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

Multiple top-contact OTFTs with various channel lengths (Lc) were successfully scaled-down to the Lc of 1.8 μm 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 °C, the parasitic resistance (Rp) at VGS = −20 V has 1.8 ± 0.2 kΩ cm, whereas for small grain pentacene (S-20) deposited at 20 °C has 4.2 ± 0.2 kΩ cm, which means that Rp depends on the grain size of pentacene. The grain size and grain boundary trap density for pentacene can be possibly origins to determine Rp, which is critically correlated with bulk transport in pentacene. The grain boundary trap density (Nt) for S-80 and S-20 was extracted as (5.6 ± 0.5) × 1011 and (1.2 ± 0.3) × 1012 cm−2 from the Levinson plots, respectively. In addition, activation energy of Rp for S-80 is in the range from 42 to 48 meV, whereas for S-20 is from 72 to 108 meV.