Dual-TFT Display Backplane Structure to Prevent Oxide Contamination
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Solution Overview
Problem
The challenge in display devices is to minimize the number of through holes while forming polysilicon and oxide semiconductor TFTs on the same substrate, as this complexity leads to increased manufacturing costs and potential contamination of oxide semiconductor TFTs during the process of forming protecting metals, which affects the stability of the TFT characteristics.
Innovation Solution
The solution involves forming a display device structure with a polysilicon semiconductor layer and an oxide semiconductor layer, where a first light shading film and a second light shading film are used between the semiconductor layers and the substrate, with specific through holes penetrating the insulating films to connect the shading films with conductive components, reducing the need for additional processes and protecting metals on the oxide semiconductor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If through holes are formed simultaneously for oxide semiconductor TFTs and polysilicon semiconductor TFTs, then the manufacturing process is simplified, but the oxide semiconductor is dissolved at the through holes causing contamination
Solution Approach 1:
A protective film is formed over the oxide semiconductor layer before through holes are formed. This preliminary protective action prevents the oxide semiconductor from being dissolved during the through hole formation process, allowing simultaneous formation of through holes for both oxide and polysilicon TFTs without contamination
Solution Approach 2:
A protective film acts as an intermediary layer between the oxide semiconductor and the etching process. This intermediary protects the oxide semiconductor from direct contact with etchants during through hole formation, enabling simplified manufacturing without compromising oxide semiconductor integrity
2Temperature
If polysilicon semiconductor TFTs are formed first on the lower layer, then the process temperature requirements are met, but additional processes and protecting metals are required for oxide semiconductor TFTs formed later
Solution Approach 1:
The protective film is formed in advance before the oxide semiconductor layer is deposited. This preliminary formation eliminates the need for subsequent protecting metal layers and additional processes when forming oxide semiconductor TFTs after polysilicon TFTs, reducing overall device complexity while maintaining temperature requirements
3Reliability
If two polysilicon semiconductor TFTs are used in series for switching elements, then the leak current is reduced, but the device structure becomes more complex
Solution Approach 1:
The invention changes the material parameter of the switching TFT from polysilicon to oxide semiconductor. This material substitution provides inherently low leak current characteristics of oxide semiconductors, eliminating the need for series-connected polysilicon TFTs and their associated structural complexity
Data Source
AI summary
A display device including: a substrate; a first thin film transistor of polysilicon semiconductor, a second thin film transistor of oxide semiconductor; a first light shading film opposing to the polysilicon semiconductor, and a second light shading film opposing to the oxide semiconductor; a first insulating film, a second insulating film which is constituted from plural insulating films, and a third insulating film superposed in this order; a first through hole penetrating the second insulating film and not penetrating the first insulating film and the third insulating film; a second through hole penetrating the first insulating film and the third insulating film; the first light shading film connects with a first conductive component, a part of the first conductive component exists on the third insulating film, through the second through hole.