Impact of semiconductor/metal interfaces on contact resistance and operating speed of organic thin film transistors

Abstract

The contact resistance of field effect transistors based on pentacene and parylene has been investigated by experimental and numerical analysis. The device simulation was performed using finite element two-dimensional driftdiffusion simulation taking into account field-dependent mobility, interface/bulk trap states and fixed charge density at the organic/insulator interface. The width-normalized contact resistance extracted from simulation which included an interface dipole layer between the gold source/drain electrodes and pentacene was 91 k cm. However, contact resistance extracted from the simulation, without consideration of interface dipole was 52.4 k cm, which is about half of the experimentally extracted 108 k cm. This indicates that interface dipoles are critical effects which degrade performances of organic field effect transistors by increasing the contact resistance. Using numerical calculations and circuit simulations, we have predicted a 1 MHz switching frequency for a 1 µm channel length transistor without dipole interface between gold and pentacene. The transistor with dipole interface is predicted, via the same methods, to exhibit an operating frequency of less than 0.5 MHz.

Modeling and Simulation of Organic Field Effect Transistor (OFET) Using Artificial Neural Networks

“…Increasing the electric field will help these trapped charges to exit the trap. The release of these charge carriers will result in a large increase in the drain current of the device [13].…”

Influence of active layer thickness, device architecture and degradation effects on the contact resistance in organic thin film transistors

“…TC-TFTs presented mobilities one order of magnitude higher (4.8 × 10 -2 cm 2 /V•s) than BC-TFTs (1 × 10 -3 cm 2 /V•s). Changes in mobility on BC-TFTs have been attributed to contact (semiconductor/metal) effects due to a dipole barrier that can shift the vacuum level upward by more than 1 eV, avoiding carriers to reach the HOMO level [22][23][24]. However, mobility is not dependent on the contacts used in the TFT and is normally dictated by the dielectric/semiconductor interface in both TC and BC structures.…”

Solution processed copper tetrabenzotriazaporphyrin films for organic field effect transistors

“…estimated to be ∼1.33 × 10 −2 cm 2 /V 3/2 s from the slope of the linear fit to the plot of ln μ sat vs √V on a log-linear scale and this positive value of β implies that the positional order is small in comparison with the width of the Gaussian density of energy states. 40 Similarly configured OFETs using the seven monolayer thick Langmuir-Blodgett film of liquid crystalline 2,3,9,10,16,17,23,24-octakis((2cinnamyl) ethoxy) phthalocyaninato copper molecules exhibit a similar field dependence of the saturated mobility μ sat with the highest value of 1.8 × 10 −2 cm 2 V −1 s −1 at V G ¼ 40V, 41 which is found to be smaller than the corresponding value of the 6CuTBTAP molecule by a factor of more than three. The release of these charge carriers at high gate voltages results in a large increase in the drain current of the device due to the field enhanced thermal excitation.…”