Mass Producing Printed Electronics
The Engineer posted on April 04, 2017 |
A memory test devices on a polyimide foil. (Image courtesy of Huber et al.)
A memory test devices on a polyimide foil. (Image courtesy of Huber et al.)
Memory devices—as a subset of electronic functions that includes logic, sensors and displays—have undergone an exponential increase in integration and performance. 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 lags behind. But now, thanks to a group of researchers at Munich University of Applied Sciences in Germany and INRS-EMT in Canada, this is about to change.

In an article appearing this week in Applied Physics Letters, the group presents a proof of concept, using resistive memory (ReRAM), that could pave 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’,” explained Bernhard Huber, a doctoral student at INRS-EMT and working in the Laboratory for Microsystems Technology at Munich University of Applied Sciences. “For ReRAM devices, these two states are defined by the resistance of the memory cell."

“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," Huber 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."

Christina Schindler and Bernhard Huber in front of their inkjet printer in the laboratory. (Image courtesy of Huber et al.)
Christina Schindler and Bernhard Huber in front of their inkjet printer in the laboratory. (Image courtesy of Huber et al.)
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.

"We not only demonstrated that a complete additive process was possible but also that the performance parameters are comparable to cleanroom-fabricated devices," Schindler said. "The biggest technological appeal is the mechanical flexibility of our memory tiles, and the fact that all materials required for processing are commercially available."

"From our proof of concept, we're paving a road toward optimization," Schindler said. "Our biggest surprise was how little device performance depends on the fabrication process."

"Print-on-demand electronics are another large field of possible applications," Ruediger said. "At present, the main source of versatile electronics is field-programmable gate arrays that provide a reconfigurable circuitry that can be adopted for different purposes with predefined limitations."

"Just imagine supermarkets printing their own smart tags or public transport providers customizing multifunctional tickets on demand. 'Wearables' that explicitly require flexible electronics may also benefit," Schindler said.

According to the researchers, the costs for such a printer, after optimization of the process steps, could drop to within the range of current inkjet printers.

For more printable electronics news, find out how these Printed Electronics Heal in Record Time.

Source: American Institute of Physics

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