January 30, 2011

Molybdenite better than silicon and in some ways graphene for computer chips

Molybdenite can make smaller and 100,000 times more energy-efficient electronic chips. Molybdenite is abundant in nature, is often used as an element in steel alloys or as an additive in lubricants. 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.

One of molybdenite's advantages is that it is less voluminous than silicon, which is a three-dimensional material. "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," explains Kis. "But it's not currently possible to fabricate a sheet of silicon as thin as a monolayer sheet of MoS2." (H/T nanopatents and innovations)

Another advantage of molybdenite is that it can be used to make transistors that consume 100,000 times less energy in standby state than traditional silicon transistors. A semi-conductor with a "gap" must be used to turn a transistor on and off, and molybdenite's 1.8 electron-volt gap is ideal for this purpose.

Graphene doesn't have a bandgap, and it is very difficult to artificially reproduce one in the material. Molybdenite has a bandgap.

Nature Nanotechnology - Single-layer MoS2 transistors

Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS2 have a large intrinsic bandgap of 1.8 eV, previously reported mobilities in the 0.5–3 cm2 V−1 s−1 range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS2 mobility of at least 200 cm2 V−1 s−1, similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10^8 and ultralow standby power dissipation. Because monolayer MoS2 has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS2 could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.

6 pages of supplemental material


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