Effects of post-annealing on Schottky contacts of Pt/ZnO films toward UV photodetector

The Schottky contact of Pt/ZnO was formed by depositing ZnO films oriented along c-axis by pulsed-laser deposition on Pt/Ti buffer layer supported by SiO₂/Si substrate. Effects of the post-annealing on the crystallinity, uniformity and native defects of ZnO film as well as Schottky contacts of Pt/ZnO films were investigated. Results show that the annealing can improve the crystallinity of ZnO film, suppress the native defects, and enhance the performance of Pt/ZnO Schottky contacts dramatically. The best Schottky diode shows the largest barrier height of 0.8 eV with reverse leakage current of 1.5 × 10⁻⁵ A/cm². The zero-biased photodetector based on the best Schottky diode possesses responsivity of 0.265 A/W at 378 nm, fast photo-response component with rise time of 10 ns and fall time of 17 ns. This report demonstrates possibility of ZnO films/Pt hetero-junction with large area Schottky contact, and establishes the potential of this material for use in UV photodetector devices.     

LiCoO2 cathode thin film fabricated by RF sputtering for lithium ion microbatteries

Thin films of lithium cobalt oxide were deposited on Pt or Pt/Ti/quartz glass substrates by radio frequency (RF) magnetron sputtering at the substrate temperatures from room temperature to 500 °C. As the substrate temperature increased, the film structure changed from amorphous structure to crystallinity with a strong (003) texture as characterized by X-ray diffraction. The surface morphology and cross-section were observed using scanning electron microscopy. It was found that the films tended to crack at a high substrate temperature. Charge-discharge tests of these films were conducted and compared. The different electrochemical characteristics of these films were attributed to the modified crystallography, morphology, and thermal stress. The LiCoO₂ film deposited at 400 °C showed a well-defined 4.0 V voltage plateau on charge and a 3.9 V plateau on discharge, and delivered 54.5 μAh/cm² μm at the first discharge capacity, with good cycling performance, giving evidence that such films could be used as the thin film cathodes for lithium microbatteries.     

Tunable characteristics of (Ba0.5Sr0.5) TiO3 (BST) capacitors using (Ba0.5Sr0.5) RuO3 (BSR) interfacial layers onto Pt/Ti/SiO2/Si substrates

The conducting oxide electrodes (Ba, Sr) RuO₃ (BSR) similar in structure and chemical composition to (Ba, Sr) TiO₃ (BST) were deposited by metalorganic chemical vapor deposition (MOCVD) onto Pt/Ti/SiO₂/Si substrates to improve the structural and dielectric properties of BST films. The BSR interfacial layers between the BST and Pt bottom electrode influenced the preferred orientation, surface morphologies, and dielectric properties of BST films. The structural and dielectric properties of BST films depended on the thickness of the BSR layers. BST films with (100) texturing up to 150 Å thickness of BSR showed a smoother and smaller grain size than those without interfacial layers, and a tunability and dielectric constant of about 70% and 1300 at an interfacial layer of 150 Å, respectively. On the other hand, BST films with above 300 Å thickness in BSR layers showed a (110) texturing similar to those without BSR layers and a slight decrease of tunability and dielectric constant compared with those of (100) texturing BST films. The increase of the dielectric loss of BST films with BSR layers was attributed to the carbon contamination diffused from MOCVD-BSR layers.     

Ferroelectric properties of dysprosium-doped Bi4Ti3O12 thin films crystallized in various atmospheres

Dysprosium-doped Bi4Ti3O12 （Bi3.4Dy0.6Ti3O12, BDT） ferroelectric thin films were deposited on Pt（111）/Ti/SiO2/Si（111） substrates by chemical solution deposition （CSD） and crystallized in nitrogen, air and oxygen atmospheres, respectively. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. The results show that the crystallization atmosphere has significant effect on determining the crystallization and ferroelectric properties of the BDT films. The film crystallized in nitrogen at a relatively low temperature of 650 ℃, exhibits excellent crystallinity and ferroelectricity with a remanent polarization of 2Pr = 24.9 ℃/cm^2 and a coercive field of 144.5 kV/cm. While the films annealed in air and oxygen at 650 ℃ do not show good crystallinity and ferroelectricity until they are annealed at 700 ℃. The structure evolution and ferroelectric properties of BDT thin films annealed under different temperatures （600-750 ℃） were also investigated. The crystallinity of the BDT films is improved and the average grain size increases when the annealing temperature increases from 600 ℃ to 750 ℃ at an interval of 50 ℃. However, the polarization of the films is not monotonous function of the annealing temperature.     

Electrochemical synthesis of polypyrrole films over each of well-aligned carbon nanotubes

Polypyrrole (PPy) films were uniformly electropolymerized over each carbon nanotube of the well-aligned carbon nanotube arrays. For comparison, PPy films were also coated on flat metallic titanium (Ti) and platinum (Pt) substrates by the same technique. The synthesis and the redox performance of the PPy films were conducted by cyclic voltammetry (CV). The structural characterization including the thickness and uniformity of the PPy films was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is observed that the coating of the PPy film over carbon nanotubes is much faster than that on flat Ti/Pt surface. Furthermore, the redox performance of the PPy-coated carbon nanotube electrodes over flat Ti/Pt electrodes was significantly improved due to the high accessible surface area of the carbon nanotubes in the aligned arrays, especially in large film formation charge (Q_film). It is very promising that the electrode developed in this study could be used as high performance electrode in rechargeable batteries.     

Deposition of BN films on metal substrates from a fluorine-containing plasma

Boron nitride (BN) films were deposited on Mo, W, Ni, Ti and Zr substrates by DC arc jet chemical vapor deposition using a gas mixture of Ar-N₂-BF₃-H₂ at 50 Torr, a substrate temperature of 850-1150 °C, and a − 85 V substrate bias. Cubic BN (c-BN) films showing clear c-BN Raman peaks were obtained on Mo and W, but they did not adhere well to the substrates. Hexagonal or turbostratic BN was deposited predominantly on Ni substrates, which is similar to the preferable deposition of graphitic carbons in diamond CVD. High quality c-BN films with good adhesion were obtained on Ti and Zr. The reasons for these differences among metal substrates are discussed.     

磁控溅射法ZnO-TiO2复合薄膜的制备及性能

采用双靶共溅射的方法在FJL600EI型超高真空多功能磁控溅射仪上制备不同复合量的ZnO-TiO2复合薄膜,对不同工艺参数制备的ZnO-TiO2复合薄膜进行形貌结构分析、光催化性测定和亲水性检测。结果表明,当Ti靶材的溅射功率为150 W时,得到了颗粒大小均匀的ZnO-TiO2复合薄膜,且复合薄膜对甲基橙的降解率最高,亲水性最优。ZnO-TiO2薄膜的光催化性明显高于单一ZnO薄膜。     

不同工艺制备的铁电薄膜底电极Pt／Ti

采用高真空电子束蒸与直流溅射在ＳｉＯ２／Ｓｉ基底上制备Ｐｔ／Ｔｉ底电极,对Ｐｔ／Ｔｉ在不同热处理温度下的结构与形貌进行对比研究。结果表明;由于采用不同的制备工艺,Ｐｔ晶粒在成核与生长方式上有所不同,导致了Ｐｔ薄膜在结构与形貌的差异。     

Leakage currents in Ti−O/Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin film deposited on Ta/Ti/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The electrical characteristics of Ta/Ta₂O₅ films and Ta/Ti−O/Ta₂O₅ films deposited by RF reactive sputtering on Ta/Ti/Al₂O₃ substrates were investigated. Ta was used for the bottom and upper electrodes in order to simplify the fabrication process. Dielectric materials were annealed at 700°C for 60 sec under vacuum. XRD analysis showed that Ta was crystalline and Ta₂O₅ was amorphous in an as-deposited state, but amorphous Ta₂O₅ was transformed to a crystalline state by rapid thermal heat treatment. We compared lnJ-E², C−V, and C−F of both as-deposited and annealed dielectric thin films deposited on the Ta bottom electrode. From these results, we concluded that introducing a Ti−O buffer layer could reduce the leakage current. The conduction mechanisms of Ti−O/Ta₂O₅ could be interpreted appropriately by hopping conduction and space-charge-limited current.     

In-situ thermal evolution of Ni/Ti multilayer thin films

Nickel and titanium alternated nanolayers were deposited from Ti and Ni targets. The multilayer thin films were designed in order to have equiatomic overall chemical composition with a period from 5 to 70 nm. The chemical composition, morphology, structure and phase transformation behaviour were studied. The surface and cross-section morphology of the as-deposited thin films was analysed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The Ni/Ti thin films present in their surface nanograins and for higher periods in cross section it was possible to distinguish the alternated layers and measure their thickness. The structural evolution with temperature was analysed by in-situ hot stage X-ray diffraction (XRD). The as-deposited multilayer thin films exhibit a tendency to a transitory disorder as the period decreases. For the smaller periods a disordered phase forms during the deposition process, while in Ni/Ti multilayers with higher periods this phase is only observed during annealing. By increasing the temperature an exothermic reaction occurs with the formation of the B2-NiTi austenitic phase. In spite of moderate enthalpy of mixing, the multilayers with intermediate modulation period of Ni/Ti films show potential to be used for joining purposes.     

SnO2 coated Ni particles prepared by fluidized bed chemical vapor deposition

A Fluidized Bed Metal–Organic Chemical Vapor Deposition (FB-MOCVD) process was developed for the growth of tin oxide thin films on large hollow Ni particles. Tetraethyl tin was used as tin source and dry air both as fluidization gas and oxidant reagent. The SnO₂ films were grown in a FBCVD reactor under reduced pressure (13.3 kPa) in the temperature range of 633–663 K. A series of specific experiments was carried out to optimize the design of the reactor and to determine the range of experimental parameters (flow rate, pressure, temperature) leading to good fluidization of the large hollow Ni particles used as base material. The SnO₂ films deposited on particles exhibited a dense nodular surface morphology similar to that previously observed on flat substrates. The relative thickness of the films was determined by EDS analyses and the real values were measured by SEM on cross-sections of particles. The SnO₂ films exhibit satisfactory thickness uniformity from one particle to another in the same batch and from run to run. XRD studies revealed that the films exhibited good crystallinity with the cassiterite structure. Traces of NiO were found at the SnO₂/Ni interface. Finally, the SnO₂ CVD coated-Ni particles were used as anodes in an electrochemical cell. The potential limit of oxygen evolution measured was that of the SnO₂ layer despite the initial porosity of the hollow Ni particles inherent to their preparation. This work is the first step towards the preparation of high specific surface area electrodes.     

Epitaxial PMN-PT thin films grown on buffered Si substrates using ceramic and single-crystal targets

Epitaxial 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (PMN-PT) thin films were deposited on LSCO/CeO₂/YSZ tri-buffered Si substrate by pulsed laser deposition (PLD) using sintered ceramic and single-crystal targets. The PMN-PT films deposited using both targets were single crystalline and exhibited cube-on-cube growth epitaxy with the substrate. The films deposited using the single-crystal target showed higher crystallinity and a smoother surface morphology than those grown using the ceramic target. The crystallinity of films can be affected by the in-plane lattice mismatch of PMN-PT/LSCO interfaces. The low density and low absorption coefficient of the sintered ceramic target were responsible for the severe compositional deviation from the desired stoichiometry of the PMN-PT films. Dielectric constants of approximately 1926 and 1540 at 10 kHz were obtained for the films deposited using the single-crystal and sintered ceramic target, respectively. In addition, the PMN-PT films fabricated using the single-crystal target exhibited well-developed polarization hysteresis loops with a remnant polarization of 11.9 μC/cm². Single-crystal targets are an indispensable candidate for the growth of epitaxial PMN-PT films with high crystallinity and good electrical properties.     

The effect of thickness on the properties of Ti-doped ZnO films by simultaneous r.f. and d.c. magnetron sputtering

For Ti-doped ZnO (ZnO:Ti) films, the crystallinity and degree of orientation of the ZnO:Ti films were closely related to the film thickness. The crystal size increased with the increase of film thickness. With decreasing film thickness, there were more defects existing in the ZnO:Ti films and surface roughness decreased. The resistivity increased with the decrease of film thickness. The main scattering mechanism in the thin ZnO:Ti films was defect scattering. The transmission in UV region decreased strongly with the increase of film thickness. Such behavior was due to the films with different thickness showing different structural and electrical properties. As the results, film thickness affected the properties of ZnO:Ti films significantly.     

Epitaxial SrRuO3 thin films deposited on SrO buffered-Si(001) substrates for ferroelectric Pb(Zr0.2Ti0.8)O3 thin films

SrRuO₃ thin film electrodes are epitaxially grown on SrO buffered-Si(001) substrates by pulsed laser deposition. The optimum conditions of the SrO buffer layers for epitaxial SrRuO₃ films are a deposition temperature of 700 °C, deposition pressure of 1 × 10^?6 Torr, and thickness of 6 nm. The 100 nm thick-SrRuO₃ bottom electrodes deposited above 650 °C on SrO buffered-Si (001) substrates have a rms (root mean square) roughness of approximately 5.0 Å and a resistivity of 1700 µω-cm, exhibiting an epitaxial relationship. The 100 nm thick-Pb(Zr_0.2Ti_0.8)O₃ thin films deposited at 575 °C have a (00l) preferred orientation and exhibit 2P_r of 40 µC/cm², E_c of 100 kV/cm, and leakage current of about 1 × 10^?7 A/cm² at 1 V. The silicon oxide phase which presents within PZT and SrRuO₃ films, influences the crystallinity of the PZT films and the resistivity of the SrRuO₃ electrodes.     

钛酸铋薄膜的磁控溅射及其退火处理

采用射频磁控溅射技术,在Pt/Ti/SiO2/Si衬底上制备了钛酸铋(Bi4Ti3O12,简称BIT)薄膜。研究了衬底温度及后续退火处理对薄膜结构和表面形貌的影响。结果表明:适宜的衬底温度为200℃。随着退火温度(650~800℃)的升高,BIT薄膜的结晶性变好,晶粒尺寸增大,c轴取向增强。当退火温度达到850℃时,开始出现焦绿石相;700~800℃为适宜的退火温度,在此条件下得到的BIT薄膜结晶良好,尺寸均匀,表面平整致密。     

Characteristics of IZSO films deposited by a co-sputtering system

In−Zn−Sn−O films were deposited on a polycarbonate (PC) substrate by a magnetron co-sputtering system using two cathodes (DC, RF) without substrate heating. Two types of ITO targets (target A: doped with 5 wt.% SnO₂, target B: doped with 10 wt.% SnO₂) were used as an In−Sn−O source. The ITO and ZnO targets were sputtered by DC and RF discharges, respectively, and the composition of the In−Zn−Sn−O films was controlled via the power ratio of each cathode. In the case of ITO target A, the lowest resistivity (4.3×10⁻⁴ Ωcm) was obtained for the film deposited at the RF power (ZnO) of 55W. In the case of ITO target B, the lowest resistivity (2.9×10⁻⁴ Ωcm) of the film was obtained at the RF power (ZnO) of 30W, which was attributed to the increase in carrier density. Hall mobility decreased with increasing carrier density, which could be explained by the increase in ionized impurity scattering.     

Composite fluorocarbon/ZnO films prepared by R.F. magnetron sputtering of Zn and PTFE

In this paper, composite fluorocarbon/ZnO films were prepared by R.F. sputtering used polytetrafluoroethylene (PTFE) and Zn target on polyethylene terephthalate (PET) substrate. Argon was used as the working gas and oxygen used as reacting gas. The obtained films were characterized by means of SEM, XPS and UV-visible spectrophotometer. It was found, the surface morphology of composite fluorocarbon/ZnO films vary as the deposited time of ZnO. The growing mode of composite films is the deposition and expansion. The ultraviolet absorbance of composite fluorocarbon/ZnO films is equal to that of fluorocarbon films' when deposited time of ZnO is within 2 min, while distinctively increases when deposited time of ZnO exceeds 5 min, the absorbance value is larger than the ZnOs'. The composite films exhibit multi-enhanced ultraviolet absorption due to π-conjugated molecular structure, nanoparticle-pore reflection and the absorption effect of nanosized ZnO particles.     

Highly adhesive Pt-electrode films directly deposited on SiO2 by electron-cyclotron-resonance plasma sputtering

Pt films directly deposited on SiO₂ by electron-cyclotron-resonance (ECR) plasma sputtering and DC-magnetron sputtering have been compared in terms of their performance as electrodes. The DC-magnetron sputtered Pt film consisted of sharply (111) oriented crystallites, which was reflected in hexagonal crystallites observed in atomic force microscopy images. While ECR-sputtered Pt film was also (111) oriented, the X-ray diffraction rocking curve of the (111) peak was broader than that of the DC-magnetron sputtered film. The surface image revealed fine grains, thus having a flatter surface. A scratch test revealed that ECR-sputtered films had an adhesive strength about twice that of DC-magnetron-sputtered films, which was consistent with our tape-test results. Possible reasons for the different adhesion characteristics are discussed.     

Dielectric properties of ZrTiO<Subscript>4</Subscript> thin films synthesized by sol-gel method

ZrTiO₄ thin films were successfully prepared on Pt/Ti/SiO₂/Si(100) substrates by a sol-gel process and gel films were heat-treated at various temperatures. The surface morphology, crystal structure, and dielectric properties of the thin films were investigated. It was possible to obtain ZrTiO₄ phase at temperatures above 650 °C for 2 h, which is much lower than the bulk sintering temperature. The microstructure of well-crystallized ZrTiO₄ thin films was a fine-grained microstructure less than 70 nm in grain size and the surface morphology was smooth with 22.4 rms roughness. The dielectric constant and loss of ZrTiO₄ thin films were 38 and 0.006, respectively, for thin films with 450 nm thickness heat-treated at 900 °C for 2 h.     

Effects of substrate temperature and RF power on the formation of aligned nanorods in ZnO thin films

We report on the effects of substrate temperature and RF power on the formation of aligned nanorod-like morphology in ZnO thin films. ZnO thin films were sputter-deposited in mixed Ar and N₂ gas ambient at various substrate temperatures and RF powers. We find that the substrate temperature plays more important role than RF power in the formation of ZnO nanorod-like morphology. At low substrate temperatures (below 300°C), ZnO nanorod-like morphology does not form regardless of RF powers. High RF power helps to promote the formation of aligned ZnO nanorod-like morphology. However, lower RF powers usually lead to ZnO films with better crystallinity at the same substrate temperatures in mixed Ar and N₂ gas ambient and therefore better photoelectrochemical response.