Showing papers on "Microheater published in 2014"

Technological Journey Towards Reliable Microheater Development for MEMS Gas Sensors: A Review

Abstract: Micromachined silicon platforms, owing to some of its inherent advantages including miniaturized dimensions, ultralow power consumption, reduced batch fabrication cost, long-term reliability, and compatibility with standard CMOS fabrication technology, attracted the attention of solid-state gas sensor researchers, particularly since the last decade. As the semiconducting gas sensing thin film on top of micromachined platforms often needs an elevated temperature to activate the sensing mechanism, the suitable electrothermal and structural design of a microheater, i.e., having fast response, uniform temperature distribution over sensing area, and minimal residual/thermal-stress-induced membrane deflection, are of prime concern. In this paper, the technological developments related to the various designs and geometries of microheaters and their fabrication technology employing different suitable heating materials, for closed- and suspended-type silicon membranes have been discussed critically with particular emphasis on the relative merits and demerits with reference to heater parameters such as power consumption, temperature distribution, response time, and mechanical stability/reliability.

A Single Cell Extraction Chip Using Vibration-Induced Whirling Flow and a Thermo-Responsive Gel Pattern

Abstract: We propose a single cell extraction chip with an open structure, which utilizes vibration-induced whirling flow and a single cell catcher. By applying a circular vibration to a micropillar array spiral pattern, a whirling flow is induced around the micropillars, and target cells are transported towards the single cell catcher placed at the center of the spiral. The single cell catcher is composed of a single-cell-sized hole pattern of thermo-responsive gel. The gel swells at low temperatures (≲32 ◦C) and shrinks at high temperatures (≳32 ◦C), therefore, its volume expansion can be controlled by an integrated microheater. When the microheater is turned on, a single cell is trapped by the hole pattern of the single cell catcher. Then, when the microheater is turned off, the single cell catcher is cooled by the ambient temperature. The gel swells at this temperature, and the hole closes to catch the single cell. The caught cell can then be released into culture wells on a microtiter plate by heating the gel again. We conducted single cell extraction with the proposed chip and achieved a 60% success rate, of which 61% cells yielded live cells.

The implementation of a thermal bubble actuated microfluidic chip with microvalve, micropump and micromixer

Abstract: This paper presents the implementation of a thermal bubble actuated microfluidic chip with microvalve, micropump and micromixer, based on a simple process with SOI wafer. Only two photolithography processes were required to provide an effective means of manufacturing the vertical bulk microheater and high-aspect-ratio microchannel for microfluidic applications. The static and dynamic electro-thermal coupling behaviors of the proposed resistive silicon-based microheater were evaluated by finite element analysis to provide an applicable design. The feasibility of each actuation element has also been verified by experiments. Experimental results show that the sizes of thermal bubbles, at flow rates less than 4.5 μl/s, can be controlled steadily by applying the magnitude of direct current that meets the requirement of a microvalve to modulate flow rate. When applying an alternating current with high frequency to the microheater, thermal bubbles could grow cyclically and collapse rapidly, so the liquid stream could be regulated by the repeated volume change of thermal bubbles. A maximum volume flow rate of 4.5 μl/s was obtained, under the driving voltage with a frequency of 60 Hz and 30% duty ratio. The mixing test of the multi-layer fluidics with laminar flow also was successfully implemented by using the volume of thermal bubble to create turbulent flow in the fluids. With no moving parts, the proposed microfluidic chip is well designed with high performance and reliability.

Design, Fabrication, and Characterization of Liquid Metal Microheaters

Abstract: This paper reports design, fabrication, and characterization of liquid metal-based microheaters. Liquid metal microheaters designed via finite element simulation were fabricated by simply injecting eutectic gallium indium into polydimethylsiloxane (PDMS) microfluidic chips bonded to either silicon or PDMS substrates. Considering the net positive volume change of the microheater upon heating, both nonpressurized and pressurized contacts between the power supply and the liquid metal wires were investigated. The pressurized contact was found to provide more reliable electrical connection, thus more stable long-term operation than the nonpressurized contact. Due to higher thermal conductivity, liquid metal microheaters with silicon substrate exhibit better temperature uniformity than ones with PDMS substrate. However, liquid metal microheaters with PDMS substrate are flexible and deformable, thus more suitable than ones with silicon substrate when microheaters should be applied to nonflat objects.

Numerical Investigation of Saturated Flow Boiling in Microchannels by the Lattice Boltzmann Method

Abstract: Bubble formation in saturated flow boiling in 2D microchannels, generated from a microheater under constant wall heat flux or constant wall temperature conditions, is studied numerically based on a newly developed lattice Boltzmann model for liquid-vapor phase change. Simulations are carried out to study effects of inlet velocity, contact angle, and heater size on saturated flow boiling of water under constant wall heat flux conditions. Important information, such as effects of static contact angle on nucleation time and nucleation temperature, which was unable to be obtained by other numerical simulation methods, is obtained. Furthermore, effects of inlet velocity, contact angle, and superheat on nucleate boiling heat transfer in steady flow boiling of water under constant wall temperature conditions are also presented. It is found that the nucleate boiling heat transfer at the microheater is higher if the heater surface is more hydrophilic, because the superheated vapor at the hydrophilic wall has a thi...

Thermoelectric voltage measurements of atomic and molecular wires using microheater-embedded mechanically-controllable break junctions

Abstract: We developed a method for simultaneous measurements of conductance and thermopower of atomic and molecular junctions by using a microheater-embedded mechanically-controllable break junction. We find linear increase in the thermoelectric voltage of Au atomic junctions with the voltage added to the heater. We also detect thermopower oscillations at several conductance quanta reflecting the quantum confinement effects in the atomic wire. Under high heater voltage conditions, on the other hand, we observed a peculiar behaviour in the conductance dependent thermopower, which was ascribed to a disordered contact structure under elevated temperatures.

CO Sensor Using ZnO Thin Film Derived by RF Magnetron Sputtering Technique

Abstract: In this paper, the fabrication and results of zinc oxide (ZnO) thin-film CO gas sensor are discussed The thin film of c-axis oriented ZnO is deposited on Si/SiO2 substrate at room temperature using RF magnetron sputtering technique The deposited ZnO film is annealed at different temperatures starting from 200 °C to 400 °C The crystalline structural properties are analyzed by X-ray diffraction technique and the preferred orientation of ZnO thin film (along 002 direction) is found at 400 °C Further, ZnO thin film is characterized by scanning electron microscopy and surface profilometer to analyze the surface properties and thickness The deposited ZnO film is supported by Au electrodes and Pt microheater to couple the sensing signal with outer circuitry A measurement system is also developed to measure the gas sensing properties and the results are discussed in detail

On-Chip Gel-Valve Using Photoprocessable Thermoresponsive Gel

Abstract: Microfluidic chips are powerful tools for biochemical experiments. High speed and precise flow control can be achieved by using microvalves on a chip. Several types of microvalves that can be integrated into a microfluidic chip have been reported. Among them, gel microvalves have certain advantages over other valves because of their soft structure, which will contribute to prevent mechanical damage the cells passing though the valve. Here we use Bioresist, a photoprocessable thermoresponsive gel, as a key component of the microvalve. Since Bioresist is photopatternable, we can create any arbitrary 2D shape from the thermoresponsive gel using photolithography. Moreover, Bioresist has the unique feature of a phase transition around 30°C, and swells and shrinks repeatedly with temperature change. By integrating the patterned thermoresponsive gel with a microheater, we developed a gel actuator and designed a gel-valve. The gel-valve has the advantages of a simple actuation mechanism: high leakage pressure, high speed actuation and low power consumption. The valve is biocompatible and easily integrated into a chip by using conventional photolithography. Using this valve, we achieved on-chip flow control, and applied it to cell sorting on a chip.

Design considerations for a CMOS Lab-on-Chip microheater array to facilitate the in vitro thermal stimulation of neurons

Abstract: This paper identifies and addresses key design considerations and trade-offs in the implementation of a CMOS high-resolution microheater array for Lab-on-Chip (LOC) applications. Specifically, this is investigated in the context of facilitating the in vitro thermal stimulation of single neurons. The paper analyses the electro-thermal response (by means of COMSOL simulations) and reliability issues (such as melting and electromigration) of different microheater designs. The analysis shows that a small-area heater is more efficient in terms of power, but it has more reliability problems essentially due to electromigration effects. For the proposed heater designs, the expected lifetime is a few days (in continuous operation) in the worst scenario, which is still generally acceptable for LOC applications.

Thermal characterization of a thin film heater on glass substrate for lab-on-chip applications

Abstract: This paper presents for the first time an accurate thermal characterization of thin film heaters manufactured on glass substrates. The characterization has been performed on Cr/Al/Cr meandered heaters. Techniques commonly adopted for measuring the temperature coefficient of resistance, the thermal resistance and thermal capacitance in the case of Si-based microheaters have been conveniently modified to take into account the fundamentally different thermal parameters of a heater manufactured on glass. In order to reduce power consumption, 250 μm wide trenches were manufactured on the back side of the heaters, obtaining an increase of the thermal resistance of about 50% when the glass is in good thermal contact with a heat sink. The measured values of thermal resistance and time constants on a heat sink and in air have been justified with simple physical considerations. Guidelines are also given for a further increase of the thermal resistance of the thin film heaters.

Optofluidic microvalve-on-a-chip with a surface plasmon-enhanced fiber optic microheater

Abstract: We present an optofluidic microvalve utilizing an embedded, surface plasmon-enhanced fiber optic microheater. The fiber optic microheater is formed by depositing a titanium thin film on the roughened end-face of a silica optical fiber that serves as a waveguide to deliver laser light to the titanium film. The nanoscale roughness at the titanium-silica interface enables strong light absorption enhancement in the titanium film through excitation of localized surface plasmons as well as facilitates bubble nucleation. Our experimental results show that due to the unique design of the fiber optic heater, the threshold laser power required to generate a bubble is greatly reduced and the bubble growth rate is significantly increased. By using the microvalve, stable vapor bubble generation in the microchannel is demonstrated, which does not require complex optical focusing and alignment. The generated vapor bubble is shown to successfully block a liquid flow channel with a size of 125 μm × 125 μm and a flow rate of ∼10 μl/min at ∼120 mW laser power.

Pulse-Heating Ionization for Protein On-Chip Mass Spectrometry

Abstract: An on-chip pulse-heating ionization source for protein samples was developed for the realization of miniaturized mass spectrometry. A protein analyte was ionized on a chip by applying only thermal energy to the solid phase sample without a laser, high voltage, or heated ambient gases. A fabricated ionization source consisting of a Pt/Cr microheater (width: 30 μm; length: 100 μm) on a silicon substrate was coupled with a time-of-flight mass filter to analyze a protein sample of bovine serum albumin (BSA, M = 66 kDa). A singly charged BSA ion and other multiply charged BSA ions were generated in the presence of 2,5-dihydroxybenzoic acid as a matrix. To detect the singly charged BSA ion, the required surface energy density of 1.65 × 10–2 μJ/μm2 was applied to the microheater for 500 ns. The use of the 2,5-dihydroxyacetophenone matrix resulted in the generation of the multiply charged protein analyte, while the use of the sinapic acid matrix showed abundant peaks in the low m/z region.

Comparative Study on Temperature Coefficient of Resistance (TCR) of the E-beam and Sputter Deposited Nichrome Thin Film for Precise Temperature Control of Microheater for MEMS Gas Sensor

Abstract: Nichrome (Ni–Cr 80/20 wt %), alloy of Ni and Cr is used as a microheater element of the MEMS microhotplate embedded in the metal oxide based gas sensor. Nichrome is used as a heater element for its unique properties like high resistivity, low cost, low Temperature Coefficient of Resistance (TCR), anti oxidant, anti corrosive nature, no need for extra adhesive layer as required for Pt or Au and also compatibility with standard silicon fabrication technology. Microheater with low TCR is the very important property to avoid localized hotspot and precisely controlling the active area temperature of the microhotplate for sensing the gases at different temperature. In this paper, Temperature Coefficient of Resistance (TCR) of the thin film of nichrome was studied by depositing two popular physical vapor deposition (PVD) methods one is Electron Beam Evaporation and other is DC Sputtering. The TCR parameter was extracted by placing the resistor in wafer level on the thermal chuck and measurement was done by varying the temperature of the thermal chuck using ATT System from room temperature up to 200 °C and measuring the resistance of the microheater using Agilent 4284A LCR meter. The structural characterization was carried out for finding the grain size and elemental composition of Ni/Cr of the as-deposited thin film using FESEM and EDX respectively. The effect of annealing at 300 °C temperature in N2 ambient of the e-beam deposited nichrome thin film on the TCR was also analyzed.

On-chip tuning of the resonant wavelength in a high-Q microresonator integrated with a microheater

Abstract: We report on fabrication of a microtoroid resonator of high-quality (high-Q) factor integrated with an on-chip microheater. Both the microresonator and microheater are fabricated using femtosecond laser three-dimensional (3D) micromachining. The microheater, which is located about 200 micron away from the microresonator, has a footprint size of 200 micron by 400 micron. Tuning of the resonant wavelength in the microresonator has been achieved by varying the voltage applied on the microheater. The drifting of the resonant wavelength shows a linear dependence on the square of the voltage applied on the microheater. We found that the response time of the microresonator is less than 10 secs which is significantly shorter than the time required for reaching a thermal equilibrium on conventional heating instruments such as an external electric heater.

Highly insulating, fully porous silicon substrates for high temperature micro-hotplates

Abstract: As alternative to established thermal substrates and thin membranes, we have investigated fully porous silicon substrates as highly insulating material for thermal devices. Exhibiting a thermal conductivity similar to silica glass and considerably lower than silicon nitride due to increased phonon scattering, thick mesoporous silicon also offers improved thermal and mechanical stability. Our work has focused on full wafer thickness porosification as a not extensively documented use of porous silicon and its application to thermal devices. Here we present measurement and finite element simulation results for our latest generation thin film microheaters on fully porous silicon substrates as proof of concept devices. Porosity, mass density, and specific heat capacity of porous silicon are deduced from fabrication parameters, thermal conductivity is determined by the so-called 3ω-measurement method, and all material properties are validated by fitting measurement data to our finite element models. For thick fully porous domains we estimated a thermal conductivity of ≈0.9 W/m/K, as well as a density of ≈1200 kg/m3, a specific heat capacity of ≈780 J/kg/K and a corresponding volumetric porosity of ≈50%. Thin film fabrication of nitride passivation and molybdenum meander microheaters on fully porous domains allowed characterization of thermal performance and insulation. For 10 mm2 microheaters we measured a power efficiency of 0.40 K/mW stable up to a maximum temperature of 475 °C, compared to 0.37 K/mW stable up to 440 °C on silica glass. Both static and dynamic heater measurements show superior performance of fully porous silicon substrates compared to reference samples on thin silica glass substrates.

Microthermal sensors for determining fluid composition and flow rate in fluidic systems

Abstract: To analyze fluid mixtures a simple and low cost measurement method is realized using a microthermal sensor that introduces a short heat pulse into the fluid under test whilst the resulting temperature increase reflects thermal parameters of the fluid. For methanol in water this principle showed an almost linear dependence of the temperature increase on the methanol content for the volume concentration range 0–20 %. The sensitivity was determined to S = 0.19 K/(% (V/V)) for a heat pulse of 0.5 s duration and a heater power of 30 mW. The accuracy achieved in stopped-flow single pulse measurements is ~0.5 % (V/V). By integrating additional temperature sensors in front and behind the microheater the flow rate of the liquid can also be determined using thermal anemometry. The low cost sensor construction and simple signal analysis make this principle promising for use in low cost mobile applications like DMFC power supplies for laptops.

Analysis of local heating of liquid samples in multiparametric capillary sensors

Abstract: The local heating enables liquid classification in multiparametric capillary sensors. The dispersion of capillary and microheater parameters may determine the sensor action. Therefore, this paper focuses on the analysis of a local heating implemented in mentioned sensor. The microheater consist of 4H-SiC volume heating unit, alundum ceramic base and a glass capillary is modeled and simulated using CoventorWare™. We use finite element method (FEM) to determine thermo-mechanical parameters of the designed structure. Obtained results are then compared and verified with experimental research. The influences of a capillary to microheater distance and capillary’s thickness on the output results are examined.

Capillary-driven microfluidic chips with evaporation-induced flow control and dielectrophoretic microbead trapping

Abstract: This work reports our efforts on developing simple-to-use microfluidic devices for point-of-care diagnostic applications with recent extensions that include the trapping of microbeads using dielectrophoresis (DEP) and the modulation of the liquid flow using integrated microheaters. DEP serves the purpose of trapping microbeads coated with receptors and analytes for detection of a fluorescent signal. The microheater is actuated once the chip is filled by capillarity, creating an evaporation-induced flow tuned according to assay conditions. The chips are composed of a glass substrate patterned with 50-nm-thick Pd electrodes and microfluidic structures made using a 20-μm-thick dry-film resist (DFR). Chips are covered/sealed by low temperature (50°C) lamination of a 50-μm-thick DFR layer having excellent optical and mechanical properties. To separate cleaned and sealed chips from the wafer, we used an effective chip singulation technique which we informally call the “chip-olate” process. In the experimental section, we first studied dielectrophoretic trapping of 10-μm beads for flow rates ranging from 80 pL s−1 to 2.5 nL s−1 that are generated by an external syringe pump. Then, we characterized the embedded microheater in DFR-covered chips. Flow rates as high as 8 nL s−1 were generated by evaporation-induced flow when the heater was biased by 10 V, corresponding to 270-mW power. Finally, DEP-based trapping and fluorescent detection of functionalized beads were demonstrated as the flow was generated by evaporation-induced flow after the microfluidic structures were filled by capillarity.

CNT bundles growth on microhotplates for direct measurement of their thermal properties

Abstract: Vertically aligned Carbon Nanotubes (CNT) arrays were successfully grown on top of a freestanding microhotplate, to investigate the thermal dissipation properties of CNT bundles and their applicability as heat exchanger. Two CNT configurations are employed: a group of six bundles, each with a diameter of 20 μm, and a single CNT bundle with a diameter of 200 μm. In both configurations the bundles are 70 μm high. The microhotplate consists of a platinum thin film microheater integrated on a freestanding silicon nitride membrane. The microhotplate is used as heat source and as temperature sensor. Results show that at 300 °C, 20% and 31% of power can be saved with the circular six and single bundle configurations, respectively.

Capillary-driven microfluidic chips with evaporation-induced flow control and dielectrophoretic microbead trapping

Abstract: This work reports our efforts on developing simple-to-use microfluidic devices for point-of-care diagnostic applications with recent extensions that include the trapping of microbeads using dielectrophoresis (DEP) and the modulation of capillary-driven flow using integrated microheaters. DEP serves the purpose of trapping microbeads coated with receptors and analytes for detection of a fluorescent signal. The microheater is actuated once the chip is filled by capillarity, creating an evaporation-induced flow tuned according to assay conditions. The chips are composed of a glass substrate patterned with 50-nm-thick Pd electrodes and microfluidic structures made using a 20-μm-thick dry-film resist (DFR). Chips are covered/sealed by low-temperature (50 °C) lamination of a 50-μm-thick DFR layer having excellent optical and mechanical properties. To separate cleaned and sealed chips from the wafer, we used an effective chip singulation technique that we informally call the "chip-olate" process. In the experimental section, we first studied dielectrophoretic trapping of 10 μm beads for flow rates ranging from 80 pL s -1 to 2.5 nL s -1 and that are generated by an external syringe pump. Then, we characterized the embedded microheater in DFR-covered chips. Flow rates as high as 8 nL s -1 were generated by evaporation-induced flow when the heater was biased by 10 V, corresponding to 270 mW power. Finally, DEP-based trapping and fluorescent detection of functionalized beads were demonstrated as the flow was generated by the combination of capillary filling and evaporation-induced flow.

Design and characterization of embedded microheater on CMOS-MEMS resonator for application in mass-sensitive gas sensors

Abstract: In utilizing CMOS-MEMS resonators as mass-sensitive platforms, a uniform temperature distribution on the membrane surface is critical. In this paper, a novel design of CMOS-MEMS resonator with embedded microheater to control the temperature over the sensing layer was successfully designed and characterized. The CMOS-MEMS resonator was fabricated using 0.35 μm CMOS and post-CMOS micromachining process. Temperature coefficient of resistance (TCR) of aluminum temperature sensor embedded in the membrane was determined by measurement of resistance variation as a function of temperature from 27°C and 150°C. The TCR of the temperature sensor is found to be 0.00386 and 0.00379 for measurements carried out while temperature is increasing and decreasing, respectively. The total resistance of the temperature sensor and the wire interconnects was theoretically determined to be 74.23 Ω and 94.82 Ω, respectively, making a total resistance of 169.05 Ω when measurements are made through the pads. On the other hand the measured resistance at 27°C is found to be 169.06 Ω which is in very good agreement with a difference of 0.006 %. The experimental results and analytical values of resistance of the temperature sensor as a function of temperatures shows a good agreement (1.07%). TCR of Al is found to 0.00382 with percentage difference of about 2.05 % from standard value (39 ×10 -4 C -1 ).

Demonstration of Reduced Power Consumption MEMS LEL Sensor Prepared by a Novel Digital Microfluid Technique

Abstract: A low power consumption micro electro-mechanical system catalytic combustible low explosion limit (LEL) sensor was fabricated. The microheater was characterized by a suspending microhotplate over the silicon substrate. The alumina slurry and Pd-Pt catalyst solution were precisely and repeatedly coated on the microhotplate by a novel digital microfluid technique, respectively. Furthermore, the alumina layer and the alumina/catalyst layer on the microheater showed the collinear resistance versus voltage thermal characteristic curves during the solidification, which indicated that a good match could be directly made between them. During aging, the alumina/catalyst element demonstrated a high initial signal and then fell rapidly before coming to a stable value. Through pairing the alumina reference and alumina/catalyst sensitive elements in the wheatstone bridge, the output voltage could be up to 36 mV at the 50% LEL level of CH4 at the working temperature of 400 °C and the operation voltage was 2.6 V. The power consumption and the signal sensitivity could be also down to 75 mW and up to 0.702 mV/LEL%, respectively.

Electro-thermal analysis of an embedded boron diffused microheater for thruster applications

Abstract: One of the important design criteria of micropropulsion systems in particular VLM is the type of microheater, its layout and placement with a view to achieve uniform heating of propellant, fast heat transfer efficiency with minimum input power. Thrust produced by microthruster not only depends on the structural geometry of the thruster and propellant flow rate, but also on the chamber temperature to produce super saturated dry stream at the exit nozzle. Detailed design of microheater in thermal and electrical domains using co-solvers available in MEMS software tools along with material’s thermal property, temperature dependence of electrical resistivity and thermal conductivity have been considered in the present work to achieve precise modeling and experimental accuracy of heater operation. The chamber temperature was analytically calculated and subsequently the required resistance and power were estimated. The boron diffused microheaters of meanderline configuration in silicon substrate has been designed and its finite element based electro-thermal modeling was employed to predict the heater characteristics. The variation of microheater temperature with time, applied voltage and along chamber length has been determined from the modeling. Subsequently the designed microheater was realized on silicon wafer by lithography and boron diffusion process and its detailed testing was evaluated. It was found that boron diffused resistor of 820 Ω can generate 405 K temperature with applied input power 2.4 W. Finally the simulated results were validated by experimental data.

Accurate analog temperature control of a thin film microheater on glass substrate for lab-on-chip applications

Abstract: This paper presents a new methodology to accurately manage the temperature of microheaters manufactured on glass, based on an analog control circuit built around a single operational amplifier. The first step is an accurate electro-thermal characterization of the microheater, using a 4-terminal topology, in order to extract i) the microheater active area temperature as a function of both heating power and 2-wire electrical resistance and ii) the thermal resistances and capacitances of a thermal model. Then experimental measurements are shown and compared with simulations obtained using PSpice modelling.

Effects of material and membrane structure on maximum temperature of microheater for gas sensor applications

Abstract: The material selection for membrane is important in designing a microheater. A membrane is used as an insulator layer to prevent heat dissipation from the microheater to the substrate. At the same time, the thermal characteristic of the microheater is influenced by the insulator layer. A study on the effects of material and membrane structure on the maximum temperature of the microheater for gas sensor applications has been carried out using Heat Transfer Module of COMSOL 4.2. Three different membrane materials namely silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ) and polyimide and two types of membrane structures namely full-membrane and bridgemembrane have been chosen for the study. Their effects on the microheater temperature are presented. The resistive meander type of microheater is used in this study. The heater material is platinum. The thickness and the area of the heater are 2 μm and 600 μm × 680 μm respectively. The thickness of each membrane is 5 μm. The area of the full-membrane and the bridgemembrane are 2500 μm × 2500 μm and 850 μm × 850 μm respectively.

Microelectrode patterning of metal films using pulsed UV-laser system

Abstract: This study presents a maskless method to conduct microelectrode patterning of metal films using pulsed UV-laser-writing technology. The experimental procedures involved designing the ablation region of a glass substrate, ablation path planning, and determining detailed laser-writing parameters. The various parameters used in a UV-laser-writing system were investigated and analyzed using an optical microscope and a three-dimensional confocal laser scanning microscope. This technique was successfully applied in patterning aluminum (Al) thin film on a glass substrate for use in microheater devices. The measurements of electrical resistance and temperature distribution on the substrate demonstrated that no short circuiting occurred in the microheater, confirming the quality of the electrical isolation values.

Methane detection with high temperature all-silicon microheater

Abstract: Detection of methane (CH4) below the Lower Explosive Limit (LEL) with large-signal output based on thermal conduction was demonstrated by an ultra-high temperature all-silicon cantilever-type microheater. Thermal conductivity measurement is powerful for gas sensing in chromatography, however, the thermal conductivity method is nearly never used for detection of the methane below the LEL in coal mine due to deficiency in sensitivity. In this paper, a cantilever-type all-silicon microheater with high temperature capability was designed and fabricated from Silicon-On-Insulator (SOI) substrate; and corresponding output signal at least 10 mV for per 1 vol% methane was obtained in the range from 0~5 vol%. It offers the potential application in underground coal mining for monitoring the methane concentration below the LEL with replacement of the bead-type catalytic pellistor devices.

Graphene microheater and method of manufacturing the same

Abstract: A microheater and a method of manufacturing the same are disclosed. The microheater includes a substrate, graphene disposed on the substrate and formed in a pattern; and a passivation layer disposed on the graphene. The method of manufacturing a microheater involves transferring graphene to a substrate, forming a first pattern for supplying electric power to the graphene, forming an electrode on the first pattern, forming a second pattern for focusing heating in the graphene, and forming a passivation layer on the graphene having the electrode and the second pattern formed therein.