Micro-nano acoustic image sensor capable of large-scale integration and control method thereof

Abstract

The application discloses a micro-nano acoustic image sensor capable of large-scale integration and a control method thereof. The micro-nano acoustic image sensor comprises a plurality of pixel sensing units arranged in an array; each pixel sensing unit comprises a micro-mechanical ultrasonic transducer located at a top layer, a pixel circuit located at a bottom layer and an inter-electrode metal bonding layer connecting the two; wherein the micro-mechanical ultrasonic transducer is an acoustic-electric conversion unit with an inverted diaphragm structure, and is connected to the pixel circuit through a lower electrode layer; the pixel circuit is an integrated circuit internal unit with a "3T1D" structure, has a peak sound pressure rectification function, and synchronously senses and addresses samples the sound pressure signal of each pixel sensing unit through an inverse correlation double sampling method, and the sampling method has a global shutter function. The application can perform large-scale array integration on the pixel sensing unit, and perform tomographic sampling on the spatial distribution of ultrasonic echoes, and can directly realize dynamic intensity imaging and distance tomographic imaging of a target sound field.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of acoustic imaging, and further belongs to the field of ultrasonic imaging, and particularly relates to a micro-nano acoustic image sensor capable of large-scale integration and a control method thereof. BACKGROUND

[0002] In view of the problems of low integration and poor consistency of a conventional transducer splicing to form a sensing array, researchers began to try to design a new type of ultrasonic transducer using MEMS technology, i.e., a micromachined ultrasonic transducer (MUT), in the 1990s. The C.S. Draper Laboratory in the United States first reported the research on MUT array sensing imaging technology. In 1997, the laboratory first deposited a PZT thin film using a sol-gel technology, and then combined a MEMS process to prepare a sensing array with an effective area of 6x6 pixels, and completed an imaging test of 141x141 pixels by scanning and splicing on the focal plane of an underwater acoustic lens. Considering the time-domain vibration characteristics of ultrasonic signals, the device uses a multi-channel parallel sampling method to obtain real-time acoustic pressure signals of each array element.

[0003] After that, with the help of the micro-nano manufacturing capability of the MEMS process, after more than 20 years of development, people have made a series of research achievements in MUT and its array technology. These achievements are divided into two categories according to the sensing mechanism, i.e., capacitive (Capacitive) and piezoelectric (Piezoelectric), namely CMUT and PMUT. At present, MUT devices can be realized on a silicon substrate to achieve large-scale integration, but still have to use a large number of channels in parallel to sample the acoustic pressure signals of each array element in real time. For example, the most outstanding portable product Butterfly iQ developed by the American Butterfly Network Company, which represents the highest level in the industry. The device is highly integrated with an ASIC, although it has a CMUT array of 64x140, but its real effective receiving channel is only 1 / 8 of the number of array elements. The main reason is that the acoustic pressure signal of each array element needs to be sampled in real time by an independent channel. Even if it is integrated with the front end of the ASIC, a large number of channels for parallel sampling are inevitable for a large-scale array. Therefore, with the increase of the array size, the parallel sampling of a large number of array elements has always restricted the further integration of MUT devices.

[0004] In view of the above problems, in recent years, scholars at home and abroad have proposed a sensing scheme of row-column intersection addressing and row-column scanning, for example, a miniature ultrasonic imaging system based on PMUT array scanning imaging, namely an ultrasonic fingerprint sensor. In 2016, Tang et al. of the University of California reported a highly integrated on-chip ultrasonic fingerprint sensor, which is composed of a 110x56 PMUT array and an ASIC. For a fingerprint target with a small and constant distance, in order to avoid the coupling crosstalk of adjacent elements, Tang et al. adopt a multi-column phased focusing transmission, a single-column detection sampling method of echo amplitude, and finally complete the projection intensity imaging of the fingerprint echo through column scanning. Although this scheme reduces the number of parallel sampling channels through column scanning and realizes large-scale integration of the MUT array, it cannot realize synchronous sampling and real-time imaging of the spatial distribution of the ultrasonic signal.

[0005] In summary, due to the imaging system of the conventional acoustic B-scan (azimuth-distance), the above schemes need to use a large number of channels to parallel sample the sound pressure signals of each element, and the array size of the sensor device is limited. Secondly, due to the flexible and variable target area and detection distance, even if the imaging real-time performance is not considered, the above schemes cannot be used for conventional acoustic imaging of a large field of view target. SUMMARY

[0006] Therefore, the present application provides a large-scale integrated micro-nano acoustic image sensor and a control method thereof, which are used for realizing two-dimensional intensity imaging of the spatial distribution of an ultrasonic echo. The micro-nano acoustic image sensor is integrated by a large-scale array of pixel sensing units, each of which adopts an independent pixel circuit to realize synchronous sensing and addressing readout of the sound pressure signal. In addition, a sensing control method with a global shutter function can be used to perform spatial tomographic sampling on the ultrasonic echo received by all pixel sensing units. The micro-nano acoustic image sensor and the control method thereof provided by the present application can directly realize dynamic intensity imaging and distance tomographic imaging of a target sound field.

[0007] To achieve the above purpose, the present application provides a large-scale integrated micro-nano acoustic image sensor, which comprises a plurality of pixel sensing units arranged in an array; each pixel sensing unit comprises a micro-mechanical ultrasonic transducer located at the top layer, a pixel circuit located at the bottom layer, and an electrode interconnection layer connecting the two;

[0008] The micro-mechanical ultrasonic transducer is an inverted acoustic-electric conversion unit with a diaphragm structure, which is electrically interconnected with the corresponding pixel circuit at the wafer level through the lower electrode layer;

[0009] The pixel circuit is an internal pixel array unit of a micro-nano acoustic image sensor application specific integrated circuit, and has a "3T1D" circuit structure; the pixel circuit of each pixel sensing unit is connected to a corresponding column bus CS j of each column of pixel sensing units in units of columns, and the column bus is used as a column addressing signal line at the same time; each row of pixel sensing units is connected to a corresponding row addressing signal line RS i in units of rows; all pixel circuits are connected to the same reset signal line.

[0010] The pixel circuit is controlled by using a double correlated sampling method, and the signal voltage of each pixel sensing unit is read out by row and column addressing sampling.

[0011] Preferably, the micro-mechanical ultrasonic transducer comprises a diaphragm and a support substrate; the diaphragm is of an inverted structure, comprising a Si layer, a SiO2 layer, an upper electrode layer, a piezoelectric layer and a lower electrode layer arranged in sequence from top to bottom; the support substrate is an insulating layer fixed around the periphery of the diaphragm; the diaphragm, the support substrate and the pixel circuit form a cavity required for diaphragm vibration.

[0012] Preferably, the lower electrode layer is pixelated and etched separately, or the lower electrode layer and multiple layers of the Si layer, the SiO2 layer, the upper electrode layer and the piezoelectric layer are all pixelated and etched separately.

[0013] Preferably, the pixel circuit comprises a transistor T1, a transistor T2, a transistor T3 and a diode D1.

[0014] The source of the transistor T1 is connected to the lower electrode layer of the micro-mechanical ultrasonic transducer, the drain is connected to a reference voltage, and the gate is connected to a reset signal line.

[0015] The gate of the transistor T2 is connected to the source of the transistor T1, the source is connected to the drain of the transistor T3, and the drain is connected to a power supply voltage.

[0016] The gate of the transistor T3 is connected to a corresponding row addressing signal line RS i of the pixel circuit, the drain is connected to the source of T2, and the source is connected to a corresponding column bus CS j of the pixel circuit.

[0017] The positive and negative electrodes of the diode D1 are connected to the source of T1 and the reference voltage respectively, and the positive electrode of the diode D1, the source of T1 and the gate of the transistor T2 are connected to form a floating node FG.

[0018] Preferably, the transistor T1, the transistor T2 and the transistor T3 are NPN transistors or PNP transistors.

[0019] The second aspect of the present application provides a control method of a micro-nano acoustic image sensor which can be mass integrated, the control method performs peak rectification sampling control on the sound pressure signal in the whole echo cycle, and comprises:

[0020] 1.1: at the beginning of the sensing sampling period, the voltage of each row addressing signal line RS of the pixel circuit is converted from high level to low level, the reset signal RST is maintained to low level, the external sound source is driven to start radiating ultrasonic pulses, and the spatial distribution of the ultrasonic echo sound pressure signal is received by the micro-nano acoustic image sensor; i

[0021] 1.2: the voltage of each row addressing signal line RS of the pixel circuit and the reset signal RST are maintained to low level, the diode D1 is used to rectify the ultrasonic echo sound pressure signal sensed by the lower electrode layer of the micro-mechanical ultrasonic transducer, so that the voltage of the floating node FG is clamped to the sum of the conduction threshold voltage of the diode D1 and the reference voltage; i

[0022] 1.3: after the ultrasonic echo action ends, the voltage of each row addressing signal line RS of the pixel circuit is converted from low level to high level, and the voltage of the floating node FG of all pixel circuits is sampled for the first time through row-column addressing, and the sampling result is read out by each column bus CS i j

[0023] 1.4: after the first sampling is completed, the reset signal RST is converted from low level to high level, and the reference voltage is converted from low voltage state to high voltage state, and the pixel circuit charges the reset charge to the lower electrode layer of the micro-mechanical ultrasonic transducer connected thereto; j

[0024] 1.5: after the reset charge is fully charged, the reset signal RST is converted from high level to low level, and the reference voltage is converted from high voltage state to low voltage state, and after the voltage of the floating node FG returns to the reset state, the second sampling is performed through row-column addressing, and the sampling result is read out by each column bus CS i

[0025] 1.6: after the second sampling is completed, the voltage of each row addressing signal line RS of the pixel circuit is converted from high level to low level, and each pixel circuit stops sampling and reading out, the difference between the voltage of the two samplings of each pixel circuit is the signal voltage corresponding to the peak sound pressure of the ultrasonic echo at the pixel point, and the signal voltages of all pixel circuits form a two-dimensional image of the ultrasonic echo sound pressure intensity according to the array arrangement of the pixel sensing units;

[0026] ​​​​​​1.7: Based on the actual imaging requirements, repeating the sensing sampling cycle from 1.1 to 1.6 allows for multiple sensing and imaging of the spatial distribution of ultrasonic echo sound pressure intensity.

[0027] A third aspect of this invention proposes a control method for a scalably integrated micro / nano acoustic image sensor. This control method is a sensing timing control method with a global shutter function. The method performs peak rectification sampling control on the sound pressure signals of the echo during different flight distances and time periods, including:

[0028] 2.1: Connect the RS addressing signal lines of each row of the pixel circuit. i The voltage changes from high level to low level, maintaining the reset signal RST at a low level, and then driving the external sound source to start radiating ultrasonic pulses. The spatial distribution of the ultrasonic echo sound pressure signal is received by the micro-nano acoustic image sensor.

[0029] 2.2: Before the start of the flight time period set within the echo cycle, the reset signal RST is changed from low level to high level, and the reference voltage is changed from low voltage state to high voltage state. The floating node FG is charged with reset charge. After the reset charge is fully charged, at the start of the sampling time period, the reset signal RST is changed from high level to low level again, and the reference voltage is changed from high voltage state to low voltage state, so that the micro-nano acoustic image sensor can start to receive the spatial distribution of ultrasonic echo sound pressure signal again.

[0030] 2.3: During the flight time of the echo cycle, maintain the RS addressing signal lines of each row of the pixel circuit. i The voltage and reset signal RST are low. At the same time, diode D1 is used to detect and rectify the ultrasonic echo sound pressure signal sensed by the lower electrode layer of the micromechanical ultrasonic transducer so that the voltage of the floating node FG is the sum of the conduction threshold voltage of diode D1 and the reference voltage.

[0031] 2.4: After the flight time of the echo cycle ends, the RS addressing signal lines of each row of the pixel circuit are... i The voltage transitions from low to high, and the voltage of all floating nodes FG in the pixel circuit is sampled for the first time using row and column addressing. The sampling results are then processed by the CS of each column bus. j Read it aloud;

[0032] 2.5: After the first sampling is completed, the reset signal RST is changed from low level to high level, and the reference voltage is changed from low voltage state to high voltage state. The pixel circuit charges the lower electrode layer of the micromechanical ultrasonic transducer connected to it with reset charge.

[0033] 2.6: After the reset charge is fully charged, the reset signal RST is switched from high to low, and the reference voltage is switched from high to low. After the voltage of the floating node FG returns to the reset state, a second row-column addressing sampling is performed. The sampling results are then processed by the CS of each column bus. j Read it aloud;

[0034] 2.7: After the second sampling is completed, the RS addressing signal lines of each row of the pixel circuit are... i When the voltage changes from high to low, each pixel circuit stops sampling and reading. The difference between the two sampling voltages of each pixel circuit is the signal voltage corresponding to the peak sound pressure of the pixel point during the flight time of the ultrasonic echo at the corresponding distance. The signal voltages of all pixel circuits are arranged according to the array of pixel sensing units to form a two-dimensional image of the ultrasonic echo intensity distribution at that distance.

[0035] The beneficial effects of this invention are:

[0036] (1) The micro-nano acoustic image sensor that can be integrated on a large scale is integrated by an array of pixel sensing units. Each pixel sensing unit has its own independent and dedicated pixel circuit for synchronous real-time sampling of its sensing signal. Therefore, the acoustic image sensor can be integrated on a large scale and can perform real-time synchronous sampling of the spatial distribution of sound pressure signal. It can solve the problem that the array size of the sensor device is limited by a large number of array elements being read out synchronously in the prior art.

[0037] (2) In the micro-nano acoustic image sensor that can be integrated on a large scale, the micro-mechanical ultrasonic transducer in each pixel sensing unit of the present invention is pixelated by diaphragm etching, which can avoid vibration crosstalk between pixels; moreover, by flipping the diaphragm of the micro-mechanical ultrasonic transducer, wafer-level bonding interconnection between the sensing electrode and the pixel circuit can be achieved, thereby reducing the spatial gap between the two, reducing circuit parasitic parameters, and reducing sampling noise.

[0038] (3) In the micro-nano acoustic image sensor that can be integrated on a large scale in this invention, the pixel circuit in each pixel sensing unit has peak detection and rectification function. The synchronous sensing and addressing sampling of the sound pressure signal of each pixel sensing unit is performed by the inverse correlation double sampling method. This sampling method can eliminate the reset transistor switching noise, diode conduction threshold voltage difference, flicker noise and thermal noise of each transistor in the pixel circuit, which can effectively reduce signal noise and improve the sampling accuracy of the device.

[0039] (4) The micro-nano acoustic image sensor that can be integrated on a large scale has a global shutter function, which can perform synchronous tomographic sampling of the spatial distribution of ultrasonic echoes at different distances, and can realize direct visualization imaging, dynamic intensity imaging and distance tomographic imaging of the target sound field.

[0040] In summary, the micro-nano acoustic image sensor proposed in this invention can be integrated into a large-scale array of pixel sensing units, and each pixel sensing unit realizes real-time sensing and addressing sampling of sound pressure signals through its independent pixel circuit, without the need for a large number of parallel channels, thus improving the scalability of the sensor device. The pixel circuit has peak detection and rectification functions, and senses and samples the sound pressure signals of each pixel sensing unit through an inverse correlation double sampling method, reducing sampling noise and improving sensing accuracy. The sensing sampling control method of this micro-nano acoustic image sensor can realize direct visualization imaging, dynamic intensity imaging, and distance tomography imaging of the target sound field.

[0041] After being fitted with an acoustic lens, the micro-nano acoustic image sensor of the present invention, which can be integrated on a large scale, can achieve high-resolution ultrasonic imaging with a large field of view that conforms to human vision and resembles optical images, and has strong practicality. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of the micro-nano acoustic image sensor in an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of the cross-sectional structure of a single pixel sensing unit of the micro-nano acoustic image sensor in an embodiment of the present invention.

[0044] Figure 3 This is a schematic diagram of a partial structure of the pixel circuit array of a micro / nano acoustic image sensor dedicated integrated circuit in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the pixel circuit structure of the micro-nano acoustic image sensor in an embodiment of the present invention;

[0046] Figure 5 This is a timing diagram of the sensing sampling control of the micro-nano acoustic image sensor for a complete echo cycle in an embodiment of the present invention;

[0047] Figure 6 This is a timing diagram of the tomographic sensing control of the micro-nano acoustic image sensor for ultrasonic echoes during different flight distances and time periods in an embodiment of the present invention.

[0048] In the figure: 1. Micro-nano acoustic image sensor 1-A. Micromechanical ultrasonic transducer 1-B. Electrode metal bonding layer 1-C. Pixel circuit 1-A-1. Si layer 1-A-2. SiO2 layer 1-A-3. Upper electrode layer 1-A-4. Piezoelectric layer 1-A-5. Lower electrode layer 1-A-6. Supporting substrate. Detailed Implementation

[0049] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

[0050] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0051] This invention provides a micro / nano acoustic image sensor that can be scalably integrated, as an example of... Figure 1 As shown, the micro-nano acoustic image sensor includes multiple pixel sensing units arranged in an array. Each pixel sensing unit includes a micromechanical ultrasonic transducer 1-A on the top layer, a pixel circuit 1-C on the bottom layer, and an inter-electrode metal bonding layer 1-B connecting the two.

[0052] like Figure 2 As shown, the micromechanical ultrasonic transducer 1-A includes a diaphragm and a supporting substrate 1-A-6. The diaphragm includes, from top to bottom, a Si layer 1-A-1, a SiO2 layer 1-A-2, an upper electrode layer 1-A-3, a piezoelectric layer 1-A-4, and a lower electrode layer 1-A-5. In this embodiment, the piezoelectric layer 1-A-4 is made of PZT, and the upper electrode layer 1-A-3 and the lower electrode layer 1-A-5 are made of Al. The supporting substrate 1-A-6 is an insulating layer fixed around the diaphragm, and in this embodiment, its material can be SiO2. The supporting substrate 1-A-6, the pixel circuit 1-C, and the diaphragm of the micromechanical ultrasonic transducer 1-A form the cavity required for diaphragm vibration.

[0053] The aforementioned micromechanical ultrasonic transducer 1-A achieves pixelation through diaphragm etching, which serves to avoid vibration crosstalk between pixels during sensing. In this embodiment, the micromechanical ultrasonic transducer 1-A is an acoustic-electric conversion unit with an inverted diaphragm structure, which facilitates wafer-level electrical bonding interconnection between the sensing electrode (lower electrode layer 1-A-5) of the micromechanical ultrasonic transducer and the pixel circuit 1-C (internal array unit of the ASIC), reducing the spatial gap between the two and decreasing circuit parasitic parameters.

[0054] As an example, the lower electrode layer 1-A-5 of the micromechanical ultrasonic transducer 1-A is separated by pixelated etching; as another example, the lower electrode layer 1-A-5 and multiple layers among the Si layer 1-A-1, SiO2 layer 1-A-2, upper electrode layer 1-A-3 and piezoelectric layer 1-A-4 are all separated by pixelated etching.

[0055] like Figure 3As shown, pixel circuit 1-C is an internal pixelated array unit of the dedicated integrated circuit for micro / nano acoustic image sensors. All pixel circuits 1-C of the pixel sensing units are integrated on the dedicated integrated circuit of the micro / nano acoustic image sensor. As an example, the pixel circuit 1-C of each pixel sensing unit is arranged in columns, connecting each column of pixel sensing units to the corresponding column bus CS. j Above, each column of bus CS j It is also used as a column addressing signal line, connecting each row of pixel sensing units to the corresponding row addressing signal line RS on a row-by-row basis. i All pixel circuits 1-C are connected to the same reset signal line and are reset by the same reset signal RST, which facilitates the synchronous reset of all pixel sensing units in the micro-nano acoustic image sensor.

[0056] As another embodiment, the above-mentioned columns of bus CS can also be used. j RS and row addressing signal lines i Make the swap.

[0057] As an example, pixel circuit 1-C is as follows Figure 4 The diagram shows a "3T1D" circuit structure, specifically including transistor T1, transistor T2, transistor T3, and diode D1. The source of transistor T1 is connected to the lower electrode layer of the micromechanical ultrasonic transducer, the drain is connected to the reference voltage, and the gate is connected to the reset signal line. The gate of transistor T2 is connected to the source of transistor T1, the source is connected to the drain of transistor T3, and the drain is connected to a low level. The gate of transistor T3 is connected to the row addressing signal line RS corresponding to the pixel circuit it belongs to. i The drain of T2 is connected to the source of T2, and the source is connected to the column bus CS corresponding to the pixel circuit. j Above; the positive and negative terminals of diode D1 are connected to the source of T1 and the reference voltage, respectively. The positive terminal of diode D1, the source of T1, and the gate of transistor T2 are connected to form a floating node FG.

[0058] The transistors T1, T2 and T3 mentioned above are NPN type transistors or PNP type transistors.

[0059] Each of the aforementioned pixel circuits 1-C uses an inverse correlation double sampling method for sensing and sampling control. This involves first synchronously sensing the sound pressure signal of each pixel sensing unit, and then using the row addressing signal line RS... i CS and column addressing signal lines j The cross-selection transmits the signal voltage of the corresponding pixel sensing unit (i, j) to each column bus CS. j Then, the signal is sampled and read out using the same amplifier and the same AD device. Finally, the related reset signal is sampled again and the difference is calculated to eliminate circuit noise and obtain the real sound pressure signal corresponding to the pixel.

[0060] As an example, there are two control methods for the micro-nano acoustic image sensor of the present application: one is to perform peak rectification sampling control on the sound pressure signal in the entire echo cycle; the other is a sensing timing control method with a global shutter function, which can perform peak rectification sampling control on the sound pressure signal of the echo in the time-of-flight period at different distances according to the imaging needs of targets at different distances, so as to realize the tomographic imaging of the target. The detailed processes of the two control methods are introduced as follows:

[0061] (1) The first one is to perform peak rectification sampling control on the sound pressure signal in the entire echo cycle, which is described in combination with the sensing control timing diagram shown in FIG. 2: Figure 5

[0062] At time t0, that is, at the end of the previous sensing sampling period T and the beginning of the new sensing sampling period T, the reference voltage V ref is kept at a low level. First, the voltage of each row addressing signal line RS i of the pixel circuit is converted from a high level to a low level, turning off all the transistors T3 of the pixel circuit, while keeping the reset signal RST at a low level to turn off the transistor T1. At this time, the lower electrode layer voltage of the micro-mechanical ultrasonic transducer of each pixel sensing unit (that is, the voltage of the floating node FG) is floating, and the voltage is equal to the sum of the conduction threshold voltage V th-D1 of the diode D1 and the reference voltage V ref . Then, an external sound source is driven to start radiating ultrasonic pulses, and the spatial distribution of the ultrasonic echo sound pressure signal is received by the micro-nano acoustic image sensor.

[0063] During the period from t0 to t1, the voltage of each row addressing signal line RS i of the pixel circuit and the reset signal RST are kept at a low level. Under the action of the ultrasonic echo, the micro-mechanical ultrasonic transducer converts the sound pressure excitation into a corresponding signal voltage and conducts it to the floating node FG through the lower electrode layer. Due to the detection and rectification effect of the diode D1, the peak part of the voltage of the floating node FG higher than the initial voltage V th-D1 + V ref is clamped, which is manifested as a positive charge discharging through the diode D1, so that the voltage of the floating node FG is the sum of the conduction threshold voltage of the diode D1 and the reference voltage.

[0064] After the action of the ultrasonic echo ends, the diaphragm of the micro-mechanical ultrasonic transducer returns to the initial equilibrium state. At this time, the voltage of each row addressing signal line RS i of the pixel circuit is converted from a low level to a high level, and the voltage of the floating node FG of all the pixel circuits is sampled for the first time (1#) through row-column addressing, and the sampling results are transmitted to each column bus CS j ​superior;

[0065] After the first sampling is completed, at time t2, the reset signal RST changes from low to high, at which point the reference voltage V... ref It also transitions from a low voltage state to a high voltage state, and the increase in voltage is greater than the turn-on threshold voltage V of diode D1. th-D1 The pixel circuit charges the lower electrode of the micromechanical ultrasonic transducer with reset charge;

[0066] After the reset charge is fully charged, at time t3, the reset signal RST is switched from high to low. At this time, the reference voltage V... ref It also transitions from a high-voltage state to a low-voltage state due to the conduction threshold voltage V of diode D1. th-D1 Due to the clamping effect, the excess reset charge ΔQ charged into the lower electrode layer of the micromechanical ultrasonic transducer during the t2-t3 stage will be discharged through diode D1, restoring the voltage of the floating node FG to the reset state. Subsequently, a second row-column addressing sampling (2#) is performed, and the sampling results are obtained from each column bus CS. j Read it aloud;

[0067] After the second sampling is completed, the RS addressing signal lines of each row of the pixel circuit are... i When the voltage changes from high level to low level, each pixel circuit stops sampling and reading. The difference between the two sampling voltages of each pixel circuit is the signal voltage corresponding to the peak sound pressure of the ultrasonic echo at that pixel point. The signal voltages of all pixel circuits are arranged according to the array of pixel sensing units to form a two-dimensional image of the ultrasonic echo sound pressure intensity.

[0068] The above process can be repeated according to the actual imaging needs, based on the sensing sampling period T, to perform multiple sensing and imaging of the spatial distribution of ultrasonic echo sound pressure intensity.

[0069] (2) The second method is a sensor timing control method with global shutter function, combined with Figure 6 The sensor control timing diagram shown is used for explanation and comparison. Figure 5 The sensor control timing sequence for the complete ultrasonic echo cycle shown has the following characteristics: during the ultrasonic echo cycle, the voltage of the levitated node FG can be reset to its initial state before the start of a flight time period at any distance.

[0070] First, connect the RS addressing signal lines of each row of the pixel circuit. i The voltage changes from high level to low level, turning off transistor T3, keeping the reset signal RST at low level, turning off transistor T1, and then driving the external sound source to start radiating ultrasonic pulses. The spatial distribution of the ultrasonic echo sound pressure signal is received by the micro-nano acoustic image sensor.

[0071] Then, before the start of the flight time period F set in the echo cycle T, the reset signal RST is converted from low to high, and the reference voltage is converted from low to high, the reset charge is charged to the floating node FG, and after the reset charge is charged, the reset signal RST is converted from high to low at the start of the flight time period F, and the reference voltage is converted from high to low, so that the micro-nano acoustic image sensor starts to receive the spatial distribution of the ultrasonic echo pressure signal again.

[0072] The above two-step process is the idle stage before the start of the flight time period F in the echo cycle T.

[0073] Then, the flight time period F in the echo cycle T is entered, and the process is basically the same as the control method process for the complete echo cycle, except that the flight time period F can start at any time in the echo cycle T. For example, Figure 6 As shown in FIG. 6, at the start time t0 of the flight time period F, the ultrasonic echo has acted for a period of time, at which time the voltage of each row addressing signal line RS i of the pixel circuit is kept at a low level to turn off transistor T3, and the reset signal RST is also kept at a low level to turn off transistor T1, and the micro-nano acoustic image sensor will start to receive the ultrasonic echo excitation again.

[0074] After the ultrasonic echo action ends, the voltage of each row addressing signal line RS i of the pixel circuit is converted from low to high, and the voltage of the floating node FG of all pixel circuits is sampled for the first time by row-column addressing, and the sampling result is transmitted to each column bus CS j In this embodiment, the end time of the flight time period F in the echo cycle T is the end time of the echo cycle T, but in fact it is not limited to this case, and the start time and end time of the flight time period in the echo cycle can be adjusted.

[0075] Next, after the first sampling is completed, the floating node FG is reset, and the voltage after the reset is sampled for the second time, and the sampling result is transmitted to each column bus CS j The specific operation is the same as the second sampling operation in the first control method.

[0076] Finally, after the second sampling is completed, the voltage of each row addressing signal line RS iThe voltage of each pixel circuit is converted from high level to low level, and each pixel circuit stops sampling and reading out, and the difference between the two sampling voltages of each pixel circuit is the signal voltage corresponding to the peak sound pressure of the ultrasonic echo in the time-of-flight period of the corresponding distance.

[0077] The above process has a global shutter function, can sample and sense any time period within the action period of the ultrasonic echo, and can reduce the length of the time-of-flight period by adjusting the reset time of the floating node FG voltage, realize short-time fast "explosion", and be used for dynamic acoustic imaging. In addition, by using the global shutter function, the time-of-flight period of the echo of different distance targets in the ultrasonic echo can be intercepted, and the cross-sectional image of the echo intensity of the target, i.e. the tomographic image, can be obtained. Therefore, the micro-nano acoustic image sensor and the control method thereof can realize dynamic acoustic imaging and distance tomographic imaging.

[0078] It should be clear to those skilled in the art that the acoustoelectric conversion unit of each pixel in the micro-nano acoustic image sensor of the present application is a piezoelectric micro-mechanical ultrasonic transducer (PMUT) with an inverted diaphragm structure, which functions to realize the acoustoelectric conversion of the micro-nano acoustic image sensor of the present application to the sound pressure signal. In the present application, only the piezoelectric inverted diaphragm structure of the PMUT is replaced with an inverted capacitive cavity diaphragm structure, and the capacitive micro-mechanical ultrasonic transducer (CMUT) can also be used to perform acoustoelectric conversion on the sound pressure signal. Therefore, based on the inventive concept of the present application, replacing the piezoelectric micro-mechanical ultrasonic transducer (PMUT) with the capacitive micro-mechanical ultrasonic transducer (CMUT), and adaptively replacing and modifying the remaining structures of the present application, all fall within the protection scope of the present application.

Claims

1. A micro- and nano-acoustic image sensor that can be mass- integrated, characterized in that, The micro-nano acoustic image sensor comprises a plurality of pixel sensing units arranged in an array; each pixel sensing unit comprises a micro-mechanical ultrasonic transducer located at a top layer, a pixel circuit located at a bottom layer, and an inter-electrode metal bonding layer connecting the two; The micro-mechanical ultrasonic transducer is an acoustic-electric conversion unit with an inverted diaphragm structure, and the lower electrode layer thereof is electrically interconnected with the corresponding pixel circuit at a wafer level; The pixel circuit is an internal pixelated array unit of a micro-nano acoustic image sensor integrated circuit, and has a "3T1D" circuit structure, wherein the pixel circuit comprises a transistor T1, a transistor T2, a transistor T3, and a diode D1; The source electrode of the transistor T1 is connected to the lower electrode layer of the micro-mechanical ultrasonic transducer, the drain electrode is connected to a reference voltage, and the gate electrode is connected to a reset signal line; The gate electrode of the transistor T2 is connected to the source electrode of the transistor T1, the source electrode is connected to the drain electrode of the transistor T3, and the drain electrode is connected to a power supply voltage; The gate of the transistor T3 is connected with the row addressing signal line RS corresponding to the pixel circuit i The drain of the transistor T3 is connected with the source of the transistor T2, and the source is connected with the column bus CS corresponding to the pixel circuit j ; The positive and negative electrodes of the diode D1 are connected to the source electrode of T1 and the reference voltage, respectively, and the positive electrode of the diode D1, the source electrode of T1, and the gate electrode of the transistor T2 are connected to form a floating node FG; The pixel circuit of each pixel sensing unit is connected to the corresponding column bus CS in column unit j , which is used as the column addressing signal line at the same time j ; the pixel circuit of each row pixel sensing unit is connected to the corresponding row addressing signal line RS in row unit i ; and all the pixel circuits are connected to the same reset signal line. The pixel circuit is controlled by using an inverse double correlation sampling method, and the signal voltage of each pixel sensing unit is row-column addressed, sampled, and read out.

2. The massively integrable micro / nano-acoustic image sensor according to claim 1, wherein, The micro-mechanical ultrasonic transducer comprises a diaphragm and a support substrate; the diaphragm is an inverted structure comprising a Si layer, a SiO2 layer, an upper electrode layer, a piezoelectric layer, and a lower electrode layer arranged in order from top to bottom; the support substrate is an insulating layer fixed around the periphery of the diaphragm; the diaphragm, the support substrate, and the pixel circuit form a cavity required for diaphragm vibration.

3. The massively integrable micro / nano-acoustic image sensor according to claim 2, wherein, The lower electrode layer is pixelated and etched to separate, or multiple layers of the lower electrode layer, the Si layer, the SiO2 layer, the upper electrode layer, and the piezoelectric layer are all pixelated and etched to separate.

4. The massively integrable micro / nano-acoustic image sensor according to claim 1, wherein, The transistor T1, the transistor T2, and the transistor T3 are NPN transistors or PNP transistors.

5. A method of controlling a large-scale integrable micro / nano-acoustic image sensor using the large-scale integrable micro / nano-acoustic image sensor according to any one of claims 1 to 4, characterized by, The control method performs peak rectification sampling control on the sound pressure signal in the entire echo cycle, comprising: 1.1: At the beginning of the sensing sampling period, the RS addressing signal lines of each row of the pixel circuit are... i The voltage changes from high level to low level, while the reset signal RST is maintained at low level, and then the external sound source is driven to start radiating ultrasonic pulses, and the spatial distribution of ultrasonic echo sound pressure signal is received by micro-nano acoustic image sensor. 1.2: Address signal line RS of each row of the pixel circuit is maintained i The voltage of the floating node FG is clamped to the sum of the on- threshold voltage of the diode D1 and the reference voltage, while the ultrasonic echo pressure signal sensed by the micro-mechanical ultrasonic transducer lower electrode layer is detected and rectified by the diode D1. 1.3: After the ultrasonic echo effect ends, the RS addressing signal lines of each row of the pixel circuit are... i The voltage transitions from low to high, and the voltage of all floating nodes FG in the pixel circuit is sampled for the first time using row and column addressing. The sampling results are then processed by the CS of each column bus. j Read it aloud; 1.4: After the first sampling is completed, the reset signal RST is converted from low level to high level, and the reference voltage is converted from low voltage state to high voltage state, and the pixel circuit charges the reset charge to the lower electrode layer of the micro-mechanical ultrasonic transducer connected thereto; 1.5: After the reset charge is filled, the reset signal RST is converted from high level to low level, and the reference voltage is converted from high voltage state to low voltage state. After the voltage of the floating node FG returns to the reset state, it is addressed by row and column for the second time sampling. The sampling result is output by each column bus CS j read out; 1.6: After the second sampling is completed, the RS addressing signal lines of each row of the pixel circuit are... i When the voltage changes from high level to low level, each pixel circuit stops sampling and reading. The difference between the two sampling voltages of each pixel circuit is the signal voltage corresponding to the peak sound pressure of the ultrasonic echo at the pixel point. The signal voltages of all pixel circuits are arranged in an array according to the pixel sensing unit to form a two-dimensional image of the ultrasonic echo sound pressure intensity. 1.7: According to the actual imaging requirements, repeat 1.1-1.6 according to the sensing sampling period, and perform multiple sensing imaging on the spatial distribution of the ultrasonic echo sound pressure intensity.

6. A method of controlling a large-scale integrable micro / nano-acoustic image sensor using the large-scale integrable micro / nano-acoustic image sensor according to any one of claims 1 to 4, characterized by, The control method is a sensing timing control method with a global shutter function, which performs peak rectification sampling control on the sound pressure signal in different distance time-of-flight periods, comprising: 2.1: Connect the RS addressing signal lines of each row of the pixel circuit i The voltage changes from high level to low level, maintaining the reset signal RST at a low level, and then driving the external sound source to start radiating ultrasonic pulses. The spatial distribution of the ultrasonic echo sound pressure signal is received by the micro-nano acoustic image sensor. 2.2: before the start of the time-of-flight period set within the echo cycle, the reset signal RST is converted from low to high level, and the reference voltage is converted from low voltage state to high voltage state, the floating node FG is charged with reset charge, after the reset charge is charged, at the start of the time-of-flight period, the reset signal RST is converted from high to low level, and the reference voltage is converted from high voltage state to low voltage state, so that the micro-nano acoustic image sensor starts to receive the spatial distribution of the ultrasonic echo pressure signal again; 2.3: During the time-of-flight period of the echo cycle, the row address signal lines RS of the pixel circuits are held at a voltage and the reset signal RST is low while the ultrasound echo pressure signal sensed by the micromechanical ultrasound transducer lower electrode layer is rectified by diode D1 to clamp the voltage of the floating node FG to the sum of the turn-on threshold voltage of diode D1 and the reference voltage; i 2.3: During the time-of-flight period of the echo cycle, the row address signal lines RS of the pixel circuits are held at a voltage and the reset signal RST is low while the ultrasound echo pressure signal sensed by the micromechanical ultrasound transducer lower electrode layer is rectified by diode D1 to clamp the voltage of the floating node FG to the sum of the turn-on threshold voltage of diode D1 and the reference voltage; 2.4: After the end of the time-of-flight period of the echo cycle, the row addressing signal lines RS of the pixel circuits are switched from low to high voltage, and the voltage of all pixel circuit floating nodes FG is sampled for the first time by row and column addressing, the result being read out by the column buses CS i . 2.5: The row addressing signal lines RS are switched from high to low voltage, and the voltage of all pixel circuit floating nodes FG is sampled for the second time by row and column addressing, the result being read out by the column buses CS j . 2.5: after the first sampling is completed, the reset signal RST is converted from low to high level, and the reference voltage is converted from low voltage state to high voltage state, and the pixel circuit charges the micro-mechanical ultrasonic transducer lower electrode layer connected thereto with reset charge; 2.6: After the reset charge filling is completed, the reset signal RST is converted from high level to low level, and the reference voltage is converted from high voltage state to low voltage state. After the voltage of the floating node FG returns to the reset state, it is addressed for the second time and sampled. The sampling result is output by each column bus CS j read out; 2.7: After the second sampling is completed, the RS addressing signal lines of each row of the pixel circuit are... i When the voltage changes from high to low, each pixel circuit stops sampling and reading. The difference between the two sampling voltages of each pixel circuit is the signal voltage corresponding to the peak sound pressure of the pixel point during the corresponding distance flight time. The signal voltages of all pixel circuits are arranged according to the array of pixel sensing units to form a two-dimensional image of the ultrasonic echo intensity distribution at that distance.

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