Analog Characteristics of Fully Printed Flexible Organic Transistors Fabricated With Low-Cost Mass-Printing Techniques

Fully printed organic field effect transistors (OFETs) are fabricated on a flexible, 100-μm-thick, polyethylene terephthalate substrate using high-throughput printing techniques: 1) Cyflex; 2) gravure; 3) screen; and 4) flexographic printing without using a cleanroom, and below 130°C. The dependence of the transconductance g_m, transit-frequency f_T, and intrinsic-gain on the bias drain current I_D are measured. The OFETs show intrinsic gain for I_D >10 nA mm (per millimeter width), and reach f_T=64 kHz at I_D = 16 μA/mm, whereas the g_m loss with frequency is 10% up to f_T. Unlike silicon MOSFETs, the dependence of the OFET g_m on the f_T in the subthreshold region is found to be weaker than I_D^1.0. In addition, the overlap capacitance of the staggered-geometry OFET shows strong frequency dependence, and this is shown to be related to the overlap semiconductor. For the first time, it is found that the impact of process variations and bias stress on the OFET analog characteristics can be significantly attenuated by biasing the device at a fixed I_D. This approach is tested on an array of five amplifiers, reaching the gain-bandwidth product of 32 kHz, within ±3.7% variations.