C. Daniel Frisbie Group
Chemical Engineering & Materials Science
University of Minnesota - Twin Cities 		Films & Interfaces,
Molecular Crystals,
Molecular Electronics,
Organic Semiconductors,
Scanning Probe Microscopy

Siddharth Mohapatra Siddharth Mohapatra
OrganicID
M.S. Materials Science, 2004

Structural, Morphological and Electrical Characterization of new thiophene based organic semiconductors for understanding structure-property relationships

Increasing use of organic semiconductors as the conducting layer in thin film transistors demands evolution of the existing semiconductors to obtain progressively improved properties. Parameters that are central to obtaining high performance TFTs include but are not limited to high mobilities, a high ratio of the currents in the on state to off state, low sub threshold swings, reasonable environmental stability and the ability to conduct both electrons and holes (ambipolar).

Although the properties of certain materials like pentacene have seen a dramatic improvement in the last few years due to improved understanding of the processing conditions, these conditions however remain quite stringent for obtaining mobilities of > 1 cm^2/Vs.

My research revolves around developing new materials by conceptualizing new molecules in collaboration with other group members having expertise in synthetic chemistry for functionalizing existing thiophene based semiconductors in order to obtain improved structural and electrical properties. My work also involves relating the thin film structure to electrical properties.

Thin films of these semiconductors are characterized using instruments like AFM (morphological characterization) and XRD (structural characterization). Electrical characterization is performed in a TFT configuration with the semiconductor as the conducting layer. Source, drain and 2 additional probes in the channel region (to correct for potential drops at the source and drain contacts) are defined by contact metallization using shadow masking. Additionally I do variable temperature measurements in vacuum and partial pressures of gases like H2 to study the effect of traps on conduction and if possible to quantify and predict the distribution of the same using existing models and rules like MTR and MNR.

Additionally I am also involved in a project where I do some device engineering to obtain high mobility ambipolar devices with low off currents and distinct onset voltages for hole and electron conduction.

Publications
"Organic Thin Film Transistors based on tolyl substituted oligothiophenes," Mohapatra, S.; Holmes, B. T.; Newman, C. R.; Prendergast, C. F.; Frisbie, C. D.; Ward, M. D., Advanced Materials 2004, (in press)

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