Transversely-excited film bulk acoustic resonator with thick dielectric layer for improved coupling

A mass sensor device comprising:

• a substrate having a surface;
• a piezoelectric plate having front and back surfaces;
• an interdigital transducer (IDT) at the front surface of the piezoelectric plate;
• a first half-lambda dielectric layer at the front surface of the piezoelectric plate, such that the first half-lambda dielectric layer at least partially covers the IDT at the front surface of the piezoelectric plate;
• a second half-lambda dielectric layer at the back surface of the piezoelectric plate;
• and
• an acoustic Bragg reflector sandwiched between the surface of the substrate and the back surface of the piezoelectric plate, the acoustic Bragg reflector configured to reflect a primary acoustic mode, wherein a thickness td of each of the first and second half-lambda dielectric layers is defined as 0.85λ0,d≤2td≤1.15λ0,d, where λ0,d is a wavelength of a fundamental shear bulk acoustic wave resonance in the respective first and second half-lambda dielectric layers, wherein the thickness td of the first and second half-lambda dielectric layers is in a direction normal to the surface of the substrate,
• wherein the acoustic Bragg reflector comprises alternating layers of a first material and a second material having a higher acoustic impedance than the first material, and
• wherein a top layer of the second material of the alternating layers of the acoustic Bragg reflector contacts the second half-lambda dielectric layer.

A bulk acoustic resonator comprising:

• a substrate having a surface;
• a piezoelectric plate having front and back surfaces;
• an interdigital transducer (IDT) at the front surface of the piezoelectric plate;
• a half-lambda dielectric layer on the back surface of the piezoelectric plate;
• and
• an acoustic Bragg reflector sandwiched between the surface of the substrate and the back surface of the piezoelectric plate, the acoustic Bragg reflector configured to reflect a primary acoustic mode,
• wherein the acoustic Bragg reflector comprises alternating layers of a first material and a second material having a higher acoustic impedance than the first material,
• wherein a top layer of the alternating layers of the acoustic Bragg reflector contacts the half-lambda dielectric layer,
• wherein the IDT is configured to excite a primary shear acoustic mode within the piezoelectric plate, and
• wherein a thickness td of the half-lambda dielectric layer is defined as 0.85λ0,d≤2td≤1.15λ0,d, where λ0,d is a wavelength of a fundamental shear bulk acoustic wave resonance in the half-lambda dielectric layer, and the thickness td of the half-lambda dielectric layer is measured in a direction normal to the surface of the substrate.