The importance of resistive random access memory which functions by means of a memristor has wide attractive features compared to other memory devices. They are known to function at faster timescale and lower voltage applications coupled with their desired small-sized structures. These attractive features make them practically applicable for challenges faced in non-volatile memory devices.
Despite this, the issue of sneak peak current interference which occurs at larger crossbar arrays lowers the capacity of a resistive random access memory due to increased power consumption. This can be minimized by increasing the resistive switching ratios between the high and low resistant states, but ability of these devices to read and detect data during the switching process which relies on current measurements remains a bane to this approach. It is therefore important to develop ways of controlling these challenges faced from the sneak path current interference.
In line with this, researchers led by Professor Jinho Bae at Jeju National University and in collaboration with Dr. Sangho Shin at Rowan University and Professor Nobuhiko Kobayashi at University of California Santa Cruz proposed a flexible and ultra-low non-volatile resistive random access memory NVRRAM which consists of crossbar memristor with poly (4-vinylphenol) PVP layer and a pull-up resistor connected to each column bar. They made use of the electrohydrodynamic printing technique to fabricate a 3 ´ 3 flexible dimensional non-volatile resistive random access memory array to further ascertain its functionality. The research work is now published in Organic Electronics.
They made investigations on a single bit memory cell; fabricated on a polyethylene terephthalate substrate was investigated upon series connection between the pull-up resistor and memristor. A timing diagram of the single bit read/write cycle was also provided. A low voltage level was set as logic 0 and the high voltage level as logic 1. The write mode voltage was ±2 V while read mode voltage of 0.5 V was applied.
The team observed the current-voltage curve of the poly (4-vinylphenol) based memristor to have a high and low resistance state to be 10 Gῼ and 10 Mῼ respectively, implying a high OFF/ON resistive switching ratio of about a thousand which operated at low operating current of 10-100 nA.
They also observed long retention performance when the high and low resistance states where measured for a period of 180 days. The steadiness observed in the resistance values of both the high and low resistance states was maintained when measured at a time more than 180 days. This was achieved due to their further encapsulation with plydimethylsiloxane.
The non-volatile resistive random access memory also exhibited some level of bendability down to 10mm when tested for 1000 cycles. They also observed very low power consumption less than 8.33 nW which makes them applicable for non-volatile memory technologies.
The authors of the study were able to fabricate a flexible memory device with high resistive switching ratios, ultra-low power consumption coupled with a high level of detection margins in data for reading and writing operations which could be applicable to other non-volatile random access memory device.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (NRF-2016R1A2B4015627).
Ali, S., Bae, J., Lee, C.H., Shin, S., Kobayashi, N.P. Ultra-low Power Non-Volatile Resistive Crossbar Memory Based on Pull up Resistors, Organic Electronics 41 (2017) 73-78.Go To Organic Electronics