Sasikanth Manipatruni

Columbia University, New York City, NY, United States

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Publications (61)104.82 Total impact

  • 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 logic. Improvement of its performance—switching speed vs. required current—is critical for its competitiveness. In this paper, (a) we identify an optimized layout of the gate comprised of thin magnetic wires with in-plane magnetization; (b) we optimize geometries of perpendicular magnetization spin torque majority gates. Micromagnetic simulations demonstrate an improvement in switching current for in-plane magnetization (with less than 1 ns switching time) from 6 mA in the original scheme to 1.5 mA in the present one. Additionally, failures of switching caused by vortex formation are eliminated and desired output magnetization is achieved. Various geometries of STMG with perpendicular magnetization are explored. The scheme with a straight cross proves to be the most advantageous. It is predicted to operate with the switching current of 50 μA and less than 4 ns switching time.
    Journal of Applied Physics 04/2014; 115(17). · 2.21 Impact Factor
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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.
    IEEE Transactions on Electron Devices 01/2014; 61(5):1553-1560. · 2.06 Impact Factor
  • 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.
    Journal of Applied Physics 01/2014; 115(17):17B754-17B754-3. · 2.21 Impact Factor
  • V. Calayir, D.E. Nikonov, S. Manipatruni, I.A. Young
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    ABSTRACT: Spin-based devices, in which information is carried via electron spin rather than electron charge, are potential candidates to complement CMOS technology due to the promise of non-volatility and compact implementation of logic gates. One class of such devices is all-spin logic (ASL) which is based on switching ferromagnets by spin transfer torque and conduction of spin-polarized current. Using previously developed physics-based circuit models for ASL, we develop a complete logic family for static ASL comprising of majority logic gates. We compare its performance metrics by means of circuit simulations using our Verilog-A compact models. We also show the novel implementations of sequencing elements (e.g., latch and D flip-flop) to enable clocked ASL. We also refine the models for ferromagnets to include spin relaxation inside ferromagnetic metals (FMs).
    Circuits and Systems I: Regular Papers, IEEE Transactions on 01/2014; 61(2):393-406. · 2.24 Impact Factor
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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.
    IEEE Transactions on Electron Devices 01/2014; 61(8):2905-2911. · 2.06 Impact Factor
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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.
    Applied Physics Letters 01/2014; 104(26):262407-262407-5. · 3.79 Impact Factor
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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.
    IEEE Transactions on Magnetics 01/2014; 50(9):1-13. · 1.42 Impact Factor
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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.
    IEEE Transactions on Magnetics 01/2014; 50(9):1-11. · 1.42 Impact Factor
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    Dmitri E. Nikonov, Sasikanth Manipatruni, Ian A. Young
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    ABSTRACT: We simulate automotion, the spontaneous transport of a magnetic domain wall under the influence of demagnetization and magnetic anisotropy, in nanoscale spintronic interconnects. In contrast to spin transfer driven magnetic domain wall motion, the proposed interconnects operate with only a transient current pulse and provide favorable scaling down to the 20nm scale. Cases of both in-plane and perpendicular magnetization are considered. Analytical dependence of the velocity of domain walls on the angle of magnetization are compared with full micromagnetic simulations. Deceleration, disappearance, and reflection of domain walls are demonstrated. Dependences of the magnetization angle on the current pulse parameters are studied. The energy and delay analysis suggests that automotion is an attractive option for spintronic logic interconnects.
    Journal of Applied Physics 11/2013; 115(21). · 2.21 Impact Factor
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    ABSTRACT: A squeezed light source, i.e. a source with ultra low noise level, below the standard quantum limit (SQL), can enable quantum enhanced sensing, spectroscopy[1, 2], metrology[3] and quantum information processing[4,5]. To date, such a non classical light source on-chip, scalable, compact and robust has not been demonstrated. Such a source could not only enable ultrasensitive measurements on chip, but also provide squeezing over high bandwidths in contrast to most sources which usually rely on large optical cavities with narrow bandwidths. Here, we report the observation of squeezed light in an on-chip monolithically integrated platform, generated in a micron-size silicon nitride oscillator[6] with GHz cavity linewidth. We show 1.7dB noise squeezing, i.e. reduction of the noise level below the standard quantum limit, of the intensity difference between two beams generated by an on-chip optical parametric oscillator.
    09/2013;
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    Sasikanth Manipatruni, Dmitri E. Nikonov, Ian A. Young
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    ABSTRACT: We propose an all-spin state element using spin currents and nanomagnets to enable all-spin state machines for digital computing. We demonstrate via numerical simulations the operation of the state element, a critical building block for synchronous, sequential logic computation. The numerical models encompass Landau-Lifshitz-Gilbert nanomagnet dynamics with stochastic models and vector spin-transport in metallic magnetic and non-magnetic channels. Combined with all-spin combinatorial logic, the state elements can enable synchronous and asynchronous computing elements.
    Applied Physics Letters 08/2013; 103(6). · 3.79 Impact Factor
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    ABSTRACT: We report the first observation of squeezing in an on chip integrated platform based on SiN Optical parametric oscillator ring resonator. We demonstrate 1.7 dB squeezing in the intensity difference between the signal and idler beams.
    CLEO: QELS_Fundamental Science; 06/2013
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    Sasikanth Manipatruni, Dmitri E. Nikonov, Ian A. Young
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    ABSTRACT: In this letter, we show that Giant Spin Hall Effect (GSHE) MRAM can enable better energy- delay and voltage performance than traditional MTJ based spin torque devices at scaled nanomagnet dimensions (10-30 nm). Firstly, we derive the effect of dimensional scaling on spin injection efficiency, voltage-delay and energy-delay of spin torque switching using MTJs and GSHE and identify the optimum electrode geometry for low operating voltage (<0.1 V), high speed (>10 GHz) operation. We show that effective spin injection efficiency >100 % can be obtained using optimum spin hall electrode thickness for 30 nm nanomagnet widths. Finally, we derive the energy-delay trajectory of GSHE and MTJ devices to calculate the energy-delay product of GSHE and MTJ devices with an energy minimum at the characteristic time of the magnets. Optimized GSHE devices when combined with PMA can enable MRAM with scaled nanomagnets (30 nm X 60 nm), ultra-low voltage operation (< 0.1 V), fast switching times (10 ps) and switching energy as low as 100 aJ/bit.
    Applied Physics Express 01/2013; · 2.73 Impact Factor
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    Sasikanth Manipatruni, Dmitri E. Nikonov, Ian A. Young
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    ABSTRACT: All-spin logic devices are promising candidates to augment and complement beyond-CMOS integrated circuit computing due to non-volatility, ultra-low operating voltages, higher logical efficiency, and high density integration. However, the path to reach lower energy-delay product performance compared to CMOS transistors currently is not clear. We show that scaling and engineering the nanoscale magnetic materials and interfaces is the key to realizing spin logic devices that can surpass energy-delay performance of CMOS transistors. With validated stochastic nano-magnetic and vector spin transport numerical models, we derive the target material and interface properties for the nanomagnets and channels. We identified promising new directions for material engineering/discovery focusing on systematic scaling of magnetic anisotropy (Hk) with saturation magnetization (Ms), use of perpendicular magnetic anisotropy, and interface spin mixing conductance of ferromagnet/spin channel interface (Gmix). We provide systematic targets for scaling spin logic energy-delay product toward a 2 aJ.ns energy-delay product, comprehending the stochastic noise for nanomagnets.
    12/2012;
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    Sasikanth Manipatruni, Michal Lipson, Ian A. Young
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    ABSTRACT: We introduce an analytical framework to understand the path for scaling nanophotonic interconnects to meet the energy and footprint requirements of CMOS global interconnects. We derive the device requirements for sub 100 fJ/cm/bit interconnects including tuning power, serialization-deserialization energy, optical insertion losses, extinction ratio and bit error rates. Using CMOS with integrated nanophotonics as an example platform, we derive the energy/bit, linear and areal bandwidth density of optical interconnects. We also derive the targets for device performance which indicate the need for continued improvements in insertion losses (<8dB), laser efficiency, operational speeds (>40 Gb/s), tuning power (<100 {\mu}W/nm), serialization-deserialization (< 10 fJ/bit/Operation) and necessity for spectrally selective devices with wavelength multiplexing (> 6 channels).
    IEEE Journal of Selected Topics in Quantum Electronics 07/2012; · 4.08 Impact Factor
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    ABSTRACT: We demonstrate experimentally the synchronization of two coupled micro-optomechanical oscillators. The mutual coupling is purely optical and fully tunable. Upon synchronization, the phase noise drops in agreement with the prediction.
    05/2012;
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    ABSTRACT: We demonstrate the generation of error-free binary-phase-shift-keyed (BPSK) data at 5 Gb/s using a silicon microring modulator. The microring-modulated BPSK signal is propagated at fiber lengths up to 80 km, maintaining error-free performance, while demonstrating resilience to chromatic dispersion. Bit-error-rate measurements and eye diagrams show near equivalent performance of a microring-based BPSK modulator as compared to commercial LiNbO₃ phase modulators.
    Optics Express 04/2012; 20(8):8681-8. · 3.55 Impact Factor
  • S. Manipatruni, D.E. Nikonov, I.A. Young
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    ABSTRACT: We present a theoretical and a numerical formalism for analysis and design of spintronic integrated circuits (SPINICs). The formalism encompasses a generalized circuit theory for spintronic integrated circuits based on nanomagnetic dynamics and spin transport. We propose an extension to the modified nodal analysis technique for the analysis of spin circuits based on the recently developed spin conduction matrices. We demonstrate the applicability of the framework using an example spin logic circuit described using spin Netlists.
    Circuits and Systems I: Regular Papers, IEEE Transactions on 01/2012; 59(12):2801-2814. · 2.24 Impact Factor
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    ABSTRACT: For the past 40 years, relentless focus on Moore's Law transistor scaling has delivered ever-improving CMOS transistor density. This paper discusses architectural and materials options which will contribute to the ultimate CMOS device. In addition, the paper reviews device options beyond the ultimate CMOS device.
    Electron Devices Meeting (IEDM), 2012 IEEE International; 01/2012
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    ABSTRACT: Synchronization, the emergence of spontaneous order in coupled systems, is of fundamental importance in both physical and biological systems. We demonstrate the synchronization of two dissimilar silicon nitride micromechanical oscillators, that are spaced apart by a few hundred nanometers and are coupled through optical radiation field. The tunability of the optical coupling between the oscillators enables one to externally control the dynamics and switch between coupled and individual oscillation states. These results pave a path towards reconfigurable massive synchronized oscillator networks.
    Physical Review Letters 12/2011; 109(23). · 7.73 Impact Factor

Publication Stats

764 Citations
104.82 Total Impact Points

Institutions

  • 2010–2012
    • Columbia University
      • Department of Electrical Engineering
      New York City, NY, United States
  • 2007–2012
    • Cornell University
      • Department of Electrical and Computer Engineering
      Ithaca, NY, United States