• The Journal of the Acoustical Society of Korea
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• v.30 no.4
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• pp.215-222
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• 2011

In order to obtain high resolution images, a focusing ultrasonic transducer operated in very high frequency (VHF) range was fabricated and its characteristics were evaluated. A 9-${\mu}m$ thick PVDF film with only one metalized surface for electric ground was adhered to a CCP (Copper-clad polyimide) film by using epoxy. It was pressed by a metal ball to form a concave surface and its rear side was filled with the epoxy. The radius of curvature and the f-number of the fabricated transducer are 7.5 mm and 1.7, respectively. The pulse-echo measurement results from a target located at the focal point showed that the frequency bandwidth was 35.0 MHz and the insertion loss near the peak frequency of approximately 40 MHz was about 60 dB. Those values agreed well with the simulation results by the KLM equivalent circuit analysis including the effect of the epoxy bonding layer. When the image of thin copper lines by the 35 MHz transducer of the UBM (Ultrasonic Backscattering Microscope) system was compared with the image by the transducer fabricated in this study, the fabricated transducer was observed that the axial resolution was improved although the lateral resolution was degraded.

• Journal of the Korean Vacuum Society
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• v.16 no.2
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• pp.79-90
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• 2007

Prototype of $800{\ell}$ vacuum web coater (Vic Mama) consisting of ion source with low energy less than 250 eV for high speed surface modification and 4 magnetron sputter cathodes was designed and constructed. Its performance was evaluated through fabricating the adhesiveless flexible copper clad laminate (FCCL). Pumping speed was monitored in both upper noncoating zone pumped down by 2 turbo pumps with 2000 l/sec pumping speed and lower surface modification and sputter zone vacuumed by turbo pumps with 450 1/sec and 1300 1/sec pumping speed respectively. Ion current density, plasma density, and uniformity of ion beam current were measured using Faraday cup and the distribution of magnetic field and erosion efficiency of sputter target were also investigated. With the irradiation of ion beams on polyimide (Kapton-E, $38{\mu}m$) at different fluences, the change of wetting angle of the deionized water to polyimide surface and those of surface chemical bonding were analyzed by wetting anglometer and x-ray photoelectron spectroscopy. After investigating the deposition rate of Ni-Cr tie layer and Cu layer was investigated with the variations of roll speed and input power to sputter cathode. FCCL fabricated by sputter and electrodeposition method and characterized in terms of the peel strength, thermal and chemical stability.

• Macromolecular Research
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• v.17 no.12
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• pp.976-986
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• 2009

With the study goal of firstly elucidating the anisotropic interactions between oriented polymer chain segments and liquid crystal (LC) molecules, and secondly of determining the contributions of the chemical components of the polymer segments to the film surface topography, LC alignment, pretilt, and anchoring energy, we synthesized three dianhydrides, 1,4-bis(4'-t-butylphenyl)pyromellitic dianhydride (BBPD), 1,4-bis(4'-trimethylsilylphenyl)pyromellitic dianhydride(BTPD), and 2,2'-bis(4"-tert-butylphenyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (BBBPAn), and a series of their organosoluble polyirnides, BBPD-ODA, BBPD-MDA, BBPD-FDA, BTPD-FDA, and BBBPAn-FDA, which contain the diamines 4,4'-oxydianiline (ODA), 4,4'-methylenediamine (MDA), and 4,4'-(hexafluoroisopropylidene)dianiline (FDA). All the polyimides were determined to be positive birefringent polymers, regardless of the chemical components. Although all the rubbed polyimide films exhibited microgrooves which were created by rubbing process, the film surface topography varied depending on the polyimides. In all the rubbed films, the polymer chains were unidirectionally oriented along the rubbing direction. However, the degree of in-plane birefringence in the rubbed film varied depending on the polyimides. The rubbing-aligned polymer chains in the polyimide films effectively induced the alignment of nematic LCs along their orientation directors by anisotropic interactions between the preferentially oriented polymer chain segments and the LCs. The azimuthal and polar anchoring energies of the LCs ranged from $0.45{\times}10^{-4}\;-\;1.37{\times}10^{-4}\;J/m^2$ and from $0.86{\times}10^{-5}\;-\;4.26{\times}10^{-5}\;J/m^2$, respectively, depending on the polyimides. The pretilt angles of the LCs were in the range $0.10-0.62^{\circ}$. In summary, the soluble aromatic polyimides reported here are promising LC alignment layer candidates for the production of advanced LC display devices.

• Analytical Science and Technology
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• v.19 no.5
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• pp.400-406
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• 2006

Hydrogen analysis by elastic recoil detection has been performed utilizing polyimide film as a reference sample of known hydrogen content assuming the soundness of ion beam current integration. However beam current integration at higher incidence angle is not reliable. Scattering yield per unit fluence by current integration which is normalized per unit path length decreases as the sample tilt angle is getting higher. Moreover because beam current integration at high tilt angle is incomplete, hydrogen evaluation is very risky by direct comparison of sequentially collected recoil spectra between reference and target sample. In this study, primary ion beam dose is determined by backscattering spectrum that is collected simultaneously with recoil spectrum instead of ion beam current integration in order to reduce uncertainty arising in the process of current integration and to enhance the reliability of quantitative analysis. Three test samples are selected $-7.6{\mu}m$ polyimide film, hydrogen implanted silicondioxide and Au deposited carbon wafer- and analyzed by two methods and compared.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.818-821
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• 2006

We demonstrate the vertical alignment of liquid crystal on $a-SiO_x$ film surface using the ion beam exposure. Liquid crystal can be aligned vertically by the rotational oblique evaporation of $a-SiO_x$ film. However, the electro-optic switching behavior of liquid crystal along random directions results in disclination lines. We found that we can achieve highly uniform alignment of liquid crystal without disclination lines by using the ion beam exposure. We found from XRD and XPS data that the vertical alignment can be achieved when x approaches 1.5 at the $a-SiO_x$ film surface. We have shown that the pretilt angle can be controlled by changing ion beam parameters, such as the ion beam energy, the angle of incidence, and the exposure time. We found that whether liquid crystals can be aligned vertically or homogeneously on $a-SiO_x$ film can be predicted simply by measuring the change in optical transmittance by deposition of $a-SiO_x$ thin film layers. We also have shown that a liquid crystal cell aligned vertically by the ion beam exposure exhibits the voltage-transmittance curve similar to that of a rubbed polyimide cell.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.10
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• pp.1100-1106
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• 2004

In this paper, we intend to make fringe-field switching (FFS) mode cell by the ion beam (IB) alignment method on the a-C：H thin film, to analyze electro-optical characteristics in this cell. We studied on the suitable inorganic thin film for fringe-field switching (FFS) cell and the aligning capabilities of nematic liquid crystal (NLC) using the alignment material of a-C：H thin film as working gas at 30 W rf bias condition. A high pretilt angle of about 5 $^{\circ}C$ by ion beam (IB) exposure on the a-C：H thin film surface was measured. Consequently, the high pretilt angle and the good thermal stability of LC alignment by the IB alignment method on the a-C：H thin film surface as working gas at 30 W rf bias condition can be achieved. An excellent voltage-transmittance (V -T) and response time curve of the IE-aligned FFS-LCD was observed with oblique IB exposure on the a-C：H thin films. Also, AC V-T hysteresis characteristics of the IB-aligned FFS-LCD with IE exposure on the a-C：H thin films is almost the same as that of the rubbing-aligned FFS cell on a polyimide (PI) surface.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.264-264
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• 2011

Poly [(N, N'-oxydiphenylene) pyromellitimide], polyimide (PI) film은 기계적 강도가 매우 우수하고 열적, 화학적 안정성이 뛰어난 재료로서 전자제품의 소형화, 경령화, 고성능화를 위한 차세대 flexible electronic device에 적용하기 위하여 많은 연구가 진행되고 있다. 그러나 PI의 특성상, 매우 낮은 표면에너지로 인해 금속과의 접촉력이 좋지 않은 단점을 가지고 있다. 본 연구에서는, 금속박막과 PI film 과의 접촉력을 증가시키기 위해 remote-type modified dielectric barrier discharge (DBD) module을 이용하여 대기압 플라즈마 표면처리를 하였다. 실험에 사용된 gas composition은 각각 $N_2$/ He/ $SF_6$, $N_2$/ He/ $O_2$, $N_2$/ He/ $SF_6$/ $O_2$, $N_2$/ He/ $SF_6$/ $O_2$ 이다. $N_2$/ He/ $SF_6$/ $O_2$ gas composition을 이용하여 PI 표면을 플라즈마 처리한 경우, C=O 결합이 PI film 위에 생성됨으로써, 접촉각이 매우 낮게 형성됨을 관찰할 수 있었다. 이와는 반대로 $N_2$/ He/ $SF_6$ gas composition 을 사용하였을 경우에는 C-Fx 화학적 결합이 생성되기 때문에 가장 높은 접촉각이 형성됨을 관찰할 수 있었다. 특히, $N_2$ (40 slm)/ He (1 slm)/ $SF_6$ (1.2 slm) gas composition에 $O_2$ gas를 0.2 slm부터 1.0 slm까지 변화시켜가며 PI film 표면을 처리한 결과, $O_2$ gas를 0.9 slm 첨가하였을 때, 가장 낮은 $9.3^{\circ}$의 접촉각을 얻을 수 있었다. 이는 0.9 slm의 $O_2$ gas를 첨가하였을 때, 가장 많은 양의 $O_2$ radical이 생성되기 때문에 많은 양의 C=O 결합이 생성되기 때문이다. 최적화된 $N_2$ (40 slm)/ He (1 slm)/ $SF_6$ (1.2 slm)/ $O_2$ (0.9 slm) gas composition 조건에서 Ag film과 PI film과의 접촉력을 관찰할 결과, 111 gf/mm를 얻을 수 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.604-609
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• 2019

In this study, we fabricated a capacitive humidity sensor with interdigitated (IDT) electrodes using a thermosetting polyimide as a humidifying material. First, the number of electrodes, thickness, and spacing of the polyimide film were optimized, and a mask was designed and fabricated. The sensor was fabricated on a silicon substrate using semiconductor processing equipment. The area of the sensor was $1.56{\times}1.66mm^2$, and the width of the electrode and the gap between the electrodes were each $3{\mu}m$. The number of electrodes was 166, and the length of an electrode was 1.294 mm for the sensitivity of the sensor. The sensor was then packaged on a PCB for measurement. The sensor was inserted into a chamber environment with a temperature of $25^{\circ}C$ and connected to an LCR meter to measure the change in capacitance at relative humidity (RH) of 20% to 90%, 1 V, and 20 kHz. The results showed a sensitivity of 26fF/%RH, linearity of < ${\pm}2%RH$, and hysteresis of < ${\pm}2.5%RH$.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.105-111
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• 2023

Electronic devices have been evolved to be mechanically flexible that can be endured repetitive deformation. This evolution emphasizes the importance of long-term reliability in metal wiring connecting electronic components, especially under bending fatigue in compressed environments. This study investigated methods to enhance adhesion between copper (Cu) and polyimide (PI) substrates, aiming to improve the reliability of copper wiring under such conditions. We applied oxygen plasma treatment and introduced a chromium (Cr) adhesion layer to the polyimide substrate. Our findings revealed that these adhesion enhancement methods significantly affect compression fatigue behavior. Notably, the chromium adhesion layer, while showing weaker fatigue characteristics at 1.5% strain, demonstrated superior performance at 2.0% strain with no delamination, outperforming other methods. These results offer valuable insights for improving the reliability of flexible electronic devices, including reducing crack occurrence and enhancing fatigue resistance in their typical usage environments.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.195-198
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• 2008

In this paper, it was demonstrated that organic thin-film transistors (OTFTs) were fabricated with the organic passivation layer by vapor deposition polymerization (VDP) processing. In order to form polymeric film as a passivation layer, VDP process was also introduced instead of spin-coating process, where polymeric film was co-deposited by high-vacuum thermal evaporation from 6FDA and ODA followed by curing. In order to investigate by compared with different passivation layer, the other OTFTs is fabricated to passivation by Polyvinylalcohol using spincoating. We can see that two different ways of passivation layer affect electric characteristic of OTFTs. The initial electric characteristic of OTFTs before passivation such as field effect mobility, threshold voltage, and on-off current ratio are $0.24cm^2/Vs$, -3V, and $10^6$, respectively. Then after polyimide passivation layer, field effect mobility change from $0.24cm^2/Vs$ to $0.26cm^2/Vs$, threshold voltage from -3V to 1V and on-off current ratio from $10^6$ to $10^6$, respectively. In the case of polyvinylalcohol passivation, the initial electric characteristic of OTFTs before passivation such as field effect mobility, threshold voltage, and on-off current ratio are $0.13cm^2/Vs$, 0V, and $10^6$, respectively. Then after polyvinylalcohol passivation layer, field effect mobility changes from $0.13cm^2/Vs$ to $0.13cm^2/Vs$, threshold voltage from 0V to 2V, and on-off current ratio from $10^6$ to $10^5$, respectively.