Bulk acoustic wave device with integrated temperature sensor and heater
An acoustic-wave device includes a first electrode located over a substrate. A piezoelectric film is located over the first electrode and at least partially overlaps the first electrode. A second electrode is located over the piezoelectric film and at least partially overlaps the first electrode and the piezoelectric film. A temperature sensor is located in a same layer level as the first or second electrode. A heater may also be located in a same layer level as the first electrode. A closed-loop system may operate using the temperature sensor and the heater to maintain an operating temperature that provides highly stable operation.
1. An acoustic-wave device, comprising:
a first electrode located over a substrate;
a piezoelectric layer over the first electrode;
a second electrode over the piezoelectric layer and at least partially overlapping the first electrode; and
a temperature sensor in a same layer level as the first or second electrode.
2. The device of claim 1 , wherein each of the temperature sensor and the second electrode includes at least one of molybdenum, platinum, or aluminum.
3. The device of claim 1 , wherein the temperature sensor includes:
a resistive member having a first end and a second end and including multiple line segments between the first and second ends.
4. The device of claim 3 , wherein the resistive member follows a serpentine path between the first and second ends.
5. The device of claim 3 , wherein a group of line segments of the multiple line segments are parallel to a side of the second electrode and serve as resonate confiners during operation of the device.
6. The device of claim 5 , wherein:
the first and second electrodes and the piezoelectric layer are configured to generate an acoustic wave having a wavelength, and each line segment of the group of line segments has a linewidth about equal to half the wavelength; and
a separation distance between nearest neighbor line segments of the group of line segments is about equal to half the wavelength.
7. The device of claim 1 , further comprising a thermal coefficient of frequency (TCF) dielectric layer between the second electrode and the piezoelectric layer.
8. The device of claim 7 , wherein the TCF dielectric layer has a thickness in a range between about 20 nm and about 35 nm.
9. The device of claim 1 , wherein the temperature sensor is formed in the same layer as one of the first and second electrodes, and further comprising a heater in the same layer as the other of the first and second electrodes.
10. The device of claim 9 , further comprising a controller configured to control the heater in response to a temperature-dependent property of the temperature sensor.
11. The device of claim 10 , wherein the controller is configured to control the heater to maintain an elevated temperature of the piezoelectric layer in response to the temperature-dependent property.
12. The device of claim 11 , wherein the elevated temperature is in a range between about 100° C. and about 165° C.
13. A method of forming a resonator, comprising:
forming a first electrode and a first resistor from a first metallic film over a substrate;
forming a piezoelectric film over the first electrode;
forming a second electrode over the first electrode from a second metallic film; and
forming a second resistor from the second metallic film,
configuring a controller to maintain an operating temperature of the piezoelectric film by directing current to a first one of the first and second resistors in response to a resistance of a second one of the first and second resistors, the operating temperature being greater than a specified maximum ambient temperature of the resonator.
14. The method as recited in claim 13 , where a resonant frequency of the resonator varies by less than about #1 ppm while the piezoelectric film is maintained at the operating temperature.
15. The method as recited in claim 13 , further comprising forming a dielectric layer having a thickness in arrange between about 20 nm and about 35 nm between the piezoelectric film and the second electrode.
16. The method as recited in claim 13 , further comprising forming a silicon oxide layer having a thickness in arrange between about 20 nm and about 35 nm between the piezoelectric film and the second electrode.
17. The method as recited in claim 13 , further comprising forming first and second power terminals of the first or the second resistor, wherein the first and second power terminals are immediate neighbors.
18. A resonator, comprising:
a first electrode and a first resistor in a first metallic layer over a substrate;
a piezoelectric film over the first electrode and the first resistor;
a second electrode over the first electrode in a second metallic layer; and
a second resistor from the second metallic layer,
a controller configured to maintain an operating temperature of the piezoelectric film by directing current to a first one of the first and second resistors in response to a resistance of a second one of the first and second resistors, the operating temperature being greater than a specified maximum ambient temperature of the resonator.
19. The resonator as recited in claim 18 , where a resonant frequency of the resonator varies by less than about +1 ppm while the piezoelectric film is maintained at the operating temperature.
20. The resonator as recited in claim 18 , further comprising a dielectric layer having a thickness in arrange between about 20 nm and about 35 nm between the piezoelectric film and the second electrode.
21. The resonator as recited in claim 18 , further comprising a silicon oxide layer having a thickness in arrange between about 20 nm and about 35 nm between the piezoelectric film and the second electrode.
22. The resonator as recited in claim 18 , further comprising first and second power terminals of the first or the second resistor, wherein the first and second power terminals are immediate neighbors.