Polysilicon TFT Segmented Doping Suppresses Hot Carrier Effect
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Solution Overview
Problem
The high electric field intensity in low-temperature polysilicon thin film transistors (LTPS-TFTs) leads to the hot carrier effect, causing degradation in MOS characteristics and reliability issues due to increased electron mobility and leakage currents, which are not adequately addressed by existing doping methods.
Innovation Solution
A polysilicon thin film transistor structure with a specific doping pattern and ion implantation process, where passivated doped regions form stable covalent bonds with silicon atoms, reducing boundary defects and suppressing the hot carrier effect by controlling the diffusion rate of ions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heavy doping is conducted on polysilicon layer to form source and drain regions, then doping concentration is high and manufacturing is simplified, but strong electric field is produced near source and drain regions causing hot carrier effect and increased leakage current
Solution Approach 1:
The doped regions are segmented into multiple zones with different doping concentrations: heavily doped regions (first and second doped regions) and lightly doped regions (third and fourth doped regions). This segmentation allows the source and drain areas to have high doping for easy manufacturing while the channeladjacent regions have low doping to reduce electric field intensity and suppress hot carrier effect, thus improving reliability.
Solution Approach 2:
Different doping concentrations are applied to different locations within the source and drain regions. The regions far from the channel have heavy doping for ease of manufacture, while the regions adjacent to the channel have light doping to reduce electric field intensity. This local differentiation resolves the contradiction between manufacturing ease and hot carrier effect suppression.
2Reliability
If light doping is conducted on drain region to reduce leakage current by decreasing electric field at drain boundary, then leakage current is reduced, but boundary defect increases and manufacturing complexity increases
Solution Approach 1:
The source and drain regions are segmented into heavily doped areas (first and second doped regions) and lightly doped areas (third and fourth doped regions). This segmentation reduces leakage current through light doping near the channel while maintaining manufacturing simplicity through a systematic multi-zone structure, avoiding excessive complexity.
Solution Approach 2:
The doping structure employs asymmetric doping concentrations positioned symmetrically: heavily doped regions are located at the outer edges of source and drain, while lightly doped regions are positioned adjacent to the channel. This asymmetric doping pattern within a symmetric layout reduces leakage current while maintaining manufacturing feasibility.
3Manufacturing precision
If multiple ion implantation processes are conducted to form different doped regions, then doping precision is improved and hot carrier effect is suppressed, but manufacturing process complexity increases
Solution Approach 1:
The ion implantation process is segmented into multiple steps, each targeting specific regions with specific doping concentrations. First ion implantation forms heavily doped regions, second ion implantation forms lightly doped regions. This segmented approach achieves precise doping distribution to suppress hot carrier effect while organizing the complex process into manageable stages.
Solution Approach 2:
The heavily doped regions are formed first through preliminary ion implantation, establishing the basic source and drain structure. Subsequently, lightly doped regions are formed through additional ion implantation to refine the doping profile and suppress hot carrier effect. This preliminary action sequence manages process complexity by building the structure step-by-step.
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 proposed solution stabilizes the performance of TFTs by effectively suppressing the hot carrier effect and reducing leakage currents, enhancing the reliability and stability of LTPS-TFTs.
Implementation Method 1
doping ions for passivation that form stable covalent bonds with silicon atoms are included in the passivated doped regions
Implementation Method 2
a first ion implantation process is conducted to form heavily doped regions; a second ion implantation process is conducted, so as to form lightly doped regions
Implementation Method 3
the diffusion rate of ions in other two regions can be restrained
Data Source
AI summary
A polysilicon thin film transistor, a manufacturing method thereof, an array substrate involve display technology field, and can repair the boundary defect and the defect state in polysilicon, suppress the hot carrier effect and make the characteristics of TFTs more stable. The polysilicon thin film transistor includes a gate electrode, a source electrode, a drain electrode and an active layer, the active layer comprises at least a channel area, first doped regions, second doped regions and heavily doped regions, and the first doped regions are disposed on two sides of the channel area, the second doped regions are disposed on sides of the first doped regions away from the channel area; the heavily doped regions are disposed on sides of the second doped regions opposed to the first doped regions; and dosage of ions in the heavily doped regions lies between that in the first doped regions and that in the second doped regions.