Effect of active layer thickness on device properties of organic thin-film transistors based on Cu(II) phthalocyanine

We investigated the device properties of Cu(II) phthalocyanine (CuPc)-based bottom-contact thin-film transistors (TFTs) with various active layer thicknesses. The operating performance of the TFTs depended on the thickness, and a device with a CuPc layer of 80 nm showed the maximum field-effect mobility. We found that the field-effect mobility of the thinnest and thickest devices exhibited a marked source–drain bias dependence. The characteristics of these devices were not as good as those of the other TFTs. We attributed the source–drain bias dependence to a significantly trap-affected carrier transport process in a conduction channel formed in the vicinity of the gate insulator. We concluded that, in these TFTs, the conduction channel was formed at a different position in the CuPc layer depending on the thickness, and the thickness dependent operating performance originated from variations in the effect of carrier trapping on the carrier transport process in these conduction channels.