Oxide Semiconductor TFT with Protective Film Opening
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Solution Overview
Problem
The existing photodiode arrays using oxide semiconductors face challenges with membrane stress and hydrogen penetration, leading to degraded semiconductor characteristics, particularly due to the sensitivity of oxide semiconductors to environmental factors and the difficulty in preventing hydrogen plasma from affecting the oxide semiconductor layer.
Innovation Solution
A semiconductor device structure is implemented with a thin film transistor featuring an oxide semiconductor layer and a hydrogenated amorphous silicon photodiode, where a protective film is configured with an opening portion above the channel region to reduce membrane stress and facilitate post-processing for enhancing semiconductor characteristics, allowing for effective gas annealing and improved reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective film is formed over the oxide semiconductor layer to prevent hydrogen penetration, then reliability is improved, but membrane stress increases and degrades semiconductor characteristics
Solution Approach 1:
The protective film is segmented by forming an opening portion that divides the continuous film into regions, allowing the channel region to be exposed while maintaining protection in other areas. This segmentation reduces the overall membrane stress while preserving the protective function where needed.
Solution Approach 2:
The protective film is selectively removed only in the region corresponding to the channel, creating a local opening. This allows the protective film to maintain its stress-reducing function in the opened region while preserving protection in other critical areas, achieving local optimization of both protection and stress management.
2Stress or pressure
If the oxide semiconductor layer is exposed to reduce membrane stress, then semiconductor characteristics are improved, but hydrogen penetration risk increases
Solution Approach 1:
The opening portion is localized specifically to the channel region, exposing only this critical area to reduce stress. The rest of the oxide semiconductor layer remains covered by the protective film, maintaining protection against hydrogen penetration in non-channel regions.
Solution Approach 2:
The protective film structure is segmented to create a controlled exposure zone. This segmentation allows the system to benefit from stress reduction in the exposed channel region while maintaining protective coverage in other areas, balancing both requirements.
3Reliability
If gas annealing is performed to enhance oxide semiconductor characteristics, then mobility is improved, but process complexity increases
Solution Approach 1:
The opening portion is formed in advance before final device completion, preparing the structure for subsequent gas annealing. This preliminary action allows gas molecules to access the oxide semiconductor layer more easily during annealing, enhancing characteristics without requiring complex additional processing steps.
Solution Approach 2:
The opening portion acts as an intermediary structure that facilitates gas molecule access to the oxide semiconductor layer. This simple structural feature enables effective gas annealing by serving as a diffusion pathway, avoiding the need for complex processing equipment or procedures.
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 reduces membrane stress, enhances the initial characteristics of the oxide semiconductor, and improves reliability by allowing for efficient post-processing and easier gas molecule diffusion, thereby stabilizing the threshold and preventing hydrogen penetration.
Implementation Method 1
In the mechanism thereof, photoelectric conversion of light is performed using the photodiode, and acquired electric charge is read from a signal line through the TFT.
Implementation Method 2
In the oxide semiconductor, oxide ions form a valence band, and a metal cation forms a conduction band. Thus, here, in a case where the oxide ions come out, remaining electrons present in a remaining site after the oxide ions come out move from the valence band to the conduction band, thereby electricity flows. At this time, the remaining site after the coming-out of the oxide ions is called oxygen vacancy.
Implementation Method 3
it is known that the conductivity increases in a case where hydrogen is introduced into oxide semiconductor
Implementation Method 4
in a case where annealing is performed in oxygen atmosphere containing water vapor, as the humidity is higher, the mobility is improved more, and a threshold shift and an S value decrease
Implementation Method 5
photoelectric conversion of light is performed using the photodiode
Data Source
AI summary
A semiconductor device includes: a thin film transistor including an oxide semiconductor layer that is formed in an island shape and contains at least one or more elements among indium, gallium, zinc, and tin and oxygen, a source and a drain that are connected to the oxide semiconductor layer; a protective film of at least one or more layers that is formed in an upper layer of the oxide semiconductor layer, and an opening portion that is disposed in the protective film and has a position and a size for including a channel region or a back channel region of the oxide semiconductor layer; and a photodiode that is disposed in an upper layer upper than the oxide semiconductor layer of the thin film transistor and includes a hydrogenated amorphous silicon layer.