View
2
Download
0
Category
Preview:
Citation preview
MEMS: Characterization
Characterization of MEMS Devices
Prasanna S. GandhiAssistant Professor,Department of Mechanical Engineering,Indian Institute of Technology, Bombay,
Recap
Fabrication of MEMSConventional VLSI fabricationNonconventional methods
Design and analysis of MEMS
Characterization of MEMS
Today’s Class
Why characterization?? Why optics?? Principles of optics useful in characterizationTools for optical characterization
ProfilometerMicroscope
Methods for characterization of mechanical propertiesSPM based tools: STM and AFM
Why Characterization?
Material properties change at micro-scale, different from bulk properties due to grain boundary effectSuccessful design/manufacturing of MEMS devices need reliable knowledge of MEMS material propertiesVerification of design and validation of models proposedCalibration of devices and signalsElectronic analysis: noise vs signalResearch various new effects: example Biosensor devices
Why Optics for Characterization?
Noninvasive techniqueDoes not disturb sensitive MEMS deviceVery high resolutions possibleHigher measurement range possibleSeveral optical phenomenon can be made use of
Principles of Optics
Wave nature of light
InterferenceWave divisionAmplitude division
Diffraction + Diffr. gratingMoire interferenceHolography
Principles of Optics
InterferenceWave divisionAmplitude division
Beam splitter
Michaelsons InterferometerAnalysis??
Young’s double slit
Referencemirror
Principles of OpticsInterference
Testdevice
Mach-Zehnder Interferometer
Used for laser-doppler vibrometer
Polarization
Concept of polarization of light
Principles of OpticsInterference
Febry-Parot Interferometer
Partially Reflecting Mirrors
Lens
Screen
Source
Another method for interference
Principles of OpticsDiffraction grating
Diffraction Fringes
Source
Diffraction Grating
Diffraction Grating Fringes
Principles of OpticsMoire Fringes
Specimen Grating
FringesMaster Grating
Rotational Mismatch Translational Mismatch
Profilometer
Laser-photodetectorcombinationAs the scanning of sample is done the laser spot moves on the photodetector (PSD) because of bending of cantilever over asperitiesThe movement results in differential voltage output from the PSD
Profilometer principle
BA
D C
ProfilometerAnother technology
Sensor Camera
Spot size [µm] 1,5 Integrated in-axis camera
Vertical resolution [µm] 0,020 Field of view [mm]
0,6x0,8
Measurement frequency [Hz] 10,000
Stand off [mm] 2 or 5 Laser diode Class I
Linearity [%] <0,08 Wavelength [nm] 630 copyright © Solarius Development Inc. 2003-04
ProfilometerAnother technology
copyright © Solarius Development Inc. 2003-04
Sensor Camera
Spot size [µm] 2 Integrated off-axis camera
Vertical resolution [µm] 0,1 Magnification 200x
Measurement frequency [Hz] 1400
Stand off [mm] 5 Laser Class II
Linearity [%] ±0.5 Wavelength [nm] 670
Microscope for Measurement of Dimensions
Taking image on CCD camera and processing with precalibration for measurement of MEMS device dimensionsVarious types of microscopesGrating used in CD ROM
Limitations of Microscope
Q: is it possible to increase the magnification of microscope indefinitely and expect improved resolution??
Minimum resolution possible is comparable with wavelength of light
SPM: STM and AFM
STM invented in early 80s by Binnigand Rohrer.Real limitations: only used to image conducting materials. Cannot distinguish between atoms of different elements within a compound material.
Atomic Force Microscope
AFM Image
Kriptan- polymer surface characteristics using AFM
Conclusions
Various optical principles Characterization tools
MicroscopeEllipsometerProfilometer
Various methods of characterization of mechanical properties
Recommended