JPH06224487A - Manufacturing piezoelectric composite - Google Patents

Abstract

(57) Abstract: To provide a method of manufacturing a grooving-filled composite or a method of enabling production of an acoustic device using PZT elements with different and / or complementary properties. A method of making a piezoelectric composite for constructing an acoustic transducer from two or more pieces of piezoelectric material. Each piece of material is cut to form slots or trenches of uniform pitch as well as material portions of uniform width such that the material portion of one piece of material is contained within the slot or trench of the other. It These pieces of material are then mutually digitalized and bonded to make a piezoelectric composite.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to the manufacture of ultrasonic transducers, and more particularly to the manufacture of very fine pitch piezoelectric transducer components.

[0002]

2. Description of the Related Art Ultrasonic devices such as those used in the medical ultrasonic imaging market typically use zirconate-lead titanate (PZ) for both transmission and reception of ultrasonic waves.
Use a piezoelectric ceramic material such as T). To maintain formability and improve electroacoustic performance, it may be beneficial to use composite piezoelectric materials rather than PZT monolithic slabs. The composite typically consists of individual small pieces of PZT dispersed and separated within a support of epoxy or other polymeric plastic matrix material. PZT material strips usually consist of small strips or posts embedded in a flexible, acoustically lossy host matrix material.

In the case of embedded strips of piezoelectric material,
The composite is said to be "one-dimensional" and the width of each embedded strip can be several acoustic wavelengths long. However, array transducers used in medical ultrasound applications require piezoelectric strips, posts or rods with an aspect ratio (width to height) of less than 0.7. The piezoelectric elements of such medical transducers often must be below this value to achieve satisfactory sector, linear or vector type phased array transducer performance. As is often the case, one must resort to techniques for finely chopping the elements so that the strips or elements of each element are below the aspect ratio requirements above. One way to fabricate such a device is to first "fine-cut" all the subelements on a fine pitch piece, and then to form macro transducer elements on a coarser pitch piece. First, two, three, or even four or more of these subelements are electrically linked. A two-dimensional piezoelectric device is formed by dicing or cutting subelements in two diagonal directions to form posts or rods, rather than strips formed by dicing in only one direction.

A common and convenient method of making one-dimensional composites is to start with a monolithic slab of piezoelectric material and then use a dicing saw to cut slots, trenches or gaps in the slab. Is. After cutting, these slots, trenches or gaps may be backfilled with a polymer matrix material such as epoxy. Two-dimensional composites can be made by further cutting diagonal slots. For this bidirectional material, a method of cutting and filling in each direction may be selected in order to facilitate manufacturing. After filling the slots, the exposed flat surface of the composite structure is ground and lapped, then metallized or electroded, and repoled, if necessary, as a necessary step. (repoling). The resulting structure essentially comprises a semi-flexible mat consisting of strips, posts or rods of piezoelectric material laterally encapsulated by a polymer matrix material such as epoxy. The isolated strips, posts or rods (which are typically made of PZT) have their opposite exposed edges or edges in contact with the metallized or electroded surface.

Composite piezoelectric materials have been shaped and formed to provide mechanical focusing of ultrasonic waves. Composites have also been manufactured for use in specialized applications to provide improved electroacoustic characteristics compared to those obtained with monolithic piezoelectric materials. Examples of such applications include mechanical scanning low pass devices and annular arrays commonly used in the field of medical ultrasound.

To meet the demand for even higher frequency transducers, adjacent PZ
It is necessary to find a way to make composites with very fine pitch pieces between the T strips. This is based on the fact that the thickness must decrease as the operating ultrasonic wavelength decreases, and the pitch must also decrease in order to meet the aforementioned aspect ratio criteria.

At present, the dicing technology utilizes a thin foil blade of diamond-polished 30,000 to 60,000 revolutions per minute. However, the use of such blades is limited with respect to constantly narrower trenches or kerfs or deeper cuts required to produce finer pitch composites. 15 micron (15 x 10 ^-6 m)
Blades of the following thickness are difficult to machine with them and difficult to obtain. Moreover, such blades become mechanically quite unstable when cutting very thin slots at great depths. Moreover, as the cutting depth / blade thickness (and kerf width) ratio increases, blade life shortens, kerf taper fails, and the frequency of fatal blade failures increases. Obviously, if dicing is performed at a very fine pitch and the dimensions of the composite are very macro, then blade failure during dicing as a whole is likely to destroy that part.
Much of the added value that was put in to reach the point of failure is lost as such meaningless. Therefore, it is difficult to achieve narrower cuts, or slots, so that it is limited or impossible to produce finer pitch composites with higher yields.

[0008]

SUMMARY OF THE INVENTION A first object of the present invention is to use ultrasonic transducers, especially those having a very fine pitch and more closely spaced PZT elements as required for high frequency devices. It is to provide a better method of assembling and manufacturing "dice and fill" composites.

A second object of the present invention is an improvement which allows the manufacture of acoustic devices using PZT elements with different and / or complementary properties, an advantage not possible with monolithic structures. To provide a method.

An important feature of the present invention is the formation of two phase slabs or diced piezoceramics by using conventional dicing blade or laser cutting techniques. Each of these two slabs is diced to provide a relatively wide slot or groove on a common pitch or spacing. The diced surface of each slab is then
Moistened with epoxy so that the slot or notch is partially or fully filled. These two diced surfaces are then brought together in a face-to-face relationship with the aligned surfaces, such that one strip or post is received in the slot of the other, thereby mutual digitizing, Form a composite slab with strips or posts that have half the pitch dimension of these two starting slabs and double the depth. Depending on the application, epoxy can
It is possible to completely fill the spacing between the strips or posts, and if the epoxy is only applied to the parts of the slab mentioned above, the result is an almost "air filled" composite. The epoxy is then cured and the interdigitated and cured slab is conventionally ground, lapped, and, if necessary, prepared for metallization and repoling.

The invention disclosed herein allows a composite PZT with a groove width that can be reduced to near zero dimensions and a pitch of the subelements that is much tighter than is possible with the same tool and the monolithic method described above. It becomes possible to manufacture an audio device. By this method
Relatively wide cuts made using laterally stiff and thin blades can be employed, and even very fine pitch composites can be produced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a pair of slabs 10 and 11. Each slab is formed of a piezoelectric material according to the preferred embodiment of the present invention. Each slab is complementary to each other and is diced or cut to form a notch or slot 12 of width K and depth D, as shown. The slot 12 clearly shows within it a plurality of posts or strips of width W 2. As shown, the posts 13 of one slab are interdigitated with the posts of the other slab, thereby creating a gap 14 between the posts of one slab and the adjacent posts of the other slab. I have left. This arrangement allows the piezoelectric composite of the transducer to be formed with a plurality of gaps 14, which can be much narrower than is possible using conventional manufacturing techniques.

It may be desirable for the posts and strips to be implemented such that they have slightly sloping sidewalls and are not perfectly rectangular in cross section. This facilitates the process of mutual digitalization because the gaps 14 are not formed until the opposing slabs are completely mutual digital. Such post or strip taper rings also provide additional acoustic design freedom. Furthermore, it may also be acoustically desirable that a thickness taper be present in slab 10 and / or 11 for the purpose of manipulating the acoustic spectrum.

The two slabs 10 and 11 may be electrically repolled in that direction, ie in the sense 15 direction, as is customary prior to dicing. However, poling can also occur after dicing as long as the appropriate electrodes are available and accessible.

To simplify FIGS. 1 and 2, a slab
It was shown that 10 and 11 were cut to a thickness D (less than the slab thickness). Slab 10 as an option
And 11 may be mounted on a separate carrier plate which allows the value of D to be greater than the thickness of the slab. Yet another option is slab 10 and / or
An additional acoustic layer, such as an acoustic matching layer, may be laminated to itself before performing such cutting and mutual digitization on itself. In this way, the component is acoustically aligned with what it ultimately must couple into.

The gap 14 may be filled with a polymeric material, as is conventional and standard in the manufacture of composite transducers, or may be left unfilled, at least partially. The choice of whether or not to use a gap filling material is largely a matter of tradeoffs. The use of gap-filling material makes the structure more complete, but degrades in terms of acoustic isolation between the elements. The void-filling material may include microspheres, which are, for example, polystyrene or plasticizer spheres, of the appropriate size mixed in at a sufficient concentration so that all voids have the same size. Will be things. However, using too many microspheres can increase acoustic crosstalk and make mutual digitalization more difficult. It is believed that the size or diameter of the microspheres should be selected to be approximately the same as the size of the preferred gap 14. If this microsphere is elastic or imparts, as is the case with polymer spheres in general, then the sphere will ensure that the posts have the correct uniform spacing between the microsphere and the adjacent post. It is advantageous to deliberately design mild mechanical interference to ensure that it is placed.

There are essentially three methods of mutual digitization and gap filling. The first method is to dry assemble the slabs 10 and 11 and then introduce the gap filling material. The second method is to pre-wet these slabs and / or their slots with a filled matrix material such that the two slabs merge and the strips or posts of one of them are mutually digitalized by those of the other. , Is a method of forcibly removing the excess amount. The third process of filling the gap is a modification of the second method, in which the slab is pre-wetted, interdigitized, and then the excess filling material is controlled and removed to cause capillary action. It attracts each other through force and / or atmospheric forces to bring them together. The microspheres, if used, are either present in the epoxy, or use a polymer matrix material, or are instead placed in the notch without epoxy.
The epoxy may then be added and is present in the polymer matrix.

A fourth possible scheme is to fill air gaps completely or temporarily in order to provide air gaps to maximize acoustic isolation between the elements, wet etching and This method removes some or all of the filler by dry etching, melting or sublimation.

As can be seen in FIG. 1, the portions of slabs 10 and 11 extending below pseudowire 16 and above pseudowire 17 have been grinded or lapped during further processing of the manufacturing cycle. The remaining center or center between the pseudowires 16 and 17, as indicated by the double arrow line 18, is an isolated post made of piezoelectric material, cased or laterally enclosed by a mat of polymeric material. Or it constitutes a single composite mat consisting of strips. The exposed end surface of the post is metallized to form the required electrodes.

Removal of the gap-filling polymer is easiest and convenient to perform after removing the piezoelectric material above and below each of the pseudowires 16 and 17, if partial air gaps are desired.

FIG. 2 shows the final PZT composite component used in the transducer after the excess piezoelectric material on the opposite side of the interdigitated assembly of FIG. 1 has been removed. As shown, the surface is metalized or coated with an electrically conductive layer 19. This is done using conventional sputtering, evaporation or other thick film deposition processes.

While the preferred embodiment of the invention has been illustrated and described, various modifications and changes can be made without departing from the spirit and scope of the invention and each such modification and change is expected. Has been done.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a pair of piezoelectric slabs that have been diced and mutually digitalized according to a preferred embodiment of the present invention.

FIG. 2 is a cross-digitized cross-section shown in FIG. 1 depicting how the grinding and lapping processes were performed on the top and bottom surfaces, and how these surfaces appeared after being metalized or electrodeized. Sectional drawing which showed the similarity of a slab.

[Explanation of Codes] 10, 11 Slab 12 Slot 13 Post 14 Gap

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[Procedure amendment]

[Submission date] September 16, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H04R 31/00 330 9181-5H (72) Inventor John, Paul, Mall, The, Third California, USA , Los, Altos, Hills, Oneonta, Drive, 24931

Claims (20)

[Claims] 1. A method of making a piezoelectric composite from two or more pieces of piezoelectric material or electrostrictive material, each of which:
Forming two structures consisting of piezoelectric elements of width W separated by a gap distance K on the pitch-spaced piece P; making two structures mutually digital, An element is interdigitated with an element of the other structure; and the step of combining the interdigitized elements to form a composite suitable for use in an acoustic transducer. How to characterize. 2. A method according to claim 1, characterized in that the elements made of piezoelectric material are coupled in a relationship of P>K> W. 3. The method of claim 1 or 2 further comprising: pre-wetting each structure with a curable polymer prior to mutual digitalization, the polymer being The method, further comprising the step of joining the elements of the two structures during mutual digitalization and solidification. 4. A method according to any one of claims 1 to 3, wherein the gaps or grooves between the elements of the at least one structure are coated or filled with microspheres prior to mutual digitization, The method according to claim 1, wherein the intervals between the elements digitized by the microspheres are made uniform. 5. A method of manufacturing a composite piezoelectric device from two or more pieces of piezoelectric material and / or electrostrictive material: 2
Cutting a slot, trench or through cut in each of the two pieces of material, the slot, trench or cut separating two or more portions of each piece by a gap distance K. Forming cuts on the pitch-spaced pieces P and further forming material parts or elements of width W to make the two material pieces mutually digitalizable; the step of mutually digitizing the two material pieces. To accommodate a portion of the first piece of material in the slot, trench or cut of the second piece of material and, conversely, to place the second piece of material in the slot, trench or cut of the first piece of material. Accommodating steps;
Combining two mutually digitalized pieces of material to form a composite device. 6. A method according to claim 5, wherein the elements of piezoelectric material are bonded such that P>K> W. 7. A method according to claim 5 or 6, further comprising: prior to mutual digitalization, the slots in each piece of material to be mutual digitalized are pre-filled with a curable polymer or are curable. A step of wetting with a polymer, wherein the polymer binds the two pieces of material together by mutual digitalization and subsequent solidification. 8. The method according to claim 5, wherein the material is a piezoelectric material or an electrostrictive material, and the width W is less than 7/10 of the thickness D. A method characterized by being cut to form a. 9. A method according to any one of claims 5 to 8 further comprising: starting materials consisting of two structures formed by the method of claim 5.
A method for producing a final composite of a two-dimensional structure utilizing a cutting step, a mutual digitalization step, and a step of joining two material pieces together. 10. A method according to any one of claims 5 to 9 including the step of vertically stacking and stacking structures to form a three-dimensional piezoelectric composite. 11. The method according to claim 5, wherein the composite structure is subsequently deformed on a curved surface for the purpose of mechanically focusing the transmitted or received ultrasonic waves to some extent. A method characterized by blaming. 12. The method according to claim 5, wherein the mechanical grinding saw, laser cutting, ultrasonic cutting, electric discharge machining and wet etching or dry etching are combined in any combination. A method characterized by completing the steps of cutting by utilizing. 13. A method according to any one of claims 5 to 12, wherein the composite structure is formed with a plurality of different thicknesses than the piezoelectric activator material to achieve broad band functionality. A method characterized by being performed. 14. A method according to any one of claims 5 to 13, characterized in that the two pieces of material are cut so as to form a plurality of complementary aligned arrays of slots, strips or posts. Method. 15. A method according to claim 14, characterized in that the strips or posts of the composite structure are subsequently replaced by metal elements for the purpose of electrical connection or impedance tuning. 16. A method of making a composite piezoelectric device from two or more slabs of piezoelectric material, each slab having a substantially flat surface at least initially: a plurality of parallel slots in the surface of each slab. Forming a trench or a through cut, the slot, trench or through cut being formed on the pitch spacing piece P,
In the meantime, limit the material part or element of width W,
Each slot, trench or through cut with a gap K
The steps of separating adjacent element parts and mutually digitizing the material parts of the two slabs; the step of mutually digitizing the two slabs, wherein the first slab part is the second slab In a slot, trench, or through cut, and vice versa; and then joining two slabs to form a composite device. 17. A method according to claim 16, characterized in that the slab is cut or minced so that P>K> W. 18. A method of manufacturing a two-dimensional or three-dimensional composite piezoelectric device comprising the steps of claim 16 for forming a first acoustic transducer having one dimension, formed in each slab. A plurality of second slots perpendicular to the slots are formed, and the second slots separate two or more portions by a gap distance K1, and the slots are formed on the pitch spacing piece P1 to form a width W1. Forming a plurality of parallel slots in the surface of the third slab of piezoelectric material, said slots being formed on the pitch spacing piece P1, between which a section of material of width W1 is formed. And separating each portion where each slot is adjacent by a gap distance K1; and interdigitizing the third slab with the first acoustic transducer, the portion of the third slab In the second slot of the first acoustic transducer and vice versa; then combining the two structures to form a composite acoustic transducer structure of two or more dimensions. And a step; 19. The method according to claim 18, wherein P1> K.
A method characterized by cutting or carving the first acoustic transducer and the third slab such that 1> W1. 20. A composite piezoelectric device formed by mutual digitizing and bonding a pair of complementary slabs of piezoelectric or electrostrictive material, with a spacing therebetween defining a slab portion. Slicing each slab to form parallel slots, trenches or through cuts placed, the gap width of the slots, trenches or cuts being greater than the width of the slab portion, the slab portion of one slab being the slot of the other slab. , A device for accommodating in a trench or a cut and vice versa.