TY - GEN
T1 - On the crucial role of the insulator-semiconductor interface in organic thin-film transistors
AU - Horowitz, Gilles
AU - Mottaghi, Mohammad
AU - Lang, Philippe
AU - Rodriguez, Fernand
AU - Yassar, Abderrahim
AU - Lenfant, Stéphane
AU - Vuillaume, Dominique
PY - 2006/12/1
Y1 - 2006/12/1
N2 - This paper reports on two sets of data. In the first one, organic thin-film transistors (OTFTs) where fabricated by vapor depositing a pentacene layer on a gate dielectric made of alumina. The devices divide in two sets, depending on whether the alumina surface was or was not modified with a self-assembled monolayer (SAM) of eicosanoic acid. Atomic force microscopy (AFM) images show that the presence of the SAM strongly reduces the size of the crystal grains. A careful analysis of the current-voltage characteristics of the devices, which includes the use of the Transfer Line Method (TLM), allowed the extraction of the gate voltage (VG) dependent mobility corrected for contact resistance. A remarkable feature is that the mobility decreases with V G at high gate bias, which is interpreted by assuming that the mobility in the layer close to the insulator-semiconductor interface is substantially lower than that in the bulk of the film. Modeling the charge distribution in the conducting channel allowed us to extract the bulk mobility, which is found to saturate at around 5 cm2/Vs in SAM-modified devices and 3 cm2/Vs in devices with bare alumina. The difference is interpreted in terms of more or less defective grains. The second set of results deals with a transistor, in which the active element is reduced to a single monomolecular layer. This was achieved by using a SAM of a bifunctional molecule comprising a quaterthiophene moiety linked to a short alkyl chain. AFM images of the SAM after various adsorption times show that the size of the well-organized domains is around 25 ± 5 nm. Working transistors could only be realized by reducing the channel length L down to a magnitude comparable to that of the domain size, which was achieved with the help of e-beam lithography. In one occasion, well-defined current-voltage characteristics was recorded, which allowed to extract a gate-voltage independent mobility of 0.0035 cm2/Vs.
AB - This paper reports on two sets of data. In the first one, organic thin-film transistors (OTFTs) where fabricated by vapor depositing a pentacene layer on a gate dielectric made of alumina. The devices divide in two sets, depending on whether the alumina surface was or was not modified with a self-assembled monolayer (SAM) of eicosanoic acid. Atomic force microscopy (AFM) images show that the presence of the SAM strongly reduces the size of the crystal grains. A careful analysis of the current-voltage characteristics of the devices, which includes the use of the Transfer Line Method (TLM), allowed the extraction of the gate voltage (VG) dependent mobility corrected for contact resistance. A remarkable feature is that the mobility decreases with V G at high gate bias, which is interpreted by assuming that the mobility in the layer close to the insulator-semiconductor interface is substantially lower than that in the bulk of the film. Modeling the charge distribution in the conducting channel allowed us to extract the bulk mobility, which is found to saturate at around 5 cm2/Vs in SAM-modified devices and 3 cm2/Vs in devices with bare alumina. The difference is interpreted in terms of more or less defective grains. The second set of results deals with a transistor, in which the active element is reduced to a single monomolecular layer. This was achieved by using a SAM of a bifunctional molecule comprising a quaterthiophene moiety linked to a short alkyl chain. AFM images of the SAM after various adsorption times show that the size of the well-organized domains is around 25 ± 5 nm. Working transistors could only be realized by reducing the channel length L down to a magnitude comparable to that of the domain size, which was achieved with the help of e-beam lithography. In one occasion, well-defined current-voltage characteristics was recorded, which allowed to extract a gate-voltage independent mobility of 0.0035 cm2/Vs.
KW - Gate-voltage dependent mobility
KW - Pentacene
KW - Self-assembled monolayers
KW - e-beam lithography
U2 - 10.1117/12.680345
DO - 10.1117/12.680345
M3 - Conference contribution
AN - SCOPUS:33751419565
SN - 0819464155
SN - 9780819464156
T3 - Proceedings of SPIE - The International Society for Optical Engineering
BT - Organic Field-Effect Transistors V
T2 - Organic Field-Effect Transistors V
Y2 - 13 August 2006 through 15 August 2006
ER -