Self-Heating and Quality Factor: Thermal Challenges in Aluminum Scandium Nitride Bulk Acoustic Wave Resonators

Understanding the thermal properties of piezoelectric thin films is essential in studying the performance and ultimate dissipation limits of bulk acoustic wave resonators. Here, we present the experimental and modeled results of thermal conductivity of the in-demand piezoelectric material aluminum scandium nitride (Al 1-x Sc x N), with x = Sc/(Sc+Al) ratio. We construct the three-dimensional (3D) finite-element modeling (FEM) of a back-side etched thin-film bulk acoustic wave resonator (FBAR) with aluminum nitride (AlN) and Al 0.7 Sc 0.3 N thin films. Comparison reveals a 26% more temperature rise in Al 0.7 Sc 0.3 N FBAR with equal input surface heat density of 2 W/mm2. The trend is consistent with the drastic decrease of thermal conductivity with increasing x in Al 1-x S cx N. Consequently, as we study the upper limit of the frequency (f), quality factor (Q) product (f. Q) under phonon interactions, Al 1-x S cx N exhibits a greater amount of degradation due to self-heating. This work reports the first comparison of thermal properties of AlN and Al 1-x S cx N resonators, critical in material selection for resonator operation under high power levels.