Vikas Saini

Bio: Vikas Saini is an academic researcher from Central Electronics Engineering Research Institute. The author has contributed to research in topics: Thin film & Sputtering. The author has an hindex of 2, co-authored 9 publications receiving 17 citations. Previous affiliations of Vikas Saini include Council of Scientific and Industrial Research.

Nickel oxide (NiO) thin film optimization by reactive sputtering for highly sensitive formaldehyde sensing

Abstract: Trace level detection of formaldehyde (HCHO) is of utmost importance due to its harmful effects (carcinogenic) on humans. In the present work, we have deposited nickel oxide (NiO) using reactive sputtering technique with varying Ar:O2 ratio. It was found that NiO developed with Ar:O2 ratio of 70:30 exhibited the best response (operating temperature 200 °C) for formaldehyde. Developed metal oxide material is highly sensitive to formaldehyde with limit of detection as low as 50 ppb. Developed films were characterized for crystal structure using XRD, and surface morphology using AFM and SEM. Crystallographic assessment confirms the presence of face centered cubic phase of NiO and surface morphology of the film clearly shows the granular structure of the metal oxide film. Deposited NiO is found to be p-type which is confirmed by hotpoint probe, hall measurement as well as gas sensing behavior. The developed material was tested for various other indoor gases such as benzene (C6H6), carbon monoxide (CO), toluene (C7H8), and ammonia (NH3) and the material exhibited high selectivity towards HCHO. HCHO gas concentration ranging from 0.3 ppm to 2.5 ppm was tested on the sample. The material also showed good stability over the period of 3 months.

Effect of IDE placement on response in metal oxide gas sensors

Abstract: Sensitivity and response of metal oxide based gas sensors depend on various aspects including design as well as environmental parameters. This paper discusses the positioning of interdigitated electrodes (IDE) with respect to sensing film, for sensor response optimization. Two arrangements of IDE were considered, one with electrodes below the sensing film and other with electrodes above the sensing film; both schemes were further characterized for ammonia sensing, at different temperatures. Tin-oxide (SnO2) film was used as the sensing film to discern the gas sensing behavior of the two schemes. The film was also characterized by atomic force microscopy and UV-visible spectroscopy. The scheme with electrodes on top of the sensing film, showed about two times better response (~2×) than the other case, when examined in the presence of 10 ppm ammonia (NH3). The same was earlier validated by the simulations performed using COMSOL. Electrodes on top configuration has shown improved response for hydrogen sulphide (H2S) as well.

Metal Oxide Semiconductor-based gas sensor for Acetone sensing

Abstract: Acetone constitutes 58% of the volatile organic compounds found in human breath. Acetone in breath is proven to be a biomarker for type I diabetes. Portable and sensitive metal oxide semiconductor-based gas sensor with Tungsten Oxide (WO 3 ) thin film as the sensing layer has been used to measure the concentration of Acetone in breath. Acetone gas being a reducing gas decreases the resistance of thin film when it comes in contact of the sensor. The gas sensor is fabricated, characterized and tested for various concentrations of Acetone gas. A linear calibration curve is obtained on the log scale for predicting any concentration in the novel range of 10 ppm to 300 ppm at 300 °C in the sensor fabricated using RF Magnetron sputtering method. The gas sensor is portable and easy to handle with the chip size of 5mm × 5mm and thin film thickness of 100 nm. The efficiency is optimized by operating it at temperature 300 °C with minimum response time and recovery time

Development and reliability analysis of micro gas sensor platform on glass substrate

Abstract: In this paper, technology for a gas sensor platform with borofloat as the substrate material is presented. Comprehensive characterization of the platform, its comparison with silicon and alumina, fabrication yield improvement and a study of reliability of the micro-heater platform have been carried out. Usually, the chips are suspended in air to reduce power consumption. However, the presented technology is a non-MEMS technique and doesn’t require any complex packaging. Borofloat has much lower thermal conductivity in comparison to silicon and alumina, thereby reducing the thermal losses, making it possible to operate the device with low power consumption. The process adapted for the fabrication of the gas sensor platform has lesser complexities and the process cost is reduced compared to conventional gas sensor fabrication, as it does not require thermal oxidation and bulk micromachining. Different substrates (silicon, alumina and glass) have been simulated using COMSOL to depict the benefit of lower thermal conductivity. Micro-heater has also been fabricted on all the three above mentioned substrates and the power consumption is compared. Various reliability analysis have been carried out on the glass based platform such as maximum temperature test, long term ON test and ON–OFF pulse test.

Gold-Doped Tin Oxide Film for Highly Sensitive Carbon Monoxide Sensing

Abstract: This paper presents the development of gold-doped tin oxide (SnO2) film, realized by radiofrequency (RF) sputtering, which is highly sensitive for carbon monoxide (CO) gas. According to the Occupational Safety and Health Administration (OSHA), human exposure to 50 ppm CO is safe up to 8 h (as permissible exposure limit), but inhalation of higher concentrations of CO can cause headache, dizziness, nausea, etc. Hence, it is imperative to detect CO gas in low concentrations. The receptor films were prepared via reactive co-sputtering of high-purity Sn and Au targets and characterized by x-ray diffraction (XRD), which confirmed the presence of SnO2 and gold. The thin films of pristine SnO2 and gold-doped SnO2 were also examined through field emission scanning electron microscopy (FESEM) images, showing the distinction in their structures. A reasonably enhanced response of ~ 56.4% was exhibited by gold-doped SnO2 compared to 15.5% for pristine SnO2 for 50 ppm CO at operating temperature of each film.

Selective determination of ammonia, ethanol and acetone by reduced graphene oxide based gas sensors at room temperature

Abstract: This work reports a new technique for the selective determination of three organic vapors– ammonia, ethanol and acetone by employing two resistive sensors. These two resistive sensors are based on reduced graphene oxide (RGO) and RGO– rosebengal (RB) composites. The chemically synthesized RGO and RGO–RB based sensors were tested for four different concentrations of ammonia (400–2800 ppm) and two different concentrations (1000, 2000 ppm) of ethanol and acetone each, at room temperature. The RGO sensor was found to exhibit response of 10.3% to 25.3% to 400–2800 ppm of ammonia, 1.01% to 1.15% to 1000 and 2000 ppm of acetone respectively, and 1.05% to 1.56% to 1000 and 2000 ppm of ethanol respectively. The RGO–RB composite-based sensor exhibited an enhanced response ranging from ~17% to 36.6% for 400–2800 ppm of ammonia, 1.6% to 3.2% for 1000 and 2000 ppm of acetone and 1.1% to 1.7% for 1000 and 2000 ppm of ethanol at room temperature. An algorithm, based on the soft margin classifier was developed to accurately determine the concentrations of all the three organic vapors. The initial 100 s of the response values of both the sensors for all the targeted vapors were considered for this purpose. This resulted into classification of all the concentrations of the three organic vapors much before the full-scale response of the sensors. It is believed that this work will aid in development of portable devices comprising of array of sensors having the capability of determining the vapors and their concentrations accurately.

Inkjet‐Printed rGO/binary Metal Oxide Sensor for Predictive Gas Sensing in a Mixed Environment

Abstract: Selectivity for specific analytes and high‐temperature operation are key challenges for chemiresistive‐type gas sensors. Complementary hybrid materials, such as reduced graphene oxide (rGO) decorated with metal oxides enables realization of room‐temperature sensors with enhanced sensitivity. However, sensor training to identify target gases and accurate concentration measurement from gas mixtures still remain very challenging. This work proposes hybridization of rGO with CuCoOx binary metal oxide as a sensing material. Highly stable, room‐temperature NO2 sensors with a 50 ppb of detection limit is demonstrated using inkjet printing. A framework is then developed for machine‐intelligent recognition with good visibility to identify specific gases and predict concentration under an interfering atmosphere from a single sensor. Using ten unique parameters extracted from the sensor response, the machine learning‐based classifier provides a decision boundary with 98.1% accuracy, and is able to correctly predict previously unseen NO2 and humidity concentrations in an interfering environment. This approach enables implementation of an intelligent platform for printable, room‐temperature gas sensors in a mixed environment irrespective of ambient humidity.