Investigation of brittle failure in transparent conductive oxide and permeation barrier oxide multilayers on flexible polymers

An oxide multilayer structure—consisting of an indium zinc oxide (IZO) conductive layer, a silicon oxide (SiO_x, x = 1.8) water vapor permeation barrier, and an aluminum oxide (Al₂O₃) interlayer—coated on polyethylene terephthalate (PET) is proposed as a transparent flexible substrate for display and photovoltaic applications. Vital properties of the multilayer, such as the low water vapor impermeability of the SiO_x barrier and the high conductance of the IZO film, degraded considerably because of the crack formation in bend geometries, attributed to the large difference between elastic properties of the oxide films and polymers. In order to suppress the crack formation, a 10-nm-thick Al₂O₃ interlayer was sputtered on Ar ion-beam treated PET surfaces prior to a SiO_x plasma-enhanced chemical vapor deposition (PECVD) process. Changes in the conductance and water vapor impermeability were investigated at different bending radii and bending cycles. It was found that the increases in resistance and water vapor transmission rate (WVTR) were significantly suppressed by the ion-beam PET pretreatment and by the sputtered Al₂O₃ interlayer. The resistance and WVTR of IZO/SiO_x/Al₂O₃/PET systems could be kept low and invariable even in severely bent states by choosing the SiO_x thickness properly. The IZO (135 nm)/SiO_x (90 nm)/Al₂O₃ (10 nm)/PET system maintained a resistance of 3.2 × 10^− 4 Ω cm and a WVTR of < 5 × 10^− 3 g m² d^− 1 after 1000 bending cycles at a bending radius of 35 mm.     

Effect of N2O/SiH4 flow ratios on properties of amorphous silicon oxide thin films deposited by inductively-coupled plasma chemical vapor deposition with application to silicon surface passivation

Silicon oxide (SiO_x) thin films have been deposited at a substrate temperature of 300 °C by inductively-coupled plasma chemical vapor deposition (ICP-CVD) using N₂O/SiH₄ plasma. The effect of N₂O/SiH₄ flow ratios on SiO_x film properties and silicon surface passivation were investigated. Initially, the deposition rate increased up to the N₂O/SiH₄ flow ratio of 2/1, and then decreased with the further increase in N₂O/SiH₄ flow ratio. Silicon oxide films with refractive indices of 1.47-2.64 and high optical band-gap values (>3.3 eV) were obtained by varying the nitrous oxide to silane gas ratios. The measured density of the interface states for films was found to have minimum value of 4.3 × 10¹¹ eV⁻¹ cm⁻². The simultaneous highest τ_eff and lowest density of interface states indicated that the formation of hydrogen bonds at the SiO_x/c-Si interface played an important role in surface passivation of p-type silicon.     

Plastic substrate with gas barrier layer and transparent conductive oxide thin film for flexible displays

A novel plastic substrate for flexible displays was developed. The substrate consisted of a polycarbonate (PC) base film coated with a gas barrier layer and a transparent conductive thin film. PC with ultra-low intrinsic birefringence and high temperature dimensional stability was developed for the base film. The retardation of the PC base film was less than 1 nm at a wavelength of 550 nm (film thickness, 120 µm). Even at 180 °C, the elastic modulus was 2 GPa, and thermal shrinkage was less than 0.01%. The surface roughness of the PC base film was less than 0.5 nm. A silicon oxide (SiO_x) gas barrier layer was deposited on the PC base film by a roll-to-roll DC magnetron reactive sputtering method. The water vapor transmission rate of the SiO_x film was less than 0.05 g/m²/day at 40 °C and 100% relative humidity (RH), and the permeation of oxygen was less than 0.5 cc/m² day atm at 40 °C and 90% RH. As the transparent conductive thin film, amorphous indium zinc oxide was deposited on the SiO_x by sputtering. The transmittance was 87% and the resistivity was 3.5 × 10^− 4 ohm cm.     

Optical and structural properties of SiOx films from ion-assisted deposition

This study investigates the optical and structural properties of SiO_x (x ∼ 1) films prepared by an ion-assisted deposition (IAD) process. The films were prepared by evaporating silicon monoxide, with and without simultaneous Ar⁺ bombardment. The stoichiometry of each film was determined as measured by the infrared spectrometry and X-ray photoelectron spectrometry. The variation in the stoichiometry revealed that the oxygen content of the SiO_x thin films varied slightly under the different conditions of the Ar⁺ bombardment. The results of the X-ray diffraction and transmission electron microscopy (TEM) measurements illustrated that all of the films had amorphous structures. However, a different interfacial appearance between the film and the substrate was observed from the TEM image. The optical constants of the SiO_x thin films were determined by a spectroscopic ellipsometry. The extinction coefficient of all of the films approached zero in the infrared wavelength range from 2 to 7 μm, but the refractive index was varied by the IAD process. The variation of these refractive indices is mainly related to the packing density of the films.     

Electrode effect on resistive switching of Ti-added amorphous SiOx films

Ti-added amorphous SiO_x films were sputter-deposited into stacks of Pt/SiO_x/Pt and Cu/SiO_x/Pt. Optimally prepared Pt/SiO_x/Pt exhibits unipolar resistive switching over 10² cycles, resistance ratio ∼ 10³, yet wide voltage distribution (2 ∼ 7 V for SET, 0.5 ∼ 1.5 V for RESET). Cu/SiO_x/Pt exhibit similar endurance, resistance ratio up to 10⁷, and SET and RESET voltages reduced to 1.8 ∼ 4.2 V and 0.5 ∼ 1 V, respectively. Cu diffusion into SiO_x at the virgin state may play a role in resistive switching of Cu/SiO_x/Pt stack besides of filament conduction. Ti-added amorphous SiO_x films incorporating Cu electrode shows potential for resistive memory.     

Application of plasma polymerized siloxane films for the corrosion protection of titanium alloy

Organosilicon film and SiO_x-like film are deposited on titanium alloy (Ti6Al4V) surfaces by atmospheric pressure (~ 10⁵ Pa) dielectric barrier discharge to improve its corrosion resistance in Hanks solution. Hexamethyldisiloxane (HMDSO) is used to be the chemical precursor. The organosilicon film deposited in Ar/HMDSO system has high growth rate (75 nm/min) and low surface roughness (3 nm), while the SiO_x-like film deposited in Ar/O₂/HMDSO system has lower growth rate (35 nm/min) and slightly higher surface roughness (9 nm). The potentiodynamic polarization tests show that both the two siloxane films coated Ti6Al4V samples have more positive corrosion potential and one order of magnitude lower corrosion current density than the substrate, indicating the corrosion resistance of Ti6Al4V can be improved by depositing siloxane film on its surface. In particular, as the surface is more compact and cross-linked, the SiO_x-like film has better corrosion resistance than the organosilicon film.     

Effect of TiOx seed layer on the texture and electric properties in La and Ca modified PbTiO3 thin films

Lanthanum-and calcium-modified PbTiO₃ (PLCT) ferroelectric thin films were successfully prepared on Pt(111)/Ti/SiO₂/Si substrates by pulsed laser deposition. Influence of TiO_x seed layer on texture and electric properties of PLCT films was investigated. It is found the PLCT films without seed layer exhibited highly (100)-textured, while using about 9 nm TiO_x as seed layer lead to highly (301)-textured. The PLCT film with TiO_x seed layer possess higher remnant polarization (Pr = 26 µC/cm²), better pyroelectric coefficient and figure of merit at room temperature (p = 370 µC/m²k, F_d = 190 × 10^− 5 Pa^− 1/2) than that of film without seed layer. The mechanism of the enhanced electric properties was also discussed.     

Deposition and characterization of ultra-high barrier coatings for flexible electronic applications

A barrier structure consisting of SiO_x and SiN_x films was deposited on the polymer substrate at 80 °C via plasma-enhanced chemical vapor deposition (PECVD). However, the low radius of curvature (R_c) of the barrier-coated substrate may cause the inconvenience of the following fabrication processes. By depositing a 150 nm-SiN_x film, the R_c of the barrier-coated polycarbonate (PC) substrate can increase from 80 to 115 mm without inducing any cracks in the barrier structure. Furthermore, the thermal stress of the barrier structure can be adjusted via extending the PECVD process duration in the chamber and replacing PC by the polyethersulone (PES) substrate. The R_c can increase to ∼356 mm by depositing the 150 nm-SiN_x film on the other side of the PES substrate. Finally, the calcium test result of the barrier films/PES/SiN_x sample was calculated to be around 3.05 × 10⁻⁶ g/m²/day, representing that the barrier structure did not fail after modification.     

Large area Ba1 − xSrxTiO3 thin films for microwave applications deposited by pulsed laser ablation

Large area Ba_1 − xSr_xTiO₃ (BST) thin films with x = 0.4 or x = 0.5 were deposited on 75 mm diameter Si wafers in a pulsed laser deposition (PLD) chamber enabling full-wafer device fabrication using standard lithography. The deposition conditions were re-optimized for large PLD chambers to obtain uniform film thickness, grain size, crystal structure, orientation, and dielectric properties of BST films. X-ray diffraction and microstructural analyses on the BST films grown on Pt/Au/Ti electrodes deposited on SiO₂/Si wafers revealed films with (110) preferred orientation with a grain size < 100 nm. An area map of the thickness and crystal orientation of a BST film deposited on SiO₂/Si wafer also showed (110) preferred orientation with a film thickness variation < 6%. Large area BST films were found to have a high dielectric tunability of 76% at an electric field of 400 kV/cm and dielectric loss tangent below 0.03 at microwave frequencies up to 20 GHz and a commutation quality factor of ~ 4200.     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.     

Leakage current characteristics of Bi3.15Nd0.85Ti3 − xZrxO12 thin films

Thin films of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) and Bi_3.15Nd_0.85Ti_3 − xZr_xO₁₂ (BNTZ_x, x = 0.1 and 0.2) were fabricated on Pt/TiO₂/SiO₂/Si(100) substrates by a chemical solution deposition (CSD) technique at 700 °C. Structures, surface morphologies, leakage current characteristics and Curie temperature of the films were studied as a function of Zr ion content by X-ray diffraction, atomic force microscopy, ferroelectric test system and thermal analysis, respectively. Experimental results indicate that Zr ion substitution in the BNT film markedly decreases the leakage current of the film, while almost not changing the Curie temperature of the film, which is at about 420-460 °C. The decrease of the leakage current in BNTZ_x films is that the conduction by the electron hopping between Ti⁴⁺ and Ti³⁺ ions is depressed because Zr⁴⁺ ions can block the path between two adjacent Ti ions and enlarge hopping distance.     

Electroluminescence of as-sputtered silicon-rich SiOx films

Si-rich oxide films (SiO_x, 0 < x < 2) were synthesized by reactive magnetron sputtering of a single Si target in a gas mixture of argon and oxygen. Intense visible electroluminescence was observed from the as-deposited SiO_x film. The microstructure of the as-sputtered SiO_x films was characterized by Raman and X-ray photoelectron spectroscopy techniques. Nanoscale amorphous Si clusters formed in the as-sputtered films. The electroluminescence was attributed to the oxygen-deficient defect luminescent centres and the formation of the amorphous Si nanoclusters.     

Pyroelectric Ta-modified LiNbO3 thin films and devices for thermal infrared detection

High-performance pyroelectric infrared (IR) detectors have been fabricated using tantalate-doped lithium niobate LiNb_1 − xTa_xO₃ (abbreviated as LNT, with x = 0-1.0) thin films deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by diol-based sol-gel processing, in which, tantalate (Ta) is adopted as dopant in lithium niobate. The randomly oriented LNT thin film exhibits a relatively small dielectric constant and a large pyroelectric coefficient. The pyroelectric characteristics of detectors with various tantalate contents, as a function of modulation frequency, were investigated. It was found that LiNb_0.8Ta_0.2O₃ had the largest voltage responsivity of 7020 (V/W) at 70 Hz, and a specific detectivity (D^?) of 7.76 × 10⁷ cm Hz^1/2/W at 200 Hz. These results indicate that the LNT thin film with x = 0.20 is most suitable for application as high-performance pyroelectric thin-film detectors.     

Effects of oxygen addition on electrochromic properties in low temperature plasma-enhanced chemical vapor deposition-synthesized MoOxCy thin films for flexible electrochromic devices

Electrochromic organomolybdenum oxide (MoO_xC_y) films are deposited onto 60 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates by low temperature plasma-enhanced chemical vapor deposition (PECVD) using a precursor of molybdenum carbonyl vapor, which is carried by argon gas, mixed with oxygen gas and synthesized by radio frequency power at room temperature (23 °C). The MoO_xC_y films with modified surface morphology and compositions of varying oxygen contents are proven to offer noteworthy electrochromic performance. Porous surface of the MoO_xC_y film (398 nm thick) provides Li⁺ ion diffusion coefficient value of 1.7 × 10^− 10 cm²/s for Li⁺ de-intercalation at a potential scan rate of 2 mV/s. High x/y value at high surface composition of oxygen to carbon in the MoO_xC_y film offers light modulation with transmittance variation of up to 63% and coloration efficiency of 36 cm²/C at a wavelength of 800 nm for 200 cycles of Li⁺ intercalation and de-intercalation. PECVD-synthesized MoO_xC_y thin films show promising electrochromic properties for applications in flexible electrochromic devices.     

Ion beam synthesis of the diamond like carbon films for nanoimprint lithography applications

Ion beam deposited hydrogenated undoped as well as SiO_x (SiO_x + N₂, SiO_x + Ar) doped DLC thin films were deposited and evaluated as possible anti-adhesive layers for nanoimprint lithography. Film surface contact angle with water was investigated as a measure of the surface free energy and anti-sticking properties. Contact angle of the DLC films was independent of SiO_x doping and ion beam energy. Air-annealing resistance in terms of the contact angle with water of the synthesized diamond like carbon films was investigated. Optical transmittance spectra of the DLC films in UV-VIS range were measured to investigate it as possible anti-sticking layers for UV imprint lithography applications. DLC films with the most promising combination of the UV absorption and anti-sticking properties were revealed. Preliminary imprint tests with uncoated and thin DLC film coated hot imprint stamps were performed.     

Preparation of homogeneous VOX thin films by ion beam sputtering and annealing process

Polycrystalline VO_x thin films that were prepared for thermal-sensitive material of far infrared sensor had been deposited on Si substrates by ion beam sputtering deposition. Scanning electron microscopy images indicated that VO_x thin films (oxygen pressure of 1.5×10⁻³ Pa) were grown into compact and ultra-fine grains (?50 nm), the film surfaces seemed smooth and uniform. Four-point probe measurements showed that the homogeneity of the films was better than 98% in a size of 30×30 mm². The four-point probe measurement on hot plate presented the sheet resistance and the temperature coefficient of resistance of the VO_x thin film that were 50 kΩ/square and −0.021 K⁻¹ at 28°C, respectively. In addition, some samples annealed in Ar atmosphere had their resistance decreased. Thus, vanadium oxide films containing more amount VO₂ were obtained.     

Physico-chemical, structural and physical properties of hydrogenated silicon oxinitride films elaborated by pulsed radiofrequency discharge

Films prepared by radiofrequency pulsed plasma enhanced chemical vapor deposition from a mixture of silane (SiH₄) and nitrous oxide (N₂O) were studied. Variation of operating conditions (flow rate, deposition temperature ...) resulted in films with chemical compositions changing from hydrogenated silicon oxynitride (SiO_xN_y:H) to silicon oxide (SiO_x:H). Infrared and Rutherford backscattering spectroscopy studies of the as-deposited films revealed different SiO_x arrangements disturbed by Si-N bonds and H-Si ≡ Si_(3 − x)O_x clusters depending on the substrate temperature and the N₂O/SiH₄ ratio. For films obtained using low N₂O/SiH₄ rations and annealed at temperature higher than 1273 K, Raman spectroscopy and microscopy analyses revealed the presence of silicon nanocrystals embedded in a matrix containing Si, O, and N. Spectroscopic ellipsometry revealed the presence of silicon nanocrystals along with two other amorphous phases (SiO_xN_y and SiO₂) in annealed samples. The electrical characteristics of annealed films obtained from capacitance-voltage measurements indicated a stable charge trapping in ultra-thin SiO_xN_y layers. These preliminary results suggest that Si-nc containing silicon oxynitride layers can be potential candidates to be used in the floating gate fabrication of memory devices.     

V-doping effects on ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

V-doped K_0.5Bi_4.5Ti₄O₁₅ (K_0.5Bi_{4.5 − x/3}Ti_4 − xV_xO₁₅, KBTiV-x, x = 0.00, 0.01, 0.03, and 0.05) thin films were prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. The thin films were annealed by using a rapid thermal annealing process at 750 °C for 3 min in an oxygen atmosphere. Among them, KBTiV-0.03 thin film exhibited the most outstanding electrical properties. The value of remnant polarization (2P_r) was 75 μC/cm² at an applied electric field of 366 kV/cm. The leakage current density of the thin film capacitor was 5.01 × 10⁻⁸ at 100 kV/cm, which is approximately one order of magnitude lower than that of pure K_0.5Bi_4.5Ti₄O₁₅ thin film capacitor. We found that V doping is an effective method for improving the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ thin film.     

The roles of B-site ions in lead strontium zirconate titanate thin films for electrically tunable device applications

B-site modification lead strontium zirconate titanate Pb_0.4Sr_0.6Zr_xTi_1 − xO₃ (PSZT, x = 0-0.7) thin films were prepared on Pt/TiO₂/SiO₂/Si substrates by a sol-gel method. The XRD results indicate that paraelectric PSZT thin films at room temperature are obtained as x approaches 0.2. The temperature-dependent dielectric and hysteresis loop measurements reveal that the thin films have diffuse phase transition characteristics and relaxor-like behavior with nano-polar regions in the paraelectric films at room temperature. The Curie temperature of the PSZT thin films varies with the Zr contents, exhibiting a complex trend. This can be attributed to two competitive factors: higher mobility of Ti⁴⁺ than Zr⁴⁺ and smaller open space left for the displacement of Ti ions with the increase of Zr content. The further increase of the Zr contents leads to the simultaneous decrease of dielectric constant, dielectric loss and tunability. PSZT (x = 0.4) thin film shows the largest figure of merit of 24.3 with a moderate tunability of 55.8% and a dielectric loss of 0.023. This suggests that B-site ions have different roles in modifying the electrically tunable performance of PSZT thin films for tunable microwave device applications.     

Influence of lithium doping on the structural and electrical characteristics of ZnO thin films

Thin films of undoped and lithium-doped Zinc oxide, (Zn_1 − xLi_x)O; x = 0, 0.05, 0.10 and 0.20 were prepared by sol-gel method using spin-coating technique on silicon substrates [(111)Pt/Ti/SiO₂/Si)]. The influence of lithium doping on the structural, electrical and microstructural characteristics have been investigated by means of X-ray diffraction, leakage current, piezoelectric measurements and scanning electron microscopy. The resistivity of the ZnO film is found to increase markedly with low levels (x ≤ 0.05) of lithium doping thereby enhancing their piezoelectric applications. The transverse piezoelectric coefficient, e₃₁^? has been determined for the thin films having the composition (Zn_0.95Li_0.05)O, to study their suitability for piezoelectric applications.