• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.8
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• pp.110-116
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• 2020

Aircraft hydraulic oil reservoirs made with aluminum 7075 have an anodized coating to enable airtightness and corrosion resistance. To maintain a stable oil pressure, the internal surface roughness of the reservoir should be less than approximately 0.2 ㎛. To this end, precision polishing must be performed. However, ensuring the processing quality is challenging, as most polishing operations are performed manually, owing to which, the inner surface roughness is not uniform, and the product quality is irregular. Therefore, we developed a special superfinishing machine to realize the efficient inner polishing of an aircraft hydraulic oil reservoir, by using an abrasive film to improve the process throughput and uniformity. In the experiment involving the superfinishing of an anodized aluminum 7075 cylinder specimen by using the proposed machine, a higher surface roughness than that achieved in the repetitive manual polishing process could be realized.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.9 s.240
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• pp.1169-1174
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• 2005

Imprint lithography is a promising method for high-resolution and high-throughput lithography using low-cost equipment. In particular, ultraviolet-nanoimprint lithography (UV-NIL) is applicable to large area imprint easily. We have proposed a new UV-NIL process using an elementwise patterned stamp (EPS), which consists of a number of elements, each of which is separated by channel. Experiments on UV-NIL are performed on an EVG620-NIL using the EPS with 3mm channel width. The replication of uniform sub 70 nm lines using the EPS is demonstrated. We investigate the nonuniformity of residual layer caused by wafer deformation in experiment with varying wafer thickness. Severely deformed wafer works as an obstacle in spreading of dropped resin, which causes nonuniformity of thickness of residual layer. Numerical simulations are conducted to analyze aforementioned phenomenon. Wafer deformation in the process is simulated by using a simplified model, which is a good agreement with experiments.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.3
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• pp.175-184
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• 2001

In this study, the improved throughput and stability in device fabrication could be obtained by applying CMP process to STi structue in 0.18 um semiconductor device. To employ the CMP process in STI structure, the Reverse Moat Process used to be added after STI Fill, as a result, the process became more complex and the defect were seriously increased than they had been,. Removal rate of each thin film in STI CMP was not uniform, so, the device must have been affected. That is, in case of excessive CMP, the damage on the active area was occurred, and in the case of insufficient CMP nitride remaining was happened on that area. Both of them deteriorated device characteristics. As a solution to these problems, the development of slurry having high removal rate and high oxide to nitride selectivity has been studied. The process using this slurry afford low defect levels, improved yield, and a simplified process flow. In this study, we evaluated the 'High Selectivity Slurry' to do a global planarization without reverse moat step, and also we evaluated EPD(Eend Point Detection) system with which 'in-situ end point detection' is possible.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.155-156
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• 2006

UV-NIL is a promising technology for the fabrication of sub-100 nm features. Due to non-uniformity of the residual layer thickness (RLT) and a strong possibility of defects, many UV-NIL processes have been developed and some are commercially available at present, most are based on the 'step-and-repeat' nanoimprint technique, which employs a small-area stamp, much smaller than the substrate. This is mainly because, when a large-area stamp is used, it is difficult to obtain acceptable uniform residual layer thickness and/or to avoid defects such as air entrapment. As an attempt to enable UV_NIL with a large-area stamp for high throughput, we propose a new UV-NIL tool that is able to imprint 4 inch wafer in a low vacuum environment at a single step.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.4050-4067
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• 2014

In wireless sensor networks, link scheduling is a fundamental problem related to throughput capacity and delay. For a given set of communication requests $L=\{l_1,l_2,{\cdots},l_n\}$, the MLS (maximum link scheduling) problem aims to find the largest possible subset S of Lsuch that the links in S can be scheduled simultaneously. Most of the existing results did not consider bidirectional transmission setting, which is more realistic in wireless sensor networks. In this paper, under physical interference model SINR (signal-to-noise-plus-interference-ratio) and bidirectional transmission model, we propose a constant factor approximation algorithm MLSA (Maximum Link Scheduling Algorithm) for MLS. It is proved that in the same topology setting the capacity under unidirectional transmission model is lager than that under bidirectional transmission model. However, compared with some work under unidirectional transmission model, the capacity of MLSA is improved about 28% to 45%.

• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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• pp.199-204
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• 2008

Sensor nodes have various energy and computational constraints because of their inexpensive nature and ad-hoc method of deployment. Considerable research has been focused at overcoming these deficiencies through faster media accessing, more energy efficient routing, localization algorithms and system design. Our research attempts to provide a method of improvement MAC performance in these issues. We show that traditional carrier-sense multiple access(CSMA) protocols like IEEE 802.11 do not handle the first constraint adequately, and do not take advantage of the second property, leading to degraded latency and throughput as the network scales in size, We present more efficient method of a medium access for real-time wireless sensor networks. Proposed MAC protocol is a randomized CSMA protocol, but unlike previous legacy protocols, does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports, it carefully decides a fixed-size contention window, non-uniform probability distribution of transmitting in each slot within the window. We show that it can offer up to several times latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using widely used simulator ns-2. We, finally show that proposed MAC scheme comes close to meeting bounds on the best latency achievable by a decentralized CSMA-based MAC protocol for real-time wireless sensor networks which is sensitive to latency.

• Journal of Communications and Networks
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• v.18 no.4
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• pp.639-648
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• 2016

Next-generation (4G) systems are designed to support universal frequency reuse (UFR) to achieve best use of valuable spectra. However, it leads to undesirable interference level near cell borders. To control this, 4G systems adopt techniques, such as network multiple-input multiple-output (MIMO) and inter-cell interference coordination (ICIC), to improve cell-edge throughput. Network MIMO aims at mitigating inter-cell interference towards cell-edge users (CEUs) through multi-cell cooperation, where each collaborative base station serves both cell-center users (CCUs) and CEUs, including other cells' CEUs, under a power constraint. The present ICIC strategies cannot be directly applied to network MIMO because they were designed in absence of multi-cell coordination. In the presence of network MIMO, this paper investigates antenna orientations in ICIC and the method of power management. Results show that a proper antenna orientation can improve the cell-edge capacity and meantime lower the interference to CCUs. Capacity inconsistency between CCUs and CEUs is detrimental to mobile communications. Simulation results show that the proposed power management for ICIC in network MIMO systems can achieve a uniform data rate regardless users' position.

• Journal of the Semiconductor & Display Technology
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• v.9 no.2
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• pp.91-96
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• 2010

In recent years there have been considerable attentions on nanoimprint lithography (NIL) by the display device and semiconductor industry due to its potential abilities that enable cost-effective and high-throughput nanofabrication. Although one of the current major research trends of NIL is large-area patterning, the technical difficulties to keep the uniformity of the residual layer become severer as the imprinting area increases more and more. In this paper we consider the roll-to-plate type imprinting process. In the process a glass mold, which is placed upon the 2nd generation TFT-LCD glass sized substrate(370${\yen}$470 mm), is rolled by a rubber roller to achieve a uniform residual layer. The pressure distribution on the glass mold by rolling of the rubber roller is crucial information to analyze mold deformation, transferred pattern quality, uniformity of residual layer and so forth. In this paper the quantitative pressure distribution induced by rolling of the rubber roller was calculated with finite element analysis under the assumption of Neo-Hookean hyperelastic constitutive relation. Additionally the numerical results were verified by the experiments.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.11
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• pp.44-52
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• 1998

In this paper, we proposed a node architecture and cell routing strategies for ATM applications in WDM multihop networks. The proposed node architecture employs the optical delay loop for storing the cell which is failed in out-link contention. This optical delay loop allows the delay of one cell without the electro-optic conversion. Therefore, we can get the advantages of S&F(Store-and-Forward) routing in Deflection-based all-optical networks. To support the ATM applications efficiently. we considered the transmission priority of ATM cell so that high priority cell can be transmitted with lower loss and shorter delay than low priority one. Two kinds of routing strategies are designed for this architecture: Scheme-Ⅰand Scheme-Ⅱ. Scheme-Ⅰapplies S&F routing to high cell and Deflection routing to low cell, i.e., high cells are routed along the shortest path based on S&F routing, but low cells are deflected or lost. Schem-Ⅱ is similar to Scheme-Ⅰexcept that low cells can occupy the optical loop if it is available. This Scheme-Ⅱ increases the utilization of network resources without decreasing the throughput of high cell by reducing the low cell loss rate when traffic load is low. Simulation results show that our routing strategies have better performance than conventional ones under non-uniform traffic as well as uniform traffic.

• Journal of KIISE:Information Networking
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• v.35 no.3
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• pp.192-206
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• 2008

Multihop is the main communication style for wireless sensor networks composed of tiny sensor nodes. Until now, most applications have treated the periodic small sized sensing data. Recently, the burst traffic with the transient and continuous nature is increasingly introduced due to the advent of wireless multimedia sensor networks. Therefore, the efficient communication protocol to support this trend is required. In this paper, we propose a novel PIGAB(Packet Interval Gap based on Adaptive Backoff) protocol to efficiently transmit the burst data in multihop wireless sensor networks. The contention-based PIGAB protocol consists of the PIG(Packet Interval Gap) control algorithm in the source node and the MF(MAC-level Forwarding) algorithm in the relay node. The PIGAB is on basis of the newly proposed AB(Adaptive Backoff), CAB(Collision Avoidance Backoff), and UB(Uniform Backoff). These innovative algorithms and schemes can achieve the performance of network by adjusting the gap of every packet interval, recognizing the packet transmission of the hidden node. Through the simulations and experiments, we identify that the proposed PIGAB protocol considerably has the stable throughput and low latency in transmitting the burst data in multihop wireless sensor networks.