Selective Laser Annealing for Dual-Mobility TFTs in Displays
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Solution Overview
Problem
Conventional polysilicon thin film transistors (TFTs) exhibit high currents in both ON and OFF states, making them unsuitable for both pixel and drive circuit applications, and existing manufacturing methods are complex and time-consuming, failing to provide TFTs with different electron mobility for varied functions.
Innovation Solution
A display apparatus with a first thin film transistor for pixels and a second thin film transistor for drive circuits, where the channel regions have distinct electrical characteristics, achieved by forming a first channel region with both amorphous silicon and polysilicon regions and a second channel region with only polysilicon regions, using a partial irradiation laser annealing method to selectively crystallize the amorphous silicon layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional laser annealing method is used to manufacture polysilicon TFTs, then the manufacturing process can be simplified, but both ON-state current and OFF-state current are high making the TFTs unsuitable for both pixel and drive circuit applications
Solution Approach 1:
The patent applies local quality by creating different crystalline structures in different regions of the same substrate. Specifically, the drive circuit region undergoes laser annealing to form high-crystallinity polysilicon for high ON-state current, while the pixel region maintains low-crystallinity amorphous silicon for low OFF-state current. This regional differentiation allows a single manufacturing process to produce TFTs with different electrical characteristics suitable for different functions.
Solution Approach 2:
The patent segments the substrate into distinct functional regions (drive circuit region and pixel region) that receive different laser annealing treatments. By dividing the manufacturing process into region-specific steps, the patent achieves different electrical characteristics in different areas without requiring completely separate manufacturing lines.
2Reliability
If different TFTs with different electron mobility are provided for different functions, then suitable functioning for pixels and drive circuits is achieved, but complicated steps and much time are required using conventional laser annealing method
Solution Approach 1:
The patent merges the manufacturing of different TFT types into a single integrated process. By combining drive circuit TFTs and pixel TFTs on one substrate and applying selective laser annealing in different regions, the patent produces multiple TFT types simultaneously in one manufacturing run, dramatically reducing the time and complexity compared to conventional separate manufacturing approaches.
3Power
If whole substrate crystallization is performed to increase ON-state current, then drive circuit TFTs achieve high current, but OFF-state current also increases making pixel TFTs unsuitable
Solution Approach 1:
The patent applies local quality by controlling laser annealing parameters (such as laser power, scanning speed, and number of passes) to achieve different crystalline structures in different regions. The drive circuit region receives higher energy density laser treatment for high crystallinity and high ON-state current, while the pixel region receives lower energy density treatment maintaining amorphous structure for low OFF-state current.
Solution Approach 2:
The patent uses partial laser annealing action on specific regions rather than treating the entire substrate uniformly. By applying laser energy selectively and with controlled intensity to only the drive circuit region, the patent achieves the necessary crystallization for high ON-state current without subjecting the pixel region to excessive crystallization that would increase OFF-state current.
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 allows for suitable functioning of TFTs for pixels by reducing OFF-state current and for drive circuits by increasing ON-state current, while simplifying the manufacturing process by eliminating the need for whole substrate crystallization and etching steps.
Implementation Method 1
The P-Si TFT is manufactured by laser-annealing method of irradiating a whole surface of a substrate with laser beams
Implementation Method 2
a first channel region including a first part of the first amorphous silicon layer, the first part being a part between the source electrode and the drain electrode of the first thin film transistor in a top view; the second channel region including a second part of the first amorphous silicon layer
Data Source
AI summary
There are provided a display apparatus and a method of manufacturing the display apparatus. The display apparatus includes a pixel having a first thin film transistor and a drive circuit having a second thin film transistor and driving the pixel, wherein a first channel region of the first thin film transistor and a second channel region of the second thin film transistor are configured to have different electrical characteristics (for example, electron mobility, thereby enabling the first thin film transistor and the second thin film transistor to function suitably for the each role thereof).