NONDESTRUCTIVE EVALUATION OF SAW DEVICES USING A HIGH-RESOLUTION OPTICAL-DETECTION TECHNIQUE

A nondestructive high-resolution technique for the optical detection o f surface acoustic wave (SAW) devices is presented. The probing techni que allows for the measurement of the phase and amplitude of microacou stic fields and waves of SAW components in operation. The phase veloci ty which is a fundamental design parameter in SAW technology can be de termined directly from the measurements with a relative accuracy of up to 1.5 . 10(-5). The measurement system incorporates a mode-locked pi cosecond laser, harmonic mixing, and coherent detection. Dynamic range and minimum detectable surface displacement are 50 dB and 1 pm/root H z, respectively. We present new experimental results of microacoustic wave propagation phenomena including anisotropic phase velocity, diffr action, and field distribution in SAW interdigital transducers and res onators. Up to now, the SAW designer has to rely only on the character ization of the electrical terminal behavior performed mostly by S para meter measurements. We demonstrate that by using highly accurate laser probing the designer is for the first time able to get a correct phys ical insight of the functioning of SAW components. This is extremely b eneficial and adds a basically new tool to the SAW design procedure.