Title Page
ABSTRACT
Contents
Chapter 1. Introduction 20
1.1. Memory trends 20
1.1.1. Memory wall 20
1.1.2. In-memory processing 22
1.2. SCM technologies 23
1.2.1. Phase change memory 23
1.2.2. Magnetic memory 25
1.2.3. Ferroelectric memory 26
1.2.4. Resistive memory 27
1.3. Thesis content overview 31
1.3.1. Thesis objectives 31
1.3.2. Thesis outline 32
Chapter 2. Overview on conduction mechanisms 33
2.1. Electrode-limited conduction mechanisms 33
2.1.1. Schottky emission 34
2.1.2. Fowler-Nordheim (F-N) and direct tunneling 36
2.2. Bulk-limited conduction mechanisms 37
2.2.1. Poole-Frenkel (P-F) emission 37
2.2.2. Ohmic conduction 38
2.2.3. Space charge limited conduction (SCLC) 39
Chapter 3. LFN applications for RRAM analysis 42
3.1. Introduction to 1/f 42
3.2. LFN application (1): Resistive switching analysis 45
3.3. LFN application (2): Analysis of mechanisms in MLC operation 49
3.4. LFN application (3): Degradation analysis 54
Chapter 4. Analysis of conduction mechanism using LFN in RRAMs 58
4.1. Thermochemical mechanism RRAM (TCM RRAM) 58
4.1.1. Fabrication 58
4.1.2. Experimental results: RS and I-V characteristics 59
4.1.3. Experimental results: LFN characteristics 65
4.2. Valence change mechanism RRAM (VCM RRAM) 69
4.2.1. Fabrication 69
4.2.2. Experimental results: RS and I-V characteristics 71
4.2.3. Experimental results: LFN characteristics 74
4.3. Comparative analysis of conduction mechanism (VCM vs. EEM) 77
4.3.1. Fabrication 77
4.3.2. Experimental results: RS and I-V characteristics 80
4.3.3. Experimental results: LFN characteristics 82
Chapter 5. Random telegraph noise (RTN) in RRAM 86
5.1. Introduction to RTN 86
5.2. RTN in RRAM 88
5.2.1. Methodology for extracting trap information in RRAM 88
5.2.2. Experimental results 92
Chapter 6. Conclusions 97
Bibliography 99
초록 109
List of Publications 111
Fig. 1.1. Example of memory hierarchy in an ICT system. 22
Fig. 1.2. Schematic view of PCM cell and programing schemes of the cell. 24
Fig. 1.3. Schematic drawing of a typical magnetic tunnel junction memory element and corresponding memory states. 26
Fig. 1.4. Schematic structure of the MFIS FeFET and the P-E hysteresis curve. 27
Fig. 1.5. (a) Simple MIM structure and (b) basic operation of RRAM devices. 30
Fig. 2.1. Classification of conduction mechanisms in dielectric films.. 34
Fig. 2.2. Schematic energy band diagrams of (a) Schottky emission, (b) F-N tunneling, and (c) Direct tunneling. 35
Fig. 2.3. Schematic energy band diagrams of (a) P-F emission and (b) Ohmic conduction. 38
Fig. 2.4. A typical current density-voltage (I-V) characteristic of the SCLC mechanism. Vtr is the transition voltage. VTFL is the trap-filled limit voltag.[이미지참조] 41
Fig. 3.1. (a) Conduction mechanism and its corresponding 1/f noise model. (b) Bias dependence of the current noise spectral density according to 1/f noise model. 45
Fig. 3.2. (a) I-V characteristic and (b) Si/I2 of the CF-type RRAM. (c) Schematic illustration explaining the difference in noise level between the two resistance states....[이미지참조] 48
Fig. 3.3. Predominant noise origin depending on device conditions in MOSFET, TFT, and RRAM. 49
Fig. 3.4. (a) Schematic illustration and (b) I-V characteristics of MLC operation in the Icc mode. (c) Dependence of resistance and reset current in LRS according to...[이미지참조] 51
Fig. 3.5. (a) Schematic illustration and (b) I-Vread characteristics of MLC operation in the Vreset mode.[이미지참조] 53
Fig. 3.6. Si/I2 according to the MLC operation in (a) Icc and (b) Vreset mode.[이미지참조] 54
Fig. 3.7. (a) I-V curves (HRS to LRS) and (b) Cycle to cycle variation of the current in LRS and HRS at Vread of 0.1 V for 500 DC cycles.[이미지참조] 56
Fig. 3.8. (a) Si/I2 according to the switching cycle. (b) Cycle to cycle variation of the Si/I2 in HRS (left) and LRS (right) at frequencies 20, 40, and 100 Hz for 500...[이미지참조] 57
Fig. 4.1. (a) Process flow, (b) schematic structure, and (c) cross-sectional TEM image of the device used in experiments. 59
Fig. 4.2. (a) I-V curves of the fabricated Pt/TiO₂/Pt device, (b) linear fitting of I-V characteristics for LRS on a logarithmic scale, (c) I-V-T measurement, and (d) the... 61
Fig. 4.3. Fitting results for (a) Schottky emission, (b) PF emission, and (c) F-N tunneling. (d) the schematic energy band diagram of the Pt/TiO₂/Pt structure. 64
Fig. 4.4. (a) Fitting results for (a) Schottky emission at different temperatures. (b) ln(J/T²) vs. 1000/T curves for extraction of SBH. (c) The variation in SBH as a... 65
Fig. 4.5. (a) Si/I2 according to the voltage in LRS. (b) The logarithmic plot of the voltage dependence of the Si/I2 at frequencies 20, 40, and 100 Hz in LRS.[이미지참조] 68
Fig. 4.6. (a) Si according to the voltage in HRS. (b) The logarithmic plot of the current dependence of the Si at frequencies 20, 40, and 100 Hz in HRS.[이미지참조] 68
Fig. 4.7. (a) Process flow, (b) schematic structure, and (c) cross-sectional TEM image of the device used in experiments. 70
Fig. 4.8. (a) I-V curves of the fabricated Al/αTiO₂/Al device. The arrows indicate the direction of the voltage sweep. (b) I-V characteristics for both LRS and HRS on... 73
Fig. 4.9. Fitting results for (a) Schottky emission, (b) PF emission, and F-N tunneling ((c) LRS and (d) HRS). 74
Fig. 4.10. Si/I2 as the voltage increases in (a) LRS and (b) HRS. Logarithmic plots of the voltage dependence of the Si/I2 at frequencies of 20, 40 and 80 Hz for (c) LRS...[이미지참조] 76
Fig. 4.11. Process flows of (a) SL- and (b) DLRRAM. Cross-sectional TEM images of (c) SL- and (d) DLRRAM. 79
Fig. 4.12. Fitting results for (a) SCLC and (b) Schottky emission in SLRRAM. Fitting results for (c) SCLC and (d) Schottky emission in DLRRAM. 81
Fig. 4.13. Si/I2 according to the voltage in (a) LRS and (b) HRS. (c) The logarithmic plot of the voltage dependence of the Si/I2 at 20 Hz in LRS (circle) and HRS (square).[이미지참조] 84
Fig. 5.1. Schematic tow-level RTN signal showing its parameters (△I, τc, and τe).[이미지참조] 87
Fig. 5.2. (a) Illustration of two-level RTN mechanism in RRAM device. (b) Energy band diagram of the MIM structure considering the trap energy level (ET) and depth (xT).[이미지참조] 91
Fig. 5.3. Energy band diagram illustrating various capture/emission processes and their corresponding bias dependences of τc and τe.[이미지참조] 91
Fig. 5.4. Read current fluctuations (△I) for SLRRAMs with a cell size of 〈 100 x 100 nm² in HRS. 94
Fig. 5.5. (a) △Iread according to the voltage in the time domain. (b) Enlarged graph of △Iread at -0.14 V showing the clear two-level RTN.[이미지참조] 95
Fig. 5.6. (a) τc and τe on the voltage. (b) Dependence of ln(τc/τe) on the voltage.[이미지참조] 95
Fig. 5.7. Dependence of ln(τc/τe) about the trap corresponding the process (a) ④, (b) ③, and (c) ② on the voltage. (d) Energy band diagram showing the...[이미지참조] 96