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 material for connection electrodes, thus enhancing the aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photosensitive resin material is thickly applied to achieve sufficient flattening effect and load capacitance reduction, then the flattening effect and power consumption reduction are improved, but the exposure time and aperture diameter need to be increased to reliably expose the lower layer, which increases the area occupied by the contact hole and reduces transmittance
Solution Approach 1:
The patent introduces a vertical dimension solution by forming a raised electrode structure (pedestal portion) beneath the contact hole. This elevates the electrode in the thickness direction, allowing the contact hole to be formed shallower in the photosensitive resin layer while still achieving reliable electrical connection. This dimensional change resolves the contradiction by reducing the required exposure depth without compromising the flattening effect of the thick photosensitive resin layer.
Solution Approach 2:
The patent applies preliminary action by forming the raised electrode structure (pedestal portion) before forming the contact hole. This pre-established structure allows subsequent contact hole formation to be shallower, as the electrode is already positioned at an elevated level. This preliminary structural preparation enables reduced exposure parameters while maintaining reliable electrical connection.
2Object-affected harmful factors
If a light blocking layer is provided to block light near the contact hole and suppress light leakage, then the contrast ratio and display quality are improved, but the area contributing to display in the pixel region is reduced, causing transmittance to decrease
Solution Approach 1:
The patent extracts and removes the light blocking layer from the structure. By eliminating this layer, light leakage is permitted to occur naturally at the contact hole periphery, but this is compensated for by the raised electrode structure that minimizes the contact hole aperture diameter. This extraction approach resolves the contradiction by removing the harmful light blocking effect while maintaining acceptable display quality through alternative structural means.
Solution Approach 2:
The patent converts the potential harm of light leakage near the contact hole into a beneficial outcome. By using the raised electrode structure to minimize the contact hole size, the light leakage effect is naturally reduced without requiring additional light blocking layers. This approach transforms what would normally be a harmful effect into an acceptable characteristic that does not require separate mitigation.
3Length of stationary object
If a complicated structure with pedestal portion is formed to make the contact hole shallow, then the contact hole depth is reduced and transmittance is improved, but light leakage concerns remain and additional light blocking is required, which further reduces transmittance and increases process load
Solution Approach 1:
The patent merges multiple functions into the raised electrode structure (pedestal portion). This single structure simultaneously achieves: (1) elevating the electrode to reduce contact hole depth, (2) providing electrical connection, and (3) minimizing the contact hole aperture diameter to reduce light leakage. By combining these functions into one integrated structure, the need for separate light blocking layers is eliminated, reducing overall device complexity and process load.
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 effectively reduces the aperture diameter of the contact hole, minimizes light leakage, and increases transmittance without additional light blocking layers, improving display quality and contrast ratio in high-resolution liquid crystal display devices.
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.