Oxide Semiconductor TFT with Cladding Unit for High Mobility
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Solution Overview
Problem
Conventional thin film transistors (TFTs) face challenges with low mobility when using amorphous silicon and non-uniform threshold voltage when using polycrystalline silicon, while manufacturing methods like low temperature poly-silicon (LTPS) are expensive and difficult to control, especially for large area substrates.
Innovation Solution
A TFT with a cladding unit on the side surfaces of source/drain electrodes is developed, using an oxide semiconductor layer of GaInZnO (GIZO) doped with Ga and In, which covers the entire outer side surfaces of the electrodes to prevent damage during etching and maintain performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon is used as the active layer, then manufacturing cost is reduced, but mobility becomes low
Solution Approach 1:
The patent changes the material parameter from conventional silicon-based semiconductors to oxide semiconductor (GaInZnO), which enables high mobility comparable to polycrystalline silicon while maintaining compatibility with low-temperature manufacturing processes. This material substitution resolves the contradiction by achieving high mobility without requiring expensive laser annealing or high-temperature processing.
Solution Approach 2:
The patent uses a composite structure combining oxide semiconductor layer with metal source/drain electrodes (Ti/Al/Ti or Ti/Ag/Ti) and introduces a cladding unit made of the same oxide semiconductor material. This composite approach protects the electrodes from oxidation while maintaining the high mobility benefits of the oxide semiconductor channel.
2Speed
If polycrystalline silicon is used as the active layer, then mobility is improved, but threshold voltage becomes non-uniform
Solution Approach 1:
The patent transitions from polycrystalline silicon to amorphous oxide semiconductor, eliminating grain boundaries that cause threshold voltage non-uniformity. The oxide semiconductor layer is deposited as a uniform amorphous structure that provides consistent electrical characteristics across the device area, while still achieving high mobility through material composition optimization (Ga and In doping in ZnO).
3Speed
If low temperature poly-silicon (LTPS) method is used, then mobility is improved, but manufacturing complexity and cost increase due to laser heat treatment
Solution Approach 1:
The patent changes the material system from silicon-based LTPS to oxide semiconductor, which inherently achieves high mobility without requiring laser annealing or other complex post-deposition treatments. The oxide semiconductor layer can be deposited directly with desired properties through sputtering or other PVD/CVD methods, simplifying the manufacturing process while maintaining high mobility.
Solution Approach 2:
The patent replaces expensive and complex laser heat treatment processes with simpler, more cost-effective deposition and low-temperature annealing processes. The oxide semiconductor material system allows achieving high performance through less expensive manufacturing equipment and processes that are more suitable for large-area production.
4Device complexity
If conventional TFT structure is used, then source/drain electrodes are exposed, but electrodes become damaged during processing
Solution Approach 1:
The patent introduces a cladding unit made of oxide semiconductor material that acts as a protective intermediary layer between the metal source/drain electrodes and the processing environment. This cladding unit prevents oxidation and damage to the electrodes during subsequent processing steps, while being electrically isolated from the active channel region to avoid affecting device performance.
Solution Approach 2:
The patent extends the protective oxide semiconductor layer from the conventional two-dimensional planar configuration to a three-dimensional structure that wraps around the side surfaces of the source/drain electrodes. This vertical/dimensional extension of the cladding unit provides comprehensive protection of the electrode surfaces that would otherwise be exposed to damage.
Data Source
AI summary
A TFT includes a substrate, a source electrode and a drain electrode on the substrate, the source and drain electrodes separated from each other, an active layer on the substrate between the source electrode and the drain electrode, a cladding unit on side surfaces of the source electrode and the drain electrode, a gate insulating layer on the substrate, the gate insulating layer overlapping the active layer and the cladding unit, and a gate electrode on the gate insulating layer, the gate electrode overlapping the active layer.