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This paper present a method of rapid replication of polymeric high aspect ratio microstructures (HARMs) and a method of rapid reproduction of metallic micromold inserts for HARMs using polydimethylsiloxane (PDMS) casting and standard LIGA processes. A high aspect ratio (HAR) metallic micromold insert, featuring a variety of test microstructures made of electroplated nickel with 15:1 height-to-width ratio for 300 μm microstructures, was fabricated by the standard LIGA process using deep X-ray lithography (DXRL). A 10:1 mixture of pre-polymer PDMS and a curing agent were cast onto the HAR metallic micromold insert, cured and peeled off to create reverse images of the HAR metallic micromold insert in PDMS. In addition to the replication of polymeric HARMs, replicated PDMS HARMS were coated with a metallic sacrificial layer and electroplated in nickel to reproduce another metallic micromold insert. This method can be used to rapidly and massively reproduce HAR metallic micromold inserts in low cost mass production manner without further using DXRL.

This paper reports a research effort to design, microfabricate and test a DC type magnetohydrodynamic (MHD) micropump using LIGA method (Menz et al., 1991). The micropump is driven using the Lorentz force and can be used to deliver electrically conductive fluids. In operation, a DC voltage is supplied across the electrodes to generate the distributed body force on the fluid in the pumping chamber, and therefore a constant pressure difference along the pumping chamber. The external magnetic field was supplied using permanent magnets. The major advantage of a MHD-based micropump is that it does not contain any moving parts. It may have potential applications in medicine delivery, biological and biomedical studies. The test of the DC prototype micropump shows that bubble generation mechanism affect the performance significantly and an AC driving mechanism may be used to improve the performance.

High aspect ratio microposts of bismuth telluride alloy with heights of up to 500 μm and a diameter of 150 μm have been fabricated with the LIGA technique. This work is part of an on-going research effort to develop a microprobe based on the Peltier effect for highly localized temperature manipulation on the microscale. Bismuth telluride alloys were electrodeposited galvanostatically into microfeatures on a titanium substrate using an acidic solution containing Bi3+and HTeO- 2 ions in 1 mol/dm3 nitric acid (pH∼0). The Bi–Te alloy microposts were monophasic, had a polycrystalline structure, demonstrated excellent adhesion to the substrate, and good mechanical strength. The chemical composition of the microposts was dependent on the electrolyte composition of the deposition bath and the current density used in electroplating; by controlling these two factors either p- or n-type Bi–Te alloy microposts may be produced. This research demonstrates that the microfabrication of Peltier effect probes is feasible.

Copper is widely used as a plating base for soft magnetic alloy electrodeposition in sensors and actuators. PMMA, the X-ray resist used in the LIGA process, typically has poor adhesion with copper. The use of black oxide of copper to enhance PMMA-copper adhesion was investigated. In this work, peel strength as a function of treatment time and the method of bonding was evaluated using an ASTM standard T-peel test. Peel strength increased with increasing treatment time. The feasibility of producing microstructures with predictable 3-D geometry for use in resonating sensors was investigated using the process developed. Nickel-iron structures of 100-1000 micrometers wide and 500 micrometers tall were successfully electrodeposited. Growth of other representative microstructures is being investigated.

The Louisiana State University (LSU) Microsystems Engineering Team (μSET) is developing techniques for producing microstructures with predictable 3-D geometry. One approach is based on controlled anodic dissolution of electroplated structures to obtain desired shapes. A finite element model was developed to predict the resulting shapes. As a demonstration of the shaping process, development of LIGA-based scanning probe microscope tips was investigated. An array of micro-posts 1.8 micrometers in diameter and 12 micrometers high was produced using x-ray lithography and subsequent electrodeposition. The posts were sharpened electrochemically. Other geometries are being investigated.