4F-5 An Improvement of the Picosecond Ultrasonic Technique Based on a Tunable Laser: Application to Bulk Acoustic Wave Resonator Characterizations

The control of the frequency is a challenging question for the mass production of bulk acoustic wave (BAW) filters. It passes through a precise control of mechanical properties of the active layer but also of the thicknesses of the whole stack. But performing mechanical measurements at such a scale is not so easy and we may say that BAW resonators constitute a challenging object for metrology. Picosecond ultrasonics is an optical technique which uses ultrashort optical pulses to generate and detect very short acoustic pulses. It is a non-contact and non-destructive technique that is well adapted to mechanical measurements in thin films. Here we show that this technique is a well-adapted tool for the control of BAW technology. Furthermore, we propose an improvement of this technique based on the use of a tunable laser which offers two major improvements of the technique, the first being the number of measured parameters and the second being the measurement precision