Magnetic Tunnel Junction Based on MgO Barrier Prepared by Natural Oxidation and Direct Sputtering Deposition

Magnetic tunnel junctions(MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have been formed by a multi-step deposition and natural oxidization of Mg layer. Mg layer thickness,oxygen flow rate and oxidization time were adjusted and the tunnel magnetoresistance(TMR) ratio of optimal MTJs is over 60% at annealing temperature 385. The(001) MgO crystal structure was obtained when the separation distance between MgO target and substrate is less than 6 cm. The TMR ratio of most MgO based MTJs are over 100% at the separation distance of 5 cm and annealing temperature 340. The TMR ratios of MTJs are almost zero when the separation distance ranges from 6 to 10 cm, due to the amorphous nature of the MgO film.

Effect of Anti-Diffusion Oxide Layer on Enhanced Thermal Stability of Magnetic Tunnel Junctions

Magnetic tunnel junctions （MTJs） with one proper oxidized FeOx layer placed between the Al oxide barrier and the top CoFe pinned layer show large tunnelling-magnetoresistance （TMR） signals as high as 39% after anneal at 380℃. The increased TMR signal may originate from the as-deposited Fe/FeOx （non-magnetic） layers changing to Fe＋magnetic FeOy layer （some Fe3O4 and mostly other kind of magnetic Fe oxide） after high temperature anneal. The maximum TMR value （TMR ） and the corresponding temperature Ts where the TMRmax occurs upon annealing are closely associated with the oxidation time of the AlOx and FeOx layers, too long oxidation for the Fe layers is detrimental for the TMR value. In addition to the enhanced AlOx barrier quality upon anneal, the improved thermal stability is also attributed to the Mn diffusion retardation by the presence of the FeOx layer which acts as an antidiffusion layer. For MTJs without the interposed FeOx layer, the TMR signal reduction at 300℃ originates from the Mnlr/CoFe partially decoupling and CoFe/AlOx interface polarization loss due to the significant Mn diffusion.

Sol-Gel Relative Humidity Sensors: Impact of Electrode Geometry on Performance in Soil Suction Measurements

This paper describes the experimental procedure followed to fabricate and validate sol-gel based RH sensors which will be incorporated in soil specimens for standard laboratorial tests. It is the first time such sensors were used for soil suction measurement. They are microfabricated relative humidity sensors (footprint area 11,000 μm × 22,000 μm) operating based on changes in electrical resistivity detected by a cerium doped silica titania film deposited using a sol-gel technique. Their design required gathering experts in several engineering specialties. The working principle of the sensors is based on water vapour equilibrium between the air in the soil and in the sol-gel pores, due to the contact between the two porous materials. The spacing between interdigitated aluminium electrodes was optimized to improve the sensing properties of the sol-gel. The calibration of the different prototypes was done against compacted clay, varying the spacing between 100 and 700 μm. The sensors were also incorporated in soil samples for suction measurement during wetting and drying paths. They were validated by comparing the readings with those from a water dew point potentiometer. From this study it was possible to determine the optimum electrodes spacing of 200 μm. Error was explained by sol-gel heterogeneity effect and by the resolution of the sensing area provided by the electrodes spacing. When comparing with other sensors operating inside soil specimens in standard laboratorial tests, these sol-gel sensors extend the operation range available with the alternative technologies: while conventional tensiometers measure suction ranges from 0 to 1.8 MPa, our sensors demonstrate good results between 1 to 10 MPa (and higher).

A 96-wells fluidic system for high-throughput screenings under laminar high wall shear stress conditions

The ability of endothelial cells to respond to blood flow is fundamental for the correct formation and maintenance of a functional and hierarchically organized vascular network.Defective flow responses,in particular related to high flow conditions,have been associated with atherosclerosis,stroke,arteriovenous malformations,and neurodegenerative diseases.Yet,the molecular mechanisms involved in high flow response are still poorly understood.Here,we described the development and validation of a 96-wells fluidic system,with interchangeable cell culture and fluidics,to perform high-throughput screenings under laminar high-flow conditions.We demonstrated that endothelial cells in our newly developed 96-wells fluidic system respond to fluid flow-induced shear stress by aligning along the flow direction and increasing the levels of KLF2 and KLF4.We further demonstrate that our 96-wells fluidic system allows for efficient gene knock-down compatible with automated liquid handling for high-throughput screening platforms.Overall,we propose that this modular 96-well fluidic system is an excellent platform to perform genome-wide and/or drug screenings to identify the molecular mechanisms involved in the responses of endothelial cells to high wall shear stress.