Sree Vidyanikethan Engineering College

Rotational Capacitive Micromachined

Ultrasonic TransducersGuided byMrs.A.Yasmine Begum

ByD.Sai lohith11121A1017

Contents

Transducers- Acostic transducersWhat are MEMS?Difference between normal UT and CMUTCMUT- Structure, principle, fabricationComparison of piezo-electric and CMUTRotational CMUT- Fabrication,experiment and it’s resultsApplicationsconclusionReferences

Acoustic TransducersUltrasonic transducers

What is the difference between normal ultrasonic transducer and CMUT?

• Piezoelectric property• Capacitive transducer

Where ,C is the capacitance, ε0 is the permittivity of free space constant, K is the dielectric constant of the material in the gap, A is the area of the plates, and d is the distance between the plates.

where S is the area of capacitor plates, V is the applied bias voltage,  is the permittivity of free space between capacitor plates, and d is the distance between the capacitor plates. 

CMUT structure

Operation priciple

Fabrication

• Sacrificial release process• Wafer bonding,etc

Step 1: Starting waferStep 2: Deposition of sacrificial layerStep 3: Deposition of structural layerStep 4: Pattern the top polysilicon layerStep 5: Deposit a second sacrificial layerStep 6: Pattern and Etch the sacrificial layersStep 7: Deposit polysilicon structural layer.Step 8: Pattern Polysilicon.Step 9: Sacrificial layer removal and freeing of structures

Why we are going to CMUT over Piezoelectric Ultrasonic transducer?

batch-production wide bandwidth easier to fabricate integration with supporting electronic

circuits Wider temperature range

Why we are going to Rotational CMUT instead of normal CMUT?

• no internal damping • negligible thermal mechanical noise • enables lower resonant frequencies• higher compliance to acoustic signals• frequency response up to 200 kHz

Rotational Capacitive Micromachined UltrasonicTransducers

Sacrificial release Process

SEMs

Applications

2D and 3D arraysIntravascular ultrasound (IVUS)Second-harmonic imagingHydrophonesPhoto-Acostic imaging

ConclusionConclusion

Rigorous modeling and acoustic characterization of the rotational cMUT

as does a detailed comparison of the device technology against other airborne ultrasonic transducers

1 μm deflection, implying that at least 10× higher compliance diaphragms are realizable by use of the beam-coupled design.

References

Some referable websites about cMUTs

• http://www.kyg.stanford.edu/khuriyakub/opencms/en/research/cmuts/Principles/

• http://www.microfab.de/mems/ultrasonictransducers/cmut.html

• http://www-kyg.stanford.edu/khuriyakub/opencms/en/research/cmuts/general/index.html

• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3158704/

• http://www-old.me.gatech.edu/mist/cmut.htm

Thank you