Mass production of low-cost, flexible inkjet-printed electronics

Researchers demonstrate by producing an inkjet-printed flexible resistive memory
April 5, 2017

Experimental flexible resistive memory printed on a polyimide foil. The lines are silver contacts; four memory cells can be seen around the lines by zooming in. (credit: Michael Kaiser)

A group of researchers at Munich University of Applied Sciences in Germany and INRS-EMT in Canada is paving the way for mass-producing low-cost printable electronics by demonstrating a fully inkjet-printable, flexible resistive memory.*

Additive manufacturing (commonly used in 3-D printing), allows for a streamlined process flow, replacing complex lithography (used in making chips), at the detriment of feature size, which however is usually not critical for memory devices in less computationally demanding uses.

Inkjet printing allows for roll-to-roll printing, making possible mass-produced printable electronics. In an open-access paper appearing this week in Applied Physics Letters, from AIP Publishing, the group presents a proof of concept for using inkjet printing of resistive memory (ReRAM).

“We use functional inks to deposit a capacitor structure — conductor-insulator-conductor — with commercially available materials** that have already been deployed in cleanroom processes,” said Bernhard Huber, a doctoral student at INRS-EMT and working in the Laboratory for Microsystems Technology at Munich University of Applied Sciences. “This process is identical to that of an office inkjet printer, with an additional option of fine-tuning the droplet size and heating the target material.”

The process enables extremely low-cost flexible electronics and may lead to print-on-demand electronics, which shows huge potential for small, flexible lines of production and end-user products, the researchers suggest.

Examples include supermarkets printing their own smart tags, public transport providers customizing multifunctional tickets on demand, and wearables.

* Currently, computing devices use two different types of memory: a non-volatile but slow storage memory like Flash and a fast but volatile random access memory (RAM) like DRAM. Resistive RAM combines non-volatile behavior and fast read-and-write access in one device. The two memory states (0 and 1) are defined by the resistance of the memory cell.

** Silver/spin-on-glass (SOG)/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) cells were fabricated by inkjet printing alone. The cells feature low switching voltages, low write currents, and a high ratio between high and low resistance state of 10,000.

UPDATE April 9. 2017: “3D-printed” removed and new higher-resolution image used.

Abstract of Fully inkjet printed flexible resistive memory

Resistively switching memory cells (ReRAM) are strong contenders for next-generation non-volatile random access memories. In this paper, we present ReRAM cells on flexible substrates consisting of Ag/spin-on-glass/PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate).

The complete cell is fabricated using a standard inkjet printer without additional process steps. Investigations on the spin-on-glass insulating layer showed that low sintering temperatures are sufficient for good switching behavior, providing compatibility with various foils. The cells feature low switching voltages, low write currents, and a high ratio between high and low resistance state of 104. Combined with excellent switching characteristics under bending conditions, these results pave the way for low-power and low-cost memory devices for future applications in flexible electronics.