The object of this study is to clarify the material interaction mechanism between laser and copper nanoparticle by physical/chemical analysis and to fabricate optimal copper electrode. Fabrication of copper electrode by copper nanoparticle laser sintering process has magnificent advantages in material cost compare to gold, silver nanoparticle laser sintering. So, Fabrication of high performance copper electrode by laser patterning with copper nanoparticle is spotlighted as a next-generation technology to substitute conventional lithography process. Therefore, clarification of copper nanoparticle laser material interaction such as oxidation tendency is hot issue recently. Previous copper nanoparticle laser sintering research has many problems because of absence of pure copper nanoparticle ink. So it has limitation in clarifying copper nanoparticle laser material interaction. For this reason, performance of fabricated copper electrode is very low and there is no research about exact copper nanoparticle laser material interaction mechanism. In this study, I propose the experimental clarification of the material interaction mechanism between laser and copper nanoparticle which is motivated by pure copper nanoparticle ink to solve the previous copper nanoparticle laser sintering problems. To verify the research, We decide and optimize main parameters by experiment. With comprehensive optimization by physical SEM analysis and chemical XPS Depth analysis, we could fabricate low resistivity (4.56μ??cm) copper electrode at 200mm/s laser scan rate. To show the industrial usefulness of copper nanoparticle laser sintering process we applicate these technology to fabricate high functional electrode pattern on flexible substrate (PI, PEN) and transistor source, drain electrode as well. First, pure copper nanoparticle ( 50 nm, 100 nm Bi modal size distribution ) are spin coated on the glass substrate. Source selection process is done before processing pure copper nanoparticle. If we provide photon energy to copper nanoparticle, it absorbs photon energy and cause photo-thermal reaction. By this photo-thermal reaction, compact copper nanoparticles are melted and sintered together which results in continuous metal electrode. There are many variables to fabricate high conductive metal layer such as laser power, laser scan rate and etc. To fabricate copper pattern, non irradiated area is washed by organic solvent such as dichloro benzene, toluene and etc. Second, through the SEM ( Scanning electron microscope), XPS ( X-ray photoelectron spectroscopy ) analysis of fabricated copper electrode, we analyze thermal sintering characteristic, oxidation tendency and organic residue that is left after laser processing. Sintering is done well under 200mm/s laser scanning speed since too fast scan speed cannot sinter copper nanoparticle perfectly because of marangoni effect. Copper oxidation decreases rapidly over 200mm/s laser scan rate. The electrode fabricated at over 400mm/s laser scan speed has much organic residue. With these results we can make comprehensive conclusion that optimal copper electrode can be fabricated at 200mm/s scan rate. In this study, by confirming the proper scanning speed, laser power to minimize the oxidation, organic residue and maximize the sintering, we could fabricate high performance copper electrode (4.56μ??cm). Third, we could applicate this technology to fabricate various electrodes and devices to verify that copper nanoparticle laser sintering has potential in industrial usefulness. We fabricate copper electrode on the PI ( Poly Imide ), PEN ( Polyethylene naphthalate ) substrate with the resistivity of 5.752μ??cm and 12.43μ??cm. Since the thermal properties such as glass transition temperature is not good compared to glass, laser processing is done with lower laser intensity. Therefore, copper electrode fabricated on the PI, PEN film shows higher resistivity compared to optimized resistivity. Lastly, fabrication of transistor source, drain electrode is done with copper nanoparticle laser processing. Substrate is p-type doped ( Boron doped ) and it is used as a gate electrode and dielectric layer is formed by SiO2 deposition on the doped silicon wafer. CuO ( Cupric oxide ) material which has 1.2eV band gap is applied as a semiconducting material and on the top of CuO layer, copper nanoparticle laser processed copper electrodes are introduced as source, drain electrode. Fabricated CuO transistor shows -0.2V threshold voltage, 130 current on/off ratio and 0.22856 ( cm²/V·s ) mobility and these properties can be applicated to 13.56MHz RFID ( Radio Frequency Identification) chip.
본 연구의 목적은 물리적 화학적 분석을 통한 레이저와 구리 나노입자간의 상호작용메커니즘에 대한 고찰 및 이를 통한 고성능의 구리 전극 제조이다. 구리 나노입자 레이저 소결을 이용한 구리 전극 제조는 기존의 금 (Au), 은 (Ag) 나노입자 기반 레이저 패터닝 공정에 비해 재료 비용 면에서 혁신적인 이점을 가지고 있어서 구리 나노입자 레이저 패터닝을 통한 고전도성의 구리 전극 제조는 기존의 포토리소 공정을 대체할 차세대 기술로 주목 받고 있다. 그러므로 산화경향과 같은 구리 나노입자 레이저 상호작용 메커니즘 규명에 관한 연구가 매우 중요한 Issue로 존재하고 있다. 기존의 구리 나노입자 레이저 소결 연구는 저 순도 또는 순도규명조차 되지 않은 구리 나노입자 잉크를 사용하여 진행되었기 때문에 구리 나노입자 상호작용 메커니즘을 실험적으로 규명하는데 한계가 존재하였다. 이러한 결과, 제작된 구리 전극의 성능이 매우 낮고 실질적인 구리 나노입자 상호작용 메커니즘 분석에 관련된 연구가 전무한 실정이다.
본 연구에서는 이러한 기존 연구의 문제점을 해결하기 위해 순수한 구리 나노입자 잉크를 이용한 정확한 레이저와 구리 나노입자간의 상호작용 메커니즘의 실험적 규명 및 이를 이용한 고전도성의 구리 전극을 제조하고자 한다. 이를 위해 공정 변수를 선정하고 실험을 진행 하였고 제작된 구리 전극의 물리적 화학적 분석을 통해 종합적인 결론을 내렸다. 결과적으로 200mm/s 레이저 스캔 속도에서 비저항 4.56μ??cm 의 고 전도성 구리 전극을 제조 할 수 있었고 이의 산업적 효용성을 입증하기 위해 유연기판 PI (Poly Imide), PEN (Poly Ethylene Naphthalate) 에도 전극을 형성할 수 있었으며 트랜지스터의 소스 (Source), 드레인 (Drain) 전극 제조를 통해13.56Mhz RFID (Radio Frequency Identification) 용 CuO 트랜지스터 제작 가능성을 확인 하였다.
