Microstructure and dielectric response of SrTiO3/NdGaO3 interdigitated capacitors

Epitaxial strontium titanate (SrTiO₃ or STO) thin films were prepared by an off-axis pulsed laser deposition technique on neodymium gallate (NdGaO₃ or NGO) substrates held at temperature of 820 °C. This technique allows different film growth rates in a deposition. Coplanar capacitors were fabricated and dielectric responses were measured at 1 MHz and at 2 GHz, and from 300 K to 4 K. The electric field tunability of the dielectric constant and loss tangent were taken with a range of electric field. The structure and morphology of the films were analyzed using high-resolution X-ray diffractometry and atomic force microscopy, respectively. The results showed that the films are crystalline with (1 0 0) orientation and the grains are columnar. Increased in-plane grain size and reduced surface to volume ratio were found to play a major role in improved performance of the film coplanar capacitors. The film with the growth rate of approximate 40 Å/min showed the highest change in the dielectric constant with an electric field of 4 V/μm. The film also showed the largest in-plane grain size of about 3000 Å.     

Magnetic properties of Co- and Mn-implanted BaTiO3, SrTiO3 and KTaO3

Implantation of Co or Mn into single-crystal BaTiO₃(K), SrTiO₃ or KTaO₃(Ca), followed by annealing at 700 °C, produced ferromagnetic behavior over a broad range of transition metal concentrations. For BaTiO₃, both Co and Mn implantation produced magnetic ordering temperatures near 300 K with coercivities 70 Oe. The M–T plots showed either a near-linear decrease of magnetization with increasing temperature for Co and a non-Brillouin shaped curve for Mn. No secondary phases were detected by high-resolution X-ray diffraction. The same basic trends were observed for both SrTiO₃ and KTaO₃, with the exception that at high Mn concentrations (5 at.%) the SrTiO₃ was no longer ferromagnetic. Our results are consistent with recent reports of room temperature ferromagnetism in other perovskite systems (e.g. LaBaMnO₃) and theoretical predictions for transition metal doping of BaTiO₃ [Nakayama et al., Jap. J. Appl. Phys. 40 (2001) L1355].     

Laser micromachining of SrTiO3 single crystal

Laser micromachining of piezoelectric materials has many advantages over other etching techniques for the fabrication of ultrasound transducer linear arrays for medical imaging. It can achieve high aspect ratios and high etch rates without the use of complicated photolithography techniques. We have investigated a laser projection etch technique to make linear arrays in single crystal (0 0 1) SrTiO₃ substrates as a model of epitaxial piezoelectric thick film heterostructure. Feature sizes of 17.5 μm were obtained with depth to width aspect ratios of 4:1. The effect of laser fluence on etching was studied and it was found that straighter sidewalls and flatter trench floors were achieved as laser fluence increases. On the other hand, higher laser fluence caused increase in heat affected zone by post-pulse plasma and made the top surfaces rougher because of the accumulation of evaporated materials. Clean top surfaces of the features were achieved by deposition and subsequent lift off of a YBa₂Cu₃O₇ sacrificial layer. In addition, the phases of recast layers on the sidewalls were characterized by four-circle X-ray diffraction with 2-D area detector before and after removed with a wet chemical etch solution. It was found that the use of the wet etchant could remove the thin polycrystalline recast layers.     

Occurrence of ferroelectricity in epitaxial BiMnO3 thin films

In this paper, we report evidence of ferroelectricity in perovskite manganite (BiMnO₃) thin films synthesized via r.f. magnetron sputtering method on a single-crystal (1 0 0)-oriented SrTiO₃:Nb 0.1% and Pt/TiO₂/SiO₂/Si substrates. X-ray diffraction measurements were used to analyse the crystal structure of the thin films, revealing epitaxial growth for BiMnO₃ films with their (1 1 1) and (2 2 2) planes parallel to the (0 0 1) and (0 0 2) planes of the SrTiO₃ substrate. AFM measurements were performed to investigate surface morphology; quantitative values of roughness and grain size are in the range between 300 and 500 nm. Ferroelectric characterization was conducted at low temperatures and at 300 K. Hysteresis loops (polarization vs. voltage) were obtained, showing saturation polarizations of , and at 105, 122, and 300 K. Resistance vs. temperature measurements were performed, which indicated this to be very robust insulating material.     

低温烧结改性PbTiO3压电陶瓷材料的研究

研制了一种添加Bi(Cd1/2Ti1/2)O3、MnO2、SiO2的新型低温结改性PbTiO3压电陶瓷材料,实验发现低熔物SiO2是影响烧结的主要因素,除能明显降低该材料烧结温度外,还能起掺杂性作用。该材料具有低烧结温度、高压电活性、大压电各向异性、较高机械品质因素及低介电常数等特点,960℃烧成时主要性能参数为：厚度机电耦合系数kt=0.49;径向机电耦合系数kp=0.027;压电各向异性比kt/kp=18;压电应变常数d33=65pC.N∧-1;机械品质因素Qm=541,密度ρv=7.4g.cm∧-3,居里温度Tc=312℃,介电常数ε∧T33/Eo=177,介质损耗tanδ=0.63%,该材料在叠层压电滤波器和叠层压电和压变压器方面显示出很好的应用前景。     

Dielectric enhancement in interface-modified BaTiO3/SrTiO3 multilayered films prepared by pulsed laser deposition

Pulsed-laser-deposited polycrystalline BaTiO₃/SrTiO₃ multilayered films on Pt/Ti/SiO₂/Si substrates have been fabricated with interfacial modification through lowering the oxygen pressure during the time interval in between two adjacent depositions. It is found that the formation of the heterolayered structure is essential to get the dielectric enhancement. Such heterolayered films have large dielectric constant of 1201 with a loss tangent below 0.1 at 10 KHz. This is about two times that of the identically prepared Ba_0.5Sr_0.5TiO₃/Ba_0.5Sr_0.5TiO₃ homolayered and uniform Ba_0.5Sr_0.5TiO₃ films. The enhancement of dielectric properties is attributed to the presence of the interfacial regions with controllable space charges due to the formation of oxygen vacancies at lower oxygen pressure.     

Numerical analysis of a PbTiO3 ferroelectric thin-filminfrared optical diode

A thin PbTiO₃-n-p⁺ silicon diode has been developed, in which the conductivity increases with the infrared light power. The infrared-sensitive part consists of PbTiO₃ ferroelectric thin film deposited by RF sputtering. The diode has smaller heat capacity compared with other conventional infrared sensors because the tunneling current is allowed through the PbTiO₃ layer so that the PbTiO₃ film thickness can be thinned. Numerical analysis of the operational mechanism, such as the effects of infrared light power on the depletion layer width, n-p⁺ junction voltage, surface depletion region voltage drop, and voltage drop across the thin PbTiO₃ film, are reported in detail. Furthermore, some experimental measurements, such as the effects of infrared light power on current-voltage (I-V) curves and the dielectric constant of PbTiO₃ film, are compared with the theoretical analysis     

The syntheses and microstructures of tabular SrTiO3 crystal

In the present paper, the microstructures of SrTiO₃ particles obtained in two different methods were examined by scanning electron microscopy (SEM) and X-ray diffraction pattern (XRD). The two synthesis techniques included a conventional mixed solid method and a molten salt synthesis method (MSS), which proceeded through two steps. In the first, precursor Sr₃Ti₂O₇ particles were synthesized. Tabular SrTiO₃ crystals were synthesized via the superposition of the SrTiO₃ basic cell on the interface of Sr₃Ti₂O₇ particles. The microstructures of SrTiO₃ particles synthesis in those two ways were quite different. The microstructures of SrTiO₃ obtained by MSS method were high purity and obviously tabular in structure. Oriented growth faces included typical (0 0 1), (1 0 0), (1 1 0), etc. The mechanism of the oriented growth of tabular SrTiO₃ could be considered as the superposition of coordination polyhedron Ti–O₆ octahedron basic cell on the interface of Sr₃Ti₂O₇ particles.     

SrTiO3环型压敏电阻器的研制及商品化生产

采用液氨分解制备的75%H2+25%N2混合气体形成还原性气氛,同时掺杂Nb2O5等添加剂使晶粒半导化,通过在空气中热处理使晶界绝缘,制得SrTiO3环型压敏电阻器,并在国内较早投入大规模商品化生产.笔者对产品进行了常规电性能测试,特殊试验及寿命试验,并与国内外同类产品进行了比较.结果表明产品主要电气性能达到或接近国外同类产品水平,成品率达到90%以上.     

Dielectric properties of single crystals of Al2O3, LaAlO3, NdGaO3, SrTiO3, and MgOat cryogenic temperatures

A dielectric resonator technique has been used for measurements of the permittivity and dielectric loss tangent of single-crystal dielectric substrates in the temperature range 20-300 K at microwave frequencies. Application of superconducting films made it possible to determine dielectric loss tangents of about 5×10^-7 at 20 K. Two permittivity tensor components for uniaxially anisotropic samples were measured. Generally, single-crystal samples made of the same material by different manufacturers or by different processes save significantly different losses, although they have essentially the same permittivities. The permittivity of one crystalline ferroelectric substrate, SrTiO₃, strongly depends on temperature. This temperature dependence can affect the performance of ferroelectric thin-film microwave devices, such as electronically tunable phase shifters, mixers, delay lines and filters