Piezoelectric stack, method for manufacturing piezoelectric stack, and piezoelectric element

A method for manufacturing a piezoelectric stack, the method comprising:

• depositing a bottom electrode film on a substrate;
• and
• depositing a piezoelectric film on the bottom electrode film, the piezoelectric film being constituted by an alkali niobium oxide containing potassium, sodium, niobium, and oxygen, wherein
• the depositing of the piezoelectric film involves firstly depositing a first piezoelectric film as a part of the piezoelectric film at a first temperature at which a (001) orientation ratio becomes 95% or more and a film stress becomes 100 MPa or less, and then depositing a second piezoelectric film as another part of the piezoelectric film on the first piezoelectric film at a second temperature at which the second piezoelectric film becomes a spontaneous polarization film.

A piezoelectric element comprising:

• a substrate;
• a bottom electrode film deposited on the substrate;
• a piezoelectric film deposited on the bottom electrode film, the piezoelectric film being constituted by an alkali niobium oxide containing potassium, sodium, niobium and oxygen;
• and
• a top electrode film deposited on the piezoelectric film, wherein
• in a hysteresis curve representing a correlation between a polarization amount and an applied electric field, a median value of a coercive electric field between a coercive electric field EC+ on a positive electric field side and a coercive electric field EC− on a negative electric field side is a positive value, the hysteresis curve being obtained by applying an electric field to the piezoelectric film under a predetermined condition,
• a relative dielectric constant of the piezoelectric film is 490 or less, and
• a film stress of the piezoelectric film is 150 MPa or less.