IN A QUIET corner of Microsoft鈥檚 sprawling campus in Redmond, Washington
state, you can forget Windows. The aim of the Microsoft Research Hardware
Laboratories is to dream up new ideas. And, as 快猫短视频 has
discovered, they have delivered the goods. The lab has developed a new type of
micromotor that could become a workhorse in the switching centres essential to
the optical Internet of the future.
The minuscule motors produce many times the force available from today鈥檚 puny
micromachines, while taking up less room on a chip, says Microsoft research
engineer Michael Sinclair.
Micromotors are needed to drive microelectromechanical systems鈥攖iny
machines etched onto silicon slivers sometimes fractions of a millimetre across.
MEMS are most commonly used as acceleration sensors in vehicle air bags and are
making inroads in medicine
(快猫短视频, 8 September, p 21).
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But today鈥檚 micromotors, which are driven by electrostatic forces, lack
power, says Sinclair. More efficient and powerful motors are needed to drive the
mirrors used as switches in optical communications networks. These mirrors will
swivel frantically to bounce your e-mails and phone calls down the appropriate
optical fibres鈥攁voiding the need to convert signals to electricity at an
exchange. 鈥淏ut moving large mirrors very rapidly could consume a lot of energy,鈥�
he says.
Most micromotors are fairly simple. For example, an electrostatic actuator
can produce movement by making interleaved polysilicon combs attract and repel
each other. But this produces little useful force and takes up large amounts of
expensive 鈥渞eal estate鈥� on a chip.
Microsoft鈥檚 solution is to replace this with what Sinclair calls a 鈥渂uckle
beam thermal actuator鈥�. Polysilicon heats up when a current passes through it,
making it expand. Although the movement from this expansion is negligible on its
own, it can easily be put to good use.
Arranged in pairs, joined in the centre and anchored at their ends, rods made
of this material will buckle when heated. The force from the expansion is
exerted in the direction of the buckling motion. The connecting member in the
middle then acts like a miniature battering ram that wiggles forwards and
backwards. A pair of actuator arrays mounted at right angles can work together
to drive a cog (see Graphic).
An array of Sinclair鈥檚 actuators is capable of producing 240 micronewtons.
This may not sound like much, says Sinclair, but to produce the same force using
other thermal actuators would require a device nearly 2000 times the size. In
early tests, Microsoft was surprised at the system鈥檚 strength: the first bending
beam force measurement device Sinclair used was actually shattered by the
actuators.
Later, Sinclair hopes to develop 鈥渁 single MEMS device capable of producing a
colour video raster for use as a personal retinal display or projection on a
small screen鈥�. But to do this he will have to increase the frequency at which
his micromotors work. At the moment, he can make a cog spin at 1600 revolutions
per minute.
But it鈥檚 not all good news. Sinclair鈥檚 actuators use considerably more
electrical power than rival electrostatic devices and generate a lot of heat.
But he says this shouldn鈥檛 be a major problem. 鈥淚f you keep below the glass
melting or deformation limit of the polysilicon, the device should be good for a
very long life.鈥�