Sasikanth Manipatruni

Cornell University, Ithaca, NY, United States

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Publications (77)122.55 Total impact

  • Sou-Chi Chang · Nickvash Kani · Sasikanth Manipatruni · Dmitri Nikonov · Ian Young · Azad Naeemi

    No preview · Article · Jan 2016 · IEEE Transactions on Magnetics
  • Sou-Chi Chang · Sasikanth Manipatruni · Dmitri Nikonov · Ian Young

    No preview · Article · Jan 2016
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    Sasikanth Manipatruni · Dmitri E. Nikonov · Ian A. Young
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    ABSTRACT: As nanoelectronics approaches the nanometer scale, a massive effort is underway to identify the next scalable logic technology beyond Complementary Metal Oxide Semiconductor (CMOS) computing. Such computing technology needs to improve switching energy & delay at reduced dimensions, allow improved interconnects and provide a complete logic/memory family. However, a viable beyond-CMOS logic technology has remained elusive. Here, we propose a scalable spintronic logic device which operates via spin-orbit transduction combined with magneto-electric switching. The proposed Magneto-Electric Spin Orbit (MESO) logic enables a new paradigm to continue scaling of logic performance to near thermodynamic limits for GHz logic (100 kT switching energy at 100 ps delay). The proposed MESO devices scale strongly and favorably with critical dimensions of the device, showing a cubic dependence of switching energy on size, (E_m proportional to W^3), and square dependence on voltage (E_m proportional to V^2). The excellent scaling is obtained thanks to the properties of the spin orbit effects (e.g. Inverse Spin Hall Effect (ISHE) and Inverse Rashba-Edelstein Effect (IREE)) and the dependence of capacitance on size. The operating voltages for these devices are predicted to be < 100 mV allowing a significant jump ahead of historic trends of scaling voltage with size and corresponding reduction of energy. Interconnect resistance is a critical obstacle for scaling beyond 10 nm dimensions. We project a less detrimental impact of interconnect resistance and show that MESO logic is amenable for highly resistive interconnects (100 uOhm.cm-1 mOhm.cm) which opens a possibility to use nano-metallic (width < bulk electron mean free path) or doped semiconducting wires (width<5 nm). A scalable, CMOS compatible, non-volatile logic family proposed here may enable the next multi-generational scaling of computing devices.
    Preview · Article · Dec 2015
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    Conference Paper: Spintronic Majority Gates
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    ABSTRACT: In this paper we present an overview of two types of majority gate devices based on spintronic phenomena. We compare the spin torque majority gate and the spin wave majority gate and describe work on these devices. We discuss operating conditions for the two device concepts, circuit implication and how these reflect on materials choices for device implementation.
    Full-text · Conference Paper · Dec 2015
  • Sourav Dutta · Dmitri E. Nikonov · Sasikanth Manipatruni · Ian A. Young · Azad Naeemi
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    ABSTRACT: The possibility of achieving phase-dependent deterministic switching of the magnetoelectric spin wave detector in the presence of thermal noise has been discussed. The proposed idea relies on the modification of the energy landscape by partially canceling the out-of-plane demagnetizing field and the resultant change in the intrinsic magnetization dynamics to drive the nanomagnet towards a preferential final magnetization state. The remarkable increase in the probability of successful switching can be accounted for by the shift in the location of the saddle point in the energy landscape and a resultant change in the nature of the relaxation dynamics of the magnetization from a highly precessional to a fairly damped one and an increased dependence on the initial magnetization values, a crucial requirement for phase-dependent spin wave detection.
    No preview · Article · Nov 2015 · Applied Physics Letters
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    Asif Khan · Dmitri E. Nikonov · Sasikanth Manipatruni · Tahir Ghani · Ian A. Young
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    ABSTRACT: There is no abstract available for this article.
    Preview · Article · Nov 2015 · Applied Physics Letters
  • Sourav Dutta · Dmitri E. Nikonov · Sasikanth Manipatruni · Ian A. Young · Azad Naeemi
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    ABSTRACT: We propose a formalism of a compact physical model for crosstalk noise analysis between two coplanar backward volume spin-wave interconnects. Comparing the amplitudes of the signal in the active line and the noise in the victim line, we introduce a figure of merit for crosstalk-the longitudinal or line-to-line coupling. It is shown that the crosstalk becomes prohibitively high as the edge-to-edge spacing between the lines goes down, and thus putting a limitation on the routing and placement in a spin-wave bus network. The position of the peak crosstalk noise coupling for different spacings and frequencies of excitation reveals a new limitation to the maximum interconnect length. Furthermore, the technique of superposition analogous to RLC interconnects is exploited to explain the complicated nature of crosstalk noise and develop a mechanism for modeling crosstalk. Finally, a compact physical model is derived using analytical expressions, which demonstrate a reasonably good agreement with the actual full micromagnetic simulation results.
    No preview · Article · Nov 2015 · IEEE Transactions on Electron Devices
  • Dmitri E Nikonov · Sasikanth Manipatruni · Ian A Young
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    ABSTRACT: Spin torque majority gate (STMG) is one of the promising options for beyond-complementary metal-oxide-semiconductor non-volatile logic circuits for normally-off computing. Modeling of prior schemes demonstrated logic completeness using majority operation and nonlinear transfer characteristics. However significant problems arose with cascade-ability and input output isolation manifesting as domain walls (DWs) stopping, reflecting off ends of wires or propagating back to the inputs. We introduce a new scheme to enable cascade-ability and isolation based on (a) in-plane DW automotion in interconnects, (b) exchange coupling of magnetization between two FM layers, and (c) 'round-about' topology for the majority gate. We performed micro-magnetic simulations that demonstrate switching operation of this STMG scheme. These circuits were verified to enable isolation of inputs from output signals and to be cascade-able without limitations.
    No preview · Article · Jul 2015 · Physica Scripta
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    Tanay Gosavi · Sasikanth Manipatruni · Dmitri Nikonov · Ian A. Young · Sunil Bhave
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    ABSTRACT: Efficient generation of spin currents from charge currents is of high importance for memory and logic applications of spintronics. In particular, generation of spin currents from charge currents in high spin-orbit coupling metals has the potential to provide a scalable solution for embedded memory. We demonstrate a net reduction in critical charge current for spin torque driven magnetization reversal via using spin-orbit mediated spin current generation. We scaled the dimensions of the spin-orbit electrode to 300 nm and the nanomagnet to 270 nm X 68 nm in a three terminal spin-orbit torque, magnetic tunnel junction (SOT-MTJ) geometry. Our estimated effective spin Hall angle is 0.15-0.20 using the ratio of zero temperature critical current from spin Hall switching and estimated spin current density for switching the magnet. We show bidirectional transient switching using spin-orbit generated spin torque at 100 ns switching times reliably. We finally compare the static and dynamic response of the SOT-MTJ with transient spin circuit modeling showing the performance of scaled SOT-MTJs to enable nanosecond class non-volatile MTJs.
    Preview · Article · Jun 2015
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    ABSTRACT: The possibility of using spin waves for information transmission and processing has been an area of active research due to the unique ability to manipulate the amplitude and phase of the spin waves for building complex logic circuits with less physical resources and low power consumption. Previous proposals on spin wave logic circuits have suggested the idea of utilizing the magneto-electric effect for spin wave amplification and amplitude- or phase-dependent switching of magneto-electric cells. Here, we propose a comprehensive scheme for building a clocked non-volatile spin wave device by introducing a charge-to-spin converter that translates information from electrical domain to spin domain, magneto-electric spin wave repeaters that operate in three different regimes - spin wave transmitter, non-volatile memory and spin wave detector, and a novel clocking scheme that ensures sequential transmission of information and non-reciprocity. The proposed device satisfies the five essential requirements for logic application: nonlinearity, amplification, concatenability, feedback prevention, and complete set of Boolean operations.
    No preview · Article · May 2015 · Scientific Reports
  • Sou-Chi Chang · Sourav Dutta · Sasikanth Manipatruni · Dmitri Nikonov · Ian Young · Azad Naeemi

    No preview · Article · Jan 2015
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    Gary Allen · Sasikanth Manipatruni · Dmitri E. Nikonov · Mark Doczy · Ian A. Young
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    ABSTRACT: We have measured the spin torques of beta-Tantalum / Co20Fe60B20 bilayers versus Ta thickness at room temperature using an FMR technique. The spin Hall coefficient was calculated both from the observed change in damping coefficient of the ferromagnet with Ta thickness, and from the ratio of the symmetric and anti-symmetric components of the FMR signal. Results from these two methods yielded values for the spin Hall coefficient of -0.090+/-0.005 and -0.11+/-0.01, respectively. We have also identified a significant out-of-plane spin torque originating from Ta, which is constant with Ta thickness. We ascribe this to an interface spin orbit coupling, or Rashba effect, due to the strength and constancy of the torque with Ta thickness. From fitting measured data to a model including interface spin orbit coupling, we have determined the spin diffusion length for beta-Tantalum to be ~2.5 nm.
    Full-text · Article · Nov 2014 · Physical Review B
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    ABSTRACT: Spin-resolved conductivities in magnetic tunnel junctions are calculated using a semiempirical tight-binding model and non-equilibrium Green's functions. The performance of half-metallic electrodes is studied by comparing conventional Fe-MgO-Fe structures to Co2FeAl-MgO-Co2FeAl structures. The results show higher tunneling magnetoresistance and resistance-area product for Co2FeAl devices across a wide bias range.
    No preview · Conference Paper · Sep 2014
  • Sou-Chi Chang · Sasikanth Manipatruni · D.E. Nikonov · Ian A. Young · Azad Naeemi
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    ABSTRACT: An Si spin interconnect for all-spin logic (ASL) is analyzed by a comprehensive physical model, including spin injection, spin transport, and stochastic magnetization dynamics. It is shown that the spin current density and spin polarization of the current can be improved by changing material properties, interface conditions, and structure dimensions. Furthermore, with the help of an electric field, spin information can preserve and propagate between magnets in a highly doped micrometer-scale Si channel. Different from metallic ASL, instead of the short spin relaxation length, the main constraint of an Si spin interconnect is the high bias voltage required to minimize the energy-delay product (EDP). The minimum EDP and corresponding bias voltage can be reduced significantly by downscaling the nanomagnet. This improvement in the magnetic response allows Si to provide a compatible low-power interconnect technology to metallic ASL.
    No preview · Article · Sep 2014 · IEEE Transactions on Magnetics
  • Sourav Dutta · D.E. Nikonov · Sasikanth Manipatruni · Ian A. Young · Azad Naeemi
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    ABSTRACT: We propose a formalism of a compact model for circuit simulations of spin wave interconnects. The developed SPICE Spin Wave model is based on the theory of numerical micromagnetics, and serves as a building block for a hierarchical circuit simulation tool for spintronic circuits and systems. We demonstrate excellent agreement between the SPICE model simulations and full micromagnetic solver results. We also present a scheme of exciting spin waves in spin wave bus having perpendicular magnetic anisotropy. Spin waves are excited with an oscillating change of magnetocrystalline anisotropy in a magnetoelectric cell. We use our proposed SPICE model to analyze this structure: determine the length of spin wave attenuation, delay in the bus, and the dependence of amplitude on the change of anisotropy.
    No preview · Article · Sep 2014 · IEEE Transactions on Magnetics
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    ABSTRACT: In this paper, a conventional spin-valve configuration combined with spin-torque-driven switching is used as an energy efficient interconnect structure for all-spin logic. Both Cu and Al interconnect materials are analyzed based on physical models for spin injection, spin transport, and magnetization dynamics. The results indicate proposed metallic interconnects dissipate less energy as compared with all-spin logic interconnects based on the nonlocal spin-valve configuration. Compared with a similar spin interconnect with an Si channel, the spin currents and injection efficiencies are predicted to be higher when a metal like Cu or Al is used due to no Schottky barrier at the interface. Because of the longer spin relaxation length (SRL) in Al as compared with Cu, the delay and energy dissipation are lower when Al is used especially at longer lengths where signal loss becomes important. While metallic spin interconnects are faster and more energy efficient in short lengths because of their smaller resistances and higher spin injection efficiencies, they are outperformed by spin interconnects with Si channels at long lengths because the SRLs in Si can be as long as many micrometers, whereas in metals they are limited to a few hundred nanometers.
    No preview · Article · Aug 2014 · IEEE Transactions on Electron Devices
  • Asif Khan · Dmitri E. Nikonov · Sasikanth Manipatruni · Tahir Ghani · Ian A. Young
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    ABSTRACT: A spintronic device, called the “strain assisted spin transfer torque (STT) random access memory (RAM),” is proposed by combining the magnetostriction effect and the spin transfer torque effect which can result in a dramatic improvement in the energy dissipation relative to a conventional STT-RAM. Magnetization switching in the device which is a piezoelectric-ferromagnetic heterostructure via the combined magnetostriction and STT effect is simulated by solving the Landau-Lifshitz-Gilbert equation incorporating the influence of thermal noise. The simulations show that, in such a device, each of these two mechanisms (magnetostriction and spin transfer torque) provides in a 90° rotation of the magnetization leading a deterministic 180° switching with a critical current significantly smaller than that required for spin torque alone. Such a scheme is an attractive option for writing magnetic RAM cells.
    No preview · Article · Jun 2014 · Applied Physics Letters
  • Sasikanth Manipatruni · Dmitri E. Nikonov · Ian A. Young
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    ABSTRACT: Integration and co-design of CMOS and spin transfer devices requires accurate vector spin conduction modeling of magnetic tunnel junction (MTJ) devices. A physically realistic model of the MTJ should comprehend the spin torque dynamics of nanomagnet interacting with an injected vector spin current and the voltage dependent spin torque. Vector spin modeling allows for calculation of 3 component spin currents and potentials along with the charge currents/potentials in non-collinear magnetic systems. Here, we show 4-component vector spin conduction modeling of magnetic tunnel junction devices coupled with spin transfer torque in the nanomagnet. Nanomagnet dynamics, voltage dependent spin transport, and thermal noise are comprehended in a self-consistent fashion. We show comparison of the model with experimental magnetoresistance (MR) of MTJs and voltage degradation of MR with voltage. Proposed model enables MTJ circuit design that comprehends voltage dependent spin torque effects, switching error rates, spin degradation, and back hopping effects.
    No preview · Article · May 2014 · Journal of Applied Physics
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    ABSTRACT: The energy-per-bit and delay of All-Spin Logic (ASL) interconnects have been modeled. Both Al and Cu interconnect channels have been considered and the impact of size effects and dimensional scaling on their potential performance has been quantified. It is predicted that size effects will affect ASL interconnects more severely than electrical interconnects.
    No preview · Conference Paper · May 2014
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    ABSTRACT: In this paper, compact circuit models for spintronic devices have been developed by manipulating the underlying physical equations. We have simulated, via circuit simulation: 1) the magnetization dynamics governed by the Landau–Lifshitz–Gilbert (LLG) equation and 2) the spin transport physics governed by the spin drift–diffusion equation. The models have been validated using numerical and analytical solutions of the LLG equation and the spin drift–diffusion equations, respectively. Simulations of an all-spin logic device demonstrate the applications of the developed models in device and circuit simulation.
    Full-text · Article · May 2014 · IEEE Transactions on Electron Devices