应用于DRAM的BST薄膜制备与性能研究

BaxSr1-xTiO3(BST)是动态随机存取存储器(DRAM)中常规电容介质SiO2的替代材料。用溶胶-凝胶(Sol-Gel)法在Si及Pt/Ti/SiO2/Si基片上制备出了较高品质的BST薄膜。系统地研究了在不同退火条件下薄膜的结晶情况、微结构和电学性能。在室温100kHz下,薄膜的介电常数为230。在3V的偏压下,薄膜的漏电流密度为1.6×10-7A/cm2。利用HCl/HF刻蚀溶液成功获得了分辨率达到微米量级的BST薄膜微图形。     

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。     

VCO电路测试新型BST电容器的可变电容特性

基于新型BST电容器的变容机理,采用集成芯片MC12148设计VCO(压控震荡器)测试电路,通过测量不同控制电压对应的频率,计算出材料的电容与介电常数,研究了新型BST的压控特性,推导出该BST材料的电压与电容关系式。结果显示:新型BST材料加正反偏压电容都发生变化;最大耐压值为40 V;其电容调谐率与压控灵敏度都很小,分别为10.691%和5.717 kHz/V;材料应用在频率合成器的微调上,可提高合成频率的灵敏度与精度。     

先进DRAM驱动高深宽比刻蚀的发展

DRAM器件制造商通过缩小设计规则、芯片尺寸来提高存储器性能和密度的方法，正面临着众多挑战。增大电容面积，使用更高介电常数的材料，以及减薄介电材料厚度等方法都能够继续延续电容的形式和功能。     

BST红外探测器阵列像元信号检测电路设计(英文)

针对铁电材料BST的电容在直流偏场下电性能随温度变化,设计了一种用来检测微小差分电容的电路。采用性能、形状较为一致的BST铁电陶瓷单元电容器配对结构,以电脉冲的方式读取不同温度下材料的充放电电荷数,从而探测辐射到铁电材料上的红外信息。实验结果与理论分析较为吻合,中心频率10Hz、带宽2Hz、放大倍数9000倍。这种BST红外探测器阵列像元信号检测电路具有抗寄生电容干扰强、灵敏度高、容易实现、成本低等优点。改进该探测电路,有望开发出结构简单、性能优良的新一代红外探测器。     

Ba_(0.5)Sr_(0.5)TiO_3薄膜电容的尺寸效应研究

采用射频磁控溅射和微细加工技术制备了不同尺寸的钛酸锶钡(Ba0.5Sr0.5TiO3,BST)平行板电容,研究了低频和高频条件下不同尺寸BST平行板电容的电容密度和Q值的变化情况。结果表明,由于存在边缘效应,BST薄膜电容的电容密度及Q值都具有尺寸效应。低频时,随着电容面积增大,电容密度减小,Q值增大。高频时,随着电容面积增大,电容密度及Q值减小。     

双面蚀刻薄介质材料埋容芯板可行性研究

用蚀刻薄膜材料法制作埋嵌式电容，其电容介质材料较薄，常用的电容介质材料厚度在8μm～50μm之间，因此在制作电容层图形时，容易出现皱折、破损的情况。目前可行的方法是用单面蚀刻法制作电容层图形。探讨运用双面蚀刻法制作电容层图形对电容值精度的影响及其可行性分析。     

升压电源和高压DAC为天线和滤波器提供调谐信号

天线阵列和滤波器常常通过改变钛酸钡锶(BST)电容上的电压来进行调谐。将这种铁电材料应用于电容时,只需施加一个电压,即可导致其晶体结构发生细小的变化,从而改变其介电常数,电容值因而随之改变。相比于传统的变容二极管,电子可调     

相对介电常数大于100的BST(钛酸锶钡)薄膜

南京电子器件研究所采用 RF磁控溅射法成功研制出室温下相对介电常数高于 1 0 0的 BST薄膜。采用具有自主知识产权的工艺技术制作了大直径 BST溅射靶材 ,用这种靶材制作 Pt/BST/Pt薄膜电容 ,在 Si/Si O2 衬底上溅射 BST,其膜厚典型值 2 80 nm。该技术采用了在 RF磁控溅射 BST时     

BST移相器的优化设计算法

近年来,人们在微波应用领域对BST移相器进行了很多研究。本文对BST铁电移相器电路进行了等效分析,就电路中重要部分-BST电容加载的方法进行研究,创新地提出了BST电容非周期性加载的设计思路。用M atlab编程实现并论证这种设计思路。使用这种优化方法设计出的非周期性加载移相器各项指标均优于周期性加载移相器,现已申请专利(专利号:200510028313.9)。     

Low-Dielectric-Loss Barium Strontium Titanate Thin Films with MgO Buffer Layer for Tunable Microwave Devices

The dielectric and microwave properties of Ba_0.6Sr_0.4TiO₃ (BST60) thin films with a MgO buffer layer deposited on Al₂O₃ substrates were investigated. Insertion of the MgO buffer layer is demonstrated to be an effective approach to fabricate low-dielectric-loss BST thin films. x-Ray pattern analysis indicates that the thin films exhibit good crystalline quality with a pure perovskite phase and that insertion of the MgO buffer layer does not change the crystal structure of BST. The nonlinear dielectric properties of the BST films were measured by using an interdigital capacitor (IDC). At room temperature, the tunability of the BST films with a MgO buffer layer was 24.1% at a frequency of 1 MHz with an applied electric field of 80 kV/cm. The dielectric loss of the BST thin films is only 0.005 to 0.007 in the frequency range from 20 Hz to 2 MHz, the same as for BST films prepared on single-crystal MgO substrates. The microwave dielectric properties of the BST thin films were also measured by a vector network analyzer from 50 MHz to 10 GHz.     

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.     

RF磁控溅射制备钛酸锶钡BST纳米薄膜

钛酸锶钡(BST)薄膜作为一种高K介质材料在微电子和微机电系统等领域具有广阔的应用前景,人们已对BST薄膜的制备工艺技术和介电性能进行了大量的研究。BST纳米薄膜的制备工艺直接影响和决定着薄膜的介电性能(介电常数、漏电流密度、介电强度等)。对RF磁控反应溅射制备BST纳米薄膜的工艺技术进行了综述。从溅射靶的制备、溅射工艺参数的优化、热处理、薄膜组分的控制,及制备工艺对介电性能的影响等方面,对现有研究成果进行了较全面的总结。     

Sol-Gel法制备BST铁电薄膜及其性能分析

用Sol-Gel法制备出表面致密,界面清晰的BST铁电薄膜。分析了BST薄膜的J-V特性,由于使用了不同的上下电极,导致J-V曲线的不对称,且在外延生长的Pt电极上制备的BST薄膜有较低的漏电流。分别在大气和干燥气氛下测量了BST薄膜的介电特性,分析结果表明:湿度对BST薄膜的介电特性有很大的影响,为了得到正确的介电特性,其测量必须在真空或干燥气氛下进行。     

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。     

A stacked capacitor technology with ECR plasma MOCVD(Ba,Sr)TiO3 and RuO2/Ru/TiN/TiSixstorage nodes for Gb-scale DRAMs

A Gb-scale DRAM stacked capacitor technology with (Ba,Sr)TiO₃ thin films is described, The four-layer RuO₂/Ru/TiN/TiSi_x, storage node configuration allows 500°C processing and fine-patterning down to the 0.20 μm size by electron beam lithography and reactive ion etching. Good insulating (Ba_0.4Sr_0.6)TiO₃ (BST) films with an SiO₂ equivalent thickness of 0.65 nm on the electrode sidewalls and leakage current of 1×10^{-/6 A}cm² at 1 V are obtained by ECR plasma MOCVD without any post-deposition annealing, A lateral step coverage of 50% for BST is observed on the 0.2 μm size storage node pattern, and the BST thickness on the sidewalls is very uniform, thanks to the ECR downflow plasma. Using this stacked capacitor technology, a sufficient cell capacitance of 25 fF for 1 Gb DRAMs can be achieved in a capacitor area of 0.125 μm² with only the 0.3 μm high-storage electrodes     

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.     

Dielectric Characteristics of Ba0.65Sr0.35TiO3 Thin Films by Sol-Gel Method

Ferroelectric Ba0.65Sr0.35TiO3 (BST) thin films on the Pt/Ti/SiO2/Si substrate have been successfully prepared by sol-gel. Such films have approximately 300 nm thicknesses with a remnant polarization of about 2.95 C/cm2 and a coercive field of about 21.5 kV/cm. The investigations of X-ray diffraction and atomic force microscopy show that the BST films annealed at 650 ℃ exhibit a tetragonal structure and that the films dominantly consist of large column or grains of about 89 nm in diameter. The curves of the temperature dependence of dielectric coefficient in different frequencies display the curie transition at the temperature around 23 ℃. The dielectric loss tangent of BST thin films at 100 kHz is less than 0.04. As a result, the BST thin films are more applicable for fabrication of infrared detector compared with the BST thin films reported previously.     

Dielectric Characteristics of Ba_(0.65)Sr_(0.35)TiO_3 Thin Films by Sol-Gel Method

Ferroelectric Ba0.65Sr0.35TiO3(BST) thin films on the Pt/Ti/SiO2/Si substrate have been successfully prepared by sol-gel. Such films have approximately 300 nm thicknesses with a remnant polarization of about 2.95 μC/cm2 and a coercive field of about 21.5 kV/cm. The investigations of X-ray diffraction and atomic force microscopy show that the BST films annealed at 650 °C exhibit a tetragonal structure and that the films dominantly consist of large column or grains of about 89 nm in diameter. The curves of the temperature dependence of dielectric coefficient in different frequencies display the curie transition at the temperature around 23 °C. The dielectric loss tangent of BST thin films at 100 kHz is less than 0.04. As a result,the BST thin films are more applicable for fabrication of infrared detector compared with the BST thin films reported previously.     

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.