Showing papers by "Chang-Min Keum published in 2011"

Surface modification of a ferroelectric polymer insulator for low-voltage readable nonvolatile memory in an organic field-effect transistor

Abstract: We demonstrate that the sequential surface modification of a ferroelectric polymer insulator plays an essential role in both the enhancement of the carrier mobility and the shift in the turn-on voltage (Von) in an organic ferroelectric field-effect transistor (FeFET) for nonvolatile memory. The surface of a ferroelectric polymer insulator, poly(vinylidene fluoride-trifluoroethylene), is physicochemically modified by the successive treatments of ultraviolet-ozone (UVO) and CF4 plasma to understand how the surface morphology and the hydrophobicity affect the grain size, the mobility, and Von in the FeFET. In a pentacene-based FeFET, the CF4 plasma irradiation leads to the mobility enhancement by a factor of about 5 as well as the shift in Von toward a positive voltage direction while the UVO treatment results in only the shift in Von toward a negative voltage direction. It is found that the sequence of the two successive treatments is critical for tailoring interfacial interactions between the ferroelectric polymer insulator and the pentacene layer. The underlying mechanism for the mobility enhancement and the shift in Von is described in terms of the surface morphology and the nature of the built-in electric field.

Chevron-type gate configuration of short channel top-contact organic thin-film transistors for large saturated drain current

Abstract: We demonstrate a chevron-type gate configuration of a short channel top-contact organic thin-film transistor (OTFT) showing large saturated drain current with the help of a polymeric edge support. The channel length (L) depends on the geometrical shape of the edge support which can be controlled by thermal treatment. Oblique deposition of Au onto the substrate with the edge support allows a self-defined channel length down to a submicrometre scale. The chevron-type top-contact OTFT with L = 0.8 µm exhibits a drain current per channel width as large as 80 µA mm−1 at the operating voltage of −3 V. The leakage current associated with a gate insulator AlOx is systematically investigated in a metal–insulator–metal structure and a metal–insulator–semiconductor–metal structure by varying the O2 plasma treatment and the pentacene thickness. Using the optimized gate insulator AlOx, a saturation behaviour of the output characteristic curve, low current leakage and low voltage operation are achieved in our chevron-type OTFT.