• 반도체디스플레이기술학회지
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• 제20권4호
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• pp.49-54
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• 2021

The display industry is transitioning from traditional rigid products such as flat panel displays to flexible or wearable ones designed to be folded or rolled. Accordingly, colorless and optically transparent polyimide (CPI) films are one of the prime candidates to substitute traditional cover glass as a passivation layer to accommodate product flexibility. However, CPI films subjected to repetitive pure bending loads inevitably entail an accumulation of residual strain that can eventually cause wrinkles or delamination in the underlying component after a certain number of static and cyclic loading. The purpose of this study is to establish an experimental method to systematically evaluate the bending residual strain of CPI films. Films were monotonically and cyclically wrapped on mandrels of various diameters to ensure a constant strain in each. After unwrapping the wound CPI film, the residual radius of curvature remaining on the film was measured and converted into residual strain. The critical radius of curvature at which residual strain does not remain was about 5 mm, and the residual strain decreased in proportion to the log time. It is expected that flexible displays can be reliably designed using the data between the applied bending strain and the residual strain.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.341-341
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• 2012

Recently, oxide semi-conductor materials have been investigated as promising candidates replacing a-Si:H and poly-Si semiconductor because they have some advantages of a room-temperature process, low-cost, high performance and various applications in flexible and transparent electronics. Particularly, amorphous indium-gallium-zinc-oxide (a-IGZO) is an interesting semiconductor material for use in flexible thin film transistor (TFT) fabrication due to the high carrier mobility and low deposition temperatures. In this work, we demonstrated improvement of flexibility in IGZO TFTs, which were fabricated on polyimide (PI) substrate. At first, a thin poly-4vinyl phenol (PVP) layer was spin coated on PI substrate for making a smooth surface up to 0.3 nm, which was required to form high quality active layer. Then, Ni gate electrode of 100 nm was deposited on the bare PVP layer by e-beam evaporator using a shadow mask. The PVP and $Al_2O_3$ layers with different thicknesses were used for organic/inorganic multi gate dielectric, which were formed by spin coater and atomic layer deposition (ALD), respectively, at $200^{\circ}C$. 70 nm IGZO semiconductor layer and 70 nm Al source/drain electrodes were respectively deposited by RF magnetron sputter and thermal evaporator using shadow masks. Then, IGZO layer was annealed on a hotplate at $200^{\circ}C$ for 1 hour. Standard electrical characteristics of transistors were measured by a semiconductor parameter analyzer at room temperature in the dark and performance of devices then was also evaluated under static and dynamic mechanical deformation. The IGZO TFTs incorporating hybrid gate dielectrics showed a high flexibility compared to the device with single structural gate dielectrics. The effects of mechanical deformation on the TFT characteristics will be discussed in detail.

• 한국전기전자재료학회논문지
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• 제28권11호
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• pp.698-703
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• 2015

In this study, we fabricated the dual gate (DG) ion-sensitive field-effect-transistor (ISFET) with flexible polyimide (PI) extended gate (EG). The DG ISFETs significantly enhanced the sensitivity of pH in electrolytes from 60 mV/pH to 1152.17 mV/pH and effectively improved the drift and hysteresis phenomenon. This is attributed to the capacitive coupling effect between top gate and bottom gate insulators of the channel in silicon-on-transistor (SOI) metal-oxide-semiconductor (MOS) FETs. Accordingly, it is expected that the PI-EG based DG-ISFETs is promising technology for high-performance flexible biosensor applications.

• JSTS:Journal of Semiconductor Technology and Science
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• 제9권3호
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• pp.174-180
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• 2009

A new flexible electronics technology, named P-FCB (Planar Fashionable Circuit Board), is introduced. P-FCB is a circuit board technology implemented on the plain fabric patch for wearable electronics applications. In this paper, the manufacturing of P-FCB, and its electrical characteristics such as sheet resistance, maximum current density, and frequency characteristics are reported. The fabrication methods and their electrical characteristics of passive devices such as resistor, capacitor, and inductor in P-FCB are discussed. In addition, how to integrate silicon chip directly to the fabric for the flexible electronics system are described. Finally, examples of P-FCB applications will be presented.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2012년도 춘계학술발표대회
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• pp.63.1-63.1
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• 2012

In recent years, the functional inks for printed electronics that can be combined with a variety of printing techniques have attracted increasingly significant interest for use in low cost, large area, high performance integrated electronics and microelectronics. In particular, the development of solution-processable conductor, semiconductor and insulator materials is of great importance as such materials have decisive impacts on the electrical performance of various electronic devices, and, therefore, need to meet various requirements including solution processability, high electrical performance, and environmental stability. Semiconductor inks such as IGO, CIGS are synthesized by chemical solution method and microwave reaction method for TFT and solar cell application. Fine circuit pattern with high conductivity, which is valuable for flexible electrode for PCB and TSP devices, can be printed with highly concentrated and stabilized conductor inks such as silver and copper. Solution processed insulator such as polyimide derivatives can be use to all printed TFT device. Our research results of functional inks for printed electronics provide a recent trends and issues on this area.

• 반도체디스플레이기술학회지
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• 제19권2호
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• pp.72-76
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• 2020

The author demonstrated organic ferroelectric thin-film transistors with ferroelectric materials of P(VDF-TrFE) and an amorphous oxide semiconducting In-Ga-Zn-O channel on the silicon substrates. The organic ferroelectric layers were deposited on an oxide semiconductor layer by Langmuir-Blodgett method and then annealed at 128℃ for 30min. The carrier mobility and current on/off ratio of the memory transistors showed 9 ㎠V^-1s^-1 and 6 orders of magnitude, respectively. We can conclude from the obtained results that proposed memory transistors were quite suitable to realize flexible and werable electronic applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.115-116
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• 2012

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has increased due to their advantages of excellent portability, conformal contact with curved surfaces, light weight, and human friendly interfaces over present rigid electronic systems. This seminar introduces three recent progresses that can extend the application of high performance flexible inorganic electronics. The first part of this seminar will introduce a RRAM with a one transistor-one memristor (1T-1M) arrays on flexible substrates. Flexible memory is an essential part of electronics for data processing, storage, and radio frequency (RF) communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. The cell-to-cell interference between neighbouring memory cells occurs due to leakage current paths through adjacent low resistance state cells and induces not only unnecessary power consumption but also a misreading problem, a fatal obstacle in memory operation. To fabricate a fully functional flexible memory and prevent these unwanted effects, we integrated high performance flexible single crystal silicon transistors with an amorphous titanium oxide (a-TiO2) based memristor to control the logic state of memory. The $8{\times}8$ NOR type 1T-1M RRAM demonstrated the first random access memory operation on flexible substrates by controlling each memory unit cell independently. The second part of the seminar will discuss the flexible GaN LED on LCP substrates for implantable biosensor. Inorganic III-V light emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps and OLED. However, due to the brittle property of bulk inorganic semiconductor materials, III-V LED limits its applications in the field of high performance flexible electronics. This seminar introduces the first flexible and implantable GaN LED on plastic substrates that is transferred from bulk GaN on Si substrates. The superb properties of the flexible GaN thin film in terms of its wide band gap and high efficiency enable the dramatic extension of not only consumer electronic applications but also the biosensing scale. The flexible white LEDs are demonstrated for the feasibility of using a white light source for future flexible BLU devices. Finally a water-resist and a biocompatible PTFE-coated flexible LED biosensor can detect PSA at a detection limit of 1 ng/mL. These results show that the nitride-based flexible LED can be used as the future flexible display technology and a type of implantable LED biosensor for a therapy tool. The final part of this seminar will introduce a highly efficient and printable BaTiO3 thin film nanogenerator on plastic substrates. Energy harvesting technologies converting external biomechanical energy sources (such as heart beat, blood flow, muscle stretching and animal movements) into electrical energy is recently a highly demanding issue in the materials science community. Herein, we describe procedure suitable for generating and printing a lead-free microstructured BaTiO3 thin film nanogenerator on plastic substrates to overcome limitations appeared in conventional flexible ferroelectric devices. Flexible BaTiO3 thin film nanogenerator was fabricated and the piezoelectric properties and mechanically stability of ferroelectric devices were characterized. From the results, we demonstrate the highly efficient and stable performance of BaTiO3 thin film nanogenerator.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.164-164
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• 2010

The impurity doped ZnO has been extensively studied because of its optoelectric properties. GIZO (Ga-In-Zn-O) amorphous oxide semiconductors has been widely used as transparent flexible semiconductor material. Recently, various amorphous transparent semiconductors such as IZO (In-Zn-O), GIZO, and HIZO (Hf-In-Zn-O) were developed. In this work, we examined the local structures of IZO, GIZO, and HIZO. The local coordination structure was investigated by the extended X-ray absorption fine structure. The IZO, GIZO and HIZO thin films ware deposited on the glass substrate with thickness of 400nm by the radio frequency sputtering method. The targets were prepared by the mixture of $In_2O_3$, ZnO and $HfO_2$ powders. The percent ratio of In:Zn in IZO, Ga:In:Zn in GIZO and Hf:In:Zn in HIZO was 45:55, 33:33:33 and 10:35:55, respectively. In this work, we found that IZO, GIZO and HIZO are all amorphous and have a similar local structure. Also, we obtained the bond distances of $d_{Ga-O}=1.85\;{\AA}$, $d_{Zn-O}=1.98\;{\AA}$, $d_{Hf-O}=2.08\;{\AA}$, $d_{In-O}=2.13\;{\AA}$.

• 반도체디스플레이기술학회지
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• 제13권1호
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• pp.7-12
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• 2014

In this study, we investigate the effects of corona-discharge pre-treatment on the properties of carbon nanotubes (CNTs) which are used as flexible transparent electrodes. The CNTs are deposited on PET (polyethylene terephthalate) substrates using a spray coating method. Prior to the deposition of CNTs, the PET substrates are corona-treated by varying the feeding directions of the PET substrate and the numbers of treatments. The variations in the surface morphologies and roughnesses of the PET substrates due to corona-treatment are characterized via atomic force microscopy (AFM). Dynamic contact angles (DCAs) of the corona-treated PET substrates are measured and analyzed as functions of the treatment conditions. Also, the sheet resistances and visible-range transmittances of the CNTs deposited on PET substrates are measured before and after bending test. The experimental results obtained in this study provide strong evidences that the adhesive forces between CNTs and PET substrates can be substantially enhanced by corona-discharge pretreatment.

• 반도체디스플레이기술학회지
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• 제13권4호
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• pp.15-20
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• 2014

The fracture analysis of $SiN_x$ layers, which were deposited by low-temperature plasma enhanced chemical vapor deposition (LT-PECVD) and could be used for an encapsulation layer of a flexible organic light emitting display (OLED), was performed by an electrical method. The specimens of metal-insulator-metal (MIM) structure were prepared using Pt and ITO electrodes. We stressed MIM specimen mechanically by bending outward with a bending radius of 15mm repeatedly and measured leakage current through the top and bottom electrodes. We also observed the cracks, were generated on surface, by using optical microscope. Once the cracks were initiated, the leakage current started to flow. As the amount of cracks increased, the leakage current was also increased. By correlating the electrical leakage current in the MIM specimen with the bending times, the amount of cracks in the encapsulation layer, generated during the bending process, was quantitatively estimated and fracture behavior of the encapsulation layer was also closely investigated.