摘要
随着微机电系统(MEMS)的快速发展及市场前景越来越好,对MEMS产品可靠性、经济性、高效性等方面的要求越来越高,从而对MEMS中所用材料的性能也提出了更多的要求,对MEMS中各种微细加工方法也提出了更高精度、更高效率等方面的要求。锆钛酸铅(PZT)陶瓷是MEMS中最为常用的功能材料之一,它不仅可以作为高性能的驱动材料,也可以作为高灵敏度的传感材料;同时作为一种铁电材料,PZT还具有铁电性、热释电效应、电光效应、声光效应、光折变效应和其他非线性光学效应等,在微电子和光电子等技术领域也显示出十分重要的现实应用以及潜在应用的前景。目前,随着PZT陶瓷制备方法的不断发展,各种基于PZT陶瓷的MEMS微器件被成功开发出来。但是仍存在一些问题限制了PZT陶瓷更好、更广的应用。比如,溶胶-凝胶法制备PZT薄膜过程中,热处理时间过长、效率较低;使用普遍的PZT薄膜底电极Pt其价格昂贵,与钙钛矿相铁电体兼容性较差,长时间高温热处理使铁电体界面出现扩散现象,易表现出明显的疲劳特性以及其不透光性限制了PZT薄膜在某些方面的应用;满足更高驱动能力的高质量PZT厚膜制备困难,实现PZT厚膜高精度、高效率的图形化相对较难等。
针对PZT陶瓷材料在制备及应用过程中的若干问题,提出本论文的主要研究内容,包括以下几个方面:
1.在透明导电材料氧化铟锡(ITO)基底上制备高性能PZT铁电薄膜。
氧化铟锡(ITO)是一种重要的透明导电氧化物,具有电阻率低、高温稳定性好等优点,在光电子、太阳能转换装置等领域有着广泛的应用。本文首先用磁控溅射等方法在Si/SiO2基底上沉积高性能ITO薄膜作为底电极材料;然后基于溶胶-凝胶法,加快热处理速度,在ITO表面制备出性能优异的PZT铁电薄膜。其介电、铁电性能都与Pt基底上制备的PZT薄膜相当,且对其疲劳特性有明显的改善作用。借助ITO薄膜优异的光电特性,PZT铁电薄膜优良的铁电﹑电光、光折变以及非线性光学等特性将能得到更好的发挥。
2.设计、制作用于无阀微泵的PZT压电厚膜驱动器。
微泵作为微流体系统中的关键部件之一,高效率、小型化、批量化等已经成为其发展趋势,而使用PZT陶瓷作为驱动材料的压电微泵相比于其他类型的微泵,具有结构简单、响应时间快、驱动能力强、耗能低、无电磁干扰等优点。针对目前压电微泵驱动电压普遍较高、不易于批量制造等局限,提出制作在较低驱动电压下有较高驱动能力且响应频率高的PZT厚膜驱动器。在分析压电膜片驱动原理以及收缩/扩散口模型的基础上,设计、制作了PZT压电层厚度40um的膜片式驱动器,并将其用于无阀微泵测试。测试表明,驱动器具有高的谐振频率(29KHz)和较强的驱动能力(30Vpp-3.6um),在高性能微泵中有广泛的应用前景。
3.利用飞秒激光加工技术实现对PZT陶瓷的烧蚀及图形化。
飞秒激光加工技术作为一种高精度的无掩模加工技术,具有真三维、亚微米级分辨率、热影响小等优点,在微细加工领域应用越来越广泛。飞秒激光具有超短的脉冲时间(100fs)、超强的功率密度(1014W/cm2以上),能够激发材料的双光子/多光子吸收效应,所以可以用来高精度的加工几乎所有类型的材料。本文中以飞秒激光烧蚀材料的阈值模型作为理论基础,利用烧蚀加工孔径大小与能量密度的相互关系进行PZT烧蚀阈值的研究,通过毫焦(mJ)能量飞秒激光脉冲成功实现对PZT陶瓷的烧蚀,并在此基础上,以适当功率和扫描参数飞秒激光实现对PZT压电厚膜驱动进行了图形化研究。通过对实验结果的测试、分析可以得出,飞秒激光加工技术能够满足对PZT陶瓷的高精度、高效率的图形化要求。
Along with the fast development, better and better market price of the Microelectromechanical system (MEMS), MEMS productions are required to be more reliable, economical and efficient;so, it puts forword more and more requirement for the capability of the material used in MEMS; at the some time, the precision and efficency of the micromachining methods is required to be batter and batter. PZT is one of the most useful functional materials, it is not only used as excellent driven material, also as sensitive transducer material. PZT also has potential application in the field of micro-electronics and photoelectron for its excellent ferroelectric capability. At present, more and more PZT preparation methods are developed, so more and more productions based on PZT are fabricated. But, there are also some problems that limit its application. For example, in the sol-gel preparation process, Pt bottom electrode has the problem of compatibility and fatigue properties, and the thermal annealing process is time-consuming; it is difficult to get PZT film more than 10um, also the micromachnining of PZT thick film is difficult.
Aim at some problems of PZT preparation and micromachnining, the main research contents of the dissertation are:
1. Fast preparation of high performance PZT film on ITO bottom electrode. ITO has high conductivity and high transparency in visible region of the Spectrum. First, high performance ITO thin film is prepared on SiO2 substrate by RF magnetron sputtering in Ar atmosphere, then, PZT thin film is prepared on ITO bottom electrode by sol-gel process and rapid thermal annealing. Finally the required PZT film has high dielectric and ferroelectric properties, and the fatigue property is improved.
2. Design and fabrication of PZT thick film actuator used for valveless micropump.
Micropump is one of the most important parts in micro fluid system. PZT drived actuator has the advantage of high resonance frequency, low actuation voltage, simple structure and good stability compared to other driving methods. In this research, PZT thick film that has piezoelectric constant d31 of about 260 pmV-1 and Young’s modulus of about 60GPa is prepared by PZT-Si bonding and spray etching process. Then, PZT thick film actuator is designed and fabricated with large driving force and high resonance frequency. Finally the flow rate is measured.
2. Ablation and micromachining of PZT thick film using Femtosecond laser.
Fs laser micromachining which does not need mask is widely used for its unique technological advantages, such as true three dimentional fabrication ability, sub-micro resolution, low heat effect et al. For its ultrashort pulse duration and ultra high instantaneous power, it can ablate most materials with high precision. Based on the relationship of ablated crater size and applied laser fluence, the ablation threshold fluence of PZT ceramic is received. Finally, PZT thick film acruator is patterned using fs laser undering determinate laser parameters and feed rate.
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