As conventional CMOS technologies are running into multiple barriers that are likely to slow down or even stop Moore?s Law scaling sometime during the next decade, there is a need for new material discoveries and new nanodevice and circuit paradigms that allow new applications that would be impractical or even impossible using traditional methods. This work focuses on modeling, fabrication and applications for spin torque oscillators (STOs), with an emphasis on nano-arrays. Using multiferroic materials and an electric field, the team will tune both the frequency of a spin torque oscillator and also the coupling between adjacent STOs. This electric field will change the coercive field of the free layer which, in turn, will adjust the precessional frequency of the STO and the coupling between STOs. When presented with a continuous stream of real-time disparate data records that could come from different types of environmental and/or biological sensors an STO array can extract knowledge by analyzing the stream and providing a degree of match information about various data instances in the stream and their class membership. The associative memory capabilities of STO arrays are agnostic to the source of data, thus they can be used for computation and composition of data streams from hybrid sources working in different modes of operation. This special form of machine learning can be done in real time with no need for excessive local buffering of data. It can also accommodate concept drift as the underlying statistics used for data mining can easily be changed over time by controlling the inputs to the individual STOs. Such applications as real-time data stream mining as enabled by the proposed technology are critical to the safety and security of the country.
The multidisciplinary activities exploit fundamental nanoelectronics and spintronics concepts through contributions in materials science, circuit design and novel nano-computing paradigms. The PIs have a strong track record of collaborating across disciplines and of involving their undergraduate and graduate students in these collaborative activities, and this project will enable further collaboration between material scientists, physicists, and electrical and computer engineers.
This project focuses on the fabrication, modeling, simulation, design space exploration and applications for Spin Torque Nano-Oscillators (STNOs), with special emphasis on arrays of such oscillators formed using magnetic tunnel junctions (MTJs) and spin valve/MTJ hybrid structures. The multi- and inter-disciplinary activities reported here exploit fundamental nanoelectronics and spintronics concepts and made contributions to materials science, device and circuits, and allow novel nanocomputing paradigms. This effort has providing enough proof of concept results necessary to put together a future larger effort where the size of the nano-array and the number of coupled STOs will be scaled up to enable a thorough exploration of the application space. Through modeling and simulation has shown that this novel new paradigm for computing has the capability of a truly disruptive change in the way that images and other "Big Data" issues are handled. This new type of data processing will have broad impacts in many fields where high throughput data needs to be analyzed in real time. The STNO mutilayer structures with non-conventional ferrimagnets, i.e. L10 MnAl and the full Heusler CoFeAl2 was fabricated for the first time. The introduction of the crystalline and interfacial magnetic anisotropies led to the STNO with the perpendicular magnetizations. The results from the new design of the tri-layer hybrid STNO fabrication results in the realization of the electrical coupling between STNO devices, which translates a significant improvement in the performance of STNO arrays. One of the most exciting aspects of this project is the incredible range of possible applications of this potentially disruptive technology. The nanoscale dimensions, coupled with the possibility of CMOS integration, low power, tunable frequency through magnetic fields and electrical currents, high quality factor Q (>10,000) and the control of coupling using multiferroics opens many possibilities, from RF applications, filters and mixers, to on-chip clock generation, to non-Boolean computation schemes based on coupled oscillators. Northrop Grumman expressed great interests in using STO for band-pass filter application in microwave frequencies. The research findings also provide an exciting basis for outreach and for integrating research and education. The PIs will include both undergraduate and graduate students in all aspects of this research. In addition to the students to be funded by this project, many aspects of the project will make good senior thesis, independent study, or course projects.
