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Organic Electronic Materials and Devices

An organic semiconductor material technology that employs printing methods to produce organic thin-film transistors and other electronic devices makes it possible to simply fabricate large-area devices on film.

Organic Semiconductor Material Technology Revolutionizes the Semiconductor Device Manufacturing Process

Electronic products, which have permeated every nook and cranny of society and our lives, are currently made using silicon semiconductor devices. However, today's semiconductor devices, cut from silicon wafers using a process such as photolithography, require large-scale, energy-intensive industrial facilities. Therefore, miniaturization and mass production of standardized devices is necessary. On the other hand, organic semiconductor materials, which can be made into an ink solution, have the potential to greatly transform the semiconductor device manufacturing process (Figure 1). For instance, the application of inkjet printing makes it possible to offer electronic devices that accommodate diverse needs in minute detail. This development is expected to result in a new electronics.

Figure 1:Fabrication process comparison
Figure 1:Fabrication process comparison

Ricoh has pioneered practical application of the first genuine organic photoconductors (OPCs) and mounted them on copiers and printers that lead the industry in high sensitivity and durability. Building on the foundation of the organic semiconductor material technologies nurtured in OPC material development, we are actively engaged in the research and development of electronic devices, beginning with organic thin-film transistors. Taking materials technology as the starting point and making the most of one of Ricoh's strengths, the capability to comprehensively engage in research and development of device application technologies and inkjet printing and other process technologies to create product functions, we are focusing on advanced R&D to create new products such as e-paper and displays (Figure 2).

Figure 2: Thin-film transistors (TFTs) for display devices
Figure 2: Thin-film transistors (TFTs) for display devices

Original Organic Semiconductor Polymer Capitalizing on In-depth Expertise

To apply organic semiconductors to a printing process, it is necessary to produce ink with high solvent resolvability and viscosity suited to the printing process. Also, in the production of thin-film transistors (TFT), uniform film-forming characteristics are required because it is necessary to fabricate thin film free of minute voids as small as several dozen nanometers. Accordingly, Ricoh judged that an amorphous polymer had the potential to become the semiconductor material with the highest utility and proceeded with development on that basis. Ordinarily, amorphous polymer utility tends to entail a trade-off with charge carrier mobility. However, pursuing a molecular structure suited to carrier mobility, for which Ricoh's experience in development of OPC materials was utilized, we were able to design a semiconductor polymer maximizing solubility, film deposition characteristics, and mobility. This made it possible to simply fabricate TFTs using spin coating and inkjet printing and to increase FET hole mobility to approximately 0.01cm2/Vs, the level required for practical applications (Figure 3).

Figure 3: Relation between carrier mobility and solubility of organic semiconductors
Figure 3: Relation between carrier mobility and solubility of organic semiconductors

Expectations for Creation of New Electronics

With the highly practical organic semiconductor polymer obtained in this way, it will be possible to fabricate the TFTs that drive e-paper and display pixels using printing processes and apply them to light, flexible film-based display devices. This is expected to be the first step toward the concrete realization of organic electronics satisfying customer needs in the age of ubiquitous computing. The application of printing processes to large-scale displays has the potential to open the way to new advertising media. Furthermore, the application of these printing processes to the production of information tags may give rise to new document management systems. Organic electronics is expected to lead to the creation of a new electronics.

Related Papers

"The Stilbene Polymers for Organic Field-Effect Transistors." , 2003 MRS Fall meeting (December, 2003)