Theoretical Approach to Electroresistance in Ferroelectric Tunnel Junctions

In this paper, a theoretical approach, comprising the non-equilibrium Green's function method for electronic transport and Landau-Khalatnikov equation for electric polarization dynamics, is presented to describe polarization-dependent tunneling electroresistance (TER) in ferroelectric tunnel junctions. Using appropriate contact, interface, and ferroelectric parameters, measured current-voltage characteristic curves in both inorganic (Co/BaTiO$_{3}$/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$) and organic (Au/PVDF/W) ferroelectric tunnel junctions can be well described by the proposed approach. Furthermore, under this theoretical framework, the controversy of opposite TER signs observed experimentally by different groups in Co/BaTiO$_{3}$/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ systems is addressed by considering the interface termination effects using the effective contact ratio, defined through the effective screening length and dielectric response at the metal/ferroelectric interfaces. Finally, our approach is extended to investigate the role of a CoO$_{x}$ buffer layer at the Co/BaTiO$_{3}$ interface in a ferroelectric tunnel memristor. It is shown that, to have a significant memristor behavior, not only the interface oxygen vacancies but also the CoO$_{x}$ layer thickness may vary with the applied bias.Comment: 12 page

Roadmap on ferroelectric hafnia- and zirconia-based materials and devices

Ferroelectric hafnium and zirconium oxides have undergone rapid scientific development over the last decade, pushing them to the forefront of ultralow-power electronic systems. Maximizing the potential application in memory devices or supercapacitors of these materials requires a combined effort by the scientific community to address technical limitations, which still hinder their application. Besides their favorable intrinsic material properties, HfO2–ZrO2 materials face challenges regarding their endurance, retention, wake-up effect, and high switching voltages. In this Roadmap, we intend to combine the expertise of chemistry, physics, material, and device engineers from leading experts in the ferroelectrics research community to set the direction of travel for these binary ferroelectric oxides. Here, we present a comprehensive overview of the current state of the art and offer readers an informed perspective of where this field is heading, what challenges need to be addressed, and possible applications and prospects for further development

Beyond-CMOS spintronic logic and ferroelectric memory

The objective of this thesis is to explore spintronic logic and ferroelectric memory as potential solutions to beyond complementary metal-oxide-semiconductor (CMOS) technologies, since devices based on ferromagnetism and ferroelectricity hold great promise for the next-generation non-volatile digital computing and storage. In the first part of this thesis, novel device and interconnect structures using spintransfer torque (STT) on ferromagnetic metals and spin diffusive transport through non-magnetic materials are presented for low-power spintronic logic. Comprehensive physical models including spin injection, spin transport and stochastic magnetization dynamics are developed to justify the proposed concepts. On the other hand, recently ferroelectric tunnel junctions (FTJs) have been an active research topic in emerging memory technologies due to an extremely high on/off ratio originated from the giant tunneling electroresistance (TER) effect. Consequently, in the second part of this thesis, an original theoretical approach comprising quantum transport and thermodynamics is presented to describe measured I-V characteristics in various FTJs. Under the proposed formalism, the controversy of the opposite TER signs reported from different groups is explained by interface termination effects.Ph.D

Thermosensitive nanoplatforms for photothermal release of cargo from liposomes under intracellular temperature monitoring

Control of cargo release from nanoscale carriers is an important technology for maximizing the benefits of nanoparticulate drug delivery systems. Herein, we attempt to trigger the release of cargo from liposomes by photothermal conversion of water with a 980 nm near-infrared (NIR) laser. This study examined liposomes of two types formulated by 1,2-dipalmitory-sn-glycero-3-phosphocholine (DPPC) or a mixture of DPPC/cholesterol with an anionic lipid and PEG-lipid as stabilizers encapsulating calcein as a cargo at different ionic strengths. Liposome formulation encapsulating a hypertonic solution with a lipid membrane shows that a gel to liquid-crystalline phase transition at around 40 degrees C effectively released the cargo from liposomes at temperature above 40 degrees C with NIR irradiation. Our proof of concept has been further demonstrated in a cancer cell with monitoring the actual "intracellular temperature" using a fluorescent thermosensor. Intracellular thermometry revealed that it was not until the intracellular temperature reached around 40 degrees C by NIR irradiation that the release of the cargo started gradually, showing good agreement with the result from the extracellular in vitro study. This targeted release of cargo from thermosensitive liposomes based on a photothermal effect using a NIR laser offers a potent nanoscale platform for the on-demand release of drugs in intracellular space with local hyperthermia. The intracellular thermometry facilitates the quantitative monitoring and control of the hyperthermia at the cellular level.116Nsciescopu

Key Process Indicators of Mortality in the Implementation of Protocol-driven Therapy for Severe Sepsis

Severe sepsis and septic shock are life-threatening disorders. Integrating treatments into a bundle strategy has been proposed to facilitate timely resuscitation, but is difficult to implement. We implemented protocol-driven therapy for severe sepsis, and analyzed retrospectively the key process indicators of mortality in managing sepsis. Methods: Continuous quality improvement was begun to implement a tailored protocol-driven therapy for sepsis in a 24-bed respiratory intensive care unit (RICU) of Taichung Veterans General Hospital from January 2007 to February 2008. Patients, who were admitted to the RICU directly, or within 24 hours, were enrolled if they met the criteria for severe sepsis and septic shock. Disease severity [Acute Physiology and Chronic Health Evaluation (APACHE) II and lactate level], causes of sepsis, comorbidity and site of sepsis onset were recorded. Process-of-care indicators included resuscitation time (Tr-s), RICU bed availability (Ti-s) and the ratio of completing the elements of the protocol at 1, 2, 4 and 6 hours. The structure and process-of-care indicators related to mortality at 7 days after RICU admission and at RICU discharge were identified retrospectively. Results: Eighty-six patients (mean age, 71 ± 14 years; 72 men, 14 women; APACHE II, 25.0 ± 7.0) were enrolled. APACHE II scores and lactate levels were higher for mortality than survival at 7 days after RICU admission (p < 0.01). For the process-of-care indicators, Ti-s (562.2 ± 483.3 vs.1017.3 ± 557.8 minutes, p = 0.03) and Tr-s (60.7 ± 207.8 vs. 248.5 ± 453.1 minutes, p = 0.07) were shorter for survival than mortality at 7 days after RICU admission. The logistic regression study showed that Tr-s was an important indicator. The ratio of completing the elements of protocols at 1, 2, 4 and 6 hours ranged from 70% to 90% and was not related to mortality. Conclusion: Protocol-driven therapy for sepsis was put into clinical practice. Early resuscitation and ICU bed availability were key process indicators in managing sepsis, to reduce mortality