Micro-fabricated gyroscope accuracy beats MEMS
"TFGs [tuning-fork gyroscopes] have hit the wall in terms of performance, but bulk acoustic wave gyroscopes have overcome these obstacles," said Sreeni Rao, vice president of Vertical Markets at Qualtre told EE Times. "And we have a head start by holding the patents on that which could improve those tuning-fork gyros."
The single crystal silicon disk (center) moves to track angular motion, which is sensed capacitively by the electrodes around the edge.
(Source: Qualtre)
According to Rao, since licensing the basic patents from Georgia Tech, Qualtre has been busy improving and perfecting the BAW gyroscope by improving it in ways tuning forks could also be improved. So far they have over 30 granted patents with more pending. Their first generation gyroscope, four years in development, is a three-axis unit that Qualtre has been sampling to select customers since June 2014.
Since it is more expensive but higher performance, than three-axis tuning-fork MEMS gyros, its first customers are manufacturers of heavy industrial machinery who are willing to pay for higher performance, and platforms that must maintain absolutely perfect stability — or as close to it as they can get. For instance, satellite and other antennae on military ships must maintain near perfect aim at the antennae with which they are communicating. Qualtre claims its BAW-based gyroscopes outperform all other types for stabilising ship antenna platforms as the ship yaws, rolls and pitches.
Its newest single axis BAW gyroscope, on the other hand, has capitalszed on those 30 granted patents to make it even higher performance than the most expensive single-axis tuning fork gyroscope, as well as lower in cost.
"In the course of sampling our three-axis products and interacting with customers we found significant interest in a single axis version. Our second-generation single-axis gyroscope beats the very excellent single-axis gyroscopes from Analog Devices, and yet is cheaper than ADI’s," Rao told us. "The second generation includes improvements all round — we have improved noise, bias instability, as well as our hallmark vibration rejection."
The tiny 200 nanometer gap between the central disk and the electrodes around the edge changes its capacitance as the disk rolls, yaws and pitches.
Both its first and second generation gyros use an improved version of a process many MEMS devices use — called HARPSS for High Aspect-Ratio Poly and Single-crystalline Silicon. Generation two improves the design and packaging, and has optimised some of the process steps.
The HARPSS process qualifies Qualtre’s BAW as a MEMS device, but with moving parts that only move a few nanometers. A circular disk is surrounded by electrodes that today are spaced by about a 200-nanometers gap from the single crystal silicon disk in the middle. To improve performance further, all they have to do is scale that gap to smaller sizes.
Eventually, Qualtre intends to come out with models inexpensive enough for the burgeoning consumer market for gyroscopes, but for now it is satisfied with its industrial and military cliental. The package size is 7-by-7-by-2.1 millimeters, but Qualtrer’s goal is and 5-by-5-by-1 millimeter.
— R. Colin Johnson, Advanced Technology Editor, EE Times
Article originally posted on EE Times
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