Grain size effects on contact resistance of top-contact pentacene TFTs

Multiple top-contact OTFTs with various channel lengths (L-c) were successfully scaled-down to the L-c of 1.8 mu m by using the membrane shadow mask and the interface between the evaporated Au and pentacene was analyzed based on the channel resistance method. For large grain pentacene (S-80) deposited at 80 degrees C, the parasitic resistance (R-p) at VGs =-20 V has 1.8 +/- 0.2 k Omega cm, whereas for small grain pentacene (S-20) deposited at 20 degrees C has 4.2 +/- 0.2 k Omega cm, which means that R-p depends on the grain size of pentacene. The grain size and grain boundary trap density for pentacene can be possibly origins to determine R-p which is critically correlated with bulk transport in pentacene. The grain boundary trap density (N-t) for S-80 and S-20 was extracted as (5.6 +/- 0.5) x 10(11) and (1.2 +/- 0.3) x 10(12) cm(-2) from the Levinson plots, respectively. In addition, activation energy of R-p for S-80 is in the range from 42 to 48 meV, whereas for S-20 is from 72 to 108 meV. (c) 2005 Elsevier B.V. All rights reserved.