referring now to the drawings , fig1 through 3 illustrate an internally grounded feedthrough capacitor assembly 10 comprising a feedthrough 12 supporting a filter discoidal capacitor 14 . the feedthrough filter assembly 10 is useful with medical devices , preferably implantable devices such as pacemakers , cardiac defibrillators , cardioverter defibrillators , cochlear implants , neurostimulators , internal drug pumps , deep brain stimulators , hearing assist devices , incontinence devices , obesity treatment devices , parkinson &# 39 ; s disease therapy devices , bone growth stimulators , and the like . the feedthrough 12 portion of the assembly 10 includes terminal pins 16 that provide for coupling , transmitting and receiving electrical signals to and from a patient &# 39 ; s heart , while hermetically sealing the interior of the medical instrument against ingress of patient body fluids that could otherwise disrupt instrument operation or cause instrument malfunction . while not necessary for accomplishing these functions , it is desirable to attach the filter capacitor 14 to the feedthrough 12 for suppressing or decoupling undesirable emi signals and noise transmission into the interior of the medical device . more particularly , the feedthrough 12 of the feedthrough filter capacitor assembly 10 comprises a ferrule 18 defining an insulator - receiving bore formed by a ferrule sidewall extending from a first ferrule end 18 a to a second ferrule end 18 b , the ferrule sidewall surrounding an insulator 20 . suitable electrically conductive materials for the ferrule 18 include titanium , tantalum , niobium , stainless steel or combinations of alloys thereof , the former being preferred . the ferrule 18 may be of any geometry , non - limiting examples being round , rectangle , and oblong . a surrounding flange 22 extends from the ferrule 18 to facilitate attachment of the feedthrough 10 to the casing ( not shown ) of , for example , one of the previously described implantable medical devices . the method of attachment may be by laser welding or other suitable methods . the insulator 20 is of a ceramic material such as of alumina , zirconia , zirconia toughened alumina , aluminum nitride , boron nitride , silicon carbide , glass or combinations thereof . preferably , the insulating material is alumina , which is highly purified aluminum oxide , and comprises a sidewall 24 extending to a first upper side or end 26 and a second lower side or end 28 , the insulator 20 is also provided with bores 30 that receive the terminal pins 16 passing therethrough . a layer of metal 32 , referred to as metallization , is applied to the insulator sidewall 24 and to a bore sidewall 33 of the terminal pin bores 30 to aid a braze material 34 in hermetically sealing between the ferrule 18 and the outer sidewall 24 of the insulator 20 and between the terminal pins 16 and the bore sidewall 33 of the insulator 20 , respectively . specifically , the metallization layer 32 is preferably applied to a portion of the outer surface of the insulator sidewall 24 and to a portion of the surface of the inside sidewall 33 of the terminal pin bores 30 . these surfaces are intended to contact and bond with the ferrule 18 and terminal pins 16 , respectively , of the feedthrough assembly 10 , establishing a hermetic seal therebetween . according to one embodiment of the present invention , as shown in fig4 and 5 , the metallization 32 comprises a composite of a first metal layer 50 and a second metal oxide layer 52 . as illustrated , the second metal oxide layer 52 resides on a first metal top surface 54 of the first metal layer 50 , the metal layer 50 being deposited on a surface of the insulator 20 . more specifically , the second metal oxide layer 52 is bonded to the first metal top surface 54 of the first metal layer 50 which is bonded to a portion of a surface of the insulator sidewall 24 and / or a portion of a surface of the bore sidewall 33 . in a preferred embodiment , the first metal layer 50 is composed of titanium and titanium alloys . the second metal oxide layer 52 is preferably composed of oxidized titanium or oxidized titanium alloys thereof . examples of titanium oxide may comprise ti 2 o 3 or tio 2 . although the use of titanium and its associated alloys are preferred , it is contemplated that other metals such as molybdenum , niobium , tungsten , aluminum , vanadium and their associated alloys may also be used as the first metal layer 50 . furthermore , the associated oxides of these metals or their associated alloys may comprise the second metal oxide layer 52 . in a preferred embodiment , the metallization 32 has an overall thickness ranging from about 0 . 01 um to about 25 um . in a more preferred embodiment , the metallization 32 has a thickness ranging from about 0 . 50 um to about 5 . 0 um . most preferably , the metallization 32 has a thickness ranging from 1 . 0 um to about 2 . 0 um . the thickness of the second metal oxide layer 52 comprises from about 25 percent to about 50 percent of the total metallization layer thickness . the thickness of the first metal layer 50 comprises from about 50 percent to about 75 percent of the total metallization layer thickness . therefore , the second metal oxide layer 52 may comprise a thickness ranging from about 0 . 0025 um to about 12 . 5 um , more preferably from about 0 . 25 um to about 1 . 0 um . in a preferred embodiment , the first metal layer 50 is initially applied to the surface of the insulator 20 . the first metal layer 50 may be applied to the surface of the insulator 20 by various means including , but not limited to , sputtering , electron - beam deposition , pulsed laser deposition , plating , electroless plating , chemical vapor deposition , vacuum evaporation , thick film application methods , and aerosol spray deposition , and thin cladding . once the first metal layer 50 is applied to the surface of the insulator 20 , the metalized substrate is subsequently heat treated in an ambient atmosphere . although the use of an ambient atmosphere is preferred , the metalized insulator may also be heat treated in an oxygen rich atmosphere . such an oxygen rich atmosphere may be used to control the attributes of the second metal oxide layer 52 such as its thickness , density , molecular oxygen ratio , and / or morphology of the oxide layer . “ morphology ” is herein defined as the texture of a surface , such as that of the second oxide layer 52 . the oxide layer 52 may have a surface morphology that is smooth , rough or undulated . a “ smooth ” morphology is primarily characterized by a planar surface . a “ rough ” morphology is primarily characterized by a surface comprising jagged edges and an “ undulated ” morphology is primarily characterized by a surface comprising a series of elevated regions . in a preferred embodiment , the titanium is heat treated at a temperature ranging from about 600 ° c . to about 1 , 000 ° c . for about 30 minutes to about 180 minutes . more preferably , the first metal layer 50 is heat treated at a temperature ranging from about 750 ° c . to about 850 ° c . for about 60 to about 120 minutes . this heat treating process preferably diffuses oxygen into the chemical structure of the first metal layer 50 , thereby transforming a portion of the metal into a layer of oxidized metal , such as that of the second metal oxide layer 52 , as shown in fig4 . it is noted that the heat treatment process may be performed within the metal deposition instrument or outside the metal deposition instrument , such as in a heat treating oven ( not shown ). for example , the first metal layer 50 may be applied using sputtering and subsequently heat treated within the sputtering chamber of the instrument , thereby eliminating the need to remove the metalized insulator 20 . in a specific example , the surface of an alumina insulator 20 is metalized with about 1 . 5 um of titanium , forming the first metal layer 50 . the metalized layer of titanium is then heat treated at about 800 ° c . for about 90 minutes to form the second metal oxide layer 52 of titanium oxide . in a second embodiment , as illustrated in fig5 , a third metal layer 58 may be applied to the second metal oxide layer 52 . more specifically , an additional layer of metal , such as titanium , may be applied to a surface 56 of the second metal oxide layer 52 . although titanium and its associated alloys are preferred , the third metal layer 58 may comprise other metals comprising molybdenum , niobium , tungsten , aluminum , vanadium and their associated alloys . in a preferred embodiment , the third metal layer 58 having a thickness ranging from about 0 . 01 um to about 5 . 0 um , more preferably a thickness ranging from about 0 . 10 um to about 2 . 0 um is deposited on the surface 56 of the second metal oxide layer 52 . the insulator 20 , now comprising an additional third metal layer 58 , is again heat treated in an ambient atmosphere at a temperature ranging from about 200 ° c . to about 500 ° c . for about 10 minutes to about 60 minutes . more preferably the insulator 20 , comprising the first metal layer 50 , the second metal oxide layer 52 and the third metal layer 58 , is heat treated at a temperature ranging from about 300 ° c . to about 400 ° c . for about 30 minutes . similarly to the first heat treatment , as previously discussed , an oxygen rich atmosphere may also be used . the second heat treatment process preferably forms a fourth metal oxide layer 62 that resides on a surface 60 of the third metal layer 58 . more specifically , the fourth metal oxide layer 62 is chemically bonded to the surface 60 of the third metal layer 58 . therefore , as shown in fig5 , the metallization 32 comprises a four layer composite comprising the first metal layer 50 , the second metal oxide layer 52 , the third metal layer 58 and the fourth metal oxide layer 62 . it is contemplated that the metallization layer 32 could also be constructed with additional alternating layers of similar or dissimilar metals and metal oxides . in a specific example of the second embodiment of the present invention , the surface of an alumina insulator 20 is metalized with a first metal layer 50 of titanium with a thickness of about 0 . 5 um . the first layer of titanium is then heat treated at about 800 ° c . for about 90 minutes to form the second metal oxide layer 52 . after the first heat treatment , an additional layer of about 1 . 0 um of titanium , i . e ., the third metal layer 58 is applied to the surface 56 of the second layer of titanium oxide . this third metal layer 58 of titanium is then heat treated a second time at about 350 ° c . for about 30 minutes . similar to the application of the first metal layer 50 , the third metal layer 58 and subsequent metal layers may be applied using various means including , but not limited to , sputtering , electron - beam deposition , pulsed laser deposition , plating , electroless plating , chemical vapor deposition , vacuum evaporation , thick film application methods , and aerosol spray deposition , and thin cladding . the composite construction comprising alternating layers of metal and metal oxide establish a metallization layer 32 with improved bonding characteristics , particularly compared to those comprising distinct layers of titanium and molybdenum as well as titanium and niobium . the composite metal and oxide layers are bonded together such that diffusion of the metal layer , particularly that of titanium , into the gold braze material is impeded . in other words , the present invention provides a layered metallization 32 that provides improved boding between the insulator 20 and the first metal layer 50 as well as the oxide metal layers 58 , 62 comprising the top layer of the metallization 32 , and the braze material . as illustrated in fig6 and 7 , the first metal layer 50 , at the bottom side of the metallization , is shown forming a bond between the insulator material . in an embodiment , a bond comprising tial , ti 3 al or combinations thereof is preferably formed between the first metal layer 50 and the surface of the insulator 20 . likewise at the opposite side or top layer of the metallization 32 , a bond between the oxidized metal , particularly oxidized titanium and gold is formed . referring to fig1 through 3 , non - limiting examples of terminal pins 16 include platinum , platinum alloys , particularly platinum - iridium alloys , palladium and palladium alloys . furthermore , it is contemplated that the terminal pin 16 may comprise an exterior outer terminal pin coating or layer of platinum , platinum alloys , gold , silver , palladium and palladium alloys . the core terminal pin material may be selected from the group consisting of niobium , tantalum , nickel - titanium ( nitinol ®), titanium , particularly beta titanium , titanium alloys , stainless steel , molybdenum , tungsten , platinum , and combinations thereof . the means of coating may include sputtering , cladding , and or plating . the coating may be applied through a process of sputtering , electron - beam deposition , pulsed laser deposition , plating , electroless plating , chemical vapor deposition , vacuum evaporation , thick film application methods , aerosol spray deposition , and thin cladding . in addition , non - limiting examples of braze materials include gold , gold alloys , and silver . then , if the feedthrough 10 is used where it will contact bodily fluids , the resulting brazes do not need to be covered with a biocompatible coating material . in other embodiments , if the brazes are not biocompatible , for example , if they contain copper , they are coated with a layer / coating of biocompatible / biostable material . broadly , the biocompatibility requirement is met if contact of the braze / coating with body tissue and blood results in little or no immune response from the body , especially thrombogenicity ( clotting ) and encapsulation of the electrode with fibrotic tissue . the biostability requirement means that the braze / coating remains physically , electrically , and chemically constant and unchanged over the life of the patient . as further shown in fig1 through 3 , the feedthrough filter capacitor 10 includes the filter capacitor 14 that provides for filtering undesirable emi signals before they can enter the device housing via the terminal pins 16 . the filter capacitor 14 comprises a ceramic or ceramic - based dielectric monolith 36 having multiple capacitor - forming conductive electrode plates formed therein . the capacitor dielectric 36 preferably has a circular cross - section matching the cross - section of the ferrule 18 and supports a plurality of spaced - apart layers of first or “ active ” electrode plates 38 in spaced relationship with a plurality of spaced apart layers of second or “ ground ” electrode plates 40 . the filter capacitor 14 is preferably joined to the feedthrough 12 adjacent to the insulator side 26 by an annular bead 42 of conductive material , such as a solder or braze ring , or a thermal - setting conductive adhesive , and the like . the dielectric 36 includes lead bores 44 provided with an inner surface metallization layer . the terminal pins 16 pass there through and are conductively coupled to the active plates 38 by a conductive braze material 46 contacting between the terminal pins 16 and the bore metallization . in a similar manner , the ground plates 40 are electrically connected through an outer surface metallization 48 and the conductive material 42 to the ferrule 18 . it is appreciated that various modifications to the invention concepts described herein may be apparent to those of ordinary skill in the art without departing from the scope of the present invention as defined by the appended claims .
a metallization that includes a composite of alternating metal and metal oxide layers for incorporation into feedthrough filter capacitor assemblies is described . the feedthrough filter capacitor assemblies are particularly useful for incorporation into implantable medical devices such as cardiac pacemakers , cardioverter defibrillators , and the like , to decouple and shield internal electronic components of the medical device from undesirable electromagnetic interference signals .