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Transparent zinc tin oxide thin-film transistors (ZTO-TFTs) [Zn:Sn = 4:1-2:1] have been fabricated so as to estimate the electrical instability under constant current stress. The relative intensity of the drain current noise power spectra density has been shown to have a typical 1/f-noise character, and it is implied that the mobility fluctuation in ZTO-TFT [Zn:Sn = 4:1] can be enhanced by a short-range ordering in amorphous Zn-Sn-oxide, causing a larger shift of the threshold voltage (deltaV(th)).

We have investigated the effects of Ti doping on the structural, optical, and electrical properties of indium tin oxide (ITO) thin films prepared by direct-current (DC) sputtering at room temperature. It is observed that the Ti doping changes the microstructure of the ITO films from amorphous to polycrystalline improving the electrical properties. The optimized ITO:Ti thin film after annealing shows a carrier concentration of 6.24 × 1020 cm−3, a mobility of 34 cm2/V s, and a resistivity of 2.3 × 10−4 Ω cm. The ITO:Ti film also shows a better thermal stability up to 450 °C.

The effects of zinc on the zinc-doped CaTiO 3 :Pr 3+ phosphors have been investigated by varying the zinc concentrations from 0 to 100 mol%. The variation of zinc concentration influences the crystallinity and morphology of the phosphors. The crystallinity and PL intensity increase as zinc content increases from 0 to 25 mol%. (Zn,Ca)TiO 3 :Pr 3+ at 25 mol% Zn exhibits nearly 3.6 times enhanced PL intensity compared to CaTiO 3 :Pr 3+ . Moreover, the red emitting phosphor developed in this study can be very effectively excited at the wavelengths of 400 nm. We think that (Zn,Ca)TiO 3 :Pr 3+ can be used as a complementary phosphor in the red region for the white LEDs.

Using ZnO, and three compositional In 2 O 3 -Ga 2 O 3 -ZnO (IGZO, In:Ga:Zn=1:1:1, 2:1:2, 2:2:1, atomic ratio) semiconductors, we have made and evaluated several double layered oxide thin-film transistors (TFTs). The drain current was mainly affected by the nearer channel material to a gate insulator. From the positive bias stress (PBS) tests, however, the electrical stability showed a complicated result, depending on both channel structures and post-heat treatments.

This paper reports on the structural and optical properties of ZnCuO thin films that were prepared by co-sputtering for the application of p-type-channel transparent thin-film transistors (TFTs). Pure ceramic ZnO and metal Cu targets were prepared for the co-sputtering of the ZnCuO thin films. The effects of the Cu concentration on the structural, optical, and electrical properties of the ZnCuO films were investigated after their heat treatment. It was observed from the XRD measurements that the ZnCuO films with a Cu concentration of 7% had ZnO(002), Cu2O(111), and Cu2O(200) planes. The 7% Cu-doped ZnO films also showed a band-gap energy of approximately 2.05 eV, an average transmittance of approximately 62%, and a p-type carrier density of approximately 1.33 x 10(19) cm-3 at room temperature. The bottom-gated TFTs that were fabricated with the ZnCuO thin film as a p-type channel exhibited an on-off ratio of approximately 6. These results indicate the possibility of applying ZnCuO thin films with variable band-gap energies to ZnO-based optoelectronic devices.

We investigate the effects of interfacial dielectric layers (IDLs) on the electrical properties of top-gate In-Ga-Znoxide (IGZO) thin film transistors (TFTs) fabricated at low temperatures below 200°C, using a target composition of In:Ga:Zn = 2:1:2 (atomic ratio). Using four types of TFT structures combined with such dielectric materials as Si3N4 and Al2O3, the electrical properties are analyzed. After post-annealing at 200°C for 1 hour in an O2 ambient, the sub-threshold swing is improved in all TFT types, which indicates a reduction of the interfacial trap sites. During negative-bias stress tests on TFTs with a Si3N4 IDL, the degradation sources are closely related to unstable bond states, such as Si-based broken bonds and hydrogenbased bonds. From constant-current stress tests of Id = 3 µA, an IGZO-TFT with heat-treated Si3N4 IDL shows a good stability performance, which is attributed to the compensation effect of the original charge-injection and electron-trapping behavior.

Transparent top‐gate Al‐Zn‐Sn‐O (AZTO) thin‐film transistors (TFTs) with an Al2O3 protective layer (PL) on an active layer were studied, and a transparent 2.5‐inch QCIF+AMOLED (active‐matrix organic light‐emitting diode) display panel was fabricated using an AZTO TFT backplane. The AZTO active layers were deposited via RF magnetron sputtering at room temperature, and the PL was deposited via two different atomic‐layer deposition (ALD) processes. The mobility and subthreshold slope were superior in the TFTs annealed in vacuum and with oxygen plasma PLs compared to the TFTs annealed in O2 and with water vapor PLs, but the bias stability of the TFTs annealed in O2 and with water vapor PLs was excellent.

We report on the growth and the properties of Sb-doped ZnMgO thin films deposited using radiofrequency (rf) magnetron sputtering for applications as transparent thin film transistors (TFTs) with p-type channels. The target was prepared with high-purity MgO mixed with ZnO and Sb2O5 as doping agents. Thin films were heat-treated in vacuum, oxygen, and nitrogen atmospheres. The eects of the working gas (Ar/O 2) ratios and the annealing conditions on the structural and the electrical properties were investigated. The atomic ratio of Zn/Mg in the films, and accordingly the films properties, depended on the post-annealing conditions and on the oxygen partial pressure in the working gas during sputtering.

A novel hybrid device structure for efficient white organic light emitting diodes has been developed, which has a high hole injection barrier between a fluorescence blue emission layer and a electron transporting layer, and therefore excitons could be confined in the emission layer close to the electron transporting layer. A phosphorescent red dopant has been introduced into the electron transporting layer to harvest triplet states of the fluorescent blue emission layer and we have succeeded in obtaining the balanced white emission from blue singlet excitons and red triplet excitons with high efficiency. The optimized device showed the maximum external quantum efficiency of about 25% at 100 cd/m2.

A blue light emitting diode based on wide band gap host for a blue fluorescence light emitting layer has been developed to fabricate hybrid white organic light emitting diode comprising of a fluorescence blue and a phosphorescence red light emitting layers. We have tested various wide band gap host materials including CBP, BAlq, and TcTa, and among them the device with TcTa host has shown good performance which could be attributed to tight exciton confinement. A phosphorescence red dopant (RD) has been introduced into BAlq layer to harvest triplet states of the fluorescence blue emission layer and we have succeeded in obtaining the balanced emission of the blue and the red emissions with high efficiency. The device showed the maximum external quantum efficiency of 16% at 0.1 mA/cm2 and 13% of external quantum efficiency with (0.29, 0.23) of CIE coordinates at 10 mA/cm2.

Top-emission organic light-emitting diodes (TEOLEDs) using chromium anode have been fabricated by employing two techniques: direct-current magnetron sputtering and e-beam evaporation. Atomic force microscopy and work function taken on the chromium film surfaces obtained from both techniques revealed that using dc magnetron sputtering is advantageous over e-beam evaporation in terms of surface characteristics particularly when the film is deposited. The anode having a triple-layer structure of Cr/Al/Cr was deposited on a Si wafer. The device structure of the TEOLED was Cr (20 nm)/Al (100 nm)/Cr (20 nm)/α-napthylphenylbiphenyl diamine (NPB) (60 nm)/tris(8-hydroxyquinoline) aluminum (Alq3) (60 nm)/LiF (1 nm)/Al (2 nm)/Ag (20 nm)/NPB (200 nm). The TEOLED containing the Cr layer deposited by dc magnetron sputtering method showed higher luminance and efficiency than that containing the Cr layer deposited by e-beam evaporation. The superior device characteristics of the TEOLED containing the chromium layer deposited by dc magnetron sputtering have been investigated.

A top emission organic light emitting diode (TEOLED) comprised of a Cr anode on PES film/NPB/Alq 3 /cathodes has been fabricated. The triple layer structure of Cr/Al/Cr allowed for fabrication of a crack-free anode and provided better thermal stability and higher work function than a conventional ITO anode. For the Cr/Al/Cr anodes, a series of Cr layers with various surface morphology has been tested. A Cr layer with a smooth surface morphology was found to be optimal. The TEOLED fabricated on PES film having good anode surface morphology showed similar device characteristics to that on a Si wafer. TEOLEDs on PES film and Si wafer exhibited a maximum luminous efficiency of 2.87 and 3.0 cd/A, respectively, at 1000 cd/m 2 with a NPB/Alq 3 /LiF/Al/Ag structure on a Cr/Al/Cr anode.

The stability of ZnO TFT under bias stress was investigated. Transparent ZnO thin films deposited by means of atomic layer deposition(ALD) and plasma enhanced atomic layer deposition(PEALD) at 100 °C were used as the active channel. The TFT with PEALD grown ZnO layer has better stability under bias stress than the TFT with ALD grown ZnO layer.

ZnO TFT was fabricated using ALD deposited materials. The temperature dependence of transfer characteristics and the degradation behavior under gate bias stress was observed. The shift of Vth under gate bias stress was explained through electron trapping and H movement.

Red-emitting CaTiO3:Pr phosphor thin films were deposited on glass, ZnO/ITO/glass, and ITO/glass substrates by RF magnetron sputtering. The effects of various substrates and heat treatment on the structural and luminous properties were investigated. The films deposited on ZnO/ITO/glass exhibited superior crystallinity and more enhanced PL and CL properties compared with those on ITO/glass. The intermediate ZnO layer between phosphor film and ITO contributed to the growing behaviors and the roughening of CaTiO3:Pr phosphor thin films, and consequently, to the excellent luminescence. The luminescent properties of the films were improved by following heat-treatment due to a combination of factors, namely the transformation from amorphous to poly crystalline phases, the activation of the activators, and the elimination of microdefects.

ZnGa 2 O 4 :Mn thin film phosphors were prepared on ITO/glass by rf magnetron reactive sputtering. The effects of the oxygen partial pressure in sputtering and annealing atmospheres on crystallinity, compositional variations, and luminescent properties of thin films were investigated. Atomic ratio of Ga/Zn in films strongly depended on the postannealing conditions, as well as the oxygen partial pressure in sputtering gas during sputtering, and accordingly affected the luminous properties.

ZnGa2O4:Mn phosphor thin films were deposited on ZnO:Ga/glass, ZnO:Al/glass, ZnO/ITO/glass, and ITO/glass by rf magnetron sputtering. Effects of substrates and heat treatment on the structural and luminescent properties were investigated. The surface morphology, growing behavior, and luminescent properties of thin films depend on the crystallinity of the substrates. Thin film phosphors were heat-treated in a N2+vacuum, vacuum (∼10−3 Torr), and air atmosphere, respectively. The annealing conditions did not affect the surface morphology and crystallinity of the films. However, the Ga/Zn atomic ratios and luminescent characteristics were dependent on these conditions.

We demonstrate that the voltage-dependent average mobility of In–Ga–Zn–O (IGZO) thin-film transistors (TFTs) can be excellently fitted by an empirical mobility function based on the exponential density of deep and tail states. The proposed mobility function needs only 5 parameters and does not need the concept of the threshold voltage which is inherently ambiguous in amorphous oxide TFTs. Both the transfer and output curves of the device are well reproduced by integrating the mobility function.

ZnGa2O4:Mn and CaTiO3:Pr thin-film phosphors which emit green and red light, respectively, were deposited on ZnO/ITO/glass and ITO/glass substrates by a rf reactive magnetron-sputtering method. To improve photo- and cathodoluminescent properties of the thin-film phosphors, ZnO buffer layers were deposited between the thin-film phosphor and the ITO-coated glass substrate. A transparent c-axis preferentially oriented ZnO thin-film buffer layer could be obtained on the ITO film, while ITO had an amorphous-like structure. ZnGa2O4:Mn and CaTiO3:Pr thin-film phosphors were used to evaluate the effects of the ZnO buffer layer. The crystal structures of thin-film phosphors deposited on ZnO/ITO/glass substrates were developed better than those on ITO/glass, consequently, the former showed photo- and cathodoluminescent intensity at least twice as high as the latter.

This paper reports on the thin film transistor (TFT) based on TiOx prepared by direct current (DC) magnetron sputtering for the application of n-type channel transparent TFTs. A ceramic TiOx target was prepared for the sputtering of the TiO2 films. The structural, optical, and electrical properties of the TiO2 films were investigated after their heat treatment. It is observed from XRD measurement that the TiO2 films show anatase structure having (101), (004), and (105) planes after heat treatment. The anatase-structure TiO2 films show a band-gap energy of approximately 3.20 eV and a transmittance of approximately 91% (@550 nm). The bottom-gate TFTs fabricated with the TiO2 film as an n-type channel layer. These devices exhibit the on-off ratio, the field-effect mobility, and the threshold voltage of about 10(4), 0.002 cm2/Vs, and 6 V, respectively. These results indicate the possibility of applying TiO2 films depositied by DC magnetron sputtering to TiO2-based opto-electronic devices.

Selective energy transfer from triplet states of the fluorescent blue emission layer to a red phosphorescent dye in a neighbored triplet harvesting layer has been achieved, which has provided improved efficiency with emissions from fluorescent and phosphorescent dyes. First of all, it is crucial to find a wide band gap host for a fluorescent blue emission layer which has larger triplet state band gap than green or red phosphorescent dye. It was found that TcTa is a good wide band gap host for fluorescent blue dopant(BD) and a efficient blue device was obtained. A phosphorescent red dopant (RD) was introduced into a neighboring electron transporting layer to harvest triplet states in the fluorescent blue emission layer and by optimizing the distance between the blue emission layer and the red triplet harvesting layer, we have succeeded in obtaining the balanced emission of the blue and the red emissions with high efficiency from the device structure of NPB/TcTa:BD/BAlq/BAlq:RD/BAlq/LiF/Al. The device showed maximum external quantum efficiency of 16 % at 0.1 mA/cm2 and 13 % of external quantum efficiency, (0.29, 0.23) of CIE coordinates and 920 cd/m2 at 10 mA/cm2. To realize RGB WOLED, a fluorescent green dopant was introduced into the blue emission layer. The RGB WOLED was successfully obtained through optimization of doping concentration for green dopant and it showed 10 % of external quantum efficiency, (0.36, 0.36) of CIE coordinates and 1400 cd/m2 at 10 mA/cm2.

We have investigated ZnO-incorporated CaTiO3:Pr3+, a red phosphor, and its application for the solid-state lighting. Efficient red emission from the phosphor was obtained by the excitation of wavelength 400 nm. Potentially, ZnO-incorporated CaTiO3:Pr3+ can be used as a complementary phosphor in the red region for the white LEDs.

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The effects of active thickness on the characteristics of oxide TFTs were investigated for the case of ZnO TFT and IGZO TFT. As the decrease of active thickness, the Von (Turn-on Voltage of TFT) was shifted to near zero Volt and negative shift of Von as decrease of channel length was also diminished. The overall performance (including subthreshold swing and leakage currents) was improved with thinner active layer. This behavior could be explained under the consideration of unintentional n-type doping in active layer. But, for the constant-current stress, thinner active layer TFT showed less stable behavior.

We have fabricated transparent bottom gate thin film transistors (TFTs) using Al-doped zinc tin oxide (AZTO) as active layers. The AZTO active layer was deposited by rf magnetron sputtering at room temperature. The AZTO TFT showed good TFT performance without postannealing. The field effect mobility and the subthreshold swing were improved by postannealing below 180 °C. The AZTO TFT exhibited a field effect mobility (μFET) of 10.1 cm2/V s, a turn-on voltage (Von) of 0.4 V, a subthreshold swing (S/S) of 0.6 V/decade, and an on/off ratio (Ion/Ioff) of 109.

White light emitting diodes with high efficiency and brightness have been fabricated using phosphorescent materials by spin coating an emission layer. The emission layer consisted of sky blue and orange light emitting materials based on iridium complexes, which were dissolved in toluene solvent with 4,4'-bis(carbazoyl-9-yl)biphenyl (CBP) as a host and polystyrene as a binder. The introduction of polystyrene binder resulted in not only good film forming properties but also better device performance than that of poly(vinyl carbazole) conventionally used as a host material. The device structure was ITO/PEDT:PSS/emission layer/BAlq/LiF/Al. The color of the devices varied according to the composition of light emitting materials and the device having the closest to white emission showed CIE coordinates of (0.33,0.39) with an external quantum efficiency and a current efficiency of 6.1% and 13 cd/A, respectively, at 100 cd/m2.

We have fabricated 2.15 inch AM-OLED panel composed of 176 × 144 (106 dpi) transparent pixels driven by ZnO-TFT. Transparent ZnO thin film deposited by means of atomic layer deposition at 100°C was used for the active channel. The ZnO TFT had a mobility of 1.13cm2/V.s, a threshold voltage of 0.8V, and an on/off ratio of 106. The fabrication of the ZnO TFT array for AM-OLED display has been carried out with four-mask process. and the integration of the ZnO TFT array and the transparent OLED consisted of a transparent anode and cathode and organic layers led to really transparent display.