Mainstream CMOS technology in today’s electronics continues to scale down in its feature size. However, power dissipation per unit area and variability post two major issues and challenges for the continuing scaling. Spintronics, as an emerging technology that exploits the intrinsic spin of the carriers, could potentially offer power savings, low variability and improved scalability. In the talk, we will address the importance of functional oxides such as MgO in field controlled spin FET devices and magnetic tunnel junctions.

 

Toward the realization of spin logic devices, electric-field manipulation of ferromagnetism offers a potential for achieving low power dissipation. The control of collection of spins is critical in accomplishing room - temperature s pin field effect transistors for dilute magnetic semiconductors such as MnxGe1-x. We found that by using high-quality MgO as gate oxide, the ferromagnetism of the quantum dots can be modulated up to 300 K, which opens the possibility to build room-temperature spin FETs.In addition, MgO was also shown to be effective for unpinning Schottky barrier height and improving the spin injection. U sing an epitaxially grown Fe/MgO/n-Ge tunnel junction, we have obtained single crystalline and atomically smooth Fe/MgO on Ge. This high quality Fe/MgO/Ge junction not only passivates the Ge surface states to favor electronic transport, but also leads to an enhanced spin injection efficiency due to the symmetry induced spin filtering property of the MgO. By using this junction, we show electrical spin injection to bulk Ge.

 

We also studied the effect of MgO tunnel barrier thickness on the spin-transfer torque-induced switching of CoFeB-MgO-CoFeB magnetic tunnel junction (MTJ) devices used for nonvolatile memory. We studied the effect of MgO thickness on the resistance-area product (RA) and tunneling magnetoresistance (TMR) of the structures using both film-level current-in-plane tunneling (CIPT) and device-level electrical transport measurements. The TMR showed a large distribution for RA values lower than 4 Ω-µm2 (corresponding to an MgO thickness ~0.85 nm), while it increased to ~150% for larger RA > 6 Ω-µm2. The results allow for optimization of RA and MgO thickness for low write energy and high-density of magnetoresistive random access memory (MRAM) switched by spin-transfer torque (STT). We obtained switching times < 1 ns and write energies < 0.3 pJ for CoFeB-MgO-CoFeB MTJ devices. We also studied the effect of CoFeB free layer composition and thickness on device performance.