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학위논문 상세정보

(A) study on SWCNT based stretchable device and 3-dimensional stretchable electronics 원문보기

  • 저자

    윤장열

  • 학위수여기관

    Graduate School, Korea University

  • 학위구분

    국내박사

  • 학과

    化工生命工學科

  • 지도교수

    河貞淑

  • 발행년도

    2014

  • 총페이지

    xviii, 181장

  • 키워드

    SWCNT stretchable electronics 3-dimensional;

  • 언어

    eng

  • 원문 URL

    http://www.riss.kr/link?id=T13541920&outLink=K  

  • 초록

    Abstract Flexible and stretchable electronics have shown remarkable development due to the growing number of potential applications in wearable computer and bio-implantable electronic systems. Various channel materials have been explored, including amorphous silicon, poly-silicon, organic materials, metal-oxide, and single-walled carbon nanotubes (SWCNTs). SWCNTs, in particular, exhibit excellent mechanical, thermal, chemical, optically transparent, and electronic properties, applicable to flexible/stretchable electronics. In addition, SWCNT-based electronic devices can be fabricated at low temperatures. Owing to these superior properties of SWCNTs, complicated logic circuits including diodes, inverters, NANDs, NORs, and ring oscillators have been successfully demonstrated so far. Currently, the growth of the aligned SWCNTs by chemical vapor deposition (CVD) is given much attention due to the relative ease of the selective removal of metallic SWCNTs in the mixture of metallic and semiconducting SWCNTs by electrical breakdown. This thesis reports on the fabrication of aligned SWCNT intra-tube junction devices by partially coating pristine SWCNTs with β- nicotinamide adenine dinucleotide, reduced dipotassium salt (NADH). Aligned SWCNTs were first transferred onto the SiO2 substrate using thermal tapes. After the selective removal of metallic tubes by electrical breakdown, NADH solution was spin-coated on half of the SWCNT channel, and it was post-annealed at 150 °C. The SWCNT intra-junction formed by this method exhibited rectifying behavior, with a large rectification ratio > 103 at a low bias of 1 V. The pn-junction formed in this way also showed a strong gate dependence, making it useful as a gate-modulated rectification device. When compared to the randomly networked SWCNT pn-intratube junctions, a much higher rectification ratio and lower reverse current were observed. This thesis also presents the fabrication and characteristics of the p-n hetero-junction diode made from the networked p-SWCNTs and n-SnO2 nanowires (NWs). SWCNTs and SnO2 NWs were transferred onto the patterned device substrate, making a crossed junction from the as-grown substrates via direct transfer methods; transfer of the SWCNTs was done using thermal tape and that of SnO2 NWs using the sliding method. The fabricated p-n hetero-junction diode showed a rectifying behavior, with a rectification ratio larger than 102 at ±5 V. Gate-dependent measurement of I-V curves exhibited the amplification of both the forward and reverse currents, with positive gate bias. In addition, the high sensitivity of the p-n hetero-junction under ultraviolet (UV) light suggested a high potential for its future application in optoelectronic devices. The simple fabrication of stretchable complementary metal oxide semiconductor (CMOS) inverter arrays consisting of p-type and n-type SWCNTs as channel materials is also demonstrated in this thesis. Both the channel and electrode regions of the fabricated CMOS inverter arrays showed excellent stretchable behavior during the stretching and releasing steps. The NADH coating of the pristine SWCNT field-effect transistor (FET) showed n-type semiconducting behavior, with an on/off current ratio of ~103, while the fabricated SWCNT CMOS inverter showed a gain value of ~9. A stretchable SWCNT inverter array on a thin polyimide (PI) film could be successfully attached onto a thin polydimethylsiloxane (PDMS) film using the simple magic tape transfer technique. Device performance of the fabricated CMOS inverter array had not deteriorated after stretching up to 33% and the 103-time repetition of stretching and releasing. This work demonstrates that SWCNT devices can be exploited in soft systems and are well suited for use in implantable electronics and wearable computer applications. Finally, this thesis proposes a novel design concept for 3D stretchable devices. This stretchable substrate consists of relatively stiff island arrays (PDMS) for active devices on both sides of the soft thin film (mixture of PDMS and Ecoflex); these active devices are electrically connected by embedded liquid metal interconnections of EGaIn. According to the analysis of strain distribution by the finite element method (FEM), a local strain of less than 1% is estimated in the active device island while the whole device array is stretched to 30%. Depending on the size of the stiff island relative to that of the soft thin film between adjacent islands, the maximum stretchability can be increased up to 70% without any deterioration in the performance of active devices including light-emitting diodes (LEDs) and micro super-capacitors attached on top of the stiff island. Integration of active devices on both sides of this stretchable substrate can double the fill factor when compared to that of conventionally used planar substrate. The embedded interconnections can simplify the fabrication process, including the encapsulation for protection from external impact, and can additionally increase the fill factor by reducing the length when compared to that of the serpentine type interconnection. Integrated devices of μ-LEDs, SnO2 nanowire UV sensors, SWCNT FETs, and micro-supercapacitors showed mechanically stable device performances upon bending, twisting, and uni-axial stretching. This work presents newly designed deformable devices, outlines their successful performance, and demonstrates the high potential for their application in the field of wearable nano-electronics.


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