Effect of Introducing H[sub 2]O Vapor on Properties of RF Sputter-Grown ITO Anode Layer for OLEDs

Abstract

We report the effects of introducing H 2 O vapor on the structural, surface, and electrical properties of radio-frequency ͑rf͒ sputtered indium tin oxide ͑ITO͒ anode layer for organic light-emitting diodes ͑OLEDs͒. By introducing H 2 O vapor during rf sputtering, we obtained an ITO anode film with lower resistivity, higher transmittance, and a smoother surface relative to the conventional rf-sputter-grown ITO anode even though it was grown at a substrate temperature of 200°C. Secondary ion mass spectroscopy analysis clearly shows that OH content in the rf-sputter-grown ITO anode film was significantly increased by adding H 2 O vapor. In addition, the current density-voltage-luminance result of an OLED fabricated on an H 2 O-vapor-incorporated ITO anode showed a lower turn-on voltage and higher luminescence than those of OLEDs fabricated on the reference ITO anode. This suggests that the introduction of H 2 O vapor during rf sputtering is an effective technique employed to improve the ITO anode layer for both topand bottom-emitting OLEDs.Indium tin oxide ͓SnO 2 -doped In 2 O 3 ͑ITO͔͒ has been commonly used in organic light-emitting diodes ͑OLEDs͒ and flexible OLEDs as anode materials both academically and commercially, due to its low resistivity and high transmittance in a visible range. 1-3 To obtain a high-quality ITO anode layer, it is necessary to raise glass substrate temperatures up to 300-400°C during the radio-frequency ͑rf͒ sputtering process. However, high substrate temperature could lead to crystallization of the ITO anode film with a preferred orientation and a rough surface. Because protrusions and spikes on the rough ITO surface act as field emission positions, which have higher voltage than their surroundings, it is important to deposit an ITO anode layer with a very smooth surface for high-performance OLEDs. Although the ITO film grown at room temperature has a very smooth surface, it is difficult to apply in OLEDs as anode materials due to the fairly high resistivity. 4 For these reasons, the ITO anode layer grown at a high substrate temperature is required to apply the chemical and mechanical polishing process. To solve those problems, Ishibashi et al. reported that an ITO film with low resistivity could be obtained at a substrate temperature below 200°C by adding H 2 O gas during an inline dc sputtering process. 5 They showed that the addition of H 2 O gas during ITO sputtering resulted in suppression of ITO crystallization and reduction in ITO film resistivity. Although the technique of H 2 O vapor introduction during ITO sputtering has been reported, the effect of H 2 O vapor introduction on properties of ITO anode materials and the use of the H 2 O-incorporated ITO anode in OLEDs has not yet been reported in detail.In this work, we report on growth of the ITO anode with an extremely smooth surface and low resistivity for normal and flexible OLEDs by the addition of H 2 O vapor to ambient Ar during ITO sputtering. The H 2 O-incorporated ITO anode exhibited lower resistivity, higher transmittan...

Crystallisation Phenomena of In2O3:H Films

“…Indeed, using a fixed leak rate of the needle valve feeding water vapour, a higher p tot should result in a smaller p (H 2 O) and, hence, in a smaller concentration of hydroxyl in In 2 O 3 . In turn, the impact of hydroxyl on the crystalline growth of In 2 O 3 is a known phenomenon, thus, the (400)-orientation can be suppressed if water is present in a sputtering gas [27]. This is consistent with our results.…”

Effect of Rapid Thermal Annealing on the Electrical, Optical and Structural Properties of ZnO-Doped In<SUB>2</SUB>O<SUB>3</SUB> Films Grown by Linear Facing Target Sputtering

“…12 In our previous report, we also reported on the effects of oxygen gas during the sputtering process on the preferred orientation of the ITO film. 13 Therefore, the different preferred orientation of the ZIO film grown at different Ar/O 2 flow ratios could result in different electrical and optical properties of the ZIO films.…”

Effects of the Ag Layer Embedded in NIZO Layers as Transparent Conducting Electrodes for Liquid Crystal Displays

“…Indium tin oxide (ITO) films deposited on glass substrates have been widely used as a transparent conducting electrode for its applications in devices such as solar cells, touch panels, organic light-emitting diodes, and liquid crystal display (LCD) s due to their visible transparency (~90%) and low resistivity (2-4×10 -4 Ω/cm) [1][2][3][4][5][6][7][8][9]. However, undesirable damage to the optoelectronic device may be caused during deposition of ITO films by direct current (DC) or radio frequency (RF) sputtering [10].…”