Characterization of MEMS Devices

Transcription

1 MEMS: Characterization Characterization of MEMS Devices Prasanna S. Gandhi Assistant Professor, Department of Mechanical Engineering, Indian Institute of Technology, Bombay,

2 Recap Fabrication of MEMS Conventional VLSI fabrication Nonconventional methods Design and analysis of MEMS Characterization of MEMS

3 Today s Class Why characterization?? Why optics?? Principles of optics useful in characterization Tools for optical characterization Profilometer Microscope Methods for characterization of mechanical properties SPM based tools: STM and AFM

4 Why Characterization? Material properties change at micro-scale, different from bulk properties due to grain boundary effect Successful design/manufacturing of MEMS devices need reliable knowledge of MEMS material properties Verification of design and validation of models proposed Calibration of devices and signals Electronic analysis: noise vs signal Research various new effects: example Biosensor devices

5 Why Optics for Characterization? Noninvasive technique Does not disturb sensitive MEMS device Very high resolutions possible Higher measurement range possible Several optical phenomenon can be made use of

6 Principles of Optics Wave nature of light Interference Wave division Amplitude division Diffraction + Diffr. grating Moire interference Holography

7 Principles of Optics Interference Wave division Amplitude division Beam splitter Young s double slit Reference mirror Michaelsons Interferometer Analysis??

8 Principles of Optics Interference Test device Mach-Zehnder Interferometer Used for laser-doppler vibrometer

9 Polarization Concept of polarization of light

10 Principles of Optics Interference Source Partially Reflecting Lens Mirrors Febry-Parot Interferometer Screen Another method for interference

11 Diffraction Grating Fringes Principles of Optics Diffraction grating Source Diffraction Fringes Diffraction Grating

12 Principles of Optics Moire Fringes Specimen Grating Fringes Master Grating Rotational Mismatch Translational Mismatch

13 Profilometer Profilometer principle A B D C Laser-photodetector combination As the scanning of sample is done the laser spot moves on the photodetector (PSD) because of bending of cantilever over asperities The movement results in differential voltage output from the PSD

14 Profilometer Another 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 copyright Solarius Development Inc Stand off [mm] 2 or 5 Laser diode Class I Linearity [%] <0,08 Wavelength [nm] 630

15 Profilometer Another technology Sensor Camera copyright Solarius Development Inc 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

16 Microscope for Measurement of Dimensions Grating used in CD ROM Taking image on CCD camera and processing with precalibration for measurement of MEMS device dimensions Various types of microscopes

17 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

18 SPM: STM and AFM STM invented in early 80s by Binnig and Rohrer. Real limitations: only used to image conducting materials. Cannot distinguish between atoms of different elements within a compound material.

19 Atomic Force Microscope

20 AFM Image Kriptan- polymer surface characteristics using AFM

21 Conclusions Various optical principles Characterization tools Microscope Ellipsometer Profilometer Various methods of characterization of mechanical properties