Papers by Keyword: Gauge Factor

Abstract: Hybrid laminates consisting of fibre-reinforced thermoplastic films and metallic thin sheets are successively replacing thermoset based systems due to their obvious advantages of higher formability and aptitude for mass production. In order to monitor the material under operating conditions, hybrid laminates need to be equipped with smart sensor units. Artifact-free integration of commercial strain gauges into hybrid laminates is almost impossible. Therefore, a new thin film strain sensor based on a PVD sputtering process was developed.The aim of this work was to evaluate the influence of the layer thickness as well as the elevated temperature during the sputtering process on the electrical performance of Ni-C strain sensors. The Ni-C films with different layer thickness and different sputtering temperatures manufactured by means of a magnetron sputtering process were investigated for the sheet resistance and the change of temperature coefficients of resistance. In addition, Raman spectroscopy was utilized to investigate the phase development with regard to different sputtering temperatures. It can be seen that the gauge factor gets doubled while optimizing the layer thickness. When the sputtering temperature was increased, the graphitic phase formation was preferred and the impurities were reduced. These results are discussed in this paper and appropriate solution concepts are provided.

Abstract: Strain sensors are devices used in applications such as electronic skin, prosthetic limbs, and e-textile applications, etc., for the purpose of measuring the physical elongation of a desired structure under a given or applied force. An artificial throat, using a strain sensor, was recently developed as an aid for speech impaired individuals. Strain sensors have been developed using graphene and polydimethylsiloxane (PDMS), with a reported gauge factor ranging from (5~120). We have developed a strain sensor through laser scribing. Using laser scribing is a recent and facile technology, used for printed electronics. Complex geometries and patterns can be drawn very easily using this method. The laser scribing method relies on the property of certain materials to form a graphene-like conductive material upon irradiation by lasers. Polyimide and graphene oxide (GO) are two such materials.In these experiments, 2×2 cm sheet of polyimide were taken and printed 1×1 cm box on the sheet using a laser patterning setup of 450 nm wavelength. Graphene oxide solution was drop-casted on the reduced polyimide sheet of 1×1cm, to increase its sensitivity, and then the drop-casted graphene oxide was reduced using the same laser. The strain sensor was characterized by a micro-strain testing machine. The normalized resistance was plotted against strain and the gauge factor was calculated. The effect of the laser intensity was investigated and different gauge factors were calculated by varying the intensity of the laser. The gauge factors were found to be in the range of 49-54 and was compared with the polyimide reduced strain sensor (without drop-casting the GO).

Abstract: This paper presents an experimental investigation of microstructure and piezoresistive properties of phosphorus-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The phosphorus-doped nc-Si:H thin films (5% doping ratio of PH₃ to SiH₄) were deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The microstructure and surface morphology of the deposited thin films was characterized and analyzed with Raman spectroscopy and atomic force microscopy (AFM), respectively. The piezoresistive properties of the deposited thin films were investigated with a designed four-point bending-based evaluation system. In addition, the influence of temperature on the piezoresistive properties of these thin films was evaluated with the temperature coefficient of resistance (TCR) measurements from room temperature up to 80°C. The experimental results show that phosphorus-doped nc-Si:H thin films prepared by PECVD technique are a two-phase material that constitutes of nanocrystalline silicon and amorphous silicon, and they present a granular structure composed of homogeneously scattered nanoclusters formed by nanocrystalline silicon grains (6nm). Moreover, phosphorus-doped nc-Si:H thin films exhibit negative GF at room temperature and show good thermal stability from room temperature up to 80°C, and the value of GF and TCR is about-31 and-509ppm/°C, respectively. These features could make phosphorus-doped nc-Si:H thin films act as a promising material for piezoresistive-based MEMS sensor.

Abstract: A new strain gauge based on graphene piezoresistivity was fabricated by a novel low cost technique which suits mass production of micro piezoresistor sensors. The strain gauge consists of a monolayer graphene film made by chemical vapor deposition on a copper foil surface, and transferred to Si/SiO₂ surface by using a polymethyl-methacrylate (PMMA) assisted transfer method. The film is shaped by laser machine to work as a conductive-piezoresistive material between two deposited electrical silver electrodes. This method of fabrication provides a high productivity due to the homogeneous distribution of the graphene monolayer all over the Si/SiO₂ surface. The experimentally measured gauge factor of graphene based device is 255, which promises a new strain gauge sensor of high sensitivity.

Abstract: The polycrystalline silicon films with same doping concentration and different thickness were prepared by low pressure chemical vapor deposition. The gauge factors of the films samples were tested, the results show that the piezoresistive properties of nanopolycrystalline silicon film (NPSF) exceed that of common polycrystalline silicon film (CPSF). To apply the NPSF to MEMS piezoresistive device effectively, the Youngs modulus of the NPSF were tested by in-situ nanomechanical test system, the results show that the Youngs modulus of the NPSF is about between 155GPa and 158GPa. It is very useful to investigate the piezoresistive and mechanics properties of NPSF, the results show that NPSF is a suitable material in MEMS piezoresistive device.

Abstract: We introduce a novel high temperature PECVD process and use it for the deposition of silicon carbide thin films on oxidized silicon wafers at 900°C substrate temperature. A variation of the atomic composition over a wide range is achieved by altering the flow ratio of the precursors silane (SiH₄) and acetylene (C₂H₂). XPS analysis is performed to verify the silicon to carbon ratio in the deposited layers. The resistivity of the obtained thin films shows a strong dependence on the Si/C-ratio. Four point measurements show the resistivity ranging between 5•10^-3Ωcm for C-rich layers and >10⁷Ωcm for near stoichiometric layers. We investigate the piezoresistivity of the SiC layers at room temperature under compressive and tensile strain using the four point bending method. The same method is used to analyze selected layers at elevated temperatures up to 600°C. Based on the results we evaluate the applicability of the obtained thin films for strain transducing in harsh environment MEMS sensors.

Abstract: The objective of this paper is to use the Noninvasive Strain Measurement System to monitor the pulse pressure of the blood’s undulation in the artery as an index for the clinical diagnosis of arteriosclerosis. In the study, a strain-measuring device (350Ω) is affixed to the left side of the radial styloid process, on the surface of the skin, and is connected to the Strain FleXense. An artery-pressuring tape is set on the left humerus, and the measurement of the wavelength and frequency of the heartbeat is taken to compare with the clinical artery wave. The results show that when the subject is in a comfortable position with moderate physiological levels, the heartbeat has no connection whatsoever with blood pressure. The greatest heartbeat strain, which occurs when the veins and arteries respectively are being cleared, displays as a linear change.

Abstract: The objective of this paper is to use the Noninvasive Strain Measurement System to monitor the pulse pressure of the blood’s undulation in the artery as an index for the clinical diagnosis of arteriosclerosis. In the study, a strain-measuring device (350Ω) is affixed to the left side of the radial styloid process, on the surface of the skin, and is connected to the Strain FleXense. An artery-pressuring tape is set on the left humerus, and the measurement of the wavelength and frequency of the heartbeat is taken to compare with the clinical artery wave. The results show that when the subject is in a comfortable position with moderate physiological levels, the heartbeat has no connection whatsoever with blood pressure. The greatest heartbeat strain, which occurs when the veins and arteries respectively are being cleared, displays as a linear change.

Abstract: In this paper, graphene grown by Chemical vapor deposition (CVD) on a Cu foil in a cold-wall furnace was used to fabrication the graphene strain gauge. The graphene membrane was patterned to wire grid shape on the Cu substrate by photolithography method in the clean room. The pattern was transferred to PDMS substrate and seal by it also to make graphene in a stable surroundings. Through the standard calibration, it was calculated that the linearity and multiplicity of the graphene strain gauge both were 0.0076%F.S.. Which indicated the good quality of the gauge. The gauge factor was 2.4, as the highest value as that of the alloy strain gauge. We also find the graphene strain gauge output increase proportionally with increasing curvature of its deformation.

Abstract: The piezoresistive and ohmic contact properties of polycrystalline silicon nano thin films were investigated in this paper. The polycrystalline silicon films with different thicknesses and doping concentrations were deposited by LPCVD and doped with boron highly, and then the cantilever beam samples were fabricated by photolithography and wet etching. By measuring the gauge factor and specific contact resistivity, the specific contact resistivity of Al contacts can reach 2.4×10^-3Ω·cm² after the alloying at 450 °C for 20 min; the enhanced piezoresistive effect of highly doped polycrystalline silicon nano thin films was discovered. The conclusions indicated that the enhanced piezoresistive sensitivity of PNTFs is due to the modification of depletion region barrier by ultra high doping and film thickness thinning and the enhancement of tunneling piezoresistive effect. The distinct piezoresistive phenomenon of PNTFs could be utilized for the development and fabrication of miniature piezoresistive sensors.