Strain Gauge Material Research Articles

Investigation on Strain Sensitivity and Temperature Behaviour of Nitrogen Doped 3C-SiC Thin Films

Electrical resistance-strain behaviour of nitrogen doped 3C-SiC thin films was investigated to determine whether they could be used as strain gauges. Using a hot wall vertical low pressure chemical vapour deposition (LPCVD) reactor, these films were deposited on thermally oxidised Si (100) and alumina substrates at 2.5 mbar pressure and 1040°C temperature from methyltrichlorosilane (MTS) precursor. The nitrogen doping gas utilised was ammonia (NH3). Using four-point bending method, the gauge factor (GF) was determined for all thin films (0, 9, 17, and 30 atomic % nitrogen doped). Systematic annealing of films in a vacuum atmosphere was used to determine the TCR of nitrogen doped 3C-SiC (111). Film sheet resistance was evaluated using a four-probe approach, and it was observed to decrease as the temperature rises from 40 to 550°C. The resistivity, average TCR, and strain sensitivity of film doped with 17 atomic % nitrogen concentration were 0.14 cm, -103 ppm/°C, and -9.6, respectively, indicating that it can be employed as a strain gauge material in high temperature applications. However, film doped with 30 atomic % of nitrogen concentration showed an increase in the resistivity, TCR and strain sensitivity.

ОПТИМІЗАЦІЯ ВИМІРЮВАЛЬНИХ ЗАСОБІВ НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ЗА ДОПОМОГОЮ ТЕНЗОДАТЧИКІВ

In the article, the principles of construction, design and mathematical modeling of deformation and stresses of complex technical constructions are developed with the help of strain gauges and strain gauges taking into account destabilizing factors, which allows to significantly reduce the level of errors in relation to existing measurement methods and known analogs.The method of digital compensation provides a more significant reduction in the errors of measuring transducers compared with the method of analog compensation. Features and technical indicators of this method are considered on an example of measuring pressure transducer with foil strain gauges.This method is universal, allows us to adjust not only the errors of the measurement channel nonlinearity and additional errors but also the errors associated with the effect of interferences of the general type due to ground resistance, which induces the connection between the measuring channels of the main and destabilizing factor.The disadvantages of this method include a significant amount of computations, which sharply increases with increasing order of approximating polynomials.The purpose is to develop a method and means of measuring stress-strain state using strain gauge, free from the above - mentioned shortcomings.The main destabilizing factors that limit the measurement accuracy using strain gauge are:- random processes (noises, obstacles, etc.);- changes in parameters of measuring transducers due to aging and physical degradation;- effects of external climatic and mechanical factors (temperature, humidity, etc.).The influence of the main destabilizing factors limiting the accuracy of the measurement of the stress-strain state of complex technical constructions with the help of strain gauges was analyzed, among which the influences of external climatic and mechanical factors are one of the most important ones. Regarding the systematic components, the most important in statistical measurements are the errors of nonlinearity and the temperature component of the error.For the study, two main alloys were taken, which today has the widest use as a material for strain gauges - it is constantan and karma. For these materials, the influence of the range of temperature changes, the spread of the values of temperature error on the mean-square value of the error of approximation by power polynomials was investigated.Using the NUMERY package, the dependence of the approximation error on the order of the approximating polyphony was determined. It is established that the mean square error value in the wide temperature range for both constantan and karma has a weak correlation with the order of a polynomial.

Titanium Nitride as a Strain Gauge Material

The performance of titanium nitride (Ti-N) thin films deposited by reactive magnetron sputtering for use as a strain gauge material was investigated. Films of different composition ranging from pure titanium to over-stoichiometric Ti-N were prepared by varying the nitrogen flow to total flow ratio ( $\alpha )$ . The atomic composition was measured using Rutherford backscattering spectrometry and energy-dispersive X-ray spectroscopy. The structure of the films was studied using X-ray diffraction and scanning electron microscopy, revealing the formation of a columnar film morphology consisting of cubic-Ti-N grains with preferential crystal orientations depending on the flow ratio $\alpha $ . The stability of the film resistivity was studied at 200 °C for 360 h. Films deposited at low ( $\alpha \leq 0.08$ ) and high ( $\alpha = 0.60$ ) nitrogen flows exhibited a stable behavior relative to films deposited with intermediate nitrogen flows. The longitudinal piezoresistive gauge factor was found to increase with increasing nitrogen flow before settling at values of 6–6.35. Finally, the temperature coefficient of resistivity was found to be less than 300 ppm/°C for the films with the highest gauge factors. The results demonstrate that the Ti-N films have a good potential as a strain gauge material, especially due to the relatively high gauge factor. [2016-0040]

Load Vector Sensors Using Strain‐Sensitive Cr‐N Thin Films and Their Applications

SUMMARYCr‐N thin films, which have a gauge factor of about 16 and a temperature coefficient of resistivity close to zero, are a promising new next‐generation strain gauge material. In this paper, the fabrication and characterization of a single‐module system of the load vector sensor using the Cr‐N strain‐sensitive thin films, which can be applied to sole sensors, are reported.

Load Vector Sensors using Strain Sensitive Cr-N Thin Films and Their Application

A Cr-N thin film shows a gauge factor of about 16 and a temperature coefficient of resistivity (TCR) of about zero, which is expected as a new strain gauge material in the next generation. In this paper, the fabrication and characterization of a single module system of the load vector sensor using the Cr-N strain sensitive thin films, which can be applied for a sole sensor, are reported.

A molecular template approach to integration of polyaniline into textiles

A molecular template (a sulfonated polyaniline) has been used to facilitate integration of a complementary conductive polymer (polyaniline) into wool-based textiles. The efficiency of the polymerisation/coating process is enhanced since the template localises the reaction within the textile. The presence of the molecular template results in the formation of an adherent, uniform and stable conducting polymer layer. The poly(2-methoxyaniline-5-sulfonic acid) (PMAS) molecular templated fabric had a surface resistivity of 28 MΩ/□, but after the integration of polyaniline the surface resistivity decreased to 342 kΩ/□. The integration of polyaniline also improved the electrochemical reversibility of the coating. The coated textiles were found to be suitable for application as wearable strain gauge materials to be used for biomechanical monitoring.

G1001-5-3 Cr-N薄膜ひずみゲージを用いた高感度力センサ((5)計測・測定)

We have developed a Cr-N alloy thin film showing a gauge factor of about 10 and a temperature coefficient of resistivity (TCR) of about zero, which is expected as a new strain gauge material in the next generation. We have prepared a force sensor using the film strain gauge, and found that the sensitivity of the sensor is about five times higher than those of a conventional metal foil gauge.

탄소섬유의 게이지 계수 측정 및 센서 응용

In this paper we report on the electrical properties of carbon fiber which is an attractive material for strain gauges and can also be applied to resonating micro sensors. The carbon fibers used in this research was manufactured from polyactylonitrile (PAN). The fabricated carbon fibers had about <TEX>$10\;{\mu}m$</TEX> in length and several centimeters in length. We employed a micro structure to measure electrical properties of the carbon fiber. The measured electrical resistivity of the carbon fibers were about <TEX>$3{\times}10^{-3}{\Omega}{\cdot}cm$</TEX> A gauge factor of the carbon fiber is also observed with the same system and it was about 400, depending on the structure of the carbon fiber. For the sensor applications of the carbon fiber, it is selectively placed between the gap of Al electrodes using a dielectrophoresis method. When the carbon fiber is resonated by a piezoelectric ceramic, resistance change at a variety of resonance mode was observed through an electrical system.

Measurement of the gauge factor of carbon fiber and its application to sensors

The electrical properties of carbon fiber (CF), an attractive material for strain gauges that can also be applied to resonating sensors, are reported in this paper. The CFs were manufactured from polyactylonitrile (PAN). The fabricated CFs had a 10μm diameter and a length of several cm. The electrical resistivity of the CFs was found to be about 3×10−3Ωcm. The gauge factor of the CF was also observed, and it was found to be about 100–400, depending on the structure of the CF. For the resonating sensor applications of the CF, it was selectively placed in the gaps between the Al electrodes through dielectrophoresis. When the CF was resonated at the 5th resonance mode, a large change of its resistance was observed through an electrical system. The results of the experiment were found to coincide with the calculation results.

Piezoresistive gauge factor of hydrogenated amorphous carbon films

In this paper we report on the transport properties of hydrogenated amorphous carbon (a-C:H) which is an attractive material for strain gauges and can also be used in flow meters, accelerometers and vibrational sensors. The a-C:H films were deposited at −350 V bias voltage on silicon (Si) substrates using plasma assisted chemical vapor deposition (PACVD). Current–voltage characteristics of a-C:H/n-Si heterojunctions show ohmic behavior within operating voltages of ±1 V. In the higher voltage range the Frenkel–Poole mechanism is dominant. Conduction is thermally activated at temperatures ranging from 23 °C to 150 °C. The activation energy amounts to 0.48 eV. A-C:H resistors are successfully integrated as strain gauges in Si bulk micromachined force sensors. Piezoresistive gauge factors are measured for the a-C:H strain gauge resistors in the temperature range 23–60 °C. The measured piezoresistive gauge factors are in between 40 and 90 for a-C:H with resistivities in the range 100–700 MΩ cm.

Dressware: wearable hardware

Conventional fabrics coated with a thin conducting polymer layer are described which possess remarkable properties of strain and temperature sensing. Sensing figures of merit are comparable to those of sensitive strain gauge materials and inorganic thermistors. Also, spun conductive polymer fibers show electromechanical actuation. The isometric contractile stress of the actuating fibers is higher than skeletal muscle, between 1 and 15 times. The fabrication of active electronic and electromechanical systems onto substrates which are not only flexible, but ideally conformable to the human body may represent a breakthrough in man–machine interface technology.

The strain sensitivity coefficient of resistance for an FeMnAlCr antiferromagnetic alloy

Experimental investigations on the strain-electric resistance relationships of an FeMnAlCr antiferromagnetic alloy show that resistance changes linearly with strain in both elastic and plastic areas. In the elastic area the strain sensitivity coefficient of resistance K = 4.0 - 4.8, and K decreases with increasing Cr content. In the plastic area . It is suggested that the high K of the FeMnAlCr alloy in elastic areas may be related to its antiferromagnetic spin structure. Finally the possibility of developing FeMnAlCr ambient temperature and cryogenic strain gauge materials are briefly discussed.

Noble Metal Alloys as Strain Gauge Materials

The development of materials which contain the noble metals for use in high temperature strain gauges is reviewed, with particular emphasis being placed upon work done by the Institute of Precious Metals, in China. Three alloy systems displaying excellent resistance to oxidation and good overall properties when used in high temperature strain gauges, are singled out for examination. These are platinum-tungsten-rhenium-nickel-chromium-yttrium, gold-palladium-chromium-platinum-iron-aluminium-yttrium and palladium-chromium. Their development and the suitability of these alloys for use in measuring high temperature static strain are discussed.

In situ calibration of stress chips

A novel procedure employing moire interferometry has been successfully implemented for the accurate in-situ calibration of stress chips. Strains were measured by this accurate and extremely sensitive technique at the locations of the gauges and related to corresponding gauge-resistance changes. The approach is immune from many of the drawbacks of earlier calibration procedures and has eliminated the need to know the piezoresistive properties of the strain-gauge material, which constituted a major difficulty in properly interpreting gauge-resistance changes in terms of strains at the gauge locations. A characteristic gauge factor, S, for each type of strain gauge has been introduced and shown to be the only gauge character to be determined. It reflects how different gauge types react to the same strain. It is suggested that the strain gauges be designed such that the gauge factor is as high as possible, thereby minimizing sensitivity to measurement errors. In addition to being flexible and applicable to new and existing stress chips, the procedure is expected to spread the use of diffused-resistor strain gauges as a realistic monitor of chip strains in addressing reliability concerns. >

Temperature compensation of amorphous silicon strain gauges

The applied potential of amorphous silicon as a strain gauge material has been investigated. Measurements of the gauge factor, K, were carried out on a-Si/a-SiN x thin-film structures deposited from a glow discharge plasma on polished stainless steel substrates. The conductance changes of phosphorus-doped a-Si under uniaxial strain lead to room temperature K values between −20 and −40, depending on the potential applied to the substrate. The control of K by the field effect makes it possible in principle to compensate for the temperature coefficients of the gauge factor.

Piezoresistive effect of hydrogenated microcrystalline silicon films

Microcrystalline silicon films are expected to have promising properties for a strain gauge material. We have investigated in detail the gauge factor, and its temperature dependence, of hydrogenated microcrystalline silicon films as a function of doping gas ratio. Samples were prepared by glow discharge decomposition of silane gas. It was found that the films show relatively high sensitivity and low temperature dependence. The gauge factor depends on the electrical conductivity of the films. The temperature coefficient of the gauge factor is deduced from the temperature dependence of the conductivity. The coefficient increases in proportion to the activation energy.

Polycrystalline silicon as a strain gauge material

A theoretical model for piezoresistance in both n- and p-type polycrystalline silicon is described. This model considers the contribution to piezoresistance from the grain and the Schottky-type barrier regions around the grain boundaries. Comparison between theory and experiment shows reasonable agreement for both longitudinal and transverse strain measurements. The difference in magnitude between longitudinal and transverse gauge factors depends on texture and is found to be explained by the anisotropy of piezoresistance in silicon. Experimental results for the temperature coefficients of resistance and gauge factor in conjunction with the model for piezoresistance may be used to optimise sensor characteristics within the confines of available processes.

Polycrystalline silicon-on-metal strain gauge transducers

The characteristics of polycrystalline silicon-on-metal strain gauge transducers are reported. This strain gauge material is stable, rugged, operates over a wide temperature range, and has a gauge factor intermediate between that of single-crystal Si, having the same carrier concentration, and that of metal wires and thin films. A model relating the polycrystalline silicon gauge factor and its temperature dependence to that of single-crystal Si strain gauges is developed and shown to adequately describe transducer properties.

Temperature and strain dependences of electrical resistance of Ni-Si-B amorphous alloys

Ni-Si-B amorphous alloys were prepared from the melt by a rapid quenching method in order to investigate the temperature and strain dependences of electrical resistance. The room-temperature coefficient of electrical resistance becomes very small in a wide temperature range by adjusting the metalloid content, and its sign changes around the total conduction electron CE≊1.5 with the resistivity ρ≊150 μΩ cm. A linear relationship between the strain and the change in the electrical resistance is observed, and the strain gauge factor is estimated to be about 2.0. In addition, the electrical resistivity of these amorphous alloys is much higher than that of conventional strain gauge alloys, and shows no anisotropy in magnetic fields because they are paramagnetic. From these results, it is concluded that Ni-Si-B amorphous alloys are suitable for applications to strain gauge materials.

Cu-Ag-P系非磁性非晶質合金の電気抵抗歪係数について

The strain gauge factor K at room temperature, the electrical resistivity ρ at 20°C and its mean temperature coefficient Cf, and the mean thermal electromotive force Emf in the temperature range of 0° to 40°C have been measured with ribbons of amorphous Cu-Ag-P alloys. Compared with conventional strain gauge materials, these amorphous alloys exhibit comparable K(1.8∼3.1), high ρ (135.6∼154.3×10−8 Ω·m), negative Cf(−0.67∼−1.23×10−4/°C) and low Emf(1.02∼1.07 μV/°C). From the above results, these amorphous alloys are expected to serve as strain guage alloys below the crystallization temperatures.