Deposition of Highly Oriented Ta₂O₅ Piezoelectric Thin Films on Silicon for Fabricating Film Bulk Acoustic Resonator Structure by RF Magnetron Sputtering

Abstract

X -axis-oriented tantalum pentoxide (Ta 2 O 5 ) piezoelectric thin films were deposited on Si using an RF magnetron sputtering system with the aim of obtaining a film bulk acoustic resonator (FBAR) structure. First, the degree of orientation and the coupling factor K 2 for the surface acoustic wave were evaluated. The K 2 of the first mode of the Ta 2 O 5 thin film deposited on the unprocessed Si(100) was almost the same as that of the zeroth mode of the Ta 2 O 5 thin film/SiO 2 glass substrate for a similar thickness. However, the K 2 of the Ta 2 O 5 thin film deposited on a silicon oxide layer formed on the Si was small because the (200) plane spacing slightly increased. Then, a process in which the Ta 2 O 5 thin film itself was used as an etch stop layer was adopted and an FBAR structure was fabricated. The resonance response corresponding to a longitudinal bulk wave was observed. #

Evaluation of Piezoelectric Ta2O5 Thin Films Deposited on Sapphire Substrates

“…Piezoelectric thin films with high coupling, high stability, low loss, and high phase velocity are required for the development of high-performance piezoelectric devices, such as surface acoustic wave (SAW) and film bulk acoustic resonator (FBAR) devices. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] An X-axis-oriented Ta 2 O 5 piezoelectric thin film is a relatively new material developed by Nakagawa and coworkers and has a strong piezoelectric property similar to that of ZnO thin films and a high dielectric constant. [16][17][18][19][20][21][22] In the deposition of X-axis-oriented Ta 2 O 5 piezoelectric thin films using an RF magnetron sputtering system with a long-throw sputter (LTS) cathode, Kakio, one of the authors, and colleagues found the optimum deposition conditions for obtaining a strong preferential (200) orientation and a high electromechanical coupling factor K 2 for a Rayleigh-type SAW (R-SAW) on synthetic fused silica (SiO 2 ) glass substrates, 23) and demonstrated the application of the optimum deposition conditions to the fabrication of an FBAR with a Si substrate.…”

“…[16][17][18][19][20][21][22] In the deposition of X-axis-oriented Ta 2 O 5 piezoelectric thin films using an RF magnetron sputtering system with a long-throw sputter (LTS) cathode, Kakio, one of the authors, and colleagues found the optimum deposition conditions for obtaining a strong preferential (200) orientation and a high electromechanical coupling factor K 2 for a Rayleigh-type SAW (R-SAW) on synthetic fused silica (SiO 2 ) glass substrates, 23) and demonstrated the application of the optimum deposition conditions to the fabrication of an FBAR with a Si substrate. 1) However, there is a problem in that a large propagation loss for the R-SAW or bulk wave occurs in the oriented Ta 2 O 5 thin films.…”

Deposition and evaluation of Ta2O5 piezoelectric thin film on Pt crystal film

“…24) Moreover, a film bulk acoustic resonator (FBAR) comprising a Ta 2 O 5 thin film and a Si support substrate has been fabricated. 25) However, a large propagation loss (PL) of R-SAWs or BAWs was observed in X-axis-oriented Ta 2 O 5 thin films. The large PL is considered to be due to the crystal grain boundaries inside the thin films.…”

Surface Acoustic Wave Properties of Amorphous Ta2O5 and Nb2O5 Thin Films Prepared by Radio Frequency Sputtering

“…6) However, optimization of the deposition conditions to reduce the propagation loss and decrease temperature coefficient is required. Similar optimization is also required for an X-axis-oriented Ta 2 O 5 piezoelectric thin film, which can be deposited at a substrate temperature higher than 400 C. [7][8][9][10][11][12][13][14][15] Moreover, the elastic constants of amorphous Ta 2 O 5 thin films have not yet been reported, which are required for the design of SAW devices.…”