Erwin Berenschot

Silicon micromachined hollow microneedles for transdermal liquid transport

This paper presents a novel process for the fabrication of out-of-plane hollow microneedles in silicon. The fabrication method consists of a sequence of deep-reactive ion etching (DRIE), anisotropic wet etching and conformal thin film deposition, and allows needle shapes with different, lithography-defined tip curvature. In this study, the length of the needles varied between 150 and 350 micrometers. The widest dimension of the needle at its base was 250 /spl mu/m. Preliminary application tests of the needle arrays show that they are robust and permit skin penetration without breakage. Transdermal water loss measurements before and after microneedle skin penetration are reported. Drug delivery is increased approximately by a factor of 750 in microneedle patch applications with respect to diffusion alone. The feasibility of using the microneedle array as a blood sampler on a capillary electrophoresis chip is demonstrated.

Electrostatic curved electrode actuators

This paper presents the design and performance of an electrostatic actuator consisting of a laterally compliant cantilever beam and a fixed curved electrode, both suspended above a ground plane. A theoretical description of the static behavior of the cantilever as it is pulled into contact with the rigid fixed-electrode structure is given. Two models are presented: a simplified semi-analytical model based on energy methods, and fully three-dimensional (3-D) coupled electromechanical numerical simulations using CoSolve-EM. The two models are in qualitative agreement with each other, and predict stable actuator behavior when the beam deflection becomes constrained by the curved electrode geometry before electrostatic pull-in can occur. The pull-in behavior depends on the shape of the curved electrode. Test devices have been fabricated by polysilicon surface micromachining techniques. Experimental results confirm the basic theoretical results. Stable behavior with relatively large displacements and forces can be generated by these curved electrode actuators. Depending on the design, or as a result of geometrical imperfections, regions of unstable (pull-in) deflection behavior are also observed.

Wet anisotropic etching for fluidic 1d nanochannels

In this paper a method is proposed to fabricate channels for fluidic applications with a depth in the nanometer range. Channels with smooth and straight sidewalls are constructed with the help of micromachining technology by etching shallow trenches into langle110rangle silicon using native oxide as a mask material and OPD resist developer as the etchant. Sub-50 nm deep fluidic channels are formed after bonding the nanopatterned wafers with silicon or borofloat-glass wafers. The nanofabrication process is significantly simplified by using native oxide as the main mask material. The etch depth of the nanochannels is limited by the thickness of the native oxide layer, and by the selectivity of the oxide/silicon etch rate (estimated to be at least 250 for langle110rangle silicon at room temperature).

Nanometer arrays of functional light harvesting antenna complexes by nanoimprint lithography and host--guest interactions

We show an approach based on a combination of site-directed mutagenesis, NIL and multivalent host-guest interactions for the realization of engineered ordered functional arrays of purified components of the photosynthetic system, the membrane-bound LH2 complex. In addition to micrometer-scale patterned structures, we demonstrated the use of nanometer-scale hard NIL stamps to generate functional protein arrays approaching molecular dimensions.

Advancements in Technology and Design of Biomimetic Flow-Sensor Arrays

This paper reports on recent developments to increase the performance of biomimetic flow-sensor arrays by means of several technological advancements in the fabrication procedures and corresponding sensor design optimizations. Advancements include fabrication procedures with higher process latitude and geometrical modifications of several parts of the flow sensor. The conclusive measurements in this paper support our sensor-model predictions for a 100-fold increase in acoustic sensitivity (down to oscillating flow amplitudes in the order of 1 mm·s-1) translating to substantially higher capacitive outputs in comparison to our first-generation biomimetic flow-sensor arrays.

Integrated Lithographic Molding for Microneedle-Based Devices

This paper presents a new fabrication method consisting of lithographically defining multiple layers of high aspect-ratio photoresist onto preprocessed silicon substrates and release of the polymer by the lost mold or sacrificial layer technique, coined by us as lithographic molding. The process methodology was demonstrated fabricating out-of-plane polymeric hollow microneedles. First, the fabrication of needle tips was demonstrated for polymeric microneedles with an outer diameter of 250 mum, through-hole capillaries of 75-mum diameter and a needle shaft length of 430 mum by lithographic processing of SU-8 onto simple v-grooves. Second, the technique was extended to gain more freedom in tip shape design, needle shaft length and use of filling materials. A novel combination of silicon dry and wet etching is introduced that allows highly accurate and repetitive lithographic molding of a complex shape. Both techniques consent to the lithographic integration of microfluidic back plates forming a patch-type device. These microneedle-integrated patches offer a feasible solution for medical applications that demand an easy to use point-of-care sample collector, for example, in blood diagnostics for lithium therapy. Although microchip capillary electrophoresis glass devices were addressed earlier, here, we show for the first time the complete diagnostic method based on microneedles made from SU-8.

Etching technology for microchannels

Various ways of fabricating channels in silicon are discussed. Some new channels are presented: the GPSICs and the LPCVD covered channels. Also some attention is paid to the problem of making connections of these channels to the outside world.

Fabrication of 3D fractal structures using nanoscale anisotropic etching of single crystalline silicon

When it comes to high-performance filtration, separation, sunlight collection, surface charge storage or catalysis, the effective surface area is what counts. Highly regular fractal structures seem to be the perfect candidates, but manufacturing can be quite cumbersome. Here it is shown-–for the first time—that complex 3D fractals can be engineered using a recursive operation in conventional micromachining of single crystalline silicon. The procedure uses the built-in capability of the crystal lattice to form self-similar octahedral structures with minimal interference of the constructor. The silicon fractal can be used directly or as a mold to transfer the shape into another material. Moreover, they can be dense, porous, or like a wireframe. We demonstrate, after four levels of processing, that the initial number of octahedral structures is increased by a factor of 625. Meanwhile the size decreases 16 times down to 300 nm. At any level, pores of less than 100 nm can be fabricated at the octahedral vertices of the fractal. The presented technique supports the design of fractals with Hausdorff dimension D free of choice and up to D = 2.322.

Versatile trench isolation technology for the fabrication of microactuators

A trench isolation technology employs trenches refilled with dielectric material to create, in a single layer, electrical isolation between mechanically joined components. This paper explores further use of this technology for MEMS fabrication, particularly the fabrication of electrostatic microactuators. Adding extra features to a two-mask trench isolation process new design opportunities, like isolation structures and isolation bumps, are created. The isolation structures can be employed as flexible or rigid connections between movable or fixed components or can serve to prevent the short-circuiting by maintaining the end distance between movable electrodes. The isolation bumps reduce stiction during release and operation, prevent short-circuiting due to an out-of-plane displacement and can serve as etch holes at the same time. The trench isolation technology is used to improve fabrication process of an actuator consisting of a large number of elastic electrodes connected in parallel and in series and to develop a novel low volume, large force (> 1 mN) and nanometer resolution electrostatic actuator for low displacement applications.

High performance bidirectional electrostatic inchworm motor fabricated by trench isolation technology

We report on an electrostatic linear micromotor, which employs built-in mechanical leverage to convert normal deflection of a flexible plate into a small in-plane step and two clamps to enable bidirectional inchworm motion. The motor, measuring 412 /spl mu/m /spl times/ 286 /spl mu/m, is fabricated by a combination of trench isolation technology and standard surface micromachining in a relative simple process. The maximum achieved travel range was /spl plusmn/70 /spl mu/m, limited only by flexure design. Depending on the plate actuation voltage, two operation modes, below and above pull-in of the plate, are demonstrated with an adjustable step size from 0.6 to 7 nm and 49 to 62 nm, respectively. The motor was driven in a broad cycling frequency range from 0 to 80 kHz. Output forces of 1.7 mN are measured at 55 V for both the clamps and plate. The motor was operated for 5 days at a stepping frequency of 80 kHz and has completed a cumulative distance of more than 1500 m in about 34/spl middot/10/sup 9/ steps without any performance deterioration.