Spanish fabless CMOS MEMS firm Baolab Microsystems has announced its first product, a single chip three axis magnetic compass that it claims will be cheaper than competitors.
"Until now, 3D compasses have typically used magneto-resistive materials or Hall-effect structures combined with magnetic field concentrators to detect the direction of the Earth’s magnetic field," claimed the firm. "Baolab is the first to design a pure CMOS Lorentz force MEMS sensor. A unique feature resulting from this integration is that the device auto-calibrates to maintain consistent accuracy."
Most MEMS are made of silicon or SiO2, and processing details mean that they are difficult to combine with CMOS circuitry.
Baolab's MEMS are built entirely in the metallisation layers above the silicon surface - the layers usually used for interconnections - allowing analogue and digital circuits to be fabricated underneath.
The firm's significant intellectual property includes a method of selectively etching away unwanted SiO2 to release the moving parts without wrecking the rest of the chip, and a way to cap-off the die using aluminium sputtering to retain a vacuum without sticking the proof mass to nearby structures.
Vapour hydrogen fluoride etching is required.
"vHF is a capability in almost every CMOS fab these days," Baolab CEO Dave Doyle told Electronics Weekly.
It is notoriously difficult to get new technology designed into the conservative mobile phone industry.
Doyle said cost savings over other compass technology will allow him to establish his supply chain and generate first revenues where, providing you can meet the specs of the incumbent, price is king - amongst Tier 3 and 4 phone makers in China.
“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,” said Doyle. “Allowing for the fixed costs of testing, tape & reel, pick and place and packaging, the only way to hit this target price and still have a margin for profit is to use our technology as traditional approaches are several times more expensive."
Hot on the heels of the compass and using almost exactly the same physical technology - a moveable aluminium plate suspended by springs - will come a 3D linear accelerometer combined with a 3D compass "towards the end of next year", then a stand-alone 3D gyro.
The compass, the BLBC3-D NanoCompass will be sampling in 2012 along with its evaluation kit and an Android driver.
It will provide 5° heading resolution and 13-bits per axis.
The commercial product will have an I2C or SPI serial interface and a choice of either a 3x3x0.9mm 10pin DFN "which provides drop in compatibility with existing solutions", said Baolab, or a 2x2x0.75mm BGA.
Lorentz force?
When a current passes through the suspended plate, it experiences a 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 chip.
"Hall effect sensors work well for magnetic field in the z-direction perpendicular to the chip, 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," claimed Baolab. "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 claimed for 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.