Liquid metals come to the rescue of semiconductors
Possible pathway to fast-switching, ultra-low energy electronics based on
2D materials

Date:
October 12, 2020
Source:
ARC Centre of Excellence in Future Low-Energy Electronics
Technologies
Summary:
Two-dimensional semiconductors offer a possible solution to the
limited potential for further shrinking of traditional silicon-based
electronics: the long-predicted end of 'Moore's Law'. 2D-based
electronics, which could eliminate wasted dissipation of heat and
allow for very fast, ultra-low energy operation, could be enabled
by a new liquid-metal deposition technique.



FULL STORY ========================================================================== Moore's law is an empirical suggestion describing that the number of transistors doubles every few years in integrated circuits (ICs). However, Moore's law has started to fail as transistors are now so small that
the current silicon-based technologies are unable to offer further opportunities for shrinking.


==========================================================================
One possibility of overcoming Moore's law is to resort to two-dimensional semiconductors. These two-dimensional materials are so thin that they can
allow the propagation of free charge carriers, namely electrons and holes
in transistors that carry the information, along an ultra-thin plane. This confinement of charge carriers can potentially allow the switching of
the semiconductor very easily. It also allows directional pathways for
the charge carriers to move without scattering and therefore leading to infinitely small resistance for the transistors. This means in theory
the two-dimensional materials can result in transistors that do not waste energy during their on/ off switching. Theoretically, they can switch very
fast and also switch off to absolute zero resistance values during their non-operational states. Sounds ideal, but life is not ideal! In reality,
there are still many technological barriers that should be surpassed for creating such perfect ultra-thin semiconductors. One of the barriers
with the current technologies is that the deposited ultra-thin films
are full of grain boundaries so that the charge carriers are bounced
back from them and hence the resistive loss increases.

One of the most exciting ultra-thin semiconductors is molybdenum
disulphide (MoS2) which has been the subject of investigation for the
past two decades for its electronic properties. However, obtaining very large-scale two-dimensional MoS2 without any grain boundaries has been
proven to be a real challenge. Using any current large-scale deposition technologies, grain-boundary-free MoS2 which is essential for making
ICs has yet been reached with acceptable maturity.

However, now researchers at the School of Chemical Engineering, University
of New South Wales (UNSW) have developed a method to eliminate such
grain boundaries based on a new deposition approach.

"This unique capability was achieved with the help of gallium metal in
its liquid state. Gallium is an amazing metal with a low melting point
of only 29.8 DEGC. It means that at a normal office temperature it is
solid, while it turns into a liquid when placed at the palm of someone's
hand. It is a melted metal, so its surface is atomically smooth. It is
also a conventional metal which means that its surface provides a large
number of free electrons for facilitating chemical reactions." Ms Yifang
Wang, the first author of the paper said.

"By bringing the sources of molybdenum and sulphur near the surface of
gallium liquid metal, we were able to realize chemical reactions that
form the molybdenum sulphur bonds to establish the desired MoS2. The
formed two- dimensional material is templated onto an atomically smooth
surface of gallium, so it is naturally nucleated and grain boundary
free. This means that by a second step annealing, we were able to obtain
very large area MoS2 with no grain boundary. This is a very important
step for scaling up this fascinating ultra-smooth semiconductor." Prof
Kourosh Kalantar-Zadeh, the leading author of the work said.

The researchers at UNSW are now planning to expand their methods to
creating other two-dimensional semiconductors and dielectric materials
in order to create a number of materials that can be used as different
parts of transistors.


========================================================================== Story Source: Materials provided by ARC_Centre_of_Excellence_in_Future_Low-Energy_Electronics
Technologies. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Yifang Wang, Mohannad Mayyas, Jiong Yang, Jianbo Tang, Mohammad B.

Ghasemian, Jialuo Han, Aaron Elbourne, Torben Daeneke, Richard
B. Kaner, Kourosh Kalantar‐Zadeh. Self‐Deposition of 2D
Molybdenum Sulfides on Liquid Metals. Advanced Functional Materials,
2020; 2005866 DOI: 10.1002/adfm.202005866 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201012120015.htm

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