Low-power Gas Research Articles

Fabrication and packaging of MEMS based platform for hydrogen sensor using ZnO–SnO2 composites

Thin films of metal-oxide with integrated microheater on micromachined silicon substrate have attracted great deal of interest towards the development of extremely small and highly sensitive gas sensor. Fabrication of MEMS microheater which is the key component for the development of low power gas sensor is reported here. The microheater is fabricated in a novel co planer fashion where the heating element and the inter-digitated electrode are place side by side. The fabricated device is structurally and electrically characterized by SEM and I---V measurements. Using ZnO---SnO2 composite material, hydrogen sensor was constructed on the microheater platform. A suitable package for encapsulating the fabricated device is designed and the device was successfully mounted on it. The sensing behavior of the packaged sensor is performed by exposing the sensor to hydrogen.

Towards a fully printed electrochemical NO2 sensor on a flexible substrate using ionic liquid based polymer electrolyte

An electrochemical amperometric nitrogen dioxide sensor with solid polymer electrolyte was fabricated by means of screen printing technology on both rigid and flexible substrates. The sensor concept is based on a semi-planar, three-electrode topology that enables low power, high performance, thin, and selective gas sensors to be produced on poly(ethylene terephthalate) (PET) and/or Kapton foil. The sensor response mechanism, i.e. the reduction of nitrogen dioxide at the boundary of a solid polymer electrolyte/working electrode/gas analyte, was predicted by using a Langmuir adsorption isotherm. It was demonstrated that a new platform for the electrochemical NO2 sensor can be completely manufactured by screen printing, which allows the fabrication of a flexible and low cost device suitable for mass production. Further, it was demonstrated that the fully printed sensor can be fabricated without using metal-based printing pastes, which is important from the point of view of the environment. The fully-printed, metal-free electrochemical sensor exhibited a linear response in the range of 0–10ppm, fast response/recovery times (70/60s, respectively), a resolution of 0.2ppm, and a sensitivity of 590nA/ppm, which enables the sensor to be used for both the monitoring of NO2 exposure in the workplace as well as environmental air pollution.

Fast response integrated MEMS microheaters for ultra low power gas detection

Semiconducting metal oxide (SMO) gas sensors typically operate at a few hundred degrees Celsius and consume hundreds of milliwatts of power, limiting their application in battery-powered devices. An analytical model is presented for the optimization of the heater dimensions, which suggests the minimal power consumption is achieved when heat loss through air conduction and supporting beam conduction are equal. We demonstrate micromachined SMO sensors with optimized microheaters, which consume only ∼2mW of power when operated continuously at 300°C. We also measure an ultra-fast thermal response time of 33μs via a transient temperature–resistivity response method. The short response time allows the heaters to be operated in ultra-short pulsing mode decreasing the average power consumption to the μW level. These micromachined SMO sensors are used in proof-of-principle experiments as ultralow power hydrogen sulfide SMO gas sensors.

Locally Grown SnO2 NWs as Low Power Ammonia Sensor

Localized growth of SnO2 nanowires on top of CMOS compatible micromembranes that incorporate a buried heater and prepatterned interdigitated electrodes has been achieved that presents the advantage that it allows to easily and directly integrate the advantageous properties of quasi-one dimensional structures in an advanced electronic device by a Vapor Liquid Solid (VLS) mechanism. A NWs based sensor of this type is characterized as a low power gas sensor towards NH3 at different temperatures. Stable and reproducible response is obtained, that allows detecting concentrations below the time-weighted average exposure limit for 8h.

A Low-cost Approach to Low-power Gas Sensors Based on Self-Heating Effects in Large Arrays of Nanostructures

The usual operation of a conductometric sensor device requires of an external energy source (i.e. an embedded heater). In the last years, the Joule effect in the sensing material, the so called self-heating effect, offered and alternative method to provide this energy: the probing current (or voltage) applied to measure the sensor signal also serves to heat up the sensor active film. Here, evidences of self-heating effects occurring on large arrays of nanostructures fabricated with low-cost methods are provided. The methodology is proven to be suitable to sense gases (humidity, NH3 and NO2) with low-powered heater-free devices.

Fast, Versatile, and Low-Cost Interface Circuit for Electrochemical and Resistive Gas Sensor

Chemical sensors for gas detection nowadays are widely used in several applications; basically, electrochemical sensors and semiconductor devices are used for this purpose. In both cases, the sensor value estimation is usually implemented as a current measurement and they are often referred as current-output sensors. In this paper, a versatile and low-cost interface circuit for such kind of sensors is presented. The proposed solution is characterized by a wide measurement range, yielding flexibility of use with sensors showing different baseline values. In addition, the fast readout time, on the order of tens of milliseconds, guarantees an accurate acquisition of the sensor data even in presence of fast transients, for example when using sensors operated in pulsed thermal regimes. The front-end works with a single-voltage power supply and furnishes a time-coded digital output signal, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process, data elaboration, and presentation. Simplicity and compactness of the electronic interface make possible the integration in a single-chip solution, together with the digital electronics. Reproducibility of the circuit, for applications requiring the simultaneous acquisition of multiple sensors, is furthermore facilitated. The proposed approach has been validated with experimental tests conducted on a discrete component prototype. The system characterization has shown a maximum linearity error in the estimation of the sensor current or resistance of ~ 5% over a measurement range of seven decades; the measurement time is in all the considered input range. Fast thermal transients of different semiconductor sensors for gas sensing have been successfully acquired, demonstrating the validity of the proposed approach. Power dissipation ( at 3.3 V) and the front-end cost ( ~ 10 $) make the presented solution suitable for the employment in low-cost and low-power gas detection systems.

Artificial Neural Network–Based System Identification for a Single-Shaft Gas Turbine

During recent decades, artificial intelligence has been employed as a powerful tool for identification of complex industrial systems with nonlinear dynamics, such as gas turbines (GT). In this study, a methodology based on artificial neural network (ANN) techniques was developed for offline system identification of a low-power gas turbine. The processed data was obtained from a SIMULINK model of a gas turbine in matlab environment. A comprehensive computer program code was generated and run in matlab for creating and training different ANN models with feed-forward multilayer perceptron (MLP) structure. The code consisted of various training functions, different number of neurons as well as a variety of transfer (activation) functions for hidden and output layers of the network. It was shown that the optimal model for a two-layer network with MLP structure consisted of 20 neurons in its hidden layer and used trainlm as its training function, as well as tansig and logsid as its transfer functions for the hidden and output layers. It was also observed that trainlm has a superior performance in terms of minimum mean squared error (MSE) compared with each of the other training functions. The resulting model could predict performance of the system with high accuracy. The methodology provides a comprehensive view of the performance of over 18,720 ANN models for system identification of the single-shaft gas turbine. One can use the optimal ANN model from this study when training from real data obtained from this type of GT. This is particularly useful when real data is only available over a limited operational range.

Temperature compensated CMOS ring VCO for MEMS gas sensor

This paper presents a CMOS voltage controlled ring oscillator with temperature compensation circuit suitable for low-cost and low-power gas sensor. To operate at low frequency, a control voltage generated by a CMOS bandgap reference is described and the measurement results of the fabricated chips are presented. The output voltage of the reference is set by resistive subdivision. In order to achieve small area and low power consumption, n-well resistors are used. This design features a reference voltage of 1 V. The chip is fabricated in AMS 0.35 μm CMOS process with an area of 0.032 mm2. Operating at 1.25 V, the output frequency is within 200 ± l0 kHz over the temperature range of −25 to 80 °C with a power consumption of 810 μW.

Low power gas discharge plasma mediated inactivation and removal of biofilms formed on biomaterials

The antibacterial activity of gas discharge plasma has been studied for quiet some time. However, high biofilm inactivation activity of plasma was only recently reported. Studies indicate that the etching effect associated with plasmas generated represent an undesired effect, which may cause live bacteria relocation and thus contamination spreading. Meanwhile, the strong etching effects from these high power plasmas may also alter the surface chemistry and affect the biocompatibility of biomaterials. In this study, we examined the efficiency and effectiveness of low power gas discharge plasma for biofilm inactivation and removal. Among the three tested gases, oxygen, nitrogen, and argon, discharge oxygen demonstrated the best anti-biofilm activity because of its excellent ability in killing bacteria in biofilms and mild etching effects. Low power discharge oxygen completely killed and then removed the dead bacteria from attached surface but had negligible effects on the biocompatibility of materials. DNA left on the regenerated surface after removal of biofilms did not have any negative impact on tissue cell growth. On the contrary, dramatically increased growth was found for these cells seeded on regenerated surfaces. These results demonstrate the potential applications of low power discharge oxygen in biofilm treatments of biomaterials and indwelling device decontaminations.

A robust platform for textile integrated gas sensors

Fabrication, textile integration and post-weaving characterization of a robust platform for monolithically integrated, low-power gas and temperature sensing are presented. The platform, consisting of an interdigitated planar capacitor for gas sensing and a resistive temperature sensor, is fabricated on a 50 μm thick flexible Kapton E® film using a simple roll-to-roll compatible process, and particularly targets disposable textile products, such as smart air filters, and medical garments. In order to demonstrate the versatility of the platform, the sensors are functionalized for humidity sensing by spray-coating of a 10 μm thick Cellulose Acetate Butyrate (CAB) polymer layer. In commercial machine weaving processes, any functional device undergo significant mechanical deformation, mostly due to high bending, and shear forces associated with the process. Bending radii in textiles can be as small as 165 μm during weaving, corresponding to a strain of about 15%. This imposes stringent mechanical requirements on the textile integrated sensors. Furthermore, the sensors integrated in textiles are exposed to harsh physical and chemical environments during operation. To avoid device failure, the sensor active area is fully encapsulated for protection during singulation, weaving, and operation, and is demonstrated to retain full functionality after weaving and repeated strain and stress tests. Despite the simple sensor structure, rapid and accurate sensor response is demonstrated in differential sensing mode.

Dielectric barrier discharge micro-plasma emission source for the determination of thimerosal in vaccines by photochemical vapor generation

A fast, simple and green approach to direct determinate thimerosal in vaccines by photochemical vapor generation (PVG) coupled to optical emission spectrometry (OES) using dielectric barrier discharge (DBD) as excitation/emission source was described in this paper. With the exception of dilution and formic acid addition, the sample was not subjected to other treatment. This method eliminated the need for using strong oxidizing conditions and conventional chemical reducing agents. In addition, the DBD micro-plasma emission source was operated with low power (≤18W) and low gas consumption (120mLmin−1). A sample throughput of 30h−1 was obtained with the proposed flow injection-PVG-DBD-OES. The main operation parameters and the potential interferences affecting the determination were investigated. The detection limits for Hg2+ and thimerosal (as Hg) were calculated to be 0.19μgL−1 and 0.17μgL−1. Repeatability, expressed as the relative standard deviation of the spectral peak height, was 0.99% (n=11) and 1.9% (n=11) for 20μgL−1 Hg2+ and thimerosal standard, respectively. The proposed method was successfully applied to the analysis of commercial vaccines. All these results demonstrated that PVG-DBD-OES could provide a green way for the rapid detection of thimerosal in vaccines.

Zinc Oxide Nanowires Deposited on Polymeric Hotplates for Low-power Gas Sensors

Zinc oxides (ZnO) nanowires were successfully deposited on plastic low-power micro-hotplates using the thermal oxidation technique. Metallic zinc layer was deposited on the sensing transducer by RF magnetron sputtering and then oxidized in a controlled atmosphere in order to obtain ZnO nanostructures. Morphological investigations confirmed the nanometric dimensions of the fabricated nanostructures. The n-type behavior of the nanostructured material was evaluated towards different chemical species to highlight the electrical properties of the materials. Calibration curves for the detection of several chemical species were defined. © 2012 The Authors. Published by Elsevier Ltd.

Scalable Fabrication of Individual SWNT Chem-FETs for Gas Sensing

Abstract We present a scalable, Deep-UV (220 nm) photolithography based process for fabricating low-power gas sensors integrating an individual single-walled carbon nanotube (SWNT) as a sensing element. SWNTs grow from defined catalyst (ferritin) islands, and their density is controlled by controlling the catalyst particle density. By designing the electrode dimensions based on the length distribution of SWNTs, a single-SWNT bridging yield of 30% has been achieved. Furthermore, we show that exposure to NO2 at room temperature results in a positive shift of the threshold voltage. A threshold shift of approximately 2 V for 500 ppb of NO2 is observed. The presented process also enables the possibility of fabricating carbon nanotube sensor arrays, as a large number of single-tube devices can be fabricated in each process run.

Flexible and Low-cost Interface Circuit for Electrochemical and Resistive Gas Sensors

This work presents a low-cost interface circuit for both electrochemical and semiconductor sensors for gas detection. The proposed circuit offers a high sampling rate, on the order of 25 ms, allowing the monitoring of the sensor behaviour even in presence of fast transients. The front-end has a single-voltage 3.3 V power supply and a time-coded digital signal output, thus it is suitable to be directly interfaced to a microcontroller for the management of the measurement process. Possible integration in a single-chip solution, together with the digital electronics is furthermore facilitated. Experimental results, conducted on a discrete component prototype and with sample resistors to emulate the sensor, have shown a maximum linearity error in the estimation of the sensor current or resistance of about 5% over a measurement range of seven decades, demonstrating the validity of the proposed solution. The power dissipation of the front-end is less than 30 mW (at 3.3 V) and the front-end cost less than 10 EUR, making it suitable for the employment in low-cost and low-power gas detection systems.

Decomposition of Ethanol in a Surface Wave Discharge at Atmospheric Pressure

Surface wave discharges at atmospheric pressure for synthesis processes are attractive since low power and flow gas are required; in addition, no catalyst is necessary. These features have been used to develop a process for hydrogen production using ethanol as a reagent. Different plasma gas flows have been used, resulting in a different magnitude of alcohol decomposition. Images of the resulting plasmas are presented.

Adaptation of small capacity natural gas engine for producer gas operation

This article addresses the adaptation of a low-power natural gas engine for using producer gas as a fuel. The 5.9 L natural gas engine with a compression ratio of 10.5:1, rated at 55 kW shaft power, delivered 30 kW using producer gas as fuel in the naturally aspirated mode. Optimal ignition timing for peak power was found to be 20° before top dead centre. Air-to-fuel ratio (A/F) was found to be 1.2 ± 0.1 over a range of loads. Critical evaluation of the energy flows in the engine resulted in identifying losses and optimizing the engine cooling. The specific fuel consumption was found to be 1.2 ± 0.1 kg of biomass per kilowatt hour. A reduction of 40 per cent in brake mean effective pressure was observed compared with natural gas operation. Governor response to load variations has been studied with respect to frequency recovery time. The study also attempts to adopt a turbocharger for higher power output. Preliminary results suggest a possibility of about 30 per cent increase in the output.

Design and Fabrication of Low-Power Planar Type Gas Sensor

In this paper we describe the fabrication steps and the implementation of a planar type gas sensing applications with suspended structure, which presents very low power consumption. Simulations with the finite element model tool show homogeneous temperature distribution across the sensitive film. The device attached with a spin-coated thin layer of SnO2 showed a reasonable sensing performance to hydrogen.

A System for the Dynamic Control and Thermal Characterization of Ultra Low Power Gas Sensors

This paper describes a system for the simultaneous dynamic control and thermal characterization of the heating and cooling phases of an ultralow-power (ULP) micromachined sensor, featuring thermal characteristics that are quite similar to those of innovative ULP semiconducting metal-oxide gas sensors. A pulsewidth-modulated (PWM) excitation system has been realized using a microcontroller featuring an ARM7 core to characterize the thermal behavior of a device formed by a Pt microheater and a Pt temperature sensor, over an insulating membrane. Three operating modes, i.e., constant target heater resistance, constant heating power, and cooling phase monitoring, were implemented. Objectives of the research were to analyze the relation between the time period and duty cycle of the PWM signal and the operating temperature of such ULP micromachined systems, to observe the thermal time constants of the device during the heating and cooling phases, and to measure the total thermal conductance. Experiments indicated that an approximately constant heater temperature in the constant target heater resistance regime (i.e., after the initial thermal transient due to the heating algorithm) can only be obtained if the time period of the heating signal is smaller than 50 μs, i.e., much faster than the time constant of the device. Constant power experiments show quantitatively a unique time constant τ for both the heater and the temperature sensor (T-sensor) in the heating phase (with a known applied power) and the cooling phase (with zero power). This time constant decreases during heating in a range of 2.3-2 ms as a function of an increasing temperature rise Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> between the ambient and the operating temperature. Moreover, we observed that, in the chosen operating temperature range, the thermal conductance is a linear function of Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> . Finally, repeatability of experimental results was assessed by guaranteeing that the standard deviation of the controlled temperature was within ±5.5°C in worst-case conditions.

Comparison of gas sensor technologies for fire gas detection

We selected a variety of low-power gas sensors in order to compare their performance with respect to fire detection applications. Gas sensitive field effect transistor (GasFET)-arrays, metal oxide sensors (MOS) and electrochemical cells (EC) were measured in test fire scenarios. Beside the investigation of the performance of the sensor elements itself, we additionally focused on the propagation behavior of different gas components in time and space. For that case we mounted the gas sensors on PCBs which were setup into a vertical “multi-sensor” chain. Comparing the response times at the ceiling, the MOS were the fastest sensors. However they are prone to false alarms due to cross sensitivities to solvent vapors. The response of the GasFET-array was slower but shows advantages with respect to low power consumption and pattern recognition capabilities. The EC carbon monoxide sensor has a good selectivity but a high price comparing to semiconductors. This paper demonstrates the usability of gas sensor technologies for fire detection to enhance the performance of conventional smoke detectors.

Hybrid integration of microfabricated chemοcapacitor arrays with miniaturized read-out electronics towards low-power gas sensing module

A hybrid gas sensing module consisting of an array of 8 polymer coated capacitive sensors and low power read-out electronics is introduced. The chemocapacitor array is fabricated with standard microelectronics/micromachining processes allowing for the realization of planar InterDigitated Electrodes (IDEs). The read-out electronics sub- module consists of an analog multiplexer for the sequential measurement of the sensor array elements, a capacitance to 24-bit converter and a USB to I2C interface. The compact hybrid module has been successfully applied in the detection of sub-100ppm concentrations of p-xylene and toluene. The responses to various humidity levels have been also evaluated.