Film bulk acoustic sensors using thin LN-LT layer

1. An acoustic sensor device comprising:

a piezoelectric plate having a front surface and a back surface opposite the front surface;

an electrically floating back-side conductor pattern formed on the back surface;

first and second front-side conductor patterns formed on the front surface opposite the back-side conductor pattern; and

a sensing layer formed over at least a portion of the floating back-side conductor pattern, wherein the sensing layer is configured to capture a target species from a liquid or gaseous environment, and

wherein the piezoelectric plate is configured such that an RF signal applied between the first and second conductor patterns excites shear bulk acoustic waves in the piezoelectric plate.

2. The device of claim 1 , wherein the piezoelectric plate is one of lithium niobate and lithium tantalate.

3. The device of claim 2 , wherein the piezoelectric plate is one of Y-cut and rotated Y-cut.

4. The device of claim 1 , wherein a resonance frequency of the device depends, in part, on an amount of the target species captured by the sensing layer.

5. The device of claim 1 , wherein the sensing layer is one of an antigen, an antibody, an enzyme, a nucleic acid, a DNA molecule, an organic material with a selected functional group, and an inorganic layer.

6. The device of claim 1 , further comprising a substrate,

wherein a portion of the piezoelectric plate forms a diaphragm spanning a cavity in the substrate, and

at least portions of the first and second front-side conductor pattern, the back-side conductor pattern, and the sensing layer are on the diaphragm.

7. The device of claim 6 , wherein the diaphragm forms a seal across the cavity such that the first and second front-side conductor patterns are not exposed to the environment around the sensing layer.

8. The device of claim 1 , wherein the first and second front-side conductor patterns comprise interleaved fingers connected to respective first and second busbars.

9. The device of claim 1 , wherein an equal number of fingers is connected to each of the first and second busbars.

10. The device of claim 1 , wherein a portion of the piezoelectric plate between the first and second front-side conductor patterns is recessed.

11. The device of claim 1 , wherein at least one of the first front-side conductor pattern, the second front-side conductor pattern, and the floating back-side conductor pattern has a non-rectangular shape.

12. A sensor system comprising:

an acoustic sensor device comprising:

a piezoelectric plate having a front surface and a back surface opposite the front surface;

an electrically floating back-side conductor pattern formed on the back surface;

first and second front-side conductor patterns formed on the front surface opposite the back-side conductor pattern; and

a sensing layer formed over at least a portion of the floating back-side conductor pattern,

wherein the piezoelectric plate is configured such that an RF signal applied between the first and second conductor patterns excites shear bulk acoustic waves in the piezoelectric plate;

a measurement system to determine a presence of a target species in an environment based on a resonant frequency of the acoustic sensor device; and

means for presenting the environment to the sensing layer of the acoustic sensor device.

13. The sensor system of claim 12 , wherein the measurement system comprises:

a reference frequency generator to provide a reference frequency; and

a frequency comparator to compare the resonance frequency of the acoustic sensor device and the reference frequency.

14. The sensor system of claim 13 , wherein the reference frequency generator includes a reference acoustic resonator.