Intentional Substrate Heating Research Articles

InOx thin films deposited by plasma assisted evaporation: Application in light shutters

An integration of undoped InOx and commercial ITO thin films into laboratory assembled light shutter devices is made. Accordingly, undoped transparent conductive InOx thin films, about 100 nm thick, are deposited by radiofrequency plasma enhanced reactive thermal evaporation (rf-PERTE) of indium teardrops with no intentional heating of the glass substrates. The process of deposition occurs at very low deposition rates (0.1–0.3 nm/s) to establish an optimized reaction between the oxygen plasma and the metal vapor. These films show the following main characteristics: transparency of 87% (wavelength, λ = 632.8 nm) and sheet resistance of 52 Ω/sq; while on commercial ITO films the transparency was of 92% and sheet resistance of 83 Ω/sq. The InOx thin film surface characterized by AFM shows a uniform grain texture with a root mean square surface roughness of Rq∼2.276 nm. In contrast, commercial ITO topography is characterized by two regions: one smoother with Rq∼0.973 nm and one with big grains (Rq∼3.617 nm). For the shutters assembled using commercial ITO, the light transmission coefficient (Tr) reaches the highest value (Trmax) of 89% and the lowest (Trmin) of 1.3% [13], while for the InOx shutters these values are 80.1% and 3.2%, respectively. Regarding the electric field required to achieve 90% of the maximum transmission in the ON state (Eon), the one presented by the devices assembled with commercial ITO coated glasses is 2.41 V/μm while the one presented by the devices assembled with InOx coated glasses is smaller, 1.77 V/μm. These results corroborate the device quality that depends on the base materials and fabrication process used.

The Influence of Al Underlayer on the Optical and Electrical Properties of GZO/Al Thin Films

100 nm thick Ga doped ZnO (GZO) thin films were deposited with DC and RF magnetron sputtering at room temperature on glass substrate and Al coated glass substrate, respectively. and the effect of the Al underlayer on the optical and electrical properties of the GZO films was investigated. As-deposited GZO single layer films had an optical transmittance of 80% in the visible wavelength region, and sheet resistance of 1,516 , while the optical and electrical properties of GZO/Al bi-layered films were influenced by the thickness of the Al buffer layer. GZO films with 2 nm thick Al film show a lower sheet resistance of 990 , and an optical transmittance of 78%. Based on the figure of merit (FOM), it can be concluded that the thin Al buffer layer effectively increases the performance of GZO films as a transparent and conducting electrode without intentional substrate heating or a post deposition annealing process.

Effects of Ar ion beam treatment on properties of roll-to-roll sputtered Sn-doped In2O3 films on colorless polyimide substrate

We report on the effects of Ar ion beam treatment on the electrical, optical, and mechanical properties of flexible Sn-doped In2O3 (ITO) films grown on colorless polyimide (CPI) by roll-to-roll (R2R) sputtering. Effective Ar ion beam treatment on ITO films led to the reduction of sheet resistance without degradation of optical transmittance of ITO films even though they were prepared at room temperature. In addition, Ar ion beam treatment resulted in crystallization of the R2R-sputtered ITO films without intentional substrate heating. At optimized conditions, the Ar ion beam treated ITO film showed a sheet resistance of 54.6Ω/square and an optical transmittance of 80.1%. A flexible organic solar cell (FOSC) fabricated with the Ar ion beam treated ITO film exhibited a power conversion efficiency (PCE) of 3.137%, which was higher than that of a FOSC made with untreated ITO film. This indicates that the in-situ Ar ion treatment is a promising method for fabrication of crystalline ITO films on flexible substrates without intentional substrate heating in a R2R sputtering process.

Effect of a TiO2Buffer Layer on the Properties of ITO Films Prepared by RF Magnetron Sputtering

Sn-doped In2O3 (ITO) thin films were prepared by radio frequency magnetron sputtering without intentional substrate heating on bare glass and TiO2-deposited glass substrates to investigate the effect of a TiO2 buffer layer on the electrical and optical properties of ITO films. The thicknesses of TiO 2 and ITO films were kept constant at 5 and 100 nm, respectively. As-deposited ITO single layer films show an optical transmittance of 75.9%, while ITO/TiO 2 bi- layered films show a lower transmittance of 76.1%. However, as-deposited ITO/TiO2 films show a lower resistivity (9.87×10 -4 Ωcm) than that of ITO single layer films. In addition, the work function of the ITO film is affected by the TiO 2 buffer layer, with the ITO/TiO2 films having a higher work-function (5.0 eV) than that of the ITO single layer films. The experimental results indicate that a 5-nm-thick TiO2 buffer layer on the ITO/TiO2 films results in better performance than conventional ITO single layer films.

Improved electrical and optical properties of GZO films with a thin TiO2 buffer layer deposited by RF magnetron sputtering

Abstract Ga-doped ZnO (GZO) thin films were prepared by radio frequency magnetron sputtering without intentional substrate heating on bare glass and TiO 2 -deposited glass substrates to investigate the effect of a thin TiO 2 buffer layer on the optical and electrical properties of the films. The thicknesses of the TiO 2 buffer layer and GZO films were kept constant at 5 and 100 nm, respectively. As-deposited GZO/TiO 2 bi-layered films show a higher transmittance of 83.0% than that of the GZO films, and GZO/TiO 2 films show a lower resistivity (1.03×10 −2 Ω cm) than that of the GZO single layer films. In addition, the work function of the GZO film was affected by the TiO 2 buffer layer, where the GZO/TiO 2 films had a higher work-function (4.86 eV) than that of the GZO single layer films. The experimental results indicate that a 5-nm-thick TiO 2 buffer layer in the GZO/TiO 2 films results in better electrical and optical performance than conventional GZO single layer films.

Low-temperature deposition of µc-Si : H thin films by a low-frequency inductively coupled plasma for photovoltaic applications

Low-temperature depositions of Si films from hydrogenated amorphous silicon (a-Si : H) to highly crystallized hydrogenated microcrystalline silicon (µc-Si : H) were realized by the low-frequency inductively coupled plasma (LF-ICP) technique, with low hydrogen dilution (50%) and without any intentional substrate heating. µc-Si : H films with a thin incubation layer (<100 nm), a small grain size (<14 nm), a weak [1 1 1] or [2 2 0] preferred orientation, and a low hydrogen content (4–8%) were obtained (at deposition rates ∼0.4–0.7 nm s−1). The increased crystallinity due to the increasing rf power is accompanied by the improved structural order, lowered impurity contamination and decreased hydrogen content. The compactness of the µc-Si : H film is positively related to crystallinity and independent of the high microstructure factor (>0.8). Low-temperature growth of µc-Si : H is attributed to high atomic H flux and suppression of high-energy ion bombardment due to the high density of low-temperature electrons in the plasma. A µc-Si : H solar cell with a less dense intrinsic layer (on a SnO2 : F glass substrate) exhibits a high Voc (584 mV), showing great potential for photovoltaic applications.

Effects of annealing temperature on thermoelectric properties of Bi2Te3 films prepared by co-sputtering

N-type thermoelectric bismuth telluride (Bi2Te3) films were grown on SiO2/Si substrates by RF magnetron co-sputtering without intentional substrate heating. The effects of annealing temperature (150–350°C) on surface morphology, crystal structure and thermoelectric properties of the Bi2Te3 films were investigated. Its crystallization was significantly improved by increasing the annealing temperature, giving rise to the enhanced charge carrier mobility. It is found that the optimum of Seebeck coefficient and power factor was about −242μV/K and 21μW/K2cm, respectively, obtained at the annealing temperature of 300°C.

HfO2-Si의 조성비에 따른 HfSiOx의 IZO 기반 산화물 반도체에 대한 연구

본 연구에서는 IZO를 활성층으로 하고 HfSiO<SUB>x</SUB>를 절연층으로 한 TFT에 대하여 그 성능을 측정하였다. HfSiO<SUB>x</SUB>는 HfO₂ target과 Si target을 co-sputtering 하여 증착하였으며 RF power를 달리 하여 네 가지의 HfSiO<SUB>x</SUB> 박막을 제작하였다. 공정의 간소화를 위해 게이트 전극을 제외한 모든 층들은 RF-magnetron sputtering system과 shadow mask만을 이용하여 증착하였으며 공정의 간소화를 위해 어떠한 열처리도 하지 않았다. 네 가지 HfSiO<SUB>x</SUB> 박막의 구조적 변화를 X-ray diffraction(XRD), atomic force microscopy(AFM)을 통해 분석하였고, 그 전기적 특성을 확인하였다. 박막 내 HfO₂와 Si의 조성비에 따라 그 특성이 현저히 차이가 남을 확인하였다. HfO₂(100W)-Si(100W)의 조건으로 증착한 HfSiO<SUB>x</SUB> 박막을 절연층으로 한 소자의 특성이 전류 점멸비 5.89E+05, 이동도 2.0[cm2/V.s], 문턱전압 -0.5[V], RMS 0.263[nm]로 가장 좋은 결과로 나타났다. 따라서 HfSiO<SUB>x</SUB> 박막 내의 적절한 HfO₂와 Si의 조성비가 계면의 질을 향상시킴은 물론, HfO₂자체의 trap이나 defect를 효과적으로 줄여 줌으로써 소자의 성능 향상에 중요한 요소라 판단된다.

Effect of the Cu Bottom Layer on the Properties of Ga Doped ZnO Thin Films

Ga doped ZnO (GZO)/copper (Cu) bi-layered film was deposited on glass substrate by RF and DC magnetron sputtering and then the effect of the Cu bottom layer on the optical, electrical and structural properties of GZO films were considered. As-deposited 100 nm thick GZO films had an optical transmittance of 82% in the visible wavelength region and a sheet resistance of 4139 <TEX>${\Omega}/{\Box}$</TEX>, while the GZO/Cu film had optical and electrical properties that were influenced by the Cu bottom layer. GZO films with 5 nm thick Cu film show the lower sheet resistance of 268 <TEX>${\Omega}/{\Box}$</TEX> and an optical transmittance of 65% due to increased optical absorption by the Cu metallic bottom layer. Based on the figure of merit, it can be concluded that the thin Cu bottom layer effectively increases the performance of GZO films as a transparent and conducting electrode without intentional substrate heating or a post deposition annealing process.

Dye-sensitized 1D anatase TiO 2 nanorods for tunable efficient photodetection in the visible range

TiO 2 films with enhanced photosensitivity were deposited on alkali free glass substrates without intentional substrate heating by pulsed DC magnetron reactive sputtering with an average thickness of about 2 μm. Three dyes, commercial N719 and two new organic dyes were impregnated in order to control the optical spectral selectivity of such films. The type of dye used proved to dramatically influence the device's response to radiation pulses. The practical breakthrough is the use of different dyes according to the region of the electromagnetic spectrum one wants to detect. Devices with photocurrent 6 orders of magnitude higher than the dark current (from ∼2 × 10 −12 to 2 × 10 −6 A for a 100 V bias) were fabricated with a spectral response within the visible range of the electromagnetic spectrum. In addition, this approach is likely to allow for the fabrication of hybrid photodetectors on cheap heat sensible flexible polymeric substrates.

The influence of Au thickness on the structural, optical and electrical properties of ZnO/Au/ZnO multilayer films

Transparent and conductive ZnO/Au/ZnO (ZAZ) multilayer films were deposited on glass substrates by magnetron sputtering without intentional substrate heating. The thickness of Au interlayer was set at 1, 2 and 3 nm. The observed structural, optical and electrical properties were dependent on the thickness of the Au interlayer. For all of the ZAZ films, the diffraction peaks in the XRD pattern were identified as the (002) and (103) planes of a ZnO films and the (111) plane of an Au interlayer. The ZAZ films with a 2 nm thick Au interlayer showed a higher figure of merit than the other ZAZ films prepared in this study, and they also demonstrated the relatively high work function of 5.13 eV. From these results, we concluded that a ZAZ film with a 2 nm thick Au interlayer is an alternative candidate for use as a transparent electrode in OLEDs and various flat panel displays.

Effect of Substrate Bias Voltage on the Properties of Hafnium Nitride Films Deposited by Radio Frequency Magnetron Sputtering Assisted by Inductive Coupled Nitrogen Plasma

Hafnium nitride (HfN) thin films were deposited onto a silicon substrate by inductive coupled nitrogen plasma-assisted radio frequency magnetron sputtering. The films were prepared without intentional substrate heating and a substrate negative bias voltage () was varied from -50 to -150 V to accelerate the effects of nitrogen ions () on the substrate. X-ray diffractometer patterns showed that the structure of the films was strongly affected by the negative substrate bias voltage, and thin film crystallization in the HfN (100) plane was observed under deposition conditions of -100 (bias voltage). Atomic force microscopy results showed that surface roughness also varied significantly with substrate bias voltage. Films deposited under conditions of -150 (bias voltage) exhibited higher hardness than other films.

구리 기저 층이 In2O3/Cu 박막의 광학적, 전기적 특성에 미치는 영향

Indium oxide (In₂O₃) single layer and In₂O₃/copper (Cu) bi-layer films were prepared on glass substrates by RF and DC magnetron sputtering without intentional substrate heating. In order to determine the effect of the Cu bottom layer on the optical, electrical and structural properties of In₂O₃ films, 3-㎚-thick Cu film was deposited on the glass substrate prior to deposition of the In₂O₃ films. As-deposited In2O3 films had an optical transmittance of 79% in the visible wavelength region and a sheet resistance of 2,300 Ω/□, while the In₂O₃/Cu film had optical and electrical properties that were influenced by the Cu bottom layer. In₂O₃/Cu films had a lower sheet resistance of 110 Ω/□ and an optical transmittance of 71%. Based on the figure of merit, it can be concluded that the Cu bottom layer effectively increases the performance of In2O3 films for use as transparent conducting oxides in flexible display applications.

Improvements in the device characteristics of IZO-based transparent thin-film transistors with co-sputtered HfO 2–Al 2O 3 gate dielectrics

Transparent oxide thin-film transistors (TFTs) have been fabricated by RF magnetron sputtering at room temperature using amorphous indium zinc oxide (IZO) as both active channel and source/drain electrodes and co-sputtered HfO 2–Al 2O 3 (HfAlO) as gate dielectric. In spite of its high dielectric constant, HfO 2 has some drawbacks including a high leakage current and rough surface morphologies due to its small band gap (5.31 eV) and microcrystalline structure. In this work, the incorporation of Al 2O 3 into hafnium (Hf) was achieved by co-sputtering of HfO 2 and Al 2O 3 without any intentional substrate heating, and its structural and electrical properties were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and spectroscopic ellipsometry (SE) analyses, depending on the Hf:Al compositional ratio. The XRD studies confirmed that the microcrystalline structures of HfO 2 were transformed to amorphous structures of HfAlO at approximately Hf:Al = 3:1 at% ratio. According to the AFM analysis, the HfAlO films (0.54 nm) were considerably smoother than the HfO 2 films (4.27 nm) due to their amorphous structure. The band gap ( E g) deduced by spectroscopic ellipsometry was increased from 5.31 eV (HfO 2) to 5.58 eV (HfAlO). The electrical performances of the TFTs, which were made of well-controlled active/electrode IZO materials and co-sputtered HfAlO dielectric material, exhibited a field-effect mobility of more than 10 cm 2/V s, a threshold voltage of about 1.5 V, a sub-threshold swing of about 0.5 V/decade, and an I on/off ratio of about 10 5.

Effect of RF Sputtering Power on the Structural, Optical and Hydrophobic Properties of SiN&lt;sub&gt;x&lt;/sub&gt; Thin Film

With a mixture gas of N2 and Ar, silicon nitride thin films were deposited on glass substrates by different radio frequency (RF) magnetron sputtering power without intentional substrate heating. The chemical composition, phase structure, surface morphology, optical properties, refractive index, hydrophobic properties of the films were characterized by X-ray energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), ultraviolet-visible spectroscopy(UV-Vis), nkd-system spectrophotometer and CA-XP150 contact angle analyzer, respectively. The results showed that silicon nitride thin films were amorphous and rich in Si; the transmittance reduced but refractive index and surface roughness increased; and the hydrophobic properties of SiNx became better with the increase of RF power.

Characterization of Hydrogen Gas Sensitivity of ZnO Thin Films

ZnO thin films were prepared on a glass substrate by radio frequency (RF) magnetron sputtering without intentional substrate heating and then surfaces of the ZnO films were irradiated with intense electrons in vacuum condition to investigate the effect of electron bombardment on crystallization, surface roughness, morphology and hydrogen gas sensitivity. In XRD pattern, as deposited ZnO films show a higher ZnO (002) peak intensity. However, the peak intensity for ZnO (002) is decreased with increase of electron bombarding energy. Atomic force microscope images show that surface morphology is also dependent on electron bombarding energy. The surface roughness increases due to intense electron bombardment as high as 2.7 nm. The observed optical transmittance means that the films irradiated with intense electron beams at 900 eV show lower transmittance than the others due to their rough surfaces. In addition, ZnO films irradiated by the electron beam at 900 eV show higher hydrogen gas sensitivity than the films that were electron beam irradiated at 450 eV. From XRD pattern and atomic force microscope observations, it is supposed that intense electron bombardment promotes a rough surface due to the intense bombardments and increased gas sensitivity of ZnO films for hydrogen gas. These results suggest that ZnO films irradiated with intense electron beams are promising for practical high performance hydrogen gas sensors.

Thickness Dependence of Indium-Tin Oxide Thin Films Deposited by RF Magnetron Sputtering

Indium-tin oxide is a ceramic material that exhibits electrical conductivity and optical transparency. It is used as transparent electrode in many optoelectronic devices. Among the possible deposition methods, magnetron sputtering is one of the most attractive techniques due to its good reproducibility and possibility of uniform deposition over large areas. In this work, indium-tin oxide thin films with different deposition times were obtained by radio frequency magnetron sputtering without intentional substrate heating. Their optical, electrical, physical and chemical properties were investigated.

Influence of CuSn thickness on the work function and optoelectrical properties of ZnO/CuSn/ZnO multilayer films

Transparent and conductive ZnO/CuSn/ZnO (ZCSZ) multilayer films were deposited on glass substrates by magnetron sputtering without intentional substrate heating. The thicknesses of CuSn layer was varied from 5 to 20 nm. In the XRD patterns, ZCSZ films with a 5 nm thick CuSn layer had a ZnO (0 0 2) peak, while the 20 nm thick CuSn intermediate films had ZnO (0 0 2) and CuSn (6 6 0) peaks. As the CuSn thickness increased, the sheet resistance decreased from 44 to 16 Ω/□ and the optical transmittance deteriorated due to increased optical absorption. The ZCSZ films with the 5 nm thick CuSn interlayer had the best figure of merit of 4.5 × 10 −3 Ω −1. The work function of the films with a 5 nm thick CuSn interlayer was 4.55 eV. These results indicate that the film with a 5 nm thick CuSn interlayer is an alternative candidate for use as a transparent electrode in OLEDs and various displays.

Enhancement of Methanol Gas Sensitivity of Cu Intermediate ITO Film Gas Sensors

Sn doped (ITO) and ITO/Cu/ITO (ICI) multilayer films were prepared on glass substrates with a reactive radio frequency (RF) magnetron sputter without intentional substrate heating, and then the influence of the Cu interlayer on the methanol gas sensitivity of the ICI films were considered. Although both ITO and ICI film sensors had the same thickness of 100 nm, the ICI sensors had a sandwich structure of ITO 50 nm/Cu 5 nm/ITO 45 nm. The ICI films showed a ten times higher carrier density than that of the pure ITO films. However, the Cu interlayer may also have caused the decrement of carrier mobility because the interfaces between the ITO and Cu interlayer acted as a barrier to carrier movement. Although the ICI films had two times a lower mobility than that of the pure ITO films, the ICI films had a higher conductivity of due to a higher carrier density. The changes in the sensitivity of the film sensors caused by methanol gas ranging from 50 to 500 ppm were measured at room temperature. The ICI sensors showed a higher gas sensitivity than that of the ITO single layer sensors. Finally, it can be concluded that the ICI film sensors have the potential to be used as improved methanol gas sensors.

Effects of Ag interlayer on the optoelectrical properties of TiON films

A sandwich structure of TiON/Ag/TiON (TAgT) multilayer films was prepared onto glass substrates using RF and DC magnetron sputtering without intentional substrate heating. The thicknesses of each layer in the TAgT films were set at 50 nm, 5 nm and 45 nm. The optoelectrical properties of the TiON films were strongly influenced by the presence of an Ag interlayer. Although the optical transmittance of the film deteriorated when an Ag interlayer was added, the films had a low resistivity of 9.0 × 10 −4 Ω cm due to increased carrier density. In addition, the TAgT films show work functions of 4.4 eV, which are suitable for organic light emitting diode (OLED) applications. The experimental results indicate that TiON film manufactured with a 5-nm thick Ag interlayer is an attractive candidate for use as a transparent electrode in large area electronic applications such as solar cells and displays.