EPFL researchers used MoS2 to create an energy-efficient memory processor that is composed of more than 1,000 transistors. This processor can efficiently perform vector matrix multiplication operations, represents a shift from the traditional von Neumann architecture, and can promote the development of the European semiconductor industry.
The first large-scale memory processor using two-dimensional semiconductor materials developed by EPFL researchers could significantly reduce energy consumption in the information and communications technology sector.
When information and communications technologies (ICT) process data, they convert electrical energy into heat. Today, the global ICT ecosystem’s carbon dioxide emissions are as much as those of the aviation industry. However, it turns out that most of the energy consumed by computer processors is not used to perform calculations. Instead, most of the energy spent processing data is used to transfer bytes between memory and the processor.
In a paper published on November 13 in the journal Nature Electronics, researchers from the Laboratory of Nanoelectronics and Structures (LANES) at EPFL's School of Engineering introduce a new type of processor that solves this inefficiency by integrating data processing and storage into a single device, a so-called memory processor. They created the first memory processor composed of more than 1,000 transistors based on two-dimensional semiconductor materials, opening up a new field. This is an important milestone on the road to industrial production.
Von Neumann's legacy
Andras Kis, who led the research, believes that the main culprit of today's CPU inefficiencies stems from the commonly used von Neumann architecture. Specifically, the physical separation of components used to perform computations and store data. Because of this separation, the processor needs to retrieve data from memory to perform calculations, which requires moving charges, charging and discharging capacitors, and transmitting current along wires, all of which dissipate energy.
Until 20 years ago, this architecture was justified because data storage and processing required different types of equipment. However, the von Neumann architecture is increasingly challenged by more efficient alternatives. "Today, there are efforts to merge storage and processing into a more general-purpose memory processor that contains components that can function as both memory and transistors," explained Keith. "His lab has been exploring how to achieve this using a semiconductor material called molybdenum disulfide (MoS2)."
New 2D processor architecture
In their Nature Electronics paper, LANES PhD assistant Guilherme Migliato Marega and his co-authors introduce a MoS2-based memory processor dedicated to one of the fundamental operations in data processing: vector-matrix multiplication. Such operations are ubiquitous in the implementation of digital signal processing and artificial intelligence models. Improving its efficiency could save significant amounts of energy across the information and communications technology sector.
Their processor combines 1,024 elements onto a one centimeter square chip. Each element consists of a two-dimensional MoS2 transistor and a floating gate, which is used to store charge in memory and thereby control the conductivity of each transistor. Coupling processing and memory together in this way fundamentally changes the way processors perform computations. "By setting the conductivity of each transistor, we can perform an analog vector-matrix multiplication simply by applying a voltage to the processor and measuring the output," Keith explained.
A big step towards practical applications
In the process of developing memory processors, the choice of material MoS2 plays a crucial role. First, MoS2 is a semiconductor, which is necessary to develop transistors. Unlike silicon, the most widely used semiconductor in today's computer processors, MoS forms a stable monolayer only three atoms thick that interacts only weakly with its surroundings. Its thinness makes it possible to produce extremely compact devices. Finally, this is a material that Kis Labs is very familiar with. In 2010, they used Scotch tape to create the first single-layer MoS2 transistor using a single layer of MoS2 material peeled off the crystal.
Over the past 13 years, their craft has matured, and Migliato Marega's contribution is indispensable. "The key advance from a single transistor to more than 1,000 transistors is the quality of the material we are able to deposit. After extensive process optimization, we can now produce entire wafers covered with a uniform layer of MoS2. This allows us to design integrated circuits on the computer using industry-standard tools and translate these designs into physical circuits, opening the door to mass production," said Keith.
Revitalizing European chip manufacturing industry
In addition to its purely scientific value, Kis believes that this result demonstrates the importance of close scientific cooperation between Switzerland and the EU, especially in the context of the European Chip Act, which aims to strengthen Europe's competitiveness and adaptability in semiconductor technologies and applications. "EU funding has been crucial for this and previous projects, including funding the work on the first MoS2 transistor, which shows how important EU funding is for Switzerland," said Kees. "At the same time, it shows how the work done by Switzerland can benefit the EU in the process of revitalizing electronics manufacturing. For example, the EU can focus on developing non-von Neumann processing architectures for artificial intelligence accelerators and other emerging applications, rather than competing with others in the same race. By defining its own competition, the EU can get a head start and secure a favorable position in the future."