M.Sc Thesis

M.Sc StudentAvrahamov Talia
SubjectTransistors Based on Thin Film Metal Oxides
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Nir Tessler


In the display industry, transistors are expected to have different characteristics than in the processors industry. Transparency is the most crucial property as it dictates the display’s power requirements. In addition, low-temperature fabrication would make for a cheap, plastic-substrate-compatible production process. Today, a-Si is used for display transistors, however, it has reached its performance limit.

Transparent Conducting Oxides (TCOs) exhibit transparency in the visible light spectrum along with relatively high mobility. These properties which are attributed to their special electronic structure make them promising candidates for the next generation of semiconductor technology in the display industry. In addition, TCOs can be deposited at low-temperatures, making their processing compatible with plastic substrate. This could open the door for a flexible display technology which would include products such as electronic papers, wearable electronics and more. 

This work explores the feasibility of fabricating thin film transistors based on TCOs as the semiconducting active layer. Two TCOs were examined: ZnO and IGZO. As a first step, the behavior of these TCOs was studied in lateral transistors. ZnO was taken to be the first case study, however, its conductivity was found to sensitively depend on environmental conditions. This ignited a study of the ZnO impurities and environmental effects. Following this, IGZO was considered as a TCO which is less sensitive to environmental conditions. The IGZO conductivity dependence on the deposition process and the post-deposition handling was examined, again in a lateral transistor.

Our final step was the fabrication of a novel vertical transistor design. The uniqueness of the vertical transistor is that the channel length (L dimension) of the transistor is defined from the active layer thickness, rather than from the technology dimensions. This is advantageous as it enables a fabrication of a short L dimension with low cost methodologies. For this unique transistor architecture, the choice of metal for the source electrode is very important. In addition, the patterning of the source electrode is crucial for obtaining a functioning transistor.