OLED Driving Transistor Reverse Bias Threshold Shift Compensation
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Solution Overview
Problem
The existing display apparatuses using organic transistors for active matrix driving suffer from threshold voltage shifts, leading to variations in OLED luminance and inoperative TFTs, which cannot be effectively compensated by existing driving circuits, resulting in increased power consumption and susceptibility to luminance variations.
Innovation Solution
The display apparatus employs a driving method that includes selection and driving transistors with capacitors, where a reverse bias is applied to the transistors during non-emission periods to correct threshold voltage shifts, thereby maintaining consistent OLED luminance and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If organic TFTs are used as active elements for driving OLEDs, then the display can be formed on flexible substrates at low cost, but threshold voltage shifts occur causing luminance variations and inoperative transistors
Solution Approach 1:
The patent applies a reverse bias voltage to the gate of the organic TFT before normal operation begins. This preliminary action prevents threshold voltage shifts from occurring during subsequent driving, thereby maintaining transistor reliability while preserving the manufacturing advantages of organic TFTs on flexible substrates.
Solution Approach 2:
The patent changes the electrical parameter (gate voltage) from a constant forward bias to a dynamically adjusted voltage that includes reverse bias periods. By varying the gate voltage parameter, the threshold voltage shift is suppressed, maintaining transistor stability without compromising the low-cost flexible manufacturing benefits.
2Reliability
If existing driving circuits are used to compensate for threshold voltage shifts, then some luminance control is achieved, but power consumption increases and luminance variations persist
Solution Approach 1:
The patent converts the harmful threshold voltage shift phenomenon into a beneficial effect by applying reverse bias. The reverse bias intentionally induces a controlled voltage shift that counteracts the unwanted threshold shift during operation, thereby maintaining luminance consistency without increasing power consumption.
Solution Approach 2:
The patent implements periodic application of reverse bias voltage to the gate during non-emission periods. This periodic action maintains transistor characteristics without continuous power consumption, achieving luminance consistency while avoiding the increased power usage associated with existing compensation circuits.
3Productivity
If forward bias is continuously applied to transistors during operation, then normal driving function is maintained, but threshold voltage shifts accumulate causing inoperative transistors
Solution Approach 1:
The patent implements periodic switching between forward bias (during emission) and reverse bias (during non-emission periods). This periodic action maintains the driving function when needed while preventing threshold voltage shift accumulation during reverse bias periods, thereby ensuring continuous transistor operability.
Solution Approach 2:
The patent applies reverse bias as a preliminary anti-action to counteract the harmful effects of continuous forward bias. By introducing this opposing action during non-emission periods, the threshold voltage shift is prevented before it can cause transistor failure, maintaining both driving function and reliability.
Data Source
AI summary
Disclosed is a display apparatus which can improve the characteristics of TFTs used to select and drive self-emissive elements such as OLEDs. The display apparatus has row electrodes, column electrodes, and a driving unit. The self-emissive elements are formed in regions corresponding to intersections of the row electrodes with the column electrodes. Element driving circuits are formed for driving the self-emissive elements. Each of the element driving circuits includes a selection transistor, a capacitor, and a driving transistor. The driving unit applies a reverse bias to a control terminal of the driving transistor in a non-emission period in which the self-emissive element is not supplied with a driving current.