ASIC数据采集与处理的实现

介绍了数据采集的原理和ASIC的基本功能实现以及JTAG的边界扫描测试技术。该ASIC已经在各种控制外设中得到了广泛的应用。     

Dielectric properties for Tantalum-doped strontium barium titanate thin films prepared by sol-gel method

In this work, Sr_0.5Ba_0.5Ti_1-zTa_zO₃ (SBT) thin films were prepared on a Pt/SiO₂/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The influences of Ta on the microstructure and dielectric properties of SBT thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Ta⁵⁺ doping fines the grain of SBT thin films. It is found that Ta⁵⁺ doping decreases dielectric loss for SBT thin films.     

Observation of Long Transients in the Electrical Characterization of Thin Film BST Capacitors

Charge trapping is responsible for long transient leakage currents observed in parallel plate thin film BST capacitors. The presence of such time dependence complicates the measurement of leakage current as a function of an applied voltage, with the voltage sweep introducing hysteresis in the absence of ferroelectricity. The effect of long transients on current-voltage sweeps is discussed, as well as a method of obtaining current-voltage characteristics in the presence of transient leakage currents.     

Optimum Reflection-Type Phase Shifter Using (Ba,Sr)TiO3 Thin Film

In this paper, in order to obtain a large differential phase shift with a little change in applied voltage, a ferroelectric reflective load circuit has been designed on top of barium strontium titanate (Ba,Sr)TiO₃ [BST] thin film. The design of the ferroelectric reflection-type phase shifter is based on a reflection theory of terminating circuit, which has a reflection-type analogue phase shifter with two ports terminated in symmetric phase-controllable reflective networks. To achieve large amounts of phase shift in low bias-voltage range, the effects of change of capacitance and transmission line connected with two coupled ports of a 3-dB 90° branch-line hybrid coupler have been investigated. A large phase shift with a small capacitance change in the parallel terminating circuit has been demonstrated in the paper.     

Investigation of the effects of milling ceramic targets on the optical and electrical properties of BST thin films deposited by RF sputtering

Abstract

The RF sputtering method was utilized to deposit thin films of Ba_1-xSr_xTiO₃ (BST). The targets utilized in these experiments were prepared from ceramic powders with different particle size. The goal of this work is to examine whether the particle size distribution of the target can affect the properties of the thin films fabricated by the sputtering method. The Atomic Force Microscope (AFM) was used to examine the grain size in the thin films. The composition of the thin films and the bulk materials were examined by Fourier Transform Infrared (FTIR) spectroscopy. The dielectric properties of the thin films were measured and compared to its bulk counterparts. It was found that on lattice matched electrodes of SrRuO₃ on LaAlO₃ substrates, the thin films deposited from ceramic targets manufactured from ball-milled powders had finer grain size than those deposited from targets made from unmilled powders. However, this phenomenon was not observed in the case of polycrystalline films deposited on platinized silicon wafers.     

Influence of preheating on crystallization and growing behavior of Ce and Mn doped Ba0.6Sr0.4TiO3 film by sol–gel method

Cerium and manganese codoped Ba_0.6Sr_0.4TiO₃ (CeMn-BST) film and pure BST, Ce-BST and Mn-BST films were prepared. Influence of preheating on film crystallization and growing behavior was studied. X-ray diffraction (XRD) reveals that all films mainly grow along (110) orientation and show cubic ABO₃ perovskite structures, and the preheating promotes Ce^3 + and Mn^4 + ions enter into B-sites and substitute Ti^4 + ions. Preheating enhances crystallization and causes the strongest crystallization with CeMn-codoping. Atomic force microscopy (AFM) exhibits that films preheated show layered growth, while those not preheated show island growth, which are related to layer number and doping. Therefore, the films preheated show larger permittivities, higher tunabilities, and lower dielectric losses except the pure BST film and higher figures of merit (FOMs). Preheating with CeMn-codoping causes best dielectric properties with 56% tunability, 0.0037–0.0091 loss and near 150 FOM, meeting the needs of tunable microwave applications.     

水基金属有机物分解法制备Ba0.5Sr0.5TiO3薄膜的研究

制备了水基Ｂａ＾２＋、Ｓｒ＾２＋、Ｔｉ＾４＋三元有机物溶液。根据红外光 谱测定及对比实验分析了溶液配制过程中化学反应机理。采用金属有机物分解法（ＭＯＤ）制备Ｂａ０．５Ｓｒ０．５ＴｉＯ３（ＢＳＴ）薄膜。通过ＸＲＤ、ＳＥ趱 阻抗分析仪等分析测试手段,薄膜的相结构、微观形态及电性能。结果表明,所制备ＢＳＴ薄 数矿晶相结构,结晶完整晶粒小（１０－５０ｎｍ）,显微结构均匀致密,并具有良好的电性能（电容密度为     

Dielectric tunable properties of (Ba1−xSrx)TiO3 thin films on LaAlO3 substrate

(Ba_1−xSr_x)TiO₃ (1−x=0.8, 0.7, 0.6 and 0.5) thin films were prepared on (0 0 1) LaAlO₃ substrates by sol–gel method. The films were found to be crystallized in preferential (0 0 1) orientation after post-deposition annealing at 750°C for 1.5 h and 1100°C for 2 h in air, respectively. We investigated the dependence of tunability and dissipation factor on annealing temperature and different Ba/Sr ratios. It was found that the tunability increased dramatically and dissipation factor decreased obviously with increasing annealing temperature, and Ba_0.6Sr_0.4TiO₃ thin films annealed at 1100°C for 2 h have a tunability of 46.9% at 80 kV/cm bias filed and a dissipation factor of 0.008 at 1 MHz.     

Implementation of GaAs Monolithic Microwave Integrated Circuits with On-Chip BST Capacitors

GaAs microwave monolithic ICs with novel on-chip BST (Ba _X Sr_{1 –X} TiO₃) capacitors are demonstrated. MOD (Metal Organic Decomposition) technique was employed to make the BST thin film. The fabricated BST capacitor has the dielectric constant as high as 300, which is 50 times higher than the conventional Si₃N₄ one. The implemented GaAs MMIC with on-chip BST capacitor provides both high gain and low power dissipation characteristics. These MMIC can be packaged in a compact outline with reduced pin counts. BST capacitors also show the suppressed harmonics due to their low-pass filtering characteristics of the frequency roll-off around 2 GHz. The present technology will reduce the system size for a variety of the mobile communication systems.     

Electrical properties of sputtered (Ba, Sr)TiO3 thin films prepared by two-step deposition method

The influence of two-step deposition on the electrical properties of sputtered (Ba,Sr)TiO₃ thin films was investigated. BST thin films with thickness 40 nm were deposited by a simple two-step radio frequency-magnetron sputtering technique, where the BST thin film consisted of a seed layer and a main layer. The dielectric constant was strongly dependent on the thickness of seed layer, but there was no dependence on deposition temperature of the seed layer. For a 2 nm seed layer, the dielectric constants were higher by about 29% than those of single-step BST thin films due to higher crystallinity and the leakage current was nearly the same as that of a single-step sample in bias voltage from −2 to 2.5 V. However, an improvement of the dielectric constant was not observed for samples having above 4 nm thick seed layers. A 40 nm thick BST film with 2 nm thick seed layer deposited by a two-step method exhibited a SiO₂ equivalent thickness of 0.385 nm and a leakage current density of 2.74 × 10⁻⁸A/cm²at+1.5V after post-annealing under an atmosphere of flowing N₂ for 30 min at 750°C.