Walter Fix

Fast polymer integrated circuits

Using soluble polymers for the active layer and insulating layer, we report on a concept for the fabrication of fast integrated circuits based on p-type organic transistors only. Ring oscillators with frequencies above 100 kHz and propagation stage delays below 0.7 μs are presented. They show a very stable performance over time even without encapsulation, when stored and measured under ambient conditions. Regioregular poly(3-alkylthiophen) is used as the active semiconducting layer, a polymer blend as the insulator, a flexible polyester film as the substrate and metal electrodes. To enable vertical interconnects, the insulating layer is patterned.

Stability of polythiophene-based transistors and circuits

Detailed investigations on shelf life and operation lifetime of polymer field-effect transistors (PFETs) and circuits are reported. All examined devices consisted entirely of polymer materials except the electrodes. Regioregular poly(3-alkylthiophene) was used as a semiconductor. Unencapsulated devices were produced, stored, and measured under ambient conditions. The performance of PFETs was maintained for more than 12 months after production. Even under extreme conditions of 85 °C and 85% relative humidity, a stable shelf life of more than 1400 h was measured. Transistors exceeded a continuous operation time of 1000 h. Operation lifetimes showed that the degradation did not follow the Arrhenius lifetime-temperature relationship. Similar results were found for ring oscillators.

Dynamic and lifetime measurements of polymer OFETs and integrated plastic circuits

Organic Field-effect Transistors (OFETs) with poly(3-alkylthiophene) (P3AT) as semiconductor on flexible polymeric substrate and organic insulator in top gate construction were prepared. These transistors show a high field-effect mobility, good saturation behavior for low biases and rather high on-off ratio. The transistors were characterized through dynamic and lifetime measurements. A switching speed of 38 kHz at a 3 dB modulation depth was reached in a single transistor. The shelf-lives of the transistors exceeded six months without any special encapsulation. In addition different integrated plastic circuits (IPC) were constructed consisting of several organic transistors including NAND/NOR gates, bi-stable flip-flops and ring-oscillators with a oscillating frequency of 68 Hz.

Fast Polymer Integrated Circuits Based on a Polyfluorene Derivative

Low-cost fabrication of integrated circuits on flexible substrates is best realised by using semiconducting and insulating polymers from solution. We report on a novel concept based on p-type organic transistors only. A poly(fluorene bithiophene) derivative is used as active semiconducting layer, a copolymer blend as insulator, a flexible polyester film as substrate and metal electrodes. To enable vertical interconnects, the insulating layer is patterned. Polymer FETs (PFET) with a mobility of 0.015 cm/Vs and an on/off ratio above 10 are presented as well as ring oscillators with frequencies of 10 kHz and propagation stage delays of 10 μs. These results clearly indicate, that integrated plastic circuits (IPC) based on soluble polymer semiconductors and processed on flexible films are very suitable for inexpensive high volume electronic applications.