Etching of silicon in alkaline solutions: a critical look at the {111} minimum

Anisotropic wet-chemical etching of silicon in alkaline solutions is a key technology in the fabrication of sensors and actuators. In this technology, etching through masks is used for fast and reproducible shaping of micromechanical structures. The etch rates Image depend mainly on composition and temperature of the etchant. In a plot of etch rate versus orientation, there is always a deep, cusped minimum for the {1 1 1} orientations. We have investigated the height of the {1 1 1} etch-rate minimum, as well as the etching mechanisms that determine it. We found that in situations where masks are involved, the height of the {1 1 1} minimum can be influenced by nucleation at a silicon/mask-junction. A junction which influences etch or growth rates in this way can be recognized as a velocity source, a mathematical concept developed by us that is also applicable to dislocations and grain boundaries. The activity of a velocity source depends on the angle between the relevant {1 1 1} plane and the mask, and can thus have different values at opposite {1 1 1} sides of a thin wall etched in a micromechanical structure. This observation explains the little understood spread in published data on etch rate of {1 1 1} and the anisotropy factor (often defined as Imag

Simulation of anisotropic wet-chemical etching using a physical model

We present a method to describe the orientation dependence of the etch rate of silicon, or any other single crystalline material, in anisotropic etching solutions by analytical functions. The parameters in these functions have a simple physical meaning. Crystals have a small number of atomically smooth faces, which etch (and grow) slowly as a consequence of the removal (or addition) of atoms by rows and layers. However, smooth faces have a roughening transition (well known in statistical physics); at increasing temperature they become rougher, and accordingly the etch and growth rates increase. Consequently, the basic physical parameters of our functions are the roughness of the smooth faces and the velocity of steps on these faces. This small set of parameters describes the etch rate in the two-dimensional space of orientations (on the unit sphere). We have applied our method to the practical case of etch rate functions for silicon crystals in KOH solutions. The maximum deviation between experimental data and simulation using only nine physically meaningful parameters is less than 5% of the maximum etch rate. This method, which in this study is used to describe anisotropic etching of silicon, can easily be adjusted to describe the growth or etching process of any crysta

Magnetoelectric Effect in Ni-PZT-Ni Cylindrical Layered Composite Synthesized by Electro-deposition

The magnetoelectric (ME) coupling of cylindrical trilayered composite was studied in this paper. The Ni-lead zirconate titanate (PZT)-Ni trilayered cylindrical composite was synthesized by electro-deposition. The maximum ME voltage coefficient of cylindrical ME composite is 35V/cm Oe, about three times higher than that of the plate trilayered composite with the same raw materials and magnetostrictive- piezoelectric phase thickness ratio. The high ME voltage coefficient of cylindrical composite owes to the self-bound effect of circle. Moreover, the resulting complex condition can induce a double peak in the field dependence of ME coefficient.Comment: 11 pages, 5 figure

Investigation of biferroic properties in La0.6Sr0.4MnO3/0.7 Pb(Mg1/3Nb2/3)O3 0.3 PbTiO3 epitaxial bilayered heterostructures

Epitaxial bilayered thin films consisting of La0.6Sr0.4MnO3 (LSMO) and 0.7 Pb(Mg1/3Nb2/3)O3 0.3 PbTiO3 (PMN-PT) layers of relatively different thicknesses were fabricated on LaNiO3 coated LaAlO3 (100) single crystal substrates by pulsed laser ablation technique. Ferroelectric and ferromagnetic characteristics of these heterostructures confirmed their biferroic nature. The magnetization and ferroelectric polarization of the bilayered heterostructures were enhanced with increasing PMN-PT layer thickness owing to the effect of lattice strain. Dielectric properties of these heterostructures studied over a wide range of temperature under different magnetic field strength suggested a possible role of elastic strain mediated magnetoelectric coupling behind the observed magneto-dielectric effect in addition to the influence of rearrangement of the interfacial charge carriers under an applied magnetic field

Giant Magnetoelastic Effects in BaTiO3-based Extrinsic Multiferroic Hybrids

Extrinsic multiferroic hybrid structures consisting of ferromagnetic and ferroelectric layers elastically coupled to each other are promising due to their robust magnetoelectric effects even at room temperature. For a quantitative analysis of these magnetoelectric effects, a detailed knowledge of the piezoelectric and magnetoelastic behavior of both constituents as well as their mutual elastic coupling is mandatory. We here report on a theoretical and experimental study of the magnetic behavior of BaTiO3-based extrinsic multiferroic structures. An excellent agreement between molecular dynamics simulations and the experiments was found for Fe50Co50/BaTiO3 and Ni/BaTiO3 hybrid structures. This demonstrates that the magnetic behavior of extrinsic multiferroic hybrid structures can be determined by means of ab-initio calculations, allowing for the design of novel multiferroic hybrids

Ni-PZT-Ni Trilayered Magnetoelectric composites Synthesized by Electro-deposition

We report the high strength of magnetoelectric (ME) coupling of trilayered composites prepared by electro-deposition. The ME coupling of Ni-lead zirconate titanate (PZT)-Ni trilayered structure was measured ranged from1 kHz to 120 kHz. The trilayered composites exhibit high magnetoelectric voltage coefficient because of good bonding between piezoelectric and magnetostrictive layers. The maximum magnetoelectric voltage coefficient can be up to 33 V/cm Oe at the electromechanical resonance frequency. This magnetoelectric effect shows promising application in transducers for magnetoelectric energy conversion.Comment: 13 pages, 4 figure

Frequency Dependence of Magnetoelectric Interactions in Layered Structures of Ferromagnetic Alloys and Piezoelectric Oxides

Magnetoelectric (ME) interactions in layered structures of magnetostrictive and piezoelectric phases are mediated by mechanical deformation. Here we discuss the frequency dependence of ME coupling in bilayers and trilayers of Permendur, a ferromagnetic alloy, and lead zirconate titanate. Data on ME voltage coefficient versus frequency profiles reveal a giant ME coupling at electromechanical resonance. The maximum voltage coefficient of 90 V/cm Oe is three orders of magnitude higher than low-frequency values. The ME interactions for transverse fields is an order of magnitude stronger than for longitudinal fields. These results are in agreement with theory. The resonance ME effect, therefore, is a novel tool for enhancing the magnetic-to-electric field conversion efficiency in the composites.Comment: accepted for publication as rapid communication in Applied Physics