Oxide TFT with Segmented Channel for Vth Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing oxide TFTs face challenges in suppressing threshold voltage (Vth) depletion and reducing parasitic capacitances (Cgs, Cgd) when a channel protection film is provided, which affects the stability and performance of liquid crystal display devices.
Innovation Solution
A bottom gate thin film transistor design is implemented, featuring a first oxide semiconductor layer as the channel layer, a channel protection layer, and a second oxide semiconductor layer with a higher oxygen-to-indium ratio, where the second oxide semiconductor layer is thicker than the first layer, and both include indium and oxygen, to enhance stability and reduce parasitic capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a channel protection film is provided on the oxide semiconductor layer, then the stability of the transistor is improved, but the threshold voltage depletes and parasitic capacitances increase
Solution Approach 1:
The oxide semiconductor layer is divided into two distinct layers: a first oxide semiconductor layer serving as the channel layer, and a second oxide semiconductor layer with higher oxygen content formed on top of it. This segmentation allows the channel layer to maintain stability while the upper layer suppresses threshold voltage depletion and reduces parasitic capacitances, resolving the contradiction between stability and harmful factors.
Solution Approach 2:
Different regions of the oxide semiconductor structure are given different oxygen concentrations tailored to their specific functions. The first layer (channel region) has a specific oxygen content optimized for stability, while the second layer has higher oxygen content specifically to suppress threshold voltage depletion and reduce parasitic capacitances. This local differentiation of material properties resolves the contradiction by addressing different requirements in different locations.
2Object-generated harmful factors
If the oxide semiconductor layer is made thicker to reduce parasitic capacitance, then parasitic capacitance is reduced, but the threshold voltage becomes unstable
Solution Approach 1:
The oxide semiconductor structure is segmented into two layers with different thicknesses and oxygen concentrations. The first layer provides the channel function with appropriate thickness for stability, while the second layer is specifically designed with higher oxygen content to reduce parasitic capacitance without compromising threshold voltage stability, thus resolving the contradiction between reducing parasitic capacitance and maintaining stability.
Solution Approach 2:
The invention uses a composite oxide semiconductor structure where two oxide semiconductor layers with different compositions (different oxygen contents) are combined. This composite structure leverages the advantages of both layers: the first layer ensures stability while the second layer with higher oxygen content reduces parasitic capacitance, resolving the contradiction between these two parameters.
3Stability of the object's composition
If a gate shielding structure is applied to prevent Vth shift, then Vth stability is improved, but parasitic capacitances increase
Solution Approach 1:
The invention extracts and eliminates the need for a separate gate shielding structure by incorporating the Vth stabilization function directly into the oxide semiconductor layer composition. By controlling the oxygen content in the oxide semiconductor layers, particularly the higher oxygen content in the second layer, the patent achieves Vth stability without requiring additional shielding structures, thus avoiding the increase in parasitic capacitance that would result from such structures.
Solution Approach 2:
The oxide semiconductor layer structure serves multiple functions simultaneously: it acts as the channel layer, provides threshold voltage stability through controlled oxygen content, and reduces parasitic capacitances. This multi-functionality eliminates the need for separate gate shielding structures, resolving the contradiction between Vth stability and parasitic capacitance by integrating multiple benefits into a single structure.
Data Source
AI summary
A thin film transistor includes a first oxide semiconductor, a source electrode, a drain electrode, a gate insulating film and a gate electrode. A second oxide semiconductor layer is between the first oxide semiconductor layer and the source electrode. A third oxide semiconductor layer is between the first oxide semiconductor layer and the drain electrode. The content ratio of oxygen/Indium in each of the second semiconductor layer and the third oxide semiconductor layer is equal to or larger than that of the first semiconductor layer. A thickness of each of the second semiconductor layer and the third oxide semiconductor layer is bigger than that of the first semiconductor layer.