Researchers are developing an approach to the manufacture of high-performance transistors based on 2D semiconductors.

Two-dimensional (2D) semiconductor materials have distinct optoelectronic properties that can be useful for the development of ultra-thin and customizable electronic components. Despite their potential advantages over volumetric semiconductors, the optimal interaction of these materials with the gate dielectrics has so far proven to be a difficult task, which often led to the formation of interphase traps that quickly deteriorated the characteristics of transistors.

Researchers from King Abdullah University of Science and Technology (KAUST), Suzhou University and other institutions around the world have recently presented an approach that can create more efficient transistors based on 2D semiconductors. Their proposed design, set out in an article in the journal Nature Electronics, involves the use of dielectrics made of hexagonal boron nitride (h-BN) and metal shutter electrodes with high cohesion energy.

"Initially, we found that when we use platinum (Pt) as an anode, the h-BN battery is less likely to cause a dielectric breakdown," Yaqing Shen, the first author of the article, told Tech Xplore. "Based on this discovery, we developed our experiments and found that Pt/h-BN valve stacks show 500 times less leakage current than Au/h-BN gate stacks, and demonstrate high dielectric strength of at least 25 MV/cm. This gave us the idea of using CVD h-BN as a gate dielectric in 2D transistors."

Shen, Professor Mario Lanza and their colleagues produced more than 1,000 devices using chemical vaporized h-BN as a dielectric. When they evaluated these devices, they found that the h-BN gate dielectrics are best compatible with metals with high cohesion energy, such as Pt and tungsten (W).

"To manufacture transistors with a vertical structure of Pt/h-BN/MoS2, we started by cleaning the SiO2/Si substrate using ultrasonic baths in acetone, alcohol and deionized water," Shen explained. "The source and drain electrodes (Ti/Au) were applied to this substrate using electron beam lithography and applied by electron beam deposition. Subsequently, MoS2 was detached from the natural crystal and transferred to these electrodes to form a channel. CVD h- The BN film was transferred to this structure by wet transfer".

At the last stage of the transistor manufacturing process, the researchers applied a drawing to the platinum shutter electrode using electron beam lithography, and then applied it using a method known as electron beam evaporation. The clean Van der Waals interface between MoS2 and h-BN in the command transistor increases its reliability and performance by minimizing defects and improving shutter control.

"We found that contrary to the idea that CVD h-BN is a bad gate dielectric, the choice of the right metal electrodes allows it to be used effectively in field-effect transistors with MoS2 channels," Shen said. "MoS2 and h-BN form a clean Van der Waals interface, which increases reliability. Our results show that the use of metals with high cohesion energy, such as Pt and W, makes CVD h-BN an effective gate dielectric in 2D transistors".

The approach of this research group to the manufacture of two-dimensional semiconductor transistors has now turned out to be very promising, as it reduces current leakage and provides a high dielectric strength of at least 25 MV cm-1. Initial tests showed that Pt and W-based gate electrodes reduce the leakage current through h-BN dielectrics by about 500 times compared to similar transistors with gold (Au) electrodes.

The recent work of Shen and her colleagues can facilitate the use of 2D materials for the manufacture of reliable solid-state microelectronic circuits and devices.