Characterization and Design of Organic Field-Effect Transistor Circuits for Sensing Bioelectromagnetism NSF Summer Undergraduate Fellowship in Sensor Technologies

Current scanning technology for the brain and heart requires electrodes to be placed on the surface, with a wire connected to each electrode. Because the electrodes are large, it is impossible to achieve a high sampling resolution of the signals from the tissue being scanned. Silicon based structures are not very suitable for this application. They have a rigid planar surface which prevents them from capturing a high degree of information from the three dimensional structure of the brain or the heart. However, an organic transistor, fabricated on flexible plastics, should be able to conform to and output a high degree of information from a three-dimensional structure. To test the ability of organic transistors to read data, an organic field-effect transistor was placed in a common source configuration. This configuration, when used with an organic transistor, allows the electrodes to conform to the structure, appear in higher density, and cover a larger area. A 50μm channel length transistor was able to operate with a low frequency gain of 0.97V/V and with a cutoff frequency of 91Hz. Organic field-effect transistors fabricated into circuits that are more complex were analyzed so that they could be considered for amplification purposes. A 6μm channel length inverter showed a low frequency gain of 3.2V/V and a cutoff frequency of 145Hz. A 10μm channel length cascode showed a low frequency gain of 2V/V with a cutoff frequency of 220Hz. These results suggest that organic field-effect transistors have the ability to measure and amplify a small signal and become an effective tool for mapping high-density signals of the brain and the heart.