臺灣博碩士論文加值系統

摘要
近年來鐵電記憶體元件在下世代的高度整合性電路中引起很大的注意。其中，隨機存取記憶體(DRAM)中所使用高介電常數的薄膜是廣大的研究與發展。但無論如何，DRAM是揮發性記憶體而且非揮發性記憶體是值得被發展的。有主要兩種非揮發性鐵電記憶體：用鐵電蓄電電容器及金屬-鐵電-（絕緣層）-半導體的場效電晶體（MFISFET）。尤其是，從記憶體在非壞性的讀取方式看來，後者為較好的記憶體元件。然而，有許多朝此方向進行的阻礙的挑戰，此種型式的記憶體有一個不好的介面和矽基板之間，並且保存時間也不長。為了克服這些問題，必須在鐵電薄膜和矽基板之間的阻擋層。
有好的閘極結構的鐵電材料結構Pt/SrBi2Ta2O9/Si3N4/p-Si (100)的MFIS記憶體的電性是被研究。245nm厚的SBT薄膜被旋塗在Si3N4/p-Si (100)的基底接著一分鐘的熱退火分別在溫度700∼800℃。試著再低的工作電壓有著大的記憶視窗，備用在不同超薄的Si3N4緩衝層分別為3.5nm，2nm及0.9nm厚。Si3N4緩衝層是用低壓化學氣相沈積方式除了0.9nm氮化物SixNy薄膜外。從C-V測量的結果0.9nm氮化物SixNy薄膜在退火溫度為750℃、偏壓為5V的情形下記憶視窗大約為0.8V。完整的perovskite結晶構造可以被x-ray繞射量測認定。在持久力上扮演重要的角色的漏電流是比2.5 x 10-8 A/cm2 at 200kV/cm SBT用在Pt/SBT (245nm)/ Si3N4 (0.9nm)/p-Si (100)上。其可以達成寫入1010次及超過2小時的持久時間。SBT薄膜可被相信用在進行低電壓的運作、高密度及可能的1T的非揮發性鐵電隨機存取記憶體。

Abstract
In recent years ferroelectric memory devices have attracted much attention from the viewpoint of the next generation of highly integrated circuits. Research and development in dynamic random access memory (DRAM) using high dielectric constant films are extensive. However, DRAM is volatile memory, and it is desirable that nonvolatile memory should be developed. There are mainly two kinds of ferroelectric nonvolatile memories: a memory cell using a ferroelectric storage capacitor, and metal-ferroelectric-(insulator)-semiconductor FET (MFISFET). Especially, the latter is superior among memory devices since the memory is read out nondestructively. In practice, however, there are many challenges which have held back the progress in that direction, a major one being the difficulty of making an electrically switchable ferroelectric thin film on Si with good interface properties and long retention time. To overcome these problems, buffer layers are usually inserted between the ferroelectric layer and silicon substrate.
The electrical properties of the MFIS memories with stacked gate configuration of ferroelectric Pt/SrBi2Ta2O9/Si3N4/p-Si (100) were investigated. 245nm-thick SBT thin films were spin-coated on the Si3N4/Si substrate followed by 1 min. rapid thermal crystallization annealing at the temperatures regime of 700~800℃. In an attempt to operate memory at low voltage with sufficient large memory window, various ultra thin Si3N4 buffer layers in thickness of 3.5, 2, and 0.9nm were employed. The Si3N4 buffer layers were deposited by means of LPCVD with the exception of surface nitridation for 0.9nm SixNy thin film. From the results of C-V measurements, the memory window can be as large as 0.8V at the bias amplitude of 5 V for the sample with 0.9 nm SixNy buffer layer and 750℃ annealing temperature. Complete perovskite crystalline structure can also be affirmed by the spectra of X-ray diffraction measurements. The leakage current, which plays a very important role in the data retention, of Pt/SBT (245nm)/ Si3N4 (0.9nm)/p-Si (100) is as low as 2.5 x 10-8 A/cm2 at 200kV/cm. The 1010 write cycles and greater than 2hr retention time can be achieved. Optimization and scaling of SBT thin films are believed to be effective in pursuing extremely low voltage operation, high-density and liable 1T nonvolatile ferroelectric random access memories.

CONTENTS
ABSTRACT (in Chinese)i
ABSTRACT (in English)iii
ACKNOWLEDGEMENTv
CONTENTSvi
TABLE CAPTIONSviii
FIGURE CAPTIONSix
Chapter 1
Introduction1
1-1General Background1
1-2Motivation3
1-3Thesis Organization4
Chapter 2
Characteristics of ferroelectrics5
2-1Ferroelectricity5
2-1.1 Ferroelectric hysteresis loop6
2-1.2 Dielectric and ferroelectric theory8
2-2Ferroelectric memory9
2-2.1 Type of ferroelectric memory9
2-2.2 Operation mechanism11
2-2.3 Scaling Rule of Ferroelectric Memories12
2-3Reliability13
2-3.1 Fatigue14
2-3.2 Retention15
2-3.3 Imprint16
2-3.4 Leakage current17
Chapter 3
Experimental details19
3-1 Experimental proces19
3-2 Physical Characterization Techniques20
3-2.1 X-Ray Diffraction Analysis (XRD)20
3-2.2 Atomic force microscopy (AFM)21
3-2.3 Scanning Electron Microscopy(SEM) 21
3-3 Electrical Characterization Techniques21
3-3.1 Current-voltage (I-V) measurements21
3-3.2 Capacitance-voltage (C-V) measurements21
3-3.3 Fatigue Meausrements22
Chapter 4
Results and discussion23
4-1Effect of substrate temperature on properties of SBTN films23
4-2The MFIS Structure23
4-3Reliability studies of SBT films27
4-3.1 Retention Characteristics27
4-3.2 Fatigue Characteristics28
Chapter 5
Conclusions29

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