Director's Message: C-SPIN Annual Review
Since C-SPIN opened its doors a year ago, I’ve had a front-row seat for a productive whirlwind of meetings, reports and world-class spintronics research. The Center is meeting (if not exceeding) its administrative and research goals, so we can all take pride in what’s been accomplished and the groundwork that’s been laid for at least the next four years. And by “we,” I mean everyone: my co-directors and Center manager, the Theme leaders, PIs, grad students and post-docs, undergraduate assistants, administrators, and even me. Thank you all for your exceptional work. I would also like to again thank our sponsors for their support of the STARnet program, including DARPA, Applied Materials, GlobalFoundries, IBM, Intel, Micron, Raytheon, Texas Instruments and United Technologies.
We are well-positioned for another excellent year. Now that our administrative wheels are in place, I expect that we’ll be able to conduct more research, build stronger relationships with our academic and industry partners, and communicate with all of you more effectively in 2014. More on that below, along with a summary of our 2013 accomplishments.
A Brief History
First, though, a short history for all the colleagues in and out of C-SPIN who have asked, “How did the Center get started?”
From my perspective, the history of the Center goes back to 2002, when I took my current position at the University of Minnesota. My education and research work in Singapore had exposed me to spintronics, but coming to the U.S. enabled me to concentrate on making the theoretical advantages of spin-based memory and computing a reality. However, by early 2003, when I began my metallic spintronics research for logic and memory applications, this field was not well funded and there were different opinions about its future. I still remember submitting a white paper in 2004 on non-volatile magnetic logic that was turned down within one month. Since 2007 the field has been brimming with exciting technical and theoretical advances, partly because of the looming limits of CMOS technology. Sponsors like DARPA, the Semiconductor Research Corporation (SRC) and their individual members, NSF, and others were casting their nets wide in hopes of generating the innovations necessary to propel the industry well beyond 2020.
Through my own research, I became more involved in the extensive network of spintronics researchers over the next eight years. This network, along with impressive results from SRC centers, led me to think about the possibility of an SRC center devoted entirely to spintronics with a vertical framework that integrated research into materials, devices, and systems. The positives of such a center were obvious: a world-class research team would have the support to conduct focused, accelerated spintronics research, and the innovations and discoveries from such a center would be enormously helpful to many inside and outside the computer industry.
In the end, my conviction that the computer industry needed a spintronics center was the decisive factor. It was – and remains – hard to imagine the computers of the future without using spin devices, and I wanted to be a part of a team that was making that happen. Enthusiastic responses from fellow researchers around the country, along with support from colleagues and administrators at the University of Minnesota, definitely pushed me to the SRC application process. After countless scientific discussions, negotiations, budget meetings, initial proposal drafts, and final proposal drafts, the C-SPIN team submitted its 320- page proposal to SRC in September 2012. When we received word that the Center would be funded, I knew that a new era in spintronics research in the U.S. had begun.
I realize that “a new era in spintronics research” sounds bold, but it’s hard to think otherwise when I consider the work that C-SPIN PIs did in 2013. Here’s a much-condensed list of our accomplishments:
Goal: Develop materials with perpendicular magnetic anisotropy that can be used as magnetic tunnel junctions, giant magnetoresistance structures, and voltage-controlled devices.
- Observed the first inverse spin Hall effect in a ferromagnetic metal
- Developed CoFeB-based perpendicular MTJs with ultra-low switching current density (2 x 104 A/cm2)
- Developed two low damping non-interface perpendicular magnetic materials and one all-optical switching perpendicular magnetic material
- Developed boron-doped Cr2O3, which had an elevated Néel temperature, a boundary spin polarization with the correct minority spin density of states, and a larger switching field than Cr2O3
- Developed block copolymer patterning techniques that form close-packed dots or lines with order and feature sizes of near 50 nm
- Calculated magnetic damping produced by the Kambersky mechanism
Goal: Develop novel spin channel materials for lateral spin transport devices.
- Developed the growth of MoS2(1-x)Se2x alloys, the post-growth processing of single-layer films based on low-energy Ar+ sputtering, and MoS2 transistors with top gates and a HfO2 dielectric
- Developed back-gated topological insulator devices with ferromagnetic tunnel contacts from MBE-grown thin films of (Bi,Sb)2Te3 using SrTiO3 as the substrate
- Developed nearly all of the process modules needed to fabricate graphene spin valves using a CMOS-compatible hard mask process
- Developed a series of spin valves based on the integration of the Heusler alloy Co2Mn1-xFexSi with n-GaAs with approximately twice the spin polarizations of that in comparable structures based on Fe
- Developed a new approach to measure spin polarization in the regime of very large spin currents and used this approach to measure spin transport in III-IV semiconductor channels
Goal: Determine how interfaces limit spin injection efficiencies and explore the effects of interfacial structural, chemical and magnetic disorder on spin injection.
- Demonstrated that it is possible to make full Heusler alloys that are half-metallic and have perpendicular anisotropy
- Discovered a Heusler alloy that is half-metallic at the interface as well as in bulk, has zero moment in bulk, and has perpendicular anisotropy
- Grew and imaged the Heusler alloy Co2MnSi on GaAs by molecular beam epitaxy for carrying out lateral spin valve experiments
- Developed a new technique for using electron microscopy on two-dimensional spin-transport materials
Goal: Design and model spin-based logic, memory and interconnect devices
- Performed a series of experiments using the longitudinal spin Seebeck effect to determine the spin Hall angle in a variety of materials
- Developed a spin valve with semiconductor detection arms in lieu of a second ferromagnetic contact
- Developed a spin pumping device and performed a series of experiments to determine the spin Hall angle and damping constant in a variety of materials.
- Used simple field-effect transistor structures to analyze the reproducibility of chemical doping of graphene and MoS2
- Designed a new scheme of spin-optical interconnection and performed initial calculations of energy efficiency in these structures
- Developed circuit models for spin transfer torque devices driven by the giant spin-Hall effect
Goal: Develop spin-based circuits and architectures for low-power and high-performance spin-based memory and computation
- Developed a devices-to-circuits simulation framework that captures effects of spin transport and magnetization dynamics at the device level during circuit level simulations
- Analyzed the power and performance overhead due to the additional signal buffers in a spin-based Intel Core i7 processor
- Designed an ultra-low voltage and high-speed current-mode bipolar lateral spin valve neuron and unipolar domain wall neuron device model
- Designed a spintronic processor for deep learning networks
- Investigated an approximate computing technique using stochastic bit streams that can tolerate errors when implemented using spintronic devices
- Designed a general purpose graphics processing unit on-chip cache hierarchy using Domain Wall Memory
As expected, Steve Koester, Paul Crowell, and I devoted a lot of time this year to Center administration. We hired Marie Rahne as our Center Manager and Kieran Dhital as our Center accountant and, together, have put most of the necessary procedures in place for financial reporting, research updates, review planning, and internal communications. This administrative foundation will allow us to devote more time to research and build stronger relationships with industry and academic partners in the years ahead. I believe all of you who have met Marie would agree that she has been an excellent addition to C-SPIN.
Our Theme leaders definitely deserve kudos for their work in 2013. In addition to carrying out excellent research on their own, they oversaw the research of Theme PIs and helped put together quarterly SRC research updates. Most importantly, they have carried out the vision of the Center by enthusiastically embracing the cross-disciplinary work necessary to move spintronics research in the direction of viable spin-based prototypes. To put it another way, they have happily stepped outside of their specialties in order to become a powerful research team.
One other highlight is worth noting. The annual review in September – which all the Theme leaders, 25 of 27 PIs, and over 60 grad students and post-docs attended – was a success. The STARnet assessment that came out of the review was very positive. The Center was commended for its research, its leadership, and its teamwork. The write-up also gave me, my co-Directors, and the Theme leaders helpful suggestions for making the Center even better. In addition, the entire review process gave all of us opportunities to learn from each other and grow as a team.
I am looking forward to another year of world-class spintronics research in 2014. My hope is that, through WebEx, phone, and face-to-face meetings, all PIs will get a better sense of Theme and Center goals and become more collaborative. The more we share our research with one another, the better our research will be and the better we will prepare high-level research timelines for the next annual review.
We also plan to increase C-SPIN student engagement this year. Specifically, we will host bi-monthly student-to-student presentations via WebEx, and we will provide a “Best Poster” award for each Theme and for the best cross-Theme collaboration at the annual review.
To further promote the scientific collaboration within and outside C-SPIN, we intend to 1) expand Center communication efforts and 2) strengthen relationships with academic and industry partners.
- Expand Center Communications. We plan to get newsletters like this out on a quarterly basis. We are very glad to have Mike Lotti, a fantastic professional writer, to help produce pieces for the newsletter and other publications. Don’t be surprised if he contacts you in 2014 to learn more about your research.
- Strengthen Relationships with Industry and Academic Partners. We want to find every opportunity outside the STARnet review process to let our industry partners know about our accomplishments and to collaborate with them on research. I visited DARPA, Intel, Micron, Applied Materials, and Global Foundries last year, and we are planning 5-7 industry visits in 2014. We also hope to engage industry partners through a more formal presence at conferences, and we will try to expand our research collaborations with our sister STARnet centers. It is possible that each PI will be asked to engage in at least one industry interaction in 2014.
We also want our academic partners – namely, your institutions – to know more about C-SPIN and the research you are doing for the Center. If your department or college regularly posts information about faculty research, please connect either me or Marie Rahne with the appropriate personnel.
Again, thank you all for a wonderful 2013 at C-SPIN. I look forward the progress we will make in 2014.