Research On Photoelectric Thin Film Processes And Devices Using Atomic Layer Deposition

Atomic layer deposition(ALD) method has already shown its versatility in industrial use for deposition of dielectric and luminescent films for electroluminescent flat panel displays. Organic light-emitting diodes(OLEDs) have attracted increasing attention due to their potential application for display and lighting. The encapsulation process is a key technology which influences both the lifetime and reliability of OLEDs. The long-time devices require encapsulation materials to protect them from water and oxygen. Thin film encapsulation(TFE) is considered as one of the most potential methods to protect devices from moisture and oxygen penetration in electronic devices. Recently, several researches have focused on the multilayered nanolaminate structure for TFE which comprised of alternating layer of different materials with an individual layer of nanometer-scale thickness. However, there still are some issues which need to be investigated and improved in TFE. In this thesis, we have developed the novel TFE fabrication process based on ALD. Thin films are successfully applied to OLED and TFT. Some results have been obtained as follows:First, the effect of the pulse and purge time on the properties of the deposited films were studied at 85 ℃, including Al2O3, Zr O2, alucone and zircone films. Al2O3 films were fabricated using H2 O and trimethylaluminum(TMA) as precursors with a depositon rate of 1 ?/ cycle and 1.89 % uniformity. The root-mean-square(RMS) surface roughness of the Al2O3 film was 1.12 nm.The light transmission of the Al2O3 layer was above 99.2%. The water vapor transmission rate(WVTR) values of 200 nm Al2O3 films are as low as 1.55×10-4 g/m2/day at 25℃, 65% RH. H2 O and tetrakis(dimethylamido) zirconium(TDMAZ) were used as precursors for Zr O2 with a deposition rate of 1.22 ?/ cycle and 1.95 % uniformity. Alucone films were grown using TMA and ethylene glycol(EG) using 0.1 s of TMA pulse, 10 s of N2 purge, 0.3 s of EG pulse with carrier gas and 15 s of N2 purge. Zircone films were deposited through TDMAZ and EG pulse and general reactions between the TDMAZ and EG was demonstrated by FTIR spectra.Secondly, a hybrid nanolaminates consisting of Al2O3/ Zr O2/ alucone(aluminum alkoxides with carbon-containing backbones) grown by ALD were investigated for an encapsulation of OLEDs. The electrical Ca test in this study was designed to measure WVTR of nanolaminates. We found that moisture-barrier performance was improved with the increasing number of dyads(Al2O3/ Zr O2/ alucone) and the WVTR reached 8.5×10-5g/m2·day at 25 ℃, RH 65 %. The half lifetime of a green OLED with the initial luminance of 1500 cd/m2 reached 350 h using three pairs of the Al2O3(15 nm)/Zr O2(15 nm)/alucone(80 nm) as encapsulation layers. We have optimized a new structure based on the Zr Alx Oy-aluminate phase with higher packing density that formed at the interfaces between Al2O3 and Zr O2. This structure creates a tortuous path resulting in very long effective diffusion pathways increasing the barrier performance with WVTR of 4.76×10-5g/m2/day.Thirdly, Zr O2/Zircone composite thin films with a configuration of distributed Bragg reflectors(DBR) are fabricated by using ALD. The full width at half maximums(FWHMs) of green OLEDs spectra decreases as the number of Zr O2/ Zircone pairs increases, and the minimum value of FWHMs reaches 12 nm. Compared with the reference device, the current efficiency and the power efficiency of OLEDs have been improved more than 40% and 60%, respectively, by using a microcavity including four-pairs Zr O2/Zircone thin films. Zr O2/Zircone composite thin films show that the permeability was as low as 4.5×10-4 g/m2/day measured by a Ca degradation test at 25 ℃ and a relative humidity of 65 %. It demonstrates that the DBRs with hybrid structure also have good barrier performance.Finally,the Zr O2-Al2O3 ultra nano composite layer were prepared based on atomic layer deposition technology and applied in TFT, the study found that this composite insulation layer can be combined with the advantages of each monolayer film, not only retained the properties of high-k materials of high capacitance coupling ability, the leakage performance of the device has also been greatly improved. This is mainly due to that the amorphous alumina can suppress the formation of polycrystalline structure in high-k zirconium oxide. The ultra nano composite can avoid the disadvantage that the single material once produced defects will be along the direction of the continuous generation of defects. The property of the device that with ultra nano composite are good. The switch of the device is greater than 107, which exhibits high open current, low off current, result in a fast response, low power consumption, and meet the driving OLED. The threshold voltage is only 0.15 V, the mobility is as high as 14.3 cm2 /Vs. In addition, the use of temperature-stress method to quantitative characterization of the active device layer with internal energy and density, reveal the inherent mechanism of influence the stability of the device, device exhibits more stable is due to the smaller density of states.