One-step Photolithography Research Articles

Tight focusing of laser light using microlens array combined with radially polarised light converter

ABSTRACT A facile method to prepare a liquid crystal polarisation conversion microlens array (LCPC MLA) is reported. One-step photolithography was used to form a microhole array patterned fluoropolymer poly (butenyl vinyl ether) (CYTOP) layer on the front and back side of a thin glass substrate. On the front side, LC droplets are radially aligned in the microholes, and a twisted radial arrangement texture is formed by the integration of another glass substrate coated with a parallel alignment layer to create the LCPC array. The MLA is located at the rear side of the thin glass substrate and each microlens centre is completely aligned with the centres of the LC droplets in the LCPC array. The LCPC array can convert linearly polarised light to radially polarised light and the MLA can focus the radially polarised light to a spot array. This tightly focused array has a high intensity and at each focused spot, a large component of the electric field is in the longitudinal direction. The LCPC MLA has a compact structure, good stability, and highly uniformity, and it shows potential for applications such as material processing, phase modulation, polarisation compensation, and polarisation imaging.

Optical gain based on NaYF4: Er3+, Yb3+ nanoparticles-doped polymer waveguide under convenient LED pumping

The relative optical gains at three near infrared wavelengths (1550 nm, 1064 nm, and 980 nm) were achieved in NaYF4: Er3+, Yb3+ nanoparticle-doped SU-8 waveguides when using two low-cost light-emitting diodes (LEDs) instead of traditional 980 nm semiconductor laser as pump source. The polymer waveguides were fabricated by one-step photolithography process. The fluorescence bands around 1550 nm and 1000 nm wavelengths due to the 4I13/2 → 4I15/2 transition of Er3+ ions and 2F5/2 → 2F7/2 transition of Yb3+ ions were observed under the excitation of 405 nm and 520 nm LEDs. By using the vertical top pumping mode of LEDs, the relative gains of 4.2 dB, 1.7 dB, and 2.1 dB at 1550 nm, 1064 nm, and 980 nm wavelengths were achieved, respectively, on a 10-mm-long waveguide.

Skin-like Ultrasensitive Strain Sensor for Full-Range Detection of Human Health Monitoring.

The development of strain sensors with high sensitivity and stretchability, which can accurately detect different human activities such as subtle physiological signals and large-scale joint motions is essential for disease diagnosis and human health monitoring. However, achieving both high sensitivity and stretchability is still an enormous challenge at the moment, particularly for intrinsically stretchable strain sensors. Herein, utilizing large differences in the conductivity and stretchability of micropatterned Au and SWCNTs, we present an ultrasensitive intrinsically stretchable strain sensor by a one-step photolithography process. Its high sensitivity is inspired from spiders' slit organ and the high stretchability is enlightened from spiders' neural pathway. The skin-like sensor exhibits many superior merits, including ultrahigh sensitivity (gauge factors of 7.1 × 104 to 3.4 × 106), wide detection range (up to 100% strain), excellent durability (1000 cycles), ultralow limit of detection (0.1% strain), fast response (1.3 ms), and minimal feature size (≤100 μm). These fascinating merits allow the strain sensor to precisely detect diverse human activities. This work opens up a feasible path to fabricate highly sensitive and stretchable strain sensors, presenting their promising potential in future personalized healthcare, as electronic skins, and being a portable friendly human-machine interaction system.

Microprobe electrode array with individual interconnects through substrate using silicon through-glass via

This paper presents the fabrication and measurements of a vertical out-of-plane microprobe electrode array with individual interconnects through the substrate using a silicon through-glass via (TGV) with transparent properties. The TGV was fabricated using a low-resistance silicon (LRS) via and the glass reflow process. The microprobe structure was formed by multiple deep reactive ion etching and reactive ion etching processes using one-step photolithography and a single etch mask. The height and pitch of the microprobe are designed to be 90 μm and 210 μm, respectively. Cr and Au conductive layers were deposited and patterned on the silicon microprobe structure. A parylene-C thin film was used as an insulating layer and it was etched only at the tip-end through the self-alignment fabrication process using a thick photoresist to expose the conductive part. Each microprobe electrode was independently connected to the backside of the substrate through the silicon TGV. The single via resistance was measured to be 1.26 ± 0.041 Ω. To verify the electrochemical characteristics of the microprobe electrodes with individual interconnects, the steady-state limiting current through the redox reaction was measured by the cyclic voltammetry method for each electrode. The measured steady-state peak current of the microprobe electrode was compared with the theoretical calculation. Further, the electrode impedance was measured and the equivalent circuit analysis was constructed using the Zview impedance modeling software. Experiments were conducted to measure the impedance of 16 microprobe electrodes, and it was confirmed that the impedance did not exceed 1 MΩ at 1 kHz. Then, primary rat cortical neuron cells (DIV 7) were cultured on the fabricated microprobe electrodes and neural spike signals were successfully measured. Also, the light transmittance experiment was conducted to measure the transparency of the TGV structure fabricated through the glass reflow process.

Fabrication of Magnetically Driven Microvalve Arrays Using a Photosensitive Composite

Microvalves play an important role in fluid control in micro total analysis systems (µTAS). Previous studies have reported complex fabrication processes for making microvalve elements in a channel. Hence, there is a need for a simpler microvalve fabrication method for achieving throughput improvement and cost reduction in µTAS. In this study, we propose a simple fabrication method for a magnetically driven microvalve array using a photosensitive composite. The composite was prepared by mixing a photoresist and magnetic particles of pure iron. The simple fabrication process was performed by using a laminating layer composed of a sacrificial part and the composite in a channel. The microvalve elements were fabricated by one-step photolithography using the processability of the sacrificial layer and composite. Further, we demonstrated the magnetic driving property of the fabricated microvalve array device. Compared to devices containing non-driving microvalves, the flow rate was decreased by 50%, and the pressure difference between the inlet and outlet increased by up to 4 kPa with increase in driving microvalve elements. These results imply that our proposed device could be useful for practical µTAS applications.

Engineering the Charge Transport of Ag Nanocrystals for Highly Accurate, Wearable Temperature Sensors through All-Solution Processes.

All-nanocrystal (NC)-based and all-solution-processed wearable resistance temperature detectors (RTDs) are introduced. The charge transport mechanisms of Ag NC thin films are engineered through various ligand treatments to design high performance RTDs. Highly conductive Ag NC thin films exhibiting metallic transport behavior with high positive temperature coefficients of resistance (TCRs) are achieved through tetrabutylammonium bromide treatment. Ag NC thin films showing hopping transport with high negative TCRs are created through organic ligand treatment. All-solution-based, one-step photolithography techniques that integrate two distinct opposite-sign TCR Ag NC thin films into an ultrathin single device are developed to decouple the mechanical effects such as human motion. The unconventional materials design and strategy enables highly accurate, sensitive, wearable and motion-free RTDs, demonstrated by experiments on moving or curved objects such as human skin, and simulation results based on charge transport analysis. This strategy provides a low cost and simple method to design wearable multifunctional sensors with high sensitivity which could be utilized in various fields such as biointegrated sensors or electronic skin.

Preparation and luminescence properties of patterned SOG/Sr2MgSi2O7:Eu2+, Dy3+ long-persistent luminescence composite thin films by one-step photolithography

In this paper, patterned photosensitive silicon-organic hybrid glass material/Sr2MgSi2O7:Eu2+, Dy3+ (SOG/SMS) long persistent luminescence composite films with lines (widths 50μm and 250μm), dots (50μm) and holes (50μm) patterns on silicon wafer were fabricated by one-step photolithography. SMS particles were first synthesized by sol–gel method and their structure was analyzed by XRD. Patterned SOG/SMS composite films containing 5wt% of SMS particles were then fabricated by one-step photolithography. SEM, fluorescent microscope and spectrofluorophotometer were used for the characterization of the patterned SOG/SMS composite films. It was found that the obtained patterns are of good shapes and order. The fluorescent emission band of the composite films shows a major peak at 468nm. Decay curves of the composite films have a similar tendency with that of the pure SMS particles, except for slightly lower intensity for the former.

An effective passive micromixer with shifted trapezoidal blades using wide Reynolds number range

In this paper, a novel micromixer design, called the shifted trapezoidal blades (STB) micromixer, has been designed and fabricated to provide high mixing efficiency even at low Reynolds number (Re) based on the combination of several mixing principles, including vortices, transversal flows and chaotic advection. Although the STB micromixer has 3D geometrical structure, it can be easily fabricated by one-step photolithography technique, using only one mask and two inclined exposures and an aluminum base with 15° inclines. We conducted intensive numerical study to evaluate the performance of the proposed STB micromixer using COMSOL Multiphysics package with a wide range of Reynolds number from 0.5 to 100. We have fabricated STB micromixers for testing and verification. Both experiment and simulation results demonstrated that the STB micromixer had stable mixing efficiency of 80% or above for Reynolds number values in the range from 0.5 to 100. The most effective mixing performance was achieved at Re=40 in which the STB micromixer had the highest mixing efficiency value (95%) and a moderate pressure drop ΔP=30.27kPa. The proposed STB micromixer provided better mixing performance and smaller footprint compared to the previous micromixers presented in literatures. With a high mixing efficiency and the advantage of being easy to fabricate, the STB micromixer can be utilized in various microfluidic, point-of-care, point-of-need, central automatic diagnosis, and pre-treatment systems including sensor control systems.

Superhydrophobic properties of a hierarchical structure using a silicon micro-tip array decorated with ZnO nanowires

In this study, wetting properties of a hierarchical structure using a silicon micro-tip array covered with ZnO nanowire are characterized, and compared with hierarchical structures composed of micro-pillars for micro-scale roughness. The superhydrophobicity of a surface can be efficiently enhanced by using a micro-tip array, compared with a micro-pillar structure, because a micro-tip structure with high aspect ratio and small apex radius can significantly reduce fractions of liquid droplet area in contact, maintaining the droplet in the regime of the Cassie state. The micro-tip array was simply fabricated by combining anisotropic and isotropic silicon etching processes with one-step photolithography and a single etch mask. The measured height and aspect ratio of the fabricated micro-tip was around 40 μm and 8, respectively, when the center-to-center distance between micro-tips was 30 μm. The maximum CA on the hierarchical surface using the micro-tip array was measured to be 165.0 ± 2.3° with a period of 30 μm, while the hierarchical surface using the micro-pillar array showed the maximum CA of 158.6 ± 1.1° with 20 μm-diameter and 70 μm-gap between micro-pillars. The smallest CAH on the hierarchical micro-tip array was measured to be 5.0 ± 0.3° for the center-to-center distance between micro-tips of 30 μm.

A one-step photolithography method for fabrication of a staggered herringbone mixer using inclined UV lithography

We present a facile method for fabrication of a staggered herringbone mixer using inclined UV lithography, in which the incident UV angle is not perpendicular to the wafer. With this fabrication method, we were able to fabricate staggered herringbone ridges and microchannels simultaneously. As a result, complicated photolithography processes were reduced to a single step. Herein, we describe the fabrication method and performance of the resulting mixers in detail, including the effects of ridge height on mixing. This fabrication technique can be applied directly to the fabrication of other 3D structures on microfluidic chips.

Optical Manipulation of Microparticles in an SU-8/PDMS Hybrid Microfluidic Chip Incorporating a Monolithically Integrated On-Chip Lens Set

An SU-8/PDMS microfluidic chip incorporating a monolithically integrated on-chip lens set for transport and manipulation of microparticles is developed. The components, including the on-chip lens set, the microfluidic channel, and the fiber grooves, are defined in a single layer of SU-8 by one-step photolithography. The design of the on-chip lens set and the fabrication of the microfluidic chip are fully described. The influence of the beam-waist radius on the manipulation performance is theoretically analyzed and experimentally verified for the first time. In the cross-type optofluidic architecture, the evaluation is performed by measuring the particle displacement with different beam-waist radii under different fluid-flow rates. The on-chip lens set is designed to have a specific dimension to achieve the required beam-waist radius. It is revealed that the particle displacement is counter-proportional to the beam-waist radius. An experiment is performed. The results show that the particle displacement is increased by reducing the beam-waist radius. The optical manipulation of microparticles is also demonstrated by using two counter-propagating light beams that are perpendicular to the fluid-flow direction with the beam-waist radius determined by two on-chip lens sets placed on the two sides of the microfluidic channel. The proposed architecture could be used to enhance the performance in particle transport, separation, and concentration.

Planar high-numerical-aperture low-loss focusing reflectors and lenses using subwavelength high contrast gratings

We propose planar, high numerical aperture (NA), low loss, focusing reflectors and lenses using subwavelength high contrast gratings (HCGs). By designing the reflectance and the phase of non-periodic HCGs, both focusing reflectors and lenses can be constructed. Numerical aperture values as high as 0.81 and 0.96 are achieved for a reflector and lens with very low losses of 0.3 and 0.2 dB, respectively. The design algorithm is also shown to be readily extended to a 2D lens. Furthermore, HCG optics can simultaneously focus the reflected and transmitted waves, with important technological implications. HCG focusing optics are defined by one-step photolithography and thus can be readily integrated with many devices including VCSELs, saturable absorbers, telescopes, CCDs and solar cells.

Various shapes of silicon freestanding microfluidic channels and microstructures in one-step lithography

In this research, we have developed and demonstrated a fabrication method for the formation of various shapes of silicon freestanding microfluidic channels and microstructures in one-step photolithography. The fabrication process utilizes the silicon direct wafer bonding with silicon nitride as an intermediate layer, local oxidation of the silicon (LOCOS) process and wet anisotropic etching. Two different types of etchants (non-ionic surfactant (Triton-X-100) added and pure 25 wt% TMAH solutions) are used in series to perform silicon anisotropic etching. Surfactant-added tetramethyl ammonium hydroxide (TMAH) is employed to define the shapes of the structures, while pure TMAH is used to get high undercutting for their fast releasing. The non-ionic surfactant is preferred considering the complementary metal-oxide semiconductor (CMOS) post process issue of wet anisotropic etching. The undercutting at sharp and rounded concave corners, edges aligned along ⟨1 0 0⟩ directions, is measured and analyzed in both pure and surfactant-added TMAH solutions. Mask design issues that must be taken into consideration for the fabrication of desired shape and size structures are also presented.

A SU-8/PDMS Hybrid Microfluidic Device with Integrated Optical Fibers for Online Monitoring of Lactate

A microfluidic device with integrated optical fibres was developed for online monitoring of lactate. The device consists of a SU-8 waveguide, microfluidic channels and grooves for the insertion of optic fibres. It was fabricated by one-step photolithography of SU-8 polymer resist. Different channel widths (50-300 microm) were tested in terms of detection sensitivity. A wide range of flow rates were applied to investigate the influence of flow rate on signal fluctuations. The separation between optical fibre sensor and microfluidic channel and the width of fluidic channel have been optimized to maximize the detection sensitivity. It was revealed that 250 microm of channel width is the optimum light path length for a compromise between detection sensitivity and interference of ambient light. The independence of detection signals on flow rates was demonstrated within the range of flow rate (0.5-5 ml/hr) tested. Compared with conventional lactate detection, the device is proved to have high accuracy, relatively low limit of detection (50 mg/L) and reasonably fast response time (100 sec). The fabrication of device is simple and low cost. The present work has provided some fundamental data for further system optimization to meet specific detection requirements.

グレイスケールマスクを用いたガラスの三次元微細加工技術

A cost-effective gray-scale mask fabrication technique and three dimensional micromaching of photo sensitive glass has been developed. The gray-scale mask was fabricated with wide use computer apparatus, a 1/20 projector and an emulsion glass mask. Multi level structures can be achieved with one-step photolithography and etching process using a gray-scale mask which is modified with gray-scale patterns to vary the energy of UV-light. High aspect ratio complex 3-D structures with different depths of 0.1mm to 1.5mm have been fabricated by use of this technique. These surfaces of fabricated structures can be made smooth by polysilazane coating. The technique can be applied to fabrication of the elements in optical and biomedical applications.

Fabrication of multilevel phase computer-generated hologram elements based on effective medium theory

A conventional method to synthesize diffractive optical elements and computer-generated holograms (CGH's) with high diffraction efficiency relies on an increase of phase levels. To fabricate such a device, one should perform electron-beam (e-beam) lithography with multiple-dose exposures or multiple-step photolithography. Here we describe a one-step method, which is based on the effective medium theory, for the fabrication of a multilevel phase CGH. The phase modulations required in cells of a CGH are constructed by means of dividing these cells into fine (subwavelength) structures. The surface features of these fine structures control their corresponding indices, and their values can be calculated according to the effective medium theory. By proper selection of the fine structures, based on the requirements of the phase modulation of the cells, a CGH with multilevel phases is synthesized when a binary structure is relieved on the dielectric material. Then the CGH can be fabricated by direct e-beam lithography or one-step photolithography through an amplitude mask followed by an ion-etching treatment. The experimental results showed that the reconstructed wave field is in good agreement with that simulated by a computer, indicating the effectiveness of the proposed method.