Holding Capacitor Electrode Oxidation Resistance
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Solution Overview
Problem
In high-definition liquid crystal devices, the reduced area for holding capacitors leads to insufficient electric capacitance, causing flickering and instability in pixel electrode potential control due to oxidation and light leakage issues during high-temperature treatments, which affect the light shielding property and physical strength of metal electrodes.
Innovation Solution
The electro-optical device incorporates a holding capacitor with a first capacitance electrode containing tungsten silicide, a second electrode layer with a metal more stabilized through silicidation, and a third electrode layer of silicon, stacked together, along with a capacitance insulation film, to maintain thermal stability and prevent oxidation, ensuring desired electric capacitance and light shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal electrode (tungsten, molybdenum, tantalum, chromium, titanium, or niobium) is used in the holding capacitor, then the electrode can be formed with good conductivity, but the electrode may be oxidized during high temperature treatment, reducing light shielding property
Solution Approach 1:
A silicon-containing layer is introduced as an intermediary between the metal electrode and the external environment. This silicon layer reacts with oxygen during high temperature treatment to form a protective silicon oxide layer, preventing oxygen from reaching and oxidizing the metal electrode. The silicon acts as a sacrificial protective layer that shields the metal from oxidation.
Solution Approach 2:
The electrode structure is transformed from a single metal material into a composite structure consisting of multiple layers: the metal electrode layer combined with a silicon-containing layer. This composite structure provides both the electrical conductivity of the metal and the oxidation resistance of the silicon oxide formation, resolving the contradiction between conductivity and oxidation resistance.
2Reliability
If silicide of metal is used in the electrode, then conductivity can be improved, but silicon is liberated during high temperature treatment causing film quality changes and reduced light shielding property
Solution Approach 1:
Different regions of the electrode structure are assigned different functions: the metal silicide layer provides conductivity in the bulk, while the silicon-containing layer (with higher silicon concentration) is positioned at the surface to prevent oxidation. This local differentiation of material composition and function prevents silicon liberation issues while maintaining conductivity.
Solution Approach 2:
The silicon concentration distribution is optimized by controlling deposition parameters. The silicon-containing layer is designed with sufficient silicon content to form a complete protective oxide layer, preventing silicon liberation from the metal silicide layer during high temperature treatment. Parameter control in the silicon layer prevents the harmful effects of silicon liberation.
3Manufacturing precision
If the area for holding capacitor is reduced to achieve high definition, then pixel density increases, but the electric capacitance of the holding capacitor becomes insufficient, causing flickering
Solution Approach 1:
The capacitance insulation film is designed with a porous structure containing silicon particles. This porous structure increases the effective surface area and volume of the insulation film within the same physical footprint, thereby increasing the electric capacitance of the holding capacitor without increasing the pixel area, resolving the contradiction between high definition and sufficient capacitance.
Solution Approach 2:
The dielectric constant of the capacitance insulation film is enhanced by incorporating silicon particles and optimizing the film structure. This parameter change in the insulation film's electrical properties increases the capacitance value, allowing sufficient holding capacitance to be achieved within the reduced pixel area required for high definition displays.
4Manufacturing precision
If high temperature treatment is performed to form the semiconductor layer, then the semiconductor layer can be properly formed, but the electrode may be oxidized or silicon may be liberated, reducing light shielding property and causing light leakage current
Solution Approach 1:
The silicon-containing layer is formed on the electrode surface before the high temperature treatment step. This preliminary action ensures that when high temperature treatment is subsequently applied to form the semiconductor layer, the silicon layer is already in place to react with oxygen and form a protective oxide barrier, preventing electrode oxidation and silicon liberation during the heating process.
Solution Approach 2:
The silicon-containing layer serves as an intermediary protective barrier between the metal electrode and the high temperature environment. During semiconductor layer formation, this intermediary layer absorbs the thermal stress and prevents direct interaction between oxygen and the metal electrode, maintaining electrode integrity and light shielding properties throughout the high temperature processing.
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 configuration effectively suppresses the reduction of light shielding property and physical strength, even at high temperatures, maintaining stable pixel electrode control and preventing light leakage, thus providing a high-quality display with desired electric capacitance.
Implementation Method 1
silicidation proceeds owing to the heat applied to the second electrode layer, and silicon becomes difficult to liberate
Implementation Method 2
the first capacitance electrode... capable of blocking incident light by the first capacitance electrode
Implementation Method 3
the electrode formed by using a metal, an alloy, or polysilicon described above and being in contact with the interlayer insulation film or the capacitance insulation film may be oxidized
Data Source
AI summary
A liquid crystal device as an electro-optical device includes a base substrate as a substrate, a TFT as a transistor, and a holding capacitor, and the holding capacitor includes a first capacitance electrode disposed on the base substrate side and a second capacitance electrode disposed on the first capacitance electrode via a capacitance insulation film, and the first capacitance electrode includes a first electrode layer containing tungsten silicide, a second electrode layer containing silicide of a metal more stabilized through silicidation than tungsten, and a third electrode layer containing silicon stacked one on another.