James W. Reiner

Origin of the magnetoelectric coupling effect in Pb(Zr0.2Ti0.8)O{3}/La{0.8}Sr{0.2}MnO{3} Multiferroic heterostructures.

The electronic valence state of Mn in Pb(Zr0.2Ti0.8)O{3}/La{0.8}Sr{0.2}MnO{3} multiferroic heterostructures is probed by near edge x-ray absorption spectroscopy as a function of the ferroelectric polarization. We observe a temperature independent shift in the absorption edge of Mn associated with a change in valency induced by charge carrier modulation in the La0.8Sr0.2MnO3, demonstrating the electronic origin of the magnetoelectric effect. Spectroscopic, magnetic, and electric characterization shows that the large magnetoelectric response originates from a modified interfacial spin configuration, opening a new pathway to the electronic control of spin in complex oxide materials.

Crystalline oxides on silicon.

This review outlines developments in the growth of crystalline oxides on the ubiquitous silicon semiconductor platform. The overall goal of this endeavor is the integration of multifunctional complex oxides with advanced semiconductor technology. Oxide epitaxy in materials systems achieved through conventional deposition techniques is described first, followed by a description of the science and technology of using atomic layer-by-layer deposition with molecular beam epitaxy (MBE) to systematically construct the oxide-silicon interface. An interdisciplinary approach involving MBE, advanced real-space structural characterization, and first-principles theory has led to a detailed understanding of the process by which the interface between crystalline oxides and silicon forms, the resulting structure of the interface, and the link between structure and functionality. Potential applications in electronics and photonics are also discussed.

Ferroelectric Field Effect Transistors for Memory Applications

The non-volatile polarization of a ferroelectric is a promising candidate for digital memory applications. Ferroelectric capacitors have been successfully integrated with silicon electronics, where the polarization state is read out by a device based on a field effect transistor configuration. Coupling the ferroelectric polarization directly to the channel of a field effect transistor is a long-standing research topic that has been difficult to realize due to the properties of the ferroelectric and the nature of the interface between the ferroelectric and the conducting channel. Here, we report on the fabrication and characterization of two promising capacitor-less memory architectures.

Active Silicon Integrated Nanophotonics: Ferroelectric BaTiO3 Devices

The integration of complex oxides on silicon presents opportunities to extend and enhance silicon technology with novel electronic, magnetic, and photonic properties. Among these materials, barium titanate (BaTiO3) is a particularly strong ferroelectric perovskite oxide with attractive dielectric and electro-optic properties. Here we demonstrate nanophotonic circuits incorporating ferroelectric BaTiO3 thin films on the ubiquitous silicon-on-insulator (SOI) platform. We grow epitaxial, single-crystalline BaTiO3 directly on SOI and engineer integrated waveguide structures that simultaneously confine light and an RF electric field in the BaTiO3 layer. Using on-chip photonic interferometers, we extract a large effective Pockels coefficient of 213 ± 49 pm/V, a value more than six times larger than found in commercial optical modulators based on lithium niobate. The monolithically integrated BaTiO3 optical modulators show modulation bandwidth in the gigahertz regime, which is promising for broadband applications.

The realization and performance of vibration energy harvesting MEMS devices based on an epitaxial piezoelectric thin film

This paper focuses on the fabrication and evaluation of vibration energy harvesting devices by utilizing an epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) thin film. The high quality of the c-axis oriented PZT layer results in a high piezoelectric coefficient and a low dielectric constant, which are key parameters for realizing high performance piezoelectric energy harvesters. Different cantilever structures, with and without a Si proof mass, are realized using micro-patterning techniques optimized for the epitaxial oxide layers, to maintain the piezoelectric properties throughout the process. The characteristics and the energy harvesting performances of the fabricated devices are experimentally investigated and compared against analytical calculations. The optimized device based on a 0.5 µm thick epitaxial PZT film, a cantilever beam of 1 mm × 2.5 mm × 0.015 mm, with a Si proof mass of 1 mm × 0.5 mm × 0.23 mm, generates an output power, current and voltage of, respectively, 13 µW g − 2, 48 µA g − 1 and 0.27 V g − 1 (g = 9.81 m s − 2) at the resonant frequency of 2.3 kHz for an optimal resistive load of 5.6 kΩ. The epitaxial PZT harvester exhibits higher power and current with usable voltage, while maintaining lower optimal resistive load as compared with other examples present in the literature. These results indicate the potential of epitaxial PZT thin films for the improvement of the performances of energy harvesting devices.

NON-FERMI-LIQUID BEHAVIOR OF SRRUO3 : EVIDENCE FROM INFRARED CONDUCTIVITY

The reflectivity of the itinerant ferromagnet SrRuO{sub 3} has been measured between 50 and 25thinsp000thinspthinspcm{sup {minus}1} at temperatures ranging from 40 to 300thinspthinspK, and used to obtain conductivity, scattering rate, and effective mass as a function of frequency and temperature. We find that at low temperatures the conductivity falls unusually slowly as a function of frequency (proportional to 1/{omega}{sup 1/2} ), and at high temperatures it even appears to increase as a function of frequency in the far-infrared limit. The data suggest that the charge dynamics of SrRuO{sub 3} are substantially different from those of Fermi-liquid metals. {copyright} {ital 1998} {ital The American Physical Society }

Epitaxial piezoelectric MEMS on silicon

This paper reports on the microfabrication and characterization of piezoelectric MEMS structures based on epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) thin films grown on silicon wafers. Membranes and cantilevers are realized using a sequence of microfabrication processes optimized for epitaxial oxide layers. Different issues related to the choice of materials and to the influence of the fabrication processes on the properties of the piezoelectric films are addressed. These epitaxial PZT transducers can generate relatively large deflections at low bias voltages in the static mode. Estimations of the piezoelectric coefficient d31 of the epitaxial PZT thin film (100 nm) yield 130 pm V−1. In the dynamic mode, the performance of the epitaxial PZT transducers in terms of the resonant frequency, modal shape and quality factor are examined. An epitaxial PZT/Si cantilever (1000 × 2500 × 40 µm3) resonating in air and in vacuum exhibits a deflection of several microns with quality factors of 169 and 284, respectively. For a 1500 µm diameter membrane, the quality factor is 50 at atmospheric pressure, and this rises to 323 at a pressure of 0.1 mbar. These results indicate the high potential of epitaxial piezoelectric MEMS, which can impact a variety of technological applications.

Tuning the Structure of Nickelates to Achieve Two-Dimensional Electron Conduction

Metallic electronic transport in nickelate heterostructures can be induced and confined to two dimensions (2D) by controlling the structural parameters of the nickel-oxygen planes.

Atomically Engineered Oxide Interfaces

New solid-state phenomena emerge when interfaces between different oxides are created with atomic-scale precision.