P-Channel TFT Threshold Control via Selective Doping
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Solution Overview
Problem
Existing display devices face challenges in controlling threshold voltage of thin film transistors, leading to issues with image quality and reliability, especially in varying environmental temperatures, due to contamination and work function differences.
Innovation Solution
Incorporating p-channel and n-channel thin film transistors with controlled impurity concentrations in the channel formation regions, where the p-channel transistors in the driver circuit have a higher threshold for high-speed operation and those in the pixel have a lower threshold, and selectively doping semiconductor layers to manage cutoff current and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If channel doping is applied to control threshold voltage, then threshold voltage control is improved, but manufacturing complexity increases due to selective doping requirements
Solution Approach 1:
The patent applies different impurity concentrations to different transistor types (p-channel vs n-channel) and different circuit locations (driver circuit vs pixel). Specifically, p-channel TFTs in driver circuits receive higher impurity concentrations for high-speed operation, while p-channel TFTs in pixels receive lower impurity concentrations for low cutoff current. This localized differentiation resolves the contradiction by tailoring doping levels to specific functional requirements rather than applying uniform doping.
Solution Approach 2:
The patent changes the impurity concentration parameter selectively across different transistor regions. By adjusting the impurity concentration (a key physical parameter) to different values for driver circuit transistors versus pixel transistors, the patent achieves precise threshold voltage control and optimized electrical characteristics without requiring complex additional processing steps.
2Reliability
If p-channel thin film transistor threshold is lowered for pixel operation, then image quality improves, but cutoff current increases leading to higher power consumption
Solution Approach 1:
The patent differentiates impurity concentration based on the specific functional location of the transistor. Pixel p-channel TFTs use lower impurity concentrations to minimize cutoff current and power consumption during display operation, while driver circuit p-channel TFTs use higher impurity concentrations for fast switching. This spatial differentiation of material properties resolves the contradiction between image quality and power consumption.
3Productivity
If driver circuit p-channel thin film transistor operates at high speed, then productivity improves, but threshold voltage control becomes more difficult
Solution Approach 1:
The patent changes the impurity concentration parameter specifically for driver circuit p-channel TFTs to higher levels, which enables high-speed operation through improved carrier mobility. This parameter adjustment is applied selectively only to driver circuit transistors, maintaining precise threshold voltage control where needed while optimizing speed where required.
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 results in improved image quality, reduced power consumption, and enhanced reliability of display devices, maintaining performance even in high-temperature environments, with reduced luminance in black display states and improved contrast.
Implementation Method 1
an impurity element imparting one conductivity (typically, P, As, B, or the like) is added to at least a channel formation region of a TFT
Data Source
AI summary
In a case where a p-channel thin film transistor is used as a thin film transistor that is electrically connected to a light-emitting element and drives the light-emitting element, a value of cutoff current of the p-channel thin film transistor is made lower than that of a p-channel thin film transistor of a driver circuit. Specifically, channel doping is selectively performed on a semiconductor layer of a thin film transistor included in a pixel.