With 3D printing in miniature to microelectronics

Notebooks, smartphones and many other electronic devices are based on microelectromechanical systems (MEMS). Their reliability and service life are influenced by mechanical shock (drops), vibrations and their environment. However, it is not yet possible to test mechanical reliability under realistic conditions. In addition, the design and choice of materials of these MEMS, which are crucial for the functionality of our electronics, are limited by the way they are manufactured.

In order to overcome these challenges, the European Research Council (ERC) is now supporting the research of Dr. Rajaprakash Ramachandramoorthy with a Starting Grant of 1.5 million euros for five years. The head of the "Extreme Nanomechanics" and "Additive Manufacturing" groups at the Max Planck Institute for Iron Research (MPIE) in Düsseldorf wants to research a way to produce and test three-dimensional metal microarchitectures for use in MEMS. The microarchitectures are to be 3D printed in order to overcome the current limitations of manufacturing.

3D printing enables a wider range of designs

"I am very happy, grateful and proud that the ERC is funding my project. The grant enables me to pursue my research further and is an important step in my career," says Ramachandramoorthy. The microelectronics currently used in smartphones, laptops and other electronic devices are currently manufactured using UV lithography. This method is stable and can be easily adapted to industrial needs. However, the design possibilities and choice of materials are limited, as the method is only suitable for silicon and a few metals.

3D printing and mechanical testing of 3D metal microarchitectures. © R. Ramachandramoorthy, T. You, Max Planck Institute for Iron Research

"In my project, I will use additive manufacturing, i.e. 3D printing of metals, to print 3D architectures in the micro and nanometer range. These are structures that are sometimes 100 times thinner than a human hair. Additive microfabrication expands the design freedom for microelectronic applications. In addition, production is based on local galvanic deposition. This method allows printing with a variety of different metals such as copper, gold, cobalt, nickel and silver," says Ramachandramoorthy. Localized electrodeposition in liquids uses an electrochemical salt solution that flows through a small orifice and contains metal ions. These are reduced at the working electrode to form a microscale metal droplet. Drop by drop, 3D metal micro-objects are formed.

Another major advantage of the new production method is that liquids can be encapsulated in the metal microarchitectures. This is interesting for the administration of medication or temperature measurement, for example. In addition, the printed microarchitectures could also be filled with liquids containing fluorescent markers that flow out locally in the event of impact/deformation and thus serve as damage sensors. Knowing where and when an electronic device is damaged helps in the search for ways to repair the device - a step towards sustainability.

Desired application determines choice of manufacturing technique

After fabricating the metallic 3D microarchitectures, Ramachandramoorthy and his team will develop further reliability protocols to verify the micro/nanomechanical properties under application-relevant extreme speeds, shocks and temperatures.

UV lithography is very costly in the early stages, but becomes less expensive when mass producing MEMS devices. Setting up the additive microfabrication process to be researched in this ERC project is less costly, and once the process goes into mass production, it becomes even cheaper. "I think that a combination of both processes will be ideal in the future. UV lithography will remain the method of choice when it comes to producing 2.5D silicon-based microarchitectures. Additive microfabrication, on the other hand, will become interesting whenever 3D microarchitectures with a wider range of metals are required or the integration of liquids is desired," explains Ramachandramoorthy.

Rajaprakash Ramachandramoorthy joined the MPIE as a group leader in August 2020. Previously, he was a Marie Curie postdoctoral researcher at the Swiss Federal Laboratories for Materials Science and Technology (Empa). Ramachandramoorthy holds a PhD in theoretical and applied mechanics from Northwestern University (USA). His research focuses on the mechanical behavior of materials at small scales, mainly using scanning and transmission electron microscopy and additive techniques for the fabrication of microarchitectures.

Funding from the European Research Council is considered one of the most prestigious international research funding schemes. In this application round, 2932 proposals were submitted across Europe, of which 408 scientists were successful.