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Microdome-gooved Gd_2O_2S:Tb scintillator for flexible and high resolution digital radiography
Jung, Phill Gu,Lee, Chi Hoon,Bae, Kong Myeong,Lee, Jae Min,Lee, Sang Min,Lim, Chang Hwy,Yun, Seungman,Kim, Ho Kyung,Ko, Jong Soo The Optical Society 2010 Optics express Vol.18 No.14
<P>A flexible microdome-grooved Gd(2)O(2)S:Tb scintillator is simulated, fabricated, and characterized for digital radiography applications. According to Monte Carlo simulation results, the dome-grooved structure has a high spatial resolution, which is verified by X-ray image performance of the scintillator. The proposed scintillator has lower X-ray sensitivity than a nonstructured scintillator but almost two times higher spatial resolution at high spatial frequency. Through evaluation of the X-ray performance of the fabricated scintillators, we confirm that the microdome-grooved scintillator can be applied to next-generation flexible digital radiography systems requiring high spatial resolution.</P>
Replication of polyethylene nano-micro hierarchical structures using ultrasonic forming
Lee, Chi Hoon,Jung, Phill Gu,Lee, Sang Min,Park, Sang Hu,Shin, Bo Sung,Kim, Joon-Ho,Hwang, Kyu-Youn,Kim, Kyoung Min,Ko, Jong Soo IOP 2010 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.20 No.3
<P>We present the replication of polyethylene (PE) nano-micro hierarchical structures and their application for superhydrophobic surfaces. A commercial ultrasonic welding system was used to apply ultrasonic vibration energy to the forming of nano-micro hierarchical structures. To evaluate ultrasonic formability, Ni nanomold and nano-micro hierarchical mold were designed and fabricated. The optimal weld times were 1.5 s and 3.0 s for PE nanoprotrusions and nano-micro hierarchical structures, respectively. The forming process was conducted at atmospheric pressure. The PE structures were well replicated without a vacuum. The trapped air in the microcavity of the nano-micromold was dispersed and absorbed into the molten PE. Ultrasonic nano-microreplication technology showed an extremely short processing time and did not require a vacuum environment. To investigate the applicability of ultrasonic forming, the fabricated nanoprotrusions and nano-micro hierarchical structures were coated with plasma polymerized fluorocarbon (PPFC) of a hydrophobic nature and were applied to modify superhydrophobic surfaces. The contact angle was increased from 106° (smooth surface) to 125° (nanostructured surface) and finally to 160° (nano-microstructured surface) so that the surface became superhydrophobic.</P>
Dry etching of polydimethylsiloxane using microwave plasma
Hwang, Sung Jin,Oh, Dong Joon,Jung, Phill Gu,Lee, Sang Min,Go, Jeung Sang,Kim, Joon-Ho,Hwang, Kyu-Youn,Ko, Jong Soo IOP 2009 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.19 No.9
<P>This paper presents a new polydimethylsiloxane (PDMS) dry-etching method that uses microwave plasma. The applicability of the method for fabricating microstructures and removing residual PDMS is also verified. The etch rate of PDMS was dominantly influenced by the gas flux ratio of CF<SUB>4</SUB>/O<SUB>2</SUB> and the microwave power. While the PDMS etch rate increased as the flux ratio of CF<SUB>4</SUB> was increased, the etch rate decreased as the flux ratio of O<SUB>2</SUB> was increased. The maximum etch rate of 4.31 µm min<SUP>−1</SUP> was achieved when mixing oxygen (O<SUB>2</SUB>) and tetrafluoromethane (CF<SUB>4</SUB>) at a 1:2 ratio at 800 W power. The PDMS etch rate almost linearly increased with the microwave power. The ratio of the vertical etch rate to the lateral etch rate was in a range of 1.14–1.64 and varied with the gas fluxes. In consideration of potential applications of the proposed PDMS etching method, array-type PDMS microwells and network-type microprotrusion structures were fabricated. The contact angle was dramatically increased from 104° (non-etched PDMS surface) to 148° (etched PDMS surface) and the surface was thereby modified to be superhydrophobic. In addition, a thin PDMS skin that blocked holes and PDMS residues affixed in nickel microstructures was successively removed.</P>
KMPR을 이용한 다층구조물 제작 및 전해도금을 이용한 니켈몰드 제작
황성진(Sung Jin Hwang),정필구(Phill Gu Jung),고정상(Jeung Sang Ko),고종수(Jong Soo Ko),정임덕(Im Deok Jeong),김인곤(In Gon Kim) 한국정밀공학회 2006 한국정밀공학회 학술발표대회 논문집 Vol.2006 No.5월
In this paper, we proposed XP KMPR-1050 negative tone resist to replace SU-8 resist for multi-layer microstructures and thick plating mold fabrication using UV-LIGA process. XP KMPR resist proposed in this paper can be easily striped using a common stripping solution such as NMP without damage of micro-structure. The conditions for the fabrication of XP KMPR micro-structure were optimized by adjustment of exposure and post-exposure bake(PEB). The 140㎛-thick and an aspect ratio at least 10 micro-structure and multi-layer structures were successfully fabricated through the process conditions. Through-mold electroplating and PR striping of XP KMPR has been successfully demonstrated.
Pixel-Structured Scintillator with Polymeric Microstructures for X-Ray Image Sensors
Im Deok Jung,Min Kook Cho,Kong Myeong Bae,Sang Min Lee,Phill Gu Jung,김호경,김성식,고종수 한국전자통신연구원 2008 ETRI Journal Vol.30 No.5
We introduce a pixel-structured scintillator realized on a flexible polymeric substrate and demonstrate its feasibility as an X-ray converter when it is coupled to photosensitive elements. The sample was prepared by filling Gd2O2S:Tb scintillation material into a square-pore-shape cavity array fabricated with polyethylene. For comparison, a sample with the conventional continuous geometry was also prepared. Although the pixelated geometry showed X-ray sensitivity of about 58% compared with the conventional geometry, the resolving power was improved by about 70% above a spatial frequency of 3 mm-1. The spatial frequency at 10% of the modulation-transfer function was about 6 mm-
Evaluation of the waterproof ability of a hydrophobic nickel micromesh with array-type microholes
Lee, Sang Min,Oh, Dong Joon,Jung, Im Deok,Jung, Phill Gu,Chung, Kwang Hyo,Jang, Won Ick,Ko, Jong Soo IOP 2009 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.19 No.12
<P>Hydrophobic nickel micromeshes with array-type circular holes were designed and fabricated, and their waterproof abilities with respect to the hole diameter were theoretically and experimentally evaluated. The hole diameter increased from 20 mu m to 100 mu m in steps of 10 mu m, while the hole pitch was fixed at 200 mu m. Photolithography and nickel electroforming processes were used to fabricate 10 mu m thick nickel micromeshes. In order to enhance the waterproof ability of nickel micromeshes, a plasma-polymerized fluorocarbon (PPFC) layer was coated on the nickel micromeshes. The contact angle of the micromesh increased from 63 degrees for the non-coated nickel flat film to 106 degrees for the PPFC-coated film. The maximum allowable hydraulic pressure decreased as the hole size increased and was inversely proportional to the hole diameter. The micromesh with a hole diameter of 20 mu m showed the highest waterproof performance, with a water height of 111 cm in the experiment. The measured maximum allowable hydraulic pressures were about 31% lower than the calculated pressures on average.</P>
A microcasted PDMS vacuum pad and its application for stacking thin ceramic layers
Hwang, Sung Jin,Lee, Sang Min,Jung, Im Deok,Jung, Phill Gu,Go, Jeung Sang,Ko, Jong Soo IOP 2009 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.19 No.8
<P>A PDMS vacuum pad for stacking very thin green sheets with a 3 µm thick dielectric layer is introduced and fabricated. Its applicability for producing multi-layer ceramic capacitors (MLCCs) is evaluated. Five micro-holes with a diameter and depth of 70 µm are formed on a single vacuum-line unit that is of 120 µm width, 100 µm depth and 2 mm length. Each vacuum-line unit with five micro-holes is deployed at 6 mm intervals on a PDMS vacuum pad of size 166 mm × 166 mm. To fabricate the PDMS vacuum pads, a mold with an obverse structure to that of the PDMS vacuum pad is needed. The metal mold has a two-stage nickel microstructure, the first stage for forming the vacuum lines and the second stage for forming the micro-holes. To fabricate the mold, micromachining processes, including photolithography, nickel/copper electroforming and chemical mechanical polishing, were conducted twice on a precision-machined SUS substrate with a size of 210 mm × 210 mm. The PDMS vacuum pads were fabricated through a microcasting process. Using the PDMS vacuum pad, 320 layers of green sheets, upon which nickel electrodes were patterned on 3 µm thick dielectric layers, were consecutively stacked. It has been observed that the stacked green sheets were very flat and uniform without any distortion or wrinkles. It is believed that the uniform stacking will greatly help to improve the production yield as well as enhance the reliability of MLCCs.</P>