Gold Printing with the Exaddon CERES µAM system

The Exaddon CERES µAM system is a unique technology for printing microscale metal structures with submicron resolution, using additive manufacturing. Exaddon has developed and released gold as a production ready print material, in addition to their copper printing capabilities.

This advance brings their unique additive micromanufacturing (µAM) technology to industries needing minute gold structures in complex geometries.

GOLD µAM. An array of pure gold micropillars, produced by additive micromanufacturing.

GOLD μAM. An array of pure gold micropillars, produced by additive micromanufacturing. Image Credit: Exaddon AG

Introduction

Exaddon took the big step of focusing R&D efforts on gold, with a view to supplying it to market as a mature product, following analysis of market feedback and recognizing the growing role of gold within microelectronic applications.

Winter 2020 saw the culmination of that process, and Exaddon is extremely proud to show off their great advance in the additive manufacturing (AM) of complex metal objects at the microscale, this time in pure gold.

MULTIPURPOSE. The CERES system allows different metals to be printed by changing only the consumable printing tip and associated chemicals.

MULTIPURPOSE. The CERES system allows different metals to be printed by changing only the consumable printing tip and associated chemicals. Image Credit: Exaddon AG

Exaddon’s electrochemists and engineers started to develop and optimize the same process with gold while refining and researching the electrodeposition of copper on both polymer and metal substrates.

Printing complex microscale metal objects using electrodeposition means that any alteration in print material has huge implications for the whole electrochemical print process, and a great deal of time and effort has been invested in this area.

Why Gold?

It is abundantly clear that gold has a key value in microscale applications after extensive collaboration and feedback from numerous partners in different industries.

Gold is frequently utilized within the MEMS area for structural layers and electrical connections because of its corrosion resistance and high conductivity. This article will outline two use cases where µAM of gold has huge potential.

Use Case 1 – Neuronal Interfaces

Recently, neuronal interfaces like implantable electrodes or multiple-electrode arrays have been the focus of much media coverage, and for good reason. They have great value as transformative tools for monitoring and modifying neural electrophysiology, both for the diagnosis and treatment of neurological disorders and for fundamental studies of the nervous system.

In order to enhance recording fidelity and minimize background noise, these neuronal interfaces require high electrical conductivity 1.

Gold has seen extensive utilization as a material of choice for implantable electrodes within this field because of its conductivity and durability together with the material’s inherent cell compatibility. Additive micromanufacturing in medical applications is seen as the next step.

MICROSCALE AM. A micropillar printed in pure gold.

MICROSCALE AM. A micropillar printed in pure gold. Image Credit: Exaddon AG

Use Case 2 – Biosensors & Bioreceptors

Similarly, biocompatible biosensors which utilize a gold contact layer have proven efficacy in the detection of carcinogenic cells and tumor biomarkers.

Additive manufacturing’s ability to create intricate geometries has resulted in its identification as the ideal technology for pharmaceutical applications which need a high degree of personalization and accuracy.

Wearable electrochemical biosensors have proven their worth for real-time reporting and continuous management of diseases in recent years, these include detection of biotoxins or glucose monitoring 2. Many studies have exhibited the conductivity and durability of gold as an electrode in this arena 3.

The market value and forecast for biosensors show great growth, which is an indication of the importance of these devices. As of Sept 2020, the global biosensors market is expected to grow from USD 21.5 bn in 2019 to USD 41.29 bn by 2027, this is a CAGR of 8.5 % 4.

Benefits of Electroplating vs Other Methods of Fabrication

In modern-day microelectronics, electrodeposition of gold is a crucial process and has been for some years. Notably, gold can be electroplated quite easily, enabling higher film thickness than can be achieved with physical vapor deposition (PVD) techniques like sputtering, whilst also permitting higher rates of deposition.

One key point here is that both thermal expansion and sputtering need to be conducted in a high vacuum chamber. Additionally, these techniques cannot be utilized to build 3D objects, but only to coat whole areas of an object (masks are needed if partially coating an object).

In the case of Exaddon's unique electrodeposition process, their CERES print system operates in normal atmospheric conditions at room temperature and permits almost free form 3D design possibilities.

In terms of printing choices, this opens up a wide scope of possibilities, and indeed the types of pre-existing structures which can be modified and printed upon. Microelectronic components can be very sensitive to conventional manufacturing environments like adverse pH or heat.

In order to minimize the probability of possible damage to delicate components, Exaddon's µAM technology uses a very benign room temperature process.

Complexity of Gold Printing R&D

There are many technical challenges to developing a microscale gold AM. It is not just a case of changing the printing ink from copper to gold and starting to print. The electrochemistry is extremely complex, and extensive R&D and technical knowledge are needed for successful configuration.

In µAM, replicability and accuracy are crucial, and these attributes only result from robust electrochemical R&D.

The first challenge is that gold ions are not stable in solution, unlike ionic copper, and so they require the addition of certain chemical agents to stop the ionic gold precipitating out of solution, which might otherwise clog the printing tip and exhaust the supply of gold available for printing.

Due to the interaction with the chemicals, to achieve successful gold deposition Exaddon had to develop modified iontips with a protective coating.

Exaddon Gold µAM Capabilities

Exaddon can print voxels of 800 nm to 4.5 µm in diameter by utilizing their standard 300 nm aperture iontips, enabling an extremely small minimum feature size. The surface quality of objects printed with their gold ink is excellent, which is vital for end-use applications like neuronal interfaces or bioreceptors, where durability and precision are vital.

SURFACE QUALITY. Through extensive electrochemistry R&D, we have achieved exceptional surface quality with our gold print process.

SURFACE QUALITY. Through extensive electrochemistry R&D, we have achieved exceptional surface quality with our gold print process. Image Credit: Exaddon AG

In terms of print substrates, the substrate surface has to be conductive and compatible with electroplating. Exaddon’s standard metal substrates like copper and gold are viable, as are flexible polymers such as PEDOT.

Exaddon’s development of an industry-ready gold µAM solution is a genuine breakthrough in the application of Industry 4.0 technologies to real-world use cases, and one which is a potential gamechanger.

References

  1. Chapman C.A., Chen H., Stamou M., et al. Nanoporous gold as a neural interface coating: effects of topography, surface chemistry, and feature size. ACS Appl Mater Interfaces. 2015 Apr 8;7(13):7093-100.
  2. Gao Y., Xin Z., Zeng B., et al. Plasmonic interferometric sensor arrays for high-performance label-free biomolecular detection. Lab Chip. 2013 Dec 21;13(24):4755- 64.
  3. Chan Y., Skreta M., McPhee H., et al. Solutionprocessed wrinkled electrodes enable the development of stretchable electrochemical biosensors. Analyst. 2018 Dec 17;144(1):172-179.
  4. http://bit.ly/3mnTHV6

This information has been sourced, reviewed and adapted from materials provided by Exaddon AG.

For more information on this source, please visit Exaddon AG.

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