Organic materials have been drawing attention for variety of applications in optics and electronics due to the enormous possibility of designing the material function by controlling the molecular structure. For the development of practical devices, these functional organic materials are often required in the form of stable thin films. The conventional methods of forming organic thin films include casting and spin coating from their solutions. However, these films do not necessarily fulfill the recent requirement for advanced device technology. In many cases, uniform and stable thin films of several nanometer thick are required. Some of the functional materials are insoluble to any common solvents. For such advanced requirements, the physical vapor deposition can be a strong candidate for the fabrication technology of functional organic devices.
Physical Vapor Deposition
Many organic materials can be evaporated by heating in vacuum, and can be formed into thin films by condensing the vapor on substrates. This vacuum deposition technique has the advantage of depositing a desired film thickness, even in nanometer range, in the clean environment of high vacuum. Although the vacuum deposition is widely used for film preparation of inorganic materials in industrial scale, it has sparsely been applied for organic materials except for academic purpose, since the solution-based methods are considered to have higher throughput and cost performance. On the other hand, recent advancement of organic light emitting diode was made possible by constructing multi-layered structure by vacuum deposition method. It indicates that the physical vapor deposition might be an indispensable technique for the development of future organic devices. It is therefore industrially, as well as academically, important to pursue a new technology for depositing functional and high quality organic thin films.
The concept of vacuum deposition.