氧化物薄膜晶体管的制备与物性研究

发布时间：2018-03-13 05:16

  本文选题：氧化物TFT　切入点：原子层沉积技术　出处：《上海大学》2015年博士论文　论文类型：学位论文

【摘要】：薄膜晶体管(TFT)是有源矩阵有机发光二极管(OLED)驱动电路的核心元件。OLED是电流驱动型器件,传统的非晶硅TFT迁移率低,难以满足OLED驱动的需要,而多晶硅TFT制备成本高、存在晶界、均匀性差等缺点限制了其在市场上的竞争力。近年发展的氧化物TFT具有迁移率高、可见光区透明、制备工艺简单、成本低等优点,成为最有发展潜力的TFT技术。本文就氧化物TFT的制备、电学性质、稳定性做了研究,主要的研究内容和创新点如下:1.绝缘层材料和生长方法的选择——Al2O3和原子层沉积技术(ALD)的应用。绝缘层是TFT器件的重要组成部分,绝缘材料及制备工艺的选择是器件好坏的关键。本文对比了分别以低介电常数Si O2(ε=3.9)和高介电常数HfO2(ε=25)为绝缘层的TFT特性。研究表明采用高介电常数材料作为绝缘层的器件迁移率有了明显的提高,以磁控溅射氧化硅为绝缘层的器件的迁移率为2 cm2/Vs,以氧化铪与氧化硅为复合绝缘层的器件的迁移率为8.6 cm2/Vs。通过对比证实高介电常数绝缘层能够提高器件的迁移率,降低驱动电压。然而它有较大的漏电,严重影响器件性能,这是因为高介电常数材料多形成多晶态,晶粒间界形成漏电通道,造成漏电。理想的绝缘材料应呈非晶态,且具有较高介电常数。在金属氧化物中,满足此条件的只有Al2O3(ε=9),因此Al2O3应成为绝缘材料的首选。选定了材料后就是选择制备方法。首先本文研究了磁控溅射氧化铝作为绝缘层的器件的性能,发现器件的稳定性还是不尽如意,采用传统的热氧化硅作为绝缘层的器件的最大界面态为4.2×1011 cm-2,而采用氧化铝作为绝缘层的器件的最大界面态为3.4×1012 cm-2。本文发现氧化铝的界面态较大是由制备方法造成的,磁控溅射虽然被广泛采用,但是由于溅射过程粒子能量较大,会造成界面的损伤,影响器件的稳定。于是本文又采用更加先进的原子层沉积技术(ALD),以充分发挥Al2O3的优势。采用ALD制备Al2O3作为绝缘层的器件与溅射Al2O3作为绝缘层的器件相比,迁移率从4.4 cm2/Vs增加到了5.2 cm2/Vs,阈值电压从9.9 V降低到4.3 V,界面态从3.4×1012 cm-2降低到了9.1×1011 cm-2,性能都有提高。本文后面的研究所制备的器件都是以ALD-Al2O3为基的器件。2.以ALD-Al2O3为绝缘层的TFT稳定性的研究:本文研究了ALD生长条件及绝缘层厚度对IGZO-TFT电学性能及稳定性的影响。通过优化Al2O3的生长温度及厚度得到较高迁移率和稳定性的器件。然而由于Al2O3的介电常数不够高,提升迁移率受到限制。我们使用高介电常数的Zr O2(ε=25),并使用ALD-Al2O3作为缓冲层进行修饰,不仅将Zr O2的漏电减少了两个数量级,还使迁移率从9.8 cm2/Vs上升到14 cm2/Vs,开关比从4×105提高到了3.5×106,最大界面态从4.3×1012 cm-2减小到了2.5×1012 cm-2,器件的稳定性得到了显著的提高,经过2个小时的偏压的老化,阈值电压漂移从1.6 V降低到0.79 V。利用ALD-Al2O3作为高介电常数绝缘层的修饰层既保有Al2O3低漏电、好界面的优点,又提高了介电常数。3.态密度的导出和稳定性的关联:TFT的不稳定性不仅和有源层/绝缘层界面的缺陷有关(如正偏压stress),还和有源层半导体中的带内能级有关,特别是在光照和热激发下的偏压stress下,都表现出阈值电压的漂移。研究有源层半导体的带内能级态密度Subgap density of states(DOS)是TFT稳定性研究的重要课题。本文采用Temperature Stress方法,通过提高温度热激电子、研究激活能随栅极电压变化的速度,来确定态密度DOS,进而解释影响器件稳定性的内在机理。本文制备的器件是在150 nm ALD-Al2O3上制备的IZO-TFT,器件的阈值电压为-0.46 V,迁移率高达17.9 cm2/Vs,开关比108,亚阈值摆幅为0.13 V/dec。通过Temperature Stress实验和计算,得到器件的最大激活能为0.96 e V,激活能的变化率为1.39 e V(V)-1,器件的态密度在1017到1015e V-1 cm-3量级,小于目前报道的1018 to 1016e V-1 cm-3,,器件稳定性良好。还研究了不同有源层厚度对于器件态密度和稳定性的影响,研究表明稳定性好的器件态密度低。同样也研究了不同有源层溅射功率密度下的态密度和稳定性,同样得到稳定性和态密度的关联性。4.双有源层的应用:有源层是TFT器件的又一个重要组成部分。最为当前广泛应用的有源材料,IZO和IGZO各有千秋。IZO具有高载流子浓度,IGZO有高稳定性,当我们用IZO和IGZO双层复合结构作为有源层,不仅表现出类似IGZO-TFT的稳定性,还表现出类似IZO-TFT的高迁移率,采用该结构制备的TFT有理想的阈值电压0.8 V,高的迁移率14.4 cm2/Vs,亚阈值摆幅仅仅为0.13V/dec,并且器件的态密度小于单纯的用IGZO或者IZO作为有源层的TFT,稳定性良好。
[Abstract]:Thin film transistor (TFT) is an active matrix organic light emitting diode (OLED) driver circuit is the core component of.OLED current driven devices, low mobility of the amorphous silicon TFT tradition, it is difficult to meet the need of OLED driver, and polysilicon TFT high preparation cost, the presence of grain boundaries, poor uniformity limits its competitiveness in the on the market development in recent years. The oxide TFT has high transfer rate, visible light transparency, simple preparation process, low cost, become the most promising TFT technology. In this paper, the nature of the preparation, electrical stability of the oxide of TFT, to do the research, the main research content and innovation points are as follows: 1. insulation materials and methods growth layer Al2O3 and atomic layer deposition (ALD). The application of the insulation layer is an important part of the TFT device, insulation material and preparation process of selection is the key device of good or bad. This paper contrasts respectively. The low dielectric constant of Si O2 (=3.9) and high dielectric constant HfO2 (=25) TFT. The results indicate that the properties of the insulating layer with high dielectric constant material as insulation layer of device mobility has been significantly improved, with magnetron sputtering of silicon oxide insulating layer of the device for the migration rate is 2 cm2/ Vs, with hafnium oxide and silicon oxide composite insulation layer of the device transfer rate of 8.6 cm2/Vs. confirmed by comparing the high dielectric constant insulating layer can improve the mobility of the device, the driving voltage is reduced. However, it has large leakage, seriously affecting the performance of the device, this is because of high dielectric constant materials forming crystalline grain boundaries form a leakage channel, causing leakage of insulating material. The ideal was amorphous, and has a high dielectric constant. The metal oxide, meet this condition only Al2O3 (=9), so Al2O3 should be the preferred insulation material selected materials. Is the choice of preparation method. At first this paper studies the performance of magnetron sputtering device of alumina as insulating layer, found that the stability of the device is still unsatisfactory, the maximum interface state by thermal oxidation of silicon devices as the traditional insulating layer is 4.2 * 1011 cm-2, the maximum interface state and alumina as a device for insulating layer 3.4 x 1012 cm-2. we found that the larger alumina interface state is caused by the preparation method, magnetron sputtering, although widely adopted, but due to the sputtering process of particle energy is large, will cause the interface damage, affect device stability. So this paper adopts the technique of atomic layer deposition is more advanced (ALD), in order to give full play to the advantages of Al2O3. Using Al2O3 as insulating devices and sputtered Al2O3 layer as compared to insulation device using ALD system, the migration rate increased from 4.4 cm2/Vs to 5.2 cm2/Vs, the threshold voltage from 9.9 V Reduced to 4.3 V, the interface state is reduced from 3.4 cm-2 to 9.1 * 1012 * 1011 cm-2, the performance has improved. The research behind the devices fabricated on the stability of TFT based on ALD-Al2O3.2. devices with ALD-Al2O3 as the insulating layer: This paper studies the ALD growth conditions and insulation effect the layer thickness on the electrical properties and stability of IGZO-TFT. The device high mobility and stability by optimizing Al2O3 growth temperature and thickness of the dielectric constant. However, Al2O3 is not high enough, to enhance mobility is limited. We use high dielectric constant Zr O2 (E = 25), and as the buffer layer was modified the use of ALD-Al2O3 Zr O2, not only the leakage is reduced by two orders of magnitude, the migration rate increased from 9.8 cm2/Vs to 14 cm2/Vs, the switching ratio from 4 * 105 to 3.5 * 106, the maximum interface state decreases from 1012 cm-2 to 4.3 * 2.5 * 1012 cm-2 devices Stability has been greatly improved, after 2 hours of aging bias, drift of threshold voltage reduced from 1.6 V to 0.79 V. using ALD-Al2O3 as a high dielectric constant insulating layer not only has modified Al2O3 low leakage, has the advantages of good interface, but also improves the stability and correlation derived dielectric constant.3. density of states TFT: the instability of the active layer and the insulating layer not only / interface defects (such as stress, but also positive bias) and the active layer in a semiconductor with energy levels, especially stress bias in the light and thermal excitation, have shown a drift pressure threshold electric active layer with semiconductor research. Energy level density of States of Subgap (DOS) density of States is an important subject of TFT stability. This paper uses the Temperature Stress method, by raising the temperature of hot electron, on activation energy changed with the speed of the gate voltage, to determine the density of states DO S, and then explain the influence mechanism of the stability of the device. This device is prepared in 150 nm ALD-Al2O3 on the preparation of IZO-TFT, the threshold voltage of the device is -0.46 V, the migration rate as high as 17.9 cm2/Vs, switch 108, sub threshold swing is 0.13 V/dec. through the Temperature Stress experiment and calculation, get the maximum activation energy 0.96 e V devices, the activation energy of the rate of change was 1.39 e V (V) -1, the density of states of the device in 1017 to 1015e V-1 cm-3 magnitude is less than 1018, reported to 1016e, V-1 cm-3, the device has good stability. We also research the influence of different thickness of the active layer on the device density and stability. The research show that the device has good stability and low density. Also study the different active layer sputtering power density under the state density and stability, also applied.4. correlation stability and density of double active layer: the active layer is TFT devices and An important part of the active material. The most widely used IGZO, IZO and.IZO with high carrier concentration, each one has its own merits, IGZO has high stability, when we use the IZO and IGZO double layer composite structure as the active layer, not only showed stability similar to IGZO-TFT, IZO-TFT also showed a similar high mobility, adopting the structure the preparation of TFT is an ideal threshold voltage of 0.8 V, the high mobility of 14.4 cm2/Vs, the sub threshold swing is only 0.13V/dec, the density of States and the device is less than pure IGZO or IZO as the active layer of TFT, the stability is good.

【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TN321.5
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本文编号：1604977