Storage Capacitor Conductive Film Stack for LTPS Display Voltage Dependency
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Solution Overview
Problem
In active matrix display devices using polycrystalline semiconductor thin film transistors (LTPS-TFTs), the high resistance of polycrystalline semiconductor films in storage capacitors leads to voltage dependency and reduced display quality, making it difficult to achieve desired capacitance and high-resolution displays.
Innovation Solution
A conductive film is stacked above the polycrystalline semiconductor film used as the lower electrode of the storage capacitor, allowing for the formation of a storage capacitor that is independent of voltage and improving display quality by achieving desired capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a polycrystalline semiconductor film is used as the lower electrode of a storage capacitor, then the desired capacitance can be achieved, but the high resistance of the polycrystalline semiconductor film causes voltage dependency and reduces display quality
Solution Approach 1:
The patent applies composite materials by forming a stacked structure consisting of a polycrystalline semiconductor film layer and a conductive film layer. The polycrystalline semiconductor film provides the desired capacitance characteristics, while the conductive film layer compensates for the high resistance issue. This composite structure combines the advantages of both materials to achieve both precise capacitance control and low resistance, thereby resolving the contradiction between capacitance precision and display quality.
2Measurement precision
If the thickness of the insulating film is reduced to achieve high-resolution displays, then the resolution is improved, but the capacitance of the storage capacitor becomes insufficient
Solution Approach 1:
The patent applies parameter changes by introducing a conductive film layer with different electrical parameters (higher conductivity) to compensate for the reduced capacitance caused by thinner insulating films. This allows the system to maintain the desired capacitance value even when the insulating film thickness is reduced for high-resolution displays, thus resolving the contradiction between resolution and capacitance value.
3Reliability
If a conductive film is added above the polycrystalline semiconductor film, then the resistance is reduced and voltage dependency is eliminated, but the device structure becomes more complex
Solution Approach 1:
The patent applies universality by designing the conductive film layer to serve multiple functions: it acts as an electrode for the storage capacitor, provides electrical connection, and compensates for the high resistance of the polycrystalline semiconductor film. This multi-functional design reduces the need for additional separate components, thereby minimizing the increase in device complexity while achieving voltage independence.
Data Source
AI summary
In a thin film transistor using a polycrystalline semiconductor film, when a storage capacitor is formed, it is often that a polycrystalline semiconductor film is used also in one electrode of the capacity. In a display device having a storage capacitor and thin film transistor which have a polycrystalline semiconductor film, the storage capacitor exhibits a voltage dependency due to the semiconductor film, and hence a display failure is caused. In the display device of the invention, a metal conductive film 5 is stacked above a semiconductor layer 4d made of a polycrystalline semiconductor film which is used as a lower electrode of a storage capacitor 130.