Asymmetric LDD-TFT Pixel Circuit for Display Leakage and Speed
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Solution Overview
Problem
Conventional lightly doped drain thin film transistors (LDD-TFTs) in pixel circuits of display devices face challenges with high leakage current and low operation speed due to the symmetric structure of lightly doped drains, which affects the performance of organic light-emitting displays.
Innovation Solution
The proposed solution involves a dual gate transistor with asymmetric lightly doped drains, where one lightly doped drain is lengthened to reduce leakage current and the others are shortened or canceled to decrease series resistance, thereby increasing electron drift and operation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If symmetric lightly doped drains are used in conventional LDD-TFTs, then leakage current is reduced, but operation speed decreases due to increased series resistance
Solution Approach 1:
The patent applies asymmetry by configuring the first lightly doped drain with a first length and the second lightly doped drain with a second length different from the first length. This asymmetric structure allows one drain to optimize for leakage reduction while the other optimizes for speed, resolving the contradiction between reducing leakage current and maintaining operation speed.
2Length of moving object
If channel region length is reduced to achieve compact TFT size, then device integration is improved, but threshold voltage decreases and hot electron effects increase
Solution Approach 1:
The patent segments the drain structure into lightly doped drain regions with different lengths, positioned at specific locations within the channel. This segmentation allows the channel to remain short for compact size while the segmented LDD structures provide localized field control to maintain threshold voltage stability and reduce hot electron effects.
Solution Approach 2:
The patent applies local quality by creating regions with different dopant concentrations and geometries within the drain structure. The first and second lightly doped drains have different lengths and are positioned at different locations, providing localized electrical field management that addresses hot electron effects specifically where they occur without requiring a longer channel.
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 effectively reduces leakage current and enhances the operation speed of the transistor by optimizing the length of lightly doped drains, improving the overall performance of the pixel circuit in display devices.
Implementation Method 1
a lightly doped drain (LDD) structure is proposed in the prior art so as to reduce the electric field at the junction of the drain, thereby lowering the hot electron effects
Implementation Method 2
the hot electron effects, a total of which affects the operational performance of the conventional TFT structure
Implementation Method 3
The lightly doped drains 140, 142 respectively have higher resistance than the sources/drains 144, 146 due to low dopant concentration
Data Source
AI summary
A pixel circuit for driving a plurality of pixel units within a display includes: a plurality of scanning lines formed within the display for transmitting scanning signals to the pixel units; a plurality of data lines formed within the display and transversely crossing the scanning lines for transmitting data signals to the pixel units, respectively; and a plurality of LDD-TFTs. The LDD-TFT is coupled to a respective scanning line, a respective data line and a driving transistor. The LDD-TFT includes a first lightly doped drain that is closest to the driving transistor and that has a first length, and a second lightly doped drain that has a second length shorter than the first length.