Microwave dielectric properties of W-doped Ba0.6Sr0.4TiO3 thin films grown on (001) MgO by pulsed laser deposition with a variable oxygen deposition pressure

The microwave dielectric properties of Ba_0.6Sr_0.4TiO₃ 1 mol% W-doped thin films deposited using pulsed laser deposition, are improved by a novel oxygen deposition profile. The thin films were deposited onto (001) MgO substrates at a temperature of 720 °C. A comparison is made between three different oxygen ambient growth conditions. These include growth at a single oxygen pressure (6.7 Pa) and growth at two oxygen pressures, one low (6.7 Pa) and one high (46.7 Pa). Films were deposited in a sequence that includes both a low to high and a high to low transition in the oxygen deposition pressure. Following deposition, all films were post-annealed in 1 atm of oxygen at 1000 °C for 6 h. The dielectric Q (defined as 1 / tanδ) and the dielectric constant, ε_r, were measured at room temperature, at 2 GHz, using gap capacitors fabricated on top of the dielectric films. The percent dielectric tuning (defined as (ε_r(0 V) − ε_r(40 V)) / ε_r(0 V) × 100) and figure of merit (FOM) (defined as percent dielectric tuning × Q(0 V)) were calculated. The film deposited using the two-stage growth conditions, 6.7 / 46.7 Pa oxygen, showed a maximum Q(0 V) value with high percent dielectric tuning and gave rise to a microwave FOM twice as large as the single stage growth condition. The improved dielectric properties are due to initial formation of a film with reduced interfacial strain, due to the formation of defects at the film/ substrate interface resulting in a high Q(0 V) value, followed by the reduction of oxygen vacancies which increases the dielectric constant and tuning.     

Effects of reduction treatment on the photorefractive properties of Pb0.5Ba0.5Nb2O6

Lead barium niobate is a new photorefractive material of high interest for a variety of applications including holographic storage. Pb_0.5Ba_0.5Nb₂O₆ crystals have been grown by the Bridgman method, and the effects of heat treatments on their photorefractive properties were investigated using Ar ion laser at λ=514.5 nm. The color and absorption spectrum of the crystals varied depending on the oxygen partial pressure during heat treatment. The oxygen diffusivity was estimated to be in the order of 10⁻⁶ and 10⁻⁵ cm²/h at 425 and 550 °C, respectively. Reduction treatment at an oxygen pressure of 215 mTorr increased the effective density of photorefractive charges about three times from 8.0×10¹⁵ to 2.2×10¹⁶ cm⁻³ and made the charge transport more electron-dominant. As a result, the maximum gain coefficient improved from 5.5 to 13.8 cm⁻¹. A diffraction efficiency as high as 70% was achieved in a reduced crystal.     

Preparation of Pt-PtOx thin films as electrode for memory capacitors

Pt-PtO_x thin films were prepared on Si(100) substrates at temperatures from 30 to 700°C by reactive r.f. magnetron sputtering with platinum target. Deposition atmosphere was varied with O₂/Ar flow ratio. The deposited films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Resistively of the deposited films was measured by d.c. four probe method. The films mainly consisted of amorphous PtO and Pt₃O₄ (or Pt₂O₃) below 400°C, and amorphous Pt was increased in the film as a deposition temperature increased to 600°C. When deposition temperature was thoroughly increased, (111) oriented pure Pt films were formed at 700°C. Compounds included in the films strongly depended on substrate temperature rather than O₂/Ar flow ratio. Electrical resistivity of Pt-PtO_x films was measured to be from the order of 10⁻¹ Ω cm to 10⁻⁵ Ω cm, which was related to the amount of Pt phase included in the deposited films.     

Deposition and dielectric properties of CaCu3Ti4O12 thin films on Pt/Ti/SiO2/Si substrates using pulsed-laser deposition

CaCu₃Ti₄O₁₂ (CCTO) thin films were successfully deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates using pulsed-laser deposition technique. The crystalline structure and the surface morphology of the CCTO thin films were greatly affected by the substrate temperature and oxygen pressure. Thin films with a (2 2 0) preferential orientation were obtained at the substrate temperature above 700 °C and oxygen pressure above 13.3 Pa. The 480-nm thin films deposited under 720 °C and 26.6 Pa have a fairly high dielectric constant of near 2000 at 10 kHz and room temperature. The values of the dielectric constant and loss and their temperature-dependence under different frequency are comparable with those obtained in the epitaxial CCTO films grown on oxide substrates.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Electrochromic properties of nanocrystalline MoO3 thin films

Electrochromic MoO₃ thin films were prepared by a sol–gel spin-coating technique. The spin-coated films were initially amorphous; they were calcined, producing nanocrystalline MoO₃ thin films. The effects of annealing temperatures ranging from 100 °C to 500 °C were investigated. The electrochemical and electrochromic properties of the films were measured by cyclic voltammetry and by in-situ optical transmittance techniques in 1 M LiClO₄/propylene carbonate electrolyte. Experimental results showed that the transmittance of MoO₃ thin films heat-treated at 350 °C varied from 80% to 35% at λ = 550 nm (ΔT =  45%) and from 86% to 21% at λ ≥ 700 nm (ΔT =  65%) after coloration. Films heat-treated at 350 °C exhibited the best electrochromic properties in the present study.     

Atomic layer deposition growth of zirconium doped In2O3 films

Zirconium doped indium oxide thin films were deposited by the atomic layer deposition technique at 500 °C using InCl₃, ZrCl₄ and water as precursors. The films were characterised by X-ray diffraction, energy dispersive X-ray analysis and by optical and electrical measurements. The films had polycrystalline In₂O₃ structure. High transparency and resistivity of 3.7×10⁻⁴ Ω cm were obtained.     

Al2O3 formation on Si by catalytic chemical vapor deposition

Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al₂O₃) thin films on silicon (Si) crystals using N₂ bubbled tri-methyl aluminum [Al(CH₃)₃, TMA] and molecular oxygen (O₂) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min⁻¹ at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10¹² cm⁻², small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10⁻⁷ A cm⁻² at a gate bias of 1 V.     

Characterization of indium zinc oxide thin films prepared by pulsed laser deposition using a Zn3In2O6 target

Using a Zn₃In₂O₆ target, indium-zinc oxide films were prepared by pulsed laser deposition. The influence of the substrate deposition temperature and the oxygen pressure on the structure, optical and electrical properties were studied. Crystalline films are obtained for substrate temperatures above 200°C. At the optimum substrate deposition temperature of 500°C and the optimum oxygen pressure of 10⁻³ mbar, both conditions that indeed lead to the highest conductivity, Zn₃In₂O₆ films exhibit a transparency of 85% in the visible region and a conductivity of 1000 S/cm. Depositions carried out in oxygen and reducing gas, 93% Ar/7% H₂, result in large discrepancies between the target stoichiometry and the film composition. The Zn/In (at.%) ratio of 1.5 is only preserved for oxygen pressures of 10⁻²–10⁻³ mbar and a 93% Ar/7% H₂ pressure of 10⁻² mbar. The optical properties are basically not affected by the type of atmosphere used during the film deposition, unlike the conductivity which significantly increases from 80 to 1400 S/cm for a film deposited in 10⁻² mbar of O₂ and in 93% Ar/7% H₂, respectively.     

Molecular beam epitaxial growth of SmBa2Cu3O7−δ thin films and effect of substrate temperature on the surface roughness

Stoichiometrically optimized, epitaxial SmBa₂Cu₃O_7-δ thin films with high T_{c, R = 0} and high critical current densities j_c have been prepared for the first time in a tightly controlled molecular beam epitaxy process in non-reactive molecular oxygen, followed by an in situ loading process with molecular oxygen. The surface roughness (on a submicrometre scale) of single-crystal films with their c axes perpendicular to the surface depends markedly on the surface temperature of the substrate during the deposition of the epitaxial films, within a range of only a few degrees centigrade. The calibrated optimal temperature for the preparation of epitaxial films 200 nm thick of this single orientation is found to be 680 ± 5 °C. In scanning tunnelling microscopy investigations, they show a surface roughness of less than 6 nm (five SmBa₂Cu₃O_7−δ unit cells) on a 2 μm × 2 μm scale. At deposition temperatures below this optimal deposition temperature, the well-known a-axis growth increases rapidly, whereas higher temperatures give a significantly higher surface roughness, which can be observed by scanning electron microscopy.     

Epitaxial growth of RuO2 thin films by metal-organic chemical vapor deposition

Conductive RuO₂ thin films were epitaxially grown on LaAlO₃(100) and MgO(100) substrates by metal-organic chemical vapor deposition (MOCVD). The deposited RuO₂ films were crack-free, and well adhered to the substrates. The RuO₂ film is (200) oriented on LaAlO₃ (100) substrates at deposition temperature of 600°C and (110) oriented on MgO(100) substrates at deposition temperature of 350°C and above. The epitaxial growth of RuO₂ on MgO and LaAlO₃ is demonstrated by strong in-plane orientation of thin films with respect to the major axes of the substrates. The RuO₂ films on MgO(100) contain two variants and form an orientation relationship with MgO given by RuO₂(110)//MgO(100) and RuO₂[001]//MgO[011]. The RuO₂ films on LaAlO₃(100), on the other hand, contain four variants and form an orientation relationship with LaAlO₃ given by RuO₂(200)//LaAlO₃(100) and RuO₂[011]//LaAlO₃[011]. Electrical measurements on the RuO₂ thin films deposited at 600°C show room-temperature resistivities of 40 and 50 μΩ cm for the films deposited on the MgO and LaAlO₃ substrates, respectively.     

Fabrication of robust Bi3.25La0.75Ti3O12 thin film resistant to hydrogen damage

Ferroelectric bismuth lanthanum titanate (Bi_3.25La_0.75Ti₃O₁₂; BLT) thin films were deposited on Pt/TiO₂/SiO₂/Si substrate by chemical solution deposition method. The films were crystallized in the temperature range of 600–700 °C. The spontaneous polarization (P_s) and the switching polarization (2P_r) of BLT film annealed at 700 °C for 30 min were 22.6 μC/cm² and 29.1 μC/cm², respectively. Moreover, the BLT capacitor did not show any significant reduction of hysteresis for 90 min at 300 °C in the forming gas atmosphere.     

Structural, electrical, and optical studies on rapid thermally processed ferroelectric BaTiO3 thin films prepared by metallo-organic solution deposition technique

Polycrystalline BaTiO₃ thin films having the perovskite structure were successfully produced on platinum coated silicon, bare silicon, and fused quartz substrate by the combination of the metallo-organic solution deposition technique and post-deposition rapid thermal annealing treatment. The films exhibited good structural, electrical, and optical properties. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) and metal-ferroelectric-semiconductor (MFS) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 255 and 0.025, respectively, and the remanent polarization and coercive field were 2.2 μC cm⁻² and 25 kV cm⁻¹, respectively. The resistivity was found to be in the range 10¹⁰–10¹² Ω·cm, up to an applied electric field of 100 kV cm⁻¹, for films annealed in the temperature range 550–700 °C. The films deposited on bare silicon substrates exhibited good film/substrate interface characteristics. The films deposited on fused quartz were highly transparent. An optical band gap of 3.5 eV and a refractive index of 2.05 (measured at 550 nm) was obtained for polycrystalline BaTiO₃ thin film on fused quartz substrate. The optical dispersion behavior of BaTiO₃ thin films was found to fit the Sellmeir dispersion formula well.     

Low-temperature epitaxial growth of conductive LaNiO3 thin films by RF magnetron sputtering

Epitaxial growth of LaNiO₃ (LNO) thin films was successful on CeO₂/YSZ/Si(100), MgO(100) and SrTiO₃ (STO)(100) substrates by RF magnetron sputtering at 300 °C, although pulsed laser deposition requires 600 °C to prepare epitaxial LNO films according to the literature. Epitaxial LNO films deposited on CeO₂/YSZ/Si(100) and STO(100) had single orientation of LNO[100]//CeO₂[110]//YSZ[110]//Si[110]) and LNO[100]//STO[100], respectively. On the other hand, epitaxial LNO films deposited on MgO(100) had mixed orientations of LNO[100]//MgO[100] and LNO[100]//MgO[110]. The lattice parameter, composition and resistivity of the LNO thin films were strongly dependent on the substrate temperature. The minimum resistivity of LNO films was approximately 5×10⁻⁶ Ω m, which value almost agrees with the resistivity in the literature. It was found that the temperature to achieve minimum resistivity was 200 °C, irrespective of the type of substrate. The surface of the LNO films was smooth and flat.     

Optical and electrical properties of p-type AgInSnxS2−x (x = 0–0.04) thin films prepared by spray pyrolysis

AgInSn_xS_2−x (x = 0–0.2) polycrystalline thin films were prepared by the spray pyrolysis technique. The samples were deposited on glass substrates at temperatures of 375 and 400 °C from alcoholic solutions comprising silver acetate, indium chloride, thiourea and tin chloride. All deposited films crystallized in the chalcopyrite structure of AgInS₂. A p-type conductivity was detected in the Sn-doped samples deposited at 375 °C, otherwise they are n-type. The optical properties of AgInSn_xS_2−x (x < 0.2) resemble those of chalcopyrite AgInS₂. Low-temperature PL measurements revealed that Sn occupying an S-site could be the responsible defect for the p-type conductivity observed in AgInSn_xS_2−x (x < 2) thin films.     

Fabrication and characterization of (1−x)SrBi2Ta2O9–xBi3TaTiO9 layered structure solid solution thin films for ferroelectric random access memory (FRAM) applications

We report on the properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi₂Ta₂O₉. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi₃TaTiO₉ content in the solid solution. Ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films were significantly improved compared to SrBi₂Ta₂O₉. For example, the observed remanent polarization (2P_r) and coercive field (E_c) values for films with 0.7SrBi₂Ta₂O₉–0.3Bi₃TaTiO₉ composition, annealed at 650°C, were 12.4 μC/cm² and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 10¹⁰ switching cycles and good memory retention characteristics after about 10⁶ s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films compared to SrBi₂Ta₂O₉, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.     

Preparation and characterization of YBa2Cu3O7−x high Tc superconducting thin films deposited by S-gun sputtering

We have prepared YBa₂Cu₃O_7−x high T_c superconducting (HTS) thin films on (100) yttria-stabilized zirconia (YSZ) and LaAlO₃ (LAO) substrates, using a 2 kW S-gun in an off-axis mode. By varying the temperature of the substrates, films with a axis and c axis orientations were readily obtained. The X-ray diffraction pattern and Laue pattern confirmed that films with a axis orientation exhibited a single-crystal texture. All films had a good mirror-like surface. For films grown on YSZ substrates, scanning electron microscopy (SEM) revealed a clear distinction between the surfaces of the films grown at various temperatures (520–780°C). Films grown on LAO substrates exhibited even smoother and flatter surfaces. The SEM changes will be discussed in correlation with J_c. The best HTS thin films were obtained on LAO substrates at a temperature of 820°C, with T_c=89 K and J_c=1×10⁶ A cm^-2 (77 K).     

Tungsten chemical vapor deposition using tungsten hexacarbonyl: microstructure of as-deposited and annealed films

Tungsten (W) films were deposited on Si(100) from tungsten hexacarbonyl, [W(CO)₆], by low-pressure chemical vapor deposition (CVD) in an ultra-high vacuum (UHV)-compatible reactor. The chemical purity, resistivity, crystallographic phase, and morphology of the deposited films depend markedly on the substrate temperature. Films deposited at 375°C contain approximately 80 at.% tungsten, 15 at.% carbon and 5 at.% oxygen. These films are polycrystalline β-W with a strong (211) orientation and resistivities of >1000 μΩ cm. Vacuum annealing at 900°C converts the metastable β-W to polycrystalline -W, with a resistivity of approximately 19 μΩ cm. The resultant -W films are porous, with small randomly oriented grains and nanoscale (<100 nm) voids. Films deposited at 540°C are high-purity (>95 at.%) polycrystalline -W, with low resistivities (18–23 μΩ cm) and a tendency towards a (100) orientation. Vacuum annealing at 900°C reduces the resistivity to approximately 10 μΩ cm, and results in a columnar morphology with a very strong (100) orientation.     

Atomic-layer doping in Si by alternately supplied PH3 and SiH4

Atomic-layer doping of P in Si epitaxial growth by alternately supplied PH₃ and SiH₄ was investigated using ultraclean low-pressure chemical vapor deposition. Three atomic layers of P adsorbed on Si(100) are formed by PH₃ exposure at a partial pressure of 0.26 Pa at 450°C. By subsequent SiH₄ exposure at 220 Pa at 450°C, Si is epitaxially grown on the P-adsorbed surface. Furthermore, by 12-cycles of exposure to PH₃ at 300–450°C and SiH₄ at 450°C followed by 20-nm thick capping Si deposition, the multi-layer P-doped epitaxial Si films of average P concentrations of 10²¹ cm⁻³ are formed. The resistivity of the film is as low as 2.4×10⁻⁴ Ω cm. By annealing the sample at 550°C and above, it is found that the resistivity increases and the surface may become rough, which may be due to formation of SiP precipitates at 550°C and above. These results suggest that the epitaxial growth of very low-resistive Si is achieved only at a very low-temperature such as 450°C.