Engineered crystals could make computers more energy efficient

Researchers at the University of California, Berkeley (UC Berkeley) have made a major breakthrough in the design of a component of transistors that could make them more energy-efficient without compromising their speed, size or performance.

According to them, the component called gate oxide, a thin layer of material that converts the applied voltage into an electric charge, plays a key role in switching the transistor on and off.

The researchers attribute this boost in efficiency to an effect called negative capacitance that can boost the performance of the gate oxide by reducing the amount of voltage required to achieve a given electrical charge. However, the effect can be achieved in just any material. Previously, negative capacitance has only been achieved in ferroelectric materials called perovskites, whose crystal structure is not compatible with silicon.

In this new study, the researchers showed that the effect can also be achieved in an engineered crystal structure called a superlattice, which is composed of hafnium oxide and zirconium oxide. By incorporating the material into model transistors, the study demonstrates how the negative capacitance effect can dramatically reduce the amount of voltage required to control transistors, and ultimately the amount of energy consumed by computers.

The team found that a superlattice structure composed of three atomic layers of zirconium oxide sandwiched between two single atomic layers of hafnium oxide, totaling less than 2nm in thickness, provided the best negative capacitance effect.

To test the performance of superlattice structure as a gate oxide, they fabricated short channel transistors and found that these transistors would require approximately 30% less voltage while maintaining semiconductor industry benchmarks and with no loss of reliability, compared to existing transistors.

"We have been able to show that our gate-oxide technology is better than commercially available transistors: What the trillion-dollar semiconductor industry can do today — we can essentially beat them," said study senior author Sayeef Salahuddin, the TSMC Distinguished professor of Electrical Engineering and Computer Sciences at UC Berkeley.

The findings are published in the journal Nature. More information can be found here.