1차원 반도체 나노구조체의 화학적 변환 및 직접인쇄법에 의한 전자소자 제작 및 특성 평가

Abstract

Nanotechnology represents an exciting and rapidly evolving research area that crosses the boundary between basic science and engineering. Much of the excitement in nanotechnology has arisen from recognition that (i) the properties can be significantly altered as their dimensions are reduced to the nanometer due to classical size effects and quantum confinement and (ii) the ability to further miniaturize and integrate multi-functionality into device/system. In order to build highly performance nanodevices, it is essential to synthesize nanoscale building blocks with precisely controlled and tunable chemical composition, crystal structure, size, and morphology since these characteristics determine their corresponding properties. Among various nanoengineered materials, one-dimensional (1-D) nanostructures received great attentions because of their unique applications in mesoscopic physics and fabrication of nanoscaled devices. Although intensive studies have been carried out on the synthesis of 1-D nanostructures, there is a great need to develop novel synthesis techniques which enables rational design and predictable synthesis for 1-D nanostructure. In addition, synthesis methods must be low cost and high throughput (e.g., the fabrication of electric circuits on flexible substrate using nanostructured materials). The overarching objective of this dissertation is (i) to develop cost-effective and scalable synthesis method to form 1-D hollow nanostructures from solid nanostructures using various cost-effective and scalable chemical transformation and (ii) development of novel inks for non-contact direct printed conductive features formed on flexible substrate. Chemical transformation methods including thermal oxidation using Kirkendall effect and galvanic displacement reaction (GDR) were used convert 1-D metal nanowires or nanofibers, which were synthesized by template-directed electrodeposition or electrospinning methods, to 1-D metal, metal oxide, and chalcogenide nanotubes with controlled diameter, wall thickness, composition, crystal structure and morphology. In addition, the reaction mechanism was investigated in detail, and the structure and properties of synthesized 1-D hollow nanostructures including phase, morphology, composition, microstructure, and electrical property were systematically characterized and correlated. In the area of non-contact direct printing, stable Cu complex ion inks were developed for non-contact direct printing to form Cu interconnects on flexible substrates. The printed Cu interconnects show an excellent electrical and mechanical properties after thermal treatment. During this work, an UV/ozone pretreatment was employed to further enhance the hydrophilicity of polyimide film which led to reduce the feature size. Furthermore, the adhesion was enhanced by adding silane coupling agent to the Cu complex ion ink. The improvement of mechanical properties of non-contact direct printed pattern was demonstrated by employing two-dimensional Ag nanoplatelets instead of zero-dimensional Ag nanoparticles. In this dissertation, the work was divided into four chapters. Chapter 1 compares state-of-the-art nanomaterials synthesis and their advantages and disadvantages. Chapter 2 describes the synthesis of 1-D hollow nanostructures with the controlled morphology (porous and hollow structure), phase (valence state and chemical composition) and size (diameter and aspect ratio) using chemical transformation processes (i.e., thermal oxidation and galvanic displacement) using electrodeposited and electrospun sacrificial metal nanowires or nanofibers. Chapter 3 describes the fabrication of Cu ions and Ag nanoplatelets based conductive inks and their application toward ink-jet or dispense printing to form conductive patterns. In this chapter, novel inks (i.e., copper complex ions and silver nanoplatelets) were successfully prepared by utilizing modified electrolysis and solvothermal approaches. Printed conductive features on flexible substrates show excellent electrical conductivity and superior mechanical stability. Chapter 4 summarizes the findings and recommends future works. |나노 기술(nanotechnology)은 물리, 화학, 재료과학 및 공학, 생명과학을 하나의 범주로 융합하여 종래의 기술과는 지배법칙 및 발상이 다른 혁신기술로서 매우 큰 관심을 받고 있다. 이러한 나노 기술은 물질의 크기를 나노 스케일(nanoscale)로 제어하여 매우 큰 비표면적(surface to volume ratio) 및 양자 구속 효과(quantum confinement effect)를 통해 기존 물질이 발현하지 못하는 새로운 특성을 갖는 물질을 합성, 이용하거나 또는 기존 재료의 특성을 개선시킬 수 있는 기술이다. 더 나아가 이러한 나노 물질(nanomaterials)을 이용하여 신 개념의 시스템을 구축하고, 기존의 다양한 기능성 시스템을 더욱 소형화(miniaturization)하거나 다기능성(multifunctionality)을 갖도록 유도할 수 있는 기술을 의미한다. 다양한 나노 물질 중에서 1차원 구조의 나노 재료(one-dimensional nano-materials)는 벌크(bulk), 박막(thin film) 및 0차원의 나노입자(nanoparticle)와는 다른 독특한 물리적, 화학적 특성과, 그들의 1차원 형상을 통해 발현되는 다양한 장점으로 인해 학문적 및 실용적으로 많은 관심을 받고 있다. 최근 1차원 나노재료를 합성하여 기본적인 특성을 탐구하고, 더 나아가 이러한 재료를 기초 물질로 하여 다양한 기능성 소자를 제작하기 위한 많은 연구가 진행되고 있다. 1차원 나노재료의 물리적, 화학적 특성은 재료의 화학조성, 형상, 크기 및 결정 구조에 의해 결정되기 때문에 이를 각각의 응용분야가 필요로 하는 특성으로 정확하게 제어하는 것이 반드시 필요하다. 이러한 재료의 기본적 특성은 1차원 나노재료를 합성하는 기술, 즉 공정(process)에 의해 많은 영향을 받는다. 따라서 우수한 특성을 갖는 다양한 나노시스템(nanosystems)을 구현에 필요한 1차원 나노재료를 합리적이면서도 손쉽게 그 특성을 제어할 수 있는 합성 방법을 개발하는 것이 필요하다. 나노시스템의 구현에 있어 또 하나의 중요한 기술은 각 시스템의 중요한 구성 인자, 예를 들면 시스템에 전기적 특성을 부여하는 전기적 회로(electrical circuit) 또는 전극(electrode)을 나노 재료를 이용하여 구현하는 것이다. 최근 비 접촉 방식의 인쇄 기술(printing technique)은 기존의 사진석판술(photolithography) 공정이 갖는 단점을 극복할 수 있는 기술로 각광을 받고 있으며, 다양한 반도체(semiconductor), 절연체(insulator) 및 전도체(conductor)를 부품화함에 있어 생산 비용 절감, 수율 증대 및 대면적화에 가장 효율적인 기술로 많은 연구가 진행되고 있다. 이 중 전도체는 전기 소자(electronic devices), 광 소자(optical devices), 가스 및 바이오 센서(Gas & bio sensors) 및 태양전지(solar cell) 등을 구현함에 있어 필수적인 요소로서, 특히 유연 기판(flexible substrate)에 전도체를 형성하는 것은 앞서 언급한 시스템을 유연 소자(flexible electronics)로 발전시키는 데 반드시 필요한 기술이다. 본 학위 논문의 첫 번째 목적은 다양한 1차원 나노재료 중에서 중공 구조(hollow structure)로 인해 더욱 큰 비표면적을 나타내고, 매우 작은 크기의 벽(wall)을 갖기 때문에 양자 구속 효과의 발현에 유리한 나노 튜브(nanotubes)를 매우 간단하며, 생산적 및 가격적인 측면에서 유리하고, 대량으로 제조가 가능한 합성 기술을 개발하는 것이다. 기존 합성 방법의 한계를 극복하기 위해 템플레이트(template) 기반의 전해증착(electrochemical deposition) 방법 및 전기방사법과 Kirkendall effect 및 galvanic displacement와 같은 화학적 변환을 결합시켜 산화물 나노튜브, 금속 나노튜브 및 칼코지나이드 나노 튜브를 합성하였고, 나노 튜브의 직경, 벽 두께, 화학 조성 및 종횡비(aspect ratio)를 제어하는 연구를 수행하였다. 더 나아가 변환 과정을 체계적으로 관찰함으로써 중공 구조가 형성되는 메커니즘(mechanism)을 확인하였고, 재료의 결정 구조, 형상, 조성, 미세구조 및 전기적인 특성을 고찰하였다. 다양한 유연 소자(flexible electronics)를 구현하기 위해 기존 나노입자 기반의 전도성 배선을 위한 인쇄 기술의 문제점을 극복하고 유연 기판(flexible substrate)에 우수한 전기적, 기계적 특성을 갖는 배선을 비 접촉형태로 인쇄하는 것이 본 연구의 두 번째 목적이다. 이를 위해 안정성 및 토출성이 우수한 착이온(complex ions) 형태의 잉크를 전기분해(electrolysis) 방법을 이용하여 합성하였고, 또한 충진성의 문제를 해결하기 위해 판상형태(platelet type)를 기본 물질로 하는 잉크를 제조하였다. 잉크젯 인쇄 기술(ink-jet printing)과 디스펜싱 기술(dispensing printing)를 사용하여 제조된 잉크를 박막 형태의 배선으로 형성하였고, 잉크를 구성하는 기본 물질이 잉크 및 배선에 미치는 영향을 체계적으로 고찰하였으며, UV/Ozone 처리를 통해 기판의 표면 에너지를 제어하여 전도성 배선을 원하는 형상 및 폭을 갖도록 인쇄하였다. 또한 실란 커플링제(silane coupling agent)를 이용하여 인쇄된 배선과 유연 고분자 기판의 접착력을 향상시켰다. 더 나아가 판상 물질을 함유한 전도성 잉크를 이용하여 기존 나노입자 기반의 배선보다 외부에서 가해지는 휨 응력(bending strength)에 뛰어난 안정성 및 우수한 전기적 특성을 보유한 배선을 제작하였다.; Nanotechnology represents an exciting and rapidly evolving research area that crosses the boundary between basic science and engineering. Much of the excitement in nanotechnology has arisen from recognition that (i) the properties can be significantly altered as their dimensions are reduced to the nanometer due to classical size effects and quantum confinement and (ii) the ability to further miniaturize and integrate multi-functionality into device/system. In order to build highly performance nanodevices, it is essential to synthesize nanoscale building blocks with precisely controlled and tunable chemical composition, crystal structure, size, and morphology since these characteristics determine their corresponding properties. Among various nanoengineered materials, one-dimensional (1-D) nanostructures received great attentions because of their unique applications in mesoscopic physics and fabrication of nanoscaled devices. Although intensive studies have been carried out on the synthesis of 1-D nanostructures, there is a great need to develop novel synthesis techniques which enables rational design and predictable synthesis for 1-D nanostructure. In addition, synthesis methods must be low cost and high throughput (e.g., the fabrication of electric circuits on flexible substrate using nanostructured materials). The overarching objective of this dissertation is (i) to develop cost-effective and scalable synthesis method to form 1-D hollow nanostructures from solid nanostructures using various cost-effective and scalable chemical transformation and (ii) development of novel inks for non-contact direct printed conductive features formed on flexible substrate. Chemical transformation methods including thermal oxidation using Kirkendall effect and galvanic displacement reaction (GDR) were used convert 1-D metal nanowires or nanofibers, which were synthesized by template-directed electrodeposition or electrospinning methods, to 1-D metal, metal oxide, and chalcogenide nanotubes with controlled diameter, wall thickness, composition, crystal structure and morphology. In addition, the reaction mechanism was investigated in detail, and the structure and properties of synthesized 1-D hollow nanostructures including phase, morphology, composition, microstructure, and electrical property were systematically characterized and correlated. In the area of non-contact direct printing, stable Cu complex ion inks were developed for non-contact direct printing to form Cu interconnects on flexible substrates. The printed Cu interconnects show an excellent electrical and mechanical properties after thermal treatment. During this work, an UV/ozone pretreatment was employed to further enhance the hydrophilicity of polyimide film which led to reduce the feature size. Furthermore, the adhesion was enhanced by adding silane coupling agent to the Cu complex ion ink. The improvement of mechanical properties of non-contact direct printed pattern was demonstrated by employing two-dimensional Ag nanoplatelets instead of zero-dimensional Ag nanoparticles. In this dissertation, the work was divided into four chapters. Chapter 1 compares state-of-the-art nanomaterials synthesis and their advantages and disadvantages. Chapter 2 describes the synthesis of 1-D hollow nanostructures with the controlled morphology (porous and hollow structure), phase (valence state and chemical composition) and size (diameter and aspect ratio) using chemical transformation processes (i.e., thermal oxidation and galvanic displacement) using electrodeposited and electrospun sacrificial metal nanowires or nanofibers. Chapter 3 describes the fabrication of Cu ions and Ag nanoplatelets based conductive inks and their application toward ink-jet or dispense printing to form conductive patterns. In this chapter, novel inks (i.e., copper complex ions and silver nanoplatelets) were successfully prepared by utilizing modified electrolysis and solvothermal approaches. Printed conductive features on flexible substrates show excellent electrical conductivity and superior mechanical stability. Chapter 4 summarizes the findings and recommends future works.