Contact effects analyzed by a parameter extraction method based on a single bottom-gate/top-contact organic thin-film transistor

Abstract

Contact effects in organic thin-film transistors (OTFTs) were examined by using our previously proposed parameter extraction method from the electrical characteristics of a single staggered-type device. Gate-voltage-dependent contact resistance and channel mobility in the linear regime were evaluated for bottom-gate/top-contact (BGTC) pentacene TFTs with active layers of different thicknesses, and for pentacene TFTs with contact-doped layers prepared by coevaporation of pentacene and tetrafluorotetracyanoquinodimethane (F4TCNQ). The extracted parameters suggested that the influence of the contact resistance becomes more prominent with the larger active-layer thickness, and that contact-doping experiments give rise to a drastic decrease in the contact resistance and a concurrent considerable improvement in the channel mobility. Additionally, the estimated energy distributions of trap density in the transistor channel probably reflect the trap filling with charge carriers injected into the channel regions. The analysis results in this study confirm the effectiveness of our proposed method, with which we can investigate contact effects and circumvent the influences of characteristic variations in OTFT fabrication.

Use of doping to achieve low contact resistance in bottom-gate top-contact type organic transistor with liquid-crystalline organic semiconductor, Ph-BTBT-10

“…In order to reduce the contact resistance and threshold voltage and improve various characteristics of FETs, depositing acceptor dopants on the surface of organic semiconductors and mixing of organic semiconductors with dopants are common techniques. [16][17][18][19][20][21][22][23][24][25][26][27][28][29] In the case of depositing acceptor dopants, regarding contact resistance, it is difficult to reduce the bulk resistance of the organic semiconductor layer under the source/drain electrode in a BGTC-type FET because the dopant molecules are only located on the surface of the organic semiconductor layer. Therefore, in order to reduce the contact resistance in BGTC-type FETs, it would be necessary for the dopant molecules to diffuse into the bulk under the source/drain electrodes.…”