Nanoelectronics Spintronic MEMS devices (collaboration with INL Spintronics Group)


The convergence of MEMS and spintronics technology to create a new breed of hybrid devices with a set of features exclusive to these cross-technology devices is one of the areas where INL is well positioned as a result of its micromachining and magnetic processing capabilities. Accelerometers, magnetoresistive AFM tips and ultra-low magnetic field sensors are currently being developed.

Among many possibilities, MEMS based accelerometers have been selected to demonstrate the power of this technological convergence, since these are widespread sensors that are integrated in every modern automobile as e.g. actuators of airbags, a critical safety system, as well as in aircraft devices for navigation purposes. Present day MEMS accelerometers are based in variable capacitors where the plate electrodes consist of interdigitated finger structures micro-fabricated in Si and attached to inertial masses acting as the acceleration-sensing element. Acceleration results in a variation of the gap between the fingers, which in turn leads to a capacitance change. The minute capacitance changes during operation require complex conditioning electronics. In addition, for such variations to be comfortably measured, the area of plates must be sufficiently large thus making the whole device large as well. Significant device size reduction is being accomplished by replacing the capacitive transduction scheme by permanent magnet / magnetic field sensor pairs whose resistance variations can be easily probed up to the GHz range.

Another type of device currently being investigated is an AFM-like tip integrating magnetoresistive sensors, which can be used to scan a surface, much like a conventional AFM tip, extracting information concerning the magnetic fields present at the surface. Such features are required in magnetic imaging applications (used to monitor electrical currents, image magnetic domains, detect magnetic nanoparticles and magnetically tagged surfaces/biological elements) with a broad spectrum of end-uses (electronics, medicine, biology, structural analysis, critical structure monitoring, etc...). The integration of these magnetoresistive sensors in AFM platforms consists of first defining the magnetic elements on the frontside of the silicon wafer, isotropically machine the surrounding area into a mesa structure, contacting, defining sharp tip and through etching the base by DRIE.