Oxide Semiconductor Dual-Gate TFT for Low Off-State Current
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Solution Overview
Problem
Existing transistors using oxide semiconductors face challenges with low field-effect mobility, high off-state current, and unstable electrical characteristics due to variations in stoichiometric composition and hydrogen bonding, which are not suitable for high-definition displays requiring fast operation and low power consumption.
Innovation Solution
A semiconductor device is developed using an intrinsic or substantially intrinsic oxide semiconductor layer with a crystalline region in the surface portion, and a dual-gate structure with conductive films on opposite sides separated by insulating films to control channel position and reduce off-state current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a transistor is formed using amorphous silicon, then it can be formed over a glass substrate with a larger area, but the field-effect mobility is low
Solution Approach 1:
The invention changes the material parameter from amorphous silicon to oxide semiconductor, which enables formation on large-area glass substrates while achieving higher field-effect mobility through controlled intrinsic or substantially intrinsic semiconductor characteristics
Solution Approach 2:
The invention uses a composite structure combining oxide semiconductor layer with insulating films and conductive layers, creating a transistor that achieves both large-area manufacturability and high mobility performance
2Speed
If a transistor is formed using crystalline silicon, then the field-effect mobility is high, but a crystallization step such as laser annealing is necessary and it is not suitable for a larger glass substrate
Solution Approach 1:
The invention changes the material phase from crystalline silicon requiring high-temperature laser annealing to oxide semiconductor that can be deposited at lower temperatures and formed into intrinsic or substantially intrinsic state, enabling large-area substrate compatibility while maintaining high mobility
Solution Approach 2:
The invention replaces the mechanical/thermal crystallization process (laser annealing) with a deposition and purification process that forms oxide semiconductor layers with controlled intrinsic characteristics, eliminating the need for high-temperature crystallization steps
3Object-generated harmful factors
If an oxide semiconductor with electron carrier concentration less than 10^18/cm^3 is used, then the off-state current is reduced, but the on/off ratio is only 10^3 due to large off-state current
Solution Approach 1:
The invention changes the key parameter of electron carrier concentration to achieve intrinsic or substantially intrinsic state (even lower concentration), and combines this with dual-gate voltage control to simultaneously reduce off-state current and achieve high on/off ratio exceeding 10^8
Solution Approach 2:
The invention introduces dynamic control through dual-gate voltage application, where the channel position and conductivity can be dynamically adjusted by gate voltages, enabling the transistor to switch between low-off-state-current state and high-conductivity state for superior on/off ratio
4Measurement precision
If the screen resolution is increased for higher definition, then the number of pixels is significantly increased, but the writing time for one pixel is shortened requiring high speed operation
Solution Approach 1:
The invention changes the semiconductor material parameters to achieve higher field-effect mobility and faster carrier transport, enabling transistors to operate at higher speeds required for driving high-resolution displays with increased pixel counts
5Area of stationary object
If the screen size is increased towards larger displays, then the area coverage is improved, but the power consumption increases
Solution Approach 1:
The invention changes the electrical characteristics parameters including lower off-state current and optimized threshold voltage, reducing the power consumption per pixel and enabling large-screen displays to maintain acceptable power consumption levels
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 solution enhances transistor performance with improved mobility, reduced off-state current, and stable electrical characteristics, enabling high-speed operation and low power consumption suitable for large, high-definition displays.
Implementation Method 1
an oxide semiconductor layer which is intrinsic or substantially intrinsic and includes a crystalline region in a surface portion
Data Source
AI summary
An oxide semiconductor layer which is intrinsic or substantially intrinsic and includes a crystalline region in a surface portion of the oxide semiconductor layer is used for the transistors. An intrinsic or substantially intrinsic semiconductor from which an impurity which is to be an electron donor (donor) is removed from an oxide semiconductor and which has a larger energy gap than a silicon semiconductor is used. Electrical characteristics of the transistors can be controlled by controlling the potential of a pair of conductive films which are provided on opposite sides from each other with respect to the oxide semiconductor layer, each with an insulating film arranged therebetween, so that the position of a channel formed in the oxide semiconductor layer is determined.