Electro-optic Substrate Stray Light Shielding via Insulating Layer Refraction
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Solution Overview
Problem
Display devices, particularly those with liquid crystal devices, face issues with light leakage currents due to obliquely incident stray light, which worsen with the use of single-crystal silicon transistors, leading to increased noise and decreased image quality.
Innovation Solution
An electro-optic substrate design featuring a transparent substrate, light-shielding layers, and strategically positioned insulating layers to minimize light penetration, with specific layer thickness and refractive index relationships to prevent stray light from reaching the channel and LDD regions, as defined by Rayleigh's diffraction conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light-shielding layer is formed on the substrate surface to block obliquely incident stray light, then light-shielding performance is improved, but the structural complexity and manufacturing difficulty increase
Solution Approach 1:
An insulating layer with specific refractive index is introduced as an intermediary between the light-shielding layer and the semiconductor layer. This intermediary layer modifies the optical path of obliquely incident light through refraction, preventing stray light from reaching the channel region while maintaining a relatively simple overall structure.
Solution Approach 2:
The patent specifies precise parameters for the insulating layer including refractive index (1.4-1.7) and thickness (50-200 nm), and defines the light-shielding layer thickness (100-500 nm) to optimize light-blocking performance. By controlling these parameters, effective light shielding is achieved without excessive structural complexity.
2Object-affected harmful factors
If the insulating layer thickness is increased to improve light shielding, then light leakage current is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent defines an optimal thickness range of 50-200 nm for the insulating layer, balancing light-shielding effectiveness with manufacturability. This specific range achieves sufficient refraction of oblique light while remaining within standard thin-film deposition capabilities, avoiding excessive precision requirements.
Solution Approach 2:
The patent employs a composite structure combining the light-shielding layer (metal or semiconductor material) with the insulating layer (oxide or nitride material). This composite approach distributes the light-blocking function across two layers with different optical properties, reducing the precision burden on any single layer while maintaining overall effectiveness.
3Reliability
If a light-shielding layer is added to prevent stray light, then image quality is improved, but the device complexity increases
Solution Approach 1:
The light-shielding function is segmented into two distinct layers: a light-shielding layer for primary light blocking and an insulating layer for refraction-based stray light prevention. This segmentation allows each layer to be optimized for its specific function while keeping the overall structure manageable and integrated with the existing thin-film transistor architecture.
Solution Approach 2:
The insulating layer serves multiple functions: it acts as a refractive barrier to oblique light, provides electrical insulation, and can serve as a base for subsequent electrode patterns. This multi-functionality reduces the need for additional dedicated layers, thereby limiting the increase in device complexity while improving image quality.
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 design effectively reduces light leakage currents and noise, enhancing image quality by positioning the channel and LDD regions beyond the penetration depth of stray light, thereby improving light-shielding performance and maintaining high image intensity.
Implementation Method 1
a first insulating layer having a refraction index n and a layer-thickness t (nm), as an insulating layer sandwiched between the first light-shielding layer and the transparent substrate
Implementation Method 2
a first light-shielding layer disposed on at least one part of a region surrounding an opening in a plane view, at a side of a first surface of the transparent substrate
Data Source
AI summary
Stray light in an oblique direction penetrates a channel part of a thin-film transistor, which sometimes causes light leakage current. This phenomenon becomes more pronounced in the case of using an optical system with high intensity, leading to deterioration in an image quality.To prevent the light that possibly penetrates an equivalent optical waveguide from reaching the channel part, on the condition that a first insulating layer is set to have a layer-thickness t (nm) and a refraction index n, a relation is to be expressed by the following expression. t<(0.61×λ)/(n×sin θ) A value of λ is set to a lower limit 400 (nm) of a visible light wavelength and a value Lc (nm) is set to a distance between an end of a light-shielding layer and an end of a channel region. With those values, an expression of nt2/244 (nm)<Lc (nm) is set up. By controlling a layer-thickness of the first insulating layer and a distance between the end of the light-shielding layer and the end of the channel region in a manner to fulfill the above expression, the deterioration in the image quality due to the stray light in the oblique direction can be minimized.