Gate insulators influencing electronic transport in organic FETs

Low‐k Insulators as the Choice of Dielectrics in Organic Field‐Effect Transistors

“…Stray capacitances were negligible. In some cases, the frequency dependence of the capacitance was also studied [24].…”

“…We have recently been developing multiple layer gate insulators comprising a high permittivity layer to maximize the capacitance and a thin, low polarity layer adjacent to the semiconductor, which minimizes trapping at the interface. [24] The gate-insulator effect described here is a unique feature of organic materials, the majority of which exhibit no electronic bands. Conventional semiconductors are insensitive to it because random dipoles at the interface are unlikely to affect significantly a large extended state or a wide band.…”

Effect of the hydrophobicity and thickness of polymer gate dielectrics on the hysteresis behavior of pentacene-based field-effect transistors

“…8, a hysteresis with clockwise loop direction is found in the presence of a large number of polar functionalities, and water molecules, ionic impurities in the thick gate dielectric. These species cause slow polarization, [23][24][25][26][27][28][29][30] in the same way as the charges injected from the gate electrode trapped in the gate dielectric. [43][44][45] In this study, however, the above issue can be excluded as a cause of clockwise hysteresis because hysteresis was only observed in ambient air.…”

“…[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Gu et al 15,16 found that in the case of pentacene-based OFETs containing octadecyltrichlorosilanemodified SiO 2 gate dielectrics, the hysteresis observed during the full swing of a gate is due to long-lived charge traps present at the interface between semiconductor and gate dielectric, where trapping and detrapping of holes and electrons take place under an applied gate bias. [15][16][17][18] Further, water molecules in the air could create hysteresis-causing charge traps at the semiconductor/dielectric interface.…”

“…Although these results indicate that the formation of hysteresis-causing traps at the semiconductor/gate dielectric interface is strongly responsible for the observed hysteresis, the presence ͑in the dielectric bulk͒ of chemical species that cause slow polarization ͑e.g., polar functionalities, ionic impurities, and diffused water molecules͒ is also an important cause for the hysteresis observed in the OFETs. [23][24][25][26][27][28][29][30] When a polymer is used as the gate dielectric in an OFET, the end functionalities present both at the polymer surface and in the bulk have an important influence on the device performance ͑e.g., drain current, mobility, threshold voltage, and hysteresis͒. 7,31-33 Although polar functionalities, such as hydroxyl groups, are known to seriously affect the hysteresis observed during the operation of polymer-dielectric-based OFETs, 17,18,[22][23][24][25]28,29 there are only a few research papers that discuss in detail how each constituent of the polymer gate dielectric contributes to the origin and mechanism of the hysteresis.…”