Sommawan Khumpuang

Plain-pattern to cross-section transfer (PCT) technique for deep x-ray lithography and applications

This paper presents a novel fabrication method for three-dimensional microstructures using deep x-ray lithography. The microstructures were fabricated including sloped sidewalls and curved surfaces by exposing a synchrotron radiation beam to a moving x-ray resist. The technique, the so-called plain-pattern to cross-section transfer (PCT) technique, has been developed as an extension to conventional 2.5-dimension lithography. The fabrication of PMMA microstructures has been demonstrated with surfaces as smooth as 10 nm of RMS roughness. Various applications, e.g., micro-optic, bio-medical and some components of MEMS devices have been realized. Two microstructures have been given as examples: microlens arrays and microneedle arrays. The resulting arrays can be employed to fabricate moulds by electro-deposition for further batch-processing using the LIGA process.

Design and Fabrication of 1D and 2D Micro Scanners Actuated by Double Layered Lead Zirconate Titanate (PZT) Bimorph Beams

Micro scanners including 1D scanner beams and 2D scanning micromirrors are designed and fabricated. In order to yield large bending force, the sol-gel derived double layered lead zirconate titanate (PZT) structures are developed to be the actuator components. In our developed fabrication process, the use of thermal treatment and the addition of one platinium/titanium film played an important role to yield the well-crystallized perovskite phase and decrease the residual strss of total cantilever structures successfully. In the case of 1D scanner beams with the size of 750×230 µm2, the optical scanning angle was 41.2 deg with respect to actuation with AC 5 V at 2706 Hz. Under the applied bias of 10 V, the bimorph beam bended upward and the deflection angle of 34.3 deg was measured. A 2D scanning micromirror supported by four suspended double layered PZT actuators was designed to rotate around two orthogonal axes by the operation at different resonant frequencies. While resonating with AC 7.5 V at 3750 Hz and 5350 Hz, the maximum scanning area of 24°×26° was obtained.

Design and fabrication of a coupled microneedle array and insertion guide array for safe penetration through skin

Ordinary flat hollow tip, microneedles have been designed and fabricated for biomedical MEMS applications. With the facilitation of an insertion guide, the needles can be pushed down through the viable-epidermis with less bending. The microneedle array has the ability of integration with microfluidic devices since the needles are hollow so that the liquid can flow through the holes. 100 microneedles are contained in a 5 /spl times/ 5 mm/sup 2/ array chip and the same size of another array chip contains 100 insertion guide holes. A standard silicon micromachining process was employed to fabricate both arrays. The shape of microneedle is as simple as a tube so that the designed theories and simulations can be more precise than the complicated shape. The result of testing shows that there was no microneedle broken during the penetration to the skin via the guiding holes. The finite-element analyses of stresses and deformed shapes have been carried out with the explanation of deformed shape and stress occurred in the needle structure.

Microneedle fabrication using the plane pattern to cross-section transfer method

In this paper, microneedle fabrication using the PCT (plane pattern to cross-section transfer) method is summarized. Three types of microneedle array have been developed: the single-tip, quadruplet, and hollow microneedle arrays. A brief introduction to the fabrication process using PCT and detailed design concepts for optimizing the fabrication steps for shape improvement of the three types of microneedle are provided. The microneedle structures have controllable angled sidewalls, exhibiting an extraordinarily geometrical level of accuracy compared to what is achieved using other existing fabrication methods based on deep x-ray lithography by synchrotron radiation. Furthermore, the improvements reported in this work as compared to the results from the existing methods are: sharper tips for the single-tip microneedles, strength improvement for the quadruplet microneedles, and cost reduction for the hollow microneedles. Each type of microneedle was designed to serve a different biomedical need.

Development of Bio-chemical Sensor System Integrated with Blood Extraction Device

The fabrication of a blood extraction device integrated with an electrolyte-monitoring system is reported in this paper. The device has advantages in precise controlled dosage of blood extracted including the slightly damaged blood vessels and nervous system. Main components of the portable system are; the blood extraction device and electrolyte-monitoring system. The monitoring system consists of ISFET (ion selective field effect transistor) for measuring the concentration level of minerals in blood. In this work, the authors measured the level of 3 ions; Na+, K+ and Cl-. The 100 hollow-microneedles fabricated by synchrotron radiation deep X-ray lithography through PCT (plane-pattern to cross-section transfer) technique were revealed in 5times5 mm2 area. The total size of the blood extraction device is 2times2times2 cm3. The package is made from an acrylic socket consisting of microneedle array block, ion-sensors block, blood and reference reservoirs. ISFET was connected to an electrical circuit for monitoring the potential different.

Portable blood extraction device integrated with biomedical monitoring system

Painless and portable blood extraction device has been immersed in the world of miniaturization on bio-medical research particularly in manufacturing point-of-care systems. The fabrication of a blood extraction device integrated with an electrolyte-monitoring system is reported in this paper. The device has advantages in precise controlled dosage of blood extracted including the slightly damaged blood vessels and nervous system. The in-house blood diagnostic will become simple for the patients. Main components of the portable system are; the blood extraction device and electrolyte-monitoring system. The monitoring system consists of ISFET (Ion Selective Field Effect Transistor) for measuring the concentration level of minerals in blood. In this work, we measured the level of 3 ions; Na+, K+ and Cl-. The mentioned ions are frequently required the measurement since their concentration levels in the blood can indicate whether the kidney, pancreas, liver or heart is being malfunction. The fabrication of the whole system and experimentation on each ISM (Ion Sensitive Membrane) will be provided. Taking the advantages of LIGA technology, the 100 hollow microneedles fabricated by Synchrotron Radiation deep X-ray lithography through PCT (Plane-pattern to Cross-section Transfer) technique have been consisted in 5x5 mm2 area. The microneedle is 300 μm in base-diameter, 500 μm-pitch, 800 μm-height and 50 μm hole-diameter. The total size of the blood extraction device is 2x2x2 cm3. The package is made from a plastic socket including slots for inserting microneedle array and ISFET connecting to an electrical circuit for the monitoring. Through the dimensional design for simply handling and selection of disposable material, the patients can self-evaluate the critical level of the body minerals in anywhere and anytime.

Microneedle array and insertion guide array for safe use of biomedical applications

A new method of using silicon microneedle array in Bio-Medical applications is introduced in this work. The hollow microneedle array with the facilitation of an insertion guide array have been designed and fabricated. The needles can be pushed down through the second layer of human skin with less-bending. The tip of microneedle will be led by the insertion guide to pierce the skin perpendicularly. The silicon bulk micromachining technique using an inductively coupled plasma (ICP) etcher has been employed to fabricate the microneedle array and the insertion guide array. The array chips are 5x5 mm2 for both structures. The needle array chip contains 100 microneedles with 100μm and 30 μm of the outer diameter and the hole diameter respectively. The guide array chip is 100 μm-thick and contains 100 guiding holes with 120 μm diameter. A buckling test of microneedle shows the result that there was no microneedle broken during the test via the guiding holes. Contrary, there were several microneedles broken during the penetration without the facilitation of the guide. The finite-element analysis also supports the test result. After the insertion with guiding has been tested and proved, a wet etching process was added in order to obtain sharper tips.

Novel pressure-gradient driven component for blood extraction

Portable blood analysis devices are usually appreciable for applications in blood diagnostic system. We have designed and fabricated a low-cost and simple deal blood extraction device for a biomedical analysis. The device mainly composes of blood extraction tool and a functional bio-chemical analyzing element. In this work, we report the fabrication and pressure-gradient testing results of the blood extraction tool which consists of painless microneedle array and pressure-gradient tank. Microneedle array was fabricated by X-ray lithography using PCT (Plane-pattern to Cross-section Transfer) technique. The idea of our extraction device was simple but capability which is just to hold a sufficient pressure gradient between the tank and blood vessel. The device can draw the volume of blood up to 237 μl. The device was made of low-cost and disposable materials since it is expected to be used for single blood analysis system. In this work, we introduce design, fabrication and mechanism of the pressure gradient driven component including the extraction test results. The fabrication method of microneedle used in our system is also described.

Method for accurate shape prediction of 3D structure fabricated by x-ray lithography

The paper describes about a useful study on the deformed shapes of microstructures fabricated by PCT (Plane-pattern to Cross-section Transfer) Technique. Previously, we have introduced the PCT technique as an additional process to conventional X-ray lithography for an extension of 2.5-dimensional structure to 3-dimensional structure. The PMMA (poly-methylmethacrylate) has been used as the X-ray resist. So far, microneedle and microlens arrays have been successfully fabricated in various shapes and dimensions. The production cost of X-ray mask has been known as the most expensive process for LIGA step, therefore, to predict the resulting shapes of structure precisely before fabricating the mask is relatively important. Although, the 2-D pattern on the X-ray mask can form a similar shape resulting in 3-D structure, the distorted shapes of microstructures have been observed. A linear-edged pattern on the X-ray mask resulted as an exponential-edged structure and an exponential-edged pattern resulted as an exceeding curvature, for example. This problem causes a change in the functional property of the array. In the case of our microneedle array, the linear-edge is highly required since it increases the strength of microneedle. We have investigated and suggested a calculation method fir a shape-prediction of microstructure fabricated by PCT technique in this work. The compensation calculation by our theories for an X-ray mask design can solve the undesired shape resulting after X-ray exposure. Moreover, the dosage control and suitable developing time are given in order to see through the current condition of the currently used synchrotron radiation light-source.

Advanced simulation for shape-prediction of microstructures fabricated by PCT technique

Simulations for deformed shape-predictions of the 3-dimensional microstructures fabricated by Plane-pattern to Crosssection Transfer (PCT) Technique and Synchrotron Radiation (SR) lithography are described in this paper. We have attempted to study on a nonlinear relation between X-ray dosage and depth of the structure in the past work. The shapeprediction was investigated from two pairs of parameters influencing the structural deformation; dose-depth and position-dose. However, the above simulations resulted as, the higher height of the structure, the more error margin observed. A possible cause could be the etching direction dependent on the developing time. Thus, we currently emphasize on the factor causing this error. In order to comprehend the mechanism of the factor, the mathematical system of X-ray energy distribution onto PMMA (poly-methylmethacrylate) resist has been developed. The shape-prediction is consequent of the simulations based on calculations from the mathematics software. The investigation of the system enhances a possibility for higher accuracy of the prediction. In addition, the desired shapes can be confirmed by the simulations before the mask design and running experiments. The mathematical system for energy distribution dependents on the SR light source, X-ray mask specification, and resist specification. As a result, the predicted structures relevant to the absorbed energy-depth-position parameter set and absorbed energy-etching rate parameter set were obtained from this system. The simulations for shape-prediction were completed by the above parameter sets with the simulation software, MATHEMATICA(R). Graphic displays of predicted shapes are provided in the paper for clearly understanding.