Freestanding hydride vapor phase epitaxy grown GaN(Gallium Nitride) substrates subjected to various polishing methods were characterized for their surface and subsurface conditions. Although CMP(Chemical Mechanical Polishing) is one of the best approaches for reducing scratches and subsurface damages, the removal rate of Ga-polar surface in CMP is insignificant(0.1-0.3㎛/hr) as compared with that of N-polar surface. Therefore, conventional MP(Mechanical Polishing) is commonly used in the GaN substrate fabrication process.
MP of (0001) surface of GaN has been demonstrated using diamond slurries with different abrasive sizes. Diamond abrasives of size ranging from 30㎚ to 100nm were dispersed in ethylene glycol solutions and mineral oil solutions, respectively. Significant change in the surface roughness (R_a 0.15㎚) and scratch-free surface were obtained by diamond slurry of 30㎚ in mean abrasive size dispersed in mineral oil solutions. However, MP process introduced subsurface damages confirmed by TEM (Transmission Electronic Microscope) and PL(Photo-Luminescence) analysis.

Light guide plate is one of most important components which are composed of back light unit, affecting the quality and performance of LCD. Average brightness and uniformity are especially key factors for designing the light guide unit. These qualities are affected and controlled by the pattern being attached to the back of light guide unit. In order to obtain high brightness and uniformity the optimized pattern design is adopted for LGP. In this study, optimized molding condition for LGP with 0.4 ㎜ thickness was obtained by using the Moldflow simulation software and the optimized pattern for better brightness uniformity was designed for the thickness of the 0.4 ㎜ by trial and error method. The brightness was measured for the different LGP thicknesses and the residual stress analysis was performed for 0.4 ㎜ thickness by the photoelasticity and the results are compared with 0.5 ㎜, 0.6 ㎜ thickness.

As multiple functions are required in a robot controller, RTOS(Real Time Operating System) should be adopted to manage complex situations, such as choosing most urgent task among competing ones. In this paper, we implemented RTAI(Real Time Application Interface) based robot controller for wafer handling robots including graphic simulator. We showed how multiple tasks are organized and also explained in detail about task priorities and execution periods. Finally, we presented simulation results.

The traditional engine valve train in a combustion engine is the mechanically driven camshaft system that provides one-fixed valve timing. The variable valve timing (VVT), however, is highly required to achieve the significant improvement in fuel economy. To achieve VVT in combustion engine, the solenoid type of actuator had been developed in past years, but it requires current in all operation period, the starting is difficult and the efficiency is low. In this paper, a new linear actuator using permanent magnet (PM) is proposed and verified its feasibility by finite element (FE) analysis.

Polynomial is used to optimize crown bowl shape of a marine medium speed diesel engine piston. The primary goal of this paper is that it's for an original design through a thermal stress and highest temperature minimum. Piston is modeled using solid element with 6 design variables defined the positional coordinate value. Global optimum of design variables are found and evaluated as developed and integrated with the optimum algorithm combining genetic algorithm(GA) and tabu search(TS). Iteration for optimization is performed based on the result of finite element analysis. After optimization, thermal stress and highest temperature reduced 0.68% and 1.42% more than initial geometry.

Microcellular foaming plastics create a sensation at polymer industrial for lowering product costs and overcoming a lowering of mechanical intensity. Among many advantages, microcellular foaming plastics is well known to have a good acoustical properties. This research based on the experiment of sound absorption and transmission characteristics inquire into acoustical properties of microcellular foaming plastics. Difference of transmission loss of microcellular foaming plastics and solid materials was defined as cell effect. Also, cell effect is expressed by sound reflection and sound absorption. This study is expected to fundamental research to present economical, functional alternative plan for products using sound absorption and transmission materials.

Piezoelectric materials have been investigated as vibration energy converters to power wireless devices or MEMS devices due to the recent low power requirements of such devices and the advancement in miniaturization technology. Piezoelectric power generation can be an alternative to the traditional power source-battery because of the presence of facile vibration sources in our environment and the potential elimination of the maintenance required for large volume batteries. This paper represents the new power source which supplies energy device node. This system, called "energy harvesting system", with piezo materials scavenges extra energy such as vibration and acceleration from the environment. Then it converts the mechanical energy scavenged to electrical energy for powering device This paper explains the properties of piezo material through theoretical analysis and experiments The developed system provides a solution to overcome the critical problem of making up wireless device networks.

A total stroke of an opening or closing motion of a hinge mechanism in a folder-type mobile phone is composed of two portions. In the first portion, human fingers act a force to open or close the folder. In this portion, the rotating folder compresses the coil spring installed in the mechanism. In the last portion, this compressed coil spring generates a torque to rotate the folder. The main merit of this study is that we have designed a hinge mechanism to be operated by a uniform torque in the first portion of the total stroke. The uniform torque means that it is constant along the folder's swing angle. This mechanism will give softer feeling to human fingers. A pair of contours in the mechanism plays an important role. It transforms rotation into translation in the first portion; on the other hand, it transforms translation into rotation in the last portion. In this study, we have developed an algorithm to obtain the pair of contour curves. We divided the total contour curves into finite sub-intervals. Assuming that the curves in every sub-interval are parabolas, we have obtained the coefficients of them by solving systems of nonlinear equations recursively.

A miniature metal bellows is used to minimize the excessive flow of the cryogenic gas in Joule-Thomson micro cryocooler. It is made of metal alloy and its geometry is axisymmetric. The bellows is filled with high pressure gas. It contracts or expands in the axial direction for a wide change of temperature, because the pressure and volume inside the bellows must be satisfied with state equation of the gas. Therefore, in order to design the bellows in Joule-Thomson micro-cryocooler, it is important to evaluate deformation of the bellows under internal pressure exactly. Considering geometric nonlinearity, deformations analysis of the bellows were obtained by a commercial finite element code ANSYS. The bellows was modeled by 3-node axisymmetric shell elements with reduced integration. Experiments were also performed to prove the validity of proposed numerical analysis. The results by numerical analysis and experiments were shown in good agreements.

In-plane shear tests were performed to investigate the shear property change of FRP by plasma modification. Graphite/epoxy prepreg was used as a test material and plasma source was a microwave (2.4㎓) type. Plasma was induced by oxygen gas and its flow rate was kept 4~5sccm with low vacuum state of 10?³ Torr. Prepreg was stacked unidirectionally ([0?]?) after plasma modification. Wettability was determined by measuring a contact angle. The results showed that the contact angle was decreased from 86° to 45° after plasma modification. Shear strength was also improved by~10%. SEM examination was made on the fracture surface and functional group produced by the plasma modification was investigated by XPS.

The cleaning process of contaminant particles adhering to the microchips, integrated circuits (ICs) or the like is essential in modem microelectronics industry. In the cleaning process particularly working with the application of inert gases, the removal of contaminant particles of submicron scale is very difficult because the particles are prone to reside inside the boundary layer of the working fluid. The use of cryogenic CO₂ cleaning method is increasing rapidly as an alternative to solve this problem. In contrast to the merits of high efficiency of this process in the removal of minute particles compared to the others, even fundamental parametric studies for the optimal process design in this cleaning process are hardly done up to date. In this study, we attempted to measure the cleaning efficiency with the variations of some principal parameters such as mass flow rate, injection distance and angle, and tried to draw out optimal cleaning conditions by measuring and evaluating an effective cleaning width called d??.