Efficient and Stable Acoustical Coupling for GHz Subsurface Probe Microscopy

Efficient and Stable Acoustical Coupling for GHz Subsurface Probe Microscopy

Quesson, B.A.J.
van Neer, P.L.M.J.
van Riel, M.C.J.M.
van Es, M.H.
Piras, D.
Hatakeyama, K.
Mohtashami, A.
Navarro, V.
Duivenvoorde, T.
Sadeghian Marnani, H.

2018

Many techniques are under development for the detection of subsurface defects or cracks. One such method is GHz subsurface probe microscopy (GHz SSPM). Here, modulated GHz elastic waves are transmitted through the bottom of a sample. The waves are scattered by buried features and detected using the probe of an atomic force microscope (AFM), which scans the top of the sample. To ensure that sufficient acoustical energy reaches the sample surface, an efficient and stable acoustical and mechanical coupling between the transducer and the sample is essential. As the GHz excitation is continuous, the attenuation and the standing wave patterns lead to a requirement on the coupling layer thickness and its stability in the micrometer and nanometer order, respectively. This study describes the design and modelling of a clamp and the associated acoustic measurement method to monitor and control the coupling thickness with nanometer accuracy. A 1 GHz transducer transmitted modulated elastic waves through the bottom of a sample. The out-of-plane sample surface displacement was read-out with an AFM. Samples typically measured 10xl Oxl mm3, The coupling layer was water. Evaporation of the coupling layer was counteracted using a basin and the capillary action. The combined acoustic behavior of the piezo, delay line, coupling layer and sample was modeled using the KLM model. The time dependent behavior of the coupling layer liquid was modeled analytically. The coupling layer thickness was controlled using the custom designed clamp and monitored in real-time using pulse-echo measurements and custom signal processing based on detecting the acoustic resonances of the transducer-coupling layer-sample stack. The acoustic measurements showed that the clamp allowed for stable coupling layers (< 1 um in thickness with 3o variations < 8 nm) over a span of hours, allowing for successful BA GHz SSPM measurements.

Acoustical coupling
Atomic force microscopy
GHz excitation
Scanning probe microscopy
Stability analysis
Subsurface
Acoustic measuring instruments
Acoustic variables measurement
Atomic force microscopy
Elastic waves
Scanning probe microscopy
Transducers
Mechanical coupling
Monitor and control
Pulse echo measurements
Stability analysis
Standing wave patterns
Time dependent behavior
Thickness measurement

http://resolver.tudelft.nl/uuid:5c00fc7b-4ea6-4f49-81e9-eba4e1c43197

861883

IEEE Computer Society

9781538634257

1948-5719

IEEE International Ultrasonics Symposium, IUS 2018, 22-25 October 2018, Kobe, Japan

8579802

conference paper