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Title Page

Abstract

Contents

Chapter 1. Introduction 12

1.1. Background and Motivation 12

1.2. Organization of the dissertation. 14

References 15

Chapter 2. Time-domain current measurement 17

2.1. Introduction 17

2.2. Measurement scheme 17

2.3. Pulse measurement verification 22

References 31

Chapter 3. Radio frequency electrical pulse characterization of defect states in a GaAs/AlGaAs narrow channel field effect transistor 32

3.1. Introduction 32

3.2. Device fabrication and measurement setup 34

3.3. Pulse measurement data 36

3.4. Analysis and modeling 41

3.5. Conclusions 54

References 55

Chapter 4. Probing continuous radio frequency spectrum of water relaxation using carbon nanotube 61

4.1. Introduction 61

4.2. Device fabrication and measured data 62

4.3. Modeling and analysis 67

4.4. Conclusions 72

References 73

Chapter 5. Conclusions 75

국문 요약 77

List of tables

Table 2.1. Exponential fitting result of 1 MΩ, 10 MΩ resistance and substrate 27

Table 3.1. Summary of the time variation of various charges of the device 44

Table 3.2. Fitting parameters obtained from Eq. (2) 49

Table 3.3. Fitting parameters obtained from Eq. (3) 49

Table 4.1. Fitting results in air 68

Table 4.2. Fitting results in vacuum 68

Table 4.3. Fitting result of the second device in air 72

Table 4.4. Fitting result of the second device in vacuum 72

List of figures

Figure 2.1. The schematic of time-domain current detection system. The methods of time-domain current detection consist of real-time current measurement and time averaged current measurement 18

Figure 2.2. Labview program for time-domain current measurement. This program can control all of condition which include pulse frequency, pulse amplitude, DC bias and measurement methods. 19

Figure 2.3. MW substrate which is designed to enable high-frequency transmission 20

Figure 2.4. PCB mount was designed by using CPW structure. The device was connected to equipment by using PCB mount. The pads of device were wire-boned on CPW signal line in PCB mount. 21

Figure 2.5. Measured S-parameter (S₂₁) of CPW gate in substrate with PCB and RF cable 22

Figure 2.6. The real-time drain current of substrate when a series of pulse was applied on gate of the substrate with zero DC bias 23

Figure 2.7. The real-time current measurement system for verifying the current amplifier with various resistances 24

Figure 2.8. The real-time current when resistances are 50Ω and 100Ω at f＝5 KHz, VPP＝1V(이미지참조) 24

Figure 2.9. The real-time current of 1 MΩ resistance at various sensitivities and pulse amplitudes 25

Figure 2.10. (a) the real-time current and exponential fitting of 1 MΩ, 10 MΩ resistance and substrate at 105 sensitivity(이미지참조) 26

Figure 2.10. (b) the real-time current and exponential fitting of 1 MΩ, 10 MΩ resistance and substrate at 106 sensitivity(이미지참조) 27

Figure 2.11. Q3D simulation model for calculating the capacitance in substrate 28

Figure 2.12. The real-time current measurement method by subtracting the current when drain bias zero from the current with drain bias 28

Figure 2.13. Schematic of the time-averaged drain current measurement 29

Figure 2.14. The time-averaged current and integral current of same MOSFET 31

Figure 3.1. SEM image of the fabricated NCFET, schematic of the RF pulse measurement setup, and schematic of the RF fixture. The bandwidth of this RF fixture is〉 5 GHz which is higher than the highest pulse frequency of 3 GHz.... 34

Figure 3.2. (a) IDS-VGS characteristics at several VDS values. The inset shows gm.(이미지참조) 36

Figure 3.2. (b) IDS* measured as a function of f at VPP＝0.5 to 3 V in 0.5 V steps (solid lines). The symbols denote IDS* calculated from the real-time IDS (shown in figure 3.3). The symbols are in good agreement with the solid lines....(이미지참조) 37

Figure 3.3. Real time current IDS(t) measured at various pulse frequencies when VDS＝2V, VPP＝2V. The waveforms are strongly changing as a function of f.(이미지참조) 40

Figure 3.4. Schematic band diagrams of the IPG and the channel at (a) various steady states, (b) pulse low, and (c) pulse high. Four different trap dynamics (τDS (decay of the surface trap), τFS (filling of the surface trap), τDB (decay of the bulk trap), and τFB (filling...(이미지참조) 42

Figure 3.5. (a) Calculated IDS* using Eq. (1)-(3). (b) Calculated dIDS*/d(logf). They show quantitative agreement with the measured results.(이미지참조) 48

Figure 3.6. (a) IDS* measured as a function of VGS, at f＝1 kHz, (b) IDS* measured as a function of VGS, at f＝10 kHz(이미지참조) 52

Figure 3.6. (c) IDS* measured as a function of VGS, at f＝1 GHz. (d) Ideal IDS* calculated from DC current (when VDS＝2 V). The traces at 1 kHz are in agreement with the ideal IDS*....(이미지참조) 53

Figure 4.1. (a) IDS-VGS characteristics obtained from our CNT FET (shown in the inset) in air (solid lines) and in vacuum (dotted lines). VDS was fixed at 1, 3 and 5 V. (b) Schematic of the CPW, on top of which a single-walled CNT bundle bridges Au electrodes. (c)...(이미지참조) 63

Figure 4.2. Typical IDS (t) (a) in air and (b) in vacuum. (c) dIDS*/d(logT) in air and vacuum taken at Vpp＝1, 2, 3, 4, 5, and 6 V. Each inset show the magnified data at high frequency (small T) region....(이미지참조) 65

Figure 4.3. (a) Calculated dIDS*/d(logT). Schematics of water molecule polarization for (b) positive switching and (c) negative switching.(이미지참조) 67

Figure 4.4. dIDS*/d(logT) vs. T measured from the second device. 70

Figure 4.5. Calculated dIDS*/d(logT) vs. T to fit the measured data of the second device 71

초록보기

본 논문은 나노 소자의 전류 변화를 시간영역에서 측정하는 방법과 이를 이용한 실험 결과에 대하여 설명하고 있다. 시간영역에서 전류 변화를 확인하기 위해서는, 신호의 손실을 최대한 줄이고 신호의 왜곡 없이 증폭하는 작업이 매우 중요하다. 50Ω impedance matching을 위해 substrate와 PCB 마운트에 coplanar wave guide(CPW) 구조가 적용되었다.

시간영역에서 나노 소자의 전류 측정방법은 오실로스코프를 이용한 실시간 전류 측정과 Loss pass 필터를 통과한 DC성분을 측정하는 평균 전류 측정법으로 나뉜다. 두 측정법을 검증하기 위해 저항과 MOSFET를 이용한 실험을 진행하였으며, 이를 통해 측정법을 검증하고, 시간영역 전류 측정의 핵심 역할을 하는 current amplifier의 특징을 확인할 수 있었다.

우선, GaAs/AlGaAs 기반의 in-plane gate 전계효과 트랜지스터를 이용하여 시간영역에서의 전류 측정을 수행하였다. 소자의 게이트에 연속된 pulse를 DC bias와 함께 인가한 후 평균전류 측정법을 이용하여 3GHz까지 drain 전류를 측정하였다. 주파수가 증가함에 따라 전류의 변곡점이 나타남을 확인 할 수 있었다. Trap dynamics에 기반한 분석과 모델링을 이용하여 소자의 surface trap 및 bulk deep level 과 관련된 특성 주파수를 확인 할 수 있었고, 소자가 pulse 변화에 응답 할 수 있는 intrinsic response 주파수 등을 구할 수 있었다.

같은 측정법을 카본나노튜브 소자에 적용하여 카본나노튜브의 표면에 흡착된 물 분자의 변화를 감지할 수 있는 방법을 도출하였다. CPW 구조가 적용된 substrate를 이용하여 카본나노튜브 전계효과 트랜지스터를 제작하였고, 소자의 게이트에 pulse를 인가해 준 후, 그에 따른 드레인 전류의 변화를 공기중과 진공에서 측정하였다. 인가된 Pulse에 따라 변화하는 물 분자의 relaxation dynamics를 이용한 데이터의 분석 및 모델링을 통하여 물 분자의 relaxation processes 와 관련된 characteristic time 등을 확인할 수 있었다.

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