Tunable film bulk acoustic resonators and filters

A tunable film bulk acoustic resonator FBAR for forming a tunable microwave acoustic filter and a tunable oscillator for microwave applications, comprises

• at least a substrate with a substrate thickness;
• an acoustic wave isolation region with an acoustic wave isolation region thickness;
• a bottom support membrane with a bottom support membrane thickness;
• a bottom electrode of a bottom electrode material with a bottom electrode thickness;
• at least a first piezoelectric layer with a first piezoelectric layer thickness, said first piezoelectric layer is a piezoelectric semiconductor with a first conducting type and doped to a first impurity concentration, said first piezoelectric layer has a first piezoelectric layer depletion region with a first piezoelectric depletion region thickness and a first piezoelectric layer neutral region with a first piezoelectric neutral region thickness;
• a third piezoelectric layer with a third piezoelectric layer thickness, said third piezoelectric layer is a piezoelectric semiconductor with a third conducting type and doped to a third impurity concentration, said third conducting type is opposite to said first conducting type, wherein said third piezoelectric layer has a third piezoelectric layer depletion region with a third piezoelectric depletion region thickness and a third piezoelectric layer neutral region with a third piezoelectric neutral region thickness;
• and
• a top electrode of a top electrode material with a top electrode thickness,
• said first piezoelectric layer depletion region and said third piezoelectric layer depletion region forms a combined first piezoelectric active layer having a combined first piezoelectric active layer thickness, said active layer thickness is controlled and adjusted by a first DC voltage applied between said bottom electrode and top electrode to effect interactions between RF electrical signals applied between said top electrode and bottom electrode and mechanical vibrations to excite acoustic waves to achieve control, selection and adjustment of resonant frequencies of said TFBAR when forming a microwave filter.

A tunable microwave film bulk acoustic filter comprising, at least one first series tunable resonators;

• at least one second parallel tunable resonators, each pair connected at a first contact point;
• at least a first coupling capacitor and at least a second coupling capacitor for blocking of a DC voltage;
• at least a first isolation inductor for blocking of RF signals;
• at least a first DC voltage source VDC1 with a voltage value V1s applied through said first isolation inductor and across the combination of said first series resonator and second parallel resonator to establish biasing of said first series resonator and second parallel resonator and to control and adjust central frequency of resonant and transmission of an RF signal applied to a first RF input contact so that microwaves signals at and around said central frequency of resonant are allowed to propagate through said first resonators to reach an RF output contact so that central frequency of transmission of microwaves of said tunable microwave bulk acoustic filter is selected and controlled to a desired value by value of said first DC voltage source.