Dissertation Defense NackBong Choi

Title: Metal Oxide Thin Film Transistors on Paper Substrate: Fabrication, Characterization, and Printing Process

Flexible electronics is an emerging next-generation technology that offers many advantages such as light weight, durability, comfort, and flexibility. These unique features enable many new applications such as flexible display, flexible sensors, conformable electronics, and so forth. For decades, a variety of flexible substrates have been demonstrated for the application of flexible electronics. Most of them are plastic films and metal foils so far. For the fundamental device of flexible circuits, thin film transistors (TFTs) using poly silicon, amorphous silicon, metal oxide and organic semiconductor have been successfully demonstrated. Depending on application, low-cost and disposable flexible electronics will be required for convenience. Therefore it is important to study inexpensive substrates and to explore simple processes such as printing technology.
In this thesis, paper is introduced as a new possible substrate for flexible electronics due to its low-cost and renewable property, and a-IGZO TFTs are realized as the promising device on the paper substrate. The fabrication process and characterization of a-IGZO TFT on the paper substrate are discussed. a-IGZO TFTs using a polymer gate dielectric on the paper substrate demonstrate excellent performances with field effect mobility of ~20 cm2 V-1 s-1, on/off current ratio of ~106, and low leakage current, which show the enormous potential for flexible electronics application. In order to complement the n-channel a-IGZO TFTs and then enable CMOS circuit architectures, cuprous oxide is studied as a candidate material of p-channel oxide TFTs.
In this thesis, a printing process is investigated as an alternative method for the fabrication of low-cost and disposable electronics. Among several printing methods, a modified offset roll printing that prints high resolution patterns is presented. A new method to fabricate a high resolution printing plate is investigated and the most favorable condition to transfer inks from a blanket to a cliché is studied. Consequently, a high resolution cliché is demonstrated and the printed patterns of 10?m width and 6?m line spacing are presented. In addition, the top gate a-IGZO TFTs with channel width/length of 12/6?m is successfully demonstrated by printing etch-resists.
This work validates the compatibility of a-IGZO TFT on paper substrate for the disposable microelectronics application and presents the potential of low-cost and high resolution printing technology.

Prof. Miltiadis K. Hatalis(Advisor)
Prof. James Hwang
Prof. Svetlana Tatic-Lucic
Dr. Ruiqing Ma