This paper describes the development of a phasesensitive laser probe with fast mechanical scan for RF surface and bulk acoustic wave (SAW/BAW) devices. The Sagnac interferometer composed of micro-optic elements was introduced for the selective detection of RF vertical motion associated with RF SAW/BAW propagation and vibration. A high-pass characteristic of the interferometer makes the measurement very insensitive to low-frequency vibration. This feature allows us to apply the fast mechanical scan to the interferometric measurement without badly sacrificing its SNR and spatial resolution. The system was applied to the visualization of a field pattern on the vibrating surface of an RF BAW resonator operating in the 2 GHz range. The field pattern was obtained in 17 min as a 2-D image (500 × 750 pixel with 0.4 μm resolution and SNR of 40 dB). The system was also applied to the characterization of an RF SAW resonator operating in the 1 GHz range, and the applicability of the system was demonstrated.

This paper describes the development of a new laser probe for radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices. The Sagnac interferometer was introduced for the selective detection of RF vertical motion associated with RF SAW/BAW propagation and vibration. A high-pass characteristic of the interferometer makes the measurement very insusceptible to the low-frequency vibration. Combining such a feature with *he advanced scanning technique and optimized detection system, we were successfully able to maximize the scanning speed without sacrificing the signal-tonoise ratio and sensitivity of the measurement. The system was applied to the characterization of RF SAW/BAW devices and showed its effectiveness in device diagnosis. INDEX TERMS -SAGNAC INTERFEROMETER, LASER PROBE, SURFACE ACOUSTIC WAVE, BULK ACOUSTIC WAVE978-1-4244-1780-3/08/$25.00

This paper describes the application of the developed fast-scanning laser probe system to the diagnosis of frequency dependence of lateral energy leakage occurring in RF bulk acoustic wave (BAW) devices. According to wavenumber domain analyses, dispersion relation for the device under test is derived, the leakage behaviors at different frequencies are shown as images, and energy of each lateral mode is evaluated quantitatively. The cause of the lateral energy leakage and its frequency dependence are discussed. It is shown that the cause of lateral energy leakage is the higher order transverse modes which are not excited at frequency higher than a cut-off frequency ( f c ) for the longitudinal extension mode. It is demonstrated that by using this laser probe system, the lateral energy leakage variation upon frequency can be seen intuitively, and the underlying mechanism for the leakage can be analyzed and explained clearly.

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