Driving Transistor Gate Electrode Covering for Bootstrap Gain
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Solution Overview
Problem
The bootstrap gain decreases when driving transistors are formed over semiconductors or insulators, leading to deteriorated image quality in display devices due to parasitic capacitors, which affects the operation of pixel circuits in flat panel display devices.
Innovation Solution
A display device configuration where the driving transistor's gate electrode and source/drain electrode are stacked, with the source/drain electrode covering the peripheral portion of the gate electrode, reducing parasitic capacitors between the gate and other metal layers and increasing the bootstrap gain by altering the capacity values attached to the gate electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the driving transistor is formed over semiconductor or insulator, then the device can be manufactured with standard processes, but the bootstrap gain decreases due to parasitic capacitors
Solution Approach 1:
The invention extracts the parasitic capacitor between the gate electrode and other metal layers by covering the peripheral portion of the gate electrode with the source/drain electrode. This removes the harmful parasitic capacitance while maintaining the standard manufacturing process compatibility.
Solution Approach 2:
The invention changes the spatial arrangement by stacking the gate electrode and source/drain electrode in the vertical dimension, with the source/drain electrode covering the peripheral portion of the gate electrode. This three-dimensional configuration reduces parasitic capacitance while maintaining planar manufacturing compatibility.
2Device complexity
If the gate electrode peripheral portion is exposed, then the structure is simpler, but parasitic capacitors are generated between the gate and other metal layers
Solution Approach 1:
The invention converts the potentially harmful exposure of the gate electrode peripheral portion into a benefit by having the source/drain electrode cover it. This covering structure eliminates the parasitic capacitor harm while the source/drain electrode serves its primary function of current conduction.
3Reliability
If the source/drain electrode covers the peripheral portion of the gate electrode, then parasitic capacitors are reduced and bootstrap gain increases, but the manufacturing process becomes more complex
Solution Approach 1:
The invention merges the function of the source/drain electrode to not only conduct current but also to cover and protect the peripheral portion of the gate electrode. This combined function reduces parasitic capacitance without adding separate structural elements, thereby limiting the increase in manufacturing complexity.
Data Source
AI summary
There is provided a display device including pixel circuits which are arranged and each of which includes a driving transistor to drive an electro-optical element and a capacitor connected between a gate electrode and one source/drain electrode of the driving transistor. The driving transistor is configured by stacking the gate electrode and the source/drain electrode and a peripheral portion of the gate electrode is covered by the source/drain electrode.