Step-Shaped Via Hole Prevents Pixel Electrode Fracture

Solution Overview

Problem

Conventional display devices face the challenge of pixel electrode fracture at the joint with the via hole, while attempting to reduce parasitic capacitance by increasing the thickness of the organic insulation layer, which leads to a higher axial height of the via hole.

Innovation Solution

A step-shaped via hole is designed with a larger upper end surface area connected to the pixel electrode and a smaller lower end surface connected to the drain, allowing for a good contact and preventing fracture, while maintaining a thin film transistor structure with an organic and inorganic insulation layer configuration that penetrates the via hole.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the thickness of the organic insulation layer is increased to reduce parasitic capacitance, then the parasitic capacitance decreases, but the axial height of the via hole increases causing pixel electrode fracture

Engineering Contradiction:

Improvepixel electrode fracture resistanceVSAvoidparasitic capacitance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The via hole is divided into two distinct portions: a first via portion extending through the organic insulation layer to the inorganic insulation layer, and a second via portion extending through the inorganic insulation layer to the drain. This segmentation allows each portion to be optimized independently for its specific function and structural requirements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the via hole are given different cross-sectional areas to match the local structural requirements. The first via portion has a larger cross-sectional area to provide sufficient contact area with the pixel electrode at the upper level, while the second via portion has a smaller cross-sectional area appropriate for connection to the drain at the lower level. This local quality differentiation ensures reliable electrical connection without requiring excessive via hole height.

Inventive Principle:

Principle #3Local quality

2Reliability

If the thickness of the organic insulation layer is increased to reduce parasitic capacitance, then the parasitic capacitance decreases, but the axial height of the via hole increases making the pixel electrode more likely to fracture

Engineering Contradiction:

Improvepixel electrode joint strengthVSAvoidvia hole structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The via hole is divided into two distinct portions: a first via portion extending through the organic insulation layer to the inorganic insulation layer, and a second via portion extending through the inorganic insulation layer to the drain. This segmentation allows each portion to be optimized independently for its specific function and structural requirements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The via hole transitions from a simple vertical structure to a stepped three-dimensional structure with different cross-sectional areas at different heights. This dimensional change allows the via hole to accommodate the thickness of the organic insulation layer without proportionally increasing the overall via hole height, as the larger cross-sectional area of the first via portion provides sufficient contact area without requiring excessive height.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS9508755B2Pixel unit and method of fabricating the same, array substrate and display device

Publication Date: 2016.11.29 BOE TECHNOLOGY GROUP CO LTD

AI summary

The present invention provides a pixel unit including a thin film transistor and a pixel electrode, the thin film transistor includes a gate, a source and a drain, and the pixel electrode is electrically connected to the drain through a via hole. An upper end surface of the via hole is connected to the pixel electrode, and a lower end surface of the via hole is connected to the drain. The via hole is a step-shaped hole, and an area of the upper end surface of the via hole is larger than that of the lower end surface of the via hole. The present invention also provides a method of fabricating the pixel unit, an array substrate including the pixel unit, and a display device including the array substrate.