Duke University Develops 3D Printing Technique That Could Enable Flexible Digital Storage

Every day, our society gets a little bit more digital. CDs still exist, but when was the last time you bought one? For people who hate clutter, the digitization of our everyday lives is a wonderful thing – our music, our documents, our photos, our books are all stored in neat little digital devices. (I’ll never stop reading actual physical books, though, despite my distaste for clutter – it’s just not going to happen.) And those devices keep getting smaller and smaller, which can be a nightmare. I have at least four or five flash drives lying around my office, but whenever I need one, they magically disappear.

What if those flash drives were incorporated directly into everyday objects, though? That’s the idea behind the new technology that Duke University researchers have come up with. The technology involves the use of an aerosol jet printer, which sprays nanoparticle inks onto substrates to create digital memory devices, analogous to 4-bit flash drives, that can be incorporated directly into products such as pill bottles or even clothing.

The device is the first 3D printed digital memory technology suitable for practical use in electronics such as RFID tags or environmental sensors – and because it’s printed at low temperatures using aerosol jetting, it can also be used to build programmable electronics on flexible materials like plastic, paper or even fabric.

“We have all of the parameters that would allow this to be used for a practical application, and we’ve even done our own little demonstration using LEDs,” said graduate student Matthew Catenacci.

The postage-stamp-sized device is composed of a copper nanowire material capable of storing information.

“Memory is kind of an abstract thing, but essentially it is a series of ones and zeros which you can use to encode information,” said associate chemistry professor Benjamin Wiley.

Those ones and zeros, when programmed into the silicon transistors that make up flash drives, correspond to charged and uncharged states, respectively. The material developed by the Duke team, which is composed of silica-coated copper nanowires encased in a polymer matrix, encodes information in states of resistance rather than states of charge. A low voltage, applied to the device, can switch it between a state of low resistance, which allows electric current to flow, and high resistance, which stops the current. The copper and polymer can also be melted, allowing them to be sprayed through a nozzle.

“We have developed a way to make the entire device printable from solution, which is what you would want if you wanted to apply it to fabrics, RFID tags, curved and flexible substrates, or substrates that can’t sustain high heat,” Wiley said.

Wiley and Catenacci documented their research in a recently published paper entitled “Fully Printed Memristors from Cu-Si O₂ Core-Shell Nanowire Composites,” which you can access here. Catenacci started by using commercially available gold nanoparticle ink to print several gold electrodes onto a glass slide. He then printed the copper nanowire material over the gold electrodes, followed by a series of copper electrodes. Finally, he connected the whole device to a circuit on which four LED lights were attached, to demonstrate how the device could be used to program the lights to flash on and off in different patterns.

The Duke team’s device, while similar to some that have been created by other researchers, is the first of its kind to have the potential for any kind of practical use. The write speed – aka the time it takes to switch back and forth between states of resistance – is about three microseconds, which is close to the speed of flash drives. Testing showed that the information written into the device could be retained for 10 years, and that the material could be rewritten several times without degrading.

The device won’t be replacing flash drives; its memory is very low, but it could be used in applications that require low cost and flexibility.

“For example, right now RFID tags just encode a particular produce number, and they are typically used for recording inventory,” Wiley said. “But increasingly people also want to record what environment that product felt — such as, was this medicine always kept at the right temperature? One way these could be used would be to make a smarter RFID tags that could sense their environments and record the state over time.”

Additional authors of the research paper include Patrick F. Flowers, Changyong Cao, Joseph B. Andrews and Aaron D. Franklin. The research was supported by a National Science Foundation CAREER Award and the Duke SMF Voucher Program. Discuss in the Duke University forum at 3DPB.com.