Eric Belloy

The introduction of powder blasting for sensor and microsystem applications

We introduce powder blasting using a pressurised nozzle and a metallic mask as a new promising technology for microsystem fabrication. We study basic parameters of this powder blasting erosion process as well as mask-geometry effects on the erosion rate. We demonstrate the application potential of this technique in three important fields of microsystems research: (i) the realisation of microfluidic chips for biochemical separations, (ii) the micropatterning of composite hard magnetic layers for mechatronic and magnetic sensor applications, and (iii) the realisation of inertial sensors in glass. We present for the first time a mechanical and electrical characterisation of powder-blasted accelerometer devices.

Printed circuit board integrated fluxgate sensor

We have developed a cheap and simple trilayer printed circuit board (PCB)-based technology, adapted for the fabrication of fluxgate magnetic sensors. The two outer layers of the PCB stack comprise the electrical windings of the fluxgate, while the inner layer is made of patterned amorphous magnetic core with extremely high relative magnetic permeability (µr100,000). The output voltage and the sensitivity of the fluxgate devices have been studied as a function of the external field and of the geometry of the magnetic core. We have found a relatively high sensitivity of 18 V/T at an excitation current frequency of 10 kHz. The results obtained clearly show the potential of this miniaturised fluxgate device for application as a magnetic field sensor. Keywords: Fluxgate sensor; Sensitivity; High permeability; Compass; Vitrovac®; Printed circuit board (PCB)

Micromachining of glass inertial sensors

We demonstrate the feasibility of a powder blasting micro-erosion process for the micromachining of accelerometer devices in glass. Using high-speed abrasive microparticles and a metal contact mask, we structure millimeter-size cantilever beams from simple glass slides. By metalizing one side of the glass substrate, we demonstrate both capacitive and piezoresistive/strain gauge detection of the vibrating cantilever mass and measure the frequency response of mechanically excited cantilever beams. We think that our approach opens new perspectives for manufacture of inertial sensing devices in a technology alternative to Si.

Powder blasting for three-dimensional microstructuring of glass

We report on powder blasting as a promising technology for the three-dimensional structuring of brittle materials. We investigate the basic parameters of this process, which is based on the erosion of a masked substrate by a high-velocity eroding powder beam, using glass substrates. We study the effect of various parameters on the etching rate, like the powder velocity and the mask feature size, which induces geometrical effects to the erosion process. We introduce oblique powder blasting and investigate, in particular, sidewall effects of the micropatterned structures. A few examples of devices micromachined by powder blasting are also presented.

Microfabrication of high-aspect ratio and complex monolithic structures in glass

We present a novel approach for the realization of complex three-dimensional microstructures in brittle materials, like glass. Our technology is based on a beam of eroding powder particles, etching a masked rotating substrate. By using an oblique powder beam and mask under-etching effects, we fabricate monolithic millimeter-high microstructures with an aspect ratio of 5 to 10. This intrinsically very simple microfabrication method also allows to realize in a unique way free-standing monolithic glass microstructures, suspended over many millimeters.

New hybrid technology for planar fluxgate sensor fabrication

We have adapted a new printed circuit board (PCB) technology to the fabrication of ultraflat and sensitive fluxgate magnetic field sensors. The two outer layers of the PCB stack compose the electrical windings of fluxgates, while the inner layer is made of a micro-patterned amorphous magnetic ribbon with extremely high relative magnetic permeability (/spl mu//sub r//spl ap/100 000). Two basic configurations were considered: one based on a toroidal magnetic core and the other on a rectangular core with and without an air gap. The field response and sensitivity of the fluxgate devices have been studied as a function of the gap length, the excitation current, and excitation frequency. Compared to fluxgate sensors of similar size, a relatively high sensitivity of 60 V/T was found at 30 kHz for a five-winding detection coil wound around a rectangular E-shaped magnetic core. This high performance is primarily attributable to the high-permeability magnetic core. The results clearly show the potential of this fluxgate device for application as a magnetic sensor.

Powder blasting patterning technology for microfabrication of complex suspended structures in glass

We present a powder blasting microfabrication method and realize with it complex three-dimensional and monolithic suspended microstructures in glass. We also compare the usual metal contact mask to an alternative photosensitive flexopolymer. At normal incidence of the powder beam, the obtained profiles are similar for both methods and both the metal contact mask and the flexopolymer erosion selectivity with respect to glass is ∼ 50. By controlling the underetching induced by oblique powder blasting, suspended structures are realized, using a metal contact mask directly into the substrate. These structures can be realized in a single oblique erosion step or by a two-step normal/oblique erosion process.

High inductance planar transformers

We have developed a new printed circuit board PCB technology adapted for the fabrication of ultra-flat microtransformers. The two outer layers of the PCB stack comprise the electrical windings of the inductive devices, while the inner layer is made of a micro-patterned . amorphous magnetic ribbon with extremely high relative magnetic permeability m f 100,000 . The electrical properties of the toroidal r microtransformers have been studied as a function of frequency. Inductances were found to be as much as 30 mH at 1 kHz, a relatively high value compared to microtransformers of similar size. Despite a relatively high leakage flux, the voltage transformation efficiency is measured at 89%. The high performance of these devices is primarily due to the use of the high permeability magnetic core. q 2000 Elsevier Science S.A. All rights reserved.

Oblique Powder Blasting for Three-dimensional Micromachining of Brittle Materials

We present oblique powder blasting as a three-dimensional micromachining technology for brittle materials. Powder blasting is a microfabrication process, based on the use of a pressurised air beam containing eroding Al2O3 particles. By varying the angle of incidence of the incoming particles to a substrate, covered by a mask, one can exploit the oblique slopes of micropatterned holes and mask underetching phenomena to generate new options for three-dimensional microstructuring. We have identified and quantified the role of secondary rebounding particles in mask underetching.

Development of a novel printed circuit board technology for inductive device applications

Abstract This paper describes the fabrication and characterisation of 2-dimensional inductive devices integrated inside printed circuit boards (PCB) and flex-foils. These devices basically are composed of three layers of which the outer layers bear the printed coil patterns and the inner layer is a high permeability ferromagnetic sheet core. Both magnetic metal and copper layers are patterned using standard lithographic techniques. Electroplated interconnections between the outer layers complete the windings. We have fabricated both transformers and fluxgate magnetic field sensing devices with a thickness of 200 μm for the flex-foil devices and 600 μm for the PCB-based devices. Lateral dimensions are approximately 1 cm. We realise relatively high inductances of 1–10 μH at a frequency of 1 kHz for the transformers and a magnetic field detection limit of 43 μT at 20 kHz for the fluxgate devices.