Sunipa Roy

Ultrasensitive Pd–Ag/ZnO/Nickel Alloy-Based Metal–Insulator-Metal Methane Sensor on Micromachined Silicon Substrate

A novel Pd-Ag/ZnO/Nickel alloy Metal-Insulator-Metal (MIM) sensor on micromachined silicon platform, for efficient methane detection, is reported in this letter. The co-planar microheater and lower electrode of the MIM sensor were fabricated using an alloy (called DilverP1) of nickel. The Ni-alloy was found to offer an Ohmic contact with ZnO sensing layer. Nanostructured ZnO was deposited on lower electrode by a low temperature chemical process and Pd-Ag (70%) was used as the top catalytic electrode to ZnO. A study of the current-voltage characteristics of the MIM structure in pure N2 with the presence and absence of desired concentration of methane revealed that the device can be used as a low-temperature methane sensor with ultrahigh sensitivity and fast response. The response magnitude and response/recovery time were studied at different temperatures (100, 130, 160, 190, and 220°C) for different methane concentrations. 190°C was found to be the optimum temperature for maximum response of ~316% and minimum time of response of 18 s at 1% methane in N2.

Notice of Violation of IEEE Publication Principles Design and simulation of MEMS based piezoresistive pressure sensor for enhanced sensitivity

The application of MEMS to the measurement of pressure is a mature application of micromachined silicon mechanical sensors. The present paper describes the design and simulation of surface micromachined piezo resistive type pressure sensor for enhanced sensitivity. The principle of the sensing mechanism is based on the deflection of sensing silicon nitride diaphragm. In order to achieve better sensor performance, a FEM analysis using mechanical analysis module of Intellisuite software is performed to evaluate the system output sensitivity of the pressure sensor. The deflections of the diaphragms (for square as well as circular) have been studied for different applied pressure. From this, the operating range as well as the sensitivity of the sensors can be easily determined. A detailed analysis of the deflection with different applied pressure is presented graphically. The output voltage and material elasticity of diaphragm are affected by temperature variations. So, use of heat sink is required for temperature compensation purpose. This simulation results depict that proper selection of the diaphragm geometry and piezoresistor location can enhance the sensor sensitivity with lower power consumption.

Electro thermal analysis and fabrication of low cost microheater using a nickel alloy for low temperature MEMS based gas sensor application

A stable and low power heating characteristics of a microheater are very important for the gas sensor platform. In this paper, we present a complete electrothermal and coplanar structure of a microheater for MEMS based gas sensor platform using a low cost nickel alloy Dilver PI (alloy of Ni, Co, Fe) having high resistivity 49∗10–8Ωm and high yield stress 680MPa with low thermal conductivity 17.5W/m/°C. A comparative study has also been made with six different types of heater structures. Thermal electrical analysis was done using finite element modeling of Intellisuite 8.2. Microheater device of size 5mm × 5mm with a 50μ thick membrane of size 2mm∗2mm are fabricated using a single lithographic mask. The maximum temperature of 200 °C with a distribution of ± (2–3) % over the entire microheater membrane region has been achieved with 5V excitation. The power consumption 146 mW has been achieved.

Facile Synthesis of Multi-Layer Graphene by Electrochemical Exfoliation Using Organic Solvent

Abstract This paper presents a facile method of producing graphene nanosheets by organic liquid-assisted electrochemical exfoliation using tetramethyleammonium hydroxide (TMAH) as organic electrolyte. The process involves low-cost copper as ground electrode and carbon block as anode or cathode. The application of organic electrolyte eliminates the presence of unwanted metal ions on the graphene nanosheets. To the best of our knowledge, this is a maiden effort of producing graphene with pure organic electrolyte using TMAH with low-cost copper electrode. By the use of TMAH, conformal large-area graphene nanosheets of 4.3 nm thickness with an average sheet diameter of 3–4 μm have been obtained. Graphene nanosheets are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, ultraviolet-visible spectroscopy, Fourier transform infrared, Raman spectroscopy, and atomic force microscopy. Raman characterization confirms the conservation of the intrinsic nature of few-layer graphene. Graphene nanosheets are dissolved in a polar aprotic solvent dimethylformamide and are drop coated on the Si/SiO2 substrate to make a thin film of graphene. Films are annealed to remove any residual solvent attached to it. Different annealing temperatures (50–200°C) were reported. Sheet resistances were measured before and after annealing, with a remarkable decrease afterward. Current-voltage characteristics were studied to evaluate the conductivity of the graphene nanosheets produced.

Development of Integrated microsystem for Hydrogen Gas Detection

A low-power microelectromechanical system-based metal-oxide gas sensor along with integrated signal conditioning unit is presented in this study to detect and quantify the variation of H 2 gas concentrations. The interface circuit controls the sensor operating temperature, measures the H 2 gas concentration, contributes a user-friendly interface and can be used with any suitable sensor network. A PIC16F877A microcontroller has been used for this purpose. The temperature of the sensors was stabilised by controlling the actuating voltage of the microheater. Temperatures of the microheater depend on the output voltage of the digital-to-analogue converter (DAC) and were measured by sampling the heater resistance through the use of a voltage divider and analogue-to-digital converters (ADCs). A microcontroller accordingly adjusts the output of DACs in order to apply the appropriate steering voltage to the heaters. The method employed to measure the concentration of gases is to sample the voltage drop over the resistances of the sensors by ADCs. Alarming system for safety measure was also implemented in this design. The preventive action was taken by introducing an additional feature of wireless communication by sending short message service via global system for mobile modem to the designated emergency number.