Organic Light Emitting Display Pixel Circuit Using Mixed NMOS PMOS TFTs

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Solution Overview

Problem

Conventional organic light emitting displays face challenges in simplifying the TFT process steps and achieving high resolution pixels, particularly due to the need for additional mask processes in NMOS type TFTs and limited power consumption reduction in low refresh modes.

Innovation Solution

Implementing TFTs as a combination of oxide TFTs and LTPS TFTs, including some as NMOS type and others as PMOS type, and using a second capacitor to minimize luminance issues and power consumption by electrically separating data and initialization voltage supply paths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If NMOS type TFTs are used in conventional organic light emitting displays, then response characteristics are improved, but additional mask processes are required increasing manufacturing complexity

Engineering Contradiction:

Improveresponse characteristicsVSAvoidmanufacturing process complexity

Core Design Contradiction:

SpeedVSEase of manufacture

Solution Approach 1:

The pixel circuit is divided into two types of TFTs: oxide TFTs for switching functions and LTPS TFTs for driving functions. This segmentation allows each TFT type to be optimized for its specific function, with LTPS TFTs providing good response characteristics without requiring additional mask processes

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the pixel circuit use different TFT types based on functional requirements. Switching TFTs (ST1-ST3) use oxide TFTs for low leakage, while the driving TFT (DT) uses LTPS TFT for high response characteristics, achieving local optimization of circuit performance

Inventive Principle:

Principle #3Local quality

2Reliability

If oxide TFTs are used for switching TFTs to reduce leakage current, then off-current characteristics are improved, but response characteristics deteriorate

Engineering Contradiction:

Improveoff-current characteristicsVSAvoidresponse characteristics

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

3Speed

If LTPS TFTs are used for all TFTs to improve response characteristics, then response characteristics are improved, but power consumption increases

Engineering Contradiction:

Improveresponse characteristicsVSAvoidpower consumption

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

4Use of energy by moving object

If refresh period is lengthened to reduce power consumption, then power consumption is reduced, but video data leakage increases

Engineering Contradiction:

Improvepower consumptionVSAvoidvideo data maintenance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10355062B2Organic light emitting display

Publication Date: 2019.07.16 LG DISPLAY CO LTD

AI summary

An organic light emitting display is disclosed. In the disclosure, only one switching TFT among TFTs constituting a pixel is implemented as an NMOS type TFT, and at least some of a driving TFT and the remaining switching TFTs are implemented as a PMOS type TFT. Therefore, the disclosure simplifies TFT process steps and provides an organic light emitting display suitable for realizing a high resolution pixel implementation.