Integrated Heating Elements Research Articles

High-speed epitaxial growth of AlN above [formula omitted] by hydride vapor phase epitaxy

Aluminum nitride (AlN) epitaxial layer on sapphire (0 0 0 1) substrate was grown at high temperatures above 1200 ∘ C by hydride vapor phase epitaxy (HVPE). A high-temperature growth system was built by combining a conventional hot-wall type furnace and a heating susceptor with integrated heating element. This system realized growth of AlN by HVPE above 1200 ∘ C even in the quartz reactor. Growth rates of AlN stay constant in the temperature range of 1280 – 1410 ∘ C . This result was consistent with the results expected from thermodynamic analysis, and represents that growth of AlN by HVPE is under mass transportation limited process even at high temperatures. Epitaxial growth of AlN with growth rate of 85 μ m / h was achieved at 1380 ∘ C .

Characterization of liquid and gaseous micro- and nanojets using microcantilever sensors

This paper reports the development of microelectromechanical metrology tools to characterize liquid and gaseous jets generated from microfabricated nozzles with diameters ranging from 1 to 12 μm. Microcantilever sensors with either piezoresistive elements or integrated heating elements have been fabricated and applied to measure thrusts, velocities, and heat transfer characteristics of micro/nanojets. Piezoresistive cantilever measurements showed that liquid butane microjets from a 6 μm diameter nozzle achieved velocities 40–60 m/s for driving pressures 0.6–1.4 MPa. Jet velocities estimated from cantilever measurements agreed well with shadowgraphy results within 12.5% without any correction factor. A microcantilever with integrated heating elements measured cooling capacities of liquid butane microjets on the order of 10 −5 W/K.

Quality Control of Coffee Using an Electronic Nose System

An electronic nose system for quality control of coffee is designed and tested. The system uses the Figaro TGS800 series sensors with an integrated heating element. The testing of the system is carried out using different types of coffee where it is proved successful in classifying the tested coffees and actual discrimination of ingredients into different classes[10]. Database based software is designed to interface the built hardware and to process the electronic nose signals before being classified.

"Smart" mobile affinity matrix for microfluidic immunoassays.

There is a current need for simple methods for immobilizing biomolecules within microfluidic channels. Here, a technique is reported for reversibly immobilizing immunoassay components in a channel zone that can be simply controlled by integrated heating elements. Latex beads were modified with the temperature-responsive polymer poly(N-isopropylacrylamide)(PNIPAAm) and co-modified with biotinylated poly(ethylene glycol)(PEG). PNIPAAm undergoes a hydrophilic-to-hydrophobic transition when the temperature is raised above the lower critical solution temperature (LCST)( approximately 28 degrees C in the solutions used here). This reversible transition drives the aggregation and dis-aggregation of the modified beads in heated zones within poly(ethylene terephthalate)(PET) microchannels. Biotinylated monoclonal antibodies for the drug digoxin were bound via streptavidin to the biotin-PEG-coated beads. These antibody-functionalized beads were then reversibly immobilized by aggregation and hydrophobic adhesion to the surface of PET microfluidic channels in response to a thermal stimulus. The antibodies on the beads immobilized in the channel were shown to bind digoxin and a competitor fluorescent ligand from a flow stream in a quantitative competitive assay format that reported the digoxin concentration. The antibodies could be replenished for each immunoassay trial, using the reversible, temperature-controlled immobilization process. This technique allows reagent immobilization immediately prior to an analytical procedure, following the removal of previously utilized beads, guaranteeing fresh and active immobilized biomolecules. Furthermore, it provides a simple approach to multiplexing through the simultaneous or sequential injection of different antibody-coated bead species, potentially at multiple sites in the integrated device channels.

Ceramic sol–gel composite coatings for electrical insulation

Electrically insulative alumina and silica-based coatings up to 500 μm in thickness have been deposited on steel substrates using a sol–gel composite technology. Coatings are produced by spray depositing a ceramic paint consisting of fine ceramic powders dispersed in a sol–gel solution to form a coating. Coatings are then dried at 343 K and fired at 723 K to pyrolyze the organic components. A room temperature dielectric strength up to 5000 V AC has been achieved at coating thicknesses as low as 300 μm on a steel substrate. Coatings have been fabricated that pass a ‘hi-pot’ test of 1275 V AC for 1 s at operating temperatures as high as 673 K. These results have been achieved through control of coating microstructure and the elimination of surface porosity. This technology provides cost effective electrical insulation for a wide range of applications including low profile integrated heating elements based on inexpensive steel and aluminum substrate materials.

High-density data storage based on the atomic force microscope

The atomic force microscope (AFM), with its ability to image and modify surfaces on the nanometer scale, offers the potential for simple, compact, high-density data storage devices. At the heart of the technique is a microfabricated cantilever with a sharp tip on the end. Using modern micromachining techniques, it is possible to batch fabricate cantilevers with tips that are sharp on the scale of 100 /spl Aring/. We have pursued a particular AFM storage scheme based on mechanical readback of topographic data using high-frequency piezoresistive silicon cantilevers. Areal densities of 65 Gbit/in/sup 2/ have been demonstrated, with readback rates greater than 10 Mbit/s. Nanoreplication techniques have been used to produce read-only disks. In addition, a write-once scheme was developed that uses integrated heating elements on the cantilevers in order to perform thermomechanical writing on a polymer substrate. Considerable progress has been made in addressing critical issues such as data rate, reliability, and practical implementation, but significant challenges still remain, both in the technology and in finding the most suitable applications.

Laser patterning of thin-film electrochemical gas sensors

We have patterned a CO2 thin film electrochemical sensor using Xe laser ablation of Pt, Nasicon and Na2CO3 thin films. A thin metallic absorbing layer on Nasicon is used to achieve reproducible ablation of the ionic conductor with no piercing of the buried Pt electrode. Processing conditions are 10 J/cm2 pulses with a scanning velocity of 500 μm/s for Pt and 6.3 J/cm2 pulses with a scanning velocity of 100 μm/s for Nasicon. Nasicon is ablated in the form of flakes suggesting an ablation in the solid phase. Fabrication of an integrated heating element and a micro-thermometer by laser ablation is also presented.

A new microstructured silicon substrate for ultrathin gas-sensitive films

Microstructured substrates featuring interdigitated electrodes with a high length-to-width ratio allow the evaluation of thin films with very high sheet resistivity even in environments with large electromagnetic interference. However, thin phthalocyanine (Pc) films vacuum evaporated on substrates with conventional interdigitated (ID) electrodes deposited on top of a planar surface, develop cracks at the edges of the contact stripes. For samples with a film thickness of 200 monolayers (ML) corresponding to 80 nm this causes a resistance two orders of magnitude higher than expected for the chosen length-to-width ratio. A new microstructured Si substrate with in-plane interdigitated (IPID) electrodes is designed to achieve minimum height differences on the surface. This substrate features interdigitated electrodes with a length-to-width ratio of 52 000:1 and, additionally, an integrated heating element and a temperature-sensitive resistor. Thin Pc films with various thicknesses between 50 ML ( = 20 nm) and 500 ML ( = 200 nm) exhibit sheet resistivities as were expected for the chosen length-to-width ratio. These sensing elements were successfully employed in the detection of diesel exhaust gases in ambient air and they have proven their stability and sensitivity in polluted air during several months.

In-plane interdigitated (IPID) electrodes for thin film applications

Microstructured substrates featuring interdigitated electrodes with a large length to width ratio allow the evaluation of thin films with very high sheet resistivity even in environments with large electromagnetic interference. However thin phthalocyanine (Pc) films, vacuum evaporated on substrates with conventional interdigitated (ID) electrodes deposited on top of a planar surface, develop cracks at the edges of the contact stripes. For samples with a film thickness of 200 monolayers (ML) corresponding to 80 nm this causes a resistance two orders of magnitude higher than that expected for the chosen length to width ratio. A new microstructured Si-substrate with in-plane interdigitated (IPID) electrodes has been designed to achieve minimum height differences on the surface. This substrate features interdigitated electrodes with a length to width ratio of 52,000:1 and additionally an integrated heating element and a temperature sensitive resistor. Thin Pc-films with various thicknesses between 50 ML (=20 nm) and 500 ML (=200 nm) exhibit sheet resistivities as were expected for the chosen length to width ratio. These sensing elements were successfully employed in the detection of NOx emissions in cars and their stability and sensitivity have been proved over several months in polluted air.