钛酸锶钡/铋锌铌多层复合薄膜的制备及性能

采用溶胶一凝胶法在Pt/Ti/SiO2/Si衬底上制备了钛酸锶钡/铋锌铌多层复合薄膜样品.研究了不同退火温度下多层复合薄膜的结构、微观形貌及介电性能.结果表明:在退火温度高于700℃时,所得复合薄膜中会出现立方焦绿石结构的铋锌铌和钙钛矿结构的钛酸锶钡.750℃退火处理得到的多层复合薄膜,表面致密,无裂纹,其相对介电常数...     

高度(100)取向的BST薄膜及其高介电调谐率

用脉冲激光沉积法制备(Ba1-xSrx)TiO3(x=0.35,0.50简称BST35和BST50)介电薄膜。在650℃原位退火10min,获得高度(100)取向柱状生长的晶粒。BST35薄膜的平均晶粒尺寸为50nm,BST50薄膜的晶粒尺寸为150~200nm。在室温和1MHz条件下,BST35的最大εr和调谐率分别达到810和76%,其介电调谐率高于国内外同类文献报道的数据;BST50的εr和调谐率最大分别达到875和63%。薄膜为(100)取向生长,因为薄膜沿平面c轴极化而产生应力,在电场作用下,而获得高介电调谐率。     

BST-MEMS移相器开关

为了提高MEMS电容开关性能,介绍了移相器的一种新型结构——分布式电容周期性加载结构。分析发现移相器的相移度和单元可变电容的变化率有关。目前MEMS可变电容单元采用的介质基本上是氮化硅。BST薄膜作为一种性质优良的介电材料,其介电常数远大于氮化硅。从MEMS移相器开关性能的几个关键指标出发,探讨在MEMS移相器开关中,用BST薄膜代替氮化硅介质的可能性。     

Characteristics of smooth and periodic HTS coplanar resonators on ferroelectric/dielectric substrates

Characteristics of smooth and periodic (consisting of sections with different dimensions) high temperature superconducting (HTS) thin film coplanar waveguide (CPW) resonators with a ferroelectric component were calculated. Frequency tunability and microwave (MW) losses of the structure were analyzed using the obtained formulas. It was shown that for the ferroelectric layer thickness less than 100 nm, the MW losses are determined by the losses of HTS electrodes, while for thicker layers, the MW losses are completely determined by the loss tangent of the ferroelectric. Experimental aspects of the problem were investigated in the example of a YBCO/Ba/sub x/Sr/sub 1-x/TiO/sub 3/ smooth CPW resonator at 77 K and information about the permittivity and the loss tangent of the ferroelectric was obtained.     

Recent progress of (Ba,Sr)TiO<Subscript>3</Subscript> thin films for tunable microwave devices

The (Ba_1−xSr_x)TiO₃ (BST) ferroelectric thin films exhibit outstanding dielectric properties, even at high frequencies (>1 GHz), and large, electric-field dielectric tunability. This feature makes them suitable for developing a new class of tunable microwave devices. The dielectric properties and dielectric tuning property of BST thin films are closely related to the film compositions, substrate types, and post-deposition process. The successful implementation of BST films as high-frequency dielectrics in electrically tunable microwave devices requires a detailed understanding of both their processing and material properties. This paper will review the recent progress of BST thin films as active dielectrics for tunable microwave devices. The technical aspects of BST thin films, such as processing methods, post-annealing process, film compositions, film stress, oxygen defects, and interfacial structures between film and substrate, are briefly reviewed and discussed with specific samples from the recent literature. The major issues requiring additional investigations to improve the dielectric properties of BST thin films for tunable microwave applications are also discussed.     

BST铁电薄膜的制备及介电性能研究

通过射频磁控溅射法,采用高温溅射、低温溅射高温退火两种不同的工艺制备了钛酸锶钡（BST）薄膜。分析两种不同的工艺对BST薄膜的结构、微观形貌及介电性能的影响。采用X线衍射（XRD）分析了样品的微观结构。采用扫描电镜（SEM）和台阶仪分别测试了样品的微观形貌和表面轮廓。通过能谱分析（EDS）得到了薄膜均一性的情况。最后通过电容 电压（C V）曲线测试得到BST薄膜的介电常数偏压特性。结果表明,与低温溅射高温退火工艺制备的BST 薄膜相比,高温溅射制备的BST薄膜结晶度好,致密性高,表面光滑,薄膜成分分布较均一。因此,采用高温溅射得到的BST薄膜性能较好。在频率300 kHz时,采用高温溅射制备的BST薄膜介电常数为127.5~82.0,可调谐率为23.86%~27.9%。     

BST薄膜铁电移相器研究进展

钛酸锶钡(BST)薄膜因其具有高的介电调谐量,相对低的损耗tgδ和快的开关速度,在微波移相器的应用中显示出巨大优势。介绍了改善BST薄膜的介电性能的有效方法,衬底材料的选择,以及BST薄膜铁电移相器的结构类型和研究进展。     

A Si MMIC compatible ferroelectric varactor shunt switch for microwave applications

This letter describes a ferroelectric thin-film based varactor shunt switch, for microwave and millimeterwave switching applications. Our implementation is based on a coplanar waveguide transmission line shunted by a ferroelectric varactor. The concept of switching ON and OFF is based on the dielectric tunability of the ferroelectric barium strontium titanium oxide (BST) thin-films. From experimental verification, the isolation of a switch with a varactor area of 75/spl mu/m/sup 2/ was approximately 20dB at 35GHz and the insertion loss was below 4.5dB up to 35GHz. This letter addresses the design and experimental verification of the first ferroelectric varactor shunt switch with an Si monolithic microwave integrated circuit compatible process.     

用正交法优化BST/MTO铁电移相器材料性能

利用正交试验方法研究了Bi2O3、MnCO3、SnO2等添加剂对钛酸锶钡/钛酸镁(BST/MTO)复合铁电移相器材料介电常数r、介质损耗tg以及调谐性T等性能的影响,并对影响机理作了初步探讨。实验结果表明选择合适种类与数量的添加剂能有效提高铁电移相器材料的性能。通过正交试验获得综合性能优异的移相器材料性能:r=315,tg=0.002 8,T=14.27%。     

水基前驱体法制备BST铁电薄膜的研究

Ba1-SrxTiO3(BST)薄膜具有非线性强、漏电流小、不易疲劳等特点,在高密度动态随机存储器的应用,受到x了极大关注。以水基溶液为前驱体,调整Ti(OC4H9)4与H2O的配比以改变溶胶的黏度,并采用旋涂法制备了BST铁电薄膜。对水基BST前驱体溶液进行了DSC/TG和XRD分析。实验表明,采用较高浓度的水基前驱体,有利于薄膜的形成和均匀性。薄膜的相结构研究表明,随着退火温度的上升,BST薄膜的结晶度上升,而晶粒尺寸随之略有下降。     

Bi_(1.5)Zn_(1.0)Nb_(1.5)O_7/Ba_(0.5)Sr_(0.5)TiO_3复合薄膜介电性能的频率特性研究

采用射频磁控溅射法在蓝宝石基片上制备了Bi1.5Zn1.0Nb1.5O7(BZN)/Ba0.5Sr0.5TiO3(BST)双层复合薄膜,并研究了该薄膜在100 kHz~6 GHz频率范围内的介电性能。研究结果表明,BZN/BST复合薄膜的介电性能具有良好的频率稳定性。该复合薄膜的介电常数在研究的频率范围内基本与频率无关;其介电损耗在频率低于1 GHz时与频率无关,在频率高于1 GHz时随频率的上升而略微增大;薄膜在研究的频率范围内具有稳定的介电调谐率。     

快速退火对Pt/BST/Pt电容器结构和性能的影响

采用脉冲激光沉积(PLD)法在Pt/Ti/SiO2/Si(001)基片上制备了Ba0.6Sr0.4TiO3(BST)薄膜,对Pt/BST/Pt电容器在空气中进行400℃快速退火(RTA)处理,研究了快速退火对Pt/BST/Pt电容器的结构和性能的影响。结果表明:快速退火虽然对BST薄膜的结晶质量影响较小,但却极大改善了Pt/BST/Pt电容器的电学性能。当测试频率为100kHz、直流偏压为0V时,介电损耗从快速退火前的0.07减小到0.03,介电常数和调谐率略有增加。快速退火后负向漏电流过大现象得到了明显抑制,正负向漏电流趋于对称,在300×103V/cm电场强度下,漏电流密度为4.83×10–5A/cm2。     

Comparison of Microwave Dielectric Properties of Ba0.6Sr0.4TiO3 Thin Films Grown on (100) LaAlO3 and (100) MgO Single-Crystal Substrates

The microwave properties of barium strontium titanate (Ba_0.6Sr_0.4TiO₃) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single-crystal substrates through the sol–gel technique were investigated. The interdigital capacitor (IDC) technique was used to measure the nonlinear dielectric properties in the frequency range from 1 GHz to 10 GHz. The results show that the Curie temperature, capacitance, and tunability of the films are strongly dependent upon the substrate. The film fabricated on the LaAlO₃ substrate has a higher tunability of 16.77% than that grown on the MgO substrate (～8.38%), measured at 10 GHz with an applied voltage of 35 V. The loss tangent is a linear function of the frequency in the microwave range, and the film grown on the MgO substrate has a lower loss tangent than that grown on the LAO substrate. This work reveals the great potential of Ba_0.6Sr_0.4TiO₃ (BST) films for application in tunable microwave devices.     

X‐Band Phased Array Antenna Using Ferroelectric (Ba,Sr)TiO3 Coplanar Waveguide Phase Shifter

A phased array antenna was fabricated using four‐element ferroelectric phase shifters with a coplanar waveguide (CPW) transmission line structure based on a Ba0.6Sr0.4TiO3(BST)/MgO structure. Epitaxial BST films were deposited on MgO (001) substrates by pulsed laser deposition. To attain the large differential phase shift and small losses for a ferroelectric CPW phase shifter, an impedance‐matching‐part adding technique between the effective transmission line and connecting cable was used. The return loss and insertion loss for this technique‐adapted BST CPW device were improved with respect to those for a normal BST CPW device. For an X‐band phased array antenna system consisting of ferroelectric BST CPW phase shifters, power divider, dc block, patch antenna, and programmed dc power, the steering beam could be tilted by 15° in either direction.     

Tunable barium strontium titanate thin film capacitors for RF andmicrowave applications

The measurement results for thin film barium strontium titanate (BST) based voltage tunable capacitors intended for RF applications are reported. At 9 V DC, BST capacitors fabricated using MOCVD (metalorganic chemical vapor deposition) method achieved 71% (3.4:1) tunability. The measured device quality factor (Q) for BST varactors is comparable with the device Q for commercially available varactor diodes of similar capacitance. The typical dielectric loss tangent was in the range 0.003-0.009 at VHF. Large signal measurement and modeling results for BST thin film capacitors are also presented     

Electrically tunable split-ring resonators at microwave frequencies based on barium-strontium-titanate thick films

Split-ring resonators (SRRs) implemented using ferroelectric materials to modify their resonance frequency by means of a tuning voltage are presented for the first time. SRRs have been used to load a microstrip transmission line on a multilayered substrate including a thick film of barium-strontium-titanate (BST) to obtain a tunable stopband response. The characteristics of the BST layer allow the application of 140 V as tuning voltage to obtain frequency tunability values of around 12.5 . The applied technology is suitable for the fabrication of cost-effective and reliable planar microwave devices.     

Characterization of pulsed laser deposited Ba0.6Sr0.4TiO3 on Pt-coated silicon substrates

The high dielectric constant (Ba,Sr)TiO₃ (BST) films have been widely used to realize capacitors integrated on silicon with a high value of capacitance. The multilayer Pt/Ti/SiO₂/Si is one of the most currently used bottom electrodes for the integration of BST on silicon. However, the crystal orientation and the dielectric properties of ferroelectric thin films are greatly influenced by the underlying Pt/Ti metallization, and particularly by the out-diffusion of titanium towards the platinum surface during thermal treatments. In this study, we show that the heating stage of the Pt/Ti/SiO₂/Si substrate before the BST pulsed laser deposition is of primary importance in both favoring the (1 1 1) growth of the BST material within a wide range of oxygen deposition pressure and in reducing drastically the loss tangent values of Al/BST/Pt capacitors because of the oxygen saturation of platinum. Electrical measurements indicate the existence of an interfacial layer degrading the capacitance. They support the presence of an interfacial depleted layer. The dramatic increase of the loss tangent under positive polarities applied on the platinum electrode is attributed to the ohmic contact of the BST/Al interface. Except this increase, all of the electrical properties are very promising in view to realize capacitors with high capacitance value and low dispersion.     

Wide-Tunable Low-Field Interdigitated Barium Strontium Titanate Capacitors

This letter reports low-field wide-tunable interdigitated barium strontium titanate (BST) capacitors. The capacitors consisting of BST thin film dielectric, silicon substrate, and gold metallization have been fabricated. The capacitance exhibits 0.2 pF at zero-bias and shows a tunability of 63% with an applied electric field of 1.4 V/mum. This corresponds to a 3.5 mum electrode gap width and a 5 V dc bias. Microwave measurements reveal a zero bias film quality of 50 around 30 GHz.     

Structural and Electrical Characters of Ba0.6Sro.4TiO3/La0.5Sr0.5CoO3 Thin Films by Plus Laser Deposition

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). Xray relationship of BST/LSCO/LAO was [001] BST//[001]LSCO//[001] LAO. The atomic force microscope (AFM)revealed a smooth and crackfree surface of BST films on LSCOcoated LAO substrate with the average grain size of 120 nm and the RMS of 1.564 nm for BST films.Pt/BST/LSCO capacitor was fabricated to perform CapacitanceVoltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.63×107 A/crm2 under an applied filed of 200 kV/cm. Furthermore, it was found that epitaxial BST (60/40) films demonstrate wellbehaved ferroelectric properties with the remnate polarization of 6.085 μC/cm2 and the coercive field of 72 kV/cm. The different electric properties from bulk BST (60/40)materials with intrinsic paraelectric characteristic are attributed to the interface effects.     

Structural and Electrical Characters of Ba0.6Sr0.4TiO3/La0.5Sr0.5CoO3 Thin Films by Plus Laser Deposition

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). X-ray diffraction ~2 and Ф scan showed that the epitaxial relationship of BST/LSCO/LAO was [001] BST//[001] LSCO//[001] LAO. The atomic force microscope (AFM) revealed a smooth and crack-free surface of BST films on LSCO-coated LAO substrate with the average grain size of 120 nm and the RMS of 1.564 nm for BST films. Pt/BST/LSCO capacitor was fabricated to perform CapacitanceVoltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.6310-7 A/cm2 under an applied filed of 200 kV/cm. Furthermore, it was found that epitaxial BST (60/40) films demonstrate well-behaved ferroelectric properties with the remnate polarization of 6.085 C/cm2 and the coercive field of 72 kV/cm. The different electric properties from bulk BST (60/40) materials with intrinsic paraelectric characteristic are attributed to the interface effects.