UC San Diego

Organic semiconducting materials have attracted intense attentions for electronic and chemical sensing applications. The fundamental understanding of charge transport properties of organic thin-films is critical for both applications. This thesis investigates the charge transport properties of phthalocyanine thin-film devices and couples these properties with chemical sensor developments. In chapter 1, the basic charge transport processes in the two- and three- terminal devices are reviewed. In chapter 2 & 3, we have investigated the AC and DC charge transport properties of the CoPc two- terminal devices. The frequency dispersive charge transport property in CoPc thin-films has been characterized and applied for analyte identification. The Ohmic conduction and Space-charge-limited conduction (SCLC) processes have been characterized by both macroscopic and microscopic measurements. A practical sensing technique has been developed based on the fundamental understanding of the charge transport process: operating in the SCLC region to enhance the device to device repeatability. In chapter 4, the bias-induced charge trapping is identified as the major source of electrical instability of OTFT sensors. A pulsed gating method has been developed to obtain ultra-low drift even for low vapor pressure analytes, such as organophosphonate nerve agent simulants. In chapter 5, the chemical sensing properties of phthalocyanine thin-film transistors have been investigated using n-type and p-type devices. The effects of surface pre-adsorbed oxygen in channel conductivity and chemical responses have been investigated. In chapter 6, ultrathin organic transistors have been reported for chemical sensing by maximizing the charge trapping effect in chemical sensor responses, thereby, greatly enhance the chemical sensitivity