Engineers at Stanford identify ultrathin semiconductor materials for future electronics

Source: Xinhua| 2017-08-13 10:57:56|Editor: Song Lifang
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SAN FRANCISCO, Aug. 12 (Xinhua) -- Electrical engineers at Stanford University have identified two semiconductors, hafnium diselenide and zirconium diselenide, that share or exceed some of silicon's desirable traits, starting with the fact that all three materials can "rust," which insulates its tiny circuitry.

Described in a paper published Friday in the journal Science Advances, the new materials can be shrunk to functional circuits just three atoms thick and they require less energy than silicon circuits.

Among several qualities that have led silicon to become the bedrock of electronics, one is that it is blessed with a very good "native" insulator, silicon dioxide or, in plain English, silicon rust.

Exposing silicon to oxygen during manufacturing gives chip-makers an easy way to isolate their circuitry. Other semiconductors do not "rust" into good insulators when exposed to oxygen, so they must be layered with additional insulators, a step that introduces engineering challenges.

Both of the diselenides the Stanford researchers tested formed this elusive, yet high-quality insulating rust layer when exposed to oxygen. Both ultrathin semiconductors form what are called "high-K" insulators, which enable lower power operation than is possible with silicon and its silicon oxide insulator.

In addition, as they started shrinking the diselenides to atomic thinness, the researchers realized that the semiconductors share another of silicon's secret advantages: the energy needed to switch transistors on, a critical step in computing called the band gap, is in a just-right range.

While both materials were in the same optimal range as silicon, any other semiconductors that need too low energy to switch transistors on could result in leaky and unreliable circuits, and others that need too high could lead to circuits taking too much energy to operate and becoming inefficient.

The combination of thinner circuits and desirable high-K insulation means that the two ultrathin semiconductors could be made into transistors 10 times smaller than anything possible with silicon today.

Although still experimental, the researchers believe the materials could be a step toward the kinds of thinner, more energy-efficient chips demanded by devices of the future.

Next, they need to refine the electrical contacts between transistors on their ultrathin diselenide circuits, work to better control the oxidized insulators to ensure they remain as thin and stable, then begin to integrate with other materials and to scale up to working wafers, complex circuits and eventually complete systems.

As there is much work ahead, the researchers acknowledge that silicon will not go away for quite a long time.