Accelerometers, compasses, gyros and RF switches can be made cheaply in the metal layers over CMOS , claims Barcelona-based Baolab Microsystems.
"We use exactly the same lithography process as CMOS and we use existing metal," CEO Dave Doyle told EW. "It is not a new idea, a good number of people have tried. In reality, it is very hard to do."
Dubbed NanoEMS, "it significantly reduces the costs of a MEMS by up to two thirds and even more if several different MEMS are created together on the same chip", claimed the firm.
The aluminium MEMS structures are made alongside conductors during the repeated SiO2-metal-SiO2-metal- deposition that is part of all CMOS chip making.
The tough bit has been to predictably release the MEMS by introducing a reagent that will dissolve the surrounding SiO2, and do this without the chemical going on to dissolve the oxide supporting nearby conductors.
Although Baolab is not revealing much about its techniques, Doyle did say that some form of grid structure in the top metal layer acts as a window through which vHF (vapour HF) etchant is introduced and "another technique controls etching sideways. We figured out a way to stop etching dead in its tracks" using something already available on a CMOS line.
Once the MEMS is cut free, the top metal grid provides a scaffold on which to deposit an undisclosed sealing layer which, according to Doyle, allows the micromachine to be left in a vacuum or protective gas, and is strong enough for the finished die to be run through a conventional packaging process.
Most MEMS are made from polysilicon, which is stiff, robust and well characterised, although it can be brittle.
Aluminium is not a traditional MEMS material, and is more prone to fatigue fracture.
"Our technique is not all things to all people. We are focussing on how to build MEMS cheaply for huge volumes. " said Doyle. "From aluminium and eventually copper we can build extremely effective switches and sensors."
Formed in 2003, the firm has spent much of its time designing structures that are suited to switches and sensors made of metals.
MEMS have been made on standard 0.18um 200mm volume CMOS wafers with four or more metal layers, with features down to 200nm.
Doyle claims that RF switches that can operate for the tens of billions of cycles demanded by phone makers are in the lab being tested.
The firm is aiming its switches at mobile phone power amplifiers where they are used to change operating band, and has found a way to make the contacts last.
"If you just use aluminium to aluminium contact, there is nothing left of the switch after a million cycles," said Doyle. "We are still in the middle of testing, but we are confident we can get the necessary reliability."
He sees one nine or 11-way micromechanical switch replacing multiple three of four way GaAs FET or PIN diode switches in LTE phones. "The solution is going to cost around $2 for GaAs or PIN switches, which could go down to $1.20. We could do it for substantially less: in the low tens of cents."
The firm has also built a single 2x2mm chip that implements a three-axis magnetic compass, plus a three-axis accelerometer, including conditioning electronics. According to Doyle, this is a pad-limited design and the sensors only occupy approximately 100x100um of the die.
Aimed at handsets as well as power amplifier and RF front ends, evaluation samples will be available later this year, including RF switches, electronic compasses and accelerometers.
The top mesh is a window to allow etchant to release underlying metal structures - in this case a fine aluminium mesh test structure hanging over pegs on the silicon surface.
