M.Sc Thesis

M.Sc StudentChen Zetian
SubjectStudy and Characterization of Organic-Metal Oxide Hybrid
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Nir Tessler


There was a rapid development of organic and metal oxide semiconductor materials during recent decades. On the one hand, organic materials, due to their diverse compositions, have attractive optical properties over traditional semiconductor materials. On the other hand, thin-film transistors (TFTs) composed of metal oxide semiconductors, especially amorphous indium gallium zinc oxide (IGZO), are believed to be a good substitute for amorphous Si TFTs in backplane technology. Making use of the advantages of both materials by integrating them into a single device, is a promising route for a range of optoelectronic applications.

In this work, we have studied a phototransistor consisting of solution-processed IGZO TFT and vacuum deposited small organic molecules. The research started by investigating the process of fabricating high performance IGZO TFT. Next, we focused on studying the device physics of organic-metal oxide hybrid phototransistor. It is found that depending on the configuration of organic materials, either bulk heterojunction (BHJ) or planar heterojunction (PHJ), the said phototransistor assumes the functionality of either a photo-sensor or a photo-induced memory, respectively. The photo-sensor device shows relatively fast response, together with tunable responsivity and sensitivity by gate bias. The mechanism of the memory device is studied by device simulation, as well as experimentally, by implementing surface potential measurement and examining the performance of different device structures and material compositions. It is revealed that the memory effect is due to long charge retention time at the organic PHJ interface, whose sub-gap tails states determine the retention efficiency. The memory device with C70 and DBP results in ~75 % of charge retention over 9 days. The presented integration
of the PHJ with the transistor constitutes a new design of write once read many times (WORM) memory device that is likely to be attractive for low cost applications.