Thin Film Temperature Sensors Research Articles

A cost-effective flexible MEMS technique for temperature sensing

A simplified, cost-effective flexible micro-electronic-mechanical systems (MEMS) technology has been developed for realizing a temperature-sensing array on a flexible polyimide substrate. The fabrication technique utilized liquid polyimide to form flexible film on the rigid silicon wafer using a temporary carrier during the fabrication. The platinum thin film is employed as temperature sensitive material and 8×8 temperature-sensing arrays were micromachined on the polyimide, from which the silicon wafer carrier was removed at the end of fabrication. The platinum thin film temperature sensor exhibits excellent linearity and its temperature coefficient of resistance reaches 0.00291°C−1. Because of the effective thermal isolation, the flexible temperature sensors show a high sensitivity of 1.12Ω/°C at 10mA to the constant drive current. The flexible MEMS technology based on liquid polyimide enables the development of flexible, compliant, robust, and multi-modal sensor skins for many other important applications, such as robotics, biomedicine, and wearable microsystems.

EPMA and XRD study on nickel metal thin film for temperature sensor

During the measurement and analysis of Micro Total Analysis System (μ-TAS), the bulk of the injected sample is about nano-liter, so that the study of microfluidic sensor has been becoming an important aspect of the analytical instrument. The microfluidic sensor based on the principle of the thermal distribution could be used to measure the micro flow by measuring the asymmetry of temperature profile around the heater. The precision of micro flow measurement depends on the precise of the temperature measurement. Ni thin film was chosen as the material of the temperature sensor, and it was sputtered on different substrates by dc magnetron method. The adhesion between Ni thin film and different substrates were investigated by EPMA (Electron Probe Micro Analyzer). The results indicate that nickel thin film can be used as a suitable material for fabricating temperature sensor, and the arrangement order of the adhesion between Ni thin film and wafer are Si 3N 4/SiO 2/Si, SiO 2/Si and Si, respectively. The TCR of the Ni thin film temperature sensor fabricated in this paper is about 6.3 × 10 −3 °C −1, which has satisfied the requisition of microfluidic sensor, and it could be used in many fields.

Flexible thin film temperature and strain sensor array utilizing a novel sensing concept

Flexible arrays of resistive temperature and strain sensors have been designed, and fabricated on polyimide sheets. We describe a novel sensor design concept, utilizing materials selection combined with specific device layout design, such that both temperature and strain values can be determined from resistance values of parallel sensor pairs, regardless of complex strain fields or temperature distribution. Fabrication of thin film Pt and NiCr resistive sensor arrays, with Cu conducting lines, on polyimide demonstrates the sensing concept. Temperature and strain sensing capabilities are demonstrated for temperatures up to 200°C and up to 2% tensile strain.

Effect of surface condition on boiling heat transfer from silicon chip with submicron-scale roughness

Boiling heat transfer on treated silicon surfaces was studied. Experiments were conducted to investigate the effects of submicron-scale roughness on the boiling heat transfer at a subcooled condition in FC-72 at the ambient pressure. Two-type of treated silicon surfaces were prepared for boiling surfaces using anodisation with HF (hydrofluoric acid) based electrolyte and DMF (dimethylforamide) based one. The back side of the treated surface was glued to the back side of the other silicon chip on which thin film heaters and thin film temperature sensors were fabricated using conventional MUPs processes with doped polysilicon. The treated chips with submicron-scale roughness which provide many possible nucleation sites showed considerable enhancement in the nucleate boiling heat transfer coefficients compared to the untreated silicon surface. Further, the critical heat flux (CHF) of the treated surfaces increase linearly to the increase in the effective area for boiling.

Convection Heat Transfer in Microchannels With High Speed Gas Flow

This paper presents an experimental investigation of convective heat transfer for laminar gas flow through a microchannel. A test stand was set up to impose thermal boundary conditions of constant temperature gradient along the microchannel length. Additionally, thin film temperature sensors were developed and used to directly measure the microchannel surface temperature. Heat transfer experiments were conducted with laminar nitrogen gas flow, in which the outlet Ma was between 0.10 and 0.42. The experimental measurements of inlet and outlet gas temperature and the microchannel wall temperature were used to validate a two-dimensional numerical model for gaseous flow in microchannel. The model was then used to determine local values of Ma, Re, and Nu. The numerical results show that after the entrance region, Nu approaches 8.23, the fully developed value of Nu for incompressible flow for constant wall heat flux if Nu is defined based on (Tw−Tref) and plotted as a function of the new dimensionless axial length, X*=(x∕2H)(Ma2)∕(RePr).

Bi0.5Sb1.5Te3/Bi2Te2.4Se0.6 thin film thermoelectric sensors

In order to make thin film thermoelectric sensors, p-type (Bi0.5Sb1.5Te3) and n-type (Bi2Te2.4Se0.6) thermoelectric thin films were deposited on Pyrex and Teflon substrates by the flash evaporation technique. Their thermoelectric properties were investigated for annealed (473 K, 1 h) films. Thin film temperature sensors were fabricated and their thermal emf, sensitivity, and time constant were measured and evaluated. The sensor deposited on Teflon substrate showed better performance than that on the Pyrex substrate. The sensitivity and time constant were 2.54 V/W and 13.7 s, respectively, for the sensor with a leg size of 3 mm (w)×16mm (l)×4μm (t).

Dynamic performance of a thin film temperature sensor in a lubricated contact

A thin film temperature sensor integrated onto mechanical component surface is promising for real-time machine condition monitoring. In this article, a one-dimensional heat conduction model has been developed to study the dynamic performance of the thin film sensor designed for monitoring the temperature distribution in an elastohydrodynamic lubrication contact. A control volume approach was used to numerically analyse the effects of sensor film thickness (from 0.1 to 100 μm), sensing materials, and substrate materials on the transient time response of the thin film sensor. The numerical model was evaluated by an analytical solution in a semi-infinite domain. The sensor time constant is obtained on the basis of a constant heat load and sensor sensitivity is studied when a typical elastohydrodynamic pressure distribution in a lubricated contact is applied. Faster response time and short time delay of a thin film sensor are expected in a higher conductivity of substrate. It is also clear that the response time decreases with increasing sensor film thickness and with increasing conductivity of the substrate. The results show that when the thickness of the sensor is < 1 μm, the sensor is feasible to capture transient temperature profile in real time for machine health monitoring under various operating conditions. One of the experimental validations given in this article has proven the robustness of the developed model.

極薄ジルコニア基板を使用したフィルム形ニッケル箔温度センサ

We propose a highly reliable thin film temperature sensor of 3x8x0.1mm, for which Nickel foil with a thickness of approx. 0.003mm is bonded onto a Zirconia baseboard of 0.05mm thickness using epoxy resin. The baseboard is then affixed to a ceramic reinforcing board of 0.40mm thickness with polyimide tape, and the fine resistance patterns in the nickel foil are fabricated using photo-etching technology. The resulting resistance patterns are then covered with another Zirconia baseboard using epoxy resin to protect from damage, moisture and acid in the air. Some of the key performance characteristics are a response time of about 6s in air and an accuracy drift of only ±0.01°C/year. As a result this temperature sensor will be applied to the precision manufacturing, semiconductor, and other industries where high accuracy and high reliability are demanded.

Thin film temperature sensor for real-time measurement of electrolyte temperature in a polymer electrolyte fuel cell

This paper describes a technique for the measurement of the electrolyte temperature in an operating polymer electrolyte fuel cell (PEFC). A patterned thin film gold thermistor embedded in a 16 μm thick parylene film was laminated in the Nafion ® electrolyte layer for in situ temperature measurements. Experimental results show that the sensor has a linear response of (3.03 ± 0.09) × 10 −3 °C −1 in the 20–100 °C temperature range and is robust enough to withstand the electrolyte expansion forces that occur during water uptake. An electrolyte temperature increase of 1.5 °C was observed in real-time when operating the fuel cell at 0.2 V and a current density of 0.19 A/cm 2. The temperature sensitivity of the present sensor is in an order of magnitude better than the conventional micro-thermocouples that have been reported. Additionally, use of micro-fabrication techniques allows for an accurate placement of the temperature sensor within the fuel cell. Simulation results show that the sensor has no significant effect on the local temperature distribution.

Simulation and experimental validation of a SU-8 based PCR thermocycler chip with integrated heaters and temperature sensor

We present a SU-8 based polymerase chain reaction (PCR) chip with integrated platinum thin film heaters and temperature sensor. The device is fabricated in SU-8 on a glass substrate. The use of SU-8 provides a simple microfabrication process for the PCR chamber, controllable surface properties and can allow on chip integration to other SU-8 based functional elements. Finite element modeling (FEM) and experiments show that the temperature distribution in the PCR chamber is homogeneous and that the chip is capable of fast thermal cycling. With heating and cooling rates of up to 50 and 30 °C/s, respectively, the performance of the chip is comparable with the best silicon micromachined PCR chips presented in the literature. The SU-8 chamber surface was found to be PCR compatible by amplification of yeast gene ribosomal protein S3 and Campylobacter gene cadF. The PCR compatibility of the chamber surfaces was enhanced by silanization.

Heat flux measurement techniques

Heat flux measurement is used in the field of fluid mechanics and heat transfer to quantify the transfer of heat within systems. Several techniques are in common use, including: differential temperature sensors such as thermopile, layered resistance temperature devices or thermocouples and Gardon gauges; calorimetric methods involving a heat balance analysis and transient monitoring of a representative temperature, using, for example, thin-film temperature sensors or temperature sensitive liquid crystals; energy supply or removal methods using, for example, a heater to generate a thermal balance; and, finally, by measurement of mass transfer which can be linked to heat transfer using the analogy between the two. No one method is suitable to all applications because of the differing considerations of accuracy, sensitivity, size, cost and robustness. Recent developments including the widespread availability and application of thin-film deposition techniques for metals and ceramics, allied with advances in microtechnology, have expanded the range of devices available for heat flux measurement. This paper reviews the various types of heat flux sensors available, as well as unique designs for specific applications. Critical to the use of a heat flux measurement technique is accurate calibration. Use of unmatched materials disturbs the local heat flux and also the local convective boundary layer, producing a potential error that must be compensated for. The various techniques in common use for calibration are described. A guide to the appropriate selection of a heat flux measurement technique is provided according to the demands of response, sensitivity, temperature of operation, heat flux intensity, manufacturing constraints, commercial availability, cost, thermal disturbance and acceleration capability for vibrating, rotating and reciprocating applications.

Thin film TiC/TaC thermocouples

TiC and TaC thin films were investigated, for the first time, for thin film thermocouple applications. Thin films of TaC and TiC were deposited on electronic grade alumina substrates using the r.f. sputter deposition technique. Sheet resistance of the thin films was measured using a four point probe. It was observed that the sheet resistance of the films depends critically on the deposition parameters such as substrate temperature during deposition, sputter gas pressure and r.f. power used. The deposition parameters were optimized to yield the lowest sheet resistance of the thin films at room temperature. The thermoemf of the deposited films was measured as a function of temperature in a vacuum using a home made device. It was observed that thin films of TaC and TiC yield fairly high and stable thermoemf throug hout the temperature range of stability. Under the optimized deposition conditions, thin film thermocouples were fabricated. The thermocouples were calibrated against temperature and the output was measured in vacuum (pressure <10−6 Torr). TiC/TaC thermocouples yield stable output up to 1350 K, temperatures above which breakdown occurs. The thermocouple output was theoretically estimated from the thermoemf measured, and compared. It was observed that these thermocouples yield reproducible output in the temperature range of stability and hold excellent potential for high temperature thin film temperature sensor applications in vacuum or inert atmospheres.

Active cavity absolute radiometer based on high-Tc superconductors

To implement the detector-based radiometric scale in the new Medium Background Infrared (MBIR) facility at the National Institute of Standards and Technology (NIST), we have developed an electrical-substitution cavity radiometer that can be operated just above liquid-nitrogen temperature. This MBIR active cavity radiometer (ACR) utilizes a temperature-controlled receiver cone and an independently temperature-controlled heat sink. Being a thermal-type detector, low noise and drift of the radiometer signal depends mainly on low-noise temperature control of the receiver and heat sink. Using high critical-temperature (Tc) superconducting thin-film temperature sensors in the active control loops, we have achieved closed-loop temperature controllability of better than 10 µK at 89 K for a receiver having an open-loop thermal time constant of about 75 s. For a flux level of 1 µW to 10 µW, the rms noise floor over a measurement cycle time is below 20 nW. This is the lowest noise level yet reported for a liquid-nitrogen-cooled electrical-substitution radiometer, and it is the first demonstration of the use of high-Tc superconductors in such a radiometer. Potential uses for this ACR in the MBIR facility include absolute measurement of the broadband radiance of large-area 300 K cryogenic black-body sources, and absolute measurement of the spectral radiance of laser-illuminated integrating spheres for improved spectral responsivity measurements of infrared transfer standard radiometers.

Magnetoresistance of the new ceramic “Cernox” thermometer from 4.2 K to 300 K in magnetic fields up to 13 T

Measurements of the resistance and the magnetoresistance of a new ceramic thin-film temperature sensor (Cernox-1080, Lake Shore Cryotronics Inc.) are reported for magnetic fields up to 13 T in the temperature range 4.2 to 300 K. The zero-field resistance changes monotonically over more than three orders of magnitude with a negative temperature coefficient. The magnetoresistance is small at temperatures above 10 K and exhibits partially compensating positive and negative components. The magnetic-field induced temperature reading error at 13 T is about 2% at 4.2 K and less than 0.3% at 10 K and above. In the temperature range 80 to 300 K, the magnetoresistance can be approximated by a fourth-order polynomial, allowing for an estimation and correction of the apparent temperature reading error of the Cernox thermometer in high magnetic fields.

Sensors for Detecting Molecular Hydrogen Based on Pd Metal Alloys

A simple process using a shadow mask is described to fabricate Pd/Ni resistors for detecting . The performance of the resistive sensors is studied in relation to annealing the devices at different temperatures in 2% in for 2 h. The Pd/Ni film surface morphology is also examined in relation to the resistor response when exposed to . The detailed information learned about the performance of the prototype resistors is used to fabricate wide‐range‐hydrogen microsensors, which combine a Pd/Ni chemiresistor and metal‐oxide semiconductor capacitor along with a thin film metal heater and temperature sensor. These studies provide an important step for improving the reliability of microsensors used to detect over concentrations ranging from 1 mTorr to 700 Torr.

液体ヘリウムλ点近傍での冷却によるＨｅ Ｉ‐Ｈｅ ＩＩ相界面の現出とその伝播現象

The investigation of the cooling process in the vicinity of λ-transition in liquid helium is of crucial importance for cryogenic engineering. In spite of the 2nd order transition, when the temperature crosses downward over the λ-point, a He I-He II interface appears. In this study, the dynamic behavior of a He I-He II phase boundary was experimentally investigated. When He I under the condition of saturated vapor pressure is suddenly cooled from an initial state at a temperature slightly higher than Tλ by vapor evacuation, an interface appears and propagates downward from the liquid helium-free surface in a cryostat. We investigated the interface behavior by measuring the temperature with a superconductive thin-film temperature sensor. It was confirmed that the He I-He II interface propagates downward at a speed of several centimeters per second in direct proportion to the cooling rate and that the interface speed decreases as the distance from the free surface increases. A preliminary theoretical approach for the phenomena is also discussed briefly. It was confirmed that a modified Stefan problem can be a fundamental model for the construction of the theory.

Transient heat transfer in channel of liquid or supercritical helium

Thin-film temperature sensors fabricated on alumina chips have been used to study heat transfer across a rectangular channel of liquid or supercritical helium. Step input heating power is applied to a sensor embedded in the bottom channel surface. The temperature response is also monitored at the top of the channel by a purely passive sensor. Temperature traces obtained for varying power inputs, helium pressures (1.0–3.0 bar) and channel heights (0.2 and 0.4mm) display the evolution of steady state conditions. Steady state behaviour suggests that at low powers (in the nucleate boiling regime) only the sensor surface (≈9% of the whole chip face) is heated, and at high powers (in the film boiling regime) the entire chip face is heated; intermediate powers produce large thermal fluctuations, probably corresponding to fluctuations in the extension of the helium film. It is conjectured that the redistribution of heat flow during the onset of film boiling accounts for the comparatively gradual ‘take-off’ observed in the heat pulse temperature responses. Temperature fluctuations are reduced at higher pressures. The time elapsed until the passive sensor temperature begins to rise is comparable to the time required to evaporate enough helium to fill the volume between the sensors. Reducing the channel gap reduces this response time. Take-off times on the active sensor are generally too short for appreciable confinement effects to be observed.

Electrical resistance drift of molybdenum silicide thin film temperature sensors

For a thermometer to be of practical use, its accuracy of temperature indication must be within a tolerable range. In this paper, patterned molybdenum disilicide (MoSi 2) thin film temperature sensors were fabricated to study their thermoresistance, i.e. resistance vs. temperature ( R- T) characteristics. The R- T characteristic of MoSi 2 thin films exhibits a positive deviation from linearity (termed “superlinearity”) instead of showing a simple linearity as for most metals. This superlinear behavior was attributed to thermal expansion and the consequent decrease in the Debye characteristic temperature of MoSi 2. For long-term duration at elevated temperatures, the variation in thickness and composition of the sensor film due to oxidation and other factors may produce drift in the electrical resistance. In this study, the electrical resistance drifts of the sensors as a function of time at temperatures of 1200, 1300 and 1350 °C are presented. For the sensor film tested at 1300 °C, the resistance drift due to the thickness change of the sensor layer was well corrected with the help of an analysis of the oxidation rate of the sensor material. On the other hand, the in-depth composition profile analyzed by Auger electron spectroscopy (AES) indicated no significant composition variation, implying that we could neglect the correction factor for the composition variation in the present study. After the thickness factor was corrected for, a minor drift was still observed; this was also found for the same sensor film tested in an Ar ambient. The exact source of the minor drift is not well understood; further investigations are required.

Thin film thermocouples for advanced ceramic gas turbine engines

Thin film temperature sensors were developed for both the rotating and non-rotating components of ceramic-based gas turbine engines. These type-S thin film thermocouples were fabricated on hot isostatically pressed Si 3N 4 substrates (Norton-TRW NT154), whose surfaces were altered to maximize adhesion. Annealing cycles and sputtered oxide interlayers were utilized in the fabrication to prevent blistering of the metallic thin films and enhance adhesion. Completed sensors were tested at temperatures up to 1300°C, with a variety of temperature gradients applied along the length of the test bars. Both oxidizing and inert gas atmospheres were used to investigate environmental effects on sensor performance. Sensor tests performed in oxidizing atmospheres resulted in the formation of volatile platinum and rhodium oxides, which caused significant drift and ultimate failure. Sensor tests performed in inert gas environments had drift rates 5–10 times lower than those observed in oxidizing atmospheres. Therefore, sputtered oxide overcoats were employed to minimize adverse reactions between the sensor elements and the atmosphere, the results of which will be discussed in terms of sensor performance.

Effects of activated reactive evaporation process parameters on the microhardness of polycrystalline silicon carbide thin films

Polycrystalline ß-SiC is expected to be an excellent material for thin film temperature sensors for the measurement of the surface temperature of gas turbine engine components operated at high temperatures (up to 1500°C). In this paper, Vickers and Knoop indentation microhardness tests were carried out on the silicon carbide films grown on Si(100) substrates by the activated reactive evaporation (ARE) process to measure one of the important mechanical properties, i.e. hardness of the films. The results of these tests are presented as a function of the ARE process parameters, such as C2H2 pressure PC2H2, substrate temperature Tsub, ARE electrode voltage VARE for the generation of d.c. glow discharge and substrate bias Vsub. It was found that the hardness of the films is very much dependent on these process parameters. A Vickers hardness value of 3680 kgf mm−2 (36.1 GPa) at 25 gf load (0.25 N) and a Knoop hardness value of 2060 kgf mm−2 (20.2 GPa) at 100 gf load (0.98 N) are obtained for polycrystalline ß-SiC films (C-to-Si ratio, 1.17) prepared under the following deposition conditions: C2H2 pressure, 3 mTorr (0.4 Pa); substrate temperature, 700°C; ARE electrode voltage, +150 V; substrate bias, −50 V.Microhardness variation of the ß-SiC films with applied load on the indenter was also studied. It was found that the hardness of the films decreases with increasing load, which is believed to be due to indentation size and substrate hardness effects.