Effects of bottom electrodes on the orientation of AlN films and the frequency responses of resonators in AlN-based FBARs

Synthesis of c-Axis Inclined AlN Films in an Off-Center System for Shear Wave Devices

“…Therefore, a substrate which facilitates nucleation of inclined islands, or that creates conditions for inclined islands and grain growth, is favorable. In our case, the lattice mismatch between the AlN (002) plane and the Pt (111) plane is only 6.9% with nanoscale surface roughness, which leads to a large number of inclined islands, 22 meaning that columns that are aligned with the inclined net flux direction grow faster than columns in other directions due to competitive growth. The induction of c-axis inclination is facilitated by the Pt film.…”

Fabrication and analysis of ZnO thin film bulk acoustic resonators

“…Furthermore, in this study, when the thickness of each layer of FBAR was controlled at a certain level, a longer acoustic wave path had no significant impact on frequency change. Therefore, the major probable cause of this phenomenon is that the mass densities of these two kinds of bottom electrodes are related according to the acoustic wave rate [10,11], since the mass density of Mo 10,200 (kg/m 3 ) is less than that of Pt 21,400 (kg/m 3 ), and its acoustic wave rate 6290 (m/s) appears to be faster than the acoustic wave rate of Pt 4152 (m/s). Thus, the Mo bottom electrode FBAR component would naturally have a higher frequency.…”

Comparative study of c-axis AlN films sputtered on metallic surfaces

“…lack three-fold symmetry. Other authors have also achieved AlN with good quality on {110} Mo [3,5]. Therefore, it seems that the bhexagonalQ symmetry of the surface is not so indispensable to obtain AlN of good quality.…”

“…Good results have been obtained on metallic surfaces with three-or six-fold symmetry ({111} Al, {111} Pt, {00d 2} Ti, {111} Au), compatible with the three-fold symmetry of c-axis AlN [1,9]. However, AlN films of good quality have also been obtained on {110} Mo [3,5], which does not have three-or six-fold symmetry. Very good results have been reported on metallic surfaces which are stable with regard to the nitrogen plasma, such as Pt [1,6].…”

“…The fabrication of FBAR or MEMS devices requires the growth of c-axis AlN on a metallic film acting as the bottom electrode. The most commonly used metallic substrates are Al and its alloys [1,[3][4][5], Mo [3][4][5], Ti [1,3,5] and Pt [1,6], although many others have also been employed [3][4][5][7][8][9]. It is widely agreed that the nature of the surface on which AlN is deposited affects the AlN properties as much as the sputtering conditions.…”