Y. Huang

Preparation of single high-Tc phase BiPbSrCaCuO superconductor by the EDTA precursor solution method

Abstract High fraction of 110 K phase Bi-based superconductor was prepared by the EDTA precursor solution method. The process is based on the formation of EDTA complexes to form a submicron-size fine powder of the correct stoichiometry without segregation. Using this simple technique more than 90% fraction of high- T c phase can be obtained with 100 hours sintering at 858°C.

Poly-Si Based Two-Axis Differential Capacitive-Sensing Accelerometer

This paper reports the design and implementation of a two-axis capacitive-type accelerometer using well-known two poly-Si processes. The accelerometer design consists of a pendulum proof-mass (bulk Si), a gimbal-spring (poly-Si film), and vertical-comb sensing electrodes. This design has three merits: 1) pendulum proof-mass to produce torque by in-plane acceleration; 2) high-aspect-ratio-micromachined (HARM) gimbal-springs enable the detection of two-axis accelerations; and 3) vertical-combs of different vertical positions enable the differential sensing electrodes design to detect the angular motion. In short, this paper exploits the vertical-comb electrodes for differential capacitive sensing to detect the two-axis in-plane accelerations. Measurement results show that the sensitivities (nonlinearity) of etch direction are 17.87 mV/G (2.65%) of X-axis, and 16.54 mV/G (2.71%) of Y-axis in the excitation range of 0.6~2 G. Due to the HARM gimbal-spring design, the cross axis sensitivity introduced by the Z-axis excitation is less than 0.3% for both X-axis and Y-axis sensing. However, the cross-axis error between the X-axis and the Y-axis sensing elements still need to be improved.

Effect of solution pH on the synthesis of the YBa2Cu4O8 superconductor via an EDTA solution process

High critical temperature, Tc, YBa2Cu4O8 superconducting oxides have been prepared by a solution technique using ethylenediaminetetraacetic acid (EDTA) as complexing agent. The use of an appropriate complexing agent leads to complete mixing of the Y3+, Ba2+ and Cu2+ cations, and thus facilitates formation of YBa2Cu4O8 at a lower temperature. The effect of pH on the homogeneity of samples is discussed. The superconducting YBa2Cu4O8 sample with Tc = 80 K was obtained after heat treatment at 820°C. Characterization of the sample by X-ray diffraction (XRD), thermal analysis, scanning electron microscopy (SEM), electron-probe microanalysis (EPM), electrical resistivity, magnetic susceptibility and other spectroscopic analyses are reported.

A poly-Si based 2-axis differential capacitive-sensing accelerometer

This study reports the design and implementation of a 2-axis capacitive-type accelerometer design consists of a pendulum-proofmass (bulk Si), a gimbal-spring (poly-Si film), and vertical-comb sensing electrodes. This design has three merits, (1) pendulum-proofmass to produce torque by in-plane acceleration (offset-axis inertial force), (2) gimbal-springs enable the detection of 2-axis accelerations, and (3) high-aspect-ratio-micromachined (HARM) vertical-combs as the differential sensing electrodes to detect angular motion. In short, this study implements the HARM vertical-comb electrodes for differential capacitive sensing to detect the 2-axis in-plane accelerations. Measurement results show that sensitivities (non-linearity) of etch direction are 20.3mV/G (10.36%) of X-axis, and 17.67mV/G (4.25%) of Y-axis (measurement range: 0.05G∼3G). The resolution is 50mG for both axes. The cross-axis errors range from 0.75% to 19.18%.

Magnetic levitation of YBa2Cu3Oy single crystals

Abstract By using an ordinary electric balance, we are able to measure the magnetic levitation forces acting on a superconducting YBa 2 Cu 3 O y (YBCO) single crystal. It is found that when the external magnetic field is parallel to the c -axis of the single crystal, the hysteretic levitation curve is similar to that of a melt-processed YBCO superconducting sample. However, when the external magnetic field is perpendicular to the c -axis of the YBCO single crystal, the levitation forces are too small to be measured by our equipment. Also, we have introduced a simple model with the Beans approximations to explain the levitation forces. The critical current density derived from this model by fitting with experimental data is quite close to the value obtained from magnetization measurements.

Spin-valve transistor

A spin transistor consisting of a metallic pseudo-spin-valve emitter, a copper base, and a p‐n junction collector was prepared on a Si(100) wafer. This spin transistor can provide high magnetocurrent output, high magnetocurrent variation, and high transfer ratio. The common collector configuration with an emitter bias of 5.12V at 77K gives a large magnetocurrent variation of more than 95.5μA in the collector, and the change is more than 3400% with a transfer ratio of 2.59×10−3. At room temperature, these changes go down to 98.3μA and 55.3%, respectively, and the transfer ratio rises to 5.98×10−3. The high performance of this spin-valve transistor is due to the use of a p‐n junction as an energy barrier to select spin electrons.

Growth of YBa2Cu3Oy single crystals from a mixture of YBa2Cu3Oy and Ag2O

Single crystals of the superconductor YBa2Cu3Oy have been grown from a mixture of solid phase YBa2Cu3Oy and liquid phase silver. Crystals with a thickness of up to 1 mm along the c axis can be obtained when the mixture is soaked at 1005 °C for more than 8 h. Silver melt enhances the peritectic partial melting of the YBa2Cu3Oy solid phase, and induces the solution and reprecipitation process during sintering at 1005 °C. Stacked plate‐like YBa2Cu3Oy grains grow through a coalescence process. Crystals are heavily twinned after 20 h of O2 annealing at 500 °C. They exhibit a sharp superconducting transition with an onset temperature of 93 K in zero field.

Room temperature stability study in silicon base magnetic tunneling transistor

A spin tunneling transistor (STT) was designed by growing a magnetic tunneling junction (MTJ) on a p-n junction. The magnetocurrent (MC) ratio of the collector can be stabilized roughly above 40% at V/sub E/=1.25/spl plusmn/0.25 V with the transfer ratio (I/sub C//I/sub E/) of 2.88%, while the transistor is operated in the common collector circuitry with an emitter bias and a base resistor at room temperature. The output current can be more than 4 /spl mu/A when the magnetic moment of the base layer is oriented parallel to that of the emitter layer. The high performance is achieved mainly due to the base resistor, which can push our STT to the right working region and enlarge the MC ratio of the collector.

Synthesis of YBa2Cu4O8 superconductor via EDTA solution-mix process

Abstract YBa 2 Cu 4 O 8 has been prepared by a solution-mix technique. The use of an appropriate complexing agent leads to a complete mixing of the Y 3+ , Ba 2+ and Cu 2+ cations. The superconducting YBa 2 Cu 4 O 8 sample with Tc=80 K have been obtained after heat treatment at 820°C. Characterization of the sample by X-ray diffraction, thermal analysis, electrical resistivity, magnetic susceptibility are reported.

The optimum magneto-current of collector in a silicon base spin valve transistor

New samples of a new type of spin transistor consisting of a metallic pseudo spin-valve emitter, a copper base, and a Si (100) p-n junction collector were made. For better operating conditions, the magneto-resistance between the emitter and base (MR/sub EB/) had different ratios. The value of MR/sub EB/ is an important factor for better magneto-current (MC) ratios; however, the working range for the emitter bias, V/sub E/, is largely improved and the maximum of MC could be enhanced by one order of the magnitude of MR/sub EB/.