SPIN

In the era of big data, massive data requires processing efficiently. However, the limited data bandwidth between the memory and the processor in conventional computer systems could not meet the requirement of data transferring. Computing in-memory has been considered an effective solution to address this problem. In this paper, based on the spin transfer torque-magnetic random access memory (STT-MRAM), a computing in-memory architecture with as few peripheral circuits as possible is proposed. This computing in-memory architecture gives the specific reference cell so that two rows in one array can be activated simultaneously to perform bitwise logic operations, such as OR/NOR and AND/NAND. In addition, with technology scaling down, STT-MRAM suffers from high sensitivity to process variation, which results in more device mismatch in a sense circuit. Additionally, the negative bias temperature instability (NBTI) seriously affects the life of PMOS transistors used in a sense circuit. In this paper, a high-reliability sense amplifier for computing in-memory with STT-MRAM is proposed. By using two self-enabled switching transistors, the proposed sense amplifier not only can decrease the NBTI effect on PMOS transistors but also can achieve a low sensing error rate. Using a CMOS 40nm design-kit and an accurate compact model of the STT magnetic tunnel junction (MTJ), mixed transient and statistical simulations have been present to demonstrate the functionality and performance of the proposed circuits.

Physical unclonable function (PUF) is considered as a promising primitive for variety of security applications since its appearance, such as authentication, key generators and random oracle. With the fast development of Internet of Things (IoT), the requirement for low complexity, high power efficiency and enhanced security level of PUF becomes urgent. Meanwhile, the conventional PUF instances based on optical effect and semiconductors fail to meet the requirements due to poor scalability and sensitivity to attacks. This paper proposes a circuit design of PUF by utilizing the spin transfer torque magnetic random access memory (STT-MRAM). The performance of presented circuit design is thoroughly investigated from the aspects of uniqueness, reliability, uniformity, diffuseness, access speed and energy consumption. The simulation results show that the inter-Hamming distance can achieve 50% and the intra-Hamming distance can be reduced as low as 0%, resulting in perfect security. Meanwhile, the circuit behaves high immunity to environmental variations such as high and low temperature. With the rapid development of artificial intelligence, many powerful attack methods emerge. To defend against these attacks, the user reconfigurable function has been proposed. Moreover, design space including programming voltage, device parameters and thermal conditions has been explored to optimize the reliability of this function.

Due to their nonvolatility and intrinsic current integration capabilities, spintronic devices that rely on domain wall (DW) motion through a free ferromagnetic track have garnered significant interest in the field of neuromorphic computing. Although a number of such devices have already been proposed, they require the use of external circuitry to implement several important neuronal behaviors. As such, they are likely to result in either a decrease in energy efficiency, an increase in fabrication complexity, or even both. To resolve this issue, we have proposed three individual neurons that are capable of performing these functionalities without the use of any external circuitry. To implement leaking, the first neuron uses a dipolar coupling field, the second uses an anisotropy gradient and the third uses shape variations of the DW track.

One of the most interesting solutions for decreasing the static power of computational circuits is to use approximate computing. Approximate computing has been extensively considered to trade-off limited accuracy for improvements in other circuit metrics such as area, power and performance. On the other hand, the increasing leakage power and limited scalability have become serious obstacles that prevent the continuous miniaturization of conventional CMOS-based logic circuits. Spintronic devices are being considered as a promising alternative technology for silicon-based FET to implement digital circuits. In this paper, an approximate 5-2 compressor cell is presented using spin-based devices. The proposed circuit is designed by majority gates which can be implemented very easily and efficiently by spintronic threshold device (STD). The proposed design has been simulated comprehensively for both quantitative and qualitative metrics. The results show that the spin-based compressor decreases the power consumption about 7X compared to the best state-of-the-art design. Also, the application simulations using the multiplier implemented by the proposed compressor indicate the acceptable results.

In the present work we have performed self-consistent ab-initio calculation using the full-potential linearized augmented plane-wave method (FP-LAPW), based on the density functional theory (DFT) as implemented in the Wien2k code to study the structural, electronic, magnetic, thermodynamic and thermoelectric properties of the half-heusler compound CrYSn ($\mathrm{\text{Y}}=\mathrm{\text{Ca}}$, Sr) using generalized gradient approximation (GGA) described by Perdew–Burke–Ernzerhof (PBE), GGA+U and the modified Beck–Johnson correction (mBJ), the obtained results show that the compound is stable in the ferromagnetic state (FM) in $\alpha$ phase on one hand and has a half-metallic character (metallic nature in spin up channel and semiconductor one in spin down channel with an indirect gap) on the other hand thus, the compound is a good candidate for spintronic applications, moreover it shows a very interesting thermoelectric predisposition in the minority spin or spin down channel at room temperature consisting of a very high Seebeck coefficient, high electrical conductivity and figure of merit near unity for the two compounds. The thermodynamic properties of CrCaSn and CrSrSn compounds using Gibbs code are studied for the first time. This study showed that these compounds can be used in extreme thermodynamic conditions. Since no experimental data were reported until now concerning this compound, our theoretical predictions of electronic, thermodynamic and thermoelectric properties are likely to be experimentally verified.

The structural, elastic, electronic and thermodynamic properties of skutterudite binary compound CoP₃ and the ternary alloy FeCoP₃ were investigated by using the full-potential linearized augmented plane-wave plus local orbitals method within the approximation GGA-PBEsol functional. The computed lattice constants, bulk moduli and the pressure derivative of the bulk moduli at the equilibrium are in good agreement with the published experimental data. The brittleness and ductility of these materials were studied by the analysis of the elastic constants and other mechanical parameters, where we have found that both CoP₃ and FeCoP₃ are ductile materials. The electronic band structure calculation, using the modified Becke-Johnson potential (TB-mBJ), shows that the skutterudite binary compound CoP₃ at equilibrium, present a narrow indirect bandgap of 0.524eV where the ternary alloy FeCoP₃ is a metal behavior. Finally, we investigated the impact of pressure $P$ and temperature $T$ on the lattice parameters, heat capacities $C_V$, Debye temperatures ${\theta }_D$ and the entropies $S$ using the quasi-harmonic Debye model.

The current-driven magnetization precession dynamics stimulated by Spin-Transfer Torque (STT) in a trilayer spin-valve device (typically Spin-Torque Nanooscillator (STNO)) is numerically investigated by solving the Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation. We have devised four STNO devices made of ferromagnetic alloys such as CoPt, CoFeB, Fe${}_{85}$B${}_{13}$Ni₂ and EuO, which act as free and fixed layers. Here, copper acts as a nonmagnetic spacer for all the devices. In this work, we have introduced the current-induced Oersted field, which is generated when a spin-polarized current passes through the device. The generated Oersted field strength is varied by increasing the diameter of the STNO device. Frequency tunability is achieved in all the four devices, whereas the power of the individual device reduces. The frequency and power of the devices depend entirely on the saturation magnetization of the material, which inherently reflects in the current density and the coherence of the spin-polarized DC. In all devices, the frequency increases, whereas the power decreases by increasing the strength of the Oersted field. Among the four devices, the maximum frequency can be tuned up to 104GHz with 40nm device diameter, which is obtained for EuO material. This opens a promising source and paves a glittering future for the nanoscale spintronic devices.

The electronic structure and magnetic properties of diluted Ca${}_{1-x}$TM_xS (TM$=$V, Cr and Co) in the rocksalt structure at concentrations $x=0.0625$, 0.125 and 0.25 were studied using the full-potential linearized augmented plane wave approximation of the density functional theory with the Wu-Cohen generalized gradient approximation (WC-GGA) and the Tran–Blaha-modified Becke–Johnson (TB-mBJ) potential. Features such as lattice constant, bulk modulus, spin-polarized band structures, total and local densities of states and magnetic properties have been computed. The electronic structure show that Ca${}_{1-x}$(V, Cr)_xS at all the studied concentrations and the diluted Ca${}_{1-x}$Co_xS with $x=0.0625$ compounds are half-metallic ferromagnets with spin polarization of 100%. The calculated total magnetic moments for Ca${}_{1-x}$V_xS and Ca${}_{1-x}$Co_xS show the same integer value of 3${\mu }_B$ per formula unit and Ca${}_{1-x}$Cr_xS exhibit a total magnetic moment of 4${\mu }_B$, which confirm the half-metallic behavior of these compounds. We also calculated the values of the band edge spin splitting of the valence and conduction bands and the exchange constants. We have found that the ferromagnetic state is stable by the p-d exchange associated with the double-exchange mechanism. The diluted Ca${}_{1-x}$(V,Cr,Co)_xS are found to be new promising candidates for spintronic applications.

In this work, the structural, electronic and optical properties of Si-doped barium chalcogenide [barium sulfide (BaS)] with different Si concentrations ($0\le x\le 0.25$) are investigated by the first-principles calculations based on the density functional theory (DFT). The band structures, charge densities and complex dielectric functions of the pure as well as Si-doped BaS were presented and analyzed in detail using TB-mBJ approach by WIEN2k package. It is found that silicon concentration can control the bandgap by reducing it to values around 1.4eV and 1.6eV for 12.5% and 6.25% of Si-doped BaS, respectively. The electron charge density indicates the ionic bonding between silicon and sulfur atoms due to the high electronegativity between them. In fact, the results show that the absorption peaks of Si-doped BaS are enhanced compared with pure BaS. These results suggest that the Ba${}_{1-x}$Si_xS original structure displays excellent physical properties thereby revealing that it is a promising material in advanced optoelectronic and solar cell applications.