Effect of processing on the properties of Bi3.15Nd0.85Ti3O12 thin films

Various crystallization parameters were studied during the fabrication of Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) thin films on Pt/Ti/SiO₂/Si (100) by metal organic solution decomposition method. The effect of crystallization processes, crystallization ambients on the properties of BNdT thin films such as orientation, ferroelectric properties were examined. By adopting different fabrication processes, it is possible to get both highly c-axis oriented as well as randomly oriented thin films. Highly c-axis oriented BNdT thin film showed a large remnant polarization (2P_r) of 70 μC/cm² at an applied voltage of 10 V and exhibited a fatigue free behavior unto 2 × 10⁹ switching cycles. The improved ferroelectric properties of BNdT thin films suggest their suitability for high density ferroelectric random access memory applications.     

Dielectric properties of sol-gel derived barium strontium titanate thin films

Barium strontium titanate (Ba_xSr_1−xTiO₃) films were deposited by sol-gel technique on platinized silicon substrate for the composition range x = 0.0 to 1.0 in steps of 0.1. The as-deposited films were found to be amorphous. The films crystallize on annealing in air at 700 °C for 1 h. Dielectric constant (ε′) and loss tangent (tanδ) were measured in the temperature range − 180 °C to 150 °C in the frequency range 0.1 to 100 kHz. Both ε′ and tanδ show a small dispersion for all the compositions. This dispersion is more at the peak value than at room temperature. A comparison of the room temperature and peak value of the dielectric constant for various compositions are made with the reported values. Transition temperatures are reported for the entire composition range. All the compositions show a transition from ferroelectric to paraelectric phase except strontium titanate. Transition temperature shows a systematic decrease with increase in strontium content. The variation is at a rate of 3.4 °C/mol% of SrTiO₃. Curie constants are also reported for the entire composition range.     

Estimation of nonlinear interfacial capacitance from domain switching current of ferroelectric thin films

We introduce a methodology to estimate the nonlinear capacitance of interfacial “passive” layers of ferroelectric thin films from domain switching currents directly. The methodology has the advantage over the traditional extrapolation technique of a linear plot of the inversed capacitance against the film thickness which neglects the size effect on the ferroelectricity. Expectedly, this technique remains suitable in ultrathin films with the thickness scaling down into a few nanometers, where the size effect is important. From our measurements, we found that the interfacial capacitance increases nonlinearly with the reduction of the applied voltage in a tendency similar to the capacitance-voltage curve of ferroelectric thin films above the coercive voltage. Nevertheless, the capacitance at a high field drops down closely to a value derived from the traditional extrapolation technique. The pertinent physics is discussed in this work. Finally, we observed the reduction of the interfacial capacitance with the rising temperature, which suggests the thickening of interfacial layers at high temperatures.     

Characterization of lanthanum-doped bismuth titanate thin films prepared by polymeric precursor method

Lanthanum-modified bismuth titanate, Bi_4−xLa_xTi₃O₁₂ (BLT), with x ranging from 0 to 0.75 was grown on Pt/Ti/SiO₂/Si substrates using a polymeric precursor solution and spin-coating method. The dielectric constant of highly doped bismuth titanate was equal to 148 while dielectric losses remained low (tan δ=0.0018), and the films showed well-saturated polarization-electric field curves (2P_r=40.6 μC/cm² and V_c=0.99 V). The leakage current densities improve for the lanthanum-doped system. For five-layered BLT films with x=0.75, a charge storage density of 35 fC/μm² and a thickness of 320 nm were found.     

金属有机物分解法制备SrBi2Ta2O9铁电薄膜的开关特性

用金属有机物分解（MOD）以及sol-gel方法制备了SiBi2Ta2O9（STB）铁电薄膜。经测量在750℃晶化的SBT薄膜具有很好的铁电性能。通过对SBT样品极化反转过程进行测试,得出了外加电压（0．5－5V）与SBT薄膜的开关时间（100－600ms）及极化反转电荷的关系。并研究了不同气氛不退火对SBT铁电薄膜形状特性的影响。     

Growth mechanism and characterization of chemical oxide films produced in peroxide mixtures on Si(100) surfaces

The growth kinetics of silicon chemical oxides in H₂O₂-containing solutions at various pH values and temperatures was studied by electrochemical impedance spectroscopy (EIS), ellipsometry and X-ray photoelectron spectroscopy. Infrared (IR) spectroscopy was also used to investigate the evolution of the surface chemistry from the initial hydrogen coverage as Si-H bonds to the subsequent oxidation states by analysing the Si-O-Si stretching vibration modes. Successive EIS diagrams obtained as a function of time constituted a series of semicircles indicating that the semiconductor/oxide/electrolyte junction can be modelled as a resistance-capacity (RC) circuit. It was then observed that the resistance term increased with time to almost 1 MΩ cm² after 3 h in SC1 solution. It is generally known that, in alkaline solutions such as SC1, the oxidation rate reaches rapidly a steady regime controlled by the interfacial charge transfer reaction and the subsequent dissolution of the generated oxide. Accordingly, a mechanism involving a diffusion process of reactants through the oxide barrier followed by a simultaneous dissolution of the layer is proposed. Likewise, in acidic media such as SC2, even though the solubility is extremely low, we have extended our model based on the competition between the oxidation rate at the surface and the dissolution of the built-up oxide, and thus it was possible to evidence oxide solubility at the nanoscopic scale. In addition, thickness measurements by ellipsometry together with the observed gradual change in the IR spectrum of the Si-O-Si vibration mode were interesting parameters revealing that the oxide growth proceeds simultaneously with an evolution of the structure leading to a more compact and insulating dielectric layer. The whole of the results lead to a model for the oxidation process accounting for the observed structure and complex impedance properties under various conditions of chemical treatment.     

Microstructure and ferroelectric properties of dysprosium-doped bismuth titanate thin films

Bi₄Ti₃O₁₂ (BIT) ferroelectric thin films with Dy³⁺ substitution (Bi_4−xDy_xTi₃O₁₂, x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively) were grown on Pt(111)/Ti/SiO₂/Si(100) substrates using sol–gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that after annealing at 710 °C for 10 min, all Bi_4−xDy_xTi₃O₁₂ films became polycrystallites. Among all the deposited thin films, the Bi_3.4Dy_0.6Ti₃O₁₂ specimen exhibits improved ferroelectric properties with the largest average remanent polarization (2Pr) of 53.06 μC/cm² under applied field of 400 kV/cm and fatigue free characteristics (16% loss of 2Pr after 1.5 × 10¹⁰ switching cycles), indicating that it is suitable for non-volatile ferroelectric random access memories applications.     

The ac conductivity and dielectric properties of Europium-Indium oxide films prepared on silicon (100) substrate

Thin Eu-In oxide films were prepared on glass and Si (P) substrates to form metal-oxide-semiconductor (MOS) devices. These films were annealed at different conditions and characterised by UV-absorption spectroscopy, X-ray fluorescence (XRF), and X-ray diffraction (XRD). The ac-conductance and capacitance of the devices were studied as a function of frequency in the range of (500 Hz-100 kHz), temperature in the range of (293-363 K), and gate voltage. It was observed that the frequency dependence of the ac-conductivity and capacitance of the insulator is controlled by the “corrected barrier hopping” model, which based on the relaxation processes of hopping of current carriers between equilibrium sites. The temperature dependence of ac-conductance showing small activation energy characterises the hopping process. The method of capacitance-gate voltage (C-V_g) and conductance-gate voltage (G-V_g) were used to investigate the effect of annealing in air or in vacuum on the trapped-charge density in the oxide and the surface density of states (N_ss) at the insulator/semiconductor interface. It was observed that the prepared solid solution (SS) of Eu₂O₃-In₂O₃ has a sufficiently high dielectric constant (ε), around 30, which suggests that it is a promising candidate for high-ε dielectric applications.     

Integration of BiFeO3 thin films on Si wafer via a simple sol-gel method

Integration of BiFeO₃ (BFO) films on Si substrate is desirable from an application point of view. The growth of (110)-textured BFO thin films with high quality on Si(100) substrate was realized by a seeding technique via a simple sol-gel method. Obviously switchable ferroelectric domains were observed, and in the meantime, the BFO films also exhibited a weak magnetization which somewhat showed dependence on the film thickness. Such an integration of the BFO films on Si constructed a metal/ferroelectric/insulator/semiconductor structure, which presented a memory feature as evidenced by capacitance-voltage hysteresis.     

Electrical properties of thin PbTe films on Si substrates

An attempt was made to reduce the carrier concentration in thin PbTe films on Si substrates by optimizing deposition conditions. A modified hot-wall method was used for reproducible growth ofp-type films with 5 × 10¹⁵ < p(77 K) < 5 × 10¹⁷ cm^-3 andn-type films with 3 × 10¹⁵ < n(77 K) < 5 × 10¹⁶ cm^-3. The IR irradiation was found to have a significant effect on the temperature variation of film resistance. The activation energy of the IR-sensitivity centers was determined to be 0.11 ± 0.005 eV at room temperature and 0.18 ± 0.005 eV between 150 and 180 K.     

Barium titanate thin films deposited by electrophoresis on p-Doped Si (001) substrates

Barium titanate (BaTiO3) thin films have been prepared by electrophoretic deposition on p-doped and platinum covered silicon (Si) substrates. Their structure, nanostructure and dielectric properties were characterized. The as-deposited films were polycrystalline and composed by barium titanate nanograins with an average grain size approximately 9 nm. Annealing at high temperatures promoted grain growth, so that the samples annealed at 600 degrees C presented average grain sizes approximately 24 nm. From Raman spectroscopy measurements it was found that the tetragonal (ferroelectric) BaTiO3 phase was stabilized on the films. Also, at higher annealing temperatures, cation disorder was reduced on the films. From measurements of the temperature dependence of the dielectric permittivity the corresponding paraelectric-ferroelectric phase transition was determined. The observed transition temperature (approximately 100 degrees C) was found to be below the BaTiO3 bulk or thick film values, due to the small nanosized grains composing the films.     

Electrical properties of silver selenide thin films prepared by reactive evaporation

The electrical properties of silver selenide thin films prepared by reactive evaporation have been studied. Samples show a polymorphic phase transition at a temperature of 403 ± 2 K. Hall effect study shows that it has a mobility of 2000 cm²V^?1s^?1 and carrier concentration of 10¹⁸ cm^?3 at room temperature. The carriers are ofn-type. X-ray diffraction study indicates that the as-prepared films are polycrystalline in nature. The lattice parameters were found to bea= 4.353 Å,b= 6.929 Å andc = 7.805 Å.     

低能Ar+离子束辅助沉积择优取向Pt(111)膜

采用低能Ar+离子束辅助沉积方法,在Mo/Si(100)基底上沉积Pt膜,离子/原子到达比分别为0.1、0.2、0.3.若Ar+离子的入射角为0°,XRD谱分析表明,沉积的Pt膜均呈(111)和(200)混合晶向;当Ar+离子的入射角为45°,沉积的Pt膜均呈很强的(111)择优取向.因此若合理控制Ar+离子束的入射角,可在Mo/Si(100)衬底上制备出具有显著择优取向的Pt(111)薄膜.本文采用Monte Carlo方法模拟低能Ar+离子注入 Pt单晶所引起的原子级联碰撞过程,得出Ar+离子入射单晶铂(200)晶面时,Ar+离子的溅射率与入射角的关系,对Pt膜择优取向的机理作了初步的探讨和分析.     

掺杂SnS薄膜的制备及电学性能

硫化锡（SnS）具有很高的光吸收系数和合适的禁带宽度，又无毒性，因此在太阳电池等光电器件中具有潜在应用价值。本文用真空蒸发法制备掺杂的SnS薄膜，掺杂源有Sb、Sb：O3、Se、Te、In、In2O3、Se和In2O3的混合物。对各种掺杂SnS薄膜的厚度、电流-电压（Ⅰ—Ⅴ）特性等进行了表征，并计算了其电阻率和光电导与暗电导的比值（Gphoto／Gdark）。结果表明较有效的掺杂源是Sb，Sb掺杂的薄膜电阻率比纯薄膜的电阻率降低四个数量级，Gphoto／Gdark增加约一倍。同时，研究了Sb掺杂量对SnS薄膜电学性能的影响，表明Sb的最佳掺入量约为1．3wt％～1．5wt％。     

Structure and electrical properties of bismuth thin films prepared by flash evaporation method

Polycrystalline Bi thin films with thickness in the range 40-160 nm have been successfully deposited on glass substrates at 453 K by flash evaporation method for the first time. XRD and FE-SEM were performed to characterize their structure and surface morphology respectively. Electrical resistivity measurement was carried out in the temperature range 300-350 K. Hall coefficient, electron concentration and mobility were measured at 300 K. A distinctly oscillatory behavior has been observed for the electrical properties of the Bi thin films.     

Characteristics of yttrium substituted sodium bismuth titanate thin films

Sodium bismuth titanate (NBT) thin films substituted with yttrium for Na site were prepared by a modified sol-gel processing and their dielectric properties were investigated. The stability of perovskite structure was highly affected by the amount of Y substitution and the annealing temperatures. Y substituted NBT thin films post-annealed at 750 °C exhibited uniform microstructures associated with grain growth inhibition. Relative permittivity and remnant polarization were maximized at 5 mol% Y substitution and loss tangents for all the prepared films were relatively stable with less than 0.03. It was also found that the substitution of yttrium led to the enhancement of diffuse phase transition for the NBT thin films.     

On the optical properties of bismuth oxide thin films prepared by pulsed laser deposition

The optical properties of bismuth oxide films prepared by pulsed laser deposition (PLD), absorption in the photon energy range 2.50-4.30 eV and optical functions (n, k, ?₁, and ?₂) in the domain 3.20-6.50 eV, have been investigated. As-prepared films (d=0.05-1.50 μm) are characterized by a mixture of polycrystalline and amorphous phases. The fundamental absorption edge is described by direct optical band-to-band transitions with energies 2.90 and 3.83 eV. The dispersion of the optical functions provided values of 4.40-6.25 eV for electron energies of respective direct transitions. In the spectral range 400-1000 nm, bismuth oxide films show a normal dispersion, which can be interpreted in the frame of a single oscillator model.     

Electrical properties of chemically prepared nonstoichiometric CuIn(S,Se)2 thin films

Polycrystalline thin films of copper indium sulphoselenide [CuIn(S,Se)₂] were deposited on glass substrate by chemical bath deposition technique. The deposition parameters such as pH, temperature and time were optimized. A set of films having different elemental compositions was prepared by varying Cu/In ratio from 1·87–12·15. The films were characterized by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX). The chemical composition of the CuIn(S,Se)₂ was found to be nonstoichiometric. The d.c. conductivities of the films were studied below and near room temperature. The thermo-electric power of the films was also measured and type of semiconductivity was ascertained.     

Electrical properties of silicon nitride films deposited by catalytic chemical vapor deposition on catalytically nitrided Si(100)

Thin film transistor incorporating silicon nitride (SiN_x) films deposited by catalytic chemical vapor deposition (Cat-CVD) on silicon exhibit some problems such as a large-threshold voltage shift and a large hysteresis loop width of the capacitance vs. voltage (C–V) characteristics. In this work, in order to solve these problems, the surface of the silicon substrate is catalytically nitrided before SiN_x deposition. Inserting the nitridation layer, injection-type hysteresis loop of C–V curve is reduced from 1.3 to 0.05 V and large threshold voltage shift to the negative direction is reduced from 4 to 1.8 V.