Xiaofeng Yao

University of Minnesota Duluth, Duluth, Minnesota, United States

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Publications (16)38.12 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic tunneling junction (MTJ)-based programmable logic devices have been proposed and studied for future reconfigurable and nonvolatile computation devices and systems. Spin transfer torque (STT)-based switching has advantages in device scaling compared to the field-switching mechanism. However, the previously proposed MTJ logic devices have operated independently and, therefore, are limited to only basic logic operations. Consequently, the MTJ device has only been used as an ancillary device, rather than the main computation device. As a result, the full benefits of MTJ-based computation have not been explored. New designs are needed to accelerate the development of the MTJ-based logic devices. Specifically the realization of direct communication between the MTJ devices is crucial to fully utilize the MTJ devices in the circuits to implement more advanced logic functions. In this paper, new MTJ-based spintronic logic units (building blocks) for spintronic circuits using the STT switching mechanism have been proposed and investigated, which includes the designs of a basic STT-MTJ logic cell, a direct communication between the MTJ logic cells, a three-MTJ logic unit and a spintronic logic circuit acting as an arithmetic logic unit.
    IEEE Transactions on Nanotechnology 02/2012; 11(1-11):120 - 126. DOI:10.1109/TNANO.2011.2158848 · 1.83 Impact Factor
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    ABSTRACT: We investigated magnetic tunnel junction (MTJ)-based circuit that allows direct communication between elements without intermediate sensing amplifiers. Two- and three-input circuits that consist of two and three MTJs connected in parallel, respectively, were fabricated and are compared. The direct communication is realized by connecting the output in series with the input and applying voltage across the series connections. The logic circuit relies on the fact that a change in resistance at the input modulates the voltage that is needed to supply the critical current for spin-transfer torque switching the output. The change in the resistance at the input resulted in a voltage swing of 50-200 mV and 250-300 mV for the closest input states for the three and two input designs, respectively. The two input logic gate realizes the AND, NAND, NOR, and OR logic functions. The three-input logic function realizes the majority, AND, NAND, NOR, and OR logic operations.
    IEEE Transactions on Magnetics 11/2011; 47(10-47):2970 - 2973. DOI:10.1109/TMAG.2011.2158527 · 1.39 Impact Factor
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    ABSTRACT: Early recognition and prevention of chronic disease, such as lung cancer, require a fast, accurate detection and longitudinal monitoring on potential biomarkers, which could identify the molecule change in the initial stage of the chronic disease. Here we report the realization of specific and accurate quantification of a low-abundance serum protein in unprocessed human sera, using our novel giant magnetoresistive (GMR) biosensing system with uniform high-magnetic-moment nanoparticles and a competition based detection scheme. Only one antibody is needed for such detection scheme. The quantification of interleukin-6 (IL-6, a low-abundance protein and a potential cancer biomarker), as low as 125 fM IL-6 proteins, directly in 4 muL of unprocessed human sera was demonstrated within 5 minutes by such system. The results nicely differentiate normal individuals and lung cancer patients. This platform has great potential to facilitate the identification and validation of disease biomarkers.
    12/2010; 1311. DOI:10.1063/1.3530018
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    ABSTRACT: We experimentally demonstrated a magnetic tunnel junction (MTJ) based circuit that allows direct communication between elements without intermediate sensing amplifiers. The input of the circuit consists of three MTJs connected in parallel. The direct communication is realized by connecting the output in series with the input and applying voltage across the series connections. Combining the circuit with complementary metal oxide semiconductor current mirrors allows for fan-out to multiple outputs. The change in resistance at the input resulted in a voltage swing across the output of 150–200 mV for the closest input states which is sufficient to realize all of the Boolean primitives.
    Applied Physics Letters 11/2010; 97(15-97):152504 - 152504-3. DOI:10.1063/1.3499427 · 3.30 Impact Factor
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    ABSTRACT: The electrical behavior of a magnetic tunnel junction (MTJ) using spin-torque-transfer (STT) switching was modeled using a SPICE subcircuit. The subcircuit is a two-terminal device that exhibits the electrical characteristics of an STT-MTJ. These characteristics include all the major transient characteristics of an MTJ, including the hysteresis, bias voltage dependence of the resistance, and the critical switching current versus the critical switching time. The model was designed to work over a wide range of operating conditions. Simulation and analysis of an MTJ-based D flip-flop are presented to demonstrate possible applications of the model.
    IEEE Transactions on Electron Devices 07/2010; 57(6-57):1425 - 1430. DOI:10.1109/TED.2010.2047073 · 2.47 Impact Factor
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    ABSTRACT: We investigated spin-polarized current controlled magnetic tunnel junctions (MTJs) connected with a nano-magnetic channel using micromagnetic simulations. A spin polarized current is used to switch the MTJ and form a domain wall in the nanochannel that is captured at a notch in the channel. A current can then be applied along the nanochannel to drive the domain wall to the other MTJ. The nanochannel design was optimized by varying MTJ pillar size, nanochannel width, material, and notch sizes. Both in-plane and perpendicular anisotropy were simulated. Perpendicular anisotropy was found to be the most beneficial by alleviating the dominate effect of shape anisotropy. Four different nanochannels were connected to a single MTJ with perpendicular anisotropy and a domain wall formed in each channel. This allows fan out to be realized and consequently more complex logic functions. The current densities to switch the MTJ elements and drive the domain wall were found to be on the order of 1 × 10<sup>8</sup> A/cm<sup>2</sup> and 6 × 109 A/cm<sup>2</sup>, respectively.
    IEEE Transactions on Magnetics 07/2010; 46(6-46):2216 - 2219. DOI:10.1109/TMAG.2010.2045355 · 1.39 Impact Factor
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    ABSTRACT: A novel giant magnetoresistive sensor and uniform high-magnetic-moment FeCo nanoparticles (12.8 nm)-based detecting platform with minimized detecting distance was developed for rapid biomolecule quantification from body fluids. Such a system demonstrates specific, accurate, and quick detection and quantification of interleukin-6, a low-abundance protein and a potential cancer biomarker, directly in 4 muL of unprocessed human sera. This platform is expected to facilitate the identification and validation of disease biomarkers. It may eventually lead to a low-cost personal medical device for chronic disease early detection, diagnosis, and prognosis.
    Journal of the American Chemical Society 03/2010; 132(12):4388-92. DOI:10.1021/ja910406a · 12.11 Impact Factor
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    ABSTRACT: The discovery of spin torque transfer (STT) has lead to a significant advance in the development of spintronic devices. Novel structures and materials have been studied in order to improve the performance of the magnetic tunnel junctions (MTJs) performances and understand the fundamental physics in spin torque transfer. The adiabatic spin torque effect, which is due to the spatial non-uniformity of magnetic properties, has been predicted in theory and demonstrated experimentally in magnetic nanowires. However, this important spin torque has been rarely concerned in the magnetic tunnel junctions (MTJ) because of its extremely weak effect in conventional MTJs. This paper reports for the first time a giant adiabatic spin torque in MTJ devices with a hybrid free layer structure. The generation of the giant adiabatic spin torque was realized through the introduction of a spatial magnetic non-uniformity in a hybrid free layer along the current direction. It is observed that the giant adiabatic spin torque can substantially promote the current-induced switching process in the MTJ devices: the adiabatic spin torque can be larger than the in-plane spin torque, which allows for the switching with a single-polar current under different bias fields. Moreover, the adiabatic spin torque, which is proportional to the level of spatial non-uniformity, increases during the switching process. The observed effects are confirmed by numerical simulations. These results have far-reaching implications for the future of high-density STT-MRAM devices. Comment: Total 26 pages with 7 figures. Submitted to Nature Materials, June 25th 2009
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    ABSTRACT: Zeptomole detector: A highly sensitive giant-magnetoresistive chip and FeCo nanoparticles can be used to linearly detect 600-4500 copies of streptavidin. Under unoptimized conditions, this system also detects human IL-6 with a sensitivity 13-times higher than that of standard ELISA techniques.
    Angewandte Chemie International Edition 03/2009; 48(15):2764-7. DOI:10.1002/anie.200806266 · 11.26 Impact Factor
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    ABSTRACT: In this paper, we present a ultra high sensitive (Zeptomole, 10(-21)) technique to enable the detection of any potential low abundance biomarkers. We demonstrated for the first time the detection of sub 13nm high-moment magnetic nanoparticle and the implementation of a novel magnetoresistive (GMR) biosensor concept with higher sensitivity and 10 times lower external field in real biomarker sensing schemes. A potential lung cancer biomarker, interleukin-6 (IL-6), was successfully detected with extremely low concentration (as few as only 200 pieces of IL-6). Together with other features of GMR sensor systems like low-cost, portability, easy-to-use, our demonstrated device may lead to future family-based personalized medicine for cancer prevention.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:5432-5. DOI:10.1109/IEMBS.2009.5332479
  • Xiaofeng Yao · Roger Malmhall · Rajiv Ranjan · Jian-Ping Wang ·
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    ABSTRACT: The current-induced magnetization switching was studied in the MTJ devices with composite free layer (CoFeB/CoFeB-oxide/CoFeB). The stable intermediate state was observed due to the multi-domain structure induced by the dipole field and large device size. Two different stable intermediate states were observed in different applied current direction. The switching mechanisms of those two intermediate states are different, which is also indicated by the switching current distribution. Reversible intermediate state was also observed at low applied current, which may be due to the domain nucleation.
    IEEE Transactions on Magnetics 12/2008; 44(11-44):2496 - 2499. DOI:10.1109/TMAG.2008.2003072 · 1.39 Impact Factor
  • Xiaofeng Yao · Hao Meng · Yisong Zhang · Jian-Ping Wang ·
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    ABSTRACT: The asymmetry of the switching current in magnetic tunneling junction (MTJ) and giant magnetoresistance (GMR) spin torque transfer devices was reported in both theory and experiment. This is one of the key challenges for future magnetic random access memory applications. In this work, the switching symmetry was greatly improved by inserting a nano-current-channel (NCC) structure in both MTJ and GMR devices. With the NCC structure, the current induced magnetization switching is nonuniform with initiation cites induced by locally high current density. The critical switching current density in both switching directions was successfully reduced while the degree of switching asymmetry {[(JcP-AP−JcAP-P)/JcAP-P]×100%} was improved as well.
    Journal of Applied Physics 03/2008; 103(7):07A717-07A717-3. DOI:10.1063/1.2837485 · 2.18 Impact Factor
  • Jian-Ping Wang · Xiaofeng Yao ·
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    ABSTRACT: Non-volatile and programmable logic devices are desirable for future reconfigurable computer on chip. Spintronic logic devices, which use both electron spin and charge, can satisfy these requirements. Moreover, small device size, low power consumption, fast switching speed and programmable "on the fly" make it the most promising candidate for the next generation logic devices. First, this paper reviews the different types of spintronic logic devices. Secondly, we review the proposal and experimental demonstration of the magnetic tunnel junction (MTJ) and giant magnetoresistance element (GMR) based logic devices with the focus on the development of single MTJ logic device with programmable functions and a MTJ-based full-adder logic circuit. Thirdly, a new generation of spintronic logic devices based on spin torque transfer switching mechanism (or so-called current-induced-magnetization switching) is introduced. The last part gives an outlook of future prospective of spintronic logic devices and challenges.
    Journal of Nanoelectronics and Optoelectronics 02/2008; 3(1):12-23. DOI:10.1166/jno.2008.006 · 0.39 Impact Factor

  • Journal of Medical Devices 01/2008; 2(2). DOI:10.1115/1.2936202 · 0.42 Impact Factor
  • Xiaofeng Yao · Hao Meng · Jian-Ping Wang ·
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    ABSTRACT: This paper investigates the design of a hybrid (composite) free layer in order to implement a new spin switching configuration to reduce the switching current. The hybrid free layer consists of one and two free layer and couples to a magnetic granular structured nano-current-confined (NCC) layer. The magnetic tunnel junction (MTJ) devices were patterned into 180 nmtimes250 nm ellipse shape by using phase-shift lithography. The current-induced magnetization switching of the MTJs with and without NCC structure was measured by four-point probe method. Results show that for MTJ with NCC structure, the critical switching current decreased dramatically .
    01/2008; DOI:10.1109/DRC.2008.4800811
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    ABSTRACT: Conventional electronics technology uses an electron's charge to store information and a current of electrons to transfer information. Spintronics technology, in contrast, uses an electron's 'spin' in addition to its charge to transfer and store information. Magnetic Tunnel Junctions (MTJ) are spintronic devices that exhibit two distinct resistance states due to the tunneling magnetoresistance (TMR) effect. Their properties can provide significant advantages over conventional electronics in the design of computer systems. We characterize some of the challenges in using spintronic technology in large systems, and describe a novel design technique called 'union with neutralization' to combine individual component designs into multi-functional units. We use this technique to present the design of an arithmetic and logical unit (ALU) using 20 MTJs and two CMOS-based sense amplifiers. The spintronics-based ALU has the potential to offer considerable area, timing, and power advantages over a conventional CMOS-based ALU.
    Proceedings of the 5th Conference on Computing Frontiers, 2008, Ischia, Italy, May 5-7, 2008; 01/2008

Publication Stats

217 Citations
38.12 Total Impact Points


  • 2008-2012
    • University of Minnesota Duluth
      • Department of Electrical Engineering
      Duluth, Minnesota, United States
    • University of Minnesota Twin Cities
      • Department of Electrical and Computer Engineering
      Minneapolis, Minnesota, United States