Rewritable ITO Patterning for Nanophotonics

Indium tin oxide (ITO) targets possess good performances, thereby used to produce high-quality ITO films in transparent electrodes of various optoelectronic devices. The performance of the target greatly affects the performances of prepared ITO films. However, effect of the overall performance of ITO targets on ITO films performance is still not fully understood. ITO films were prepared with four targets by magnetron sputtering in the similar condition in this study. Effects of crystal structure, resistivity, and oxygen content of the targets on photoelectric performances of ITO films were all evaluated. Results showed the important effect of target properties on obtained film characteristics. ITO films prepared by low resistivity targets are more evenly distributed on the substrate surface. Meanwhile, oxygen content of obtained ITO films decreased as oxygen content of ITO targets used in sputtering process increased. This also significantly improved the photoelectric performances. ITO thin films deposited using targets with low resistivity and low oxygen content exhibited excellent photoelectric performances. In this experiment, the prepared ITO film illustrated the lowest resistivity of 1.75×10−4 Ω·cm and average transmittance of 90.5%. In sum, these findings provided a certain experimental basis for further improving the performances of ITO films.

Optical Kerr nonlinearity (n2) in n-type indium tin oxide (ITO) films coated on glass substrates has been measured using Z-scans with 200-fs laser pulses at wavelengths ranging from 720 to 780 nm. The magnitudes of the measured nonlinearity in the ITO films were found to be dependent on the carrier concentration with a maximum n2-value of 4.1 x 10-5 cm2/GW at 720-nm wavelength and an electron density of Nd = 5.8 x 1020 cm-3. The Kerr nonlinearity was also observed to be varied with the laser wavelength. By employing a femtosecond time-resolved optical Kerr effect (OKE) technique, the relaxation time of OKE in the ITO films is determined to be ~1 ps. These findings suggest that the Kerr nonlinearity in ITO can be tailored by controlling the carrier concentration, which should be highly desirable in optoelectronic devices for ultrafast all-optical switching.

Roll-to-Roll fabrication of ITO thin film for flexible optoelectronics applications: The role of post-annealing

Transparent conductive indium tin oxide (ITO) films with thin Ni-doped surface layers were prepared for organic light emitting diode (OLED) application. The top Ni-doped ITO surface layer were synthesized using Ni (RF) and ITO (DC) co-sputtering method at 120°C and annealed at 300°C for 10 minutes in vacuum to form a modulated work function layer in contact with the subsequently deposited light emitting organic layers. OLED devices with an Al/Alq3/NPB/Ni-doped ITO/ITO/glass structure were fabricated to investigate the effect of the Ni-doped ITO layer on the characteristics of the luminescence efficiency. The depositions of the Al/Alq3/NPB stacked films on top of the Ni-doped ITO/ITO/glass sample were conducted using thermal evaporation in a cluster tool without breaking the vacuum. Initial results show that the device turn-on voltage decreases from 10 volts to 6 volts and the luminescence efficiency was improved by 36% due to the existence of the Ni-doped ITO layer. It was also found that the optical transmittance of the ITO film decreased with the Ni concentration, resulting in external quantum efficiency deterioration by 3%. It was suspected that the presence of Ni (Φ~5.2eV compared to that of ITO ~4.2eV) on ITO surface decreases the heterojunction barrier height at the ITO/NPB interface, allowing more effective transportation of hole-carriers and hence an enhancement on the external quantum efficiency. However the optical impurity scattering of the Ni atoms in the ITO matrix caused the deterioration of the optical transparency and negative effect on the external quantum efficiency.

Indium Tin Oxide (ITO) films deposited by magnetron sputtering are widely used as transparent conducting layers for InGaN based light-emitting diodes (LEDs). Compared to ITO films deposited by electron beam evaporation, tthe ITO films deposited by magnetron sputtering typically have higher optical transmittance and greater electrical conductivities, which can result in higher efficiency for LEDs. However, the surface of LEDs could be damaged due to bombarding of highly energetic ITO particles during magnetron sputtering, which can cause a higher ITO/p-GaN contact resistance. In addition, the n-electrode/n-GaN contact can also be affected by different ITO treatment processes. Therefore, there is still a need to optimize the ITO deposition and treatment processes to minimize the working voltage In this work, the relationship of the ohmic contacts of ITO/p-GaN and n-electrode/n-GaN with ITO deposition and treatment process have been investigated in details, by Circle Transport Line method (CTLM) and Transport Line method (TLM). It is found that a special pre-treatment process for magnetron sputtering ITO films can reduce the working voltage by 0.1V compared to the conventional processes by further lowering the n-electrode/n-GaN contact resistivity. This work can help further improve the luminous efficacy of white LEDs especially in the high power working conditions.

A systematic study to optimize the electrical properties of ITO–graphene composite films deposited by spray pyrolysis method was investigated. The Hummers method was used for the synthesis of graphene oxide (GO) powder. Graphene was prepared by chemical reduction method from GO. To reduce GO, the most common reducing agent hydrazine hydrate at 3 ml per 100 mg of GO was used, Then, “ITO–graphene” composite films deposited by spray pyrolysis method. Structural, electrical and optical properties of films by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, two-point probe method, Hall Effect experiment and UV–Vis were analyzed. The results show that graphene sheets and “ITO–graphene” composite have been produced. The obtained ITO–graphene composite films showed an energy band gap from 3.62 to 3.57 eV and sheet resistance from 7.5 to 1.5 KΩ/sq in comparison with undoped ITO films. This study showed that adding graphene to ITO film without causing much change in structural properties and energy gap, reduces the resistance of ITO film about 75 % and increases its transparency up to 90 %. The results of this study may lead to ITO–graphene composite films be more interested in sensing and solar cells applications and composites.

ITO(indium tin oxide) 박막을 RF 마그네트론 스퍼터링법에 의해 산소 분압을 0에서 <TEX>$6{\times}10^{-5}$</TEX> Pa로 변화시킨 조건 하에서 PET 기판 위에 증착하였고, 산소 분압에 따른 ITO 박막의 전기적, 광학적 특성과 결정성의 변화를 조사하였다. 산소 분압이 <TEX>$1{\times}10^{-5}$</TEX> Pa 이하에서는 증착된 ITO 박막은 비정질 구조를 가지는 반면에 <TEX>$2{\times}10^{-5}$</TEX> Pa 이상에서는 결정질임을 확인하였다. 이러한 구조적 변화와 더불어 전하 캐리어 농도와 비저항이 증가하였다. 산소 분압이 <TEX>$4{\times}10^{-5}$</TEX> Pa에서 최소 비저항(<TEX>$9.8{\times}10^{-4}{\Omega}{\cdot}cm$</TEX>)을 얻을 수 있었다. ITO/PET 박막의 광투과율도 산소 분압이 증가함에 따라 증가하였으며 산소 분압 <TEX>$4{\times}10^{-5}$</TEX> Pa에서 80 % 이상을 나타내었다. 본 연구를 통하여 최적의 산소 분압 선정이 ITO 박막의 결정성 향상, 캐리어 밀도 향상 그리고 전기전도도 향상 효과를 나타냄을 확인하였다. Indium tin oxide (ITO) films with various oxygen partial pressure from 0 to <TEX>$6{\times}10^{-5}$</TEX> Pa were prepared onto polyethylene terephthalate (PET) using RF magnetron sputtering at room temperature. The structural, electrical and optical properties of the grown ITO films were investigated as a function of the oxygen partial pressure. The amorphous nature of the ITO films was dominant at the partial pressure below <TEX>$1{\times}10^{-5}$</TEX> Pa and the degree of crystallinity increased as the oxygen concentration increased further. This structural change comes with the increased carrier concentration and reduction of the electrical resistivity down to <TEX>$9.8{\times}10^{-4}{\Omega}{\cdot}cm$</TEX>. The average transmittance (at 400~800 nm) of the ITO deposited on the PET substrates increased as the oxygen partial pressure increased and transmittance above 80 % was achieved with the partial pressure of <TEX>$4{\times}10^{-5}$</TEX> Pa. The results show that the choice of optimal oxygen partial pressure can present improved film crystallinity, the increased carrier concentration, and the enhancement in the electrical conductivity.

The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low resistivity and high transmittances in the visible range of the electromagnetic spectrum. Fabricating ultra-thin indium tin oxide (ITO) films (sub-50 nm) using conventional methods has presented a number of challenges; however, a novel method involving chemical shaving of thicker (greater than 80 nm) RF sputter deposited high-quality ITO films has been demonstrated. This study investigates the effect of oxygen concentration on the etch rates of RF sputter deposited ITO films to provide a detailed understanding of the interaction of all critical experimental parameters to help create even thinner layers to allow for more finely tune plasmonic resonances. ITO films were deposited on silicon substrates with a 98-nm, thermally grown oxide using RF magnetron sputtering with oxygen concentrations of 0, 0.4 and 1.0 sccm and annealed at 300 °C air ambient. Then the films were etched using a combination of water and hydrochloric and nitric acids for 1, 3, 5 and 8 min at room temperature. In-between each etching process cycle, the films were characterized by X-ray diffraction, atomic force microscopy, Raman Spectroscopy, 4-point probe (electrical conductivity), and variable angle spectroscopic ellipsometry. All the films were polycrystalline in nature and highly oriented along the (222) reflection. Ultra-thin ITO films with record low resistivity values (as low as 5.83 × 10−4 Ω·cm) were obtained and high optical transparency is exhibited in the 300–1000 nm wavelength region for all the ITO films. The etch rate, preferred crystal lattice growth plane, d-spacing and lattice distortion were also observed to be highly dependent on the nature of growth environment for RF sputter deposited ITO films. The structural, electrical, and optical properties of the ITO films are discussed with respect to the oxygen ambient nature and etching time in detail to provide guidance for plasmonic enhanced a-Si:H solar PV cell fabrication.

Interfacial barrier height modification of indium tin oxide/a-Si:H(p) via control of density of interstitial oxygen for silicon heterojunction solar cell application

Influence of oxygen/argon pressure ratio on the morphology, optical and electrical properties of ITO thin films deposited at room temperature

In this study, indium tin oxide (ITO) films were deposited at 300°C on glass substrates by low-frequency (60 Hz) magnetron sputtering technique. The influence of oxygen flow rate on the structural, electrical and optical properties of ITO thin films was investigated. The oxygen flow rate was varied from 0 to 8 sccm. We obtained the most superior property of ITO films at oxygen flow rate of 0.5 sccm. The films are found to show preferential orientation both (222) and (400) planes in the XRD patterns. The resistivity of the films with the thickness of 140 nm is 2.1 × 10−4 ohm · cm with 88% optical average transmittance in visible range (500–800 nm). Therefore, we conclude that transparent conducting ITO films prepared by low-frequency magnetron sputtering can be applied for various flat panel displays.

Surface characterisation of indium-tin oxide thin electrode films for use as a conducting substrate in DNA sensor development

Electric resistance change of indium-tin oxide (ITO) film was investigated when dielectric oxide films such as Sr(Zr0.2Ti0.8)O3 and Y2O3 for an electroluminescent device were deposited on the ITO by the rf magnetron sputtering method using oxide ceramic targets. In order to understand the mechanism of the resistance change, a dc voltage of -70∼+70 V was biased to an ITO film during the sputtering of dielectric oxide films. The resistance of the ITO film became higher in the positive bias region. The cause of the increase in resistance of the ITO films was confirmed to be oxidation by the oxide targets and the sputtering gas. The amount of the resistance change could be qualitatively explained by the ratio of the oxygen introduced into the ITO film and the combined oxygen forming O2 gas at the ITO surface incident to the ITO film at the sputtering of the dielectric oxide films.

In this work, rapid thermal annealing (RTA) was applied to indium tin oxide (ITO) films in ambient atmosphere, resulting in significant improvements of the quality of the ITO films that are commonly used as conductive transparent electrodes for photovoltaic structures. Starting from a single sintered target (purity 99.95%), ITO thin films of predefined thickness (230 nm, 300 nm and 370 nm) were deposited at room temperature by radio-frequency magnetron sputtering (rfMS). After deposition, the films were subjected to a RTA process at 575 °C (heating rate 20 °C/s), maintained at this temperature for 10 minutes, then cooled down to room temperature at a rate of 20 °C/s. The film structure was modified by changing the deposition thickness or the RTA process. X-ray diffraction investigations revealed a cubic nanocrystalline structure for the as-deposited ITO films. After RTA, polycrystalline compounds with a textured (222) plane were observed. X-ray photon spectroscopy was used to confirm the beneficial effect of the RTA treatment on the ITO chemical composition. Using a Tauc plot, values of the optical band gap ranging from 3.17 to 3.67 eV were estimated. These values depend on the heat treatment and the thickness of the sample. Highly conductive indium tin oxide thin films (ρ = 7.4 × 10−5 Ω cm) were obtained after RTA treatment in an open atmosphere. Such films could be used to manufacture transparent contact electrodes for solar cells.

Development of indium tin oxide film texture during DC magnetron sputtering deposition