本文選題：氧化物TFT　切入點(diǎn)：原子層沉積技術(shù)　出處：《上海大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：薄膜晶體管(TFT)是有源矩陣有機(jī)發(fā)光二極管(OLED)驅(qū)動電路的核心元件。OLED是電流驅(qū)動型器件,傳統(tǒng)的非晶硅TFT遷移率低,難以滿足OLED驅(qū)動的需要,而多晶硅TFT制備成本高、存在晶界、均勻性差等缺點(diǎn)限制了其在市場上的競爭力。近年發(fā)展的氧化物TFT具有遷移率高、可見光區(qū)透明、制備工藝簡單、成本低等優(yōu)點(diǎn),成為最有發(fā)展?jié)摿Φ腡FT技術(shù)。本文就氧化物TFT的制備、電學(xué)性質(zhì)、穩(wěn)定性做了研究,主要的研究內(nèi)容和創(chuàng)新點(diǎn)如下:1.絕緣層材料和生長方法的選擇——Al2O3和原子層沉積技術(shù)(ALD)的應(yīng)用。絕緣層是TFT器件的重要組成部分,絕緣材料及制備工藝的選擇是器件好壞的關(guān)鍵。本文對比了分別以低介電常數(shù)Si O2(ε=3.9)和高介電常數(shù)HfO2(ε=25)為絕緣層的TFT特性。研究表明采用高介電常數(shù)材料作為絕緣層的器件遷移率有了明顯的提高,以磁控濺射氧化硅為絕緣層的器件的遷移率為2 cm2/Vs,以氧化鉿與氧化硅為復(fù)合絕緣層的器件的遷移率為8.6 cm2/Vs。通過對比證實(shí)高介電常數(shù)絕緣層能夠提高器件的遷移率,降低驅(qū)動電壓。然而它有較大的漏電,嚴(yán)重影響器件性能,這是因?yàn)楦呓殡姵?shù)材料多形成多晶態(tài),晶粒間界形成漏電通道,造成漏電。理想的絕緣材料應(yīng)呈非晶態(tài),且具有較高介電常數(shù)。在金屬氧化物中,滿足此條件的只有Al2O3(ε=9),因此Al2O3應(yīng)成為絕緣材料的首選。選定了材料后就是選擇制備方法。首先本文研究了磁控濺射氧化鋁作為絕緣層的器件的性能,發(fā)現(xiàn)器件的穩(wěn)定性還是不盡如意,采用傳統(tǒng)的熱氧化硅作為絕緣層的器件的最大界面態(tài)為4.2×1011 cm-2,而采用氧化鋁作為絕緣層的器件的最大界面態(tài)為3.4×1012 cm-2。本文發(fā)現(xiàn)氧化鋁的界面態(tài)較大是由制備方法造成的,磁控濺射雖然被廣泛采用,但是由于濺射過程粒子能量較大,會造成界面的損傷,影響器件的穩(wěn)定。于是本文又采用更加先進(jìn)的原子層沉積技術(shù)(ALD),以充分發(fā)揮Al2O3的優(yōu)勢。采用ALD制備Al2O3作為絕緣層的器件與濺射Al2O3作為絕緣層的器件相比,遷移率從4.4 cm2/Vs增加到了5.2 cm2/Vs,閾值電壓從9.9 V降低到4.3 V,界面態(tài)從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備的器件都是以ALD-Al2O3為基的器件。2.以ALD-Al2O3為絕緣層的TFT穩(wěn)定性的研究:本文研究了ALD生長條件及絕緣層厚度對IGZO-TFT電學(xué)性能及穩(wěn)定性的影響。通過優(yōu)化Al2O3的生長溫度及厚度得到較高遷移率和穩(wěn)定性的器件。然而由于Al2O3的介電常數(shù)不夠高,提升遷移率受到限制。我們使用高介電常數(shù)的Zr O2(ε=25),并使用ALD-Al2O3作為緩沖層進(jìn)行修飾,不僅將Zr O2的漏電減少了兩個數(shù)量級,還使遷移率從9.8 cm2/Vs上升到14 cm2/Vs,開關(guān)比從4×105提高到了3.5×106,最大界面態(tài)從4.3×1012 cm-2減小到了2.5×1012 cm-2,器件的穩(wěn)定性得到了顯著的提高,經(jīng)過2個小時的偏壓的老化,閾值電壓漂移從1.6 V降低到0.79 V。利用ALD-Al2O3作為高介電常數(shù)絕緣層的修飾層既保有Al2O3低漏電、好界面的優(yōu)點(diǎn),又提高了介電常數(shù)。3.態(tài)密度的導(dǎo)出和穩(wěn)定性的關(guān)聯(lián):TFT的不穩(wěn)定性不僅和有源層/絕緣層界面的缺陷有關(guān)(如正偏壓stress),還和有源層半導(dǎo)體中的帶內(nèi)能級有關(guān),特別是在光照和熱激發(fā)下的偏壓stress下,都表現(xiàn)出閾值電壓的漂移。研究有源層半導(dǎo)體的帶內(nèi)能級態(tài)密度Subgap density of states(DOS)是TFT穩(wěn)定性研究的重要課題。本文采用Temperature Stress方法,通過提高溫度熱激電子、研究激活能隨柵極電壓變化的速度,來確定態(tài)密度DOS,進(jìn)而解釋影響器件穩(wěn)定性的內(nèi)在機(jī)理。本文制備的器件是在150 nm ALD-Al2O3上制備的IZO-TFT,器件的閾值電壓為-0.46 V,遷移率高達(dá)17.9 cm2/Vs,開關(guān)比108,亞閾值擺幅為0.13 V/dec。通過Temperature Stress實(shí)驗(yàn)和計(jì)算,得到器件的最大激活能為0.96 e V,激活能的變化率為1.39 e V(V)-1,器件的態(tài)密度在1017到1015e V-1 cm-3量級,小于目前報(bào)道的1018 to 1016e V-1 cm-3,,器件穩(wěn)定性良好。還研究了不同有源層厚度對于器件態(tài)密度和穩(wěn)定性的影響,研究表明穩(wěn)定性好的器件態(tài)密度低。同樣也研究了不同有源層濺射功率密度下的態(tài)密度和穩(wěn)定性,同樣得到穩(wěn)定性和態(tài)密度的關(guān)聯(lián)性。4.雙有源層的應(yīng)用:有源層是TFT器件的又一個重要組成部分。最為當(dāng)前廣泛應(yīng)用的有源材料,IZO和IGZO各有千秋。IZO具有高載流子濃度,IGZO有高穩(wěn)定性,當(dāng)我們用IZO和IGZO雙層復(fù)合結(jié)構(gòu)作為有源層,不僅表現(xiàn)出類似IGZO-TFT的穩(wěn)定性,還表現(xiàn)出類似IZO-TFT的高遷移率,采用該結(jié)構(gòu)制備的TFT有理想的閾值電壓0.8 V,高的遷移率14.4 cm2/Vs,亞閾值擺幅僅僅為0.13V/dec,并且器件的態(tài)密度小于單純的用IGZO或者IZO作為有源層的TFT,穩(wěn)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.

【學(xué)位授予單位】：上海大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TN321.5
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本文編號：1604977