多铁性自旋过滤隧道结的制备与多态存储研究
发布时间：2018-11-22 17:53
【摘要】：传统铁电随机存取存储器的基本单元是一个铁电电容,需要一定的电容面积获得足够的电荷量来存储信息,难以实现高密度存储。其读出方式是破坏性的,在读出后需要重写信息,限制了读出时间。近年来出现的铁电隧穿存储以铁电隧道结为基本单元,是一种铁电极化调控的阻性存储方案,有望实现高密度、低功耗非易失性存储。在这样的背景之下,结合自旋阀磁隧道结,本文设计制备了一种多铁性自旋过滤阀隧道结,可在一个存储单元内同时实现铁电隧道结和磁隧道结的功能,获得四态非易失性存储,同时还研究了超薄铁电薄膜的极化弛豫行为。论文主要研究内容与结果如下:(1)在(001)取向的SrTiO3单晶衬底上制备了一系列不同相对厚度的Pr0.8Ca0.2MnO3/BaTiO3异质结,磁滞回线测量表明厚度为9个晶胞高度(u.c.)的Pr0.8Ca0.2MnO3薄膜在10K以下处于铁磁相,压电力显微镜表征表明5u.c.厚的BaTiO3仍有铁电性,确定优化的复合势垒为Pr0.8Ca0.2MnO3(9 u.c.)/BaTiO3(5 u.c.)。(2)制备了 LaNiO3/Pr0.8Ca0.2MnO3/BaTiO3/La0.7Sr0.3MnO3 外延异质结构,通过紫外光刻、离子束刻蚀等微加工手段获得多铁性隧道结原型器件。测试结果表明,器件具有区别明显的四种非易失性阻值状态,隧穿电致电阻约为100%,隧穿磁致电阻约为24%,并且发现铁电势垒的极化方向可调制Pr0.8Ca0.2Mn03的自旋极化率,进而影响器件的隧穿磁致电阻值。(3)不同厚度的BaTiO3薄膜铁电畴弛豫现象不同,7 u.c.的超薄BaTiO3膜中,铁电畴的面积变化缓慢,而极化强度逐渐变小;40nm厚的BaTiO3薄膜中,弛豫通过铁电畴面积不断变小完成。温度对Pb(Zr0.1Ti0.9)O3薄膜的铁电畴保持性有很大影响,温度越高,畴保持性越差。铁电畴形状影响弛豫时间,形状越接近圆的铁电畴弛豫越慢,保持性越好。
[Abstract]:The basic unit of traditional ferroelectric random access memory (FRAM) is a ferroelectric capacitance. It is difficult to realize high density storage because it needs a certain capacitance area to obtain enough charge quantity to store information. The readout method is destructive and needs to be rewritten after reading, which limits the readout time. In recent years ferroelectric tunneling storage, which is based on ferroelectric tunneling, is a kind of resistive storage scheme regulated by iron electrode, which is expected to achieve high density, low power consumption and non-volatile storage. In this context, combined with the spin valve magnetic tunnel junction, a multi-iron spin filter valve tunnel junction is designed and fabricated, which can realize the functions of ferroelectric tunnel junction and magnetic tunnel junction simultaneously in a memory cell. The four-state nonvolatile storage is obtained, and the polarization relaxation behavior of ultrathin ferroelectric thin films is also studied. The main contents and results are as follows: (1) A series of Pr0.8Ca0.2MnO3/BaTiO3 heterojunctions with different relative thickness have been prepared on (001) oriented SrTiO3 single crystal substrates. The hysteresis loop measurements show that the thickness is 9 unit cell height (u. C.) The Pr0.8Ca0.2MnO3 films are in ferromagnetic phase below 10K, and the results of PPM show that 5u. C. Thick BaTiO3 still has ferroelectric properties. It is determined that the optimized composite barrier is Pr0.8Ca0.2MnO3 (9 u. C.) / BaTiO3 (5 u. C.). (2) to prepare LaNiO3/Pr0.8Ca0.2MnO3/BaTiO3/La0.7Sr0.3MnO3 epitaxial heterostructure. The prototype devices of multi-iron tunneling junctions were obtained by ion beam etching and other micromachining methods. The test results show that the device has four distinct non-volatile resistance states, the tunneling resistance is about 100 and the tunneling magnetoresistance is about 24. It is also found that the polarization direction of the ferroelectric barrier can modulate the spin polarizability of Pr0.8Ca0.2Mn03. Furthermore, the tunneling magnetoresistance of the device is affected. (3) the ferroelectric domain relaxation phenomenon of BaTiO3 thin films with different thickness is different, 7 u. C. In ultrathin BaTiO3 films, the area of ferroelectric domains changes slowly, but the polarization intensity becomes smaller, while in BaTiO3 thin films with 40nm thickness, the relaxation is achieved by decreasing the area of ferroelectric domains. The temperature has a great influence on the ferroelectric domain retention of Pb (Zr0.1Ti0.9) O 3 thin films, and the higher the temperature, the worse the domain retention. The shape of ferroelectric domain affects the relaxation time, and the closer the ferroelectric domain is to the circle, the slower the relaxation is, and the better the retention is.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP333;O484.4
，
本文编号：2350125
[Abstract]:The basic unit of traditional ferroelectric random access memory (FRAM) is a ferroelectric capacitance. It is difficult to realize high density storage because it needs a certain capacitance area to obtain enough charge quantity to store information. The readout method is destructive and needs to be rewritten after reading, which limits the readout time. In recent years ferroelectric tunneling storage, which is based on ferroelectric tunneling, is a kind of resistive storage scheme regulated by iron electrode, which is expected to achieve high density, low power consumption and non-volatile storage. In this context, combined with the spin valve magnetic tunnel junction, a multi-iron spin filter valve tunnel junction is designed and fabricated, which can realize the functions of ferroelectric tunnel junction and magnetic tunnel junction simultaneously in a memory cell. The four-state nonvolatile storage is obtained, and the polarization relaxation behavior of ultrathin ferroelectric thin films is also studied. The main contents and results are as follows: (1) A series of Pr0.8Ca0.2MnO3/BaTiO3 heterojunctions with different relative thickness have been prepared on (001) oriented SrTiO3 single crystal substrates. The hysteresis loop measurements show that the thickness is 9 unit cell height (u. C.) The Pr0.8Ca0.2MnO3 films are in ferromagnetic phase below 10K, and the results of PPM show that 5u. C. Thick BaTiO3 still has ferroelectric properties. It is determined that the optimized composite barrier is Pr0.8Ca0.2MnO3 (9 u. C.) / BaTiO3 (5 u. C.). (2) to prepare LaNiO3/Pr0.8Ca0.2MnO3/BaTiO3/La0.7Sr0.3MnO3 epitaxial heterostructure. The prototype devices of multi-iron tunneling junctions were obtained by ion beam etching and other micromachining methods. The test results show that the device has four distinct non-volatile resistance states, the tunneling resistance is about 100 and the tunneling magnetoresistance is about 24. It is also found that the polarization direction of the ferroelectric barrier can modulate the spin polarizability of Pr0.8Ca0.2Mn03. Furthermore, the tunneling magnetoresistance of the device is affected. (3) the ferroelectric domain relaxation phenomenon of BaTiO3 thin films with different thickness is different, 7 u. C. In ultrathin BaTiO3 films, the area of ferroelectric domains changes slowly, but the polarization intensity becomes smaller, while in BaTiO3 thin films with 40nm thickness, the relaxation is achieved by decreasing the area of ferroelectric domains. The temperature has a great influence on the ferroelectric domain retention of Pb (Zr0.1Ti0.9) O 3 thin films, and the higher the temperature, the worse the domain retention. The shape of ferroelectric domain affects the relaxation time, and the closer the ferroelectric domain is to the circle, the slower the relaxation is, and the better the retention is.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP333;O484.4
，
本文编号：2350125
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