Roll-to-roll sputtered, indium-free ZnSnO/AgPdCu/ZnSnO multi-stacked electrodes for high performance flexible thin-film heaters and heat-shielding films

Seok, Hae-Jun,Jang, Hyeon-Woo,Lee, Dong-Yeop,Son, Beom-Gwon,Kim, Han-Ki Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.775 No.-

<P><B>Abstract</B></P> <P>As a cost-effective, indium-free, flexible, and highly transparent electrode for flexible thin-film heaters and heat-shielding films, ZnSnO(ZTO)/AgPdCu(APC)/ZTO multi-stacked films were fabricated by using 1500-mm–width, roll-to-roll (RTR) sputtering at room temperature. The optimized RTR-sputtered ZTO/APC/ZTO film showed a very low sheet resistance (3.43 ohm/square), high optical transmittance (80.99%), and small inner/outer critical bending radii (1 and 2 mm, respectively), even when it was processed at room temperature. In particular, the better flexibility of the ZTO/APC/ZTO films, relative to typical ITO films, was confirmed by lab-scale bending, rolling, twisting, and folding tests. Due to the very low sheet resistance, superior flexibility, and low transmittance in the near-infrared wavelength region, flexible and transparent thin-film heaters (TFHs) and flexible heat-shielding films (HSFs) made with the ZTO/APC/ZTO films showed better performance than typical ITO-based TFHs and HSFs. This suggests that the RTR–sputtered, indium-free ZTO/APC/ZTO films can be applied as transparent and flexible electrode materials in cost-effective and multi-functional smart windows for buildings and automobiles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electrical, optical, and mechanical properties of ZTO/APC/ZTO multilayers. </LI> <LI> Outstanding flexibility of roll-to-roll sputtered ZTO/APC/ZTO films. </LI> <LI> Flexible thin-film heater and heat-shielding films for smart windows. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

투명 유연 박막 트랜지스터의 구현을 위한 열처리된 산화아연 박막의 전사방법 개발

권순열 ( Soon Yeol Kwon ),정동건 ( Dong Geon Jung ),최영찬 ( Young Chan Choi ),이재용 ( Jae Yong Lee ),공성호 ( Seong Ho Kong ) 한국센서학회 2018 센서학회지 Vol.27 No.3

Zinc oxide (ZnO) thin films have the advantages of growing at a low temperature and obtaining high charge mobility (carrier mobility) [1]. Furthermore, the zinc oxide thin film can be used to control application resistance depending on its oxygen content. ZnO has the desired physical properties, a transparent nature, with a flexible display that makes it ideal for use as a thin-film transistor. Though these transparent flexible thin-film transistors can be manufactured in various manners, manufacturing large-area transistors using a solution process is easier owing to the low cost and flexible substrate. The advantage of being able to process at low temperatures has been attracting attention as a preferred method. However, in the case of a thin-film transistor fabricated through a solution process, it is reported that charge mobility is lower. To improve upon this, a method of improving the crystallinity through heat treatment and increasing electron mobility has been reported. However, as the heat treatment temperature is relatively high at 500°C, an application where a flexible substrate is absent would be more suitable.

Laser processing of indium tin oxide thin film to enhance electrical conductivity and flexibility

Park, Taesoon,Ha, Jeonghong,Kim, Dongsik Elsevier 2018 THIN SOLID FILMS - Vol.658 No.-

<P><B>Abstract</B></P> <P>This work reports a method that uses a KrF excimer laser to enhance the electrical and mechanical properties of amorphous indium tin oxide (ITO) thin films on flexible substrates. Irradiation with nanosecond laser pulses induces thermal crystallization of ITO, and thereby increases the electrical conductivity and flexibility of film deposited on polyethylene terephthalate substrates. The shallow optical (~45 nm) and thermal penetration (~100 nm) of the laser beam confines the thermal effect to within the ITO layer without damaging the substrate. The laser treatment changed the crystallinity of ITO film from amorphous to poly-crystalline; as a result, its electrical-conductivity increased by 20–25%. Moreover, the treatment decreased the critical bending radius to avoid loss of electrical property from 8 mm to 5 mm. The adhesion strength and transparency of the ITO film were not affected significantly by the laser treatment. This work suggests that laser treatment can be an effective tool to enhance the crystallinity, of sputtered ITO thin film, and its electrical and mechanical properties on flexible substrate.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Laser irradiation enhances the properties of sputtered ITO thin films on flexible substrates. </LI> <LI> Nanosecond laser irradiation can crystallize amorphous ITO thin film. </LI> <LI> The laser treatment increases the electrical conductivity by 20–25%. </LI> <LI> The critical bending radius to avoid loss of conductivity is decreased from 8 to 5 mm. </LI> </UL> </P>

Excimer laser sintering of indium tin oxide nanoparticles for fabricating thin films of variable thickness on flexible substrates

Park, Taesoon,Kim, Dongsik Elsevier 2015 THIN SOLID FILMS - Vol.578 No.-

<P><B>Abstract</B></P> <P>Technology to fabricate electrically-conducting, transparent thin-film patterns on flexible substrates has possible applications in flexible electronics. In this work, a pulsed-laser sintering process applicable to indium tin oxide (ITO) thin-film fabrication on a substrate without thermal damage to the substrate was developed. A nanosecond pulsed laser was used to minimize thermal penetration into the substrate and to control the thickness of the sintered layer. ITO nanoparticles (NPs) of ~20nm diameter were used to lower the process temperature by exploiting their low melting point. ITO thin film patterns were fabricated by first spin coating the NPs onto a surface, then sintering them using a KrF excimer laser. The sintered films were characterized using field emission scanning electron microscopy. The electrical resistivity and transparency of the film were measured by varying the process parameters. A single laser pulse could generate the polycrystalline structure (average grain size ~200nm), reducing the electrical resistivity of the film by a factor of ~1000. The sintering process led to a minimum resistivity of 1.1×10<SUP>−4</SUP> Ω·m without losing the transparency of the film. The thickness of the sintered layer could be varied up to 150nm by adjusting the laser fluence. Because the estimated thermal penetration depth in the ITO film was less than 200nm, no thermal damage was observed in the substrate. This work suggests that the proposed process, combined with various particle deposition methods, can be an effective tool to form thin-film ITO patterns on flexible substrates.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Excimer laser sintering can fabricate ITO thin films on flexible substrates. </LI> <LI> The laser pulse can form a polycrystalline structure without thermal damage. </LI> <LI> The laser sintering process can reduce the electrical resistivity substantially. </LI> <LI> The thickness of the sintered layer can be varied effectively. </LI> </UL> </P>

Metal-containing thin-film encapsulation with flexibility and heat transfer

권정현,김응택,임현균,배병수,장기수,박상희,최경철 한국정보디스플레이학회 2015 Journal of information display Vol.16 No.2

The thin-film encapsulation (TFE) technology is a salient technique for the realization of flexible organic light-emitting diodes. To reliably fabricate bendable and lightweight displays, ultra-thin and flexible encapsulation is required. Reported herein is a moisture-resistant, flexible, and thermally conductive TFE technology created by inserting a metal thin film with an inorganic–organic multibarrier structure to resolve the reliability and heat dissipation issues. Silica-nanoparticleembedded sol-gel organic/inorganic hybrid nanocomposite (S-H) and Al2O3 were used as organic and inorganic materials, respectively. A silver (Ag) thin film used as a metal was deposited through thermal evaporation, and it had slight barrier properties, outstanding ductility, and high thermal conductivity. The proposed structure, which consists of three materials, resulted in a low water vapor transmission rate of 10−5 g/m2/day for a 240-nm-thick thin film, and showed improvement of the resistance to bending stress compared with the previous structure formed without an Ag thin film in terms of flexibility. A comparative analysis of the heat transfer properties of encapsulation structures was also performed through the investigation of the thermal conductivity of the materials, and thermal imaging measurement. The heat dissipation performance was confirmed to have been improved by the insertion of Ag thin films into the inorganic/organic multibarrier.

Functional Design of Dielectric–Metal–Dielectric-Based Thin-Film Encapsulation with Heat Transfer and Flexibility for Flexible Displays

Kwon, Jeong Hyun,Choi, Seungyeop,Jeon, Yongmin,Kim, Hyuncheol,Chang, Ki Soo,Choi, Kyung Cheol American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.32

<P>In this study, a new and efficient dielectric-metal-dielectric-based thin-film encapsulation (DMD-TFE) with an inserted Ag thin film is proposed to guarantee the reliability of flexible displays by improving the barrier properties, mechanical flexibility, and heat dissipation, which are considered to be essential requirements for organic light-emitting diode (OLED) encapsulation. The DMD-TFE, which is composed of Al2O3, Ag, and a silica nanoparticle-embedded sol-gel hybrid nanocomposite, shows a water vapor transmission rate of 8.70 X 10(-6) g/m(2)/day and good mechanical reliability at a bending radius of 30 mm, corresponding to 0.41% strain for 1000 bending cycles. The electrical performance of a thin-film encapsulated phosphorescent organic light-emitting diode (PHOLED) was identical to that of a glass-lid encapsulated PHOLED. The operational lifetimes of the thin-film encapsulated and glass-lid encapsulated PHOLEDs are 832 and 754 h, respectively. After 80 days, the thin-film encapsulated PHOLED did not show performance degradation or dark spots on the cell image in a shelf-lifetime test. Finally, the difference in lifetime of the OLED devices in relation to the presence and thickness of a Ag film was analyzed by applying various TFE structures to fluorescent organic light-emitting diodes (FOLEDs) that could generate high amounts of heat. To demonstrate the difference in heat dissipation effect among the TFE structures, the saturated temperatures of the encapsulated FOLEDs were measured from the back side surface of the glass substrate, and were found to be 67.78, 65.12, 60.44, and 39.67 degrees C after all encapsulated FOLEDs were operated at an initial luminance of 10 000 cd/m(2) for sufficient heat generation. Furthermore, the operational lifetime tests of the encapsulated FOLED devices showed results that were consistent with the measurements of real-time temperature profiles taken with an infrared camera. A multifunctional hybrid thin-film encapsulation based on a dielectric-metal-dielectric structure was thus effectively designed considering the transmittance, gas-permeation barrier properties, flexibility, and heat dissipation effect by exploiting the advantages of each separate layer.</P>

용액공정을 이용한 열처리된 산화아연 박막의 투명한 박막 트랜지스터 구현을 위한 전사방법 개발

권순열,정동건,최영찬,이재용,공성호 한국반도체디스플레이기술학회 2018 반도체디스플레이기술학회지 Vol.17 No.2

Recently, Thin-film transistors (TFTs) are fundamental building blocks for state-of-the-art microelectronics, such as flat-panel displays and system-on-glass. Zinc oxide thin films have the advantage that they can grow at low temperature and can obtain high charge movility. Also the zinc oxide thin film can be used to control the resistance according to the oxygen content, so it is very easy to obtain the desired physical properties. In this paper, we fabricated a zinc oxide thin film on a polished copper substrate through a solution process, then improved the crystallinity through a geat treatment porcess, and studied to transfer it on a flexible substrate after the heat treatment was completed.

Quantitative analysis of bending fracture resistance of nanoscale Cu-buffered ZnO:Al thin films on a polymer substrate

Kim, Seung Won,Choi, Hong Je,Cho, Yong Soo Elsevier 2018 Journal of alloys and compounds Vol.731 No.-

<P><B>Abstract</B></P> <P>Improving the fracture resistance of fragile inorganic thin films under various bending conditions is critical in flexible thin-film systems. Here, we introduce a Cu-buffer-layer approach to evaluate the level of enhancement in the bending fracture behavior of Al-doped ZnO (AZO) thin films on the basis of quantitative mechanical parameters such as fracture energy, film strength and fracture toughness. These fracture behaviors of thin films sputter-deposited onto polyethersulfone substrates were observed to depend largely on the thickness of the Cu buffer layer. In the case of thin films with a 20 nm-thick Cu buffer layer, crack-initiating bending strain was substantially improved from ∼1.04% to ∼1.37%; this corresponds to an improvement of ∼31.7%. The substantial improvement is attributed to the presence of the Cu buffer layer, which helps prevent the formation of cracks by absorbing crack-initiating tensile stress. The calculated values of fracture energy and film strength support well the Cu thickness dependence of fracture behavior under bending operation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bending fracture resistance of Cu-buffered Al:ZnO thin films is investigated. </LI> <LI> Flexibility of the films is largely improved with the nanoscale Cu layer. </LI> <LI> A 20 nm-thick Cu layer induces a ∼31.7% improvement in fracture resistance. </LI> <LI> An estimated fracture energy of ∼224.7 Jm<SUP>−2</SUP> supports the mechanical improvement. </LI> <LI> Film strength and fracture toughness are correlated to the bending fracture behavior. </LI> </UL> </P>

A review of highly reliable flexible encapsulation technologies towards rollable and foldable OLEDs

정은교,권정현,강기석,정소영,최경철 한국정보디스플레이학회 2020 Journal of information display Vol.21 No.1

As the demand for flexible, rollable, and foldable displays grows, various state-of-the-art component technologies, including thin-film transistors (TFTs), electrodes, thin-film encapsulations (TFEs), and touch screen panels, have been developed based on organic light-emitting diodes (OLEDs) with flexible organic layers. Developing highly reliable flexible OLEDs is essential to realize flexible displays, but the flexible encapsulation technology still has technical difficulties and issues to be addressed. This review covers the recent developments in encapsulation technologies, particularly their material and structural designs, for highly reliable, flexible OLEDs. The solution concepts for the existing technical hurdles in flexible encapsulations are addressed. Among the various advanced flexible encapsulation technologies developed so far, neutral-axis engineering with a thin metal layer and a crack arrester is introduced.

Performance enhancement of thin-film silicon solar cells by development of core component layers

Cho, Jun-Sik,Jang, Eunseok,Lim, Dongmin,Ahn, Seungkyu,Yoo, Jinsu,Park, Joo Hyung,Kim, Kihwan,Yun, Jae Ho,Choi, Bo-Hun Elsevier 2018 Solar energy Vol.159 No.-

<P><B>Abstract</B></P> <P>High efficiency thin-film silicon (Si) solar cells were prepared on flexible substrates by the plasma-enhanced chemical vapor deposition method. To improve their performance, the microstructural, electrical, and optical properties of the core component layers including the metal rear reflectors, p- and n-type doped layers, and intrinsic absorber layers were controlled sophistically. To enable the use of flexible substrates with low heat resistance as well as to enhance light-scattering properties, nanotextured rear reflectors with a Ag/Al:Si bilayer structure were developed by dc magnetron sputtering at a low substrate temperature of below 150 °C. Highly crystalline n-doped seed layers (which effectively eliminate a defect-dense amorphous region formed in the initial growth stage of intrinsic nanocrystalline silicon (nc-Si:H) absorber layers) and p-type wide-bandgap nanocrystalline silicon carbide (nc-SiC:H) window layers (which reduce the parasitic absorption loss in the short-wavelength region and increase the open circuit voltage (V<SUB>OC</SUB>)) were successfully applied to enhance the performance characteristics of the solar cells. Through the combination of the developed core component layers, high conversion efficiencies of 8.84% (V<SUB>OC</SUB> = 0.53 V, J<SUB>SC</SUB> = 25.28 mA/cm<SUP>2</SUP>, and fill factor (FF) = 0.66, where J<SUB>SC</SUB> is the short circuit current) and 7.48% (V<SUB>OC</SUB> = 0.50 V, J<SUB>SC</SUB> = 21.07 mA/cm<SUP>2</SUP>, and FF = 0.71) were obtained for nc-Si:H solar cells fabricated on stainless steel (SUS) and polyimide substrates, respectively, at a low substrate temperature of below 150 °C. Flexible a-Si:H/nc-Si:H double-junction solar cells fabricated on SUS substrates showed a high conversion efficiency of 11.46% (V<SUB>OC</SUB> = 1.38 V, J<SUB>SC</SUB> = 11.53 mA/cm<SUP>2</SUP>, and FF = 0.72) when the nc-Si:H solar cells developed in this study were applied as a bottom cell.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We developed the core component layers for thin-film Si solar cells. </LI> <LI> The substrate temperature does not exceed 150 °C. </LI> <LI> Enhanced performance was achieved in flexible thin-film Si solar cell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>