Increasing Measurement Temperature Research Articles

Optimization of magnetoresistive sensor current for on-chip magnetic bead detection using the sensor self-field

We investigate the self-heating of magnetoresistive sensors used for measurements on magnetic beads in magnetic biosensors. The signal from magnetic beads magnetized by the field due to the sensor bias current is proportional to the bias current squared. Therefore, we aim to maximize the bias current while limiting the sensor self-heating. We systematically characterize and model the Joule heating of magnetoresistive sensors with different sensor geometries and stack compositions. The sensor heating is determined using the increase of the sensor resistance as function of the bias current. The measured temperature increase is in good agreement with a finite element model and a simple analytical thermal model. The heat conductance of our system is limited by the μ 1 m thick electrically insulating silicon dioxide layer between the sensor stack and the underlying silicon wafer, thus the heat conductance is proportional to the sensor area and inversely proportional to the oxide thickness. This simple heat conductance determines the relationship between bias current and sensor temperature, and we show that μ 2 5m wide sensor on a μ 1 m oxide can sustain a bias current of 30 mA for an allowed temperature increase of 5 °C. The method and models used are generally applicable for thin film sensor systems. Further, the consequences for biosensor applications of the present sensor designs and the impact on future sensor designs are discussed.

INVESTIGATION OF LEAKAGE CURRENT BEHAVIOR OF Pt/Bi0.975La0.025Fe0.975Ni0.025O3/Pt CAPACITOR MEASURED AT DIFFERENT TEMPERATURES

Polycrystalline Bi 0.975 La 0.025 Fe 0.975 Ni 0.025 O 3 (BLFNO) film is fabricated on Pt / Ti / SiO 2/ Si (111) substrate by sol–gel method. It is found that the well-crystallized BLFNO film is polycrystalline, and the Pt / BLFNO / Pt capacitor possesses good ferroelectric properties with remnant polarization of 74 μC/cm2 at electric field of 833 kV/cm. Moreover, it is also found that the leakage current density of the Pt / BLFNO / Pt capacitor increases with the increase of measurement temperature ranging from 100 to 300 K. The leakage density of the Pt / BLFNO / Pt capacitor satisfies space-charge-limited conduction (SCLC) at higher electric field and shows little dependence on voltage polarity and temperature, but shows polarity and temperature dependence at lower applied electric field. With temperature increasing from 100 to 300 K at lower applied electric field, the most likely conduction mechanism is from Ohmic behavior to SCLC for positive biases, but no clear dominant mechanism for negative biases is shown.

The sympathetic release test: a test used to assess thermoregulation and autonomic control of blood flow

When a subject is heated, the stimulation of temperature-sensitive nerve endings in the skin, and the raising of the central body temperature, results in the reflex release of sympathetic vasoconstrictor tone in the skin of the extremities, causing a measurable temperature increase at the site of release. In the sympathetic release test, the subject is gently heated by placing the feet and calves in a commercially available foot warming pouch or immersing the feet and calves in warm water and wrapping the subject in blankets. Skin blood flow is estimated from measurements of skin temperature in the fingers. Normally skin temperature of the fingers is 65-75°F in cool conditions (environmental temperature: 59-68°F) and rises to 85-95°F during body heating. Deviations in this pattern may mean that there is abnormal sympathetic vasoconstrictor control of skin blood flow. Abnormal skin blood flow can substantially impair an individual's ability to thermoregulate and has important clinical implications. During whole body heating, the skin temperature from three different skin sites is monitored and oral temperature is monitored as an index of core temperature. Students determine the fingertip temperature at which the reflex release of sympathetic activity occurs and its maximal attainment, which reflects the vasodilating capacity of this cutaneous vascular bed. Students should interpret typical sample data for certain clinical conditions (Raynaud's disease, peripheral vascular disease, and postsympathectomy) and explain why there may be altered skin blood flow in these disorders.

SPICE Network Simulation to Calculate Thermal Runaway in III–V Solar Cells in CPV Modules

Current injection into solar cells may occur if cells in modules are connected in parallel without the protection of string diodes. This current injection can cause heating of the cell, which increases the recombination currents and, thus, the current injection. In this manner, a self-feeding process called thermal runaway is started. In concentrator photovoltaics modules, thermal runaway can cause substantial damage. In this paper, a model is introduced that calculates the conditions causing thermal runaway. This model is based on the two-diode model. As inputs for the model, three dependences were experimentally determined from dark IV measurements on the triple-junction cell: 1) series resistance on cell temperature, 2) saturation currents for each of the three junctions on cell temperature, and 3) cell temperature on the injected current. The model was tested by comparing the simulated and measured temperature increase in a triple-junction cell and their dependencies on the applied voltage. A reasonable agreement between the experiment and model was found whereby the voltage at which a thermal runaway occurred differs slightly by 0.04 V. The model was then applied to estimate the dependence of an expected temperature increase in a shaded solar cell on the number of cells connected in parallel and on the concentration factor of the sunlight.

Study of microstructure and semiconductor to metallic conductivity transition in solid state sintered Li0.5Mn0.5Fe2O4−δ spinel ferrite

Li0.5Mn0.5Fe2O4 ferrite has been prepared by solid state sintering route. XRD pattern showed single phased cubic spinel structure. The samples exhibited typical character of plastoferrite with ring shaped surface microstructure. New feature observed in the present ferrite is the frequency activated conductivity transition from semiconductor to metallic state above 800 K. The increase of conductivity with frequency in the semiconducting regime follows Jonscher power law, while decrease of conductivity in metallic regime obeys Drude equation. The conductivity in semiconductor regime has been understood by hopping mechanism of localized charge carriers among the cations in B sites of cubic spinel structure. At higher temperatures, overlapping of electronic orbitals from neighbouring ions and free particle like motion of lighter Li+ ions among interstitial lattices contributed metallic conductivity. The samples provided evidence of localized nature of the charge carriers at lower temperatures and increasing delocalized character with the increase of measurement temperature. From application point of view, such ferrites behave as semiconductor at low temperature and allow electromagnetic wave to pass through, but transform into a metallic reflector with negative dielectric constant at high temperature.

Effect of acid‐ethanol treatment on physicochemical properties and in vitro digestibility of maize starches varying in AM content

In the current work, three maize starches with different AM/AP content were treated with hydrochloric acid in ethanol solvent to prepare modified starches and to study the effect of acid‐ethanol treatment on starches. Results showed that with increase of treatment time, the hydrolysis rate of maize starches increased. Native WMS had the highest hydrolysis rate. After treatment, starch granules exhibited decreased birefringent and morphology was destroyed. The modified Hylon V retained its granular appearance with only some slight breakage. Solubility of acid‐ethanol treatment starches profoundly increased with increasing measurement temperature and decreased with increasing AM content. Crystalline type of modified starches was not changed and the relative crystallinity increased. The gelatinization temperatures after acid‐ethanol treatment increased except To, while ΔH decreased. The average rate of digestion for each acid‐ethanol treated starch was higher than that of its counterpart native starch. With increasing AM content, the digestion rates of native and modified starches decreased.

Structural and optical properties of nanoparticles (V, Al) co-doped ZnO synthesized by sol–gel processes

ZnO, Zn0.9V0.1O and Zn0.89V0.1Al0.01O nanoparticles have been prepared by a sol–gel method and their structural and optical properties have been investigated. The obtained nanopowder was characterised by various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. After thermal treatment at 500°C in air, the powder of Zn0.89V0.1Al0.01O with an average particle size of 25nm presents a strong luminescence band in the visible range. The PL band energy position presents a small blue shift with the increase of measurement temperature. Different possible attributions of this emission band will be discussed.

Effect of Tungsten (W) Substitution on the Physical Properties of Bi-(2223) Superconductors

The superconducting Bi1.6Pb0.4Sr2Ca2Cu3−x W x O10+y (x=0.00, 0.05, 0.10, 0.15) bulk samples were prepared by the solid-state reaction method. The effects of W substitution on the BSCCO system have been investigated by the electrical resistivity (ρ-T), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), magnetic hysteresis and critical current density measurements. It has been found that the Bi-(2212) low-T C phase is formed for all the substitution levels, together with the Bi-(2223) high-T C phase. The results obtained from the XRD data show that the Bi-(2223) phase gradually transforms into the Bi-(2212) phase with increasing W substituting for Cu. In addition, from the magnetization measurements at the temperatures below the zero resistance temperatures of the samples, we have observed that a decreasing in magnitude of |M| with the increasing measurement temperature and W concentration. Therefore, the decreasing of |M| related to superconducting volume seems to imply an existence of flux-pinning centers in our samples.

극저온에서 나노스케일 무접합 p-채널 다중 게이트 FET의 전기적 특성

In this paper, the electrical properties of nanoscale junctionless p-channel MuGFET at cryogenic temperature have been analyzed experimentally. The experiment was performed using a cryogenic probe station which uses the liquid Helium. It has been observed that the drain current oscillation at low drain voltage and cryogenic temperature was more pronounced in junctionless transistor than in accumulation mode transistor. The reason for more marked oscillation is due to the smaller electrical cross section area of the inversion channel which is formed at the center of silicon film in junctionless transistor. It was also observed that the drain current and maximum transconductance were increased as the measurement temperature increased. This is resulted from the increase of hole mobility and the decrease of the threshold voltage as the measurement temperature increases. The drain current oscillation due to the quantum effects can be occurred up to the room temperature when the device size scales down to the nanometer level.

Temperature Dependence and Postirradiation Annealing Response of the $1/f$ Noise of 4H-SiC MOSFETs

The temperature dependence of the low-frequency noise of 4H-silicon carbide (SiC) MOSFETs with nitrided oxides is reported over the temperature range 85-510 K. The 1/f noise decreases significantly with increasing measurement temperature. This decrease in noise results primarily from a decrease in the density of interface traps at increasing temperatures. The 1/f noise is also characterized after total ionizing dose irradiation and postirradiation annealing. No significant change in the 1/f noise is observed after the devices are irradiated to 1 Mrad (SiO2) and then annealed under bias at elevated temperature. These results show that the 1/f noise in 4H-SiC MOSFETs is dominated by the interaction of channel carriers with slow interface traps at temperatures 360 K. This result contrasts with most experience with Si/SiO2-based MOSFETs, and results from the wider bandgap and greater density of slow interface traps in SiC/SiO2-based MOSFETs than in Si/SiO2-based MOSFETs.

TU‐C‐144‐02: Antivascular Ultrasound for Cancer Treatment: The Role of Thermal Effects

Purpose: Tour previous studies1 have demonstrated that low‐intensity ultrasound (1∼2 W/cm2, 0.2‐0.3 MPa) in the presence of microbubbles disrupt tumor vasculature and behaves as an antivascular agent for the treatment of cancer. Although the antivascular effect is potent and reproducible, the mechanism of action is not fully understood. The goal of this study we evaluate the role of thermal effects in antivascular ultrasound. Methods: Studies were performed in mice with subcutaneous melanoma (K1735). Antivascular ultrasound (AVUS) therapy was performed at 1 and 3 MHz. During treatment temperature was measured with a fine wire thermocouple. Tumor vascularity (percentage area of perfusion, PAF) was assessed before and after each test and sham treatment with contrast‐enhanced Doppler US imaging. Simulations of microbubble induced heating were performed for mono‐and polydisperse (lognormal distribution) microbubbles under varying conditions of experiments and blood flowResults and Conclusions: AVUS reduced the tumor vascularity at both 1 MHz and 3 MHz. The vascularity reduction at 3 MHz was two times greater than with 1 MHz treatment. The enhanced antivascular action at 3 MHz was significant (P=0.02). The measured temperature increase was 5.2 ± 1.4°C for the 1 MHz ultrasound and 10.2 ± 2.7°C for 3 MHz ultrasound. Consistent with the experimental observations modeling showed that microbubble induced temperature increased more rapidly at 3 MHz than at 1 MHz. The observation that there is greater neovascular disruption and temperature change 3 MHz than at 1 MHz suggests that the ultrasound antivascular activity is primarily thermal in nature, although inertial cavitational effects cannot be excluded. The tissue response to antivascular ultrasound injuries could further stimulate an immune response and induce endogenous vaccination.1. Wood et al, Acad. Rad., 15, 1133, 2008; Levenback et al, JASA, 131, 540, 2012; IEEE Ultrasonics 2012.

High‐Temperature Electromagnetic Wave Absorption Properties of ZnO/ZrSiO4 Composite Ceramics

Owing to the widespread presence of electromagnetic interferences, it is necessary to develop new materials with excellent high‐temperature electromagnetic wave (EM) absorption properties. In the present work, ZnO is infiltrated into porous ZrSiO4 substrates to form ZnO/ZrSiO4 composite ceramics using sol‐gel process. The doping of aluminum results in the improvement of electrical conductivity and the significant change in the morphology of ZnO. With the increase in environment temperature during measurement, the permittivity of the composite ceramics increases first and then decreases dramatically, which is attributed to the change in conductive loss. The electrical conductivity increases with increasing measurement temperature. However, the concentration of oxygen vacancies decreases under air atmosphere when the measurement temperature increases continuously, which results in the reduction in conductivity. Therefore, permittivities of the undoped and doped ceramics measured at 673 K are higher than the ones at the other temperatures. The composite ceramics maintain a relatively high EM absorption coefficient, low reflection coefficient (RC), and wide effective absorption bandwidth at environment temperatures up to 773 K. As a result, we conclude that the ZnO/ZrSiO4 composite ceramics exhibit a promising prospect as a kind of high‐temperature EM absorbing material.

Hall mobility, electrical resistivity, and dielectric properties of reduced La0.01Ba0.99TiO3

The La0.01Ba0.99TiO3 sample was reduced at 1380 °C under about a 10−14-atmosphere oxygen partial pressure. After the sample had been reduced under these conditions, the resistivity and the Hall mobility of the reduced La0.01Ba0.99TiO3 were investigated experimentally within a temperature range of 300 to 600 K. The electrical resistivity decreased linearly with increasing measurement temperature, indicating that the conduction mechanism in this system was thermally activated. Evidence of an excess of charge carriers was observed at high temperatures. The dielectric property data showed that the known phase-transition temperature shifted to a higher temperature (425 K). Thus the reduction of the sample has an influence on both the dielectric constant and the transition temperature. In-situ high-temperature electrical-conductivity and Hall measurements are useful tools for establishing the donor-doping effect in perovskite La0.01Ba0.99TiO3 and for screening it for more industrial applications.

Magnetization reversal in antiferromagnetically coupled [Pt/CoFeB]N1/Ru/[CoFeB/Pt]N2 structures with perpendicular anisotropy

Magnetic interlayer coupling and magnetization switching characteristics have been investigated in synthetic antiferromagnetically coupled [Pt/CoFeB]N1/Ru/[CoFeB/Pt]N2 structures with perpendicular anisotropy. We observe an oscillatory behavior of the antiferromagnetic coupling with a period of 0.7 nm and a maximum coupling strength of 0.09 erg/cm2. The coupling field is shown to decrease rapidly with the increase of repetition number and measurement temperature. Depending on the repetition numbers of the two multilayers, magnetic hysteresis loops may or may not display a reversal feature of the net magnetic moment. Samples with large N have a bow-tie loop shape due to the formation of multi-domains. The analysis of magnetic moments and exchange coupling fields show that there exists a ∼0.4 nm thick magnetic dead layer mostly at the CoFeB/Ru interface.

Room temperature ferromagnetism in epitaxial In2O3 films with embedded nano-sized Fe3O4 columns

Epitaxial In2O3 films with embedded Fe3O4 oriented nanocolumns were deposited by pulsed laser deposition (PLD) on Y-stabilized ZrO2 (111) substrates. The resulting films show ferromagnetism at room temperature with strong magnetic anisotropy, which can be attributed to the presence of Fe3O4 nanocolumns. Magnetotransport measurements demonstrate a transition from negative magnetoresistance to positive magnetoresistance as the measuring temperature increases. Quantitative coincidence between the anomalous Hall resistivity as a function of the magnetic field and the magnetic hysteresis loop is observed at room temperature, indicating the spin polarization nature of carriers.

Synthesis and Conductivity of Nano Crystalline Ceria

Nanoparticles of cerium oxide were synthesized by the co-precipitation method. Synthesis conditions were optimized for phase purity, particularly the effect of pH (=14,13,11) of solutions during reaction, was studied. The phase analysis and structural properties of the prepared particles were determined by X-ray diffraction analysis. The average crystallite size decreased with the increase in pH of solution. The temperature-dependent DC conductivity was measured in the temperature range 300 °C to 700 °C and was found to be increasing with the increase in measurement temperature. AC conductivity and dielectric constants were measured in the frequency range of 1 kHz to 3 MHz and also at different temperatures.

Moving cracks in viscoelastic materials: Temperature and energy-release-rate measurements

A novel set up is proposed to measure the energy release rate vs. crack propagation speed in viscoelastic materials. The new test is referred to as the square sample tear test. In comparison to other techniques as the pure shear specimen and the pure tensile specimen tests, the square sample geometry guarantees at the same time: (i) a constant flux of elastic energy at the crack tip, (ii) the full development of the annular dissipative region around the crack tip, where the material is in the transition region of the viscoelastic response spectrum. Both conditions allow to precisely control the crack propagation speed and to test the predictions of existing theories. By employing the new set-up we measure the energy release rate as a function of the crack propagation speed. We also measure with a high precision infrared camera the increase of temperature at the crack tip, showing that, notwithstanding the low speed regime considered during the experiments, the viscoelastic dissipation at the crack tip leads to a measurable temperature increase of about 1°C.

Effect of high-temperature aging on the thermal conductivity of nanocrystalline tetragonal yttria-stabilized zirconia

The thermal conductivity of yttria-stabilized zirconia (YSZ) thermal barrier coatings increases with high-temperature aging. This common observation has been attributed to the densification of the coatings as porosity sinters out and pores and cracks spheroidize to minimize their surface energy. We show that the thermal conductivity of fully-dense 3mol.% Y2O3 stabilized zirconia (3YSZ) also increases with high-temperature aging, indicating that densification and pore shape changes alone are not responsible for all the observed increase in thermal conductivity of coatings. Instead, there are also increases due to a combination of phase separation and grain growth. The increase in thermal conductivity can be described by a Larson–Miller parameter. It is also found that the increase in thermal conductivity with aging is greatest when measured at room temperature and decreases with increasing measurement temperature. Measured at 1000°C, the thermal conductivity of zirconia is almost temperature independent and the changes in thermal conductivity with aging are less than 15%, even after aging for 50h at 1400°C.

4C code analysis of thermal–hydraulic transients in the KSTAR PF1 superconducting coil

The KSTAR tokamak, in operation since 2008 at the National Fusion Research Institute in Korea, is equipped with a full superconducting magnet system including the central solenoid (CS), which is made of four symmetric pairs of coils PF1L/U–PF4L/U. Each of the CS coils is pancake wound using Nb3Sn cable-in-conduit conductors with a square Incoloy jacket. The coils are cooled with supercritical He in forced circulation at nominal 4.5K and 5.5bar inlet conditions. During different test campaigns the measured temperature increase due to AC losses turned out to be higher than expected, which motivates the present study.The 4C code, already validated against and applied to different types of thermal–hydraulic transients in different superconducting coils, is applied here to the thermal–hydraulic analysis of a full set of trapezoidal current pulses in the PF1 coils, with different ramp rates. We find the value of the coupling time constant nτ that best fits, at each current ramp rate, the temperature increase up to the end of the heating at the coil outlet. The agreement between computed results and the whole set of measured data, including temperatures, pressures and mass flow rates, is then shown to be very good both at the inlet and at the outlet of the coil. The nτ values needed to explain the experimental results decrease at increasing current ramp rates, consistently with the results found in the literature.

Temperature dependence of the contact resistance of ohmic contacts to III–V compounds with a high dislocation density

A new mechanism describing the rise in the contact resistance ρc of ohmic contacts to n-n+-n++-GaAs(GaP, GaN, InP) structures with increasing measurement temperature T, experimentally observed in the temperature range 100–400 K, is suggested on the basis of a theoretical analysis of the temperature dependence of ρc. Good agreement between the experimental and theoretical ρc(T) dependences is obtained and explained for a case where there is a high density of dislocations (on which metallic shunts are localized) in the near-contact region of the semiconductor.