The first 2D microprocessor — based on a layer of just 3 atoms

May one day replace traditional microprocessor chips as well as open up new applications in flexible electronics
April 24, 2017

Overview of the entire chip. AC = Accumulator, internal buffer; PC = Program Counter, points at the next instruction to be executed; IR = Instruction Register, used to buffer data- and instruction-bits received from the external memory; CU = Control Unit, orchestrates the other units according to the instruction to be executed; OR = Output Register, memory used to buffer output-data; ALU = Arithmetic Logic Unit, does the actual calculations. (credit: TU Wien)

Researchers at Vienna University of Technology (known as TU Wien) in Vienna, Austria, have developed the world’s first two-dimensional microprocessor — the most complex 2D circuitry so far. Microprocessors based on atomically thin 2D materials promise to one day replace traditional microprocessors as well as open up new applications in flexible electronics.

Consisting of 115 transistors, the microprocessor can run, simple user-defined programs stored in an external memory, perform logical operations, and communicate with peripheral devices. The microprocessor is based on molybdenum disulphide (MoS2), a three-atoms-thick 2D semiconductor transistor layer consisting of molybdenum and sulphur atoms, with a surface area of around 0.6 square millimeters.

Schematic drawing of an inverter (“NOT” logic) circuit (top) and an individual MoS2 transistor (bottom) (credit: Stefan Wachter et al./Nature Communications)

For demonstration purposes, the microprocessor is currently a 1-bit design, but it’s scalable to a multi-bit design using industrial fabrication methods, says Thomas Mueller, PhD., team leader and senior author of an open-access paper on the research published in Nature Communications.*

New sensors and flexible displays

Two-dimensional materials are flexible, making future 2D microprocessors and other integrated circuits ideal for uses such as medical sensors and flexible displays. They promise to extend computing to the atomic level, as silicon reaches its physical limits.

However, to date, it has only been possible to produce individual 2D digital components using a few transistors. The first 2D MoS2 transistor with a working 1-nanometer (nm) gate was created in October 2016 by a team led by Lawrence Berkeley National Laboratory (Berkeley Lab) scientists, as KurzweilAI reported.

Mueller said much more powerful and complex circuits with thousands or even millions of transistors will be required for this technology to have practical applications. Reproducibility continues to be one of the biggest challenges currently being faced within this field of research, along with the yield in the production of the transistors used, he explained.

* “We also gave careful consideration to the dimensions of the individual transistors,” explains Mueller. “The exact relationships between the transistor geometries within a basic circuit component are a critical factor in being able to create and cascade more complex units. … the major challenge that we faced during device fabrication is yield. Although the yield for subunits was high (for example, ∼80% of ALUs were fully functional), the sheer complexity of the full system, together with the non-fault tolerant design, resulted in an overall yield of only a few per cent of fully functional devices. Imperfections of the MoS2 film, mainly caused by the transfer from the growth to the target substrate, were identified as main source for device failure. However, as no metal catalyst is required for the synthesis of TMD films, direct growth on the target substrate is a promising route to improve yield.

Abstract of A microprocessor based on a two-dimensional semiconductor

The advent of microcomputers in the 1970s has dramatically changed our society. Since then, microprocessors have been made almost exclusively from silicon, but the ever-increasing demand for higher integration density and speed, lower power consumption and better integrability with everyday goods has prompted the search for alternatives. Germanium and III–V compound semiconductors are being considered promising candidates for future high-performance processor generations and chips based on thin-film plastic technology or carbon nanotubes could allow for embedding electronic intelligence into arbitrary objects for the Internet-of-Things. Here, we present a 1-bit implementation of a microprocessor using a two-dimensional semiconductor—molybdenum disulfide. The device can execute user-defined programs stored in an external memory, perform logical operations and communicate with its periphery. Our 1-bit design is readily scalable to multi-bit data. The device consists of 115 transistors and constitutes the most complex circuitry so far made from a two-dimensional material.