Researchers at the Korea Institute of Science and Technology (KIST) and the Gwangju Institute of Science and Technology (GIST) designed an optoelectronic logic gate (OELG) made from organic-inorganic perovskite photodiodes. The OELG architecture will help computers quickly calculate and process large amounts of information, the researchers said. A logic gate platform that can accurately compute extensive data sets, while consuming less power, is needed to support the trend toward data-intensive technologies such as artificial intelligence. Existing electronic circuits and processors are limited by performance shortfalls in switching, operation, computing, and decision-making. The perovskite OELG is based on the bipolar spectral photoresponse characteristics of a self-powered perovskite photodetector (SPPD) that has a back-to-back (p+-i-n-p-p+) diode structure consisting of low-band and high-band perovskites. The key components used in the SPPD OELG to execute Boolean logics are a back-to-back configuration (i.e., p+-i-n-p-p+) based on two vertically stacked perovskite diodes, and optical gate modulation using visible and near-infrared light. The SPPD OELG uses light as an input signal. The desired binary logic operation is achieved by inputting two different wavelengths of light. Conceptual image of an optical processor chip for optical computers using perovskite optoelectronic logic gates (OELGs). The OELG designed by a team of researchers from KIST and GIST could be applied to health care sensing, as well as multiple applications in optical computing and communication. Courtesy of KIST. The output discrimination of the SPPD OELG is based on the polarity of the photocurrent, which can be tuned by optical gate modulation using visible (625 nm) and near-infrared (940 nm) light. The output state of 1 or 0 is determined by the positive or negative output photocurrent, respectively, allowing the SPPD OELG to execute more than one logic gate operation for the same input. The researchers demonstrated five basic logic operations — AND, OR, NAND, NOR, and NOT — with a single SPPD. An 8 × 8 logic array consisting of 64 SPPD pixels comprises the OELG platform, which executed all five logic gates at 100% yield without any errors, regardless of electrical noise or current variation between the pixels. The ability of one logic gate to perform the functions of five could enable high spatial efficiency and integration in optical processors. “The optoelectronic logic gate developed through this research is an outcome of optical computing R&D that realizes five basic logic operations into one device, and will greatly contribute to next-generation optical communication, optical networks, and health care R&D,” GIST professor Gun Young Jung said. In addition to its high-speed and high-efficiency characteristics, the SPPD OELG demonstrated low energy loss physically, and can operate without an electrical power supply by using only light energy. In contrast, electronic semiconductor logic gates, which serve as the “brains” of today’s computers, have a limited capacity to perform high-speed data calculation and processing. They also consume a lot of energy and generate considerable heat. Data processing with specific instructions (e.g., add, multiply, or count) could be implemented with a combinational circuit of multiple SPPD-OELGs in a single chip, the researchers said. This would be more efficient spatially and economically, compared to conventional logic circuits based on electronic transistors. In the future, SPPD-OELGs could improve applications for optical computing, optical communication, and logic memory. In the short term, the new OELGs could be applied to light-fidelity (Li-Fi) transmission, security circuits, and health care sensors, using to advantage the optoelectronic output states based on the photocurrent polarity. “Perovskite optoelectronic logic gates that execute multiple logic operations in response to optical input are expected to be used for ultrasmall and low-power universal optical sensor platforms in the future,” KIST researcher Yusin Pak said. The research was published in Nature Communications (www.doi.org/10.1038/s41467-022-28374-w).
