High Mobility Solution Processed Organic Semiconducting Blends for Ultra-High Frequency Operation

IoT (Internet of Things) is thought to be one possible key-aspect for a future technological revolution, in which specific functionality are cost-effectively integrated in daily objects, creating an extended network of interacting devices via wireless communication. This would be very helpful in many application-fields, ranging from health-care to distributed-sensing. In this scenario, organic electronics has the potential to be a promising technology tanks to its compatibility with simple large-area and low-cost fabrication processes. Moreover, the possibility of using flexible and conformable substrates is highly desirable to realize wearable and light-weight devices. However, to ensure wireless communications one has to face many challenges. In particular, to maximize operational frequency of a single organic transistor it is highly desirable downscale device dimensions to reduce unwanted parasitism and increase channel transconductance, since they directly depend on channel and overlap length. Unfortunately, this is not trivial since many undesired phenomena will occur at small scale, among which contact limitations are maybe the most relevant, reducing the overall performances and nullifying all the results obtained in many years in improving transport properties. In this work it is demonstrated the successful use of a solution-processed dopant injection layer in short channel and low overlap (<i>L_C</i> = 2um, <i>L_OV</i> = 3um) field-effect transistors in combination with C₈-BTBT: C₁₆-IDT-BT (1:4) blend as active material, which is among the best performing solution processed poly-crystalline existing organic semiconductors, yet to be exploited in downscaled devices. This approach was successful to reduce contact resistance, therefore allowing to retain good mobility in short channel devices, reaching values as high as 3 cm²/Vs in downscaled structures with a suitable geometry for high-frequency. This fundamental step, in combination with direct-writing approaches for device fabrication, is fundamental for the development of next-generation organic field-effect transistors operating in the UHF regime, which was thought for a long time to be out of reach for organic electronics, especially for solutions based approaches.