Strong Rashba parameter of two-dimensional electron gas at CaZrO/SrTiO heterointerface.

We synthesized a CaZrO/SrTiO oxide heterostructure, which can serve as an alternative to LaAlO/SrTiO, and confirmed the generation of 2-dimensional electron gas (2-DEG) at the heterointerface. We analyzed the electrical-transport properties of the 2-DEG to elucidate its intrinsic characteristics. Based on the magnetic field dependence of resistance at 2 K, which exhibited Weak Anti-localization (WAL) behaviors, the fitted Rashba parameter values were found to be about 12-15 × 10 eV*m.

Quantum interference probed by the thermovoltage in Sb-doped BiSe nanowires.

The magnetic-flux-dependent dispersions of sub-bands in topologically protected surface states of a topological insulator nanowire manifest as Aharonov-Bohm oscillations (ABOs) observed in conductance measurements, reflecting the Berry's phase of π because of the spin-helical surface states. Here, we used thermoelectric measurements to probe a variation in the density of states at the Fermi level of the surface state of a topological insulator nanowire (Sb-doped BiSe) under external magnetic fields and an applied gate voltage. The ABOs observed in the magnetothermovoltage showed 180° out-of-phase oscillations depending on the gate voltage values, which can be used to tune the Fermi wave number and the density of states at the Fermi level.

Implementation of Flip-Chip Microbump Bonding between InP and SiC Substrates for Millimeter-Wave Applications.

Flip-chip microbump (μ-bump) bonding technology between indium phosphide (InP) and silicon carbide (SiC) substrates for a millimeter-wave (mmW) wireless communication application is demonstrated. The proposed process of flip-chip μ-bump bonding to achieve high-yield performance utilizes a SiO-based dielectric passivation process, a sputtering-based pad metallization process, an electroplating (EP) bump process enabling a flat-top μ-bump shape, a dicing process without the peeling of the dielectric layer, and a SnAg-to-Au solder bonding process. By using the bonding process, 10 mm long InP-to-SiC coplanar waveguide (CPW) lines with 10 daisy chains interconnected with a hundred μ-bumps are fabricated.

Hysteretic temperature dependence of resistance controlled by gate voltage in LaAlO/SrTiO heterointerface electron system.

For two-dimensional electron gas device applications, it is important to understand how electrical-transport properties are controlled by gate voltage. Here, we report gate voltage-controllable hysteresis in the resistance-temperature characteristics of two-dimensional electron gas at LaAlO/SrTiO heterointerface. Electron channels made of the LaAlO/SrTiO heterointerface showed hysteretic resistance-temperature behavior: the measured resistance was significantly higher during upward temperature sweeps in thermal cycling tests.

First Observation of Ferroelectricity in ∼1 nm Ultrathin Semiconducting BaTiO Films.

The requirements of multifunctionality in thin-film systems have led to the discovery of unique physical properties and degrees of freedom, which exist only in film forms. With progress in growth techniques, one can decrease the film thickness to the scale of a few nanometers (∼nm), where its unique physical properties are still pronounced. Among advanced ultrathin film systems, ferroelectrics have generated tremendous interest.

Polarity-tunable magnetic tunnel junctions based on ferromagnetism at oxide heterointerfaces.

Complex oxide systems have attracted considerable attention because of their fascinating properties, including the magnetic ordering at the conducting interface between two band insulators, such as LaAlO3 and SrTiO3. However, the manipulation of the spin degree of freedom at the LaAlO3/SrTiO3 heterointerface has remained elusive. Here, we have fabricated hybrid magnetic tunnel junctions consisting of Co and LaAlO3/SrTiO3 ferromagnets with the insertion of a Ti layer in between, which clearly exhibit magnetic switching and the tunnelling magnetoresistance effect below 10 K.