Showing papers on "Microheater published in 2021"

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.

ITO-based microheaters for reversible multi-stage switching of phase-change materials: towards miniaturized beyond-binary reconfigurable integrated photonics.

Abstract: Inducing a large refractive-index change is the holy grail of reconfigurable photonic structures, a goal that has long been the driving force behind the discovery of new optical material platforms Recently, the unprecedentedly large refractive-index contrast between the amorphous and crystalline states of Ge-Sb-Te (GST)-based phase-change materials (PCMs) has attracted tremendous attention for reconfigurable integrated nanophotonics Here, we introduce a microheater platform that employs optically transparent and electrically conductive indium-tin-oxide (ITO) bridges for the fast and reversible electrical switching of the GST phase between crystalline and amorphous states By the proper assignment of electrical pulses applied to the ITO microheater, we show that our platform allows for the registration of virtually any intermediate crystalline state into the GST film integrated on the top of the designed microheaters More importantly, we demonstrate the full reversibility of the GST phase between amorphous and crystalline states To show the feasibility of using this hybrid GST/ITO platform for miniaturized integrated nanophotonic structures, we integrate our designed microheaters into the arms of a Mach-Zehnder interferometer to realize electrically reconfigurable optical phase shifters with orders of magnitude smaller footprints compared to existing integrated photonic architectures We show that the phase of optical signals can be gradually shifted in multiple intermediate states using a structure that can potentially be smaller than a single wavelength We believe that our study showcases the possibility of forming a whole new class of miniaturized reconfigurable integrated nanophotonics using beyond-binary reconfiguration of optical functionalities in hybrid PCM-photonic devices

A rapid and controllable acoustothermal microheater using thin film surface acoustic waves

Abstract: Temperature control within a microreactor is critical for biochemical and biomedical applications. Recently acoustothermal heating using surface acoustic wave (SAW) devices made of bulk LiNbO3 substrates have been demonstrated. However, these are generally fragile and difficult to be integrated into a single lab-on-a-chip. In this paper, we propose a rapid and controllable acoustothermal microheater using AlN/Si thin film SAWs. The device’s acoustothermal heating characteristics have been investigated and are superior to other types of thin film SAW devices (e.g., ZnO/Al and ZnO/Si). The dynamic heating processes of the AlN/Si SAW device for both the sessile droplet and liquid within a polydimethylsiloxane (PDMS) microchamber were characterized. Results show that for the sessile droplet heating, the temperature at a high RF power is unstable due to significant droplet deformation and vibration, whereas for the liquid within the microchamber, the temperature can be precisely controlled by the input power with good stability and repeatability. In addition, an improved temperature uniformity using the standing SAW heating was demonstrated as compared to that of the travelling SAWs. Our work shows that the AlN/Si thin film SAWs have a great potential for applications in microfluidic heating such as accelerating biochemical reactions and DNA amplification.

Pt Nanostructures Fabricated by Local Hydrothermal Synthesis for Low-Power Catalytic-Combustion Hydrogen Sensors

Abstract: Hollow, microrod-like Pt nanostructures are locally synthesized on a small, suspended microheater platform (9 μm × 110 μm) as the catalytic layer of a low-power hydrogen (H2) catalytic combustion s...

Low-power thermocatalytic hydrogen sensor based on electrodeposited cauliflower-like nanostructured Pt black

Abstract: A thermocatalytic hydrogen (H2) gas sensor based on pseudo-porous networks of cauliflower-like nanostructured Pt crystals (Pt black), as the catalytic material, has been fabricated through electrodeposition onto a strip-type suspended microheater (9 μm × 110 μm) for low power sensor operation (8 mW) and fast response speed (1.8 s). The electroplating parameters (solution concentration, current strength, and time) have been tuned for maximum sensitivity and an ionic solution of platinic acid with lead acetate has been used for high adhesion of the catalytic layer. The high catalytic activity of the Pt black, small size of the device, and highly localized electroplating method used allow for sensitive H2 detection: ∼0.75% resistance change per %H2 and an estimated 75-ppm lower limit of detection. Additionally, the sensor shows high selectivity against other flammable gases, while consuming much lower power than the commercial catalytic combustion based H2 sensors. The low power consumption attained in this work is expected to help in the constant need for miniaturization of portable devices using catalytic gas sensor for selective detection in industry and for personalized applications.

MEMS hydrogen gas sensor for in-situ monitoring of hydrogen gas in transformer oil

Abstract: Dissolved hydrogen gas analysis (DHGA) is a key aspect that defines the operational status of a transformer and is vital to the maintenance of safety standards in the power grid. In this report, we proposed, MEMS gas sensor arrays for DHGA with a specially designed system having a Wheatstone bridge circuitry with two pairs of resistors. The optimal temperature of the sensor was controlled using a monolithically integrated in-plane microheater and a temperature sensor to monitor the temperature change in the oil and to compensate for the temperature variations in resultant hydrogen sensor signals. The fabricated sensor in a transformer oil showed excellent H2 response (ΔVout = 62μV to 10 ppm and 4.71 mV to 2000 ppm). In addition, long-term stability of sensor performance was observed, confirming that the Al2O3 passivation layer and packaging were effective to enhance the robustness of the sensor in an oil environment. A customized, compact, and portable sensor interface electronics was developed and applied to the sensor system. The results obtained with the developed sensor interface were very similar to those measured with a digital multimeter. Our results demonstrate that the developed sensor system and packaging are very promising for long term monitoring of the operational status of transformers.

Optimization of a Low-Power Chemoresistive Gas Sensor: Predictive Thermal Modelling and Mechanical Failure Analysis.

Abstract: The substrate plays a key role in chemoresistive gas sensors. It acts as mechanical support for the sensing material, hosts the heating element and, also, aids the sensing material in signal transduction. In recent years, a significant improvement in the substrate production process has been achieved, thanks to the advances in micro- and nanofabrication for micro-electro-mechanical system (MEMS) technologies. In addition, the use of innovative materials and smaller low-power consumption silicon microheaters led to the development of high-performance gas sensors. Various heater layouts were investigated to optimize the temperature distribution on the membrane, and a suspended membrane configuration was exploited to avoid heat loss by conduction through the silicon bulk. However, there is a lack of comprehensive studies focused on predictive models for the optimization of the thermal and mechanical properties of a microheater. In this work, three microheater layouts in three membrane sizes were developed using the microfabrication process. The performance of these devices was evaluated to predict their thermal and mechanical behaviors by using both experimental and theoretical approaches. Finally, a statistical method was employed to cross-correlate the thermal predictive model and the mechanical failure analysis, aiming at microheater design optimization for gas-sensing applications.

A Highly Sensitive and Stable rGO:MoS2-Based Chemiresistive Humidity Sensor Directly Insertable to Transformer Insulating Oil Analyzed by Customized Electronic Sensor Interface.

Abstract: Reduced graphene oxide and molybdenum disulfide (rGO:MoS2) are the most representative two-dimensional materials, which are promising for a humidity sensor owing to its high surface area, a large number of active sites, and excellent mechanical flexibility. Herein, we introduced a highly sensitive and stable rGO:MoS2-based humidity sensor integrated with a low-power in-plane microheater and a temperature sensor, directly insertable to transformer insulating oil, and analyzed by a newly developed customized sensor interface electronics to monitor the sensor's output variations in terms of relative humidity (RH) concentration. rGO:MoS2 sensing materials were synthesized by simple ultrasonication without using any additives or additional heating and selectively deposited on titanium/platinum (Ti/Pt) interdigitated electrodes on a SiO2 substrate using the drop-casting method. The significant sensing capability of p-n heterojunction formation between rGO and MoS2 was observed both in the air and transformer insulating oil environment. In air testing, the sensor exhibited an immense sensitivity of 0.973 kΩ/%RH and excellent linearity of ∼0.98 with a change of humidity from 30 to 73 %RH, and a constant resistance deviation with an inaccuracy rate of 0.13% over 400 h of continual measurements. In oil, the sensor showed a high sensitivity of 1.596 kΩ/%RH and stable repeatability for an RH concentration range between 34 and 63 %RH. The obtained results via the sensor interface were very similar to those measured with a digital multimeter, denoting that our developed total sensor system is a very promising candidate for real-time monitoring of the operational status of power transformers.

Well-connected ZnO nanoparticle network fabricated by in-situ annealing of ZIF-8 for enhanced sensitivity in gas sensing application

Abstract: Low-power microheater platforms are promising in lowering power consumption during gas sensing processes. However, the small amount of activated-material and poor electrical contact greatly affect the sensitivity. Here, via in-situ annealing of a porous metal organic framework (MOF), ZIF-8, using a miniature heater electrode with a fast ramp rate (ca. 60 °C/s), we demonstrate the formation of a well-connected nanoparticle network with high porosity. Nanoparticle networks prepared in-situ exhibit significantly enhanced response to ethanol, defined as the ratio of sensor’s resistance before and after gas exposure, compared to ex-situ annealed counterparts (>10 times larger response) and to commercially available nanoparticles (∼4 times larger response) at a sensing temperature of 250 °C. The mechanism of the enhanced performance is studied using AC impedance spectroscopy. The results indicate that the large number of highly accessible and effective adsorption sites on the in-situ annealed material are responsible for the enhancement.

Coupling-Controlled Multiport Thermo-Optic Switch Using Polymer Waveguide Array

Abstract: A multiport thermo-optic switch based on parallel polymer waveguides and microheater array is proposed. The basic unit is a $1\times3$ switch for Up Transfer, Isolation, and Down Transfer operations. By introducing refractive index perturbation along the selected waveguides through microheaters, the Transfer /Isolation condition can be switched locally, and light is then steered into different paths. A $1\times5$ switch is demonstrated experimentally as an example. Colorless ( $1.50~\mu \text{m}$ to $1.62~\mu \text{m}$ ) and polarization independent operation is achieved with crosstalk suppression ratio larger than 10 dB, which can be further optimized. The design requires less waveguides and tuning sections than conventional Mach-Zehnder interferometer-based switches. 6 microheaters are placed but only 3 need to be powered on simultaneously to reach any of the 5 output ports. The maximal heater power is 33.8 mW over a coupling length of $1331.6~\mu \text{m}$ . This design can easily scale up to form an arbitrary cascaded M $\times1$ and $1\times $ N switch network for high-density photonic integration.

Free-standing, thin-film sensors for the trace detection of explosives.

Abstract: In a world focused on the development of cybersecurity, many densely populated areas and transportation hubs are still susceptible to terrorist attacks via improvised explosive devices (IEDs). These devices frequently employ a combination of peroxide based explosives as well as nitramines, nitrates, and nitroaromatics. Detection of these explosives can be challenging due to varying chemical composition and the extremely low vapor pressures exhibited by some explosive compounds. No electronic trace detection system currently exists that is capable of continuously monitoring both peroxide based explosives and certain nitrogen based explosives, or their precursors, in the vapor phase. Recently, we developed a thermodynamic sensor that can detect a multitude of explosives in the vapor phase at the parts-per-trillion (ppt) level. The sensors rely on the catalytic decomposition of the explosive and specific oxidation-reduction reactions between the energetic molecule and metal oxide catalyst; i.e. the heat effects associated with catalytic decomposition and redox reactions between the decomposition products and catalyst are measured. Improved sensor response and selectivity were achieved by fabricating free-standing, ultrathin film (1 µm thick) microheater sensors for this purpose. The fabrication method used here relies on the interdiffusion mechanics between a copper (Cu) adhesion layer and the palladium (Pd) microheater sensor. A detailed description of the fabrication process to produce a free-standing 1 µm thick sensor is presented.

Laser multifunctional fabrication of metallic microthermal components embedded in fused silica for microfluidic applications

Abstract: Microheaters as tiny in-situ heating elements are of great importance for developing many thermal-sensitive microdevice applications. A facile technique for the fabrication of embedded metallic microheaters, microheater arrays, and microthermal sensors based on the combination of femtosecond laser-assisted chemical etching, electroless plating, and mechanical polishing has been proposed. With the proposed technique, uniform and controllable temperature distributions in the central area of fabricated microheaters have been achieved. Moreover, flexible manipulation of localized temperature in a microheater array as well as precise calibration of microheaters based on a simultaneously integrated microthermal sensor has been demonstrated. Furthermore, precise control of temperature in glass channels and acceleration of a chemical reaction in microfluidics using monolithically integrated microheaters have been realized, showing great potential for developing laser manufacturing of multifunctional thermal-control microfluidic devices.

High-Q-Factor Tunable Silica-Based Microring Resonators

Abstract: A high-Q-factor tunable silica-based microring resonator (MRR) is demonstrated. To meet the critical-coupling condition, a Mach–Zehnder interferometer (MZI) as the tunable coupler was integrated with a racetrack resonator. Then, 40 mW electronic power was applied on the microheater on the arm of MZI, and a maximal notch depth of about 13.84 dB and a loaded Q factor of 4.47 × 106 were obtained. The proposed MRR shows great potential in practical application for optical communications and integrated optics.

Low power perforated membrane microheater

Abstract: Heat loss to the membrane of a microheater is one of the major sources of heat loss in a micro heater. In this paper, we present a low power consuming micro heater. We show that power consumption can be decreased by decreasing heat loss in the supporting membrane on which the heating resistor sits on. We designed a modified structured two beams suspended membrane microheater with a perforated dielectric layer. The test result shows an 18.6 % reduction in power consumption with 15.18mW and a response time of 0.42ms at 400 °C. It was observed to be thermally stable and should provide a good platform for exploitation in the design of commercial MEMS sensors that have microheaters as one of its components.

Direct integration of carbon nanotubes on a suspended Pt microheater for hydrogen gas sensing

Abstract: The gas-sensing equipment experienced a greater demand in different workplace environments owing to its high capability to detect the unburnt poisonous gases in the boilers or analyzing the airborne pollution levels. The recent trend toward achieving an efficient gas sensor depends on the low-power consumption and miniaturization. In addition, emerging nanomaterials have shown great potential toward gas sensing along with their outstanding electrochemical properties. This work aims toward the sensing of hydrogen gas utilizing carbon nanotubes (CNTs) directly integrated onto a Pt microheater. The pristine CNTs detect hydrogen gas through the change in the electrical resistance. The chemical reaction between the hydrogen molecule and CNTs is promoted at high temperatures by utilizing the microheater. The suggested spray-coated CNT layer survives subsequent microfabrication processes, demonstrating a robust integration method of nanomaterials into conventional microelectromechanical systems (MEMS). CNTs integrated Pt microheater is batch fabricated using a microfabrication technique, allowing a high device yield of over 90%. The fabricated gas sensors demonstrate a low power budget of a few mW and owe a fast response time. The temperature is elevated up to 420 °C by supplying 2.19 mW power for gas sensing, and the change in the rate of resistance change reached 1.82% by supplying hydrogen gas of 10% concentration. The response and recovery time from the microheater are found to be 39 and 35 seconds, respectively. Besides, the decrease in drift factor occurs when the sensor operates at too high temperatures. The gas concentration is controlled and simultaneously the rate of resistance change is evaluated which further helps to obtain a LOD value of 1200 ppm. The Raman spectra of CNTs before and after the gas-sensing experiment confirm that there is no change or degradation of the CNTs during the experimental process. The fabricated CNTs integrated Pt microheater-based gas sensor has immense potential toward sensing hydrogen gas.

Photocurrents Recovery in GaN UV Sensors Using Microheaters at Low Temperatures

Abstract: At various low-temperature conditions, it is difficult to obtain an accurate sensing response due to temperature-dependent material properties such as bandgap and resistivity of semiconductors. In this study, a gallium nitride (GaN)-based ultraviolet (UV) photodetector with a microheater was demonstrated to compensate for the low-temperature effects. A parallel-type platinum microheater array was fabricated to supply thermal energy by Joule heating. In addition, a silicon oxide layer was deposited between the heater and the GaN surface, allowing an independent voltage supply. Therefore, the change in the signal level was successfully recovered to the initial state in the temperature range of $-27.4-11.5 ^{\circ }\text{C}$ within ~0.64% error without electrical interference. This study supports an active, accurate, and reliable method for the stable measurement of UV signals in various low-temperature environments such as freezer warehouses, Antarctic research stations, and in space.

Semi-Automatic Lab-on-PCB System for Agarose Gel Preparation and Electrophoresis for Biomedical Applications

Abstract: In this paper, a prototype of a semi-automatic lab-on-PCB for agarose gel preparation and electrophoresis is developed. The dimensions of the device are 38 × 34 mm2 and it includes a conductivity sensor for detecting the TAE buffer (Tris-acetate-EDTA buffer), a microheater for increasing the solubility of the agarose, a negative temperature coefficient (NTC) thermistor for controlling the temperature, a light dependent resistor (LDR) sensor for measuring the transparency of the mixture, and two electrodes for performing the electrophoresis. The agarose preparation functions are governed by a microcontroller. The device requires a PMMA structure to define the wells of the agarose gel, and to release the electrodes from the agarose. The maximum voltage and current that the system requires are 40 V to perform the electrophoresis, and 1 A for activating the microheater. The chosen temperature for mixing is 80 ∘C, with a mixing time of 10 min. In addition, the curing time is about 30 min. This device is intended to be integrated as a part of a larger lab-on-PCB system for DNA amplification and detection. However, it can be used to migrate DNA amplified in conventional thermocyclers. Moreover, the device can be modified for preparing larger agarose gels and performing electrophoresis.

Demonstration of green and UV wavelength high Q aluminum nitride on sapphire microring resonators integrated with microheaters

Abstract: We demonstrate a high Q aluminum nitride (AlN) on sapphire microring resonators at green (532 nm) and ultraviolet (UV) (369.5 nm), which are two important wavelengths for sensing and quantum information processing. The quality factors (Q) of these resonators are characterized using integrated microheaters and based on thermo-optic resonance sweeping around those wavelengths for which tunable lasers are typically less available. We measure a record of high intrinsic Q of 147 000 with a propagation loss of 7.3 dB/cm at 532 nm wavelength, and an intrinsic Q of 25 500 with a propagation loss of 60.4 dB/cm at UV 369.5 nm wavelength. We also investigate the thermal crosstalk between the adjacent resonators when temperature change is applied by the microheater of one of the resonators on the same chip. A large thermal crosstalk and resonance shift are observed on other microring resonators even at millimeter(s) distance away from a microheater. This study provides further insight on the functionalities and capabilities of this promising integrated photonic platform for the ultraviolet (UV) and visible range.

High Sensitivity and Power Efficient Heater Structure for Bulk Micromachined Thermal Accelerometer

Abstract: In MEMS based thermal convective accelerometers, the structure of the constituent microheater plays a crucial role in determining the sensitivity of the accelerometer. This paper reports the sensitivity improvement of a dual axis thermal accelerometer using a cross shaped heater structure. In a conventional heater design, the peak heater temperature generated at the center of the cavity offers lower temperature gradient at the position of the temperature sensors situated afar. As a result, the sensitivity obtainable from the thermal accelerometer becomes low. The sensitivity can be improved by generating the peak temperature at the side arms which are used to suspend the heater structure. This has been accomplished in this work using a cross shaped heater where the peak temperature is generated at the cross arms of the heater. Hence, the temperature gradient is higher near the temperature sensors, leading to improved sensitivity of the accelerometer. The sensitivity achieved using such a cross shaped heater is 0.36 K/g at a peak heater temperature of 615 K and having power requirement of 29.6 mW. The proposed heater structure can also be employed in other microsystem devices like gyroscope and thermal flow sensor for improving their performance.

Gas Sensing with Two-Dimensional Materials Beyond Graphene

Abstract: The semiconductor industry is intensely working towards the functional integration of devices beyond digital logic, such as sensors and RF circuits, on the same chip. For gas sensors, this requires that future devices can be fabricated with the same technologies as future digital logic transistors, likely using mature complementary metal oxide semiconductor (CMOS) fabrication techniques, due to the inherent low costs and scalability they offer. While chemoresistive semiconductor metal oxide (SMO) sensors have garnered significant attention in the last decades, resulting in their commercialization, they require high temperatures to initiate the surface chemical reactions for sensing, meaning that a complex integration of a microheater on a MEMS structure is required. This is not ideal and room temperature solutions are readily sought after. Two-dimensional (2D) materials appear to offer precisely that: Potential for integration with CMOS technology, while also being highly sensitive to many relevant gases at room temperature. This manuscript explores several types of 2D materials which have the potential to be used as channel materials in digital logic transistors and sensing films, due to the presence of a relatively wide band gap. Therefore, this excludes graphene from our discussion and we look into recent gas sensing trends with reduced graphene oxide, transition metal dichalcogenides (TMDs), and phospho-rene and arsenene.

Microfabrication of Metal Oxide Based Gas Sensors

Abstract: Metal Oxide (MOX) materials have attracted a great interest for sensing applications in both chemiresistive and mass sensitive (QCM; quartz crystal microbalance, SAW; surface acoustic wave) types due to their low cost, easy production, and high sensor response against wide range of gases. However, device fabrication is a key issue for the development of sensor technologies in terms of miniaturization, portability, and power consumption. Recently, researchers have been focused on monolithic sensor device platforms which consist of interdigital electrodes (IDEs) and a microheater. They are controlled electronically on the same chip. In this study, we fabricated a sensor device platform by microfabrication techniques. Then, we coated fabricated sensor platforms with vanadium oxide (V2O5) thin film as a gas sensing layer by RF sputtering for the testing of microchips. Structural and morphological characterization of sensing layer was performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Sensing properties against different alcohol groups such as ethanol and isopropanol were discussed.

Microelectromechanical system component or a microfluidic component comprising a free-hanging or free-standing microchannel

Abstract: The invention relates to a microelectromechanical system (MEMS) component or microfluidic component comprising a free-hanging or free-standing microchannel (1), as well as methods for manufacturing such a microchannel, as well as a flow sensor, e.g. a thermal flow sensor or a Coriolis flow sensor, pressure sensor or multi-parameter sensor, valve, pump or microheater, comprising such a microelectromechanical system component or microfluidic component. The MEMS component allows to increase the flow range and/or decrease the pressure drop of for instance a micro Coriolis mass flow meter by increasing the channel diameter, while maintaining its advantages.