Oxide Semiconductor Transistor Power Reduction in Displays
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Solution Overview
Problem
Active matrix display devices face challenges in reducing power consumption while maintaining display quality, as long break periods and low-frequency alternating-current driving signals can lead to increased off-state current and flicker in pixels.
Innovation Solution
Incorporating a highly purified oxide semiconductor layer in transistors with minimal impurities, such as hydrogen and oxygen deficiencies, to reduce off-state current and improve display stability, even during extended break periods and low-frequency driving signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the rewriting frequency of display is decreased to reduce power consumption, then power consumption is reduced, but display quality deteriorates due to increased off-state current effects
Solution Approach 1:
The patent applies parameter changes by modifying the rewriting frequency from the conventional 60 Hz to a lower frequency (e.g., 1 Hz or less), and by introducing a break period where no data signal is input. This parameter change enables significant power consumption reduction while the oxide semiconductor transistor maintains display quality through its extremely low off-state current characteristics.
Solution Approach 2:
The patent employs oxide semiconductor transistors with extremely low off-state current (1×10^-21 A or less) that can maintain data signals for extended periods without refresh. This allows the system to use a 'short-living' low-frequency refresh approach instead of continuous high-frequency refreshing, effectively making the display refresh mechanism more economical in terms of energy consumption.
2Use of energy by stationary object
If a long break period is used to reduce power consumption, then power consumption is reduced, but the data signal varies due to off-state current, causing display quality deterioration
Solution Approach 1:
The patent changes the parameter of break period length to be equal to or longer than the scanning period, enabling extended periods without data signal input. The oxide semiconductor transistor's extremely low off-state current ensures data signal stability throughout this extended break period, maintaining display quality while maximizing power savings.
3Use of energy by stationary object
If an alternating-current driving signal with low frequency is supplied in the break period, then power consumption is reduced, but flicker is generated in display due to potential variation
Solution Approach 1:
The patent changes the frequency parameter of the alternating-current driving signal to be equal to or lower than the data signal frequency (e.g., 60 Hz or lower). The oxide semiconductor transistor's ability to maintain stable potential despite off-state current allows this low-frequency AC signal to be used without generating visible flicker, thus reducing power consumption while maintaining display quality.
Data Source
AI summary
An object is to reduce power consumption of a display device and to suppress deterioration of display quality. As a transistor provided for each pixel, a transistor including an oxide semiconductor layer is used. Note that off-state current of the transistor can be decreased when the oxide semiconductor layer is highly purified. Therefore, variation in the value of a data signal due to the off-state current of the transistor can be suppressed. That is, display deterioration (change) which occurs when writing frequency of the data signal to the pixel including the transistor is reduced (when a break period is lengthened) can be suppressed. In addition, flickers in display which generates when the frequency of an alternating-current driving signal supplied to a signal line in the break period is reduced can be suppressed.