Researchers from the University of Applied Sciences Munich have developed resistive non-volative memory cells (ReRAM) flexible substrates made using a standard ink-jet printer.

The cells feature switching voltages at 0.5V, low write currents and a high ratio between high and low resistance state of 10^4. The high ratio also allows distinguishing of up to eight state of Ron and 3bit multibit storage in a single memory cell.

The cell is made up of a silver top electrode over silicon-dioxide-based spin-on-glass insulation layer over PEDOT-PSS (poly [3,4-ethylenedioxythiophene] polystyrene sulfonate) bottom layer on a 125μm thick PEN foil (Teonex Q65HA from Dupont Teijin Film).

The nano-porous spin-on-glass acts as an insulator and as a matrix for ion migration and growth of a metallic filament in the manner of a conductive-bridging RAM (CBRAM). The memory cell was approximately 100μm x 100μm cross-point. To avoid dealing with array addressing issues the memories were composed multiple cells on a single word line.

A standard FujiDimatix DMP 2831 inkjet printer was used for the printing of all 3 layers of the memory cells, the researchers said.

In an un-flexed state at a voltage of approximately 0.5V, the cells switch from the high resistance off-state to the low resistance on-state and return back to off at −0.05V. The low switching voltages combined with the small write currents, due to the high resistance of the underlying PEDOT polymer electrodes enable low power consumption memory devices. No electroforming was required as the switching mechanism is via defects in the SOG, the researchers said.

The cells feature low switching voltages, low write currents, and a high ratio between high and low resistance state of 10^4. 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.

The cells were also tested under bending and Roff and Ron, and showed no significant dependence on the bending radius down to values of 15mm, researchers said. For bending radii smaller than 15mm, the on-resistance increased substantially, but returned to the value of the non-distorted cell when brought back to a larger bending radius.

The memory cells showed an endurance of more than 1,000 switching cycles and the maximum retention time of the cells at room temperature was approximately 1.6 x 10^4 seconds (3 hours 26 minutes).

If combined with printable select transistors the cells could be used for crossbar memory arrays and because the process is not depended on any sacrificial layers the process could be transferred to roll-to-roll printing for high-throughput production. However, both the endurance and retention will require further improvements to meet industrial expectations, the authors said.

The work was reported in Applied Physics Letters.