Active Matrix Substrate Contact Hole Layout for Higher LCD Transmittance
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Solution Overview
Problem
In liquid crystal display devices with active matrix substrates, contact holes formed in flattened layers lead to reduced transmittance due to light leakage and alignment disturbances of liquid crystal molecules, which decreases contrast ratio and display quality, especially in high-resolution displays like head-mounted displays.
Innovation Solution
The active matrix substrate design includes a pixel contact hole that overlaps both the lower and upper gate electrodes, allowing for reduced exposure time and aperture diameter, eliminating the need for light blocking layers and improving transmittance by using a transparent conductive connection electrode to connect the drain contact region with the pixel electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light blocking layer is provided near the contact hole to prevent light leakage, then contrast ratio and display quality are improved, but transmittance decreases due to reduced light transmission area
Solution Approach 1:
The patent removes the light blocking layer from the pixel region, extracting the harmful element that was reducing transmittance. The contact hole is repositioned to overlap with the gate electrode, allowing the gate electrode itself to serve as the light blocking structure, thereby eliminating the need for separate light blocking layers in the pixel area and improving light transmission efficiency.
Solution Approach 2:
The patent merges the light blocking function with the gate electrode structure. By positioning the contact hole to overlap with the gate electrode, the gate electrode simultaneously serves as both the control electrode for the TFT and the light blocking structure, eliminating the need for separate light blocking layers and improving overall transmittance.
2Reliability
If the contact hole aperture diameter is increased to ensure reliable exposure and formation, then exposure reliability is improved, but transmittance decreases due to larger light blocking area
Solution Approach 1:
The patent changes the spatial arrangement from a traditional side-by-side layout to a vertical overlap configuration. The contact hole is positioned to overlap with the gate electrode in the vertical direction, utilizing the third dimension (depth) to resolve the contradiction between exposure reliability and transmittance.
Solution Approach 2:
The patent applies local quality by creating different functional zones: the contact hole region provides reliable exposure and electrical connection, while the gate electrode region provides light blocking. The overlap configuration allows each structure to fulfill its specific function optimally without compromising the other.
3Ease of manufacture
If a pedestal portion structure is added to raise the electrode and shallow the contact hole, then contact hole depth is reduced and formation is easier, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes the pedestal portion structure, extracting the unnecessary intermediate layer that was complicating the device structure. By repositioning the contact hole to overlap with the gate electrode, the patent achieves shallow contact hole formation without requiring additional pedestal structures, thereby simplifying the overall device architecture.
Solution Approach 2:
Instead of raising the electrode upward with a pedestal to shallow the contact hole, the patent inverts the approach by repositioning the contact hole downward to overlap with the gate electrode, achieving the same effect of reduced contact hole depth through a different spatial configuration.
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 enhances transmittance by reducing the aperture diameter of the contact hole and minimizing light leakage, thereby improving the contrast ratio and display quality without increasing manufacturing complexity or costs.
Implementation Method 1
it is necessary to provide sufficient exposure energy to the photosensitive resin material during exposure to allow the photosensitive resin material to be sufficiently exposed in a depth direction
Data Source
AI summary
An active matrix substrate includes a first TFT disposed in each of pixel regions, a first flattened layer covering the first TFT, and a pixel electrode provided on the first flattened layer. The first TFT includes a lower gate electrode, a lower gate insulating layer, an oxide semiconductor layer, an upper gate insulating layer, and an upper gate electrode. The active matrix substrate further includes a first connection electrode for electrically connecting a drain contact region of the oxide semiconductor layer and the pixel electrode. The first flattened layer includes a pixel contact hole formed so as to expose a part of the first connection electrode. The bottom face of the pixel contact hole at least partially overlaps, of a lower gate metal layer including a lower gate electrode and an upper gate metal layer including an upper gate electrode, at least the lower gate metal layer when viewed from the normal direction of the substrate. The first connection electrode is formed from a transparent conductive material.