OLED TFT Contact Structure for Etch Uniformity and Low Resistance
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Solution Overview
Problem
In the manufacturing of organic light emitting display devices with multi-type thin film transistors, residual inorganic layers and non-uniform etch uniformity can occur due to thick insulating layers, leading to issues with contact resistance and spot defects.
Innovation Solution
The design of an asymmetric structure for the active layer under contact holes in LTPS thin film transistors, allowing side contact with source and drain electrodes, reduces the influence of residual inorganic layers and improves etch uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If thick insulating layers are stacked to form multi-type thin film transistors on different layers, then device functionality is improved, but residual inorganic layers remain and etch uniformity deteriorates
Solution Approach 1:
The active layer is designed with an asymmetric structure where the first region (under contact hole) has different thickness or composition compared to the second region (channel region). This asymmetry allows the first region to be etched more effectively while preserving the channel region, thereby improving etch uniformity across the thick insulating layers without compromising the multi-type transistor functionality.
Solution Approach 2:
Different regions of the active layer are given different properties: the first region has modified characteristics (thickness, composition, or structure) to facilitate better etching and reduce residual inorganic layers in contact areas, while the second region maintains properties optimized for transistor channel function. This local differentiation resolves the contradiction between etchability and device functionality.
2Adaptability or versatility
If thick insulating layers are stacked to form multi-type thin film transistors on different layers, then device functionality is improved, but contact resistance increases due to residual inorganic layers
Solution Approach 1:
The asymmetric active layer structure creates a first region with enhanced etchability that extends deeper into the contact hole, effectively removing residual inorganic layers that would otherwise increase contact resistance. This maintains low contact resistance while preserving the thick insulating layer structure needed for multi-type transistor functionality.
Solution Approach 2:
The asymmetric design converts the potential harm of thick insulating layers (which cause residual inorganic layers and high contact resistance) into a benefit by creating a localized region that facilitates complete etching through the thick layers, thereby eliminating the harmful residual layers while maintaining the necessary insulating layer thickness for device functionality.
3Manufacturing precision
If asymmetric active layer structure is implemented, then residual inorganic layer influence is reduced, but device complexity increases
Solution Approach 1:
The complexity is localized only to the first region of the active layer under the contact hole, while the second region (channel) maintains a conventional structure. This localized modification achieves residual inorganic layer reduction without significantly increasing overall device complexity, as only a specific area requires the asymmetric design.
Solution Approach 2:
The active layer is segmented into functionally distinct regions: a first region with asymmetric structure optimized for contact hole etching and a second region with conventional structure optimized for transistor operation. This segmentation allows each region to be optimized independently, reducing residual inorganic layers where needed without complicating the entire device structure.
Data Source
AI summary
An organic light emitting display device may include a first thin film transistor disposed above a substrate and including a first active layer that is formed of a first material and includes a first source region, a first channel region, and a first drain region, a first gate electrode, and a first source electrode and a first drain electrode, at least one insulating layer disposed on the first gate electrode and a second thin film transistor disposed on the insulating layer and including a second active layer that is formed of a second material and includes a second source region, a second channel region, and a second drain region, a second gate electrode, and a second source electrode and a second drain electrode, wherein the first source electrode and the first drain electrode are electrically connected to the first active layer through a first contact hole, and wherein the first active layer under the first contact hole has an asymmetric structure.