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
• in the deposition of the piezoelectric film, a first piezoelectric film as a part of the piezoelectric film is firstly deposited 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 a second piezoelectric film as another part of the piezoelectric film is deposited on the first piezoelectric film at a second temperature at which a piezoelectric constant e31 of the second piezoelectric film becomes 10 C/m2 or more and at which when a negative voltage is applied to a top electrode film deposited on the second piezoelectric film in such a manner that an electric field of 300 kV/cm is generated between the bottom electrode film and the top electrode film, time up to when the density of a leakage current flowing through the second piezoelectric film exceeds 30 mA/cm2 becomes 5 hours or more.

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
• a piezoelectric constant e31 of the piezoelectric film is 10 C/m2 or more,
• when a negative voltage is applied to the top electrode film at a temperature of 200° C. in such a manner that an electric field of 300 kV/cm is generated between the bottom electrode film and the top electrode film, time from the start of the negative voltage application up to when the density of a leakage current flowing through the piezoelectric film exceeds 30 mA/cm2 is 5 hours or more, and
• a film stress of the piezoelectric film is 150 MPa or less.