Lamb wave device
There is provided a lamb wave device with small variations in frequency, the device including: a piezoelectric thin film; an IDT electrode which is provided on a main surface of the piezoelectric thin film; and a support structure which supports a laminate of the IDT electrode and the piezoelectric thin film, and is formed with a cavity that isolates the laminate, wherein a film thickness h of the piezoelectric thin film and a pitch p of a finger of the IDT electrode are selected such that a lamb wave is excited at a target frequency, the lamb wave making dispersibility of a sonic velocity v with respect to the film thickness h of the piezoelectric thin film small.
1. A lamb wave device, comprising:
a piezoelectric thin film;
an IDT electrode which is provided on a main surface of said piezoelectric thin film; and
a support structure which supports a laminate of said piezoelectric thin film and said IDT electrode, wherein
a film thickness h of said piezoelectric thin film and a pitch p of a finger of said IDT electrode are selected such that a lamb wave, with which an absolute value of a change coefficient Δv/Δ (h/λ) of a sonic velocity v with respect to a ratio h/λ of said film thickness h of said piezoelectric thin film to a wavelength λ is not larger than 2000 m/s, is excited at a target frequency.
2. The lamb wave device according to claim 1 , wherein a vibration mode of the lamb wave is an S 0 mode.
3. The lamb wave device according to claim 1 , wherein
said support structure includes:
a support substrate; and
a support film which bonds said support substrate and said laminate, and is also formed with a cavity that isolates an excitation section of said laminate from said support substrate, and wherein
an orientation of said piezoelectric thin film is selected such that an etching rate of the main surface on said support structure side of said piezoelectric thin film to a solution containing hydrogen fluoride or a gas containing hydrogen fluoride at 65° C. is not larger than one half of that of the main surface on said support substrate side of said support film.
4. The lamb wave device according to claim 3 , wherein the orientation of said piezoelectric thin film is selected such that the etching rate of the main surface on said support structure side of said piezoelectric thin film to the solution containing hydrogen fluoride or the gas containing hydrogen fluoride at 65° C. is not larger than one twentieth of that of the main surface on said support substrate side of said support film.
5. The lamb wave device according to claim 1 , wherein
said support structure includes
a support substrate, and wherein
an orientation of said piezoelectric thin film is selected such that an etching rate of the main surface on said support structure side of said piezoelectric thin film to a solution containing hydrogen fluoride or a gas containing hydrogen fluoride at 65° C. is not larger than one half of that of the main surface on the opposite side to said piezoelectric thin film side of said support substrate.
6. The lamb wave device according to claim 5 , wherein the orientation of said piezoelectric thin film is selected such that the etching rate of the main surface on said support structure side of said piezoelectric thin film to the solution containing hydrogen fluoride or the gas containing hydrogen fluoride at 65° C. is not larger than one twentieth of that of the main surface on the opposite side to said piezoelectric thin film side of said support substrate.