Transparent-Oxide TFT Light Shielding for Stable OFF-Current
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Solution Overview
Problem
Transparent amorphous oxide semiconductor films used in thin-film transistors (TFTs) exhibit changes in electrical conductivity due to photocarrier generation under visible light, affecting the stability of the TFTs.
Innovation Solution
Incorporating a light-shielding structure in the TFTs to shield the active layer from visible light and electromagnetic waves, particularly in the 300 to 800 nm range, using materials with low transmittance to maintain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent amorphous oxide semiconductor film is used as the active layer to achieve high light transmittance, then the transparency and flexibility of the TFT are improved, but the electrical conductivity becomes unstable due to photocarrier generation under visible light
Solution Approach 1:
The device is segmented into multiple functional layers: a transparent active layer for light transmission and a separate light-shielding layer for stability. This segmentation allows each layer to perform its specific function without compromising the other, resolving the contradiction between transparency and electrical stability.
Solution Approach 2:
A light-shielding layer is introduced as an intermediary element between the transparent active layer and the incident light. This intermediary layer blocks harmful light from reaching the active layer, preventing photocarrier generation while preserving the active layer's transparency for necessary light transmission.
2Reliability
If a light-shielding structure is added to shield the active layer from visible light, then the electrical conductivity stability is improved, but the device complexity and manufacturing process become more complicated
Solution Approach 1:
The light-shielding layer is merged with existing device components or integrated into the substrate structure. By combining the light-shielding function with other structural elements, the patent avoids adding excessive complexity while still achieving the necessary protection against light-induced conductivity changes.
Solution Approach 2:
The patent optimizes parameters such as the thickness and material composition of the light-shielding layer to achieve effective light blocking with minimal structural complexity. By carefully controlling these parameters, the device achieves stability without requiring complex multi-layer structures.
3Reliability
If a light-shielding layer is provided between the substrate and the active layer, then photocarrier generation is reduced, but the manufacturing precision and alignment requirements increase
Solution Approach 1:
The light-shielding function is extended into the vertical dimension by providing protection from both the substrate side and the opposite side. This multi-directional approach ensures comprehensive light blocking while allowing each shielding layer to be independently positioned, reducing the stringency of alignment requirements between layers.
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
The light-shielding structure significantly reduces deviations in OFF-current, ensuring stable operation of TFTs by minimizing photocarrier generation, with transmittance reduced to less than 0.01% for visible light and shorter wavelengths.
Implementation Method 1
Incorporating a light-shielding structure in the TFTs to shield the active layer from visible light and electromagnetic waves, particularly in the 300 to 800 nm range
Implementation Method 2
a change in electrical conductivity occurs, namely, photocarriers are practically generated by irradiation with light in a certain visible light region
Data Source
AI summary
A field-effect transistor includes a substrate, a source electrode, a drain electrode, a gate electrode, a gate-insulating film, and an active layer. The active layer contains an oxide having a transmittance of 70% or more in the wavelength range of 400 to 800 nm. A light-shielding member is provided as a light-shielding structure for the active layer, for example, on the bottom face of the substrate.