Papers by Keyword: Nanoimprint Lithography

Abstract: A wide range of Light Emitting Diodes (LEDs) applications, from general lighting to transmission sources of the Visual Light Communication (VLC) system, makes the LEDs very important to be developed. This research focuses on comparing LED performance due to the variation in surface size and shape of the LED. The research method is carried out with a simulation and an experimental approach. Before the experiment, the LED was simulated with nanopattern variations to determine the best fabrication parameter. The simulation method is carried out using Ansys Lumerical FDTD 2021. The experiment method used to fabricate nanopatterns on the surface of a semiconductor LED layer uses the nanoimprint lithography method. Stamps for nanoimprint lithography are made using Polydimethylsiloxane (PDMS), and the nanopattern sources are obtained from DVD and Blu-ray grating patterns. The characterization of nanoscale patterns was carried out using a Scanning Electron Microscope (SEM). The light emission intensity is measured using a lux meter at a series of emission angles. The results obtained from this research are that the smaller the width and the periodicity of the grating nanopattern, the light produced will be distributed at a wider angle, but the light intensity will decrease; conversely, for a planar surface without a grating nanopattern, level of focus and intensity of light will be higher. In addition, the thicker the ZnS:Cu layer, the better the intensity of the light produced.

Abstract: This paper introduces research situation and prospect of nanoimprint lithography technology. The process of three common lithography (Such as hot press printing, UV curing stamping and Micro Contact stamping) is discussed. For getting better quality, the method and main factors of nanoimprint lithography pattern are analyzed. Furthermore, some key problems of the nanoimprint lithography process are solved for the purpose of the further understands for this process. A new way of thinking is provided for development new nanoimprint lithography technology in the paper.

Abstract: Although nanoimprint lithography (NIL) can successfully fabricate structures down to 10 nm [1], it is difficult to produce perforated pores with diameters less than 100 nm in freestanding polymer membranes. Since it requires molding using a stamp with extremely high aspect ratio to achieve high mechanical stability for the membrane fully released from a substrate. We utilized silicon microneedle structures as an imprinting mold that overcomes these issues. Also, pressed self-perfection (PSP) process was employed after nanoimprinting to further reduce the pore size. Additionally, the membranes were integrated with microfluidic devices to measure current-voltage curves in order to determine pore size indirectly.

Abstract: Lift-off process is a critical combined process in semiconductor manufacturing field. However, traditional methods of lift-off process can hardly be carried out in Ultraviolet Nanoimprint Lithography due to the poor solubility of ultraviolet imprint resist. In this paper, a modified lift-off process using a multi-layer transfer method has been introduced to solve this problem. More importantly, this method could bring an improved result even if the aspect ratio of hard stamp is small. By applying this method, we succeeded in fabricating pillar photonic crystal stamp using hole pattern mother stamp and using the newly defined stamp to fabricate nanopattern sapphire substrate. Depth of the nanopattern is 250nm and the profile of the pattern is pyramid type which is very suitable for subsequent epitaxy.

Abstract: The nanimprint lithography technology was used on the optical glass substrate of organic light-emitting diodes (OLED). By optimizing nanoimprint process 2-dimensional micro-structures were fabricated on the substrate. The parameters of micro-structures such as period, diameter and length were optimized using Finite-difference time-domain (FDTD) and finally, the optical crystal micro-structure with 500nm period, 300nm diameter and 500nm length was fabricated. The basic structure of the devices fabricated on the micro-structure substrate is Glass/ LTO/photonic / ITO/ MoO3/NPB/Alq/LiF/Al. The light outcoupling efficiency can be increased effectively due to the photonic band gap effect produced by photonic crystal structures on the substrate of OLED. The measuring result showed that both the emission spectrum and the light intensity were increased.

Abstract: Transferable microlens-structures were fabricated on the substrate of OLED by using nanoimprint lithography. As a result, the waveguide effect on each organic layer was reduced, which can facilitate the optical coupling of the substrate and is expected to increase luminous efficiency, and finally, the device with high brightness can be fabricated. Firstly, ultraviolet exposure and wet etching technology were combined to fabricate high-precision nanoimprint template with quartz glass; secondly, the cleaning and anti-adhesion treatment were used and finally transferable microlens-structures were fabricated on the substrate of OLED by using hot nanoimprint lithography. The result shows that the lens micro-structures are characterized by good flatness, high nanoimprinting precision. The parameters of micro-structures such as period, diameter and length were optimized using Finite-difference time-domain (FDTD) and finally, the optical crystal micro-structure with the photonic band gap effect was fabricated. The light outcoupling efficiency can be increased effectively due to the photonic band gap effect produced by photonic crystal structures on the substrate of OLED. The measuring result showed that both the emission spectrum and the light intensity were increased.

Abstract: It is very hard to fabricate nano-strctures on PEDOT:PSS film by conventional Nanoimprint Lithography for its non-thermoplastic property. Here we demonstrated a new nanoimprint process to pattern the PEDOT:PSS film at low temperature and low pressure by adding proper amount of Glycerol into PEDOT:PSS solution and pressing the Si-mold into Glycerol-PEDOT:PSS film under a pressure of 6.2Mpa for 45min at 80°C. We also compared our result to L. Tan and co-workers’. They found that positive replica was left on PEDOT:PSS film after pressing the Si-mold into Glycerol-PEDOT:PSS film under a pressure of 10Kpa for 5min at 80°C, but our work showed negative replica formed. Pressing time maybe is the critical reason to explain the different results. Holding the pressure longer gave the PEDOT:PSS enough time to flow into Si-mold and also gave Glycerol enough time to evaporate so that PEDOT:PSS became strong enough when separated the Si-mold from the PEDOT:PSS film. At last, Roman spectra was measured to confirm adding glycerol to PEDOT:PSS will not influence its molecular structure.

Abstract: We have successfully fabricated light emitting diodes (LEDs) based on patterned sapphire substrates (PSSs) fabricated by employing nanoimprint lithography (NIL) technique. The nano-patterns were designed as regular triangles consisting of columns, whose diameters and pitches were 100, 150, 200, 250 nm and 200, 300, 400, 500 nm, respectively. 412 nm wavelength LEDs grown by metal organic chemical vapor deposition (MOCVD) method were also demonstrated. The NIL technique and nano-etching by employing RIE were demonstrated in details. The qualities of all LEDs based on PSSs are superior compared with that non-patterned sapphire substrate LED. The experimental results showed that the light output power was increased by using the PSS structure. At a driving current of 20 mA, the light output powers of LEDs based on PSSs with 200, 300, 400 and 500 nm pitches are enhanced by 59%, 79%, 42% and 48%, compared with the conventional LEDs. These results provide promising potential to increase output powers of commercial light-emitting devices.

Abstract: An InGaN/GaN-based photodetector with nano-structure on the surface is present. Surface nano-structure was formed by nanoimprint lithography (NIL) and reactive ion etching (RIE) techniques. The NIL technique and nano-structure etching by employing RIE were demonstrated in details. The nano-pattern was designed as regular triangles consisting of columns, whose diameter and period were around 105 and 210 nm, respectively. The height of nano-columns was around 66 nm. The photo-voltage of this type of photodetector had very good wave characteristics with 60° period, and it presented different waveform at different angles and wavelengths of incident light. The periodic characteristics took not only on minimum voltage but also peak voltage. We demonstrated this characteristic by employing Bragg formulation.

Abstract: Flexible polymer stamps are considered as an attractive alternative to rigid, brittle and expensive stamps made of inorganic materials because of their low cost and ease of fabrication. In this paper, we present a nanoimprint process to fabricate large area, high-resolution nanograting patterns using flexible polymer stamp made from fluoropolymer. The flexibility and low surface energy of polymer stamp provide a clean release without fracture or deformation of the stamp and of the replicated nanograting. Large-area, high-density nanograting patterns with good shape homogeneity and size uniformity have been successfully fabricated using the flexible polymer stamp with advantages of its good conformal contact and low adhesion. Using flexible polymer stamps can resolve many serious issues in NIL and therefore can bring it to real industrial applications.