OLED has many advantages such as possibility to make micro size, tiny driving power, and fast response time with high resolution. However, significant commercial level problems are being recognized resulting from the damage of emitting layer, degradation of organic layers, and generation of dark spot. It is therefore necessary to overcome the problems for the development of high performance products. Deposition characteristic associated with the materials failure in OLED has been determined, firstly, by means of the analysis of the surface morphology and roughness of thin film. Physical vapor deposition technique was employed to develop test specimens, and atomic force microscopy has been used to identify the uniformity of emitting layer. In addition, optimal control set enabling the roughness of thin film surface to be minimized is presented, and the results obtained are compared with the experimental data. Generally good agreement has been achieved. It is known that the luminance decay mechanisms are directly related to the reliability of finished products, and thus further investigation has been carried out using the luminance decay curves. As shown by the results, the luminance decay may be divided into two major components during the failure processes. One is simple exponential during operation and the other is rapid decline in the initial stages of operation. It can be thought that the simple exponential decline is related to a chemical degradation of Hole Transport Layer, whereas the rapid decline is probably due to the generation of an internal electric field.