Mechanical resonating structures including a temperature compensation structure
Mechanical resonating structures are described, as well as related devices and methods. The mechanical resonating structures may have a compensating structure for compensating temperature variations.
1. A device comprising:
a mechanical resonating structure configured to support Lamb waves, the mechanical resonating structure including:
an active layer; and
a compensating structure coupled to the active layer, the compensating structure comprising
a first layer having a stiffness that increases with increasing temperature over at least a first temperature range,
a third layer having a stiffness that increases with increasing temperature over at least the first temperature range, and
a second layer between the first layer and the third layer.
2. The device of claim 1 , wherein the active layer comprises a piezoelectric material.
3. The device of claim 2 , wherein the piezoelectric material is aluminum nitride.
4. The device of claim 1 , wherein the compensating structure is configured to provide the mechanical resonating structure with a temperature coefficient of frequency (TCF) having an absolute value of less than 10 ppm/K over a second temperature range from approximately −40° C. to approximately 85° C.
5. The device of claim 4 , wherein the TCF has an absolute value of less than 3 ppm/K over the second temperature range.
6. The device of claim 4 , wherein the TCF has an absolute value of less than 1 ppm/K over the second temperature range.
7. The device of claim 1 , wherein the compensating structure is configured to provide the mechanical resonating structure with a TCF having an absolute value of less than 4 ppm/K over a second temperature range spanning at least 40° C. and centered approximately at 25° C.
8. The device of claim 1 , wherein the first layer and the third layer of the compensating structure are formed of a first material.
9. The device of claim 1 , wherein the first layer and the third layer of the compensating structure have approximately the same thickness as each other.
10. The device of claim 1 , wherein the first layer of the compensating structure is formed of a first material and wherein the second layer is formed of a second material different than the first material.
11. The device of claim 10 , wherein a ratio of a total thickness of one or more layers of the mechanical resonating structure comprising the first material to a thickness of the active layer is between 1:0.1 and 1:1.25.
12. The device of claim 10 , wherein a ratio of a total thickness of one or more layers of the mechanical resonating structure comprising the first material to a thickness of the active layer is between 1:0.2 and 1:0.75.
13. The device of claim 1 , wherein the first layer is formed of silicon dioxide.
14. The device of claim 1 , wherein the second layer is formed of a material selected from the group consisting of silicon, silicon carbide, sapphire, quartz, germanium, gallium arsenide, aluminum nitride and diamond.
15. The device of claim 1 , wherein the first temperature range spans at least 200° C.
16. The device of claim 1 , wherein the first temperature range is between −55° C. and 150° C.
17. The device of claim 1 , wherein the first temperature range is between −40° C. and 85° C.
18. The device of claim 1 , wherein the active layer is formed of silicon.
19. The device of claim 1 , wherein the active layer is formed on the compensating structure.
20. The device of claim 1 , wherein each of the first and third layers includes silicon dioxide, and wherein the second layer includes single crystal silicon.
21. The device of claim 20 , wherein the silicon dioxide comprises thermal silicon dioxide.
22. The device of claim 1 , wherein the first and third layers include silicon dioxide, and wherein the second layer includes a single crystal material.
23. The device of claim 22 , wherein the silicon dioxide comprises thermal silicon dioxide.
24. The device of claim 1 , wherein:
the mechanical resonating structure further includes at least one patterned electrode; each of the first and third layers of the compensating structure includes thermal silicon dioxide;
the second layer of the compensating structure includes single crystal silicon; and the device further comprises first and second anchors coupled to the mechanical resonating structure and substantially in plane with the mechanical resonating structure.
25. A device comprising: a mechanical resonating structure configured to support Lamb waves, the mechanical resonating structure comprising an active layer and a compensation structure coupled to the active layer and configured to compensate temperature-induced variations in stiffness of at least the active layer, the compensation structure comprising a first layer, a second layer, and a third layer, wherein the first and third layers are formed of a first material and wherein the second layer is formed of a second material different than the first material, and wherein the second layer is disposed between the first layer and the third layer.