Ms. Seema Dhull Profile

Seema Dhull

at Indian Institute of Technology Roorkee

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Proceedings Article | 20 August 2020 Presentation + Paper

Design of an efficient VCMA controlled spintronic random number generator

Arshid Nisar, Seema Dhull, Brajesh Kumar Kaushik, Farooq Ahmad Khanday

Proceedings Volume 11470, 114703X (2020) https://doi.org/10.1117/12.2567531

KEYWORDS: Magnetism, Switching, Spintronics, Resistance, Energy efficiency, Stochastic processes, Modulation, Ferromagnetics

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Random number generators play an essential role in stochastic circuits, neuromorphic computing and cryptographic systems. Existing CMOS based true random number generators (TRNGs) incur a significant performance, power and area overheads. The systems based on magnetic tunnel junctions (MTJs) offer favorable features such as high resilience, low energy consumption, good performance, and less complexity. Compared with the conventional MTJ switching approaches, voltage controlled magnetic anisotropy switching (VCMA) features low switching current, minimal control circuitry and calibration process, and insensitivity to the write pulse duration. In this paper an efficient design for TRNG based on VCMA using MTJ is presented. The proposed magnetic TRNG consists of a standard two-terminal MTJ connected to the drain terminal of a PMOS transistor which controls the pulse width of the applied bias voltage. MTJ is used as a noise source device and its precessional switching characteristics are exploited to design the TRNG. The resistance of the device fluctuates while operating in precessional switching regime and the magnetization state is selected randomly via thermal fluctuations. The voltage developed across the MTJ corresponding to its random state results into a random bit. A 64-bit parallel random number generator has been implemented and evaluated using Spice simulating tool (with 45 nm CMOS technology node). The proposed circuit has an advantage of less circuit complexity and high energy efficiency. It achieves a high throughput of 64Gbps with an energy consumption of 5.6 fJ/bit.

Proceedings Article | 20 August 2020 Poster + Paper

High frequency current induced domain wall motion based nano oscillator

Seema Dhull, Arshid Nisar, Brajesh Kumar Kaushik

Proceedings Volume 11470, 114703Y (2020) https://doi.org/10.1117/12.2568313

KEYWORDS: Magnetism, Oscillators, Motion models, Spintronics, Signal generators, Signal detection, Ferromagnetics

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In recent years, nano-oscillators have gained enormous interest in the research domain of spintronics. These nanooscillators generate microwave signals using spin-transfer torque (STT) mechanism and demonstrate key features in terms of scalability, frequency tunability, wide operating temperature, and high integrability with CMOS technology. Spin devices such as STT, domain wall (DW), and spin-orbit torque (SOT) devices can be interchangeably used to build these nano-oscillators. The magnetic domain wall in nanowires shows stable chirality induced by interfacial Dzyaloshinskii–Moriya Interaction (DMI) and exhibit ultra-high-speed DW motion. A spin current injecting into the nanowire create magnetic oscillations by moving the DW between the ends of DMI confined region. In this manuscript, current driven domain wall motion (DWM)-based nano-oscillator has been presented to achieve a high tuneable frequency. Furthermore, a comparative study of STT, SOT, and current induced DWM based nano-oscillators has been carried out. The potential applications of these nano-oscillators include frequency signal generation, signal modulation, neuromorphic computing, and microwave signal detection/generation. The capability of spintronic oscillators to communicate together, their long lifetime, and low energy consumption unfolds the path for the fast and parallel computation systems.

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