JPH03274899A - Ultrasonic converter - Google Patents

Abstract

PURPOSE:To form a small-sized sensor which can obtain an image by being inserted into a minute part such as a blood vessel, etc., by connecting a thin film piezoelectric converting part and a signal processing circuit part of the piezoelectric converting part concerned by a pattern wiring in the extreme vicinity of the piezoelectric converting part and installing them on a semiconductor substrate. CONSTITUTION:On a silicon substrate 10, a circuit part 15 consisting of a driver circuit for exciting a piezoelectric thin film, a pre-amplifying circuit, a transmission/reception separating circuit, etc., is formed. Thereafter, an ultrasonic converting part is constituted by forming first the lower electrode 11 consisting of, for instance, platinum, etc., and laminating successively a thin film 12 of 10mum film thickness mainly composed of lead titanate, and also, the upper electrode 13 consisting of aluminum. The thin film 12 mainly composed of lead titanate is formed by a high frequency magnetron spattering method. After the upper electrode 13 is formed, a sample is held at 150 deg.C, a voltage of 100V is applied between the upper and the lower electrodes 11, 13 for ten minutes, and a polarization processing is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film type ultrasonic transducer used in ultrasonic diagnostic devices, ultrasonic exploration imaging devices, ultrasonic microscopes, and the like.

[Conventional technology]

In imaging devices that apply ultrasound, an ultrasound transducer that mutually converts electricity and sound waves plays an important role. Ultrasound waves of several MHz are mainly used for medical purposes, but there is also a growing demand for ultrasonic waves to be inserted into the body or into blood vessels to view minute areas with high resolution. For this reason, higher frequencies have been attempted, and 30 MH2 linear array converters have recently been realized.

On the other hand, for flaw detection, a wide range of frequencies ranging from several MHz to IGHz are used depending on the application. This is because while increasing the frequency improves the resolution, the attenuation of the ultrasonic waves within the sample increases, making it impossible to reach a sufficient depth. Furthermore, in the case of flaw detection, a surface at a certain depth is often imaged, and therefore, the scanning method is generally mechanical scanning using a single sensor.

In an ultrasonic transducer, the piezoelectric body is designed to resonate through its thickness at the ultrasonic frequency used. In the frequency band of several tens of MHz or higher, the thickness of the piezoelectric material is several tens of micrometers or less, so the piezoelectric material is formed by a thin film process.In the case of this thin film type ultrasonic transducer, a substrate supporting the thin film As a material, considering acoustic properties and crystallographic consistency,
Selecting suitable materials. ZnO as a thin film piezoelectric material
is widely used, and sapphire (α-AI, ◯) is generally used as the substrate material.

Transducers of this type are discussed, for example, in Solid State Physics, Vol. 17, pp. 51-57.

[Problem to be solved by the invention] Conventionally, it was necessary to send an RF pulse to a piezoelectric material to excite the piezoelectric material (driver), and to provide a circuit around the piezoelectric transducer to sample and amplify the returned echoes. . Normally, drivers and preamplifiers consist of elements on the order of lci'' and capacitors, and even if the piezoelectric transducer that transmits and receives ultrasonic waves is made small using microfabrication technology, the problem is that the overall size of the device cannot be reduced. There was this.
This makes it difficult to form a small sensor that can be inserted into a minute part such as a blood vessel to obtain an image.

Furthermore, even when circuits are integrated using recent IC technology, if there is a distance between the circuit and the piezoelectric converter, it is necessary to connect them with a coaxial cable, etc. requires the ability to drive this cable capacity. For this reason, the transistors constituting the circuit must have a large area to allow a sufficient current to flow, and there is also a problem in that the circuit area cannot be expected to be reduced to an extent commensurate with the reduction of the piezoelectric conversion section.

Furthermore, it is necessary to perform wiring etc. to a large number of micro elements.
This is a difficult problem in terms of implementation, and the resulting increase in variation in implementation is also a major problem.

The present invention has been made in view of the above circumstances, and its purpose is to solve the above-mentioned problems in the conventional technology and to provide a small sensor that can be inserted into minute parts such as blood vessels to obtain images. An object of the present invention is to provide an ultrasonic transducer that can be used for forming an ultrasonic transducer.

Another object of the present invention is to compress the signal processing circuit section! An object of the present invention is to provide an ultrasonic transducer that can reduce loss, simplify mounting, and reduce variations in performance between elements by being installed very close to a converter.

Still another object of the present invention is to provide an ultrasonic transducer with high sensitivity.

[Means for Solving the Problems] The above object of the present invention is to provide a thin film piezoelectric transducer and a signal processing circuit section of the piezoelectric transducer on a semiconductor substrate very close to the piezoelectric transducer by pattern wiring. An ultrasonic transducer characterized in that they are connected and installed, and in the ultrasonic transducer, the thin film piezoelectric transducer is formed by a large number of fine elements arranged in an array. This is accomplished by an ultrasonic transducer.

[Function] The ultrasonic transducer according to the present invention includes a driver circuit for generating ultrasonic waves (longitudinal waves) from the piezoelectric thin film, and a bridge and a prism for amplifying the electric signals converted from the ultrasonic waves returned from the sample. Since the circuit sections are integrated and formed on a semiconductor substrate, there is no need for coaxial cable wiring between the piezoelectric conversion section and the circuit section, and the driving capacity of the output section can be significantly reduced. , the area of the transistors forming the circuit becomes smaller. This makes it possible to significantly reduce the occupied space.

Furthermore, since the piezoelectric conversion section and the circuit section are formed on the same semiconductor substrate and are connected by a wiring pattern on the substrate, there is no need to conduct wiring by wire bonding or the like, and loss due to wiring is reduced. Furthermore, since weak signals can be amplified near the receiving section, the S/N ratio is improved.

Furthermore, in order to perform high-speed imaging, even when a large number of minute elements are arranged in an array and configured to perform electronic scanning, multiplexers, drivers, transmission/reception switching circuits, and preamplifiers are required to select specific elements. etc. are formed on the same substrate as the piezoelectric transducer, so the entire device can be significantly miniaturized.

Note that since no processing is required to connect these elements, variations in performance between elements can be significantly reduced.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an ultrasonic transducer according to an embodiment of the present invention, in which (a) is a perspective view with the acoustic matching layer omitted, and (b) is a cross-sectional view. In the figure, 10 is a silicon substrate, 11 is a lower electrode, and 12 is lead titanate (P).
bTi○S) thin film, 13 is an upper electrode, 14 is an acoustic matching layer, 15 is a circuit section such as a driver, preamplifier, transmission/reception separation circuit, etc., 16.16' is a bonding pad, 17.17
' indicates a lead wire.

In the ultrasonic transducer shown in this embodiment, as shown in FIG. 1, a circuit section 15 consisting of a driver circuit for exciting a piezoelectric thin film, a preamplifier circuit, a transmission/reception separation circuit, etc. is formed on a silicon substrate 10. ing.

Thereafter, as an ultrasonic transducer, a lower electrode 11 made of, for example, platinum is first formed, a thin film 12 with a thickness of 10 μm mainly composed of lead titanate is formed thereon, and an upper electrode 13 made of aluminum is further formed. It is constructed by sequentially laminating layers.

The thin film 12 whose main component is lead titanate is formed by high frequency magnetron sputtering. Note that here, the sputtering conditions are a high frequency power of 50 to 200 W.
The substrate temperature was 500 to 600° C., argon-oxygen (90%-10%) mixed gas was used as the introduced waste, and the gas pressure was 4 to 5 Pa. As a result of X-ray diffraction, this thin film mainly composed of lead titanate was found to be a polycrystalline film.

After forming the upper electrode 13, the sample was held at 150° C., and a voltage of 100 V was applied between the upper and lower electrodes II and 13 for 10 minutes to perform polarization treatment. On top of the ultrasonic transducer, a 10 μm thick Sin film 14 was formed by CVD as an acoustic matching layer and a protective film.

Next, after pulling out the lead wire from the bonding pad 16, 16' of the upper electrode by wire bonding,
The entire structure was molded with resin, and an experiment was conducted to transmit ultrasonic waves into water. For comparison, the driver.

A conventional ultrasonic transducer with a separate preamplifier circuit was also constructed, and the ultrasonic transducer was excited in the usual way, and the echoes from the underwater reflector were amplified and detected by the preamplifier.

FIG. 2 shows a comparison of echoes from a reflector placed in water using the two ultrasonic transducers described above. Compared to the underwater reflector echo (A) produced by the conventional ultrasonic transducer, the integrated ultrasonic transducer according to this embodiment has improved sensitivity by about 6 dB and reduced noise. This brings the piezoelectric conversion part and the circuit part close together,
This shows that because the wiring is performed using a pattern, the loss is reduced and the probability of taking in unnecessary responses is also reduced, leading to improvements in sensitivity and S/N.

In addition, in the conventional converter in which an electronic circuit using individual elements is placed on a separate board, the size is 20 to 30 mm, but in the converter of this embodiment, the size is 2U. Ta.

Next, the configuration of an ultrasonic array transducer according to a second embodiment of the present invention will be explained using FIG. 3. (a) is a perspective view with the acoustic matching layer omitted, and (b) is a cross-sectional view. The ultrasonic array transducer shown in this example has three elements.
60 array transducers, in the figure, symbols 10 to +
5 (15-1-15-n) indicates the same components as shown in FIG. Further, 21 is a multiplexer for selecting a specific element, and 22-1 to 22-n are individual elements.

The ultrasonic array transducer shown in this example has a width of 5 mm and a length of 2 mm.
On a 5 mm silicon substrate 10, a multiplexer 21,
A circuit section 15 such as a driver, a preamplifier, a transmission/reception separation circuit, etc. is arranged, and then, as an ultrasonic conversion section, a lower electrode II made of platinum or the like, a thin film 12 mainly made of lead titanate, etc. are arranged. The upper electrode 13 made of aluminum is constructed by sequentially stacking layers in the same manner as in the first embodiment, and is further aligned with the circuit section 15 to form a width of 50 μm, a gap of 5 μm, and the number of elements by photolithography. 360 resist patterns are formed, and the upper electrode and the lead titanate thin film are sequentially etched to form an array of ultrasonic transducer elements 22-1 to 22-2.
2-n is formed. Incidentally, an acoustic matching layer is finally formed to complete the ultrasonic array transducer shown in this example.

As mentioned above, the ultrasonic array transducer shown in this example has five
It is possible to accommodate 360 channels within a size of mm x 25 mm. If this was created using the conventional method of arranging electronic circuits using individual elements on separate substrates, the size would be 100 x 100 mm or more.

Moreover, in the ultrasonic array transducer according to this embodiment, the noise level is suppressed to a low level. This is because, as described above, the piezoelectric conversion section and the circuit section are placed close to each other and wiring is performed using a pattern.

In addition, in an ultrasonic array transducer, variation in the characteristics of each element has a large effect on image quality, but the ultrasonic array transducer shown in the above example eliminates the need for packaging and bonding, which are the causes of variation. As a result, the above-mentioned variations were eliminated and the uniformity of sensitivity was improved.

On the other hand, in an ultrasonic array transducer, the pitch and width of each element are determined based on the need to form an ultrasonic beam with few side lobes. Regarding this, in the ultrasonic array transducer shown in the above embodiment, the circuit sections 15 are arranged alternately on both sides of the elements 22-1 to 22-n, thereby making it possible to utilize the space effectively. .

FIG. 4 shows an ultrasonic beam profile obtained by exciting 16 elements of the ultrasonic array transducer shown in the above embodiment by applying signals with slightly different phases to each element. The beam width at −6 dB was approximately 40 μm, which agreed with the calculated value. The ultrasonic beam thus formed can be electronically scanned by shifting the array elements used one by one.

Next, an ultrasonic thin film array transducer which is a third embodiment of the present invention will be explained with reference to FIG.

In Figure 9, (a) is a perspective view with the acoustic matching layer omitted, and (b) is a cross-sectional view, symbols 10 to 15 (151
15-n), 21.22-1 to 22-n indicate the same components as shown in FIGS. 1 and 3. Further, 31 indicates a groove provided in the silicon substrate 10 for a complex resonance mode to be described later, and 32 indicates a backing material filled in the groove 31.

The ultrasonic thin film array transducer shown in this embodiment is manufactured by grinding a silicon substrate 10 from the back side using a method such as anisotropic etching to make the silicon substrate thinner in the area where the piezoelectric thin film 12 is to be formed. This utilizes a composite resonance mode in which the 10 and 10 resonate together.

In the ultrasonic thin film array transducer shown in this embodiment, a circuit section +5-1-15- n and ultrasonic conversion elements 22-1~
22-n is formed. Next, after protecting these element formation parts with resin, a resist pattern was formed on the back surface, and the silicon substrate was anisotropically etched with an aqueous potassium hydroxide solution to form grooves 31. In addition, lead titanate thin film 1
The thickness of the film 2 is 5 μm, the thickness of the substrate of the groove 31 is 20 μm,
The width of one element was 90 μm, and the gap was 10 μm.

First, they excited a single element and examined its waveform. 6th
The waveform is shown in the figure. As a result, although the vibration tail is slightly longer, the frequency is approximately 100 MH2, and a high frequency vibrator can be obtained. Note that this is a mode in which the thin film and the entire substrate resonate together (
It corresponds to the complex resonance mode). Regarding ultrasonic transducers that utilize complex resonance modes, US Pat.
25935 (corresponding to Japanese Patent Application Laid-Open No. 63-82100) can be effectively applied.

Next, an acoustic matching layer 14 was formed on the ultrasonic transducer, and a backing material 32 was filled in the groove 31 of the silicon substrate. When this ultrasonic transducer was used to form an ultrasonic beam using 16 elements in the same manner as in the second example, a convergent beam was also obtained, and the beam width was about 80 μm. Furthermore, compared to the case where the groove portion 31 of the silicon substrate was not filled with the backing material 32, the effect that the tail of the beam was considerably shortened was obtained.

As mentioned above, the size of this ultrasonic transducer is lOam
The size is about 40mm x 40mm, and if it was created using the conventional method of arranging an electronic circuit using individual elements on a separate board, the size would be more than +00mm x 100mm.

Note that as the backing material, for example, an epoxy resin is effective, and an epoxy resin containing a filler is particularly effective.

As an improved version of the ultrasonic thin film array transducer shown in the third embodiment, a structure capable of transmitting and receiving ultrasonic waves with even higher sensitivity is shown in FIG. FIG. 7(a) shows its cross-sectional structure. In each of the above-mentioned examples, the thin film containing lead titanate as a main component is formed as an unoriented polycrystalline body. is particularly high, high sensitivity can be achieved by forming a C-axis oriented film.

For this purpose, in this embodiment, fine sawtooth gratings 41 with a pitch of 0.2 to 0.3 μm are formed on the silicon substrate 10 in the area where the ultrasonic transducer elements are formed. The details will be explained below.

Submicron pitch serrated grating 4 described above
1 is formed using laser holography exposure technology and silicon anisotropic etching technology. In this case, the grating 41 was formed only in the portions corresponding to the elements of the array, and the other portions were left flat. This substrate is thermally oxidized to form a grating 1141 of Sin,
After that, electronic circuit parts 15-1 to 15-n were formed using the same procedure as shown in the second and third embodiments.

Thereafter, a platinum film was formed on the grating formation surface by electron beam evaporation, and heat treatment was performed.

Since platinum is a crystal with an f, c, c structure, it is easily (111) oriented on a flat plate. When this platinum is formed on the sawtooth gratings 41 facing each other at an angle of 70.5 degrees, each surface is (111) oriented, so that an apparently upward (100) oriented film is formed.

This situation is shown in FIGS. 7(b) and (c).

A thin film 12 containing lead titanate as a main component was formed on the (100) platinum film formed as described above by high frequency magnetron sputtering. When this thin film was evaluated by X-ray diffraction, only the (OOQ) (Q=1.2.3) diffraction line was detected. Therefore, it has been revealed that the thin film material 2 containing lead titanate as a main component has C-axis orientation. Furthermore, an upper electrode 13 was formed and patterned into an array, thereby forming an ultrasonic transducer.

Next, after protecting this ultrasonic converting section with a resin, the silicon substrate was etched from the back side as in the third embodiment. Then, when one of these elements was excited with the same voltage as before and the sensitivity was compared, an improvement in sensitivity of lod 8 or more was achieved. The effective electromechanical coupling coefficient keff as complex resonance was also sufficiently large at 0.35. This shows that piezoelectricity was greatly improved by forming lead titanate with C-axis orientation.

It goes without saying that the crystal growth method using a grating shown in the above embodiment can also be used in the thickness resonance mode ultrasonic transducer shown in the first and second embodiments. Regarding an ultrasonic transducer using a crystal growth method using a grating, US Pat.
It is possible to effectively apply the technique disclosed in No. 446 (corresponding to Japanese Patent Application Laid-open No. 61-177900).

Next, as another embodiment of the present invention, a needle tip section for observing minute parts such as blood vessels will be described with reference to FIG.

(a) shows a side sectional view, and (b) shows a main part plan view.

A silicon substrate 10 is placed inside a thin tube 51 made of transparent nylon, poly-4-methylpentene, etc.
On top of this, an ultrasonic array conversion section 22 and an electronic circuit section 15 are provided.
are integrated and formed.

The ultrasonic waves pass through the filler 14 with low attenuation and enter the window 52.
radiated from.

In this embodiment as well, by integrating the ultrasonic array conversion section 22 with the other electronic circuit section 15, the size can be significantly reduced. The overall size is 2 mmφ, and this device can be inserted into a blood vessel to examine the stenosis within the blood vessel.

It goes without saying that each of the above embodiments is an example of the present invention, and that the present invention is not limited thereto.

〔Effect of the invention〕

As described above in detail, according to the present invention, the thin film piezoelectric transducer and the signal processing circuit section of the piezoelectric transducer are connected on the semiconductor substrate very close to the piezoelectric transducer by pattern wiring. By installing the ultrasonic transducer, it is possible to realize an ultrasonic transducer that can be used to form a small sensor that can be inserted into minute parts such as blood vessels to obtain images. Moreover, it is possible to realize an ultrasonic transducer that can reduce variations in performance between elements.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an ultrasonic transducer according to an embodiment of the present invention, and FIG. 2 is a comparison diagram of detected two-row waveforms between the transducer shown in FIG. 1 and a conventional transducer. FIG. 3 is a block diagram showing a second embodiment of the present invention, FIG. 4 is a profile of an ultrasonic beam formed using the transducer shown in FIG. 3, and FIG. 5 is a diagram showing a third embodiment of the present invention. FIG. 6 is a block diagram showing the detected echo waveform of the converter shown in FIG. 5. FIG. 7 is a block diagram of main parts showing another embodiment of the present invention. FIG. FIG. 7 is a main part configuration diagram showing still another embodiment. 10. Silicon substrate, 11. Lower electrode, 12. Thin film of lead titanate, 13. Upper electrode, 14. Acoustic matching layer, 15.
:Circuit part, 16.16' :Bonding pad, 17
．． 17 lead wire, 21. Multiplexer, 22: Individual ultrasonic conversion element, 31 Groove, 32: Packing material, 41
．． Serrated grating, 51: tubule, 52: window. (a) Figure ■ Figure 2 Figure 111 → - 0ns Distance from the center of the Figure (rrm) Figure fa) Figure (al 1 2 Figure 6 on s Figure fa) (b) (111) ↑ (c) (100)

Claims (8)

[Claims] 1. 1. An ultrasonic transducer characterized in that a thin film piezoelectric transducer and a signal processing circuit of the piezoelectric transducer are installed on a semiconductor substrate in close proximity to the piezoelectric transducer, connected by pattern wiring. 2. The ultrasonic transducer according to claim 1, wherein the semiconductor substrate is a silicon substrate. 3. 3. The ultrasonic transducer according to claim 1, wherein a thin film containing lead titanate as a main component is formed in the piezoelectric transducer. 4. 1. The thin film piezoelectric transducer is formed by arranging a large number of fine elements in an array.
4. The ultrasonic transducer according to any one of 3 to 3. 5. 5. The ultrasonic transducer according to claim 1, wherein the signal processing circuit sections are arranged alternately on both sides of the thin film piezoelectric transducer section. 6. On the back side of the thin film piezoelectric conversion section of the semiconductor substrate,
The ultrasonic transducer according to any one of claims 1 to 5, characterized in that a groove is formed. 7. 7. The ultrasonic transducer according to claim 6, wherein the groove on the back side of the semiconductor substrate is filled with an ultrasonic absorbing material. 8. A sawtooth grating is formed in the piezoelectric conversion lower layer of the semiconductor substrate, and an electrode made of a metal film and a piezoelectric conversion part made of a thin film mainly composed of lead titanate are formed on the grating. The ultrasonic transducer according to any one of claims 1 to 7, characterized in that: