Pixel Circuit Transistor Segmentation for Leakage Current Reduction
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Solution Overview
Problem
Display devices with light emitting elements face issues of leakage current, which reduces luminance and causes flicker, especially in low-frequency driving, due to the electric field between the channel and source/drain regions of thin film transistors.
Innovation Solution
The display device incorporates a pixel circuit with specific transistor configurations and capacitors to control driving currents, including first and second transistors connected in series, and additional transistors for initialization and emission control, to increase gate voltage driving ranges and minimize leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thin film transistor is used to control the light emitting element, then the device can be manufactured with simple processes and low cost, but leakage current flows when the transistor is turned off, reducing luminance and causing flicker
Solution Approach 1:
The first transistor is divided into two series-connected transistors (first-first transistor and first-second transistor), each with its own gate electrode. This segmentation allows independent control of the two transistors, enabling one to compensate for leakage current of the other, thereby reducing total leakage while maintaining the simplicity of thin film transistor manufacturing processes
2Use of energy by moving object
If the thin film transistor is turned off to control pixel state, then power consumption is reduced, but leakage current still flows due to electric field between channel and source/drain regions
Solution Approach 1:
The second transistor acts as an intermediary element connected in parallel with the first-first transistor. It provides an alternative current path that compensates for the leakage current of the first-first transistor, thereby reducing the net leakage current while maintaining low power consumption when the pixel is not actively being updated
3Use of energy by moving object
If low-frequency driving is used to reduce power consumption, then energy efficiency improves, but luminance drops and flicker occurs due to leakage current accumulation
Solution Approach 1:
The pixel circuit uses the interaction between the two series-connected transistors to create a self-compensating mechanism. The leakage current from one transistor is compensated by the other transistor in the series connection, providing continuous feedback that maintains stable luminance even during low-frequency driving periods when power consumption is minimized
Data Source
AI summary
A display device includes: a plurality of pixels on a substrate, each of the plurality of pixels including a light emitting element and a pixel circuit configured to drive the light emitting element, wherein the pixel circuit of each of the plurality of pixels comprises: a first-first transistor configured to control a driving current flowing through the light emitting element based on a voltage of a first node; a first-second transistor connected in series with the first-first transistor and configured to control the driving current based on a voltage of a second node; a second transistor configured to selectively supply a data voltage to a third node which is a first electrode of the first-first transistor; a third-first transistor connected between the first node and a fourth node which is a second electrode of the first-second transistor; and a third-second transistor connected between the second node and the fourth node.