Integration of high-k dielectric materials in a-IGZO thin film transistors by ALD

High field-effect mobility of Amorphous Oxide Semiconductor Thin Film Transistors (AOS TFT’s) has become more critical in switching devices for active matrix OLED’s (AMOLED). 

Out of many AOS materials, stable a-IGZO (Indium Gallium Zinc Oxide) TFT’s has shown high performance in display devices. However, the process integration of TFT’s is very complicated where a high number of parameters are to be considered and optimized to obtain maximum device performance. Therefore, it is essential to develop each process step through various device structure of thin film transistors using Back Channel Etch and self-aligned TFT. 

An example: Magnified image of the AMOLED screen on the Google Nexus One smartphone using the RGBG system of the PenTile matrix family (Wikipedia).

Currently, incorporation of high–k dielectric materials such as Al2O3 and HfO2 as a passivation layer and gate insulating material shows promising results in obtaining high performance of TFT’s in terms of low operating voltages, bias stability and reducing degradation by isolation from the external environment. A primary focus is on Al2O3 films by ALD technique, where the doping of film to the active layer (a-IGZO) is investigated through back channel etch (BCE) device structure by two different deposition temperatures followed by annealing studies. The performance of the self-aligned TFT's is primarily determined by the two factors :

I. Deposition temperatures of the passivation layer (Al2O3) 

II. Etching rate. 

The conclusions drawn from the studies of BCE applied to a-IGZO 10% O2 aelf–aligned (SA) device structures where Al2O3 layer deposited by ALD at 150 °C as a gate insulating material. The electrical characteristics of fabricated Thin Film Transistors are obtained to be very promising for further engineering applications. 

A deep study and understanding of each step in process flow and significance of Atomic Layer Deposition gave a fruitful insight into many aspects.
---------------------
Guest Blog by: Ravi Pendurthi, imec, Leuven, Belgium LinkedIn Profile