Membrane-type longitudinal mode resonator

A microacoustic resonator comprising:

• a dielectric layer comprising a first surface and a second surface opposite the first surface;
• a piezoelectric layer having a first surface and a second surface opposite the first surface, wherein the piezoelectric layer is disposed on the first surface of the dielectric layer with the second surface of the piezoelectric layer facing the first surface of the dielectric layer, and wherein the piezoelectric layer is LiNbO3 having a crystallographic orientation defined by a set of Euler angles of λ=90+/−1.5°, μ=90+/−1.5°, θ=40+/−1.5°;
• and
• an electrode structure comprising an interdigital transducer disposed on the first surface of the piezoelectric layer,
• wherein the second surface of the dielectric layer faces an air gap.

A method of fabricating an microacoustic resonator, the method comprising:

• providing a piezoelectric layer having a first surface and a second surface opposite the first surface wherein the piezoelectric layer has an orientation configured to excite a longitudinal mode in the microacoustic resonator;
• depositing a temperature compensation layer on the first surface of the piezoelectric layer;
• structuring a sacrificial layer on the temperature compensation layer;
• depositing an intermediate layer over the sacrificial layer and the temperature compensation layer;
• bonding a bulk substrate on the intermediate layer;
• grinding and polishing the second surface the piezoelectric layer to a target thickness for the piezoelectric layer;
• fabricating an interdigital transducer on the second surface of the piezoelectric layer;
• forming a passivation layer over the interdigital transducer and the second surface of the piezoelectric layer;
• etching a release hole through the passivation layer, the piezoelectric layer, and the temperature compensation layer to the sacrificial layer;
• and
• release etching the sacrificial layer to form an air gap against the temperature compensation layer opposite the interdigital transducer.

A method comprising:

• providing a piezoelectric layer having a first surface and a second surface opposite the first surface, wherein the piezoelectric layer has an orientation configured to excite a longitudinal mode in a microacoustic resonator and configured to suppress a shear horizontal mode;
• depositing a temperature compensation layer on the first surface of the piezoelectric layer;
• forming a first passivation layer on the temperature compensation layer;
• bonding a bulk substrate on the first passivation layer;
• grinding and polishing the second surface of the piezoelectric layer to a target thickness for the piezoelectric layer;
• fabricating an interdigital transducer on the second surface of the piezoelectric layer;
• forming a second passivation layer over the interdigital transducer and the second surface of the piezoelectric layer;
• and
• forming an air gap through the bulk substrate to the first passivation layer in an area opposite the interdigital transducer.