TFT Backplane with Mixed Oxide and LTPS Transistors
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Solution Overview
Problem
Conventional TFT backplanes employing a single type of TFTs are limited in reducing power consumption and touch scan capability, as they require continuous signal supply to all pixels, leading to inefficiencies and noise interference, which are exacerbated by the need for high refresh rates in modern displays.
Innovation Solution
A TFT backplane that combines oxide TFTs and LTPS TFTs, allowing for adjustable refresh rates by turning off signals to pixel circuits during low-speed frames and using different TFT types for driving circuits and pixel circuits to optimize power usage and touch recognition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If a conventional TFT backplane employs a single type of TFTs and continuously supplies signals to all pixels, then the display maintains stable operation, but power consumption increases and touch scan capability deteriorates
Solution Approach 1:
The display is divided into multiple zones with different refresh rates. The gate driver sequentially scans gate lines and can selectively refresh only certain zones, allowing parts of the display to operate at lower refresh rates or remain static, thereby reducing overall power consumption while maintaining stability in critical areas
Solution Approach 2:
The refresh rate of different display zones is made dynamic and adjustable based on content requirements. The system can adaptively change refresh rates for different regions, enabling power savings in static or low-change areas while maintaining high refresh rates in areas requiring smooth updates
2Ease of manufacture
If a conventional TFT backplane employs a single type of TFTs, then the manufacturing is simplified, but touch scan capability is limited due to noise from continuous display driving
Solution Approach 1:
The backplane uses two types of TFTs with different characteristics in different functional areas. LTPS TFTs are used in touch scan circuits for low noise and high precision, while a-Si TFTs are used in display pixel circuits for ease of manufacture. This segmentation allows both manufacturing simplicity and high touch recognition accuracy
Solution Approach 2:
Different TFT types are strategically placed in different locations based on functional requirements. The touch scan region uses LTPS TFTs for superior electrical characteristics and low noise, while the display region uses a-Si TFTs for manufacturing efficiency, achieving local optimization of both manufacturing ease and measurement precision
3Stability of the object's composition
If oxide TFTs are used to implement the driving circuit on a TFT backplane, then voltage holding ratio is improved, but the sensing of Vth takes significantly longer and the size of non-display area increases
Solution Approach 1:
Oxide TFTs are used specifically in pixel circuits where excellent voltage holding ratio is critical for maintaining display state during low refresh periods. LTPS TFTs are used in driving circuits where fast switching and low parasitic capacitance are needed for rapid Vth sensing and signal processing, thus achieving both stable voltage holding and fast operation
4Use of energy by stationary object
If the refresh rate is reduced for power savings, then power consumption decreases, but the display may not maintain stable driving voltage during periods when data is not processed
Solution Approach 1:
Before entering low refresh mode, the pixel circuit performs preliminary actions to prepare for extended periods without data updates. The circuit pre-charges capacitors and adjusts transistor states to maintain stable driving voltage throughout the low refresh period, ensuring voltage stability is established in advance rather than deteriorating over time
Solution Approach 2:
The pixel circuit is designed to self-maintain its driving voltage during low refresh periods through internal capacitor charging and transistor configuration. The circuit automatically compensates for voltage decay without requiring external intervention, maintaining stable operation throughout the extended frame period
Data Source
AI summary
There is provided a TFT backplane having at least one TFT with oxide active layer and at least one TFT with poly-silicon active layer. In the embodiments of the present disclosure, at least one of the TFTs implementing the circuit of pixels in the active area is an oxide TFT (i.e., TFT with oxide semiconductor) while at least one of the TFTs implementing the driving circuit next to the active area is a LTPS TFT (i.e., TFT with poly-Si semiconductor).