Oxide Semiconductor Channel Protection for Display Circuits
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Solution Overview
Problem
In display devices using oxide semiconductors, the electrical characteristics of the oxide semiconductor layer deteriorate over time, leading to increased conductivity and electrical short-circuiting with upper interconnects, which lowers the breakdown voltage at interconnect intersection points, causing functional issues in the circuit.
Innovation Solution
The implementation of a circuit design where the oxide semiconductor layer and channel protective layer are stacked with a gate insulating film, with the channel protective layer interposed between the oxide semiconductor layer and upper interconnects, preventing electrical short-circuiting even as the oxide semiconductor deteriorates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the film thickness of the interlayer insulating film is set large at the interconnect intersection part to prevent interlayer short circuit, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The interlayer insulating film is segmented into multiple functional layers: a first interlayer insulating film (gate insulating film) and a second interlayer insulating film (channel protective film). This segmentation allows each layer to have optimized thickness for its specific function, with the channel protective film providing the necessary insulation at the interconnect intersection part without requiring the entire structure to be unnecessarily thick.
Solution Approach 2:
The channel protective film is selectively positioned at the interconnect intersection part where the upper interconnect crosses over the lower interconnect. This local quality approach ensures that the increased film thickness is applied only where needed for breakdown voltage prevention, rather than uniformly across the entire device, thus maintaining reliability while minimizing overall device complexity.
2Speed
If the oxide semiconductor layer is used as the channel layer, then the carrier mobility is improved, but the reliability deteriorates over time due to oxygen loss
Solution Approach 1:
The channel protective film is formed in advance over the oxide semiconductor layer before the oxide semiconductor undergoes oxygen loss. This preliminary protective layer prevents direct exposure of the oxide semiconductor to environmental factors that cause oxygen loss, thereby maintaining the electrical characteristics stability while preserving the high carrier mobility benefits.
Solution Approach 2:
The channel protective film acts as an intermediary layer between the oxide semiconductor layer and the upper interconnect. This intermediary structure protects the oxide semiconductor from direct contact with potentially harmful environmental factors and prevents electrical short-circuiting, allowing the oxide semiconductor to maintain its high carrier mobility without suffering from reliability deterioration.
Data Source
AI summary
Disclosed herein is a device using an oxide semiconductor, the device including a circuit part configured to include a thin film transistor using the oxide semiconductor as a channel material, wherein the circuit part has a lower interconnect, an upper interconnect, and an interlayer insulating film, the interlayer insulating film includes an oxide semiconductor layer and a channel protective layer, and the channel protective layer is interposed between an outer circumferential surface of a rising part of the oxide semiconductor layer corresponding to thickness of the lower interconnect and the upper interconnect.