Tangyou Sun

Accurate characterization of nanoimprinted resist patterns using Mueller matrix ellipsometry.

In order to control nanoimprint lithography processes to achieve good fidelity, accurate characterization of structural parameters of nanoimprinted resist patterns is highly desirable. Among the possible techniques, optical scatterometry is relatively ideal due to its high throughput, low cost, and minimal sample damage. Compared with conventional optical scatterometry, which is usually based on reflectometry and ellipsometry and obtains at most two ellipsometric angles, Mueller matrix ellipsometry (MME) based scatterometry can provide up to 16 quantities of a 4 × 4 Mueller matrix in each measurement and can thereby acquire much more useful information about the sample. In addition, MME has different measurement accuracy in different measurement configurations. It is expected that much more accurate characterization of nanoimprinted resist patterns can be achieved by choosing appropriate measurement configurations and fully using the rich information hidden in the measured Mueller matrices. Accordingly, nanoimprinted resist patterns were characterized using an in-house developed Mueller matrix ellipsometer in this work. We have experimentally demonstrated that not only more accurate quantification of line width, line height, sidewall angle, and residual layer thickness of nanoimprinted resist patterns can be achieved, but also the residual layer thickness variation over the illumination spot can be directly determined, when performing MME measurements in the optimal configuration and meanwhile incorporating depolarization effects into the optical model. The comparison of MME-extracted imprinted resist profiles has also indicated excellent imprint pattern fidelity.

Porous Light-Emitting Diodes With Patterned Sapphire Substrates Realized by High-Voltage Self-Growth and Soft UV Nanoimprint Processes

Nanostructured GaN-based light-emitting diode (LED), with its high performance on light extraction efficiency, has attracted significant attention for the potential application in solid state lighting. However, patterning structures at nanoscale feature size with large area and low cost is of great importance and hardness. In this paper, a 2 inch anodic aluminum oxide (AAO) template was used as the initial mold to copy the photonic-crystal-like structures (PCLSs) on a blue-light LED by soft UV nanoimprint lithography. An additional solute, aluminum oxalate hydrate, is employed to overcome the burn-through issue in the high-voltage anodization which is critical for the fabrication of the large-pore (250-500 nm) AAO. The photoluminescence and electroluminescence enhancements of the patterned LED device with 150-nm-deep PCLSs are, respectively, 45% and 11.4% compared with the un-patterned LED device. A 3-D finite-difference time-domain simulation confirms that the light extraction efficiency is enhanced when PCLSs are formed. The proposed method is simple, cheap, repeatable in large area and compatible with the high volume production lines.

Resistive switching behavior of photochemical activation solution-processed thin films at low temperatures for flexible memristor applications

This study explores deep ultraviolet photochemically activated solution-processed metal-oxide thin films at room temperature for fabrication of flexible memristor active resistive layers. An annealing treatment was not required during the process. Solution processed undoped and Mn-doped ZnO thin films served as active layers in the resistive random access memory structure, prepared at 145 °C. The carrier transports in high and low electrical fields were dominated by Frenkel–Poole emission and thermionic emission, respectively. The trap energy level, which originated primarily from Vo or the singly charged oxygen vacancy, was calculated at 0.49 eV. A flexible structure consisting of Ag/DUV-ZnO/indium tin oxide/polyethylene terephthalate was fabricated successfully and its mechanical performance was investigated.

Polymer nanopillar array with Au nanoparticle inlays as a flexible and transparent SERS substrate

We report a facile and efficient way to fabricate a highly flexible, transparent and efficient surface-enhanced Raman scattering (SERS) substrate, in which Au nanoparticles (NPs) were embedded into the polymeric nanopillars via a nanoimprint lithography (NIL) method and using an anodic aluminum oxide (AAO) template. The obtained substrate exhibits prominent reproducibility and high sensitivity to Rhodamine 6G (R6G). Moreover, it possesses excellent transparency and flexibility. The SERS intensity acquired from these substrates almost remains constant after 200 bending cycles. Compared with traditional SERS substrates, this substrate represents a novel format with unique advantages, such as being highly flexible, transparent, lightweight, portable and easy to handle. More importantly, it can be scaled up for high-throughput production with low cost.

First-principles study of optical absorption properties of perovskite PbZrxTi1-xO3

The energetic stability, the structural and the electronic properties of perovskite PbZrxTi1-xO3 are systematically investigated by the first-principles. when the x=0.5, the light absorption properties of PZT in non Zirconium-Rich area is the hightest.

Resistive Switching Behaviors In ZnO Thin Films Prepared By Photochemical Activation At Room Temperature

ZnO thin films based resistive switching layer in the Ag/ZnO/ITO structure was fabricated by photochemical activation at low temperature through sol-gel process. The resistive switching characteristics of as fabricated Ag/ZnO/ITO structure are studied.

Uniform and Duty Cycle Tunable Photonic Crystal LEDs Fabricated by Intermediate Mask Layer: Soft UV Nanoimprint Lithography

As an improvement of the conventional nanoimprint lithography, an intermediate mask layer process is invited for photonic crystal pattern transfer on LEDs. Benefit from the smooth effect of the under-layer resist, uniform photonic crystal structure is successfully transferred to the p-GaN surface. The intermediate SiO2 layer has a high etching selectivity to the under-layer resist, which can be used to fabricate nanostructures with tunable duty cycle via one single initial mold. The photonic crystal LED fabricated by the process of intermediate mask layer nanoimprint lithography shows a 3.31 fold PL enhancement to that of the un-patterned LED.

Photonic crystal structures on nonflat surfaces fabricated by dry lift-off soft UV nanoimprint lithography

The surface nonflatness induced from the material itself or the production atmosphere can lead to serious non-uniformity consequences in nanoimprint lithography (NIL) which is used for providing a low cost and high throughput nano-fabrication process. In this paper, soft UV NIL (SUNIL) processes are used for photonic crystal (PC) pattern transfer of a GaN-based light-emitting diode (LED) with patterned sapphire substrate (PSS). The results reveal a significant incompatibility between the conventional SUNIL and the nonflat p-GaN surface. Ellipse-shaped rather than circle-shaped PC structure is obtained on the p-GaN surface due the deformation of the soft mold in nonflat NIL. A dry lift-off (DLO) SUNIL is proposed to overcome the non-uniformity issue in nonflat NIL as well as the collapse problem of the free-standing pillar-shaped resist in wet lift-off. The photoluminescence enhancements of the LED fabricated by the DLO SUNIL method compared to those with conventional SUNIL and unpatterned LED are 1.41 fold and 3.48 fold, respectively. Further study shows that the DLO SUNIL is applicable in the fabrication of the PC structure with tunable duty cycle via one single initial PC mold.