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Pentacene is a good candidate for organic thin film transistors. We have studied charge injection and electrical properties of the top and bottom metal/pentacene thin film contacts using I-V characterization and electric force microscopy. Between the top and bottom contact, the top contact is known to perform better. When pentacene is deposited on a metal substrate, an amorphous wetting layer is known to form initially before crystalline layers form. Therefore, bottom electrode metal makes a contact with pentacene amorphous layer but top electrode metal makes a contact with crystalline pentacene. To study how the two interfaces are different, we prepared pentacence thin films sandwiched between top and bottom contacts. When the top and bottom electrodes were made of different metal, we obtained diode-like I-V curves which could be explained in terms of the Schottky barrier difference at the top and bottom interface. When the same metal was used for the top and bottom electrodes, I-V curves were also asymmetric which seemed due to the different amount of charge injection into pentacene. We also found that the mechanical bonding between the sidewall of bottom electrode and pentacene molecules strongly depended on the geometry of an electrode. We will also show an example of how the pentacene device performance can be limited because of the poor bottom contact. This work was supported by the Korea Science and Engineering Foundation through NCRC program of Seoul National University. |