Elastic wave device
An elastic wave device includes a spacer layer on or above a support substrate and outside a piezoelectric film as seen in a plan view from a thickness direction of the support substrate. A cover layer is disposed on the spacer layer. A through electrode extends through the spacer layer and the cover layer and is electrically connected to the wiring electrode. The wiring electrode includes a first section overlapping the through electrode as seen in the plan view from the thickness direction, a second section overlapping the piezoelectric film as seen in the plan view from the thickness direction, and a step portion defining a step in the thickness direction between the first section and the second section. The spacer layer includes an end portion embedded in the cover layer.
1. An elastic wave device comprising:
a support substrate;
a piezoelectric film disposed on or above the support substrate;
a functional electrode disposed on or above the piezoelectric film;
a wiring electrode electrically connected to the functional electrode;
a spacer layer disposed on or above the support substrate, and disposed outside the piezoelectric film as seen in a plan view from a thickness direction of the support substrate;
a cover layer disposed on the spacer layer; and
a through electrode extending through the spacer layer and the cover layer and electrically connected to the wiring electrode; wherein
the wiring electrode includes:
a first section overlapping the through electrode as seen in the plan view from the thickness direction;
a second section overlapping the piezoelectric film as seen in the plan view from the thickness direction;
a first step portion defining a step in the thickness direction between the first section and the second section; and
a second step portion;
in the first step portion, a distance from the support substrate in the thickness direction gradually increases along a direction from the first section toward the second section;
in the second step portion, the distance from the support substrate in the thickness direction decreases along the direction from the first section toward the second section;
the spacer layer covers both of the first step portion and the second step portion as seen in the plan view from the thickness direction; and
the spacer layer includes an end portion embedded in the cover layer.
2. The elastic wave device according to claim 1 , wherein the cover layer includes:
a first sublayer; and
a second sublayer disposed on or above the first sublayer; wherein
the first sublayer is closer to the support substrate than the second sublayer; and
a Young's modulus of the first sublayer is larger than a Young's modulus of the second sublayer.
3. The elastic wave device according to claim 2 , wherein a depth of the end portion embedded in the cover layer is not larger than a thickness of the first sublayer.
4. The elastic wave device according to claim 2 , wherein
the first sublayer is made of an epoxy-based resin; and
the second sublayer is made of a polyimide-based resin.
5. The elastic wave device according to claim 1 , wherein a depth of the end portion embedded in the cover layer is not smaller than about 2.0 μm.
6. The elastic wave device according to claim 1 , further comprising:
an insulating layer disposed on the support substrate; wherein
the support substrate is a silicon substrate;
a portion of the wiring electrode is disposed on the insulating layer;
the spacer layer is disposed on the wiring electrode and the insulating layer; and
the through electrode is disposed on the wiring electrode.
7. The elastic wave device according to claim 6 , wherein a Young's modulus of the insulating layer is smaller than a Young's modulus of the piezoelectric film.
8. The elastic wave device according to claim 1 , wherein the functional electrode is an interdigital transducer electrode.
9. The elastic wave device according to claim 8 , wherein the interdigital transducer electrode is made of at least one of aluminum, copper, platinum, gold, silver, titanium, nickel, chromium, molybdenum, and tungsten, or an alloy including any of aluminum, copper, platinum, gold, silver, titanium, nickel, chromium, molybdenum, and tungsten.
10. The elastic wave device according to claim 1 , further comprising an external connection terminal electrically connected to the through electrode.
11. The elastic wave device according to claim 1 , wherein the piezoelectric film is made of lithium tantalite, lithium niobate, zinc oxide, aluminum nitride, or PZT.
12. The elastic wave device according to claim 1 , wherein a high acoustic velocity film and a low acoustic velocity film are disposed between the piezoelectric film and the support substrate.
13. The elastic wave device according to claim 12 , wherein
the high acoustic velocity film is disposed on the support substrate;
the low acoustic velocity film is disposed on the high acoustic velocity film; and
the piezoelectric film is disposed on the low acoustic velocity film.
14. The elastic wave device according to claim 12 , wherein the high acoustic velocity film is made of at least one of diamond-like carbon, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon, sapphire, lithium tantalite, lithium niobite, crystal, alumina, zirconia, cordierite, mullite, steatite, forsterite, and magnesia diamond.
15. The elastic wave device according to claim 12 , wherein the low acoustic velocity film is made of a compound in which fluorine, carbon, or boron is added to silicon oxide, glass, silicon oxynitride, tantalum oxide, or silicon oxide.
16. The elastic wave device according to claim 1 , further comprising a protective film covering the functional electrode.
17. The elastic wave device according to claim 16 , wherein the protective film is made of silicon oxide.