Oxide Semiconductor Back Gate Threshold Voltage Control
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Solution Overview
Problem
Transistors using oxide semiconductors for semiconductor layers face issues with impurity entry, such as hydrogen or moisture, which generate carriers and alter the threshold voltage, affecting their electrical characteristics.
Innovation Solution
Incorporating a back gate structure with specific insulating films and conductive films to control the threshold voltage, where the first conductive film has a higher potential than the second conductive film, and using an oxide semiconductor layer with indium, gallium, and zinc, with a c-axis aligned crystal part, to manage potential application and reduce impurity effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If oxide semiconductors are used for semiconductor layers, then field-effect mobility is improved and manufacturing is simplified, but impurity entry (hydrogen or moisture) generates carriers and changes threshold voltage
Solution Approach 1:
The patent applies preliminary action by forming a protective inorganic insulating film (such as silicon oxide or silicon nitride) over the oxide semiconductor layer before impurity contamination can occur. This protective film is deposited in advance to prevent hydrogen or moisture from entering the oxide semiconductor, thereby maintaining threshold voltage stability while preserving the high field-effect mobility benefits of oxide semiconductors.
Solution Approach 2:
The patent introduces an intermediary protective inorganic insulating film between the oxide semiconductor layer and the external environment (sources of impurities like hydrogen and moisture). This intermediary layer acts as a barrier that prevents impurity entry while allowing the oxide semiconductor to maintain its electrical characteristics, thus resolving the contradiction between high mobility and threshold voltage stability.
2Device complexity
If driver circuits are integrated with pixel transistors, then frame width and peripheral IC cost are reduced, but transistors require better electrical characteristics than pixel transistors alone
Solution Approach 1:
The patent applies local quality by providing selective protection to transistors in the driver circuit region through the inorganic insulating film, ensuring that these specific transistors (which require better electrical characteristics) are protected from impurity contamination. This allows integration of driver circuits with pixel transistors while maintaining the required electrical characteristics for driver circuit operation.
Data Source
AI summary
A semiconductor device includes: a transistor including a gate electrode, a gate insulating film over the gate electrode, a semiconductor layer over the gate insulating film, and a source electrode and a drain electrode over the semiconductor layer; a first insulating film comprising an inorganic material over the transistor; a second insulating film comprising an organic material over the first insulating film; a first conductive film over the second insulating film and in a region overlapping with the semiconductor layer; a third insulating film comprising an inorganic material over the first conductive film; and a second conductive film over the third insulating film and in a region overlapping with the first conductive film. The absolute value of a first potential applied to the first conductive film is greater than the absolute value of a second potential applied to the second conductive film.