Tunnel barriers are the basis for many electronic (charge-based) and spintronic (spin-based) device structures. Fabrication of ultra-thin and defect-free barriers is an ongoing challenge in materials science.
Sometimes there is really nothing a writer can add to the information contained in the original press release. That is clearly the case with the big graphene advance made by scientists at the Washington based, U. S. Naval Research Laboratory and announced recently. The properties of graphene make it an ideal tunnel barrier, and will lead to its adoption in “more complex graphene-based devices for highly functional nanoscale circuits, such as tunnel transistors, non-volatile magnetic memory and reprogrammable spin logic.”
While this development seems more end decade-next decade before commercial product reaches the general public, I suspect that in military/space uses it will be more mid decade-end decade. Below, the new discovery in their own words. Did I mention that the future looks bright for the emerging carbon/graphite age.
Fabrication of ultra-thin and defect-free barriers is an ongoing challenge in materials science. Typical tunnel barriers are based on metal oxides (e.g. aluminum oxide or magnesium oxide), and issues such as non-uniform thicknesses, pinholes, defects and trapped charge compromise their performance and reliability. Such oxide tunnel barriers have several limitations which hinder future performance. For example, they have high resistance-area (RA) products which results in higher power consumption and local heating; they allow interdiffusion at the interfaces, which reduces their performance and can lead to catastrophic failure; and their thickness is generally non-uniform, resulting in "hot spots" in the current transport. In contrast, Dr. Jonker explains, the inherent material properties of graphene make it an ideal tunnel barrier. Graphene is chemically inert and impervious to diffusion even at high temperatures. The atomic thickness of graphene represents the ultimate in tunnel barrier scaling for the lowest possible RA product, lowest power consumption and fastest switching speed.
Navy Scientists Demonstrate Breakthrough in Tunnel Barrier Technology
07/27/2012 07:00 EDT
Scientists at the Naval Research Laboratory have demonstrated, for the first time, the use of graphene as a tunnel barrier — an electrically insulating barrier between two conducting materials through which electrons tunnel quantum mechanically. They report fabrication of magnetic tunnel junctions using graphene, a single atom thick sheet of carbon atoms arranged in a honeycomb lattice, between two ferromagnetic metal layers in a fully scalable photolithographic process. Their results demonstrate that single-layer graphene can function as an effective tunnel barrier for both charge and spin-based devices, and enable realization of more complex graphene-based devices for highly functional nanoscale circuits, such as tunnel transistors, non-volatile magnetic memory and reprogrammable spin logic.
—-The research initiates a "paradigm shift in tunnel barrier technology for magnetic tunnel junctions (MTJs) used for advanced sensors, memory and logic," explains NRL's Dr. Berend Jonker. Graphene has been the focus of intense research activity because of its remarkable electronic and mechanical properties. In the past, researchers focused on developing graphene as a conductor, or perhaps a semiconductor, where the current flows in-plane parallel to the carbon honeycomb sheet. In contrast, the NRL researchers show that graphene serves as an excellent tunnel barrier when current is directed perpendicular to the plane, and in fact, also preserves the spin polarization of the tunneling current.
U. S. Naval Research Laboratory.
—- NRL researchers believe that the graphene-based magnetic tunnel junctions they have demonstrated will eclipse the performance and ease of fabrication of existing oxide technology. These graphene-based MTJs would be a breakthrough for nascent spin-based technologies like MRAM and spin logic, and enable the electrically accessible non-volatile memory required to initiate a revolution in computer architecture. These results also pave the way for utilization of other two-dimensional materials such as hexagonal boron nitride for similar applications.