Baolab Microsystems has developed innovative, pure CMOS MEMS devices that use Lorentz force sensors to detect the strength and direction of the Earth’s magnetic field. The new 3D Digital NanoCompass™ technology matches existing performance benchmarks for sensitivity, power consumption and package size at dramatically lower cost. An additional unique feature is autocalibration for consistent accuracy.
The new compass chips utilise Baolab’s NanoEMS™ technology, which allows nanoscale MEMS devices to be fabricated using standard high-volume CMOS lines and fully integrated monolithically with analogue and digital electronics. The MEMS elements are defined within the existing metal interconnect layers on the wafer as part of the normal CMOS production process. Conventional 3D compass devices typically use magnetoresistive materials or Hall-effect devices combined with magnetic field concentrators to detect the direction of the Earth’s magnetic field.
The Lorentz force approach has not been used extensively up to now due to the cost of manufacture using conventional MEMS techniques, but it is perfectly suited to the mechanical structures that can be fabricated using Baolab’s NanoEMS technology. The MEMS structure, consisting of a moveable aluminium plate suspended by springs, is constructed from the metal interconnect layers of the CMOS chip by using vapour HF to etch away the intermetal dielectric. A current flowing through the plate experiences a force (the Lorentz force) proportional to the strength of the surrounding magnetic field. The resulting displacement is measured by detecting the capacitance between the moveable plate and fixed electrodes around it, allowing the magnetic field to be sensed in the X, Y and Z directions with a single device.
Engineering samples of the first compass product, the BLBC3-D NanoCompass, will be available in 2012, along with a comprehensive evaluation kit providing 5° heading resolution and 13 bits per axis. Commercial products will have an I²C or SPI digital serial interface and a choice of a DFN package for drop-in compatibility with existing solutions or a BGA package.
Image: Baolab Microsystems