Cheng-Tang Pan

New NaSrPO4:Sm3+ phosphor as orange-red emitting material

Sm3+-activated NaSrPO4 phosphors could be efficiently excited at 403 nm, and exhibited a bright red emission mainly including four wavelength peaks of 565, 600, 646 and 710 nm. The highest emission intensity was found for NaSr1−xPO4: xSm3+ with a composition of x = 0.007. Concentration quenching was observed as the composition of x exceeds 0.007. The decay time values of NaSr1−xPO4: xSm3+ phosphors range from around 2.55 to 3.49 ms. NaSr1−xPO4: xSm3+ phosphor shows a higher thermally stable luminescence and its thermal quenching temperature T50 was found to be 350°C, which is higher than that of commercial YAG:Ce3+ phosphor and ZnS:(Al, Ag) phosphor. Because NaSr1−xPO4: xSm3+ phosphor features a high colour-rendering index and chemical stability, it is potentially useful as a new scintillation material for white light-emitting diodes.

Study of micro-lens array by reflow process

In this study, different diameters of photoresist AZ4620 are defined using lithography. According to the specification of the back light module (BLM) for a liquid crystal display (LCD), the diameters of micro-lenses are divided into two groups. The first group includes lenses with diameters of 90, 95, 100, 105, 110 and 150 µm at a 100 µm pitch; the reflow temperatures for this first group range from 175–300°C with heating times of 6–24 h. The second group includes lenses with diameters of 10, 20, 30, 40, and 50 µm at pitches of 40, 30, 20, 10, and 25 µm, respectively; the reflow temperatures are the same as for the first group with heating times of 1–12 h. In this study, the parametric effects of reflow time and temperature on micro-opticals are characterized and discussed, and optical properties such as the focal length of micro-lenses are measured and analyzed. Then, each micro-lens is sputtered with a conductive seed layer of silver (Ag) for the subsequent eletroforming process, which is the mold for hot embossing. The mold is further incorporated with hot embossing materials and hot embossing techniques to produce the micro-lens required.

A parametric study on synthesis of Ag nanowires with high aspect ratio

In this study, the effect of the experimental parameters of the polyol process on the aspect ratio of silver nanowires (AgNWs) was investigated. The one-factor-at-a-time method was adopted to analyze the effect of various parameters, such as the amount of reducing agent, seeds and the ratio of PVP/Ag, on the growth of AgNWs. The optimal parameters were determined to obtain a high aspect ratio of AgNWs. Synthesized AgNWs were analyzed by SEM, TEM, and XRD, and the four-point probe method was applied to measure the average aspect ratio, morphology, crystal direction, crystalline structure, and the electrically property of its sheet resistance. From the result of the morphology measurement, a high aspect ratio of 74.85 can be fabricated, where the average diameter and length were about ~55 and 4117xa0nm, respectively. Regarding electrical property, the sheet resistance of AgNWs with a high aspect ratio is about ~16.34xa0kΩ/sq with the film thickness of 142.1xa0nm. However, when the film thickness was increased to 1.123xa0µm, the resistance decreased to 3.012xa0Ω/sq.

Fibers and conductive films using silver nanoparticles and nanowires by near-field electrospinning process

The silver nanowires (AgNWs) and silver nanoparticles (AgNPs) were synthesized. With near-field electrospinning (NFES) process, fibers and thin films with AgNPs and AgNWs were fabricated. In the NFES process, 10 k voltage was applied and the AgNPs and AgNWs fibers can be directly orderly collected without breaking and bending. Then, the characteristics of the fibers were analyzed by four-point probe and EDS. The conductive film was analyzed. When the thickness of films with AgNWs and AgNPs was 1.6 µm, the sheet resistance of films was 0.032Ω/sq which was superior to that of the commercial ITO. The transmissivity of films was analyzed. The transmissivity was inversely proportional to sheet resistance of the films. In the future, the fibers and films can be used as transparent conductive electrodes.

Fabrication of high fill factor optical film using two-layer photoresists

A new process to fabricate gapless triangular micro-lens array (GTMA) optical film is realized in this study. Two-layer photoresists are used to define a triangular column array template. The upper and lower layer photoresists are AZ 4620 and AZ 9260, respectively. The two-layer photoresists form a higher aspect ratio than the individual photoresist does. This process includes a two-layer ultraviolet (UV) lithography, photoresist reflow process, Ni–Co electroplating and the hot embossing technique. After a triangular column array of two layers of photoresist is defined by UV lithography, the reflow technique is applied to melt the triangular column array into the shape of a triangular micro-lens array. With this reflowed triangular micro-lens array, Ni–Co alloy is electroplated and covered uniformly on the triangular micro-lens array to form the GTMA mould. After this electroplating process, a mould of GTMA is obtained, which serves as the primary mould. Next, with the passivation technique applied on this primary moulds surface, a secondary mould is obtained by applying the electroplating process again. This secondary mould serves as a master for the subsequent hot embossing process to replicate the GTMA pattern onto a polymethyl methacrylate (PMMA) sheet. The Ni–Co mould with a hardness over 650 Hardness of Vicker (Hv) is obtained. The stiffness and hardness of the mould play important roles in the GTMA hot embossing process. In addition, this PMMA-based GTMA film used as optical film offers a 100% fill factor and high optical coupling efficiency to improve the luminance. The optical measurement shows that this optical film with GTMA pattern increases 18.39% of luminance for a backlight module (BLM) of a liquid crystal display (LCD).

Effect of O2/Ar Gas Flow Ratios on Properties of Cathodic Vacuum Arc Deposited ZnO Thin Films on Polyethylene Terephthalate Substrate

Cathodic vacuum arc deposition (CVAD) can obtain a good quality thin film with a low growth temperature and a high deposition rate, thus matching the requirement of film deposition on flexible electronics. This paper reported the room-temperature deposition of zinc oxide (ZnO) thin films deposited by CVAD on polyethylene terephthalate (PET) substrate. Microstructure, optical, and electrical measurements of the deposited ZnO thin films were investigated with various O2/Ar gas flow ratios from 6u2009:u20091 to 10u2009:u20091. The films showed hexagonal wurtzite crystal structure. With increasing the O2/Ar gas flow ratios, the c-axis (002) oriented intensity decreased. The crystal sizes were around 16.03u2009nm to 23.42u2009nm. The average transmittance values in the visible range of all deposited ZnO films were higher than 83% and the calculated band gaps from the absorption data were found to be around 3.1 to 3.2u2009eV. The resistivity had a minimum value in the 3.65 × 10?3u2009?·cm under the O2/Ar gas flow ratio of 8u2009:u20091. The luminescence mechanisms of the deposited film were also investigated to understand the defect types of room-temperature grown ZnO films.

Magnetically-actuated bending-mode microactuators with excimer laser ablation

Abstract Bending-mode polyimide-based (PI) electromagnetic microactuators with different geometries were fabricated and tested. Fabrication of the electromagnetic microactuator consists of electroplated 10 μm thick Ni/Fe (80 : 20) permalloy on a PI diaphragm, high aspect ratio electroplating of a copper planar micro-coil, bulk micromachining, low-temperature bonding, and 248 nm excimer laser selective ablation. They were fabricated by a novel concept avoiding the etching selectivity and residual stress problems which occur during wafer etching. The magnetic field generated by the planar micro-coil was used to provide an external magnetic field (H ext) to interact with Ni/Fe on the PI diaphragm, by which a repulsive force can be induced to provide a large deflection angle. The deflection angle of the microactuator with different H ext values was measured. Preliminary results show that 82° can be obtained. In addition, to provide a high strength and low temperature bonding process for the microactuator system, a polymer-based photoresist with patternable characteristics was used as the adhesive bonding material. The bonding results for different photoresists are compared and discussed.