A memory device readable through both electrical and optical methods

One material with two functions could lead to faster memory.

A newly developed device uses just a single semiconductor known as perovskite to store and visually transmit data simultaneously. The device, developed by National Taiwan Normal University and Kyushu University, is a step toward developing higher performance memory devices.

To develop this new device, scientists integrated a light-emitting electrochemical cell with a resistive RAM. Both are based on perovskite semiconductors. This integration enabled the parallel and synchronous reading of data both electrically and optically in a ‘light-emitting memory.’

With the growing need for data storage, scientists are looking for alternatives to improve speed further and simplify fabrication.

RRAM stores charge in materials that can switch between high and low resistance states to represent ones and zeros. However, the electrical measurements needed to check the resistance and read zeros and ones from RRAM can limit the overall speed.

Chun-Chieh Chang, professor at National Taiwan Normal University, said, “Recently, to overcome this issue, RRAMs have been combined with LEDs to develop something called light-emitting memories. In this case, the data can also be read by checking if the LED is on or off. This additional optical reading also opens new routes for carrying large amounts of information.”

“However, previous versions of light-emitting memories required the integration of two separate devices with differing materials, complicating fabrication.”

Scientists overcome this limitation by selecting perovskite. By controlling the ion migration, perovskite scientists have been constructing new materials with unique properties.

light emitting memory
A scanning electron microscope image of the light-emitting memory, with each key layer labeled. (Kyushu University/ Ya-Ju Lee)

Using perovskite consisting of cesium lead bromide (CsPbBr3), the team demonstrated that data could be electrically written, erased, and read in one of the perovskite devices acting as an RRAM. Simultaneously, the second perovskite device can optically transmit whether data is written or erased through light emission by working as a light-emitting electrochemical cell with a high transmission speed.

National Taiwan Normal University’s Ya-Ju Lee, who also led the study, said, “Using just one perovskite layer between contacts, we could fabricate a device that works both as an RRAM and a light-emitting electrochemical cell. By taking advantage of the fast, electrically switchable ionic motion that enables this dual functionality in a single layer of perovskite, we were able to connect two devices and develop an all-inorganic perovskite light-emitting memory.”

Later on, by using perovskite quantum dots of two different sizes for the two devices in the light-emitting memory, scientists achieved different emission colors depending on whether the memory was being written or erased. This provided a real-time indicator of the ones and zeros.

Kaoru Tamada, a distinguished professor at Kyushu University’s Institute for Materials Chemistry and Engineering, said“This demonstration significantly broadens the scope of applications of the developed all-perovskite light-emitting memory and can serve as a new paradigm of synergistic combination between electronic and photonic degrees of freedom in perovskite materials.”

“From multicast mesh network to data encryption systems, these findings have the potential for numerous applications in next-generation technologies.”

Journal Reference:
  1. Meng-Cheng Yen, Chia-Jung Lee et al. All-inorganic perovskite quantum dot light-emitting memories. Nature Communications (2021). DOI: 10.1038/s41467-021-24762-w

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