Oxide TFT Source Drain Transition Layer Process Simplification
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Solution Overview
Problem
The existing fabrication processes for oxide TFTs require multiple mask steps, including an etch stop layer, which complicates the process, affects the threshold voltage, and increases costs, while also impacting the stability and performance of the TFTs.
Innovation Solution
The introduction of heavily doped semiconductor source and drain transition layers between the oxide active layer and the source and drain, which are formed in the same patterning process as the source and drain, eliminating the need for an etch stop layer and simplifying the process, and an annealing treatment under specific conditions to convert the active layer into a conductor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an etch stop layer is used in the fabrication process, then the oxide active layer can be protected during etching, but the fabrication process becomes more complex and requires additional mask steps
Solution Approach 1:
The patent removes the etch stop layer from the traditional TFT fabrication process. Instead of adding a separate protective layer, the invention uses the source and drain transition layers themselves to provide protection during etching, thereby eliminating the need for the etch stop layer and reducing process complexity while maintaining reliability
Solution Approach 2:
The source and drain transition layers are designed to serve multiple functions: they act as both the transition region for electrical characteristics and as the protective layer during etching processes. This multi-functionality eliminates the need for a separate etch stop layer, reducing fabrication complexity while maintaining the protection of the oxide active layer
2Reliability
If an etch stop layer is used, then the oxide active layer is protected, but fabrication cost increases due to additional mask processes
Solution Approach 1:
The patent eliminates the etch stop layer and its associated mask process, thereby reducing fabrication costs. The protective function is transferred to the source and drain transition layers, which are already required for electrical functionality, thus achieving cost reduction without sacrificing protection
3Reliability
If an etch stop layer is used, then etching protection is provided, but threshold voltage drift and thermal stability deteriorate
Solution Approach 1:
The patent removes the etch stop layer that was causing threshold voltage drift and thermal stability issues. The invention achieves etching protection through alternative means (the transition layers) that do not have the harmful side effects of the traditional etch stop layer
Solution Approach 2:
The patent modifies the doping concentration and material composition of the source and drain transition layers to achieve both etching protection and improved electrical stability. By carefully controlling the doping parameters (e.g., boron doping concentration between 1×10^19 to 1×10^21 atoms/cm³), the invention achieves threshold voltage stability and thermal stability while maintaining protective functionality
4Reliability
If source and drain transition layers with heavy doping are used, then conductor characteristics are achieved in contact regions, but the active region must maintain semiconductor characteristics
Solution Approach 1:
The patent applies different doping concentrations to different regions of the source and drain transition layers. The portions contacting the source/drain electrodes are heavily doped to achieve conductor characteristics, while the portions adjacent to the active region are lightly doped or undoped to maintain semiconductor characteristics. This spatial variation in doping quality resolves the contradiction between contact conductivity and active region functionality
5Productivity
If the fabrication process is simplified by removing the etch stop layer, then productivity increases, but manufacturing precision may be affected
Solution Approach 1:
The patent combines the formation of source/drain electrodes and source/drain transition layers into a single patterning process. By merging these steps and using the transition layers to provide etching protection, the invention achieves both improved productivity (fewer process steps) and maintained precision (single patterning operation reduces alignment errors)
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 approach reduces the number of patterning processes, improves the stability and switching performance of the TFTs, enhances thermal stability, and reduces threshold voltage drift, while maintaining semiconductor characteristics in the active region and conductor characteristics in the contact regions.
Implementation Method 1
the source transition layer and the drain transition layer comprising heavily doped semiconductor material including at least one element of B, Si, Ge and Te
Implementation Method 2
annealing treatment on an oxide active layer and a source and drain transition layer under a certain condition
Data Source
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AI summary
The present invention discloses a thin film transistor (TFT), an array substrate, and fabrication methods thereof, and a display device. The TFT includes a gate, an oxide active layer, a source, and a drain formed on a substrate, wherein a source and drain transition layer is provided between the oxide active layer and the source, the drain. One patterning process is reduced and one mask process is saved through forming the source and drain transition layer between the oxide active layer and the source, the drain, thus effectively simplifying the fabrication procedure. At the same time, the additionally provided source and drain transition layer may prevent the oxide active layer from being corroded during etching, also effectively reduce threshold voltage (Vth) drift of the TFT, improve Ion (on-state current)/Ioff (off-state current), and enhance thermal stability.