GaN stack acoustic reflector and method for producing the same
Methods of forming a thin-film piezoelectric acoustic filter, a GaN-channel/buffer Bragg reflector, and a monolithically integrated GaN HEMT PA and CMOS over a [111] crystal orientation Si handle of a SOI wafer and resulting devices are provided. Embodiments include providing a SOI wafer including a [111] crystal orientation Si handle, a BOX layer, and a top Si layer; forming a CMOS device over the top Si layer; and forming a Bragg reflector over the [111] crystal orientation Si handle wafer, the Bragg reflector including a GaN stack with alternating layers of high/low acoustic impedance.
1. A method comprising:
providing a silicon on insulator (SOI) wafer comprising a [111] crystal orientation silicon (Si) handle wafer, a buried oxide (BOX) layer, and a top Si layer;
forming a complimentary metal-oxide semiconductor (CMOS) device over the top Si layer of the SOI wafer;
forming a Bragg reflector over the [111] crystal orientation Si handle wafer, the Bragg reflector comprising a gallium nitride (GaN) stack with alternating layers of high/low acoustic impedance;
forming a sacrificial (SAC) layer over and around the thin-film acoustic filter;
forming an encapsulation layer over the SOI wafer;
forming a via through the encapsulation layer on opposite sides of the thin-film acoustic filter;
removing the SAC layer through the via, a cavity formed over and around the thin-film acoustic filter;
forming a sealing layer over the encapsulation layer; and
forming a metal contact through the sealing layer and the encapsulation layer down to a portion of the thin-film acoustic filter.
2. The method according to claim 1 , comprising forming the GaN stack by:
forming a buffer layer over the [111] crystal orientation Si handle wafer;
forming a GaN channel layer over the buffer layer; and
forming an aluminum gallium nitride (AlGaN)/aluminum nitride (AlN) barrier layer over the GaN channel layer.
3. The method according to claim 2 , further comprising forming a thin-film acoustic filter over the GaN stack by:
forming a first molybdenum (Mo) or tungsten (W) layer over the AlGaN/AlN barrier layer;
forming an aluminum nitride (AlN), scandium aluminum nitride (ScAlN), zinc oxide (ZnO), lithium niobate (LiNbO 3 ), lithium tantalite (LiTaO 3 ), lead zirconate titanate (PZT), or polyvinylidene fluoride (PVDF) layer over the first Mo or W layer;
forming a second Mo or W layer over the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
forming a via through the first Mo or W layer and the GaN stack on opposite sides of the thin-film acoustic filter; and
forming a cavity under the thin-film acoustic filter in the [111] crystal orientation Si handle wafer through the vias.
4. The method according to claim 3 , further comprising etching the second Mo or W layer in an interdigitated (IDT) pattern down to the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer.
5. The method according to claim 2 , further comprising forming a thin-film acoustic filter over the GaN stack by:
forming an AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer over the AlGaN/AlN barrier layer;
forming a Mo or W layer over the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
patterning the second Mo or W layer down to the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
forming a via through the GaN stack on opposite sides of the thin-film acoustic filter; and
forming a cavity under the thin-film acoustic filter in the [111] crystal orientation Si handle through the vias.
6. The method according to claim 1 , comprising forming GaN stack by:
forming a buffer layer over the [111] crystal orientation Si handle wafer;
forming a GaN channel layer over the buffer layer;
forming an AlGaN/AlN barrier layer over the GaN channel layer; and
forming a silicon nitride (SiN) or silicon dioxide (SiO 2 ) passivation layer over the AlGaN/AlN barrier layer.
7. The method according to claim 6 , further comprising forming a thin-film acoustic filter over the GaN stack by:
forming a first Mo or W layer over the AlGaN/AlN barrier layer;
forming an AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer over the first Mo or W layer;
forming a second Mo or W layer over the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
forming a via through the first Mo or W layer and the GaN stack on opposite sides of the thin-film acoustic filter; and
forming a cavity under the thin-film acoustic filter in the [111] crystal orientation Si handle wafer through the vias.
8. The method according to claim 1 , further comprising forming a GaN high-electron-mobility transistor power amplifier (GaN HEMT PA) in and over respective portions of the GaN stack.
9. A device comprising:
a silicon on insulator (SOI) wafer, the SOI wafer comprising a [111] crystal orientation silicon (Si) handle wafer, a buried oxide (BOX) layer, and a top Si layer
a complimentary metal-oxide-semiconductor (CMOS) device over the top Si layer;
a Bragg reflector over the [111] crystal orientation Si handle, the Bragg Reflector comprising a gallium nitride (GaN) stack with alternating layers of high/low acoustic impedance; and
a GaN high-electron-mobility transistor power amplifier (GaN HEMT PA) in and over respective portions of the GaN stack.
10. The device according to claim 9 , wherein the GaN stack comprises:
a buffer layer over the [111] crystal orientation Si handle wafer;
a GaN channel layer over the buffer layer; and
an aluminum gallium nitride (AlGaN)/aluminum nitride (AlN) barrier layer over the GaN channel layer.
11. The device according to claim 10 , further comprising a thin-film acoustic filter over the GaN stack, wherein the thin-film acoustic filter comprises:
a first molybdenum (Mo) or tungsten (W) layer over the AlGaN/AlN barrier layer;
an aluminum nitride (AlN), scandium aluminum nitride (ScAlN), zinc oxide (ZnO), lithium niobate (LiNbO 3 ), lithium tantalite (LiTaO 3 ), lead zirconate titanate (PZT), or polyvinylidene fluoride (PVDF) layer over the first Mo or W layer;
a second Mo or W layer over the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
a via through the first Mo or W layer and the GaN stack on opposite sides of the thin-film acoustic filter; and
a cavity under the thin-film acoustic filter in the [111] crystal orientation Si handle wafer,
wherein the thin-film acoustic filter is a bulk acoustic wave (BAW) filter.
12. The device according to claim 10 , further comprising a thin-film acoustic filter over the GaN stack, wherein the thin-film acoustic filter comprises:
a first Mo or W layer over the AlGaN/AlN barrier layer;
an AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer over the first Mo or W layer;
a second Mo or W layer in an interdigitated (IDT) pattern over the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
a via through the first Mo or W layer and the GaN stack on opposite sides of the thin-film acoustic filter; and
a cavity under the thin-film acoustic filter in the [111] crystal orientation Si handle wafer,
wherein the thin-film acoustic filter is a Lamb filter.
13. The device according to claim 12 , wherein the thin-film acoustic filter comprises:
an AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer over the AlGaN/AlN barrier layer;
a Mo or W layer in an IDT pattern over the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
a via through the GaN stack on opposite sides of the thin-film acoustic filter; and
a cavity under the thin-film acoustic filter in the [111] crystal orientation Si handle wafer,
wherein the thin-film acoustic filter is a Lamb filter.
14. The device according to claim 9 , wherein the GaN stack comprises:
a buffer layer over the [111] crystal orientation Si handle wafer;
a GaN channel layer over the buffer layer;
an AlGaN/AlN barrier layer over the GaN channel layer; and
a silicon nitride (SiN) or silicon dioxide (SiO 2 ) passivation layer over the AlGaN/AlN barrier layer.
15. The device according to claim 14 , further comprising a thin-film acoustic filter over the GaN stack, wherein the thin-film acoustic filter comprises:
a first Mo or W layer over the AlGaN/AlN barrier layer;
an AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer over the first Mo or W layer;
a second Mo or W layer over the AlN, ScAlN, ZnO, LiNbO 3 , LiTaO 3 , PZT, or PVDF layer;
a via through the first Mo or W layer and the GaN stack on opposite sides of the thin-film acoustic filter; and
a cavity under the thin-film acoustic filter in the [111] crystal orientation Si handle wafer,
wherein the thin-film acoustic filter is a BAW filter.
16. The device according to claim 11 , further comprising:
an encapsulation layer over the [111] crystal orientation Si handle wafer with a cavity over and around the thin-film acoustic filter;
a sealing layer over the encapsulation layer; and
a metal contact through the sealing layer and the encapsulation layer down to a portion of the thin-film acoustic filter.
17. A device comprising:
a silicon on insulator (SOI) wafer, the SOI wafer comprising a [111] crystal orientation silicon (Si) handle wafer, a buried oxide (BOX) layer, and a top Si layer;
a complimentary metal-oxide-semiconductor (CMOS) device over the top Si;
a gallium nitride (GaN) stack over the [111] crystal orientation Si handle;
a GaN high-electron-mobility transistor power amplifier (GaN HEMT PA) in and over the GaN stack;
a thin-film Lamb acoustic wave filter over the GaN stack;
a via through the first Mo or W layer on opposite sides of the thin-film Lamb acoustic wave filter; and
a cavity under the thin-film Lamb acoustic filter in a passivation layer of the GaN stack.
18. The device according to claim 17 , wherein the GaN stack comprises:
a buffer layer over the [111] crystal orientation Si handle wafer;
a GaN channel layer over the buffer layer;
an AlGaN/AlN barrier layer over the GaN channel layer; and
the passivation layer of silicon nitride (SiN) or silicon dioxide (SiO 2 ) over the AlGaN/AlN barrier layer.