Scales and read heads aid micro-machining

Special scales and readheads are being used by micro-machining researchers at the University of Southampton to provide crucial positioning for the nanometric movements required. Dean Palmer reports Special equipment, which includes a multi-axis sample stage fitted with piezo-ceramic motors and a scale and readhead system, has recently been installed at the University of Southampton, to help scientists research micro-machining. The equipment was truly a team effort. The overall system was designed by Ionoptika based at the Chilworth Science Park in Southampton, the multi-axis 'Nanomotion' sample stage was supplied by Heason Technologies of Chichester, and the scale and readhead system, whose function is the precise positioning for the nanometric movements required of the system, was supplied by Renishaw based in Gloucestershire. The whole micro-machining assembly is housed within a vacuum casing and mounted on a high-stability platform, isolated from all external vibrations. Andy Barber, technical manager at Ionoptika, commented: "The scale and readheads were specified for the critical measuring and positioning functions because they are able to maintain the necessary accuracy. They can also cope with the demanding environment. To avoid 'out-gassing' problems, the ultra high vacuum conditions require the entire development to be periodically 'baked' at temperatures of up to 120°C." And, to ensure continuous, smooth motion the sample stage was fitted with piezo-ceramic motors. Barber explained: "Matching the encoders to these motors has proved very effective. The result is smooth motion combined with high resolution, zero backlash and fine positioning accuracy, which is typical with piezoelectric devices." The sample stage uses a Renishaw RG2 linear encoder system, with 50nm resolution and an RGH25 UHV compact, robust readhead. Linear movements across the work piece can be up to 50nm, with a requirement to return to features previously worked on. The system must have high repeatability to achieve this, which, according to Barber, is the key benefit of the encoders. To achieve sub-micron precision, scientists at Ionoptika wrote their own programmes for the computer-controlled four-axis stage system, including integrated micro-machining software. To demonstrate the minute scale of this work, one programme etches the Ionoptika company logo on a metallic screen mask. The entire company name is perfectly reproduced within the width taken by a single hole, 20(m wide. According to Southampton University's Chris Finlayson, the plan is to use the new equipment to conduct studies on "the patterning of 2D photonic crystal structures into various dielectric waveguides", "the etching of sub-micron sized holes through inert metal thin-films in order to examine light/plasmon interactions" and to investigate the "lateral patterning of waveguides and integrated optical circuits." Ionoptika has facilities at its site to assemble and test ion guns, sources and other high vacuum instrumentation. Scientists at the company are 'experts' in highly specialised imaging on both elemental and molecular features, including single cell systems. With a frequent need to look at such a cell and come back to it, positioning accuracy is critical. For this particular application, a 25kV gallium liquid metal ion gun of less than 30nm special resolution was employed. Pointers * Equipment has been developed that will help scientists conduct research into micro-machining * The four-axis sample stage incorporates a linear encoder and readhead system, a piezo-ceramic motor housed within a vacuum casing and mounted on a high-stability platform to isolate the system from external vibrations * Southampton University will use the system to research patterning of 2D crystal structures, the etching of small holes through inert metal thin-films to examine light interactions and to investigate the lateral patterns of waveguides and integrated optical circuits