Silas T. Hung

Room-temperature magnetism in Cr-doped AlN semiconductor films

Synthesis and characterization of magnetic semiconductors Al1−xCrxN, in which the atomic fraction of chromium x is up to 0.357, are reported. The films, grown by reactive co-sputtering on silicon, glass, and kapton substrates, have a crystal structure of aluminum nitride. Magnetic and transport properties were studied in the temperature range of 50 to 340 K. The materials are in the dielectric regime and have variable-range-hopping type of conductance. The films are ferromagnetic at temperatures over 340 K.

Room temperature magnetism in sputtered (Zn,Co)O films

Cobalt doped zinc oxide films Zn/sub 1-x/Co/sub x/O with the atomic fraction x in the range 0.035-0.115 were prepared by sputtering from composite ZnO/Co/sub 3/O/sub 4/ targets. X-ray diffraction pattern shows the ZnO phase with [002] preferential orientation. Magnetic measurements show ferromagnetic behavior with Curie temperatures higher than 350 K.

Ferromagnetism in Mn-doped CuO

Ferromagnetic properties have been observed in CuO doped with 3.5–15 at. % of Mn. The transition from ferromagnetic to paramagnetic phase at TC=80 K is associated with the metal–insulator transition. Magnetoresistance is weakly negative in the vicinity of the transition, but positive in a wide range of temperatures below TC. The experimental results suggest a possibility of interpretation in terms of the Zener double-exchange mechanism and strong electron–phonon interactions.

A novel current-mode sensing scheme for magnetic tunnel junction MRAM

In this paper, we present two integrated circuits for sensing data nondestructively from one-transistor one-magnetic tunnel junction (1T-1MTJ) magnetoresistive random access memory (MRAM). The first one is a low-power sensing circuit for MTJs with a magnetoresistance (MR) ratio larger than 10%, and the second one is a high-sensitivity switched-current sensing circuit for MTJs with an MR ratio as low as 5%. The circuits are designed using 0.60- and 0.18-/spl mu/m CMOS processes, and their performance is verified using HSPICE. Compared with existing sensing circuits at a power supply of 3.0 V, their read access time is 1.46-3.33 times faster and power consumption is 2.67-3.85 times smaller.

A switched-current sensing architecture for a four-state per cell magnetic tunnel junction MRAM

A current-mode binary-search sensing scheme for a four-state per cell one-transistor one-magnetic tunnel junction magneto-resistive (MR) random access memory is proposed. By using the switched-current technique, it is able to read data nondestructively with a MR ratio as low as 5%. The sensing circuit is designed using a 0.18-/spl mu/m CMOS process and the performance is verified by HSPICE simulation. At a supply voltage of 1.8 V, the data can be accessed in 17.5 ns with a power consumption of 475.9 /spl mu/W. Compared to the parallel sensing approach, the proposed sensing scheme consumes less power and chip area, and requires fewer comparison steps. Compared to the conventional serial sensing approach, it allows a shorter read access time while performing the same number of comparisons.

Magneto-optical Kerr effect and photonic bandgap in cobalt nanodisc array

In this paper, we report our experimental investigation on two-dimensional (2-D) magneto-photonic crystals (MPCs) by using high-precision magneto-optical Kerr effect (MOKE) measurement. Our 2-D MPC is in the form of a periodic triangular array of cobalt (Co) circular nano-discs on a silicon (Si) substrate. Preliminary longitudinal MOKE measurement reveals a hysteresis loop that suggests a saturated Kerr rotation of ≈ 0.05°. We numerically investigate the potential photonic band gap (PBG) phenomenon of a triangular nano-disc array with the Co real refractive index = 2.26 by using 2-D finite-different time-domain (FDTD) method. We observe relatively wide TM-polarization (E-field⊥substrate) band gaps in the 1550-nm telecommunication wavelengths: 500 nm in the -M Γ direction whereas 400 nm in the -K Γ direction.

High-sensitivity switched-current sensing circuit for magnetic tunnel junction MRAM

A high-sensitivity switched-current sensing circuit for reading data non-destructively from 1T-1MTJ magneto-resistive random access memory (MRAM) is presented. Compared to the existing sensing circuits at a power supply of 3.0V, simulation results showed that the read access time and the power consumption are about 3 times faster and smaller

Room temperature magnetism in sputtered Co/sub x/Zn/sub 1-x/O films

Summary form only given. Wide gap diluted magnetic semiconductors (DMS) have been proposed for applications in magneto-optical devices. However there are very few reports of DMS which are magnetic at room temperature. In this work we describe synthesis and characterization of transparent Co-doped ZnO DMS films, prepared by single sputtering deposition. The films are ferromagnetic up to at least 350 K.

Preparation and Characterization of Cobalt Doped ZnO and TiO 2

Synthesis and characterization of transparent Co-doped ZnO and TiO 2 diluted magnetic semiconductor (DMS) films are described. The films are prepared by single sputtering deposition. They are ferromagnetic at temperatures as high as 350 K. The films were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), X-ray fluorescence (XRF). Optical transparency was measured on UV/VIS spectrometer. The Codoped ZnO films had wurtzite structure similar to ZnO with the (002) preferential texture. Neither XRD nor XPS showed any presence of pure Co or CoO in the samples. The Co-doped TiO 2 samples were amorphous, and some unoxidized Co was found in the films.