Debate on graphene

Post date: Sep 25, 2013 4:29:03 AM

There is an expanding discussion about whether graphene is a promising material for further nano electronics. Due to the limitation of graphene large-scale production and the high subthreshold current in graphene transistors, many engineers and scientists began to doubt the role of graphene in the post-silicon time. However, if graphene is not the appropriate choice, which material could replace silicon for next-generation electronic industry? Perhaps, no material could have more chances to play an important role than graphene in the future. Given that graphene has ultrahigh intrinsic carrier mobility and atomically thin body, it still possesses many opportunities to enhance the development of electronic community.

When graphene was refound firstly at 2004, authorities in the scientific world were shocked, since graphene was only an imaginary structure before. The intrinsic electron mobility of graphene is highest among all known materials, and this property could be utilized to make radio frequency devices. Until now, the value of electron mobility in graphene has been measured up to 1,000,000; the value is reached when high-quality graphene is suspended. With the same on current, the lower the subthreshold current is, the better these logical transistors are. Transistors for radio frequency are not required to have low subthreshold current, but to have high operation speed. In terms of operation speed, the higher the carrier mobility is, the faster these transistors operate. Thus, graphene transistors are best choice if we only consider this aspect.

Another advantage of graphene results from its physical characteristics, which is atomically thin body. Graphene with different layers has different electronic properties. We could employ this to make the types of electronic devices more diverse. In the other hand, graphene is not alone. Researches recently have uncovered many other two dimensional crystals, such as MoS2 and h-BN. Surprisingly, MoS2 is an excellent semiconducting material, and h-BN is an excellent insulating material. Combined with metallic large-area graphene, they could construct the foundation of furture nano electronics just like CMOS technology today. For example, J. Park’s group from Cornell University has demonstrated the possibility of atomically and preciously synthesis of structure based on these three materials. This progress will cast light on fabrication of wafer-scale graphene nano-devices.

Everything has two sides. It is the atomic thickness of graphene that leads to the high subthreshold current in graphene transistors, especially in single-layer graphene. As we know, intrinsic single-layer graphene has no bandgap, which means transistors based on this kind of graphene could not be switched off effectively. Consequently, the output characteristics of transistors based on single-layer graphene are not consistent with the requirements of logical devices for the sake of high energy dissipation. There are some methods to reduce subthreshold current, including patterning graphene into graphene nanoribbon and utilizing electric field to open the bandgap of graphene, however, each method has its own drawbacks. For instance, electron mobility in graphene nanoribbon is dramatically reduced to the same degree as silicon.

In sum, considering that graphene transistors could not be turned off completely, they may not be good candidates for logical application. Nevertheless, rich physical properties, ultrathin body and ultrahigh electron mobility of graphene have made graphene a potential material for radio-frequency application. What's more, recent investigations on graphene have shown its potential in other areas, such as display, energy storage and ultrasound transducer.

Original Link: http://blog.sina.com.cn/s/blog_5d6501970101385k.html