An Organic Thin Film Transistor Circuit

The organic thin-film transistor (OTFT) is a field-effect transistor technology that uses organic materials as the semiconductor. OTFTs have field-effect mobilities that are comparable to those of hydrogenated amorphous silicon TFTs, and OTFTs are compatible with large-area and mechanically-flexible substrates. The goal of this work is to demonstrate an integrated OTFT temperature-sensing circuit suitable for large-area and flexible substrates.

Two important differences are observed between the OTFT’s and the MOSFET’s current-voltage characteristics when temperature is varied. First, the OTFT’s current increases with temperature in both subthreshold and above-threshold regimes, whereas the MOSFET’s above-threshold current decreases with temperature. Second, the OTFT’s subthreshold slope is temperature independent over the measured range of -20 to 60°C, while the MOSFET’s subthreshold slope is proportional-to-absolute-temperature (PTAT).

Because of these differences in temperature response, the OTFT temperature-sensing “delta-VBE circuit” has a complementary-to-absolute-temperature (CTAT) response instead of an equivalent silicon circuit’s PTAT response. The OTFT circuit is scaled to an array format to enable surface thermal sensing applications.