Double-Gate NMOS Inverter for Stable Scan Driver Turn-Off

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Solution Overview

Problem

In organic light emitting displays, N-type transistors used in scan drivers face challenges with turn-off operation due to threshold voltage shifts, leading to potential erroneous operations.

Innovation Solution

The implementation of an inverter circuit using double gate NMOS transistors, where a lower voltage is applied to the second gate electrode to positively shift the threshold voltage, stabilizing the turn-off operation and improving driving reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If N-type transistors are used in scan drivers, then manufacturing cost is reduced by forming transistors in the panel, but the turn-off operation is not satisfactorily controlled due to threshold voltage shift

Engineering Contradiction:

Improvemanufacturing costVSAvoidturn-off operation control

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies parameter changes by utilizing the threshold voltage shift characteristic of N-type transistors in a beneficial way. Instead of trying to prevent the negative threshold voltage shift, the invention designs the inverter circuit to exploit this shift for achieving satisfactory turn-off operation control, thereby maintaining manufacturing simplicity while improving reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful threshold voltage shift into a beneficial effect. The negative threshold voltage shift that causes poor turn-off control is transformed into a mechanism that enables reliable turn-off operation through the specific inverter circuit design, turning a defect into an advantage

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Adaptability or versatility

If N-type transistors are used, then device integration is improved, but threshold voltage shifts cause erroneous operation

Engineering Contradiction:

Improvedevice integrationVSAvoidoperation accuracy

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the operational parameters of the N-type transistors by designing the inverter circuit to accommodate and utilize the threshold voltage shift characteristics, enabling reliable operation while maintaining high device integration

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention converts the threshold voltage shift from a source of erroneous operation into a controlled parameter that enables reliable turn-off operation, thereby maintaining device integration benefits while eliminating operation accuracy issues

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8937489B2Inverter and scan driver using the same

Publication Date: 2015.01.20 SAMSUNG DISPLAY CO LTD

AI summary

An inverter is capable of improving the reliability of driving. The inverter includes a first transistor and a second transistor. The first transistor is coupled between a first power source and an output terminal of the inverter, and has a first gate electrode coupled to a first input terminal of the inverter and a second gate electrode coupled to a third power source. The second transistor is coupled between the output terminal and a second power source, and has a first gate electrode coupled to a second input terminal of the inverter and a second gate electrode coupled to the third power source.