Oxide Semiconductor Transistor Loff Region Design for Current Control
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Solution Overview
Problem
Oxide semiconductor transistors used in light-emitting display devices have high on-state currents, leading to varying drain currents with slight changes in driving voltage, affecting luminance and requiring adjustment to reduce current without increasing transistor area, which is challenging in high-definition displays with limited pixel space.
Innovation Solution
Incorporating a Loff region in the oxide semiconductor transistor design, where the oxide semiconductor film does not overlap with the gate electrodes in specific areas, reduces the on-state current without increasing the transistor's occupied area, allowing for its use in pixels and driver circuits on the same substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the channel length of the oxide semiconductor transistor is increased to reduce the on-state current, then the on-state current decreases, but the occupied area of the transistor increases
Solution Approach 1:
The gate electrode is divided into two separate gate electrodes (first gate electrode and second gate electrode) positioned at opposite sides of the channel formation region. This segmentation allows independent control of voltage application and enables the creation of an Loff region, reducing the on-state current without requiring a longer channel length, thus maintaining a compact transistor area.
Solution Approach 2:
Instead of reducing on-state current by extending the channel length in one dimension, the invention applies voltage in another dimension by positioning gate electrodes laterally at both sides of the channel. This dimensional change allows for effective current control while preserving the original channel length and transistor area.
2Reliability
If the on-state current of the oxide semiconductor transistor is reduced to stabilize luminance, then the drain current variation decreases, but the aperture ratio of the display device decreases
Solution Approach 1:
The gate electrode is segmented into two separate gate electrodes positioned at opposite sides of the channel formation region. This segmentation enables the creation of an Loff region where the oxide semiconductor film does not overlap with gate electrodes, reducing on-state current and stabilizing drain current without increasing transistor area, thereby maintaining aperture ratio.
3Reliability
If different types of oxide semiconductor transistors (low on-state current and high on-state current) are manufactured separately on different substrates, then each transistor type can be optimized, but the number of manufacturing steps increases
Solution Approach 1:
A single oxide semiconductor transistor structure with two gate electrodes can serve multiple functions: by applying different voltage conditions to the first and second gate electrodes, it can operate as either a low on-state current transistor (for pixel circuits) or a high on-state current transistor (for driver circuits). This multi-functionality eliminates the need for separate manufacturing processes for different transistor types, reducing the number of manufacturing steps while maintaining performance optimization.
Data Source
AI summary
A semiconductor device including a first gate electrode and a second gate electrode formed apart from each other over an insulating surface, an oxide semiconductor film including a region overlapping with the first gate electrode with a gate insulating film interposed therebetween, a region overlapping with the second gate electrode with the gate insulating film interposed therebetween, and a region overlapping with neither the first gate electrode nor the second gate electrode, and an insulating film covering the gate insulating film, the first gate electrode, the second gate electrode, and the oxide semiconductor film, and being in direct contact with the oxide semiconductor film is provided.