Linghui Rao

Low voltage blue-phase liquid crystal displays

A protrusion electrode structure is proposed to dramatically lower the operation voltage of the emerging blue-phase liquid crystal displays (BP-LCDs). Simulation results indicate that the generated horizontal electric field is not only strong but also penetrates deeply into the bulk LC layer. As a result, a low voltage (∼10 Vrms) and reasonably high transmittance (∼70%) BP-LCD can be achieved. This approach enables the BP-LCDs to be addressed by amorphous silicon thin-film transistors (TFTs). Widespread application of TFT BP-LCDs is foreseeable.

Extended Kerr effect of polymer-stabilized blue-phase liquid crystals

Electric-field-induced birefringence of a polymer-stabilized blue-phase liquid crystal (BPLC) is investigated. In the low field region, conventional Kerr effect holds. As the electric field increases, the induced birefringence gradually saturates and deviates from Kerr effect. An exponential convergence model, called extended Kerr effect, is proposed to fit the experimental data. Good agreement between experiment and model is obtained. This extended Kerr effect will make a significant impact to the optimization of emerging BPLC display devices.

Modeling of Blue Phase Liquid Crystal Displays

We propose a numerical model based on Kerr effect for simulating the electro-optics of polymer-stabilized blue phase liquid crystal displays (BP-LCDs). Parameters affecting the electro-optics of BP-LCDs in in-plane-switching (IPS) structures, such as wavelength, temperature, electrode dimension, and cell gap are investigated. In addition, viewing angle and color shift of IPS BP-LCDs are studied.

A large Kerr constant polymer-stabilized blue phase liquid crystal

A polymer-stabilized blue phase liquid crystal (BPLC) composite with a large Kerr constant (K∼13.7 nm/V2) is developed and its electro-optic properties characterized. In addition to the reduced operating voltage, this BPLC also exhibits a fast response time (∼1 ms), high contrast ratio (>1000:1), and relatively small hysteresis (<6%). It will undoubtedly accelerate the emergence of BPLC for next-generation display and photonic devices.

Polymer-stabilized optically isotropic liquid crystals for next-generation display and photonics applications

Polymer-stabilized optically isotropic liquid crystals, including blue phases, are emerging as a strong contender for next-generation display technology because they exhibit some revolutionary features such as no need for surface alignment, submillisecond response time, isotropic dark state, and cell gap insensitivity. The basic material properties, including electric field-induced birefringence, dispersion relation of Kerr constant, and temperature dependent Kerr constant, are reviewed. Recent progress on blue phase liquid crystal material development and device structures for lowering the operating voltage are introduced. Promising applications and remaining technical challenges are also discussed.

Wall-shaped electrodes for reducing the operation voltage of polymer-stabilized blue phase liquid crystal displays

Polymer-stabilized blue phase liquid crystal displays based on the Kerr effect are emerging due to their submillisecond response time, wide view and simple fabrication process. However, the conventional in-plane switching device exhibits a relatively high operating voltage because the electric fields are restricted in the vicinity of the electrode surface. To overcome this technical barrier, we propose a partitioned wall-shaped electrode configuration so that the induced birefringence is uniform between electrodes throughout the entire cell gap. Consequently, the operating voltage is reduced by ~ 2.8× with two transistors. The responsible physical mechanisms are explained.

Low-voltage blue phase liquid crystal displays

Polymer-stabilised blue phase liquid crystal displays (PS-BPLCD) based on Kerr effect have become an increasingly important technology for information display applications. In comparison with conventional nematic LC devices, BPLCs exhibit several attractive features, such as sub-millisecond grey-to-grey response time, reasonably wide temperature range, no need for alignment layer, optically isotropic voltage-off state and large cell gap tolerance. However, some technical challenges such as high operation voltage, hysteresis, residual birefringence and relatively low transmittance remain to be overcome before their widespread applications can be realised. Recent progress on BPLC materials and devices has shown great promise. From material aspect, the electro-optical properties of blue phase liquid crystal material system are studied. To realise the electro-optic effect of PS-BPLC, novel device configurations that can dramatically improve the display performances are designed.

Low Voltage Blue-Phase LCDs With Double-Penetrating Fringe Fields

A blue-phase liquid crystal display (BP-LCD) with an in-plane switching (IPS) electrode and etched substrate for generating double-penetrating fringe fields is proposed. An etching depth of 1-2 helps to lower the operating voltage by 30%. This etched IPS BP-LCD also exhibits a wider viewing angle than the conventional one because of the created multi-domain structures in the etched areas. Physical mechanisms responsible for the observed phenomena are discussed.

Critical Field for a Hysteresis-Free BPLC Device

A correlation between the peak electric field and hysteresis of a polymer-stabilized blue-phase liquid crystal (BPLC) is found experimentally. If the peak electric field is below ~ 5 V/μm, hysteresis is negligible. Based on this guideline, we propose elliptical protrusion electrodes to reduce peak electric field which in turn eliminates hysteresis while keeping a high transmittance. Such a hysteresis-free BPLC device is highly desirable for display and photonic applications.

Optimisation of electrode structure to improve the electro-optic characteristics of liquid crystal display based on the Kerr effect

Liquid crystal displays based on the Kerr effect are emerging because of their attractive features, such as symmetric viewing angle, no need for alignment layer, and sub-millisecond response time. However, high operating voltage and low optical efficiency remain as challenges to be overcome. Here, we propose a new cell structure with a protrusion shape of electrode and a driving scheme using two transistors to reduce operating voltage and enhance light efficiency. Confirming simulation results are obtained.