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Keun Hyung Lee

Seoul National University, Korea; 2007
B.S. Chemical Engineering

Email: leex3432@umn.edu

Research: Optimization of Ion Gel Gate Dielectrics for Organic Thin Film Transistors (OTFTs)

An ion gel which consists of an ABA type triblock copolymer (where the B block is soluble in an ionic liquid but the A blocks are not) swollen in the ionic liquid can be used as a gate dielectric for transistors. Due to remarkably high capacitance of an ion gel, low-voltage operation (~1-2 V) and high ON/OFF current ratio (~10^5) can be realized in organic thin film transistors. To understand working mechanisms and improve the device performance, we systematically vary the thickness, area, and temperature of the ion gel. From the impedance measurements, the resistance depends linearly on the thickness, and is inversely proportional to the area. However, the interfacial capacitance and conductivity of the ion gel remains almost the same. Importantly, a gel polarization time constant of a few microseconds is achieved by reducing the ion gel thickness. Additionally, both the interfacial capacitance and conductivity of an ion gel increase with increasing temperature; the mechanism for the former dependence is not yet clear.

Publications

"Electrical Impedance of Spin-Coatable Ion Gel Films," Lee, K. H.; Zhang, S.; Lodge, T. P.; Frisbie, C. D., J. Phys. Chem. B 2011,115, 3315-3321

"Ionic Conductivity, Capacitance, and Viscoelastic Properties of Block Copolymer-Based Ion Gels," Zhang, S.; Lee, K. H.; Frisbie, C. D.; Lodge, T. P., Macromolecules 2011,44, 940-949