The disclosure relates to a sensing apparatus; in particular, the disclosure relates to a fingerprint sensing apparatus.
Currently, fingerprint recognition is widely applied in various electronic products, and most commonly in portable mobile devices such as smart phones and tablet computers. Currently in the fingerprint recognition applied to smart phones, forms of common fingerprint sensing apparatuses may be categorized into an optical form, a capacitive form, ultrasonic form, etc. By utilizing a piezoelectric micromachined ultrasonic transducer (PMUT), common ultrasonic fingerprint sensing apparatuses transmit and receive ultrasonic waves for fingerprint sensing. Since the PMUT requires a higher AC drive voltage (100 to 200V) and needs to be manufactured on a silicon substrate to be manufactured with a complementary metal-oxide semiconductor (CMOS) circuit, the manufacturing costs are relatively high, adversely affecting application to a large-area fingerprint sensing.
The disclosure provides a fingerprint sensing apparatus, in which manufacturing costs of an ultrasonic fingerprint sensing apparatus is reduced, facilitating application to large-area fingerprint sensing.
According to an embodiment of the disclosure, a fingerprint sensing apparatus includes a signal emission receiving layer, a driving circuit, a sensing circuit layer, and a substrate. The signal emission receiving layer includes a capacitive micromachined ultrasonic transducer array formed by a plurality of capacitive micromachined ultrasonic transducers. The driving circuit is coupled to the capacitive micromachined ultrasonic transducer array, and drives the capacitive micromachined ultrasonic transducer array to emit a planar ultrasonic wave to a finger during a transmission period to generate a plurality of reflected ultrasonic signals. The capacitive micromachined ultrasonic transducers receive the reflected ultrasonic signals during a receiving period to generate a plurality of sensing current signals. The sensing circuit layer includes a plurality of sensing circuits. The sensing circuits are respectively coupled to the corresponding capacitive micromachined ultrasonic transducers, and sense the sensing current signals output by the capacitive micromachined ultrasonic transducers to generate a plurality of fingerprint sensing signals. The sensing circuit layer is formed on the substrate, and the signal emission receiving layer is formed on the sensing circuit layer. The substrate is a glass substrate or a silicon substrate.
Based on the foregoing, in the embodiments of the disclosure, the driving circuit may drive the micro-machined ultrasonic transducer array to emit the planar ultrasonic wave to the finger during the transmission period to generate the reflected ultrasonic signals. The micromachined ultrasonic transducer may receive the reflected ultrasonic signals during the receiving period to generate the sensing current signals. The sensing circuit senses the sensing current signals output by the micromechanical ultrasonic transducers to generate the fingerprint sensing signals. Compared with fingerprint sensing utilizing piezoelectric micromachined ultrasonic transducers, fingerprint sensing utilizing the micromachined ultrasonic transducers requires a lower AC drive voltage. In addition, since the micromachined ultrasonic transducers may be formed on a glass substrate, compared to the manufacturing using a silicon substrate, the manufacturing costs are reduced, facilitating application to large-area fingerprint sensing.
To make the aforementioned more comprehensible, several embodiments accompanied with drawings are described in detail as follows.
The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure.
To be more specific, taking the capacitive micromachined ultrasonic transducer CM1 as an example, each capacitive micromachined ultrasonic transducer may include electrode layers E1 and E2 and a dielectric layer DE1. The dielectric layer DE1 is disposed between the electrode layers E1 and E2, and a cavity VA1 is formed between the dielectric layer DE1 and the electrode layer E2. The materials of the electrode layers E1 and E2 may, for example, include aluminum, nickel, titanium, copper, or silver. The thickness of the electrode layers E1 and E2 is between 0.1 um to 1.5 um. The material of the dielectric layer DE1 may include silicon dioxide, aluminum oxide, or silicon nitride. The thickness of the dielectric layer DE1 is between 0.1 um to 1.5 um. The gap between the dielectric layer DE1 and the electrode layer E2 is between 0.03 um and 0.5 um. The electrode layer E1 is coupled to the driving circuit 102, and the electrode layer E2 is coupled to the corresponding sensing circuit SA1. In addition, the selection circuit 110 is coupled to the sensing circuits SA1 to SA3 and the processing circuit 112. In some embodiments, the driving circuit 102 may include a direct-current voltage generating circuit Vdc and a waveform generating circuit Vac as shown in
During a transmission period, the driving circuit 102 may output a driving signal S1, and drives the capacitive micromachined ultrasonic transducer array to transmit a planar ultrasonic wave to a finger to generate a plurality of reflected ultrasonic signals. During a receiving period, each capacitive micromachined ultrasonic transducer may receive the reflected ultrasonic signals to generate a plurality of sensing current signals IS1 to ISN. To be more specific, during the transmission period, the waveform generating circuit Vac may provide an alternating-current voltage with a predetermined waveform, and the direct-current voltage generating circuit Vdc may provide a direct-current voltage. Taking the driving signal S1 shown in
After the transmission period TA ends, the waveform generating circuit Vac may stop providing the alternating-current voltage, and accordingly the capacitive micromachined ultrasonic transducer array stops emitting the planar ultrasonic wave, while the direct-current voltage generating circuit Vdc continues to provide the direct-current voltage. During the receiving period, the electric field between the electrode layers E1 and E2 of the capacitive micromachined ultrasonic transducers CM1 to CM3 is varied as the reflected ultrasonic signal is received. Thereby, the corresponding sensing current signals IS1 to ISN are generated.
The sensing circuits SA1 to SAN may respectively receive the sensing current signals IS1 to ISN, and generate a plurality of fingerprint sensing signals FS1 to FSN according to the sensing current signals IS1 to ISN. The fingerprint sensing signals FS1 to FSN are respectively proportional to the sensing current signals IS1 to ISN. The selection circuit 110 may selectively output the fingerprint sensing signals FS1 to FSN to the processing circuit 112 according to a column and row selection signal, such that the processing circuit 112 generates a fingerprint image according to the fingerprint sensing signals FS1 to FSN, and performs fingerprint recognition processing on the fingerprint image.
As such, in fingerprint sensing through the capacitive micromachined ultrasonic transducers, the required AC drive voltage is reduced. In addition, the signal emission receiving layer 104 including the capacitive micromachined ultrasonic transducers may be formed on the glass substrate with the sensing circuit layer 106 in the same TFT process, instead of being manufactured in different processes and then joined together. Compared with manufacturing utilizing a silicon substrate, the costs are reduced, facilitating application to large-area fingerprint sensing.
Notably, in some embodiments, the waveform generated by the driving circuit 102 is not limited to a square wave. For example,
During a reset period, the reset transistor M2 may be controlled by a reset control signal VRST and enter a turn-on state during the reset period, such that the reset voltage VB1 resets the voltage at the control terminal of the conversion transistor M3. During a receiving period, the conversion transistor M3 may generate the corresponding fingerprint sensing signal FS1 at the second terminal of the conversion transistor M3 in response to the sensing current signal IS1 provided by the capacitive micromachined ultrasonic transducer CM1. The reading transistor M4 may be controlled by the reading control signal VRD and enter a turn-on state during a reading period to transmit the fingerprint sensing signal FS1 through the selection circuit 110 to the processing circuit 112 for fingerprint recognition processing.
Notably, a capacitive micromachined ultrasonic transducer array is taken as an example for description in the above embodiments, but the disclosure is not limited thereto. In other embodiments, the capacitive micromachined ultrasonic transducer array may also be replaced by a piezoelectric micromachined ultrasonic transducer array formed by a plurality of piezoelectric micromachined ultrasonic transducers or a piezoelectric thin-film micromachined ultrasonic transducer array formed by a plurality of piezoelectric thin-film micromachined ultrasonic transducers for implementation.
In summary of the foregoing, in the embodiments of the disclosure, the driving circuit may drive the micro-machined ultrasonic transducer array to emit the planar ultrasonic wave to the finger during the transmission period to generate the reflected ultrasonic signals. The micromachined ultrasonic transducer may receive the reflected ultrasonic signals during the receiving period to generate the sensing current signals. The sensing circuit senses the sensing current signals output by the micromechanical ultrasonic transducers to generate the fingerprint sensing signals. Compared with fingerprint sensing utilizing piezoelectric micromachined ultrasonic transducers, fingerprint sensing utilizing the micromachined ultrasonic transducers requires a lower AC drive voltage. In addition, since the micromachined ultrasonic transducers may be formed on a glass substrate, compared to the manufacturing using a silicon substrate, the manufacturing costs are reduced, facilitating application to large-area fingerprint sensing.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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202110390381.9 | Apr 2021 | CN | national |
This application claims the priority benefits of U.S. provisional application Ser. No. 63/054,223, filed on Jul. 20, 2020, U.S. provisional application Ser. No. 63/054,249, filed on Jul. 21, 2020, and Chinese application no. 202110390381.9, filed on Apr. 12, 2020. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.
Number | Date | Country | |
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63054223 | Jul 2020 | US | |
63054249 | Jul 2020 | US |