Light-Emitting Device Pixel Circuit Current Extraction
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Solution Overview
Problem
In active matrix light-emitting devices, variation in threshold voltages of driving transistors affects the luminance of light-emitting elements, making it difficult to accurately determine electrical characteristics and correct the current supplied to pixels, leading to uneven luminance across pixels.
Innovation Solution
A light-emitting device with a pixel configuration that includes transistors with a semiconductor film structure having a higher hydrogen concentration in specific regions, allowing for accurate control of current supply and correction of image signals to reduce luminance variation, utilizing oxide semiconductors like indium, zinc, and magnesium for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current extraction is performed from pixels to determine electrical characteristics of driving transistors, then threshold voltage and mobility can be determined, but off-state current flowing through power supply lines makes it difficult to determine electrical characteristics with accuracy
Solution Approach 1:
The patent extracts the current measurement function from the pixel circuit itself by using a dedicated current extraction circuit. This separates the measurement function from the display function, allowing accurate current measurement without the interference of off-state currents in the power supply lines. The extraction circuit is specifically designed to measure only the relevant current components.
Solution Approach 2:
The patent introduces an intermediary current extraction circuit that acts as a mediator between the pixel circuit and the measurement system. This intermediary circuit filters out the off-state current interference from power supply lines and extracts only the signal current needed for electrical characteristic determination, thereby improving measurement accuracy.
2Reliability
If image signal correction is performed using extracted current, then electrical characteristics can be compensated, but off-state current interference prevents accurate current value determination
Solution Approach 1:
The patent implements a feedback mechanism where the extracted current values are used to correct image signals. The current extraction circuit provides accurate feedback information about the driving transistor characteristics, which is then used to adjust subsequent image signals. This feedback loop enables reliable luminance uniformity across the display.
Solution Approach 2:
The patent converts the potentially harmful effect of off-state currents into a benefit by designing the current extraction circuit to specifically measure and compensate for these currents. By measuring the off-state current components and incorporating this information into the correction process, the system actually uses the previously problematic current as useful information for improving luminance uniformity.
3Ease of manufacture
If all transistors in pixels have the same polarity to omit fabrication steps, then manufacturing complexity is reduced, but current control precision for luminance uniformity becomes more difficult
Solution Approach 1:
The patent changes the control parameters from relying solely on transistor polarity to using extracted electrical characteristics (threshold voltage and mobility) as correction parameters. By measuring and compensating for variations in these parameters through the current extraction circuit, the system achieves precise current control even with simplified single-polarity transistor fabrication.
Data Source
AI summary
A light-emitting device capable of suppressing variation in luminance among pixels is provided. A light-emitting device includes a pixel and first and second circuits. The first circuit has a function of generating a signal including a value of current extracted from the pixel. The second circuit has a function of correcting an image signal by the signal. The pixel includes at least a light-emitting element and first and second transistors. The first transistor has a function of controlling supply of the current to the light-emitting element by the image signal. The second transistor has a function of controlling extraction of the current from the pixel. A semiconductor film of each of the first and second transistors includes a first semiconductor region overlapping with a gate, a second semiconductor region in contact with a source or a drain, and a third semiconductor region between the first and second semiconductor regions.