Multibit optoelectronic memory

September 21, 2018, National University of Singapore
Multibit optoelectronic memory
Schematic illustration of the optoelectronic memory device fabricated by layering a monolayer WSe2 on a 20-layer BN. Credit: National University of Singapore

NUS scientists have developed multibit optoelectronic memory using a heterostructure made of two-dimensional (2-D) materials for next generation devices.

Optoelectronic memories are devices which can store photon-generated charge carriers when exposed to light. The stored charges can be accessed later for information retrieval. These devices can be used in image capture and spectrum analysis systems. 2-D atomically layered materials are promising candidates for the development of next generation memories to meet emerging requirements for device miniaturisation and structural flexibility. However, optoelectronic memories fabricated using 2-D materials have been reported to suffer from poor data storage capability with the highest reported figure at about eight distinct storage states.

A team lead by Prof Chen Wei from both the Department of Chemistry and the Department of Physics, NUS has developed a multibit, non-volatile optoelectronic memory device that is able to store up to 130 distinct states by using a tungsten diselenide/boron nitride (WSe2/BN) heterostructure. The heterostructure, made of 2-D , comprises a monolayer of WSe2 on a 20-layer BN. The programming (store data) and erasing (delete data) functions are controlled by adjusting the applied polarity to the device. A negative polarity is applied during the programming function and it causes the photon-generated electrons from the midgap donor-like states of the BN material to transfer into the WSe2 material. This leaves behind localised (non-mobile) positive charges in the BN material. For the erasing function, a positive polarity is applied. This causes the photon-generated electrons from the valence band in the BN material to recombine with the localised positive charges, returning it to a neutral state.

The amount of electrons transferred into the WSe2 material is dependent on the duration of light exposure time for the device. A longer exposure time would mean that more electrons are transferred. The researchers found that the continual accumulation of electrons in the WSe2 material corresponding up to 130 light pulses can be detected before saturation conditions set in. Each of these pulses can be treated as a distinct storage state. During performance testing, they found that the device exhibits a data retention of over 4.5×104 seconds and a cyclic programme/ erase endurance exceeding 200 cycles.

Explaining the significance of the findings, Prof Chen said, "Although there is still a performance gap when compared to commercial silicon-based memory, these devices are advantageous in electronic applications which require structural flexibility. The use of this WSe2/BN 2-D layered heterostructure provides a method to achieve multibit device and may pave the way for the development of next generation optoelectronic memories."

Explore further: An expressway for electrons in oxide heterostructures

More information: Du Xiang et al. Two-dimensional multibit optoelectronic memory with broadband spectrum distinction, Nature Communications (2018). DOI: 10.1038/s41467-018-05397-w

Related Stories

Single photon light emitting diodes for on-chip integration

September 26, 2016

Researchers from the Graphene Flagship use layered materials to create an all-electrical quantum light emitting diodes (LED) with single-photon emission. These LEDs have potential as on-chip photon sources in quantum information ...

Recommended for you

In colliding galaxies, a pipsqueak shines bright

February 20, 2019

In the nearby Whirlpool galaxy and its companion galaxy, M51b, two supermassive black holes heat up and devour surrounding material. These two monsters should be the most luminous X-ray sources in sight, but a new study using ...

Research reveals why the zebra got its stripes

February 20, 2019

Why do zebras have stripes? A study published in PLOS ONE today takes us another step closer to answering this puzzling question and to understanding how stripes actually work.

When does one of the central ideas in economics work?

February 20, 2019

The concept of equilibrium is one of the most central ideas in economics. It is one of the core assumptions in the vast majority of economic models, including models used by policymakers on issues ranging from monetary policy ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.