RAM At The Speed Of Light?

Scientists in Singapore have created a new type of random-access memory that uses light for reading out information. The prototype RAM, which is based on ferroelectrics, boasts significantly faster write/read speeds, better longevity and low energy consumption compared to current technologies. The resultant FeRAM is being billed as a possible “universal memory” contender to displace flash.

Researchers from Nanyang Technological University in Singapore based their RAM prototype on the ferroelectric material BiFeO3. Previous versions of FeRAM could only achieve read-outs by destructing the original information, thus requiring a rewrite step. The Singaporean researchers worked around this by introducing the ferroelectric photovoltaic effect, which enables light to induce electric currents. Explain the authors:

BiFeO3, a multiferroic material with robust ferroelectric and magnetic order at room temperature, and a band gap (B2.7 eV) that is within visible light range, offers a unique opportunity for memory application. As both signs of Voc and short circuit photocurrent (Isc) depend on the polarization direction they can serve as the read-out signal in a memory device.

While the writing step is performed as in regular ferroelectric random-access memories using a negative or positive voltage pulse, the information is then read out by shining light on the sample. The light gives rise to a photocurrent whose polarization reveals whether a positive or negative voltage pulse had been applied in the writing step.

A prototype 16-cell memory based on the cross-bar architecture was prepared and tested by the researchers to demonstrate the feasibility of the technique. Their results showed voltage pulses as short as 10 nanoseconds, indicating the incredibly high writing speed of the memory.

“For the reading process, as it does not require switching of polarization and the light can be kept on whenever the device is in operation, so the photovoltaic response of every cell is always ready for reading and the speed is only limited by the RC-time constant of the circuit,” adds the paper.

The memory cells were also subjected to bipolar switching for up to 108 cycles and showed no signs of fatigue, suggesting that the non-volatile memory can sustain much more read/write cycles than flash memory. This can be further mitigated by using oxide electrodes.

Compared with flash memory, the photovoltaic FeRAM reported here has much higher operation speed and lower energy consumption. It also compares favourably with other non-volatile memories that are under development currently, for example, magnetic random access memory and resistive switching random access memory. In summary, we report here a novel approach to create a non-volatile memory technology that uses the polarization-dependent photovoltaic effect in ferroelectrics.

While the photovoltaic effect in ferroelectrics is not a new discovery, this latest research could bring it one step closer to entering mainstream electronics. Furthermore, the authors note that further optimisation on the film thickness and electrode materials selection could result in even better performance.

Non-volatile memory based on the ferroelectric photovoltaic effect [Nature Communications]

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