Browsing by Subject "Magnetic tunnel junction"

Now showing 1 - 3 of 3
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    CMOS Reliability Characterization Techniques and Spintronics-Based Mixed-Signal Circuits
    (2015-09) Choi, Won Ho
    Plasma-Induced Damage (PID) has been an important reliability concern for equipment vendors and fabs in both traditional SiO2 based and advanced high-k dielectric based processes. Plasma etching and ashing are extensively used in a typical CMOS back-end process. During the plasma steps, the metal interconnect, commonly referred to as an “antenna,” collects plasma charges and if the junction of the driver is too small to quickly discharge the node voltage, extra traps are generated in the gate dielectric of the receiver thereby worsening device reliability mechanisms such as Bias Temperature Instability (BTI) and Time Dependent Dielectric Breakdown (TDDB). The foremost challenge to an effective PID mitigation strategy is in the collection of massive TDDB or NBTI data within a short test time. In this dissertation, we have developed two array-based on-chip monitoring circuits for characterizing latent PID including (1) an array-based PID-induced TDDB characterization circuit and (2) a PID-induced BTI characterization circuit using the 65nm CMOS process. As the research interest on analog circuit reliability is increasing recently, a few studies analyzed the impact of short-term Vth shift, not a permanent Vth shift, on a Successive Approximation Register (SAR) Analog-to-Digital Converter (ADC) and revealed that even short-term Vth shifts in the order of 1mV by short stress pulse (e.g., 1μs) on the comparator input transistors may cause to degrade the resolution of the SAR ADC even for a fresh chip (no experimentally verified). In this dissertation, we quantified this effect through test-chip studies and propose two simple circuit approaches that can be used to mitigate short-term Vth instability issues in SAR ADCs. The proposed techniques were implemented in 10-bit SAR ADC using the 65nm CMOS process. Spintronic circuits and systems have several unique properties including inherent non-volatility that can be uniquely exploited for achievable functional capabilities not obtainable in conventional systems. Magnetic Tunnel Junction (MTJ) technology has matured to the point where commercial spin transfer torque MRAM (STT-MRAM) chips are currently being developed. This work aims at leveraging and complimenting on-going development efforts in MTJ technology for non-memory mixed-signal applications. In this dissertation, we developed two spintronics-based mixed-signal circuit designs: (1) an MTJ-based True Random Number Generator (TRNG) and (2) an MTJ-based ADC. The proposed TRNG and ADC have the potential to achieve a compact area, simpler design, and reliable operation as compared to their CMOS counterparts.
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    Dynamics and performance optimization of spin-torque switching in magnetic tunnel junctions
    (2013-10) Dunn, Thomas Edward
    In this thesis I present a theoretical description for spin-torque switching using AC and DC spin-currents. This description builds from the standard Landau-Lifshitz-Gilbert equation with Slonczewski spin-torque. By exploiting a separation in time-scales between the fast precessional motion of the free layer magnetization about the effective field and the slow drift of the free layer towards higher or lower energies that results from ST and damping, I reduce the free layer switching dynamics to that of a one dimensional system. Using this description I characterize certain current and frequency values important to switching, such as the DC critical current and the AC upper bifurcation frequency. Finally, using this description I show how to optimize the efficiency of AC, DC, and combination AC/DC spin-current strategies to minimize the Joule heat loss associated with switching. This leads to a well-defined range of spin-current polarization and free layer anisotropy values where each spin-current strategy is optimal.
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    Spin transfer torque induced oscillation and switching in magnetic tunnel junction
    (2014-05) Zhang, Yisong
    Spin transfer torque (STT) induced magnetization switching and oscillation in nanometer scale magnetoresistance (MR) devices have been studied intensively due to its direct application in the non-volatile STT random access memory (STT-RAM) and its potential application in the high frequency spin torque oscillatior (STO). STO could be used in high-density microwave signal processor and chip-to-chip communication system due to its nanometer scale footprint and ultra high oscillation frequency. STO has also been suggested in the magnetic recoridng head for the microwave assisted magnetic recording (MAMR) and in the high-speed magnetic reader for future hard disk drive. However, several critical engineering challenges for those exciting STO applications are still remaining, including optimizing the operating condition, tuning the frequency, narrowing the linewidth and improving the output power.In this thesis work, the spin transfer torque induced oscillation is experimentally studied in MgO barrier based magnetic tunnel junctions (MTJs) with focus on the improvement of the key performances of the STO. The power angular dependence of spin torque oscillation is experimentally studied in dual MgO barrier MTJs based on the understanding of the relation between the MR and oscillation output power. It is proved that the STO electrical power increases with the polarizer canting angle. Meanwhile, the results also reveal a solution for extending the oscillation operating condition. Furthermore, the MTJ based STO device with a built-in hard axis polarizer is designed and studied. This design provides an external-field-free STO with high power, low critical current and extended operation range of the driving current for the first time. Additionally, two oscillation modes in the dual MgO barrier MTJs are observed and investigated. It is found from the field-dependent power spectra that the extra oscillation mode may come from the weakly-pinned top reference layer. A single-shot time-domain measurement to characterize the switching time of each switch under different voltages for MTJs in the nanosecond precessional regime was carried out too.