Effects of geometrically extended contact area on electrical properties in amorphous InGaZnO thin film transistors

•Amorphous InGaZnO transistors with different contact areas were fabricated.•Transistors with extended contact area have better electrical properties.•Contact resistance and channel resistivity were extracted by transmission line method.•Transfer length and specific contact resistivity were calculated.•The relationship between the contact resistance and the contact area was established.

To elucidate the effect of the contact geometry on the device performances, the amorphous InGaZnO field effect transistors with different contact areas were fabricated and compared by the transmission line method. Extended contact-area devices were found to have better electrical performances in field effect mobility and subthreshold swing than those of bar-shaped reference devices. These improvements in the device characteristics resulted from a significantly reduced contact resistance (Rc). From the comparison of specific contact resistivity and transfer length (LT), the relationship between Rc and contact area including the contact width and the LT was established and demonstrated that Rc is controllable by optimizing the contact area geometry.