Viable cell handling with high aspect ratio polymer chopstick gripper mounted on a nano precision manipulator

This paper presents the development of an optimized contact technique for viable cell manipulation utilizing a high aspect ratio polymer chopstick gripper. The gripper consists of a 2 μm thick metal heater layer and a 60 μm thick SU-8 layer and is fabricated by a typical UV-LIGA process using SiO₂ as sacrificial layer. The grippers were completely released, de-tethered and assembled as end-effectors on to a nano precision manipulator to perform cell manipulation. Successful pick-and-place of a suspended normal rat kidney cell in phosphate buffered saline solution was demonstrated. The major cell-damage mechanisms associated with contact techniques were identified and alleviated by optimizing the handling force and operating temperature of the polymer gripper. The viability of cells handled with this optimized contact technique was demonstrated by labeling cells with a fluorescent dye. The developed technique will enable incorporation of simple, viable, and repeatable cell handling capabilities into the generic micromanipulators used in the biological laboratories.     

Swelling of SU-8 structure in Ni mold fabrication by UV-LIGA technique

UV-LIGA technique is used to fabricate hot embossing mold of PMMA microfluidic chip. Pre-polished Ni plate serves as electroforming substrate and the micro channel is the only structure to be electroformed in the fabricated mold. The precision of the micro channel strongly depends on the process parameters. Experiments show that the width of micro channel varies with the electroforming time. With the electroforming time of 108, 140 and 160 min, the width of micro channel reduces to 89, 86 and 82% of patterned SU-8 mold respectively, which is caused by swelling of SU-8 in acidic, high temperature electroforming solution. This swelling is the key answer to the slope of the sidewalls of the electroformed structure. This study is beneficial to optimizing microfluidic chip mold design.     

Chip-level integration of RF MEMS on-chip inductors using UV-LIGA technique

This paper presents a chip-level integration of radio-frequency (RF) microelectromechanical systems (MEMS) air-suspended circular spiral on-chip inductors onto MOSIS RF circuit chips of LNA and VCO using a multi-layer UV-LIGA technique including SU-8 UV lithography and copper electroplating. A high frequency simulation package, HFSS, was used to determine the layout of MEMS on-chip inductors with inductance values close to the target inductance values required for the RF circuit chips within the range of 10%. All MEMS on-chip inductors were successfully fabricated using a contrast enhancement method for 50 μm air suspension without any physical deformations. High frequency measurement and modeling of the integrated inductors revealed relatively high quality factors over 10 and self-resonant frequencies more than 15 GHz for a 1.44 nH source inductor and a 3.14 nH drain inductor on low resistivity silicon substrates (0.014 Ω cm). The post-IC integration of RF MEMS on-chip inductors onto RF circuit chips at a chip scale using a multi-layer UV-LIGA technique along with high frequency measurement and modeling demonstrated in this work will open up new avenues with the wider integration feasibility of MEMS on-chip inductors in RF applications for cost-effective prototype applications in small laboratories and businesses.     

Investigations of SU-8 removal from metallic high aspect ratio microstructures with a novel plasma technique

First promising investigations of SU-8 removal experiments with a novel plasma etching technique are presented. The basic idea of this technique is to separate the highly effective generation of chemical radicals (e.g. oxygen radicals) using a traveling wave reactor (TWR) microwave source with water cooled plasma zone from the chemical reaction with the resist polymer. The etching tool operates in a remote and downstream mode with very high radical density allowing precise thermal management of the substrates on the chuck giving controlled process conditions without deviation in temperature, and generally preventing ion bombardment, at least resulting in gentle processing without jeopardizing the integrity of the metal structures. Very good removal of SU-8 with very few residues and very high etching rates up to 10 μm per minute are observed in first experiments which are offering chances to get even more than 20 μm per minute. The etching process is isotropic, and the rate stays stable during the whole removing process even for very thick films of 1 mm and more. First application examples of SU-8 removal are demonstrating the great potential of the presented microwave plasma based technique not only for the cleaning of metallic microparts but also for other more sensitive materials which is demonstrated by SU-8 removal from graphite X-ray mask substrates.     

Design and fabrication of an electrostatically suspended microgyroscope using UV-LIGA technology

A micromachined electrostatically suspended gyroscope, with a wheel-like rotor housed by top stator and bottom stator, using UV-LIGA microfabrication technology, was presented. The designed structure and basic operating principle of the gyroscope are described. The key steps in the fabrication process, such as wet etching of Pyrex glass pits for soldering, and integration of thick nickel structures by removal of SU-8 mold, were considered in detail and well solved. Cr/Pt/photoresist was used as etching mask and the etched pits, in depth of near 30 μm, with aspect ratio (depth to undercutting) of 0.75, were obtained. With metal foundations constructed for consolidation, successful integration of the nickel structures, in thickness of 200 μm, was achieved by successful removal of the SU-8 mold using oleum. After the two stators and the rotor were fabricated separately, they were assembled and soldering bonded to form axial and radial small gaps, hence, the initial prototype of the microgyroscope was realized. The key techniques described in this paper can be applied to fabrication of other micro devices. The metal foundation method, associated with removal of SU-8 mold by oleum, is expected to make SU-8 wider applications in making integrated microstructures with fabricated circuitry on the same chip.     

Submicron polymer structures with X-ray lithography and hot embossing

This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiO _x membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λ _c ≈ 0.4 nm) at a dose of 4 kJ/cm³ using a Si₃N₄ membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.     

Fabrication of chamber for piezo inkjet printhead by SU-8 photolithography technology and bonding method

The chamber is an important part of the inkjet printhead. However, the present fabrication methods of chamber suffer from a low alignment resolution between nozzle plates and piezoelectric structure and residual SU-8 removing problems during chamber fabricating process. In this paper, a SU-8 chamber was fabricated by using ultraviolet (UV) photolithography and SU-8 thermal bonding method. By this method, the infilling problem of the chamber during thermal bonding process was solved, and low alignment resolution problem of conventional UV exposure system during assembly process was avoided. The thickness of the SU-8 nozzle plate was optimized, and the influence of bonding parameters on the deformation of chamber was analyzed. The simulation results show that the optimal thickness of the SU-8 nozzle plate is 40 μm and the optimal bonding parameters are bonding temperature of 50 °C, bonding pressure of 160 kPa and bonding time of 6 min. The tensile test results show the bonding strength of the SU-8 chamber is 2.1 MPa by using the optimized bonding parameter.     

A multipurpose electrothermal microgripper for biological micro-manipulation

A novel electrothermal SU-8 microgripper with a large gripping scope and multipurpose jaws is designed and ANSYS software was used to check its performances. Then, the microgripper is fabricated by a simple UV-LIGA process followed by two performance tests. The static test results show that with only 195 mV, 111.1 mW and 53.7 °C temperature increase at the actuator, a 71.5 μm jaws gap change is obtained. The dynamic response test result shows that driven by different step-type voltages, the response time is about 0.23 s during both closing and opening jaws process. Finally, two micro-manipulation sequences are carried. The experimental results show that due to the large gripping scope and the multipurpose jaws, the microgripper can be used as a multipurpose manipulator for biological micro-manipulations including the manipulation of micro blood vessel and the operation of small size cell, such as cyanobacteria cell.     

Optimizing the performance of a Coriolis-based angular rate sensor applying an analytical approach

This paper focuses on the optimization of a novel angular rate sensor element based on the Coriolis force working principle. The device is resonantly excited and consists of two mechanically coupled oscillators representing the drive and the sense unit. In order to minimize energy losses during operation, the device employs a single point suspension to the substrate. This is especially advantageous when choosing an antiphase torsional motion for the sense mode. Furthermore, thermally-induced stress resulting in undesired drift effects of the device is minimized. The excitation frequency of the electrostatic drive unit was chosen to be in the range from 10 to 15 kHz, according to automotive requirements. The optimization process started with a complete parameterization of the sensor geometry, providing the basis for an analytical model. This was set up via the so-called deformation algorithm, applying the Ritz method. Next, the eigenfrequencies and mode shapes of the sensor were calculated analytically and compared with FEM results. The inclusion of the Coriolis force induced response of the sense unit yielded signal values from the differential capacitive pickup. An advanced hill climbing algorithm was used, varying two geometrical parameters simultaneously in such a way that the difference in drive and sense frequencies was kept at a constant value of 200 Hz. Based on this procedure an optimized design was found with an increase in signal level of about 450% as compared to earlier versions (e.g. from 3 to 17 aF/°/s). In a last step, fabrication related perforation holes which are typical for surface micromachined devices were included in the model. For this configuration, a frequency matching step was performed by FEM calculations. Resulting stiffness values were fed into the analytical model yielding a final output signal of the sensor of 16 aF/°/s.     

A novel method to fabricate complex three-dimensional microstructures

Conventional three-dimensional (3D) microstructures such as arcs or spiralities are generally fabricated using some complicated methods like LIGA or two-photon lithography. In this paper, a new approach of fabricating 3D microstructures is provided. The process is based on UV-LIGA technology yet including a novel reformation method in the post bake procedure. The fabrication process started with coating SU-8 as thick as 500 microns on the silicon substrate, and then it was followed by an exposure with patterned mask under UV light. Subsequently, a force on the exposed SU-8 photo resist was applied in the post-bake process. By adjusting the amount of force, the way in which the force was placed and the exposure dose, we directly fabricated some complicated three-dimensional structures on the SU-8 photo resist after development of the SU-8. We call this microfabrication method as Force-LIGA (F-LIGA). Firstly, orthogonal experiment method conducted to optimize the hot-press process is presented, and then we give some experiment examples using F-LIGA approach and discuss the relationships among the exposure time, pressure and the profile of microstructures. The fabrication process can be used widely in making useful three-dimensional devices.     

Application of the inclined exposure and molding process to fabricate a micro beam-splitter with nanometer roughness

This paper successfully used inclined exposure technology to fabricate a wafer-level 3D micro cube beam splitter with a 45° optical grade surface (~1.4 mm thick). This research also tests the effect of solvent loss percentage of the SU-8 3035 polymer material (85.45 % solvent removal) to optimum surface roughness on the surface roughness of inclined surfaces. The smallest surface roughness achieved in the experiments using SU-8 3035 material with a thickness of 1.4 mm was less than 34 nm (400 × 400 μm area). And the reflective surface roughness of the molding cube beam-splitter is below 2 nm. The optical power of the fabricated cube beam splitter is about 60.55 and 39.44 % for transmission and reflection, respectively. This type of micro cube beam-splitter can be used as a key component in Pico-projectors, Interferometers, bio detection systems, data storage systems, and linear encoder optic systems. And this novel technology also has the characteristics of high throughput and wafer-level assembly.     

High throughput projection UV lithography of high-aspect-ratio thick SU-8 microstructures

This paper presents a method and an ultra-violet (UV) lithography system to fabricate high-aspect-ratio microstructures (HARMS) with good sidewall quality and nice dimension control to meet the requirement for industrial high throughput and high yield production of micro devices. The advantages, equipment, working principle of UV projection scanning exposure, and scanning exposure strategies are introduced first. Following the numerical simulation for the UV projection scanning exposure of thick SU-8 photoresist, experiment results are demonstrated for different exposure strategies. With Continually Changing Focus Projection Scanning (CCFPS), SU-8 microstructures with 860 μm high and 15 μm feature size are demonstrated. For microstructure with 866 μm height, 20 μm width, from the top layer to the bottom layer, the dimension can be controlled in the range of +0.7 to ?1.7 μm; also, the vertical sidewall angle can be controlled inside 90 ± 0.16°. It approves that the CCFPS exposure for HARMS can achieve much straighter and more vertical sidewall compared with UV contact print or UV projection exposure with focusing image on the resist surface or an optimized depth.     

Fabrication of micro sloping structures of SU-8 by substrate penetration lithography

In this paper, three-dimensional (3D) micro sloping structures were fabricated by ordinary mask pattern and diffraction phenomenon. Especially, we fabricated the structures with SU-8 negative photoresist and substrate penetration lithography. In this method, exposure is performed arranging in order of a mask, a substrate and the SU-8 resist. There is a gap that is equal to the thickness of the substrate between resist and mask. In narrow slit of mask, resist is less exposed than usual because of Fraunhofer diffraction. The amount of exposure depends on slit width so that the height of SU-8 resist can be controlled. A 173 μm height of structure was obtained in the case of 27 μm width slit and 24.2 μm height of structure was obtained in the case of 7.4 μm width slit. By using this method, high aspect ratio 3D SU-8 structures with smooth sloping were fabricated in the length of 100–300 μm and in the height of 50–200 μm with rectangular triangle mask pattern. In the same way, there is influence of Fresnel diffraction on edge of aperture so that micro taper structures were fabricated. A lot of taper structures were fabricated by the method to make the surface repellency. The contact angle was achieved more than 160° in this study.     

Design and UV-LIGA microfabrication of an electro-statically actuated power relay

A novel type of micro power relay has been designed and fabricated using UV-LIGA technology. The relay is based on electrostatic actuation and SU-8 was used as a functional material. The unique character of this novel power relay is that other than two SU-8 strips used both as electrical insulators mechanical connectors, all other components are made of metal or alloys. Because UV-LIGA technology has the advantages of broad material selection and the capability of making high aspect ratio microstructures, the technology is best suited for fabricating micro electro mechanical system power relays. A multi-step, multi-layer UV-LIGA process has been successfully developed and a prototype relay has been successfully fabricated.     

Dual-axis tuning fork vibratory gyroscope with anti-phase mode vibration mechanism

In this paper, a novel micro-machined dual-axis tuning fork gyroscope (DTFG) with an anti-phase mechanism is proposed. The proposed anti-phase mechanism could effectively minimize the undesired lateral motion and ensure the anti-phase resonant mode of the two vibrating frames of DTFG. The gyroscope is fabricated by the high-aspect-ratio silicon-on-insulation bulk micromachining process with a device layer thickness of 45 μm. Furthermore, a CMOS drive/readout ASIC Chip, which is fabricated by a 0.25 μm 1P5M standard CMOS process, is integrated with the fabricated DTFG by direct wire-bonding. The experimental characterizations of DTFG demonstrate that the rate sensitivities of z-axis and x-axis sense modes are 2.2132 mV/DPS and 1.8477 mV/DPS respectively and the associated R²-linearity are 0.9995 and 0.9996.     

A Single-Crystal Silicon Symmetrical and Decoupled MEMS Gyroscope on an Insulating Substrate

This paper presents a single-crystal silicon symmetrical and decoupled (SYMDEC) gyroscope implemented using the dissolved wafer microelectromechanical systems (MEMS) process on an insulating substrate. The symmetric structure allows matched resonant frequencies for the drive and sense vibration modes for high-rate sensitivity and low temperature-dependent drift, while the decoupled drive and sense modes prevents unstable operation due to mechanical coupling, achieving low bias-drift. The 12–15-$mu m$-thick single-crystal silicon structural layer with an aspect ratio of about 10 using DRIE patterning provides a high sense capacitance of 130 fF, while the insulating substrate provides a low parasitic capacitance of only 20 fF. A capacitive interface circuit fabricated in a 0.8-$mu m$CMOS process and having a sensitivity of 33 mV/fF is hybrid connected to the gyroscope. Drive and sense mode resonance frequencies of the gyroscope are measured to be 40.65 and 41.25 kHz, respectively, and their measured variations with temperature are$+18.28~ Hz/~^circ C$and$+18.32~ Hz/~^circ C$, respectively, in$-40~^circ C$to$+85~^circ C$temperature range. Initial tests show a rate resolution around 0.56 deg/s with slightly mismatched modes, which reveal that the gyroscope can provide a rate resolution of 0.030 deg/s in 50-Hz bandwidth at atmospheric pressure and 0.017 deg/s in 50-Hz bandwidth at vacuum operation with matched modes.hfillhbox[1195]     

Integration of optical waveguide on pneumatic balloon actuator for flexible scanner in endoscopic imaging diagnosis applications

This paper reports a flexible scanner consisting of a scanning actuator and optical waveguides for medical imaging applications such as endoscopic fluorescence imaging diagnosis. The 0.3-mm-thick and 5-mm-wide functional scanner was designed to be smaller enough than the 10 mm-diameter of channel of endoscope. The proposed device can be used to introduce an excitation light into the abdominal cavity or digestive tract. A pneumatic balloon actuator (PBA) consisting of polydimethylsiloxane (PDMS) is used as the scanning actuator for the scanner in consideration of its small, soft, and safe features. The SU-8 optical waveguides with high refractive index (n_SU-8 = 1.575) are integrated onto the PBA structure made of PDMS with a lower refractive index (n_PDMS = 1.405). Excitation light at a wavelength of 405 nm is transmitted through an optical fiber to the SU-8 waveguides. The outgoing light from the waveguide can be scanned by the bending motion of the PBA. The waveguide functions as a detector as well. Our developed device has successfully scanned, excited, and detected light from fluorescence beads at a wavelength of 540 nm distributed in a pseudo-tissue.     

A wireless powered fully integrated SU-8-based implantable LC transponder

In this work, we report a SU-8-based fully integrated miniaturized inductively powered LC transponder for generic implantable wireless sensor applications. It consists of a 1 mm diameter octagonal spiral inductor and a micro fabricated MIM (metal insulator metal) capacitor. Polyvinylidene Fluoride–Trifluoroethylene (PVDF–TrFE) copolymer is applied as a dielectric material for the capacitor fabrication due to its high dielectric constant. The 1 mm diameter, 154 nH spiral inductor is built on top of the capacitor. The capacitor and the inductor are in parallel connection through SU-8 via holes. SU-8 is used as a packaging material due to its biocompatibility, and also it serves as an insulator between the capacitor and the spiral inductor. The operating frequencies of the LC tanks are decided by the sizes of the capacitors (45 × 45, 55 × 55, 95 × 95 and 100 × 100 μm), and measured operating frequency range is from 385 to 485 MHz. The fabricated LC tanks are held to the power transmitting coil coaxially at distances of 2, 5, 7 and 10 mm, and rectified induced voltage at the LC tank is 8.5 V with 29 dBm input power at a 5 mm distance.     

Fabrication of a freestanding micro mechanical structure using electroplated thick metal with a HAR SU-8 mold

In this thesis, fabrication technology of a freestanding micro mechanical structure using electroplated thick metal with a high-aspect-ratio SU-8 mold was studied. A cost-effective fabrication process using electroplating with the SU-8 mold was developed without expensive equipment and materials such as deep reactive-ion etching (DRIE) or a silicon-on-insulator (SOI) wafer. The process factors and methods for the removal of SU-8 were studied as a key technique of the thick metal micro mechanical structure. A novel method that removes cross-linked SU-8 completely without leaving remnants of the resist or altering the electroplated microstructure was utilized. The experimental data pertaining to the relationship between the geometric features and the parameters of the removal process are summarized. Based on the established SU-8 removal process, an electroplated nickel comb structure with high-aspect-ratio SU-8 mold was fabricated in a cost-effective manner. In addition, a freestanding micro mechanical structure without a sacrificial layer was successfully realized. The in-plane free movements of the released freestanding structure are demonstrated by electromagnetic actuation. This research implies that various types of MEMS devices can be developed at a low-cost with design flexibility.     

Design and fabrication of an electrochemically actuated microvalve

A microfluidic valve based on electrochemical (ECM) actuation was designed, fabricated using UV-LIGA microfabrication technologies. The valve consists of an ECM actuator, polydimethylsiloxane (PDMS) membrane and a micro chamber. The flow channels and chamber are made of cured SU-8 polymer. The hydrogen gas bubbles were generated in the valve microchamber with Pt black electrodes (coated with platinum nanoparticles) and filled with 1 M of NaCl solution. The nano particles coated on the working electrode helps to boost the surface-to-volume ratio of the electrode for faster reversible electrolysis and faster valve operation. To test the functionality of the microvalve, a simple micropump based on ECM principle was also integrated in the system to deliver a microscopic volume of fluid through the valve. The experimental results have showed that an approximately 300 μm deflection of valve membrane was achieved by applying a bias voltage of ?1.5 V across the electrodes. The pressure in the valve chamber was estimated to be about 200 KPa. Experimental results proved that the valve can be easily operated by controlling the electrical signals supplied to the ECM actuators.