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2848 |
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Design of a Six Degree of Freedom Nanopositioner for Use in Massively Parallel Probe-based Nanomanufacturing |
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Design of Precision Machines and Instruments |
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| Content |
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In probe-based nanomanufacturing a micro-scale probe tip is used to create or measure nm-scale features. The serial nature of probe-based manufacturing dictates that practical throughput rates will require the use of two-dimensional tip arrays. Even using large arrays of tips (>10,000) requires the parallel operation of many arrays in order to achieve high throughput rates. These ‘surface’ tools must be controlled in six degrees-of-freedom (DOF) in order to maintain parallelism with respect to the surface they interact with. Meso-scale, 6-DOF nanopositioners will be important for these arrays because they (1) are lower cost ($100s US rather than $10,000s US), (2) possess higher bandwidth, and (3) are more thermally stable when compared to macro-scale nanopositioners. Furthermore, their small size enables arraying many nanopositioners in a small footprint. Sensing is important as this enables closed loop control of position, and therefore some measure of control in the manufacturing process. This is important to the creation of cost-appropriate equipment that will enable the transition of nano-scale manufacturing technologies from the lab to manufacturing. We present the design and fabrication of a low-cost, microfabricated nanopositioner with nm-level accuracy and resolution that is equipped for closed-loop operation throughout a 50x50x50 μm3 work volume. The nanopositioner is designed to control the orientation of a cm2 chip containing 55,000 tips for dip pen nanolithography (DPN). Figure 1 shows the meso-scale nanopositioner (less actuators and electronics) that contains an integrated 6-DOF piezoresistive sensing system. The figure inset shows the piezoresistor arrangement, wherein a first sensor is placed along the neutral axis of the beam and the second sensor is placed at the beam’s edge. Both sensors are placed near the root of the cantilever, where the device strain is at a maximum. The sensor on the neutral axis experiences stress primarily from out-of-plane bending while the sensor on the edge of the beam experiences stress from in- and out-of-plane bending. By biasing these signals it is possible to obtain in-plane and out-of-plane measurements from the sensors while keeping them located on the same face of the flexible beam. The structure of the nanopositioner was microfabricated from a 400 μm thick silicon wafer with 500 nm polysilicon piezoresistors fabricated onto the flexural beams of the nanopositioner. Each nanopositioner costs approximately $250 US and initial tests indicate the nanopositioner will have 2nm out-of-plane resolution and 20 nm in-plane resolution. In this paper we present (1) the design and modeling of the meso-scale nanopositioner, (2) optimization of the topology and sensing system, (3) design rules and trade-offs for the nanopositioner, and (4) experimental results. The nanopositioner’s design and utility will be presented in the context of a case study for a massively parallel DPN machining center that may be used for the manufacture, measurement, and manipulation of nm-level structures and biological samples. |
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