CN105591020B - A kind of high-frequency transducer with curve focusing array and preparation method thereof - Google Patents

Abstract

The invention discloses a high-frequency ultrasonic transducer with a curved surface focusing array and a preparation method thereof. The high-frequency ultrasonic transducer includes a curved substrate, and the upper surface of the curved substrate has an arc of 60° to 180° The whole or part of the upper surface of the curved substrate is covered with a curved focusing array, the bottom of the curved focusing array is a bottom electrode with a height of 4 μm to 20 μm, and 16 to 256 arc-shaped array elements arranged in parallel, the bottom of the arc-shaped array element is a thick film of lead magnesium niobate titanate with a height of 7 μm to 100 μm, and the top is a gold electrode with a height of 100 nm to 300 nm, and the arc-shaped array element The center of the circle is located on the central axis of the upper surface of the curved substrate. Through the invention, an ultrasonic transducer with lead magnesium niobate titanate curved surface thick-film focusing array is prepared, which has a good application prospect in high-resolution high-frequency ultrasonic transducers.

Description

A high-frequency ultrasonic transducer with curved surface focusing array and its preparation method

technical field

The invention belongs to the field of high-frequency ultrasonic transducers, and more specifically relates to a high-frequency ultrasonic transducer with a curved surface focusing array and a preparation method thereof.

Background technique

The ultrasonic transducer is a device that realizes the conversion of acoustic signals and electrical signals. The lateral resolution of the ultrasonic transducer is determined by the following formula:

Among them, R is the lateral resolution, c is the speed of sound in the medium, f _c is the center frequency, F ^# is the ratio of the focal length to the aperture size, and λ is the wavelength of the sound wave, therefore, the larger the ratio of the focal length to the aperture size, the lateral The higher the resolution. When the aperture size is constant, the smaller the focal length, the higher the resolution. Figure 1 shows the sound field of a single vibration element on the ultrasonic transducer. The focal length is the distance from the focal point to the center of the array element. Since the focal point of the plane is far away, the focal length is relatively large. Therefore, the curved piezoelectric thick film can improve the lateral resolution of high-frequency ultrasonic transducers.

In the prior art, the preparation of the curved surface aggregation array in the ultrasonic transducer needs to prepare a flat piezoelectric thick film first, and then press it on the curved surface substrate by a stainless steel cylinder to form a curved piezoelectric thick film, and then perform mechanical cutting to form the array. . For example, in the non-patent literature Cylindrically shaped ultrasonic linear array fabricated using PIMNT/epoxy 1-3piezoelectric composite (Sensors and Actuators A: Physical Volume 192, 1April 2013, Pages 69–75), since the thickness of the array reaches 0.55mm, the frequency is low, only There are about 2MHz. In addition, lead zirconate titanate (PZT) is widely used as the piezoelectric material in current ultrasonic transducers, and the electric strain coefficient and electromechanical coupling coefficient of this material are low, which is difficult to meet the needs of most ultrasonic transducers. .

Contents of the invention

In view of the above defects or improvement needs of the prior art, the present invention provides a high-frequency ultrasonic transducer with a curved surface focusing array and its preparation method and its preparation method, the purpose of which is to prepare a curved surface focusing array by pad printing, so that Enhances the lateral resolution and performance of ultrasound transducers.

In order to achieve the above object, according to one aspect of the present invention, a high-frequency ultrasonic transducer is provided, including a curved substrate and a curved focusing array, the upper surface of the curved substrate is a ring with an arc of 60° to 180°, The curved surface focusing array covers all or part of the upper surface of the curved surface substrate, the bottom of the curved surface focusing array is a bottom electrode with a height of 4 μm to 20 μm, and 16 to 256 bottom electrodes are arranged on the bottom electrode Parallel arc-shaped array elements, the arc-shaped array elements are composed of a lead magnesium niobate titanate thick film with a bottom height of 7 μm to 100 μm and a gold electrode with a top height of 100 nm to 300 nm, and the arc array The arc center of the element is located on the central axis of the upper surface of the curved substrate.

Preferably, the material of the curved substrate is piezoelectric ceramics or metal oxides.

Preferably, the width of the arc-shaped array element is 24 μm-60 μm, and the pitch is 33 μm-76 μm.

Preferably, the material of the bottom electrode is an inert metal.

According to another aspect of the present invention, a kind of preparation method of this high-frequency ultrasonic transducer is also provided, and described preparation method comprises the following steps:

S1. Prepare a bottom electrode with a height of 4 μm to 20 μm on the upper surface of the curved substrate by pad printing, and the upper surface of the curved substrate is a ring with an arc of 60° to 180°;

S2. Preparing a thick film of lead magnesium niobate titanate with a height of 7 μm to 100 μm on the bottom electrode by pad printing;

S3. Prepare a gold electrode with a height of 100nm-300nm on the lead magnesium niobate titanate thick film by sputtering;

S4. Use a laser to cut the gold electrode and the lead magnesium niobate titanate thick film in parallel, thereby forming 16 to 256 arc-shaped array elements arranged in parallel, so that the bottom of the arc-shaped array elements is magnesium niobate Lead acid lead titanate thick film, the top is a gold electrode, and the arc center of the arc-shaped array element is located on the central axis of the upper surface of the curved substrate.

Preferably, the step S2 is specifically:

S21. Uniformly disperse the lead magnesium niobate lead titanate powder with a particle size of 200nm to 500nm in a 10% to 20% polyethylene glycol solution, so that the lead magnesium niobate titanate powder and the polyethylene glycol solution The mass ratio of the diol solution is 7:3 to 4:1 to obtain a piezoelectric slurry;

S22. Transfer the piezoelectric slurry to the bottom electrode by a pad printing method, form a piezoelectric coating with a height of 5 μm to 12 μm after drying, and repeat the above steps until the piezoelectric coating is stacked to a desired height;

S23. Heating at 300°C to 350°C until the polymer in the piezoelectric coating is fully decomposed by heat and volatilized;

S24. Heating at 800° C. to 1000° C. to sinter the lead magnesium niobate titanate powder in the piezoelectric coating.

As a further preference, the specific method of step S22 is to use a mold that matches the shape of the upper surface of the curved substrate to take the piezoelectric slurry and transfer it to the upper surface of the curved substrate, After heating and drying at 100° C. to 120° C., a piezoelectric coating with a height of 5 μm to 12 μm is formed, and the above steps are repeated until the piezoelectric coating is stacked to a desired height.

As a further preference, the material of the mold is silica gel.

As a further preference, in the step S21, the mass ratio of the lead magnesium niobate titanate powder to the polyethylene glycol solution is 2:1˜3:1.

As a further preference, the heating time in the step S23 is 30 minutes to 60 minutes.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects because the curved surface focusing array is prepared on the curved surface substrate by the pad printing method:

1. The curved surface focusing array is directly prepared on the circular curved surface substrate, and then cut into arc-shaped array elements. Compared with the pressing method in the prior art, the height of the arc-shaped array elements is reduced to less than 100 μm, thereby improving the ultrasonic conversion rate. The horizontal resolution of the transducer improves its conversion effect at high frequencies;

2. Using laser cutting instead of ordinary mechanical cutting improves the cutting accuracy;

3. Using lead magnesium niobate titanate powder dispersed in 10% to 20% polyethylene glycol solution to prepare a thick film of lead magnesium niobate titanate, because the material has a high electrical strain coefficient, and The electromechanical coupling coefficient, which is used to replace the traditional lead zirconate titanate thick film, improves the piezoelectric performance, electric strain coefficient and electromechanical coupling coefficient of the ultrasonic transducer.

Description of drawings

Fig. 1 is the lateral resolution schematic diagram of ultrasonic transducer;

Fig. 2 a is the front view of the curved PZT substrate of embodiment 1 of the present invention;

Fig. 2 b is the plan view of the curved PZT substrate of embodiment 1 of the present invention;

Fig. 3 a is the front view of the silicone mold of embodiment 1 of the present invention;

Fig. 3 b is the side view of the silicone mold of embodiment 1 of the present invention;

Fig. 4 is the SEM figure of the curved surface of the lead magnesium niobate titanate thick film of embodiment 1 of the present invention (respectively from the lower left corner to the upper right corner: lead magnesium niobate titanate piezoelectric thick film, Pt electrode, PZT curved surface Substrate);

FIG. 5 is a schematic diagram of the overall structure of Embodiment 1 of the present invention;

FIG. 6 is a schematic diagram of a curved surface focusing array according to Embodiment 1 of the present invention;

In all the drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-curved surface single array element, 2-plane single array element, 3-focus area of curved surface single array element, 4-plane single array element The focal area of the array element, 5-curved surface single array element beam, 6-plane single array element beam, 11-curved surface substrate, 12-bottom electrode, 13-lead magnesium niobate titanate thick film, 14-gold electrode.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

One aspect of the present invention provides a high-frequency ultrasonic transducer, including a curved substrate and a curved focusing array. On all or part of the upper surface of the curved substrate, the bottom of the curved surface focusing array is a bottom electrode with a height of 4 μm to 20 μm, and 16 to 256 widths, arc lengths, and arcs are arranged on the bottom electrode. and parallel arc array elements with the same height and arc centers located on the central axis of the upper surface of the curved substrate. The bottom of the arc array elements is lead magnesium niobate titanate with a height of 7 μm to 100 μm Lead thick film, the top is a gold electrode with a height of 100nm to 300nm.

Wherein, the material of the curved surface substrate is piezoelectric ceramics or metal oxide, and the material of the bottom electrode is an inert metal; while the width and spacing of the arc-shaped array elements are related to the wavelength of the sound wave, and the high-frequency ultrasonic transducer The frequency range is 20MHz to 200MHz, and high-frequency ultrasonic transducers are generally used in medicine to detect human tissues and organs. The propagation speed of sound in the human body is 1540m/s, and the distance between arc array elements is less than or equal to half a wavelength. Therefore, the width of the arc-shaped array element is usually 20 μm to 50 μm, and the spacing is usually 30 μm to 70 μm; its length (that is, the arc length corresponding to the arc-shaped array element) must meet the requirements of an arc of more than 60°. For example, when the curved surface substrate When the radius of the upper surface is 5 mm, the length of the arc array element is usually 5 mm to 15 mm.

The preparation method of the ultrasonic transducer comprises the following steps:

S1. Prepare a bottom electrode with a height of 4 μm to 20 μm on the upper surface of the curved substrate by pad printing, and the upper surface of the curved substrate is a ring with an arc of 60° to 180°;

S2. Preparing a thick film of lead magnesium niobate titanate with a height of 7 μm to 100 μm on the bottom electrode by pad printing;

S3. By controlling sputtering power, sputtering pressure and sputtering time, prepare a gold electrode with a height of 100nm to 300nm on the lead magnesium niobate titanate thick film as a top electrode by sputtering; for example, use radio frequency sputtering Sputtering, the power is 100w, the pressure is 0.5Pa, the rate is 0.3nm/s, and the sputtering time is 6min, a gold electrode with a thickness of 100nm can be obtained;

S4. Use a laser to cut the gold electrode and the lead magnesium niobate titanate thick film in parallel, the depth direction of the cutting is perpendicular to the upper surface of the curved substrate, and the bottom electrode can be avoided by controlling the cutting time, thereby Forming 16 to 256 arc-shaped array elements of the same size and arranged in parallel, so that the bottom of the arc-shaped array elements is a thick film of lead magnesium niobate titanate, the top is a gold electrode, and the arc-shaped array elements The arc center is located on the central axis of the upper surface of the curved substrate.

Wherein, the pad printing method in step S1 is specifically, using a mold matching the shape of the upper surface of the curved substrate to take the inert metal paste, and transfer it to the surface of the curved substrate, at 150°C to 200°C After heating, the solvent in the slurry is completely volatilized, and then sintered at 1150° C. to 1250° C. to obtain a bottom electrode with a height of 4 μm to 20 μm.

The pad printing method in the step S2 is relatively complicated, and its specific steps are:

S21. When the proportion of lead magnesium niobate titanate powder is too high, the piezoelectric slurry is too thick, which is not conducive to pad printing. When the quality of the polymer solution is too high, the piezoelectric slurry is thin, and thick films cannot be formed. ; Therefore with the mass ratio of 7:3～4:1 (preferably 2:1～3:1) lead magnesium niobate lead titanate powder is uniformly dispersed in 10%～20% polyethylene glycol solution, prepares The piezoelectric slurry is obtained, and the particle size of the lead magnesium niobate titanate powder is 200nm～500nm, so as to ensure that the formed lead magnesium niobate titanate thick film is relatively uniform; when the concentration of the polyethylene glycol solution is too low When the viscosity is too small, the powder cannot be bonded together. When the concentration is too high, the polyethylene glycol will leave a relatively large gap after volatilization, which will affect the mechanical properties of the ultrasonic transducer;

S22. Take the piezoelectric slurry with a mold matching the shape of the upper surface of the curved substrate, transfer it to the surface of the curved substrate, and heat and dry it at 100°C to 120°C to prevent the subsequent temperature from rising too quickly , the rapid evaporation of water vapor causes cracks in the piezoelectric thick film, thereby forming a piezoelectric coating with a height of 5 μm to 12 μm, and repeating the above steps until the piezoelectric coating is stacked to the required height;

S23. Heating at 300°C to 350°C for 0.5h to 1h, until the polyethylene glycol in the piezoelectric coating is thermally decomposed and volatilized;

S24. Heating at 800° C. to 1000° C. to sinter the lead magnesium niobate titanate powder in the piezoelectric coating to obtain the lead magnesium niobate titanate thick film.

The preparation of embodiment 1 piezoelectric material

Experimental Materials:

Clean PZT piezoelectric ceramic curved substrate: the custom-made PZT curved substrate has a height of 7.5mm and a width of 15mm. Its inner surface is a semi-circular ring with a diameter of 5mm. 2.5mm. Its front view and top view are shown in Figure 2a and Figure 2b, respectively. The PZT curved substrate was mechanically polished to remove the corroded part of the surface, rinsed with deionized water, then ultrasonically cleaned in alcohol for 10 minutes, rinsed with deionized water again, ultrasonically cleaned in acetone for 10 minutes, and then ultrasonically cleaned in alcohol for 10 minutes, Finally, rinse with deionized water and dry for later use.

Polymer solution: Mix in a beaker according to the mass ratio of polyethylene glycol 4000 (PEG-4000) and deionized water at 3:20. After mixing, stir on a magnetic stirrer for 20 minutes to form a 15% polymer solution.

S1. Preparation of bottom electrode

Prepare the silicone mold, its front view is shown in Figure 3a, and its side view is shown in Figure 3b; it can be seen from the figure that the semicircular end with a diameter of 5mm at the lower end matches the semicircular annular end of the inner surface of the curved substrate exactly, and the middle A rectangular segment with a width of 10mm and a height of 15mm can be used to control this mould.

Take out the refrigerated platinum slurry (M-Pt100-1, solid content 82±0.5%), and thaw it at room temperature for 20 minutes, then use the silicone mold shown in Figure 3 to transfer the platinum slurry evenly onto the PZT curved surface lining On the bottom, it only needs to be printed once. Put the sample in an oven and bake at 200°C for 30 minutes to dry the platinum slurry. Afterwards, the sample was taken out and sintered in a furnace to prepare a bottom electrode with a thickness of 18 μm. The sintering process was set to heat at 1200°C for 240 minutes, then keep the temperature for 10 minutes, and then cool naturally to room temperature. During the pad printing process, it is best to place the PZT curved substrate horizontally, while the silicone mold should be pad printed vertically after dipping the platinum slurry. The force during the pressing process should be uniform to avoid uneven bottom electrodes formed, which will affect the performance of the ultrasonic transducer. .

S21. Configuration of lead magnesium niobate titanate slurry

Mix lead magnesium niobate titanate powder and polymer solution with a particle size of 200nm to 500nm in a beaker at a mass ratio of 1:3, place on a magnetic stirrer for 30 minutes of magnetic stirring, and mix evenly to obtain magnesium niobate Lead lead titanate paste.

S22. Preparation of lead magnesium niobate titanate thick film on curved substrate

First, use a clean silicone mold to dip in an appropriate amount of lead magnesium niobate titanate slurry, transfer it vertically onto the PZT curved substrate, and press it evenly with a force of about 1N-10N to make the lead magnesium niobate titanate thick. The film was formed uniformly. Then, the pad-printed samples were dried in an oven at 100°C to slowly evaporate the water in the slurry to avoid cracks in the thick film caused by the rapid evaporation of water vapor in the subsequent sintering process. The thickness of the lead niobate magnesium titanate thick film lead piezoelectric thick film printed once is about 14 μm, and the above steps are repeated 5 times to obtain a 70 μm thick film.

S23 drying the sample for sintering. Our heating process is the first stage to raise the temperature from 0°C to 300°C after 60 minutes, and the second stage to debinding at a temperature of 300°C for 30 minutes (let PEG4000 be thermally decomposed);

S24. After 120 minutes, the temperature was raised from 300°C to 900°C, then kept at 900°C for 60 minutes for sintering, and finally the temperature was naturally lowered. After this process, the lead magnesium niobate titanate thick film was prepared on the PZT curved substrate. The Pt electrode and the lead magnesium niobate titanate thick film were sequentially formed on the curved substrate from the bottom to the top. The cross-section SEM As shown in Figure 4, from the lower left corner to the upper right corner are: lead magnesium niobate titanate piezoelectric thick film, Pt electrode and PZT curved substrate.

S3. The frequency uses radio frequency, the sputtering power is 100w, the sputtering pressure is 0.5Pa, the sputtering rate is 0.3nm/s, and the sputtering time is 30min. Finally, a gold electrode with a thickness of 100nm is formed on the thick film of lead magnesium niobate titanate As the top electrode, a bottom electrode, a lead magnesium niobate titanate thick film and a top electrode are sequentially formed on the curved substrate from bottom to top, as shown in FIG. 5 .

S4. Use laser cutting to cut the gold electrode and lead magnesium niobate titanate thick film along the arc from left to right along the upper surface of the curved substrate. By controlling the cutting time, cutting the bottom electrode can be avoided, and by controlling the size of the laser spot Width control; cutting the top electrode and lead magnesium niobate titanate thick film into a curved surface focusing array composed of 24 arc-shaped array elements arranged in parallel, and the arc center of the arc-shaped array elements is located on the curved surface substrate On the central axis of the upper surface; the length of the arc-shaped array elements is equal to the semicircumference length of the upper surface of the curved substrate, the width is 32 μm, the pitch of the arc-shaped array elements is 50 μm, the number of arrays is 24, and the center frequency is 30 MHz.

S5. The wires can be led out from the bottom electrode and the top electrode in sequence; wherein, the bottom electrode is a whole and can be directly led out by a wire. And the top electrode is on each array, respectively connected with wires from two ends. The odd-numbered arrays are wired from the left from the front to the back, and the even-numbered arrays are wired from the right to avoid short-circuiting on one side of the wiring.

Repeat Example 1 with the same steps to obtain Example 2-Example 5, and the specific parameters adjusted are shown in Table 1.

Table 1

Tests were carried out on Examples 1 to 5, and the center frequency was increased to 20MHz to 200MHz, and the piezoelectric performance, electrical strain coefficient and electromechanical coupling coefficient of the ultrasonic transducer were all improved compared with the prior art.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (8)

1. a kind of preparation method of high-frequency transducer, it is characterised in that comprise the following steps：

S1. the hearth electrode that height is 4 μm~20 μm is prepared in the upper surface of curved substrate using transfer printing, the curved substrate Upper surface is the annular of 60 °~180 ° of radian；

S2. the lead magnesio-niobate lead titanates thick film that height is 7 μm~100 μm is prepared on hearth electrode using transfer printing；

S3. the gold electrode that height is 100nm~300nm is prepared on the lead magnesio-niobate lead titanates thick film using sputtering method；

S4. using the parallel cutting gold electrode of laser and the lead magnesio-niobate lead titanates thick film, so as to form 16~256 The arc array element be arrangeding in parallel so that the bottom of the arc array element is lead magnesio-niobate lead titanates thick film, and top is gold electrode, and The arc core of the arc array element is located on the central shaft of the curved substrate upper surface；

The high-frequency transducer includes curved substrate and curve focusing array, and the curve focusing array is covered in described All or part of region of the upper surface of curved substrate, the bottom of the curve focusing array are hearth electrode, the hearth electrode it On be provided with 16~256 parallel arc array elements, the arc array element is that lead magnesio-niobate lead titanates is thick by its bottom level Film and its gold electrode at top composition, and the arc core of the arc array element is located on the central shaft of the curved substrate upper surface.

2. preparation method as claimed in claim 1, it is characterised in that the step S2 is specially：

S21., the lead magnesio-niobate lead titanates powder that particle diameter is 200nm~500nm is dispersed in 10%~20% poly- second two In alcoholic solution so that the mass ratio of the lead magnesio-niobate lead titanates powder and the polyglycol solution is 7:3~4:1, obtain Piezoelectricity slurry；

S22. the piezoelectricity slurry is transferred on hearth electrode using transfer printing, the pressure that height is 5 μm~12 μm is formed after drying Electrocoat, and above step is repeated until the Piezoelectric coating is superimposed to required height；

S23.300 DEG C~350 DEG C heating, until the polymer in the Piezoelectric coating is fully thermally decomposed and volatilized；

S24.800 DEG C~1000 DEG C heating make it that the lead magnesio-niobate lead titanates in the Piezoelectric coating is powder sintered.

3. preparation method as claimed in claim 2, it is characterised in that the specific method of the step S22 is, with the song The mould pressure plasma-based material that the pattern of the upper surface of face substrate matches, transfers them to the upper surface of the curved substrate, and 100 DEG C~120 DEG C of heat dryings after to form height be 5 μm~12 μm of Piezoelectric coating, and repeat above step until the piezoelectricity applies Stacking adds to required height.

4. preparation method as claimed in claim 2, it is characterised in that in the step S21, the lead magnesio-niobate lead titanates The mass ratio of powder and the polyglycol solution is 2:1~3:1.

5. preparation method as claimed in claim 2, it is characterised in that the time heated in the step S23 be 30min~ 60min。

6. preparation method as claimed in claim 1, it is characterised in that the material of the curved substrate is piezoelectric ceramics or gold Belong to oxide.

7. preparation method as claimed in claim 1, it is characterised in that the width of the arc array element is 20 μm~60 μm, Away from for 30 μm~70 μm.

8. preparation method as claimed in claim 1, it is characterised in that the material of the hearth electrode is inert metal.