本論文以溶膠－凝膠法及快速熱處理技術製備鉭酸鋰[LiTaO3，簡稱LT]焦電薄膜以作為紅外線感測元件之應用；以旋鍍法將薄膜沈積於Pt/SiO2/Si(100)基板上，同時選擇1,3丙二醇為溶劑以減少達到薄膜所需厚度之披覆次數，並改變升溫速率(600~3000℃/min)及熱處理溫度(500~800℃)，探討不同製程參數對薄膜成長之影響，且藉由升溫速率的改變探討其對焦電紅外線感測元件響應的影響。
實驗結果顯示，薄膜中升溫速率的快慢直接影響到LT薄膜的晶粒大小、介電性、鐵電性及焦電性，隨升溫速率的增加，LT薄膜的晶粒會有變小而緻密的趨勢。在結晶特性方面，C軸排向隨著升溫速率的提高而有增強的趨勢。在電性方面，相對介電常數從28增加到45.6，介電損失從0.033增加到0.134，而矯頑電場從122 KV/cm上升到183 KV/cm，殘留極化量從7.45 mC/cm2上升到12.12 mC/cm2，焦電係數γ從9.33×10-9 C/cm2K上升到2.66×10-8 C/cm2K。另一方面，實驗結果也顯示在熱處理溫度為700℃，升溫速率為1800℃/min之LT薄膜具有最大之優值Fv及Fm，其分別為2.19×10-10 及4.01 ×10-9 Ccm/J；且隨著升溫速率的增加，將會使電壓響應在截波頻率為80 Hz時，由LT600的5496 V/W增加到LT1800的8455 V/W，比感測率在截波頻率為300 Hz時，由LT600的1.94×108 cmHz1/2/W增加到LT1800的2.38×108 cmHz1/2/W；然而當升溫速率再增加時，電壓響度和比感測率則有下降的趨勢，結果顯示兩者皆在升溫速率為1800℃/min時具有最大值，而與優值評估相符合；因此，本研究中以LT1800薄膜最適合紅外線感測元件之應用。

The lithium tantalite [LiTaO3,abbreviated to LT] thin films were deposited on Pt/SiO2/Si substrates by spin coating with sol-gel processing and rapid thermal processing in this thesis. 1,3 propanediol was used as solvent to minimize the number of cycles of spin coating and drying processes to obtain the desired thickness of thin film. By changing the heating rate (600~3000℃/min) and the heating temperature (500~800℃), the effects of various processing parameters on the thin films growth are studied. The effects of various heating rate on the response of pyroelectric IR detector devices are studied also.
Experimental results reveal that the heating rate will influence strongly on grain size, dielectricity, ferroelectricity and pyroelectricity of LT thin films. With the increase of heating rate, the grain size of LT thin film decreases slightly, and the C-axis orientation is enhanced. The relative dielectric constant of LT thin film increases from 28 up to 45.6, the tand increases from 0.033 to 0.134, Ec increases from 122 KV/cm to 183 KV/cm, Pr increases from 7.45 mC/cm2 to 12.12 mC/cm2, and g increases from 9.33´10-9 C/cm2K up to 2.66´10-8 C/cm2K, respectively, as the heating rate increases form 600 up to 3000℃/min. In addition, the results also show that the LT thin film possesses the largest figures of merit Fv (2.19×10-10 Ccm/J) and Fm (4.01×10-9 Ccm/J) at the heating temperature of 700℃ and heating rate of 1800℃/min. The voltage responsivities (Rv) measured at 80 Hz increase from 5496 to 8455 V/W and the specific detecivities (D*) measured at 300 Hz increase from 1.94×108 to 2.38×108 cmHz1/2/W with an increase of heating rate from 600 to 1800℃/min. However, the voltage responsivity and the specific detecivity decrease with heating rate in excess of 1800℃/min. The results show that LT1800 pyroelectric thin film detector exists both the maximums of voltage responsivity and specific detecivity. Therefore, LT1800 thin film exhibits the best IR characteristics for detector material.

Abstract I
Content V
Figures Caption VIII
Tables Caption XIII
Chapter 1 Introduction 1

Chapter 2 Theory 4
2.1 The structure of LiTaO3 4
2.2 Ferroelectricity 4
2.3 Sol-Gel processing 5
2.4 The choice of precursor 6
2.5 Fabrication of the film 6
2.6 Pyroelectric effect 7
2.7 Pyrolelctric response 8
2.8 Sputtering 13
2.9 DC glow discharge 14

Chapter 3 Experiments 16
3.1 Properties of precursors 16
3.2 Thin film deposition 17
3.2.1 Cleaning of the substrate 17
3.2.2 Deposition of the bottom electrode 17
3.2.3 Spin-coating 18
3.2.4 Thermal processing 18
3.2.4.1 Pyrolysis 18
3.2.4.2 Annealing 19
3.3 RTA furnace 19
3.3.1 Infrared gold image furnace 19
3.3.2 Comparison of the CTA and RTA 20
3.4 XRD analysis 20
3.5 SEM analysis 20
3.6 Thickness analysis 21
3.7 SIMS (Secondary Ion Mass Spectroscopy) 21
3.8 Electrical measurements 21
3.9 Fabrication of IR detectors 21

Chapter 4 Results and discussion 23
4.1 The analysis of the solution 23
4.1.1 The composition analysis of the solution 23
4.1.2 Differential thermal analysis (DTA) and Thermogravimetric analysis (TGA) 23
4.2 The thickness analysis of the film 24
4.3 Orientation analysis of the films 24
4.3.1 The effects of annealing temperature 24
4.3.2 The effects of heating rate 24
4.4 Surface morphology analysis 25
4.4.1 The effect of the annealing temperature 25
4.4.2 The effect of the heating rate 26
4.5 SIMS analysis 26
4.6 Dielectric constant 26
4.7 Dielectric loss 27
4.8 Current-Voltage measurement 28
4.9 P-E measurement 28
4.10 Pyroelectric coefficient measurement 28
4.11 The characteristics of the thin film detectors 29
4.11.1 Voltage responsivity (RV) and Current reponsivity (RI) 30
4.11.2 The noise voltages (Vn) 31
4.11.3 The noise equivalent power (NEP) and the specific detectivity (D*) 32
Chapter 5 Conclusion 33

References 35


Figures Caption

Fig.2-1 Stereoscopic view of the lithium tantalum crystal structure.. 42

Fig.2-2 Stereoscopic view of the bonding topography around tantalum . 43

Fig.2-3 Hysteresis loop of the ferroelectric materials. 44

Fig.2-4 The schematic diagram of the spin coating process. 45

Fig.2-5 Pyroelectric effect. 46

Fig.2-6 A pyroelectric detector element. 47

Fig.2-7 A common pyroelectric detecting system. 48

Fig.2-8 Variation in voltage responsitivity RV with frequency. 49

Fig.2-9 Voltage versus current characteristic for three types of self-sustained discharges(p= 2 to 30 Pa). 50

Fig.2-10 Features of a dc glow discharge system. 51

Fig.3-1 Preparation procedure for LiTaO3 films. 52

Fig.3-2 The schematic diagram of the DC magnetron sputtering system. 53

Fig.3-3 The schematic diagram of the infrared gold image furnace. 54

Fig.3-4 The metal foil mask. 55

Fig.3-5 The single IR detector. 56

Fig.4-1 TGA-DTA curves of the LiTaO3 solutions. 57

Fig.4-2 The SEM cross section morphology of LiTaO3 film. 58

Fig.4-3 XRD results as a function of annealing temperature for LiTaO3 films. 59

Fig.4-4 XRD results as a function of heating rate for LiTaO3 films. 60

Fig.4-5 The f factor as a function of heating rate for LiTaO3 films. 61

Fig.4-6 The SEM surface morphologies of LiTaO3 films annealed at: (a) 500℃; (b) 600℃; (c) 700℃; and (d) 800℃ with heating rate of 1800℃/min.(bar=0.25μm) 62

Fig.4-7 The SEM surface morphologies of LiTaO3 films annealed at 700℃ with different heating rate of: (a) 600℃/min; (b) 1200℃/min; (c) 1800℃/min; (d) 2400℃/min; and (e) 3000℃/min.(bar=0.25μm). 63

Fig.4-8 The SIMS analysis for LiTaO3 thin film. 64

Fig.4-9 Heating rate dependence of dielectric properties for the LiTaO3 thin films 65

Fig.4-10 Heating rate dependence of leakage current density for LiTaO3 thin films 66

Fig.4-11 The Sawyer-Tower circuit. 67

Fig.4-12 Ferroelectric hysteresis loops of LiTaO3 films with different heating rate of: (a) 600℃/min; (b) 1200℃/min; (c) 1800℃/min; (d) 2400℃/min; and (e) 3000℃/min. 68

Fig.4-13 Heating rate dependence of the coercive field (Ec) and remnant polarization (Pr) for LiTaO3 thin films. 69

Fig. 4-14 The schematic diagram of the pyroelectric current measurement 70

Fig.4-15 Heating rate dependence of pyroelectric coefficient for LiTaO3 thin films. 71

Fig.4-16 Dependence of the figure of merit Fv and Fm on heating rate. 72

Fig.4-17 The schematic diagram of the IR detector measurement system. 73

Fig.4-18 Frequency dependence of the voltage responsivity (RV) and current reponsivity (RI) of the LiTaO3 thin film IR detector with heating rate of 600℃/min. 74

Fig.4-19 Frequency dependence of the voltage responsivity (RV) and current reponsivity (RI) of the LiTaO3 thin film IR detector with heating rate of 1200℃/min. 75

Fig.4-20 Frequency dependence of the voltage responsivity (RV) and current reponsivity (RI) of the LiTaO3 thin film IR detector with heating rate of 1800℃/min. 76

Fig.4-21 Frequency dependence of the voltage responsivity (RV) and current reponsivity (RI) of the LiTaO3 thin film IR detector with heating rate of 2400℃/min. 77

Fig.4-22 Frequency dependence of the voltage responsivity (RV) and current reponsivity (RI) of the LiTaO3 thin film IR detector with heating rate of 3000℃/min. 78

Fig.4-23 Dependence of the maximum voltage reponsivity on heating rate at 80Hz. 79

Fig.4-24 Frequency dependence of the noise voltage per unit bandwidth for LiTaO3 thin film IR detectors. 80

Fig.4-25 Frequency dependence of the noise equivalent power and the specific detectivity of the LiTaO3 thin film IR detector with heating rate of 600℃/min. 81

Fig.4-26 Frequency dependence of the noise equivalent power and the specific detectivity of the LiTaO3 thin film IR detector with heating rate of 1200℃/min. 82

Fig.4-27 Frequency dependence of the noise equivalent power and the specific detectivity of the LiTaO3 thin film IR detector with heating rate of 1800℃/min. 83

Fig.4-28 Frequency dependence of the noise equivalent power and the specific detectivity of the LiTaO3 thin film IR detector with heating rate of 2400℃/min. 84

Fig.4-29 Frequency dependence of the noise equivalent power and the specific detectivity of the LiTaO3 thin film IR detector with heating rate of 3000℃/min. 85

Fig.4-30 Dependence of the maximum specific detectivity on heating rate at 300Hz. 86


Tables Caption

Table 1 The DC sputtering deposition conditions. 87

Table 2 The ratios of the XRD inensities of LiTaO3 films with various heating rate. 88

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