Hybrid LTPS-TAOS TFT Display Layout for HF-Compatible Processing
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Solution Overview
Problem
The challenge lies in forming TFTs using both low temperature poly-Si (LTPS) and transparent amorphous oxide semiconductor (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 a first TFT using TAOS is formed with an oxide film, a gate electrode connected through specific taper-shaped holes in the oxide film, and an AlOx sacrificial layer is used to prevent hydrofluoric acid from damaging the TAOS, allowing for the formation of both LTPS and TAOS TFTs on the same substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If LTPS is used for TFT switching in pixels, then high carrier mobility is achieved, but leak current increases and two LTPS transistors are required in series connection
Solution Approach 1:
The patent combines LTPS and TAOS materials in a hybrid structure where LTPS provides high carrier mobility for drive circuits and TAOS provides low leak current for pixel switching TFTs. This merging of two different semiconductor materials allows each material to be used in its optimal application context within the same display device.
Solution Approach 2:
The patent applies different semiconductor materials to different functional regions: LTPS is used in peripheral drive circuits where high speed is critical, while TAOS is used in pixel switching TFTs where low leak current is critical. This local differentiation of material properties optimizes overall device performance.
2Reliability
If TAOS is used for TFT switching in pixels, then leak current is reduced, but carrier mobility is too low to form drive circuits
Solution Approach 1:
The patent combines LTPS and TAOS materials in a hybrid structure where LTPS provides high carrier mobility for drive circuits and TAOS provides low leak current for pixel switching TFTs. This merging of two different semiconductor materials allows each material to be used in its optimal application context within the same display device.
Solution Approach 2:
The patent applies different semiconductor materials to different functional regions: LTPS is used in peripheral drive circuits where high speed is critical, while TAOS is used in pixel switching TFTs where low leak current is critical. This local differentiation of material properties optimizes overall device performance.
3Reliability
If hydrofluoric acid is used to clean LTPS surface oxide, then LTPS TFT performance is improved, but TAOS is dissolved and cannot be used
Solution Approach 1:
The patent segments the device into two distinct regions with different semiconductor materials (LTPS and TAOS) that can be processed independently. This allows the LTPS region to receive hydrofluoric acid treatment for optimal performance while the TAOS region remains protected and unaffected by the harsh cleaning chemistry.
4Productivity
If the same substrate is used for both LTPS and TAOS TFTs, then manufacturing efficiency is improved, but process compatibility is lost due to material characteristics differences
Solution Approach 1:
The patent segments the device into two distinct regions with different semiconductor materials (LTPS and TAOS) that can be processed independently. This allows the LTPS region to receive hydrofluoric acid treatment for optimal performance while the TAOS region remains protected and unaffected by the harsh cleaning chemistry.
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.