Nanomechanical membrane-type surface stress sensor

Nanomechanical cantilever sensors have been emerging as a key device for real-time and label-free detection of various analytes ranging from gaseous to biological molecules. The major sensing principle is based on the analyte-induced surface stress, which makes a cantilever bend. In this letter, we present a membrane-type surface stress sensor (MSS), which is based on the piezoresistive read-out integrated in the sensor chip. The MSS is not a simple "cantilever," rather it consists of an "adsorbate membrane" suspended by four piezoresistive "sensing beams," composing a full Wheatstone bridge. The whole analyte-induced isotropic surface stress on the membrane is efficiently transduced to the piezoresistive beams as an amplified uniaxial stress. Evaluation of a prototype MSS used in the present experiments demonstrates a high sensitivity which is comparable with that of optical methods and a factor of more than 20 higher than that obtained with a standard piezoresistive cantilever. The finite element analyses indicate that changing dimensions of the membrane and beams can substantially increase the sensitivity further. Given the various conveniences and advantages of the integrated piezoresistive read-out, this platform is expected to open a new era of surface stress-based sensing.     

A small cantilever beam test for determination of creep properties of materials

The application of small specimen creep test techniques in the evaluation of creep properties of materials in‐service has been increasing. To obtain the creep data accurately and conveniently, a new creep test method with small cantilever beam specimens is proposed. Analytical equations are derived that can convert the load to equivalent uniaxial stress and the displacement rate to equivalent uniaxial strain rate. Three types of the cantilever beam specimens are designed. The optimal configuration of the cantilever beam specimens is recommended with the aid of finite element method, which is further validated by the cantilever beam and uniaxial specimen tests. The results show that parameters obtained from the cantilever beam tests correspond reasonably well with those from uniaxial tests at low stress levels. With a relatively large equivalent gauge length, the cantilever beam specimen allows the small creep strain rate data obtained with a high accuracy.     

Millimeter-Scale Piezoresistive Cantilevers for Accurate Force Measurements at the Nano-Newton Level

This paper reports a development of millimeter-scale cantilevers equipped with piezoresistive deflection sensing metrology as a force sensor at the micro- and nano-Newton level. The cantilevers was designed and fabricated to minimize the error during the force transfer or calibration, so that they have full-bridge type piezoresistors, a large length and width and reference marks to facilitate the positioning of probes or tips onto the piezoresistive cantilevers. Their 6 mm-long and 0.4 mm-wide dimensions can reduce the error due to incomplete contact (or loading) position. The reference marks on the cantilever can give you a range of stiffness and force sensitivity with a single piezoresistive cantilever. The stiffness can vary from 25 N m^?1 at the first mark to 0.04 N m^?1 at the last. The full-bridge piezoresistors give an electrical signal proportional to the applied force with superior temperature independency. The fabricated piezoresistive cantilevers were calibrated with the KRISS nano force calibrator (NFC). The results showed that the stiffness and the force sensitivity at the last mark was determined to be 0.0502 N m^?1 and 0.357 (mV/V) μN^?1, respectively. The performances were tested by calibrating stiffness of commercial cantilevers using the cantilever-on-cantilever method with a fabricated cantilever and comparing calibration results with stiffness obtained from calibration using the NFC. Two results match to each other within approximately 10 % discrepancy.     

焊接接头横向拉伸试验结果分析

通过一系列对比试验,研究分析了Q345焊接试板焊接接头横向拉伸性能与全焊缝和焊板母材之间的差异,探索接头横向拉伸所得屈服强度与断后伸长率的合理性。结果表明,接头横向拉伸所获得的屈服强度值介于母材与全焊缝的值之间,且试验结果受所用引伸计标距的影响较为显著;接头横向拉伸断裂位置虽在母材上,但抗拉强度值要高于母材强度近20 MPa,断后伸长率则比母材低了近10%,但仍高于全焊缝的值。     

Design of High-Sensitivity Cantilever and Its Monolithic Integration With CMOS Circuits

Rectangular piezoresistive cantilevers with stress concentration holes opened were designed and fabricated in order to increase the response signals of piezoresistive cantilever first. Both the simulations and the measurements on the cantilever sensitivity show that this design can obviously result in an improvement on the displacement sensitivity of the piezoresistive cantilever. After a characterization study on the piezoresistive cantilever, a monolithic integration of the microcantilever array with a complementary metal-oxide-semiconductor (CMOS) readout circuitry based on the silicon-on-insulator (SOI) CMOS and the SOI micromachining technologies was designed. A cantilever array, a digital controlled multiplexer, and an instrumentation amplifier compose the integrated sensor system, and post-CMOS process was designed to fabricate the integrated system. The measurement results on the SOI CMOS circuitry of the integrated system prove a feasibility of the integration design     

不锈钢拉伸试验条件与断后伸长率测量值的关系

采用单向拉伸试验研究了不同拉伸速度、不同试样规格对不锈钢冷轧薄板断后伸长率测量值的影响。结果表明:不锈钢的断后伸长率测量值随拉伸速度的提高而下降、随试样横截面的增大而提高。说明拉伸试验条件对不锈钢薄板的断后伸长率测量值影响较大,只有在拉伸试验条件一致的情况下,断后伸长率测量值才能作为选材的依据之一。     

Nanocrystalline diamond piezoresistive sensor

The design, fabrication and test of piezoresistive sensors based on nanocrystalline diamond (NCD) films are reported. The CoventorWare FEM calculations of the mechanical stress and geometrical deformations of a 3-D structure are used for a proper localization of the piezoresistor on the carrying substrate. The boron-doped piezoresistive sensing element was realized using a directed patterned growth of NCD film on SiO₂/Si by microwave plasma-enhanced chemical vapour deposition (CVD). The gauge factor of boron-doped NCD films was investigated in the range from room temperature up to 200 °C and from 0 to 5 N of the applied force. These NCD piezoresistive sensor elements are compared with a Silicon-on-Insulator (SOI) based piezoresistive sensor and their high-temperature applications are discussed.     

Epoxy based photoresist/carbon nanoparticle composites

We have fabricated composites of SU-8 polymer and three different types of carbon nanoparticles (NPs) using ultrasonic mixing. Structures of composite thin films have been patterned on a characterization chip with standard UV photolithography. Using a four-point bending probe, a well defined stress is applied to the composite thin film and we have demonstrated that the composites are piezoresistive. Stable gauge factors of 5–9 have been measured, but we have also observed piezoresistive responses with gauge factors as high as 50. As SU-8 is much softer than silicon and the gauge factor of the composite material is relatively high, carbon nanoparticle doped SU-8 is a valid candidate for the piezoresistive readout in polymer based cantilever sensors, with potentially higher sensitivity than silicon based cantilevers.     

Magnetically actuated complementary metal oxide semiconductor resonant cantilever gas sensor systems

In the present paper, an electromagnetically actuated resonant cantilever gas sensor system is presented that features piezoresistive readout by means of stress-sensitive MOS transistors. The monolithic gas sensor system includes a polymer-coated resonant cantilever and the necessary oscillation feedback circuitry, both monolithically integrated on the same chip. The fully differential feedback circuit allows for operating the device in self-oscillation with the cantilever constituting the frequency-determining element of the feedback loop. The combination of magnetic actuation and transistor-based readout entails little power dissipation on the cantilever and reduces the temperature increase in the sensitive polymer layer to less than 1 degrees C, whereas previous designs with thermally actuated cantilevers showed a temperature increase of up to 19 degrees C. The lower temperature of the sensitive polymer layer on the cantilever directly improves the sensitivity of the sensor system as the extent of analyte physisorption decreases with increasing temperature. The electromagnetic sensor design shows an almost 2 times larger gas sensitivity than the earlier design, which is thermally actuated and read out using p-diffused resistors. The gas sensor is fabricated using an industrial complementary metal oxide semiconductor (CMOS) process and post-CMOS micromachining.     

Piezoresistivity in films of nanocrystalline manganites

Rare earth manganites having perovskite structure are susceptible to lattice strain. So far most investigations have been done with hydrostatic pressure or biaxial strain. We have observed that hole doped rare-earth manganites, which are known to display colossal magnetoresistance (CMR) also show change in its resistance under the influence of uniaxial strain. We report the direct measurement of piezoresistive response of La0.67Ca0.33MnO3 (LCMO) and La0.67Sr0.33MnO3 (LSMO) of this manganite family. The measurements were carried out on nanostructured polycrystalline films of LCMO and LSMO grown on oxidized Si(100) substrates. The piezoresistance was measured by bending the Si cantilevers (on which the film is grown) in flexural mode both with compressive and tensile strain. At room temperature the gauge factor approximately 10-20 and it increases to a large value near metal-insulator transition temperature (Tp) where the resistivity shows a peak.     

Ultra-sensitive shape sensor test structures based on piezoresistive doped nanocrystalline silicon

This paper describes the manufacture of a thin skin-like piezoresistor strain-sensing membrane and the miniaturization of dense piezoresistive sensor arrays based on n-type hydrogenated nanocrystalline silicon thin-films (nc-Si:H) deposited on flexible polyimide substrates (PI). The nc-Si:H thin-films, prepared by hot-wire chemical vapor deposition, have a piezoresistive gauge factor of −32.2.Six of the sensors batch-processed on the 15-μm thick membrane, were used in a test structure to track the simulated movement of the head of a bedridden patient. The sensors were glued to both sides of a 3-mm thick acrylic rectangular plate, to collect strain data from the tensile and compressive surfaces of the plate upon bending. The electrical output signal of the sensor was obtained by inserting the sensors into Wheatstone bridge circuits and recording the output voltage of the bridge as a function of the sensor/plate deformation. The results using quarter-, half-, and full-bridge configurations were compared.In order to give a further step toward a shape sensitive electronic textile, nine sensors were glued and interconnected using a machine-sewed conductive thread and preliminary tests on their output response under random loading conditions were performed.     

Tensile testing of silicon thin films

The tensile strength of silicon thin films was investigated using a specimen chucking system dedicated for microscale specimens. The system uses electrostatic force to fix and hold the free end of the cantilever‐shaped specimens. The thin film tensile tester was built using this system. The accuracy and reliability of this method were assured by comparing it with other tensile‐testing methods using single‐crystal silicon specimens. The result shows good agreement between the testing methods. The strength properties of polysilicon thin films, such as the effect of the testing environment and the specimen size and the film fabrication conditions, were investigated.     

合金薄膜电阻应变式压力传感器的研究进展

综述了合金薄膜应变压力传感器的现状、发展趋势、技术关键及应用情况.合金敏感薄膜电阻在应变压?技 力传感器上的应用克服了粘贴式应变压力传感的缺点,使压力传感器结构更精细,性能更优越,适应各种恶劣环境测量压力的要求.     

固体推进剂储存老化力学性能双因素方差分析

采用单轴拉伸实验方法研究了固体推进剂力学性能的变化,并对结果进行双因素方差分析。测试结果表明:随老化时间延长,推进剂的抗拉强度和伸长率呈下降趋势;温度越高,下降趋势越明显;70 ℃下,抗拉强度和伸长率下降幅度明显大于50、60 ℃时。双因素方差分析显示,老化时间、老化温度对抗拉强度、伸长率、断裂能均存在显著影响。与老化温度相比,老化时间对固体推进剂力学性能产生的影响更显著。     

Investigation on the Influence of Temperature Variation on the Response of Miniaturised Piezoresistive Sensors

Abstract:  This paper deals with the analysis of temperature response of miniaturised piezoresistive strain sensors. Amorphous silicon sensors of different geometry were deposited on a glass specimen: on the basis of previous studies, each sensor has a linear response and can be compared with a full Wheatstone bridge, but dimensions and power consumption are much lower than those of ordinary resistance strain gauges. A preliminary experiment was performed to prove the robustness of sensor response, considering connections to the acquisition device having different lengths. The main experimental campaign was aimed at investigating the influence on response because of temperature variation during each test. Eight different sensor configurations were tested, both under load and no-load conditions, with three replications. This paper describes test installation and measuring chain for simultaneous acquisition of both temperature and sensor voltage output. Thermal response linearity and hysteresis effects were investigated. In addition, the results, whose repeatability over the three replications was checked, made it possible to determine and compare the sensitivities of each sensor configuration to temperature variations. Analysis of variance (anova) showed that, despite its different values for configurations with different geometry, sensitivity remains the same under load or no-load conditions.     

Piezoelectric control of delamination response in woven fabric composites under mode I loading

This paper investigates the application of piezoelectric actuators to control the delamination response in woven fabric composites subjected to Mode I loading. Experiments were conducted on a double cantilever beam (DCB) specimen of woven glass fiber reinforced polymer (GFRP) composite laminates with piezoelectric ceramic actuators bonded on the surfaces, in order to evaluate the dependence of the delamination behavior on the applied electric fields. A finite element analysis of the DCB specimen with surface-bonded actuators was also performed, and a comparison was made between the finite element predictions and the test results. In addition, the effect of the actuator location on the effectiveness of the piezoelectric control was examined numerically.     

Micromachining of a bimorph Pb(Zr,Ti)O3 (PZT) cantilever using a micro-electromechanical systems (MEMS) process for energy harvesting application

We designed and fabricated a bimorph Pb(Zr,Ti)O3 (PZT) cantilever with an integrated Si proof mass to obtain a low resonant frequency for an energy harvesting application. The cantilevers were fabricated on the micro-electromechanical systems (MEMS) scale. A mode of piezoelectric conversions were d31 and d33 mode in cantilever vibration Therefore, we designed and fabricated a single cantilever with d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes. Finally, we fabricated a device with beam dimensions of about 5,400 microm x 480 microm x 14 microm (< +/- 5%), and an integrated Si proof mass with dimensions of about 1,481 microm x 988 microm x 450 microm (< +/- 5%). In order to measure the d31 and d33 modes, we fabricated top and bottom electrodes. The distance between the top electrodes was 50 microm and the resonant frequency was 89.4 Hz. The average powers of the d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes were 3.90, 9.60, 21.42, and 22.47 nW at 0.8 g (g = 9.8 m/s2) and optimal resistance, respectively.     

The Semiconductor/Conductor Interface Piezoresistive Effect in an Organic Transistor for Highly Sensitive Pressure Sensors

The piezoresistive pressure sensor, a kind of widely investigated artificial device to transfer force stimuli to electrical signals, generally consists of one or more kinds of conducting materials. Here, a highly sensitive pressure sensor based on the semiconductor/conductor interface piezoresistive effect is successfully demonstrated by using organic transistor geometry. Because of the efficient combination of the piezoresistive effect and field‐effect modulation in a single sensor, this pressure sensor shows excellent performance, such as high sensitivity (514 kPa^?1), low limit of detection, short response and recovery time, and robust stability. More importantly, the unique gate modulation effect in the transistor endows the sensor with an unparalleled ability—tunable sensitivity via bias conditions in a single sensor, which is of great significance for applications in complex pressure environments. The novel working principle and high performance represent significant progress in the field of pressure sensors.     

UHPC单轴拉伸试验狗骨试件优化设计

单轴拉伸试验是测试超高性能混凝土(Ultra-high Performance Concrete,简称UHPC)破坏机理、抗拉性能与拉伸本构关系最有效的方法。单轴拉伸试验成功率不高。其常用的狗骨试件形状与尺寸对试验成功率有较大的影响,目前还未有统一的标准。调查表明,不带缺口的狗骨试件最适合用于UHPC单轴拉伸试验,主要有梯形、弧形和阶梯形三种类型。通过对试件的受力分析,提出两个应力均匀性指标来评价试件优劣。建立了三种共275根狗骨试件的有限元模型,通过分析,分别给出三种试件均匀性较好的参数。同时,建立了三组15根试件有限元模型,横向对比了三种狗骨试件的应力均匀性。对比结果表明,弧形狗骨试件受力均匀性最好,开展的验证性试验取得了95.8%的成功率,推荐采用。     

Localization Events and Microstructural Evolution in Ultra‐Fine Grained NiTi Shape Memory Alloys during Thermo‐Mechanical Loading

Subjecting a thin NiTi specimen to uniaxial tension often leads to a localized martensitic transformation: macroscopic transformation bands form and propagate through the specimen, separating it into regions of fully transformed martensite and original austenite. In the present study, the alternating current potential drop (ACPD) technique is used to analyze the change in electrical resistance of ultra‐fine grained NiTi wires subjected to a broad range of thermo‐mechanical load cases: (i) uniaxial tensile straining at constant temperatures (pseudoelastic deformation); (ii) cooling and heating through the transformation range at constant load (actuator load case); (iii) a combination of mechanical and thermal loading. We monitor the ACPD signals in several zones along the gauge length of specimens, and we demonstrate that a localized type of transformation is a generic feature of pseudoelastic as well as of shape memory deformation. Moreover, the ACPD signals allow to differentiate between temperature‐induced martensite (formed during cooling at no or relatively small loads), stress‐induced martensite, and reoriented martensite (formed under load at low temperatures).