BITS Faculty Publications
Permanent URI for this communityhttp://localhost:4000/handle/123456789/1867
Browse
10 results
Search Results
Item Heterogeneous CMOS-MEMS based Boost Converter for 2.4 GHz RF energy Harvester(IEEE, 2024) Rao, V. RamgopalInternet of Things (IoT) has experienced a significant growth in last few years. Billions of battery-powered wireless sensors are expected to be employed as the IoT becomes an integral part of our daily lives. Therefore, ambient energy resources such as light, RF source, EM radiation, thermal energy can be utilized to prolong the lifetime of batteries for sensors. In this work, ambient RF energy source is used for energy harvesting to power up the wireless sensors and low power electronic devices. For the first time, we experimentally demonstrated RF energy harvester to scavenge 2.45 GHz from Wi-Fi sources using commercially available CMOS-MEMS (micro electromechanical switch) hybrid switches. The use of MEMS switches in the boost converter instead of conventional NMOS switches reduces the leakage current, stabilize the ON-state resistance, and improves the overall efficiency. Our experimental result indicates that the use of MEMS switches increases the efficiency of the energy harvester more than 15% as compared to its NMOS counterpart.Item High Yield Polymer MEMS Process for CMOS/MEMS Integration(Springer, 2011-02) Rao, V. RamgopalMEMS community is increasingly using SU-8 as a structural material because it is self-patternable, compliant and needs a low thermal budget. While the exposed layers act as the structural layers, the unexposed SU-8 layers can act as the sacrificial layers, thus making it similar to a surface micromachining process. A sequence of exposed and unexposed SU-8 layers should lead to the development of a SU-8 based MEMS chip integrated with a pre-processed CMOS wafer. A process consisting of optical lithography to obtain SU-8 structures on a CMOS wafer is described in this paper.Item ZnO Nanorod Based Ultra Sensitive and Selective Explosive Sensor(IEEE, 2013-02) Rao, V. RamgopalA small scale (20 μm), ultra sensitive (50 ppb) and highly selective sensor based on ZnO nanostructures using Micro-electro-mechanical system (MEMS) platform has been reported here for the detection of explosive and Volatile Organic Compound (VOC) vapors. Flower and rod like architectures of nanorods were used as a sensing layer. The nanorods prepared via chemical synthesis were uniform with diameters of 50-80 nm and lengths about 3-4 μm. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) reveal that the nanostructures are well oriented with the c-axis, perpendicular to the substrate. A relatively higher selectivity for 2, 4, 6-Trinitrotoluene (TNT) vapors compared to other VOCs at room temperature were observed. The intensity of deep level green emission peak associated with point defects decreases after exposure as revealed from Photoluminescence (PL) spectra.Item Nano-electro-mechanical transduction and packaging solutions for polymer MEMS devices(IEEE, 2015) Rao, V. RamgopalPolymeric micro/nano electromechanical sensors and devices have recently gained much attention over their Si counterparts because of their lower cost and higher sensitivity. In this paper, we have reviewed various reported schemes for nano-electro- mechanical transduction for polymeric sensors particularly for physical, chemical and bio-sensing applications. We have also reviewed the packaging aspects and challenges for these polymeric sensors for various applications.Item A lab-on-a-chip system for detection of multiple macronutrients in the soil(IEEE, 2016) Rao, V. RamgopalIn this work, we have demonstrated for the first time the sensing of soil macronutrients nitrate and potassium with the use of MTDAN ionophore, nitrate ionophore VI and 18crown6 ether in a PVC/DOS matrix using a highly sensitive piezoresitive silicon oxide cantilevers. The complete portable electronics system along with a liquid cell for on the field experimentation has been demonstrated.Item Nanomechanical characterization of multiferroic thin films for micro-electromechanical systems(World Scientific, 2011) Rao, V. RamgopalIn this paper, the elastic properties of Dy modified BiFeO3 (BDFO) multiferroic films deposited on Si substrate are reported for the first time. The mechanical properties are extracted using nanoindentation technique. The Young's modulus and hardness of the BDFO films are found to be 140 ± 3 GPa and 7.5 ± 0.3 GPa respectively. In this study the properties in the region of penetration depth up to 20% of BDFO film thickness, are found out. For these indentation depths, Young's modulus and hardness are almost constant indicating that substrate effects are not significant. It is also confirmed that neither cracks, nor pile-ups can be observed for indentation loads up to 10 mN. However, at higher indentation loads (>10 mN), bulging and spallation are observed suggesting delamination and buckling of the film. The mechanical properties of BDFO films are similar to that reported for lead zirconate titanate (PZT), while offering many novel properties. This report is accordingly expected to facilitate the design of BDFO-based micro-electromechanical systems devices.Item A Novel SU8 Polymer Anchored Low Temperature HWCVD Nitride Polysilicon Piezoresitive Cantilever(IEEE, 2014-12) Rao, V. RamgopalIn this paper, we present a novel approach for fabricating piezoresistive silicon nitride cantilevers using polymer as an anchor. In our approach, the silicon nitride structural layers, as well as the polycrystalline silicon piezoresistive layer, are deposited by a low temperature hot-wire chemical vapor deposition process. The novelty of this process is that the silicon wafer is not consumed and is reusable, and the process also allows use of alternate materials for cantilever fabrication in place of silicon substrate. The fabricated silicon nitride cantilevers are characterized for their mechanical and electromechanical behavior.Item Polymer-Based MEMS Photodetector With Spectral Response in UV-Vis-NIR and Mid-IR Region(IEEE, 2015-08) Rao, V. RamgopalIntegrating various components on the same chip is highly sought after for various optoelectronic applications. In an attempt to provide an on-chip photodetection, a MEMS-based photodetector device with a wide spectral response is presented. The design merges the photoconductive and pyroelectric properties of nanomorphology-controlled polyvinyl alcohol as a photoactive layer. The fabrication technology is low cost with a single-layer deposition of photoactive polymer on a MEMS low thermal mass platform designed to improve the heat loss to the substrate. This fabricated device with a metal-semiconductor-metal structure shows Schottky diode behavior. The photoresponse of this device was observed from UV to mid-IR region with minimum light detection capability of 30 nW in UV, 120 nW for visible light, and 100 μW for IR light. The effect of nanomorphology and the thickness of the photoactive layer were studied to optimize the responsivity in the different waveband regions. Typically, at zero bias, under 405-nm illumination with light intensity of 170 μW/cm 2 , the photodetector exhibited responsivity of 0.53 A/W. The wavelength response of this detector was found to be similar with standard detectors of the UV visible as well as mid-IR region (6.3-10.6 μm). The proposed on-chip MEMS-based photodetection module with the broad-spectrum detection capability and lower power consumption is useful for lab-on-chip-based technologies for a wide range of optical/spectroscopic applicationsItem On-Chip Integration of Photodetector and Sensor: A Multimodal Photonic Device for Sensing Applications(IEEE, 2017-08) Rao, V. RamgopalIn this paper, we present the design and development of a novel miniaturized multimodal photonic sensor, which can be configured dually as a photodetector in the absorptive mode and as a pyro-detector in the photonic sensor mode. In this paper, we have fabricated a polyvinyl alcohol (PVA) photoactive layer-based MEMS structure and analysed the effect of effective inter-electrode separation on the photoactive area of the photoactive film using the four quadrant metal-semiconductor polymer-metal (MSM) design on the photoresponsivity of this device in terms of photoconductive and the pyroelectric responses. Our analysis reveals that the interdigitated electrode configuration is best suited for photoconductive response while the cross-electrode configuration with large effective interelectrode spacing is advantageous for pyroelectric measurement in the infrared region. Here, the unique design of this device offers the choice of electrode configurations that enables the utility of this device in various regions of the electromagnetic spectrum. In this regard, we demonstrate the optical detection of localized surface plasmon resonance of immobilized gold nanoparticle monolayer in the visible region, employing the absorptive mode and the detection of the spectroscopic signature of RDX and TNT molecules (134 μg/cm 2 ) in the midinfrared region using photonic sensor mode. This paper paves a way for designing a low-cost PVA-based miniaturized sensor architectures with huge potential for on-chip real-time detections in various fields of scientific and commercial applications.Item Piezoresistive microcantilever based lab-on-a-chip system for detection of macronutrients in the soil(Elsevier, 2017-12) Rao, V. RamgopalMonitoring of soil nutrients is very important in precision agriculture. In this paper, we have demonstrated a micro electro mechanical system based lab-on-a-chip system for detection of various soil macronutrients which are available in ionic form K+, NO3−, and H2PO4−. These sensors are highly sensitive piezoresistive silicon microcantilevers coated with a polymer matrix containing methyltridodecylammonium nitrate ionophore/ nitrate ionophore VI for nitrate sensing, 18-crown-6 ether for potassium sensing and Tributyltin chloride for phosphate detection. A complete lab-on-a-chip system integrating a highly sensitive current excited Wheatstone’s bridge based portable electronic setup along with arrays of microcantilever devices mounted on a printed circuit board with a liquid flow cell for on the site experimentation for soil test has been demonstrated.