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. 2010 Jan 1;19(1):215-228.
doi: 10.1109/jmems.2009.2032670.

A Parylene Bellows Electrochemical Actuator

Po-Ying Li  1 , Roya Sheybani, Christian A Gutierrez, Jonathan T W Kuo, Ellis Meng
Affiliations

A Parylene Bellows Electrochemical Actuator

Po-Ying Li et al. J Microelectromech Syst. .

Abstract

We present the first electrochemical actuator with Parylene bellows for large-deflection operation. The bellows diaphragm was fabricated using a polyethylene-glycol-based sacrificial molding technique followed by coating in Parylene C. Bellows were mechanically characterized and integrated with a pair of interdigitated electrodes to form an electrochemical actuator that is suitable for low-power pumping of fluids. Pump performance (gas generation rate and pump efficiency) was optimized through a careful examination of geometrical factors. Overall, a maximum pump efficiency of 90% was achieved in the case of electroplated electrodes, and a deflection of over 1.5 mm was demonstrated. Real-time wireless operation was achieved. The complete fabrication process and the materials used in this actuator are bio-compatible, which makes it suitable for biological and medical applications.

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Figures

Fig. 1
Fig. 1
Parylene bellows electrochemical actuator for ocular drug delivery: (a) Exploded view of the actuator showing the major components, (b) example of the actuator assembled into a drug delivery system, and (c) conceptual depiction of the implanted intraocular drug delivery device. The device is implanted under the conjunctiva (within the eyewall) with the cannula directed through an incision into the anterior segment of eye.
Fig. 2
Fig. 2
Illustration of wireless operation of the intraocular drug delivery system: (a) power off and (b) power on.
Fig. 3
Fig. 3
Finite-element analysis using COSMOSWorks showing stress distribution for (a) Parylene corrugated membrane and (b) bellows. Critical stress sites are also indicated in the graph.
Fig. 4
Fig. 4
Photographs of interdigitated Pt/Ti electrode layout for electrochemical actuator showing (a) fixed-width variable spacing electrodes, (b) variable width and spacing electrodes, and (c) close-up of (b). The electrode element spacing and width are also defined in (c).
Fig. 5
Fig. 5
Fabrication process flow for the pump interdigitated electrode: (a) Liftoff lithography, (b) Ti and Pt e-beam evaporation, and (c) Pt liftoff.
Fig. 6
Fig. 6
Bellows molding process. (a)–(f) Fabrication steps for the bellows. (g) Photographs of the PEG mold. (h) Parylene bellows. The inset in (h) shows a close-up of the top bellows convolution.
Fig. 7
Fig. 7
Parylene electrochemical bellows actuator. (a) Schematic diagram of the two-part assembly. (b) Image of assembled actuator.
Fig. 8
Fig. 8
Schematic diagrams of the experimental apparatus for (a) Parylene bellows load–deflection testing, (b) flow rate testing for the (top inset) electrodes and (bottom inset) assembled bellows actuator, (c) real-time pressure monitoring, and (d) wireless operation.
Fig. 9
Fig. 9
Comparison of load-deflection experimental data with linear approximation and nonlinear FEM model for the Parylene bellows diaphragm (mean ± SE, n = 4).
Fig. 10
Fig. 10
Pump efficiency optimization based on current-controlled gas generation for fixed-width variable spacing electrodes. Pump efficiency increases with decreasing element spacing (mean ± SE, n = 4).
Fig. 11
Fig. 11
Pump efficiency optimization based on current-controlled flow delivery for the constant pump area interdigitated electrodes. (a) Pump efficiency versus current density (mean ± SE, n = 4) and (b) pump efficiency versus element spacing and width results were obtained from electrodes fabricated using the optimized process. (c) Pump efficiency versus current density (mean ± SE, n = 4) and (d) pump efficiency versus element spacing and width results were obtained from electrodes fabricated using the unoptimized process.
Fig. 12
Fig. 12
High applied current experiments. [(a) and (b)] Gas generation rate and calculated pump efficiency results for fixed-width variable spacing electrodes. [(c) and (d)] Gas generation rate and calculated pump efficiency results for variable width and spacing electrodes.
Fig. 13
Fig. 13
Electroplated electrode experimental results. SEM images of the e-beam evaporated electrode surface (a) before electroplating and (b) after electroplating. Electrode electrochemical characterization before and after electroplating: (c) CV and (d) electrochemical impedance plots. Electrolysis pumping performance before and after electroplating: (e) pump flow rate and (f) pump efficiency.
Fig. 14
Fig. 14
Flow rate testing for Parylene bellows actuator: (a) Current-controlled delivery collected from 20-μm-width and 100-μm-gap device (mean ± SE, n = 4) and (b) calculated pump efficiency.
Fig. 15
Fig. 15
Real-time pressure measurement of Parylene bellows actuator: (a) In actuator chamber and (b) during on (2-min) and off (3-min) operations.
See this image and copyright information in PMC

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