advantage of capacitive mems accelerometers vs other technologies
TRANSCRIPT
Advantage capacitive MEMs vs other technologies
www.colibrys.com
1 3
4 6Advantage Colibrys
MEMs
5The right choice for capacitive MEMs
Compared technology
Introduction to Piezoelectric MEMs
Technology
2Introduction to Piezoresistive
MEMs Technology
Introduction to capacitive MEMs
Technology
ADVANTAGE CAPACITIVE MEMS VS OTHER TECHNOLOGIES
PIEZOELECTRIC DISPLACEMENT ACCELEROMETER:
A piezoelectric material is a crystal
Applying an electrical field on the crystal
generates deformation
Acceleration applied on sensor changes
crystal deformation.
The sensitivity of the sensor is therefore
given by the piezoelectric coefficients
Piezoelectric element
Seismic mass
Solid Base
Acc
eler
atio
n
Output
Measure forces, displacement
High temperature >120°C
PIEZOELECTRIC
Not suitable for measurement in static condition.
Poor bias stability over years Operates with the small electric
charge, and need high impedance cable for electrical interface.
Poor stability in temperature Sensitive to humidity
DISAVANTAGES ADVANTAGES
APPLICATIONS
Very high frequency range
High temperature up to 350°C
Large measuring range up to 6000g
Small dimensions
+
PIEZORESISTIVE DISPLACEMENT ACCELEROMETER:
Similar to piezoelectric materials
A change in mechanical stress results in a change of the materials resistivity.
Piezoresistor
Cantilever
Seismic mass
Acceleration
Silicon
SiO2
PIEZORESISTIVE
More complex to use (design, electrical)
Poor bias stability over years
Poor stability in temperature
Very poor non-linearity, low scale-factor (few mV/g)
Sensitive to humidity
Very high frequency range
High temperature up to 350°C
Large measuring range up to 6000g
Low hysteresis Small dimensions
Measure forces, pressure, displacement
High shock, industrial application
APPLICATIONS
DISAVANTAGES ADVANTAGES+
CAPACITIVE-BASED DISPLACEMENT ACCELEROMETERS
Capacitance is inversely proportional to the distance.
If this distance changes due to a movement of the proof mass, the capacitance changes and the change in the electrical potential between the electrodes can be measured.
- - - - - - -+ + + + ++ + +
Figure 1Applying a voltage to conductive objects causes positive and negative charges to collect on each object. This creates and electric field in the space between the objects
- --
- - --+ + + + +
+ ++ -
+ + + + ++ +
+
-
- -- - - --
- -
Figure 2Applying an alternative voltage causes the charges to move back and forth between the objects, creating and alternating current which is detected by the sensor
AccelerationSuspension
Conductive Electrode
AnchorMass
Substrate
CAPACITIVE MEMS
Inertial, Tilt, Vibration High shock, industrial
application
DISAVANTAGES ADVANTAGES
APPLICATIONS
DC measurement Good stability in temperature Good stability over years Good repeatability Easy to compensate
More complexe to use (design, electrical)
Sensitive to electromagnetic field change
+
ACCELEROMETER TECHNOLOGIES COMPARISONBandwidth
High g measurement rnage
Robustness to shock
Resolution
Non linearity
Long term stability
Sensitivity temperature stability
Bias temperature stability
Operating Temperature
DC measurement
0
0.5
1
Bandwidth
High g measurement rnage
Robustness to shock
Resolution
Non linearity
Long term stability
Sensitivity temperature stability
Bias temperature stability
Operating Temperature
DC measurement
0
0.5
1
Bandwidth
High g measurement rnage
Robustness to shock
Resolution
Non linearity
Long term stability
Sensitivity temperature stability
Bias temperature stability
Operating Temperature
DC measurement
0
0.5
1
Piezoelectric Piezoresistive
Capacitive MEMs
ACCELEROMETER TECHNOLOGIES COMPARISON
Bandwidth
High g measurement rnage
Robustness to shock
Resolution
Non linearity
Long term stability
Sensitivity temperature stability
Bias temperature stability
Operating Temperature
DC measurement
0
0.5
1
PiezoelectricPiezoresistiveCapacitive
Capacitive Piezzo
CAPACITIVE MEMS FULLFILL MAIN APPLICATION: THE RIGHT CHOICE FOR CAPACITIVE MEMS
Temperature [°C]
Acceleration [g]
Bandwidth [Hz]
-55 150
0
0
200
1500
350
6000
20000
App
licat
ion
requ
irem
ent
ADVANTAGE CAPACITIVE COLIBRYS
SFB : SILICON FUSION BONDING
STABILITY ROBUSTNESS
PROCESS
• temperature stability, repeatability
• own fab
• qualification• quality • perenity
• qualified in harsh environment
• own ASIC
• assembly patented
+ +
++
CONFIDENTIEL / April 3rd 2014 / DIRECTION
www.colibrys.com