Ms. Yao Fu Profile

Yao Fu

at Silverbrook Research Pty Ltd

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Proceedings Article | 23 February 2005 Paper

Fabrication of microstructures with different aspect ratios in a single layer

Yao Fu, Erol Harvey, Muralidhar Ghantasala

Proceedings Volume 5650, (2005) https://doi.org/10.1117/12.581894

KEYWORDS: Copper, Magnetism, Electroplating, Photoresist materials, Silicon, Electromagnetism, Semiconducting wafers, Resistance, Photomasks, Confocal microscopy

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Magnetic actuation has been very successful in both macro and micro scales and magnetic microactuators with different microstructures have also been extensively studied. Almost all of these microactuators are based on the electromagnetic effect and the force is generated by the electromagnetic coil, between the soft magnetic core and the (magnetic) cantilever. To integrate all of these magnetic components on the same chip, microstructures with different aspect ratios were fabricated in a single layer by using a photolithography process using the negative photoresist SU-8 2000. A copper microcoil, a permalloy core and a nickel metal post for suspending a cantilever beam were electroplated on the same seed layer with aspect ratios varying from 1:1, 5:1 to 10:1, and the dimensions of the features ranging from 25 μm to 500 μm. The three different features were fabricated separately in three layers. Different viscosity of SU-8 2000 was used in three layers. 50 μm, 80 μm and 200 μm thick SU-8 are used to pattern the molds for electroplating three different features. 25 μm thick copper microcoils with an aspect ratio 1:1 was first electroplated on the Ti/Cu/Ti seed layer. This is followed by electroplating of 50 μm thick permalloy layer with an aspect ratio 10:1 on the same seed layer. A 100 μm thick copper post with an aspect ratio 5:1 was electroplated on to the same seed layer in the next step. SU-8 resist molds were removed between each of these layers. Finally, the residual SU-8 was cleaned by CF₄ plasma etching. The coils have 19 turns with a footprint area of 10 mm². The microcoils were tested to ascertain their maximum current densities before burnout. Similarly, the magnetic properties of the Permalloy core were also tested. The profiles of different layers and the coil and permalloy core test results were discussed in detail in this paper.

Proceedings Article | 2 April 2004 Paper

Design, modeling, and fabrication of piezoelectric polymer actuators

Yao Fu, Erol Harvey, Muralidhar Ghantasala, Geoff Spinks

Proceedings Volume 5276, (2004) https://doi.org/10.1117/12.527885

KEYWORDS: Ferroelectric polymers, Polymers, Nickel, Composites, Actuators, Electroplating, Polymeric actuators, Optical simulations, Micromachining, Microelectromechanical systems

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Piezoelectric polymers are a class of materials with great potential and promise for many applications. Because of their ideally suitable characteristics, they make good candidates for actuators. However, the difficulty of forming structures and shapes has limited the range of mechanical design. In this work, the design and fabrication of a unimorph piezoelectric cantilever actuator using piezoelectric polymer PVDF with an electroplated layer of nickel alloy has been described. The modeling and simulation of the composite cantilever with planar and microstructured surfaces has been performed by CoventorWare to optimize the design parameters in order to achieve large tip deflections. These simulation results indicated that a microstructured cantilever could produce 25 percent higher deflection compared to a simple planar cantilever surface. The tip deflection of the composite cantilever with a length of 6mm and a width of 1mm can reach up to 100μm. A PVDF polymer with a specifically designed shape was punched out along the elongation direction on the embossing machine at room temperature. The nickel alloy layer was electroplated on one side of the PVDF to form a composite cantilever. The tip deflection of the cantilever was observed and measured under an optical microscope. The experimental result is in agreement with the theoretical analysis.

Proceedings Article | 14 November 2002 Paper

Laser-LIGA for Ni microcantilevers

Hengyi Jin, Erol Harvey, Jason Hayes, Muralidhar Ghantasala, Yao Fu, Karlo Jolic, Matthew Solomon, Kynan Graves

Proceedings Volume 4935, (2002) https://doi.org/10.1117/12.476113

KEYWORDS: Nickel, Excimer lasers, Copper, Polymers, Etching, Micromachining, Actuators, Temperature metrology, Laser processing, Microactuators

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This paper presents our design and experimental results of nickel microcantilevers, which were fabricated using a laser-LIGA process, based on KrF (248 nm) excimer laser micromachining. A chrome-on-quartz mask, containing the desired mask patterns was prepared for this work. The substrate of copper (30 μm thick) clad printed circuit board (PCB) was laminated with Laminar 5038 photopolymer to be laser patterned. Following laser patterning and laser cleaning, all the samples were electroformed with nickel on top of the copper layer. To release the Ni microcantilevers, the excimer laser was employed again to remove the polymer in the localised area to facilitate Cu selective etching. Here, copper acted as the sacrificial layer as well. The Cu selective etching was carried out with ~ 20 % (wt) aqueous solution of ammonium persulfate. Because the Cu selective etching is isotropic, some undercuts happened next to the anchor area. The samples were characterised using optical microscope, confocal laser scanning microscope and SEM, and some of Ni cantilevers were tested electro-thermally. Their performance was analyzed with respect to the simulation results.

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