Microheater

About: Microheater is a research topic. Over the lifetime, 814 publications have been published within this topic receiving 12478 citations.

Fabrication and integration of metal oxide nanowire sensors using dielectrophoretic assembly and improved post-assembly processing

Abstract: We report the fabrication and integration of metal oxide nanowire sensors using dielectrophoretic assembly and a novel bonding process. Metal oxide nanowires were successfully prepared by a two-step thermal oxidation process from their corresponding metal nanowires (indium, tin, and indium–tin) that have been synthesized by electroplating in nanoporous templates. Before oxidation, dielectrophoretic (DEP) assembly and a novel post-assembly bonding process were applied to integrate high-density nanowire arrays on interdigitated microelectrodes. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS) elemental analysis provide morphological and compositional informations of the metal and metal oxide nanowires. Electrical measurements of the nanowire arrays show how the resistance changed after each process, which demonstrates that the post-assembly bonding is an important and effective step in reducing contact resistance between the nanowires and interdigitated microelectrodes. Metal oxide nanowire sensor chips were fabricated using microelectrodes embedded with a microheater for temperature control. The performance of these metal oxide nanowire sensors was investigated towards common volatile organic compounds, including methanol, ethanol, isopropanol, acetone, chloroform, and benzene, and the sensors showed high sensitivity, fast response, and good repeatability. The assembly and improved post-assembly bonding processes developed in this research provide a new platform for nanowire-based sensor integration.

Flexible NO 2 gas sensor using multilayer graphene films by chemical vapor deposition

Abstract: We report a highly sensitive NO2 gas sensor based on multi-layer graphene (MLG) films synthesized by a chemical vapor deposition method on a microheater-embedded flexible substrate. The MLG could detect low-concentration NO2 even at sub-ppm (<200 ppb) levels. It also exhibited a high resistance change of ~6% when it was exposed to 1 ppm NO2 gas at room temperature for 1 min. The exceptionally high sensitivity could be attributed to the large number of NO2 molecule adsorption sites on the MLG due to its a large surface area and various defect-sites, and to the high mobility of carriers transferred between the MLG films and the adsorbed gas molecules. Although desorption of the NO 2 molecules was slow, it could be enhanced by an additional annealing process using an embedded Au microheater. The outstanding mechanical flexibility of the graphene film ensures the stable sensing re sponse of the device under extreme bending stress. Our large-scale and easily reproducible MLG films can provide a proof-of-concept for future flexible NO 2 gas sensor devices.

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.

Sensitive and Low-Power Metal Oxide Gas Sensors with a Low-Cost Microelectromechanical Heater.

Abstract: In this study, a simple and cost-effective metal oxide semiconductor (MOS) gas sensor, which can be fabricated utilizing only two photolithography steps, was designed and developed through the planar microelectromechanical systems (MEMS) technique. Ball-milled porous tin dioxide nanoparticle clusters were precisely drop-coated onto the integrated microheater region and subsequently characterized using a helium ion microscope (HIM). The spatial suspension of the silicon nitride platform over the silicon substrate provides superior thermal isolation and thus dramatically reduces the power consumption of the microheater. The well-designed microheater exhibits excellent thermal uniformity, which was verified both computationally and experimentally. The as-fabricated sensors were tested for ethanol gas sensing at various operating temperatures with different concentrations. At the optimal work temperature of ∼400 °C, our gas sensors demonstrated a respectable sensitivity to 1 ppm ethanol, which is the lower detection limit to most commercial products. Moreover, stable performance over repetitive testing was observed. The innovative sensor developed here is a promising candidate for portable gas sensing devices and various other commercial applications.