以有機金屬化學氣相沈積製備的二氧化鈦薄膜之電阻轉換特性研究

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研究生：	張櫻靖 Ying-Ching Chang
論文名稱：	以有機金屬化學氣相沈積製備的二氧化鈦薄膜之電阻轉換特性研究 Resistance switching characteristics of TiO2 films deposited by MOCVD
指導教授：	吳泰伯 Tai-Bor Wu
口試委員:
學位類別：	碩士 Master
系所名稱：	工學院 - 材料科學工程學系 Materials Science and Engineering
論文出版年：	2007
畢業學年度：	95
語文別：	英文
論文頁數：	66
中文關鍵詞：	二氧化鈦、金屬化學氣相沈積、電阻、轉換、氧氣、燈絲
外文關鍵詞：	TiO2, MOCVD, resistance, switching, oxygen, filament
相關次數：	點閱：3 下載：0
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在白金底電極以金屬化學氣相沈積(MOCVD)製備的二氧化鈦薄膜呈現出良好的電阻轉換特性，因此可應用於非揮發性記憶體(NVM)的研究。此金屬-絕緣體-金屬(MIM)結構的上下電極皆使用白金，形成對稱電極。接著將薄膜以氮、氧氣氛作熱處理(rapid thermal Annealing,RTA)，以研究其二氧化鈦薄膜的結構及成分對電性影響。另外，由於白金具有較佳的捕捉氧能力，有助於此電阻轉換機制的討論，因此在二氧化鈦薄膜中鍍製白金氧薄層，期望藉由高溫退火後，檢視其還原成的白金粒子對電性的影響。由電性量測的結果，高低阻態的穩定性與結晶性及氧化膜的計量比、氧化程度極相關。此結果也能輔助說明此過渡金屬氧化物(trasition metal oxides)的電阻轉換機制，當薄膜內含有一定程度的氧空缺和較純相的結晶，將具有穩定的電阻轉換表現。

Abstract
The TiO2 films for non-volatile memory applications were prepared on Pt bottom electrode by metal-organic chemical vapor deposition (MOCVD) method. The Pt top and bottom electrodes were made in symmetric metal-insulator-metal (MIM) structure. In order to investigate the relationships between TiO2 film structures and resistance switching behaviors, various temperatures of rapid thermal annealing under O2 and N2 atmosphere were performed. Additionally, according to the good characteristic of oxygen capture of Pt, the TiO2 films embedded with PtO thin layer was performed. The stability of high-resistance state (HRS) and low-resistance state (LRS) was dependent on the crystallinity and film composition of the TiO2 films. The results suggest that the electrical - induced resistance switching was dependent on the crystalline phases and oxygen vacancies in the TiO2 films, which affect the formation of filamentary path previously reported in binary transition metal oxide thin films exhibiting resistance switching characteristics.

Contents
Abstract    I
Contents    II
List of tables    V
List of figures    VI
Chapter 1. Introduction    1
Chapter 2. Literature review    3
2-1 Emerging non-volatile memories    3
2-1-1 FeRAM    3
2-1-2 MRAM    4
2-1-3 PCRAM    5
2-1-4 RRAM    5
2-1-5 Polymer memory    6
2-2 Mechanism of transition metal oxide (TMO) RRAM    6
2-2-1 Filamentary model    7
2-2-2 Schottky barrier and space-charged limited conduction (SCLC)    7
Chapter 3. Experimental procedures    13
3-1 M-I-M variable resistor fabrication    13
3-1-1 Process flow    13
3-1-2 Substrate preparation    14
3-1-3 TiO2 film deposition in MOCVD    14
3-1-4 TiO2 film embedded with PtO thin layer    15
3-1-5 Thermal treatments    15
3-1-6 Top electrode deposition    15
3-2 Property analysis    16
3-2-1 Film thickness and Ti valence states    16
3-2-2 Crystalline structure    16
3-3 Electrical characterization    17
Chapter 4. Results and discussion    20
4-1 Preliminary study of TiO2 films deposited by MOCVD    20
4-2 Characterization of as-deposited TiO2 films    21
4-2-1 Film thickness and composition    21
4-2-2 Crystalline structure    21
4-2-3 Electrical property    22
4-3 Effects of RTN treatment    22
4-3-1 Film thickness and composition    22
4-3-2 Crystalline structure    24
4-3-3 Electrical property    24
4-4 Effects of RTO treatment    25
4-4-1 Film thickness and composition    25
4-4-2 Crystalline structure    26
4-4-3 Electrical property    27
4-5 Effects of embedded PtO thin layer    29
4-5-1 Formation of Pt nanocrystals    29
4-5-2 Crystalline structure    29
4-5-3 Electrical property    29
Chapter 5. Conclusion    61
Chapter 6. Reference    63

List of tables
Table 3- 1 – Summary of deposition parameters.    18
Table 3- 2 -MOCVD temperature calibration.    18
Table 3- 3 – Summary of PtO deposition parameters.    19

Table 4- 1 - XPS Spectrum, Atomic Concentration Table.    31

List of figures
Fig. 2- 1 P-E characteristic curve.    9
Fig. 2- 2 Core storage is why the internal workspace of the computer is called "memory." Like magnetic disks, magnetic cores hold their content without power.    9
Fig. 2- 3 Change in magnetic polarity sensed as resistance change.    10
Fig. 2- 4 Electrical energy (heat) converts the material between crystalline    10
Fig. 2- 5 RRAM cross sectional structure.    11
Fig. 2- 6 Typical resistive switching I-V curves.    11
Fig. 2- 7 Change in resistance due to ionic transport with applied electric field.    12

Fig. 4- 1 I-V curves of the Ar/ O2：1/1 sample in voltage sweeping (0→+V) mode.    32
Fig. 4- 2 I-V curves of the Ar/ O2：2/3 sample in voltage sweeping (0→+V) mode.    32
Fig. 4- 3 I-V curves of the Ar/ O2：3/2 sample in voltage sweeping (0→+V) mode.    33
Fig. 4- 4 I-V curves of the sample in oxygen-free atmosphere in voltage sweeping (0→+V) mode.    33
Fig. 4- 5 I-V curves of the sample in oxygen-free atmosphere in voltage sweeping (0→+V) mode.    34
Fig. 4- 6 I-V curves of the sample in oxygen-free atmosphere in voltage sweeping (0→+V) mode.    34
Fig. 4- 7 I-V curves of the sample in oxygen-free atmosphere in voltage sweeping (0→+V) mode.    35
Fig. 4- 8 SEM cross sectional structure of as-deposited TiO2 films.    35
Fig. 4- 9 SEM plane view of as-deposited TiO2 films.    36
Fig. 4- 10 XPS spectra of the Ti2p region of as-deposited TiO2 films.    36
Fig. 4- 11 X-ray diffraction patterns of as-deposited TiO2 films.    37
Fig. 4- 12 Typical I-V curves of the as-deposited TiO2 films in voltage sweeping (0→+V) mode.    37
Fig. 4- 13 Dispersion in the set and reset voltage.    38
Fig. 4- 14 Resistance switching behavior of de-posited samples at room temperature against the cycling times.    38
Fig. 4- 15 Cross-sectional SEM of TiO2 after RTN 400℃, 30s.    39
Fig. 4- 16 Cross-sectional SEM of TiO2 after RTN 500℃, 30s.    39
Fig. 4- 17 Cross-sectional SEM of TiO2 after RTN 600℃, 30s.    40
Fig. 4- 18 Plane view of SEM after RTN400℃, 30s.    40
Fig. 4- 19 Plane view of SEM after RTN500℃, 30s.    41
Fig. 4- 20 Plane view of SEM after RTN500℃, 30s.    41
Fig. 4- 21 TEM cross sectional Pt/ Ti substrate of (a) RTN600℃, 30s (b) As-deposited.    42
Fig. 4- 22 XPS spectra of the Ti2p region of the TiO2 films after RTN500℃, 30s.    42
Fig. 4- 23 X-ray diffraction patterns of TiO2 films after RTN400℃, 500℃, 600℃, 30s, respectively, and compared with the pattern of the as-deposited sample.    43
Fig. 4- 24 I-V curves of the TiO2 films after RTN400℃,30s.    43
Fig. 4- 25 I-V curves (early stage) of the TiO2 films after RTN500℃,30s    44
Fig. 4- 26 I-V curves (late stage) of the TiO2 films after RTN500℃,30s.    44
Fig. 4- 27 I-V curves of the TiO2 films after RTN600℃,30s.    45
Fig. 4- 28 Dispersion in the set and reset voltage of RTN500℃, 30s.    45
Fig. 4- 29 Overlap number of Vset and Vreset values of samples under RTN500, 30s.    46
Fig. 4- 30 Dispersion in the set and reset voltage of RTN400℃, 30s.    46
Fig. 4- 31 Resistance switching behavior of TiO2 films after RTN500℃, 30s against cycling times at room temperature.    47
Fig. 4- 32 Resistance switching behavior of TiO2 films after RTN400℃, 30s against cycling times at room temperature.    47
Fig. 4- 33 Cross-sectional SEM of TiO2 after RTO 400℃, 3min.    48
Fig. 4- 34 Cross-sectional SEM of TiO2 after RTO 500℃, 3min.    48
Fig. 4- 35 Cross-sectional SEM of TiO2 after RTO 600℃, 3min.    49
Fig. 4- 36 XPS spectra of the Ti2p region of RTO400℃ TiO2 films.    49
Fig. 4- 37 XPS spectra of the Ti2p region of RTO500℃ TiO2 films.    50
Fig. 4- 38 XPS spectra of the Ti2p region of RTO600℃ TiO2 films.    50
Fig. 4- 39 X-ray diffraction patterns of TiO2 films after RTO400℃, 500℃, 600℃, 3min, respectively, and compared with the pattern of the as-deposited sample.    51
Fig. 4- 40 I-V curves of the TiO2 films after RTO400℃,3min, in voltage sweeping (0→+V) mode.    51
Fig. 4- 41 I-V curves of the TiO2 films after RTO500℃,3min, in voltage sweeping (0→+V) mode.    52
Fig. 4- 42 I-V curves of the TiO2 films after RTO600℃, 3min, in voltage sweeping (0→+V) mode.    52
Fig. 4- 43 Resistance switching behavior of TiO2 films after RTO600℃, 3min against cycling times measured at room temperature.    53
Fig. 4- 44 Dispersion in the set and reset voltage of RTO600℃, 3min.    53
Fig. 4- 45 Resistance switching behavior of TiO2 films after RTO500℃, 3min against cycling times measured at room temperature.    54
Fig. 4- 46 Dispersion in the set and reset voltage of RTO500℃, 3min.    54
Fig. 4- 47 Resistance switching behavior of TiO2 films after RTO400℃, 3min against cycling times measured at room temperature.    55
Fig. 4- 48 Dispersion in the set and reset voltage of RTO400℃, 3min.    55
Fig. 4- 49 Resistance comparison between RTO400℃, 500℃ and 600℃, 3 min, respectively.    56
Fig. 4- 50 Cross-sectional TEM structure of TiO2 films embedded with PtO ultra thin layer after MOCVD in-situ 425℃ annealing.    57
Fig. 4- 51 X-ray diffraction patterns of TiO2 films embedded PtO thin layer compared with the pattern of the as-deposited sample.    58
Fig. 4- 52 I-V curves (early stage) of the TiO2 films embedded with PtO thin layer, in voltage sweeping (0→+V) mode.    58
Fig. 4- 53 I-V curves (late stage) of the TiO2 films embedded with PtO thin layer, in voltage sweeping (0→+V) mode.    59
Fig. 4- 54 Resistance switching behavior of Pt-nanocrystals embedded TiO2 film against cycling times measured at room temperature.    59
Fig. 4- 55 Dispersion in the set and reset voltage of MOCVD in-situ annealing.    60

                                

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