Capacitive micromechanical array ultrasonic transducer

Abstract

A group of upper electrode copper columns (13) and a group of lower electrode copper columns (14) which are connected with an upper electrode bonding pad (02) and a lower electrode bonding pad (04) of a CMUTs array chip (01) are respectively arranged on a ceramic adapter plate (08), and upper electrode solder balls (09) and lower electrode solder balls (10) are respectively connected with the upper electrode copper columns and the lower electrode copper columns through transmission lines (12); a through hole for containing a CMUTs array chip is formed in the center of a PCB (16), an upper electrode bonding pad and a lower electrode bonding pad of the PCB are connected with corresponding upper electrode welding balls and lower electrode welding balls, a copper column and welding ball array is welded to the PCB through the flip-chip reflow soldering technology, and the ultrasonic transducer free of lead bonding and packaged in a three-dimensional stacking and integrated mode is achieved. And the failure risk of lead bonding in a traditional packaging scheme is reduced, so that the packaging system has better thermal adaptability, and adverse effects caused by thermal stress are prevented.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic transducers, and particularly to a capacitive micromachined array ultrasonic transducer. Background Art

[0002] A capacitive micromachined ultrasonic transducer (CMUT) is a MEMS (Micro-Electro-Mechanical Systems) acoustic sensor that uses minute capacitance changes to detect vibration signals. It has advantages such as small size, large bandwidth, good acoustic matching characteristics, and easy integration, and has broad prospects in fields such as industrial non-destructive testing and ultrasonic medical imaging.

[0003] However, in order to meet the large energy and high power required for ultrasonic imaging, multiple CMUT elements are usually combined into an ultrasonic transducer array, and each element constitutes a channel. Therefore, an ultrasonic transducer chip contains many channels (commonly 64 channels, 128 channels, 192 channels, 256 channels, etc.). To achieve independent control of each channel, it is necessary to have independent upper and lower electrodes, and the number of its leads is numerous. When integrating the ultrasonic transducer chip with other IC chips on a PCB, the more channels the ultrasonic transducer chip has, the more difficult it is to ensure that no reliability issues occur during the processes of wire bonding, integrated packaging, and probe use for each channel.

[0004] The issue of packaging reliability is one of the key factors restricting the commercial application of CMUTs. Currently, there are no ultrasonic probe products using CMUTs array chips in China. To verify the feasibility of three-dimensional integration, Chinese Patent 《CN113560158 B》 discloses a piezoelectric micromachined ultrasonic transducer, array chip, and manufacturing method, which achieves the miniaturization and high-density integration of ultrasonic transducer chips. However, its process is complex and the number of channels is limited, making it difficult to be applicable to capacitive micromachined ultrasonic transducers. Summary of the Invention

[0005] The purpose of the present invention is to provide a capacitive micromachined array ultrasonic transducer, which solves the problems of complex process and limited number of channels in the prior art. The CMUTs array chip of the present invention can reach 192 channels. A ceramic substrate is used to connect the CMUTs array chip and the PCB, and flip-chip reflow soldering technology is used to achieve leadless wire bonding between the CMUTs chip and the PCB, forming a three-dimensional stacked integrated package with high reliability.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A capacitive micromachined array ultrasonic transducer comprises the following components: 1. A CMUTs array chip, which includes a group of upper electrode pads, an acoustic functional region, and a corresponding group of lower electrode pads. The acoustic functional region contains a group of arrayed sub-acoustic functional regions. Each sub-acoustic functional region, together with the corresponding upper electrode pad and lower electrode pad, forms a channel (CMUTs element). An isolation groove surrounding the channel (CMUTs element) is provided around each channel (CMUTs element). All CMUT units in the sub-acoustic functional region are connected in series through silicon wires; Therefore, a complete CMUTs array chip contains a group of multiple upper electrode pads and lower electrode pads, the number of which is equal to the number of channels. A complete CMUTs array chip contains up to 192 channels, which is the difference between the present invention and the prior art; The acoustic functional region, as the core of the CMUTs array chip, mainly performs the transmission and reception of acoustic signals. It is located between the upper electrode pad region and the lower electrode pad region. The acoustic functional region is composed of a group of sub-acoustic functional region arrays. One sub-acoustic functional region, together with the corresponding upper electrode pad and lower electrode pad, forms a channel. An isolation groove exists between each adjacent channel to separate the channels from each other, enabling each channel to be controlled individually. The sub-acoustic functional region is formed by connecting multiple CMUT units in series. The CMUT units are circular, which belongs to the prior art.

[0007] The CMUT unit has a vibrating membrane that vibrates when excited to emit acoustic signals externally, and / or vibrates when receiving acoustic signals; A cavity structure is provided directly below the vibrating membrane. The vibrating membrane and the bottom of the cavity form a capacitor. When the vibrating membrane vibrates above the cavity, the capacitance gap of the capacitor changes, resulting in a change in capacitance. Therefore, the detection of acoustic signals can be achieved by detecting the change in capacitance; The cavity structure is a hole etched on the substrate. The unetched area around the hole is connected to the vibrating membrane to form a support structure; The CMUT units are connected through silicon wires and arranged at a certain spacing to form a dot matrix. This dot matrix forms the acoustic functional region. The array chip composed of all channels is the CMUTs array chip.

[0008] 2. A ceramic adapter plate. A sound-transmitting window is opened in the center of the ceramic adapter plate. The size of the sound-transmitting window should match the size of the CMUTs array chip to facilitate the chip's transmission and reception of acoustic signals; A group of upper electrode copper pillars and lower electrode copper pillars are respectively provided on the ceramic adapter board, and are connected to the upper electrode pad and the lower electrode pad of the CMUTs array chip, and the CMUTs array chip is connected to the ceramic adapter board through the upper electrode copper pillars and the lower electrode copper pillars; A group of upper electrode solder balls and lower electrode solder balls corresponding to the upper electrode copper pillars and the lower electrode copper pillars are also provided on the ceramic adapter board. Each upper electrode solder ball and each lower electrode solder ball are connected to the corresponding upper electrode copper pillar and the lower electrode copper pillar through corresponding transmission lines.

[0009] The ceramic adapter plate is a ceramic substrate that plays a role of adapter, and a packaging solution that realizes three-dimensional stacking integration through the ceramic adapter plate.

[0010] The ceramic adapter plate uses alumina material with a thermal expansion coefficient of 4.5~8 ppm / ℃. Compared with the thermal expansion coefficient of 12~18 ppm / ℃ of PCB materials, the alumina ceramic has better thermal compatibility with silicon-based chips (thermal expansion coefficient is about 3 ppm / ℃); further, alumina ceramics have excellent mechanical strength and an elastic modulus of more than 300 GPa, which can provide high-strength mechanical support for the CMUTs array chip, with a compressive strength higher than 2500 MPa, a bending strength higher than 300 MPa, and excellent vibration resistance, which can effectively prevent solder joint failure caused by vibration.

[0011] A rectangular through hole is opened in the center of the ceramic substrate to form an acoustic window. The size of the acoustic window should match the size of the CMUTs array chip and be slightly larger than the overall acoustic functional area of ​​the CMUTs chip so as not to hinder the chip from transmitting and receiving acoustic signals. The acoustically transparent window should not exceed the upper electrode pad and the lower electrode pad, otherwise the CMUTs array chip and the ceramic adapter board cannot be connected; Copper pillars connected to the CMUTs array chip are prepared on the ceramic substrate. The positions of the copper pillars should correspond to the positions of the upper and lower electrode pads of the CMUTs array chip. The diameter of the copper pillars does not exceed the diameter of the upper and lower electrode pads of the CMUTs array chip. The height of the copper pillars should be as small as possible while ensuring the connection strength.

[0012] A solder ball array is prepared on the ceramic substrate. Optionally, the solder balls can use lead-free solder or copper core solder balls. Lead-free solder has lower cost, simpler process, high compatibility with ceramic adapter plates and PCBs, and is suitable for medium and low power CMUTs chips; copper core solder balls have better mechanical properties and thermal and electrical conductivity, and are suitable for higher power CMUTs chips. The described solder ball array on the ceramic substrate can be evenly distributed in the solder ball area at a certain pitch, or the rows and columns of the solder balls can be staggered to increase the solder ball density, but this will correspondingly increase the difficulty of arranging the internal transmission lines of the ceramic board; A part of the described copper pillars and the described solder ball array should be interconnected through transmission lines inside the ceramic substrate, and this interconnection should have a corresponding relationship with each channel of the CMUTs array chip; The solder balls without an interconnected relationship do not require the arrangement of transmission lines and only have the functions of supporting the ceramic adapter board and strengthening the connection strength; On the surface of the PCB connected to the described ceramic adapter board, pads matching the positions and sizes of the solder balls should be prepared; III. PCB board. A through hole is prepared in the center of the PCB, and the size of the through hole is slightly larger than the overall size of the CMUTs array chip, which can ensure that the PCB does not interfere with the CMUTs array chip during integrated packaging; Connect the CMUTs array chip to the ceramic adapter board and the ceramic adapter board to the PCB to form a three-dimensional stacked integrated packaging structure; For the connection between the CMUTs array chip and the ceramic adapter board, first prepare copper pillars on the surface of the described ceramic adapter board, then invert the ceramic adapter board onto the surface of the CMUTs array chip, align the copper pillars with the corresponding electrode pads of the CMUTs, and finally use the flip-chip reflow soldering technology to weld the copper pillars and the electrode pads together. The copper pillars connected to the upper electrode pads of the CMUTs array chip are upper electrode copper pillars, and the copper pillars connected to the lower electrode pads of the CMUTs array chip are lower electrode copper pillars.

[0013] For the connection between the ceramic adapter board and the PCB, first prepare a solder ball array on the ceramic adapter board and prepare pads for connecting to the solder balls at the corresponding positions on the PCB. Then, through vertical interconnection technology inside the ceramic adapter board, connect the copper pillars to the corresponding solder balls to form upper electrode solder balls and lower electrode solder balls. The solder balls not internally connected to any copper pillars only have a supporting function and serve as supporting solder balls to strengthen the connection strength. Finally, invert the ceramic adapter board onto the PCB and use the flip-chip reflow soldering technology to weld the solder balls on the ceramic adapter board to the corresponding pads on the PCB.

[0014] Conduct wire layout inside the described PCB, and connect the upper electrode pads and the lower electrode pads to external systems, such as drive circuits, signal processors, etc., to perform the functions of driving the CMUTs array chip and signal processing.

[0015] The beneficial effects achieved by the present invention are: (1) The present invention provides a CMUTs array chip connected to a PCB through a ceramic adapter board. Compared with the PCB board, the ceramic adapter board has a lower coefficient of thermal expansion and higher mechanical strength. Compared with the traditional solution of directly connecting the CMUTs chip to the PCB, the packaging solution proposed by the present invention effectively improves the thermal adaptability, reduces the thermal stress, and at the same time provides better mechanical protection, reducing the failure risk. (2) A three-dimensional stacked integrated packaging solution provided by the present invention uses the flip-chip reflow soldering technology to solder the copper pillars on the ceramic adapter board to the pads of the corresponding electrodes of the CMUTs array chip, so that the CMUTs array chip and the ceramic adapter board are interconnected. Then, the same flip-chip reflow soldering technology is used to solder the solder ball array on the ceramic adapter board to the corresponding pads on the PCB, finally forming a leadless integrated interconnection of the CMUTs array chip, the ceramic adapter board, and the PCB. Compared with the traditional packaging that uses gold wire bonding and finally forms a solution with hundreds of leads, the connection strength is greatly enhanced, and the serious problem of product failure caused by lead breakage during the use of the ultrasonic probe product is reduced, which is beneficial to promoting the commercialization process of the capacitive ultrasonic transducer probe. Description of the Drawings

[0016] Figure 1 is an overall schematic diagram of the CMUTs array chip in the embodiment of the present invention; Figure 2 is a schematic diagram of two adjacent channels in the CMUTs array chip in the embodiment of the present invention; Figure 3 is a schematic diagram of the acoustic functional area of each channel in the CMUTs array chip in the embodiment of the present invention; Figure 4 is a schematic diagram of the ceramic adapter board in the embodiment of the present invention; Figure 5 is a cross-sectional schematic diagram of the integration of the ceramic adapter board and the CMUTs array chip in the embodiment of the present invention; Figure 6 is a schematic diagram of the PCB board in the embodiment of the present invention; Figure 7 is a cross-sectional schematic diagram of the integration of the PCB board, the ceramic adapter board, and the CMUTs array chip in the embodiment of the present invention; Figure 8 is a cross-sectional schematic diagram of the wire bonding in the traditional packaging solution.

[0017] The labels in the figure are: 01, CMUTs array chip; 02, upper electrode pad area; 03, acoustic functional area; 03a, sub-acoustic functional area; 04, lower electrode pad area; 05, channel isolation groove; 06, one CMUT channel (CMUTs element); 06a, CMUT unit; 07, unit connecting silicon wire; 08, ceramic adapter board; 09, upper electrode solder ball; 10, lower electrode solder ball; 11, support solder ball; 12, internal transmission line of ceramic substrate; 13, upper electrode copper column; 14, lower electrode copper column; 15, through hole of ceramic substrate; 16, PCB board; 17, PCB upper electrode pad; 18, PCB lower electrode pad; 19, PCB through hole; 20, gold wire lead; 21, CMUT vibrating film; 22, CMUT cavity; 23, CMUT substrate and support structure. Detailed implementation mode

[0018] A capacitive micromachined array ultrasonic transducer provided by the present invention includes the following components: I. As Figure 1 shown, the present invention provides a CMUTs array chip 01, which includes a group of upper electrode pads 02, an acoustic functional area 03, and a corresponding group of lower electrode pads 04.

[0019] A group of upper electrode pads 02 includes the upper electrode pads of all CMUTs elements in the acoustic functional area 03. Each CMUTs element (channel) corresponds to one upper electrode pad. Therefore, the number of pads in the upper electrode pad area is equal to the number of channels; A group of lower electrode pads 04 in the lower electrode pad area includes the lower electrode pads of all elements in the acoustic functional area 03. Each element corresponds to one lower electrode pad. Therefore, the number of pads in the lower electrode pad area is equal to the number of channels; The acoustic functional area 03, as the core of the CMUTs array chip 01, mainly performs the transmission and reception of acoustic signals. It is located between the upper electrode pad area 02 and the lower electrode pad area 04 and is the sum of the ultrasonic transducers of all channels.

[0020] As Figure 2 shown, each sub-acoustic functional area 03a and the corresponding upper electrode pad 02 and lower electrode pad 04 together form a channel (CMUTs element) 6. There is an isolation groove 05 between each adjacent channel (CMUTs element) 06 to separate the channels from each other. Therefore, each channel (CMUTs element) 6 can be controlled separately.

[0021] As Figure 3 shown, the sub-acoustic functional area 03a of a channel (CMUTs element) 6 is composed of multiple CMUT units 06a. The CMUT units 06a are circular, and adjacent CMUT units 06a are connected in series by silicon wires 07 to form a dot matrix.

[0022] Figure 3 In the schematic diagram of the sub-acoustic functional area of each channel in the shown CMUTs array chip, in this embodiment, the sub-acoustic functional area 03a is formed by connecting CMUTs units in series in an array of n rows and 3 columns. However, this should not be a limitation of the present invention. The form of this array is a specific design based on the size requirements of the CMUTs chip in a specific application scenario. Those skilled in the art are aware that the number of rows and columns of the array can vary, and even the form of the array can be a full array or a cross array, etc.

[0023] II. As Figure 4 shown, the present invention provides a ceramic adapter plate 08 for physically and electrically interconnecting the CMUTs array chip 01 and the PCB board 16.

[0024] The described ceramic adapter plate 08 uses alumina material with a thermal expansion coefficient of 4.5 - 8 ppm / °C. Compared with the thermal expansion coefficient of 12 - 18 ppm / °C of the material of the PCB board 16, the alumina ceramic has better thermal adaptability with the silicon-based chip (thermal expansion coefficient is about 3 ppm / °C). At the same time, the alumina ceramic has excellent mechanical strength, and its elastic modulus exceeds 300 GPa, which can provide high-strength mechanical support for the CMUTs array chip 01. Its compressive strength is higher than 2500 MPa, its flexural strength is higher than 300 MPa, and its vibration resistance performance is excellent, which can effectively prevent the solder joint failure caused by vibration.

[0025] A rectangular through-hole is opened in the center of the described ceramic adapter plate 08 to form a sound transmission window 15. The size of the sound transmission window 15 should match the size of the CMUTs array chip 01, be slightly larger than the overall acoustic functional area 03 of the CMUTs chip 01, and does not hinder the chip from emitting and receiving sound signals.

[0026] On the basis of being larger than the acoustic functional area 03, the size of the sound transmission window 15 should not exceed the upper electrode pad 02 and the lower electrode pad 03, otherwise, it will be impossible to weld the CMUTs array chip 01 and the ceramic adapter plate 08 through the pads.

[0027] Copper columns 13 and 14 for connecting the CMUTs array chip 01 should be prepared on the described ceramic adapter plate 08. The positions of the copper columns should correspond to the positions of the upper electrode pad 02 and the lower electrode pad 04 of the CMUTs array chip 01. The diameter of the copper columns does not exceed the diameter of the upper electrode pad 02 and / or the lower electrode pad 04 of the CMUTs array chip 01, and the height of the copper columns should be as small as possible while ensuring the connection strength. The copper column connected to the upper electrode pad 02 of the CMUTs array chip 01 is the upper electrode copper column 13, and the copper column connected to the lower electrode pad 04 is the lower electrode copper column 14.

[0028] On the ceramic adapter board 08, solder ball arrays 09, 10, and 11 are to be fabricated. Optionally, the solder balls can be lead-free solder or copper-core solder balls. Lead-free solder has a lower cost and simpler process, and has high compatibility with the ceramic adapter board 08 and the PCB board 16, and is suitable for medium- and low-power CMUTs chips; copper-core solder balls have better mechanical properties, thermal conductivity, and electrical conductivity, and are suitable for higher-power CMUTs chips.

[0029] Furthermore, the solder ball arrays on the ceramic adapter board 08 can be evenly distributed in different solder ball areas at a certain pitch according to the schematic diagram of this embodiment. The solder balls are interconnected with the copper pillars through the internal transmission line 12. The solder balls interconnected with the upper electrode copper pillars 13 form the upper electrode solder ball area 09, and the solder balls interconnected with the lower electrode copper pillars 14 form the lower electrode solder ball area 10. The support solder ball area 11 that does not interconnect with any copper pillars only serves as a support. Those skilled in the art are well aware that the solder ball rows and columns can also be arranged in a staggered manner to increase the solder ball density, but this will correspondingly increase the difficulty of arranging the internal transmission line 12 in the ceramic board.

[0030] When the copper pillars are interconnected with the solder ball arrays inside the ceramic adapter board 08 through the transmission line 12, they should have a corresponding relationship with each channel of the CMUTs array chip 01.

[0031] III. The present invention provides a three-dimensional stacked integrated packaging technology. First, the ceramic adapter board 08 is inverted over the CMUTs array chip 01 and welded using the flip-chip reflow soldering technology. As shown in the A-A cross-section, Figure 5 . When the CMUTs array chip 01 is working, acoustic signals can be transmitted and received through the acoustic window 15, and the upper electrode pads 02 are interconnected with the upper electrode copper pillars 13, and the lower electrode pads 04 are interconnected with the lower electrode copper pillars 14 by welding around the acoustic window 15.

[0032] Furthermore, as Figure 6 shown, a PCB board 16 interconnected with the ceramic adapter board 08 is provided. On the surface of the PCB board 16, PCB upper electrode pads 17 and PCB lower electrode pads 18 that match the positions and sizes of the upper electrode solder balls 09 and the lower electrode solder balls 10 should be fabricated.

[0033] A through hole 19 is fabricated in the center of the PCB board 16, and its size is slightly larger than the overall size of the CMUTs array chip 01, which can ensure that the PCB board 16 does not interfere with the CMUTs array chip 01 during integrated packaging and prevent the distance between the ceramic adapter board 08 and the PCB board 16 from being too small to place the CMUTs array chip 01.

[0034] According to Figure 7 for three-dimensional stacked integrated packaging, Figure 5The obtained CMUTs array chip 01 is first packaged with the ceramic adapter board 08 and then finally integrated and packaged with the PCB board 16. The ceramic adapter board 08 is inverted onto the PCB board 16, and the upper electrode solder balls 09 of the ceramic adapter board 08 are soldered to the PCB upper electrode pads 17, and the lower electrode solder balls 10 of the ceramic adapter board 08 are soldered to the PCB lower electrode pads 18 through the flip-chip reflow soldering technology.

[0035] Wiring is arranged inside the PCB board 16, and the PCB upper electrode pads 17 and the PCB lower electrode pads 18 are respectively connected to external systems such as a driving circuit and a signal processor, so as to perform the functions of driving the CMUTs array chip 01 and signal processing.

[0036] The three-dimensional stacked integrated packaging solution provided by the present invention has significant advantages compared with the traditional CMUT packaging solution using wire bonding. For example Figure 8 As shown, in the traditional wire bonding packaging solution, the CMUTs array chip 01 is directly integrated with the PCB board 16. A typical CMUT structure includes a vibrating film 21, a cavity 22, a substrate and a support structure 23, an upper electrode pad 02 and a lower electrode pad 04. In order to achieve electrical interconnection between the CMUTs array chip 01 and the PCB board 16, gold wire leads 20 need to be formed respectively between the upper electrode pad 02 of the CMUTs array chip 01 and the PCB upper electrode pad 17, and between the CMUT lower electrode pad 04 and the PCB lower electrode pad 18. For a CMUTs array chip with multiple channels (such as 192 channels), two gold wire leads need to be led out for each channel, and finally hundreds of leads are formed. These leads are prone to failure problems such as falling off, adhesion, and breakage during the packaging process and during the long-term use of the probe product. Therefore, as a product, the traditional packaging method is unreliable. The three-dimensional stacked integrated packaging proposed by the present invention not only achieves wire-bonding-free, but also realizes better thermal adaptability through the ceramic adapter board, which is of great significance to the productization of capacitive ultrasonic transducers.

Claims

1. A capacitive micromechanical array ultrasonic transducer, comprising a CMUTs array chip (01), the CMUTs array chip comprising a group of upper electrode pads (02), an acoustic functional area (03) and a corresponding group of lower electrode pads (04), the acoustic functional area comprising a group of arrayed sub-acoustic functional areas (03a), each sub-acoustic functional area (03a) and the corresponding upper electrode pad (02) and lower electrode pad (04) together forming a channel (06), i.e., a CMUTs array element (06), each CMUTs array element being provided with an isolation groove (05) surrounding the CMUTs array element, and all CMUT units (06a) in the sub-acoustic functional area (03a) being connected in series via silicon wires (07); Features include: 1) a ceramic adapter plate (08), wherein a sound-transmitting window (15) is provided at the center of the ceramic adapter plate (08), and the size of the sound-transmitting window (15) should match the size of the CMUTs array chip (01) to facilitate the chip to transmit and receive sound signals; A group of upper electrode copper pillars (13) and lower electrode copper pillars (14) respectively connected to the upper electrode pads (02) and lower electrode pads (04) of the CMUTs array chip (01) are provided on the ceramic adapter plate (08); the CMUTs array chip (01) is connected to the ceramic adapter plate (08) via the upper electrode copper pillars (13) and the lower electrode copper pillars (14); A group of upper electrode solder balls (09) and lower electrode solder balls (10) respectively connected to the upper electrode copper pillars (13) and the lower electrode copper pillars (14) are respectively provided on the ceramic adapter plate (08); each upper electrode solder ball (09) and each lower electrode solder ball (10) are respectively connected to the corresponding upper electrode copper pillars (13) and the lower electrode copper pillars (14) via corresponding transmission lines (12); 2) A PCB board (16) having a through hole (19) at the center thereof for accommodating a CMUTs array chip (01), a group of PCB upper electrode pads (17) and PCB lower electrode pads (18) respectively provided on the PCB board, each PCB upper electrode pad (17) and PCB lower electrode pad (18) respectively connected to a corresponding upper electrode solder ball (09) and each lower electrode solder ball (10) on a ceramic adapter board, and the CMUTs array chip (01) is located in the through hole (19) after the PCB board is connected to the ceramic adapter board.

2. A capacitive micromechanical array ultrasonic transducer according to claim 1, characterized in that: The ceramic adapter plate (08) is also provided with supporting solder balls (11) that cooperate with the PCB board and play a role in enhancing the connection strength.

3. A capacitive micromechanical array ultrasonic transducer according to claim 1 or 2, characterized in that: Wires are arranged inside the PCB board (16) to respectively connect the PCB upper electrode pad (17) and the PCB lower electrode pad (18) to an external system including a drive circuit and a signal processor, thereby performing the functions of driving the CMUTs array chip (01) and signal processing.

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