S Mouaziz

Submicrometer Hall devices fabricated by focused electron-beam-induced deposition

Hall devices having an active area of about (500 nm)(2) are fabricated by focused electron-beam-induced deposition. The deposited material consists of cobalt nanoparticles in a carbonaceous matrix. The realized devices have, at room temperature, a current sensitivity of about 1 V/AT, a resistance of a few kilo-ohms, and can be biased with a maximum current of about 1 mA. The room-temperature magnetic field resolution is about 10 muT/Hz(1/2) at frequencies above 1 kHz.

Polymer-based cantilevers with integrated electrodes

An innovative release method of polymer cantilevers with embedded integrated metal electrodes is presented. The fabrication is based on the lithographic patterning of the electrode layout on a wafer surface, covered by two layers of SU-8 polymer: a 10-mum-thick photo-structured layer for the cantilever, and a 200-mum-thick layer for the chip body. The releasing method is based on dry etching of a 2-mum-thick sacrificial polysilicon layer. Devices with complex electrode layout embedded in free-standing 500-mum-long and 100-mum-wide SU-8 cantilever were fabricated and tested. We have optimized major fabrication steps such as the optimization of the SU-8 chip geometry for reduced residual stress and for enhanced underetching, and by defining multiple metal layers [titanium (Ti), aluminum (Al), bismuth (Bi)] for improved adhesion between metallic electrodes and polymer. The process was validated for a miniature 2times2 mum2 Hall-sensor integrated at the apex of a polymer microcantilever for scanning magnetic field sensing. The cantilever has a spring constant of cong1 N/m and a resonance frequency of cong17 kHz. Galvanometric characterization of the Hall sensor showed an input/output resistance of 200Omega, a device sensitivity of 0.05 V/AT and a minimum detectable magnetic flux density of 9 muT/Hz1/2 at frequencies above 1 kHz at room temperature. Quantitative magnetic field measurements of a microcoil were performed. The generic method allows for a stable integration of electrodes into polymers MEMS and it can readily be used for other types of microsensors where conducting metal electrodes are integrated in cantilevers for advanced scanning probe sensing applications

Element-resolved x-ray ferrimagnetic and ferromagnetic resonance spectroscopy

We report on the measurement of element-specific magnetic resonance spectra at gigahertz frequencies using x-ray magnetic circular dichroism (XMCD). We investigate the ferrimagnetic precession of Gd and Fe ions in Gd-substituted yttrium iron garnet, showing that the resonant field and linewidth of Gd precisely coincide with Fe up to the nonlinear regime of parametric excitations. The opposite sign of the Gd x-ray magnetic resonance signal with respect to Fe is consistent with dynamic antiferromagnetic alignment of the two ionic species. Further, we investigate a bilayer metal film, Ni 80Fe20(5 nm)/Ni(50 nm), where the coupled resonance modes of Ni and Ni80Fe20 are separately resolved, revealing shifts in the resonance fields of individual layers but no mutual driving effects. Energy-dependent dynamic XMCD measurements are introduced, combining x-ray absorption and magnetic resonance spectroscopies.

Highly Sensitive Cantilevers, with and without Magnetic Tip, for Magnetic Resonance Force Microscopy

In this paper we present the fabrication and characterization of highly sensitive cantilevers, with and without magnetic tip, used for magnetic resonance force microscopy experiments. The full wafer silicon batch microfabrication was successful and the achieved production yield was about 70%. Cantilevers have been characterized in vacuum, at room temperature, and revealed promising properties for MRFM applications. A cantilever of 500times10times0.34 mum3 dimensions, a resonance frequency of 1670 Hz and a spring constant of 0.00014 N/m, we measured a quality factor of 27000 giving a minimum detectable force of 8times10-17 N/Hz1/2.

Integrated Nickel Micro-Nano-Hall Sensors on SU-8 Cantilevers for Scanning Hall Probe Microscopy

We report the fabrication and characterization of nickel Hall sensors integrated on SU-8 cantilevers. Sensors having active area down to 1 x 1 mum 2 show a magnetic field resolution better than 1 /n muT / Hz 1/2 in the thermal noise frequency range. The fabricated devices have been tested for magnetic imaging using the scanning Hall probe microscopy technique.