# Patent

## Title
Hermetically bonding ceramic and titanium with a Ti-Pd braze interface

## Abstract

A component assembly for use in living tissue comprises: a ceramic part; a metal part; and a titanium palladium (Ti—Pd) interface layer for bonding said ceramic part to the metal part. In one embodiment, the interface layer may be formed from a single titanium layer in contact with a single palladium layer, or in other embodiments, may be at least a three layer laminate (Pd—Ti—Pd). A microstimulator housing comprising a ceramic part, a titanium or titanium alloy part sandwiching the Ti—Pd interlayer may be employed to create a eutectic bond that is strong and hermetic.

## Background
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/618,076, filed Oct. 12, 2004, which application is incorporated herein by reference in its entirety.


BACKGROUND OF THE INVENTION
The present disclosure relates to implantable medical devices and, more particularly, systems and methods that permit a titanium or titanium alloy part and a ceramic part to be brazed together to achieve a hermetic seal.
Body implanted devices are generally hermetically sealed to keep fluids and water vapor from infiltrating into the device and destroying the electronic circuitry contained within the device. Typically, the medical device has an outer housing that is made of a biocompatible material such as a ceramic or a metal.
While a medical device housing may be made almost entirely of a biocompatible metal such as titanium, it may be necessary for example, in some medical applications to have a housing which is made substantially from a non-metallic material because a receiving/transmitting antenna may be included inside the housing. Such an antenna may not be operable within a housing that is completely made from metal, e.g., titanium, since metal can effectively act as a shield against RF energy transmissions.
One such application where it is often, for example, to have a composite device housing consisting of a non-metal material, e.g., a ceramic, and a metal, e.g., titanium, is an implantable microstimulator. A microstimulator has very small dimensions and can have metal electrode contacts integrated into the housing. The small dimensions allow a microstimulator to be implanted with less surgical trauma compared to a larger, implantable stimulator device.
Because of the small size of a microstimulator, it generally does not use a primary (one-time-use-only) battery but uses, instead, a replenishable power source such as a rechargeable battery. The rechargeable battery, contained in the microstimulator, is charged inductively with transcutaneous RF power transmissions. In addition, the RF transmissions may also be used to transfer data and commands between the implanted device and the external device that is connected to the secondary antenna. Such RF power/data transmissions require the use of a primary, internal antenna that may be placed inside the device housing and a secondary, external antenna that is not implanted. In order to achieve effective and efficient RF power transmissions through the stimulator housing, the housing can be made at least partly of a non-metallic material. The use of a housing that is at least partly non-metallic can improve the magnetic inductance between the internal antenna within or on the implantable device and an external antenna.
An example microstimulator that employs a rechargeable battery and derives power from transcutaneous RF power transmissions is a BION® implantable microstimulator, manufactured by Advanced Bionics® Corporation, Valencia, Calif.
The following list of applications, publications and patents, which are all herein incorporated by reference, describe various details associated with the manufacture, operation and use of BION implantable microstimulators.












Application/Patent/
Filing/Publication



Publication No.
Date
Title







U.S. Pat. No. 5,193,539
Issued
Implantable Micro-



Mar. 16, 1993
stimulator


U.S. Pat. No. 5,193,540
Issued
Structure and Method of



Mar. 16, 1993
Manufacture of an




Implantable Micro-




stimulator


U.S. Pat. No. 5,312,439
Issued
Implantable Device



May 17, 1994
Having an Electrolytic




Storage Electrode


U.S. Pat. No. 5,324,316
Issued
Implantable



Jun. 28, 1994
Microstimulator


U.S. Pat. No. 5,405,367
Issued
Structure and Method of



Apr. 11, 1995
Manufacture of an




Implantable Micro-




stimulator


PCT Publication
Published
Battery-Powered Patient


WO 98/37,926
Sep. 3, 1998
Implantable Device


PCT Publication
Published
System of Implantable


WO 98/43,700
Oct. 8,1998
Devices For Monitoring




and/or Affecting Body




Parameters


PCT Publication
Published
System of Implantable


WO 98/43,701
Oct. 8, 1998
Devices For Monitoring




and/or Affecting Body




Parameters


U.S. Pat. No. 6,051,017
Issued
Improved Implantable



Apr. 18, 2000
Microstimulator and




Systems Employing




Same



Published
Micromodular Implants



September, 1997
to Provide Electrical




Stimulation of Paralyzed




Muscles and Limbs, by




Cameron, et al.,




published in IEEE




Transactions on




Biomedical Engineering,




Vol. 44, No. 9, pages




781-790.









The BION microstimulator has a small housing that may be partly metal, e.g., titanium and partly non-metallic, e.g., a ceramic. Because the microstimulator uses a rechargeable battery and contains an antenna for receiving power and/or data transmissions, it may be necessary for example, for at least a part of the housing to be non-metallic. In addition, because the microstimulator has both anode and cathode electrode contacts, which are typically both metals, it may be necessary for example, to hermetically seal the interface between the metal electrode contacts and the non-metallic, e.g., ceramic part of the housing. Thus, the housing may comprise a metal part and a non-metallic part, which two parts exhibit different mechanical properties. The construction of such a composite housing for a microstimulator is challenging because: (1) the two dissimilar materials, ceramic and titanium have different mechanical properties, including thermal coefficients of expansions and (2) the method of joining for example, must yield a strong, hermetic seal.
Nickel has been used to create a brazed interface. U.S. Pat. No. 6,521,350 to Fey et al. employs an interlayer of pure nickel to form a bond between a ceramic part and a titanium part. U.S. Pat. No. 6,221,513 to Lasater uses a titanium nickel (Ti—Ni) alloy as interface material between ceramic and titanium. Both patents are herein incorporated by reference in their entireties.
A need exists for alternative systems and methods for hermetically sealing a medical device housing that may be partly ceramic and partly titanium.
SUMMARY OF THE INVENTION
A component assembly provides a hermetic seal between a titanium part and a ceramic part, which component assembly is implantable within living tissue, e.g., a human body. A titanium-palladium (Ti—Pd) interface layer (interlayer), e.g., a titanium layer in contact with a palladium layer in a sheet or foil form or Pd—Ti—Pd laminate form, is placed between the titanium part and ceramic part and pressed together to get intimate contact between all parts. While the complete assembly is placed in an inert gas, e.g., argon, or in a vacuum, heat is applied until a temperature is reached, where the Ti—Pd interlayer melts. After cooling, the Ti—Pd interlayer forms a eutectic bond with the titanium part and also wets the ceramic surface and forms a bond with the ceramic after the interlayer is allowed to cool. The resulting brazed interface is strong and provides a hermetic seal that is essentially impervious to the passage of gases or water.
In a particular embodiment utilizing the hermetic component assembly, an implantable microstimulator housing employs a titanium part and a ceramic part and an interface layer (interlayer) of Ti—Pd or Ti—Pd—Ti. Other Ti—Pd laminates having more than three layers may also be used. The microstimulator housing is hollow and the space inside is filled with components, e.g., a rechargeable battery and associated stimulation electronics.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects of the present disclosure will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:
FIG. 1 shows an illustration of a system for hermetically sealing an interface between a ceramic component and a titanium component;
FIG. 2 shows a representation of a ceramic part, e.g., zirconia, and titanium or titanium alloy part with a Ti—Pd interlayer;
FIG. 3 shows a solid-liquid phase diagram for titanium-palladium;
FIG. 4 shows an illustration of a microstimulator housing having a ceramic part and a titanium part and a Ti—Pd or Ti—Pd—Ti interlayer therebetween;
FIG. 5 shows a cross-sectional view of a microstimulator housing having a ceramic part and titanium part or titanium alloy part;
FIG. 6 shows a magnified detail view #1 of a brazed interface;
FIG. 7 shows a magnified detail view #2 of a brazed interface;
FIG. 8 shows a magnified detail view #3 of a brazed interface;
FIG. 9 shows a magnified detail view of a brazed interface identifying brazed areas A and B;
FIG. 10 shows a magnified detail view of brazed area A;
FIG. 11 shows a magnified detail view of brazed area B;
FIG. 12 shows a material element graph depicting the material content of Section I;
FIG. 13 shows a material element graph depicting the material content of Section II; and
FIG. 14 shows a material element graph depicting the material content of Section III.



Corresponding reference characters indicate corresponding components throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE INVENTION
The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.
FIG. 1 shows a view of a component assembly system 10 for achieving a hermetic seal between a titanium part 30 and a ceramic part 50, which system may be implanted in living tissue. The assembly system includes a titanium-palladium (Ti—Pd) interface layer (interlayer) 40 placed between the titanium part 30 and ceramic part 50.
FIG. 2 shows a cross-section of one embodiment of the Ti—Pd interlayer 40. FIG. 2 also shows the component parts of the hermetic assembly: a ceramic 50, e.g., a zirconia ceramic part, titanium part 30 and the Pd—Ti—Pd laminate interlayer 40. It will be appreciated that a Ti—Pd laminate interlayer 40 may have more than three layers. In one of many possible examples, the laminate interlayer 40 can be cold rolled into a two-layer foil or at least a three-layer laminate to achieve intimate material contact between palladium and titanium. In other embodiments the interlayer 40 may have palladium layer sputter coated over titanium layer or palladium may be vapor deposited over a titanium layer. The titanium part 30 may be a commercially pure titanium or a titanium alloy, including among others, Ti-6 Al-4 V, titanium niobium alloy or titanium tantalum. The ceramic part 50 may be, among others, zirconia, stabilized zirconia, partially stabilized zirconia, tetragonal zirconia, magnesia stabilized zirconia, ceria-stabilized zirconia, yttria stabilized zirconia, and calcia stabilized zirconia, as well as alumina, and titania, and the like.
The interlayer 40, in one embodiment, may be a three layer laminate with palladium sandwiching a middle layer of titanium, i.e., Pd—Ti—Pd. The interlayer may be produced by cold rolling a Pd—Ti—Pd layer. Alternatively, the a first palladium layer may be sputter coated or vapor deposited over one side of a layer of titanium and a second palladium layer may be sputter coated or vapor deposited over the second side of the titanium layer. This laminate interlayer 40 can be placed between the titanium part 30 and ceramic part 50 and pressure (force) of between 5 to 20 psi may be applied to urge the titanium part 30 and ceramic part 50 to firmly press against the laminate interlayer 40. While pressure is applied to achieve positive material contact, the titanium part 30, the ceramic part 50 and laminate interlayer 40 are placed in a vacuum, e.g., at about 10−6 torr or in a non-reactive gas, such as argon, and then the parts are heated to a temperature at or above the Ti—Pd eutectic temperature, e.g., 1120 degrees C., that causes the interlayer 40 and titanium part 30 to fuse together and cause wetting of the surface of the ceramic part 50. The melting temperature applied to the Ti—Pd interlayer 40, for example, is lower than a melting temperature for the titanium part 30 per se or the melting temperature for the ceramic part 50.
FIG. 3 shows a liquid-solid phase diagram for titanium-palladium (Ti—Pd). This diagram indicates an X-axis (shown at the bottom of the graph) of atomic percent of palladium relative to titanium or, alternatively, weight percent of palladium relative to titanium (shown at the top of the graph). The Y-axis indicates the temperature in degrees Celsius. The dotted line at the upper area of the graph demarcates the upper area labeled “L”, which dotted line indicates the temperatures and percentage weights of palladium wherein the palladium/titanium interlayer will begin to liquify. Below the dotted line at the upper part of the graph, the palladium/titanium is in the solid phase. It can be seen that at a 50% weight of palladium relative to titanium/palladium, the Ti—Pd will enter a liquid phase at a temperature at or above 1120 degrees C. At some melting temperature, the Pd—Ti—Pd laminate interlayer 40 will be in a liquid state and conform to the surface of the ceramic part 50 (FIG. 2). As the interlayer 40 cools, a bond forms between the ceramic part 50 and the interlayer 40. In addition, the Pd—Ti—Pd interlayer 40 will also fuse and bond with titanium part 30.
FIG. 4 shows a perspective, external view of a microstimulator housing 5 showing its various parts, which microstimulator housing 5 may have a ceramic part 50′, a titanium part 30′ and a titanium palladium interlayer 40′ therebetween. The three part housing assembly comprising the ceramic part 50′, interlayer 40′ and the titanium part 30′ make up the total component assembly 10′ needed to achieve a hermetic seal. The microstimulator housing 5, as shown, also has an electrode contact 60 and may have another interlayer 40′′ which can also be a Ti—Pd braze. Pressure (force), as shown by the arrows 20A and 20B, may be applied from both ends of the microstimulator housing to provide intimate contact between component materials during brazing of the Ti—Pd interlayer. The pressures (force), as shown by the arrows 20A and 20B, applied to the component materials may be, for example, between 5 to 20 psi. In one embodiment, the interlayer 40′ may be placed into a vacuum that is about 10−6 torr while the Ti—Pd brazing occurs.
FIG. 5 shows a cross sectional view of a microstimulator housing 5 of FIG. 4. The microstimulator housing 5 is hollow inside and contains internal electronics and parts, e.g., a rechargeable battery (not shown) and electronic circuitry (not shown) for producing electrical stimulation pulses from the electrode contact 60 and titanium part 30′, which may function as an electrode. The total length of the microstimulator housing 5, may be for example, less than about 1.5 inches and in some examples, may be less than about 1 inch. The diameter of the microstimulator may be less than about 1.5 inches and in some examples, less than about a quarter inch. The electrode contact 60 and titanium part 30′ are connected in a circuit. To achieve a hermetic seal, the interface layer 40′ between the ceramic part 50′ and titanium part 30′ is brazed with Ti—Pd. For example a Pd—Ti—Pd laminate interlayer 40′ may have a total thickness of between about 0.0001 to about 0.01 inches. A thickness of about 0.003 inches, for instance, may be a thickness for use with a microstimulator. Each palladium layer on either side of the laminate may have a thickness of between about 0.000033 to about 0.0033 inches. The titanium layer in the interlayer 40′ may have a thickness between about 0.000033 to about 0.0033 inches. It is understood that these dimensions for the interlayer 40′ are exemplary only and may vary according to the particular application.
In sum, to create a hermetic seal for an implantable housing, the Ti—Pd brazing steps include: providing a ceramic part and a titanium part, placing a Ti—Pd thin foil or a Pd—Ti—Pd laminate sheet in the interface between the ceramic and titanium parts, which parts are held together intimately under a pressure (force) in a vacuum or inert gas environment. In this environment, the Ti—Pd (or Pd—Ti—Pd) interlayer is heated to a temperature exceeding the liquid phase of the Ti—Pd interlayer, e.g., about 1120 to 1150 degrees Celsius, in order to liquify the Ti—Pd interlayer and to create a bond between the interlayer and the Ti part and between the interlayer and the ceramic part.
In may also be possible to provide a Ti—Pd interlayer in forms other than a foil or laminate. For example, a mixed powdered form or micro-bead form can also suffice. Certain applications may require the foil to be circular or annular in form to seal a cylindrical, annular, or other similar surfaces.
Compared to a nickel braze, for example, it is known that palladium and titanium are more inert in the body environment and thus more bio-compatible, i.e., relatively non-reactive within the human body. The bond created between the Ti—Pd interlayer with ceramic is strong and hermetic, and is essentially impervious to the passage of gases or water at the brazed interface. The bond created between the Ti—Pd interlayer with a commercially pure titanium part or titanium alloy part is also strong and hermetic.
While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.
Test Results
The following examples demonstrate magnified detail views of a brazed interface 100 between a ceramic material 102, e.g., zirconia, and a metal material 104, e.g., Ti6-4. A palladium/titanium laminate alloy 105 was used as the brazing material between the ceramic material 102 and a metal material 104. The laminate alloy 105 consisted of a titanium foil 106 with a thickness of 54 um and a Palladium material 108 (18 um thickness) sputtered on both sides of the titanium foil 106. The test results demonstrated a strong hermetic bond at the brazed interface.













Example #1
Shown in FIG. 6 is a magnified detail view #1 of the brazed



interface.


Example #2
Shown in FIG. 7 is a magnified detail view #2 of the brazed



interface.


Example #3
Shown in FIG. 8 is a magnified detail view #3 of the brazed



interface.









Brazed areas A and B (taken from detail views #1, #2, or #3) shown in FIG. 9 were further enlarged as shown in FIGS. 10 and 11 respectively. The three material sections, Section I, Section II, and Section III (shown in FIGS. 10 and 11), were further analyzed for material content:













Section I
For both brazed areas A and B, Section I represented the



palladium/titanium laminate alloy, 105. A material element



graph shown in FIG. 12 verified the expected material content



of Section I. As indicated by the material spikes 110 and 112,



a count of 600 elements of palladium and a count of 1020



elements of titanium were found.


Section II
For both brazed areas A and B, Section II represented the



titanium alloy material, 104. A material element graph shown



in FIG. 13 verified the expected material content of Section II.



As indicated by the material spike 114, a count of 980



elements of the titanium alloy were found.


Section III
For both brazed areas A and B, Section III represented the



Zirconia material, 102. A material element graph shown in



FIG. 14 verified the expected material content of Section III.



As indicated by the material spike 116, a count of 990



elements of the zirconia were found.









The material count found in Sections I, II, and III for brazed areas A and B confirmed the strength of the hermetic bond between the ceramic material 102, e.g., zirconia, and a metal material 104, e.g., Ti6-4.

## Claims

1. A component assembly for use in living tissue comprising:
a ceramic part;
a metal part selected from the group consisting of titanium and titanium alloys; and
an interface layer consisting essentially of titanium and palladium, the interface layer bonding the ceramic part to the metal part.

2. The component assembly of claim 1, wherein said ceramic part is selected from the group consisting or zirconia, stabilized zirconia, partially stabilized zirconia, tetragonal zirconia, magnesia stabilized zirconia, ceria-stabilized zirconia, yttria-stabilized zirconia, and calcia-stabilized zirconia, as well as alumina, and titania.

3. The component assembly of claim 1, wherein the interface layer forms a eutectic bond between said metal part and said ceramic part.

4. The component assembly of claim 1, wherein the interface layer can be heated to a temperature that is at or greater than the eutectic melting point of the interface layer.

5. The component assembly of claim 1, wherein the interface layer is a three-layer laminate comprising two palladium layers at least partially covering opposing sides of a titanium layer.

6. The component assembly of claim 5, wherein the laminate is cold rolled to provide the intimate contact between layers.

7. The component assembly of claim 1, wherein the interface layer is a two-layer laminate of comprising a titanium layer and a palladium layer.

8. The component assembly of claim 7, wherein the laminate is cold rolled to provide intimate contact between layers.

9. The component assembly of claim 7, wherein the laminate is formed by sputter coating palladium over titanium.

10. The component assembly of claim 7, wherein the laminate is formed by vapor deposition of palladium over titanium.

11. A microstimulator comprising:
a component assembly housing comprising:
a ceramic part;
a metal part selected from the group consisting of titanium and titanium alloy; and
an interface layer consisting essentially of titanium and palladium, the interface layer bonding the ceramic part to the metal part.

12. The microstimulator of claim 11, wherein said ceramic part is selected from the group consisting of zirconia, stabilized zirconia, partially stabilized zirconia, tetragonal zirconia, magnesia stabilized zirconia, ceria-stabilized zirconia, yttria-stabilized zirconia, and calcia-stabilized zirconia, as well as alumina, and titania.

13. The microstimulator of claim 11, wherein the interface layer forms a eutectic bond between said metal part and said ceramic part.

14. The microstimulator of claim 11, wherein the interface layer can be heated to a temperature that is at or greater than the eutectic melting point of the interface layer.

15. The microstimulator of claim 11, wherein the interface layer is a three-layer laminate comprising two palladium layers at least partially covering opposing sides of a titanium layer.

16. The microstimulator of claim 15, wherein the laminate is cold rolled to provide intimate contact between layers.

17. The microstimulator of claim 11, wherein the interface layer is a two-layer laminate comprising a titanium layer and a palladium layer.

18. The microstimulator of claim 17, wherein the laminate is cold rolled to provide intimate contact between layers.

19. The microstimulator of claim 17, wherein the laminate is formed by sputter coating palladium over titanium.

20. The microstimulator of claim 17, wherein the laminate is formed by vapor deposition of palladium over titanium.