【作者】 张燕；

【导师】 朱明；

【作者基本信息】 东南大学 ， 凝聚态物理， 2006， 硕士

【摘要】 近年来具有巨磁阻效应的材料及应用的研究已经成为当今磁学和磁性材料领域中最引人瞩目的课题之一。迄今为止,人们对巨磁阻材料进行了广泛的研究,但主要是集中在由外加磁场引起的磁阻效应和磁输运特性方面。目前人们对巨磁阻材料中的场致电阻效应产生的机理以及在电场下巨磁阻材料中的载流子迁移率的行为还缺乏充分的研究。迁移率随电荷密度的增加而趋于下降。随着器件尺寸的减小,摩尔定律也越来越显得重要,影响迁移率的因素也因此变的复杂起来了。尤其是,当器件尺寸小到纳米数量级时,硅是否还是最好的半导体材料,是值得探讨的。近年来人们正试图用一些具有一定功能的新型半导体材料去制备各种功能器件。其中的一种选择就是钙钛矿型（ABO₃）氧化物,这是由于钙钛矿结构的材料为人们提供了丰富的物理图像和各种引人注目的特性。但是由于在这类材料中存在着电子与晶格、电子自旋、以及电子间的强相互作用等各种复杂的作用,从而导致了载流子迁移率的大幅度减少,因而阻碍了钙钛矿材料在电子器件领域中的应用。最近,有文献报道在玻璃基底上成功地制备了巨磁阻异质结结构,发现巨磁阻中的载流子浓度随着钙锰比例的变化以及氧的化学计量比的变化而变化。为了研究巨磁阻膜La_0.8Ca_0.2MnO₃（LCMO）的电场效应,我们利用脉冲激光沉积法和溶胶-凝胶法制备了La_0.8Ca_0.2MnO₃薄膜,并利用传统的半导体工艺制备了“金属—绝缘体—巨磁阻”背栅场效应晶体管（CMRFET）的原型器件。这种背栅（back gate）场效应晶体管结构与常规的顶栅（top gate）的最大区别是,巨磁阻膜生长在PbZr_0.2Ti_0.8O₃ （PZT）上面。这种结构最突出的优点就是巨磁阻膜LCMO不影响绝缘膜—PZT栅的结构和介电性质。我们尝试了利用电场效应对LCMO中的载流子迁移率以及微分迁移率进行了定量的研究,并在一个大的温度范围内,对LCMO巨磁阻场效应结构的电流-电压（I-V）关系进行了较系统的研究。实验结果表明在大的反向电场偏置下,有效的LCMO沟道厚度变窄,非导电畴区与导电网络间的体积比随反向偏压的改变而改变,同时LCMO中的载流子迁移率也随着偏置电压的改变而改变。利用材料相变点附近的电场调制效应,可以使LCMO的场效应晶体管在大的迁移率下工作。这个结果尚属首次发现。更多还原

【Abstract】 In recent years, the study on colossal magnetoresistance （CMR） materials, as well as their application becomes more and more popular in magnetism and magnetic materials fields. Up to now, CMR materials have previously been studied for various purposes, which were mainly focus on the colossal magnetoresistance decrease and magnetotransport properties caused by magnetic field. The full study on electric-field （ER） effects coupled with magnetic field （MR） effect and the charge carrier mobility in these materials at electric field seems to be lacking.The mobility becomes compromised with increased charge density. As the device size is reduced with the trend for higher device packing density following the Moore’s law, the problem with the mobility becomes compounded. In particular when the size of the device goes down to a nano-meter level it is highly worthy of discussing if silicon is still the best choice as a semiconductor material.People are trying to fabricate functional apparatus using new semi-conductor materials with certain function in recent years. Perovskite oxide is one kind of these materials, which provides us so many physical pictures and fascinating properties. But strong reciprocity among electron- crystal lattice ,electron- electron and spin-spin in these materials leads great reduction of carrier mobility ,which blockes the applications of these materials in the field of electronic apparatus.Recently, the ferroelectric field effect transistor（FET）based on epitaxial La0.7Ca0.3MnO3 thin film heterostruture was reported. It was found the carrier density of the semiconductor varies widely with both the ratio of Ca︰Mn and oxygen stochiometry, and so the channel could be“tuned”by the ferroelectric gate.In order to study electric-field effects in La_0.8Ca_0.2MnO₃（LCMO） CMR film, an inverted metal-insulator-CMR field-effect transistor（CMR-FET） structure was chosen. This arrangement has an advantage that CMR film does not influence the structural and dielectric properties of the gate insulator-PZT, as would be the case if the PZT were grown on top of the CMR film. We carried out a quatitative investigation of carrier effective mobility and differential mobility under low and high electric field in La_0.8Ca_0.2MnO₃/PbZr_0.2Ti_0.8O₃ field-effect-transistors through the measurement of the current-voltage relationship and the capacitance-voltage relationship over a wide range of temperature. This result demonstrates, for the first time, that under a high reverse electric field that significantly narrows the thickness of the LCMO channel, a MOSFET with a material with MIT can operate with a very high mobility.更多还原