应用于MEMS的PZT铁电薄膜

薄膜制备工艺的发展使铁电薄膜很好的应用于MEMS, 使两者集成成为可能. 本文将详细论述铁电薄膜的优良性能, 及其与MEMS集成的关键工艺--图形化. 最后, 举例论述了PZT铁电薄膜在MEMS中的应用.     

MEMS集成应用的纳米结构PZT厚膜形成工艺研究

提出了制备PZT厚膜的一种新的旋转涂覆方法.采用0-3复合法将PZT溶胶与PZT纳米粉混合形成浆料,并与PZT溶胶交替涂覆在Pt/Ti/SiO2/Si衬底上,使PZT厚度达2μm,并且使PZT表面质量得到了改善.利用XRD和SEM对PZT厚膜的组织和结构进行了表征.得到的薄膜无裂纹,结晶和表面平整度良好,可用于MEMS中微型传感器和微型驱动器的制作.     

以溶胶-凝胶法PZT薄膜为驱动的微泵研制

采用溶胶-凝胶法(sol-gel)制备技术制作了Pb(Zr,Ti)O3(PZT)压电薄膜,并以PZT薄膜为驱动制作了微泵.采用了V型微阀的微泵主要利用PZT的压电效应.针对微泵的关键结构--复合驱动膜,探索了一种Si/SiO2/Ti/Au/PZT/Cr/Au多层驱动膜结构制备方法,解决了在硅基底上制备PZT薄膜的问题,同时探讨并解决了硅各向异性刻蚀微泵的微驱动腔、单向阀的工艺问题,并通过SEM照片对V型阀和多层驱动膜进行了表征.研究结果表明,采用MEMS技术成功地完成了微驱动器的研制,得到的驱动腔硅杯平坦均匀.在V型阀微泵整体设计中需要的硅片数目少,降低了器件的复杂性,可以满足功耗低、小型化和批量生产的要求.     

硅基PZT压电薄膜微开关的设计和制作

对硅基锆钛酸铅（PZT）压电薄膜微开关进行了结构和版图设计，根据MEMS加工工艺和标准硅基IC工艺的特点，获得了硅基PZT压电薄膜微悬臂梁结构系统工艺流程中的关键工艺技术和典型工艺条件，对多孔硅的选择性生长进行了较为详细的实验研究，最后成功的制备出硅基PZT压电薄膜微开关样品，这对集成化芯片系统的进一步发展打下了必要的良好的实验基础。     

溶胶-凝胶法制作PZT微驱动器的研究

采用溶胶-凝胶法(Sol-gel)制备了PZT压电薄膜,利用PZT的压电效应制作以PZT薄膜为驱动的V型阀微驱动器.针对微驱动器的关键结构驱动膜,探索了Si/SiO2/Ti/Au/PZT/Cr/Au多层驱动膜结构制备方法,解决了在硅基底上制备PZT薄膜的问题,同时详细探讨了硅各向异性刻蚀微驱动器的关键部件驱动腔、单向阀的工艺,解决了集成制作的V型阀微驱动器的关键工艺问题,并通过SEM照片对V型阀和多层驱动膜进行了表征.研究结果表明,采用MEMS与IC技术结合的方法成功地完成了微驱动器的研制,得到的驱动腔硅杯平坦均匀.在V型阀微驱动器整体设计中需要的硅片数目少,降低了器件的复杂性,可以满足低功耗、小型化和批量生产的要求.     

Sol-Gel法硅基铁电薄膜研究

介绍了用溶胶 凝胶方法制备Pb(Zr0 .53Ti0 .4 7)O3(PZT)铁电薄膜的工艺流程。以硝酸锆、醋酸铅和钛酸四丁酯为原料 ,在 90 0℃ ,30min退火条件下制备了硅基PZT铁电薄膜。实验分析结果显示 ,PZT铁电薄膜的晶化很完善。研究了PZT铁电薄膜与硅之间的界面及其对铁电薄膜品质的影响。并在此基础上实现了制备PZT铁电薄膜的低温改进工艺。     

PZT/ZnO薄膜制备及其结构特性研究

利用固相反应制备的ZnO-Li_(2.2%)陶瓷靶和RF射频磁控溅射技术在Si(100)基片上制备了高度c轴择优取向的ZnO薄膜,XRD和电性能分析表明掺杂Li离子改善了ZnO靶材的结构和性能,同时研究了不同RF溅射温度对ZnO薄膜结构与取向的影响;然后采用sol-gel前驱单体薄膜制备方法,以ZnO为过渡层淀积PZT薄膜,探讨高度c轴(002)择优取向ZnO薄膜对PZT薄膜结构与性能的影响,实验发现在PZT/ZnO异质结构中,致密、均匀和高度c轴择优取向的ZnO可作为晶核,促进PZT钙钛矿结构转化、晶粒(110)择优取向生长,相应降低PZT薄膜的退火温度.     

Sol-Gel法制备PZT铁电薄膜新进展

从底电极的选择、过渡层的引入、外延膜的生长、取代阳离子的改性四个方面介绍了Sol-Gel法制备PZT铁电薄膜的研究进展,简述了PZT的Sol-Gel机理研究现状和引起PZT铁电薄膜极化疲劳的原因,分析了Sol-Gel法制备PZT铁电薄膜研究中存在的问题,并提出展望。     

激光脉冲外延生长Pb(Zr0.52Ti0.48)O3薄膜及其特性研究

利用激光脉冲法在LaAlO3衬底上沉积制备LaNiO3薄膜作为底电极并外延生长(100) Pb(Zr0.52Ti0.48)O3铁电薄膜,系统研究了生长温度对PZT外延结构和电学特性的影响.研究发现当生长温度高于550℃时即可得到外延(100)PZT薄膜.在对所制备的PZT薄膜的结构和性能测试表明,650℃下生长的PZT薄膜外延性最佳,并且表现出优异的介电和铁电性能,介电常数ε、剩余极化Pr和矫顽场Ec分别为900、26.5 μC/cm2和52.1kV/cm.试验还证实这种外延PZT薄膜具有优良的抗疲劳特性,可用于铁电存储器的制备中去.     

Sol-gel法制备PZT铁电薄膜的疲劳影响因素研究进展

简述了PZT铁电薄膜在制备和应用当中遇到的问题.围绕提高薄膜的疲劳性能,介绍了PZT铁电薄膜近年来在热处理、底电极、过渡层和掺杂等方面的研究进展,并分析了它们对材料电性能和疲劳性能的影响.最后提出了展望.     

PZT铁电薄、厚膜及其制备技术研究进展

铁电薄、厚膜材料具有良好的铁电、压电、热释电、电光及非线性光学特性,在微电子学、光电子学、集成光学和微电子机械系统等领域有许多重要的应用.近年来,随着铁电薄、厚膜制备技术的发展,PZT厚膜材料及厚膜器件成为科学工作者研究的热点.介绍了PZT铁电薄、厚膜材料与器件的研究进展以及PZT铁电薄、厚膜制备技术及几种典型的PZT铁电薄、厚膜材料制备技术的特点,并指出了目前存在的一些问题和未来的发展方向.     

Fabrication of single crystal PZT thin films on glass substrates

 We have successfully transferred heteroepitaxial Pb(Zr,Ti)O₃ (PZT) thin films from MgO substrates on to glass substrates. The transferred PZT thin films exhibit single crystal structure with ferroelectric properties similar to the as-grown epitaxial films. The transferring process comprises coating of Cr-metallized surface of epitaxial PZT thin films, pressing and cementing the Cr-metallized surface on to the glass substrates by silicone rubber, and removing the MgO substrates by chemical etching. This process realizes a fabrication of high-temperature processed PZT thin films onto the glass at room temperature. The process is also available for the transformation of PZT thin films on organic film sheet. The present transfer process reduces the effects of the inevitable strain and/or constraint to rigid substrates for heteroepitaxial growth and has a potential for integration of single crystal piezoelectric PZT devices onto a wide variety of MEMS.     

基于锆钛酸铅薄膜的变形镜微致动器

以锆钛酸铅（PZT）薄膜作为驱动材料,制备了变形镜的微致动器阵列．使用有限元软件对致动器进行了模拟仿真,得到了驱动器上电极尺寸、Si弹性层厚度等参数对致动器性能的影响,获得了最优化的致动器结构．以钙钛矿相的镍酸镧（LNO）作为PZT薄膜在Pt衬底上生长的缓冲层,增强了PZT薄膜的（100）取向,减小了PZT薄膜的内部应力,提高了致动器的驱动性能．最终制备出的1μm厚PZT薄膜驱动的变形镜微致动器,在10V直流电压的激励下,具有2．0μm的变形量．以PZT薄膜作为驱动材料制备的变形镜微致动器阵列,对变形镜致动器的微型化和系统集成度的提高具有重要意义．     

Fabrication and characterization of piezoelectric micromachined ultrasonic transducers with thick composite PZT films

Ferroelectric microelectromechanical systems (MEMS) has been a growing area of research in past decades, in which ferroelectric films are combined with silicon technology for a variety of applications, such as piezo-electric micromachined ultrasonic transducers (pMUTs), which represent a new approach to ultrasound detection and generation. For ultrasound-radiating applications, thicker PZT films are preferred because generative force and response speed of the diaphragm-type transducers increase with increasing film thickness. However, integration of 4- to 20-microm thick PZT films on silicon wafer, either the deposition or the patterning, is still a bottleneck in the micromachining process. This paper reports on a diaphragm-type pMUT. A composite coating technique based on chemical solution deposition and high-energy ball milled powder has been used to fabricate thick PZT films. Micromachining of the pMUTs using such thick films has been investigated. The fabricated pMUT with crack-free PZT films up to 7-microm thick was evaluated as an ultrasonic transmitter. The generated sound pressure level of up to 120 dB indicates that the fabricated pMUT has very good ultrasound-radiating performance and, therefore, can be used to compose pMUT arrays for generating ultrasound beam with high directivity in numerous applications. The pMUT arrays also have been demonstrated.     

Highly polarized single-c-domain single-crystal Pb(Mn,Nb)O(3)-PZT thin films

In-plane unstrained single-c-domain/single-crystal thin films of PZT-based ternary ferroelectric perovskite, ξPb(Mn,Nb)O3-(1 - ξ)PZT, were grown on SrRuO(3)/Pt/MgO substrates using magnetron sputtering followed by quenching. The sputtered unstrained thin films exhibit unique ferroelectric properties: high coercive field, Ec > 180 kV/cm, large remanent polarization, P(r) = 100 μC/cm(2), small relative dielectric constants, ε* = 100 to 150, high Curie temperature, Tc = ~600 °C, and bulk-like large transverse piezoelectric constants, e31,f = -12.0 C/m(2) for PZT(48/52) at ξ = 0.06. The unstrained thin films are an ideal structure to extract the bulk ferroelectric properties. Their micro-structures and ferroelectric properties are discussed in relation to the potential applications for piezoelectric MEMS.     

Fabrication and characteristics of out-of-plane piezoelectric micro grippers using MEMS processes

Out-of-plane type piezoelectric micro grippers (briefly, OPPMG) actuated by micro cantilevers using sol-gel multi-coated PZT (Pb(Zr_0.52Ti_0.48)O₃) films with the thickness of 1.2 μm were newly designed and fabricated using MEMS processes. Electromechanical and gripping characteristics of fabricated micro PZT cantilevers and OPPMG using them have been investigated. Two types of micro PZT cantilevers were fabricated with two types of supporting layers, respectively. The OPPMG was formed by two micro PZT cantilevers of the same type facing each other across the spacer of polyimide (PI). Precise gripping and positioning of metallic ball with diameter of 100 μm using fabricated OPPMGs was successfully done at a low actuating voltage of 7 V, without any adhesion problems between two jaws of gripper and the ball.     

Piezoelectric films for high frequency ultrasonic transducers in biomedical applications

Piezoelectric films have recently attracted considerable attention in the development of various sensor and actuator devices such as nonvolatile memories, tunable microwave circuits and ultrasound transducers. In this paper, an overview of the state of art in piezoelectric films for high frequency transducer applications is presented. Firstly, the basic principles of piezoelectric materials and design considerations for ultrasound transducers will be introduced. Following the review, the current status of the piezoelectric films and recent progress in the development of high frequency ultrasonic transducers will be discussed. Then details for preparation and structure of the materials derived from piezoelectric thick film technologies will be described. Both chemical and physical methods are included in the discussion, namely, the sol-gel approach, aerosol technology and hydrothermal method. The electric and piezoelectric properties of the piezoelectric films, which are very important for transducer applications, such as permittivity and electromechanical coupling factor, are also addressed. Finally, the recent developments in the high frequency transducers and arrays with piezoelectric ZnO and PZT thick film using MEMS technology are presented. In addition, current problems and further direction of the piezoelectric films for very high frequency ultrasound application (up to GHz) are also discussed.     

Ultra-thin and isolated dots in polycrystalline lead zirconate titanate films

Size effects with critical thickness or minimum volume for ferroelectricity are of importance in the application of polycrystalline PZT thin films as future memory devices and as storage media. Isolated dots of perovskite phases in the matrix of pyrochlore were synthesized by isothermal annealing through transformation from amorphous to perovskite. Control of the transformation kinetics allows us to produce the isolated ferroelectric dots with a diameter of 50 nm. Domain structure of the isolated dots is also studied by piezoresponse force microscopy. As prepared, all isolated dots contain perpendicularly polarized monodomains. Domain structures and switching behaviors of the isolated dots are similar to those of the single crystalline PZT films. Polycrystalline PZT films with a thickness of 50 nm were also investigated. They show excellent piezoresponse properties and switching behaviors. Ultra-thin polycrystalline PZT films can play a major role in the application of future ferroelectric memories and field-effect transistors as well as for storage media using the local probe technique.