NEMS gyroscope from CEA-Leti at 50 kHz


Microscope image of an M & NEMS gyroscope operating at 50 kHz

Gyroscopes operate at a specific resonant frequency. When this frequency and the frequency of vibrations in the environment are too close, measurements may be distorted. The French company CEA-Leti and the Technical University of Milan said they have solved this problem by developing a gyroscope that operates at high frequencies (about 50 kHz). The operating frequency range of this gyroscope is beyond the vibration frequencies found in automotive, aerospace and industrial use cases.

“This is the first gyroscope so powerful that it can detect deviations of less than a degree per hour,” said Philippe Robert, MEMS business development manager and senior expert at CEA-Leti. “All of this is made possible by nanosensors.”

Detection with nanosensors

Over the past 10 years, there has been a great demand for inexpensive and miniature inertial sensors – gyroscopes and accelerometers. To reduce the sensors without compromising sensitivity and resolution, CEA-Leti engineers developed a piezoresistive measurement concept with silicon nanosensors. M & NEMS technology, based on 25 patents, combines nano- and microelectromechanical technologies. This technology uses a thin layer with detectors (piezoresistive nanosensor), a thick layer that defines the internal mass and deformable springs.

The use of nanosensors made it possible to increase the voltage concentration, and later “we realized that three degrees of freedom could be realized in the new sensor architecture.” Said Robert.

Six years ago, Leti started working with the Technical University of Milan on a project funded by the European Union. The Nirvana project focused on the development of advanced 9-axis inertial microsensors (3D gyroscopes, 3D accelerometers, and 3D magnetometers) based on silicon nanowires for consumer and automotive applications, as well as a 3-axis gyroscope for medical applications. The Technical University of Milan and CEA-Leti also collaborated on a MEMS gyroscope. CEA-Leti was also responsible for the design and manufacture of the accelerometer and magnetometer.

The project has shown promising results for the gyroscope in terms of offset and noise and linearity measurements. After the completion of the project, CEA-Leti and the Technical University of Milan decided to continue their research using their own funds. “We were not able to conclude an industrial contract, but we believed in our business with all our hearts and continued to cooperate,” said Robert. “Over time, we realized that one of the interesting features of using nanosensors in gyroscopes is the ability to maintain a high level of performance even as the resonant frequency of the sensors increases.”
Capacitive vs Piezoresistive

In the M & NEMS gyroscope, piezoresistive nanosensors are used not only to detect rotational speed, but also to detect motion.

Modern low-power MEMS gyroscopes are based on capacitive sensors. “The problem with capacitive detection is that it detects bias, and when you want to work at high resonant frequencies, the designs get stiffer,” Robert said. However, “the stiffer the structure, the less it deforms.”

Robert further noted that nanosensors measure “not displacement, but voltage. We have shown experimentally that it is possible to increase the resonant frequency without sacrificing performance. We even managed to improve the sensor. ” This is a significant advantage, according to Robert, because almost all gyroscopes are sensitive to vibration, and when the vibration is compared to the resonant frequency of the sensor, it loses information.

Vibration-sensitive media

To maintain acceptable sensitivity, conventional gyroscopes must operate at a relatively low frequency (15-20 kHz). In an airplane or car, environmental vibrations often exceed 20 kHz. Based on information obtained from discussions with automakers, CEA-Leti and the Technical University of Milan have been working on a gyroscope whose resonant frequency is outside this spectrum, which could allow it to “become insensitive to the environment.” Their gyroscope, which operates at frequencies of the order of 50 kHz, outperforms modern counterparts in offset recognition and noise / linearity, Robert says.

In automotive use scenarios, gyroscopes must be able to detect deflection of one degree per hour (that is, rotational speed about ten times slower than that of the Earth) in environments that are subject to strong and constant vibrations. Cars (especially unmanned vehicles) should not lose navigation even if they can no longer receive a GPS signal (for example, in tunnels or stone jungles). “We need a high-sensitivity, high-resolution backup navigation system,” said Robert. “We have proven that we can create it.”

A gyroscope with an operating frequency of about 50 kHz and a base area of ​​1.45 mm² as a result of tests showed a scale factor of 1.3 ° / s / √Hz and a stability of 0.5 °, confirming the theoretical estimates. “We were able to combine small size, low cost, performance and compatibility with other sensors,” said Robert.

“Our technology is applicable to all applications, including consumer applications, but our device can really stand out in high vibration use scenarios such as industrial, automotive, aerospace and military.”

Technology transfer

The technology is advanced and “our goal is to find industrial partners for further development,” said Robert. “A number of MEMS device manufacturers in Europe and Asia have shown interest, but the transfer is expensive and will only happen when we have a major industrial partner. We are currently working on accelerometers and pressure sensors, and we already have industrial partners for these projects. “

The technology is ready for transfer. However, Robert acknowledged that there is still a lot of work to be done before the full release. “Our solution is not yet at a high level of readiness. This means that we have proven that the technology works, but we need to improve the architecture of the chips and work on integration. “

Robert also said that depending on the application and the specific needs of the partners, it can take from one to three years to start production and release the final product.

In parallel, the Technical University of Milan and CEA-Leti continue their research. They said they had just reached a new milestone in performance, but they didn’t want to discuss it until it was confirmed experimentally. “From a component development perspective, the idea is to continue to improve performance. As for the error, now it is equal to 0.5 ° per hour, our goal is to reduce it to 0.1 ° per hour, ”concluded Robert.

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