PhD Defense: "Exploration of Graphene for Tunnel Devices and Electrodes in Next-Generation Green Electronics"

Yasin Khatami

July 30th (Tuesday), 2:00pm
HFH 4164

With the rapid scaling of metal-oxide-semiconductor field-effect transistors (MOSFET), the passive power dissipation is becoming comparable to the active power consumption. The passive power dissipation can be reduced by increasing the threshold voltage in MOSFETs. However, this leads to low drive current and higher delay for the devices. An effective way to lower the passive power is to reduce the subthreshold swing (S), which is the amount of gate voltage required to change the device current by an order of magnitude in the subthreshold region.

In this dissertation, novel applications of graphene in low-power and energy-efficient electronics are investigated. To that purpose, first the performance of MOSFET devices for gate lengths below 10 nm will be studied. It will be shown that the MOSFETs have various power dissipation issues in the sub-10 nm regime. An alternative device to MOSFET is the tunneling field effect transistor (TFET). TFETs can exhibit S values much lower than the MOSFET’s fundamental limit of 60 mV/dec. However, TFETs exhibit low ON current compared to MOSFETs. The drive current of TFETs can be improved by reducing the bandgap. The design of TFET devices based on conventional materials including silicon and germanium are discussed in this dissertation. The engineering of the bandgap with the use of silicon-germanium leads to improved performance for TFETs.

Then, the design of TFET based on graphene nanoribbons (GNRs) is investigated. The graphene nanoribbons offer several key advantages over conventional materials. These advantages include the tunable bandgap, the superb gate electrostatic control due to the atomically thin structure, the pristine surface, which reduces the trap density, the high carrier mobility, high thermal stability and high mechanical flexibility. Homojunction and heterojunction TFETs based on GNRs are proposed and their characteristics are investigated. The GNR based TFETs can exhibit very high ON currents as well as S values down to 15 mV/dec.

In addition, alternative devices and circuits based on GNRs are proposed and studied in this dissertation. A novel negative resistance device based on GNR is proposed, which can be used in design of ultra-compact memory cells. The proposed negative resistance devices have peak to valley current ration of ~105 and drive current of 700 μA/μm. Further properties of graphene such as contact resistance, trap state density and optical transparency are investigated for chips based on graphene devices and interconnects.

About Yasin Khatami:

photo of yasin khatami Yasin Khatami received the B.Sc. and M.Sc. degrees in electrical engineering from Sharif University of Technology, Tehran, Iran in 2005 and 2007, respectively. Since 2007 he has been working toward the Ph.D. degree at Prof. Banerjee’s Nanoelectronics Research Laboratory, Department of Electrical and Computer Engineering, University of California, Santa Barbara. His research emphasis is on the exploration of emerging ultra-energy efficient green transistors and circuits, emerging materials and carbon electronics. Mr. Khatami has authored or co-authored several papers published in leading journals and refereed conferences and his work has received more than 100 citations per Google Scholar at the time of his defense. He is also the co-author of a book chapter on carbon based electronics.