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Laser-induced SAW Pulse Technique

puls_mp1

We use this very fast surface acoustic wave (SAW)-based measuring system with high accuracy for investigation of mechanical und structural properties of thin films, crystals and new materials as well as for evaluation of technological process parameters. Due to its reliability this method was established as a german DIN standard (DIN50992-1).

 

Samples:

There are only a few requirements on the sample: a polished surface, a size between a 15 x 10 mm2 slab and a 4 inch diameter wafer and a thickness between 0.3 mm and 5 mm. Additionally it should be opaque for UV-light (337nm) or must be covered with an absorptive thin film like Al or Ti (thickness typically 10-50nm).

Working principle:

puls_principle

 

  1. A pulsed laser beam (red) (0.5ns @ 337nm) is focused on the substrate surface by a cylindrical lens in order to excite a line-shaped (aprox. 12µm depth in propagation direction; 8mm wide) broadband SAW pulse (blue) via a thermoelastic mechanism.
  2. A piezoelectric polymer foil pressed onto the substrate by a steel wedge is used as a detector for the SAW pulse (blue)
  3. SAW propagation measurement is performed for different propagation lengths between a few mm and some cm: The pulses are sampled by a digitizing oscilloscope delivering the data for the computation of both amplitude and phase spectra (example below: pulses at minimum and at maximum distance for a single crystalline silicon sample with a free surface (orange) and with a metallized surface (magenta), respectively)
    Impulse_0mm_20mm_engl
  4. From these data set, the SAW phase velocity (see example of dispersion curves below) is derived as a function of frequency
    LPuls_Dispersion_engl
  5. The experimental dispersion curve can be used to determine material constants of both substrate and coatings by fitting the related parameters of a SAW propagation model to the SAW phase velocity curve
  6. For the given laser pulse duration and detector bandwidth the system enables measurements at frequencies up to 600MHz for usual samples with a SAW velocity range between 3000m/s and 10000m/s

Features:

  • very fast, high accuracy SAW phase velocity measurement for single crystals, bulk materials, thin layers, hard coatings etc. (relative accuracy up to 10-5)
  • angular dependent SAW phase velocity measurements for anisotropic materials
  • possibility for evaluation of layer thickness, YOUNG's modulus, POISSON ratio, mass density for substrate and thin film (number of determinable properties depends on the sample, i.e. the shape of the velocity dispersion )
  • working frequency up to 600 MHz (depends on surface quality and defects)
  • possible temperature range: -10 ... +80°C

Contact:

Dr. Hagen Schmidt
IFW Dresden e.V.
'Magnetic and acoustic resonances' (Dept. 15)
Surface Dynamics Group
P.O.Box 270116
D-01171 Dresden, Germany
phone: ++49/351/4659 278
fax: ++49/351/4659 313
e-mail: h.schmidt + @ifw-dresden.de (Sorry, but we try to prevent automatic SPAM)

For purchase requests, please see LAwave or contact Dr. Dieter Schneider at IWS Fraunhofer-Institute: schnei@iws.fhg.de
Contact


Dr. Hagen Schmidt
IFW Dresden e.V.
'Magnetic and acoustic resonances' (Dept. 15)
Surface Dynamics Group
P.O.Box 270116
D-01171 Dresden, Germany
phone: ++49/351/4659 278
fax: ++49/351/4659 313
e-mail: h.schmidt + @ifw-dresden.de

 

(Sorry, but we try to prevent automatic SPAM)