Surface acoustic wave resonator and multiplexer including the same
A surface acoustic wave resonator ( 100 ) comprises a layered substrate including a carrier substrate ( 110 ) and a dielectric layer ( 112 ) having a low acoustic velocity. Another dielectric layer ( 122 ) is disposed on a piezoelectric layer ( 113 ) and interdigitated electrodes ( 131, 132 ) having an acoustic velocity lower than the acoustic velocity of the carrier substrate ( 110 ) and a positive temperature coefficient of frequency.
1 . A surface acoustic wave resonator, comprising:
a layered substrate, comprising:
a carrier substrate having an acoustic velocity;
a first dielectric layer having an acoustic velocity lower than the acoustic velocity of the carrier substrate, the first dielectric layer disposed on the carrier substrate;
a piezoelectric layer disposed on the first dielectric layer;
interdigitated electrodes disposed on the piezoelectric layer; and
a second dielectric layer having an acoustic velocity lower than the acoustic velocity of the carrier substrate and having a positive temperature coefficient of frequency, the second dielectric layer disposed on the piezoelectric layer and on the interdigitated electrodes,
wherein the interdigitated electrodes comprise a plurality of fingers having a pitch related to a wavelength, and
wherein a height of the second dielectric layer is between 5% and 15% of a height of the piezoelectric layer.
2 . The surface acoustic wave resonator of claim 1 , wherein the second dielectric layer has an acoustic velocity lower than the acoustic velocity of any other layer of the layered substrate.
3 . The surface acoustic wave resonator of claim 1 , wherein the carrier substrate and the piezoelectric layer have a temperature coefficient of frequency below zero and the first dielectric layer and the second dielectric layer have a temperature coefficient of frequency larger than zero.
4 . The surface acoustic wave resonator of claim 1 , wherein the first dielectric layer and the second dielectric layer have a same temperature coefficient of frequency larger than zero.
5 . The surface acoustic wave resonator of claim 1 , wherein the second dielectric layer comprises silicon dioxide.
6 . The surface acoustic wave resonator of claim 1 , wherein the second dielectric layer comprises at least one of germanium dioxide, scandium yttrium fluoride, zirconium tungsten oxide, hafnium tungsten oxide.
7 . The surface acoustic wave resonator of claim 1 , the layered substrate further comprising a layer having an acoustic velocity higher than the acoustic velocity of the carrier substrate, said layer disposed between the carrier substrate and the first dielectric layer of the layered substrate.
8 . The surface acoustic wave resonator of claim 1 , further comprising a passivation layer disposed on the second dielectric layer.
9 . The surface acoustic wave resonator of claim 1 , wherein the carrier substrate comprises one of monocrystalline silicon, aluminum oxide, silicon carbide and diamond, wherein the first dielectric layer of the layered substrate comprises one of silicon dioxide, germanium dioxide and doped silicon dioxide and wherein the piezoelectric layer comprises one of lithium tantalate, lithium niobate, aluminum nitride and quartz.
10 . The surface acoustic wave resonator of claim 9 , the layered substrate further comprising a layer having an acoustic velocity higher than the acoustic velocity of the carrier substrate, said layer comprising one of polycrystalline silicon, amorphous silicon, aluminium nitride and silicon carbide.
11 . A RF multiplexer circuit, comprising:
a first port to be coupled to an antenna;
a second port to be coupled to a transmit circuit and a transmit filter circuit coupled between the first and second ports; and
a third port to be coupled to a receive circuit and a receive filter circuit coupled between the first and third ports, wherein transmit and receive filter circuits each include resonators, and wherein a first resonator of the resonators comprises:
a layered substrate, comprising:
a carrier substrate having an acoustic velocity;
a first dielectric layer having an acoustic velocity lower than the acoustic velocity of the carrier substrate, the first dielectric layer disposed on the carrier substrate;
a piezoelectric layer disposed on the first dielectric layer;
interdigitated electrodes disposed on the piezoelectric layer; and
a second dielectric layer having an acoustic velocity lower than the acoustic velocity of the carrier substrate and having a positive temperature coefficient of frequency,
wherein the interdigitated electrodes comprise a plurality of fingers having a pitch related to a wavelength, and
wherein a height of the second dielectric layer is between 5% and 15% of a height of the piezoelectric layer.
12 . The RF multiplexer circuit of claim 11 , wherein the second dielectric layer has an acoustic velocity lower than the acoustic velocity of any other layer of the layered substrate.
13 . The RF multiplexer circuit of claim 11 , wherein the carrier substrate and the piezoelectric layer have a temperature coefficient of frequency below zero and the first dielectric layer and the second dielectric layer have a temperature coefficient of frequency larger than zero.
14 . The RF multiplexer circuit of claim 11 , wherein the first dielectric layer and the second dielectric layer have a same temperature coefficient of frequency larger than zero.
15 . The RF multiplexer circuit of claim 11 , wherein the second dielectric layer comprises silicon dioxide.
16 . The surface acoustic wave resonator-RF multiplexer circuit of claim 11 , wherein the second dielectric layer comprises at least one of germanium dioxide, scandium yttrium fluoride, zirconium tungsten oxide, hafnium tungsten oxide.
17 . The surface acoustic wave resonator of RF multiplexer circuit claim 11 , the layered substrate further comprising a layer having an acoustic velocity higher than the acoustic velocity of the carrier substrate, said layer disposed between the carrier substrate and the first dielectric layer of the layered substrate.