Active Matrix Substrate Contact Structure for Higher Aperture Ratio
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Solution Overview
Problem
The increasing thickness of the flattened layer in liquid crystal display devices to improve surface flatness and reduce load capacitance results in larger tapered contact holes, which decreases the aperture ratio and transmittance, posing challenges for high-definition displays.
Innovation Solution
The active matrix substrate incorporates a contact structure with a connection electrode made of transparent conductive material, such as ITO or IZO, and a drain region with higher impurity concentration at the contact hole overlap, overlapping both the lower and upper gate electrodes, allowing for a shallower pixel contact hole and reduced exposure time, thus improving aperture ratio and transmittance without requiring additional light blocking layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the flattened layer is formed thicker to improve surface flatness and reduce load capacitance, then surface flatness and capacitance performance are improved, but the contact hole becomes larger and deeper, which decreases the aperture ratio and transmittance
Solution Approach 1:
The contact structure is segmented into multiple components: a connection electrode extending from the drain region through the insulating layer to the flattened layer, and a separate pixel contact hole formed only in the flattened layer. This segmentation allows the connection electrode to provide electrical connection through the thick flattened layer while the pixel contact hole remains small, resolving the contradiction between thick flattened layer requirements and aperture ratio maintenance
Solution Approach 2:
The connection electrode acts as an intermediary element that bridges the drain region and the pixel contact hole. It extends through the insulating layer and flattened layer to establish electrical connection without requiring a large or deep pixel contact hole, thus maintaining aperture ratio while enabling proper electrical connection in the thick flattened layer structure
2Reliability
If the contact hole is made deeper to reach the drain region through a thick flattened layer, then electrical connection is achieved, but the tapered portion occupies more area, which is undesirable for high definition and aperture ratio
Solution Approach 1:
The electrical connection path is segmented from the pixel contact hole. The connection electrode extends through the insulating layer and flattened layer to reach the drain region, while the pixel contact hole only needs to penetrate the flattened layer. This segmentation allows the connection electrode to handle the deep connection requirement while the pixel contact hole remains shallow with minimal tapered portion area
Solution Approach 2:
The solution moves the deep connection function to a different dimensional approach by having the connection electrode extend vertically through multiple layers (insulating layer and flattened layer) while the pixel contact hole remains a shallow horizontal feature. This dimensional separation allows deep electrical connection without requiring a large or deep pixel contact hole
Data Source
AI summary
An active matrix substrate includes a substrate, TFTs, an insulating layer covering the TFTs, a flattened layer covering the insulating layer, pixel electrodes located on the flattened layer, and connection electrodes located between the insulating layer and the flattened layer respectively. The TFT includes a gate electrode, a gate insulating layer, and an oxide semiconductor layer. The oxide semiconductor layer includes a channel region facing the gate electrode with the lower gate insulating layer interposed therebetween, a source region and a drain region positioned on either side of the channel region. The insulating layer includes a contact hole at a position overlapping the drain region. The connection electrode is connected to the drain region in the contact hole. The drain region has a higher impurity concentration at least in a portion overlapping the contact hole than a concentration in a portion adjacent to the channel region.