Epson has recently made a series of announcements in the IMU space, including a new V-series that they claim features the “world’s smallest IMU” (defined as “The smallest IMU among high-performance IMUs having gyro bias instability of 10 dph or less (as of the beginning of August 2013, according to Epson’s research)”). That would be 10x12x4 mm.
Why are they not comparing themselves to the silicon guys? Because their fundamental sense element material isn’t silicon; it’s quartz, branded as QMEMS. At least for the gyroscope, which they make. The accelerator in the IMU comes from someone else; they’ve not disclosed that partner. (And they say that no one has yet successfully made a quartz-based accelerator.)
So what’s with this quartz stuff, anyway? And isn’t quartz simply SiO2, like the SiO2 on silicon chips? Well, yes and no. It is SiO2, but it’s crystalline – the dielectric layers on chips are not. They grow a specific quartz crystal – the fabrication process includes an anneal that lasts for months in a 30-m-high autoclave. The cut they make off the crystal also determines the temperature stability.
The benefit is a high-quality (i.e., high Q), stable output that requires less conditioning than a silicon element would need. In fact, they say that silicon folks sometimes use redundant elements and average them to stabilize the result. This is also different from Qualtré’s approach, which uses a resonating disk: Epson’s element vibrates, but not at resonance.
Of course, this isn’t going to compete with the gyro that’s going into your phone when it comes to price. This is a more upscale version for use where accuracy commands a premium. One application they mentioned that can take advantage is SATCOM OTM – “on the move” – used for maintaining a satellite linkup while moving. The IMU is needed for fine alignment.
They’ve announced a G-series of other industrial IMUs as well that use their older technology. The difference with the V series is the new sense element – they say they can fit eight of the new ones in the space required by one of the old ones (which they claim was already pretty small). They also don’t need mechanical isolation or vacuum chambers like some larger high-performance IMUs need.