Characteristics of post-annealed SrTiO3 thin films prepared by mirror-confinement-type ECR plasma sputtering

SrTiO₃ films were synthesized on Pt/Ti/SiO₂/Si multilayer substrates by mirror-confinement-type ECR plasma sputtering without substrate heating. All films were found to be well crystallized at a substrate temperature below 450 K. A low temperature post-annealing of the films by electromagnetic-wave radiation drastically improved the crystallographic and electric properties of Pt/SrTiO₃/Pt/Ti/SiO₂/Si capacitors. The crystallinity of the films indicated little variation by post-annealing, but irradiation of electromagnetic wave was confirmed to be effective for decreasing the post-annealing time and temperature. The electric properties of films annealed without Pt upper electrodes were better than those with them, and the film dielectric constant reached a value of 260, which is nearly equal to the bulk one, at an annealing temperature of 573 K.     

Characteristics of post-annealed SrTiO3 thin films prepared by mirror-confinement-type ECR plasma sputtering

SrTiO₃ films were synthesized on Pt/Ti/SiO₂/Si multilayer substrates by mirror-confinement-type ECR plasma sputtering without substrate heating. All films were found to be well crystallized at a substrate temperature below 450 K. A low temperature post-annealing of the films by electromagnetic-wave radiation drastically improved the crystallographic and electric properties of Pt/SrTiO₃/Pt/Ti/SiO₂/Si capacitors. The crystallinity of the films indicated little variation by post-annealing, but irradiation of electromagnetic wave was confirmed to be effective for decreasing the post-annealing time and temperature. The electric properties of films annealed without Pt upper electrodes were better than those with them, and the film dielectric constant reached a value of 260, which is nearly equal to thebulk one, at an annealing temperature of 573 K.     

KrF excimer laser crystallization of silicon thin films

A KrF excimer laser operating at 249 nm has been employed to crystallize silicon thin films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) and by RF magnetron sputtering on Corning glass and SiO₂. All films display a substantial improvement in crystallinity after ELC with the optimum laser fluence for as-deposited ECR films being higher than for sputtered films. This is probably related to the presence of Si-H_x bonds in the former. A pronounced bimodality in the Raman spectra of some amorphous, as-deposited ECR samples has been observed after laser crystallization where, in addition to the peak at 520cm^-1, a strong peak at 509cm^-1 is also present. Such behavior has not been reported previously to our knowledge in ELC silicon films. Interestingly, the XRD spectra of these samples do not exhibit any peaks suggesting the films are composed of nano-grain material. The dehydrogenation of ECR films by ELC has been demonstrated to be substantial, the hydrogen content typically decreasing from ~30 at % in an as-deposited film to ~10 at % after a single low fluence laser shot. Raman spectroscopy has shown that the film bonding changes from predominantly Si-H₂ to Si-H after ELC. Electrical resistivity measurements of phosphorus-doped films show a controllable and repeatable change with laser fluence. The results in this paper show that it is possible to crystallize and controllably change the electrical characteristics of ECR PECVD produced silicon thin films by ELC.     

电子回旋共振等离子体辅助溅射沉积锂磷氧氮薄膜

用电子回旋共振(ECR)等离子体辅助射频溅射沉积法制备快锂离子传导的锂磷氧氮(LiPON)薄膜. X射线光电子能谱、扫描电子显微镜、紫外可见吸收光谱等手段表征了在不同ECR功率辅助下沉积的薄膜. 结果显示, ECR等离子体对磁控溅射沉积薄膜的生长有明显的影响,能够提高N的插入量, 改变薄膜的组成与结构. 但是过高的ECR功率反而易破坏薄膜的结构, 不利于N的插入. 最佳的实验条件是在ECR 200W辅助下沉积的LiPON薄膜, 它的电导率约为8×10^-6S/cm. 讨论了ECR对沉积LiPON薄膜的N插入机理.     

Preparation of amorphous FexSi(1 − x) film using unbalanced magnetron sputtering

The preparation of iron-silicon films was performed onto Si (100) substrates by microwave electron cyclotron resonance (ECR) plasma source enhanced unbalance magnetron sputtering. The compositions, microstructures and properties of films under different sputtering powers and annealing conditions were characterized by AES, GAXRD, TEM and absorption spectrum techniques. The results described that the amorphous iron silicon films can be easily prepared by unbalance magnetron sputtering. Even the Fe/Si ratio deviated far from 1:2, such as Fe/Si = 1:14.8 or 1:10, the amorphous iron silicon film with semiconductor properties can also be obtained, which suggests that the Fe/Si ratio is not the only factor to determine whether the samples have semiconducting properties in iron silicon amorphous. After annealing at 850 °C for 4 h, the microstructure of nanometer β-FeSi₂ embedded into amorphous Si still possesses semiconducting characteristics.     

Structures and properties of titania thin films annealed under different atmosphere

The effects of crystallinity, phase and oxygen vacancies on optical and photocatalytic properties of titania (TiO₂) thin films were systematically studied. The as-deposited amorphous titania films were prepared by reactive sputtering titanium metal targets in argon–oxygen plasma at 100 °C and subsequently annealed at various temperatures of 400–800 °C in air, vacuum and H₂ atmosphere. The results indicate that in general the crystallinity of the annealed films is enhanced with the increasing annealing temperature. At the same temperature, the H₂ annealed films achieve better crystallinity but containing more oxygen vacancies than the films annealed in air and in vacuum. In H₂ or in vacuum, the concentration of oxygen vacancies in the annealed films increases with increasing temperature, while in air it remains constant. Oxygen vacancies in titania film not only facilitate phase transformation but also lower the band gap of titania, and make the film visible-light responsive. Photocatalytic properties of the TiO₂ films were characterized in UV and visible light irradiation by following the Ag reduction and degradation of methylene blue. The films annealed at 600–700 °C in H₂ possess the best film crystallinity and the proper concentration of oxygen vacancies and exhibit the best photocatalytic performance under both UV and visible light.     

Nanostructured tungsten and tungsten trioxide films prepared by glancing angle deposition

Nanostructured tungsten (W) and tungsten trioxide (WO₃) films were prepared by glancing angle deposition using pulsed direct current magnetron sputtering at room temperature with continuous substrate rotation. The chemical compositions of the nanostructured films were characterized by X-ray photoelectron spectroscopy, and the film structures and morphologies were investigated using X-ray diffraction and high resolution scanning electron microscopy. Both as-deposited and air annealed tungsten trioxide films exhibit nanostructured morphologies with an extremely high surface area, which may potentially increase the sensitivity of chemiresistive WO₃ gas sensors. Metallic W nanorods formed by sputtering in a pure Ar plasma at room temperature crystallized into a predominantly simple cubic β-phase with <100> texture although evidence was found for other random grain orientations near the film/substrate interface. Subsequent annealing at 500 °C in air transformed the nanorods into polycrystalline triclinic/monoclinic WO₃ structure and the nanorod morphology was retained. Substoichiometric WO₃ films grown in an Ar/O₂ plasma at room temperature had an amorphous structure and also exhibited nanorod morphology. Post-deposition annealing at 500 °C in air induced crystallization to a polycrystalline triclinic/monoclinic WO₃ phase and also caused a morphological change from nanorods into a nanoporous network.     

Phase separation in Ga and N co-incorporated ZnO films and its effects on photo-response in photoelectrochemical water splitting

Ga and N co-incorporated ZnO thin films [ZnO:(Ga:N)] with reduced bandgaps were deposited by co-sputtering at different N₂ gas flow rate in mixed N₂ and O₂ ambient at room temperature followed by postannealing at 500 °C in air for 2 h. We found that all of the ZnO:(Ga:N) films exhibited enhanced crystallinity which can suppress the recombination rate between the photogenerated electrons and holes. However, phase segregation of Zn₃N₂ occurred in ZnO:(Ga:N) thin films in nitrogen-rich sputtering ambient. We found that ZnO:(Ga:N) thin films without phase separation of Zn₃N₂ exhibited much better photoelectrochemical (PEC) response, due to the reduced bandgap and better crystallinity. Our results suggest that growth conditions must be controlled carefully to avoid phase separation in Ga and N co-incorporated ZnO thin films to improve PEC response.     

Nanocrystalline SnO2 and Au:SnO2 thin films prepared by direct current magnetron reactive sputtering

Nanocrystalline pure and gold doped SnO₂(Au:SnO₂) films were prepared on unheated glass substrates by dc magnetron reactive sputtering and, subsequently, the as deposited films were annealed in air. The films structure, surface morphology, photoluminescence, electrical and optical properties were investigated. After annealing the as deposited SnO₂ films, crystallinity increased and the surface roughness decreased. The intensity of PL peaks increases sharply with the annealing temperature. The optical transmittance of the films was around 89% after annealing the as deposited SnO₂ films at 450 °C. The as deposited Au:SnO₂ films show better crystallinity than the as deposited SnO₂ films, the average grain size was around 4.4 nm. The emission peaks of Au:SnO₂ films are slightly blue shifted as compare to undoped SnO₂ films. The Au:SnO₂ films show the lowest electrical resistivity of 0.001 Ωcm with optical transmittance of 76%, after annealing at 450 °C.     

Spectroscopic ellipsometry and positron annihilation investigation of sputtered HfO2 films

Hafnium oxide (HfO₂) films were prepared using a pulsed sputtering method and different O₂/(O₂ + Ar) ratios, deposition pressures, and sputtering powers. Spectroscopic ellipsometry (SE) and positron annihilation spectroscopy (PAS) were used to investigate the influence of the deposition parameters on the number of open volume defects (OVDs) in the HfO₂ films. The results reveal that a low O₂/(O₂ + Ar) ratio is critical for obtaining films with a dense structure and low OVDs. The film density increased and OVDs decreased when the deposition pressure was increased. The film deposited at high sputtering power showed a denser structure and lower OVDs. Our results suggest that SE and PAS are effective techniques for studying the optical properties of and defects in HfO₂ and provide an insight into the fabrication of high-quality HfO₂ thin films for optical applications.     

Structural characterization of sputtered indium oxide films deposited at room temperature

Structural evolution of indium oxide thin films deposited at room temperature by reactive magnetron sputtering and annealing in a reducing atmosphere were investigated. The as deposited indium oxide (In₂O₃) films showed a dominating randomly oriented nanocrystalline structure of cubic In₂O₃. The grain size decreased with increasing oxygen concentration in the plasma. Annealing in reducing atmospheres (vacuum, nitrogen and argon), besides improving the crystallinity, led to a partial cubic to rhombohedral phase transition in the indium oxide films. Annealing improved the optical properties of the indium oxide film and shifted the absorption edge to higher energies.     

Growth characteristics and device properties of MOD derived β-Ga2O3 films

β-Ga₂O₃ films prepared by metal organic deposition (MOD) on (000l) sapphire substrates, have been developed for ultraviolet photodectors. The structural, surface, optical properties of MOD derived β-Ga₂O₃ films depending on growth temperatures were investigated. As growth temperature increased, the crystallinity of β-Ga₂O₃ films enhanced, crystallite size and surface roughness increased. The optical band gap of β-Ga₂O₃ films maintained within 4.8–4.9 eV at different growth temperatures. Metal–semiconductor–metal ultraviolet photodetectors based on MOD derived β-Ga₂O₃ films were successfully fabricated, demonstrating the responsivity of 0.76 A/W at 20 V and the upper limits of the rise and decay time of 50 and 30 ms, respectively, indicating a promising low-cost approach for Ga₂O₃-base photoelectronics applications.     

Characteristics of sputtered Al-doped ZnO films for transparent electrodes of organic thin-film transistor

Aluminum-doped ZnO (AZO) thin-films were deposited with various RF powers at room temperature by radio frequency (RF) magnetron sputtering method. The electrical properties of the AZO film were improved with the increasing RF power. These results can be explained by the improvement of the crystallinity in the AZO film. We fabricated the organic thin-film transistor (OTFT) of the bottom gate structure using pentacene active and poly-4-vinyl phenol gate dielectric layers on the indium tin oxide gate electrode, and estimated the device properties of the OTFTs including drain current-drain voltage (I_D-V_D), drain current-gate voltage (I_D-V_G), threshold voltage (V_T), on/off ratio and field effect mobility. The AZO film that grown at 160 W RF power exhibited low resistivity (1.54 × 10^− 3 Ω·cm), high crystallinity and uniform surface morphology. The pentacene thin-film transistor using the AZO film that's fabricated at 160 W RF power exhibited good device performance such as the mobility of 0.94 cm²/V s and the on/off ratio of ~ 10⁵. Consequently, the performance of the OTFT such as larger field-effect carrier mobility was determined the conductivity of the AZO source/drain (S/D) electrode. AZO films prepared at room temperature by the sputtering method are suitable for the S/D electrodes in the OTFTs.     

A statistical parameter study of indium tin oxide thin films deposited by radio-frequency sputtering

In order to optimize the electrical and optical properties of indium tin oxide (ITO) thin films, a statistical analysis called Taguchi design was employed. It is shown that the sheet resistance and transmittance are inversely proportional to each other as a function of the process parameters. Additionally, the preferred orientation of crystalline ITO film is distinguishably changed with the increase of sputtering temperature and oxygen fraction (O₂/O₂+Ar) in the sputtering ambient. The change in crystallinity results from the content of incorporated oxygen, which significantly affects the electrical and optical properties of ITO films and causes a rearrangement of atoms to form preferred closed-packed plane orientation. Finally, the microstructure of the ITO films becomes denser with the increasing oxygen fraction. As a result of this work, we have successfully achieved low sheet resistance (7.0 Ω/□) and high transmittance (~90%) for 300 nm thick films.     

Preparation of anatase TiO2 thin films by vacuum arc plasma evaporation

Anatase titanium dioxide (TiO₂) thin films with high photocatalytic activity have been prepared with deposition rates as high as 16 nm/min by a newly developed vacuum arc plasma evaporation (VAPE) method using sintered TiO₂ pellets as the source material. Highly transparent TiO₂ thin films prepared at substrate temperatures from room temperature to 400 °C exhibited photocatalytic activity, regardless whether oxygen (O₂) gas was introduced during the VAPE deposition. The highest photocatalytic activity and photo-induced hydrophilicity were obtained in anatase TiO₂ thin films prepared at 300 °C, which correlated to the best crystallinity of the films, as evidenced from X-ray diffraction. In addition, a transparent and conductive anatase TiO₂ thin film with a resistivity of 2.6 × 10^− 1 Ω cm was prepared at a substrate temperature of 400 °C without the introduction of O₂ gas.     

Effect of sputtering power on microstructure of dielectric ceramic thin films by RF magnetron sputtering method using (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> as target

Radio frequency (RF) magnetron sputtering method was applied to prepare dielectric ceramic thin films on SiO₂ (110) substrates using (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ microwave dielectric ceramics as target. The samples were deposited at different sputtering powers in Ar atmosphere. In particular, the microstructure and morphology of the thin films were investigated as a function of sputtering powers by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results show that the thin films are polycrystalline and the sputtering power significantly influences the surface morphology and microstructure of the thin films. On increasing the sputtering power, the crystallinity improves and the grain size and roughness of the thin films reach maximum values at 200 W.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Comparison of hydrophilic properties of TiO2 thin films prepared by sol-gel method and reactive magnetron sputtering system

This article reports on preparation, characterization and comparison of TiO₂ films prepared by sol-gel method using the titanium isopropoxide sol (TiO₂ coating sol 3%) as solvent precursor and reactive magnetron sputtering from substoichiometric TiO_2 − x targets of 50 mm in diameter. Dual magnetron supplied by dc bipolar pulsed power source was used for reactive magnetron sputtering. Depositions were performed on unheated glass substrates. Comparison of photocatalytic properties was based on measurements of hydrophilicity, i.e. evaluation of water contact angle on the film surface after UV irradiation. It is shown, that TiO₂ films prepared by the sol-gel method exhibited higher hydrophilicity in the as-deposited state but has significant deterioration of hydrophilicity during aging, compared to TiO₂ films prepared by magnetron sputtering. To explain this effect AFM, SEM and high resolution XPS measurements were performed. It is shown that the deterioration of hydrophilicity of sol-gel TiO₂ films can be suppressed if as-deposited films are exposed to the plasma of microwave oxygen discharge.     

Phase transformations in sputtered Ni-Mn-Ga magnetic shape memory alloy thin films

Ni-Mn-Ga magnetic shape memory alloy films have been prepared by the DC magnetron sputtering technique. As-deposited films show a quasi-amorphous structure that crystallizes at ~ 500 K. Crystallization study using Kissinger's analysis reveals a relatively low activation energy indicating partial crystallinity in the films. In situ X-ray diffraction studies show reversible martensite phase transformations, and phase segregation to non-transforming L1₂ precipitates at higher temperatures. It was observed that the phase segregation can be suppressed by low temperature heat treatment.     

Structure, hardness and thermal stability of TiAlN and nanolayered TiAlN/CrN multilayer films

TiAlN films were deposited on silicon (1 1 1) substrates from a TiAl target using a reactive DC magnetron sputtering process in Ar+N₂ plasma. Films were prepared at various nitrogen flow rates and TiAl target compositions. Similarly, CrN films were prepared from the reactive sputtering of Cr target. Subsequently, nanolayered TiAlN/CrN multilayer films were deposited at various modulation wavelengths (Λ). X-ray diffraction (XRD), energy dispersive X-ray analysis, nanoindentation and atomic force microscopy were used to characterize the films. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of TiAlN/CrN multilayers was 3900 kg/mm², whereas TiAlN and CrN films exhibited maximum hardnesses of 3850 and 1000 kg/mm², respectively. Thermal stability of TiAlN and TiAlN/CrN multilayer films was studied by heating the films in air in the temperature range (T_A) of 500-900 °C for 30 min. The XRD spectra revealed that TiAlN/CrN multilayers were stable up to 800 °C and got oxidized substantially at 900 °C. On the other hand, the TiAlN films were stable up to 700 °C and got completely oxidized at 800 °C. Nanoindentation measurements performed on the films after heat treatment showed that TiAlN retained a hardness of 2200 kg/mm² at T_A=700 °C and TiAlN/CrN multilayers retained hardness as high as 2600 kg/mm² upon annealing at 800° C.