Showing papers on "Microheater published in 2009"

Capacitive humidity sensor design based on anodic aluminum oxide

Abstract: Capacitive humidity sensors based on anodic aluminum oxide (AAO), a material used as a sensing layer for high sensitivity, were investigated. The AAO film has many nanosized pores, giving it a large surface area for absorbing water vapor. Effects of design factors and heating were investigated. A thick porous layer or big pore diameter increases sensitivity because of increase in contact surface area. An electrode of rectangular spiral-shaped type tends to have a slightly higher hysteresis than the interdigitated type, but the rectangular spiral-shaped type is efficient and sensitive if the hysteresis and nonlinearity are reduced by controlling design factors or heating. Although heating reduced the sensitivity, it improved performance parameters such as nonlinearity, hysteresis, response time and temperature dependence. Also, a porous electrode would show a higher sensitivity than a nonporous electrode because of the larger surface area.

Polydimethylsiloxane microfluidic chip with integrated microheater and thermal sensor

Abstract: A microheater and a thermal sensor were fabricated inside elastomeric polydimethylsiloxane microchannels by injecting silver paint (or other conductive materials) into the channels. With a high-precision control scheme, microheaters can be used for rapid heating, with precise temperature control and uniform thermal distribution. Using such a microheater and feedback system, a polymerase chain reaction experiment was carried out whereas the DNA was successfully amplified in 25 cycles, with 1 min per cycle.

Thermally mediated control of liquid microdroplets at a bifurcation

Abstract: The ability to precisely control the motion of droplets is essential in droplet-based microfluidics. It serves as the basis for various droplet-based devices. This paper presents a thermal control technique for microdroplets at a bifurcation. Control was achieved using an integrated microheater that simultaneously induces a reduction in fluidic resistance and thermocapillarity. The temperature of the heater was monitored by an integrated temperature sensor. At a bifurcation with symmetric branches, a droplet can be split into two daughter droplets of controllable sizes or entirely switched into a desired branch. The physics of this phenomenon was investigated with the help of a numerical model. Splitting and switching were demonstrated within an operational temperature range 25‐38 ◦ C. The relatively low operational temperature range allows this technique to be used for droplets containing biological samples. The present control concept is not limited to bifurcations, but can be employed in other geometries.

Design, fabrication and characterization of a conducting PDMS for microheaters and temperature sensors

Abstract: In this paper, we present the design and fabrication procedure of a conducting polydimethylsiloxane (PDMS) and then evaluate its potential uses for heating and temperature sensing. The conducting PDMS was made up of a mixture of a PDMS prepolymer and metallic powder. Depending on purpose, i.e. heater or sensor, different weight ratios of the powder and geometric shapes were considered. Characterization of both the microheaters and the temperature sensors includes stability, repeatability, durability and time response. The results suggest that the microheater is feasible for constantly heating at a fixed temperature instead of running thermal cycles. The optimal heating range was estimated below 100 °C under the current setup and a power consumption of 210 ± 12 mW was needed for 92 °C. Hysteresis and time lag were observed in the temperature sensor. Accordingly, the sensor is recommended to be used for long-term monitoring instead of rapid temperature detections.

Polydimethylsiloxane-based conducting composites and their applications in microfluidic chip fabrication

Abstract: This paper reviews the design and fabrication of polydimethylsiloxane (PDMS)-based conducting composites and their applications in microfluidic chip fabrication. Owing to their good electrical conductivity and rubberlike elastic characteristics, these composites can be used variously in soft-touch electronic packaging, planar and three-dimensional electronic circuits, and in-chip electrodes. Several microfluidic components fabricated with PDMS-based composites have been introduced, including a microfluidic mixer, a microheater, a micropump, a microdroplet controller, as well as an all-in-one microfluidic chip.

Ultrashort Photonic Crystal Optical Switch Actuated by a Microheater

Abstract: We demonstrate a silicon photonic crystal (PhC) optical switch with a 20-mus response time controlled by a thermo-optic microheater. The switch consists of a dispersion engineered PhC directional coupler that is only 4.9 mum long. Optical and electrical isolation is provided by backfilling the holes and embedding the PhC in a silica cladding to produce a vertically symmetric structure that is more robust than a membrane geometry. No increase in optical loss is observed due to the silica cladding, despite operating above the lightline; the insertion loss for airbridge and silica embedded structures are comparable at 1-2 dB.

A Latchable Phase-Change Microvalve With Integrated Heaters

Abstract: This paper presents a latchable phase-change microvalve with integrated microheaters, which is suitable for lab-on-a-chip systems where minimal energy consumption is desired. The microvalve exploits low-melting-point paraffin wax, whose solid-liquid phase changes allow switching of fluid flow through deformable microchannel ceiling. Switching is initiated by melting of paraffin through an integrated microheater, with an additional pneumatic pressure used for the open-to-close switching. The valve consumes energy only during initiation of valve switching. When paraffin solidifies, the switched state is maintained passively. The microvalve was fabricated from polydimethylsiloxane through multilayer soft lithography techniques. Experiments show that the valve can switch flow within 4-8 s due to the small thermal mass and localized melting of paraffin wax; when closed, the valve can passively withstand an inlet pressure over 50 kPa without leakage. Time response of the valve can be further improved with improved heater and wax chamber designs, while the latching ability can be improved by optimizing the wax chamber/membrane design. Compared to existing latchable phase-change valves, the microvalve has no risk of cross-contamination. In addition, the improved sealing offered by the compliant membrane makes the valve robust and flexible in operation, allowing large ranges of initiation pressure from various actuation schemes.

An electrical microheater technique for high-pressure and high-temperature diamond anvil cell experiments.

Abstract: Small electrical heating elements have been lithographically fabricated onto the culets of “designer” diamond anvils for the purpose of performing high-pressure and high-temperature experiments on metals. The thin-film geometry of the heating elements makes them very resistant to plastic deformation during high-pressure loading, and their small cross-sectional area enables them to be electrically heated to very high temperatures with relatively modest currents (≈1 A). The technique also offers excellent control and temporal stability of the sample temperature. Test experiments on gold samples have been performed for pressures up to 21 GPa and temperatures of nearly 2000 K.

Thermal imaging with tapping mode using a bimetal oscillator formed at the end of a cantilever

Abstract: Thermal detection based on the thermal shift of the resonant frequency of a bimetal resonator (Al/Si) is presented and demonstrated. The bimetal oscillator with a tip is fabricated at the end of a commercial silicon cantilever. The bimetal oscillator and the silicon cantilever have a resonance frequency of 441 and 91 kHz, respectively, and the measured temperature coefficients of the resonant frequency are -127x10(-6)/K and -115x10(-6)/K, respectively. It is demonstrated that self-oscillated resonant frequency of the bimetal oscillator changes in response to heat from a microheat source. Simultaneous measurements of topography and temperature profile with the temperature resolution of 0.12 K on a glass substrate heated using a thin chromium film microheater are successfully demonstrated. These results show potential abilities of the mechanical resonant thermal sensor.

Fabrication of microheater by laser micro cladding electronic paste

Abstract: The paper presents a direct-write technique named laser micro cladding electronic paste for rapid prototyping and manufacturing of microheaters. Microheaters (5 mm × 5 mm) have been successfully fabricated on alumina substrate. RuO2 thick film resistor paste was used as heating material. Thermal characterization of the microheaters has been investigated. These microheaters were suitable for a maximum long-term operation temperature of 400 °C. Cracking of the alumina substrate was observed at higher temperature. The heating and cooling rates of microheater were about 7 °C s−1 and 4 °C s−1, respectively. The results indicate that the microheater exhibits excellent thermal performance equivalent to those of traditional thick film screen-printed microheaters.

Selective Formation of Carbon Nanotubes and Its Application to Field-Emitter Arrays

Abstract: At room-temperature ambient, carbon nanotubes (CNTs) were selectively synthesized on each bridge of the microheater array (MHA) formed on a glass substrate. Both multiwalled (MW) and single-walled CNTs could be formed by controlling the MHA temperature, which was confirmed from Raman spectroscopy. By incorporating the selectively grown MW CNTs into the lateral-gated field-emitter arrays, high current density of electron emission was observed with low device leakage.

On-chip Cell Immobilization and Monitoring System Using Thermosensitive Gel Controlled by Suspended Polymeric Microbridge

Abstract: In this paper, we describe the fabrication of a temperature-controlled microfluidic chip for cell immobilization using a thermosensitive hydrogel of poly (N-isopropylacrylamide) (PNIPAAm). A mixture of PNIPAAm solution, yeast cells, and Calcein-AM fluorescent dye is flowed in the microchannel, and the indium-tin-oxide (ITO) microheaters that were fabricated by micromachining technology heat a PNIPAAm gel. However, if the gel is very thick, it blocks the observation of the culturing cells and reduces the SNR. To address this problem, we fabricate a suspended microbridge above the microheater that limits the height of the gel, ensuring that it forms a thin and transparent layer above the heater. Microheaters and suspended biocompatible microbridge are integrated on a chip in which yeast-cell immobilization can be performed by gelation of a PNIPAAm solution.

Bacterial detection using a carbon nanotube gas sensor coupled with a microheater for ammonia synthesis by aerobic oxidisation of organic components

Abstract: In this study, the authors propose a new bacteria detection method using a carbon nanotube (CNT) gas sensor and a microheater, which were coupled into a Bio-MEMS (microelectromechanical systems)-type device. Bacteria were heated by the microheater in air so that ammonia (NH3) gas can be generated by the oxidation reaction of organic components of bacteria. Thus generated NH3 gas was detected by using the CNT gas sensor, which was fabricated by dielectrophoresis (DEP) and combined with the microheater to form a small chamber. Cyclic pulsed heating operation was employed so that the CNT response to elevated temperature did not mask NH3 response. It was demonstrated that the proposed device could detect and quantify 107 bacteria cells (Escherichia coli). Possible application of DEP to trap and enrich target bacteria on the microheater was also discussed.

Rapid patterning of slurry-like elastomer composites using a laser-cut tape

Abstract: We present a cleanroom-free, simple and low-cost fabrication approach utilizing a laser-cut tape for rapidly patterning slurry-like elastomer composites. A conductive polydimethylsiloxane (PDMS) composite was chosen for demonstration in this paper due to its wide use of sensing and heating in many applications. Two fabrication schemes were developed: embedding in a PDMS matrix and relieving on a PDMS substrate. In both schemes, the patterns were first inscribed on adhesive tape using a CO2 laser. The patterned tape then served as a positive mask when spreading the conductive PDMS over it. The patterns were eventually transferred to a substrate after scraping the excessive composite with a razor blade and then removing the tape. The feature resolution of the technique was about 90‐100 μm primarily determined by the laser beam diameter, the translational speed and the power. The height of the patterned structures was associated with the thickness of the tape, which ranged from 76.1 ± 4.3 μm to 168.9 ± 8.2 μm in this study. A thicker structure can be achieved by stacking more adhesive tapes. For a practical demonstration, the conductive PDMS was patterned on a PDMS substrate serving as a heating element. The elastomeric microheater was successfully heated to 92 ◦ C with a power of 210 ± 12 mW applied. (Some figures in this article are in colour only in the electronic version)

Development of temperature feedback control system for piezo-actuated display package

Abstract: This paper describes a temperature management system for a deformable mirrors of piezo-actuated display package (PADP). This package which is integrated in microbeam projectors is used in portable devices such as cellphones, laptops, and personal digital assistants (PDAs), to name a few. Ambient temperature change is a critical factor affecting the performance of PADP. To reduce this effect of ambient temperature change, a temperature control system using a microheater and a temperature feedback circuit is developed. A computational model of the transient thermal analysis for the feedback control system is also developed. The obtained theoretical results are in a good agreement with the experimental measurements. Under this controlled system, the magnitude of the temperature fluctuation is reduced by ±0.5 °C. In order to enhance the performance of the developed system, various values of the temperature sensor resistance are used, leading to a reduction of about 10% of the temperature fluctuation.

Theoretical and experimental investigation of spatial temperature gradient effects on cells using a microfabricated microheater platform

Abstract: While the cellular interaction with the chemical microenvironment has been studied in detail in the past, the effect of thermal signals and gradients on cells is not well understood. While almost all biological macrosystems exhibit temperature sensitivity, this has not been studied much at the cellular level. The capability of precise control of temperature and heat flux at the scale of a few microns using microfabricated structures makes microelectromechanical systems (MEMS) ideal for investigating these effects. This work describes a MEMS-based microheater platform capable of subjecting surface-adhered cells to microscale temperature gradients. This microdevice comprises a free-standing thin film based microheater platform. The design and microfabrication of this microdevice are described. A thermal conduction model is developed in order to thermally characterize the microheater platform. Protocols for culturing cells on the microheater platform are developed, making it possible to adhere cells on the microheater surface and subject them to a desired spatial temperature gradient. Experiments demonstrating the spatial control of cell viability using the microheater device are described. This is followed by experiments that explore the possibility of cellular growth in response to thermal gradients, similar to chemotaxis. Thermotactic effect is well known at the organismal level. However, cells used in this work did not exhibit any thermotactic effect. A theoretical model for predicting cell response to a spatial temperature gradient in its microenvironment is proposed. The model is based on the effect of the temperature gradient on the chemical sensory process of the cell. The model predicts that in addition to the thermal gradient, the thermotactic effect also depends on a number of other parameters that have not been well characterized in the past. The microheater platform described in this work offers a fundamental new experimental tool with which to explore the interaction of cellular systems with their thermal microenvironment. The theoretical model of thermotaxis developed here furthers the understanding of the function of a cell as a thermal and chemical sensor.

Evaluation of thermal conduction of single carbon nanotube by local heating in air

Abstract: We evaluated thermal conduction of a single carbon nanotube (CNT) in air. Heating the end of the CNT locally by a microheater, we measured temperature dependence of electrical resistance of the single CNT. First, we fabricated the microheater for local heating and four electrodes for electrical resistance measurement on a Silicon on Insulator (SOI) wafer and made a gap for heat insulation. The effectiveness of the SOI wafer and the gap was confirmed by FEM analysis. Next, the single CNT was manipulated on this pattern by nanomanipulation and fixed by Electron-Beam-Induced-Deposition (EBID) in the Scanning Electron Microscope (SEM). Finally, we measured the electrical resistance when the temperature of the microheater was changed by applying the voltage. As a result, we could evaluate the thermal conduction of a specific single CNT in air. This paper also indicates the possibility of using a single CNT as a temperature sensor.

MEMS Nanoreactor for Atomic-Resolution Microscopy of Nanomaterials in their Working State

Abstract: We present a MEMS nanoreactor that for the first time enables transmission electron microscopy (TEM) of nanomaterials at the atomic scale during exposure to reactive gases at ambient pressure. This pressure exceeds that of existing in-situ TEM systems by a factor of one hundred. The reactor integrates a shallow flow channel (35 ?m high) with a microheater and an array of robust electron-transparent windows of only 10 nm thickness. The Pt heater is embedded in a SiN x membrane. The reactor is integrated into a dedicated TEM specimen holder. Its performance is demonstrated by the live formation of a nanostructured catalyst that is normally used for the production of methanol. The formation of Cu nanoparticles on the ZnO support crystals is imaged at 1.2 bar H 2 and up to 500°C with very low thermal drift and with a spatial resolution of 0.18 nm.

Thermal Bubble Microfluidic Gate Based on SOI Wafer

Abstract: This paper presents a simple process using a silicon-on-isolator (SOI) wafer to fabricate a silicon-based vertical microheater to generate thermal bubbles for the applications in microfluidic systems. The fabrication process consists of only two photolithography masks that provide an effective way of manufacturing a resistive bulk microheater and a high-aspect-ratio microchannel. The electrothermal property of the proposed microheater has been characterized and verified by finite-element analysis and experiment. According to the design concept and experimental results, the largest temperature occurred at the smallest neck section due to the nonuniform property of the resistance along the length of the arch-type microheater, and thus, the vapor bubble was generated and attached to the vertical sidewall of the microheater. For a typical microheater design, bubble nucleation could be generated under a applied voltage of 5 V, and the bubble could obstruct the entire 100 mum width of the microchannel when the applied voltage reaches 8 V. A switching test has showed that the silicon-based microheater has a good thermal resistance behavior for long-term reliability and that the modulation of output flow rate is easily handled by the sizes of the thermal bubbles. Moreover, the bubble can be formed with a steady growth, even when the maximum fluid velocity is larger than 920 mum/s in a microchannel with a rectangular cross section 100 mum wide and 50 mum high. These results reveal that the microfluid gate presented here is well designed and that bubble sizes are stable and controllable.

Droplet-Volume-Adjustable Microinjectors Using a Digital Combination of Multiple Current Paths Connected to Single Microheater

Abstract: In this paper, we design, fabricate, and test a single-heater microinjector, whose ejected-droplet volume is adjusted by a digital combination of multiple current paths connected to a single microheater. The novel aspect of the present method includes using the single microheater having multiple current paths to achieve multilevel droplet volume adjustment. In the design process, we design four pairs of current I/O interconnection lines connected to the microheater. We numerically estimate the actually heated area whenever we vary the combination of 4-b current path through the single microheater. On the basis of the numerical and theoretical estimation results, we design the droplet-volume-adjustable microinjector having a rectangular (R)- and a circular (C)-shape single microheater. In the experimental study, we measure the sizes of the generated bubbles, as well as the volumes and velocities of the ejected droplets, according to the digital current-path combination. In the bubble generation test, we use the 1-kHz 15.0-V 3-mus pulsewidth electrical signal and DI water at room temperature. The measured input power is varied from 8.7 to 24.9 muW for the R type and from 8.1 to 43.8 muW for the C type as the current path is changed. The projected area of the generated bubble is varied from 440 to 1,360 mum2 for the R type and from 800 to 3300 mum2 for the C type at six levels, respectively. Under the same experimental condition, we measure the ejected-droplet volumes and velocities. It is found that the ejected-droplet volumes are varied from 9.4 plusmn 0.7 to 20.7 plusmn 1.8 pL at three levels for the R type and from 7.4 plusmn 0.8 to 27.4 plusmn 2.0 pL at five levels for the C type, respectively, while the ejected-droplet velocities are varied from 0.8 plusmn 0.01 to 1.7 plusmn 0.01 m/s for the R type and from 0.5 plusmn 0.02 to 2.8 plusmn 0.03 m/s for the C type, respectively.

Heat transfer and bubble detachment in subcooled pool boiling from a downward-facing microheater array in a nonuniform electric field.

Abstract: The effects of a nonuniform electric field on vapor bubble detachment and heat transfer in subcooled pool boiling from a microheater array are investigated. The heater array faced downward to simulate a -1 g gravity condition and to eliminate the dominant masking effect of the buoyancy force. Experiments were conducted at different subcooling levels for various wall temperatures and electric field magnitudes. A dielectric fluid, FC-72, was used as the working fluid at ambient pressure. The array of 3 x 3 independently controlled microheaters was maintained at constant temperature and the rate of heat transfer from each heater was measured. Bubble images were recorded using a high-speed camera. The electric field was applied between the horizontal downward-facing microheater array, which was grounded, and a spherical, off-axis electrode beneath it. Boiling heat transfer results with and without the electric field are presented in this study. In the absence of the nonuniform electric field, compared to the same bulk fluid temperature and wall superheat settings in the +1 g situation, a much larger primary bubble was formed on the heater array, due to the coalescence of the secondary bubbles that nucleated on the heater array. The vapor bubble remained on the heater array surface and no bubble detachment was observed. With the nonuniform electric field applied, bubbles were lifted and sheared off from the heater array surface. The electric field was able to break up the primary bubble into several smaller bubbles--considerably greater heat transfer enhancement was measured than under similar conditions in +1 g.

Method for forming silicon film, method for forming pn junction and pn junction formed using the same

Abstract: A method for forming a silicon film may be performed using a microheater including a substrate and a metal pattern spaced apart from the substrate. The silicon film may be formed on the metal pattern by applying a voltage to the metal pattern of the microheater to heat the metal pattern and by exposing the microheater to a source gas containing silicon. The silicon film may be made of polycrystalline silicon. A method for forming a pn junction may be performed using a microheater including a substrate, a conductive layer on the substrate, and a metal pattern spaced apart from the substrate. The pn junction may be formed between the metal pattern and the conductive layer by applying a voltage to the metal pattern of the microheater to heat the metal pattern. The pn junction may be made of polycrystalline silicon.

A plasma spectroscopic microdevice for on-site water monitoring

Abstract: Plasma spectroscopic techniques can provide a quick, on-site solution for monitoring the potability of water sources. This paper reports on a new, essentially disposable ceramic microdevice that utilizes on-chip doped DC plasmas to spectroscopically analyze the atomic and molecular composition of water samples on-site. The device is fabricated on an alumina ceramic substrate, which is ideal due to its low-cost, ability to be cast into micro-structures, mechanical robustness, and insulation of high-voltage. Water sample analysis is performed in air at atmospheric pressure, greatly reducing the cost and complexity of water quality monitoring on-site. Samples are partially evaporated with on-chip thin-film Cr microheater integrated into the cathode lead. Temperature changes as large as 47 °C can be realized with 60 mA. With the device reported here, copper and aluminum impurities are detected at 100 ppm and ammonia contaminants are observed in concentrations as low as 1%.

Integrated CMOS gas sensors

Abstract: We present a low power gas sensor system on CMOS platform consisting of micromachined polysilicon microheater, temperature controller circuit, resistance readout circuit and SnO 2 transducer film. The design criteria for different building blocks of the system is elaborated. The microheaters are optimized for temperature uniformity as well as static and dynamic response. The electrical equivalent model for the microheater is derived by extracting thermal and mechanical poles through extensive laser doppler vibrometer measurements. The temperature controller and readout circuit are realized on 130nm CMOS technology. The temperature controller re-uses the heater as a temperature sensor and controls the duty cycle of the waveform driving the gate of the power MOSFET which supplies heater current. The readout circuit, with subthreshold operation of the MOSFETs, is based on resistance to time period conversion followed by frequency to digital converter. Subthreshold operatin of MOSFETs coupled with sub-ranging technique, achieves ultra low power consumption with more than five orders of magnitude dynamic range. RF sputtered SnO 2 film is optimized for its microstructure to achive high sensitivity to sense LPG gas.

A MEMS-based dual-axis tilt sensor using air medium

Abstract: In this paper, a MEMS-based dual-axis tilt sensor, which utilizes a free-convection-based air medium, is fabricated and its operating characteristics are evaluated. The key components of the proposed tilt sensor, microheater and temperature sensors, are designed to have various patterns in order to examine an optimized geometry for achieving high sensitivity. Six different types of tilt sensors are fabricated and measured. The proposed tilt sensor operates in a wide detecting range of ±90κ on two axes. Output characteristics show excellent linearity and symmetric sensitivity. Fabrication sequence is also very simple owing to its monotonous structure and heater/sensor material, thus it fits mass production at a low cost.

Microfocusing using the thermal actuation of microbubbles

Abstract: This paper describes the microfocusing in a microchannel using the thermal actuation of a pair of microbubbles. A microbubble was produced from de-ionized (DI) water with an integrated microheater, and the volume was controlled by applying voltage. The microfocusing was demonstrated with a polydimethylsiloxane (PDMS) device consisting of two layers. The top layer included a microchannel that was 300 μm wide and 50 μm high. It was flanked by a pair of reservoirs. The bottom layer provided a microheater underneath the reservoir. Upon heating, DI water boiled immediately over the microheater and formed a microbubble that came out of the reservoir in a perpendicular direction toward the fluid. The fluid was focused from 300 to 22 μm, as the distance between the apexes of the arch-shaped microbubbles was shortened due to expansion, which was maintained at a flow velocity up to approximately 17.8 mm s−1. The temperature of the water in the reservoir was estimated to reach the boiling point within 62 or 160 ms, depending on the substrate.