Optical, electrical and dielectric properties of TiO2-SiO2 films prepared by a cost effective sol-gel process

Titanium dioxide (TiO(2)) and silicon dioxide (SiO(2)) thin films and their mixed films were synthesized by the sol-gel spin coating method using titanium tetra isopropoxide (TTIP) and tetra ethyl ortho silicate (TEOS) as the precursor materials for TiO(2) and SiO(2) respectively. The pure and composite films of TiO(2) and SiO(2) were deposited on glass and silicon substrates. The optical properties were studied for different compositions of TiO(2) and SiO(2) sols and the refractive index and optical band gap energies were estimated. MOS capacitors were fabricated using TiO(2) films on p-silicon (100) substrates. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated for the films annealed at 200°C for their possible use in optoelectronic applications.     

Microstructure and electrical properties of BaTiO<Subscript>3</Subscript> and (Ba,Sr)TiO<Subscript>3</Subscript> ferroelectric thin films on nickel electrodes

Nickel thin films have been sputtered on standard Si/SiO₂ substrates with TiO₂ as an adhesive layer. The thermal stability of these substrates was analyzed. SEM images show an increase in grain size with annealing temperature. They were found to be stable till 800°C, beyond which the nickel layer disintegrated. These substrates were used for deposition of BaTiO₃ and (Ba,Sr)TiO₃ dielectric thin films under a reducing atmosphere. The dielectric thin films were processed with various pyrolysis and annealing temperatures in order to optimize the dielectric properties. Increased pyrolysis temperatures showed an increase in the grain size. Results on these nickelised substrates were finally compared with dielectric films deposited on platinized silicon substrates under identical conditions but crystallized in an oxygen atmosphere.     

Investigation on the growth of CaCu3Ti4O12 thin film and the origins of its dielectric relaxations

Using the radio frequency magnetron sputtering, CaCu₃Ti₄O₁₂ (CCTO) thin films were deposited on platinized silicon substrates. The influence of annealing temperature on structures and morphologies of the thin films was investigated. The high annealing temperature increased the crystallinity of the films. Temperature dependence of the dielectric constant revealed an amazing different characteristic of the dielectric relaxation at ∼10 MHz, whose characteristic frequency abnormally increased with the decrease of the measuring temperature unlike the relaxations due to extrinsic origins. Meanwhile, the dielectric constant at high frequencies was close to the value derived from the first principle calculation. All these gave the evidences to ascribe this relaxation to the intrinsic mechanism.     

Recent advances in characterization of CaCu3Ti4O12 thin films by spectroscopic ellipsometric metrology

CaCu3Ti4O12 (CCTO) thin films were successfully grown on LaAlO3(100) and Pt/TiO2/SiO2/Si(100) substrates by a novel MOCVD approach. Epitaxial CCTO(001) thin films have been obtained on LaAlO3(100) substrates, while polycrystalline CCTO films have been grown on Pt/TiO2/SiO2/Si(100) substrates. Surface morphology and grain size of the different nanostructured deposited films were examined by AFM, and spectroscopic ellipsometry has been used to investigate the electronic part of the dielectric constant (epsilon2). Looking at the epsilon2 curves, it can be seen that by increasing the film structural order, a greater dielectric response has been obtained. The measured dielectric properties accounted for the ratio between grain volumes and grain boundary areas, which is very different in the different structured films.     

Substrate temperature influenced physical properties of silicon MOS devices with TiO2 gate dielectric

DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO₂) films. The films were formed on Corning glass and p‐Si (100) substrates by sputtering of titanium target in an oxygen partial pressure of 6×10^?2 Pa and at different substrate temperatures in the range 303 – 673 K. The films formed at 303 K were X‐ray amorphous whereas those deposited at substrate temperatures ≥ 473 K were transformed into polycrystalline nature with anatase phase of TiO₂. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic bonding configuration of TiO₂. The surface morphology of the films was significantly influenced by the substrate temperature. MOS capacitor with Al/TiO₂/p‐Si sandwich structure was fabricated and performed current–voltage and capacitance–voltage characteristics. At an applied gate voltage of 1.5 V, the leakage current density of the device decreased from 1.8 × 10^?6 to 5.4 × 10^?8 A/cm² with the increase of substrate temperature from 303 to 673 K. The electrical conduction in the MOS structure was more predominant with Schottky emission and Fowler‐Nordheim conduction. The dielectric constant (at 1 MHz) of the films increased from 6 to 20 with increase of substrate temperature. The optical band gap of the films increased from 3.50 to 3.56 eV and refractive index from 2.20 to 2.37 with the increase of substrate temperature from 303 to 673 K. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural and optical properties of thin silver films deposited on Si(111)

Silver films in the thickness range 3–12 nm were deposited on very clean Si(111) substrates at ambient temperature. The annealing up to temperatures of 650?°C was then studied using LEED/Auger, SEM and X-ray diffraction as well as resistivity and ellipsometry measurements. The films crack during annealing and silver islands are formed on the silicon surface. The coagulation results in a steep drop of the ellipsometric parameters Δ and Ψ in the temperature range 150–300?°C which can be attributed to the generation of surface plasmons and Mie plasmon polaritons, respectively.     

Structure and voltage tunable dielectric properties of sol–gel derived Bi1.5MgNb1.5O7 thin films

Bi_1.5MgNb_1.5O₇ (BMN) thin films were fabricated on Au/Ti/SiO₂/Si(100) substrates using a sol?Cgel spin coating process. Thermo decomposition of the BMN precursor gel was discussed. The structures, morphologies, dielectric properties and voltage tunable dielectric properties were investigated. The deposited films showed a cubic pyrochlore structure after annealing at 550?°C or higher temperatures. With the annealing temperature increased from 500 to 800?°C, the root-mean-square surface roughness of the films increased from 0.6 to 6.8?nm. Additional phase, MgNb₂O₆, emerged after annealing at 800?°C due to the volatilization of Bi element. The dielectric properties and tunability of the films were annealing temperature dependent. BMN thin films annealed at 750?°C had a high dielectric constant of 135 and low dielectric loss of 0.002 at 1?MHz. The high tunability of 31.3?% and figure of merit of 156.5 were obtained under an applied electric field of 1?MV/cm at room temperature.     

Influence of surfactant and annealing temperature on optical properties of sol–gel derived nano-crystalline TiO2 thin films

Titanium dioxide thin films have been synthesized by sol–gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 °C. The influence of surfactant and annealing temperature on optical properties of TiO₂ thin films has been studied. Optical constants and film thickness were estimated by Swanepoel's (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO₂ films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO₂ films was estimated by Tauc's method at different annealing temperature.     

Structural, morphology and electrical studies of Sm-modified bismuth titanate thin films on Si (100)

Samarium-substituted bismuth titanate (Bi_3.15Sm_0.85Ti₃O₁₂ (BSmT)) thin films have been grown on n-type Si (100) substrates by metalorganic decomposition and spin-coating technique. X-ray diffraction and scanning electron microscopy (SEM) analyses confirmed that the crystallinity of the films increases with increasing annealing temperature and the optimum temperature was found to be 700°C. The Raman measurement showed an increase in structural distortion due to the changed ionic radius and atomic mass of Sm ions. The current-voltage characteristics displayed good insulating properties for a film annealed at 700°C for 1 h. The capacitance-voltage characteristic hysteresis curves revealed that the ferroelectric property sufficiently controlled the silicon potential. The measurements of the dielectric constant and dissipation factor of BSmT as a function of frequency exhibited excellent dielectric properties.     

Ferroelectric and Pyroelectric Properties of Highly (111)-oriented Nanocrystalline Pb(Zr0:95Ti0:05)O3 Thin Films

"Lead zirconate titanate Pb(Zr0:95Ti0:05)O3 (PZT95/5) antiferroelectric thin films with 300 nm thickness were grown on Pt/Ti/SiO2/Si substrates by a sol-gel method with rapid thermal annealing processing. The X-ray diffraction results showed that the highly (111)-oriented pervoskite PZT95/5 thin films were grown on Pt/Ti/SiO2/Si substrates when annealed at 600-700 oC. Electrical measurements were conducted on PZT95/5 films in metal-ferroelectric-metal capacitor configuration. The PZT95/5 thin films annealed at 600-700 oC showed well-saturated hysteresis loops at an applied voltage of 20 V. At 1 kHz, the dielectric constant and dielectric loss of the films were 519 and 0.028, 677 and 0.029, 987 and 0.025, respectively for the thin films annealed at 600, 650, and 700 oC. The average remanent polarization (Pr) and the coercive electric field (Ec) obtained from the P-E hysteresis loops, were 19.1 1C/cm2 and 135.6 kV/cm, 29.31C/cm2 and 88.57 kV/cm, 45.3 1C/cm2 and 102.1 kV/cm, respectively for PZT95/5 thin films annealed at 600, 650 and 700 oC for 10 min in the oxygen atmosphere. This showed a good ferroelectricity of the prepared PZT95/5 films on Pt/Ti/SiO2/Si substrates by the simple sol-gel processing. The pyroelectric coeocient (p) of antiferroelectric PZT95/5 films was measured by a dynamic technique. At room temperature, the p values of the antiferroelectric PZT95/5 films at 1 kHz were 274, 238, and 212 1C/m2K."     

溶胶法制备的二氧化硅与二氧化钛复合薄膜的性能

在室温下, 采用溶胶法在玻璃基板上制备了厚度约为100 nm的均匀、透明的纳米SiO2-TiO2复合薄膜.研究了不同温度处理后薄膜的超亲水性、光催化能力等光致活性.通过XPS对薄膜表面及近表面元素的化学态的研究发现, Ti在表面及近表面不仅以Ti4＋形式存在, 也存在少量Ti3＋.紫外光照射后, 部分Ti4＋ 转变成了Ti3＋. XRD研究表明, 该薄膜中的TiO2主要以锐钛矿形式存在, 而且其晶粒大小为14～20 nm.用AFM研究了SiO2-TiO2薄膜的表面形貌及不同的温度处理对TiO2颗粒大小的影响.     

Structure and dielectric properties of HfO<Subscript>2</Subscript> films prepared by a sol–gel route

Mono- and multilayer HfO₂ sol–gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 °C for 0.5 h (after drying at 100 °C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 °C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 °C the films are totally crystallized. The HfO₂ grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO₂ layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.     

三甲基氯硅烷对纳米多孔二氧化硅薄膜的修饰

以正硅酸乙酯为先驱体,采用溶胶-凝胶法,结合旋转涂胶、超临界干燥工艺在硅片上制备了纳米多孔SiO2薄膜.用三甲基氯硅烷(TMCS)对该SiO2薄膜进行了表面修饰,采用FTIR、TG-DTA、AFM和椭偏仪等方法研究了TMCS修饰前后薄膜的结构、形貌、厚度与介电常数等性能.超临界干燥后的SiO2薄膜含有Si－O－Si与Si－OR结构,呈疏水性.在空气中250 ℃以上热处理后SiO2薄膜因含有Si－OH而呈吸水性. TMCS修饰后的SiO2薄膜在温度不高于450 ℃时可保持其疏水性和多孔结构. SiO2薄膜经TMCS修饰后基本粒子和孔隙尺寸增大,孔隙率提高,介电常数可降低至2.5以下.     

Ion bombardment-induced mechanical stress in plasma-enhanced deposited silicon nitride and silicon oxynitride films

We have studied the influence of different deposition conditions on the mechanical stress of silicon nitride and silicon oxynitride layers formed by plasma-enhanced deposition onto silicon substrates. It appears that the mechanical stress of the as-deposited silicon (oxy)nitride layer is a combined effect of the extent of ion bombardment and the deposition temperature on the hydrogen desorption rate. Deposited films show a tensile stress character when the hydrogen desorption rate is thermally controlled, whereas in the case of an ion-bombardement-controlled hydrogen desorption rate the deposited films have a compressive stress. It is also shown that due to annealing at temperatures above the deposition temperature the films are densified as a result of hydrogen desorption and cross-linking.     

Microstructure and electrical properties of lead zirconate titanate thin films deposited by sol-gel method on La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrate

(La_0.7Sr_0.3)MnO₃ thin films were deposited on SiO₂/Si substrates by a metal-organic decomposition (MOD) method, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were grown on (La_0.7Sr_0.3)MnO₃-coated SiO₂/Si substrates by a sol-gel method. The effects of annealing temperature on the crystalline phases, microstructures and electrical properties of the PZT films were investigated. X-ray diffraction analysis results indicated that the PZT films with a perovskite single phase could be obtained by annealing at 650°C. The dielectric constant and the remnant polarization of the PZT films increased with increasing annealing temperature. The remnant polarization and the coercive field of the films annealed at 650°C were 18.3 μC/cm² and 35.5 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.81, respectively.     

Preparation of CuAlO<Subscript>2</Subscript> thin films with high transparency and low resistivity using sol–gel method

CuAlO₂ thin films were deposited on quartz substrates by sol–gel process using copper acetate monohydrate and aluminum nitrate nanohydrate as starting materials and isopropyl alcohol as solvent. The influence of annealing temperature on the film structure and the phase evolution of CuAlO₂ films were investigated, so as to obtain CuAlO₂ films with superior performance. The phase compositions of the films were dependent on the annealing temperature. The films annealed at temperatures below 400 °C were amorphous while those annealed above 400 °C were polycrystalline. The phases of CuO and CuAl₂O₄ appeared gradually with the increase of annealing temperature. When the heat treatment temperature was elevated to 900 °C, the uniform and dense films with single phase of CuAlO₂ were obtained, with a resistivity of 15 Ωcm. The transmittance of the 310 nm-thick CuAlO₂ film is 79% at 780 nm and the direct optical band gap is 3.43 eV.     

Improving ferro- and piezo- electric properties of hydrogenized poly(vinylidene fluoride-trifluoroethylene) films by annealing at elevated temperatures

After annealing the solution cast P(VDF-TrFE) films at elevated temperatures, which were synthesized via a full hydrogenation process from P(VDF-CTFE) with a composition of VDF/TrFE = 80/20(mol%), a series of P(VDF-TrFE) films were fabricated in present work. The crystalline and ferroelectric phases of the films were carefully characterized and their dielectric, ferroelectric and piezoelectric properties were systematically investigated. The improved crystalline and ferroelectric phases in the films induced by annealing at elevated temperatures are responsible for the significant improved electric properties of the films. The optimized annealing temperature is found to be 130 °C and the best performance including the highest dielectric constant of 12.5 at 1 kHz, the largest maximum polarization of 11.21 μC/cm~2 and remnant polarization of 7.22 μC/cm~2, the lowest coercive electric field of 56 MV/m, and the highest piezoelectric coefficient of -25 pC/N is observed.     

Evolution of water vapor from indium-tin-oxide transparent conducting films fabricated by dip coating process

Tin-doped indium oxide In₂O₃ (indium-tin-oxide) transparent conducting films were fabricated on silicon substrates by a dip coating process. The thermal analysis of the ITO films was executed by temperature-programmed desorption (TPD) or thermal desorption spectroscopy (TDS) in high vacuum. Gas evolution from the ITO film mainly consisted of water vapor. The total amount of evolved water vapor increased on increasing the film thickness from approx. 25 to 250 nm and decreased by increasing the preparation temperature from 365 to 600°C and by annealing at the same temperature for extra 10 h. The evolution occurred via two steps; the peak temperatures for 250 nm thick films were approx. 100-120 and 205-215°C. The 25 nm thick films evolved water vapor at much higher temperatures; a shoulder at approx. 150-165°C and a peak at approx. 242°C were observed. The evolution temperatures increased by increasing the preparation and the annealing temperatures except in case of the second peak of the 25 nm thick films. The evolution of water vapor at high temperature was tentatively attributed to thermal decomposition of indium hydroxide, In(OH)₃, formed on the surface of the nm-sized ITO particles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of post-metallization annealing on the ferroelectric properties of sol-gel derived PZT thin films

A series of monolithic Pt-PZT-Pt capacitors was prepared based on sol-gel derived PZT 53/47 films fired to 700 C. After deposition of top Pt electrodes, the capacitors were subjected to post-metallization annealing (PMA) temperatures of 100 C to 700 C. Dielectric and ferroelectric (FE) characterizations were performed. Increasing the PMA temperature produced lower values of spontaneous and remanent polarizations, dielectric constant and leakage currents. The observations are correlated with a proposed FE capacitor model.     

SnO2 thin films doped indium prepared by the sol–gel method: structure, electrical and photoluminescence properties

This paper reports on the preparation, characterization, electrical and optical properties of tin oxide (SnO₂) thin films doped indium prepared by the sol–gel method and deposited on glass substrates with dip coating technique. X-ray diffraction patterns showed an increase in the crystallinity of the films with increase in annealing temperatures. Atomic force microscopy analyses revealed an increase of grain growth with raise in annealing temperature. The film surface revealed positive skewness and kurtosis values less than 3 which make them favorable for OLEDs applications. The lowest resistivity (about 10^?7) was obtained for the ITO films annealed at 500 °C. These films acquire n-type conductivity due to the non-stoichiometric in the films like (interstitial tin atoms) and also due to low indium doping concentration. The optical properties of the films have been studied from transmission spectra. An average transmittance of >80 % in ultraviolet–visible region was observed for all the films. Optical band gap energy (E _gap) of ITO films was found to vary in the range of 3.69–3.81 eV with the increase in annealing temperature. This slight shift of E _gap to higher photon energies could be related to the crystalline nature of the films associated with the decrease in the defect concentration caused by annealing. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in annealing temperature. The high temperature annealing would be expected to decrease the density of defects, improve the crystal orientation and reduce the traps for non-radiative transition and also increase the oxidation processes.