A comparative study of tunable Ba1−x Sr x TiO3 thin film capacitors prepared by rf-sputtering and liquid-phase deposition

Abstract

Ba_1?x Sr _x TiO₃ thin film capacitors have been successfully prepared using rf-sputtering and a metal organic deposition (MOD) method. The structure, microstructure and composition of the BSTO films are presented. Films grown on lanthanum aluminate LAO(100) showed c-axis preferred growth orientation. Broad paraelectric-to-ferroelectric transitions were observed in films prepared by both methods. The tunability of the capacitance by means of an appplied electric field is examined using various capacitor geometries. A decrease in the capacitance exceeding 75% at 77 K was obtained from the MOD deposited films under an electric field strength of 0.3 MV/cm. On the other hand, the tunability of the capacitance in the rf-sputtered films ranged from 5 to 10% at 77 K and at 20 kV/cm, while it exceeds 50% in some films. The results are compared with the predictions of Devonshire's phenomenological theory.     

Nd2O3掺杂对BSTO/MgO复合陶瓷显微结构和性能的影响

当掺杂0.3mol% Nd2O3时,BSTO/MgO复合陶瓷材料的介电常数为88,损耗2.8×10-3(4.1GHz),介电常数可调为6.9%(2.0 kV/mm).利用电介质理论分析了Nd2O3对BSTO/MgO复合陶瓷材料介电性质的改性机理.     

Deposition and characterization of low-loss epitaxial non-linear dielectric thin films for microwave devices

Abstract

Oxide ferroelectric thin films for frequency-tunable microwave devices, in which the dielectric constant of the non-linear dielectric is varied by application of electric fields, have been deposited using PLD. We have fabricated single phase epitaxial Ba_0.6Sr_0.4TiO₃ and KTaO₃ thin film capacitors for applications at 300K and 77K, respectively. Single phase KTaO₃ films were obtained only with excess potassium source in the target along with KTaO₃ perovskite phase. The films have been characterized for structure and morphology by X-ray diffraction and AFM. The dielectric properties were measured in the low frequency range from 100 kHz to 10 MHz, using interdigitated capacitors. Low loss tangents (0.002 at 300K) were observed for highly oriented Ba_0.6Sr_0.4TiO₃ films. The importance of low losses for various devices is discussed and the dielectric constants, loss tangents and tunability of these films are reported in this paper.     

添加CuO对Ba_(3.99)Sm_(9.34)Ti_(18)O_(54)陶瓷烧结及微波介电性能的影响

采用传统固相工艺制备了Ba3.99Sm9.34Ti18O54(BSTO)微波介质陶瓷,研究了烧结助剂CuO对BSTO的结构及介电性能的影响。结果表明,添加CuO能较好促进BSTO晶粒致密化,降低烧结温度约140℃。当添加质量分数1.0%的CuO时,1220℃保温3h烧结的BSTO样品的介电性能较好:εr=86.87,Q·f=5138GHz(f=4.95GHz),τf=–10.84×10–6℃–1。     

Ferroelectric tunable coplanar waveguide components for Ku- and K-band and applications

Abstract

The main objective of this research is to study the effect of inserting a Barium Strontium Titanate (BSTO) ferroelectric tuning layer in coplanar waveguide (CPW) and conductor-backed CPW (CBCPW) components. The modeled components include CPW and CBCPW transmission lines (with and without a dielectric filling between the center conductor and the ground planes). We have modeled the characteristic impedance (Z₀), effective dielectric constant (ε_eff), attenuation and dispersion as a function of circuit geometry and the ferroelectric thin-film's dielectric properties over the 10–20 GHz frequency range. We found that the presence of a ferroelectric layer between the transmission line and the ground planes improves the percentage change in ε_eff by almost two-fold with respect to a CPW deprived of this layer. This result is significant, as one could obtain larger frequency tunability with relatively lower applied fields compared to regular CPW or microstrip lines.     

Slow Dielectric Relaxation in Pb(Zr,Ti)O3 and (Ba,Sr)TiO3 Ferroelectric Thin Films

An impedance analysis of Ni/Pb(Zr,Ti)O₃/Pt thin-film structures based on measurements at the frequencies from 100 Hz to 100 MHz, along with the data of Grazing Angles XRD, TEM and photo-electric study, is used to obtain electronic structure of the PZT thin films deposited by sol-gel method on silicone substrates. Both slow capacitance relaxation and charging/discharging currents versus time under step-voltage excitation have been studied in (Ba,Sr)TiO₃ thin films between SrRuO₃ electrodes.     

BSTO电光材料及其制备

用ＢＳＴＯ电光材料制作的电光移相器与铁氧体移相器相比,具有非常好的性能,它以高的功率、高的相移速度、低的插入损耗、低的驱动功率、充分宽的工作温度范围以及低的成本,受到相控阵天线技术的关注。文章介绍了ＢＳＴＯ材料及其制备方法,简要概述了这种材料研究的进展,讨论了ＢＳＴＯ电光材料化学组成、工艺制备技术和非铁电相对ＢＳＴＯ电光材料性能的影响,最后提出了发展该材料的方向。     

一种用于相控阵天线的新型钛酸锶钡电光相移器

钛酸锶钡电光相移器同铁氧体相移器相比,主要优点是功率处理能力大、相移速度区动功率小、插入损耗小、体积小、重量轻、介绍了钛酸锶钡相移器及在相控在线中的应用,主要这种相移器的发展过程,工作原理及其对材料性能的要求。     

The influence of microstructure on the electronic properties of thin films of barium strontium titanium oxide composites

Abstract

Microstructural and electrical properties were investigated for barium strontium titanium oxide (BSTO) magnesium oxide doped (0 to 10 wt.%) thin films deposited by the pulsed laser deposition (PLD) method on Pt/TiO_x/SiO₂/Si substrates. The dielectric properties were found to be strongly dependent on composition and microstructure. In cross-section, all films exhibited a columnar polycrystalline microstructure with vertical orientation deviations dictated by the surface roughness of the Pt electrode. A uniform granular microstructure was observed for all films in plan view. The dielectric constant, loss tangent and grain size decreased with increasing MgO concentration.     

YF_3掺杂对Ba_(0.6)Sr_(0.4)TiO_3介电可调性的影响

采用传统工艺制备了YF_3掺杂的Ba_0.6Sr_0.4TiO_3陶瓷材料,研究了YF_3掺杂比例对钛酸锶钡材料结构及介电性能的影响.结果表明:烧结后得到的BSTO材料具有典型的钙钛矿结构;YF_3掺杂具有降低Ba_0.6Sr_0.4TiO_3材料的介电常数、细化陶瓷晶粒和提高介电常数温度稳定性的作用.在氟化钇掺杂比例1%时介电常数降至1887(100 kHz),介电可调性达到30%(1.5 kV/mm)以上, 各掺杂比例的钛酸锶钡材料的介电损耗均在1%以下.