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Sercel And Tronic’s Team Up For MEMS Based Geophones

Sercel and TRONIC'S Microsystems, have collaborated for the production of a new generation of seismic sensors, or geophones, based on MEMS. Designed by CEA Leti, the 0.1µg resolution accelerometer packaged under vacuum has been optimised and industrialized by TRONIC'S Microsystems.

Geophones comprise one of the key products of Sercel (F), the world leader in seismic equipments for oil and gas exploration. Extremely sensitive sensors, the geophones measure the reflection of acoustic waves, sent on the surface of the field, in the different geologic layers (see figure 1). The data are then used to draw geological survey maps indicating the location and size of oil and gas reserves.

Geophones, though being inexpensive electromagnetic components (see figure 2), have rather been heavy and cumbersome as they need to be linked by cables to a central processing unit. Modern oil exploration now demands ever lighter, more mobile solutions capable of very high precision.

MEMS based geophone
Sercel spent several years working with the CEA Leti (F), to show the feasibility and design a MEMS based geophone. The collaboration resulted in a prototype of a far smaller and lighter accelerometer based geophone (see figure 2 and table 1).

The prototype reached the required extreme performances: a resolution down to 0.1µg, less than a millionth of the Earth gravity, over a range of +/- 100mg.

However, one of the biggest challenges laid in moving the MEMS-based solution from the laboratory to the production line. MEMS actually present no standard fabrication processes and have extremely demanding packaging requirements and complex specific testing procedures. Sercel therefore needed a custom MEMS manufacturer that could transform its MEMS concept into a reliable industrial product.

Geophone industrialization
Experienced in industrializing and manufacturing custom MEMS accelerometers, TRONIC'S Microsystems (F) also mastered the building blocks of Sercel's geophone technology.

The company's high-end custom MEMS manufacturing business model was also particularly appropriate to Sercel's manufacturing needs. Therefore the two companies entered into a business partnership

Starting from the prototypes, Tronic's optimised the device and qualified its specific process and vacuum packaging technique. The French manufacturer then ensured the first series deliveries early 2003 and today delivers packaged and tested geophone components (see figure 3) that Sercel integrates into new digital systems.

Vacuum package for MEMS
In order to reduce the molecular noise on the structure and to reach the requisite performance levels, TRONIC'S encapsulates the silicon microstructure under a very high vacuum environment in a LCC packaging. This packaging allows the MEMS geophone to exceed a Q factor of over 10.000 (estimated vacuum in the range of 1mTorr).

Smaller and lighter, the vacuum packaged MEMS geophone even outperform some other key specifications of the traditional geophones (see table 1).

In addition, 3 MEMS geophones can also be integrated together in a very small space with its digital electronic eliminating some of the cables previously required. The new MEMS based geophone therefore facilitates the logistic for Sercel customers while allowing 3 components measurement with a higher dynamic.

Through this collaboration, TRONIC'S Microsystems has further proven its ability to transform custom MEMS concepts into reliable high performance products for demading applications.

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