Build a 900 pixel imaging sensor using atomically thin material

APS 2D. a, 3D schematic (left) and optical image (right) of a single-layer MoS₂ phototransistor integrated with a programmable gate stack. The local back-gate stacks, including an atomic layer deposition grown at 50 nm Al₂O₃ on Pt/TiN deposited by sputtering, are arranged in islands above a Si/SiO₂ substrate. Monolayer MoS₂ used in this study was grown via a MOCVD technique using carbonless precursors at 900°C on an epitaxial sapphire substrate to ensure high film quality. After growth, the film was transferred to the TiN/Pt/Al₂O₃ back-gate islands and then patterned, etched, and contacted to fabricate phototransistors for the multipixel APS platform. b, Optical image of a 900-pixel 2D APS sensor fabricated in a crossbar architecture (left) and the corresponding circuit diagram showing row and column select lines (right). Credit: Natural materials (2022). DOI: 10.1038/s41563-022-01398-9

A team of researchers from Penn State University has developed a 900-pixel imaging sensor using atomically thin material. In their article published in the journal Natural materialsthe group describes how they built their new sensor and its possible uses.

Sensors that react to light have become very common in the modern world – lights that turn on when the presence of an intruder is detected, for example. Such sensors typically consist of a grid of pixels, each of which is reactive to light. The performance of these sensors is based on reactivity measurements and what parts of the light they detect.

Most are designed with certain noise-signal constraints. In this new effort, the researchers noted that most of these sensors are also very inefficient, using far more electricity than should be the case for such devices.

To make a sensor that would be more efficient, the researchers looked at the materials used to make those currently in use – typically a silicon complementary metal oxide semiconductor serves as the backbone. And that was the backbone on which the researchers focused their efforts. To make a more efficient sensor, they replaced the traditional skeleton with a skeleton made of molybdenum disulfide, a material that, like graphene, can be grown as a sheet one atom thick.

In their work, they grew it on a sapphire base by vapor deposition. Then lift the finished product from the base and lay it on a silicon dioxide base that had already been wire etched. They then finished their product by etching additional wiring on top.

The result of their work was a 30×30 grid, where each of the pixels was its own device, which was not only able to detect light, but could also be drained using an electrode which made it ready for use after something has been detected.

By evaluating the characteristics of their sensor, they found it to be much more efficient than those currently in use, with each pixel using less than a picojoule. They also found it very easy to reset. A power surge through the network did the trick. On the other hand, the researchers discovered that it reacted much more slowly to light than the sensors currently in use. This, they note, suggests it could be used as a general purpose light sensor, but not as a device within a camera. They further suggest that it could provide an ideal sensing solution in a wide variety of IoT applications.

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