Microelectronic Gas Research Articles

Sensing Characterization of Metal Oxide Semiconductor-Based Sensor Arrays for Gas Mixtures in Air

Micro-electronic gas sensor devices were developed for the detection of carbon monoxide (CO), nitrogen oxides (NOx), ammonia (NH3), and formaldehyde (HCHO), as well as binary mixed-gas systems. Four gas sensing materials for different target gases, Pd-SnO2 for CO, In2O3 for NOx, Ru-WO3 for NH3, and SnO2-ZnO for HCHO, were synthesized using a sol-gel method, and sensor devices were then fabricated using a micro sensor platform. The gas sensing behavior and sensor response to the gas mixture were examined for six mixed gas systems using the experimental data in MEMS gas sensor arrays in sole gases and their mixtures. The gas sensing behavior with the mixed gas system suggests that specific adsorption and selective activation of the adsorption sites might occur in gas mixtures, and allow selectivity for the adsorption of a particular gas. The careful pattern recognition of sensing data obtained by the sensor array made it possible to distinguish a gas species from a gas mixture and to measure its concentration.

Microelectronic Gas sensors for Non-invasive Analysis of Exhaled Gases

Interest in the research of small-sized gas sensors (especially semiconductor) for medical applications has sharply increased in recent years. Requirements for to such sensors are their high sensitivity, performance and stability to very low concentrations of gases, mainly exhaled by a living organism. Today the doctor not only polls, and examines the patient but also sends it to the lab-tests of blood, urine, perform an electrocardiogram, etc. But, for example, today’s periodic monitoring of glucose concentrations in the blood induces acute pain, risk of virus (e.g., hepatitis B) infection from needles, and other difficulties in frequent monitoring. Even in 1784, Antoine Lavoisier wrote that of all the phenomena of life, none is more striking and worthier for physicists and physiologists than phenomena accompanying the breath. Meanwhile, one of the most important directions of modern medicine is non-invasive diagnostics of the patient, based on the analysis of exhaled air in a special device.

Microelectronic Gas sensors for Non-invasive Analysis of Exhaled Gases

Microelectronic Gas sensors for Non-invasive Analysis of Exhaled Gases

Microelectronic Gas Resistive Sensor Based on Nanocrystalline Tin Dioxide Films with Terbium and Antimony Additives

The technology of microelectronic resistive gas sensors is considered. Heater and thermistor contacts are formed on an oxidized silicon substrate by sputtering a nichrome film and subsequent photolithography in combination with reactive magnetron sputtering of a nanocrystalline tin dioxide film with terbium and antimony additives. A 1.5 × 1.5 mm sensor requires 90 mW for heating to optimal working temperature of 250–280°C. The sensor has very high sensitivity to alcohols and low sensitivity to benzene and acetone.

Микроэлектронный газовый резистивный сенсор на основе нанокристаллических плёнок диоксида олова с аддитивами тербия и сурьмы

Микроэлектронный газовый резистивный сенсор на основе нанокристаллических плёнок диоксида олова с аддитивами тербия и сурьмы

The Observations of the IR Sensitivity Enhancement, Negative Differential Resistance and Hysteresis in a Microelectronic Gas Discharge Device with GaP

In this paper, some interesting features of a microelectronic gas discharge device with GaP semiconductor are reported. The device is a complicated plasma system with a metal anode and a GaP cathode. A discharge occurs in the micro-scaled gap, when a voltage larger than the breakdown value is applied between these electrodes. Since large region of applied voltages are scanned in the microelectronic gas discharge device, both Townsend and glow regimes are clearly observed and a complete electrical and optical responses of the device has been clarified. Following the increase of U gradually, different light emission intensities occur as a result of discharge current I. An IR light source is also used in order to test the IR excitation of the microstructure. Although it has been believed that the GaP is sensitive to UV and visible regions, it has been proven for the first time that the IR sensitivity of GaP can be enhanced by using microelectronic gas discharge device, when an appropriate parameter set is applied. Moreover, a negative differential resistance regime, which is important for the high frequency microwave applications, has been observed at moderate voltages. In addition to the negative differential resistance regime, certain hysteresis behaviour is also observed in the sweep up/down cases of U. DOI: http://dx.doi.org/10.5755/j01.eee.20.1.6173

Exploration of the Townsend regime by discharge light emission in a gas discharge device

The Townsend discharge mechanism has been explored in a planar microelectronic gas discharge device (MGDD) with different applied voltages U and interelectrode distance d under various pressures in air. The anode and the cathode of the MGDD are formed by a transparent SnO2 covered glass and a GaAs semiconductor, respectively. In the experiments, the discharge is found to be unstable just below the breakdown voltage Ub, whereas the discharge passes through a homogeneous stable Townsend mode beyond the breakdown voltage. The measurements are made by an electrical circuit and a CCD camera by recording the currents and light emission (LE) intensities. The intensity profiles, which are converted from the 3D light emission images along the semiconductor diameter, have been analysed for different system parameters. Different instantaneous conductivity σt regimes are found below and beyond the Townsend region. These regimes govern the current and spatio-temporal LE stabilities in the plasma system. It has been proven that the stable LE region increases up to 550 Torr as a function of pressure for small d. If the active area of the semiconductor becomes larger and the interlectrode distance d becomes smaller, the stable LE region stays nearly constant with pressure.

Lead free packaging of Pt micro-heater for high temperature gas sensors

There is a continuing demand for the development of fast, sensitive and reliable sensors for applications in harsh industrial environments. Gas sensors are finding great importance in fuel and energy sectors. Monitoring and control of combustion related emissions result in efficient use of fuels and subsequent energy savings. Microelectronic gas sensors have advantages like small size, low power combustion, and possibility of in situ control and monitoring. These gas sensors are commonly employed in fire detectors, emission control system, CO2 operated enhanced geothermal system (EGS), supercritical water systems, organic rankine cycles used in binary power plants, high temperature gas-reactors in next-generation nuclear power plants and in gas processing. Packaging of microelectronic devices is equally important to the development practice. Input/Output connections are fabricated on these systems during this process. Thermo-mechanically strong lead attachments on sensor devices are necessary for high temperature applications. The conventional joining techniques like soldering, wire bonding, flip chip bonding and lead welding show failure in high temperature operative microelectronic systems. Present work is focused on the development and characterization of Pb free packaging of Pt micro-heaters, a main functionary of the gas sensors. Thick film Pt heater printed on ceramics substrate has been interconnected to Cu metal using Indium interlayer. The thermal and mechanical strengths of the interconnect specimen are determined and analyzed. The ultimate tensile strength (UTS) and ultimate shear strength (USS) values are plotted for different reaction parameters. The isothermal solidification morphology and crystallography are examined and discussed. The tests of thermal shock, pressure, operating life and vibration have been performed in an environmental lab to predict the compatibility of the packaging for deployment in harsh environments.

Gas Identification Based on Committee Machine for Microelectronic Gas Sensor

Gas identification represents a big challenge for pattern recognition systems due to several particular problems such as nonselectivity and drift. The purpose of this paper is twofold: 1) to compare the accuracy of a range of advanced and classical pattern recognition algorithms for gas identification for the in-house sensor array signals and 2) to propose a gas identification ensemble machine (GIEM), which combines various gas identification algorithms, to obtain a unified decision with improved accuracy. An integrated sensor array has been designed with the aim of identifying combustion gases. The classification accuracy of different density models is compared with several neural network architectures. On the gas sensors data used in this paper, Gaussian mixture models achieved the best performance with higher than 94% accuracy. A committee machine is implemented by assembling the outputs of these gas identification algorithms through advanced voting machines using a weighting and classification confidence function. Experiments on real sensors' data proved the effectiveness of the system with an improved accuracy over the individual classifiers. An average performance of 97% was achieved using the proposed committee machine

Bayesian Learning Using Gaussian Process for Gas Identification

In this paper, a novel gas identification approach based on Gaussian process (GP) combined with principal components analysis is proposed. The effectiveness of this approach has been successfully demonstrated on an experimentally obtained dataset. Our aim is the identification of different gases with an array of commercial Taguchi gas sensors (TGS) as well as microelectronic gas sensors. The proposed approach is shown to outperform both K nearest neighbor (KNN) and multilayer perceptron (MLP) classifiers

Diamond microelectronic gas sensor for detection of benzene and toluene

We have applied diamond chemical sensor to detect benzene (C 6H 6) and toluene (C 7H 8), volatile organic compounds and possible indication of environmental hazard and petroleum in soil/subsoil. Steady-state and transient responses of the sensor for both gases have been studied. These studies have shown that the sensor shows a large sensitivity, fast response, high selectivity, wider dynamic range, repeatable/reproducible response for benzene and toluene gases. The detection mechanisms of the sensor for both gases have been analyzed and models have been developed. Activation energy analysis of the sensor for both gases resulted in a very small values, confirming fast response and high sensitivity. Furthermore, the effects of structural properties of the sensor and temperature on gas sensing performance have been studied and a structurally optimum sensor has been presented in this study.

A novel microelectronic gas sensor utilizing carbon nanotubes for hydrogen gas detection

A novel microelectronic gas sensor utilizing carbon nanotubes (CNTs) in a thin-layered Pd/ CNTs/ n +- Si structure for hydrogen detection has been achieved. The sensor is fabricated on an n-type silicon wafer, which is needed as an ohmic supporting substrate. Multiwalled CNTs were grown selectively on the substrate via catalytic activation with microwave plasma enhanced chemical vapor deposition. The I– V characteristics of the sensor exhibit Schottky diode behavior at room temperature with marked sensitivity or current changes in the presence of hydrogen. Increasing detection sensitivity in hydrogen sensing was observed with increasing operating temperature. The results demonstrate that CNTs configured as a gas sensor has high sensitivity to hydrogen over a wide temperature range. Behaviors of the sensor in the presence of hydrogen and at elevated temperature were discussed. The successful utilization of CNTs in gas sensors may open a new door for the development of novel nanostructure gas-sensing devices.

A PECVD diamond device for chemical gas sensing applications

Abstract This paper presents a new diamond based microelectronic gas sensor for applications that require operation at a higher and wider temperature range and in harsh environments such as process control, exhaust emission and engine monitoring. The CO gas sensing performance and detection mechanism of the new sensor have been studied by using I – V and I – t characteristics as a function of gas concentration over a wide temperature range (50–500 °C). The gas sensitivity of the sensor is high, repeatable and reproducible. The response time is in seconds to a small concentration of CO gas. Gas detection mechanism of the new sensor is attributed to the modification of the oxygen vacancies in the SnO x layer through the reduction reaction between pre-adsorbed oxygen and CO gases.

High temperature tolerant diamond-based microelectronic oxygen gas sensor

Abstract A new diamond-based microelectronic gas sensor (catalyst/adsorptive-oxide/insulator/semiconductor, CAIS device) has been developed for the detection of oxygen and CO gases. The gas sensing performance, detection mechanisms and activation energy analysis of the sensor for oxygen and CO gases have been analyzed. The gas sensitivity of the sensor is high, repeatable, and reproducible. The response time is in seconds to a small concentration of oxygen and CO gases. The gas detection mechanism of the new sensor is attributed to the change in the oxygen vacancies of the SnO x layer upon oxygen and CO exposure, causing several milliamperes of change in device current. The adsorption activation energy analysis of the sensor reveals small values, 2.8±0.1 kcal mol −1 and 1.1±0.1 kcal mol −1 for oxygen and CO gases, respectively, confirming the high sensitivity and fast response of this new sensor. The diamond-based CAIS gas sensor could be applied for the detection of oxidizing and reducing gases over a higher and wider temperature range than is currently possible.

On the design of microelectronic water and gas flowmeters—Sensors of a new generation

We consider the sources of reduced accuracy in pressure microsensors and ways to eliminate them. We present theoretical calculations that make it possible to increase accuracy with our method. We also consider the technology for producing and designing microsensors.

A novel oxygen gas sensor utilizing thin film diamond diode with catalyzed tin oxide electrode

A novel microelectronic device utilizing the gas sensing properties of tin oxide SnO x and electrical properties of plasma enhanced chemical vapor deposited (PECVD) diamond film for oxygen gas sensing at higher and wide temperature range is presented in this paper. The sensor is fabricated as a layer of catalyst/SnO x (adsorptive oxide)/i(intrinsic)-diamond/p +-diamond CAIS structure. The performance of the new microelectronic gas sensor has demonstrated a large sensitivity to oxygen gas. The response is reproducible and repeatable. Activation energy of oxygen adsorption by the new microelectronic gas sensor is low. The sensor has also indicated CO detection in air ambient.

Diamond microelectronic gas sensors

Diamond-based microelectronic gas sensors using plasma enhanced chemical vapor deposition (PECVD) technology have been explored in our laboratory. This paper presents a new gas sensor using Pd/i-diamond structure for hydrogen detection. Hydrogen sensitivity of the device has been characterized and analyzed as a function of hydrogen partial pressure and temperature by using current-voltage (I–V) and capacitance-voltage-frequency (C-V-F) methods. The hydrogen sensitivity is high, reproducible, and repeatable over a wide temperature range including room temperature.

In Situ Atomic Force Microscopy of Pt/Ti film morphology changes on a microelectronic gas sensor operating at elevated temperatures

Thin film electronic devices that employ resistance change responses of Pt / Ti films to detect gas species have been microfabricated at the University of Michigan. Atomic force microscopy (AFM) is used to investigate morphology of the Pt / Ti sensing films deposited on the microfabricated device. These Pt / Ti sensing films are strongly influenced by many factors, making it difficult to determine the exact relationship between film structure, chemical sensitivity, and selectivity. In-situ AFM investigations of Pt / Ti films on this device at elevated temperatures provides the opportunity for real time observation of film morphology changes under controlled conditions, testing sensing film stability during device operation, and correlating film structure to resistance.Observation of the Pt / Ti film surface and in-situ resistance measurements at elevated temperatures are possible due to the construction of the sensing device. The sensors are based on chemically active thin films deposited on a micromachined silicon window, supported by a 300 μn thick silicon rim.

A selected-area CVD method for deposition of sensing films on monolithically integrated gas detectors

A novel method for deposition of thin transducing films on geometrically well-defined areas is reported. The films represent the front-end of monolithically integrated microelectronic gas detectors. These devices contain a 1 /spl mu/m thick dielectric window equipped with four-point probe electrodes and a boron-diffused silicon heater underneath the window. The central region of the window can be instantaneously switched from room temperature to several hundred /spl deg/C while maintaining excellent thermal uniformity within a 350/spl times/350 /spl mu/m area. Thermally activated CVD of Pt is realized on the heated region by raising the temperature of the central region into the regime of thermal decomposition of Pt precursors such as Pt(PF/sub 3/)/sub 4/. The growth of thin Pt films is monitored in situ by measuring film resistance, and film growth is terminated once desired film resistance values are reached by cutting off the heater current. This allows to optimize film properties for gas sensing applications. The deposited films are characterized ex situ by optical microscopy and scanning electron microscopy to correlate film morphology with resistance. This method can be easily extended to deposition of other films of interest such as TiO/sub 2/.

A polycrystalline diamond thin-film-based hydrogen sensor

A new microelectronic gas sensor utilizing polycrystalline diamond film in conjunction with a catalytic metal has been developed for hydrogen detection. The sensor is fabricated in a layered Pd/i-diamond/p-diamond metal-insulator-semiconductor (MIS) Schottky-diode configuration on a tungsten substrate. The performance of the sensor for H 2 detection has been examined in the temperature range 27-300°C. The analysis of the steady-state reaction kinetics has confirmed that the hydrogen adsorption process is responsible for the barrier-height change in the diamond-based MIS Schottky diode. The use of diamond-film technology opens the door to the development of a microelectronic gas sensor that can operate at a wider and higher temperature range than the ones based on present silicon technology.