While memory devices are becoming progressively more flexible, their ease of fabrication and integration in low performance applications have been generally been treated as being of secondary importance. But now, thanks to the work of researchers at Munich University of Applied Sciences and INRS-EMT, this is about to change. In this week's Applied Physics Letters, they presents a proof of concept, using resistive memory that now paves the way for mass-producing printable electronics.
Memory devices – as a subset of electronic functions that includes logic, sensors and displays – have undergone an exponential increase in integration and performance known as Moore's Law. In parallel, our daily lives increasingly involve an assortment of relatively low-performance electronic functions implemented in computer chips on credit cards, in-home appliances, and even smart tags on consumer products.
While memory devices are becoming progressively more flexible, their ease of fabrication and integration in low performance applications have been generally been treated as being of secondary importance. But now, thanks to the work of a group of researchers at Munich University of Applied Sciences in Germany and INRS-EMT in Canada, this is about to change.
Additive manufacturing, perhaps best known because of 3-D printing, allows for a streamlined process flow -- eliminating complex lithography and material removal steps at the detriment of feature size, which is in many cases not critical for memory devices in less computationally demanding uses.
Inkjet printing is a common office technology that competes with laser printing. It offers the added benefit of a straightforward transfer from inkjet to roll-to-roll printing. In an article appearing this week in Applied Physics Letters, from AIP Publishing, the group presents a proof of concept, using resistive memory (ReRAM) that now paves the way for mass-producing printable electronics.
The basic principle behind the group's ReRAM is simple. "In any kind of memory, the basic memory unit must be switchable between two states that represent one bit, or '0' or '1.' For ReRAM devices, these two states are defined by the resistance of the memory cell," explained Bernhard Huber, a doctoral student at INRS-EMT and working in the Laboratory for Microsystems Technology at Munich University of Applied Sciences.
For the conductive-bridge random access memory (CB-RAM) used by the group, "0" is "a high-resistance state represented by the high resistance of an insulating spin-on glass, which separates a conducting polymer electrode from a silver electrode," he continued. "The '1' is a low-resistance state, which is given by a metallic filament that grows into the spin-on glass and provides a reversible short-circuit between the two electrodes."
Rather than printing colors, "we use functional inks to deposit a capacitor structure – conductor-insulator-conductor – with materials that have already been deployed in cleanroom processes," Huber said. "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 concept of CB-RAM is already well established and the group's leaders – Andreas Ruediger of INRS-EMT in Canada and Christina Schindler of Munich University of Applied Sciences – have previously worked on more conventional CB-RAM cells.