Integrated Gas Sensor Array Research Articles

Metal-decorated 3D tin oxide nanotubes in a monolithic sensor array chip for room-temperature gas identification

Inadequate limit of detection at room temperature and unsatisfactory selectivity remain challenge for wide applications of the chemiresistive gas sensors. Nanostructured gas sensors ensure the desirable activation energy for the gas adsorption and chemical reactions, favorable for room-temperature parts-per-billion (ppb) level gas detection. In this work, we demonstrated a single-chip integrated gas sensor array (4 ×4 pixels) based on kinds of metal (Pt, Pd, Au, Ag) decorated 3D SnO2 nanotubes for ultrasensitive room-temperature gas-sensing. The nanostructured sensor array has a high surface area-to-volume ratio, enabling room temperature sensing with high detection response toward H2 (minimum 5 ppm), formaldehyde (minimum 50 ppb), toluene (minimum 50 ppb) and NO2 (minimum 100 ppb) with the detection accuracy within 5% range, respectively. In addition, the effect of metals decoration on the gas identification features were systematically conducted, and these specific response features can be mainly attributed to metal activation capability toward the gases, which enables demonstrating differentiable response patterns for the target gases identification employing a pattern recognition algorithm. These results demonstrate that the proposed strategy helps to provide an excellent route for the future low-power-consumption smart sensing devices design and fabrication.

Multi-gas detection using Fabry-Perot interferometers on silicon chip

Abstract This work presents an all optical on chip integrated gas sensor array for sensing multiple gas simultaneously using non-specific polymers as the sensing material. The individual sensors are vertically etched into silicon. They are made of two Bragg mirrors forming a Fabry-Perot cavity which is functionalized with different polymers such as polyethylene glycol (PEG), SU-8 and polydimethylsiloxane (PDMS). Multi-gas detection was achieved for various gas mixtures of isopropyl alcohol (IPA), H 2 O, valeric acid and butanol. Using a linear model, we report limits of detection as low as 8.1 parts per million (ppm) for valeric acid within mixtures.

Advanced Micro- and Nano-Gas Sensor Technology: A Review.

Micro- and nano-sensors lie at the heart of critical innovation in fields ranging from medical to environmental sciences. In recent years, there has been a significant improvement in sensor design along with the advances in micro- and nano-fabrication technology and the use of newly designed materials, leading to the development of high-performance gas sensors. Advanced micro- and nano-fabrication technology enables miniaturization of these sensors into micro-sized gas sensor arrays while maintaining the sensing performance. These capabilities facilitate the development of miniaturized integrated gas sensor arrays that enhance both sensor sensitivity and selectivity towards various analytes. In the past, several micro- and nano-gas sensors have been proposed and investigated where each type of sensor exhibits various advantages and limitations in sensing resolution, operating power, response, and recovery time. This paper presents an overview of the recent progress made in a wide range of gas-sensing technology. The sensing functionalizing materials, the advanced micro-machining fabrication methods, as well as their constraints on the sensor design, are discussed. The sensors’ working mechanisms and their structures and configurations are reviewed. Finally, the future development outlook and the potential applications made feasible by each category of the sensors are discussed.

Printable polythiophene gas sensor array for low-cost electronic noses

A route for generating arrays of printable polythiophene-based gas sensor materials suitable for low-cost manufacturing is demonstrated. Materials with complementary sensor responses are synthesized by incorporating functional groups into the molecule, either along the polymer backbone or as end-capping groups. Using these materials as printable sensor inks, a functional, integrated gas sensor array chip is fabricated using additive deposition techniques. The sensor array shows sensitivity to a range of volatile organic compounds down to concentrations of 10ppm. A three-terminal thin film transistor structure is used, allowing the extraction of multiple parameters that help to elucidate the mechanisms responsible for sensor response and the role of the functional groups in this response.

A Reusable Smart Interface for Gas Sensor Resistance Measurement

The advances of the semiconductor industry enable microelectromechanical systems sensors, signal conditioning logic and network access to be integrated into a smart sensor node. In this framework, a mixed-mode interface circuit for monolithically integrated gas sensor arrays was developed with high-level design techniques. This interface system includes analog electronics for inspection of up to four sensor arrays and digital logic for smart control and data communication. Although different design methodologies were used in the conception of the complete circuit, high-level synthesis tools and methodologies were crucial in speeding up the whole design cycle, enhancing reusability for future applications and producing a flexible and robust component.

A Monolithic Interface Circuit for Gas Sensor Arrays: Control and Measurement

The electronics for monolithically integrated gas sensor arrays fabricated using a compatible CMOS process have been developed. Circuitry includes the heater driver for temperature control and an interface circuit for inspection of the four sensors in the array. The operating temperature of the sensing resistors is between 200° and 400°C. The proposed temperature controller is capable of regulating the temperature of a 2100 × 2100 μm hotplate up to 400°C with a resolution of 2°C with 5 V supply voltage. A readout circuit based on a ring-oscillator has been included to measure the sensing resistance change upon gas exposure over a high dynamic range. Because it is robust, small, low priced and offers future capabilities with adequate signal processing, the system would be able to cover most of today's gas sensor markets.

Low-voltage and low-power optimization of micro-heater and its on-chip drive circuitry for gas sensor array

Low-voltage and low-power design is the key issue for the portable electronics applications and has become the major concern for the system design. Integrated gas sensor array allows the monolithic realization of multi-species gas sensing systems. This paper reports the developments of Si-based micro-machined micro-heater array with extremely low-power consumption, low-voltage operation, and CMOS compatibility, and low-voltage and low-power CMOS drive circuitry for the micro-heaters that can provide large drive current and voltage swing, and heater temperature is continuously adjustable in the full temperature range.

An integrated gas sensor technology using surface micro-machining

We report the first silicon based integrated gas sensor technology using surface micro-machined micro-hotplate (MHP). In this work, the thermally isolated hotplate was fabricated using surface silicon micro-machining technique. Various etching window designs for the polysilicon sacrificial etch were also explored to optimize the surface micro-machining process yield. The front-side surface micro-machined MHP provide excellent manufacturing yield compared to the bulk micro-machined counterpart and at the same time retains all the desirable thermal characteristics that are essential to the integrated gas sensor application. Integrated gas sensors with sensitivity down to 1 ppm of carbon monoxide were demonstrated using this technology. This approach has been extended to integrated gas sensor array.

Micro-machined gas sensor array based on metal film micro-heater

An integrated gas sensor array is promising to overcome the poor selectivity and drift encountered by individual gas sensor. Micro-machined gas sensor array was fabricated using the post-process micro-machining technology of silicon integrated circuit (IC). The size of a 2×4 array is 2 mm×4 mm, and the active area of each cell is 50 μm×50 μm. The electric properties, thermal characteristics, and the response to standard gases of the sensor array were investigated. The micro-heater can be driven to 400°C with about 9 mW applied power, and thermal response time constant of a micro-heater is about 10 ms. The techniques of oxygen radical assisted EB evaporation was utilized to prepare SnO 2 sensitive films that show high sensitivity and good selectivity to C 2H 5OH.

Sensitive, selective and stable tin dioxide thin-films for carbon monoxide and hydrogen sensing in integrated gas sensor array applications

This paper reports on the preparation, electrical and surface characterization of Cu doped tin dioxide thin-films for highly selective integrated gas sensor devices. The 3000 Å thin-film of 0.16 wt.% copper doped tin dioxide was deposited by reactive R.F. sputtering at room temperature and followed by 10 Å Pt on top of Cu doped tin dioxide thin-film (SnO 2–Cu/Pt). In another batch, the 100 Å SiO 2 thin-film was deposited on top of the SnO 2–Cu/Pt thin-film structure (SnO 2–Cu/Pt/SiO 2). The electrical response of these thin-films was investigated for CO and H 2 gases at different temperatures and gas concentrations. The device with the SnO 2–Cu/Pt thin-film, showed excellent electrical response towards CO gas and device with SnO 2–Cu/Pt/SiO 2 thin-film showed response towards hydrogen only. The SiO 2 thin-film prevents the diffusion of CO gas and only hydrogen gas diffuse through silicon dioxide layer. Using thin-films structure SnO 2–Cu/Pt and SnO 2–Cu/Pt/SiO 2, a highly selective sensor device for CO and H 2 gas was fabricated. The surface characterization of these thin-films was performed using scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS) techniques. The SEM picture showed that surface structure of the SnO 2 thin-film improved by copper doping.

The design of a new integrated gas sensor array based on FEA

The temperature distribution of the integrated gas sensor array is discussed. Since it is difficult to measure the surface temperature on an integrated gas sensor chip experimentally, the finite element analysis (FEA) technique is used in our simulation design of the microstructure gas sensor array. First, the model is derived from the array's exact structure and physical features. Second, we discussed the temperature distribution under steady state of the integrated gas sensor array according to the variances of material properties and the array's structure. Finally, we designed and manufactured a novel integrated gas sensor array based on FEA. The experimental results show that the above-mentioned study is feasible and satisfactory.

Field-effect-induced gas sensitivity changes in metal oxides

The sensitivity of micromachined gas sensor elements with respect to CO, NO, NO 2, CH 4, H 2O and oxygen partial pressure changes was investigated. The microsensors consisted of thin films of RGTO-SnO 2 deposited on top of resistively heated Si 3N 4 membranes. The electrical insulation between the Pt heater and SnO 2 sensing layer circuits was provided by a thin dielectric layer. Applying a bias voltage across this layer, field-effect-induced changes in the gas sensing properties could be studied. We find that bias voltage changes can be used to systematically modify the cross-sensitivity of identically prepared sensor elements. These results are relevant for the realisation of monolithically integrated gas sensor arrays.

Application of iteration technique in association with multiple regression method for identification of mixtures of gases using an integrated gas-sensor array

This paper deals with the discrimination of gases using the responses of an integrated gas sensor. The multiple regression method is used to find the sensor parameters for different gases in training mode. In sniffing mode, these parameters are used to discriminate the gases present in the ambient using the iteration technique. These methods, i.e., the multiple regression method and iteration technique, have been successfully applied to the data set obtained in our laboratory for a mixture of carbon tetrachloride and ethyl methyl ketone exposed to a fabricated integrated gas-sensor array. The methods can effectively be used for the realization of an 'intelligent gas sensor'.

Transformed cluster analysis: an approach to the identification of gases/odours using an integrated gas-sensor array

This paper deals with ‘transformed cluster analysis’, which can be used to analyse gas-sensor responses for the identification of individual gases/odours present in the ambient. The computational strategy for the analyses consists of transformation of data, graphical representation, formulation of the classification method, interpretation of results and quantification. The unknown gas/odour may be classified into five different probability groups according to the transformed responses obtained, i.e., real object, apparent object, probable object, doubt object and atypical object. This method also helps to evaluate the effect of dopants. The method is illustrated here with experimental data obtained in the laboratory. It is predicted that the technique can successfully be used for application-specific gas sensors.