Molybdenite outshines silicon and graphene for electronic applications

Researchers have uncovered a material that they say has distinct advantages over traditional silicon and even graphene for use in electronics. Called molybdenite (MoS2), this mineral is abundant in nature and is commonly used as an element in steel alloys or, thanks to its similarity in appearance and feel to graphite, as an additive in lubricant. But the mineral hadn’t been studied for use in electronics, which appears to have been an oversight with new research showing that molybdenite is a very effective semiconductor that could enable smaller and more energy efficient transistors, computer chips and solar cells.

Researchers from Ecole Polytechnique Fédérale de Lausanne (EPFL) say one of molybdenite’s advantages over silicon is its thinness. With an atomic structure consisting of a sheet of molybdenite atoms sandwiched between sheets of sulfur atoms, molybdenite is less voluminous than silicon.

“It’s a two-dimensional material, very thin and easy to use in nanotechnology. It has real potential in the fabrication of very small transistors, light-emitting diodes (LEDs) and solar cells,” says EPFL Professor Andras Kis. “In a 0.65-nanometer-thick sheet of MoS2, the electrons can move around as easily as in a 2-nanometer-thick sheet of silicon,” adds Kis, “but it’s not currently possible to fabricate a sheet of silicon as thin as a monolayer sheet of MoS2.”

Additionally, to turn a transistor on and off, a semi-conductor with a “gap” must be used and molybdenite’s 1.8 electron-volt gap is ideal for this purpose. It would allow transistors to be made that consume 100,000 times less energy in standby state than traditional silicon transistors.

But it’s not just silicon that is humbled by molybdenite. Everyone’s favorite wonder material graphene also gets a going over. In semi-conductors, electron-free spaces exist between bands of energy. These so-called “band gaps” allow certain electrons to hop across the gap if it is not too small or too large. This results in a greater level of control over the electrical behavior of the material as it can easily be turned on or off. The existence of such a gap in molybdenite gives it a distinct advantage over graphene, which has no such gap and it is difficult to artificially produce one in the material.

The EPFL team’s study showing molybdenite’s potential for use in electronics applications appears in the journal Nanotechnology Nature.

New IBM chip technology integrates electrical and optical devices on the same piece of silicon

IBM has announced another breakthrough in its long term research goal to harness the low power consumption and incredible speed promised by optical computing. Following on from the Germanium Avalanche Photodetector – a component able to receive optical information signals at 40 Gb/sec and multiply them tenfold using a mere 1.5V supply – the company has now unveiled a new chip technology that integrates electrical and optical devices on the same piece of silicon. So how far can this technology take us? Eventually, IBM hopes, all way to the Exascale – that's one million trillion calculations per second.
IBM says the new technology, called CMOS (Complementary Metal-Oxide Semiconductor) Integrated Silicon Nanophotonics, will revolutionize the way chips communicate and enable an improvement of over 10 times the integration density than is feasible with current manufacturing techniques by integrating optical devices and functions onto a silicon chip. This is possible because IBM’s new technology sees a single transceiver channel with all accompanying optical and electrical circuitry occupying only 0.5mm2, which is ten times smaller than previous efforts. This means it should be possible to manufacture single-chip transceivers as small as 4x4mm2 that can receive and transmit over a trillion bits (Terabit) per second.

Standard CMOS foundry manufacture

In addition to combining electrical and optical devices on a single chip, IBM says its new technology can be produced on the front-end of a standard CMOS manufacturing line without the need for any new or special tooling. This approach allows silicon transistors to share the same silicon layer with silicon nanophotonics devices and, to make this approach possible, IBM researchers have developed a suite of integrated ultra-compact active and passive silicon nanophotonics devices that are scaled down to the diffraction limit – the smallest size that dielectric optics can afford.
IBM says single-chip optical communications transceivers can now be manufactured in a standard CMOS foundry, rather than assembled from multiple parts made with expensive compound semiconductor technology. This is made possible through the addition of a few more processing modules to a standard CMOS fabrication flow and enables a variety of silicon nanophotonics components, such as: modulators, germanium photodetectors and ultra-compact wavelength-division multiplexers, to be integrated with high-performance analog and digital CMOS circuitry.

Shooting for an Exaflop

By dramatically increasing the speed and performance between chips, IBM expects the new technology to further its ambitious Exascale computing program, which is aimed at developing a supercomputer that can perform one million trillion calculations – or an Exaflop – in a single second. Such a supercomputer would be around one thousand times faster than the fastest machine existing today.
“The development of the Silicon Nanophotonics technology brings the vision of on-chip optical interconnections much closer to reality,” said Dr. T.C. Chen, vice president, Science and Technology, IBM Research. “With optical communications embedded into the processor chips, the prospect of building power-efficient computer systems with performance at the Exaflop level is one step closer to reality.”
The details of IBM’s research effort were presented at the major international semiconductor industry conference SEMICON held in Tokyo on the December 1, 2010.

Silicon carbide technology to take electronics to the extreme

New technology using silicon carbide electronics could enable radio transmitters that can withstand temperatures of up to 900 degrees Celsius (1,652 F). No, it’s not being developed so listeners can enjoy their favorite breakfast DJ in a worst-case global warming scenario. Rather the team behind the research envisions devices that could be dropped into the depths of the earth to provide early warning of a volcanic eruption or to provide real time data from the inside of a jet engine or nuclear power plant.

Building reliable components that will continue to work under extreme conditions has been an on-going challenge for electronic engineers. To ‘go where no technology has gone before’ and unlock the secrets of some of the world’s harshest environments, a team from Newcastle University in England is using a compound of silicon and carbon called silicon carbide (SiC), or carborundum, which is already used in high temperature/high voltage semiconductor electronics.

Strong bonds

Because of its unique molecular structure – which is more stable than silicon – SiC also has a high radiation tolerance opening up possibilities for its use in the nuclear industry. The secret of SiC is the much stronger bonds between the silicon and carbon atoms, which also require more energy to release electrons for electrical conduction. However, this also makes it more difficult to manufacture into components.

The team has successfully managed to develop the necessary components and is now working to integrate them into a device about the size of an iPhone that could be used in a variety of locations such as power plants, aircraft engines and even volcanoes.

Dr Alton Horsfall, who leads the SiC work alongside Professor Nick Wright, explains: "At the moment we have no way of accurately monitoring the situation inside a volcano and in fact most data collection actually goes on post-eruption. With an estimated 500 million people living in the shadow of a volcano this is clearly not ideal.

"We still have some way to go but using silicon carbide technology we hope to develop a wireless communication system that could accurately collect and transmit chemical data from the very depths of a volcano," Horsfall said.

Volcanic monitoring is just one of the strands of research being carried out at the Centre for Extreme Environment Technology.

Underwater and the underground

With expertise in underwater communications, Professor Bayan Sharif, Jeff Neasham and Dr Charalampos Tsimenidis have developed a micro Remotely-Operated Vehicle that can be used to feed back environmental data about our coastlines. The team is also working on through metal communications which involves transmitting a signal through almost 10cm (3.9-in) of steel and wireless sensor networks.

"If someone sets off a bomb on the underground, for example, this will still sit on the wall and tell you what’s going on," says Dr Horsfall. “If a dirty bomb has gone off you want to know what’s happened before you send anyone in."

Professor Nick Wright, pro-vice chancellor for innovation and research at Newcastle University, added: "The situations we are planning to use our technology in means it’s not enough for the electronics to simply withstand extremes of temperature, pressure or radiation – they have to continue operating absolutely accurately and reliably.

"Increasingly mankind is spreading out into harsher and more extreme environments as our population grows and we explore new areas for possible sources of energy and food in order to sustain it. But with this comes new challenges and this is why research into extreme technologies is becoming ever more important."