Transceiving integrated PMUT unit of frequency conversion self-focusing combination drive and preparation method thereof
阅读说明：本技术 变频自聚焦混合驱动收发一体化pmut单元及其制备方法 (Transceiving integrated PMUT unit of frequency conversion self-focusing combination drive and preparation method thereof ) 是由 赵立波 徐廷中 郭帅帅 李支康 杨萍 李�杰 赵一鹤 刘子晨 蒋庄德 于 2019-07-31 设计创作，主要内容包括：本发明公开了变频自聚焦混合驱动收发一体化PMUT单元及其制备方法,其将传统CMUT单元的塌陷工作模式与PMUT单元的驱动方式进行结合。在超声发射状态,通过调节偏置电压控制处于振动薄膜塌陷区域与传感器基底的贴合状态,实现对振动薄膜刚度的大范围调控。同时,结合PMUT输出灵敏度不受空腔高度约束的结构设计灵活性,实现PMUT单元的变频高能超声输出。在超声接收状态,通过各个PMUT单元处于塌陷模式下的电容变化量来对入射超声波进行感知,从而极大提高传感器的接收灵敏度。(The invention discloses transceiving integrated PMUT units of frequency conversion self-focusing combination drive and preparation method thereof, and the driving method for collapsing operating mode and PMUT unit of traditional CMUT unit is combined.In ultrasound emission state, it is in the fit-state that vibration film collapses region and sensor base by adjusting bias voltage control, realizes a wide range of regulation to vibration film rigidity.Meanwhile the structure design flexibility not constrained by cavity height in conjunction with PMUT output sensitivity, realize the frequency conversion high-energy ultrasonic output of PMUT unit.In ultrasonic reception state, incident ultrasound wave is perceived by capacitance change that each PMUT unit is under collapsed mode, so that the receiving sensitivity of sensor be greatly improved.)
1. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive, which is characterized in that including what is set gradually from top to bottom MULTILAYER COMPOSITE vibration film (1), pillar (2) and basal electrode (3), the pillar (2) are hollow structure, the film (1), branch Column (2) and basal electrode (3) are enclosed cavity (6)；
The MULTILAYER COMPOSITE vibration film (1) includes the structure sheaf (1-2) set gradually from top to bottom, Piezoelectric Driving layer (1-1) With bonded layer (1-3)；The Piezoelectric Driving layer (1-1) includes the top electrodes (1-1-1) set gradually from top to bottom, piezoresistive material The bed of material (1-1-2) and bottom electrode (1-1-3)；
The basal electrode (3) is by underlying structure (3-2) and the boss structure (3-1) being arranged on the underlying structure (3-2) It is composed, basal electrode (3) upper surface is covered with basal electrode composite insulation layer (5)；
The top electrodes (1-1-1) include multiple concentric loops, and the top electrodes (1-1-1) and cavity (6) are planar Projection it is concentric, the internal diameter of the smallest concentric loop is less than the projection radius of the upper surface boss structure (3-1) planar；It is described The planar dimension of bottom electrode (1-1-3) is greater than the projection of top electrodes (1-1-1) planar, and by top electrodes (1-1- 1) it is included.
2. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive according to claim 1, which is characterized in that described Pillar (2) includes the high fine-tuning pillar (2-1) and main corbeling (2-2) set gradually from top to bottom, the pillar (2) Height is greater than the height of boss structure (3-1).
3. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive according to claim 1, which is characterized in that described Structure sheaf (1-2) includes structural support layers (1-2-1), when the resistance value of structural support layers (1-2-1) is less than or equal to 100 Ω cm When, top electrodes insulating layer (1-2-2) is covered in structural support layers (1-2-1).
4. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive according to claim 1, which is characterized in that described Basal electrode composite insulation layer (5) includes upwards from top to down by the first basal electrode insulating layer (5-1) and the second basal electrode Material used in insulating layer (5-2), the first basal electrode insulating layer (5-1) and the second basal electrode insulating layer (5-2) is not Together.
5. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive according to claim 4, which is characterized in that described The material of first basal electrode insulating layer (5-1) is Si3N4, the material of the second basal electrode insulating layer (5-2) is SiO2。
6. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive according to claim 1, which is characterized in that described Top electrodes (1-1-1) include outer layer round loop electrode (9), central circular electrode (10), the internal layer circle set gradually from the outside to the core Ring electrode (11), the central circular electrode (10) and internal layer round loop electrode (11) and central circular electrode (10) and outer layer circle Gap between ring electrode (9) is in always within the scope of the plane projection of vibration area (8).
7. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive according to claim 1, which is characterized in that described The resistivity of basal electrode (3) is not more than 0.001 Ω cm.
8. the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive according to claim 1, which is characterized in that described Piezoelectric material layer (1-1-2) uses PZT piezoelectric material, AlN piezoelectric material, ZnO piezoelectric material or PVDF piezoelectric material.
9. a kind of preparation method of the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive described in claim 1, special Sign is, comprising the following steps:
Step 1 forms boss structure (3-1) on monocrystalline silicon piece (13), the portion other than monocrystalline silicon piece (13) boss structure (3-1) It is divided into underlying structure (3-2), boss structure (3-1) and underlying structure (3-2) composition basal electrode (3)；
Step 2, in basal electrode (3) Surface Creation basal electrode composite insulation layer (5) and pillar (2)；
Step 3 carries out thermal oxide to SOI piece, and SOI piece includes the top layer silicon (15) set gradually from bottom to top, SOI piece base silicon (16), SOI buried silicon dioxide layer (17) and top layer silicon；
Step 4, the deposited metal layer on top layer silicon (15) upper surface, and graphically form top electrodes (1-1-1)；
Step 5, the product upper surface depositing piezoelectric material layer (1-1-2) obtained in step 4；
Step 6 forms bottom electrode (1-1-3) in the piezoelectric material layer upper surface (1-1-2)；
Step 7 deposits SiO in the structure upper surface that step 6 obtains2Layer, and by the SiO of cavity (6) plane projection position2Layer subtracts It is thin, it is formed bonded layer (1-3)；
Step 8, the structure for obtaining step 2 and step 7 are bonded；
Step 9, the SOI piece base silicon (16) and SOI buried silicon dioxide layer (17) for successively removing SOI on piece, obtain frequency conversion autohemagglutination The burnt transceiving integrated PMUT unit of combination drive.
Technical field
The invention belongs to miniature ultrasonic transducer technical fields, and in particular to frequency conversion self-focusing combination drive is transceiving integrated PMUT unit and preparation method thereof.
Background technique
Miniature ultrasonic transducer (Micromachined Ultrasonic Transducer, MUT) based on MEMS technology Because have micromation, with fluid impedance matching properties it is good, can be achieved mass preparation, be easily achieved two-dimensional array processing and easily It is raw in instant ultrasonic imaging and treatment (Point of Care Diagnostics, POC), ultrasound in integrated with ICs the features such as The forward positions application fields such as the identification of object feature, 3D ultrasound gesture recognition and non-contact control have huge applications potentiality.Miniature ultrasonic Energy converter mainly includes capacitance type micromachined ultrasonic energy converter (Capacitive Micromachined UltrasonicTransducer, CMUT) and piezoelectric micromachined ultrasonic transducer (Piezoelectric MicromachinedUltrasonic Transducer, PMUT) two major classes.Relative to CMUT, based on piezoresistive materials such as AlN, ZnO Material has outstanding advantage in low-power consumption application field using the PMUT of beam mode, but due to AlN, the piezoelectricity of ZnO material Coefficient is much smaller than PZT material, and the performances such as PMUT electromechanical coupling factor, bandwidth and receiving sensitivity is caused also far to lag behind CMUT. Although part researcher improves PMUT performance by structure design, thorough improvement is not obtained yet.
Although CMUT has outstanding advantage in aspect of performance such as bandwidth, electromechanical coupling factor and receiving sensitivities, It is limited by electrostatic drive mode, very big limitation is caused to the design of its structure, while also limiting it in terms of transmitting sensitivity Raising.Therefore based on MEMS technology miniature ultrasonic transducer (Micromachined Ultrasonic Transducer, MUT) in the forward positions skill such as instant ultrasonic imaging and treatment, the identification of ultrasound biological feature, 3D ultrasound gesture recognition and non-contact control Art field still faces following technical problem urgently to be resolved:
(1) the technical requirements ultrasonic transducer such as ultrasonic imaging, 3D ultrasound gesture recognition has low-work voltage, low function immediately Consumption and portability.For example, ultrasonic fingerprint identification technology needs the power consumption of ultrasonic transducer in the even lower rank of mW, so as to hand The electronic devices such as machine reduce Overall Power Consumption after integrating use, improve stand-by time；And CMUT operating voltage conventional at present is big, function Consumption is high, when work the high DC offset voltage (tens to several hectovolts etc.) of required load limit it in portable, low-power consumption And the application in terms of long-term on-line checking；
(2) ideal ultrasonic transducer should have good ultrasonic wave transmitting and ultrasonic wave receptivity simultaneously.But at present Conventional PMUT is applicable in piezoelectric material performance and limits the raising of its receiving sensitivity.
Summary of the invention
To solve the above-mentioned problems, the present invention provides the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive and its Preparation method realizes the regulation to vibration film rigidity, improves the receiving sensitivity of sensor.
In order to achieve the above objectives, the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive of the present invention, including from upper and Under the MULTILAYER COMPOSITE vibration film that sets gradually, pillar and basal electrode, pillar is hollow structure, film, pillar and substrate electricity Pole is enclosed cavity；
MULTILAYER COMPOSITE vibration film includes the structure sheaf set gradually from top to bottom, Piezoelectric Driving layer and bonded layer；Piezoelectricity Driving layer includes the top electrodes, piezoelectric material layer and bottom electrode set gradually from top to bottom；
Basal electrode is composed of underlying structure and the boss structure being arranged in underlying structure, basal electrode upper surface It is covered with basal electrode composite insulation layer；
Top electrodes include multiple concentric loops, and top electrodes and the projection of cavity planar are concentric, the smallest concentric The internal diameter of annulus is less than the projection radius of boss structure upper surface planar；The planar dimension of bottom electrode is greater than top electrodes Projection planar, and top electrodes are included.
Further, pillar includes the high fine-tuning pillar and main corbeling set gradually from top to bottom, the height of pillar Degree is greater than the height of boss structure.
Further, structure sheaf includes structural support layers, when the resistance value of structural support layers is less than or equal to 100 Ω cm, Top electrodes insulating layer is covered in structural support layers.
Further, basal electrode composite insulation layer includes upwards from top to down by the first basal electrode insulating layer and second Basal electrode insulating layer, the first basal electrode insulating layer are different from material used in the second basal electrode insulating layer.
Further, the material of the first basal electrode insulating layer is Si3N4, the material of the second basal electrode insulating layer is SiO2。
Further, top electrodes include the outer layer round loop electrode set gradually from the outside to the core, central circular electrode, internal layer Round loop electrode, the gap between central circular electrode and internal layer round loop electrode and central circular electrode and outer layer round loop electrode are begun Eventually within the scope of the plane projection in vibration area.
Further, the resistivity of basal electrode is not more than 0.001 Ω cm.
Further, piezoelectric material layer uses PZT piezoelectric material, AlN piezoelectric material, ZnO piezoelectric material or PVDF piezoelectricity Material.
A kind of preparation method of the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive, comprising the following steps:
Step 1 forms boss structure on monocrystalline silicon piece, and the part other than monocrystalline silicon piece boss structure is underlying structure, Boss structure and underlying structure form basal electrode；
Step 2, in basal electrode Surface Creation basal electrode composite insulation layer and pillar；
Step 3 carries out thermal oxide to SOI piece, and SOI piece includes the top layer silicon set gradually from bottom to top, SOI piece substrate Silicon, SOI buried silicon dioxide layer and top layer silicon；
Step 4, the deposited metal layer on top layer silicon upper surface, and graphically form top electrodes；
Step 5, the product upper surface depositing piezoelectric material layer obtained in step 4
Step 6 forms bottom electrode in piezoelectric material layer upper surface；
Step 7 deposits SiO in the structure upper surface that step 6 obtains2Layer, and by the SiO of cavity plane projection position2Layer subtracts It is thin, form bonded layer；
Step 8, the structure for obtaining step 2 and step 7 are bonded；
Step 9, the SOI piece base silicon and SOI buried silicon dioxide layer for successively removing SOI on piece, it is mixed to obtain frequency conversion self-focusing It closes and drives transceiving integrated PMUT unit.
Compared with prior art, the present invention at least has technical effect beneficial below:
1) it uses capacitor and receives mode, overcome the low defect of conventional PMUT receiving sensitivity, made by collapsed mode The self-focusing characteristic of the PMUT unit ultrasound emission is realized at the recess of film, while being reduced and being situated between ultrasound unit by fluid It is interfered with each other caused by matter.In conjunction with the ultrasonic reception working condition under collapsed mode, the ultrasonic reception spirit of energy converter is greatly improved Sensitivity.
2) in ultrasound emission state, by adjusting bias voltage of the load on basal electrode to PMUT unit biggish It is adjusted in ultrasound emission frequency range, so as to flexibly control the super of the PMUTs array being made of this kind of cellular construction Sound emission bandwidth expands the scope of application of single chip.
3) in ultrasonic reception state, by adjusting bias voltage of the load on basal electrode to PMUT unit biggish It is adjusted in ultrasonic reception frequency range, the PMUT unit can be enable to have needle to the different supersonic frequencies in larger frequency range Property is selected, only has a kind of ultrasonic device of resonance frequency that can capture more ultrasound informations compared to tradition, thus Improve imaging precision.
4) PMUTs structure is simple, is easy to form array, is easy to be electrically connected, it can be achieved that portable on-line measurement.
One step of progress, pillar is in a thickness direction from top to down successively by high fine-tuning pillar and main corbeling group At.The height of pillar is greater than the height of boss structure.High fine-tuning pillar be responsible for the bottom surface of MULTILAYER COMPOSITE vibration film with Gap between the upper surface of boss structure is accurately controlled, to substantially reduce PMUT unit institute in the case where collapsing operating mode Need DC offset voltage VDC, and then substantially reduce bias voltage and can reduce MUT chip power-consumption, reduce its exciting circuit and swash The complexity for encouraging power supply is easy to implement low-power excitation.
Detailed description of the invention
Fig. 1 is schematic cross-section of the present invention；
Fig. 2 is ultrasound emission Work Incentive schematic diagram of the present invention；
Fig. 3 is that the present invention realizes that self-focusing and variable-frequency ultrasound emit Work Incentive schematic diagram；
Fig. 4 is ultrasonic reception operating mode schematic diagram of the present invention；
Fig. 5 is preparation method step schematic diagram of the present invention；
In attached drawing: 1, MULTILAYER COMPOSITE vibration film, 2, pillar, 3, basal electrode, 5, basal electrode composite insulation layer, 6, chamber Body, 7, collapse region, 8, vibration area, 9, outer layer round loop electrode, 10, central circular electrode, 11, internal layer round loop electrode, 12, convex Platform surface SiO2, 13, monocrystalline silicon piece, 14, non-boss surface SiO2, 15, top layer silicon, 16, SOI piece base silicon, 17, SOI buried layer two Silica, 1-1, Piezoelectric Driving layer, 1-2, structure sheaf, 1-3, bonded layer, 2-1, high fine-tuning pillar, 2-2, main corbeling, 3-1, boss structure, 3-2, underlying structure, 5-1, the first basal electrode insulating layer, 5-2, the second basal electrode insulating layer, 1-1- 1, top electrodes, 1-1-2, piezoelectric material layer, 1-1-3, bottom electrode, 1-2-1, structural support layers, 1-2-2, top electrodes are exhausted Edge layer, the top Fig. 2 camber line are ultrasonic wave transmitting signals, and the camber line on the top Fig. 3 is that ultrasonic wave reception is illustrated.
Specific embodiment
The following describes the present invention in detail with reference to the accompanying drawings and specific embodiments.
In the description of the present invention, it is to be understood that, term " center ", " longitudinal direction ", " transverse direction ", "upper", "lower", The orientation or positional relationship of the instructions such as "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outside" is It is based on the orientation or positional relationship shown in the drawings, is merely for convenience of description of the present invention and simplification of the description, rather than instruction or dark Show that signified device or element must have a particular orientation, be constructed and operated in a specific orientation, therefore should not be understood as pair Limitation of the invention.In addition, term " first ", " second " are used for description purposes only, it is not understood to indicate or imply opposite Importance or the quantity for implicitly indicating indicated technical characteristic.Define " first " as a result, the feature of " second " can be bright Show or implicitly include one or more of the features.In the description of the present invention, unless otherwise indicated, " multiple " contain Justice is two or more.In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, art Language " installation ", " connected ", " connection " shall be understood in a broad sense, for example, it may be being fixedly connected, may be a detachable connection, or It is integrally connected；It can be mechanical connection, be also possible to be electrically connected；It can be directly connected, it can also be by between intermediary It connects connected, can be the connection inside two elements.For the ordinary skill in the art, can be understood with concrete condition The concrete meaning of above-mentioned term in the present invention.
Referring to Fig.1, the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive is more including what is set gradually from top to bottom Layer complex vibration film 1, pillar 2 and basal electrode 3.Wherein, pillar 2 is hollow structure, film 1, pillar 2 and basal electrode 3 It is enclosed cavity 6.
MULTILAYER COMPOSITE vibration film 1 is by structure sheaf 1-2, Piezoelectric Driving layer 1-1 and bonded layer 1-3 successively group from top to bottom It closes；Piezoelectric Driving layer 1-1 thickness direction from top to bottom successively include top electrodes 1-1-1, piezoelectric material layer 1-1-2 and Bottom electrode 1-1-3；Structure sheaf 1-2 is successively exhausted by structural support layers 1-2-1 and top electrodes from top to down in a thickness direction Edge layer 1-2-2 composition, when structural support layers 1-2-1 insulated with material or resistance value are greater than 100 Ω cm, top electrodes insulating layer 1- The thickness minimum of 2-2 can be zero.
Top electrodes 1-1-1 includes multiple concentric loops, and top electrodes 1-1-1 and the projection of cavity 6 planar are same The heart.The internal diameter of the smallest concentric loop is greater than zero, and is less than the projection radius of the upper surface boss structure 3-1 planar.Bottom Its planar dimension of electrode 1-1-3 has to be larger than the projection of top electrodes 1-1-1 planar, and is contained in interior.Bottom electricity Pole size must be able to for top electrode being included, and imitate because only that inverse piezoelectricity could occur for the piezoelectric material between upper/lower electrode It answers.
Preferably, piezoelectric material layer 1-1-2 is using PZT piezoelectric material, AlN piezoelectric material, ZnO piezoelectric material or PVDF pressure Electric material.
Pillar 2 is successively made of high fine-tuning pillar 2-1 and main corbeling 2-2 from top to down in a thickness direction.Branch The height of column 2 is greater than the height of boss structure 3-1.Wherein, high fine-tuning pillar 2-1 is responsible for MULTILAYER COMPOSITE vibration film 1 Gap between bottom surface and the upper surface of boss structure 3-1 is accurately controlled, and is being collapsed to substantially reduce PMUT unit Required DC offset voltage V under operating modeDC.MUT chip power-consumption can be reduced by substantially reducing bias voltage in turn, reduced it and swashed The complexity for encouraging circuit and excitation power supply is easy to implement low-power excitation.It, can by the height adjustment to fine tuning pillar 2-1 To change the height on capacitance cavity between bottom crown, thus change on capacitor electrostatic force between bottom crown, to adjust capacitance cavity Collapse voltage plays the role of reducing bias voltage.Main corbeling 2-2 is the primary structure for supporting vibration film, is determined The movable area area of vibration film.
Basal electrode 3 is composed of truncated cone-shaped boss structure 3-1 and underlying structure 3-2.Boss structure 3-1 and cavity 6 Projection in the plane is concentric.3 upper surface of basal electrode is covered with basal electrode composite insulation layer 5.
Preferably, basal electrode 3 is low resistance conductive material, and resistivity is not more than 0.001 Ω cm, as electrode material, Low resistivity can reduce electrode fever, reduce energy loss.Preferably, basal electrode composite insulation layer 5 is by two kinds of differences The insulation film of material is constituted, in a thickness direction from top to down by the first basal electrode insulating layer 5-1 and the second basal electrode Insulating layer 5-2 composition.
Preferably, the first basal electrode insulating layer 5-1 selects Si3N4, the second basal electrode insulating layer 5-2 selection SiO2。
Referring to Fig. 2, the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive working mechanism under ultrasound transmission modes It is as follows:
Collapse film under inverse piezoelectric activity shown in the left side in Fig. 2 before this, followed by capacitor excitation makes suspension area in right figure Domain vibration transmitting ultrasound.
Bottom electrode 1-1-3 is grounded, normal polarity or the polar DC offset voltage of negative sense are applied to basal electrode 3 VDC, so that electrostatic masterpiece of 1 center of circle near zone of MULTILAYER COMPOSITE vibration film between bottom electrode 1-1-3 and basal electrode 3 It under, is attracted with the basal electrode composite insulation layer 5 of the upper surface boss structure 3-1, is attracted part and is known as collapsing region 7, multilayer Complex vibration film 1 is not attracted part and is known as vibration area 8.
Meanwhile identical frequency alternating voltage is loaded to each concentric ring electrode of top electrodes 1-1-1, and be based on annulus Position on locating MULTILAYER COMPOSITE vibration film 1 applies certain phase difference to loaded AC signal, so that piezoelectric material layer 1- 1-2 driving vibration area 8 under inverse piezoelectric effect effect is ultrasonic by the transmitting of the required vibration shape.
Preferably, top electrodes 1-1-1 uses three concentric loop figures, including the outer layer circle set gradually from the outside to the core Ring electrode 9, central circular electrode 10, internal layer round loop electrode 11.Central circular electrode 10 and internal layer round loop electrode 11 and center Gap between round loop electrode 10 and outer layer round loop electrode 9 is in always within the scope of the plane projection of vibration area 8.To outer layer circle Ring electrode 9, internal layer round loop electrode 11 load alternating voltage V2, low AC voltage V is loaded to center round loop electrode 101, V1With V2It Between phase difference
Referring to Fig. 3, during ultrasound emission, by adjusting load in 3 bias voltage V of basal electrodeDCAmplitude can be right The area for collapsing region 7 is adjusted, and introducing collapses area change amount △ S, to realize to 1 tension of MULTILAYER COMPOSITE vibration film Adjusting, and then change the bending stiffness of MULTILAYER COMPOSITE vibration film 1, the final regulation realized to PMUT unit resonance frequency. Realize the variable-frequency ultrasound transmitting of PMUT unit.
The recessed state of MULTILAYER COMPOSITE vibration film 1 is caused due to collapsing region 7, is realized certainly so that emitting ultrasound It focuses, reduces proposed PMUT unit under array operating mode, interfering with each other between unit.
Referring to Fig. 4, working machine of the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive under ultrasonic reception mode It manages as follows:
Bottom electrode 1-1-3 is grounded, normal polarity or the polar DC offset voltage of negative sense are applied to basal electrode 3 VDC, so that electrostatic masterpiece of 1 center of circle near zone of MULTILAYER COMPOSITE vibration film between bottom electrode 1-1-3 and basal electrode 3 Under, it is attracted with the basal electrode composite insulation layer 5 of the upper surface boss structure 3-1.Under incident ultrasound wave effect, region is collapsed 7 area changes, so that the capacitance between bottom electrode 1-1-3 and basal electrode 3 be caused to change.By this Ultrasonic reception mode under collapsed mode, is greatly improved the receiving sensitivity of PMUT.Conventional piezoelectric formula PMUT receives sensitive Spend it is low, receive ultrasound when, the output electric current very little that piezoelectric activity can produce causes output signal weak, receiving sensitivity is low； And routine CMUT capacitive ultrasound transducer is when receiving ultrasound, upper and lower plates capacitance changes, the output electric current of generation compared with Piezoelectric type is much larger, therefore its receiving sensitivity is higher.Capacitor is employed herein and receives mode, is received so overcoming conventional PMUT The low defect of sensitivity.
Simultaneously during ultrasonic reception, by adjust load 3 bias voltage of basal electrode amplitude to collapsing region 7 Area be adjusted, introduce △ S, to realize adjusting to 1 tension of MULTILAYER COMPOSITE vibration film, and then change MULTILAYER COMPOSITE The bending stiffness of vibration film 1, the final regulation realized to 1 resonance frequency of MULTILAYER COMPOSITE vibration film.It is possible thereby to according to reality Border ultrasonic reception demand, targetedly raises or lowers the receiving sensitivity to some frequency range ultrasonic wave, to improve Ultrasonic imaging precision.
Referring to Fig. 5, the transceiving integrated PMUT unit preparation method of frequency conversion self-focusing combination drive the following steps are included:
Step 1 takes a low-resistance single crystal silicon wafer 13, by thermal oxide, forms one layer of SiO in 13 upper surface of monocrystalline silicon piece2, and By the SiO on 13 surface of monocrystalline silicon piece2Graphically, retain the boss surface SiO of boss structure 3-1 plane projection position212。
Step 2 continues thermal oxide, by boss surface SiO on monocrystalline silicon piece 132The oxygen diffusion in the region of 12 coverings Rate is lower, causes on monocrystalline silicon piece 13 not by boss surface SiO2The oxidation rate of the zone monocrystalline silicon of 12 coverings faster forms non- Boss surface SiO214, so that monocrystalline silicon forms boss structure 3-1, portion of the monocrystalline silicon piece 13 in addition to boss structure 3-1 It is divided into underlying structure 3-2；By this step can the height to boss structure 3-1 accurately controlled.
Step 3, by boss surface SiO212 and non-boss surface SiO214 removals, obtain basal electrode 3.
Step 4, thermal oxide basal electrode 3, in 3 Surface Creation of basal electrode SiO in homogeneous thickness2Layer, and pass through figure Change the SiO of 2 position of pillar2Removal, SiO2The part that layer does not remove forms the second basal electrode insulating layer 5-2.
Step 5 passes through epitaxial growth or deposit polycrystalline silicon on the product that step 4 obtains, and generates main corbeling 2- 2。
Step 6 passes through low pressure chemical vapor phase deposition LPCVD deposition Si on the product that step 5 obtains3N4, and by figure Change, expose the plane projection region of high fine-tuning pillar 2-1, forms the first basal electrode insulating layer 5-1.
The product that step 7, step of thermal oxidation 6 obtain generates high fine-tuning pillar 2-1 in the upper surface main corbeling 2-2.
Step 8 carries out thermal oxide to SOI piece, and SOI piece includes the SOI piece base silicon 16 set gradually from bottom to top, SOI Buried silicon dioxide layer 17 and top layer silicon generate SiO in homogeneous thickness in 15 upper surface of top layer silicon2Top electrodes insulating layer 1-2-2, If the top layer silicon 15 of SOI piece is High Resistivity Si, this step be can be omitted；
Step 9, the deposited metal layer on top electrodes insulating layer 1-2-2, and it is according to the required vibration shape that it is graphical Form top electrodes 1-1-1；
Step 10, the product upper surface depositing piezoelectric material layer 1-1-2 obtained in step 9
Step 11, in the upper surface piezoelectric material layer 1-1-2 deposited metal layer, form bottom electrode 1-1-3；
Step 12, deposition SiO2, and it is thinned to use etching technics to carry out 6 plane projection position of cavity, most thin is zero, Form bonded layer 1-3；
It is step 13, the surface of bonded layer 1-3 and height on the multi-layer compound structure made in SOI piece top layer silicon 15 is micro- The upper surface of pillar 2-1 is adjusted to carry out vacuum fusion bonding；
Step 14 is removed 80% SOI piece base silicon 16 first using chemically mechanical polishing hair, then uses wet etching technique Or dry etching technology etches SOI buried silicon dioxide layer 17, obtains the transceiving integrated PMUT unit of frequency conversion self-focusing combination drive.
The foregoing is merely one embodiment of the present invention, it is not all of or unique embodiment, this field is common Any equivalent transformation that technical staff takes technical solution of the present invention by reading description of the invention, is the present invention Claim covered.