MEAS Switzerland SA - MEMS Processes

Sensor Technology

The pressure sensor is an assembly of a micromachined silicon part and Pyrex™ glas. Four piezo-resistances have been implemented, in the silicon, just above the sensor's membrane. The membrane is only a few micrometers thick and deflects depending on the pressure difference existing between its two sides.

For differential sensors, the Pyrex™ is drilled with a hole below the membrane (see picture left) so that pressure can be applied on both sides.

For absolute sensors, the Pyrex™ has no hole and vacuum is created in the cavity underneath the sensor when the Pyrex™ is sealed with the silicon. This step is called "Anodic bonding".

Electrical Wafer Sort (EWS)

Sensor design optimized for high output signal
Ultra-thin process for high sensitivity low-pressure sensors (10 to 200 mbar)
Standard process for medium pressure range (0.5 to 50 bar): high linearity/medium sensitivity and low linearity/high sensitivity are available
Special process for harsh environment pressure measurement applications (1 to 50 bar)
Simplified process for high volume / low cost / miniature pressure sensor products
8 Mask levels
Implanted Piezo Resistors
Low offset drift
Wafer are 100% electrically tested (EWS)
High overpressure capability

Micromachining: anisotropic KOH (thickness control with electrochemical etch-stop, time etch), Deep Reactive Ion Etching (DRIE)
Anodic bonding of Pyrex™ glass (structured or not structured, different thicknesses) to silicon on front side and backside of the wafer, direct Si-Si bonding.
Double sided wafer alignment
Reliable hermetic connection
Wafer dicing on blue or UV tape
Double sides Automatic Optical Inspection (AOI)
100% Electrical test

BR-techno7

KOH etching

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MEMS Processes

Typical products

The sensor element of the MS7801 consists of a silicon micro-machined membrane with a Pyrex glass mounted under vacuum. Implanted resistors make use of the piezo-resistive effect. The absolute pressure sensor (MS7801A) carries a sealed vacuum reference cavity underneath the membrane whereas the differential sensor (MS7801D) has a hole in the Pyrex glass at the backside of the sensor.

The MS7212 is an absolute silicon micro-machined pressure sensor for harsh environment. A vacuum reference cavity is sealed on top of the sensitive silicon membrane by the anodic bonding of a Pyrex™ cap. The pressure, applied on the backside, is converted in electrical signal by piezo-resistors implanted in the silicon membrane. To improve the sensor stability, a drilled Pyrex™ is bonded on the backside. As the pressure port consists of Pyrex™ and silicon, both stable in most of the chemicals, the MS7212 is suitable for media-resistive applications.

The MS7305D differential pressure sensor die is designed for low pressure sensor systems with the highest demands on resolution and accuracy. Its sensor element consists of a silicon micro-machined membrane bonded on a Pyrex™ glass support. The sensor signal is proportional to the pressure difference between back and front side of the membrane. The pressure is sensed by four implanted piezoresistors, giving a large output signal.

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MEMS Processes

Typical products