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Prasad M.,Indian Central Electronics Engineering Research Institute
Microelectronics Reliability | Year: 2015

In this paper, the development and reliability of a platinum-based microheater with low power consumption are demonstrated. The microheater is fabricated on a thin SiO2 bridge-type suspended membrane supported by four arms. The structure consists of a 0.6 μm-thick SiO2 membrane of size 50 μm × 50 μm over which a platinum resistor is laid out. The simulation of the structure was carried out using MEMS-CAD Tool COVENTORWARE. The platinum resistor of 31.0 Ω is fabricated on SiO2 membrane using lift-off technique. The bulk micromachining technique is used to create the suspended SiO2 membrane. The temperature coefficient of resistance (TCR) of platinum used for temperature estimation of the hotplate is measured and found to be 2.2 × 10-3/°C. The test results indicate that the microhotplate consumes only 11.8 mW when heated up to 400 °C. For reliability testing, the hotplate is continuously operated at higher temperatures. It was found that at 404 °C, 508 °C and 595 °C, the microhotplate continuously operated up to 16.5 h, 4.3 h and 4 min respectively without degrading its performance. It can sustain at least 53 cycles pulse-mode of operation at 540 °C with ultra-low resistance and temperature drifts. The structure has maximum current capability of 19.06 mA and it can also sustain the ultrasonic vibration at least for 30 min without any damage. © 2015 Elsevier Ltd. All rights reserved.

Khanna V.K.,Indian Central Electronics Engineering Research Institute | Khanna V.K.,Academy of Scientific and Innovative Research AcSIR
Sensors and Actuators, B: Chemical | Year: 2015

An early paper [1] proposed the virtual pore widening model to explain the temporal drift in the characteristics of porous aluminum oxide humidity sensor. It is shown here that this model does not provide a plausible mechanism for the decrease in sensitivity caused by aging. Instead, it predicts the contradictory behavior of an increase in sensitivity with aging, which is not true. Alternatively, hydration of the aluminum oxide on exposure to moisture provides a more cogent explanation of the aging process, as observed in an alumina-gate ion-sensitive field-effect transistor (ISFET). In this paper, the monotonic decrease in capacitance of Al2O3 humidity sensor with the extent of hydration has been established, both by equivalent circuit approach and by modeling the sensor as a heterogeneous dielectric. Capacitance calibration characteristics of the humidity sensor have been simulated by employing the theory of alumina humidity sensor. Similarities and dissimilarities of aging of this sensor with ISFET drift have been elucidated. Whereas in ISFET, a thin hydrated layer is formed only at the surface of the gate dielectric, in Al2O3 sensor, hydration of inner layers in the porous film is highly likely. Unification of aging mechanisms in sensors is briefly discussed. © 2015 Elsevier B.V.. All rights reserved.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Sensor Review | Year: 2013

Purpose - This paper aims to focus on the steps necessary to bolster marketability of ISFET-based sensors, keeping in view the present technological status of ISFET and its limitations. Design/methodology/approach - Technical problems inhibiting commercialization of ISFET-based sensors are highlighted. The problems considered include sensitivity, drift, cleaning, disposability, reference systems, chip structural designs, packaging, light, temperature, hysteresis and body effects, and instability of biosensors. Available solutions are prescribed, discussing both direct and indirect ways of addressing the problems of ISFET sensors. Findings - The history of progress of ISFET (Ion-sensitive Field-Effect Transistor) is synonymous with the ways and means devised by different researchers for surmounting (direct approach) or acclimatizing to the shortcomings of this device (indirect approach) . Signal conditioning hardware and software considerably help in obviating issues such as drift, hysteresis and thermal effects. Research limitations/implications - Reliable on-chip reference electrodes and ISFET packaging for continuous online applications are interesting research areas. Practical implications - Where a plausible solution exists, it should be readily availed; otherwise the device limitation should be understood and ingeniously bypassed. Compromising solutions targeted on the specific applications pave the way towards widespread utilization of these sensors in industrial, biomedical, food and environmental sectors. Originality/value - The study helps in understanding the problems besetting utilization of ISFETs, calling attention to essential remedies for ISFET-based products. It provides information of value to those involved in ISFET measurements. © Emerald Group Publishing Limited.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Sensors and Transducers | Year: 2012

Humidity sensors are required for diverse applications in low and high humidity ranges. Also, fast-response humidity sensors are sometimes needed. For this purpose, it is necessary to understand the hygroscopic influences and physico-chemical mechanisms underlying sensor operation as well as their correlation with the terminal properties of sensors. Several models and theories of sensors have been proposed for interpretation of their behaviour. This paper comprehensively surveys the available models and points out the utilization of selected models for tailoring sensor characteristics in accordance with intended application. Ionic salt doping is a useful technique for improving the sensitivity, linearity and hysteresis of humidity sensor characteristics. © 2012 IFSA.

Khanna V.K.,Indian Central Electronics Engineering Research Institute
Indian Journal of Pure and Applied Physics | Year: 2012

The present paper describes the fabrication of ISFET (Ion-Sensitive Field-Effect Transistor) by a four-mask, thermal diffusion-based process. The sequence of physical and chemical processes for ISFET fabrication has been elaborated. In the first photomasking step, the regions for source and drain diffusion have been opened. The second photolithography defined the gate area. In the third photolithographic step, contact windows have been opened, and in the fourth photolithographic step, the metal pattern has been delineated. After completion of the fabrication process, the wafer has been diced into chips, which have been mounted on ceramic substrates to provide electrical connections for source, drain and substrate. Except for the gate region, the whole chip and wire bonds have been protected with insulating epoxy. For process characterization, current-voltage characteristics of MOSFET test devices simultaneously fabricated on the same wafer have been measured for gate-source voltages from -5 to +5 V. These were found to be N-channel, depletion-mode devices indicating similar behaviour for ISFETs. The pH-response of ISFET has been evaluated by drawing its I DS-V GS characteristics after immersion in standard buffer solutions and applying the gate-source voltage through Ag/AgCl reference electrode. From these transfer characteristics, pH-sensitivity of ISFET has been determined by finding the gate-source voltage necessary to ensure constant I DS, V DS condition. Technological shortcomings of this work have also been pointed out, and necessary remedial measures have been suggested.

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