US 20100076318 A1
The present invention generally relates to medical devices, and more particularly to an improved medical imaging device. In one embodiment, an imaging device includes a drive shaft having proximal and distal ends received within the lumen; and an imaging transducer assembly. coupled to the distal end of the drive shaft and positioned at the distal portion of the elongate member. The imaging transducer assembly includes one or more imaging transducers formed with a piezoelectric composite plate using photolithography based micromachining.
28. An imaging device configured to be located in an imaging catheter, said imaging device comprising:
a drive shaft having proximal and distal ends; and
an imaging transducer assembly coupled to the drive shaft, wherein the imaging transducer assembly includes at least one imaging transducer, wherein the at least one imaging transducer is formed from a photolithography based micromachined piezoelectric composite plate, wherein each imaging transducer includes a plurality of posts and each of the plurality of posts has a vertical etching profile of at least 80°.
29. The imaging device of
30. The imaging device of
31. The imaging device of
32. The imaging device of
33. An ultrasound imaging transducer, comprising:
a plurality of posts formed by photolithography based micromachining of a piezoelectric composite plate, wherein each of the plurality of posts has an aspect ratio of post height to post width of at least 2 to 1;
a plurality of kerfs separating the plurality of posts, wherein the plurality of kerfs are filled with a polymeric material; and
an electrode pattern coupled to the plurality of posts.
34. The ultrasound imaging transducer of
35. The ultrasound imaging transducer of
36. The ultrasound imaging transducer of
37. The ultrasound imaging transducer of
38. The ultrasound imaging transducer of
39. The ultrasound imaging transducer of
40. A ultrasound imaging transducer assembly, comprising:
an array comprising a plurality of the ultrasound imaging transducers of
41. The ultrasound imaging transducer assembly of
42. The ultrasound imaging transducer assembly of
43. A method of fabricating an ultrasound imaging transducer, the method comprising:
forming a photoresist mask on a plate of piezoelectric material;
forming a hard metal mask on portions of the plate exposed by the photoresist mask;
removing the photoresist mask leaving the hard metal mask;
etching portions of the plate exposed by the hard metal mask to form, in the plate, a plurality of posts and a plurality of kerfs between the posts, wherein each of the plurality of posts has an aspect ratio of post height to post width of at least 2 to 1; and
filling the plurality of kerfs surrounding the plurality of posts with a polymeric material.
44. The method of
45. The method of
46. The method of
47. The method of
The field of the invention relates to imaging devices, and more particularly to micromachined imaging transducers.
Intraluminal, intracavity, intravascular, and intracardiac treatments and diagnosis of medical conditions utilizing minimally invasive procedures are effective tools in many areas of medical practice. These procedures are typically performed using imaging and treatment catheters that are inserted percutaneously into the body and into an accessible vessel of the vascular system at a site remote from the vessel or organ to be diagnosed and/or treated, such as the femoral artery. The catheter is then advanced through the vessels of the vascular system to the region of the body to be treated. The catheter may be equipped with an imaging device, typically an ultrasound imaging device, which is used to locate and diagnose a diseased portion of the body, such as a stenosed region of an artery. For example, U.S. Pat. No. 5,368,035, issued to Hamm et al., the disclosure of which is incorporated herein by reference, describes a catheter having an intravascular ultrasound imaging transducer. These are generally known in the art as Intravascular Ultrasound (“IVUS”) devices.
On the distal end of the assembly 1 is an imaging element 15, specifically, an imaging transducer 15 that includes a layer of piezoelectric ceramic (“PZT”) 80, “sandwiched” between a conductive acoustic lens 70 and a conductive backing material 90, formed from an acoustically absorbent material (e.g., an epoxy substrate having tungsten particles). During operation, the PZT layer 80 is electrically excited by both the backing material 90 and the acoustic lens 70 to cause the emission of energy pulses.
The transducer assembly 1 of
The present invention generally relates to medical devices, and more particularly to an improved medical imaging device. In one embodiment, an imaging device includes a drive shaft having proximal and distal ends received within the lumen; and an imaging transducer assembly coupled to the distal end of the drive shaft and positioned at the distal portion of the elongate member. The imaging transducer assembly includes one or more imaging transducers formed with a piezoelectric composite plate using photolithography based micromachining.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.
In order to better appreciate how the above-recited and other advantages and objects of the present inventions are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. It should be noted that the components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. However, like parts do not always have like reference numerals. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely.
As mentioned above, an imaging transducer that operates at high frequencies, e.g., frequencies higher than 20 MHz, would be desirable. Such imaging transducers can provide images with higher resolution, which is desirable in applications involving dermatology, ophthalmology, laparoscopy, intracardiac and intravascular ultrasound. One approach to develop such imaging transducers is to utilize a photolithography based micromachining process. An example of such a process 300 is illustrated in
In the first step 310, a plate or block of piezoelectric crystal material 315, such as lead magnesium niobate lead titanate (“PMN-PT”) or lead zinc niobate-lead titanate (“PZN-PT”) is obtained. The plate 315 is preferably lapped on both sides and polished on one of the sides. The lapped and unpolished side can then be bonded to a glass carrier (not shown), which is bonded to a silicon, Si, wafer (not shown). The dimensions of the plate 315 are in the range of ten (10) millimeters (“mm”)×ten (10) mm×0.5 mm to fifteen (15) mm×fifteen (15) mm×0.5 mm; however, the dimensions could be of any size. The material of the plate 315 can be a ceramic or a single crystal. Preferably, the material of the plate 315 is a single crystal PMN-PT with electroded faces oriented along the <001> or <011> crystallographic directions. As one of ordinary skill in the art would appreciate, a single crystal structure can desirably have a high piezoelectric coefficient (e.g., d33>1500 pC/N, k33>0.8, k33′>0.7). The plate 315 preferably has a dielectric constant in the range of approximately 4000 to >7700 and a dielectric loss of less than 0.01.
In the next step 320, a mask of photoresist 325 is applied to the plate of piezoelectric material 315. The mask 325 defines the desired shape and/or pattern of imaging element(s) within the piezoelectric composite material 315. In the next step 330, electroplating is applied to the plate 315 using nickel, Ni. A hard pattern of Ni 335 is formed on the plate 315 in accordance with the mask of photoresist 325. The pattern of Ni 335 can have a thickness of approximately 1 to 20 microns (“μm”). Other metals, such as platinum, Pt, may be used instead of, or in addition to, nickel. The use of hard and/or high molecular weight materials, such as Ni and Pt, is desirable for selectivity, to protect the covered underlying area of the plate 315 from being etched. The mask of photoresist 325 is removed after the Ni is applied.
In the next step 340, an etching process, such as reactive ion etching (“RIE”), is applied. Other etching processes can be used, such as wet-etching. In one preferred embodiment, chlorine, Cl2 based RIE etching is used, which has an etching rate of approximately from less than 3 microns/hour to 12 microns/hour and can cause a substantially vertical etching profile (e.g., >80°). In the alternative, or in addition, to Cl2, sulfur hexaflouride, SF6, based etching can be used, which has similar etching properties to that of Cl2. The nickel, Ni, pattern 335 protects the underlying portions of the plate 315 covered by the pattern 335 from the etching process, and thus, one or more deep posts 347 are formed in the plate 315 with one or more kerfs 345 surrounding the one or more posts 347 etched in the uncovered portions of the plate 315. The one or more kerfs 345 can have a width in the range of approximately from less than one (<1) to twelve (12) μm, and the width of the one or more posts 347 can have a width in the range of approximately from less than three (<3) to thirty-six (36) μm and have a height in the range of approximately from less than five (<5) to more than seventy (>70) μm. In one embodiment, it is preferable to have an aspect ratio (post height/post width) of at least two (2) to one (1) to dampen the effect of lateral modes. For the dimensions of the plate 315 described above, the etching process can last approximately six (6) to eight or eighteen (8 or 18) hours. After the etching step 340, the plate 315 is then rinsed with a solvent for cleaning.
In the next step 350, the kerfs 345 are filled with an epoxy 355 such as Epo-Tek-301. A vacuum (not shown) may be utilized to remove air bubbles and prevent any void within the kerfs 345. In the next step 360, the top portion of the plate 315 and epoxy 355 are lapped to a thickness of approximately forty (40) μm. An electrode pattern 375 is then applied to the plate 315 in the next step 370 to form the imaging transducer pattern. The electrode pattern 375 is preferably comprised of gold, Au, and chromium, Cr. Moreover, as one of ordinary skill in the art would appreciate, electronic circuitry, such as imaging processing circuitry, (not shown) can be bonded to the electrodes 375. Further, the electrode pattern 375 formed on the plate 315 can define any pattern of imaging transducers, including an array, e.g., an imaging transducer at each post 347, or a single imaging transducer. An epoxy layer 377 may be applied to the back of the plate 315.
Imaging transducers having an operating frequency at above 20 MHz, e.g., 30 to >80 MHz, can be developed using photolithography based micromachining, such as the process 300 described above. The higher frequency of operation increases the resolution and image depth of an imaging transducer. Furthermore, the bandwidth of the imaging transducer, particularly when single crystal PMN-PT is employed as the piezoelectric, can be close to 100%, compared to only 70 to 80% for <20 MHz transducers made with PZT ceramic. The greater bandwidth improves the transducer's axial resolution, which increases the imaging depth. This is desirable for high frequency transducers, which have very limited imaging depth due the strong attenuation of high frequency ultrasound in tissue. When single crystal is used, these advantages can be achieved with sensitivities equivalent to or better than ceramic transducers. These high frequency transducers can be applied to a number of medical procedures including the imaging of the anterior region of an eye for monitoring surgical procedures such as cataract treatment by lens replacement and laser in situ keratomileusis (LASIK) and tumor detection (preferably up to sixty (60) MHz for fifty (50) μm resolution); skin imaging for care of burn victims and melanoma detection (preferably twenty five (25) MHz for subcutaneous, fifty (50) MHz for dermis and one hundred plus (100+) MHz for epidermis); intra-articular imaging for detection of pre-arthritis conditions (preferably twenty five (25) to fifty (50) MHz); in-vivo mouse embryo imaging for medical research (preferably fifty (50) to sixty (60) MHz); Doppler ultrasound for determination of blood flow in vessels <one hundred (100) μm in diameter (preferably twenty (20) to sixty (60) MHz); intracardiac and intravascular imaging (preferably ten (10) to fifty (50) MHz); and ultrasound guidance for the biopsy of tissue.
In preferred embodiments, at least two types of imaging transducer configurations can be developed using a photolithography based micromachining process, such as the process 300 described above, the 2-2 configuration and the 1-3 configuration, which are configurations known in the art. Turning to
Using a photolithography based micromachining process, such as the process 300 described above, on a plate of piezoelectric material enables any pattern of imaging elements to be formed, including one dimensional and two dimensional arrays of imaging elements, which can, be utilized in two dimensional and three dimensional ultrasound imaging applications, respectively.
In addition, various shapes of arrays may be formed. Turning to
In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions described herein is merely illustrative, and the invention can be performed using different or additional process actions, or a different combination or ordering of process actions. As a further example, each feature of one embodiment can be mixed and matched with other features shown in other embodiments. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.