Browsing by Author "Devi, Anjana"

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    Capacitance-voltage analysis of ZrO2 thin films deposited by thermal MOCVD technique.
    (The Electrochemical Society, 2009-10-09) Mih, Thomas Attia; Paul, Shashi; Milanov, Andrian P.; Bhakta, Raghunandan; Devi, Anjana
    The capacitance-voltage (C-V) characteristics of thin films of ZrO2 deposited by thermal metal-organic chemical vapour deposition (MOCVD) have been analyzed. The films were grown at three different temperatures (500, 550 and 600 ºC) and 1 mbar pressure from a novel monomeric zirconium amide-guanidinate complex [Zr(NEtMe)2(guanidinate)2]. The true capacitance was determined from measurements made at different frequencies in order to account for the series and shunt parasitic resistances during C-V measurements. Films grown at 500 and 550 ºC showed no hysteresis while those grown at 600 ºC exhibited a very small hysteresis window 0.16 V for O2 flow of 100 sccm and 0.19 V for 50 sccm O2 flow. A very small voltage shift is also obtained for the device under 10 hr voltage stress. These preliminary in-depth electrical results suggest that quality ZrO2 can be grown from the novel [Zr(NEtMe)2(guanidinate)2] complex precursor paving the way for their use as future gate dielectrics.
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    Electrical Performance and Stability of ZnO Thin-Film Transistors Incorporating Gadolinium Oxide High-k Dielectrics
    (Science Publishing Group, 2019-01-10) Ngwashi, Divine K.; Paul, Shashi; Devi, Anjana; Cross, R. B. M.
    This work investigates the performance and gate bias stress instability of ZnO-based thin film transistors (ZnO-TFTs) incorporating amorphous gadolinium oxide, a high-k dielectric material. ZnO thin films produced via radio frequency (RF) reactive magnetron sputtering were used as channel layers. The source/drain electrodes were achieved by the thermal evaporation of aluminium on a bottom gate inverted staggered ZnO TFT structure. Gadolinium oxide (Gd2O3) deposited by metal-organic chemical vapour deposition (MOCVD) served as the gate dielectric. The electrical characterisation of the ZnO-TFTs produced showed improvement in performance and stability in comparison to thermally-grown SiO2-based ZnO TFTs fabricated under the same conditions. The effective channel mobility, on-off current ratio and subthreshold swing of the TFTs incorporating Gd2O3 dielectric were found to be 33.5 cm2 V-1s-1, 107, and 2.4 V/dec respectively when produced. The electrical characterisation of the same devices produced with SiO2 dielectrics exhibited effective mobility, on-off current ratio and subthreshold swing of 7.0 cm2 V-1s-1, 106 and 1.4 V/dec respectively. It is worth noting that, the ZnO active layer was sputtered under room temperature with no intentional heating and post-deposition annealing treatment. On application of gate bias stressing on these thin film transistors, it was observed that threshold voltage instability increased with stress period in all device types. Transistors incorporating Gd2O3 however, were found to exhibit lesser threshold voltage related instability with regards to gate bias stressing in comparison to similar devices incorporating SiO2 as gate dielectric. It was also observed that the effective mobility in both devices tend to stabilize with prolonged gate bias application. In this work, it is demonstrated that Gd2O3 dielectric is a potential alternative to SiO2 for the fabrication of ZnO TFTs with improved performance and electrical stability under prolonged use.
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    High mobility ZnO thin film transistors using the novel deposition of high-k dielectrics.
    (Cambridge University Press, 2012) Ngwashi, Divine K.; Cross, R. B. M.; Paul, Shashi; Milanov, Andrian P.; Devi, Anjana
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    Lanthanide oxide thin films by metalorganic chemical vapor deposition employing volatile guanidinate precursors.
    (2009-11-24) Paul, Shashi; Milanov, Andrian P.; Toader, Teodor; Parala, Harish; Barreca, Davide; Gasparotto, Alberto; Bock, Claudia; Becker, Hans-Werner; Ngwashi, Divine K.; Cross, R. B. M.; Kunze, Ulrich; Fischer, Roland A.; Devi, Anjana
    The application of two novel metalorganic complexes, namely the isostructural tris(N,N'diisopropyl-2-dimethlyamido-guanidinato)gadolinium(III) (1) and tris(N,N'-diisopropyl-2-dimethlyamido-guanidinato)dysprosium(III) (2) as precursors for metalorganic chemical vapor deposition (MOCVD) of Gd 2O3 and Dy2O3 is discussed. On the basis of the detailed thermal gravimetric analysis (TGA) and isothermal TGA studies, both the precursors are very volatile and able to deliver continuous mass transport into the gas phase. The extraordinary thermal stability of the precursors was revealed by nulcear magnetic resonance (NMR) decomposition studies. Depositions were carried out in the presence of oxygen at reduced pressure and varying the substrate temperature in the range 300-700 °C. Uniform films with reproducible quality were deposited on Si(100) and Al 2O3(000l) substrates over the entire temperature range. Employing a multitechnique approach (XRD, SEM, AFM, EDX, XPS, RBS, SNMS, C- V), variations of the growth characteristics and film properties with deposition temperature are studied in terms of crystallinity, structure, surface roughness, composition, and electrical properties.
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    Rare-Earth based Oxide and Nitride thin films employing volatile homoleptic guanidinate precursors.
    (The Electrochemical Society, 2009-10-09) Milanov, Andrian P.; Thiede, Tobias; Hellwig, Malte; Parala, Harish; Bock, Claudia; Becker, Hans-Werner; Ngwashi, Divine K.; Cross, R. B. M.; Paul, Shashi; Ukunze, Ulrich; Fischer, Roland A.; Devi, Anjana
    The application of the metalorganic compound tris(N,N'-diisopropyl-2-dimethlyamidoguanidinato)gadolinium(III) (1) as a precursor for MOCVD of Gd2O3 is discussed. Depositions were carried out in the presence of oxygen at reduced pressure and varying the substrate temperature in the range 300 - 700{degree sign}C. Employing a multi-technique approach (XRD, SEM, AFM, EDX, RBS, SNMS, SE, C-V), variations of the growth characteristics and film properties with deposition temperature are studied in terms of crystallinity, structure, surface roughness, composition, optical and electrical properties. In addition, the use of 1 as single source precursor for the MOCVD of GdN thin films is also demonstrated.
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    Rare-earth substituted HfO2 thin films grown by metalorganic chemical vapor deposition.
    (Elsevier, 2011-10-29) Devi, Anjana; Cwik, Stefan; Xu, Ke; Milanov, Andrian P.; Noei, Heshmat; Wang, Yuemin; Barreca, Davide; Meijerd, Jan; Rogallad, Detlef; Kahn, Divine; Cross, R. B. M.; Parala, Harish; Paul, Shashi
    Thin films of HfGdOx and HfDyOx were deposited by metalorganic chemical vapor deposition (MOCVD) utilizing guanidinate precursors for Hf, Gd and Dy. The close match in the thermal properties of the precursors enabled the MOCVD of rare-earth (RE) substituted HfO2 over a wide temperature window. Film deposition was carried out in the temperature range 300–700 °C in the presence of oxygen on Si(100) substrates. HfGdOx films were analyzed in detail for their structure, composition and morphology using X-ray diffraction, Rutherford backscattering spectrometry, proton induced X-ray emission, X-ray photoelectron spectroscopy and scanning electron microscopy. The electrical properties of HfGdOx in terms of capacitance–voltage and current–voltage characteristics of metal-insulator-semiconductor device structures were evaluated.
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    Sc2O3, Er2O3, and Y2O3 thin films by MOCVD from volatile guanidinate class of rare-earth precursors
    (Royal Society of Chemistry, 2012) Milanov, Andrian P.; Xu, Ke; Cwik, Stefan; Parala, Harish; De Los Arcos, T.; Becker, Hans-Werner; Rogalla, Detlef; Cross, R. B. M.; Paul, Shashi; Devi, Anjana