TWO SEGMENTS CANTILEVER BEAM MASS SENSOR WITH CAPACITIVE ACTUATION AND READOUT

Gabriel Vidal Álvarez

NiPS Workshop: Noise in dynamical systems at the micro and nanoscale, August 6‐8, 2010 

MEMS Applications 2

  Sensors (Pressure, acceleration, mass, etc.)   Actuators (DLP, inkjet printers, etc.)   RF Applications (Oscillators, filters, etc.)   Energy harvesting

Mass Sensing 3

Dynamic mass sensing is based on the measure of the frequency shifts in the resonant frequencies of a mechanical structure due an added mass.

Mass Sensing

Responsivity

Sensitivity

Dynamic Range

4

Frequency resolution

Mass resolution

Mass Sensing 5

State of the art

Quartz crystals microbalances have very good noise performance

MEMS mass sensors have ultrasmall mass sensitivities

6

State of the art

Mass of a gold atom ≈ 0.327 zg Mass of an hydrogen atom ≈ 0.00166 zg

7

Mass  Sensor  Type  of  Mass  Sensor  and  Experimental  

Condi6ons  Mass  Resolu6on  (zg)  

Jensen  2008    Double-­‐walled  carbon  nanotube  can0lever  beam  in  ultra  high  vacuum  and  at  room  temperature  

0.13  

Yang  2006    Magnetomo0ve  driven  and  detected  cc-­‐beam  

opera0ng  in  high  vacuum  and  at  4.7  K  7  

Ekinci  2004    Magnetomo0ve  driven  and  detected  cc-­‐beam  opera0ng  in  ultra  high  vacuum  and  at  17  K  

2530  

Verd  2008    Capaci0ve  driven  and  detected  CMOS  metal  

can0lever  beam  in  air  and  at  room  temperature  24000  

Lavrik  2003    Photothermal  actuated  and  interferometric  readout  silicon  can0lever  opera0ng  in  air  at  room  temperature  and  atmospheric  pressure  

5500000  

The idea

First segment as transducing part

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Second segment as sensing part

Euler-Bernoulli Beam Theory 9

Energetic approach to model beam-like structures

Euler-Bernoulli equation

Two Segments Cantilever Beam Mass Sensor Mechanical Behaviour

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Two Segments Cantilever Beam Mass Sensor Mechanical Behaviour

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Two Segments Cantilever Beam Mass Sensor Mechanical Behaviour

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Two Segments Cantilever Beam Mass Sensor Mechanical Behaviour

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Two Segments Cantilever Beam Mass Sensor Mechanical Behaviour

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Choosing the appropriate ratio between segments, the two segments cantilever beam improves the sensitivity of the first segment standalone.

The maximum attainable sensitivity is a little bit lower than the attainable with the second segment acting independently.

MEMS Modeling 15

MEMS Modeling 16

Capacitive Transduction 17

Capacitive Transduction 18

Two-Port configuration

Noise in MEMS 19

Thermomechanical noise is related to the Brownian motion of the molecules surrounding the mechanical structure of the MEMS device

Noise in MEMS 20

Phase noise

Two Segments Cantilever Beam Mass Sensor

21

Mass  Sensor  Mechanical  Sensi6vity  

(zg/Hz)  Two-­‐Port  Sensi6vity  (zg/

Hz)  Frequency  Resolu6on  (Hz)   Mass  Resolu6on  (zg)  

Two  Segments  Can?lever  Beam  

1.15   6.07   0.01   0.05  

First  Segment  Standalone  Can?lever  Beam  

1687.52   8881.7   0.0002   1.54  

Second  Segment  Standalone  Can?lever  

Beam  1.095   5.76   0.71   4.08  

Conclusions 22

  With a two segments cantilever beam we can obtain very good mass sensitivities.

  Thermomechanical noise has less importance for big devices than for smaller ones. The frequency resolution is better for a “big” two segments cantilever beam than for small simple cantilever beam.

  In conclusion, we can attain better mass resolutions with capacitive transduction with a two segments cantilever beam than with other structures.