Large-area Microstructures Research Articles

Atomic Depth Image Transfer of Large-Area Optical Quartz Materials Based on Pulsed Ion Beam.

The high-efficiency preparation of large-area microstructures of optical materials and precision graphic etching technology is one of the most important application directions in the atomic and near-atomic-scale manufacturing industry. Traditional focused ion beam (FIB) and reactive ion etching (RIE) methods have limitations in precision and efficiency, hindering their application in automated mass production. The pulsed ion beam (PIB) method addresses these issues by enhancing ion beam deflection to achieve high-resolution material removal on a macro scale, which can reach the equivalent removal resolution of 6.4 × 10-4 nm. Experiments were conducted on a quartz sample (10 × 10 × 1 mm) with a specific pattern mask using the custom PIB processing device. The surface morphology, etching depth, and roughness were measured post-process. The results demonstrated that precise control over cumulative sputtering time yielded well-defined patterns with expected average etching depths and surface roughness. This confirms the PIB technique's potential for precise atomic depth image transfer and its suitability for industrial automation, offering a significant advancement in microfabrication technology.

Ultrawide linear range, high sensitivity, and large-area pressure sensor arrays enabled by pneumatic spraying broccoli-like microstructures.

Large-area pressure sensor arrays with a wide linear response range and high sensitivity are beneficial to map the inhomogeneous interface pressure, which is significant in practical applications. Here, we demonstrate a pneumatic spraying method to prepare large-area microstructure films (PSMF) for high performance pressure sensor arrays. The sprayed surface morphology is designable by controlling the spraying parameters. It is worth noting that the constructed "broccoli" like morphology with a swollen top and shrunken bottom inspired a new mechanism to enlarge the linear response range by decreasing the series resistance with pressure increasing. At the same time, the pneumatic sprayed "broccoli" has a rough surface due to droplet stacking, which reduces the initial current effectively. Hence, the sensor achieves a 10 000 kPa ultrawide linear response range with a high sensitivity (98.71 kPa-1), and low detection (5 Pa). The prepared sensor has a small static response error (4.4%) and 5000 cycle full-range dynamic response durability. Finally, the constructed sensor arrays can distinguish the pressure distribution in different ranges clearly, which indicates a great potential in health care, motion detection, and the tire industry.

Numerical Simulation of Spatial Atomic Layer Deposition on Moving Substrates with Microgrooves and Porous Structures

The need of ultrathin and highly conformal coatings on large-area microstructure substrates such as photovoltaic cells, flexible displays, and Li-ion battery (LIB) electrodes has driven the development of high-efficient ALD. Spatial ALD is a promising high-throughput technique capable of producing ultrathin films on large substrates, which can reach up to two orders of magnitude faster than temporal ALD. However, spatial ALD is a complex and strong-coupled process of fluid flow, heat and mass transfer, as well as chemical reactions. Compared to the flat substrate, the diffusion process in the microstructures takes longer, limiting the substrate velocity and the deposition rate. In this work, spatial ALD on moving microgroove substrates and porous LIB electrodes are quantitatively studied through the multiscale modelling method by coupling computational fluid dynamics (CFD) with chemical kinetics. Dynamic mesh method is implemented to simulate the ALD reaction with the in-line movement of the substrate. Results show that the vortices always exist in the micro-gap with microgroove substrates. Besides, the top of the microstructure on the first contact with the precursor is the highest, and the surface coverage at the corner on the other side of the microstructure is the lowest. For porous LIB electrodes with large specific surface area, the film coating depth is limited by both the low precursor diffusion rate and the amount of precursor supply. Increasing the carrier gas flow rate increases the film coating depth by increasing the precursor supply over the same time period. Besides, the gas byproduct of ALD remaining at the electrode bottom can be more effectively removed. Quantitative process optimizations of substrate velocity and precursor concentration for different electrode structures are also carried out. It is found that the electrode gradient design with higher porosity on the top is beneficial for obtaining deeper coating depth and higher precursor utilization compared to the inverse gradient design. The present multiscale modeling work provides a comprehensive understanding and important guidance for the industrial application of the spatial ALD process on microstructure substrates.

Defocus compensation scheme for femtosecond laser direct writing of large-area non-periodic micro-structures

The optical path error, the position-independent geometric error, and the form and position tolerance of the substrate will lead to position deviations of the laser focus resulting in the inconsistency of the large area micro-structure and limiting the processing range of the femtosecond laser fabrication platform. To realize continuous defocus compensation along the processing trajectory, an autofocus scheme consisting of an optimized depth from focus (DFF) method based on grid division and the bilinear interpolation algorithm is proposed in this paper. The optimized DFF method includes the Laplace-DWT evaluation function combining the advantages of spatial domain and frequency domain sharpness evaluation function, an adaptive focusing window selection method, and an adaptive step length three-step hill-climbing search method. The optimized DFF method was used to obtain the best focus position of each grid point. Compared with the traditional DFF method, the optimized algorithm has higher focusing precision and avoids the disadvantage of time-consuming focusing. Then, to compensate for interpolating points of the processing trajectory, the bilinear interpolation algorithm was introduced to achieve online focusing during two-photon lithography processing. Finally, the feasibility and effectiveness of the auto-focusing scheme were validated by experiments. Through defocus compensation, the sharpness evaluation value of the focus image on the processing trajectory improved by 90%, which indicated the successful focus of the laser beam on the workpiece surface. Moreover, a high-precision and large-area encoded micro-polarizer array with consistent structure were fabricated successfully. This paper provides a simple way to identify and compensate the defocus errors online with high accuracy and efficiency. The proposed method can improve the machining accuracy and quality of the femtosecond laser direct writing.

Optical Millinewton Force Sensors Based on GaN Devices Integrated With Bionic-Structured PMDS Films

In this work, optical millinewton force sensors are developed by integrating GaN devices with bionic-structured polydimethylsiloxane (PDMS) films. The chip-scale GaN-on-sapphire devices incorporating light emitters and photodetectors are fabricated using wafer-level microfabrication. Large-area bionic microstructures of varying size scales are patterned on the PDMS films using four different types of plant leaves as molding templates. The deformable PDMS film can efficiently modulate the light coupled into the detector during force loading, which endows the GaN devices with high sensitivity to millinewton forces. The force-sensing capabilities of the sensors are thoroughly investigated and compared. The device integrated with optimized film exhibits sensing characteristics with a sensitivity of 0.145 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> A/mN in the range of 0–290 mN and a sub-millinewton resolution of 0.165 mN. The developed optical sensor provides the attractive features of low-cost fabrication, high compactness, fast response, and high stability, making it highly valuable for millinewton force detection in practical applications.

Preparation of Highly Stable Polymer Microstructure with Enhanced Adhesion Strength by Pushpin-like Nano/Microstructure Array.

This polymer microstructure expands more available application, which is a milestone for the development of micro-electro-mechanical system devices towards intelligence and multifunction. Poor interface bonding between the polymer and Si or metal is a particular problem, which restricts the application and promotion of polymer materials. In this study, a transition strengthening layer is proposed to obtain a highly stable polymer microstructure by enhancing the interfacial adhesion strength. The transition strengthening layer is activated by a pushpin-like nano/microstructure array with micromachining technology. Given its good graphical qualities and compatibility, epoxy negative photoresist SU-8 is applied to evaluate the strengthened capabilities of the pushpin-like nano/microstructure array. The microstructure of SU-8 is prepared by the same processes, and then the adhesion strength between the SU-8 microstructure and various activated substrates is tested by the thrust tester. It was determined that SU-8 with an activated pushpin-like microstructure array possessed a highly stable adhesion ability, and its adhesion strength increased from 6.51 MPa to 15.42 MPa. With its ultrahigh stable adhesion ability, it has been applied in fabricating three typical microstructures (hollow square microstructure, gradually increasing adjacent periodic microstructure, and slender strip microstructures) and large-area SU-8 microstructures to evaluate the feasibility of the transition strengthening layer and repeatability and universality of the microfabrication processes. The drifting and gluing phenomenon are avoided by this method compared with the traditional design. The proposed pushpin-like nano/microstructure array is promising in enhancing the stability of polymer microstructures with a substrate.

Fabrication of micro-nano multi-scale hierarchical porous structure on the surface of Inconel718 nickel-base superalloy by one-step method

A new high-efficiency composite process consisting of laser machining and abrasive belt grinding was proposed to prepare multi-scale graded microstructures on the surface of Inconel718 nickel-base superalloy for aviation. The scheme is based on the machining characteristics of abrasive belt grinding, low damage molding and high-efficiency grinding and polishing, the effective combination of ultrashort pulse laser-induced surface microstructure growth, and the thermal effect in the process of high-energy beam machining, so as to realize the efficient preparation of hierarchical microstructure. In the one-step forming process, the accuracy of the material surface is ensured by abrasive belt grinding. The porous microstructure on the surface is catalyzed by the thermal effect produced by the high-energy beam laser. The scale of the porous structure is 3 µm–6 µm, the pore surface will generate nanoparticles, the size is below 100 nm, and dense nanoparticles will be generated on the surface. The porous structure can be super hydrophilic and adsorbed to form a liquid membrane. The formation of rib-like microstructures on the surface induced by ultrashort pulse laser makes the liquid film have directional spreading properties. Rib-like microstructure height is 50 µm–150 µm and it can be adjusted by setting the scanning line width. The one-step method for preparing hierarchical microstructures proposed in this study can efficiently process large-area microstructure surfaces with different wetting properties. • The porous structure, nanoparticles, and rib-like bulges can be efficiently fabricated. • The microstructure can be easily regulated.

Large area fabrication of single micron features using two-photon polymerization with sub-nanosecond laser

Single micrometer-sized features were fabricated on ARN-4340 photoresist using a 3D additive technique of two-photon polymerization (TPP). An economic TPP setup capable of producing a large area was developed in the lab using a sub-nanosecond laser. The Photo-initiator (2, 4 Diethyl-9H-thioxanthen-9-one) with a large two-photon absorption cross-section was used to enhance the polymerization. It was theoretically determined that the dimensions of the polymerized features depend on the concentration of the photo-initiator. A novel image-based focusing technique was developed to achieve uniform microsized features on a large area. In the proposed TPP setup, the developed focusing technique was used to determine the area over the sample, which can be polymerized in one go. To demonstrate the capability of the developed setup, microstructures of about 1 µm width were fabricated over an area of 4 cm2. Further, the fabricated sample was used to develop a master mold of Polydimethylsiloxane, which can be used for a soft-lithography replication process. Also, the melt flow technique was explored to reduce the roughness in the fabricated structure. The multi-photon polymerization process using the sub-nanosecond laser is shown to be cost-effective and robust for large area microstructure fabrication.

Role of Scanning Speed in Morphological and Optical Properties of Nanosecond Laser Textured Silicon Surfaces

Laser surface texturing (LST) is a rapid single-step method for surface functionalization. Different micro and nanoscale structures can be fabricated by controlling the laser parameters, ambient conditions, and material properties. In this work, we investigated the role of laser scanning speed in the morphological and optical properties of nanosecond laser textured silicon surfaces. Keeping the laser flounce just above the threshold, we controlled the laser scanning speed in the range 50-100 μm/s to monitor the morphological and optical changes. Morphological analysis shows various randomly arranged microstructures in the processed area, and the induced structures strongly depend on the scanning speed. The total reflection spectrum (specular+diffuse) from laser textured silicon shows that a significant reduction (≈60%) in reflectivity is possible with the decrease in scanning speed from 100 μm/s to 50 μm/s. These highly absorptive and large-area microstructures have numerous possibilities in photovoltaics, optoelectronic devices, and other material science applications.

Microstructure-Forming Mechanism of Optical Sheet Based on Polymer State Transition in Injection-Rolling Process.

Polymeric optical sheets are significant components in large-scale display devices and are difficult to fabricate due to small size and high accuracy of large-area microstructures. As a newly developed molding technique, injection-rolling is capable of continuously and efficiently achieving large-area microstructures on the polymer surface with short time and high replication. However, the microstructure-forming mechanism during the injection-rolling process has not been fully understood. In this paper, a three-dimensional steady-state heat-flow coupling simulation model of the injection-rolling zone was established to obtain the distributions of the polymer state transition interfaces. According to the state transition interfaces, the entire microstructure-forming process was numerically simulated by dividing into filling and embossing stages to systematically analyze the effects of the polymer state transition interface on filling rate. After this, the relationship between process parameters such as injection temperature, rolling speed, and roll temperature and polymer state transition interface was investigated to develop a position prediction model of the state transition interface. In addition, the optical sheet injection-rolling experiments were also carried out to reveal that the filling rate of the microstructures on the optical sheet can be affected by varying the positions of the state transition interfaces. Therefore, the microstructure-forming mechanism could be revealed as theoretical guidance for the subsequent injection-rolling production with high quality and high efficiency.

Stitching error compensation for large-area microstructures based on digital oblique scanning exposure mode

We proposed an efficient method for improving the stitching precision of large-area microstructures. A clever triangular region compensation strategy based on a digital micromirror device oblique scanning exposure mode was developed, which can effectively enhance lithographic resolution and complete seamless stitching. In order to ensure the optimal stitching effect, the stage self-calibration technology was also introduced into the exposure system. The experimental results showed that the stitching region traces can be effectively eliminated and smoothed by the above strategy. The presented method will have important applications in the printed circuit board and flat panel display fields.

Fabrication of large-area microwells on Polydimethylsiloxane films by femtosecond laser ablation

In this paper, a novel technique was presented for fabricating microwell array in large areas on a Polydimethylsiloxane films using high-speed scanning of a laser beam. A femtosecond laser double pulse ablation was achieved on Polydimethylsiloxane films. Microwells with various dimensions and sub-microstructures were successfully fabricated on Polydimethylsiloxane films, which has many applications such as optical devices. In this paper, we demonstrate that the surface roughness of the microwells is related to the laser parameters and a smooth surface can be obtained. The smooth surface of the fabricated microwells could be applied in optical imaging systems as concave microlenses, in which enables the high-resolution imaging. We also demonstrated that the microwells were formed by the transient localized electron dynamics. This work could lead to a new approach to the fast fabrication of large-area microstructures using the ultrafast laser processing technologies.

Precise fabrication of large-area microstructures by digital oblique scanning lithography strategy and stage self-calibration technique

We proposed an efficient and low-cost method for precise fabrication of large-area microstructures. A programmable digital lithography system based on digital micromirror device (DMD) oblique scanning strategy was developed, which can effectively reduce pixel quantization errors and complete a sub-pixel exposure accuracy. To further reduce the cost and enhance the flexibility of the fabrication system, a two-dimensional (2D) stage self-calibration technique is studied, which can replace the laser interferometer measurement (LIM) system and ensure the calibration accuracy well. The presented method is promising for developing large-area microstructure applications such as flat panel display (FPD), organic light-emitting diodes (OLED).

面向大面积微结构批量化制造的复合压印光刻

面向大面积微结构批量化制造的复合压印光刻

Fabrication of large-area V-groove microstructures using gasbag-pressuring edge-irradiating UV imprinting

UV imprinting has been one of the most productive replication techniques due to its low imprinting pressure and temperature. The conventional UV resin is cured by direct irradiation from the bottom. Space management and energy consumption become problems as the areas are getting larger and larger. Another problem is the uniformity of imprinting pressure, which is higher near the center with conventional platen-pressuring imprinting. In this study, we develop an innovative side-emitting UV-curing gasbag-pressuring imprinting mechanism for large area microstructure replication. An imprinting system based on such integration has been designed and implemented. V-groove microstructures has been imprinted onto a PMMA plate with dimensions of 380 mm × 230 mm × 3 mm for light enhancement. The optical performance and the profile of microstructures have been verified.

Research on temperature-assisted laser shock imprinting and forming stability

Demand for forming precision and the high-temperature stability of micro-structures is growing quickly in the fields of MEMS, optoelectronic devices, aerospace and biomedical engineering. In order to improve the precision and stability of micro-structures, and to achieve the rapid manufacture of formed parts, the temperature-assisted laser shock imprinting (TALSI) technique is proposed for fabricating large-area micro-structures on the surface of metal foil. In this study, nanosecond lasers with low energy and high frequency were used to carry out laser shock imprinting (LSI) experiments on aluminium foil at different temperatures, and recovery experiments were also implemented at different temperatures. By analysing the surface morphology, profile curve and forming depth of the micro-structures, we obtain the forming law and the optimum imprinting temperature. The influence of temperature on the plasticity, flow stress, dynamic yield strength, and deformation resilience of aluminium foil was experimentally determined, and the stress distribution at imprinting temperatures of 25 °C and 200 °C were investigated by ABAQUS software. The results indicate that warm laser shock imprinting (WLSI) can improve the forming depth, forming accuracy, high temperature stability and residual stress homogenisation of formed parts.

Excimer Laser Three-Dimensional Micromachining Based on Image Projection and the Optical Diffraction Effect

An excimer laser three-dimensional (3D) micromachining system is proposed based on a mask image projection method and the optical diffraction effect. The effects of optical diffraction on the laser machining rate are evaluated using a hole-arrayed mask pattern with various feature sizes and hole-area opening ratios. The practical feasibility of the proposed method is demonstrated by machining conical, trihedral, and pyramidal 3D microstructures on polycarbonate substrates. The proposed method greatly simplifies the photo-mask design and preparation task in traditional excimer laser 3D micromachining systems and provides a powerful technique for achieving large-area 3D microstructures with complex patterns and atypical profiles.

Use of variothermal heating for the extrusion embossing of microstructured poly(methylmethacrylate) and polycarbonate optical films

The importance of microstructured parts and extrudates is rising because of the increasing functional integration in many different fields of application, for example in the automotive industry and medical technology. Variothermal extrusion embossing is a continuous process that combines plastic film production with the application of large-area microstructures. The process utilizes an embossing roll and an external heating device to continuously imprint the desired structure into film during extrusion. Through this microstructuring, it is possible to integrate innovative functions into a film. Present efforts are focused on forming optical structures (micro-optics) on polycarbonate and poly(methylmethacrylate) films. This article deals with process control requirements that are necessary to successfully apply this technology, and also demonstrate how, through suitable process parameter selection, high-quality microstructures can be effectively embossed on the films. Different microstructures between 24 and 165 µm in height and between 100 and 200 µm in width are tested. With poly(methylmethacrylate) better microstructure reproduction could be achieved than with polycarbonate.

Thermochemical micro imprinting of single-crystal diamond surface using a nickel mold under high-pressure conditions

Single-crystal diamond is an important material for cutting tools, micro electro mechanical systems, optical devices, and semiconductor substrates. However, the techniques for producing microstructures on diamond surface with high efficiency and accuracy have not been established. This paper proposes a thermochemical imprinting method for transferring microstructures from a nickel (Ni) mold onto single-crystal diamond surface. The Ni mold was micro-structured by a nanoindenter and then pressed against the diamond surface under high temperature and pressure in argon atmosphere. Results show that microstructures on the Ni mold were successfully transferred onto the diamond surface, and their depth increased with both pressure and temperature. Laser micro-Raman spectroscopy, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) analyses indicate that a graphite layer was formed over the contact area between diamond and Ni during pressing, and after washing by a mixed acid, the graphite layer could be completely removed. This study demonstrated the feasibility of a cost-efficient fabrication method for large-area microstructures on single-crystal diamond.

Area scalable optically induced photorefractive photonic microstructures

A convenient approach to fabricate area scalable two-dimensional photonic microstructures was experimentally demonstrated by multi-face optical wedges. The approach is quite compact and stable without complex optical alignment equipment. Large-area square lattice microstructures are optically induced inside an iron-doped lithium niobate photorefractive crystal. The induced large-area microstructures are analyzed and verified by plane wave guiding, Brillouin-zone spectroscopy, angle-dependent transmission spectrum, and lateral Bragg reflection patterns. The method can be easily extended to generate other more complex area scalable photonic microstructures, such as quasicrystal lattices, by designing the multi-face optical wedge appropriately. The induced area scalable photonic microstructures can be fixed or erased even re-recorded in the photorefractive crystal, which suggests potential applications in micro-nano photonic devices.