High-speed plastic integrated circuits: Process integration, design, and test

In this paper we propose the design and measurement of functional analog and digital circuits with a response time below 1 ms, based on organic thin film transistors (OTFTs) fabricated by means of contact photolithography and self-alignment procedures. An adapted amorphous Silicon TFT compact model is used both in analytic equations and in DC Spice simulations for the design of simple organic circuits. Digital circuits such as inverters and logic gates are demonstrated with DC gains of almost 19 dB. Two analog circuits are also shown: First a differential amplifier with an open loop DC gain of 10 dB and a gain-bandwidth of 3 kHz, and second, a source coupled latch comparator tested with an input frequency of 1 kHz and a clock frequency of 10 kHz. These simple circuits comprised of only a few OTFTs are fabricated directly on flexible plastic sheets and therefore are ideal front-end interfaces for the control and fast read-out of flexible sensors.