Fabrication of transparent piezoresistors using carbon nanotube films and its application for piezoresistive touch display = 탄소나노튜브 필름을 이용한 투명 압저항체의 제작 및 압저항 터치 디스플레이에 관한 응용
서명 / 저자 Fabrication of transparent piezoresistors using carbon nanotube films and its application for piezoresistive touch display = 탄소나노튜브 필름을 이용한 투명 압저항체의 제작 및 압저항 터치 디스플레이에 관한 응용 / Kang-Won Lee.
저자명 Lee, Kang-Won ; 이강원
발행사항 [대전 : 한국과학기술원, 2011].
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학술문화관(문화관) 보존서고

DME 11050

휴대폰 전송






In this study, we demonstrate the fabrication of transparent piezoresistors using carbon nanotube films (CNFs) and application for piezoresistive touch display. CNF piezoresistors have excellent mechanical property, so the resistance will increase depending on the input force and be recovered to original value. The piezoresitive touch display is proposed as the application of transparent CNFs piezoresistors and can be used as input devices in transparent display areas. Chapter 2 describes the fabrication process and materials properties of CNFs, which can be fabricated by randomly connecting a number of tubes on the large area. There are various fabrication methods of CNFs including electrophoretic deposition, drop casting from solvent, Langmuir-Blodgett deposition, and spin coating. In this study, vacuum filtration method is used because this is the best method to increase the film uniformity and control the transmittance by changing the concentration of CNT solutions. For filtration filter, an anodic aluminum oxide membrane with 20 nm pore size and 47 mm diameter is used. SEM and AFM are used to characterize the surface properties of CNFs. Material properties are measured such as Young’s modulus, transmittance and sheet resistance. For Young’s modulus measurement, the experiments are carried out and the average values are obtained in the range of 100 to 200 nm to minimize the substrate effect. The optical transmittance at 550 nm wavelength is measured and sheet resistance is measured by four point probes as a function of the amount of various CNT solutions. Although the transmittance and sheet resistance can be controlled by vacuum filtration method, several obstacles to meet the requirement of flexible displays with high transmittance and low sheet resistance still remain. For improvement of the conductivity, HNO3 treatment is carried out by dipping the CNFs on the glass substrate in a nitric acid bath. To compare with SWCNFs, MWCNFs are fabricated and the transmittance and sheet resistance are measured. Chapter 3 describes a new transfer method of micro patterned CNFs into the PDMS and the fabrication process of flexible devices with CNFs embedded in PDMS membrane. Furthermore, the gauge factor of SWCNF piezoresistors and MWCNF piezoresistors are calculated. In previous researches, the hot embossing and PDMS stamp were used to combine CNFs with the transparent electrode in micro and nano devices. In this chapter, we propose a new transfer method of patterned CNFs into the PDMS using the poor adhesion between silicon wafer and Au layer. Cr or Ti with low electronegativity can readily form oxides and generally have a high degree of adhesion to substrates, whereas noble metal, Au with high electronegativity, is poorly adherent and easily removed. The I-V characteristic is measured to verify the utility of transferred CNFs as transparent electrodes using a semiconductor parameter analyzer. The gauge factor is the strain sensitivity, so it is necessary to obtain the strain of transparent CNF piezoresistors. There are two approaches to obtain the strain: theoretical analysis and Finite Element Analysis. The theoretical strain value has the linear relation to the indentation depth because of the elastic model and rigid body assumption. The finite element analysis strain value has the nonlinear relation to the indentation depth due to the assumptions of the hyperelastic model and plastic deformation at specific local area. To calculate the gauge factor, the resistance change should be measured as a function of center deflection. The membrane is deflected with a tungsten probe tip and z-axis micro-stage and the resistance change of SWCNF piezoresistors and MWCNF piezoresistors is measured. To confirm the repeatability, the experiment is carried out in the input pressure range of 0 to 4 kPa. Chapter 4 demonstrates piezoresistive touch display using transparent CNF piezoresistors. To demon-strate the resistance change according to the mechanical loadings, the experimental setup is prepared with the indentation system which is composed of a hemisphere probe tip with 2 mm diameter, a force sensor, a DC mo-tor attached to the linear guide. This indentation system can be applied the unit step function of constant force and the resistance change is measured and the measured data is recorded at computer through GPIB communication with LabVIEW. The mechanical force is applied at 0.1 Hz during 70 sec to confirm the repeatability and experimental results show that the resistance of CNF piezoresistors increases in proportion to the strength of the applied force and the recovery to the original resistance state. To compare with the characteristic of SWCNF piezoresistors, we measure the resistance change using MWCNF piezoresistors at the same condition. The piezoresistive touch display is composed of LED display part with six LED lights and touch sensor part. Resistance of CNF piezoresistors can be operated as variable resistance depending on the strength of applied force. Without the input force, there is no LED light. The resistance of CNF piezoresistors increases in proportion to the strength of touch, so LED lights turn on in sequence. In the polymer MEMS, CNFs can be the promising materials as a piezoresistor which is compatible with micro-fabrication process and is not required the high temperature process. Therefore, CNF piezoresistors has the great potential in the low pressure sensing environment and proposed piezoresistive touch display can be performed as multi-functional input devices.

본 연구에서는 투명 전극의 역할을 수행하는 탄소나노튜브 필름과 MEMS 기술을 접목시켜 투명 압저항체의 특성을 확인하고, 이를 이용하여 압저항 방식의 터치 디스플레이에 대한 새로운 개념을 제시하였다. 기존의 터치 디스플레이가 가지고 있는 전극의 파손에 대한 내구성 문제점과 인체가 아닌 도구는 사용할 수 없다는 문제점을 해결하기 위해, 투명 전극으로써 관심을 받고 있는 탄소나노튜브 필름의 압저항 특성을 분석하고 이를 이용해 인가 압력에 대해 필름의 저항 값이 변하는 것을 이용하여 압저항 방식의 터치 디스플레이에 대한 응용 가능성을 확인하였다. 진공 필터 방식으로 제작된 탄소나노튜브 필름은 micro fabrication 공정을 이용하여 다양한 형상으로 제작이 가능하다는 장점이 있다. 그런데 투명 전극으로써의 역할을 수행하기 위해서는 실리콘이 아닌 폴리머 기판에서 사용되어야 하는데, 유연하고 투명한 성질을 가지는 PDMS는 photolithography 공정과 금속 증착 공정에서 사용하는데 문제점이 있다. 따라서, PDMS로 전사시키는 방법이 필수적이며, 본 연구에서는 실리콘 기판과 Au 층 사이의 접착력이 나쁜 것을 이용하여 새로운 전사 방법을 제시하였다. 전사 방법을 이용해 PDMS로 전사된 탄소나노튜브 필름은 I-V 측정을 통해 전극으로써 사용할 수 있다는 것을 확인하였다. 탄소나노튜브 필름의 압저항 특성을 분석하기 위해 유연 소자를 제작하는 공정을 개발하였다. 유연 소자를 이용하여 원형 membrane의 처짐에 대한 탄소나노튜브 필름의 저항 변화 값을 측정한 다음, gauge factor를 계산해보았다. 실리콘 기반의 압저항체 보다는 낮은 gauge factor를 가지지만, 낮은 공정 온도를 요구하는 폴리머 기판에서는 높은 sensitivity를 가지는 압저항체로 사용할 수 있을 것으로 판단한다. 탄소나노튜브 필름의 압저항 특성을 확인하였기 때문에, 인가 힘에 대한 저항 변화를 측정하는 실험을 수행하였다. 측정 결과 힘에 대해 저항 값이 증가하는 것을 확인하였으며, 이를 바탕으로 손이나 펜으로 PDMS를 누를 때 탄소나노튜브 필름의 저항 변화를 감지하여 인식하는 압저항 방식의 터치 디스플레이로 사용가능 할 것으로 판단한다. 또한, 인가 힘의 크기에 의해서도 저항 값의 변화가 다른 것을 이용한 multi-functional touch 디스플레이로의 응용 가능성도 있다고 판단한다.


청구기호 {DME 11050
형태사항 xi, 114 p. : 삽도 ; 30 cm
언어 영어
일반주기 저자명의 한글표기 : 이강원
지도교수의 영문표기 : Seung S. Lee
지도교수의 한글표기 : 이승섭
수록잡지명 : "Carbon nanotube film piezoresistors embedded in polymer membranes". Applied Physics Letters, v. 96, no. 1, pp. 013511 1-3(2010)
학위논문 학위논문(박사) - 한국과학기술원 : 기계공학전공,
서지주기 References : p. 101-108
주제 Carbon nanotube films
Polymer MEMS
Wafer transfer methods
Transparent piezoresistors
Piezoresistive touch display
탄소나노튜브 필름
폴리머 멤스
기판 전사 방법
투명 압저항체
압저항 터치 디스플레이
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