Sasikaran Kandasamy

Filling schemes at submicron scale: development of submicron sized plasmonic colour filters.

The pixel size imposes a fundamental limit on the amount of information that can be displayed or recorded on a sensor. Thus, there is strong motivation to reduce the pixel size down to the nanometre scale. Nanometre colour pixels cannot be fabricated by simply downscaling current pixels due to colour cross talk and diffraction caused by dyes or pigments used as colour filters. Colour filters based on plasmonic effects can overcome these difficulties. Although different plasmonic colour filters have been demonstrated at the micron scale, there have been no attempts so far to reduce the filter size to the submicron scale. Here, we present for the first time a submicron plasmonic colour filter design together with a new challenge - pixel boundary errors at the submicron scale. We present simple but powerful filling schemes to produce submicron colour filters, which are free from pixel boundary errors and colour cross- talk, are polarization independent and angle insensitive, and based on LCD compatible aluminium technology. These results lay the basis for the development of submicron pixels in displays, RGB-spatial light modulators, liquid crystal over silicon, Google glasses and pico-projectors.

Electrical characterization and hydrogen gas sensing properties of a n-ZnO∕p-SiC Pt-gate metal semiconductor field effect transistor

A new hydrogen gas sensitive n-ZnO∕p-SiC Pt-gate metal semiconductor field effect transistor (MESFET) is reported. The observed current-voltage curves for the source to drain region indicate that this MESFET operates in enhancement mode. A change in gate potential, due to different ambient atmospheres caused a change in the width of the depletion region, hence modulating the current in the n channel (ZnO layer). The H2 gas sensing mechanism of the presented MESFET structure is discussed using energy band diagrams.

Comparison between conductometric and layered surface acoustic wave hydrogen gas sensors

A comparison between the performance of conductometric and layered surface acoustic wave (SAW) hydrogen sensors is presented. Both sensor structures employ an RF magnetron sputtered tungsten trioxide (WO3) thin film as a selective layer for hydrogen (H2) sensing applications. The conductometric device is based on an alumina substrate, while the layered SAW device structure is fabricated on a 36° Y-cut, X-propagating LiTaO3 substrate with a zinc oxide (ZnO) guiding layer. The sensors were investigated for different operational temperatures and concentrations of H2 ranging between 0.06 and 1% in synthetic air. Approximately 1.4 µA current and 27 kHz frequency shifts were observed towards 1% H2 in air for the conductometric and layer SAW device, respectively.

Study of Pt/TiO/sub 2//SiC Schottky diode based gas sensor

Metal reactive oxide silicon carbide (MROSiC) is attractive for gas sensing applications in harsh, high temperature environments. We present the hydrogen and propene gas sensing performance of a Pt/TiO/sub 2//SiC device. This sensor has been employed as a Schottky diode, and is capable of operating at temperatures around 650 /spl deg/C. The sensors were exposed to different concentrations of these analyte gases over the temperature range of 300 to 650 /spl deg/C. The response was measured as the shift in voltage when a constant forward bias current 0.5 mA was applied. Voltage shifts of approximately 4.5 V for 1% hydrogen in nitrogen and up to 1 V for 1% hydrogen in synthetic air were observed. Largest responses were observed at operating temperature of 530 /spl deg/C.

Comparison between conductometric and layered SAW hydrogen gas sensor

A comparison between the performance of conductometric and layered surface acoustic wave (SAW) hydrogen sensors is presented. Both sensor structures employ an R.F. magnetron sputtered tungsten trioxide (WO3) thin film as a selective layer for hydrogen (H2) sensing applications. The conductometric device is based on an alumina substrate, while the layered SAW device structure is fabricated on a 36° Y-cut, X-propagating LiTaO3 substrate with a zinc oxide (ZnO) guiding layer. The sensors were investigated for different operational temperatures and various concentrations of H2 in synthetic air.

Modelling of a thin film thermoelectric micro Peltier module

A micro Peltier cooler/heater module has been modelled. The module consists of n-type bismuth telluride and p-type antimony telluride thermoelectric materials. The commercial software package CFD-ACE+ has been used to implement and analyse the model. A two-dimensional coupled electrical and thermal simulation was performed. This software includes the possibility to incorporate the Peltier effect. The temperature, electric field intensity and wall heat flux distributions were simulated for different applied potentials. The variation in temperature difference with respect to the Seebeck coefficient of the material was calculated and analysed.

Mixed oxide Pt/(Ti-W-O)/SiC based MROSiC device for hydrocarbon gas sensing

A highly sensitive gas sensor employing mixed oxide (Ti-W-O) has been developed for the detection of hydrocarbons. The sensing performance of the Pt/(Ti-W-O)/SiC based metal reactive oxide silicon carbide (MROSiC) devices has been investigated as a function of temperature and different concentration of propene in synthetic air. When operated at 420degC, a 2.52V shift was observed when 1% propene was introduced into an ambient containing synthetic air. The changes in the barrier height of the device were 65.5meV, approximately two times larger for the same hydrogen concentration. Material characterization of the mixed oxide was performed using atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS). We have found that the mixed oxide (Ti-W-O) showed higher catalytic activity when compared to the single compound of TiO2 and WO3, thus increasing the rate of dehydrogenation of the hydrocarbon

Investigation of layered SAW sensors based on a WO3/ZnO/64° YX LiNbO3 structure with gold catalytic layer

A layered Surface Acoustic Wave (SAW) hydrogen gas sensor, based on a delay line structure with 64 finger pairs on input and output port, is fabricated on 64° Y-cut, X-propagating LiNbO3 substrate. A guiding layer of ZnO is used to increase the sensitivity of the structure. A WO3 selective layer is employed to H2 gas sensing applications at different operating temperatures between room temperature and 300°C. In this paper, the fabrication process of WO3/ZnO/64° YX LiNbO3 sensor is described and the sensor’s response features are analyzed. The improvement of the response with the addition of a gold catalytic layer on the sensor surface is also investigated.

Development of silicon optics for an integrated micro-optical system-on-a-chip

Development of silicon-based passive optical components such as reflectors, waveguides, and beam splitters coupled with active elements such as light emitters and detectors enable miniaturisation of a low-cost system-on-a-chip sensing device. In this work, we investigate methods to fabricate passive silicon elements on a chip. We use a combination of wet and dry etching techniques to realise angled and vertical sidewalls normal to the surface of a silicon wafer, respectively. For wet etching, we used Triton-X, a surfactant, added to an alkaline solution TMAH as the etchant. This allows perfect 45° inclined sidewalls to be fabricated. Dry etching using DRIE is to be performed on the reverse-side of the same wafer to realize through-hole vias with straight vertical sidewalls. A final Au metal layer can then be coated onto the sidewalls to realize reflective surfaces. Photolithography masks used in the wet and dry etch processes were designed and fabricated. By careful alignment of these masks using a mask aligner, we can fabricate a combination of inclined and vertical sidewalls to build optical reflectors and beam splitters with complex geometries. When integrated with active Si-optical devices, a fully integrated micro-optical system-on-a-chip can be realised.

Preparation and Characterization of Tin Oxide Nanowires on SIC

Interest in nanowires of metal oxide oxides has been exponentially growing in the last years, due to the attracting potential of application in electronic, optical and sensor field. We have focused our attention on the sensing properties of semiconducting nanowires as conductometric and optical gas sensors. Single crystal tin dioxide nanostructures were synthesized to explore and study their capability in form of multi-nanowires sensors. The nanowires of SnO2 have been used to produce a novel gas sensor based on Pt/oxide/SiC structure and operating as Schottky diode. For the first time, a reactive oxide layer in this device has been replaced by SnO2 nanowires. Proposed sensor has maintained the advantageous properties of known SiC- based MOS devices, that can be employed for the monitoring of gases (hydrogen and hydrocarbons) emitted by industrial combustion processes.