Piezoresistance Research Articles

Piezoresistance Characterization of Silicon Nanowires in Uniaxial and Isostatic Pressure Variation.

Silicon nanowires (SiNWs) are known to exhibit a large piezoresistance (PZR) effect, making them suitable for various sensing applications. Here, we report the results of a PZR investigation on randomly distributed and interconnected vertical silicon nanowire arrays as a pressure sensor. The samples were produced from p-type (100) Si wafers using a silver catalyzed top-down etching process. The piezoresistance response of these SiNW arrays was analyzed by measuring their I-V characteristics under applied uniaxial as well as isostatic pressure. The interconnected SiNWs exhibit increased mechanical stability in comparison with separated or periodic nanowires. The repeatability of the fabrication process and statistical distribution of measurements were also tested on several samples from different batches. A sensing resolution down to roughly 1 pressure was observed with uniaxial force application, and more than two orders of magnitude resistance variation were determined for isostatic pressure below atmospheric pressure.

Piezoresistance in Defect-Engineered Silicon

The steady-state, space-charge-limited piezoresistance (PZR) of defect-engineered, silicon-on-insulator device layers containing silicon divacancy defects changes sign as a function of applied bias. Above a punch-through voltage ($V_t$) corresponding to the onset of a space-charge-limited hole current, the longitudinal $\langle 110 \rangle$ PZR $\pi$-coefficient is $\pi \approx 65 \times 10^{-11}$~Pa$^{-1}$, similar to the value obtained in charge-neutral, p-type silicon. Below $V_t$, the mechanical stress dependence of the Shockley-Read-Hall (SRH) recombination parameters, specifically the divacancy trap energy $E_T$ which is estimated to vary by $\approx 30$~$\mu$V/MPa, yields $\pi \approx -25 \times 10^{-11}$~Pa$^{-1}$. The combination of space-charge-limited transport and defect engineering which significantly reduces SRH recombination lifetimes makes this work directly relevant to discussions of giant or anomalous PZR at small strains in nano-silicon whose characteristic dimension is larger than a few nanometers. In this limit the reduced electrostatic dimensionality lowers $V_t$ and amplifies space-charge-limited currents and efficient SRH recombination occurs via surface defects. The results reinforce the growing evidence that in steady state, electro-mechanically active defects can result in anomalous, but not giant, PZR.

Damage sensing in multi-functional glass fiber composites under mode-I fracture loading

A detailed experimental study is performed for piezo resistance damage sensing on conductive glass fiber/epoxy composites under mode-I fracture conditions. The conductive composites are fabricated by homogeneously dispersing carbon nanotubes (CNTs) within the epoxy matrix and electro-flocking short carbon fibers onto the laminates along with a vacuum infusion process. A parametric study is done on the in-situ damage sensing properties by varying the carbon fiber lengths (150 µm and 350 µm) and the carbon fiber areal densities (500, 1000, 1500, and 2000 fibers/mm2). The change in resistance is captured with a four-point probe measuring methodology by measuring the resistance through the thickness of the composite. The crack initiation toughness value of the composites containing carbon fibers showed improvement over control composites. Composites containing 350 µm length carbon fibers and 2000 fiber/mm2 not only showed the best crack initiation toughness but also provided sensitive network for detecting crack growth.

Mobility model based on piezoresistance coefficients for Ge 3D transistor

The conventional first order piezoresistance model has commonly been used to describe carrier mobility enhancement for low levels of process induced stress in Complementary Metal-Oxide-Semiconductor Field Effect Transistor (CMOS) technology. However, many reports show it failing to describe the nonlinear behavior observed at high levels of stress. In this paper, mobility model based on the modified piezoresistance model with nine stress-independent piezoresistance coefficients is proposed such that a mobility model can be applied correctly to calculate the strain-induced carrier mobility changes. Hence, the overall accuracy is improved compared to the conventional piezoresistance (PR) model. Its validation is confirmed with the results from TCAD simulations of carrier mobility for Ge Fin Field Effect Transistors (FinFET) and nanowire transistors.

Giant, Anomalous Piezoimpedance in Silicon-on-insulator

A giant, anomalous piezo-response of fully-depleted silicon-on-insulator (FD-SOI) devices under mechanical stress is demonstrated using impedance spectroscopy. This piezo-response strongly depends on the measurement frequency, $\omega$, and consists of both a piezoresistance (PZR) and piezocapacitance whose maximum values are $\pi_R = -1100 \times 10^{-11}$ Pa$^{-1}$ and $\pi_C = -900 \times 10^{-11}$ Pa$^{-1}$ respectively. These values should be compared with the usual bulk PZR in p-type silicon, $\pi_R= 70 \times 10^{-11}$ Pa$^{-1}$. The observations are well described using models of space charge limited electron and hole currents in the presence of fast electronic traps having stress-dependent capture ($\omega_c$) and emission rates. Under steady-state conditions (i.e. when $\omega \ll \omega_c$) where the impedance spectroscopy measurements yield results that are directly comparable with previously published reports of PZR in depleted, silicon nano-objects, the overall piezo-response is just the usual, bulk silicon PZR. Anomalous PZR is observed only under non-steady-state conditions when $\omega \approx \omega_c$, with a symmetry suggesting that the electro-mechanically active fast traps are native Pb$_0$ interface defects. The observations suggest new functionalities for FD-SOI, and shed light on the debate over the PZR of carrier depleted nano-silicon.

Highly Thermal Stable TATB‐based Aluminized Explosives Realizing Optimized Balance between Thermal Stability and Detonation Performance

AbstractIn this work, a series of TATB‐based aluminized explosives were formulated from 1, 3, 5‐triamino‐2, 4, 6‐trinitrobenzene (TATB), aluminum powders and polymeric binders. The thermal stability, heat of detonation, detonation velocity and pressure of the TATB based aluminized (TATB/Al) explosives were systematically investigated by cook‐off, constant temperature calorimeter, electrometric method and manganin piezo resistance gauge, respectively. The selected PBX‐3 (70 wt% TATB/25 wt% Al/5 wt% fluorine resin) achieved optimized balance between thermal stability and detonation performance, with the thermal runaway temperature around 583 K. The thermal ignition of TATB‐based aluminized explosive occurred at the edge of the cylinder according to the experimental and numerical simulations. Moreover, the critical thermal runaway temperature for PBX‐3 was calculated based on the Semenov's thermal explosion theory and the thermal decomposition kinetic parameters of the explosive, which was consistent with the experimental value.

A Novel MEMS Device for Scanning Profile Measurement with Three Cantilever Displacement Sensors

A novel Micro Electro Mechanical System (MEMS) measurement device for straightness measurement with a three point method has been proposed. This device integrates three cantilever displacement sensors with a narrow pitch on a silicon chip. The authors determine appropriates shape, dimensions of the cantilever, and a fabrication process. According to simulation results, a triangular cantilever with altitude 12 mm long, base 4mm long, and 0.25 mm thickness was adopted to realize the target measuring range of 100 μm. Near the end of each cantilever, a square frustum probe 250 μm high which was fabricated by anisotropic wet etching was placed. Near the base of cantilevers, four piezo resistance gauges were formed; two are active gauges for measuring stress arise from a displacement at the probe and the others are dummy gauges for temperature compensation. Wiring and contact terminals were fabricated on the base substrate and the total size of the device is 20 mm × 32 mm. The fabrication process of this device was designed and result of a trial production was reported.

Development of an Anthropomorphic Gripping Manipulator: Tactile Sensor System

Background/Objectives: This research deals with alternative systems of distributed tactile systems for robotic appliances. Methods: The electric conductor disruption method and the electrolytic separation method were used to manufacture the prototype sensor elements. Numerous experiments were conducted to study various properties of sensory elements. Findings: Various circuits that rely on different physical principles, i.e. resistance, transistor, capacitive and piezo resistance, have been analyzed. A quantum tunneling sensor element has been selected for implementation. Over 100 prototype sensor elements comprising various combinations of silicone compounds and metal powders have been produced at the early stage of experimental research. Experimental measurements have been done and the effect of powder concentration and particle size and shape on sensitivity of the finished element has been analyzed. Copper powder containing dendrite-shaped particles and silicone compound of lowest possible viscosity ensuring even mixing and obtaining high powder concentration in the mixture have been selected as the material for further experiments. Experimental studies of distributed sensor elements have been done. Lines of further experiments have been determined and schedule has been compiled. Improvements: The sensor system developed will be used as a coating for contact surfaces of an anthropomorphic gripper. The proposed technology may be applied to manufacture distributed tactile sensor systems in the form of artificial skin.

Fabrication of Piezoelectric Polyvinylidene Fluoride (PVDF) Polymer-Based Tactile Sensor Using Electrospinning Method

The polyvinylidene fluoride (PVDF) nanofiber has widely investigated as a sensor and transducer material, because of its high piezo and Ferro electric properties. The novel nano structure of PVDF has attracted considerable interest in the bio sensing and biomedical application. This paper deals with PVDF Tactile sensor. Basically The PVDF acts as piezoelectric effect which convert load into electrical signals. The tactile sensor has a main role for visual handicap and robotics. Any physical activities of robotic in all industrial the tactile sensor is a crucible role, whether it can left the object or handling glass parts pressure of object is main. The Sandwich type PVDF base tactile sensor has been fabricated using nanofiber. Using electro spinning method, the PVDF based nanofiber coated over coper the electrodes. In normal, the PVDF has α-phase and while applying electric pulse the PVDF polymer would be changed from α-phase into β-phase. Only in β-phase, the PVDF act as piezo electrics sensor and measure the piezoelectricity simultaneously measure pressure and temperature in real time. The pressure was monitored from the change in the electrical resistance via the piezo resistance of the material. The enhancement of PVDF properties has been carried by using SEM. The SEM image result showed that the size of nanofiber, the size of nanofiber is varied in the range of (180 nm-400 nm) with smooth surface. The X-Ray diffraction has shown that the PVDF was aggregated with the β-phase crystalline nature. Due to β-phase it was act as a piezo electric prosperity’s and its results are very high sensitivity.

Geometric and chemical components of the giant piezoresistance in silicon nanowires

A wide variety of apparently contradictory piezoresistance (PZR) behaviors have been reported in p-type silicon nanowires (SiNW), from the usual positive bulk effect to anomalous (negative) PZR and giant PZR. The origin of such a range of diverse phenomena is unclear, and consequently so too is the importance of a number of parameters including SiNW type (top down or bottom up), stress concentration, electrostatic field effects, or surface chemistry. Here, we observe all these PZR behaviors in a single set of nominally p-type, 〈110〉 oriented, top-down SiNWs at uniaxial tensile stresses up to 0.5 MPa. Longitudinal π-coefficients varying from −800 × 10−11 Pa−1 to 3000 × 10−11 Pa−1 are measured. Micro-Raman spectroscopy on chemically treated nanowires reveals that stress concentration is the principal source of giant PZR. The sign and an excess PZR similar in magnitude to the bulk effect are related to the chemical treatment of the SiNW.

真直形状測定用 3 点法マルチカンチレバー変位計の高感度化モデルの検討

In this study, we developed a multi cantilever device for straightness measurement using the three point method. This device has three triangular cantilever works as displacement sensors. When the displacement is given at the probe placed at the end of the cantilever, stress arises in the cantilever. Displacement is measured by detecting the stress change using two piezo resistances at the root of the cantilever. This paper presents the results of sensitivity evaluation of improved device models. To improve the sensitivity, we considered the shape to make stress concentration in the strain detecting section of the device, and examined the effects by the finite element method. As a result, it was confirmed that transverse notches on both sides at the root of the cantilever and a rectangular hole between the piezo resisances are effective for sensitivity improvement and crosstalk reduction. Furthermore, we also simulate models of changing thickness of each part and models of changing position of piezo resistance.

Structured elastomeric submillimeter films displaying magneto and piezo resistivity

ABSTRACTStructured elastomer films (100–150 µm) presenting piezo and magneto resistance are described. The films are composites of filler particles, which are both electrically conductive and magnetic, dispersed in an elastomeric matrix. The particles consist of magnetite (6 nm) grouped in silver‐coated aggregates (Fe3O4@Ag). The matrix is styrene–butadiene rubber (SBR) in which diethylene glycol (DEG) is added. The particles, SBR and DEG, are dispersed in toluene and then placed between two rare earth magnets. Formation of pseudo‐chains (needles) of inorganic material aligned in the direction of the magnetic field is obtained after solvent evaporation. The addition of DEG is substantial to obtain an electrically conductive material. The electrical conductivity is anisotropic and increases when applying normal stresses and/or magnetic fields in the direction of the needles. The elastomers, particles, and needless were characterized by XRD, SEM, EDS, FTIR, DSC, TGA, VSM, profilometry, and stress–strain analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 574–586

S1320204 機械加工面うねりの機上評価のための計測デバイス

A novel micro electro mechanical system (MEMS) device for flatness measurement with a five point method has been proposed. This device integrates five cantilever displacement sensors, three are for straightness measurement and other two are for connecting results of straightness measurements, with a narrow pitch on a silicon chip. The authors designed a compact device of which size is 20 mm × 20 mm. Five triangular cantilever with altitude 6.5 mm long, base 2.5 mm long, and 0.25 mm thickness was placed oppositely and alternately on the device for downsizing the device. Near the end of each cantilever, a square frustum probe 250 μm high which was fabricated by anisotropic wet etching was placed. Near the base of cantilevers, four piezo resistance gauges were formed; two are active gauges for measuring stress arise from a displacement of the probe and the others are dummy gauges for temperature compensation. A fabrication process of this device was designed and result of a trial production was reported.

Deformation potentials for Δ1 minimum of conduction band of single crystals n-Ge

Deformation potentials  eV   and eV   for ∆1 minimum of conduction band of single crystals  n-Ge are defined on the basis of theory of the anisotropic scattering and experimental data of longitudinal piezo resistance for single crystals n-Ge for the case, when P||J||[100]. Pressure coefficients for ∆ 1 minimum under uniaxial pressure along crystallographic directions [100], [110] [111] and hydrostatic pressure have been calculated taking into account the given parameters. The results show that the inversion of (L1-∆1) type of absolute minimum in single crystals n-Ge can be implemented under hydrostatic and uniaxial pressures P||J||[100] і P||J||[110].

Piezoresistance in silicon and its nanostructures

Abstract

Evidence for giant piezoresistance effect in n-type silicon nanowire field-effect transistors

Experimental evidence for the giant piezoresistance (PZR) effect in n-type silicon nanowires (SiNWs) on silicon-on-insulator wafers, also called SiNW field-effect transistors (SiNWFETs), is demonstrated. While an external mechanical strain is applied to SiNWFETs depleted by a back-gate bias, a marked increase in the subthreshold drain current is found, thus supporting the widely reported giant piezoresistance effect. This increase can be attributed to the change in Si/SiO2 interface states, further suggesting interface trap-induced giant piezoresistance. Furthermore, through repeated cycles of tensile and released strain, the electromechanical response of the subthreshold drain current with time offers a potential for creating strain-gated SiNWFETs.

206 樹脂封止された積層半導体チップの残留応力に起因する電気特性変動評価手法(OS2-2.電子デバイス・電子材料と計算力学(2),OS・一般セッション講演)

In electronic packages such as BGA and LGA packages, it is very important for the reliability of packages to reduce the residual stress on the surface of the semiconductor chip. In this research, the authors proposed the evaluation method to predict the electronic characteristic changes of stress-induced multilayer chip in resin-molded electronic packages. The developed technique considering the stress singular field and piezo resistance matrix made it possible to predict electronic characteristic changes of multilayer chips in resin-molded electronic packages accurately.

Giant Piezoresistance Effects in Silicon Nanowires and Microwires

The giant piezoresistance (PZR) previously reported in silicon nanowires is experimentally investigated in a large number of depleted silicon nano- and microstructures. The resistance is shown to vary strongly with time due to electron and hole trapping at the sample surfaces independent of the applied stress. Importantly, this time-varying resistance manifests itself as an apparent giant PZR identical to that reported elsewhere. By modulating the applied stress in time, the true PZR of the structures is found to be comparable with that of bulk silicon.

Application of piezoresistance effect in highly uniaxially strained p‐Si and n‐Si for current‐carrier mobility increase

AbstractUniaxially strained channels occur in silicon p‐MOS transistors and n‐MOS transistors (IEDM Tech. Dig., pp. 61–64 (2002) and pp. 978–980 (2003) [1, 2]). Both longitudinal piezoresistance (PR) and transverse PR investigation in highly uniaxially strained p‐Si(B) and n‐Si(P) are presented. It is shown that the strong anisotropy of longitudinal PR and transverse PR are caused by the pressure‐induced change of isoenergetic surface shape, i.e. by the change of heavy‐hole effective mass and its anisotropy. In n‐Si the change of the longitudinal PR and transverse PR at X ∥ [100] is determined by both the change of the f‐transition probability with increasing pressure and the redistribution of electrons between the valleys with the effective mass m∥ (longitudinal PR) and m⊥ (transverse PR). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Development of Simple Dip-Stick-Type Uniaxial Stress Actuator for Alternating-Current Susceptibility Measurements

A simple dip-stick type uniaxial stress actuator for ac-susceptibility measurement is designed. Target pressure can be achieved by smooth and continues work carried out using a combination of light weight micrometer and spring. The magnitude of the pressure is directly calculated from the force constant of the spring and the surface area of the sample. Benchmark on the quality of the data under uniaxial pressure is confirmed by the Piezo resistance measurements on [100] oriented n-type Si. The system is examined and calibrated with the standard paramagnetic Gd2O3. Further, the device performance, generation of constant uniaxial pressure against temperature variations, is assured by investigating the ac-magnetic susceptibility measurements on highly anisotropic La1.25 Sr1.75 Mn2O7 bilayer single crystal.