Oxide Semiconductor Transistor Stack for Stable Display Driver Circuits
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Solution Overview
Problem
Existing display devices face challenges in achieving favorable electric characteristics and high reliability, particularly in the long-term stability of transistors used in driver circuit portions, due to shifts in threshold voltage and increased off current.
Innovation Solution
A display device is developed with a transistor featuring an oxide semiconductor layer that undergoes dehydration or dehydrogenation heat treatment, followed by a protective insulating layer formed using inorganic materials, which reduces carrier concentration and enhances reliability by stabilizing electric characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment for dehydration or dehydrogenation is performed on the oxide semiconductor layer, then reliability is improved, but threshold voltage shifts occur
Solution Approach 1:
The patent applies preliminary action by performing heat treatment for dehydration or dehydrogenation on the oxide semiconductor layer before the transistor is fully assembled and before long-term operation begins. This advance treatment removes water and hydrogen that would otherwise cause threshold voltage shifts during operation, thereby improving reliability while preventing composition instability. The protective insulating layer is also formed in advance to prevent future contamination.
Solution Approach 2:
The patent introduces a protective insulating layer as an intermediary between the oxide semiconductor layer and the external environment. This intermediate layer acts as a barrier that prevents water and hydrogen from entering the oxide semiconductor layer during subsequent processing and operation, thereby preventing threshold voltage shifts while allowing the heat treatment to improve reliability. The insulating layer mediates between the need for heat treatment and the need for composition stability.
2Reliability
If a protective insulating layer is formed using inorganic material containing oxygen, then carrier concentration is reduced and reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by carefully controlling the oxygen content and composition of the protective insulating layer. By adjusting the material parameters (using inorganic materials containing oxygen such as silicon oxide, silicon nitride oxide, or aluminum oxide) and formation conditions, the patent reduces carrier concentration in the oxide semiconductor layer while maintaining manufacturing feasibility. This resolves the contradiction between improving reliability through reduced carrier concentration and managing manufacturing complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in a transistor with stable electric characteristics and improved reliability, reducing the likelihood of threshold voltage shifts and increasing on current, thereby enhancing the overall performance and longevity of the display device.
Implementation Method 1
the oxide semiconductor layer is subjected to heat treatment for dehydration or dehydrogenation
Implementation Method 2
the oxide semiconductor layer is subjected to heat treatment for dehydration or dehydrogenation
Implementation Method 3
a protective insulating layer is formed using an insulating inorganic material containing oxygen so as to cover the oxide semiconductor layer
Data Source
AI summary
An object is to provide a display device which operates stably with use of a transistor having stable electric characteristics. In manufacture of a display device using transistors in which an oxide semiconductor layer is used for a channel formation region, a gate electrode is further provided over at least a transistor which is applied to a driver circuit. In manufacture of a transistor in which an oxide semiconductor layer is used for a channel formation region, the oxide semiconductor layer is subjected to heat treatment so as to be dehydrated or dehydrogenated; thus, impurities such as moisture existing in an interface between the oxide semiconductor layer and the gate insulating layer provided below and in contact with the oxide semiconductor layer and an interface between the oxide semiconductor layer and a protective insulating layer provided on and in contact with the oxide semiconductor layer can be reduced.