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Spintronic-based magnetic random-access memory (MRAM) implementing the tunnel magnetoresistance (TMR) effect has various advantages over conventional semiconductor base memory devices, such as non-volatility and potentially high density and scalability. Traditional MRAM design implemented in-plane magnetic switching for the read/write operation which is now recognized to suffer from poor scalability below 60 nm. With the discovery of the spin-transfer torque (STT) effect, where the spin-polarized current is used to switch the ferromagnet, the MRAM design simplified considerably as it eliminated one of the two current-carrying wires that are used to generate the magnetic field required for switching. The thermal stability is further enhanced by using magnetic materials with perpendicular magnetic anisotropy (PMA). In current devices, perpendicular anisotropy is developed at the free magnetic layer (CoFeB) interface with the tunnel barrier (MgO). It is called interfacial-perpendicular anisotropy. However, it has been shown that this design has scaling issues below 20 nm. Materials with volume (bulk) perpendicular magnetic anisotropy should show better scaling without compromising on thermal stability.This dissertation work is focused on growth and physical property investigations of thin films of novel magnetic and electronic materials which are promising for MRAM devices. Leveraging on prior identified materials (both theory and bulk materials experiment) with tetragonal and hexagonal symmetry that support PMA, we have successfully implemented several manganese-based hexagonal Heusler-like Mn3-xFexSn (X=0,1,2) alloys predicted to be high PMA materials. While Mn3Sn thin films are reported in the literature, we are not aware of any thin film reports elsewhere on Fe2MnSn and Mn2FeSn thin films discussed here. All these materials are stabilized in the hexagonal structure which inherently supports perpendicular anisotropy. Specifically, we found that Mn3Sn has low saturation magnetization and high Tc but low magnetic anisotropy. Mn2FeSn has a moderate magnetic moment but low Tc (272 K). Fe2MnSn is the most favorable material among our investigations, with high magnetic anisotropy and high Curie temperature of 548 K, but with a higher than desired magnetization value. The magnetic anisotropy value of Fe2MnSn is estimated to be 0.56 MJ/m3. Such value is in the desirable range for MRAM devices. Our thermal stability calculations indicate that STT-MRAM with Fe2MnSn free layer can scale below 20 nm lateral size for 3nm free layer thickness. While the scaling behavior remains to be investigated experimentally, my work has demonstrated that research into new materials is always an exciting prospect particularly if combined with a theory-driven design approach.

Surface tension driven flow is studied in films of viscous polymer liquid by monitoring the spreading of droplets or the capillary levelling of films with excess surface area. The research presented in this thesis is focused on three major themes where molecular details are important to flow: molecular anisotropy, interfacial friction, and the initial state of the film. The effect of molecular anisotropy is studied by examining the dynamics of partially wetting diblock copolymer droplets using optical microscopy. The shape of the droplets is measured as they evolve towards equilibrium. In this system, it is found that energy is dissipated at the base of the droplets. This is consistent with a reduced interfacial friction at the liquid-substrate interface. Flow dynamics are also found to depend on the symmetry of the initial film thickness profile. Thickness perturbations with different degrees of symmetry were created in an initially flat film using focused laser spike annealing. The films were allowed to flow under the driving force of surface tension, and using atomic force microscopy, the film thickness profile was measured as a function of time. We find the depth of the perturbations decreases as a power law in time, with a power law exponent that depends on the symmetry of the thickness perturbation. The role of interfacial effects are explored by studying the flow in a film with zero interfacial friction: a freely-suspended film. Flow is measured in films with no interfacial friction using a technique which creates a film with a sharp step in the initial thickness profile. The excess surface area at the edge of the step drives flow, and information about the dynamics of the fluid is obtained by measuring the width of the step over time with atomic force microscopy. We observe flow that is consistent with plug flow: where the velocity of the fluid in the plane of the film is constant along the direction perpendicular to the film. Finally, freely-suspended films provide a model system to study the nucleation and growth of pores in a membrane. By purposefully creating pores of different initial size, the critical radius for nucleation is measured as a function of the membrane thickness. The experimental results agree with a simple model in which the free energy cost at the perimeter of a pore is determined by the excess surface area due to the curved interface of the pore edge. / Thesis / Doctor of Philosophy (PhD)

Thin film heaters, corrosion-resistance electrode, thin film inductors / Stretchable electronics are soft and light weight. Compared with conventional wafer-based electronics, which are rigid and planar, stretchable electronics can conform to curved surfaces and movable parts. The unique properties of stretchable electronics enable their integration with the human body, and open the door for ever more compelling applications, such as advanced surgical tools, wearable monitoring electronics, implantable prosthesis, and many others. However, the development of stretchable electronics is still at an early stage since their mechanical robustness and electrical performance are still far from satisfying. In this work, I have developed a method to fabricate thin film stretchable devices by solvent-assisted transfer of wrinkled thin films from rigid polystyrene (PS) substrates to elastomeric polydimethylsiloxane (PDMS) substrates. Using this approach, structured thin films containing multiple materials and hybrid structures could be lifted off simultaneously, facilitating the fabrication of stretchable thin film devices. With this approach, I have built corrosion-resistant stretchable electrodes, stretchable thin film heaters, and stretchable thin film inductors. These applications demonstrate the simplicity and effectiveness of this stretchable electronics fabrication strategy. Finally, I made the first step towards fabricating dye-sensitized solar cells (DSSCs) with room temperature processes, including the preparation of mesoporous TiO2 layers through mechanical compression and the integration of an interdigitated electrode that was fabricated solely by bench-top patterning, alignment, and sputtering deposition. These steps lay the foundation for the future development of stretchable DSSC. I anticipate that the fabricated stretchable thin films electronic components will contribute to the advancement of wearable and implantable electronics. / Thesis / Doctor of Philosophy (PhD) / Electronics that can be deformed and conform to the irregular surfaces are attractive because they can be better integrated with the human body. For example, they could improve disease diagnostics and therapeutic treatments by providing wearable continuous monitoring devices and more advanced surgical tools. In this work, I created wrinkled thin films that could be affixed onto an elastic substrate and stretched. The principle of operation of these wrinkled devices mimics the way that the wrinkled skin on our knuckles and elbows allows us to bend our fingers and elbows. This approach makes wrinkled thin films stretchable and could lead to robust electronic devices. I have showcased this approach building a corrosion-resistant stretchable electrode, thin films heaters that can closely conform to joints, and a spiral-shaped inductor that could be used to wirelessly transfer data or power wearable devices. I believe that this work will contribute to the development of electronics that can be worn or implanted in the human body.

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<p>Nanocomposite thin films are materials that have the potential to improve and tune many properties for various applications in electronics, sensors, memory storage, and optics. Materials properties are a consequence of their structure, so being able to manipulate the nanostructure of nanocomposite thin films is important for modifying them for device purposes. One structure that has gained a lot of attention is vertically aligned nanocomposites (VANs) due to the increased vertical coupling between two or more phases of materials and the unique nanostructures achievable through controlling deposition factors. </p> <p>VAN thin film growth involves many factors: diffusion, substrate surface conditions, source material composition, and deposition temperature and rate. The two main approaches to thin film fabrication are bottom-up and top-down. Bottom-up growth focuses on the self-assembly of the nanostructure. This work focuses on the self-assembly of VAN thin film materials through controlling the thermodynamic and kinetic factors involved in thin film growth. The main factors being considered in this work are substrate manipulation, oxygen gas flow during deposition, deposition rate, and composition. The effectiveness of each of these methods is evaluated in comparison to each other and their growth of VAN thin film materials along with the future work needed to refine each nanostructure manipulation method. </p>