21 research outputs found

    Modeling and simulation of ultrahigh sensitive AlGaN/AlN/GaN HEMT based hydrogen gas detector with low detection limit

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    Presented through this work is a steady state analytical model of the GaN HEMT based gas detector. GaN with high chemical and thermal stability provides promises for detectors in hazardous environments. However, HEMT sensor resolution must be improved to develop high precision gas sensors for automotive and space applications. The proposed model aids in systematical study of the sensor performance and prediction of sensitivities. The linear relation of threshold voltage shift at thermal equilibrium is used in predicting the sensor response. Numerical model for the reaction rates and the electrical dipole at the adsorption sites at the surface and metal/semiconductor interface have been developed and the sensor performance is analyzed for various gas concentrations. The validation of the model has been achieved through surface and interfacial charge adsorption-based gate electrode work function, Schottky barrier, 2DEG and threshold voltage deduction using MATLAB and SILVACO ATLAS TCAD. Further the applicability of gd (channel conductance) as gas sensing metric is also presented. With high ID and gd percentile sensitivities of 118.5% and 92 % for 10 ppm hydrogen concentration. The sensor shows capability for detection in sub-ppm levels by exhibiting a response of 0.043% for 0.01ppm (10 ppb) hydrogen concentration. The detection limit of the sensor (1% sensitivity) presented here is 169 ppb and the device current increases by 34.2 μA for 1ppb hydrogen concentration

    Fabrication of graphene-ZnO heterostructure-based flexible and thin platform-based UV detector

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    This work presents the performance evaluation of Graphene/ZnO Schottky junctions grown on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates. The fabricated structures include chemical vapour deposition grown graphene layer on ITO-coated PET substrates. Polymethyl methacrylate assisted transfer method has been employed for the successful transfer of graphene from Cu substrate to PET. The smaller D-band intensity (1350 cm−1) compared to G-band (1580 cm−1) indicates good quality of carbon lattice with less number of defects. High-quality ZnO has been deposited through RF sputtering. The deposited ZnO with grain size 50–95 nm exhibited dislocation densities of 1.31270 × 10–3 nm−2 and compressive nature with negative strain of − 1.43156 GPa. Further, the electrical and optical characterization of the devices has been done through device I–V characterization and UV detection analysis. The UV detection capability of the device has been carried out with the aid of a UV-lamp of 365 nm wavelength. The fabricated graphene/ZnO photodetector showed good response to UV illumination. The device performance analysis has been done through a comparison of the device responsivity and detectivity with the existing detectors. The detectivity and responsivity of the fabricated detectors were 7.106 × 109 mHz1/2 W−1 and 0.49 A W−1, respectively

    GaN-HEMT on Si as a robust visible-blind UV detector with high responsivity

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    This work presents performance evaluation of GaN High Electron Mobility Transistor (HEMT) based ultraviolet (UV) detector on Si substrate. In addition to the fabrication and characterization, a systematic study is presented here using simulations extensively to investigate the UV detection mechanism. Output current has been chosen as the sensing metric, the fabricated device exhibits a high UV responsivity of 1.62 x 107 A/W at 2.5 x 10-10 W, VGS=0.5 V. Simulations have been done using optical modules available in Silvaco ATLAS TCAD to analyze the energy band bending, Two-Dimensional Electron Gas (2DEG), channel potentials and electric fields in the device. This model can aid in systematic study of HEMT based detectors in terms of dimensional and epi layer design optimizations for sensitivity enhancements. The UV response of the device is found to decrease as the wavelength approaches the visible light wavelength. This makes the photodetectors blind to visible light ensuring selective detection of UV wavelengths. It has been observed that as the area for UV absorption is increased by increasing the W/L ratio, the increases. For a W/L ratio of 100, the detector exhibits a responsivity of 1.86 x 107 A/W

    Recent development and futuristic applications of MEMS based piezoelectric microphones

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    This paper presents a comprehensive literature survey of MEMS based piezoelectric microphones along with the fabrication processes involved, application domains, and methodologies used for experimentations. Advantages and limitations of existing microphones are presented with the impact of process parameters during the thin film growth. This review identifies the issues faced by the microphone technologies spanning from the invention of microphones to the most recent state-of-the-art solutions implemented to overcome or address them. A detailed comparison of performance in terms of sensitivity and dynamic range is presented here that can be used to decide the piezoelectric material and process to be used to develop sensors based on the bandwidth requirement. Electrical and mechanical properties of different piezoelectric materials such as AlN, ZnO, quartz, PZT, PVDF, and other polymers that has great potential to be used as the sensing membrane in development and deployment of these microphones are presented along with the complications faced during the fabrication. Insights on the future of these sensors and emerging application domains are also discussed

    Influence of AlN passivation on thermal performance of AlGaN/GaN high-electron mobility transistors on sapphire substrate: A simulation study

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    This work describes the self-heating effects on the behavior of AlGaN/GaN-based high-electron Mobility Transistors (HEMTs), which are grownon Sapphire substrate, using electro-thermal TCAD simulations. The proposed device, passivated with AlN/SiN, demonstrates more excellent thermal performance than the conventional one with SiN passivation due to the introduction of additional AlN on top of the device, which acts as a heat spreader. The electro-thermal simulations have carried out for different AlN thicknesses (0 µm to 25 µm), and the device with 5 µm AlN shows better performance compared to others. The proposed AlN/SiN stacked passivation HEMT shows a comparatively small lattice temperature of 418 K, whereas the conventional HEMT with SiN passivation shows 578 K. All the devices (gate length, LG = 1 µm) switch from OFF- to ON-states using the voltage, VGS from −10 V to 0 V with fixed bias, VDS = 5 V. The values of saturation drain current density (IDSS) and transconductance (gm) are 0.7 A/mm and 173 mS/mm for the proposed HEMT with 5 µm AlN considering the thermal simulation model. In contrast, the conventional device demonstrates those of 0.42 A/mm and 109 mS/mm, respectively. The ∼ 0.32 A/mm of drain current recover for the proposed device with 5 µm AlN from a conventional device because of the reduction of self-heating effects. Our study reveals that the AlN/SiN passivation HEMTs are a promising technology for high-power switching and microwave applications without significant reduction in device performance at high drain bias

    Optimization and fabrication of MEMS based piezoelectric acoustic sensor for wide frequency range and high SPL acoustic application

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    This paper reports finite element model (FEM) simulation and fabrication of a square shaped diaphragm along with microtunnel for MEMS acoustic sensor which can be used for measurement of wide operational frequency range and high sound pressure level (SPL) 100 dB–180 dB measurement in launching vehicle and aircraft. The structure consists of a piezoelectric ZnO layer sandwiched between two aluminum electrodes on a thin silicon diaphragm. There is a microtunnel in the structure which relates the cavity to the atmosphere for pressure compensation. The microtunnel decides the lower cut-off frequency of device. Analytical and simulation approaches are used to optimize microtunnel dimension and simulation approach for diaphragm structure optimization. The change in displacement, stress, sensitivity and resonance frequency due to different diaphragm sizes with diaphragm thickness variation is also analyzed. The optimized diaphragm structure of 1750 × 1750 μm2 and microtunnel of 100 μm wide and 24 μm deep have been fabricated using bulk micromachining technique. The fabricated device response has been tested using LDV and sensitivity measurement system

    Nicotine-induced survival signaling in lung cancer cells is dependent on their p53 status while its down-regulation by curcumin is independent

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    <p>Abstract</p> <p>Background</p> <p>Lung cancer is the most lethal cancer and almost 90% of lung cancer is due to cigarette smoking. Even though nicotine, one of the major ingredients of cigarette smoke and the causative agent for addiction, is not a carcinogen by itself, several investigators have shown that nicotine can induce cell proliferation and angiogenesis. We observed that the proliferative index of nicotine is different in the lung cancer cell lines H1299 (p53-/-) and A549 (p53+/+) which indicates that the mode of up-regulation of survival signals by nicotine might be different in cells with and without p53.</p> <p>Results</p> <p>While low concentrations of nicotine induced activation of NF-κB, Akt, Bcl2, MAPKs, AP1 and IAPs in H1299, it failed to induce NF-κB in A549, and compared to H1299, almost 100 times higher concentration of nicotine was required to induce all other survival signals in A549. Transfection of WT-p53 and DN-p53 in H1299 and A549 respectively, reversed the mode of activation of survival signals. Curcumin down-regulated all the survival signals induced by nicotine in both the cells, irrespective of their p53 status. The hypothesis was confirmed when lower concentrations of nicotine induced NF-κB in two more lung cancer cells, Hop-92 and NCI-H522 with mutant p53 status. Silencing of p53 in A549 using siRNA made the cells susceptible to nicotine-induced NF-κB nuclear translocation as in A549 DN-p53 cells.</p> <p>Conclusions</p> <p>The present study reveals a detrimental role of nicotine especially in lung cancer patients with impaired p53 status and identifies curcumin as a potential chemopreventive.</p

    Sediment blue carbon stock of Avicennia officinalis in Vembanad Lake ecosystem, Kerala, India

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    Stock assessment of the blue carbon pool of selected patches of mangrove sediment in the Vembanad Lake was done using the standard protocols on a per ha basis and multiplied with the estimated area to derive the blue carbon stock of the particular fragmented mangrove stands of the species Avicennia officinalis (Indian Mangrove), twice (in the post and pre-monsoon) during October 2017-March 2018. The treatments included ‘aged’, ‘recent’, ‘healthy’ and ‘degraded’ mangroves of the selected species and ‘control’ without mangroves. The overall mean carbon stock in the A. officinalis sediments in selected locations of the Vembanad Lake area was 136.09 Mg C/ha (Mg=mega gram=1 tonne). This value is far low compared to the mean global soil organic carbon stock in the mangrove ecosystem (386 Mg C/ha). This finding suggests ample opportunity for more carbon sequestration in the selected mangrove ecosystems in Vembanad Lake, toward climate change mitigation measures. The treatments differed significantly in the cumulative stock of blue carbon and layer-wise blue carbon density in sediment (p<0.05), the highest seen in ‘healthy’ mangroves in both seasons. The overall range of layer-wise blue carbon density in sediment was found to be 0.003 to 0.56 Mg/m3. Spatial maps prepared for layer-wise blue carbon density in the sediment revealed its depth-wise increase. Layer wise blue carbon stock in sediment had a significant correlation with total organic carbon and organic matter (p<0.01) and with the C/N ratio of the sediment (p < 0.05). Based on the results, this study suggests total organic carbon and the C/N ratio of sediment as possible predictive indicators of sediment blue carbon

    Junctionfree gate stacked vertical TFET hydrogen sensor at room temperature

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    Presented through this work is an investigation of junctionfree gate-stacked (SiO 2 + high-k) double gated vertical tunnel field-effect transistor (JF-GS-VTFET) with focus on its hydrogen (H 2 ) sensing performance at room temperature (RT) for the first time. JF-GS-VTFET with vertically characterized channel length feature minimizes short channel effects (SCEs), elevates gate controllability over regular TFETs without the presence of any sharp doping gradient. A systematical study of the sensing performance is demonstrated through effective variations in Palladium (Pd) and Gold (Au) catalytic metal gate work functions corresponding to the concentration of hydrogen appearing at the gate metal surface. A concentration dependent thorough analysis has been illustrated in terms of energy band, potential, transfer and transient characteristics. Sensing capability of the device have been analyzed in terms of variations in detecting parameters such as transconductance (g m ), off current, on current, threshold voltage and sub-threshold slope in presence of the target gas using SILVACO ATLAS TCAD. At 1.04 ppm H 2 gas concentration, the optimally designed sensor exhibits high I ON /I OFF ratios in the order of ∼ 1013 and ∼ 1011 , high g m sensing responses of 99.98% and 98.93%, high off current sensing responses of ∼ 1.895×104 and ∼1 .47×104 , better sub-threshold swing sensing responses of ∼0.71 and ∼0.55, increased threshold voltage sensing responses of ∼0.27 and ∼0.25 for Pd and Au metal gates respectively at RT. Perceptible outcomes in terms of interface trap charge density have also been presented to recognize RT H 2 sensing

    A complete analytical model for MOS-HEMT biosensors: capturing the effect of stern layer and charge screening on sensor performance

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    This letter presents analytical and technology computer aided design models for analyzing the performance of biohigh-electron-mobility transistor (HEMT) sensors. Unlike existing models for these sensors in the literature, where the biolayer is modeled as semiconductor or insulator layer with analyte-induced interface charge (i.e., surface potential), the model presented in this letter provides a better design insights by taking into consideration charge screening effect and impact of electric double layer (Stern layer) on device performance. The simulation case study is focused on prostate cancer detection using prostate-specific antigen (PSA) present in human serum as the target biomarker. Application specific validation of the model has been presented through demonstration of a MOS-HEMT PSA sensor design with sensitivity large enough to detect clinically relevant concentration of PSA in human serum (1ng/ml–4ng/ml)
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