“Wireless” Direct-Write Electrodeposition and Patterning Via Bipolar Electrochemistry
Authors: Braun Trevor M , Schwartz Daniel T. 
Published: February 2020

Manufacturing industries have seen a recent shift to additive-based fabrication methods driven by efficient utilization of feedstock material, decreased reliance on hazardous chemicals, and device customization capabilities, leading to more cost-effective and sustainable manufacturing. A critical factor in commercialization of additive manufacturing technologies is the availability of easy-to-use, integrated software/hardware platforms capable of rendering computer design files into fabricated objects [1]. Despite these advances in recently commercialized additive manufacturing techniques (fused deposition modeling, selective laser sintering, etc.), a similar shift to software-reconfigurable electrodeposition-based prototyping has yet to emerge. Current commercial electrodeposition patterning methods continue to rely on a series of masks, planarization, and chemical etching steps to fully develop objects, limiting their reconfigurability. However, direct-write electrodeposition methods have the potential to combine the advantages of electrodeposition-based fabrication with user-friendly additive manufacturing techniques.
Our research group previously developed an impinging jet electrodeposition tool with full software control of electrodeposition, transport, and x-y-z motion called Electrochemical Printing (EcP) [2]. More recently, our lab modified the EcP system to operate in a bipolar manner, enabling direct-write electrodeposition without electrical connections to the workpiece [3]. This configuration, termed a scanning bipolar cell (SBC), is advantageous for advanced fabrication at the nanoscale where surfaces may be difficult to connect to, and allows for further automation of the hardware. However, operating via bipolar electrochemistry comes with a catch, namely the need to couple a simultaneous and spatially segregated oxidation reaction to the desired reduction (deposition) reaction. In this presentation, we outline design guidelines necessary to achieve bipolar electrodeposition of metals across a wide range of nobilities, and how to extend these guidelines to similar systems. Choosing an appropriate electron-donating oxidation chemistry is critical to achieving spatiotemporally stable electrodeposited patterns, with design criteria directly related to the kinetic reversibility of the desired reduction chemistry and the thermodynamic relationship of the bipolar redox couple. Simple theoretical relationships are presented to describe scale-down of the SBC for sub-micron manufacturing. Additional challenges to sub-micron electrodeposition such as reactant transport and nanoprobe design are also explored. Bipolar electrodeposition with the SBC offers improved automation for direct-write patterning by eliminating the need to electrically connect to the substrate, particularly advantageous for advanced fabrication on complex, multifaceted electronic devices.

References:

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[2] J. D. Whitaker et al, J. Micromech. Microeng., 15, 1498 (2005).
[3] T. M. Braun et al., J. Electrochem. Soc.,
163, D3014 (2016).