Showing papers on "Microheater published in 2016"

High Surface Area MoS2/Graphene Hybrid Aerogel for Ultrasensitive NO2 Detection

Abstract: A MoS2/graphene hybrid aerogel synthesized with two-dimensional MoS2 sheets coating a high surface area graphene aerogel scaffold is characterized and used for ultrasensitive NO2 detection. The combination of graphene and MoS2 leads to improved sensing properties with the graphene scaffold providing high specific surface area and high electrical and thermal conductivity and the single to few-layer MoS2 sheets providing high sensitivity and selectivity to NO2. The hybrid aerogel is integrated onto a low-power microheater platform to probe the gas sensing performance. At room temperature, the sensor exhibits an ultralow detection limit of 50 ppb NO2. By heating the material to 200 °C, the response and recovery times to reach 90% of the final signal decrease to <1 min, while retaining the low detection limit. The MoS2/graphene hybrid also shows good selectivity for NO2 against H2 and CO, especially when compared to bare graphene aerogel. The unique structure of the hybrid aerogel is responsible for the ultrasensitive, selective, and fast NO2 sensing. The improved sensing performance of this hybrid aerogel also suggests the possibility of other 2D material combinations for further sensing applications.

Thermal tuning of Kerr frequency combs in silicon nitride microring resonators

Abstract: Microresonator based Kerr frequency comb generation has many attractive features, including ultrabroad spectra, chip-level integration, and low power consumption. Achieving precise tuning control over the comb frequencies will be important for a number of practical applications, but has been little explored for microresonator combs. In this paper, we characterize the thermal tuning of a coherent Kerr frequency comb generated from an on-chip silicon nitride microring. When the microring temperature is changed by ~70 °C with an integrated microheater, the line spacing and center frequency of the comb are tuned respectively by −253 MHz (−3.57 MHz/°C) and by −175 GHz (−2.63 GHz/°C); the latter constitutes 75% of the comb line spacing. From these results we obtain a shift of 25 GHz (362.07 MHz/°C) in the comb carrier-envelope offset frequency. Numerical simulations are performed by taking into account the thermo-optic effects in the waveguide core and cladding. The temperature variation of the comb line spacing predicted from simulations is close to that observed in experiments. The time-dependent thermal response of the microheater based tuning scheme is characterized; time constants of 30.9 μs and 0.71ms are observed.

Chemically functionalized 3D graphene hydrogel for high performance gas sensing

Abstract: The performance of chemical sensors can be optimized not only by material structural design, but also via functionalization of sensing materials. For the first time, we develop a high performance, cost-effective NO2 and CO2 sensor by exploiting a 3D chemically functionalized reduced graphene oxide hydrogel (FRGOH). The self-assembly and chemical modification of the 3D FRGOH are realized using hydroquinone molecules in a simple, one-step hydrothermal synthesis process. Compared with an unmodified RGOH counterpart, the chemically derived FRGOH sensor not only displays twofold higher sensitivity in both NO2 and CO2 sensing, but also exhibits significantly faster recovery and a lower limit of detection (LOD). Thus, a theoretical LOD of 57 ppb NO2 is obtained and a low concentration of 200 ppb NO2 is detected experimentally by the FRGOH sensor. Importantly, an integrated microheater is employed not only to significantly improve the selectivity of NO2 sensing, but also to accelerate the response and recovery. This work sheds light on improving the performance of a graphene-based gas sensor by simultaneous chemical functionalization, 3D structural design and temperature modulation.

An innovative gas sensor incorporating ZnO–CuO nanoflakes in planar MEMS technology

Abstract: In this work, a simple and cost effective MEMS based gas sensor incorporating ZnO–CuO nanoflakes is presented. For ZnO–CuO nanoflakes synthesis, brass film was deposited on oxidized Si substrate by radio frequency (RF) diode sputtering and subsequently subjected to thermal oxidation process. The oxidized samples were characterized using SEM, XRD, XPS and Raman spectroscopy. For the fabrication of the complete sensor, planar MEMS technology with integrated microheater was adopted. This technology uses sputter deposited and recessed SiO 2 platform in Si substrate for providing thermal isolation to reduce the power consumption of Ni microheater and prevents heat spreading from heater area. The microheater performance was simulated and experimentally verified. The sensor was tested for different toxic gases and volatile organic compounds (VOCs) over range of operating temperatures and concentrations for optimal sensing performances. The sensing results revealed that the sensor had highest response for acetone vapours over other gases. Also, it showed reproducible and stable performance.

Platinum Nanoparticle Loading of Boron Nitride Aerogel and Its Use as a Novel Material for Low-Power Catalytic Gas Sensing

Abstract: A high-surface-area, highly crystalline boron nitride aerogel synthesized with nonhazardous reactants has been loaded with crystalline platinum nanoparticles to form a novel nanomaterial that exhibits many advantages for use in a catalytic gas sensing application. The platinum nanoparticle-loaded boron nitride aerogel integrated onto a microheater platform allows for calorimetric propane detection. The boron nitride aerogel exhibits thermal stability up to 900 °C and supports disperse platinum nanoparticles, with no sintering observed after 24 h of high-temperature testing. The high thermal conductivity and low density of the boron nitride aerogel result in an order of magnitude faster response and recovery times (<2 s) than reported on alumina support and allow for 10% duty cycling of the microheater with no loss in sensitivity. The resulting 1.5 mW sensor power consumption is two orders of magnitude less than commercially available catalytic gas sensors and unlocks the potential for wireless, battery-powered catalytic gas sensing.

A MEMS-based heating holder for the direct imaging of simultaneous in-situ heating and biasing experiments in scanning/transmission electron microscopes.

Abstract: The introduction of scanning/transmission electron microscopes (S/TEM) with sub-Angstrom resolution as well as fast and sensitive detection solutions support direct observation of dynamic phenomena in-situ at the atomic scale. Thereby, in-situ specimen holders play a crucial role: accurate control of the applied in-situ stimulus on the nanostructure combined with the overall system stability to assure atomic resolution are paramount for a successful in-situ S/TEM experiment. For those reasons, MEMS-based TEM sample holders are becoming one of the preferred choices, also enabling a high precision in measurements of the in-situ parameter for more reproducible data. A newly developed MEMS-based microheater is presented in combination with the new NanoEx™-i/v TEM sample holder. The concept is built on a four-point probe temperature measurement approach allowing active, accurate local temperature control as well as calorimetry. In this paper, it is shown that it provides high temperature stability up to 1,300°C with a peak temperature of 1,500°C (also working accurately in gaseous environments), high temperature measurement accuracy (<4%) and uniform temperature distribution over the heated specimen area (<1%), enabling not only in-situ S/TEM imaging experiments, but also elemental mapping at elevated temperatures using energy-dispersive X-ray spectroscopy (EDS). Moreover, it has the unique capability to enable simultaneous heating and biasing experiments.

Nanowire-Assembled Hierarchical ZnCo2O4 Microstructure Integrated with a Low-Power Microheater for Highly Sensitive Formaldehyde Detection

Abstract: Nanowire-assembled 3D hierarchical ZnCo2O4 microstructure is synthesized by a facile hydrothermal route and a subsequent annealing process In comparison to simple nanowires, the resulting dandelion-like structure yields more open spaces between nanowires, which allow for better gas diffusion and provide more active sites for gas adsorption while maintaining good electrical conductivity The hierarchical ZnCo2O4 microstructure is integrated on a low-power microheater platform without using binders or conductive additives The hierarchical structure of the ZnCo2O4 sensing material provides reliable electrical connection across the sensing electrodes The resulting sensor exhibits an ultralow detection limit of 3 ppb toward formaldehyde with fast response and recovery as well as good selectivity to CO, H2, and hydrocarbons such as n-pentane, propane, and CH4 The sensor only consumes ∼57 mW for continuous operation at 300 °C with good long-term stability The excellent sensing performance of this hierarchi

In Situ Localized Growth of Porous Tin Oxide Films on Low Power Microheater Platform for Low Temperature CO Detection

Abstract: This paper reports a facile method for creating a nanostructured metal oxide film on a low power microheater sensor platform and the direct realization of this structure as a gas sensor. By fast annealing the deposited liquid precursors with the microheater, a highly porous, nanocrystalline metal oxide film can be generated in situ and locally on the sensor platform. With only minimal processing, a high performance, miniaturized gas sensor is ready for use. A carbon monoxide sensor using the in situ synthesized porous tin oxide (SnO2) sensing film is made as a demonstration of this technique. The sensor exhibits a low detection limit and fast response and recovery time at a low operating temperature. This facile fabrication method is highly flexible and has great potential for large-scale gas sensor fabrication.

Pulsed laser deposition of metal oxide nanostructures for highly sensitive gas sensor applications

Abstract: Nanosecond and picosecond pulsed laser deposition (PLD) was used to prepare metal oxide nanostructures with different morphologies as gas sensing materials on top of oxidized silicon substrates and commercial SGX Sensortech SA MEMS microheater platforms. The layers were formed of different types of nanostructures including nanoparticles, agglomerates, and nanotrees with fractal-like growth. Clear dependencies between the deposition parameters, structural morphology, and gas sensing performance were found. Also, some differences in the morphologies of the layers were seen when picosecond PLD was used instead of nanosecond PLD. Many of the sensing materials were found to be highly sensitive to different types of gaseous species. We investigated inorganic gases in the ppm range (2–400 ppm) including NO, CO, and NH3, and the selectivity and sensitivity were shown to be dependent, not only on layer morphology, but also on the measurement temperature. Moreover, an investigation with volatile organic compound gases in the ppb range demonstrated that WO3 layers are highly sensitive and selective towards naphthalene at least down to 2.5 ppb.

Low power highly sensitive platform for gas sensing application

Abstract: This paper reports a low power miniaturized MEMS based integrated gas sensor with 36.84 % sensitivity (ΔR/R0) for as low as 4 ppm (NH3) gas concentration. Micro-heater based gas sensor device presented here consumes very low power (360 °C at 98 mW/mm2) with platinum (Pt) micro-heater. Low powered micro-heater is an essential component of the metal oxide based gas sensors which are portable and battery operated. These micro-heaters usually cover less than 5 % of the gas sensor chip area but they need to be thermally isolated from substrate, to reduce thermal losses. This paper elaborates on design aspects of micro fabricated low power gas sensor which includes `membrane design' below the microheater; the `cavity-to-active area ratio'; effect of silicon thickness below the silicon dioxide membrane; etc. using FEM simulations and experimentation. The key issues pertaining to process modules like fragile wafer handling after bulk micro-machining; lift-off of platinum and sensing films for the realization of heater, inter-digitated-electrodes (IDE) and sensing film are dealt with in detail. Low power platinum microheater achieving 700 °C at 267 mW/mm2 are fabricated. Temperature calculations are based on experimentally calculated thermal coefficient of resistance (TCR) and IR imaging. Temperature uniformity and localized heating is verified with infrared imaging. Reliability tests of the heater device show their ruggedness and repeatability. Stable heater temperature with standard deviation (ź) of 0.015 obtained during continuous powering for an hour. Cyclic ON---OFF test on the device indicate the ruggedness of the micro-heater. High sensitivity of the device for was observed for ammonia (NH3), resulting in 40 % response for ~4 ppm gas concentration at 230 °C operating temperature.

A Light‐Activated Microheater for the Remote Control of Enzymatic Catalysis

Abstract: The remote control of enzymatic catalysis is of significant importance in disease treatment and industrial applications. Herein, we designed a microheater composed of a porous polylactic acid (PLA) matrix and polydopamine (PDA) with notable photothermal conversion capability. Starch hydrolysis, catalyzed by using α-amylase, was accelerated in the presence of the microheater under illumination with near-infrared light or natural sunlight at room temperature. Additionally, the methodology was extended to the preparation of microwave-absorbing materials with the deposition of polyaniline on porous PLA matrix. The porous morphology improves the energy-conversion efficiency.

Flexible Poly(Amide‐Imide)‐Carbon Black Based Microheater with High‐Temperature Capability and an Extremely Low Temperature Coefficient

Abstract: Flexible poly(amide-imide)-carbon black (PAI-CB) composite films, to be applied as high performance microheater foil, have been prepared with a solution/casting technique. The CB dispersion has been carefully controlled in order to improve the thermal and electrical properties of the resulting composites. Morphology and structure of the PAI-CB composite films have been characterized by optical microscopy, atomic force microscopy and FTIR spectroscopy. The effect of the CB dispersion and its interaction with the polymer chains on the thermal and mechanical properties of the composite films have been investigated by using differential scanning calorimetry thermogravimetric analysis and dynamic mechanical analysis. The electrical characterization has evidenced high-temperature capability and an extremely low temperature coefficient of the electrical resistance. An excellent ohmic behavior of the electrical characteristics and a fast on/off-switching of the heater-foil have also been found. No mechanical and electrical changes of the polymeric heater have been observed after various mechanical bending cycles. The combination of the observed electrical and thermal properties allows the realization of stable, compact, and flexible electrical heating systems.

A high flow rate thermal bubble-driven micropump with induction heating

Abstract: A thermal bubble-driven micropump with magnetic induction heating is successfully demonstrated in this paper. Energy is transferred from the planar coil outside the microchamber to the metal heating plate inside the microchamber through the electromagnetic field, and Joule heat is induced by the eddy current in the heating plate. Sequential photographs of bubble nucleation, growth and shrink in open environment were recorded by a CCD camera. One advantage of the micropump is that there is no physical contact between the heating plate and the external power supply circuit, which resulted in an easy fabrication process. What’s more, compared with other thermal bubble-driven micropump with resistive microheater, the flow rate and the pump stroke have been improved significantly due to its larger dimension of the heating plate and larger bubbles volume. The experiments show that the maximum flow rate of this micropump is about 102.05 μL/min, which can expand the potential applications, especially for microfluidic system that requires higher flow rate.

Oscillate Boiling

Abstract: We report about an intriguing boiling regime occurring for small heaters embedded on the boundary in subcooled water. The microheater is realized by focusing a continuous wave laser beam to about $10\,\mu$m in diameter onto a 165\,nm-thick layer of gold, which is submerged in water. After an initial vaporous explosion a single bubble oscillates continuously and repeatably at several $100\,$kHz. The microbubble's oscillations are accompanied with bubble pinch-off leading to a stream of gaseous bubbles into the subcooled water. The self-driven bubble oscillation is explained with a thermally kicked oscillator caused by the non-spherical collapses and by surface pinning. Additionally, Marangoni stresses induce a recirculating streaming flow which transports cold liquid towards the microheater reducing diffusion of heat along the substrate and therefore stabilizing the phenomenon to many million cycles. We speculate that this oscillate boiling regime may allow to overcome the heat transfer thresholds observed during the nucleate boiling crisis and offers a new pathway for heat transfer under microgravity conditions.

System On Microheater for On-Chip Annealing of Defects Generated by Hot-Carrier Injection, Bias Temperature Instability, and Ionizing Radiation

Abstract: An on-chip immune system against hot-carrier stress, bias temperature instability, and total ionizing dose degradation is presented. A system on microheater provides defect annealing capability for recovering bulk trapped charges and interface states. The microheater and the system-on-chip are fabricated separately and stacked into a single package, which can be implemented on any arbitrary commercial-off-the-shelf device as a generic approach. The device annealed at 200 °C for 3 h results in sufficient recovery in drain current versus gate voltage characteristics.

Selective detection of naphthalene with nanostructured WO 3 gas sensors prepared by pulsed laser deposition

Abstract: . Pulsed laser deposition (PLD) at room temperature with a nanosecond laser was used to prepare WO3 layers on both MEMS microheater platforms and Si/SiO2 substrates. Structural characterization showed that the layers are formed of nanoparticles and nanoparticle agglomerates. Two types of layers were prepared, one at an oxygen partial pressure of 0.08 mbar and one at 0.2 mbar. The layer structure and the related gas sensing properties were shown to be highly dependent on this deposition parameter. At an oxygen pressure of 0.2 mbar, formation of e-phase WO3 was found, which is possibly contributing to the observed increase in sensitivity of the sensor material. The gas sensing performance of the two sensor layers prepared via PLD was tested for detection of volatile organic compounds (benzene, formaldehyde and naphthalene) at ppb level concentrations, with various ethanol backgrounds (0.5 and 2 ppm) and gas humidities (30, 50 and 70 % RH). The gas sensors were operated in temperature cycled operation. For signal processing, linear discriminant analysis was performed using features extracted from the conductance signals during temperature variations as input data. Both WO3 sensor layers showed high sensitivity and selectivity to naphthalene compared to the other target gases. Of the two layers, the one prepared at higher oxygen partial pressure showed higher sensitivity and stability resulting in better discrimination of the gases and of different naphthalene concentrations. Naphthalene at concentrations down to 1 ppb could be detected with high reliability, even in an ethanol background of up to 2 ppm. The sensors show only low response to ethanol, which can be compensated reliably during the signal processing. Quantification of ppb level naphthalene concentrations was also possible with a high success rate of more than 99 % as shown by leave-one-out cross validation.

In-situ integration and surface modification of functional nanomaterials by localized hydrothermal reaction for integrated and high performance chemical sensors

Abstract: We have developed a novel method for simple, rapid and selective synthesis of one dimensional nanomaterials as well as their selective surface functionalization, all in low-temperature and liquid-phase conditions, for highly integrated chemical sensor applications. In specific, localized heating by microheater allows selective synthesis and in-situ integration of ZnO nanowires on sensing electrodes. High surface area and chemical reactivity of nanowires enable high sensitivity and fast response to hydrogen (H 2 ) molecules. Furthermore, subsequent localized heating process in metal precursor solution allows facile surface functionalization of ZnO nanowires with catalytic metal nanoparticles (Pt or Pd), which dramatically enhanced the gas sensing performances. This approach has demonstrated a practical method of developing integrated chemical sensors with heterogeneous nanostructures, potentially for multiplexed chemical detection purposes.

Fabrication and packaging of MEMS based platform for hydrogen sensor using ZnO---SnO2 composites

Abstract: Thin films of metal-oxide with integrated microheater on micromachined silicon substrate have attracted great deal of interest towards the development of extremely small and highly sensitive gas sensor. Fabrication of MEMS microheater which is the key component for the development of low power gas sensor is reported here. The microheater is fabricated in a novel co planer fashion where the heating element and the inter-digitated electrode are place side by side. The fabricated device is structurally and electrically characterized by SEM and I---V measurements. Using ZnO---SnO2 composite material, hydrogen sensor was constructed on the microheater platform. A suitable package for encapsulating the fabricated device is designed and the device was successfully mounted on it. The sensing behavior of the packaged sensor is performed by exposing the sensor to hydrogen.

Design and optimization of a high temperature microheater for inkjet deposition

Abstract: Inkjet deposition has become a promising additive manufacturing technique due to its fast printing speed, scalability, wide choice of materials, and compatibility for multi-material printing. Among many different inkjet techniques, thermal inkjet, led by Hewlett-Packard and Canon, is the most successful inkjet technique that uses a microheater to produce a pressure pulse for ejecting droplets by vaporizing the ink materials in a timespan of microseconds. Thermal inkjet has been widely adopted in many commercial 3D inkjet printers (e.g., 3D Systems ProJet X60 series) due to its low cost, high resolution, and easy operation. However, the viscosity of the printable materials has been limited to less than 40 cP due to insufficient energy provided inside the nozzle to overcome the viscous dissipation of energy. This paper presents a study on the design and optimization of a high temperature microheater with a target heating temperature of more than 600 °C (compared to ~300 °C for current printhead) to increase the energy supply to the nozzle. The benefits are fourfold: (1) higher temperature will lead to faster vaporization of ink and thus higher jetting frequency and print speed, (2) higher temperature will make it possible for jetting materials with higher boiling points, (3) higher temperature will reduce the viscosity of the ink and thus the viscous dissipation of energy, and (4) higher energy supply will increase the magnitude of the pressure pulse for printing more viscous materials. In this paper, a high-temperature microheater was designed with the following objectives: to reduce thermal stress in heaters and to minimize uneven heat distribution. A literature survey was first conducted on design, fabrication, and operation of thin-film resistive microheaters. A multiphysics numerical model was then developed to simulate electrical, thermal, and mechanical responses of the microheater. The model was validated by comparison to experimental data and existing models obtained from literature. With proper parameterization of the design geometry, the geometry of the microheater is optimized using a particle swarm optimization method. Results show the optimized high-temperature microheater successfully operates at temperatures in excess of 600 °C. The design optimization enabled better characteristics for even heat distribution and minimizing stress. The design approach can serve as a fundamental means of design optimization for microheaters.

Simple Fabrication and Characterization of a Platinum Microhotplate Based on Suspended Membrane Structure

Abstract: One of the key components of a microsensor is the Micro electromechanical system (MEMS) microheater. It has a wide range of applications such as gas sensors, pressure sensors, and so on. In this study, a platinum microhotplate based on suspended membrane structure is introduced. A simple microfabrication process is adopted to form the micromachined suspended microheater. Some integrated circuit processes such as E-beam evaporation of Pt and Au, oxidation, wet etching process, and photolithography process are used to fabricate the device. As the usage of deep-reactive ion etching and low-pressure chemical vapor deposition systems are avoided, the microfabrication process of the hotplate is accessible even in laboratories with limited equipment. In order to achieve uniform temperature distribution over the active heater area and to increase the robustness of the membrane, a thin silicon island was placed underneath the dielectric membrane. Thermal and thermomechanical behaviors of this structure obtained by finite element analysis show that the designed microhotplate is relatively strong. Experimental results show that power consumption and time constant are 50mW and 4.23ms, respectively, for the temperature variation from 30°C to 500°C in the fabricated microhotplates.

Tin Oxide Microheater for Chemical Sensors

Abstract: Tin oxide is the main material utilized for the fabrication of chemical sensing pellets which operate at elevated temperatures. The heating is commonly carried out with ruthenium dioxide resistors. Here, a tin oxide-based microheater is developed for microsensor applications. These microheaters are fabricated on 0.5 mm thick alumina substrates using spray pyrolysis technique. The optimum SnO2 heaters have a sheet resistivity in the 40-70 Ω/a range. Ohmic Ag/SnO2 contacts are formed by silver paste printing followed by an appropriate thermal annealing, which provide connections to the external circuitry. Durability tests are carried out on several samples; the long-term performance of the fabricated devices is satisfactory. The method allows the elimination of the expensive ruthenium dioxide from the structure of generic gas sensors.

Modeling and experimental investigation of an integrated optical microheater in silicon-on-insulator.

Abstract: A linear piecewise model has been formulated to analyze the performance of a metallic microheater integrated with single-mode waveguides (λ∼1550 nm) in silicon-on-insulator (SOI). The model has been used to evaluate integrated optical microheaters fabricated in a SOI substrate with 2 µm device layer thickness. The Fabry–Perot modulation technique has been used to extract the effective thermo-optic phase shift and response time. The effective thermal power budget of Peff,π∼500 µW (out of actually consumed power Pπ=1.1 mW) for a π phase shift and a switching time of τ∼9 µs, have been recorded for a typical Ti heater stripe of length LH=50 µm, width WH=2 µm, and thickness tH∼150 nm, integrated with a Fabry–Perot waveguide cavity of length ∼20 mm. It has been shown that the performance of a heater improves (in terms of power budget) as the length of a microheater decreases. However, smaller heater size requires higher joule heating to obtain a desired phase shift, which is again found to be dependent on polarization of the guided mode because of thermal stress.

Thermal characteristics of temperature-controlled electrochemical microdevices

Abstract: The development of novel, miniaturized sensing systems is driven by the demand for better and faster chemical measurements with lower power consumption and smaller sample sizes. Emerging miniature sensors, or microsensors, also offer rapid thermal and diffusive transport characteristics. For instance, temperature changes, during both heating and cooling, can be achieved on micrometer-scale surfaces much more rapidly than on bulk, macro-scale surfaces. While these rapid thermal characteristics have been most successfully exploited to date in gas-phase sensing devices, the prospect of developing analogous microfabricated, temperature-controlled microsensors for use in aqueous, or solution-phase, environments has been less explored. In this work, electrodes with underlying microheaters were designed and fabricated, and thermal characterization was performed using temperature imaging, transient temperature measurements, and theoretical modeling to determine temperature distributions and thermal response times in both gas- and solution-phase environments. These results will guide the development of solution-phase electrochemical sensors. Temperature-controlled electrochemical characterization was performed using cyclic voltammetry of a model analyte, hexaamineruthenium(III) chloride, to demonstrate the use of the multilayer, microfabricated devices, which consisted of a gold disk electrode and an underlying microheater. Electrochemical signals were enhanced by up to a factor of three at elevated temperatures (up to 81 °C) compared to those measured at room temperature (21 °C). This improved signal at elevated temperatures was explained by finite element method calculations that accounted for both temperature-dependent diffusion and thermal convection near the heated electrode surface.

A Built-In Temperature Sensor in an Integrated Microheater

Abstract: Chip-based microheaters have been widely used in many applications, including gas sensors, flow meters, mass sensors, and polymerase chain reaction chambers, where accurate monitoring of temperature is critical The temperature measurement is conventionally done with the aid of a separate sensor, which may add to the cost and inaccuracy In this paper, a built-in temperature sensing method is provided for the microheaters The resistor-based microheater relies on Joule heating mechanism and its resistance is dependent upon its own body temperature, implying that the microheater has an inherent temperature sensing mechanism It is found that an intermittent temperature sampling in the middle of the heating cycle does not disturb the body temperature if the temperature sampling voltage and pulsewidth are sufficiently low and short, respectively The built-in temperature sensing is attributed to the electrical time constant being few orders of magnitude smaller than the thermal time constant The temperature estimation results using the built-in method show excellent agreement with the benchmark measurements from an infrared pyrometer

Development of microheaters for gas sensor with an AT-Mega 8535 temperature controller using a PWM (pulse width modulation) method

Abstract: Microheater is the main component in gas sensor characterized by their sensitivity, selectivity, and time response of gas sensor which is depend on the microheater temperature stability. A Cu microheater was developed and utilized AT-Mega 8535 controller using a PWM (pulse width modulation) method. This control system is interfaced to the PC to observe the real time temperature response of the microheater. Three initial resistance (R0) variations of microheater were developed in an open loop control system. The power characteristic of designed microheater depends on the specified microheater initial resistance. The smaller R0, the less power required to reach a temperature setting value. The developed microheater was designed to reach a temperature setting value of 250°C having resistance 0.531 Ω for 1.979 Watt and 0.265 Ω for 1.072 Watt respectively. The results of the investigation on the control performances shows microheater-control system achieved operating temperature up to 250°C. The response of the temperature control shows smallest R0 resulted in a high stability with short settling time, short delay time and small ripple for temperature setting values higher than 150°C. The obtained error of microheater temperature with R0 = 0.265 is 8.596 %. It is concluded that the developed microheater can be utilized as a component of a gas sensor.

Flexible polymer/multi-walled carbon nanotube composite sensor array equipped with microheater for gas sensing

Abstract: A polymer/multi-walled carbon nanotube (MWCNT) composite sensor array based on a flexible polyimide substrate equipped with a thermostatic microheater to provide different working temperatures was developed for gas sensing. The thermostatic microheater provided nine working temperatures ranging from 20°C to 60°C. Each microheater element included a 3 × 3 polymer/MWCNT composite sensor array, which is composed of MWCNTs and polymer composite, as a sensing material. The device was developed to investigate the effect of device temperature on the response of polymer/MWCNT composite gas sensor arrays. The response to ethanol at different temperatures showed resistance variation but similar performance for the proposed gas sensor array.