Ultrasonic sensor device and control method thereof

Abstract

To improve the SN ratio of an ultrasonic sensor device.SOLUTION: An ultrasonic sensor device includes a plurality of pixels each including an ultrasonic transducer, and a control circuit that controls the plurality of pixels. Each pixel of the plurality of pixels holds a received signal from the ultrasonic transducer and transmits it to the control circuit as a response signal. The control circuit acquires an excited response signal, which is a response signal transmitted from the pixel after applying excitation to the ultrasonic transducer. The control circuit acquires an unexcited response signal, which is a response signal transmitted from the pixel without applying excitation to the ultrasonic transducer. The control circuit corrects the excited response signal based on the unexcited response signal.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present disclosure relates to an ultrasonic sensor device and a control method thereof.

Background Art

[0002] Ultrasonic sensors are used in various fields, such as non-destructive inspection of objects, object detection, and fingerprint reading. For example, as fingerprint sensors, integrated MEMS ultrasonic fingerprint sensors using MEMS (Micro Electro Mechanical Systems) and TFT (Thin Film Transistor) ultrasonic fingerprint sensors have been developed. These include a pixel array composed of two-dimensionally arranged pixels, and each pixel includes an ultrasonic transducer.

[0003] The ultrasonic transducer is, for example, a piezoelectric element. The ultrasonic transducer in the pixel may be composed of a single element that transmits and receives ultrasonic waves, or may be composed of a transmitter that transmits ultrasonic waves and a receiver that receives ultrasonic waves. Specifically, the ultrasonic transducer emits ultrasonic waves in response to an electrical signal, receives the ultrasonic waves reflected by the object, and converts them into an electrical signal.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to the inventors' research, the signal-to-noise ratio (SNR) of signals from pixels containing ultrasonic transducers tends to be low. For example, problems such as large low-frequency noise and large variations in signals from trial to trial can occur. [Means for solving the problem]

[0006] One aspect of the present disclosure is an ultrasonic sensor device comprising a plurality of pixels, each including an ultrasonic transducer, and a control circuit for controlling the plurality of pixels, wherein each of the plurality of pixels holds a received signal from the ultrasonic transducer and transmits it to the control circuit as a response signal, the control circuit acquires an excitation response signal which is a response signal transmitted from the pixel after excitation is applied to the ultrasonic transducer, acquires an unexcited response signal which is a response signal transmitted from the pixel without excitation being applied to the ultrasonic transducer, and corrects the excitation response signal based on the unexcited response signal.

[0007] One aspect of the present disclosure is a control method for an ultrasonic sensor device including a plurality of pixels, each including an ultrasonic transducer, wherein an excitation response signal is obtained, which is a response signal transmitted from the pixels after excitation is applied to the ultrasonic transducer; an unexcited response signal is obtained, which is a response signal transmitted from the pixels without excitation being applied to the ultrasonic transducer; and the excitation response signal is corrected based on the unexcited response signal. [Effects of the Invention]

[0008] According to one aspect of this disclosure, the signal-to-noise ratio of an ultrasonic sensor device can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing the configuration of the ultrasonic sensor device according to the embodiment. [Figure 2] This is a circuit diagram showing the circuit configuration of pixels in a pixel array substrate of an embodiment. [Figure 3]This shows an example of a terminal configuration including an ultrasonic sensor device. [Figure 4] A schematic representation of a portion of the pixel's cross-sectional structure is shown. [Figure 5] This is a timing chart showing an example of sensing operation in one frame (one unit period) using the ultrasonic sensor device disclosed herein. [Figure 6] The measurement results of the excitation response signal when a sensing target object is present and when a sensing target object is absent are shown. [Figure 7A] This shows the measurement results of the difference between the excitation response signal when the object is present and the excitation response signal when the object is absent. [Figure 7B] This shows the measurement results of the difference between the excitation response signal when the object is present and the excitation response signal when the object is absent. [Figure 8] This diagram illustrates the operation of correcting the excited response signal using the unexcited response signal. [Figure 9] A schematic diagram of the comb-type filter configuration is shown. [Figure 10] This diagram illustrates a method for processing pixel response signals for fingerprint reading, including a two-stage correction process. [Figure 11A] This shows the results of multiple measurements of the difference between the excitation response signal Vout (with object) and the excitation response signal Vout (w / o object). [Figure 11B] This shows the results of multiple measurements of the difference between the corrected excitation response signal ^S (with object) and the corrected excitation response signal ^S (w / o object). [Figure 12] The measurement results of the relationship between the bias pulse width Tdb and several signals, including ^S (without object), are shown. [Figure 13] This flowchart shows an example of a control method for a fingerprint sensor device. [Figure 14] A schematic example of a display screen corresponding to the processing flow shown in Figure 13 is shown. [Figure 15] A schematic example of a configuration in which the pixel region 12 is divided into two subregions is shown. [Figure 16] It is a sequence diagram showing an example of a driving method for a divided pixel region.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the ultrasonic sensor device of the present disclosure will be described in detail with reference to the drawings. The size and scale of each component in each drawing are appropriately changed and described in order to ensure the visibility of the drawing. Also, the hatching in each drawing is for distinguishing each component and does not necessarily mean a cut surface. Also, although the term "transistor" is used for a non-linear element used as a switching element or an amplifying element, the transistor includes a Thin Film Transistor (TFT).

[0011] The ultrasonic sensor device of the present disclosure can be used, for example, in medical or industrial inspection fields, or for detecting fingerprints and objects. The ultrasonic sensor device according to an embodiment of this specification includes a pixel array composed of a plurality of arranged pixels. The pixel array is composed of, for example, pixels in a one-dimensional array or a two-dimensional array.

[0012] Each pixel includes an ultrasonic transducer. The ultrasonic transducer transmits and receives ultrasonic waves. The ultrasonic transducer may be composed of a single element that transmits and receives ultrasonic waves, or may be composed of a transmitter that transmits ultrasonic waves and a receiver that receives ultrasonic waves. Ultrasonic waves have a frequency outside the audible range of 20 kHz or more. The frequency of the ultrasonic waves is appropriately selected according to the application field and usage situation. The frequency of the ultrasonic waves is, for example, 5 MHz. Alternatively, in order to enhance the directivity of the ultrasonic waves, a higher frequency, for example, 20 MHz, may be used, or 1000 MHz may be used.

[0013] In one embodiment of this specification, the ultrasonic transducer is a piezoelectric element. The piezoelectric material of the piezoelectric element may be an inorganic or organic material. The ultrasonic transducer generates ultrasonic waves in response to an electrical signal from a control circuit and converts the received ultrasonic waves into an electrical signal. The pixel holds the electrical signal converted by the ultrasonic transducer. The received signal converted by the ultrasonic transducer is transmitted from the pixel to the control circuit as a response signal.

[0014] According to the inventors' research, the signal-to-noise ratio (SNR) of signals from pixels containing ultrasonic transducers that transmit and receive ultrasound tends to be low. For example, problems such as large low-frequency noise and large variations in signals from trial to trial can occur.

[0015] One embodiment of this specification acquires a response signal by exciting an ultrasonic transducer, and also acquires a response signal without exciting the ultrasonic transducer. The response signal with excitation is corrected with the response signal without excitation. This effectively removes noise from the response signal with excitation, enabling more accurate sensing of the target. Hereinafter, the response signal with excitation may be referred to as the excited response signal, and the response signal without excitation may be referred to as the unexcited response signal.

[0016] [Device configuration] Figure 1 is a block diagram showing an example configuration of an ultrasonic sensor device according to one embodiment of this specification. The ultrasonic sensor device 10 includes a pixel array substrate 11 and a control circuit. The control circuit includes a multiplexer circuit 15, a drive circuit 14, a signal detection circuit 16, and a main control circuit 18. Note that some parts of the control circuit may be omitted or other circuits may be added, and some functions of one circuit may be included in other circuits.

[0017] The pixel array substrate 11 includes an insulating substrate (for example, a glass substrate) and a pixel region 12 on the insulating substrate in which pixels 13 are arranged in a vertical and horizontal matrix. In this example, the pixel array is composed of two-dimensionally arranged pixels, but it may also be composed of one-dimensionally arranged pixels.

[0018] The multiplexer circuit 15 is formed on an insulating substrate of the pixel array substrate 11 and is connected to each signal line Dm of the vertically arranged pixel rows in Figure 1. The multiplexer circuit converts the signal into a time series, reducing the number of signal lines, which are then detected by the signal detection circuit 16.

[0019] The drive circuit 14 drives and controls the pixels 13 for the transmission and reception of ultrasonic waves. The multiplexer circuit 15 receives the ultrasonic detection signal from the pixels 13 transmitted via the signal line Dm and outputs it to the signal detection circuit 16. The signal detection circuit 16 detects the signals from each of the signal lines that have been converted into a time series by the multiplexer circuit.

[0020] The main control circuit 18 controls the drive circuit 14, the multiplexer circuit 15, and the signal detection circuit 16. The main control circuit 18 acquires the response signals output from each pixel and performs the necessary processing. In one embodiment of this specification, the main control circuit 18 corrects the excited response signal from each pixel with the unexcited response signal. Details of the processing of the response signals from pixels by the main control circuit 18 will be described later. The drive circuit 14, the signal detection circuit 16, and the main control circuit 18 may be mounted on the pixel array substrate 11, or as components separate from the pixel array substrate 11.

[0021] [Pixel configuration] Figure 2 shows the circuit configuration of a single pixel 13. Pixel 13 includes a piezoelectric element PE, which is an ultrasonic transducer. This piezoelectric element PE has both ultrasonic oscillation and reception functions. One electrode of the piezoelectric element PE is indicated by the code TX. Electrode TX is sometimes called the transmitting electrode, and the other electrode is called the receiving electrode. In the example element configuration described later, electrode TX is the upper electrode and the other electrode is the lower electrode. The side furthest from the insulating substrate is the top, and the side closer to it is the bottom.

[0022] In the piezoelectric element PE, a voltage VRX is induced in response to the received ultrasonic vibration. One pixel circuit of the ultrasonic sensor device 10 of this disclosure includes three thin-film transistors TR1, TR2, TR3, and a diode D1. The semiconductor material of the thin-film transistors is, for example, low-temperature polysilicon, oxide semiconductor, or amorphous silicon.

[0023] The cathode terminal of diode D1 is connected to node N1, which is located between the gate terminal of transistor TR1 and the source / drain terminals of transistor TR3. The anode terminal is connected to the diode bias line PA. One of the source / drain terminals of transistor TR1 is connected to the power line PP, and the other source / drain terminal is connected to one of the source / drain terminals of transistor TR2.

[0024] The gate terminal of transistor TR2 is connected to the control line Rn. The source / drain terminals of transistor TR2 are connected to the signal line Dm. The gate terminal of transistor TR3 is connected to the control line Rn+1. The signal transmitted by control line Rn+1 is the same as the signal transmitted by the control line Rn of the next pixel row. The source / drain terminals of transistor TR3 are connected to the anode and cathode terminals of diode D1, respectively.

[0025] Transistor TR1 (amplifying transistor) provides the function of amplifying the potential at one end of the piezoelectric element PE. Transistor TR2 is a switching element that provides the function of controlling the output from the pixel circuit. Transistor TR3 is a switching element that provides the function of resetting the potential at one end of the piezoelectric element PE and the gate electrode (node ​​N1) of transistor TR1.

[0026] In the ultrasonic sensor device 10 shown in Figure 1, there is one signal line Dm for each pixel array in which multiple pixels 13 are arranged vertically. All pixels 13 in the same pixel array are connected to the signal line Dm. This signal line Dm is connected to a multiplexer circuit 15 at the end of the pixel array substrate 11.

[0027] [Element structure] Figure 3 schematically shows an example of a terminal configuration including a pixel array substrate 11 according to one embodiment of this specification. The terminal includes a stacked pixel array substrate 11, a display panel 31, and a touch panel 32. The touch panel 32 can employ any type of touch detection method, such as a capacitive or resistive touch panel. The display panel 31 may be an OLED (Organic light emitting diode) display panel or another type of display panel. The display panel 31 and the touch panel 32 can be controlled together with the pixel array substrate 11 by a main control circuit 18.

[0028] The relative positions of the pixel array substrate 11, the display panel 31, and the touch panel 32 are not limited to the example in Figure 3 and are arbitrary. For example, the pixel array substrate 11 and the display panel 31 may not be stacked, but may be positioned separately in plane (viewed in the stacking direction) on one or a different side of the touch panel 32. The stack of the display panel and the touch panel and the stack of the pixel array of the ultrasonic sensor device and other touch panels may be mounted separately. The pixel array substrate 11 does not have to be stacked with other functional panels such as the display panel or touch panel.

[0029] Figure 4 schematically shows the cross-sectional structure of a portion of a single pixel. In the following description, "up" and "down" refer to the top and bottom in the drawing. The pixel array substrate 11 includes an insulating substrate 151 and a medium 200 facing the insulating substrate 151. The medium 200 is, for example, a flexible or inflexible insulating substrate made of resin or glass. As shown in Figure 3, a laminate of a display panel or touch panel that does not affect ultrasound may be placed on or in place of the medium 200. Multiple pixels are arranged between the insulating substrate 151 and the medium 200.

[0030] Ultrasonic waves emitted from the piezoelectric element are reflected by the surface of the medium 200 and return to the piezoelectric element. If, for example, human skin is present on the surface of the medium 200, the reflectivity of the ultrasound changes. The presence or absence of skin (surface irregularities) can be sensed by the strength of the reflected ultrasound.

[0031] Each pixel includes a lower electrode 162, an upper electrode 166, and a piezoelectric material layer 165 on an insulating substrate 151. These constitute a piezoelectric element, which is an ultrasonic transducer. The piezoelectric material layer 165 is positioned between the upper electrode 166 and the lower electrode 162. The piezoelectric material may be organic or inorganic; for example, polyvinylidene fluoride (PVDF) or lead zirconate titanate (PZT) can be used. Alternatively, a copolymer P(VDF / TrFE) of vinylidene fluoride (CH2CF2) and trifluoroethylene (CF2CFH) can be used.

[0032] In the configuration example shown in Figure 4, the upper electrodes 166 of multiple pixels are each different parts of a single common electrode. In one embodiment of this specification, the upper electrodes 166 of all pixels in the pixel array are different parts of a single common electrode having a shape that completely covers the entire surface of the pixel area. The piezoelectric material layer 165 is similar. The lower electrodes 162 are separated between pixels. Multiple lower electrodes 162 are arranged on the surface of the planarization film 161.

[0033] The upper electrode 166 is a transmitting electrode, and the lower electrode 162 is a receiving electrode. By applying an excitation signal to the upper electrode 166, ultrasonic waves are simultaneously emitted from the piezoelectric elements of all pixels, and a pixel-specific receiving signal is obtained by the lower electrode 162. The upper electrode and piezoelectric material layer may be separated for each pixel.

[0034] Each pixel includes a circuit containing multiple switches. This circuit drives and controls the piezoelectric element and is also called the pixel circuit. The pixel circuit is formed between the insulating substrate 151 and the lower electrode 162 layer. The pixel circuit controls the potential of the lower electrode 162 and holds the received signal from the lower electrode 162. In the configuration example shown in Figure 4, the upper electrode 166 is positioned on the side that emits ultrasonic waves and receives reflected waves (upper side of the drawing). Note that the stacking positional relationship between the piezoelectric element and the circuit may be reversed.

[0035] Figure 4 shows transistor TR3 and the gate electrode 157B of transistor TR1 in the pixel circuit. The insulating substrate 151 is formed of, for example, glass or resin, and is an inflexible or flexible substrate. An insulating underlayment 152 is formed on the insulating substrate 151, and a semiconductor active layer 155 is laminated thereon. The semiconductor active layer 155 includes a low-resistance source / drain region and a high-resistance channel region between them.

[0036] The semiconductor active layer 155 is covered by a gate insulating layer 156. A gate electrode is formed on the semiconductor active layer 155 via the gate insulating layer 156. Figure 4 shows the gate electrode 157A of transistor TR3 and the gate electrode 157B of transistor TR1. An interlayer insulating film 158 is formed on the layers of gate electrodes 157A and 157B.

[0037] Within the pixel region 12, source / drain electrodes 159 and 160 are formed on the interlayer insulating film 158. The source / drain electrodes 159 and 160 are formed of, for example, an Al-based alloy. The source / drain electrodes 159 and 160 are connected to the semiconductor active layer 155 by contact portions 168 and 169 formed in the contact holes of the interlayer insulating film 158.

[0038] The wiring portion 171 extends from the source / drain electrodes 160 of transistor TR3 and is connected to the gate electrode 157B of transistor TR1 by a contact portion 172 formed in the contact hole of the interlayer insulating film 158. The wiring portion 171 and the source / drain electrodes 160 are contained in the same metal layer and are continuous.

[0039] An insulating planarization film 161 is formed on the source / drain electrodes 159, 160 and the wiring portion 171. A lower electrode 162 is formed on the insulating planarization film 161. The lower electrode 162 is connected to the source / drain electrodes 160 by contact portions formed in the contact holes of the planarization film 161. The pixel circuit is formed on the underside of the lower electrode 162.

[0040] A piezoelectric material layer 165 is formed on the lower electrode 162. The piezoelectric material layer 165 is in contact with the upper surface of the lower electrode 162 and the upper surface of the planarized film. An upper electrode 166 is formed in contact with the piezoelectric material layer 165. The lower electrode 162, the piezoelectric material layer 165, and the upper electrode 166 constitute a piezoelectric element.

[0041] [Reading the excitation response signal] Figure 5 is a timing chart showing an example of sensing operation by the ultrasonic sensor device 10 in one frame (one unit period). The main control circuit 18 controls each pixel 13 for each consecutive frame to read out the response signal. In the operation example described with reference to Figure 5, the ultrasonic sensor device 10 emits ultrasonic waves in the initial period of the frame, stops emitting, and then receives reflected ultrasonic waves.

[0042] One frame is the period for reading response signals from at least some of the pixels in a pixel array. The example operation described below simultaneously drives the piezoelectric elements PE of all pixels to generate ultrasound within one frame, and sequentially reads the response signals from different pixel rows, one data line at a time.

[0043] Referring to Figure 5, the period from time T1 to time T2 is the ultrasonic oscillation period. At time T1, the drive circuit 14 changes the potential of control line Rn and control line Rn+1 from a low level to a high level. As a result, transistors TR2 and TR3 turn ON. The drive circuit 14 maintains the potential of the diode bias line PA at a low level. As a result, the potential of the receiving electrode (node ​​N1) of the piezoelectric element is fixed.

[0044] After transistors TR2 and TR3 are turned ON, the drive circuit 14 provides an excitation signal to the transmitting electrode TX of the piezoelectric element PE. This causes the piezoelectric element PE to vibrate and generate ultrasonic waves. Here, the transmitting electrode TX of each piezoelectric element of all pixels on the pixel array substrate 11 is part of a single common electrode. Therefore, all the piezoelectric elements of all pixels vibrate simultaneously. After that, the drive circuit 14 stops the signal to the transmitting electrode TX.

[0045] After stopping the signal to the transmitting electrode TX, at time T2, the drive circuit 14 changes the potential of control line Rn and control line Rn+1 from a high level to a low level. As a result, transistors TR2 and TR3 are turned OFF.

[0046] From time T2, the piezoelectric element PE receives reflected ultrasonic waves. Since transistor TR3 is in the OFF state, the receiving electrode of the piezoelectric element becomes floating, and an induced voltage VRX is generated in the piezoelectric element PE due to the reception of ultrasonic waves. In Figure 5, when the piezoelectric element PE is not receiving ultrasonic waves, the induced voltage VRX is 0, and when it is receiving ultrasonic waves, the induced voltage VRX is an AC voltage with an effective value greater than 0. The potential of node N1 changes according to the induced voltage VRX. Node N1 is the output node of the transducer.

[0047] At time T3, following time T2, the drive circuit 14 changes the potential of the diode bias line PA from a low level to a high level. The diode bias adjusts the potential of node N1 to the optimal bias voltage that transistor TR1 outputs to the signal line Dm.

[0048] Figure 5 shows the potential change at node N1 when the induced voltage VRX is 0 (solid line) and the potential change at node N1 when the induced voltage VRX is present (dashed line). As shown in Figure 5, the potential at node N1 changes in response to the induced voltage VRX and the diode bias. The potential at node N1 increases in response to the diode bias. Furthermore, the potential at node N1 increases further in response to the induced voltage VRX. The period Tdb during which the diode bias is applied is an important factor for accurate sensing. This point will be discussed in detail later.

[0049] At time T4, after a period Tdb has elapsed from time T3, the drive circuit 14 changes the potential of the diode bias line PA from a high level to a low level. As a result, the potential of node N1 becomes floating and is maintained at the elevated potential. In other words, the pixel holds the received signal from the piezoelectric element, which is an ultrasonic transducer, at node N1.

[0050] A high-level pulse is then applied to the control line Rn from time T5 to T6. This turns on transistor TR2, and transistor TR1 amplifies the signal held at node N1 and outputs the response signal to the signal line Dm. The drive circuit 14 sequentially outputs pulses to the control lines Rn of different pixel rows, thereby sequentially reading out the response signals from the pixels connected to the signal line Dm.

[0051] The signal detection circuit 16 receives output OUT from the data line. Output OUT indicates the response signal from sequentially selected pixels. The response signal accompanied by excitation of the piezoelectric element has a voltage ΔV higher than the response signal without excitation of the piezoelectric element. ΔV is a value based on the diode bias value, the diode bias duration, the induced voltage VRX, etc.

[0052] [Noise in the excitation response signal] Here, we will explain the noise in the excitation response signal. The excitation response signal is the response signal accompanied by the excitation of the ultrasonic transducer. Figure 6 shows the measurement results of the excitation response signal when a sensing target is present and when a sensing target is absent. The horizontal axis of the graph represents time, and the vertical axis represents the voltage of the excitation response signal.

[0053] Figure 6 shows the excitation response signals of different pixel rows read sequentially from a single data line. A silicone cube was used as the object for the measurement. This is the same for the other measurement results described below. In the example of a fingerprint sensor device, the excitation response signal of the part of the fingerprint (finger) that is in contact with the touch surface shows a value close to the excitation response signal when the sensing object is present in Figure 6. Also, the excitation response signal of the part of the fingerprint that is away from the touch surface shows a value close to the excitation response signal when the sensing object is not present in Figure 6.

[0054] In Figure 6, each pulse pair represents a pair of excitation response signals for each pixel row, one for when an object is present and one for when it is not. For example, the leftmost pulse pair represents the excitation response signal for the first pixel row R1. The 10th and 12th pulse pairs represent the excitation response signals for the 10th and 12th pixel rows, respectively. In each pair, the excitation response signal when an object is present is smaller than the excitation response signal when an object is not present.

[0055] As shown in Figure 6, the magnitude of the excitation response signal varies greatly between pixel rows. Furthermore, the difference between the excitation response signal when an object is present and the excitation response signal when no object is present is very small relative to the magnitude of the excitation response signal.

[0056] Figures 7A and 7B show the measurement results of the difference between the excitation response signal when an object is present and the excitation response signal when the object is absent. Figures 7A and 7B show the results of two separate measurements. Each measurement result represents the average value of 1000 frames. Each graph shows the difference in excitation response signals of different pixel rows read sequentially from a single data line. The horizontal axis of each graph represents time, and the vertical axis represents the difference in excitation response signals. The difference is the value obtained by subtracting the excitation response signal when the object is absent from the excitation response signal when the object is present.

[0057] In Figures 7A and 7B, the pulses represent the difference in the excitation response signals for each pixel row. For example, the leftmost pulse represents the difference in the excitation response signal for the first pixel row R1. The 10th and 12th pulse pairs represent the difference in the excitation response signals for the 10th and 12th pixel rows, respectively. As mentioned above, the excitation response signal for an object is smaller than the excitation response signal for an object that is not present, so the value of each pulse is negative.

[0058] As shown in Figures 7A and 7B, the difference in the excitation response signals of each pixel row varies greatly from measurement to measurement. Furthermore, in each measurement, the difference in the excitation response signals differs significantly between pixel rows. For example, in the measurement results of Figure 7A, the absolute value of the excitation response signal difference for pixel row R1 is much smaller than the absolute values ​​of the excitation response signal differences for pixel rows R10 and R12.

[0059] Thus, the excitation response signal contains low-frequency noise. This noise can hinder accurate sensing by the ultrasonic sensor device. One embodiment of this specification acquires an unexcited response signal, which is a response signal without excitation of the ultrasonic transducer, and uses it to correct the excitation response signal. This makes it possible to effectively remove noise from the excitation response signal.

[0060] [Response Signal Correction] Figure 8 illustrates the operation of correcting the excited response signal with the unexcited response signal. Figure 8 schematically shows the time evolution of several signals in two consecutive frames. Specifically, it shows the signal applied to the transmit electrode TX, the response signal Vout(t) from the data line, the response signal Vout(t-τ) from the previous frame period, and the difference between the response signals of the two frames (Vout(t-τ)-Vout(t)). τ is the frame period.

[0061] In the example shown in Figure 8, excitation is applied to the transmitting electrode TX only in odd-numbered frames, and not in even-numbered frames. The processing of odd-numbered frames and even-numbered frames is repeated.

[0062] Specifically, the main control circuit 18 generates ultrasonic waves by applying an excitation signal to a piezoelectric element in odd-numbered frames, and then reads out a response signal Vout(t) from each pixel. These are excitation response signals. Figure 8 shows, as an example, the reading of excitation response signals from three pixels PX1, PX2, and PX3. The excitation response signal includes the true (original) signal S due to reflected ultrasonic waves corresponding to the object (including when no object is present) and noise N.

[0063] The main control circuit 18 reads response signals Vout from each pixel in even frames without supplying an excitation signal to the piezoelectric element. These are unexcited response signals. Figure 8 shows, as an example, the reading of unexcited response signals from three pixels PX1, PX2, and PX3. The unexcited response signals do not include the signal S corresponding to the object, and consist only of noise N.

[0064] The main control circuit 18 corrects the excitation response signals of odd frames with the de-excitation response signals of even frames to obtain an estimated value ^S of the true signal S. For example, the de-excitation response signals of even frames are subtracted from the excitation response signals of odd frames, as shown in the following equation. ^S=Vout(t-τ)-Vout(t)

[0065] τ is the frame period, and Vout(t-τ) represents the response signal from one frame period ago. As described above, the excitation response signal Vout(t) for odd frames contains the true signal S and noise N, while Vout(t) for even frames contains only noise N. By subtracting the Vout(t) for even frames from the Vout(t) for odd frames, an estimate of the true signal S, ^S, can be obtained.

[0066] The signal processing (^S = Vout(t-τ)-Vout(t)) can be implemented using a comb filter. Figure 9 schematically shows the configuration of a comb filter. The comb filter includes a delay element 401 and an operator 402. The delay element 401 outputs the input signal after delaying it by time τ. The operator 402 outputs a signal obtained by subtracting the input signal from the output signal of the delay element 401. The main control circuit 18 may perform this signal processing using a processor that operates according to a program, or it may be performed using a logic circuit configured to execute the said arithmetic element.

[0067] A comb filter can attenuate low-frequency noise without attenuating the signal component. The above correction of the excitation response signal can attenuate the DC component and integer multiples of the frame frequency of the noise to virtually zero.

[0068] The above example corrects the excitation response signal of an odd-numbered frame with the de-excitement response signal of the next even-numbered frame. In other examples, the excitation signal of an even-numbered frame may be corrected with the de-excitement response signal of the next odd-numbered frame. In other examples, the de-excitement response signal of an odd-numbered frame may be corrected with the de-excitement response signal of the next even-numbered frame, or the de-excitement response signal of an even-numbered frame may be corrected with the de-excitement response signal of the next odd-numbered frame. In other examples, a single de-excitement response signal may be used to correct multiple excitation response signals, and the correction may be performed using de-excitement response signals of frames that are discontinuous with the excitation response signal frames.

[0069] In one embodiment of this specification, the main control circuit 18 acquires a corrected excitation response signal ^S(w / o object) when no object is present and a corrected excitation response signal ^S(with object) when an object is present. The main control circuit 18 corrects the response signal ^S(with object) with the response signal ^S(w / o object). For example, it subtracts the response signal ^S(w / o object) from the response signal ^S(with object).

[0070] In other applications, ultrasonic fingerprint sensor devices may include fixed pattern noise (FPN) in ^S(with object). The response signal ^S(w / o object) can effectively remove the fixed pattern noise from ^S(with object).

[0071] Figure 10 illustrates a method for processing the pixel response signal for fingerprint reading, including the two-stage correction process described above. In frame m, the main control circuit 18 reads the excitation response signal from the pixel with the finger on the device surface (451). In the next frame m+1, the main control circuit 18 reads the de-excitation response signal from the pixel with the finger on the device surface (453). Furthermore, the main control circuit 18 subtracts the de-excitation response signal from the excitation response signal to obtain a corrected excitation response signal ^S (with object) with the finger on the device surface (455).

[0072] The main control circuit 18 reads out the excitation response signal from the pixel in frame n when the finger is not placed on the touch surface (461). In the next frame n+1, the main control circuit 18 reads out the de-excitement response signal from the pixel when the finger is not placed on the touch surface (463). Frame n+1 may precede frame m, and frame m+1 may precede frame n. Furthermore, the main control circuit 18 subtracts the de-excitement response signal from the excitation response signal to obtain a corrected excitation response signal ^S(w / o object) when the finger is not placed on the touch surface (465).

[0073] Next, the main control circuit 18 subtracts the corrected excitation response signal ^S(w / o object) when the finger is not placed on the touch surface from the corrected excitation response signal ^S(with object) when the finger is placed on the touch surface (471). The main control circuit 18 compares the fingerprint image obtained from this value with a pre-stored fingerprint image and performs fingerprint authentication.

[0074] For example, in an ultrasonic fingerprint sensor device, the received sound pressure when there is no finger is greater than the received sound pressure when there is a finger. The received sound pressure when there is no finger changes depending on the excitation voltage of the ultrasonic transducer and the presence or absence of a surface protective seal. Therefore, by using ^S(w / o object), ^S(with object) can be corrected more accurately.

[0075] Next, we will explain the correction effect of the unexcited response signal on the excited response signal. Figure 11A shows the results of multiple measurements of the difference between the excited response signal Vout(with object) with an object and the excited response signal Vout(w / o object) without an object. Each measurement result is the average value over 1000 frames. The graph shows the difference in excited response signals of different pixel rows read sequentially from a single data line. The horizontal axis of the graph represents time, and the vertical axis represents the difference in the excited response signals. The difference is the value obtained by subtracting the excited response signal without an object from the excited response signal with an object.

[0076] In Figure 11A, different pulse groups represent measurements from different pixel rows (pixels) read from a single data signal. Each pulse represents a single measurement result from a single pixel row. For example, arrows are shown between two pulse groups. The arrows indicate the variability in the measurement results within a single pixel row. This variability is due to low-frequency noise. Also, as shown in Figure 11A, the relative magnitudes of Vout(with object) and Vout(w / o object) differ for some pixel rows from measurement to measurement.

[0077] Figure 11B shows the results of multiple measurements of the difference between the corrected excitation response signal ^S (with object) and the corrected excitation response signal ^S (w / o object). Each measurement result is the average value over 1000 frames. The graph shows the difference in corrected excitation response signals for different pixel rows read sequentially from a single data line. The horizontal axis of the graph represents time, and the vertical axis represents the difference in corrected excitation response signals. The difference is the value obtained by subtracting the corrected excitation response signal without an object from the corrected excitation response signal with an object.

[0078] In Figure 11B, different pulse groups represent measurements from different pixel rows (pixels) read from a single data signal. Each pulse represents a single measurement from a single pixel row. For example, two pulse groups are labeled with arrows. The arrows indicate the variability in the measurement results within a single pixel row. This variability is due to low-frequency noise.

[0079] Compared to the measurement results in Figure 11A, the variability, or low-frequency noise, has been significantly reduced. Specifically, the low-frequency noise has decreased from 0.91 mVRMS to 0.2 mVRMS. Thus, by correcting the excited response signal with the unexcited response signal, low-frequency noise can be effectively reduced.

[0080] [Adjusting the diode bias width] Next, we will explain how to adjust the pulse width Tdb of the bias applied to diode D1 in the pixel circuit shown in Figure 2. For example, when a finger is placed on the touch surface of a fingerprint sensor device, the convex part of the fingerprint is in contact with the touch surface, and the concave part is away from the touch surface. According to the inventors' research, it has been found that the magnitude relationship of the signal can change between the region where the fingerprint (object) is in contact with the touch surface and the region where the fingerprint (object) is away from the touch surface, depending on the pulse width Tdb.

[0081] More specifically, the relative magnitudes of the values ​​of (^S(with object)-^S(w / o object)) change depending on the bias pulse width Tdb between the region where the object is in contact with the touch surface and the region where the object is not in contact with the touch surface. When the pulse width Tdb is a specific value, the value is larger in the region where the object is in contact with the touch surface, and when the pulse width Tdb is any other specific value, the value is smaller in the region where the object is in contact with the touch surface.

[0082] The inventors' research revealed that the phenomenon of changing the relative magnitudes of (^S(with object)-^S(w / o object)) is strongly correlated with the corrected excitation response signal ^S(w / o object) which does not involve an object.

[0083] Figure 12 shows the measurement results of the relationship between the bias pulse width Tdb and several signals, including ^S (w / o object). The horizontal axis of the graph represents the bias pulse width Tdb. The left vertical axis represents the response signal Vout (w / o object) from a pixel without an object, and the right vertical axis represents the corrected excitation response signal ^S (w / o object) without an object.

[0084] In the graph in Figure 12, line 501 shows the excitation response signal without an object, line 502 shows the unexcited response signal without an object, and line 505 shows the corrected excitation response signal ^S (w / o object) without an object.

[0085] The signal ^S (without object) increases or decreases with increasing bias pulse width Tdb, exhibiting local maxima and minima. For example, the dashed circle 506 indicates the region containing the local maxima (@Tdb=0.98), and the dashed circle 507 indicates the region containing the local minima (@Tdb=1.08).

[0086] At Tdb=0.98, where the signal ^S(w / o object) shows a local maximum, the value of (^S(with object)-^S(w / o object)) was smaller in the region where the object was touching the touch surface than in the region where the object was not touching the touch surface. At Tdb=1.08, where the signal ^S(w / o object) shows a local minimum, the value of (^S(with object)-^S(w / o object)) was larger in the region where the object was touching the touch surface than in the region where the object was not touching the touch surface.

[0087] In the inventors' experiments, they were able to accurately acquire fingerprint images near these extreme values. On the other hand, they were unable to acquire accurate fingerprint images at intermediate values ​​far from these extremes, for example, at Tdb = 1.03. In other words, by identifying the extreme values ​​of the signal ^S(w / o object) and setting the Tdb value within a predetermined range, it is possible to accurately acquire an image of the object.

[0088] In one embodiment of this specification, the main control circuit 18 sets the bias pulse width Tdb based on the signal ^S(w / o object). The main control circuit 18 measures the relationship between the signal ^S(w / o object) and the bias pulse width Tdb and identifies an extreme value. The main control circuit 18 selects a value for the bias pulse width Tdb from a preset range based on the extreme value.

[0089] The signal ^S(w / o object), as shown in Figure 12, increases and decreases with increasing bias pulse width Tdb, and oscillates with a certain period. The period of the oscillation of ^S(w / o object) shown in Figure 12 is 0.2 μsec. The inventors discovered that the period of the oscillation of ^S(w / o object) is the same as the excitation period. Figure 12 shows the result when the excitation period is 0.2 μsec and the frequency is 5 MHz. Therefore, in order to measure the relationship between the signal ^S(w / o object) and the bias pulse width Tdb and to identify the maximum and minimum values, it is necessary to vary the bias pulse width Tdb over a time range of at least half the excitation period and measure the signal ^S(w / o object).

[0090] Figure 13 is a flowchart illustrating an example of a control method for a fingerprint sensor device. The fingerprint sensor device can be implemented in a terminal including a touch panel 32 and a display panel 31, as shown in Figure 3. Figure 14 schematically shows an example of a display screen corresponding to the processing flow shown in Figure 13.

[0091] As shown in Figure 13, when the main control circuit 18 detects a fingerprint acquisition start event (601), it determines whether the touch surface is being touched by an object such as a finger (hereinafter referred to as a finger) (602). In Figure 14, the screen 651 presents the user with information indicating the start of fingerprint authentication. This is an example of a fingerprint acquisition start event. The main control circuit 18 can determine whether a finger is being touched on the touch surface based on the signal from the touch panel 32.

[0092] If a finger is touching the touch surface (602: NO), the main control circuit 18 displays a message on the display panel 31 instructing the user to remove their finger from the touch surface (603). In Figure 14, screen 652 shows an example of this message.

[0093] If the finger is not touching the touch surface (602: YES), the main control circuit 18 measures the relationship between the bias pulse width Tdb and the signal ^S (w / o object) (604). The main control circuit 18 may, for example, acquire the signal ^S (w / o object) multiple times while changing the bias pulse width Tdb and calculate the average value of the signal ^S (w / o object) at each bias pulse width Tdb.

[0094] Next, the main control circuit 18 identifies the bias pulse width Tdb at which the signal ^S(w / o object) reaches an extremum, and sets the bias pulse width Tdb to that value (605). The bias pulse width Tdb may be a value different from the extremum in the region near the extremum.

[0095] Next, the main control circuit 18 displays a message on the display panel 31 instructing the user to place their finger in a predetermined position (606). In Figure 14, screen 653 displays an example of this message. Next, the main control circuit 18 controls the pixels with a set bias pulse width Tdb and acquires a corrected excitation response signal ^S (with object) associated with the object (finger) (607).

[0096] [Split drive] The following describes the segmented driving of the pixel region 12. In one embodiment of this specification, the ultrasonic sensor device 10 divides the pixel region 12 into a plurality of sub-regions and controls each sub-region. Figure 15 schematically shows an example of a configuration in which the pixel region 12 is divided into two sub-regions. Each sub-region is a pixel group composed of multiple pixels. The number of segmented regions is arbitrary. In one embodiment of this specification, the common electrode and diode bias wiring of the piezoelectric element are formed separately for each sub-region and driven individually. In the above configuration example, the upper electrodes of all pixels included in one pixel group are part of a single common electrode, and the diode wiring is common to all pixels.

[0097] Figure 15 shows, as an example, the separated common electrodes 701A and 701B and diode bias wirings 703A and 703B for each of the two subregions. The upper electrode 166 of each pixel in one subregion is part of the common electrode 701A, and the upper electrode 166 of each pixel in the other subregion is part of the common electrode 701B. As described above, excitation signals are supplied individually to the common electrodes 701A and 701B. The diode bias wirings 703A and 703B transmit diode biases individually.

[0098] The drive circuits that supply excitation signals to the common electrodes 701A and 701B may be provided separately, or a switch may be used to switch the output from one drive circuit between the common electrodes 701A and 701B. The diode bias wirings 703A and 703B of the two sub-regions are separated and driven individually. This configuration reduces the capacitance of the pixel's common electrode (transmitting electrode) and diode bias wire, thereby reducing the drive load. This makes it easier to enlarge the device. Alternatively, only one of the diode bias wiring or the common electrode may be formed separately for each sub-region.

[0099] Figure 16 is a sequence diagram showing an example of a method for driving divided pixel regions. Figure 16 schematically shows the excitation signal to the transmitting electrode TX and the response signal read from the pixel for a pixel region divided into two subregions.

[0100] During the period (frame) from time T50 to T51, the main control circuit 18 applies an excitation signal to the transmitting electrode TX of the first sub-region A and sequentially reads out the excitation response signals of each pixel in sub-region A. No response signals are read out from sub-region B. The processing of the first sub-region A in this frame is the same as that of the excitation-inducing frame described with reference to Figures 2 and 8.

[0101] In the next period (frame) from time T51 to T52, the main control circuit 18 sequentially reads out the unexcited response signals of each pixel in the first sub-region A without supplying an excitation signal to the transmitting electrode TX of the first sub-region A. No response signals are read out from sub-region B. The processing of the first sub-region A in this frame is the same as that of the unexcited frame described with reference to Figure 8.

[0102] During the period (frame) from time T52 to T53, the main control circuit 18 applies an excitation signal to the transmitting electrode TX of the second sub-region B and sequentially reads out the excitation response signals of each pixel in the sub-region B. No response signals are read out from sub-region A. The processing of the second sub-region B in this frame is the same as that of the excitation-inducing frame described with reference to Figures 2 and 8.

[0103] In the next period (frame) from time T53 to T54, the main control circuit 18 sequentially reads out the unexcited response signals of each pixel in the second sub-region B without supplying an excitation signal to the transmitting electrode TX of the second sub-region B. No response signals are read out from sub-region A. The processing for the second sub-region B in this frame is the same as that of the unexcited frame described with reference to Figure 8. These four frames are then repeatedly executed.

[0104] In the above example, the unexcited and excited response signals of each sub-region are acquired by two consecutive frames. In another example, the excited response signal of one sub-region and the unexcited response signal of the other sub-region may be read out in a single frame. In this case, the data lines of each pixel sequence are formed for each sub-region.

[0105] For example, in the first frame, the main control circuit 18 provides an excitation signal to the transmit electrode TX of the first sub-region A, but does not provide an excitation signal to the transmit electrode TX of the second sub-region B. Subsequently, it sequentially reads out the excitation response signals of each pixel in sub-region A, and simultaneously reads out the de-excitation response signals of each pixel in sub-region B.

[0106] Next, in the frame, the main control circuit 18 does not supply an excitation signal to the transmitting electrode TX of the first sub-region A, but supplies an excitation signal to the transmitting electrode TX of the second sub-region B. After that, it sequentially reads out the unexcited response signals of each pixel in sub-region A, and sequentially reads out the excited response signals of each pixel in sub-region B.

[0107] While embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above. Those skilled in the art can easily modify, add to, and transform each element of the above embodiments within the scope of the present disclosure. It is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and to add the configuration of another embodiment to the configuration of one embodiment. [Explanation of symbols]

[0108] 10 Ultrasonic sensor device, 11 Pixel array substrate, 12 Pixel area, 13 Pixel, 14 Driving circuit, 15 Multiplexer circuit, 16 Signal detection circuit, 18 Main control circuit, TR1, TR2, TR3 Transistors, D1 Diode, Rn, Rn+1 Control line, Dm Signal line, PE Piezoelectric element, TX Transmitting electrode, PA Diode bias wiring, PP Power line, 151 Insulating substrate, 152 Underlying insulating layer, 155 Semiconductor active layer, 156 Gate insulating layer, 157A, 157B Gate gate, 158 Interlayer insulating film, 159, 160 Source / drain electrodes, 162 Lower electrode, 165 Piezoelectric material layer, 166 Upper electrode, 171 Wiring section, 200 Medium, 701A, 701B Common electrode for partial area

Claims

1. An ultrasonic sensor device, a plurality of pixels each including an ultrasonic transducer; a control circuit that controls the plurality of pixels; Including, Each pixel of the plurality of pixels holds a signal received by the ultrasonic transducer and transmits the signal as a response signal to the control circuit; The control circuit Acquire an excitation response signal, which is a response signal transmitted from the pixel after excitation is applied to the ultrasonic transducer; Acquire a non-excitation response signal, which is a response signal transmitted from the pixel without applying excitation to the ultrasonic transducer; correcting the excitation response signal based on the non-excitation response signal; Ultrasonic sensor device.

2. The ultrasonic sensor device according to claim 1, The control circuit acquiring a first excitation response signal and a first non-excitation response signal in the absence of an object; correcting the first excitation response signal based on the first unexcited response signal; acquiring a second excitation response signal and a second non-excitation response signal in a state where the object is present; correcting the second excitation response signal based on the second unexcited response signal; determining an excitation response signal from the object based on a comparison result between the corrected first excitation response signal and the corrected second excitation response signal; Ultrasonic sensor device.

3. The ultrasonic sensor device according to claim 1, The control circuit In each of a plurality of consecutive frames, the plurality of pixels are controlled to acquire a response signal from each of the plurality of pixels; acquiring the excitation response signal in one of two consecutive frames; acquiring the unexcited response signal in the other of the two consecutive frames; Ultrasonic sensor device.

4. The ultrasonic sensor device according to claim 1, Each of the plurality of pixels includes a diode having a cathode connected to an output node of the ultrasonic transducer, The control circuit After exciting the ultrasonic transducer, a bias pulse is applied to the cathode of the excitation diode; acquiring a third excitation response signal and a third non-excitation response signal in the absence of an object; adjusting a pulse width of the bias pulse based on a difference between the third excitation response signal and the third non-excitation response signal; Ultrasonic sensor device.

5. 5. The ultrasonic sensor device according to claim 4, The control circuit Obtaining a difference between the third excitation response signal and the third non-excitation response signal for different pulse widths of the bias pulse; determining a relationship between a pulse width of the bias pulse and a difference between the third excited response signal and the third unexcited response signal; determining the extremum in said relationship; selecting a pulse width of the bias pulse from within a preset range including the extreme value; Ultrasonic sensor device.

6. The ultrasonic sensor device according to claim 1, the plurality of pixels are configured into a plurality of pixel groups, each of the pixel groups is composed of one or more pixels; the ultrasonic transducer is a piezoelectric element including a piezoelectric material layer and two electrodes sandwiching the piezoelectric material layer; One electrode of the ultrasonic transducer of each pixel group of the plurality of pixel groups is a part of one common electrode within each pixel group, The common electrodes of different pixel groups are separated from each other and individually controlled; Ultrasonic sensor device.

7. 7. The ultrasonic sensor device according to claim 6, Each of the plurality of pixels includes a diode having a cathode connected to an output node of the ultrasonic transducer, Separate diode bias wiring is laid out for each of the plurality of pixel groups. Ultrasonic sensor device.

8. A method for controlling an ultrasonic sensor device including a plurality of pixels each including an ultrasonic transducer, comprising: Acquire an excitation response signal, which is a response signal transmitted from the pixel after excitation is applied to the ultrasonic transducer; Acquire a non-excitation response signal, which is a response signal transmitted from the pixel without applying excitation to the ultrasonic transducer; correcting the excitation response signal based on the non-excitation response signal; Control method.

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