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X-ray lithography has been first proposed almost 50 years ago, and the related LIGA process around 25 years ago. It is therefore a good time to make an analysis of the technique, with its pros and cons. In this perspective article, we describe X-ray lithography’s latest advancements. First, we report the improvement in the fabrication of the high aspect ratio and high-resolution micro/nanostructures. Then, we present the radiation-assisted synthesis and processing of novel materials for the next generation of functional devices. We finally draw our conclusion on the future prospects of the technique.

As a core component of 2D ultrasound transducers, honeycomb-shaped 1–3 connectivity piezoelectric micropillar arrays have attracted enormous attention due to their unique performance and functionality. In this paper, honeycomb-shaped 1–3 connectivity piezoelectric micropillar arrays with a high aspect-ratio were designed and fabricated by means of deep X-ray lithography and powder injection molding in six steps: preparation of lost mold, powder-binder mixing, injection molding and demolding, removal of binders, and densification of powder. A polymer-based lost mold insert was generated by a synchrotron X-ray exposure and development process. The optimal volumetric ratio between the piezoelectric powder and binders was determined by torque rheology behavior, then they were homogeneously mixed with a twin extruder mixer. To fully fill in the micro-cavities of the lost mold, rheological properties of the mixture were analyzed with a capillary rheometer using different shear rates (50–5000 s−1) and temperatures (140 °C, 150 °C, and 160 °C). After the mixture was completely injected, the lost mold was chemically dissolved in acetone and rinsed in methanol without bending or clustering of the micropillar arrays during evaporation. The binders in the injection molded portion were thermally decomposed using a continuous heating schedule of 200 °C, 390 °C, and 600 °C in argon gas under atmospheric conditions. Finally, the particles in the sample were densified into a coherent, solid mass by eliminating pores at 1300 °C. Based on the proposed micro-manufacturing process, defect-free honeycomb-shaped 1–3 connectivity piezoelectric micropillar arrays with a pattern dimension of 42 μm and aspect-ratio of 5 were successfully produced. [ABSTRACT FROM AUTHOR]

Oblique submicron-scale structures are used in various aspects of research, such as the directional characteristics of dry adhesives and wettability. Although deposition, etching, and lithography techniques are applied to fabricate oblique submicron-scale structures, these approaches have the problem of the controllability or throughput of the structures. Here, we propose a simple X-ray-lithography method, which can control the oblique angle of submicron-scale structures with areas on the centimeter scale. An X-ray mask was fabricated by gold film deposition on slanted structures. Using this mask, oblique ZEP520A photoresist structures with slopes of 20° and 10° and widths of 510 nm and 345 nm were fabricated by oblique X-ray exposure, and the possibility of polydimethylsiloxane (PDMS) molding was also confirmed. In addition, through double exposure with submicron- and micron-scale X-ray masks, dotted-line patterns were produced as an example of multiscale patterning.

SyLMAND, the Synchrotron Laboratory for Micro and Nano Devices, is a recently commissioned microfabrication bend magnet beamline with ancillary cleanroom facilities at the Canadian Light Source. The synchrotron radiation is applied to pattern high‐aspect‐ratio polymer microstructures used in the area of micro‐electro‐mechanical systems (MEMS). SyLMAND particularly focuses on spectral and beam power adjustability and large exposable area formats in an inert gas atmosphere; a rotating‐disk intensity chopper allows for independent beam‐power reduction, while continuous spectral tuning between 1–2 keV and >15 keV photon energies is achieved using a double‐mirror system and low‐atomic‐number filters. Homogeneous exposure of samples up to six inches in diameter is performed in the experimental endstation, a vertically scanning precision stage (scanner) with tilt and rotation capabilities under 100 mbar helium. Commissioning was completed in late 2017, and SyLMAND is currently ramping up its user program, mostly in the areas of RF MEMS, micro‐fluidics/life sciences and micro‐optics. Microfabrication of high‐aspect‐ratio polymer structures using deep X‐ray lithography benefits from independent beam‐power and spectral tuning now available at the Synchrotron Laboratory for Micro and Nano Devices at the Canadian Light Source. [ABSTRACT FROM AUTHOR]

In combination with tapered-trench-etching of Si and SU-8 photoresist, a grayscale mask for deep X-ray lithography was fabricated and passed a 10-times-exposure test. The performance of the X-ray grayscale mask was evaluated using the TERAS synchrotron radiation facility at the National Institute of Advanced Industrial Science and Technology (AIST). Although the SU-8 before photo-curing has been evaluated as a negative-tone photoresist for ultraviolet (UV) and X-ray lithographies, the characteristic of the SU-8 after photo-curing has not been investigated. A polymethyl methacrylate (PMMA) sheet was irradiated by a synchrotron radiation through an X-ray mask, and relationships between the dose energy and exposure depth, and between the dose energy and dimensional transition, were investigated. Using such a technique, the shape of a 26-μm-high Si absorber was transformed into the shape of a PMMA microneedle with a height of 76 μm, and done with a high contrast. Although during the fabrication process of the X-ray mask a 100-μm-pattern-pitch (by design) was enlarged to 120 μm. However, with an increase in an integrated dose energy this number decreased to 99 μm. These results show that the X-ray grayscale mask has many practical applications. In this paper, the author reports on the evaluation results of SU-8 when used as a membrane material for an X-ray mask.

In deep X‐ray lithography (DXRL), synchrotron radiation is applied to pattern polymer microstructures. At the Synchrotron Laboratory for Micro and Nano Devices (SyLMAND), Canadian Light Source, a chromium‐coated grazing‐incidence X‐ray double‐mirror system is applied as a tunable low‐pass filter. In a systematic study, the surface conditions of the two mirrors are analyzed to determine the mirror reflectivity for DXRL process optimization, without the need for spectral analysis or surface probing: PMMA resist foils were homogeneously exposed and developed to determine development rates for mirror angles between 6 mrad and 12 mrad as well as for white light in the absence of the mirrors. Development rates cover almost five orders of magnitude for nominal exposure dose (deposited energy per volume) values of 1 kJ cm−3 to 6 kJ cm−3. The rates vary from case to case, indicating that the actual mirror reflectivity deviates from that of clean chromium assumed for the experiments. Fitting the mirror‐based development rates to the white‐light case as a reference, reflectivity correction factors are identified, and verified by experimental and numerical results of beam calorimetry. The correction factors are related to possible combinations of a varied chromium density, chromium oxidation and a carbon contamination layer. The best fit for all angles is obtained assuming 7.19 g cm−3 nominal chromium density, 0.5 nm roughness for all involved layers, and an oxide layer thickness of 25 nm with a carbon top coat of 50 nm to 100 nm. A simulation tool for DXRL exposure parameters was developed to verify that the development rates for all cases do coincide within a small error margin (achieving a reduction of the observed errors by more than two orders of magnitude) if the identified mirror surface conditions are considered when calculating the exposure dose. [ABSTRACT FROM AUTHOR]

Featured Application: The characterization of negative photoresists before the application on LIGA process can be a key factor to save time, money and enhance the reproducibility of the main optical components fabricated to be used in techniques such as Talbot–Lau Interferometry. The quality of high aspect ratio microstructures fabricated by deep X-ray lithography is highly dependent on the photoresist material used and the process parameters applied. Even with photoresists more suitable to this process, it is common to face defects in the final optical components, such as in case of X-ray gratings. The gratings need to be fabricated with critical dimensions on a sub-micrometer and micrometer scale, with periods of few micrometers and heights of hundreds of micrometers to be used in X-ray imaging techniques such as Talbot–Lau Interferometry. During the fabrication process, these features lead to challenges such as mechanical stability, homogeneity, and defect-free grating patterns. Usually, an epoxy-based negative photoresist is used in X-ray lithography, which needs to account for the shrinkage that takes place during polymer crosslinking in order to avoid defects in the final pattern. Nowadays, photoresist material still lacks certain suitable properties (chemical and mechanical) to fabricate gratings of high quality and with acceptable reproducibility. This work presents the results of TGA, FTIR, and MALDI-TOF analysis made on photoresists commercially available and suitable for X-ray lithography. The photoresists presented different profiles regarding the solvent content and oligomers composition, and in the case of some samples, there were high amounts of non-epoxidized oligomers. [ABSTRACT FROM AUTHOR]

In deep x-ray lithography (DXRL), synchrotron radiation is applied to transfer absorber patterns on an x-ray mask into thick photoresist to generate high quality microstructures. Fabrication of the required x-ray masks is a demanding process sequence and constitutes a bottleneck in DXRL technology. Polymer-based mask membranes offer many benefits during mask fabrication and operation, but usually suffer from large thermal distortions during x-ray exposure. These are due to the low thermal conductivity of most polymers (approximately 0.2W/m K), which results in ineffi- cient heat transfer to the cooled areas around mask and substrate. The power tuning capabilities at the Synchrotron Laboratory for Micro and Nano Devices beamline, Canadian Light Source, however, allow the beam power to be adjusted and consequently limit thermal distortions. In this study, x-ray masks based on 30 lm thick polyimide membranes are studied. Numerical simulations of the thermal and thermoelastic behavior were performed using the software package ANSYS R14.5. The beam power input parameters were calculated with the software LEX-D. For experimental verification, a process to fabricate simple test masks was developed. The polymer membranes were processed on stainless steel sacrificial wafers and were patterned with 80 lm thick nickel absorbers in two macroscopic layouts. Five chromel/alumel (K-type) thermocouples where then bonded to the absorbers to measure the heat distribution. The measurements generally validated the numerical results. The simulated thermal distributions consistently overestimate the experimental values by approximately 4-6 K, which is mainly attributed to uncertainties in the experimental proximity gap settings. The thermal simulation results indicate that the dominant heating mechanism of the resist is conduction: Energy absorbed in the mask absorbers is conducted through the helium gas in the proximity gap to the nonexposed poly(methyl methacrylate) (PMMA) areas and the substrate (cooled to 18 °C). For 500 lm thick PMMA resist, exposed with a synchrotron beam power of 19.6 W, maximum temperatures in the mask are 31.0 and 25.8 °C in the resist below. Maximum single-axis resist deformations in the mask plane amount to 4.12 lm. At 250 lm resist thickness, the observed temperatures are only 25.4 °C in the mask and 22.3 °C in the resist, with maximum mask plane deformations of about 2.3 lm. Integrated over the entire absorber size of 60 mm, these deformations roughly double. Local structure accuracy results were obtained by measuring distortions in a micropatterned polyimide mask. Deformations verify simulation results, vary with the position on the layout, and scale with the incident beam power. At 3.3W incident beam power, typical deformations around 1-1.5 lm and maximum deformations of 2.3 lm were measured in 100 lm thick resist. [ABSTRACT FROM AUTHOR]

In this study, a fabrication method of tapered microstructures with high aspect ratio was proposed by deep X-ray lithography. Tapered microstructures with several hundred micrometers and high aspect ratio are demanded owing to the high applicability in the fields of various microelectromechanical systems (MEMS) such as optical components and microfluidic channels. However, as the pattern and gap size were downsized to smaller micro-scale with higher aspect ratio over 5, microstructures were easily deformed or clustered together due to capillary force during the drying process. Here, we describe a novel manufacturing process of tapered microstructures with high aspect ratio. To selectively block the deep X-ray irradiation, an X-ray mask was prepared via conventional ultraviolet (UV) lithography. A double X-ray exposure process with and without X-ray mask was applied to impose a two-step dose distribution on a photoresist. For the clear removal of the exposed region, the product was developed in the downward direction, which encourages a gravity-induced pulling force as well as a convective transport of the developer. After a drying process with the surface additive, tapered microstructures were successfully fabricated with a pattern size of 130 μm, gap size of 40 μm, and aspect ratio over 7.

The quality of high aspect ratio microstructures fabricated by deep X-ray lithography is highly dependent on the photoresist material used and the process parameters applied. Even with photoresists more suitable to this process, it is common to face defects in the final optical components, such as in case of X-ray gratings. The gratings need to be fabricated with critical dimensions on a sub-micrometer and micrometer scale, with periods of few micrometers and heights of hundreds of micrometers to be used in X-ray imaging techniques such as Talbot–Lau Interferometry. During the fabrication process, these features lead to challenges such as mechanical stability, homogeneity, and defect-free grating patterns. Usually, an epoxy-based negative photoresist is used in X-ray lithography, which needs to account for the shrinkage that takes place during polymer crosslinking in order to avoid defects in the final pattern. Nowadays, photoresist material still lacks certain suitable properties (chemical and mechanical) to fabricate gratings of high quality and with acceptable reproducibility. This work presents the results of TGA, FTIR, and MALDI-TOF analysis made on photoresists commercially available and suitable for X-ray lithography. The photoresists presented different profiles regarding the solvent content and oligomers composition, and in the case of some samples, there were high amounts of non-epoxidized oligomers.

With the recent progress in downsizing and the sophistication of various industrial products, the need for more compact actuators is increasing. Actuators account for the larger percentage of volume and weight of a product compared with other parts and devices. We have proposed fabrication process of spiral micro coils that employs X-ray lithography. This process will be effective for fabricating coils of a high aspect ratio lines. Reducing the size of coil lines and increasing their aspect ratio are expected to reduce the size and increase the output of actuators. Using this process, we formed spiral coil lines that can be used in electromagnetic actuators. X-ray lithography was used to form a high aspect ratio helical structure on the surface of an acrylic resin pipe. As a measure to suppress void generation, which is one of the shortcomings of electroplating processes, the sputtering apparatus and plating equipment were improved, a pretreatment process was additionally provided, and the actual electroplating method was improved. As a result, a void-free metallic deposit could be formed on a thin coil line. At the final step of this research study, we etched the coil line to determine optimal etching conditions.

Coils are used in many electronic devices as inductors in mobile units such as mobile phone, digital cameras, etc. Inductance and quality factor of coils are very important value of the performance. Therefore, the requests for coils are small size, high inductance, low power consumption, etc. However, coils are unsuitable for miniaturization because of its structure. Therefore, we have proposed and developed the microcoils of high aspect ratio with the dipping method and an X-ray lithography technique. In dipping method, centrifugal force and highly viscous photoresist solution were key points to evenly apply resist in the form of thick film on metal bar. The film thickness of resist on bar was achieved about 50 μm after single coating. Using these techniques, we succeeded in creating threaded groove structure with 10 μm lines and spaces on 1 mm brass bar. In this case, the aspect ratio was achieved five. It is very expected the high performance microcoil with high aspect ratio lines could be manufactured in spite of the miniature size.

The X-ray lithography of uses synchrotron radiation is one of the microprocessing structure fabrication technology. In X-ray lithography, precision of the fabricated structure is influenced by precision of the X-ray mask considerably. Conventionally, the X-ray mask was fabricated with UV lithography. However, it is difficult to fabricate the highly precise X-ray mask because of the tapering X-ray absorber. We introduces the ability of Si dry etching technology into UV lithography in order to fabricate untapered, high precision X-ray masks containing rectangular patterns. This new X-ray mask fabrication method uses a high-precision microstructure pattern formed by Si dry etching, thereby fabricating high aspect ratio, narrow line width resist microstructures that cannot be achieved by any conventional technology. An Au for the X-ray absorber is made to the groove of the structure, and it is formed by electroplating. The silicon substrate itself is used as seed layer and the structure is fabricated with the photo resist whose resistance is higher than silicon. It can be expected the gilding growth from only the bottom layer. High-density Au functions sufficiently as an absorber. Au plating was formed only from the base of the structure ditch and could bury Au of thickness 3.5μm in a narrow place of 2.7μm in width well. The fabricated structure using X-ray lithography. Highly-precise rectangular structure could be fabricated.

The nitrogen-implanted titanium nitride-silicon oxide-hafnium oxide-silicon oxide-silicon (hereafter, N-TOHOS) device can be a candidate for total ionizing dose (TID) radiation sensor application. In this study, we mainly focus on N implantation for the improvement of the TID radiation-induced charging effect performance of the N-TOHOS device. The TID radiation-induced charging effect performance of the N-TOHOS device is improved by the implantation of nitrogen in the HfO2 trapping layer. Experimental data show that the radiation-induced charge density of a typical N-TOHOS device is approximately 4-5 times that of a conventional metal-oxide-nitride- oxide-silicon (MONOS) device reported previously. The charge retention reliability after 5 mrad gamma irradiation of the N-TOHOS device with a high implantation dose and a low implantation energy can be improved. The N-TOHOS device described in this study has demonstrated its potential for nonvolatile TID radiation sensing application in the future. [ABSTRACT FROM AUTHOR]

Deep X-ray lithography with synchrotron radiation can be successfully used in fabrication of high-aspect-ratio microstructures (HARMs) micrometers up to several millimetres high. As such microstructures are often mechanically unstable, a supporting layer incorporated into a micropattern, was developed and studied. [ABSTRACT FROM AUTHOR]

A technique of casting of thick pre-polymer layers was developed based on the proposed model of diluent evaporation. For the first time, microstructures with 7 mm height and up to 18 microns wide (an aspect ratio of up to 389) were manufactured by means of ultra deep X-ray lithography in a cured pre-polymer that can be functionalized. The microstructures were characterized. The difference in the size of patterned microstructures and their initial size on the X-ray mask decreases to 400 nm with the lessening lateral dimension of the microstructures from 1500 to 18 μm. The sidewall roughness also decreases to 20 nm. [ABSTRACT FROM AUTHOR]

The metal tantalum has many varied uses including in microelectronics (especially in capacitors) as thin films, in medical applications as an implant material or for surgical instruments, in X-ray lithography for masks, and in high-temperature structural applications. Ta is particularly useful because it is relatively ductile, refractory in nature, and does not readily react with corrosive materials. The body-centered cubic (bcc) crystal structure of pure Ta, also known as the α-phase, is the most commonly observed, but Ta is also known to exist in two other allotropes, one tetragonal and the other (much less-well-known) face-centered cubic (fcc). The tetragonal form (β-Ta) has been produced by various deposition techniques and often occurs mixed with the α-phase; the fcc phase has only previously been reported in thin films deposited by thermal evaporation. There have been other reports of 'bcc metals' such as V and Fe existing with an fcc crystal structure when the metal is deposited as a thin film. In the present study, fcc Ta with a = 0.43 nm has been observed using transmission electron microscopy in bulk samples of Ta that have been subjected to quasi-static tensile deformation that was so large as to cause fracture of the material. The fcc phase has a relatively small grain size but appears to be stable at room temperature. It is also shown that relatively large grains (10-20 nm in diameter) of Ta can also exist with an hcp structure with a = 0.304 nm and c = 0.494 nm. [ABSTRACT FROM AUTHOR]

Results are reported of direct-write X-ray lithography using a hard X-ray beam focused by a Fresnel zone plate with an outermost zone width of 40 nm. An X-ray beam at 7.5 keV focused to a nano-spot was employed to write arbitrary patterns on a photoresist thin film with a resolution better than 25 nm. The resulting pattern dimension depended significantly on the kind of underlying substrate, which was attributed to the lateral spread of electrons generated during X-ray irradiation. The proximity effect originated from the diffuse scattering near the focus and electron blur was also observed, which led to an increase in pattern dimension. Since focusing hard X-rays to below a 10 nm spot is currently available, the direct-write hard X-ray lithography developed in this work has the potential to be a promising future lithographic method. [ABSTRACT FROM AUTHOR]

A drug delivery system is used for targeting drugs to specific cells. Various drug carriers, that also reduce the side effects of unbound drugs, have been introduced and commercialized in the pharmaceutical field. Among them, synthetic biodegradable polymers have received much attention attributed to their low toxicity, controllable biodegradation rates, manufacturability, and low costs. This paper reviews the salient characteristics of biodegradable polymers as drug carriers and their microfabrication methods. The reviewed microfabrication methods include laser micromachining, rapid prototyping, replication, emulsification, microfluidic fabrication, and X-ray-lithography-based methods. For these microfabrication methods, critical dimensions, feature variety, solvent compatibility, production throughput, and tooling requirements are also summarized. [ABSTRACT FROM AUTHOR]

The morphological change of silver nano-particles (AgNPs) exposed to an intense synchrotron X-ray beam was investigated for the purpose of direct nano-scale patterning of metal thin films. AgNPs irradiated by hard X-rays in oxygen ambient were oxidized and migrated out of the illuminated region. The observed X-ray induced oxidation was utilized to fabricate nano-scale metal line patterns using sectioned WSi2/Si multilayers as masks. Lines with a width as small as 21 nm were successfully fabricated on Ag films on silicon nitride. Au/Ag nano-lines were also fabricated using the proposed method. [ABSTRACT FROM AUTHOR]

Arrays of 11.2-16.6 μm holes were patterned on 50 μm thick SU-8 photoresist layers by using synchrotron X-ray lithography. After the resist development, the chemically stable and mechanically hardened SU-8 templates with varying hole sizes were used as substrates for RF sputtering of 1.5 μm-thick cobalt (Co). By comparing hysteresis loops from inplane and out-of-plane magnetisation, the Co film on patterned substrate with average hole size of 16.6 μm was more isotropic than in the case of 15.3 and 11.2 μm. Both magnetic squareness and coercive field were at the minimum when the holes were smallest. After the removal of Co on SU-8 surfaces, the remaining Co deposits in the holes exhibited smaller squareness and anisotropy. On the other hand, the enhanced coercive field was increased with a reduction in diameter of patterned holes. [ABSTRACT FROM AUTHOR]

X-ray lenses are fabricated in polymethyl methacrylate using deep X-ray lithography beamline of Indus-2. The focussing performance of these lenses is evaluated using Indus-2 and Diamond Light Source Ltd. The process steps for the fabrication of X-ray lenses and microfocussing at 10 keV at moderate and low emittance sources are compared. [ABSTRACT FROM AUTHOR]

The X-ray lithography beamline on Indus-2 is now operational, with two modes of operation. With a pair of X-ray mirrors it is possible to tune the energy spectrum between 1 and 20 keV with a controlled spectral bandwidth. In its 'no optics' mode, hard X-rays up to 40 keVare available. Features and performance of the beamline are presented along with some example structures. Structures fabricated include honeycomb structures in PMMA using a stainless steel stencil mask and a compound refractive X-ray lens using a polyimide-gold mask in SU-8. [ABSTRACT FROM AUTHOR]

In this study, a microfluidic chip prototype having circular microchannels was replicated by microinjection molding process, employing a modularized and sectioned micromold system (MSMS). In the viewpoint of microfluidic manipulation, a microchannel with circular cross-section shows several advantages over a conventional rectangular and/or square microchannel. To achieve a mass production of the microchannels with circular or round cross-sections, the micromold was designed and fabricated based on the concept of MSMS. It consisted of several micromold modules, each having half-circular cross-sectional microstructures on its one-side surface. The modules were precisely manufactured by a deep X-ray lithography using a synchrotron radiation and a subsequent nickel electroforming process. Then, the MSMS for a microinjection molding process was constructed by assembling the nickel modules. After the molding of plastic plate with open microchannels of half-circular cross-section, a thermal bonding of microinjection-molded plates was carried out to produce the microfluidic chip prototype including the circular microchannels. Observation of the surface quality, measurement of cross-sectional profiles, and microfluidic test were carried out, which verified the usefulness of the present fabrication process. POLYM. ENG. SCI., 54:42-50, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: Scaffolds with a high surface-area-to-volume ratio (SA:V) are advantageous with regard to the attachment and proliferation of cells in the field of tissue engineering. This paper reports on the development of novel melt-spun fibers with a high SA:V, which enhanced the surface effects of a fiber-based scaffold while maintaining its mechanical strength. The cross-section of the fibers was altered to a non-circular shape, producing a higher SA:V for a similar cross-sectional area. To obtain fibers with non-circular cross-sectional shape, or shaped fibers, three different types of metal spinnerets were fabricated for the melt-spinning process, each with circular, triangular or cruciform capillaries, using deep X-ray lithography followed by nickel electroforming. Using these spinnerets, circular and shaped fibers were manufactured with biodegradable polyester, polycaprolactone. The SA:V increase in the shaped fibers was experimentally investigated under different processing conditions. Tensile tests on the fibers and indentation tests on the woven fiber scaffolds were performed. The tested fibers and scaffolds exhibited similar mechanical characteristics, due to the similar cross-sectional area of the fibers. The degradation of the shaped fibers was notably faster than that of circular fibers, because of the enlarged surface area of the shaped fibers. The woven scaffolds composed of the shaped fibers significantly increased the proliferation of human osteosarcoma MG63 cells. This approach to increase the SA:V in shaped fibers could be useful for the fabrication of programmable, biodegradable fiber-based scaffolds in tissue engineering. [Copyright &y& Elsevier]

Scanning probe instruments have expanded beyond their traditional role as imaging or "reading" tools and are now routinely used for "writing." Although a variety of scanning probe lithography techniques are available, each one imposes different requirements on the types of probes that must be used. Additionally, throughput is a major concern for serial writing techniques, so for a scanning probe lithography technique to become widely applied, there needs to be a reasonable path toward a scalable architecture. Here, we use a multilayer graphene coating method to create multifunctional massively parallel probe arrays that have wear-resistant tips of uncompromised sharpness and high electrical and thermal conductivities. The optical transparency and mechanical flexibility of graphene allow this procedure to be used for coating exceptionally large, cantilever-free arrays that can pattern with electrochemical desorption and thermal, in addition to conventional, dip-pen nanolithography. [ABSTRACT FROM AUTHOR]

The first microbeam synchrotron X-ray fluorescence (µ-SXRF) beamline using continuous synchrotron radiation from Siam Photon Source has been constructed and commissioned as of August 2011. Utilizing an X-ray capillary half-lens allows synchrotron radiation from a 1.4 T bending magnet of the 1.2 GeV electron storage ring to be focused from a few millimeters-sized beam to a micrometer-sized beam. This beamline was originally designed for deep X-ray lithography (DXL) and was one of the first two operational beamlines at this facility. A modification has been carried out to the beamline in order to additionally enable µ-SXRF and synchrotron X-ray powder diffraction (SXPD). Modifications included the installation of a new chamber housing a Si(111) crystal to extract 8 keV synchrotron radiation from the white X-ray beam (for SXPD), a fixed aperture and three gate valves. Two end-stations incorporating optics and detectors for µ-SXRF and SXPD have then been installed immediately upstream of the DXL station, with the three techniques sharing available beam time. The µ-SXRF station utilizes a polycapillary half-lens for X-ray focusing. This optic focuses X-ray white beam from 5 mm × 2 mm (H × V) at the entrance of the lens down to a diameter of 100 µm FWHM measured at a sample position 22 mm (lens focal point) downstream of the lens exit. The end-station also incorporates an XYZ motorized sample holder with 25 mm travel per axis, a 5× ZEISS microscope objective with 5 mm × 5 mm field of view coupled to a CCD camera looking to the sample, and an AMPTEK single-element Si (PIN) solid-state detector for fluorescence detection. A graphic user interface data acquisition program using the LabVIEW platform has also been developed in-house to generate a series of single-column data which are compatible with available XRF data-processing software. Finally, to test the performance of the µ-SXRF beamline, an elemental surface profile has been obtained for a piece of ancient pottery from the Ban Chiang archaeological site, a UNESCO heritage site. It was found that the newly constructed µ-SXRF technique was able to clearly distinguish the distribution of different elements on the specimen. [ABSTRACT FROM AUTHOR]

A positive tone resist for UV and X-ray lithography synthesized starting from an organically modified silicon alkoxide, bis(triethoxysilyl)benzene, through the sol-gel method, either in basic or in acid catalysis, is presented. Being directly photo-processable, the sol-gel system combines the opportunity to avoid the use of a sacrificial layer in the fabrication process, with the possibility to fit electro-optical and structural properties of the final device material to specific requirements. In addition, the positive tone behaviour allows to preserve the organic functionality of the system after irradiation. A study of the optical and structural modifications induced on the resist by irradiation has been carried out by FT-IR spectroscopy, UV-vis spectroscopy and spectroscopic ellipsometry. An interpretation of the mechanisms leading to exposed cross-linked film development is given. Experiments have demonstrated the possibility of obtaining structures on films with lateral dimensions spanning from the micron scale up to less than a hundred nm, opening the way to a possible exploitation of such positive tone functional system in the field of miniaturized sensors. [ABSTRACT FROM AUTHOR]

The article presents a study on the synchrotron X-ray optics code, SHADOW3. It mentions that the restructured X-ray tracing code follows an improved computer engineering standards and application programming interface (API). It notes that the code is used in several applications including mirror optics, X-ray lithography and variable-line spacing.

The article examines the effect induced by exposure of sol-gel thin films on hard X-rays generated by synchrotron radiation. It evaluates the effects of the radiation by fourier transform infrared spectroscopy, spectroscopic ellipsometry and atomic force microscopy. It also gives a better insight into the basic chemical-physical effects of hard X-ray interaction with oxides and hybrid organic-inorganic sol-gel materials.

The article investigates the focused hard X-ray microbeams for use in X-ray nanolithography. It confirms that the focused X-ray beam retains a high degree of collimation owing to the long focal length of the Fresnel zone plate (FZP), which facilitates hard X-ray nanoscale lithography. It also discusses the estimation of the focusing efficiency from the integrated intensity ratio between the focused beam and the unfocused direct beam.

Thermal deformations of the x-ray mask were simulated in the case of a synchrotron x-ray spectrum which was modified to decrease the incident power of synchrotron radiation (leaving the electron beam conditions at the storage ring unaltered). Effective methods are (1) the attenuation of the hard component with a grazing incidence x-ray mirror in combination with absorption filters or (2) the use of a central beamstop to suppress the center part of the synchrotron radiation beam where its harder component is concentrated. With a central beamstop combined with absorbing filters, the spectral bandwidth of the x-ray photons absorbed in a resist layer becomes narrower, which decreases the absorbed radiation power. The maximum of the spectral distribution remains at the same position for both variants by using an optimized filter combination. Also the thermal deviation of the microstructures is decreased below 3 μm in the case of an inclined exposure, and the reproducibility of the positioning precision has been demonstrated for tilted deep x-ray lithography with the necessary top and bottom dose ratios for thick SU-8 resist layers. [ABSTRACT FROM AUTHOR]

Compact reactive lumped-element circuits fabricated using a single thick metal-layer deep X-ray lithography process are presented. Vertically oriented capacitive features are combined with inductive features in > 0.25-mm-thick metal layers to realize lumped-element filter and coupler microstructures operating at up to 12 GHz. Measurements for separate thick metal reactive structures are also presented, including variable capacitors and single-turn square loop inductors. Devices feature impressive vertical structure, including a 77:1 aspect ratio, 1.3-\mum-wide cantilever gap structure in 100-\mum-thick photoresist. A 0.6-pF capacitor has Q-factors of 95 at 5.6 GHz and 214 at 3.5 GHz, and a structurally compatible 1.2-nH loop inductor has a Q-factor of 47 at 6.8 GHz and a self-resonant frequency of 18.8 GHz. Together, these types of devices could form the building blocks for various integrated reactive lumped-element-based circuits. [ABSTRACT FROM PUBLISHER]

Direct-write soft x-ray lithography with an ∼50 nm diameter beam is used to pattern features in hydrogen silsesquioxane (HSQ) thin films. Scanning transmission x-ray microscopy of the undeveloped patterns (latent patterns) at the oxygen K-edge reveals a two-stage cross-linking mechanism. Oxygen and silicon near edge x-ray absorption fine structure spectra of latent patterns show an increase in oxygen content and no change in silicon content within exposed regions. A dose and thickness dependent spatial spread of the cross-linking reaction beyond the exposure boundaries is observed and quantified in detail. Strong area-dependent exposure sensitivity (attributed to cross-linking beyond the exposed region) is observed in latent patterns. A lateral spread in the cross-linking of >70 nm (full width at half maximum) is observed on both sides of the lines created with 580 eV x-rays (λ=2.14 nm) in 330±50 nm thick HSQ films at low dose (0.6±0.3 MGy, 27±12 mJ/cm2) (1 MGy=106 J/kg absorbed energy). At a higher dose (111±29 MGy, 5143±1027 mJ/cm2), this spread increased to 150 nm. Preliminary results indicate that latent line widths increased with increasing delay between film spin-coating and exposure. Sharper lines are observed after room temperature development of the latent HSQ patterns in NaOH/NaCl solution (onset dose of 3.9±1.0 MGy, 181±36 mJ/cm2) due to the removal of material below a critical degree of cross-linking. Given the short range of low energy secondary electrons in condensed media (<10 nm at ≤580 eV), the observed spread is likely due to the propagation of reactive ions or radicals beyond the exposed regions. [ABSTRACT FROM AUTHOR]

A Fresnel zone plate (FZP) with 35nm outermost zone width has been fabricated and tested in the hard X-ray region. The FZP was made by electron beam lithography and reactive ion etching technique. The performance test of the FZP was carried out by measuring the focused beam profile for coherent hard X-ray beam at the beamline 20XU of SPring-8. The full width at half maximum of the focused beam profile measured by knife-edge scan method is 34.9 ± 2.7 nm, that agrees well with the theoretical value of diffraction-limited resolution. Applications to scanning microscopy were also carried out. [ABSTRACT FROM AUTHOR]

This paper introduces a micromachined thick single-metal-layer high aspect-ratio coplanar waveguide (CPW) wideband bandpass filter with compact unit cells based on the electromagnetic bandgap (EBG) concept. The filter is miniaturized as a result of using the EBG concept in design, and also by realizing high aspect-ratio structures with polymer-based deep X-ray lithography fabrication. Cascaded unit cells in the EBG model consist of capacitive and inductive parallel periodically loaded transmission lines, which determine the filter bandwidth. Compact unit cells are realized by using high aspect-ratio CPW stepped-impedance resonators. The main advantage of this approach is that the high aspect-ratio CPW structures make short unit cells practically realizable, resulting in a compact filter structure. A bandpass filter with 47% bandwidth is designed and fabricated using deep X-ray lithography, and the performance and physical size is compared to a conventional quarter-wave- length-based admittance inverter filter. [ABSTRACT FROM AUTHOR]

Abstract: Micro-injection molding is an important fabrication process for polymer plastics with micro-features. In micro-injection molding of products with microstructures, the ability for the polymer melt to flow into the microstructures is a crucial factor for successful molding. An analytical model in micro-injection molding is constructed in this research. It has been reported that most of the filling in microstructure is done during the packing pressure. In this analytical model, the temperature of the polymer melt near the entrance of the microstructure at the end of mold filling is estimated first. With the temperature, we can calculate the injection distance into the microstructures of the mold insert during the packing stage. The model is compared with experimental results, and shows the feasibility. The experiment uses the LIGA-like lithography process to define the micro-feature and a micro-electroforming method to form the mold insert with the replicated micro-feature. The injection distance into the microstructures predicted by this analytical model shows reasonable result as compared to the experimental measurement. [Copyright &y& Elsevier]

Abstract: The purpose of this paper was to investigate the wearing and grinding characteristics of the micro-abrasive pellet tools with 4–6μm diamond particles fabricated by a LIGA-like process that has micro-lithography with photoresist mold and nickel/diamond composite electroforming. The results showed that when the micro-pellet tool containing partial resist joint with a root on the substrate was designed and fabricated, the tool against alumina sandpaper in wear test showed lesser amount of micro-pulled-out pellets than the tools with flat joint type, which displayed the tool to have better adhesion strength. In addition, when the micro-diamond tools were used to grind silicon wafers, the surface appearance of wafers showed ductile behavior. The surface roughness of wafers ground with increased pellet tool rotation speed became better and R a=0.05μm was achieved. [Copyright &y& Elsevier]

Abstract: Selective exposures of poly(ethylene-alt-tetrafluoroethylene) (ETFE) films with hard X-rays through high aspect ratio Ni-masks were performed at the LIGA3 beamline of the “Angström Quelle Karlsruhe” (ANKA) to create patterns of radicals used as initiators for the grafting of styrene into the bulk of the ETFE films. Grafted films were then sulfonated to obtain proton-conducting membranes. The structure definition, as investigated by scanning electron microscopy (SEM), showed a perfect discrimination between exposed and shaded areas through all the film thickness. Structuring results in a more homogeneous appearance of the membrane without affecting the degree of grafting and proton conductivity in the grafted areas. In fuel cell tests the structured membranes showed slightly lower performance due to 10% lower active area, but had a significantly higher lifetime. [Copyright &y& Elsevier]

The article evaluates the effectiveness of a microfluidic filter for biochemical reactions by performing a sandwich enzyme-linked immunosorbent assay (ELISA) of mouse immunoglobulin G IgG). According to the authors, microfluidic filters were fabricated by deep X-ray lithography using synchrotron radiation. They add that mouse IgG could be quantitatively detected in the range of 0-100 mg/ml, showing the applicability of vertical microfluidic operation to the immunoassay.

We developed an enzyme-linked immunosorbent assay for an endocrine disrupter, nonylphenol, using a microreactor composed of two reaction vessels stacked vertically through a microfluid filter. The filters constructed by deep X-ray lithography possessed 2100 through-bores (ϕ40×200 μm) in polymethylmethacrylate sheets (ϕ3 mm), which are appropriate for biochemical reactions. Through the optimization of the immunoassay, nonylphenol was quantitatively detected at the range of 0.1–10 ng/ml. [Copyright &y& Elsevier]

Hot embossing is one of the main process techniques for polymer microfabrication, which helps X-ray lithography, electroplating, and molding (LIGA) to achieve low-cost mass production. Most problems in polymer micromolding are caused by demolding, especially for hot embossing of high-aspect-ratio microstructures. The demolding forces are related to the sidewall roughness of the mold insert, the interfacial adhesion, and the thermal shrinkage stress between the mold insert and the polymer. The incorporation of polytetrafluoroethylene (PTFE) particles into a nickel matrix can have the properties such as antiadhesiveness, low friction, good wear, etc. To minimize the demolding forces and to obtain high-quality polymer replicas, a Ni-PTFE composite microelectroforming has been developed, and the hot embossing process using Ni and Ni-PTFE LIGA mold inserts has been well studied in this paper. The morphologies, sidewall roughness, and friction coefficient have been explored in the fabricated Ni-PTFE LIGA mold insert. Finally, the comparison of embossed microstructures with various aspect ratios and the comparison of the embossing lifetimes of mold inserts have been carried out between Ni and Ni-PTFE mold inserts, which show a better performance of the Ni-PTFE mold and its potential applications. [ABSTRACT FROM AUTHOR]

High aspect ratio nickel microfluidic columns were fabricated using the LGA technique. The 2-m-long 50-µm-wide high aspect ratio columns will be the separation component of a handheld gas chromatograph device for detecting semivolatile and volatile compounds. As a first step, 600-µm-deep electrodeposited nickel columns were fabricated. The serpentine columns were sealed and pressure-flow rate characteristics compared with the theoretical values. The response of the sealed columns was studied by running methane gas plugs through uncoated columns with a flame ionization detector at the exit. Negligible flow-induced dispersion was observed in the sealed metal columns. Unretained peak widths of ~15 ms were measured, and the experimental pressure and flow rate distributions matched those predicted by established analytical models within ±2.5%. Columns were coated with OV-1 stationary phase using static coating methods. A mixture of four hydrocarbons C6, C8, C10, and C12 was separated in a coated 50 µm by 600 µm by 0.5 m column in less than 2 s at 70 °C. [ABSTRACT FROM AUTHOR]