Laser probe system for 5 GHz SAW/BAW devices

In 2008, the authors reported development of a type of the laser probe system based on the Sagnac interferometer for the diagnosis of radio frequency (RF) surface and bulk acoustic wave (SAW/BAW) devices. This paper describes extension of its maximum operation frequency to the low SHF (several GHz) range without performance degradation. First, electronic components used in the system were re-examined, and some of them were replaced with appropriate ones. Second, a miniature wafer probing system was newly developed for the operation under a high magnification (×100) lens with a tiny working distance (~3.4 mm). This enables us to avoid wire-bonding between a device under the test and a printed circuit board; wire inductance gives large impact to the device characteristic in the GHz range. RF SAW/BAW devices operating in 5 GHz were characterized by the laser probe, and its effectiveness was demonstrated.