Ultrasonic fingerprint sensor with acoustic shielding
Disclosed are methods, devices, apparatuses, and systems for ultrasonic fingerprint sensing with an acoustic shielding structure. One or more layers in an ultrasonic fingerprint sensing system may reflect back ultrasonic waves due to acoustic impedance mismatch that can distort a fingerprint image. An acoustic shielding structure may be configured to absorb, store, trap, or otherwise attenuate ultrasonic waves. The acoustic shielding structure may be positioned underlying an ultrasonic sensor layer. In some implementations, the acoustic shielding structure may include a plurality of periodically spaced apart geometric features or holes in a medium.
1. An apparatus comprising:
an ultrasonic sensor layer;
an ultrasonic transmitter layer over the ultrasonic sensor layer and having a piezoelectric material configured to generate ultrasonic waves;
a backing layer underlying the ultrasonic sensor layer, the backing layer including a material with an acoustic impedance different from that of the ultrasonic sensor layer; and
an acoustic attenuator layer between the ultrasonic sensor layer and the backing layer, wherein the acoustic attenuator layer includes a plurality of features periodically spaced apart in a medium, wherein each of the features includes a solid vertical component and a solid horizontal component, wherein a gap separates each solid horizontal component from a top of the acoustic attenuator layer and separates each solid vertical component from the top of the acoustic attenuator layer, the solid horizontal component intersecting the solid vertical component.
2. The apparatus of claim 1 , wherein the solid vertical component and the solid horizontal component comprise different material.
3. The apparatus of claim 1 , wherein the plurality of features includes a plurality of periodically spaced apart solid vertical components and periodically spaced apart solid horizontal components, each of the solid vertical components being discontinuous across a thickness of the acoustic attenuator layer.
4. The apparatus of claim 1 , wherein the solid horizontal component intersects a portion between a top and bottom of the solid vertical component.
5. The apparatus of claim 1 , wherein the solid horizontal component intersects a top of the solid vertical component.
6. The apparatus of claim 1 , wherein the plurality of features include a plurality of solid vertical components that are periodically spaced apart in a horizontal direction by a distance between a quarter-wavelength and a half-wavelength of the ultrasonic waves.
7. The apparatus of claim 1 , wherein the medium includes at least one of a metal, ceramic, plastic, and air, the medium having an acoustic impedance different from that of the plurality of features.
8. The apparatus of claim 1 , wherein the acoustic attenuator layer is configured to absorb or at least attenuate ultrasonic waves.
9. The apparatus of claim 1 , wherein a thickness of the acoustic attenuator layer is between about 50 μm and about 500 μm.
10. The apparatus of claim 1 , wherein the ultrasonic sensor layer includes:
a thin film transistor (TFT) substrate; and
an array of thin film transistor (TFT) pixel circuits disposed on the TFT substrate.
11. The apparatus of claim 1 , further comprising:
a control system coupled to the ultrasonic sensor layer, the control system configured to:
receive fingerprint sensor data from the ultrasonic sensor layer; and
extract fingerprint data from the fingerprint sensor data, the fingerprint data corresponding to fingerprints of a user's hand.
12. A mobile device comprising:
a platen; and
an ultrasonic fingerprint sensor system underlying the platen, the ultrasonic fingerprint sensor system including:
an ultrasonic transmitter layer including a piezoelectric material configured to generate ultrasonic waves;
an ultrasonic sensor layer underlying the ultrasonic transmitter layer; and
an acoustic attenuator layer underlying the ultrasonic sensor layer, wherein the acoustic attenuator layer includes: a plurality of periodically spaced apart features in a medium, wherein each of the features includes a solid vertical component and a solid horizontal component, wherein a gap separates each solid horizontal component from a top of the acoustic attenuator layer and separates each solid vertical component from the top of the acoustic attenuator layer, the solid horizontal component intersecting the solid vertical component.
13. The mobile device of claim 12 , wherein the ultrasonic fingerprint sensor system further includes:
a backing layer underlying the acoustic attenuator layer, wherein the backing layer includes a material with an acoustic impedance different from that of the ultrasonic sensor layer.
14. The mobile device of claim 12 , wherein the acoustic attenuator layer is configured to absorb or at least attenuate ultrasonic waves.