Display Pixel TFT Layout for LTPS and TAOS Co-Integration
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Solution Overview
Problem
The challenge lies in forming TFTs using both Low Temperature Poly-Si (LTPS) and Transparent Amorphous Oxide Semiconductors (TAOS) on the same substrate, as LTPS requires hydrofluoric acid cleaning, which dissolves TAOS, making it impossible to use the same process for both materials.
Innovation Solution
A display device is designed with a substrate where TAOS TFTs are formed using an AlOx sacrificial layer and through holes with specific taper angles, allowing for separate cleaning of LTPS and TAOS without damaging the TAOS, using AlOx as an insulating material and a sacrificial layer to prevent hydrofluoric acid from contacting the TAOS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrofluoric acid cleaning is used to remove surface oxide from LTPS, then LTPS TFT performance is improved, but TAOS is dissolved and damaged
Solution Approach 1:
A sacrificial layer made of aluminum oxide (AlOx) is introduced as an intermediary protective layer between the hydrofluoric acid cleaning process and the TAOS layer. This sacrificial layer is selectively removed after serving its protective function, allowing the TAOS to be preserved while still enabling the necessary cleaning of LTPS surfaces
Solution Approach 2:
The sacrificial layer is formed on the TAOS surface before the hydrofluoric acid cleaning process is applied to LTPS. This preliminary protective action prevents the harmful hydrofluoric acid from contacting and dissolving the TAOS during the cleaning process
2Productivity
If the same substrate is used for both LTPS and TAOS TFTs, then manufacturing efficiency is improved, but process compatibility deteriorates
Solution Approach 1:
Different regions of the substrate are treated with different protective measures. The sacrificial layer is selectively formed only in regions where TAOS TFTs will be manufactured, while LTPS regions undergo standard hydrofluoric acid cleaning. This local differentiation allows both material types to be processed on the same substrate without mutual interference
Solution Approach 2:
The manufacturing process is segmented into distinct stages: first forming TAOS TFTs with sacrificial layer protection, then cleaning LTPS surfaces with hydrofluoric acid, and finally removing the sacrificial layer. This segmentation allows each material type to receive its specific treatment without affecting the other
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables the formation of both LTPS and TAOS TFTs on the same substrate, reducing leak current and enhancing the reliability and image quality of display devices by preventing TAOS dissolution during the cleaning process.
Implementation Method 1
using an AlOx sacrificial layer and through holes with specific taper angles, allowing for separate cleaning of LTPS and TAOS without damaging the TAOS
Data Source
AI summary
The object of the present invention is to make it possible to form an LTPS TFT and an oxide semiconductor TFT on the same substrate. A display device includes a substrate having a display region in which pixels are formed. The pixel includes a first TFT using an oxide semiconductor 109. An oxide film 110 as an insulating material is formed on the oxide semiconductor 109. A gate electrode 111 is formed on the oxide film 110. A first electrode 115 is connected to a drain of the first TFT via a first through hole formed in the oxide film 110. A second electrode 116 is connected to a source of the first TFT via a second through hole formed in the oxide film 110.