Elastic wave sensor
View Patent ↗An acoustic wave sensor includes a piezoelectric substrate, a transmitting electrode configured to excite a main acoustic wave propagating through a propagation region of an upper surface of the piezoelectric substrate, a receiving electrode configured to receive the propagated main acoustic wave, a first insulating film provided on the propagation region of the upper surface of the piezoelectric substrate, a second insulating film provided on the upper surface of the piezoelectric substrate to cover the first insulating film, and a reaction section provided on the upper surface of the second insulating film above the propagation region. The reaction section is configured to react with an object. A velocity of a transverse wave propagating through the first insulating film is higher than a velocity of a transverse wave propagating through the second insulating film. The acoustic wave sensor described above has high detection sensitivity.
1. An acoustic wave sensor comprising:
a piezoelectric substrate having an upper surface;
a transmitting electrode configured to excite a main acoustic wave propagating through a propagation region of the upper surface of the piezoelectric substrate;
a receiving electrode configured to receive the propagated main acoustic wave;
a first insulating film provided on the propagation region of the upper surface of the piezoelectric substrate;
a second insulating film contacting the upper surface of the piezoelectric substrate and an upper surface of the first insulating film to cover the first insulating film; and
a reaction section provided on an upper surface of the second insulating film above the propagation region, the reaction section configured to react with an object,
wherein a velocity of a transverse wave propagating through the first insulating film is higher than a velocity of a transverse wave propagating through the second insulating film.
2. The acoustic wave sensor according to claim 1 , wherein a velocity of the transverse wave propagating through the first insulating film is higher than a velocity of the transverse wave propagating through the piezoelectric substrate.
3. The acoustic wave sensor according to claim 1 , wherein a velocity of the transverse wave propagating through the second insulating film is lower than a velocity of the transverse wave propagating through the piezoelectric substrate.
4. The acoustic wave sensor according to claim 1 ,
wherein the second insulating film is made of silicon oxide, and
wherein the first insulating film is made of silicon nitride.
5. The acoustic wave sensor according to claim 1 , wherein an end of the first insulating film is located apart from an end of the reaction section and inside the reaction section in a propagation direction in which the main acoustic wave propagates.
6. An acoustic wave sensor comprising:
a piezoelectric substrate having an upper surface;
a transmitting electrode configured to excite a main acoustic wave propagating through a propagation region of the upper surface of the piezoelectric substrate;
a receiving electrode configured to receive the propagated main acoustic wave;
a first insulating film provided on the propagation region of the upper surface of the piezoelectric substrate;
a second insulating film provided on the upper surface of the piezoelectric substrate to cover the first insulating film; and
a reaction section provided on the upper surface of the second insulating film above the propagation region, the reaction section configured to react with an object,
wherein a velocity of a transverse wave propagating through the first insulating film is higher than a velocity of a transverse wave propagating through the second insulating film
wherein the first insulating film has:
a first end facing the transmitting electrode in a propagation direction in which the main acoustic wave propagates;
a second end facing the receiving electrode in the propagation direction; and
a center part provided between the transmitting electrode and the receiving electrode in the propagation direction, and
wherein a thickness of the center part of the first insulating film is larger than a thickness of the first end or a thickness of the second end of the first insulating film.
7. The acoustic wave sensor according to claim 6 , wherein the first end of the first insulating film has a tapered shape having a thickness decreases toward the transmitting electrode.
8. The acoustic wave sensor according to claim 6 , wherein the second end of the first insulating film has a tapered shape having a thickness decreases toward the receiving electrode.
9. The acoustic wave sensor according to claim 7 , wherein the second end of the first insulating film has a tapered shape having a thickness decreases toward the receiving electrode.
10. The acoustic wave sensor according to claim 6 , wherein a velocity of the transverse wave propagating through the first insulating film is higher than a velocity of the transverse wave propagating through the piezoelectric substrate.
11. The acoustic wave sensor according to claim 6 , wherein a velocity of the transverse wave propagating through the second insulating film is lower than a velocity of the transverse wave propagating through the piezoelectric substrate.
12. The acoustic wave sensor according to claim 6 ,
wherein the second insulating film is made of silicon oxide, and
wherein the first insulating film is made of silicon nitride.
13. The acoustic wave sensor according to claim 6 , wherein an end of the first insulating film is located apart from an end of the reaction section and inside the reaction section in a propagation direction in which the main acoustic wave propagates.