Intellectual merit of the proposed research A fundamental study involving optimization of the CPP-GMR sensor stack is proposed. This will involve a fundamental theoretical study of the physics of the spintronic device, which will lead to an optimized device design, including selection of the materials, layer thicknesses, and device structure for optimized performance. The study in GMR stack deposition will emphasize optimization of thin-film deposition with particular attention being given to interfacial engineering. Furthermore, a thorough investigation of multilayer film nucleation and growth under various processing conditions, will lead to a better understanding of how to generate and control the properties of these films and their subsequent electrical and magnetic characteristics. Subsequent fabrication of the GMR sensor has sufficient complexity and will provide the student with substantial exposure to various state-of-the-art deposition, photolithography, e-beam lithography and dry and wet etch processing techniques and equipment. In-depth structural, magnetic and electrical characterization of these nanolaminates will be carried out using a wide range of advanced analytical equipment. Atomic scale characterization of the GMR stacks by transmission electron microscopy and atom probe tomography will greatly enhance the scientific merit of the proposed research. The technological motivation for this research is grounded in the desire to create novel materials, processes and structures for novel sensors for military and civilian applications. The research is interdisciplinary, involving the Metallurgical and Materials Engineering, Electrical and Computer Engineering and Physics departments.
The broader impacts resulting from the proposed activity The proposed research is interdisciplinary, integrating faculty and students from three departments (Metallurgical and Materials Engineering, Electrical and Computer Engineering and Physics). Graduate students on this project, one a minority female will receive training in disciplines of materials selection, nanolayer processing, device fabrication, and atomic, microstructural, electrical and magnetic characterization, and will gain an understanding of physics and chemistry, metallurgical, materials and electrical engineering. The project will have collaboration with the Army Research Laboratories and Veeco Instruments, which will allow the students to be exposed to a broad range of technologies - from sensor design and fabrication to vacuum technology and cathode design and development, and have direct exposure to career options at the Army Research Laboratories as well as in industry. Recruitment of minority female undergraduate students from a neighboring HBCU is also planned. This, along with having a minority female graduate student as well as a female PI, will serve as a strong and positive role model for minority women entering science and engineering, both nationally and globally.
The SST Sensors grant has enabled us to perform state-of-the-art research at the University of Alabama on giant magnetoresistive (GMR) and tunneling magnetoresistive (TMR) sensors, which can be used for data storage or for memory applications. We have fabricated the first successful current-perpendicular-to-the-plane GMR (CPP-GMR) devices at UA with the support from this grant. We have also developed a range of perpendicular anisotropy material systems as well as an understanding of interfacial anisotropy resulting from various seed and capping materials and fabricated fully perpendicular magnetic tunnel junctions with TMR values close to 40%, approaching the state of the art for these perpendicular junctions. This is very important for advancing the state of the art in these devices, which could make the difference in allowing this technology to be viable for production. In addition to this we have utilized the grant to collaborate with the University of Illinois in Chicago. This collaboration resulted in the exciting finding that combining photosynthetic membranes (PS-1) with colloidal quantum dots yields both charge and energy transfer from one to the other, enabling potential development of biosensors for light sensing as well as bio-solar cells based on this discovery. As a final research thrust, we have started fabricating TMR sensors and hard magnets for an experimental proof-of-concept of a patent on non-erasable planer readers, utilizing the TMR sensors discussed above. This grant has had significant intellectual merit, being inherently interdisciplinary in nature, and involving the theory, processing and characterization of materials and devices for sensor applications. Prof. Butler has developed a clear understanding of Heusler and half-Heusler alloys that can be "designed" to have the correct half-metallic properties, Prof. Gupta has developed from scratch a methodology for fabricating the GMR and TMR devices, as well as researching a wide range of alloys and multilayers for perpendicular and interfacial magnetic anisotropy, and Prof. Thompson has contributed his expertise in structural characterization to the understanding of these complex devices. The two PhD students funded on this grant (one on theory and one on experimental work) have either graduated: Zeenath Tadisina, PhD Metallurgical and Materials Engineering, May 2010, currently working at Intel; or will graduate soon: Tianyi Xu, PhD Physics, May 2012). Another PhD student, Anusha Natarajarathinam who received some initial support from this grant will receive her PhD in Electrical and Computer Engineering in May 2012. A postdoctoral researcher, Galina Gulis who worked briefly on this grant is now a research associate at the University of Brasilia, Brazil. These graduate students and the postdoctoral researcher have produced results on advanced GMR and TMR sensors, and well as preliminary data for a novel biosensor. One of the sensors discussed in the original proposal, a planer reader of magnetic material, patented by Dr. Alan Edelstein of Army Research Laboratories, is actually being fabricated in the final phase of this project. There have been a total of nine graduate students, eleven undergraduate students and two high school interns that have either substantially contributed to or provided significant support for the research findings herein. More than 50% of the graduate and undergraduate students who have contributed to this grant have been female, several of them minorities. There have been two McNair scholars and a Randall award and Roland Pettis scholarship winner among them. We have trained them in deposition, etch, photolithography, magnetic characterization, and transport properties of the devices. Some of the undergraduates have accompanied the senior graduate student, Zeenath Tadisina, to the National Nanoscience Infrastructure Network facility at the Georgia Institute of Technology and been exposed to state-of-the-art nanolithography at GaTech-MiRC.Collaborators from University of Illinois in Chicago, the Georgia Institute of Technology, Grandis Inc., IBM Research Laboratories, Army Research Laboratories, Adelphi, and NIST, Gaithersburg, have contributed to these findings. There have been a total of seven refereed journal publications and five refereed conference proceedings, one Master’s thesis and one PhD dissertation that have received full or partial support from this grant. Three journal articles are undergoing peer review, one has just been submitted, and three more are in preparation.
