Stress-sensitivity of wafer-level packaged SAW delay lines

This paper presents the investigation of the influence of wafer-level packaging (WLP) on the stress-sensitivity of 100 and 200 MHz delay lines aimed to wireless sensing of stresses. The devices were fabricated on YXl/128° cut of lithium niobate. The investigated WLP achieves the assembly of two wafers by a 50µm-thick layer of SU-8 photoresist. The delay line is micro-machined on top of the first wafer while the second wafer realizes the function of protective cap in a way that should not be detrimental to the stress-sensitivity of the device. The paper gives a comparison between the theoretical and experimental phase sensitivity of both packaged and raw devices submitted to a three-points bending test.