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Title: Investigation of the bend transition in Pi-cell devices
Author: Lee, Chang-Hun
ISNI:       0000 0004 2724 5542
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2011
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The Pi-cell is known to have the fastest response time amongst commercialised nematic LCD applications due to the bend configuration. The Bend configuration can be obtained when a high voltage is applied to a Pi-cell initially treated to have a splay configuration, but transition is complex because the splay and the bend states are topologically not identical. Although two possible mechanisms (anchoring breaking and order reconstruction) can explain the bend transition, it is still difficult to be certain of the mechanism in some cases. In this thesis, therefore, the bend transition mechanism in the Pi-cell is investigated. Whichever mechanism is present, the bend transition speed is expected to increase when a high voltage is applied to the cell. However, in some cases, the application of a higher voltage reduces the bend transition speed. These phenomena are discussed based on various experimental results, and the reasons are also discussed. Four different regimes are suggested depending on the bend transition speed change. From these results, it is possible to understand the best way to obtain the bend state quickly in a TFT-LCD in the Pi-cell mode. During the experiments, unexpected light leakage was observed in the extinction position. It was proved that the light leakage came from the residual twist angle caused by the manufacturing process. In addition, two new methods were suggested for measuring the residual twist angle from the light leakage. One of the methods, the analytic method, was extended to the TN-cell. Allowing for the residual twist angle in the Pi-cell, the reason for lower CR compared to other LCD modes is discussed, and methods are suggested in this thesis to improve the CR of Pi-cell devices.
Supervisor: Elston, Steve ; Raynes, Peter Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Optoelectronics ; Pi-cell ; bend transition speed ; anchoring breaking ; order reconstruction