The integration of high performance RE-TM (NdFeB and SmCo) hard magnetic films into Micro-Electro-Mechanical-Systems (MEMS) requires their patterning at the micron scale.In this paper we report on the applicability of standard micro-fabrication steps (film deposition onto topographically patterned substrates, wet etching and planarization) to the patterning of 5 µm thick RE-TM films. While NdFeB comprehensively fills micron scaled trenches in patterned substrates, SmCo deposits are characterized by poor filling of the trench corners, which poses a problem for further processing by planarization. The magnetic hysteresis loops of both the NdFeB and SmCo patterned films are comparable to those of non-patterned films prepared under the same deposition/annealing conditions. A micron-scaled multipole magnetic field pattern is directly produced by the unidirectional magnetization of the patterned films. NdFeB and SmCo show similar behavior when wet etched in an amorphous state: etch rates of approximately 1.25µm/minute and vertical side walls which may be attributed to a large lateral over-etch of typically 20 µm. ChemicalMechanical Planarization (CMP) produced material removal rates of 0.5-3µm/min for amorphous NdFeB. Ar ion etching of such films followed by the deposition of a Ta layer prior to film crystallization prevented degradation in magnetic properties compared to nonpatterned films.
A new magnetic micro-actuator with integrated permanent magnets has been developed. The design of this device with a levitating mobile magnet is a real innovation and is patented. The structure was modeled using analytical and numerical calculations. Furthermore, the fabrication feasibility, using collective micro-technology processes, has recently been demonstrated.
This paper reports on the electrodeposition at room temperature and the characterization of hard magnetic CoPtP material. An acidic bath has been set up to be compatible with the use of photoresist for micro technologies processes. X-ray diffraction (XRD) diagrams show that CoPtP alloy crystallizes in the hexagonal system. The film growth is generally columnar with a pronounced ⟨0 0 2⟩ texture associated with preferential out-of-plane magnetization. Using particular electrodeposition conditions, in-plane magnetization can be recovered and coercivities as high as 2800 Oe are reached for patterned layers. So a room temperature electroplating process able to produce patterned micromagnets usable in magnetic applications has been set up. Examples of the integration of CoPtP micromagnets are described through the fabrication of three devices: a multilayered giant magneto-resistive sensor biased by five electroplated magnets, a vertical magnetic bistable microactuator and a horizontal magnetic bistable microswitch. The main challenge for the last two devices was to demonstrate the actuation of a moving micromagnet without any mechanical guiding during commutation. The demonstrated bistability provided by the use of micromagnets emphasizes the interest in these devices for many applications.
International audienceThis paper describes the conception, designs consideration and fabrication process of a novel MEMS microphone. The presented microphone not only uses a new architecture, the sensitive part being beams moving within the plane of the substrate, but also uses an innovative detection means with Silicon piezo-resistive nanogauges. Modelization will consider acoustic and mechanical interactions. Besides, at MEMS scale, accurate simulation of the sensor must take into account thermal and viscous boundary layers in acoustics, and we will show that the presented sensor takes benefit from these short scale effects, which leads to achieve theoretical resolution as low as 24dB
We present the development of a technological platform dedicated to 3D capacitive inertial sensors. The proof of concept will be made on a 3D gyroscope. The mobile structure is made within a 30 µm thick Si top layer of a SOI substrate, while poly-Si deposited on top of a sacrificial PSG layer serves as suspended top electrodes and connection wires. This technology enables us to maintain low parasitic capacitance, which is of paramount significance for capacitive detection. After packaging and association with an analogue electronic board, functionality of the sensor is demonstrated.
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