DESIGN AND CHARACTERIZATION OF A 6 DEGREE-OF- FREEDOM MESO-SCALE NANOPOSITIONER WITH INTEGRATED STRAIN SENSING

The success of many application areas (e.g. probe-based nanomanufacturing) hinges on the ability to design and realize low-cost, highperformance multi-degree of freedom (MDOF) nanopositioners. In meso-scale MDOF nanopositioners, the sensing system must be integrated into the structure of the nanopositioner. The only viable candidates for many small-scale, low-cost sensing systems are piezoresistive sensors. A meso-scale 6-DOF nanopositioner was designed and tested. Polysilicon piezoresistors were surface micromachined onto a microfabricated silicon nanopositioner. The nanopositioner was actuated with moving magnet Lorentz force actuators. The final prototype costs less than $300 US and was found to have 10’s of μm range, nm-level resolution, and a 100 Hz 1 natural frequency. System calibration was difficult as commercially available six-axis metrology systems for smallscale devices in a nascent technology. As a result of the preceding, the measured accuracy of the sensing system can only be claimed to be better than 17% in-plane and 30% out-of-plane. Models indicate that the system should exhibit worst case errors of a few percent; therefore this paper also serves as an indicator that new, improved metrology systems are needed for small-scale devices. INTRODUCTION Meso-scale, 6-axis nanopositioners possess unique characteristics due to their small size. They (a) are lower-cost ($100s vs. $10,000s US), (b) exhibit smaller thermally-induced errors, and (c) possess higher natural frequencies than their macro-scale counterparts. To be practical, they require a missing element, i.e. a costand size-appropriate sensing system. In general, macro-scale sensors are too large and expensive to integrate within these devices. Integrated sensors are therefore required to enable 6 axis closed loop nanopositioning within a meso-scale package. Given this capability, small-scale, 6-axis nanopositioners would then enable massively parallel probe-based nanomanufacturing processes such as dip-pen nanolithography (DPN) and nano-electrical discharge machining (nEDM). NANOPOSITIONER DESIGN The nanopositioner design is based upon the 6 degree-of-freedom (DOF), monolithic HexFlex flexure system [1-3]. Figure 1 shows our mesoscale HexFlex, less actuators and electronics. This design is attractive as (i) its 21⁄2D geometry may be microfabricated and (ii) its in-plane symmetry and thin profile yield low thermal sensitivity [1]. FIGURE 1: Meso-scale HexFlex nanopositioner Figure 2 shows how in-plane stage motion is achieved by applying combinations of in-plane forces; and how out-of-plane motions are achieved by out-of-plane forces. FIGURE 2: HexFlex actuation-motion examples Each actuator tab is driven by a moving magnet Lorentz force motor [3-4]. As shown in Fig. 3, a periodic magnet array is attached to each actuator tab. Each array interacts with a set of nested coils that are contained within a flexible circuit that is attached to the bottom of a hexagonal aluminum heat spreader plate. DESIGN AND CHARACTERIZATION OF A 6 DEGREE-OF-FREEDOM MESO-SCALE NANOPOSITIONER WITH INTE ATED