Chinese scholars have realized transistors with sub-1 nm gate length for the first time

Process flow diagram, characterization diagram and physical diagram of a6021 sub-1 nano gate length transistor device provided by Tsinghua University

Transistor is the core component of chip. Smaller gate size can integrate more transistors on the chip and improve performance. Recently, Ren Tianling, a professor at the school of integrated circuits of Tsinghua University, made important progress in the research of small-size transistors. For the first time, a transistor with sub-1 nm gate length was realized, which has good electrical performance. Relevant achievements are published online in nature under the title of “vertical molybdenum sulfide transistor with sub-1 nm gate length”.

In 1965, Gordon Moore, one of the founders of Intel, proposed: “the number of transistors that can be accommodated on an integrated circuit chip will double every 18-24 months, the performance of the microprocessor will double, or the price will be reduced by half.” This assertion is also known as Moore’s law. In the past decades, the gate size of transistors has been shrinking under the impetus of Moore’s law. However, in recent years, with the physical size of transistors entering the nano scale, the short channel effects such as reduced electron mobility, increased leakage current and increased static power consumption have become more and more serious, which makes the development of new structures and new materials imminent.

According to the international device and system roadmap (irds2021), at present, the gate size of transistors in mainstream industry is more than 12 nm. How to promote the further miniaturization of key transistor sizes has attracted extensive attention of industry researchers.

In terms of very short gate length transistors, academia has also made a lot of exploration before. In 2012, the International Conference on electronic devices of the Japan Institute of industrial technology reported that the V-shaped planar junction free silicon-based transistor based on silicon on insulating substrate has an equivalent physical gate length of only 3 nm.

In 2016, Lawrence Berkeley National Laboratory and Stanford University reported in the journal Science that a planar molybdenum sulfide transistor with a physical gate length of 1 nm was realized based on metallic carbon nanotube materials.

In order to further break through the bottleneck of gate length transistors below 1 nm, Ren Tianling’s research team used the ultra-thin monatomic layer thickness and excellent conductivity of graphene film as the gate to control the switching of vertical molybdenum disulfide (MoS2) channel through graphene lateral electric field, so as to reduce the equivalent physical gate length to 0.34 nm. Then, the vertical electric field shielding of graphene is completed by depositing metal aluminum on the surface of graphene and oxidizing it naturally. After that, researchers used HfO2 deposited by atomic layer as the gate medium and single-layer two-dimensional molybdenum disulfide deposited by chemical vapor deposition as the channel, and finally completed the transistor with sub-1 nm gate length.

It is found that compared with bulk silicon material, single-layer two-dimensional molybdenum disulfide has greater effective electron mass and lower dielectric constant. Under the control of sub-1 nm physical gate length, the transistor can be turned on and off effectively, and its off current is in the order of PA.

The simulation results based on process computer aided design (TCAD) further show that the graphene edge electric field can effectively regulate the vertical molybdenum disulfide channel, and predict the electrical performance of the transistor under the condition of shortening the channel length at the same time. The researchers said that this work promoted the further development of Moore’s law to the sub-1 nanometer level, and provided a reference basis for the application of two-dimensional thin films in future integrated circuits.

Links to related papers: org/10.1038/s41586-021-04323-3

Source: China Science Daily