PT系铁电薄膜生长及其性能研究

【作者】 张才建；

【导师】 张鹰；

【作者基本信息】 电子科技大学 ， 材料科学与工程， 2010， 硕士

【摘要】 由于具有高的剩余极化强度、较大的热释电系数和介电常数,PT系铁电薄膜如锆钛酸铅Pb(Zrx,Ti1-x)O3(PZT)和钛酸铅PbTiO3(PTO)被广泛用于非易失性铁电存储器、铁电场效应晶体管、热释电红外探测器等器件。本文采用射频磁控溅射和分子束外延两种方法研究PT系铁电薄膜的生长工艺与晶相结构、表面形貌和电学性能的关系,探索并优化在低温低氧条件下生长高质量PT系铁电薄膜的工艺方法。首先,使用射频磁控溅射在Pt/Si基片上制备了非晶的PZT薄膜,通过快速热处理研究了退火温度和升温速率对薄膜结晶质量的影响。研究表明,PZT铁电薄膜的最佳退火温度为600-750°C,温度过低难以使薄膜得到充分晶化,温度过高会使薄膜中的Pb组分过度挥发。随着退火温度的提高,PZT薄膜的取向由(100)变为(110)再变为(111),说明退火温度是提供PZT薄膜晶化动能的重要因素。退火中升温速率越慢,PZT薄膜沿(100)面择优生长越明显;当升温速率变快,薄膜开始沿(110)面择优生长;当升温速率进一步变快,薄膜开始沿(111)面择优生长。这是因为升温速率的差异导致了薄膜成核机制的不同。升温速率慢,PZT薄膜以同质成核为主,易形成(100)面择优生长;而升温速率变快,PZT薄膜以异质成核为主,易形成(111)面择优生长。在适当范围内,生长温度和退火温度越大,PZT薄膜的铁电性越好;随着升温速率变慢,PZT薄膜的铁电性进一步变好(300°C生长、10°C /S升温、650°C退火得到的PZT铁电薄膜,其2Pr约为133.8μC/cm2,矫顽场约为66.1KV/cm)。然后,在低氧和较低温度条件下使用分子束外延在Pt/Si和SrTiO3基片上生长了PTO薄膜,生长过程用反射式高能电子衍射仪(Reflection High-Energy Electron Diffraction, RHEED)进行原位监控。XRD的测试表明在Pt/Si基片上长出了沿(111)面择优取向的高质量PTO薄膜,而SrTiO3基片上长出了沿(001)面择优取向的高质量PTO薄膜(其FWHM值低至0.054°,结晶质量非常好),两者均为单晶外延薄膜且具有一定的铁电性。最后,通过对比,研究TiO2缓冲层诱导PTO薄膜在GaN基片上生长。生长过程用RHEED进行原位监控,结果表明薄膜生长模式以层状生长为主,局部为岛状生长,XRD测试结果显示在GaN基片上长出了沿(00l)面择优取向的PTO薄膜,说明TiO2缓冲层可以有效地诱导PTO薄膜在GaN基片上的生长,实现PTO/GaN的集成。更多还原

【Abstract】 Owing to its excellent physical properties such as high remnant polarization, large pyroelectric coefficient, and large dielectric constant, Pb(Zr1-xTix)O3 and PbTiO3 thin films have promising applications in ferroelectric random access memories, ferroelectric field-effect transistors, pyroelectric infrared sensors, and so on. In this thesis, the Pb(Zr1-xTix)O3 and PbTiO3 thin films were prepared by RF magnetron sputtering and molecular beam epitaxy, respectively. The effects of the growth and annealing parameters on the crystalline structure, surface morphology, and electrical properties were systematically investigated, and the growth conditions to grow high-quality PTO films were optimized under low temperature and low oxygen partial pressure. The main results are as follows.i) Amorphous PZT thin films were prepared on the Pt/Si substrates by RF magnetron sputtering. Effects of temperature and heating rate of the rapid thermal annealing process on the crystallization quality of PZT thin film was studied. The results show that the optimal annealing temperature is between 600°C and 750°C. When the temperature is lower than 600°C, the PZT film can not be fully crystallized; while higher than 750°C, it will be non-stoichiometric because of the over-volatilization of Pb. This indicates that the annealing temperature is a key factor to provide the kinetic energy for crystallization. For the films grown at a moderate temperature, (100)-texture of PTO films was observed for low annealing temperature, with increasing annealing temperature, (110)-texture was observed and with further increasing temperature, (111)-texture were observed. Similarly, the thin films exhibit more obvious (100)-texture occurred under the slower heating rate, with increasing heating rate, (110)-texture was observed, with further increasing heating rate, (111)-texture were observed. This can be explained by the different nucleation mechanism of the PZT films.ii) In order to obtain high-quality ferroelectric PTO thin films on Pt/Si and SrTiO3 substrates, molecular beam epitaxy system was performed and the growth was in situ monitored by RHEED. XRD results shows that the PbTiO3 thin films with (111)-texture were grown on the Pt/Si substrates. And PTO films were epitaxially grown on SrTiO3 and Nb: SrTiO3 substrates. It is noted that the FWHM of PTO(001) is as low as 0.054°, suggesting very high crystal-quality, and better than ever reported. Such single-crystal PTO films exhibit good ferroelectric hysteretic loops.iii) The TiO2 buffer layer inducing the growth of PTO on GaN substrates in situ monitored by RHEED. The results show that layer-by-layer growth mode is predominant and island growth mode is also observed. XRD results show that (00l)PTO film was grown. This suggests that the TiO2 buffer layer is effectively to induce the PTO growth and finally realize the integration growth of ferroelectric PTO with GaN.更多还原