Researchers from KAUST have developed smart digital image sensors that can perform visual perception capabilities such as scene recognition through exploiting the Nobel-Prize-winning technology of the charge-coupled device (CCD) image sensors found in early digital cameras. The team, led by Dayanand Kumar and Nazek El-Atab, adapted and enhanced the CCD’s core structure to create light-sensitive memory devices that can be programmed by light. The research team embedded the two-dimensional material MoS2 into a semiconductor capacitor (MOSCAP) structure that underpins the charge-storing pixels of a CCD sensor. The resulting Al/Al2O3/MoS2/Al2O3/Si MOSCAP structures function as a charge-trapping “in-memory” sensor that is sensitive to visible light and can be programmed optically and erased electrically.
El-Atab explains that the “in-memory” light sensors are multifunctional memory devices that can perform the roles of multiple devices at once, including optical sensing, storage and computation. The team’s long-term goal is to demonstrate in-memory sensors that can detect different stimuli and compute. This can overcome the memory wall and allows for faster and more real-time data analysis using reduced power consumption, which is a requirement in many futuristic and state-of-the-art applications such as the Internet of Things, autonomous cars and artificial intelligence, among others.
The team showed that it was possible to perform simple binary image recognition, distinguishing between images of either a dog or an automobile, with an accuracy of 91%. Each image was 32×32 pixels in size, and only the blue information from the images was extracted since that corresponds to the device’s peak sensitivity.
The researchers are currently exploring the development of in-memory optical sensors that can be fully optically operated. In related work published in Advanced Materials, the team explored the use of black phosphorus to create an optoelectronic memristive synapse that mimics the brain’s neurons for neuromorphic computing applications. Their multilayer device consists of a thin layer of black phosphorus and hafnium oxide that is sandwiched between a lower layer of platinum and an upper layer of copper, operating as an optoelectronic memristor that can have its electrical resistance programmed by visible light.
The device offers highly stable synaptic features, such as long-term potentiation, long-term depression, and short-term plasticity, which are all important neuronal behaviors. The team constructed a 6×6 synaptic array from the devices, and in the future, they hope that larger arrays could help realize a biomimetic retina. The devices can be fabricated cost-effectively by solution processing and are flexible with stable operation with a bend radius of 1 centimeter, offering possibilities for wearable applications.
The ultimate aim of the research is to create a single optoelectronic device that can perform optical sensing and storage with computing capabilities. The research team’s groundbreaking work in developing smart digital image sensors with visual perception capabilities is a significant step in the world of technological advancement and has the potential to revolutionize various industries, from autonomous vehicles to the Internet of Things.
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