TFT Display Device Gate Leakage Control

Solution Overview

Problem

Active-matrix liquid-crystal display devices using low-temperature poly-silicon TFTs face issues with high leak current and noticeable luminance changes during intermittent driving, leading to flickering and increased power consumption.

Innovation Solution

Incorporating a second thin-film transistor between the first thin-film transistor and the gate power supply, allowing independent control to prevent electric charge from leaking to the gate-electrode/channel capacitor, thereby reducing the driving frequency and power consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by stationary object

If intermittent driving is carried out using low-temperature poly-silicon TFT, then power consumption is reduced, but luminance changes are big and easily recognized as display flickers

Engineering Contradiction:

Improvepower consumptionVSAvoidluminance stability

Core Design Contradiction:

Use of energy by stationary objectVSReliability

Solution Approach 1:

The pixel transistor is divided into two independent transistors: a first thin-film transistor for main current control and a second thin-film transistor for gate capacitance discharge control. This segmentation allows independent optimization of each transistor's function to simultaneously achieve low power consumption and stable luminance during intermittent driving

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The gate-line potential is introduced as an intermediary control mechanism. By controlling the gate-line potential through the second thin-film transistor, the gate capacitance is discharged independently to prevent charge leakage, thereby stabilizing luminance while maintaining low power consumption during intermittent driving

Inventive Principle:

Principle #24Intermediary (Mediator)

2Use of energy by stationary object

If driving frequency is reduced to 1 Hz, then power consumption is reduced, but luminance changes must be kept at a value smaller than a recognition limit

Engineering Contradiction:

Improvepower consumptionVSAvoidluminance change control precision

Core Design Contradiction:

Use of energy by stationary objectVSManufacturing precision

Solution Approach 1:

The gate capacitance is discharged in advance during the off-period through the second thin-film transistor before the next write operation. This preliminary action prevents charge accumulation that would cause luminance changes, enabling safe operation at low driving frequencies like 1 Hz while maintaining luminance stability within acceptable limits

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If the off characteristic of the pixel TFT is poor, then device complexity is reduced, but electric charge leaks out during the data holding period causing luminance changes

Engineering Contradiction:

Improvetransistor structure complexityVSAvoidcharge holding capability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The pixel transistor is divided into two independent transistors: a first thin-film transistor for main current control and a second thin-film transistor for gate capacitance discharge control. This segmentation allows independent optimization of each transistor's function to simultaneously achieve low power consumption and stable luminance during intermittent driving

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The gate-line potential is introduced as an intermediary control mechanism. By controlling the gate-line potential through the second thin-film transistor, the gate capacitance is discharged independently to prevent charge leakage, thereby stabilizing luminance while maintaining low power consumption during intermittent driving

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS9905156B2Display device

Publication Date: 2018.02.27 MAGNOLIA WHITE CORP

AI summary

A high-precision display device is capable of suppressing a leak current and operating at a low power consumption. The display device comprises a source power supply for providing a pixel electric potential to each pixel placed on a substrate through a first thin-film transistor; a gate power supply for controlling conductive and nonconductive states of the first thin-film transistor; and a second thin-film transistor disposed between the first thin-film transistor and the gate power supply, the second thin-film transistor being controllable independently of the first thin-film transistor.