Imprint System Research Articles

Portable UV nanoimprint lithography system using hydraulic pressure

Nanoimprint lithography (NIL) is the next-generation alternative to conventional photolithography involving an inexpensive and high throughput process. However, conventional NIL equipment requires a bulky air compressor which possesses a large area. This study aims to overcome this limitation by introducing a novel hydraulic ultra-violet (UV) imprint system. Hydraulic UV imprint system can be used to conduct the UV NIL process by using a simple, low-cost materials without needing complex equipment. To form various patterned layers, UV NIL was conducted with various master stamps.(diameter: micro-cones:3 μm, nanopillars:200 nm, nanoholes: 200 nm) The performance of the imprint system was verified by using scanning electron microscopy analysis of samples fabricated by new system. The results showed that the performance of the new imprint system was comparable to that of a conventional air-pressure UV imprint system.

Injection-rolling nozzle in an imprint system with continuous injection direct rolling for ultra-thin microstructure guide light plate

A novel Injection-rolling Nozzle (IRN) in an imprint system with continuous injection direct rolling (CIDR) for ultra-thin microstructure polymer guide light plates was developed to achieve uniform flow velocity and temperature at the width direction of the cavity exit. A novel IRN cavity was designed. There are eight of feature parameters of cavity were optimized by orthogonal experiments and numerical simulation. Results show that the flow velocity at the width direction of the IRN outlet can reach uniformity, which is far better than that of traditional cavity. The smallest flow velocity difference and temperature difference was 0.6 mm/s and 0.24 K, respectively. The superior performance of the IRN was verified through a CIDR experiment. Several 0.35-mm thick, 340-mm wide, and 10-m long microstructural Polymethyl Methacrylate (PMMA) guide light plates were manufactured. The average filling rates of the microgrooves with the aspect ratio 1:3 reached above 93%. The average light transmittance is 88%.

The development of a dynamic rubber balloon spring-based asymmetric photocurable imprint system

This study aims to develop a dynamic rubber balloon spring-based asymmetric photocurable imprint system. The elastic plate used in this study combined the rubber balloon supporting force and asymmetric spring to control the asymmetric imprinting, in order to achieve photocurable micro-structural asymmetric imprinting. Firs of all, designed and developed the imprinting system, and procedure for preparation of the PDMS soft mold, and an elastic plate controlled by asymmetric spring force was used to manipulate the imprinting direction, then regulating the angle of imprinting of the direction force. The experimental results showed that, after filling the rubber balloon and the air-supporting pressure, the system used the estimated spring forced from the asymmetric spring constants to control the elastic plate to imprint and replicate the asymmetric micro structure. The results are expected to provide an alternative in the process of micro-system components.

Development of a continuous injection direct rolling imprint system for microstructure thin-plate

A prototype of a continuous injection direct rolling (CIDR) imprint system was developed and applied to CIDR tests to evaluate its feasibility for the large-area replication of an optical micro device. The developed system adopts the theories of injection compression and thermal imprinting and presents the capacity to fabricate a 200 mm-wide and over 10 m-long PMMA plate and to replicate ultra-precision structures on its surface at a rolling speed range of 1.1–11.5 mm/s. Under the given CIDR conditions (injection temperature, 280 °C; injection pressure, 6 MPa; rolling force, 13 MPa; roller temperature, 85 °C), complete fabricating of a 0.7 mm-thick Polymethyl methacrylate (PMMA) plate with 17.3 μm-deep and 35 μm-wide V-groove microstructures was achieved at a rolling speed of 3.4 mm/s. Finally, a light guide plate for a backlight panel was fabricated by CIDR. The light transmittance of this plate reached 90.8 %, the maximum birefringence was ~99 nm and its average haze was 0.51 %.

Method for high temperature nanoimprint of an organic semicrystalline polymer

Performance and functionality of devices prepared from organic semicrystalline polymers strongly depend on the size and the orientation of the ordered crystalline domains, as the conductivity is distinctly different in the different lattice directions. This investigation addresses the potential of thermal nanoimprint to control the size of the ordered domains as well as their orientation with respect to the substrate. Poly-3-hexylthiophene (P3HT) is chosen as one of the prominent semicrystalline polymers available at high quality. In order to control the ordering of the domains freely, the imprint is performed at a temperature beyond the melting point to eliminate the domains already existing after spin-coating and soft-bake. To avoid a degradation of P3HT at such a high temperature under oxygen contact—the imprint system used operates in air—a novel imprint procedure is employed, where a distinct prepressure is applied already during the heating of the imprint stack (stamp/substrate with P3HT layer). To enable efficient recrystallization in the form “shaped” by the imprint mold, the novel procedure features, in addition, a slow cool-down from the processing temperature (245 °C) down to 150 °C. During recrystallization the orientation of the ordered domains is driven primarily by the interaction of the side-chains of the P3HT molecules with the antisticking layer of the mold, where the pressure still applied forces ordering, too. The potential of this approach is characterized by x-ray diffraction measurements. The results clearly show that the novel procedure investigated here is effective not only to avoid the degradation of P3HT at a high temperature but also to provide ordered domains that are more than two times larger than those existing before imprint, after spin-coating. The results obtained so far with grating patterns are encouraging and indicate new possibilities of controlling the conductivity of devices prepared from semicrystalline organic polymers.

The underestimated impact of instabilities with nanoimprint

With nanoimprint, instabilities of the polymeric layer between the substrate and the stamp are observed when incomplete filling of the stamp cavities prevails, resulting in capillary bridges and meandering structures. Experiments show that instabilities may also affect the initial situation of a thermal nanoimprint process. Already at the beginning of the actual imprint step, the polymeric surface may be highly non-uniform, with undulations of the film thickness, polymeric bridges and de-wetted regions; thus, the starting point for imprint may differ substantially from the general expectation of a uniform spin-coated layer. A detailed instability analysis considering the combined effect of van der Waals forces, electrostatic forces and temperature gradients under realistic imprint conditions clearly identifies temperature gradients to be the cause for high initial layer non-uniformities. We found that during heat-up (before imprint) temperature differences of 10 °C may exist between the top and bottom hotplate of a thermal imprint system. These temperature differences result in the non-uniformities of the polymeric layer observed, when stamp and sample are heated under low-pressure contact, where some small but locally arbitrary gaps exist between polymer and stamp. This result asks for a reconsideration of the thermal nanoimprint procedure. It also confirms the high impact of temperature control for uniform, low-defect imprint results; this is critical not only during imprint, but also during heat-up.

Aspects of cavity filling with nano imprint

The role of capillary forces with nanoimprint is addressed. As the respective capillaries are the closed cavities of the stamp used for replication, the Laplace pressure together with the pressure of the gas phase inside the cavities dictate the equilibrium pressure in the polymer. Whether the cavities can be successfully filled, depends on the external pressure available from the imprint system, setting the pressure in the polymer, and on the sorption of any gaseous phase. Gas sorption is provided by the imprint polymer itself and may differ with different imprint materials and different imprint situations (imprint temperature, residual layer thickness). With soft stamps or composite stamps also the stamp itself may contribute to the overall gas sorption. Situations typical of different imprint techniques (thermal nanoimprint, UV-assisted nanoimprint, capillary force lithography) as well as of moulding during stamp replication are discussed in view of capillary effects. The discussion is illustrated by simple analytical estimations.

Theoretical and experimental study of a circular imprint process for fabricating polylactide stents

This study presents the concept for a circular imprint process for polylactide (PLA) stent fabrication that can reduce processing time and costs compared to traditional processes. The properties of PLA were measured for the theoretical simulation of the PLA stent firstly. Two proposed simulation models were built to predict the filling rate of the PLA material in the circular imprint process by the finite volume method (FVM) and to comprehend the compressibility of the PLA stent using the finite element method (FEM). A specially designed circular mold and imprint system are employed to imprint the stent structure. Experimental results show a similar trend to the theoretical results for the circular imprint process under varying conditions. Moreover, a filling rate of up to 98.3% can be achieved, and the PLA stent, which had good material properties and compressibility, was fabricated successfully using the circular imprint system.

High-speed imprinting on plastic optical fibers using cylindrical mold with hybrid microstructures

• We developed a cylinder mold with hybrid-layered patterns. • A precise cutting was combined with 3-D photolithography using a flexible mask. • The imprint speed was improved by changing a press-force control method. • We succeeded in continuous imprinting on a POF at a feeding speed of 20 m/min. We are developing flexible and large-size e-textiles by weaving in a smart fiber. On the surface of the fiber, micro-electro-mechanical-systems (MEMS) structures, electronic circuit patterns, and guide structures for positioning during the weaving process are fabricated. In order to manufacture smart fibers in large quantities, we developed a cylindrical mold with hybrid-layered structures consisting of 260-μm-wide macro patterns and several 10-μm-wide patterns fabricated by precise cutting of substrate employing forming tools and 3-D photolithography, and using a micro-patterned flexible photomask. Initially, the polished surface of the cylinder is covered with an electroless-plated Ni–P alloy; and convex structures with rectangular cross-sections and arc shaped convex structures are cut. Next, the surface of the cylinder is coated with a positive-tone photoresist by a dipping process. Ultraviolet (UV) lights are then irradiated on the photoresist through a flexible micro-patterned photomask wrapped around the cylinder; and then the micro-patterns on the photomask are thus transferred onto the cylindrical surface. Next, following a Cu electroplating, hybrid-layered patterns are made that comprise 260-μm-wide macro and several 10-μm-wide microstructures. In the final step, the photoresist is then removed. And moreover, in order to realize high-speed imprinting, the mechanical stiffness of a reel-to-reel thermal imprint system is improved, and the press-force control method is changed. The imprint system is equipped with a completed cylindrical mold; and using the system, a plastic optical fiber (POF) comprising a 240-μm-diameter PMMA core with a 5-μm-thick fluoride clad is imprinted for a demonstration. The cylindrical mold heated up to 50 °C with an infrared lamp, is pushed into the surface of the POF to a depth of 4.5–6.7 μm. As a result, a continuous imprinting on the POF is achieved at an imprint speed of 20 m/min.

Control of self-assembly defects in thermal nanoimprint

With residual-free imprint, physical self-assembly of the polymer within partly-filled cavities has to be avoided to ensure the masking capability of nanoimprint when used as a lithography technique. In this regard we investigate the impact of the velocity of pressure application by use of a motor-driven imprint system. Slowing-down the velocity of pressure application maintains a smooth surface of the polymeric layer in the cavities, minimizing the risk of local contact between polymer and stamp with moderate filling levels of the cavities. At a high filling level of the cavities, the formation of self-assembly cannot be avoided, as van der Waals interactions between polymer surface and stamp become effective to drive the formation of instabilities. The experimental results obtained can be understood by stability analysis. Understanding of the processes leading to the formation of physical self-assembly is vital to exploit the full potential of nanoimprint for processing.

Reel-to-reel imprint system to form weaving guides on fibers

Graphical abstractDisplay Omitted Highlights? We developed a reel-to-reel imprint system to process a fiber using a cylindrical mold. ? A press force correction mechanism that suppressed the installation error was built. ? Continuous pressing with a constant force was enabled at a sending speed of 5m/min. ? We succeeded in thermal-imprinting of weaving guides on the surface of a plastic optical fiber. We developed a reel-to-reel imprint system using a cylindrical mold that could continuously process a uniform-depth microstructure on the surface of a fibrous substrate. A fiber coming out from a sending reel was placed between two rotating heated cylindrical molds under a moderate press-force, and was then fed into a receiving reel. The two cylindrical molds rotated in opposite directions to each other while synchronized with the rotations of the two reels that moved the fiber from the sending reel to the receiving reel. The cylindrical molds comprised 100-mm-diameter metal cylinders covered with a Ni electroless-plated layer on which convex mold patterns were fabricated using a high-precision machining tool. The system was equipped with a press-force control mechanism capable of adjusting the gap between the two cylindrical molds in rapid response to any variation in the press-force as detected by a load cell. This mechanism suppresses any fluctuation in the press-force that may occur due to any error made during the assembling of the cylindrical mold. This setup can also make continuous imprinting possible under a constant force. By adjusting the cylindrical mold's position within a 74-µm-wide range, the fluctuation of the press-force can be reduced from 33 to 3N. Furthermore, as a demonstration, a plastic optical fiber (POF) in a diameter of 250µm was sent at speeds of 1m/min and 5m/min; and by a continuous imprinting process, 260-µm-wide rectangle-shape, and 145-µm-radius arc-shape concave microstructures were formed on the surface of the POFs. When the sending speeds were 1 and 5m/min, the maximum standard deviations of the imprinted depths were estimated to be 0.52 and 0.14µm, respectively. These values fell within 17% of the POF's diameter variations of 3µm. The imprinted fibrous substrate will be used as fibers that constitute e-textiles; and the imprinted concave microstructures will be used as weaving guides to fix the contact positions between warps and wefts.

Mechanical characterization of a piezo-operated thermal imprint system

Dynamic agitation during imprint is investigated as a means to reduce the imprint temperature of thermoplastic materials. The imprint system used consists of a stepping motor and a piezo unit as the main components. The motor controls the working point of the system, and a sinusoidal motion of the piezo unit (3 piezos at 120° with respect to each other) superimposes an additional dynamic excitation. The system was characterized with respect to its mechanical behavior by exploiting analogies between mechanical and electrical quantities. The results show that the system can be operated at a frequency of up to about 60 Hz and that the piezos act as a dynamic motion source in the system. First imprint experiments with polystyrene at 100 °C indicate the potential of this frequency-assisted imprint technique.

A Sliding-press-type Reel-to-reel Thermal Imprint System for Fiber Substrates

A Sliding-press-type Reel-to-reel Thermal Imprint System for Fiber Substrates

Continuous roll-to-flat thermal imprinting process for large-area micro-pattern replication on polymer substrate

Conventional imprinting process in flat-pressing mode meets with the problem of limited efficiency as a discontinuous batch-wise process in many new applications that demand micro-/nano pattern replication over large area with low cost and high throughout in mass production manufacturing. To overcome such problem, alternative imprinting process in a continuous roller-pressing mode has been gaining more attention since it has many advantages. However, few studies have been reported on the investigation of filling mechanism in roller-pressing type imprinting process. In order to have a better understanding of polymer flow behavior in roller-pressing type imprinting process, it is necessary to establish a criterion of evaluation for roller-pressing type imprinting process. In this paper, an analytical model for the cavity-filling of polymer flow in roll-to-flat (R2F) imprinting process is derived based on Hertz contact pressure distribution and Navier–Stokes equation. The feasibility of the model is evaluated using a lab-scaled prototype of a R2F micro thermal imprint system for micro-pattern replication over large area on polymer substrate. Series of tests are conducted to investigate the effects of process control parameters on the replication ratio. In results, there is good agreement between the model prediction and experiments when pattern replication is examined according to the change of control parameters such as rolling speed and loading pressure.

A compact system for large-area thermal nanoimprint lithography using smart stamps

We present a simple apparatus for thermal nanoimprint lithography. In this work, the stamp is designed to significantly reduce the requirements for pressure application on the external imprint system. By MEMS-based processing, an air cavity inside the stamp is created, and the required pressure for successful imprint is reduced. Additionally, the stamp is capable of performing controlled demolding after imprint. Due to the complexity of the stamp, a compact and cost-effective imprint apparatus can be constructed. The design and fabrication of the advanced stamp as well as the simple imprint equipment is presented. Test imprints of micrometer- and nanometer-scale structures are performed and characterized with respect to uniformity across a large area (35 mm radius). State-of-the-art uniformity for µm-scale features is demonstrated.

Prototype development of a roller imprint system and its application to large area polymer replication for a microstructured optical device

In this study, the prototype of a thermal roller imprint lithography (RIL) system was developed and applied to RIL tests to evaluate its feasibility for the large area replication of an optical micro device. The developed system adapts an automatic stamp releasing

Overview on Nanoimprint Technology - Process, Tools, Applications and Technical Issues for Industrialization

Nanoimprint process is a simple and a low cost micro/nano fabrication method based on mold replication principle. Various kinds of applications such as optical devices for flat panel displays or electronic papers, patterned medias, bio-medical devices and electronics devices using nanoimprint process are expected. In the past a decade, many researches and developments on the process, the tool, the application relating to nanoimprint were carried out and partly commercialized. In this paper, overview on nanoimprint technology including recent progress is described. And important issues to be solved and solution idea for industrialization of nanoimprint process are pointed out. Also, our recent R&D activities on nanoimprint tool and process, which are UV/thermal nanoimorint tool and process, roll to roll type imprint system are introduced.

Book and Software Reviews

Allan N. Schore has authored a most impressive landmark text, Affect Regulation and the Origin of the Self: The Neurobiology of Emotional Development. Applying a broad interdisciplinary approach to the fields of child development, neurobiology and psychoanalysis, Schore makes an important contribution in demonstrating how these various crosscurrents from different areas of study interconnect and interrelate. Essentially, in reviewing this enormous range of research, Schore's thesis points to the powerful significance of emotional resonance between mother and child. The quality of this resonance imprints itself upon a complicated neurological network. Problems of emotional resonance that occur in early development invariably lay the basis for later pathological expression. This research overwhelmingly supports the view that right hemisphere or action interventions are the preferred method of intervention in repairing damage to the self. As Schore amply demonstrates, the neurological imprint system that relates to affect regulation and self-development occurs in the right frontal hemisphere of the brain. The language of the right hemisphere is one of spatial, sensory motor, visual and kinesthetic stimulation. The implications of these findings are most important for creative arts therapy practice. Expanding upon this premise, interventions that are spatial and sensory-oriented and that promote affect resonance relate to the repair of the self. Interpretations, if given too early, interfere with the repair of the self. For any reader who is thinking of purchasing this book, be forewarned that a good deal of technical expertise is required to understand the broad complexity of neurological research. Fortunately, there is a summary at the end of each chapter that serves to cut through much of the technical data. However, this is a book that one does not pick up to read

Effect of imprinting pressure on residual layer thickness in ultraviolet nanoimprint lithography

Since ultraviolet (UV) imprint lithography can be used to fabricate nanosized patterns with extremely high throughput, it is regarded as one of the most promising technologies for nanosized patterning. However, for it to become a mass production technology for the fabrication of nanosized patterns, UV imprint lithography must demonstrate the capability to perform imprinting with a uniform and minimized residual layer. In UV imprint lithography, the thickness of the imprint residual layer is determined by various process parameters, including the initial thickness of the applied resin layer dependent on the spin speed, the viscosity of the resin, the imprint pressure, and the structure of the imprint template and pattern area. Among these process parameters, the thickness of the applied resin layer and the imprint pressure are focused on in this study. In order to transfer patterns with a uniform and minimized residual layer, the imprint resin must be rearranged during imprinting. Thus, the ability to achieve uniform pressing with a high pressure (>15atm) is very important. In this study, a commercially available imprinting system was used. The imprint system is of the pressurized chamber type and uses isotropic pressure to deliver the pressing force uniformly. A commercially available UV curable imprint resin was used.

Towards the rational development of molecularly imprinted polymers: 1H NMR studies on hydrophobicity and ion-pair interactions as driving forces for selectivity

The preparation of molecularly imprinted polymers (MIP) based on non-covalent interactions has become a widely used technique for creating highly specific sorbent materials predominantly used in separation chemistry. A crucial factor in a successful imprinting protocol is the optimisation of the template/functional monomer interaction in the pre-polymerisation mixture, eventually leading to a maximum of high-affinity binding sites in the resulting polymer matrix. In order to develop more efficient preparation technologies for imprinted polymers, two separate pre-polymerisation complexes were investigated by NMR spectroscopic techniques in order to identify the types of interactions occurring in the pre-polymerisation mixture, and their implications for the subsequently formed imprinted polymer. In particular, hydrophobic effects have been followed by NMR spectroscopy and their contribution to the selectivity of the resulting MIP has been investigated. The 2,4-D imprint system is used as an example to fundamentally study whether observations at the pre-polymerisation stage correlate with properties of the finally prepared MIP, and which parameters govern success of an imprinting protocol.