Manufacturing Bits: Nov. 24

Tiny MEMS gyroscope
CEA-Leti and Politecnico di Milano (POLIMI) have developed the world’s smallest MEMS gyroscope.

Based on a nano-resistive sensing technology, the gyroscope enables a navigation-grade performance with a sensor footprint of only 1.3mm². The tiny gyroscope is targeted for high-volume markets like automotive and others. The technology was reported in a paper, entitled “1.3mm² Nav-Grade NEMS-Based Gyroscope,” in the Journal of Microelectromechanical Systems.

Used in compasses and other products, a gyroscope is a device that consists of a spinning wheel. It detects the deviation of an object from its desired orientation.

Today’s smartphones incorporate accelerometers and gyroscopes. “Accelerometers in mobile phones are used to detect the orientation of the phone,” according to GSMArena.com, a technology site. “The gyroscope, or gyro for short, adds an additional dimension to the information supplied by the accelerometer by tracking rotation or twist.”

MEMS gyroscopes are used in smartphones and other products. Microelectromechanical systems (MEMS) are systems with moving parts. MEMS gyroscopes “monitor and control device position, orientation, direction, angular motion and rotation,” according to Leti. Nanoelectromechanical systems (NEMS) are a class of MEMS that function on the nanoscale.

CEA-Leti, in collaboration with POLIMI, demonstrated a state-of-the-art ultra-miniaturized MEMS gyroscope. This new gyroscope reaches “0.004°/hr ARW and 0.02°/hr stability on average over several tested samples, unrivaled results for a 1.3mm²-size gyroscope footprint,” according to the paper from Leti and POLIMI.

The ARW and bias instability performance were highlighted on non-static operations. The tiny gyroscope can be produced in a standard MEMS foundry. Manufactured on CEA-Leti’s silicon pilot line, these gyroscopes can also be co-integrated with a high-performance 3-axis accelerometer and barometric-pressure sensor.

“This architecture enables best-in-class MEMS gyroscopes in terms of overall performance, size and resonant frequency, and our breakthrough 1.3 mm² high-frequency device is already at the state-of-the-art performance in terms of noise, bias stability, scale range and bandwidth. Several design and technology improvements are right now under investigation,” said Philippe Robert, MEMS business development manager at CEA-Leti.

“This improved performance must not come with a high cost so the device will be priced competitively in large-volume markets, such as the automotive and consumer markets,” said Robert. “The size of these new gyroscopes must therefore not exceed 2 mm² per axis, while maintaining standard MEMS technology and using wafer-level vacuum packaging.”

Photonic gyros
Anello Photonics has developed what it calls a Silicon Photonic Optical Gyroscope (SiPhOG) technology.

SiPhOG displaces a traditional fiber optic gyroscope (FOG), which is used in several systems. “A fiber optic gyroscope detects changes in position or direction using the Sagnac effect,” according to OFS Fitel. “In this way, an optical gyro functions similarly to a mechanical gyro. However, the optical gyro operates by using light passing through a coil of optical fiber.”

Anello’s SiPhOG replaces the discrete optical components of a traditional FOG. The technology combines Anello’s on-chip waveguide manufacturing process integrated with a silicon photonic chip-scale gyroscope.

It combines high precision with reduced size, weight, power and cost. The technology is targeted for automotive, trucking, construction, drones, aerospace, defense and consumer electronics.

“What we have done is replace all the discrete optical components (splitters couplers, detectors, phase shifters, filters, delay lines, etc.) with a traditional fiber optic gyroscope (FOG) and put that into one tiny integrated silicon photonic chip. In addition, Anello has developed an ultra-low-loss-on-chip waveguide manufacturing process that allows the ‘fiber’ in a FOG to be directly replaced by the planar waveguide,” according to officials from Anello.

“The SiPhOG’s principle of operation is the same as that of the classical interferometric fiber optic gyroscope (FOG). In simplest terms, the phased modulated light is launched into a waveguide where the light experiences equal but opposite additional phase shifts during rotation. This additional phase shift due to rotation is known as the Sagnac Effect. The return light from the waveguide is coupled into a photodetector, where the two return beams produce an interference signal that is linearly proportional to the angular rate,” according to the company.

Tower Semiconductor and Anello recently announced a strategic partnership for a new waveguide manufacturing process based on the technology. The new low-loss silicon nitride waveguide process approaches a 0.005dB/cm propagation loss at 1550nm wavelengths with less than a 1mm bend radius. The combination of low loss along with a small bend radius enables the fabrication of a new class of high-performing devices, including long (>10m) delays lines and tiny on-chip resonators with high-quality factors (high-Q) surpassing 100 million.

Nuclear spin gyros
The University of California, the U.S. Army Research Laboratory and others have demonstrated a diamond nuclear spin gyroscope.

Besides MEMS-based gyros, nuclear magnetic resonance (NMR) gyroscopes are emerging. These sensors use noble gas nuclei, which are confined in vapor cells. In theory, NMR gyroscopes may surpass the performance of commercial devices within the next decade.

There is a related technology to NMR gyroscopes. The University of California, the U.S. Army Research Laboratory and others demonstrated a diamond NMR gyroscope using the N nuclear spins intrinsic to nitrogen-vacancy (NV) centers.

These so-called nuclear spin gyroscopes are different than vapor-based NMR devices. The nuclear spin gyroscopes consist of a scalable and miniaturized solid-state platform, “capable of operation in a broad range of environmental conditions,” said Andrey Jarmola, a researcher and lead author of a paper in Science Advances, a technology journal. Others contributed to the work.

“An attractive feature is that a diamond sensor can be configured as a multisensor, reporting on magnetic field, temperature, and strain while also serving as a frequency reference. This multisensing capability is important for operation in challenging environments,” Jarmola said. “Its operation is enabled by direct optical polarization and readout of the N nuclear spins and a radio-frequency (RF) double-quantum pulse protocol that monitors N nuclear spin precession. This measurement technique is immune to temperature-induced variations in the N quadrupole splitting.”