CN106744642A - The hybrid ultrasonic transducer face battle array probe of broadband and preparation method of receiving-transmitting balance - Google Patents

Abstract

The invention discloses a wide-band hybrid ultrasonic transducer area array probe with balanced transmission and reception, which comprises a silicon substrate (1), the upper surface of the silicon substrate (1) is an oxide layer (2), and the oxide The upper surface of the layer (2) is provided with several cavities (3), and the several cavities (3) are arranged in rows and columns, and the upper surface of the oxide layer (2) is bonded with a vibrating film (4), and the vibrating film An isolation layer (5) is provided on the upper surface of (4), and a sunken isolation groove (6) is opened around the periphery and inside of the isolation layer (5), and the isolation groove (6) runs through the isolation layer (5) After the vibrating film (4), the bottom of the groove is set on the oxide layer (2); the upper surface of the isolation layer (5) is provided with an upper electrode (7) at the center of each cavity (3) ). The ultrasonic probe of the invention is novel in structure, small in size, wide in frequency, high in sensitivity, low in noise, good in stability and balanced in sending and receiving performance.

Description

Broadband Hybrid Ultrasonic Transducer Area Array Probe with Balanced Transceiver and Preparation Method

technical field

The invention relates to a capacitive micro-mechanical ultrasonic transducer in the field of MEMS sensors, in particular to a structural design and a preparation method of a capacitive micro-mechanical ultrasonic transducer for ranging and imaging, which has the characteristics of balanced sending and receiving capabilities.

Background technique

With the rapid development of micro-electromechanical systems (MEMS, Micro-electromechanical Systems) and micro-nano technology, the manufacture of sensors has entered a new stage. At present, there are mainly three types of ultrasonic sensors: piezoelectric, piezoresistive and capacitive. Among them, the capacitive micro-machined ultrasonic transducer (CMUT) is flexible in design and processing, is less affected by temperature, responds to a wide frequency band, has a good matching between the production material and the dielectric impedance, and is easy to array processing. The integrated circuit can also be processed on the back of the sensor to reduce the influence of parasitic capacitance between circuits and the introduction of interference signals. After the manufacturing process flow is determined, the manufacturing cost of the ultrasonic sensor can be greatly reduced.

At present, micromachined capacitive ultrasonic transducers can only make one of them have better performance in terms of receiving and transmitting capabilities. When the CMUT is used in an integrated transceiver system, the transmission capability is weak under the same conditions.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned problems in the prior art, and to propose a novel wide-band hybrid ultrasonic transducer structure with balanced transmission and reception and a preparation method thereof.

The present invention is realized by adopting the following technical solutions:

A wide-band hybrid ultrasonic transducer area array probe with balanced transmission and reception, comprising a silicon substrate, the upper surface of the silicon substrate is an oxide layer, and several cylindrical cavities are opened on the upper surface of the oxide layer, so The upper surface of the oxide layer is bonded with a vibrating film, the upper surface of the vibrating film is provided with an isolation layer, and a sunken isolation groove is provided around the periphery of the isolation layer and inside, and the isolation groove runs through the isolation layer and the vibrating film Afterwards, the groove bottom is opened on the oxide layer; the upper surface of the isolation layer is provided with an upper electrode at the center of each cylindrical cavity.

Several cylindrical cavities on the oxide layer are located in the same isolation area to form an array element; within an array element, the cylindrical cavities are divided into two diameters, A and B.

The upper surface of the isolation layer is located at the edge of an array element, and a welding pad is provided, and a pad is passed between two adjacent upper electrodes in each row and between two adjacent upper electrodes in each column in an array element. The metal lead is connected, and the pad is connected to the nearest upper electrode through a metal lead.

Alternatively, the upper surface of the isolation layer is located at the edge of an array element, and two pads are provided, and the upper electrode corresponding to the cylindrical cavity with an inner diameter A of an array element is connected to one of the pads through a metal lead. ; An upper electrode corresponding to a cylindrical cavity with an inner diameter B of an array element is connected to the other pad through a metal lead.

Phosphorus is injected into the back of the silicon substrate, and metal sputtering is performed to form a lower electrode.

A plurality of array elements are aligned in rows and columns to form a CMUT area array, and the area array is arranged as M*N to form an ultrasonic transducer area array probe.

When working, a DC voltage is applied to the upper and lower electrodes of the probe, and an electrostatic force will be generated between the two plates. Under the action of the electrostatic force, the vibrating film is deformed and pulled toward the substrate. As the strain of the film increases, the mechanical recovery force in the film also increases. , which eventually balances with the electrostatic force. This is conducive to improving the electromechanical conversion efficiency. If an alternating voltage signal with a frequency of X (the value of X is within the response range) is applied to the upper and lower electrodes at this time, the effect of the alternating voltage signal will break the balance relationship established by the film under the DC voltage, which will make the film continuously Vibrates, emits ultrasonic waves, and realizes the function of emitting ultrasonic waves; if an ultrasonic wave acts on the film, it will also cause the film to lose balance and move up and down, resulting in a change in the distance between the upper and lower plates, thereby causing a change in capacitance. The external circuit can convert the current caused by the change in capacitance It is converted into a measurable voltage signal to realize the reception of ultrasonic waves.

The preparation method of the above-mentioned broadband hybrid ultrasonic transducer area array probe with balanced transmission and reception comprises the following steps:

(1) Select silicon wafers and SOI wafers for standard RCA cleaning;

(2) Oxidize the silicon wafer to form an oxide layer on the upper and lower surfaces;

(3) Perform photolithography on the oxide layer on the upper surface of the silicon wafer to etch a cavity with a diameter of A;

(4) Perform photolithography on the oxide layer on the upper surface of the silicon wafer after photolithography again, and further etch part of the cavity with diameter A to form a cavity with diameter B;

(5) Carry out standard RCA cleaning and activation on the silicon wafer. After activation, the oxide layer on the upper surface of the silicon wafer is bonded to the SOI wafer at a low temperature;

(6) After bonding, use TMAH solution to etch the substrate silicon of the SOI wafer, and after cleaning, use BOE solution to etch off the oxide layer on the lower surface of the silicon wafer and the oxide layer on the SOI wafer. At this time, the silicon wafer is The silicon substrate and the remaining silicon layer of the SOI wafer are the vibration film;

(7) Deposit a silicon dioxide layer on the vibrating film as an isolation layer by LPCVD process;

(8) Etch the part forming the isolation groove around the edge and inside of the isolation layer, and etch the isolation groove with TMAH solution. After the isolation groove penetrates the isolation layer and the vibrating film, the bottom of the groove is opened on the oxide layer;

(9) Sputter metal on the upper surface of the isolation layer by electron beam evaporation method, and form the upper electrode and pad by stripping method;

(10) Connect the upper electrodes and pads through metal leads;

(11) Phosphorus is implanted on the back of the silicon wafer to form a good ohmic contact with the silicon wafer;

(12) Carry out metal sputtering on the silicon substrate to form the lower electrode.

When the probe receives, a signal in a wide frequency band reaches the probe, causing it to vibrate and work. When the probe emits, the emitted frequency is different because the radius of the cavity is different. The innovation of the present invention is that cavities with different diameters are designed in the same array element, so as to increase the frequency range, widen the frequency bands of the probe's transmission and reception, and balance its transceiver performance.

The design of the present invention is reasonable, and the area array probe of the novel micro-electromechanical ultrasonic transducer with balanced transceiver solves the problem of unbalanced transmitting and receiving performance in the existing capacitive micro-electromechanical ultrasonic probe, realizes the consistency of the transceiving performance of the transducer, and realizes the broadband of the transducer bring.

The ultrasonic probe of the invention is novel in structure, small in size, wide in frequency, high in sensitivity, low in noise, good in stability and balanced in sending and receiving performance.

Description of drawings

Fig. 1-1 shows a schematic structural diagram of an array element in the transducer area array probe of the present invention, wherein the upper electrodes corresponding to different cavity depths in an array element are all connected together with metal leads.

Fig. 1-2 shows a schematic diagram of the structure of an array element in the transducer surface array probe of the present invention, wherein the upper electrodes corresponding to different cavity depths in an array element are respectively connected together with metal leads.

Figure 2 shows a cross-sectional view of an array element.

Fig. 3 shows a schematic diagram of step 2) in the transducer manufacturing method of the present invention.

Fig. 4 shows a schematic diagram of step 3) in the transducer manufacturing method of the present invention.

Fig. 5 shows a schematic diagram of step 4) in the transducer manufacturing method of the present invention.

Fig. 6 shows a schematic diagram of step 5) in the transducer manufacturing method of the present invention.

Fig. 7 shows a schematic diagram of step 6) in the transducer manufacturing method of the present invention.

Fig. 8 shows a schematic diagram of step 7) in the transducer manufacturing method of the present invention.

Fig. 9 shows a schematic diagram of step 8) in the transducer manufacturing method of the present invention.

Fig. 10 shows a schematic diagram of step 9) in the transducer manufacturing method of the present invention.

Fig. 11 shows a schematic diagram of step 12) in the transducer manufacturing method of the present invention.

In the figure: 1-silicon substrate, 2-oxide layer, 3-cylindrical cavity, 4-vibrating film, 5-isolation layer, 6-upper electrode, 7-pad, 8-isolation groove, 9-metal lead , 10-lower electrode.

detailed description

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

A wide-band hybrid ultrasonic transducer area array probe with balanced transmission and reception. Multiple array elements are arranged in rows and columns to form a CMUT area array probe. The area array can be arranged as M*N, where M can take a value 16~512, N can be 16~512.

As shown in Figure 2, it shows a cross-sectional view of an element, including a silicon substrate 1, the upper surface of the silicon substrate 1 is an oxide layer 2, and several cylindrical cavities are opened on the upper surface of the oxide layer 2 3. Cylindrical cavities 3 are arranged in rows, columns or diagonally, the upper surface of the oxide layer 2 is bonded with a vibrating film 4, and the upper surface of the vibrating film 4 is provided with an isolation layer 5, surrounding the isolation layer 5 A sinking isolation groove 6 is opened on the edge and inside (the isolation groove is used to separate each element), and after the isolation groove 6 penetrates the isolation layer 5 and the vibrating film 4, the bottom of the groove is opened on the oxide layer 2; On the upper surface of the isolation layer 5, an upper electrode 7 (forming a patterned upper electrode) is provided at the center of each cavity 3; after several cavities 3 on the oxide layer 2 are located in the same isolation area, An array element is formed; within an array element, the cavity 3 is divided into two different diameters, A and B.

There are two ways to connect the upper electrodes in an array element: (a) the upper electrodes of the cells with different diameter cavities are all connected together with metal leads; (b) the upper electrodes of the cells with different diameter cavities are connected together with metal leads . details as follows:

As shown in Figure 1-1, the upper surface of the isolation layer 5 is located at the edge of an array element, and a pad 8 is provided, between two adjacent upper electrodes 7 in each row in an array element, and each Two adjacent upper electrodes 7 in a column are connected through metal leads 9 , and the pad 8 is connected with the nearest upper electrode 7 through metal leads 9 .

As shown in Figure 1-2, the upper surface of the isolation layer 5 is located at the edge of an array element. The upper electrode 7 corresponding to the cavity 3 with the inner diameter A of the element is connected to one of the pads 8 through the metal lead 9; the upper electrode 7 corresponding to the cavity 3 with the inner diameter B of an array element is connected to the other through the metal lead 9 Pad 8 connection.

Phosphorus is injected into the back of the silicon substrate 1 , and metal sputtering is performed to form an integrated lower electrode 10 .

In the present invention, the structural design of the micro-vibration unit (cell) is designed as a cylindrical structure, which is arranged more closely, repeating units increase in a limited area, and the sensitivity of the sensor is improved, and the cavity width of different radii is designed to realize Improve the problem of narrow frequency band of the transducer.

The preparation method of the above-mentioned broadband hybrid ultrasonic transducer area array probe with balanced transmission and reception comprises the following steps:

(1) Select silicon wafers and SOI wafers, and perform standard RCA cleaning to remove various organic matter, gold dust and natural oxide layers, etc.;

(2) Oxidize the silicon wafer to form an oxide layer on both the upper and lower surfaces, in preparation for the subsequent etching of the cylindrical cavity;

(3) Perform photolithography on the oxide layer on the upper surface of the silicon wafer to etch a cavity with a diameter of A. Photolithography includes surface treatment, spin coating, pre-baking, alignment and exposure, post-baking, developing, engraving Conventional steps such as etching and degumming;

(4) Perform photolithography on the oxide layer on the upper surface of the silicon wafer after photolithography again, and further etch part of the cavity with diameter A to form a cavity with diameter B;

(5) Carry out standard RCA cleaning and activation on the silicon wafer. After activation, the oxide layer on the upper surface of the silicon wafer is bonded to the SOI wafer at a low temperature;

(6) After bonding, use TMAH solution to etch the substrate silicon of the SOI wafer, and after cleaning, use BOE solution to etch off the oxide layer on the lower surface of the silicon wafer and the oxide layer on the SOI wafer. At this time, the silicon wafer is The silicon substrate and the remaining silicon layer of the SOI wafer are the vibration film;

(7) A layer of silicon dioxide is deposited on the vibrating film by LPCVD process as an isolation layer to prevent the doping of the vibrating film during the process of evaporating metal to form the upper electrode;

(8) Etch the part forming the isolation groove around the edge and inside of the isolation layer, and etch the isolation groove with TMAH solution. After the isolation groove penetrates the isolation layer and the vibrating film, the bottom of the groove is opened on the oxide layer;

(9) Sputter metal on the upper surface of the isolation layer by electron beam evaporation method, and form the upper electrode and pad by stripping method;

(10) Connect the upper electrodes and pads through metal leads;

(11) Phosphorus is implanted on the back of the silicon wafer to form a good ohmic contact with the silicon wafer;

(12) Metal sputtering is performed on the silicon substrate to form an integrated lower electrode.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although detailed descriptions have been made with reference to the embodiments of the present invention, those of ordinary skill in the art should understand that the technical solutions of the present invention are modified Or equivalent replacements do not deviate from the spirit and scope of the technical solutions of the present invention, and all of them should be included in the protection scope of the claims.

Claims (3)

1. a kind of hybrid ultrasonic transducer face battle array of broadband of receiving-transmitting balance is popped one's head in, it is characterised in that：Including silicon substrate（1）, The silicon substrate（1）Upper surface be oxide layer（2）, the oxide layer（2）Upper surface offer some cylindrical cavities （3）, the oxide layer（2）Upper surface bonding vibration film（4）, the vibration film（4）Upper surface set separation layer（5）, Around separation layer（5）Edge and its inside offer the isolation channel of sinking（6）, the isolation channel（6）Through isolation Layer（5）And vibration film（4）Afterwards, its bottom land is opened in oxide layer（2）On；The separation layer（5）Upper surface on just to each Cylindrical cavity（3）Center position be provided with Top electrode（7）；

The oxide layer（2）On some cylindrical cavities（3）An array element is formed after in same area of isolation；One battle array In first, cylindrical cavity（3）It is divided into two kinds of diameters of A, B；

The separation layer（5）Upper surface be located at an array element in edge position be provided with a pad（8）, in an array element The two adjacent Top electrodes often arranged（7）Between and each column two adjacent Top electrodes（7）Between pass through metal lead wire（9）Even Connect, the pad（8）With a Top electrode of its nearest neighbours（7）Between pass through metal lead wire（9）Connection；

Or, the separation layer（5）Upper surface be located at an array element in edge position be provided with two pads（8）, one The cylindrical cavity of array element interior diameter A（3）Corresponding Top electrode（7）By metal lead wire（9）With one of pad（8）Even Connect；One cylindrical cavity of array element interior diameter B（3）Corresponding Top electrode（7）By metal lead wire（9）With other in which Pad（8）Connection；

The silicon substrate（1）Phosphorus is injected at the back side, and row metal of going forward side by side sputters to form bottom electrode（10）；

Multiple array elements are in a row, column alignment arrangement, form CMUT faces battle array, and face battle array is arranged as M*N, and composition ultrasonic transducer face battle array is visited Head.

2. the hybrid ultrasonic transducer face battle array of the broadband of receiving-transmitting balance according to claim 1 is popped one's head in, it is characterised in that： The M values 16 ~ 512, the N values 16 ~ 512.

3. the preparation method that a kind of hybrid ultrasonic transducer face battle array of broadband of receiving-transmitting balance is popped one's head in, it is characterised in that：Including Following steps：

（1）, selection silicon chip and SOI wafer, carry out standard RCA clean；

（2）, oxidation processes are carried out to silicon chip, its upper and lower surface is all formed oxide layer；

（3）, photoetching is carried out in the oxide layer of silicon chip upper surface, etch the cavity of diameter A；

（4）, silicon chip upper surface again after photoetching oxide layer on carry out photoetching, the cavity to section diameter A is further carved Erosion, forms the cavity of diameter B；

（5）, carry out to silicon chip standard RCA clean and go forward side by side line activating, the oxide layer and SOI wafer that silicon chip upper surface is made after activation are entered Row low-temperature bonding；

（6）, the substrate silicon of SOI wafer is corroded with TMAH solution after bonding, fall silicon chip with BOE solution corrosions again after cleaning The oxide layer in oxide layer and SOI wafer on lower surface, silicon chip now is the remaining silicon layer of silicon substrate, SOI wafer i.e. It is vibration film；

（7）, layer of silicon dioxide layer deposited on vibration film as separation layer using LPCVD techniques；

（8）, etch around the edge and inside of separation layer the part to form isolation channel, and corrode with TMAH solution Isolation channel, after separation layer and vibration film, its bottom land is opened in oxide layer isolation channel；

（9）, in the upper surface of separation layer by electron beam evaporation methods splash-proofing sputtering metal, and with the method peeled off formed Top electrode with Pad；

（10）, each Top electrode and pad connected by metal lead wire；

（11）, silicon chip the back side inject phosphorus, form good Ohmic contact with silicon chip；

（12）, silicon substrate carry out metal sputtering formed bottom electrode.