Oxide TFT Drain Electrode Geometry for Mobility Peak Suppression
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Solution Overview
Problem
Thin-film transistors (TFTs) with oxide semiconductor channel layers exhibit erratic carrier mobility curves, leading to degraded display quality and reliability in liquid crystal and organic electroluminescence display devices due to extreme peaks in mobility curves when the gate voltage is close to the threshold voltage.
Innovation Solution
A TFT configuration with a channel layer, channel protection layer, and electrodes is designed such that the drain electrode's facing portion has a length less than or equal to 2.5 μm, reducing the electric field effect on the channel region and suppressing the peak of the mobility curve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If oxide semiconductor is used in the channel layer of a TFT element, then high carrier mobility and low OFF current are achieved, but the mobility curve exhibits extreme peaks when gate voltage is close to threshold voltage
Solution Approach 1:
The patent changes the geometric parameters of the drain electrode, specifically limiting the length of the facing portion to 2.5 μm or less in the channel length direction. This parameter change modifies the electric field distribution in the channel region, suppressing the formation of extreme peaks in the mobility curve while maintaining high carrier mobility characteristics of oxide semiconductor
Solution Approach 2:
The patent applies different structural characteristics to different regions: the drain electrode has a limited-length facing portion that faces the channel region, while other portions of the drain electrode extend beyond this facing region. This local differentiation allows control of the electric field in the critical channel region without compromising overall device structure
2Force
If the drain electrode has a long facing portion, then strong electric field effect is achieved, but carrier mobility variations increase and display reliability degrades
Solution Approach 1:
The patent optimizes the electric field effect by precisely controlling the length parameter of the drain electrode's facing portion to 2.5 μm or less. This parameter optimization maintains sufficient electric field effect for device operation while preventing excessive field effects that cause carrier mobility variations and reliability degradation
Data Source
AI summary
A thin-film transistor includes: a gate electrode; a channel layer not adjacent to the gate electrode; a channel protection layer exposing portion of the channel layer, a source electrode contacting the channel layer at portion of an exposed portion of the channel layer, and a drain electrode contacting the channel layer at portion of the exposed portion, in respective order. The channel layer includes oxide semiconductor. Surface of the channel protection layer includes upper surface and side surface extending from the upper surface to the exposed portion. The drain electrode has: a rising portion extending from above the exposed region to the channel layer along the side surface; and an upper surface covering portion continuous with the rising portion and extending onto portion of the upper surface. The upper surface covering portion has a facing portion facing a channel region and being 2.5 μm or less in channel length direction.