Showing papers by "Chang-Min Keum published in 2017"

Reaching saturation in patterned source vertical organic field effect transistors

Abstract: Like most of the vertical transistors, the Patterned Source Vertical Organic Field Effect Transistor (PS-VOFET) does not exhibit saturation in the output characteristics. The importance of achieving a good saturation is demonstrated in a vertical organic light emitting transistor; however, this is critical for any application requiring the transistor to act as a current source. Thereafter, a 2D simulation tool was used to explain the physical mechanisms that prevent saturation as well as to suggest ways to overcome them. We found that by isolating the source facet from the drain-source electric field, the PS-VOFET architecture exhibits saturation. The process used for fabricating such saturation-enhancing structure is then described. The new device demonstrated close to an ideal saturation with only 1% change in the drain-source current over a 10 V change in the drain-source voltage.

Vertical organic light-emitting transistor showing a high current on/off ratio through dielectric encapsulation for the effective charge pathway

Abstract: We demonstrate a vertical organic light emitting transistor (VOLET) showing a high current on/off ratio through dielectric encapsulation of a finger-like source electrode, which is placed between the bottom gate electrode and the top drain electrode. In such a VOLET configuration, the charge transport occurs largely from the source electrode to an underlying organic semiconductor (OSC) layer through the interface between the OSC and the gate insulator. Accordingly, the current leakage is greatly reduced and the transistor-type switching behavior with a high on/off current ratio is achieved. The on/off current ratio of our VOLET is about 100 times higher than that of an existing VOLET with no dielectric encapsulation. Numerical simulations of the spatial distributions of the charge densities and the charge pathways performed in the two different VOLET configurations are in good agreement with the experimental results. Our dielectric encapsulation approach will provide a versatile method for developing a ne...

Principle of topography-directed inkjet printing for functional micro-tracks in flexible substrates

Abstract: We present a general principle of topography-directed (TD) inkjet printing for functional micro-tracks embedded in a flexible elastomer substrate. The essential features of the TD inkjet printing in a micro-structured substrate with periodic grooves and ridges are described in terms of the topographic parameters for the transformation from a single droplet to a filament or an edge-disjoint pattern of ink in the groove. Silver ink, being widely used for producing conductive wires by conventional inkjet printing, is utilized as a testbed in our study. The underlying mechanisms for the spreading and drying processes of ink drops under the topographic compartment can be understood in a two-dimensional parameter space of the aspect ratio of the groove and the contact angle of ink on the substrate. The wetting morphologies of ink droplets are described in an analytical model where the Laplace pressure and the mean curvature at the vapor/ink interface are taken into account. The first principle of the TD inkjet ...