵列及专用锁相放大器设计

EW_GⅠ是基于GMR(巨磁阻)传感器,用于检测血样中特种病毒的正在研发的生物芯片系统。叙述了其巨磁阻传感器阵列以及后端锁相放大IC电路的设计及实现。该阵列包含32个GMR传感器单元和2个传感器参考单元,形成多路的半桥式惠斯通电桥,用于感应绑定磁球的附加磁场。每个单元(100μm×100μm)由长1mm、宽7μm的巨磁电阻蜿蜒而成,该电阻采用[Ag(2nm)/NiFe(6nm)/Cu(2.2nm)/CoFe(4nm)]20结构,采用Ag作为镜面层,其饱和磁场小于等于30mT,GMR值约6%,单个传感器电阻约为780Ω。配套的锁相放大芯片包括了信号通道、参考通道、前置低噪声放大器、带通滤波器、可控增益放大器、相敏检测电路、正交移相电路、差分直流放大电路八个部分,整个设计功耗小于50mW@Vcc=3V。     

Modeling of Gate Current and Capacitance in Nanoscale-MOS Structures

By applying a fully self-consistent solution of the Schrodinger-Poisson equations, a simple unified approach has been developed in order to study the gate current and gate capacitance of nanoscale-MOS structures with ultrathin dielectric layer. In this paper, the model has been employed to investigate various gate structure and material combinations, thereby demonstrating wide applicability of the present model in the design of nanoscale-MOSFET devices. The results obtained by applying the proposed model are in good agreement with experimental data and previous models in the literature. A new result concerning optimum nitrogen content in HfSiON high-k gate-dielectric structure reported in this paper requires experimental verification through device fabrication     

Multi‐Layered,Hierarchical Fabric‐Based Tactile Sensors with High Sensitivity and Linearity in Ultrawide Pressure Range

Resistive tactile sensors based on changes in contact area have been extensively explored for a variety of applications due to their outstanding pressure sensitivity compared to conventional tactile sensors. However, the development of tactile sensors with high sensitivity in a wide pressure range still remains a major challenge due to the trade‐off between sensitivity and linear detection range. Here, a tactile sensor comprising stacked carbon nanotubes and Ni‐fabrics is presented. The hierarchical structure of the fabrics facilitates a significant increase in contact area between them under pressure. Additionally, a multi‐layered structure that can provide more contact area and distribute stress to each layer further improves the sensitivity and linearity. Given these advantages, the sensor presents high sensitivity (26.13 kPa^?1) over a wide pressure range (0.2–982 kPa), which is a significant enhancement compared with the results obtained in previous studies. The sensor also exhibits outstanding performances in terms of response time, repeatability, reproducibility, and flexibility. Furthermore, meaningful applications of the sensor, including wrist‐pulse‐signal analysis, flexible keyboards, and tactile interface, are successfully demonstrated. Based on the facile and scalable fabrication technique, the conceptually simple but powerful approach provides a promising strategy to realize next‐generation electronics.     

基于四棱镜结构的分布式 SPR传感器研究

设计了一种新型的基于四棱镜结构的分布式表面等离子体共振(SPR)传感器,用数值模拟法讨论了金属膜种类、调制层厚度和折射率、棱镜结构参数对其性能的影响,得到了有用的结论。最后,提出了SPR分布式传感器的评价因子,为今后的分布式SPR传感器设计、制作和性能评价提供了有益的参考。