铁电-贵金属纳米复合薄膜的制备及其阻变行为的研究

Ferroelectric Resistive Random Access Memory (RRAM) has been one of the most important developing directions of the novel memories. Recently, owing to the ferroelectric resistive switching (RS) mechanisms are complicated and in dispute, it is still difficult to modulate the RS performance in ferroelectric RRAM. In addition, the modulation methods, such as changing thickness or element doping, always face the issue how to balance the ferroelectricity and conductivity. Thus, the RS properties including ON/OFF ratio, current density, operation voltage, cycles and retentions, can not be improved at the same time. In order to solve this key problem, Au and Pt of good conductivity and PbZrTiO3 (PZT) of good ferroelectricity will be selected to prepare noble metal-ferroelectric nanocomposite films by chemical solution deposition. In this project, the ferroelectric nanocomposite films with different concentrations, sizes and distributions of noble metal nanoparticles will be obtained to increase the conductivity meanwhile maintain the ferroelectricity. The detailed research contents are as follows: (1) The relationships between microstructure and preparation process; (2) The dependence of ferroelectric, conductivity and RS performance in nanocomposite films; (3) The RS behaviors and mechanism of ferroelectric RRAM based on noble metal-ferroelectric nanocomposite films. This project can not only improve the functional properties of ferroelectric RRAM, but also help to promote the understanding on the physical mechanism of ferroelectric RS behavior.

铁电阻变存储器被认为是最具有应用前景的新型存储器之一。目前，由于铁电阻变行为中存在多种机制，而且具体的机制尚不完全清楚，因此如何提高铁电阻变性能还面临许多问题。通过改变膜厚、元素掺杂等调控手段提高铁电阻变性能常遇到如何平衡铁电薄膜的铁电性与导电性的问题，目前还无法同时改善开关比、导通电流密度、操作电压和循环次数等铁电阻变性能。针对这一关键问题，本项目拟通过化学溶液沉积法，采用导电性良好的贵金属金、铂与铁电性优异的锆钛酸铅进行复合，制备贵金属纳米粒子不同含量、尺寸和分布的铁电-贵金属纳米复合薄膜，以期在保证具有良好铁电性同时，提高复合薄膜的导电性。具体研究内容包括：（1）制备工艺对复合薄膜微结构的影响；（2）复合薄膜的铁电性和导电性与其阻变性能的关联；（3）铁电阻变存储器的阻变行为与机制。本项目的开展不仅可以提高阻变存储器的功能特性，还有助于探讨铁电阻变行为中的物理机制。

在铁电阻变存储器中，良好的铁电性是保证器件耐久可靠的关键。在保证铁电性的同时，适当提高导电性不仅能够获得更大的开关比，还能免除外围放大设备的使用，减小器件电极面积，甚至还能降低操作电压，从而大幅提高集成密度、减小能耗。因此，铁电阻变存储器的阻变性能是由铁电材料的铁电性和导电性共同决定的。该项目的主要研究内容是制备铁电-贵金属纳米复合薄膜，研究纳米颗粒对铁电-贵金属复合薄膜微结构的影响，理解贵金属纳米粒子对复合薄膜铁电和导电性能的影响机理，调控界面构造，阐明铁电阻变存储器的阻变行为与机制。通过本项目的实施，制备得到了以铁电-贵金属纳米复合薄膜为阻变介质材料的阻变存储器器件，铁电剩余极化基本保持不变，导通电流密度提高至每平方毫米百毫安量级，开关比提高了两个数量级，操作电压降低50%以上。采用纳米复合的方法，成功实现了铁电阻变器件中铁电性与导电性的共存，为我国研发新型阻变器件提供了一条可行的技术路线。进一步通过TEM、XPS、UPS等表征手段证实了贵金属纳米粒子的复合改变了铁电与半导体电极材料的界面能带结构，理解了铁电复合薄膜器件的阻变机制。通过调控界面结构，实现了对铁电阻变行为地有效调控，厘清了铁电阻变中铁电场效应调控能力和界面耗尽层宽度可调性之间的平衡关系，丰富了铁电阻变行为调控的物理图像，为铁电材料在阻变存储器中的应用提供了理论基础支持。