Transflective LCD Boundary Leakage Suppression
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Solution Overview
Problem
Transflective LCD units face issues with leakage light at the boundary between reflective and transmissive areas, leading to degraded contrast ratio and visibility due to disturbances in LC molecule orientation caused by electric fields.
Innovation Solution
A transflective LCD unit design featuring a reverse-tilt control member near the boundary between reflective and transmissive areas, where the reflective-area common electrode protrudes into the transmissive area, controlling the reverse tilt area and suppressing the slanted electric field to maintain proper LC molecule alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transflective LCD unit uses a lateral-electric-field mode in the transmissive area, then the viewing angle characteristic is improved, but the black color or dark state in the reflective area becomes insufficient
Solution Approach 1:
The LCD unit is divided into two distinct areas with different driving modes: the transmissive area uses lateral-electric-field mode (IPS or FFS) for excellent viewing angle characteristics, while the reflective area uses longitudinal-electric-field mode for satisfactory black color display. This segmentation allows each area to be optimized independently for its specific function.
Solution Approach 2:
Different regions of the LCD unit are assigned different optical and electrical characteristics. The reflective area is equipped with a built-in retardation film having λ/2 and λ/4 film functions, and the LC layer is configured to function as a λ/2 film, creating local optical quality enhancements specifically in the reflective area to achieve proper black color display.
2Ease of operation
If two separate common electrodes are provided for the reflective area and transmissive area, then the voltage application control is improved, but the device complexity increases
Solution Approach 1:
The common electrode is segmented into two separate electrodes: a reflective-area common electrode and a transmissive-area common electrode. This segmentation enables independent voltage control for each area, allowing the reflective area to receive voltage for longitudinal-electric-field driving while the transmissive area remains at zero voltage for lateral-electric-field operation.
Solution Approach 2:
The driving signals applied to the reflective-area common electrode and transmissive-area common electrode have an inversion relationship. When the reflective-area common electrode is at high potential, the transmissive-area common electrode is at low potential, and vice versa. This inverted signaling scheme enables precise control of the electric field distribution across different areas.
3Measurement precision
If the reflective-area common electrode and transmissive-area common electrode are driven by signals with inversion relationship, then the voltage control precision is improved, but the leakage light suppression becomes insufficient
Solution Approach 1:
A boundary electrode is introduced as an intermediary element at the interface between the reflective area and transmissive area. This boundary electrode acts as a mediator to control the electric field distribution at the boundary, preventing the slanted electric field from disturbing the LC molecule orientation and thus suppressing leakage light while maintaining the inverted signaling relationship between the two common electrodes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively suppresses leakage light, enhancing the dark state display and improving contrast ratio by aligning LC molecules correctly, thereby maintaining excellent visibility.
Implementation Method 1
the LC layer in the reflective area is driven by a longitudinal electric field
Implementation Method 2
the LC layer is oriented in a direction normal to the substrate due to the longitudinal electric field
Implementation Method 3
the LC layer in the transmissive area is driven by a lateral electric field
Implementation Method 4
a lateral-electric-field mode such as an IPS (in-plane-switching) mode
Implementation Method 5
the light incident thereto is converted into a circularly-polarized light by the built-in retardation film
Implementation Method 6
passes through the LC layer upon display of a dark state while maintaining the circularly-polarized state thereof, to reach a reflection film provided in the reflective area
Data Source
AI summary
A transflective LCD unit includes a liquid crystal (LC) layer: first and second substrates sandwiching therebetween the LC layer to define an array of pixels each including a reflective area and a transmissive area; an electrode assembly for driving the LC layer such that the LC layer in the reflective area is driven in a longitudinal-electric-field mode and the LC layer in the transmissive area is driven in a lateral-electric-field mode; and a reverse-tilt control member for controlling a reverse tilt area in which a reverse tilt of LC molecules occurs near the boundary between the reflective area and the transmissive area.