Variable capacitance element and tunable filter

[0083]A buffer layer 3 having a cubic crystal structure and formed of a Pt(111) film was deposited in a thickness of 100 nm on a piezoelectric substrate 2 formed of 15° Y cut LiNbO3 through sputtering using an Ar gas at a substrate temperature of 400° C. A dielectric layer 4 formed of BaSrTiO3 was then formed on the buffer layer 3 through sputtering at a temperature of 700° C. A second electrode 5 formed of Pt was then formed as a film in a thickness of 200 nm on the dielectric layer 4 through sputtering to obtain a variable capacitance element 1. Relationships between a dielectric constant and an applied voltage and between tan δ and the applied voltage in this variable capacitance element are illustrated in FIG. 3.

[0084]FIG. 3 clearly reveals that as the applied voltage changed, the relative dielectric constant and tan δ also changed. The rate of change in the relative dielectric constant, that is, the ratio of the highest relative dielectric constant to the lowest relative dielec...

[0088]Similarly to Example 1, but a Pt(200) film having a cubic crystal structure was deposited as the buffer layer 3. The deposition conditions were as follows. The buffer layer 3 was deposited in a film thickness of 100 nm through sputtering using an Ar gas at a substrate temperature of 700° C.

[0089]Other points were the same as in those in Example 1.

[0090]Relationships between a relative dielectric constant and an applied voltage and between tan δ and the applied voltage in the variable capacitance element obtained through Example 2 are illustrated in FIG. 4. FIG. 4 clearly reveals that the relative dielectric constant and tan δ changed more greatly than in Example 1 as the applied voltage changed. The rate of change in the relative dielectric constant, which is a ratio of the highest relative dielectric constant to the lowest relative dielectric constant within a range where the applied voltage is between −5 V and +5 V, was 4.17. Accordingly, it was discovered that a variable ra...

[0092]The buffer layer 3 having a cubic crystal structure and including the Pt(111) film was formed on the piezoelectric substrate that is formed of −1° Y cut LiNbO3, and a variable capacitance element was obtained thereafter in a similar manner to Example 1. The Pt(111) film was deposited in a film thickness of 100 nm through sputtering using an Ar gas at a substrate temperature of 400° C.

[0093]Relationships between a relative dielectric constant and an applied voltage and between tan δ and the applied voltage in the variable capacitance element obtained through Example 3 are illustrated in FIG. 8. FIG. 8 clearly reveals that as the applied voltage changed, the relative dielectric constant and tan δ also changed.

[0094]Further, the rate of change in the relative dielectric constant within a range where the applied voltage is between −5 V and +5 V was 3.34, which was greater than in Example 1 but smaller than in Example 2.

[0095]As for the variable capacitance element of Example 3, th...