Thin Film Strain Gauges Research Articles

Low-cost two-dimensional digital image correlation system

A low-cost digital image correlation (DIC) system for measuring two-dimensional displacement fields is described. Using an off-the-shelf camera, lens, and open-source DIC analysis software, displacement fields in aluminum and steel dog-bone tensile specimens were measured. Correction for out-of-plane motion is used to obtain strains from the displacement fields. Proposed DIC strain measurement system is validated using conventional thin-film strain gauges for strains below 1%. Average strain measurements from the DIC system were found to be within 1% of the measurement obtained using strain gauges. For strains between 1% and 10%, strain histories from the DIC systems displayed excellent correlation with strain measurements obtained using an extensometer.

A Novel Semiconductor Piezoresistive Thin-Film Strain Gauge With High Sensitivity

A Novel Semiconductor Piezoresistive Thin-Film Strain Gauge With High Sensitivity

High-Temperature PdCr Thin-Film Strain Gauge With High Gauge Factor Based on Cavity Structure

High-Temperature PdCr Thin-Film Strain Gauge With High Gauge Factor Based on Cavity Structure

Temperature self-compensation thin film strain gauges based on nano-SiO2/AgNP composites

Nano-SiO2/AgNP temperature self-compensation thin film strain gauges for micro-strain by direct ink writing technology.

Directly Deposited Thin-Film Strain Gauges for Force Measurement at Guide Carriages

Directly Deposited Thin-Film Strain Gauges for Force Measurement at Guide Carriages

Measurements of Polymer-Derived Ceramic Thin-Film Strain Gauges at High Temperatures

Measurements of Polymer-Derived Ceramic Thin-Film Strain Gauges at High Temperatures

Temperature‐Independent Conductive Ceramic for High‐Temperature Strain‐Sensing Applications

Temperature‐independent properties are critical for high‐temperature thin‐film strain gauges (TFSGs). In this study, by controlling the electron scattering and tunneling effects in the TiB2/SiCN composites, the environmental interference of temperature fluctuations is successfully eliminated, and a temperature‐independent TFSG is fabricated. The effects of pyrolysis temperature and TiB2 content on the microstructural evolution and electrical properties of the ceramic films are studied. The temperature insensitivity is mainly attributed to the balance between the intrasheet resistance with a positive temperature coefficient of resistance (TCR) and the intersheet resistance with a negative TCR. This composite shows nearly constant resistance values over an ultrawide temperature range of 300–700 °C, with less than 0.05% deviation of the normalized resistance and TCR values as low as 1.6 ppm °C−1. In addition, the TiB2/SiCN films exhibited stable piezoresistive responses, with a gauge factor of 4.28, and the temperature‐independent strain response in the high‐temperature range is verified.

Study on the Fabrication and Characteristics of Tantalum-Nitride (TaN) Thin-Film Strain Gauges on the Silicon Substrate for Silicon-Based Heterogeneous Integration Application

Study on the Fabrication and Characteristics of Tantalum-Nitride (TaN) Thin-Film Strain Gauges on the Silicon Substrate for Silicon-Based Heterogeneous Integration Application

Piezoresistive failure behaviors and mechanisms of the ITO thin films at high temperatures

ITO is drawing enormous attention in fabrication of thin film strain gauges (TFSGs) due to its excellent oxidation resistance, high melting point and great piezoresistivity. However, the operating temperature of ITO TFSGs is far lower than its melting point. In this work, 8.9 μm ITO thin films and TFSGs were prepared using magnetron sputtering to reveal their piezoresistive failure behaviors and mechanisms at various high temperatures. Results show that surface bulges and significant thickness reduction of the ITO thin films appear at 1275 °C due to their repaid sublimation. The Hall mobility of the ITO thin films decreases sharply due to the formation of the surface bulges and significant thickness reduction at 1275 °C. The piezoresistive failure behaviors of the ITO TFSGs mainly result in their significant resistance drift and the decline of the gauge factor (GF) at 1275 °C. The drift rate of the ITO TFSG at 1275 °C is nearly 7 times higher than that at 1250 °C. The GF of the ITO TFSGs drops from 4.67 to 1.77 when the testing temperature rises from 1250 °C to 1275 °C. These can be attributed to the sharp decrease of the Hall mobility of the ITO thin films.

High-Tolerance Thin-Film Solder Joints for Electrical Interconnection in Harsh Environments

This paper presents a pioneering use of thin-film solder joint in the electrical interconnection of high-temperature thin-film sensors, which aims to improve the low tolerance of traditional soldered balls in extreme environments. The structure of the thin-film solder joint, composed of silver foil, solder joint paste, and metal wire, has a negligible mass compared to traditional soldered balls. As a result, the inertia force on the solder joint/substrate interface during vibration and force impact is greatly reduced, improving the reliability of the solder joint under thermal-mechanical coupling impacts. The thin-film solder joint has been verified using both metal (AgPd paste) and ceramic (TiB2/SiCNO paste) solders, and can withstand extreme environments such as thermal shock and high "g" loading. The designed thin-film solder joint can withstand impact energy of up to 3 J at 1000 °C without failure, which is 6 times higher than that of traditional soldered balls (with a statistical failure rate of up to 67% under 0.5 J impact). The thin-film solder joint was successfully used for electrical interconnection of high-temperature thin-film strain gauges, demonstrating excellent reliability under thermal-mechanical coupling impacts at 1000 °C. Our high-tolerance thin-film solder joints show promising potential for use in electrical interconnection in harsh environments.

Ultrafast high-temperature sintering of polymer-derived ceramic nanocomposites for high-temperature thin-film sensors

Polymer-derived ceramic nanocomposites (PDC-NCs) are promising materials for high-temperature thin-film sensor (TFS) applications. However, owing to their inherent high-resistance characteristics and the high-temperature furnace sintering process, it is difficult to integrate PDC-NCs with high-conductive and low high-temperature tolerant alloy/metal components. In this study, an ultrafast high-temperature sintering (UHS) method was employed to prepare PDC-NC TFSs in minutes. The TiB2/SiCNO film sintered by the UHS technique shows high-sensitive microstructure and properties to sintering parameters. The UHS technique allows rapid sintering toward the desired phase, controls the grain size and microstructure, promotes the precipitation of free carbon in the SiCNO matrix within minutes, and suppresses high-temperature oxygen pollution. For example, TiB2/SiCNO films show high conductivity (18.1 S cm−1 at room temperature) and high-temperature stability (up to 800 ℃). In comparison, these properties are orders of magnitude better than those of samples sintered in the furnace. High-quality films sintered using ultrafast heating and cooling rates can also withstand thermal shocks of up to 1000 ℃. With the UHS technique, high-quality and high-conductivity films can be prepared using an ultrafast sintering rate to prevent substrate thermal damage. The TiB2/SiCNO thin-film strain gauge with high sensitivity (GF = 8.6) and low thermal noise was fabricated on alloy substrates, and its high-temperature (25–800 ℃) strain sensing performance was verified. This method offers a new route for co-sintering devices with alloy/metal substrates that suffer from low high-temperature tolerance and regulating the microstructure and electrical performance of these devices.

A Bilayer Thin-Film Strain Gauge With Temperature Self-Compensation

A Karma–CuNi bilayer strain gauge with a low-temperature coefficient of resistance (TCR) is designed for temperature self-compensation. The impact of heat treatment and structural parameters on its performance is investigated. The TCR of the bilayer thin-film strain gauge can be adjusted to near 0 ppm/°C by controlling the thickness ratio and the annealing temperature. Besides, the Karma–CuNi thin films had a gauge factor (GF) of 2.2. Finally, the Karma–CuNi bilayer thin-film strain gauge was fabricated on the metal substrates and bone-like metal elastomer. An experimental setup based on bending beam theory was developed to determine the GF of the strain gauges fabricated on metal substrate. It shows promising applications for in situ strain or torque measurement of some metal component when high sensitivity and high spatial resolution is required.

A thin film force sensor on AISI 5140 steel surface with multilayer SI3N4/AL2O3 film as insulation structure

To develop a thin film force sensor on AISI 5140 steel surface, alternating stack thin films of silicon nitride and alumina were sputtered on the 5140 steel surface as the insulating structure before NiCr thin film electrodes were deposited. The insulation was investigated by measuring the resistance between different electrodes. The sample cross-section was examined and a nano-scratch test was carried out. Finally, a Ni80Cr20 thin film strain gauge was formed on the surface of a well-insulated sample with a hard masque, and its force (0 ∼ 250 kN and 0 ∼ 500 N) and temperature (25 °C ∼ 200 °C) responses were investigated. The results show that the alternating four-layer Si3N4/Al2O3 thin film structure can provide insulation close to 1.2 GΩ with a thickness of 2360 nm. The insulation layers have fine adhesion to 5140 steel, and there is no significant inter-layer diffusion which indicates the integrity of the multi-layer structure. The resistance strain coefficient of the sensor is 1.57 ∼ 1.67, and the resistance temperature coefficient is 190.3 ppm/ °C.

Multilayer co-sintered Pt thin-film strain gauge for high-temperature applications

Typical high-temperature thin-film sensors are fabricated by layer-by-layer deposition and layer-by-layer sintering, which are time and energy consuming. In this study, thin-film strain gauges (TFSGs) were fabricated on superalloy substrate by co-sintering process for the first time. The co-sintering behavior of glassy insulating layer and Pt thin-film resistance grid was studied. Compared with layer-by-layer sintering, the weak interface constraint between the top and sub layers of co-sintered TFSG allows the free in-plane shrinkage of the Pt resistance grid. In the co-sintering process, the glassy SiO2 in the insulating layer fills the pores in the Pt resistance grid, significantly improving the compactness. Further, no Pt element diffuses into the insulating layer. Owing to the remarkable advantages of the co-sintering process, the co-sintered Pt TFSG not only inherits the high-temperature insulation (2.8 MΩ at 800 °C) of the layer-by-layer sintered insulating layer, but also significantly increases the high-temperature stability of the Pt grid resistance; the resistance change rate of layer-by-layer sintered samples at 800 °C is 7.3 % h−1, while that of co-sintered samples at 800 °C is only 0.9 % h−1. Finally, the high-temperature strain response of co-sintered Pt TFSG up to 800 °C was tested.

Temperature-insensitive conductive composites for noninterference strain sensing

Very few thin-film strain gauges (TFSGs) that exhibit temperature self-compensation have been developed. Their temperature insensitivity range is typically < 100 °C, and they cannot be used for static strain sensing in variable-temperature environments. In this study, environmental interference owing to temperature fluctuations was successfully eliminated by controlling electron scattering and thermally assisted hopping transport in conductive composites. A new temperature-insensitive material was developed. The proposed strategy enables noninterference dynamic strain monitoring over an ultrawide temperature range of 30–300 °C, which is approximately 200 °C higher than that of noninterference TFSGs that have been reported. In particular, we propose the smallest feature unit of electron transport in conducting composites, that is, the pathway of an electron through a conductive particle and adjacent junction. This unit retains all the features of the entire conductive network, such as the temperature-resistivity effect, and is the smallest unit that can fully reflect the electron transport behavior. We manipulated the microstructure such that the static strain affects only the arrangement and number of temperature-insensitive feature units without destroying its internal structure, enabling temperature independence under static strain. The first noninterference TFSG was designed with a gauge factor of > 2300 for static strain sensing. The thermal output strain error at 30–200 °C was < 0.0016%.

Graphene/SiCN Thin-Film Strain Gauges Fabricated by Direct Writing

The in situ strain/stress detection of hot components in harsh environments remains a challenging task. In this study, graphene/SiCN (G-SiCN) thin-film strain gauges (TFSGs) were fabricated on alumina substrates by direct ink writing (DIW). The percolation model and the piezoresistive effect of G-SiCN composites were systematically studied. On this basis, a TFSG with high conductivity (0.1 S/cm) and high sensitivity (gauge factor (GF) 9.9) of ceramic matrix conductive composites was fabricated. The graphene/SiCN TFSG has excellent static and dynamic strain response at room temperature. Subsequently, the strain dynamic test was conducted at 400 °C, and there was no attenuation of the GF, so as to verify the high-temperature performance of the G-SiCN TFSG. Therefore, G-SiCN TFSGs provide an effective approach for the measurement of the in situ static and dynamic strain of hot components in high-temperature environments.

Green Synthesis, Characterization and Electrical Properties of Iron Doped Vanadium Oxide for Strain Gauges

A series of vanadium oxide (V2O5) nanoparticles containing small varying concentrations of iron (Fe) were synthesized using green protocol to test its suitability towards strain gauges. The morphological, structural, transmission spectral and the dielectric properties of the synthesized nanoparticles were characterized using SEM, HRTEM, XRD, FTIR and the LCR meter respectively. The structural analysis results depict a transformation from amorphous to orthorhombic cubic phased crystalline structure. The morphological data denote an improvement in the appearance of the samples without any cracks. A better electronic transition due to high activation energy was observed from the slight shift of the transmission spectral peaks towards the lower wave number. The improved conductivity from 5.37 to 12.51 S/m in conjunction with the better temperature characteristics, specially incase of 15 wt% Fe:V2O5 contributes to the enhanced sensitivity of the samples. The overall results from the characterization emphasize the synthesized nanoparticle’s remarkable attributes towards the fabrication of thin film strain gauges.

AgPd Thin-Film Strain Gauges Fabricated by Direct Writing for High-Temperature Application

In-situ strain detection of complex structures at high temperatures remains a challenging task. In this article, the feasibility and performance of silver-palladium (AgPd) high-temperature thin-film strain gauge (TFSG) fabricated by direct ink writing (DIW) based on the Weissenberg effect is investigated, providing an in-situ strain detection method for structures working at high temperatures. The micrometer-thick AgPd film was directly written on a planar alumina substrate, and its surface topography and electrical were characterized. The four-wire resistance measurement method was adopted to eliminate the wire resistance and the contact resistance at the solder joint, thereby improving the accuracy of detection. The strain test at room temperature showed that the gauge factor (GF) of AgPd TFSGs under both tension and compression was about 1.25. They also possessed excellent linearity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}$ </tex-math></inline-formula> 2 = 0.998), good static and dynamic responses, and extremely low mechanical hysteresis. To verify the high-temperature performance of the AgPd TFSG, the strain dynamic test was carried out at 600 °C. And there was no severe attenuation of the GF. AgPd TFSG fabricated by DIW provides an efficient method for in-situ static and dynamic strain detection of complex structures at high temperatures.

Abnormal Graphitization Behavior in Near-Surface/Interface Region of Polymer-Derived Ceramics.

The in situ free carbon generated in polymer-derived ceramics (PDCs) plays a crucial role in their unique microstructure and resultant properties. This study advances a new phenomenon of graphitization of PDCs. Specifically, whether in micro-/nanoscale films or millimeter-scale bulks, the surface/interface radically changes the fate of carbon and the evolution of PDC nanodomains, promotes the graphitization of carbon, and evolves a free carbon enriched layer in the near-surface/interface region. Affected by the enrichment behavior of free carbon in the near-surface/interface region, PDCs exhibit highly abnormal properties such as the skin behavior and edge effect of the current. The current intensity in the near-surface/interface region of PDCs is orders of magnitude higher than that in its interior. Ultrahigh conductivity of up to 14.47Scm-1 is obtained under the action of the interface and surface, which is 5-8 orders of magnitude higher than that of the bulk prepared under the same conditions. Such surface/interface interactions are of interest for the regulation of free carbon and its resultant properties, which are the core of PDC applications. Finally, the first PDC thin-film strain gauge that can survive a butane flame with a high temperature of up to ≈1300°C is fabricated.

Development of High-Temperature Wire-Grid Thin Film Strain Gauges.

Aero-engine turbine stator blades are often used in harsh environments with high temperatures and high pressure and are prone to fatigue fractures. Real-time and accurate monitoring of blade surface stress and strain is critical to ensure safe operation. In this study, thin-film strain gauges (TFSGs) that can be used in high-temperature environments above 1000 °C were designed and fabricated using a PtRh6 thin film as the sensitive material. The hysteresis effect of the stress transfer upon establishing a thermo-mechanical coupling finite element model of the Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSGs was analyzed and the optimal combination of thin-film thickness and longitudinal grid length of wire-grid TFSGs was determined. In order to solve the problem of high-temperature insulation, the insulating properties of a single-layer Al2O3 insulating film, a single-layer ZrO2 insulating film, a double-layer Al2O3/ZrO2 composite insulating film, and a four-layer Al2O3/ZrO2/Al2O3/ZrO2 composite insulating film at high temperature were compared and studied using scanning electron microscopy to analyze the microscopic morphology and composition of the four insulating film structures. The results showed that the four-layer Al2O3/ZrO2/Al2O3/ZrO2 composite insulating film had the best insulating properties at high temperatures. On this basis, an Al2O3/ZrO2/Al2O3/ZrO2 composite insulating film, PtRh6 sensitive layer, and Al2O3 protective film were sequentially deposited on a high-temperature nickel-based alloy equal-strength beam using DC pulsed magnetron sputtering technology to obtain an Inconel718 high-temperature nickel-based alloy equal-strength beam PtRh6 TFSG. Its gauge factor (GF) and temperature coefficient of resistance (TCR) were calibrated, and the results showed that the sensor could be used in harsh environments of 1000 °C. The above results provide new ideas for measuring stress and strain in aerospace under high-temperature and high-pressure environments.