From the discovery of GMR effect since 1988,spintronic has been extensively developed. Research and application of relative GMR, CMR and TMR topics have progressed rapidly. In the year of 2007, the Nobel prize of physics was awarded to Albert Fert and Peter Grünberg for the great achievement on the research of GMR. The application of development on MRAM is a very hot subject recently and the main operating constructions of MRAM are MTJ. In this thesis, La0.67Ca0.33MnO3¡BLa0.67Sr1.33MnO4 and La0.8Ba0.2MnO3 of CMR materials were growth to multilayer to investigate the properties and characters of the films, in order to built up the MRAM based on CMR MTJ¡¦s.

Superconductor-Insulator-Superconductor (SIS) tunnel junction mixers are now commonly used in astronomical receivers at (sub)millimeter wavelengths because of their superb sensitivity, high dynamic range and stability of operation. Niobium SIS mixers operating at frequencies well below the super- conducting gap (∼680 GHz) have already achieved quantum limited sensitivity. Therefore to further enhance the receiver sensitivity, increasing the Intermediate Frequency (IF) bandwidth of SIS mixers has became crucial. This thesis focuses on the theoretical modeling, design and experimental verifi- cation of Nb SIS mixers operating around 230 GHz with a wide IF bandwidth of 1–15 GHz. These mixers were designed for a single baseline heterodyne interferometer (GUBBINS), which is being built to observe the Sunyaev-Zel’dovich effect in the Cosmic Microwave Background. The combination of wide IF bandwidth SIS mixers and complex analogue correlators will allow GUBBINS to feature high surface brightness sensitivity, that helps to distinguish the weak SZ effect from the background noise. The SIS mixer detector system was assembled inside the GUBBINS cryostat together with the IF electronics and RF/LO optical systems. Low noise temperatures of around 71 K were then measured in the GUBBINS system. The Nb SIS mixer we have developed uses a unilateral finline and fully integrated planar circuits deposited on a silicon substrate, to couple the electromagnetic radiation from the waveguide into the SIS junction. The finline mixer allows a broad-band RF coupling, an easy integration of the on-chip planar circuits and an easy-to-fabricate mixer block. To achieve a wide IF bandwidth, the output impedance of the SIS mixer was well matched to the input impedance of the amplifier by a multi-stage microstrip circuit. Additionally, the planar circuit of the SIS mixer was also designed to have a small lumped inductance and capacitance. The SIS mixer chip was extensively simulated by rigorous electromagnetic software (HFSS) and the S-parameter was exported to a quantum mixing package SuperMix to produce a full-wave model of the mixer. Experimental testing yielded a best noise temperature of 50 K with an average noise temperature of 75 K over an RF bandwidth of 160 GHz– 260 GHz. We have performed thorough experimental and computational investigation of the IF system in particular the constraints on the bandwidth caused by the lumped element capacitance of the mixer chip and the matching of the output impedance of the mixer to the IF amplifier. Our conclusion is that a bandwidth of 1–15 GHz could be achieved using our mixer design, subject to the performance of the amplifier. Finally, a variable temperature load system was successfully developed and tested inside the cryostat, to avoid the losses from the room-temperature optics. We have showed that the noise temperature of the SIS detector could be reduced by as much as 15 K by testing the mixer using a variable temperature load inside the cryostat.

No description available.

Spintronics discusses about fundamental physics and material science in mostly nanometer size structures. Spintronics also delivers many promising technologies for now and the future. One of the interesting spintronic structures is called “Magnetic Tunnel junction” (MTJ). A typical MTJ consists of a thin (1-3nm) insulator layer sandwiched between two ferromagnetic layers. In this work, I present MTJ with perpendicular magnetic anisotropy (PMA) using an MgO tunnel barrier. The effect of different heavy metals (HMs) adjacent to the ferromagnets (FMs) on tunneling magnetoresistance (TMR) and PMA of the junctions are discussed. Namely, Ta, Mo, Ta/Mo, W, Ir, and Hf have been utilized in HM/FM/MgO structures, and magneto-transport properties are explored. It is shown that when Ta/Mo is employed, TMR values as high as 208%, and highly thermally stable PMA can be obtained. Some physical explanation based on electronic band structure and thermochemical effects are discussed. In the last part of this work, the newly discovered tunneling anisotropic magnetoresistance (TAMR) effect in antiferromagnets is studied, and clear TAMR is demonstrated for NiFe/IrMn/MgO/Ta structures.

Magnetic sensors are deployed in many applications such as automotive, consumer electronics, navigation and data storage devices. Their market’s growth is driven by demands of higher performance; primarily to assist in the advancement of the Internet of Things (IoT) and smart systems. Challenging obstacles of miniaturization and power consumptions must be overcome. A leading sensor that has the potential to accelerate the development is the magnetic tunnel junction (MTJ) devices. Corrosion causes catastrophic consequences for industries. Preventive measures could save up to 35% of annual corrosion-related costs. An advanced corrosion sensing technique is developed based on iron nanowires. The iron nanowires are magnets which lose their magnetization when corroded. Their magnetization loss is monitored using sensitive MTJ sensor. Combined, the nanowires and the MTJ sensor realize a highly integrated sensor concept that enables corrosion sensing with an ultra-low power consumption of less than 1 nW, a sensitivity of 0.1 %/min, a response time of 30 minutes and an area of 128 μm2. Surgical tool development is accelerating in the healthcare sector. Cardiac catheterization specifically is a minimally invasive surgery that relies heavily on x-ray imaging and contrast dyes. A flexible tri-axis MTJ sensor is developed to help minimizing the need for x-ray imaging during the procedure. The flexible sensor can bend to a diameter of 500 μm without compromising the performance and can endure over 1000 bending cycles without fatigue. Three flexible sensors are mounted onto the tip of a 3 mm cardiac catheter, realizing a novel sensor-on-tube (SOT) tri-axis sensor concept. The sensor has a high sensitivity of 9 Ω/° and an MR ratio of 29%. It weighs 16 μg only, adds 5 μm to the catheter’s diameter and a total size 300 μm2. The prototype system estimated the heading angle with an RMS error value of 7° and tracked the orientation of the sensor with an acceptable accuracy. However, the sensor has a misalignment issue caused by the manual placement of the sensors. A high precision tool is needed for the assembly, and any further misplacement -within a reasonable margin of error- could be corrected by calibration algorithms.

Le contenu de ce rapport vise à résumer l'ensemble des activités de recherche que j'ai menées durant ces dernières 10 années ainsi que les perspectives et les projets pour les années à venir. Le dossier se scinde en plusieurs parties. La première partie de mon rapport expose mes travaux scientifiques effectués. Leur contenu s'intègre dans le cadre de l'électronique de spin et repose essentiellement sur l'étude du magnétisme et du transport polarisé en spin dans des systèmes de jonctions tunnel magnétiques. Ce travail m'a amené à élaborer des systèmes type jonctions tunnel magnétiques et à étudier la corrélation entre leurs propriétés magnétiques et leurs propriétés de transport polarisé en spin à des échelles macroscopiques et microscopiques. Les travaux sur les JTMs epitaxiees ont démontré qu'une physique au-delà du modèle des électrons libres gouverne le transport électronique dans les systèmes cristallins. La mise en évidence directe de la corrélation entre la structure électronique et chimique de l'interface métal oxyde et le transport tunnel polarisé en spin montre un fort potentiel pour le contrôle des caractéristiques magnéto-électriques de dispositifs spintroniques. Les études actuelles sur les effets de cohérence électronique dans des structures epitaxiees à multiples barrières tunnel et le contrôle de propriétés magnétiques par des courants de spin hors-équilibre ouvrent la voie vers une nouvelle physique et de nouvelles applications. D'une part, la complexité des mécanismes de transport dans les systèmes épitaxies a généré un important investissement personnel dans les techniques de calcul de structure électronique ab-initio ainsi que dans la création des outils de modélisation des propriétés magnétiques et de transport tunnel. D'autre part, du point de vue expérimental, l'ensemble des techniques que j'ai utilise regroupe l' épitaxie par jets moléculaires et la pulvérisation cathodique en ce qui concerne l' élaboration des échantillons, ainsi que des méthodes de caractérisation in situ (diffraction d' électrons RHEED, spectroscopie Auger) ou ex-situ (AFM pour la structure, MFM pour le micro magnétisme, VSM et e et Kerr pour le magnétisme macroscopique, et des diverses techniques de mesure électriques sous champ pour le magneto-transport). Une deuxième partie du rapport résume des résultats récents obtenus sur des systèmes tunnel complexes. Une autre partie du rapport résumé mes objectifs et projets de recherche pour les années à venir. Ils consistent a poursuivre les études de magnétisme et transport polarise en spin dans des hétéro-structures complexes de faible dimensionnalité avec un accent tout particulier vers le développement d'un axe théorique orienté vers la modélisation du transport électronique par des techniques type ab-initio. Dans un rapport annexe , je présente mon Curriculum Vitae, ma production scientifique, et un résumé des activités que j'ai effectuées dans l'enseignement, l'administration de la recherche, la participation a des contrats et des responsabilités collectives.

Thermoelectricity can directly convert a temperature difference into a voltage or charge current. Recently, the development of spin caloritronics has introduced spin as another degree of freedom in traditional thermoelectrics. This discovery bodes a new generation of magnetic random access memories (MRAMs), where thermal spin-transfer torque (TSTT) rather than voltage driven spin-transfer torque (STT) is used to switch the magnetization in magnetic tunnel junctions (MTJs). To advance the rising trend of spin caloritronics, the coupling of charge, spin, and heat flow during electron transport in MTJs was systematically studied in this thesis. To begin with, the static transport properties of MTJs were studied by observing current dependent tunnel magnetic resistance (TMR). The observed decrease of TMR with a biased current is attributed to the change in spin polarization of the free ferromagnetic layer. A phenomenological model has been built based on the current dependent polarization, which agrees with our experimental results. Next, the Seebeck rectification effect in MTJs was studied. By applying microwave currents to MTJs, an intrinsic thermoelectric coupling effect in the linear response regime of MTJs was discovered. This intrinsic thermoelectric coupling contributes a nonlinear correction to Ohm's law. In addition, this effect can be controlled magnetically since the Seebeck coefficient is related to magnetization configuration. Finally, TSTT in MTJs was systematically studied. A laser heating technique was employed to apply a temperature difference across the tunnel barrier and ferromagnetic resonance (FMR) spectra were measured electrically through spin rectification. By analyzing the FMR spectra, TSTT in MTJs was observed and the angular dependence of TSTT was found to be different from dc-biased STT. By solving the Landau-Lifshitz-Gilbert equation including STT, the experimental observations were well explained. The discovery of Seebeck rectification refines the previous understanding of magneto-transport and microwave rectification in MTJs and provides a new possibility for utilizing spin caloritronics in high-frequency applications. The study of TSTT in MTJs shows clear experimental evidence of TSTT in MTJs. Further optimization of the design of MTJs may succeed in decreasing the necessary switching fields strength or even achieve a switching by only TSTT in MTJs. / February 2017

<p>This thesis is concerned with employing the statistics of charge transfer in a conductor as a tool for quantum measurement. The physical systems studied are electronic devices made by nanoscale manufacturing techniques. In this context quantum measurement appears not as a postulate, but as physical process. In this thesis I am considering a quantum system, in particular a qubit or a nanomechanical resonator, interacting with a tunnel junction. The effect of coupling a quantum system to a tunnel junction is twofold: The state of the quantum system will be changed and there will be information about the quantum system in the statistics of charge transfer of the tunnel junction. As the first example a quantum measurement process of a qubit is considered. A common description of the system and charge dynamics is found by introducing a new quantity, the charge specific density matrix. By deriving and solving a Markovian master equation for this quantity the measurement process is analyzed. The measurement is shown to be a dynamical process, where correlations between the initial state of the qubit and the number of charges transferred in the tunnel junction arise on a typical timescale, the measurement time. As another example of a quantum system a nanomechanical oscillator is considered. It is found, that the biased tunnel junction, acting as a non-equilibrium environment to the oscillator, increases the temperature of the oscillator from its thermal equilibrium value. The current in the junction is modulated by the interaction with the oscillator, but the influence vanishes for bias voltages smaller than the oscillator frequency. For an asymmetric junction and non-vanishing oscillator momentum a current is shown to flow through the junction even at zero bias. The current noise spectrum induced by the oscillator in the tunnel junction consists of a noise floor and a peaked structure with peaks at zero frequency, the oscillator frequency and double the oscillator frequency. The peak heights are dependent on the coupling strength between oscillator and junction, the occupation number of the oscillator, the bias voltage and the junction temperature. I show how the peak height can be used as a measure of the oscillator temperature, demonstrating that the noise of a tunnel junction can be used for electronic thermometry of a nanomechanical oscillator.</p>

In the next decade, technology trends--smaller dimension, lower voltage, higher operating frequency--introduce new technical considerations and challenges for radiation effects in integrated circuits. Semiconductor based circuits and traditional dynamic random-access memories will malfunction when exposed to extreme environments, such as space and nuclear reactor. The mechanisms for radiation effect are mainly attributed to the radiation-induced charging of the oxide in a CMOS device. Spintronics is an emerging area of nanoscale electronics involving the detection and manipulation of electron spin. The magnetic tunnel junctions (MTJs), based on the intrinsic spin of the electron, can be used as the storage elements in non-volatile magnetoresistive random-access memories (MRAMs). In this effort, we study radiation tolerance of MTJs by exposing the devices in gamma and neutron radiation environment. Theoretical model for the radiation-induced defects is analyzed in this work. Experiments of the MgO-based MTJs under the conditions of pre- and post-radiation are concluded. MTJs were irradiated with gamma ray to a total dose of 10 Mrad. During the neutron irradiation, total epithermal neutron fluence up to 2.9��10�����/cm�� was obtained. The experimental results show that neither the electrical nor the magnetic properties of MTJs are affected by the radiation. / Graduation date: 2013 / Access restricted to OSU community at author's request from Sept. 11, 2012 - Sept. 11, 2014

This thesis is concerned with employing the statistics of charge transfer in a conductor as a tool for quantum measurement. The physical systems studied are electronic devices made by nanoscale manufacturing techniques. In this context quantum measurement appears not as a postulate, but as physical process. In this thesis I am considering a quantum system, in particular a qubit or a nanomechanical resonator, interacting with a tunnel junction. The effect of coupling a quantum system to a tunnel junction is twofold: The state of the quantum system will be changed and there will be information about the quantum system in the statistics of charge transfer of the tunnel junction. As the first example a quantum measurement process of a qubit is considered. A common description of the system and charge dynamics is found by introducing a new quantity, the charge specific density matrix. By deriving and solving a Markovian master equation for this quantity the measurement process is analyzed. The measurement is shown to be a dynamical process, where correlations between the initial state of the qubit and the number of charges transferred in the tunnel junction arise on a typical timescale, the measurement time. As another example of a quantum system a nanomechanical oscillator is considered. It is found, that the biased tunnel junction, acting as a non-equilibrium environment to the oscillator, increases the temperature of the oscillator from its thermal equilibrium value. The current in the junction is modulated by the interaction with the oscillator, but the influence vanishes for bias voltages smaller than the oscillator frequency. For an asymmetric junction and non-vanishing oscillator momentum a current is shown to flow through the junction even at zero bias. The current noise spectrum induced by the oscillator in the tunnel junction consists of a noise floor and a peaked structure with peaks at zero frequency, the oscillator frequency and double the oscillator frequency. The peak heights are dependent on the coupling strength between oscillator and junction, the occupation number of the oscillator, the bias voltage and the junction temperature. I show how the peak height can be used as a measure of the oscillator temperature, demonstrating that the noise of a tunnel junction can be used for electronic thermometry of a nanomechanical oscillator.