Browsing by Author "Tiwari, Nidhi"

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Development of Al-doped ZnO thin film as a transparent cathode and anode for application in transparent organic light-emitting diodes
(2016-01-01)
Chauhan, Ram Narayan
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Tiwari, Nidhi
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Anand, R. S.
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Kumar, Jitendra
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光電工程學系
Aluminum doped zinc oxide thin films have been prepared by sputtering under argon gas pressure of 0.15 Pa at different radio frequency (RF) power densities to optimize the conditions for application in both bottom emitting and transparent OLEDs. The films exhibit a wurtzite-type hexagonal structure with the [0001] preferred orientation and optical transmittance of better than 80% in the visible region, but, varying energy bandgap. The sputtering at a high RF power density of 2.47 W cm(-2) yields Al-ZnO films of minimum resistivity (similar to 1 x 10(-3) U cm) and high work function (similar to 4.44 eV), appropriate for the anode in bottom emitting OLEDs. On the other hand, AZO films obtained at the low RF power density of 0.31 W cm(-2) correspond to a low work function (3.90 eV) with slightly higher electrical resistivity (5.60 x 10(-3) U cm), useful for cathodes in transparent OLEDs. The comparable performance observed for OLEDs fabricated with AZO and ITO anodes demonstrates the suitability of AZO as an alternative electrode. The increase in RF power density during sputtering leads to perceptible damage of the organic layer. The introduction of a buffer layer of Alq3/LiF/Al just above the organic layer is shown to suppress the damages significantly and improve the performance of the transparent OLEDs.
Electrical characteristics of InGaZnO thin film transistor prepared by co-sputtering dual InGaZnO and ZnO targets
(2015-01-01)
Tiwari, Nidhi
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Chauhan, Ram Narayan
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Liu, Po-Tsun
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Shieh, Han-Ping D.
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光電工程學系
A co-sputtering of dual InGaZnO and ZnO targets, abbreviated by ZnO co-sputtered IGZO, is used to fabricate a high performance indium gallium zinc oxide ( IGZO) thin film transistor in this work. The ZnO co-sputtered IGZO thin film exhibits a smooth (R-rms similar to 0.29 nm), featureless, and amorphous structure with high carrier density (n similar to 4.29 x 10(17) cm(-3)). The performance and stability of ZnO co-sputtered IGZO TFT has been investigated and compared with the counterparts fabricated by a single ZnO and a-IGZO target respectively. Highest linear field effect mobility of 16.1 cm(2) V-1 s(-1) with an I-on/I-off ratio of 1.04 x 10(7), saturation drain current of 3.8 mu A at 5 V, and the lowest threshold voltage of 2.0 V with subthreshold swing of 0.21 V per decade have been obtained for the ZnO co-sputtered IGZO TFT. Furthermore, the ZnO co-sputtered IGZO TFT exhibited only a threshold voltage shift (Delta V-th) of 2.75 V under negative biased illuminated stress conditions for 2500 s, whereas the IGZO and ZnO based TFTs suffered from a huge threshold voltage shift (Delta V-th > 6 V) under the same conditions. The obtained performance and stability of TFTs with ZnO co-sputtered IGZO film is very promising for low voltage display applications.
Electrical performance and stability of tungsten indium zinc oxide thin-film transistors
(2018-03-01)
Chauhan, Ram Narayan
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Tiwari, Nidhi
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Shieh, Han-Ping D.
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Liu, Po-Tsun
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光電工程學系
Amorphous tungsten indium zinc oxide thin film transistors (WIZO TFTs) have been prepared using radio-frequency (RF) magnetron co-sputtering system to co-sputter indium zinc oxide (IZO) and indium tungsten oxide (IWO) targets. The electrical performance parameters and positive biased stress (PBS) test of the co-sputtered WIZO TFT were investigated to obtain better characteristics with regards to the IZO and IWO TFT counterparts. The co-sputtered TFT displayed high electrical performance (field effect mobility, mu(FE) similar to 22.30 cm(2)/Vs, and sub-threshold swing, SS similar to 0.36 V/decade) and stable electrical behavior (PBS value shift, Delta V-th similar to 1.23 V) than the IZO (mu(FE) similar to 19.90 cm(2)/Vs, SS similar to 0.46 V/decade, Delta V-th similar to 7.79 V) and IWO (conducting in nature) TFTs for its application in flexible and transparent displays. (C) 2017 Elsevier B. V. All rights reserved.
Enhanced stability of thin film transistors with double-stacked amorphous IWO/IWO:N channel layer
(2018-06-01)
Lin, Dong
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Pi, Shubin
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Yang, Jianwen
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Tiwari, Nidhi
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Ren, Jinhua
In this work, bottom-gate top-contact thin film transistors with double stacked amorphous IWO/ IWO:N channel layer were fabricated. Herein, amorphous IWO and N-doped IWO were deposited as front and back channel layers, respectively, by radio-frequency magnetron sputtering. The electrical characteristics of the bi-layer-channel thin film transistors (TFTs) were examined and compared with those of single-layer-channel (i.e., amorphous IWO or IWO:N) TFTs. It was demonstrated to exhibit a high mobility of 27.2 cm(2)V(-1 )s(-1) and an on/off current ratio of 10(7).Compared to the single peers, bi-layer a-IWO/IWO:N TFTs showed smaller hysteresis and higher stability under negative bias stress and negative bias temperature stress. The enhanced performance could be attributed to its unique double-stacked channel configuration, which successfully combined the merits of the TFTs with IWO and IWO:N channels. The underlying IWO thin film provided percolation paths for electron transport, meanwhile, the top IWO:N layer reduced the bulk trap densities. In addition, the IWO channel/gate insulator interface had reduced defects, and IWO:N back channel surface was insensitive to the ambient atmosphere. Overall, the proposed bi-layer a-IWO/IWO:N TFTs show potential for practical applications due to its possibly long-term serviceability.
Modification of intrinsic defects in IZO/IGZO thin films for reliable bilayer thin film transistors
(2016-01-01)
Tiwari, Nidhi
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Chauhan, Ram Narayan
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Liu, Po-Tsun
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Shieh, Han-Ping D.
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顯示科技研究所
Dual active channel IZO/IGZO thin film transistors as such and with ZnO interlayer are fabricated and characterized to investigate the impact of ultra-thin ZnO insertion on their performance and bias stability. The ZnO interlayer suppresses the pre-existing divalent zinc vacancies and oxygen vacancies in the IZO front layer as systematically investigated by photoluminescence and XPS analysis. This interlayer leads to an enhancement of the electrical characteristics and stability of the bilayer TFT in comparison to the counterpart TFTs fabricated by a single IZO and a-IGZO-channel device. A high-field effect mobility (similar to 14 cm(2) V-1 s(-1)) IZO/IGZO transistor with excellent photo-bias stability (Delta V-th similar to -2.45 V) was obtained from 2 nm ZnO insertion in between the IZO and IGZO layer-enabling backplane electronics for high-resolution and large-sized AMOLED and TFT-LCD displays.
Photoluminescence and Reliability Study of ZnO Cosputtered IGZO Thin-Film Transistors Under Various Ambient Conditions
(2016-04)
Tiwari, Nidhi
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Chauhan, Ram Narayan
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Shieh, Han-Ping D.
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Liu, Po-Tsun
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Huang, Yi-Pai
Zinc oxide (ZnO) cosputtered indium-gallium-ZnO (IGZO) and pure IGZO thin films have been deposited at room temperature by dual RF magnetron sputtering and annealed in argon (Ar), nitrogen (N-2), and oxygen (O-2) ambients. The beneficial effect of various annealing environments appears because of a reorganization of the amorphous network with controlling the defect chemistry in the films as systematically investigated by photoluminescence analysis. The various defects, such as zinc vacancy (V-Zn), zinc interstitial (Zn-i), and oxygen vacancy (V-O), were remarkably enhanced in argon, while suppressed in N-2 and O-2 ambients-leading more reliable cosputtered structure than the IGZO to be utilized in thin-film transistors (TFTs) fabrication for transparent electronics. Furthermore, the ZnO cosputtered IGZO TFTs were also fabricated and systematically investigated the impact of various annealing environments on their performance characteristics. The characteristics were improved in N-2 ambient-displaying the field-effect mobility (mu(FE)) of 16.10 cm(2)/Vs, the threshold voltage (V-th) of 1.50 V, the subthreshold swing of 0.21 V/decade, and the negative bias illumination stress shifting of -2.75 V.
Silicon induced stability and mobility of indium zinc oxide based bilayer thin film transistors
(2016-11-14)
Chauhan, Ram Narayan
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Tiwari, Nidhi
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Liu, Po-Tsun
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Shieh, Han-Ping D.
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Kumar, Jitendra
Indium zinc oxide (IZO), silicon containing IZO, and IZO/IZO: Si bilayer thin films have been prepared by dual radio frequency magnetron sputtering on glass and SiO2/Si substrates for studying their chemical compositions and electrical characteristics in order to ascertain reliability for thin film transistor (TFT) applications. An attempt is therefore made here to fabricate single IZO and IZO/IZO: Si bilayer TFTs to study the effect of film thickness, silicon incorporation, and bilayer active channel on device performance and negative bias illumination stress (NBIS) stability. TFTs with increasing single active IZO layer thickness exhibit decrease in carrier mobility but steady improvement in NBIS; the best values being mu(FE) similar to 27.0, 22.0 cm(2)/Vs and Delta(Vt)h similar to -13.00, -6.75V for a channel thickness of 7 and 27 nm, respectively. While silicon incorporation is shown to reduce the mobility somewhat, it raises the stability markedly (Delta V-th similar to -1.20V). Further, IZO (7 nm)/IZO: Si (27 nm) bilayer based TFTs display useful characteristics (field effect mobility, mu(FE) = 15.3 cm(2)/Vs and NBIS value, Delta V-th = -0.75V) for their application in transparent electronics. Published by AIP Publishing.
Structural, optical, and photoluminescence study of ZnO/IGZO thin film for thin film transistor application
(2015-07-15)
Tiwari, Nidhi
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Shieh, Han-Ping D.
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Liu, Po-Tsun
;
光電工程學系
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顯示科技研究所
Highly transparent and c-axis oriented zinc oxide (ZnO)/indium gallium zinc oxide (IGZO) thin films have been fabricated by R.F. sputtering. The effect of annealing on physical properties of the films was investigated and compared with a-IGZO thin films. The films are wurtzite-type hexagonal structure similar to ZnO with [0 0 0 2] preferred direction and exhibit less density of defects. The TFTs fabricated with ZnO/IGZO films after annealing at 450 degrees C reveal smaller sub-threshold swing (SS similar to 0.52 V/dec) and threshold voltage (Vth similar to 1.3 V) than the TFTs (SS similar to 0.82 V/dec, Vth similar to 13.3 V) of a-IGZO thin film annealed at the same temperature. (C) 2015 Elsevier B.V. All rights reserved.