New York University (NYU), USA: Important breakthrough in 2D semiconductor device fabrication process!

Background

Currently, the traditional semiconductor materials represented by silicon are facing serious challenges. Through principle innovation, structural improvement, and process advancement, it is difficult for researchers to significantly improve the overall performance of silicon-based semiconductor devices. The "post-Moore era" has quietly arrived. As a new generation of semiconducting materials expected to replace silicon-based semiconductor materials, research on 2D semiconductors has progressed rapidly in recent years.

Graphene, with its advantages of high mechanical strength, good electrical and thermal conductivity, thinness, flexibility, transparency, etc., was once known as the "king of new materials", and has made 2D materials a hotspot for attention. Unfortunately, the unique arrangement of carbon atoms in graphene, although conducive to the easy high-speed flow of electrons, but also makes it unsuitable as a semiconductor. Graphene does not have a bandgap and cannot be selected to "turn on" or "turn off" current, the binary switching mechanism that underlies modern electronics.

However, in addition to graphene, more and more 2D materials are being discovered and studied, and many of them can be used as semiconductors, such as transition metal sulfur compounds and black phosphorus. Scientists have already created many semiconductor devices from these 2D materials, such as:

However, in the manufacturing process of 2D semiconductor devices represented by molybdenum disulfide (MoS2), the use of electron-beam lithography to nano-engrave metal electrodes onto the layers of this atomic-level 2D material is currently creating problems that result in "non-ohmic contacts" and "non-ohmic contacts". " and "Schottky barriers".

Innovation

Recently, a team led by Elisa Riedo, a professor in the Department of Chemical and Biomolecular Engineering at the School of Engineering at New York University, reported an important breakthrough in the fabrication process for atomically thin processors. This discovery will not only have a profound impact on the nano-chip manufacturing process, but will also inspire scientists in labs around the world who are exploring the application of two-dimensional materials to smaller and faster semiconductors.

The team published their findings in a recent issue of the journal Nature Electronics.

Technology

The etching technique they demonstrated, which uses a probe heated to more than 100 degrees Celsius, goes beyond the common method of making metal electrodes on two-dimensional semiconductors such as molybdenum disulfide. The scientists believe that this transition metal belongs to the class of materials that are expected to replace silicon in atomic-scale microchip applications. The new fabrication method developed by the team, called thermal scanning probe etching (t-SPL), offers a number of advantages over current electron beam lithography (EBL) techniques.

Values

First, thermal etching significantly improves the quality of the 2D transistor, canceling out the Schottky barrier. The Schottky barrier impedes electron flow at the junction of the 2D substrate and metal. Second, unlike EBL, thermal etching allows chip fabricators to easily obtain an image of the 2D semiconductor and then etch the electrodes at the desired locations. Third, t-SPL fabrication systems are expected to significantly reduce initial investment as well as operating costs: they dramatically reduce power consumption by operating under normal ambient conditions, eliminating the need to generate high-energy electrons as well as ultra-high vacuum. Finally, this thermal processing method can be easily scaled up to industrial production by using "parallel" thermal probes.

Riedo said she expects t-SPL to bring many processes out of the rarefied clean room and into the personal lab. In the clean room, researchers have to buy time for these expensive devices; in the personal lab, they will rapidly advance materials science and chip design. the precedent of the 3D printer is a good analogy. One day, these sub-10-nanometer-resolution t-SPL tools, running on a standard 120-volt power supply under ordinary environmental conditions, will be available in research labs like hers.

References

1/articles/ncomms8702

3Xiaorui Zheng, Annalisa Calò, Edoardo Albisetti, Xiangyu Liu, Abdullah Sanad M. Alharbi, Ghidewon Arefe, Xiaochi Liu, Martin Spieser, Won Jong Yoo, Takashi Taniguchi, Kenji Watanabe, Carmela Aruta, Alberto Ciarrocchi. Andras Kis, Brian S. Lee, Michal Lipson, James Hone, Davood Shahrjerdi, Elisa Riedo. Patterning metal contacts on monolayer MoS2 with vanishing Schottky barriers using thermal nanolithography . Nature Electronics, 2019; 2 (1): 17 DOI: 10.1038/s41928-018-0191-0