Baolab Microsystems has designed pure CMOS Lorentz force
MEMS based 3D Digital NanoCompass sensor matches performance
benchmarks for sensitivity, power consumption and package
size, but at a lower cost. Baolab says it's the industries
first CMOS Lorentz force MEMS sensor. The unique feature
of this device is it auto-calibrates to maintain consistent
accuracy.
Baolab says the BLBC3-D NanoCompass is made using its NanoEMS
technology. NanoEMS enables nanoscale MEMS (Micro Electro
Mechanical Systems) to be built using standard high-volume
CMOS lines and fully integrated monolithically with the
analogue and digital electronics.
"As the market for 3D Compasses grows for smartphones
and other mobile devices, the ASP will be rapidly driven
down from around a dollar to 50 cents and lower," explained
Dave Doyle, Baolab's CEO. "Allowing for the fixed costs
of testing, tape & reel, pick and place, packaging,
etc., the only way to hit this target price and still have
a margin for profit is to use our NanoEMS technology, as
traditional approaches are several times more expensive.
When several devices are integrated onto a single chip to
create a multi-sensor device using NanoEMS, the cost savings
compared to conventional MEMS become even more significant
especially as different sensors require different production
processes, unlike NanoEMS."
The MEMS structure, a moveable aluminium plate suspended
by springs, is constructed using the metal interconnect
layers of the CMOS chip by etching away the Inter Metal
Dielectric (IMD) using vHF (vapour HF). When a current passes
through the plate, it experiences a force (the Lorentz force)
proportional to the surrounding Earth's magnetic field.
The resulting displacement is measured using capacitive
detection between the moveable plate and fixed electrodes
around it, sensing the magnetic field in the x, y and z
directions with a single NanoEMS chip explained by Baolab.
Hall effect sensors work well for magnetic field perpendicular
to the chip (z direction) but less so in the x and y planes,
and are not pure CMOS solutions as they require post processing
to deposit some magnetic material on top of the wafer to
increase their sensitivity (Integrated Magnetic Concentrator).
This adds to the cost of manufacture, as does the additional
processing required to realise compass devices from magneto-resistive
technologies such as AMR and GMR (Anisotropic Magnetoresistance
and Giant Magnetoresistance). Other benefits of Lorentz
over Hall include lower power consumption due to the use
of metallic conductors to carry the current, increased sensitivity
using mechanical resonance and no magnetic saturation issues.
As per Baolab the Lorentz force approach has not been used
until now extensively due to the cost of manufacture using
conventional MEMS techniques, but it is perfectly suited
to the mechanical structures supported by Baolab's NanoEMS.
Built in a standard CMOS process flow, NanoEMS makes it
possible to manufacture the devices at a fraction of the
cost, opening the market for a new generation of mobile
devices that take advantage of Baolab's lower cost 3D NanoCompasses,
claims Baolab.
Engineering samples of the BLBC3-D NanoCompass will be
available in 2012 along with a comprehensive evaluation
kit. It provides 5 degree heading resolution and 13-bits
per axis. Commercial product will have an I2C or SPI digital
serial interface and a choice of either a 3x3x0.9mm 10-pin
DFN/0.5mm pitch package, which provides drop in compatibility
with existing solutions, or a 2x2x0.75mm BGA package. Full
details are at www.baolab.com/compass.htm