Study for performance enhancement of vertical FETs by tailoring interfacial of 2D materials

다국어 초록 (Multilingual Abstract)

Vertical Field-Effect Transistors (VFETs) based on two-dimensional (2D) materials exhibit significant potential for achieving the ultimate scaling limit of integrated circuits. However, VFETs face critical performance limitations attributable to electron tunneling leakage from the extremely short vertical transport length and adverse interface defects induced by metal deposition, which significantly degrade the on/off current ratio.
This study advances a multifaceted interface engineering strategy to address this performance degradation. Initially, the formation of an ultrathin tungsten oxide layer via an oxidation process successfully realized a physical tunneling blockade. This layer effectively suppressed leakage current, substantially improving the VFET's on/off ratio and substantiating the efficacy of the physical blocking mechanism.
To circumvent the fixed characteristics and processing limitations of the inorganic approach, this study pioneered an active interface control strategy utilizing the Dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) organic semiconductor (OSC) as a functional interlayer. The DNTT film was formed via a low-energy, layer-by-layer growth mode, which provides a critical processing prerogative by precluding the structural damage to the 2D channel associated with high-energy deposition. The DNTT-integrated device exhibited a remarkable performance amplification, achieving an on/off current ratio magnified by a factor of nearly 104 Crucially, DNTT was elucidated not as a passive insulator but as an electronic functional layer that dynamically modulates the potential barrier via the applied gate voltage. This active barrier modulation mechanism optimizes channel performance by boosting charge injection while curtailing leakage.
By integrating the study of physical barriers (tungsten oxide) and active electronic barrier control (OSC), this dissertation establishes a comprehensive and extensible design platform for high-performance 2D VFETs, constituting a significant academic and technological contribution.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• 1.1 Two-dimensional (2D) Materials 1
• 1.2 Organic Semiconductors (OSCs) 3
• 1.3. Background and Fundamentals of 2D Field Effect Transistor (FET) 5
• 1.3.1. Fundamentals and Limitation of 2D Planar FET 6
• 1.3.2. Transition to Vertical Field-Effect Transistors (VFETs) 7
• 1.3.3. Prior Research on VFETs 9
• 1.4. Scope and Objective of a Dissertation 11
• Chapter 2. Physical Tunneling Barrier Engineering Using WOx Interlayers 12
• 2.1. Device Fabrication Process 12
• 2.2. Formation Mechanism of Self-Limited Monolayer WOx on WSe2 14
• 2.3. Structural and Chemical Characterization for Monolayer WOx 17
• 2.4. Device Performance 20
• 2.4.1. Transfer Characteristics of WSe2/WOx/Pt VFETs 21
• 2.4.2. Transfer Characteristics of WSe2/WOx/NbSe2 VFETs 23
• 2.5. Electronic Characteristics of NbSe2 Compared to Semiconducting TMDs 25
• 2.6. Band Structure Interpretation and Performance Comparison 27
• Chapter 3. Active Interface Modulation Using 2D- OSCs Interlayers 30
• 3.1. Field Tunable Barrier Mechanism 30
• 3.2. Layer-by-Layer Growth of DNTT films 31
• 3.3. Formation of 2D-OSCs Heterojunctions 32
• 3.4. Device Fabrication and Characterization 34
• 3.4.1. Device Fabrication Process 35
• 3.4.2. Structural and Morphological Characterization 37
• 3.5. Transfer Characteristics of MoS2/Au and MoS2/DNTT/Au 40
• 3.6. Band Diagram Analysis and Comparative Interpretation 43
• Chapter 4. Conclusion 45
• 4.1. Summary 45