Abstract:
A housing of an active medical device includes a metal wall having at least one feedthrough for an electrical connection through the wall. In the area of the feedthrough, the housing wall includes a contour groove extending through the thickness of wall, defining a metal islet electrically and physically isolated from the rest of the wall. The housing wall further includes an electrically insulating outer layer on the outer side of the wall extending over a region in alignment with the groove and beyond either side of the groove. The insulating outer layer includes a recess formed in alignment with the islet. The wall further includes an electrically conductive outer layer formed outside of the insulating layer and extending over the region in alignment with the groove and beyond either side of the groove. The islet is mechanically supported by the insulating and conductive outer layers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to French Patent Application No. 13/61056, filed Nov. 13, 2013, which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     The invention relates to “active implantable medical devices” as defined by the 90/395/CEE directive of Jun. 20, 1990 of the European community counsel. This definition notably includes the devices that continuously monitor the cardiac activity and deliver if necessary to the heart electrical pulses of stimulation, cardiac resynchronization, cardioversion and/or defibrillation in case of a rhythm disorder detected by the device. It also includes the neurological devices, the cochlear implants, etc., as well as the device for pH measurement or other intracorporeal parameters. 
     These devices include a generator consisting of a metal housing, usually made of titanium, on which a connector head is mounted. The connector is provided with housings for mechanically and electrically connecting one or more leads to the generator housing, the leads having at their distal end various electrodes of sensing, pacing and defibrillation. The connection of the connector to various electronic circuits involves the realization of several electrical feedthroughs, between connectors assembled on the upper surface of the housing (outer side), and the interior volume of the housing where these circuits are (inner side). 
     Besides the connection pins on the connector head, other feedthroughs can also be provided, for example to ensure a connection with a surface electrode placed on the outside of the housing, or at the sensor integrated with a lead of the device. These feedthroughs can also be found in sub-components of medical devices such as batteries and capacitors. Such a feedthrough is for example described in EP2377573 A1 (Sorin CRM SAS). 
     The technique described in the EP2377573 A1 document is to superficially oxidize the outer side of the titanium housing or to deposit an insulating layer (e.g. silicon dioxide) on the outer side, and, on the inner side, to dig into the wall throughout its thickness, so as to form a contour groove defining a closed area or “islet” dedicated to the electrical conduction. This islet, created in the mass of the wall of the housing, is physically and therefore electrically isolated from the rest of the body of the housing. 
     An electrical connection is then performed on each side of the islet by providing on each side thereof a contact pad on which for example a connection wire to a terminal of the electronic circuit, or a connection pin of the connector, is welded. The presence on the outer side of the insulating layer, which is not inground, ensures a perfect hermeticity of the feedthrough and prevents penetration of fluid inside the housing. This layer also has the advantage of being biocompatible, biostable and resistant to corrosion. 
     The method can also be developed without significant additional cost, in so far as it uses only proven conventional techniques. However, this technique leaves some mechanical fragility. Indeed, after excavation of the peripheral groove surrounding the islet, the latter is completely detached from the rest of the wall of the housing (which is precisely essential to ensure the electrical insulation of the feedthrough) and is only connected to this wall by the thin superficial layer that forms an oxide “membrane” or “diaphragm” whose thickness is typically 10 to 15 microns (for a wall thickness of about 300 microns). 
     This residual fragility, which is intrinsic to the thinness of the oxide layer, is further increased by the rather average tolerances achieved downhole during the digging of the groove. This can locally lead to the appearance of cracks or other micro-defects, precisely near the thin oxide layer which holds the islet and wherein stress biasing the structure may be concentrated, for example because of the wires or pins welded onto the central islet. 
     Certain proposed embodiments of the present invention provide a solution of mechanical reinforcement of this known structure to make it more robust and tolerant to the presence of micro-defects. 
     Another inherent drawback in the structure described above is that it only allows to passively convey (ohmic, purely resistive conduction) an electrical signal between the inside and outside of the housing. Therefore, to provide a filter (series or parallel) to the feedthrough, it is necessary to provide an external capacitive disc carried on the inner face of the feedthrough, to which the disc is mechanically and electrically connected, for example by a conductive adhesive. This is a relatively expensive step from the industrial viewpoint since it requires numerous sub-steps that can also cause reliability problems. 
     Certain proposed embodiments of the present invention provide various collateral advantages, including the ability to integrate into the known structure, improved according to the invention, additional functional elements, such as an RF antenna (for the purpose of RF telemetry), electrodes, sensor elements etc. Indeed, the RF antennas, for example, are currently made from a metal wire outside the housing, which is connected to the internal electronic circuitry through a dedicated feedthrough which is then overmolded in a biocompatible plastic matrix. Again, the connection and industrialization are complex and induce an overall volume significantly higher than that of devices without RF antenna. 
     SUMMARY 
     The present disclosure relates to a housing of an active medical device (or housing element) including a metal wall having an outer side and an inner side, said wall being provided with at least one electrically insulated and hermetic feedthrough for electrical connection through the wall. The housing further includes in the region of the feedthrough: on the inner side of the wall, a closed contour groove delimiting in the wall a metal islet physically and electrically isolated from the rest of the wall, said groove extending throughout the thickness of the wall; and on the outer side of the wall, an external electrically insulating layer formed above the wall and extending over a region located at least to the right of the groove and beyond either side of the groove, this external insulating layer including a recess formed to the right of the islet in the entire thickness of the insulating outer layer. 
     According to certain embodiments, this housing further includes, on the outer side of the wall in the region of the feedthrough, an outer electrically conductive layer formed over the insulating outer layer and extending over said region. The electrically conductive layer at least in alignment with the groove and beyond each side of the groove, the islet being mechanically supported and sealed by both conductive and insulating outer layers. The electrically conductive outer layer can be a metal layer of titanium, platinum, palladium, gold or alloys thereof. The insulating outer layer may be an oxide layer of the metal of the wall, formed on a fraction of the thickness of this wall, or an insert layer, deposited on the surface of the wall. 
     According to a first embodiment of the invention, the recess also extends throughout the thickness of the conductive outer layer, so as to provide in the bottom of the recess a contact pad to the islet at the outer side of the housing block in the area of the feedthrough. In this case, the conductive outer layer may extend beyond the region of the feedthrough defining on an area a first plate of a parallel filter capacitor of the feedthrough, the other plate of the capacitor being formed by the region of the wall extending opposite the first plate. 
     According to a second embodiment of the invention, the recess is filled with the material of the conductive outer layer, thereby electrically connecting the islet to the conductive outer layer in the region of the feedthrough. In this case, the housing may further include in the region of the feedthrough, on the inner side of the wall, an electrically insulating inner layer formed on top of the wall and extending over the region of the islet It further includes an electrically conductive inner layer formed over the inner insulating layer and extending over the region of the islet, so as to form a contact pad to the islet, inner side of the housing. The conductive inner layer thus defines a first plate of a series filter capacitor through the feedthrough, the other plate of the capacitor being formed by the region of the wall extending opposite the first plate. 
     On the other hand, the conductive outer layer may extend beyond the region of the feedthrough according to a predetermined pattern defining a RF antenna, a sensor electrode or a detection/stimulation electrode element. 
     Finally, the housing may include in the region of the feedthrough, on the outer side of the wall, a stack formed in the insulating outer layer of alternately conductive and insulating multiple additional outer layers. 
     According to another embodiment, a method of creating a feedthrough in a housing of an active implantable medical device is provided. The method includes providing a housing having an outer wall and an inner wall, creating an electrically insulating outer layer on the outer wall of the housing, and creating an electrically conductive outer layer on the outside of the electrically insulating outer layer. The method further includes forming a recess in at least the electrically insulating outer layer, extending through the electrically insulating outer layer to the outer wall of the housing and forming a contour groove in the inner wall of housing, extending through the width of the wall, at a location not aligned with the recess formed in the electrically insulating outer layer. The contour groove creates an islet in the wall of the housing, the islet being electrically and physically isolated from the rest of the wall. The islet is aligned with the recess formed in the electrically insulating outer layer. 
     According to yet another embodiment, a method of preparing a substrate for creation of a feedthrough is provided. The method includes providing a first and a second substrate, creating a first electrically insulating layer on a first side of the first substrate, and creating a second electrically insulating layer on either the second side of the first substrate or a first side of the second substrate. The method further includes welding together the first substrate and the second substrate forming a welded structure. The welded structure includes a first electrically insulating layer on the outside of the welded structure, a second electrically insulating layer between the first and the second substrate, one of the first and second substrate between the first and second electrically insulating layers forming the retained substrate, and the other of the first and second substrate forming an exposed substrate. The method further includes thinning the exposed substrate so as to form an outer conductive layer from the substrate. 
    
    
     
       DRAWINGS 
       Further features, characteristics and advantages of the present invention will become apparent to a person of ordinary skill in the art from the following detailed description of preferred embodiments of the present invention, made with reference to the drawings annexed, in which like reference characters refer to like elements and in which: 
         FIG. 1  is an elevation view, in section, of a feedthrough according to the prior art. 
         FIG. 2  is an elevation view, in section, of a feedthrough according to a first embodiment of the invention. 
         FIG. 3  is an elevation view, in section, of a feedthrough according to a second embodiment of the invention. 
         FIG. 4  is a top view showing an RF antenna integrated to the housing of the active device and realized by applying the teachings of the second embodiment of the invention. 
         FIGS. 5 and 6  are counterparts of  FIGS. 2 and 3  to illustrate an improvement wherein the feedthrough further includes a filtering series capacitor. 
         FIG. 7  illustrates an improvement of the second embodiment of the invention implementing a multi-layer structure. 
         FIG. 8  shows the successive steps for producing the structure of  FIG. 2  according to the first embodiment of the invention. 
         FIG. 9  shows the successive steps for producing the structure of  FIG. 3  according to the second embodiment of the invention. 
         FIG. 10  illustrates an alternative preparation of the substrate for the realization of the feedthrough according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a structure according to the prior art, such as that described in the abovementioned EP 2377573 A1. Reference  10  designates the titanium metal housing of the generator, or a separate titanium plate is a metal part which is then attached to the housing and welded thereto. An insulating layer  12  is formed above the wall  10 , at least on the external face of the housing. This insulating layer  12  may be formed by oxidation of the titanium of the housing  10  on a controlled depth, or by depositing a layer of insulating material, for example silicon dioxide, on the surface of the thickness  10  of the titanium housing. The thickness of the insulating oxide layer  12  is for example of the order of 10 microns for a thickness of the housing of about 300 microns. 
     The structure further includes a conductor islet  14  formed in the thickness of the housing  10  by digging a groove  16 . In the direction of depth, the groove  16  is recessed from the inner side of the housing in the entire thickness of the wall  10  of the metal housing. However, the insulating layer  12  is left intact, so that the islet  14  can be supported by the bridge of material formed by the insulating layer  12  between the area of the islet and the remainder of the metal layer of the housing. The outer insulating layer  12  also forms a hermetic barrier between the inside of the case and the external environment. In the plane of the surface of the housing, the groove  16  is recessed on a closed contour, so as to physically and electrically completely insulate the islet  14  from the remainder of the housing  10  around its entire periphery. 
     This structure also has an opening  18  formed in the outer side of the thickness of the insulating oxide layer  12  in alignment with the islet  14 , so as to expose an area on which a wire  20  or a pin can be soldered to ensure electrical contact, via solder  22 , with the central conductor islet  14 . On the inner side, the islet  14  is connected to a connection wire to the electronic circuits enclosed in the housing of the generator  10 . The connection is, for example by soldering of a connection wire (not shown), so as to produce a feedthrough insulated and sealed from the housing, from this internal connection wire to the pin or outer wire  20 , at the opposite side of the housing  10 . Other connection techniques may alternatively be used, such as soldering, wire bonding or contacting via a conductive elastic member. 
     This structure has the characteristic that the islet  14  is only connected, and mechanically supported, by the thin bridge of material  24  of the oxide layer  12 . This region, particularly the bottom  26  of the groove  16 , is particularly fragile. Defects or micro-cracks that weaken the bridge or “diaphragm”  24 , already fragile due to its very low thickness, can appear during the process of manufacturing. 
       FIG. 2  illustrates a first embodiment according to the invention. The preferred embodiments deposit on top of the insulating outer oxide layer  12  an additional, conductive outer layer  28 , e.g. by depositing a metallization of titanium or of another material such as platinum, palladium, gold and alloys thereof in a thickness of the order of several hundred nanometers to several micrometers. Titanium is preferred because of its higher affinity to the thickness of the underlying wall  10  (same expansion coefficient) and of its well-known properties of biocompatibility. 
     In the embodiment illustrated in  FIG. 2 , the conductive outer layer  28  is deposited before digging the opening  18  designed to achieve the initial contact with the conductor islet  14 , which reduces handling constraints on the structure, strengthening thereof particularly during excavation of the groove  16 . The method thus comprises forming the outer insulating layer  12  (deposition of an insert material or of the surface oxidation of the titanium of the wall  10 ) then the conductive outer layer  28  (metalizing) on the whole extent of the outer side of the wall  10 . The opening  18  is formed in a subsequent step, so as to expose a contact with the central conductor islet  14  for soldering of a wire or a pin, as in the configuration illustrated in  FIG. 1 . 
     Along with the recessing of the opening to make contact  18 , it is possible to etch the contours of the metallization  28  and of the insulating outer layer  12  on a predetermined surface, so as to define a structure of capacitor C 1 , the layers  10  and  28  forming the plates of this capacitor and the insulating oxide layer  12  forming the dielectric. If the conductive outer layer  28  is connected to the ground, an element for parallel filtering integrated to electrical feedthrough of the housing is thus obtained. The oxide insulating layer  12  is structured in the desired method, for example by photolithography. 
     The resulting structure allows for strengthening of the mechanical rigidity of the material bridge mechanically connecting the islet  14  to the rest of the wall of the housing  10  (due to the increase in thickness of material by adding the outer layer  28 ) as well as of sealing. This embodiment also provides integration of a filtering capacitive element (of a typical value in the order of 500 pF), without any mounted additional components. Furthermore, the arrangement of  FIG. 2  provides the possibility of structuring the conductive outer layer  28  and the insulating outer layer  12  so as to produce elements such as a sensing electrode, a capacitive sensor element or a biochemical sensor, etc. 
       FIG. 3  illustrates a second embodiment of the invention. Compared to the foregoing, in this embodiment the oxide insulating layer  12  is structured, particularly to release the contact area to form the opening  18 , before depositing the conductive outer layer (metallization)  28 . Therefore, when the material of the conductive layer  28  is deposited during the step of metallization, the material enters the opening  18  formed in the oxide layer  12  and comes into contact  30  with the conductor islet  14 , thus ensuring electrical continuity between first the islet  14  and the circuits to which it is connected inside, and then the outer conductive layer  28 . 
     In addition to strengthening the mechanical strength and the tightness of the material bridge connecting the islet to the rest of the housing (in the same method as in the first embodiment shown in  FIG. 2 ), this technique allows to widen the electrical connectivity with the outside, through direct contact between the outer metallization (conductive layer  28 ) and the central islet  14 . 
     One advantage of this embodiment is the ability to deport the external connecting elements elsewhere than at the vertical of the islet, thus avoiding mechanically stressing the fragile micro-structured area directly through a wire or a pin providing electrical contact at this very location. Another advantage is the ability to etch the conductive outer layer  28  so as to define the electronic elements to be electrically connected to the islet For example, as illustrated in  FIG. 4 , a loop-shaped RF antenna  32  extends in a perfectly controlled geometry between two contact points  30  and  30 ′ to respective conductor islets, interior, connected to the electronic circuits of the generator. Such an antenna may particularly be used for wireless communication (telemetry) and/or battery charging via an inductive coupling. The technique of the invention makes it easy to give any suitable shape such as a loop, a spiral, a square, etc. or even a single straight antenna. 
     It is also possible to structure the conductive outer layer  28  so as to define a detection/stimulation electrode or a surface for a sensor for physico-chemical variables or physical parameters detected by resistive and/or capacitive impedance variations. The metal electrode provides a greater and independent sensing surface compared to that of titanium micromachining. On the other hand, the outer metallization may also be used for a capacitive detection, using the structure of the capacitor defined by the conductive layers  10  and  28  separated by the insulating layer  12 . 
       FIGS. 5 and 6  are counterparts of  FIGS. 2 and 3 , forming a series capacitor filter directly integrated to the feedthrough. This improvement is applicable to any of the embodiments described above. To realize this series filter, the wall  10  of the housing, on the inner side, includes an insulating layer  34  coated with a conductive layer  36 . The inner layers  34 ,  36  are made in the same method as the corresponding outer layers  12 ,  28 , by implementation of similar techniques, these layers  34 ,  36  being deposited on the inner side of the wall  10  before digging of the groove  16 . 
     In the plane of the surface of the housing, these layers  34 ,  36  extend on the surface of the islet  14  and define a capacitor C 2  whose armatures are formed of the titanium of the wall  10  in the region of the islet and by the inner conductive layer  36  on the one hand, and the dielectric is formed by the inner insulating layer  34 , on the other hand. If the welding on the inner conductive layer  36  of a wire connecting to the internal circuits of the generator is performed, a feedthrough incorporating a series filter capacitor C 2  is thus produced, without reporting any additional component, for example for the purpose of additional filtering. 
       FIG. 7  illustrates a further embodiment, applicable to the embodiment of  FIG. 3 . In this case, additional, alternately insulating or conductive, layers  38 ,  40 , are formed on the above conductive outer layer  28  so as to define a multiple stack on the outer side of the housing. Stacking these multiple layers has the double advantage of being able to constitute an element such as a sensor or an advanced electronic function requiring several layers (e.g. a transistor); and further strengthening the structure from the mechanical and sealing point of view, the successively deposited layers increasing the thickness of the material bridge connecting the conductor islet  14  to the rest of the housing. 
       FIG. 8  shows the successive steps for producing the structure of  FIG. 2  according to the first embodiment of the invention. The starting element is the titanium housing  10  (step a), on which insulating layers are created on both sides, with an outer insulating layer  12  and an inner insulating layer  34  (step b). These layers can be made by oxidation of the titanium housing  10  on a controlled depth, or by depositing a layer of insulating material, for example of silicon dioxide on the surface  10  of the housing thickness. The thickness of each of the layers  12 ,  34  is for example of the order of 10 microns to a thickness of the housing of about 300 microns. 
     These layers  12  and  34  may be made for example by thermal oxidation or by any other method such as plasma oxidation or chemical deposition. It is also possible to proceed by anodization, by subjecting the housing to a potential difference, and by simultaneously keeping it in contact with a solution of water and sulfuric acid, by soaking or with help of a brush-electrode. 
     The next step (step c) consists in forming the conductive layer  28  outer side, for example by vacuum deposition. 
     The next step (step d) is a step of structuring of the conductive outer layer  28 , in particular to define the opening  18  that will subsequently achieve the contact, and to delimit the extent of the metal layer  28  to notably adjust the value of the series capacitor C 1  ( FIG. 2 ) associated with the feedthrough. 
     The next step (step e) is a step of etching the insulating outer oxide layer  12 , in particular to realize the exposure of the conductive layer  10  on the outer side of the housing by the opening  18 . This step may also be accompanied by an optional deletion of the insulating oxide layer  34  on the inner side of the housing. 
     The next step (step f) is to make the conductor islet  14  physically isolated in the thickness of the housing  10  by digging the groove  16  in the entire thickness of the housing. The widening of the groove can be made by various processes in themselves known, e.g. by chemical (interaction of species reactive with the titanium) or physical (ion bombardment) selective etching, or by any micro-structuring method, laser engraving, etc. These methods may also be combined with each other to minimize the time necessary for titanium cutting. The structure, illustrated in  FIG. 2 , is finally obtained after the step f. 
     Note also that the groove is not necessarily cylindrical. It can also have a conical shape, for example if one uses a wet etching technique that is not perfectly directional. Also note that in this implementation, the step of forming the islet (step f) is performed after the steps of deposition of the metallization (step c) and of structuring of the outer insulating oxide layer (step e). Thus, the stresses optionally suffered by the material bring no risk of weakening the final structure, to the extent that the wall of the housing  10  is still solid, because it has not yet been reduced by the digging of the groove  16 . 
       FIG. 9  shows the successive steps for producing the structure of  FIG. 3  according to the second embodiment of the invention. The first steps a and b are identical to those of  FIG. 8  of the previous embodiment. 
     However, the following step (step c) is a step of structuring the insulating outer oxide layer  12 , using comparable techniques to those that have been mentioned in connection with step e in  FIG. 7 , including for forming the opening  18 . 
     The next step (step d) is the depositing of the conductive outer layer  28  by metallization according to comparable techniques to those set forth above with respect to step c of Figure, with the only difference that this deposition occurs after structuring of the underlying oxide layer  12 . This in particular allows filing the opening  18 , formed in the preceding step, so as to make the direct contact catch  30  with the titanium of the wall of the housing  10 . 
     The next step (step e) is a structuring of the conductive outer layer  28 , according to comparable techniques to what has been exposed above in step d of  FIG. 8 . This step may be followed by an optional step of removing the oxide insulating inner layer  34  over the whole extent of the substrate. 
     The final step (step f) is the formation of islet  14  by digging of the groove  16  in the same method as that of the corresponding step f of  FIG. 8 . The final structure obtained after this step f is the one illustrated in  FIG. 3 . 
       FIG. 10  illustrates a variant for the preparation of the substrate for the realization of the feedthrough according to the invention. In this variant, instead of using a homogeneous titanium substrate on which a metallization layer is deposited, two titanium substrates  10  and  10 ′, are separately prepared. The substrates  10  and  10 ′ may have a substantially equal thickness (typically 300 microns), but in other embodiments may have differing thicknesses. On one of the substrates (as illustrated), or on both, an oxide layer  12 ,  34  is formed in the same method as the one described above for step b illustrated in  FIG. 8 . 
     The two substrates are superimposed and then welded to one another by a thermal process, thermo-compression or the like. To facilitate this welding step, an additional layer may previously be added to one or the other of the substrates  10  or  10 ′. At the end of this operation, a composite substrate is obtained including an oxide inner layer  12  (which originally was present on one and/or the other of the substrates  10 ,  10 ′ prior to welding) and supporting an outer conductive layer, namely the thickness of the titanium substrate  10 ′. After thinning, the layer  10 ′ may play the same role as the metallization  28  of the preceding embodiments, the basic structure obtained being comparable to that previously obtained at the end of step c illustrated in  FIG. 8 . The process continues with steps similar to what has been described above for steps d to f in  FIG. 8 , starting from this composite basis structure.