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-mu m-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 degrees 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 mu A/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.