Presented at the THIC Meeting at the DoubleTree Hotel Del Mar CA on January 18, /24/00

Transcription

1 Simultaneous 5-wavelength Interferometry for Head/Media Spacing Measurement Jiasheng Zhu and Prof. F. E. Talke Center for Magnetic Recording Research University of California at San Diego 9500 Gilman Drive, La Jolla CA Phone: , FAX: /24/00 Presented at the THIC Meeting at the DoubleTree Hotel Del Mar CA on January 18, 2000

2 Simultaneous 5-wavelength Interferometry for Head/Media Spacing Measurement Jiasheng Zhu and Prof. F. E. Talke Center for Magnetic Recording Research UC, San Diego

3 Outline Motivation Implementation of simultaneous 5-wavelength interferometry Spacing measurement in a tape drive Tape asperity compliance measurement Comparison between 3- and 5-wavelength interferometry Summary

4 Motivation Measurement reliability can be further improved by using more than 3 wavelengths Simultaneous measurement is required to measure the spacing in a tape drive

5 5-wavelength interferometry Monte Carlo Error Analysis: 5 vs. 3-wavelength3 All units in nm. Spacing: 35 nm Spacing: 50 nm Spacing: 80 nm Technique Mean Std. Dev. Mean Std. Dev. Mean Std. Dev. 3-wavelength wavelength

6 Two-step sequential 5-wavelength interferometry Sequential measurement--- asperity compliance Synchronized by video frame frequency Data Acquisition PC Data Acq. PC RG T G B Parallel Out Trigger Circuit Red light 650 nm Blue light 480 nm Green light 535 nm Red light 620 nm Blue light 450 nm R G B 3-CCD Camera Head/Tape Interface Video Out Video Monitor Data acq.. in 2 steps Switch wavelengths manually: (a) 650, 535, 480 nm (b) 620, 535, 450 nm

7 Simultaneous 5-wavelength interferometry 2 possible choices for simultaneous measurement : One 3-CCD 3 camera Two 3-CCD 3 cameras data acq.. must be done in 2 steps (With a switching of wavelengths) w difficult to align the two cameras (No switching of wavelengths)

8 Simultaneous 5-wavelength interferometry Data acquisition using 3CCD camera Odd Field 1 Video Frame (1 image) + Vertical interval (1.3 ms) Even Field Sequential acquisition Simultaneous acquisition 1 Frame 1 Frame Odd Field Even Field Image 1 (650,480,535) Manual switching (1 min.) Image 2 (620,450,535) Image 1 (650,480,535) Shutter switching (1.3 ms) Image 2 (620,450,535)

9 Simultaneous 5-wavelength interferometry 5-wavelength measurement 3-wavelength 3 measurement Synchronized by video field frequency Data Acq. Acquisition PC PC R T G B Parallel Out Trigger Circuit Red light 620 nm Green light 535 nm Blue light 450 nm Red light 650 nm Green light 550 nm R G B 3-CCD Camera Head/Tape Interface Video Out Video Out Video Monitor Data acq. to 5 wavelengths is done in 1.3 ms Image 1 650,480, ms Image 2 620,450,535

10 Simultaneous 5-wavelength interferometry Physical setup Computer 3CCD camera Camera controller Triggering circuit Light sources Microscope Shutters Tape drive 5-in-1 fiber cable

11 Spacing measurement on DLT4000 tape drive Unloading Device 4π I h = A + B cos( λ φ) Loading/Unloading rod

12 Spacing measurement on DLT4000 tape drive Envelope calibration (a) Moving fringe pattern I 4πh = A + B cos( λ φ) (b) Envelope extract Upper envelope 535 nm Lower envelope Fringe moving direction

13 Spacing measurement on DLT4000 tape drive Envelope check (a) A selected contact zone I 4πh = A + B cos( λ φ) (b) Envelope check for 535 nm Upper envelope 535 nm Lower envelope Odd field(620,535,450 nm)

14 Spacing measurement on DLT4000 tape drive Spacing map of a contact zone

15 Tape asperity measurement Application in asperity compliance measurement 60 Asperity compliance of DLT4 tape 50 Spacing (nm) DLT4 tape Contact pressure (kpa)

16 Precision comparison Spacing measurement on DLT4000 drive Standard deviation in 10 measurements (spacing is averaged over 200x200 pixels) Mean spacing (nm) Std. Deviation(nm) 3-wavelength 5-wavelength 25.9 ± 29.9 ± Robustness: 5-wavelength > 3-wavelength3

17 Precision comparison Asperity compliance measurement Standard deviation of spacing in 10 measurements (spacing is averaged over 200x200 pixels) Pressure: 9 psi Mean spacing (nm) Std. Deviation(nm) 3-wavelength 5-wavelength 36.9 ± 37.7 ± Robustness: 5-wavelength > 3-wavelength3

18 Summary Implemented simultaneous 5 wavelength interferometry Measurement accuracy is better with 5 wavelengths than with 3 wavelengths