Preparation of Ferroelectric PZT Thin Films by Photoenhanced CVD and an Application to Memory Devices

光增强CVD铁电PZT薄膜的制备及其在存储器件中的应用

基本信息

批准号：
04452176
负责人：
SHIOSAKI Tadashi
金额：
$ 3.52万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04452176/
关键词：
Photo-MOCVD PZT thin film O_3 breakdown voltage two step growth process PbTiO_3 buffer layr switching time reversed domain Pb(Zr,Ti)0_3薄膜光励起CVD 比誘電率 D-Eヒステリシスメモリデバイススイッチング特性ペロブスカイト

项目摘要

In photo-MOCVD of PZT,effects of a use of O_3 as an oxidizing gas instead of O_2 and a photoirradiation on the growth were investigated. A decrease in the growth temperature and an improvement in the crystallinity of the PZT thin films were not observed. However, when O_3 and O_3+UV irradiation during the growth run were used, an improvement in the breakdown voltage was observed. This improvement may have been caused by microscopic change in film structure.At high Zr content region, ZrO_2 and pyrochlore phase films were grown and it required high growth temperature to grow rhombohedral PZT thin films. In order to obtain perovskite rhombohedral PZT thin films at high Zr content regions, a two step growth process was proposed. In this method, at first stage, PbTiO_3 buffer layr as an intial layr were deposited and in succeeding process PZT film were grown. Rhombohedral PZT thin films were successfully obtained at higher Zr content regions and at lower substrate temperatures than when this two step growth process was not used.The pulse switching kinetics of ferroelectric PZT thin films grown by MOCVD was also investigated. The switching time was proportionally shortened as the area of ferroelectric thin film capacitor became smaller. On the other hand, both the switching time and the switched charge density had an activation-field dependence on the pulse voltage. It was proven that the pulse switching speed of ferroelectric PZT films is determined by the nucleation rate of reversed domains because the nucleation rate is lowered by the large effective time constant of the measurement system.

在PZT的光MOCVD中,研究了用O_3代替O_2作为氧化气体以及光照射对生长的影响。没有观察到生长温度的降低和PZT薄膜结晶度的提高。然而，当在生长过程中使用O_3和O_3+UV照射时，观察到击穿电压的改善。这种改善可能是由薄膜结构的微观变化引起的。在高Zr含量区域，生长了ZrO_2和烧绿石相薄膜，生长菱面体PZT薄膜需要较高的生长温度。为了在高Zr含量区域获得钙钛矿菱形PZT薄膜，提出了两步生长工艺。该方法首先沉积PbTiO_3缓冲层作为初始层，随后生长PZT薄膜。与未使用两步生长工艺时相比，在较高 Zr 含量区域和较低衬底温度下成功获得了菱形 PZT 薄膜。还研究了通过 MOCVD 生长的铁电 PZT 薄膜的脉冲切换动力学。随着铁电薄膜电容器的面积变小，开关时间成比例地缩短。另一方面，切换时间和切换电荷密度都对脉冲电压具有激活场依赖性。事实证明，铁电 PZT 薄膜的脉冲切换速度由反转域的成核率决定，因为测量系统的有效时间常数大会降低成核率。