Hsin-Han Tsai

Improvement in uniformity of emission by ZrO2 nano-particles for white LEDs

The high luminous efficiency and superior uniformity of angular-dependent correlated color temperature (CCT) white light-emitting diodes have been investigated by ZrO₂ nano-particles in a remote phosphor structure. By adding ZrO₂ nano-particles with silicone onto the surface of the phosphor layer, the capability of light scattering could be enhanced. In particular, the intensity of blue light at large angles was increased and the CCT deviations could be reduced. Besides, the luminous flux was improved due to the ZrO₂ nano-particles with silicone providing a suitable refractive index between air and phosphor layers. This novel structure reduces angular-dependent CCT deviations from 1000 to 420 K in the range of -70° to 70°. Moreover, the enhancement of lumen flux was increased by 2.25% at a driving current 120 mA, compared to a conventional remote phosphor structure without ZrO₂ nano-particles. Consequently, the ZrO₂ nano-particles in a remote phosphor structure could not only improve the uniformity of lighting but also increase the light output.

Enhanced Luminous Efficiency of WLEDs Using a Dual-Layer Structure of the Remote Phosphor Package

This study demonstrates how the insertion of a thin silicone layer into a dual-layer remote phosphor structure enhances light extraction in white light-emitting diodes (WLEDs). In the experiment, a dual-layer phosphor structure yielded a higher intensity of blue and yellow components than a conventional structure. Moreover, the lumen flux was 5% higher than a conventional remote phosphor package at the same correlated color temperature (CCT). Using a TFCalc32 simulation, the electric field intensity was calculated for different thicknesses of the dual-layer remote phosphor structures, and the enhanced use of blue rays was verified. Additionally, the dual-layer structure reduces chromaticity deviations as the driving current increases.

An Investigation of the Optical Analysis in White Light-Emitting Diodes With Conformal and Remote Phosphor Structure

An effective emission model of phosphor film is proposed by using bidirectional scattering distribution function system (BSDF), and the model is verified by white light-emitting diodes (LEDs) with conformal and remote phosphor structure. The emission model is built to clarify the optical characteristics by analyzing the angular-dependent distribution of emission and excitation behaviors in phosphor film. The white LEDs with conformal and remote phosphor structure are also fabricated for experimental comparison. The uniformity of angular correlated color temperature (CCT) in white LEDs can be determined by the angular distribution of blue and yellow light, which is in turns decided by the refractive index variation between chip a©nd phosphor layers. Finally, the experimental results are found to have good agreement with the simulation results performing by the Monte Carlo method.

Operations of poly-Si nanowire thin-film transistors with a multiple-gated configuration

In this study, a novel multiple-gated (MG) thin-film transistor (TFT) with poly-Si nanowire (NW) channels is fabricated using a simple process flow. In the proposed new transistors, poly-Si NWs were formed in a self-aligned manner and were precisely positioned with respect to the source/drain, and the side-gate. Moreover, the NW channels are surrounded by three gates, i.e., top-gate, side-gate and bottom-gate, resulting in much stronger gate controllability over the NW channels, and greatly enhanced device performance over the conventional single-gated TFTs. Furthermore, the independently applied top-gate and/or bottom-gate biases could be utilized to adjust the threshold voltage of NW channels in a reliable manner, making the scheme suitable for practical applications.

Improving the Angular Color Uniformity of Hybrid Phosphor Structures in White Light-Emitting Diodes

This letter examines a hybrid phosphor structure for white light-emitting diodes. The hybrid phosphor structure produces more efficient luminosity and more uniform angular correlated color temperature (CCT) than the conventional dispensing method. The experimental results show that the CCT deviation improved from 453 to 280 K between -70° and 70 °. This was likely caused by the large blue light divergent angle. The lumen output produced was higher than that produced by dispense and conformal phosphor structures. Therefore, the results show that the hybrid phosphor structure can be used in solid-state lighting.

Enhancement of angular CCT by hybrid phosphor structure in white light-emitting diodes

The hybrid phosphor structure for white light-emitting diodes application was reported. It was demonstrated that the improvement of the luminous efficiency as well as the good uniform angular correlated color temperature (CCT) in hybrid phosphor structure compared with the conventional dispense method. The experimental results showed the CCT deviation was improved from 453K to 280K in the range of -70 to 70 degrees, which could be attributed to the large divergent angle of blue light. Moreover, the high lumen output was also achieved, as compared with dispense and conformai phosphor structures. Therefore, the experimental results indicated that the hybrid phosphor structure was feasible to use in the solid state lighting.

High-quality quantum-dot-based full-color display technology by pulsed spray method

We fabricated the colloidal quantum-dot light-emitting diodes (QDLEDs) with the HfO2/SiO2-distributed Bragg reflector (DBR) structure using a pulsed spray coating method. Moreover, pixelated RGB arrays, 2-in. wafer-scale white light emission, and an integrated small footprint white light device were demonstrated. The experimental results showed that the intensity of red, blue, and green (RGB) emissions exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increased the use in the UV optical pumping of RGB QDs. In this experiment, a pulsed spray coating method was crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film was used as the interface layer between each RGB color to avoid crosscontamination and self-assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remained constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures was observed in the integrated device. The resulting color gamut of the proposed QDLEDs covered an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high-quality display technology.

Improvement of angular-dependent CCT uniformity by ZrO 2 nano-particles in remote phosphor white LEDs

The superior uniformity of angular-dependent CCT white LEDs have been investigated by ZrO2-type remote phosphor structure. This novel structure reduces angular-dependent CCT deviations from 1000K to 420K in range of -70 to 70 degrees.

A full-color, white light emission of quantum-dot-based display technology using pulsed spray method with distributed Bragg reflector

A colloidal quantum dot light-emitting multi-layer structure with HfO2/SiO2 distributed Bragg reflector is manufactured by pulse spray method. A pure white light with strong enhancement due to better utilization of UV pump was demonstrated.