Friday, September 6, 2019

Hydrogen diffusion barrier using thermal ALD Al2O3 encapsulation for IGZO TFTs

Amorphous phase In-Ga-Zn-O(IGZO), the typical oxide TFT compositions, has 20 to 50 times higher of field-effect mobility than that of a-Si TFTs and excellent SS (Sub-Threshold Voltage Swing) properties as well as has been very promising to apply for high performance and large area displays and for transparent displays due to their superior properties and good uniformity.

But IGZO TFTs with PECVD SiNx as an encapsulation layer have degraded their superb properties because hydrogen included in SiNx from 20% to 30% has passed through OLED layers and then diffused into IGZO layers.



Comparison of I-V characteristic of a-IGZO TFTs with and without hydrogen diffusio


If this performance degradation by hydrogen diffusion showed in typical I-V graph, SS slop would be decreased, Ioff increased and Vth shifted to negative direction from the original I-V curve.

In case of applying to OLED display with IGZO TFTs using SiNx encapsulation layers including hydrogen, Al2O3 layers would be the very excellent barriers not to degrade IGZO TFTs properties by diffusion of hydrogen from SiNx.

However it is not good choice to apply PEALD Al2O3 using plasma to the first encapsulation layer because oxygen plasma could cause the side effect such as cathode oxidation during the process. So IGZO TFTs and thermal ALD Al2O3 encapsulation layers without plasma damage could be optimum combination.

NCD Lucida GD Series that is thermal ALD batch equipment for mass production to deposit on large substrates up to 6th generation glasses could provide superior Al2O3 hydrogen barriers preventing diffusion into IGZO TFTs from PECVD SiNx encapsulation layers including hydrogen as well as expect to apply to transparent fordable OLED displays by using Al2O3/Polymer/Al2O3 encapsulation layers.


NCD’s LucidaTM GD Series ALD

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