Low-noise near-ballistic BN-graphene-BN heterostructure field-effect transistors for energy efficient electronic applications

Ballistic electron conduction offers a new possible approach to the development of low-power high-speed logic circuits [1-3]. Ultra-high mobility of graphene allows achieving the ballistic or near-ballistic transport regime at room temperature (RT) in devices with relatively long channels [4-5]. In this presentation, we show that heterostructure field-effect transistors (HFETs) with graphene channel encapsulated between two layers of hexagonal boron nitride (h-BN) combine extremely high electron mobility (~36,000 cm
²
/Vs) with a strongly reduced 1/f noise level (f is the frequency). Low-frequency 1/f noise hampers the operation of numerous devices and can be a major impediment to development of practical low-power low-voltage applications of graphene and other 2D van der Waals materials [6-8]. The low noise level is beneficial for the low-voltage electronic applications. The prototype h-BN-graphene-h-BN HFETs were fabricated using the mechanically exfoliated h-BN and graphene flakes on Si/SiO2 wafers. The viscoelastic materials adhered to glass slides were used as transparent stamps for the layer transfer. The stamps were spin coated with poly-propylene carbonate (PPC). A micromanipulator was used for careful positioning of h-BN flakes on the stamp over graphene flakes. Following this procedure, the h-BN layer was added to the stack resulting in a fully encapsulated graphene monolayer. The stack was then released onto target Si/SiO
₂
substrate by heating the stage to an appropriate temperature. The resulting heterostructure was etched to expose the edges of graphene and create one-dimensional Cr/Au (10/100 nm) electrical contacts. Figure 1 shows the schematics and an optical microscopy image of a representative device. Figure 2 (a) shows the current-voltage (I-V) characteristics of the representative HFET. Both the effective and field-effect mobility extractions gave consistent results showing the mobility of ~36,000 cm
²
/Vs at the carrier concentration of 7×10
¹¹
cm
²
. Figure 2 (b) presents the normalized 1/f noise spectral density of the graphene encapsulated device. The channel-area normalized noise spectral density in BN-graphene-BN HFET is factor of ×5-×10 smaller than that in typical reference graphene FETs without the channel encapsulation. The observed strong noise reduction can be explained by screening of the traps in SiO
₂
by the BN barrier. Other possible physical mechanisms and prospects of further noise suppression will be discussed at the presentation.