Improved Performance of Pentacene OTFT with HfLaO Gate Dielectric by Annealing in NH_3

摘要

Organic thin-film transistors (OTFTs) have attracted wide attention due to their advantages such as low cost, low-temperature processing, and use of flexible substrate in large area when compared with their inorganic counterparts (1). Thus OTFTs can be potentially applied to RF identification card, large-area flexible display, electronic paper and so on (2), (3), (4). Pentacene OTFTs with SiO_2 as gate insulator have achieved a performance comparable to that of amorphous-silicon thin-film transistors in terms of carrier mobility (5). However, the operating voltage is usually too high (> 15 V). This is especially a challenge for the development of portable instruments. To solve this problem, dielectrics with high dielectric constant have been used as the gate insulator of the OTFTs (6), (7), (8). Sputtering is extensively used for the synthesis of thin films, and is favorable for the preparation of gate insulator in OTFTs due to the fact that this method can realize large-area films at low processing temperature. In this work, pentacene OTFT with HfLaO gate dielectric prepared by sputtering method is studied in details due to its relatively high carrier mobility. To improve the surface characteristics of the dielectric, the HfLaO film is annealed in N_2, NO and NH3 respectively. Results show that the NH3 annealing gives better performance in terms of carrier mobility and noise characteristics due to its better passivation effects on the surface of the gate dielectric.