AMPLIFICATION CIRCUITS AND PATTERNING METHODS OF ORGANIC FIELD-EFFECT TRANSISTORS NSF Summer Undergraduate Fellowship in Sensor Technologies

Organic transistor technology holds great promise for creating a conformal, human-safe electronic neural interface. These interfaces must amplify the low, microvolt-range brain signals so they can be utilized in analog and digital applications. Brain signals from sensors must be relayed to the transistor’s gate through the dielectric and semiconductor layers, as well as through an encapsulant which keeps the device shielded in the aqueous brain environment. In order to test their amplification gains, silicon wafer-based ambipolar organic transistors with a pentacene semiconductor were tested under nitrogen in amplifying configurations including common source and cascode. Gains for common source amplifiers with resistors were up to 3.5V/V. Gains for the cascode setup revealed the same results as common source. Both the common source and cascode topologies exhibited very low bandwidth with -3dB points of 35 and 25 hertz, respectively. Parylene C, a biologically safe polymer, is a leading candidate to encapsulate pentacene transistors and serve as a dielectric layer between the devices and sensing electrodes. We tested etching of this parylene as well as the dielectric materials benzocyclobutene (BCB) and spin-on-glass (SoG) using both oxygen and SF6 plasma etching. Parylene was etched at a rate of 0.2μm/min with O2 plasma. BCB and SoG did not exhibit useful etching under O2 or SF6 plasma.