Dual-Gate Oxide TFT Layout for Integrated Display Drivers
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Solution Overview
Problem
The manufacturing cost of display devices increases with the number of gate lines and signal lines, making it difficult to integrate IC chips for driving, especially as display size and pixel density increase, and existing thin film transistors using amorphous or polycrystalline silicon have limitations in mobility and suitability for large substrates.
Innovation Solution
A semiconductor device using an oxide semiconductor with a dual-gate structure, where the oxide semiconductor layer is interposed between two gate electrodes, allowing for high dynamic characteristics and reduced parasitic capacitance, enabling high-speed operation and low power consumption, and can be formed over a larger substrate without increasing the number of manufacturing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a thin film transistor is formed using amorphous silicon, then it can be formed over a glass substrate with a larger area, but it has low electric field effect mobility
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical properties while maintaining the low-temperature processing capability. This enables high mobility (comparable to polycrystalline silicon) on large-area glass substrates without requiring high-temperature crystallization processes.
2Speed
If a thin film transistor is formed using polycrystalline silicon, then it has high electric field effect mobility, but a crystallization process such as laser annealing is necessary and such a transistor is not always suitable for a larger glass substrate
Solution Approach 1:
The patent changes the material system from polycrystalline silicon to oxide semiconductor, eliminating the need for high-temperature crystallization processes like laser annealing. The oxide semiconductor can be deposited at low temperatures (below 400°C) while achieving high mobility, simplifying the manufacturing process for large-area substrates.
Solution Approach 2:
The patent replaces the mechanical/thermal process of laser annealing with a low-temperature deposition process using oxide semiconductor materials. This substitution eliminates the need for complex high-temperature equipment and multiple processing steps, making large-area manufacturing more feasible.
3Manufacturing precision
If the size of a display region is increased and the number of pixels is increased, then the definition is improved, but the number of gate lines and signal lines is increased making it difficult to mount IC chips
Solution Approach 1:
The patent merges the driver circuit functionality directly into the display substrate by forming thin film transistors using oxide semiconductors. This integration eliminates the need for separate IC chip mounting, reducing the complexity associated with increasing numbers of gate lines and signal lines while maintaining high display definition.
4Speed
If a thin film transistor using oxide semiconductor is employed, then high dynamic characteristics are achieved, but the manufacturing process must be optimized for low temperature formation
Solution Approach 1:
The patent changes the material properties of the semiconductor layer to oxide semiconductor, which has unique characteristics allowing high mobility at low temperatures. This material parameter change enables the formation of high-performance transistors without requiring high-temperature processing, though it does require optimized low-temperature deposition processes.
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
The dual-gate oxide semiconductor structure enhances the reliability and dynamic characteristics of thin film transistors, reducing manufacturing costs by allowing high-speed operation and low power consumption, while enabling the integration of driver circuits and pixel portions on the same substrate without increasing the complexity of the manufacturing process.
Implementation Method 1
The oxide semiconductor film can be formed by a sputtering method or the like at a temperature of 300° C. or lower.
Data Source
AI summary
As a display device has a higher definition, the number of pixels, gate lines, and signal lines are increased. When the number of the gate lines and the signal lines are increased, a problem of higher manufacturing cost, because it is difficult to mount an IC chip including a driver circuit for driving of the gate and signal lines by bonding or the like. A pixel portion and a driver circuit for driving the pixel portion are provided over the same substrate, and at least part of the driver circuit includes a thin film transistor using an oxide semiconductor interposed between gate electrodes provided above and below the oxide semiconductor. Therefore, when the pixel portion and the driver portion are provided over the same substrate, manufacturing cost can be reduced.