IGZO Shift Register Node Segmentation for Leak Current Stability

Solution Overview

Problem

Monolithic gate drivers with IGZO-TFTs face operational abnormalities due to leak currents, leading to changes in transistor characteristics from enhanced to depression characteristics, affecting the reliability of liquid crystal display devices, especially when used in configurations with in-cell touch panels.

Innovation Solution

A shift register design with a unit circuit configuration that includes a first and second control node, along with specific transistors and capacitors, is implemented to manage clock signals and reset signals effectively, preventing operational abnormalities by maintaining the potential of control nodes within optimal ranges despite potential leak currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If IGZO-TFTs are used in monolithic gate drivers, then manufacturing integration is improved, but operational reliability deteriorates due to leak currents causing characteristic changes

Engineering Contradiction:

Improveintegration of gate driverVSAvoidoperational stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The control node is divided into two separate nodes: a first control node connected to the gate of the output transistor and a second control node connected to the gates of the set and reset transistors. This segmentation isolates the output control function from the input control functions, preventing leak currents from affecting the output signal stability while maintaining the integrated monolithic structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A capacitor is introduced as an intermediary element connected between the first and second control nodes. This capacitor acts as a mediator that blocks the transmission of leak currents from the second control node to the first control node, while still allowing controlled signal transfer during normal operation. The capacitor serves as a protective barrier that maintains output signal integrity despite the presence of leak currents in the IGZO-TFTs.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If leak current is present in transistors, then device simplicity is maintained, but output signal stability deteriorates due to discharge capacity changes

Engineering Contradiction:

Improveunit circuit structureVSAvoidoutput signal stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The control node is divided into two separate nodes: a first control node connected to the gate of the output transistor and a second control node connected to the gates of the set and reset transistors. This segmentation isolates the output control function from the input control functions, preventing leak currents from affecting the output signal stability while maintaining the integrated monolithic structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A capacitor is introduced as an intermediary element connected between the first and second control nodes. This capacitor acts as a mediator that blocks the transmission of leak currents from the second control node to the first control node, while still allowing controlled signal transfer during normal operation. The capacitor serves as a protective barrier that maintains output signal integrity despite the presence of leak currents in the IGZO-TFTs.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Area of stationary object

If control nodes are not separated, then circuit area is minimized, but operational abnormality increases due to potential fluctuations

Engineering Contradiction:

Improvegate driver areaVSAvoidoperation stability

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The control node is divided into two separate nodes: a first control node connected to the gate of the output transistor and a second control node connected to the gates of the set and reset transistors. This segmentation isolates the output control function from the input control functions, preventing leak currents from affecting the output signal stability while maintaining the integrated monolithic structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first and second control nodes are connected through a capacitor, merging their functions in a controlled manner. This allows the circuit to benefit from the separation of control functions while maintaining a compact structure through the shared capacitive connection, achieving a balance between area minimization and operational stability.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS11955097B2Shift register, scanning signal line driving circuit including same, and display device including same

Publication Date: 2024.04.09 SHARP DISPLAY TECHNOLOGY CORP

AI summary

A shift register includes stages each constituted by a unit circuit provided with a thin-film transistor (separation transistor) that separates a control node into an output-side first control node and an input-side second control node and a capacitor whose first end is connected to the second control node. The thin-film transistor (separation transistor) has a control terminal that is supplied with a high-level DC power supply voltage. Typically, the channel width of a thin-film transistor (first output control transistor) that controls output from a unit circuit is ten or more times greater than the channel width of the thin-film transistor (separation transistor).