Liquid Metal RAM: FlexRAM a Breakthrough for Wearables

• Researchers from Tsinghua University have developed a groundbreaking liquid metal RAM (FlexRAM), introducing a novel approach to data storage that could revolutionise flexible electronics.
• FlexRAM utilises the reversible electrochemical oxidation and reduction of gallium-based liquid metals, enabling binary data storage with significant resistance differences, mimicking brain cell memory processes.
• This technology demonstrates remarkable durability and data integrity, even under extreme physical deformations such as stretching, bending, and twisting, making it ideal for wearable and implantable devices.
• The size of FlexRAM memory elements can range from millimeters to nanometers, with smaller droplets showing increased sensitivity and performance, highlighting the potential for scalability and precision in future electronic applications.

Introduction

Flexible electronics are said to be the next wave of technology that will unlock numerous applications and potential, but while they promise much, they are yet to be developed into practical devices. Recently, researchers demonstrated a fully flexible memory technology that may one day empower flexible electronics. What challenges do flexible electronics face, what did the researchers demonstrate, and how could it empower future devices?

What challenges do flexible electronics face?

Over the past decade, engineers have conducted countless amounts of research into developing flexible electronics, hoping that one day they will become mainstream. If achieved, flexible electronics could allow for countless applications, including advanced body sensors, intelligent clothing, smart labels, and disposable sensors. 

Furthermore, if these technologies can be made environmentally friendly and utilise renewable sources, then the industry would have minimal environmental impact and be guaranteed to last for hundreds of years to come. However, while the idea of flexible electronics is truly amazing, actually achieving this is far easier said than done. 

By far, the biggest challenge faced in developing flexible electronics is finding materials with electrical properties that are flexible. Most electronic components used in the industry today are based on materials which are inherently ridged, meaning that they cannot be easily bent. 

Some parts which do exhibit a degree of flexibility are rarely able to flex significantly, and even if they can, the solder joints used to keep them attached to a substrate can easily crack. These components are generally reserved for environments involving strong vibration (such as automotive systems), where flexing is already at a minimum.

One area that has shown great promise is organic electronics, which, as the name suggests, utilises organic compounds. By taking advantage of special polymers, it is possible to create semiconductor components that are fully flexible, and this has been demonstrated by PragmatIC with their flexible ARM core. However, even though these devices are fully flexible, they still suffer from some major limitations, including their transistor size, lack of complementary logic, and unreliability.

In other cases, flexible electronics are often too weak to survive extended use, making them only suitable for use in the lab. Another issue that flexible electronics can see is the need for flexible power supplies, which are practically non-existent. This means that even a sensor that is fully flexible requires a physical connection to a power source that is ridged. 

Overall, research into flexible electronics is certainly yielding positive results, but as far as truly flexible electronics go, they are still very much a niche development, far from being ready for mass production.

Researchers develop liquid metal RAM

Recognising the need for flexible components, researchers from Tsinghua University recently published their findings on a newly developed memory concept that could potentially lead to flexible RAM solutions. 

Taking inspiration from how brain cells involved with memory go through polarization and non-polarization phases, the researchers utilise a gallium-based liquid metal to hold data depending on its oxidation state. When integrated into a flexible biopolymer substrate (Ecoflex), the oxidation of the liquid metal can be controlled via a small external voltage (whose polarisation determines whether the metal is oxidised or not). 

As the resistance of the liquid metal greatly depends on the oxidation state, it is possible to store binary data in the droplet. Furthermore, the liquid is able to retain its oxidation state for extended periods of time (around 12 hours), meaning that while it isn’t non-volatile, it could very easily survive power outages.

With regards to data speed, the researchers utilised a pulse width modulated signal operating around 33Hz, and the droplet was subjected to over 3,500 write cycles while still demonstrating memory retention capabilities. To create the memory device, the researchers utilised a 3D printer to create Ecoflex molds, and a solution containing the liquid metal and polyvinyl acetate hydrogel were then applied. 

Taking the concept further, the researchers then manufactured 8 bits of storage and used a computer to read and write data to the memory array.

The pioneering work by Tsinghua University, as highlighted in their publication in Advanced Materials, showcases the potential of liquid metal memory in revolutionising flexible electronics. This novel memory technology, which utilizes the reversible electrochemical oxidation and reduction of gallium-based liquid metals, demonstrates an impressive 11-order magnitude difference in resistance. This feature enables the encoding of binary data in a highly flexible format. The memory's resilience under physical deformations—such as stretching, bending, and twisting—combined with its ability to maintain data integrity over thousands of cycles, underscores its suitability for next-generation wearable and implantable electronic devices. The research not only addresses the critical challenge of developing flexible components but also opens new avenues for the application of such technologies in soft robotics, wearable electronics, and bio-inspired artificial intelligence systems.

One major benefit of the technology is that, according to the researchers, the droplets worked better as they were shrunk, meaning that shirking the technology will only yield performance improvements. This is likely due to the surface being the active component of the memory cell (as this is the layer that gets oxidised), and so the ratio of the surface area to the volume will be critical.

"The FlexRAM technology exhibits a remarkable range of possible sizes for its memory elements, extending from millimeters down to nanometers. Notably, the research findings reveal that reducing the size of these droplet-based memory elements enhances their responsiveness. According to the research team, this increased sensitivity in smaller droplets underscores the technology's versatility and potential for precision applications in flexible electronics," the researchers have noted. This detail underscores the adaptability and future possibilities of FlexRAM, showcasing its potential to revolutionise flexible electronic devices with its scalable and responsive design.

How does this new memory technology empower future devices?

While the newly developed RAM is by no means anywhere close to commercialisation, it demonstrates how there are countless materials and concepts that engineers have yet to exploit. If further refined, this memory technology could be key to creating truly flexible electronics that could be used in all manner of applications, ranging from smart labels to intelligent clothing.

The use of gallium is also critical in that it is an environmentally friendly material that is non-toxic to humans. As such, electronics utilising this memory technology would not be dangerous to the environment if disposed of in landfills (however, this would depend on what other compounds have been used in that device). 

Finally, the use of liquid metals helps to simplify the use of printing technologies, which are undoubtedly the future of flexible electronics. If combined with other organic inks and compounds, it becomes possible to construct entire electronic circuits via printing, which not only helps to significantly reduce the price of electronics but aids in the ease of manufacturing. 

Overall, what the researchers have demonstrated with their FlexRAM is nothing but brilliant, and it shows plenty of potential in its ability to store data and be flexible at the same time.