Surface Potential Imaging of Solution Processable Acene-Based Thin Film Transistors

Scanning Kelvin probe microscopy (SKPM) of functioning solution processed thin film transistors is used to correlate film microstructure with device performance. As the channel length increases in these spun-cast devices, significant changes occur in the film microstructure within the device channel.These changes are observed with SKPM and show a strong structure-function relationship.

Thin film electronic devices fabricated using organic semiconductors, insulators and conductors are expected to greatly impact the semiconductor electronics industry by significantly reducing manufacturing costs and expanding the applicability of active thin film electronics. With that, organic thin film transistors (OTFTs) have been a topic of intense interest for over a decade. Despite significant improvements to the electrical performance of OTFTs over this time, surprisingly little is known about the fundamental mechanisms governing charge injection and transport in the transistor channel. In this work we present SKPM measurements of the potential distribution in solution-processed, bottom-contact OTFTs to determine the role of film microstructure on device performance. By examining devices with a series of channel lengths, we are able to correlate the potential profile across the device and the morphology of the organic layer within the channel to the measured device mobility. Our SKPM results have provided a platform in which we were able to simultaneously probe the topography and the local potential drops within working OTFT devices (see Figure at right). Our results, explicitly demonstrate a correlation between organic thin film microstructure and potential drops within the working device. The nature and specific location of the potential drop varies with the device channel length for these systems. Short channel devices are dominated by the barriers at the organic-electrode interfaces. As the channel length increases, however, grain boundaries and regions of poorly nucleated material play a more important role in determining the mobility of the system. This work illustrates the importance of processing and metrology in the development of optimal low cost, solution processable organic electronic devices.

• Scanning Kelvin Probe Measurement of functioning devices
• Measure interdependence of film microstructure, voltage drops within the active device and device mobility
• Development of metrology tool for organic thin film transistors