Fabrication of a two-step Ni stamp for blind via hole application on PWB

This study examined imprint lithography with a two-step Ni stamp to solve the laser process problems and simultaneously form a blind via and layer pattern. The Ni stamp was fabricated by electroplating on a dry-etched Si mold, made from a SOI (silicon on insulator) wafer, and pattern replication. For the pattern transfer of the Ni stamp, hot embossing was performed on SU8-coated BT and Si wafer substrates. The residual layer was of a uniform thickness with an embossed shape of acceptable squareness.     

Fabrication of metallic nanocavities by soft UV nanoimprint lithography

We propose a process combining UV-assisted nanoimprint lithography (NIL) and shadow mask evaporation techniques to fabricate metallic nanoparticles with cavities. A bi-layer transparent soft stamp with a hard top layer containing the high resolution patterns was obtained by spin coating and casting methods of PDMS. Then, it was used to mold the top photo-curable resist on a thick PMMA layer. After removal of the residual NIL resist layer, high density and high aspect ratio PMMA nanopillar arrays were obtained by reactive ion etching. Afterward, a four step evaporation under oblique angle was performed to deposit the gold nanostructures at the top of nanopillars. After lift-off, uniformly sized gold nanocavities were collected. Dark-field microscopy imaging of the fabricated nanocavities shows a clear geometry dependence of the emission peak wavelength, thereby providing a novel types of bio-sensing nano-objects.     

Development of a very large-area ultraviolet imprint lithography process

We propose a very large-area ultraviolet imprint lithography process as a promising alternative to expensive conventional optical lithography for the production of display panels. This process uses a large-area hard stamp in a low vacuum environment. The hard quartz stamp is used to achieve high overlay accuracy, and the vacuum environment is required to ensure that air bubble defects do not occur during imprinting. We demonstrate that the quartz stamp with microscale patterns can be used for imprinting 18-in. diagonal substrates via single-step UV imprint in a low vacuum environment to obtain a practical residual layer thickness (RLT) for micro pattern transfer to the substrate. Numerical analysis is performed to clarify the physical phenomena underlying imprint process.     

The influence of stamp deformation on residual layer homogeneity in thermal nanoimprint lithography

This work studies the relation between the residual layer thickness and the patterned area size, fill factor and stamp thickness for identical stamps with opposite polarity (positive and negative) made in silicon and nickel. Important and different variations in the homogeneity of the residual layer are obtained in comparison with the values predicted by the theory. This will help to optimize stamp designs and choose appropriate process setups and parameters for nanoimprint with improved pattern transfer capability.     

Two-tone metal pattern transfer technique using a single mold surface

There is growing demand for a fine metal-patterning technique to fabricate devices of the next generation, such as patterned media, plasmon photonics, and nanoscale electrodes. Nanotransfer printing (nTP) using a nanoscale patterned stamp has recently received considerable attention because of its high throughput and high resolution. To increase the throughput of the process further, it will be necessary to be able to use the stamp repeatedly, because fabrication of the stamp is a comparatively lengthy process. However, after the first transfer process, residual metal in the concave areas of the stamp obstructs the continuation of the transfer process. We examined a two-tone metal pattern transfer technique using a single mold after the first transfer process. The obstructive gold pattern in the mold could be removed and obtained as a negative tone by using a layer of polymer as a transfer substrate.     

A 4-in.-based single-step UV-NIL tool using a low vacuum environment and additive air pressure

Ultraviolet nanoimprint lithography (UV-NIL) is a promising technology for the fabrication of sub-10-nm features. Research has focused on employing a large-area stamp to improve UV-NIL throughput, but a large-area stamp makes it difficult to obtain an acceptable uniform residual layer thickness and/or avoid defects such as air entrapment. This paper presents the development of a single-step UV-NIL tool in which a 4-in. Pyrex stamp is first used to imprint coated resin against a 4-in. Si wafer in a low vacuum environment. Pressurized N₂ is subsequently applied to the wafer bottom to improve the quality of imprint results. This UV-NIL tool was used to successfully imprint a 4-in. stamp with recessed patterns engraved over the entire stamp areas onto a 4-in. Si wafer.     

Tunable erbium-doped fiber ring laser precisely locked to the 50-GHz ITU frequency grid

A discretely tunable, single-frequency erbium-doped fiber ring laser demonstrates frequency locking to the 50-GHz ITU frequency grid with an accuracy of /spl plusmn/0.3 GHz and stability of /spl plusmn/0.05 GHz over a 50-nm tuning range. An output power of 7 mW and an extinction ratio of 45 dB make this single-frequency laser useful for a variety of DWDM applications.     

A new reconstruction approach in the SRTS method

The synchronous residual time stamp (SRTS) is widely implemented for the transport of the service clock associated with continuous bit-rate services in asynchronous transfer mode adaptation layer 1. We present a new approach to service clock regeneration, which is simple to implement and can be proven to be correct.     

Press and release imprint: Control of the flexible mold deformation and the local variation of residual layer thickness in soft UV-NIL

We report on a two step soft UV nanoimprint process termed “Press and Release Imprint (PRI) that enables the reduction of both the mold deformation and the local variation of the residual layer thickness, thereby allowing high fidelity pattern replication with a uniform local residual layer thickness. The effect of imprint pressure on the mold deformation, local variation of residual layer thickness as well as required mold release time has been investigated for microscale patterns in the range of 10-100 μm. The potentials of PRI are demonstrated by high fidelity replication of micro-patterns with a uniform residual layer of minimum thickness.     

Effect of p-contact metallization on the performance ofgain-coupled DFBs with oxide-defined surface gratings

The effect of p-contact metallization on the performance of a single-growth-step ridge waveguide InGaAs-GaAs distributed feedback (DFB) laser with a silicon dioxide defined titanium surface grating is analyzed. The metallic surface grating introduces a periodic variation of the loss in the cavity to promote single-frequency emission. Device characteristics for DFBs with 50, 150, and 300 Å of titanium are compared. Under continuous-wave (CW) conditions, the devices with a titanium adhesion layer of only 50 Å operate on single-longitudinal and single-lateral modes, with threshold currents of roughly 14 mA, slope efficiencies of 0.16 W/A and sidemode suppression ratios (SMSRs) of greater than 40 dB     

Wafer deformation in ultraviolet-nanoimprint lithography using an element-wise patterned stamp

Nanoimprint lithography is a promising method for high-resolution, low-cost nanopatterning. In particular, ultraviolet-nanoimprint lithography (UV-NIL), which requires low imprint pressure, is effective for multi-layer processes. In this study, we investigated the non-uniformity of the residual layer thickness caused by wafer deformation in an experiment that examined different wafer thicknesses using UV-NIL with an element-wise patterned stamp (EPS). The EPS consisted of a number of elements, each separated by a channel. Experiments using the EPS were performed on an EVG620-NIL. Severe deformation of the wafer served as an obstacle to the spread of resin drops, which caused non-uniformity of the residual layer thickness. We also simulated the imprint process using a simplified model and finite element method to analyze the non-uniformity.     

Pattern‐Transfer Fidelity in Soft Lithography: The Role of Pattern Density and Aspect Ratio

Using high‐aspect‐ratio nanostructures fabricated via two‐photon laser‐scanning lithography, we examine the deformation of elastomeric stamps used in soft nanolithography and the fidelity of patterns and replicas made using these stamps. Two‐photon laser‐scanning lithography enables us to systematically regulate the aspect ratio and pattern density of the nanostructures by varying laser‐scanning parameters such as the intensity of the laser beam, the scanning speed, the focal depth inside the resist, and the scanning‐line spacing. Two commercially available stamp/mold materials with different moduli have been investigated. We find that the pattern‐transfer fidelity is strongly affected by the pattern density. In addition, we demonstrate that true three‐dimensional structures can be successfully replicated because of the flexible nature of elastomeric poly(dimethylsiloxane).     

Nanoprint lithography of gold nanopatterns on polyethylene terephthalate

Nano-order metal pattern printing on plastic substrates was established by using hard stamp nanoprint lithography (NPL). A spin-on-glass (SOG) material, which is almost the same as quartz in composition, was used as the material for the hard stamp. The SOG acted as a positive-tone electron beam (EB) resist. Nanopatterns were fabricated by using electron beam lithography (EBL), and a developed pattern of SOG was used as the hard stamp. Further, two types of release coating methods were utilized. One method used a conventional silan coupling agent and the other, a chromium layer. After comparing the results of the methods, we found that the chromium layer formed a smooth surface and therefore used this layer as the release layer. In addition, chromium was changed to Cr₂O₃ because of the exposure to atmospheric air. Gold was used as the transfer metal and was deposited on the hard stamp covered with the chromium release layer. This stamp was then placed in contact with a PET substrate at 80 °C for 30 min. A gap width of less than 30 nm of gold was transferred onto the PET substrate. This process is very simple, and yet, it makes it possible to obtain a very high resolution metal pattern transfer by using hard stamp NPL.     

Reversal μCP using hard stamps

In this work, we present a new method of Micro-Contact Printing (μCP) which we call reversal μCP using hard stamps which can be used for the fabrication of different structures like negative index materials, e.g., split ring resonators (SRRs), dots and squares made of gold. Typically soft stamps made of PDMS (polydimethylsiloxane) inked with thiols are used for μCP. The softness of the stamp material entails a lot of problems like deformation of the structures, sagging and pairing of the protruding features and reliability of the process. We use hard stamps which are spin coated with a thiol solution so that the thioles stay in the recessed areas of the stamp. In the following μCP process an EVG^®620 is used to bring the stamp and substrate into contact so that the thiols on the stamp diffuse and bind to the gold surface and serve as an etch mask for succeeding wet chemical etching. Using this method overcomes the disadvantage of a soft stamp material. Smallest feature sizes down to 100 nm are shown.     

激光冲击参数对残余应力场影响的三维数值模拟

数值模拟是预测激光冲击残余应力场、研究激光冲击参数对残余应力场影响的一种有效方法。采用显式动力有限元软件ANSYS/LS-DYNA对激光冲击处理(LSP)40Cr钢残余应力场进行三维数值模拟;建立了激光冲击处理40Cr钢残余应力场有限元分析(FEA)模型,实现了激光冲击处理40Cr钢残余应力场的数值模拟;模拟研究了激光功率密度、激光脉冲持续时间、激光光斑尺寸对40Cr钢残余应力场的影响。数值模拟结果表明,残余应力模拟值与实测值之间有着较好的一致性;在激光脉冲持续时间一定的条件下,要想获得最大的表面残余压应力,存在一个最佳的激光功率密度;在激光功率密度一定并且脉宽大于45ns的情况下,表面残余压应力随激光脉冲持续时间的增加而减小;在激光功率密度、激光脉冲持续时间一定的条件下,表面残余压应力随光斑直径增大而增大。     

AM50镁合金激光冲击强化实验研究

为了研究激光冲击强化对镁合金性能的影响,采用钕玻璃脉冲激光(波长1054 nm,脉冲宽度23 ns)对AM50镁合金试样表面进行冲击强化处理,并对其表面形貌、微观组织、显微硬度、残余应力进行实验测试与分析。结果表明,在激光功率密度为3.1 GW/cm2的强脉冲激光作用下,试样表面留下光亮致密的微凹坑,凹坑深约27μm;表层材料发生高应变速率的塑性变形,材料内产生大量位错与孪晶,强化层深度约0.8 mm;冲击区的显微硬度明显增加,表层材料的显微硬度比基体约提高58%;冲击区表面存在残余压应力,数值高达-146 MPa。实验结果表明,激光冲击镁合金的强化效果明显。     

LD抽运的Nd:YAG单频倍频激光器

在20mm激光腔内,Nd:YAG一端切成布氏角,与倍频晶体KTP组合构成双折射滤波片选择单纵模.用国产激光二极管(LD)纵向抽运,在会聚抽运光功率为500mW时,获得4mW单频连续运转的532nm绿光输出,同时获得约50mW的单频连续1064nm红外输出.     

Widely tunable single-frequency Er-doped fiber laser with longlinear cavity

A widely tunable single-frequency Er-doped fiber laser is demonstrated in a 21-m-long linear cavity incorporating all-fiber acoustooptic frequency shifters and a saturable absorption grating. Stable single-frequency operation is achieved with a sidemode suppression ratio higher than 50 dB and a wavelength tuning range greater than 40 nm     

Mode selection in lasers

This is a tutorial review on the subject of mode selection in lasers. We begin with a historical review. After an introduction to the subject of modes in laser resonators and a brief review of the theory of laser gain saturation, the main body of the paper is devoted to a discussion of various mode-selection techniques, many which can be used to produce single-frequency laser operation. We discuss some systems for frequency stabilization of single-frequency lasers, and conclude with examples of laser applications where mode-selection techniques are required.     

Polarization states of a single-mode (microchip)Nd3+:YAG laser. I. Theory

We present a microscopic mathematical model for the polarization states of a single-frequency Nd³⁺:YAG laser. It is a plane wave, mean field, vector model carried to all orders in the laser field. The crystal is assumed to be optically pumped longitudinally with a laser of specified polarization. For D₂ site symmetry and an odd number of electrons, we establish the phase relationships between the components of the electric dipole matrix elements between the Kramers states. These relationships are central in determining the site-specific coupling between both, the pump and laser fields to the Nd ³⁺ ions. The laser cavity is assumed to be linear and quasi-isotropic. The residual optical anisotropies are included using a round-trip Jones matrix formalism