Andreas Ullmann

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.