Dual-Gate Oxide TFT Layout for Integrated Display Driver Circuits
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Solution Overview
Problem
The manufacturing cost of display devices increases with the number of gate lines and signal lines required for larger display regions, and existing thin film transistors using amorphous or polycrystalline silicon have limitations in terms of mobility and scalability.
Innovation Solution
A thin film transistor using an oxide semiconductor with a dual-gate structure, where gate electrodes are provided above and below the oxide semiconductor layer, enhancing mobility and reliability, and allowing for high dynamic characteristics and reduced parasitic capacitance, thereby reducing manufacturing costs and enabling high-speed operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a thin film transistor using amorphous silicon is employed, then the transistor can be formed over a glass substrate with a larger area, but the electric field effect mobility is low
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical properties and enables high mobility while maintaining large substrate compatibility. The oxide semiconductor material inherently provides higher carrier mobility compared to amorphous silicon, resolving the contradiction between substrate area and mobility.
2Speed
If a thin film transistor using polycrystalline silicon is employed, then the electric field effect mobility is higher than amorphous silicon, but a crystallization process such as laser annealing is necessary
Solution Approach 1:
The patent uses oxide semiconductor material that can be deposited as an amorphous film and directly crystallized into a functional state without requiring complex laser annealing processes. This approach replaces the expensive and complex polycrystalline silicon manufacturing process with a simpler, more cost-effective oxide semiconductor process that achieves comparable or superior mobility.
3Measurement precision
If the number of pixels is increased for larger display region or higher definition, then the display quality is improved, but the number of gate lines and signal lines is increased making IC chip mounting difficult and manufacturing cost increased
Solution Approach 1:
The patent employs oxide semiconductor thin film transistors with dual gate electrodes that can function as both switching elements and driver circuit elements on the same substrate. This multi-functional approach allows the display device to integrate both pixel switching and driving functions, eliminating the need for separate IC chip mounting and reducing the complexity associated with numerous external connections.
4Reliability
If gate electrodes are provided above and below the oxide semiconductor layer, then the on characteristics and reliability are improved, but the device structure becomes more complex
Solution Approach 1:
The patent merges the function of two gate electrodes (top and bottom gates) into a unified dual-gate structure that works synergistically to control the oxide semiconductor channel. This combined structure provides enhanced reliability and electrical characteristics while the manufacturing process integrates both gates into a single fabrication sequence, minimizing the actual increase in manufacturing complexity.
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 thin film transistor improves on characteristics and reliability, reducing manufacturing costs and enabling high-speed operation while maintaining low power consumption, suitable for large display devices.
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 higher definition, the number of pixels is increased and thus, the number of gate lines and signal lines is increased. When the number of gate lines and signal lines is increased, it is difficult to mount IC chips including driver circuits for driving the gate lines and the signal lines by bonding or the like, whereby manufacturing cost is increased. A pixel portion and a driver circuit for driving the pixel portion are provided on the same substrate, and at least part of the driver circuit comprises a thin film transistor including an oxide semiconductor sandwiched between gate electrodes. A channel protective layer is provided between the oxide semiconductor and a gate electrode provided over the oxide semiconductor. The pixel portion and the driver circuit are provided on the same substrate, which leads to reduction of manufacturing cost.