Current Saturation and Transient Behavior of Graphene [GOI] Transistors

Graphene has attracted much interest for transistor applications, initially due to its high carrier mobility. Drift velocity saturation at high field in graphene, at values several times higher than in silicon. However, velocity saturation alone is not sufficient for current saturation because the carrier density can continue to increase with drain voltage in a zero-band-gap material, where the channel cannot be fully pinched off. Current saturation is important for low output conductance go and amplifier gain it has been partly achieved through a combination of velocity saturation and electrostatic charge control. High-field transport in graphene is also influenced by self-heating as revealed by recent infrared and Raman thermal imaging Current saturation in submicron graphene transistors on SiO2/Si. Self heating is partly responsible for current saturation but degrades current densities above 1 mA/μm by up to 15%. Heating effects are reduced if the supporting insulator is thinned or, in shorter channel devices, by partial heat sinking at the contacts. The transient behavior of such devices has thermal time constants of 30-300 ns, which is dominated by the thickness of the supporting insulator and that of the device capping layers.