Two-stage lateral bulk acoustic wave filter
View Patent ↗Acoustic wave filter devices are disclosed. A device includes a layer providing or on a topmost layer of an acoustic reflector. The intermediary layer has a first region and a second region. The first region has a first layer thickness and the second region has a second layer thickness different from the first layer thickness. The device includes a first multilayer stack on the first region and a second multilayer stack on the second region of the intermediary layer. Each of the first and the second stacks includes a piezoelectric layer on a counter electrode that is located on the respective region, an input and an output electrode. Application of a radio frequency voltage between the input electrode and the counter electrode layer of the first stack creates acoustic resonance modes in the piezoelectric layer between the input and output electrodes of the first and the second stack.
1. An acoustic wave filter device comprising:
a first electrode comprising a first input electrode and a first output electrode;
a second electrode comprising a second input electrode and a second output electrode, the second input electrode being electrically connected to the first output electrode;
a piezoelectric layer beneath the first electrode and the second electrode;
a counter electrode beneath the piezoelectric layer;
an intermediary layer beneath the counter electrode, the intermediary layer comprising a first region and a second region, the first region having a first layer thickness and the second region having a second layer thickness different from the first layer thickness; and
an acoustic reflector beneath the intermediary layer, the acoustic reflector comprising one or more layers,
wherein the first electrode is located over the first region of the intermediary layer, and the second electrode is located over the second region of the intermediary layer, and
wherein the filter device is configured such that application of a radio frequency voltage between the first input electrode and the counter electrode creates acoustic resonance modes in the piezoelectric layer between the first input and output electrodes and between the second input and output electrodes.
2. The device of claim 1 , wherein the second layer thickness is greater than the first layer thickness.
3. The device of claim 1 , wherein the radio frequency voltage between the first input electrode and the counter electrode creates second-order acoustic thickness-shear (TS2) resonance mode in the piezoelectric layer between the first input and output electrodes and between the second input and output electrodes, and
wherein the second layer thickness is different than the first layer thickness so that a first resonance frequency of TS2 resonance mode created between the first input and output electrodes of the first electrode differs from a second resonance frequency of TS2 resonance mode created between the second input and output electrodes of the second electrode.
4. The device of claim 3 , wherein the first resonance frequency differs by 1% to 8% from the second resonance frequency.
5. The device of claim 3 , wherein the first resonance frequency differs from the second resonance frequency by at least 50 MHz.
6. The device of claim 1 , wherein the second layer thickness is 1% to 10% greater than the first layer thickness.
7. The device of claim 1 , wherein the second electrode has a second thickness that is less than a first thickness of the first electrode.
8. The device of claim 7 , wherein the second thickness is 1% to 10% thinner than the first thickness.
9. The device of claim 1 , wherein each of the first input and output electrodes has multiple first extensions, the multiple first extensions of the first input electrode are interdigitated with the multiple first extensions of the first output electrode, and each of the second input and output electrodes has multiple second extensions, the multiple second extensions of the second input electrode are interdigitated with the multiple second extensions of the second output electrode.
10. The device of claim 9 , wherein each of the first input and output electrodes is a comb structure having the multiple first extensions and wherein each of the second input and output electrodes is a comb structure having the multiple second extensions.
11. The device of claim 9 , wherein the multiple first extensions are thicker than the multiple second extensions.
12. The device of claim 11 , wherein a second extension in the multiple second extensions has a thickness that is 5% to 20% smaller than a thickness of a first extension in the multiple first extensions.
13. The device of claim 9 , wherein the multiple second extensions have a second extension thickness that is greater than a first extension thickness of the multiple first extensions so that a first resonance frequency of TE1 resonance mode created between the first input and output electrodes is within 1% from a second resonance frequency of TE1 resonance mode created between the second input and output electrodes.
14. The device of claim 11 , wherein the multiple second extensions are substantially parallel to the multiple first extensions.
15. The device of claim 11 , wherein the multiple second extensions form an angle greater than zero with respect to the multiple first extensions.
16. The device of claim 1 , wherein the first output electrode and the second input electrode are parts of a common electrode shared between the first electrode and the second electrode.
17. The device of claim 1 , wherein the first output electrode is connected to the second input electrode through a conductive connector.
18. The device of claim 17 , wherein the conductive connector has a length extending parallel to a long axis of extensions extending from at least one of the first input or output electrodes or the second input or output electrodes, the length being greater than a width of the extensions measured perpendicular to the long axis of the extensions.
19. The device of claim 1 , wherein the first output electrode is substantially parallel to the second input electrode.
20. An acoustic wave filter device comprising:
a first electrode comprising a first input electrode and a first output electrode;
a second electrode comprising a second input electrode and a second output electrode, the second input electrode being electrically connected to the first output electrode;
a piezoelectric layer beneath the first electrode and the second electrode;
a counter electrode beneath the piezoelectric layer;
an intermediary layer beneath the counter electrode, the intermediary layer comprising a first region and a second region, the first region having a first layer thickness and the second region having a second layer thickness different from the first layer thickness; and
an acoustic reflector beneath the intermediary layer, the acoustic reflector comprising one or more layers,
wherein the first electrode is located over the first region of the intermediary layer, and the second electrode is located over the second region of the intermediary layer, and
wherein the filter device is configured such that application of a radio frequency voltage between the first input electrode and the counter electrode creates one or more acoustic thickness-extensional resonance modes in the piezoelectric layer between the first input and output electrodes and between the second input and output electrodes.