钛酸铋基铁电薄膜的Sol-gel法制备及改性研究

发布时间：2018-05-17 15:50

本文选题：铁电存储器 + Bi_4Ti_3O_(12)铁电材料　；参考：《武汉大学》2010年博士论文

【摘要】： 稀土离子掺杂的Bi4Ti3O12(BTO)基铁电薄膜具有优异的铁电和抗疲劳特性,在新型非易失性铁电存储器等方面具有潜在的应用前景。本论文采用溶胶-凝胶工艺制备了A位镧系元素(La, Nd,Tb)、A位Nd和B位Mn共掺杂的BTO基铁电薄膜,研究了掺杂离子对BTO薄膜结构和电性能的影响；研究了不同晶种层对Bi3.25La0.75Ti3O12(BLT)薄膜的结晶取向和铁电性能的影响；最后采用绝缘性能好的Bi3.15Nd0.85Ti3O12(BNT)铁电薄膜作为缓冲层,与多铁材料BiFeO3 (BFO)复合制成BNT/BFO多层薄膜,研究了BNT铁电薄膜对BFO多铁薄膜电性能的影响。主要内容如下： 1.利用溶胶-凝胶法在Pt/TiO2/SiO2/Si衬底上制备了具有随机取向的单相层状钙钛矿结构的BLT和BNT薄膜。扫描电镜(SEM)的观测显示了这些薄膜具有50—100纳米大小的晶粒构成的均匀致密的的表面形貌。这些薄膜电容显示了很好的饱和电滞回线。在最大外加场强为400kV/cm时,得到BLT薄膜的剩余极化强度(2Pr)和矫顽电场(2Ec)分别为25.1μC／cm2和203kV／cm,BNT薄膜的分别为44.2μC／cm2和296kV／cm。而且,在1MHz频率测试下经过1.75×1010次读写循环后,由BLT和BNT薄膜组成的电容器几乎没有表现出疲劳,呈现很好的抗疲劳特性。分析比较了La和Nd掺杂对薄膜结构及铁电性能的影响及其机理。 2.首次采用Sol-gel技术在Pt/TiO2/SiO2/Si衬底上制备了高价Tb4+掺杂BTO的Bi4-xTbxTi3O12(BTTx)薄膜。BTTx薄膜表现出多晶钙钛矿结构,具有饱和的电滞回线。相比于纯BTO薄膜,BTT薄膜具有以下改善的性能：(i)在外加最大电场为540kV/cm时,具有饱和的电滞回线、大的剩余极化值(Pr～60μC／cm2)及小的矫顽电场(Ec～298 kV／cm)；(ii)在经过1.0×1010极化反转后,BTT薄膜表现出无疲劳特征。这表明高价Tb4+的掺杂明显提高了BTO薄膜的铁电性能和抗疲劳特性,这可能归因于Tb4+的掺杂引起的薄膜的晶格畸变和可能降低的氧空位浓度。 3.采用Sol-gel法在Pt/TiO2/SiO2/Si衬底上制备了A位Nd和B位Mn掺杂的Bi3.15Nd0.85Ti3-xMnxO12 (BNTMX,x=0,0.01,0.03,0.05和0.1)薄膜。BNTM薄膜具有单相钙钛矿的多晶微结构和均匀致密的的表面形貌。Mn的掺杂使BNTM薄膜的晶格产生明显畸变。随着Mn掺杂浓度的增加,BNTM薄膜的2Ec值逐渐降低,而2Pr值在x=0.05时具有最大值；Mn掺杂量为x=0.05的样品具有最佳的电性能,在最大测试场强为400kV/cm时,其2Pr和2Ec分别为38.3μC／cm2和180kV/cm。在f=1MHz时,其介电常数和介电损耗分别为290和0.08。疲劳测试表明,经过1.0×1010次读写循环后,该薄膜电容器呈现优良的抗疲劳特性。 4.采用Sol-gel技术在Pt／TiO2／SiO2／Si(100)衬底上分别制备了以Bi2O3、TiO2和BTO为晶种层的BLT铁电薄膜。XRD结果表明不同的晶种层对BLT薄膜的取向具有不同的影响。含不同晶种层的BLT薄膜的表面形貌也不同,其结果同XRD分析结果相对应。不同的晶种层对BLT薄膜的漏电流产生不同的影响,以TiO2晶种层制备的BLT薄膜的漏电流密度最小。铁电性能分析表明在BTO晶种层上沉积BLT薄膜的剩余极化2Pr最大,为62.6μC／cm2,疲劳测试表明各薄膜均具有良好的抗疲劳特性,其中以TiO2为晶种层制备的BLT薄膜的抗疲劳特性最优。 5.采用Sol-gel法在Pt／TiO2／SiO2／Si(100)衬底上制备了BFO/BNT多层薄膜。研究了室温下复合薄膜的结构、漏电流、铁电和抗疲劳特性。相对于纯的BFO薄膜,BFO/BNT多层薄膜具有更低的漏电流,能承受更高的测试电场而获得充分极化,从而表现出优良的铁电性,在350kV/cm的测试电场强度下,剩余极化强度为55μC／cm2。在6V的测试电压下,BFO/BNT薄膜的漏电流密度比纯BFO薄膜的漏电流密度要低两个数量级。
[Abstract]:Bi4Ti3O12 (BTO) based ferroelectric thin films doped with rare earth ions have excellent ferroelectric and fatigue properties, and have potential applications in the new nonvolatile ferroelectric memory. In this paper, the A bit lanthanide elements (La, Nd, Tb), A bit Nd and B Mn Co doped BTO based ferroelectric thin films were prepared by the sol-gel process. The influence of the sub layer on the structure and electrical properties of BTO film was studied. The influence of different seed layers on the crystalline orientation and ferroelectric properties of Bi3.25La0.75Ti3O12 (BLT) thin films was studied. Finally, the Bi3.15Nd0.85Ti3O12 (BNT) ferroelectric thin film was used as the buffer layer and the BiFeO3 (BFO) of the polyiron material was combined to make the BNT/BFO multilayer film, and the BNT iron was studied. The effect of electric thin film on the electrical properties of BFO multiferroic thin films is as follows:
1. BLT and BNT films with random orientation of single-phase layered perovskite structure were prepared on Pt/TiO2/SiO2/Si substrate by sol-gel method. The observation of scanning electron microscopy (SEM) shows that these films have uniform and dense surface morphology composed of 50 to 100 nanocrystalline grains. These films show good saturated hysteresis. When the maximum applied field intensity is 400kV/cm, the residual polarization (2Pr) and coercive electric field (2Ec) of the BLT film are 25.1 mu C / cm2 and 203kV / cm respectively. The BNT thin films are respectively 44.2 mu C / cm2 and 296kV / cm. After 1.75 * 1010 cycles of reading and writing under the frequency test, the capacitor is almost no more. Fatigue and good fatigue resistance were observed. The effects of La and Nd doping on the structure and ferroelectric properties of the films were analyzed and compared.
2. the Bi4-xTbxTi3O12 (BTTx) thin film.BTTx film of high valence Tb4+ doped BTO was prepared on Pt/TiO2/SiO2/Si substrate by Sol-gel technology for the first time, showing a polycrystalline perovskite structure with a saturated hysteresis loop. Compared with the pure BTO film, the BTT thin film has the following improved properties: (I) with the maximum applied electric field as 540kV/cm, it has saturated electricity. The hysteresis loop, large residual polarization (Pr ~ 60 / C / cm2) and small coercive electric field (Ec to 298 kV / cm). (II), after 1 x 1010 polarization reversal, BTT film has no fatigue characteristics. This indicates that the doping of high price Tb4+ obviously improves the ferroelectric and fatigue resistance of BTO films, which may be attributed to the film caused by Tb4+ doping. Lattice distortion and possible reduced oxygen vacancy concentration.
3. A Nd and B bit Mn doped Bi3.15Nd0.85Ti3-xMnxO12 (BNTMX, x=0,0.01,0.03,0.05 and 0.1) thin film.BNTM films were prepared on Pt/TiO2/SiO2/Si substrates by Sol-gel method. The polycrystalline microstructures of single-phase perovskite and homogeneous and dense surface morphology were doped to make the lattice of the BNTM thin film produced obvious distortion. The 2Ec value of the BNTM film decreases gradually and the 2Pr value has the maximum value at x=0.05; the sample with Mn doping amount of x=0.05 has the best electrical properties. When the maximum test field strength is 400kV/cm, its 2Pr and 2Ec are 38.3 mu C / cm2 and the dielectric loss is 290 and the fatigue test shows that the dielectric constant and the dielectric loss are respectively indicated by the fatigue test. After 1 x 1010 cycles, the film capacitors exhibit excellent fatigue resistance.
4. Sol-gel technique was used to prepare BLT ferroelectric thin film.XRD with Bi2O3, TiO2 and BTO as the crystal layer on Pt / TiO2 / SiO2 / Si (100) substrate. The results show that different crystal layers have different influences on the orientation of BLT film. The surface morphology of the BLT films with different seed layers is different, and the results are different from those of the analytical results. The crystal layer has a different effect on the leakage current of the BLT film. The leakage current density of the BLT film prepared in the TiO2 seed layer is the smallest. The ferroelectric performance analysis shows that the maximum residual polarization 2Pr of the BLT film deposited on the BTO seed layer is 62.6 mu C / cm2. The fatigue test shows that the thin films have good anti fatigue properties, and TiO2 is the crystal seed. The anti fatigue properties of the BLT films prepared by the layer are the best.
5. the BFO/BNT multilayer films were prepared on Pt / TiO2 / SiO2 / Si (100) substrates by Sol-gel method. The structure, leakage current, ferroelectric and anti fatigue properties of the composite films at room temperature were studied. Relative to pure BFO films, BFO/BNT multilayer films have lower leakage current and can withstand a higher test electric field. Under the test electric field of 350kV/cm, the residual polarization intensity is 55 mu C / cm2. at the test voltage of 6V, and the leakage current density of BFO/BNT thin film is two orders of magnitude lower than that of pure BFO film.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2010
【分类号】：O484.1

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