Carrier dynamics and fast switching by dipole engineering in solution processed thin film transistors

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

Abstract: Non-Technical: Low-cost, large area, solution processed, thin film polymer transistors are emerging as a next-generation technology, allowing electronic components to be integrated into flexible substrates. However, polymer thin film transistors suffer from low switching times, rendering their use in analytical and digital logic circuits problematic. Fast switching times in polymer transistors may be achieved by miniaturizing the device size, but this requires nanolithography, which is impractical for low-cost printing methods. This project utilizes low-cost strategies for materials engineering to improve switching times by orders of magnitude compared to the present state-of-the-art thin film polymer transistors, which will open up the printed polymer circuit technology for many new applications. Furthermore, a new experimental method based on non-linear optics will be developed for probing and visualizing the motion of charges in polymer transistors. This technique allows an accurate determination of the carrier mobility, which is a crucial parameter that controls switching times. The connection between technology and education will be reinforced by designing projects where undergraduate students will print polymer logic circuits as part of their Advanced Physics Laboratory course. The international scope will provide US students transferable skills that are essential for employment in industry and academia. Graduate and undergraduate students will gain expertise in a multidisciplinary range of technical skills, and thus be trained to contribute to the US workforce in the area of flexible electronics. Hands-on workshops for high school students and mentoring programs for underrepresented graduate students will also be part of the project. Technical: The objective of this program is to improve switching times in all-polymer thin film transistors and to develop a non-linear optical method for visualization of carrier transport. Dipole engineering of the dielectric layer, using low-cost solvent processing and poling polymer ferroelectric dielectrics, is likely to have a transformative impact on technology where fast switching times may be realized in long-channel printable thin film organic field-effect transistors and logic circuits. A new series of side-chain substituted donor-acceptor copolymers will be used as the active semiconductor layer. Carrier mobilities of organic semiconductors in field-effect transistors are strongly impacted by device geometry, physical/chemical attributes of the organic semiconductor, and the various interfaces: metal-semiconductor and semiconductor-insulator. Transient electric field-induced second-harmonic generation methods, based on the third-order susceptibility, will be established, allowing direct and selective probing of dynamic carrier motion in field-effect transistors. This technique will be a powerful methodology for visualizing transport in a new generation of donor-acceptor ambipolar transistors and pave the way for predicting accurate carrier mobilities, free from contact resistance issues and device geometrical factors. Grazing angle X-ray scattering studies from polymer films in transistor architectures will reveal not just the structure of the polymer, but also the changes in structure upon bias stress.