Patent Description:
Electronic devices can be used inside the human body for sensing (e.g., temperature, fluid composition, pressure, conductivity, chemical properties, strain) or for active treatment (e.g., cardiovascular stimulation, nerve stimulation, brain stimulation, drug delivery, drug activation). However, electronic devices should not be placed directly in the human body. Since the body environment has an average pH-value from <NUM> to <NUM> and of a temperature <NUM>-<NUM> it is potentially corrosive. Ordinary metal and plastic components are likely to degrade in such an environment, releasing toxic substances. Usually, electronic devices used as implants are sealed in housings. Titanium or titanium alloy housings are widely used for cardiac stimulation. However, they are large, heavy and bulky if they are to be made hermetic. Glass as an enclosure material could be a lightweight but robust alternative. For example, European Patent <CIT> shows a method for manufacturing a transparent component for protecting an optical component. A new laser welding method is used therein.

Some electronic devices require housings having electrical feedthroughs in order to provide electrical connections to the outside. <CIT> discloses a hermetic glass enclosure with vias to establish an electrical contact from the inside of the enclosure to the outside, e.g., for contacting a contact pad at the outside of the enclosure.

Such Through Glass Vias (TGV) are made of metals, mostly tungsten, that connect the inside surface of the glass substrate with the outside surface. However, when subjected to a corrosive environment the materials of the through glass vias can corrode and can even be released out of the glass.

<CIT> discloses a micro-electro-mechanical system (MEMS) device. In one embodiment, a cap of the device comprises an insulating material such as fused silica and the cap is provided with hermetically sealed through-glass vias (TGV). Bonding sites are formed at the positions of the TGVs, wherein the bonding sites comprise a bonding material such as gold formed on an adhesion layer such as tantalum.

It is an object of the invention to provide an improved electrical feedthrough through a glass substrate of a hermetic housing which is suitable for use in corrosive environments and in particular suitable for use as a medical implant.

A hermetic enclosure according to claim <NUM> comprising at least one glass substrate having at least one electrical feedthrough configured as a through glass via is proposed. The via comprises an electrically conductive rod electrically connecting the inside of the enclosure to the outside through the glass substrate. The part of the conductive rod's surface facing towards the outside of the enclosure is completely covered with an electrically conductive coating, wherein the electrically conductive coating is a multilayer structure comprising at least an adhesion layer in direct contact with the conductive rod and a corrosion resistant layer, wherein the electrical feedthrough comprises a depression in or an elevation on an outside facing surface of the glass substrate and/or on an inside facing surface of the glass substrate and the recess or elevation surrounds the conductive rod.

Such hermetic enclosures are formed by two or more substrates which are hermetically bonded together to hermetically enclose a function area or a cavity. For example, the hermetic enclosure may comprise three substrates. A base formed by the glass substrate comprising the at least one electrical feedthrough, a spacer substrate and a cover substrate. In this example, the base glass substrate defines a bottom wall of an enclosed cavity, the spacer substrate defines side walls of the enclosed cavity, and the cover substrate defines a top wall of the enclosed cavity. In a further example, the hermetic enclosure may comprise two substrates, a base glass substrate comprising the at least one electrical feedthrough, and a cavity substrate. The cavity substrate has a cavity produced, for example, by etching, laser assisted etching, CNC machining or laser ablation and defines side walls and a top wall of an enclosed cavity, and the base glass substrate defines a bottom wall of the enclosed cavity.

The hermetic enclosure may be directly obtained by stacking the respective substrate and subsequently bonding of the substrates. An efficient method for obtaining a large number of hermetic enclosures involves stacking and bonding of entire wafers and subsequently separating the formed enclosures, e.g., by saw dicing. In one example, a spacer wafer comprises several openings which define the cavities in conjunction with adjacent base and cover wafers. In another example, individual cavities formed in a cavity wafer define the cavities in conjunction with an adjacent base wafer.

Bonding of the substrates or wafers may, for example, be performed by means of laser bonding and/or laser welding, anodic bonding, fusion bonding, contact bonding or glass frit bonding. Bonding processes which allow direct bonding of two adjacent substrates or wafers without any intermediate material or adhesive material, such as laser bonding, are particularly preferred.

The bonding is preferably performed such that a hermetic enclosure is formed, wherein the cavity or function area is enclosed within such an enclosure. As used herein, hermetically sealed means in particular an enclosure that has a helium leakage rate of less than <NUM>·<NUM>-<NUM> mbar·l/sec and is preferably in the range <NUM>·<NUM>-<NUM> mbar·l/sec to <NUM>·<NUM>-<NUM> mbar·l/sec.

In a preferred laser bonding process, a short-pulsed laser beam from a laser source, for which at least one of the substrates is transparent, is focused to a spot inside the formed substrate stack. By choosing the repetition rate and a scan rate of the laser, the individual laser pulses are arranged so closely together that a resulting nonlinear absorption zone of a laser pulse within the material is in contact with a neighboring nonlinear absorption zone of a further laser pulse, or even overlaps with it, such that heat accumulation can occur. Due to the accumulated heat, the material of the substrate stack is locally melted and a continuous welding "line" can be obtained. For creating such a continuous welding line, a focus plane of the laser beam is arranged close to but not at the interface between the two substrates. The laser beam is arranged at a distance below the interface between the two substrates such that the accumulated heat causes the material of the first and second substrate to locally melt and mix so that a hermetic bond is formed. The area, in which the accumulated heat of the incident laser causes the material of the two substrates to melt and to mix is designated as laser treated zone. In an area surrounding said laser treated zone, the heat introduced by the laser is insufficient to melt the material but may cause modifications of the material and/or the electrically conductive coating arranged on the glass substrate. This area is in the following referred to as heat affected zone.

Preferably, the glass substrate comprising the at least one electrical feedthrough is bonded to a further substrate, such as a spacer substrate or cavity substrate, by means of laser bonding, wherein at least one bond line is formed in which material of the glass substrate and the further substrate has been melted and mixed, wherein a distance between a laser bond line and a through glass via is preferably at least <NUM>. Additionally or alternatively, the distance between a laser bond line and a through glass via is chosen such that the through glass via is outside of the heat affected zone.

The enclosed cavity provided by the proposed hermetic enclosure is in particular suited for housing an electronic device. The device is preferably electrically connected to the electrical feedthroughs and is thus capable of sending and/or receiving of electrical signals and/or electrical current from the outside of the hermetic enclosure.

The electrical feedthroughs are configured as through glass vias and comprise conductive rods that are embedded in the glass substrate such that their front and back surfaces are accessible. Preferably, the conductive rods are made from or comprise metals like tungsten, titanium, an iron/nickel alloy, gold, silver, copper or (doped) silicon and combinations of said materials.

A length of the conductive rods is chosen such that an electrical contact may be established through the glass substrate. A thickness of the glass substrate is preferably in the range of from <NUM> to <NUM>, more preferably from <NUM> to <NUM>. A length of the conductive rods is preferably in the range of from <NUM> to <NUM>, more preferably from <NUM> to <NUM>. The lengths of the conductive rods may be chosen to be identical to the thickness of the glass substrate.

The material of the glass substrate is a glass that is preferably chosen from a borosilicate glass, such as BOROFLOAT® <NUM> or D263® T eco or MEMpax® available from SCHOTT AG, a quartz glass, fused silica, an alumino-borosilicate glass such as AF <NUM>® available from SCHOTT AG, alkali-free glasses, SCHOTT B270®, or alkali-silicate glasses such as AS87.

The materials of the further substrate(s), such as the spacer substrate, the cover substrate and/or the cavity substrate, are preferably selected from a glass, a glass ceramic, a ceramic, silicon, sapphire, diamond, or other inorganic crystals. Suitable glass materials include the materials described for the glass substrate.

In case of a glass material, glasses suitable for the glass substrate are also suitable as material for the further substrate(s).

In order to protect the electrical feedthroughs from damage, for example by corrosion, the electrically conductive coating in form of a multilayer structure is provided such that the material of the conductive rod(s) of the feedthrough(s) which is exposed on the outward facing side of the enclosure and thus of the outward facing side of the glass substrate is completely covered. Thus, an outward facing side of the conductive rod is covered which includes the front surface of the conductive rod facing towards the environment and which is not surrounded by the glass substrate and is thus exposed from the glass substrate. However, the inventors have found that it is not sufficient to apply a corrosion resistant coating layer to only said front surface of the conductive rod. For example, a gold coating arranged only on said front surface of a conductive rod made from tungsten will not reduce the corrosion. Instead, it has been surprisingly found that such a gold coating will even accelerate corrosion. In order to achieve the desired corrosion resistance, not only the front surface, but the entire exposed surface of the conductive rods must be completely covered. It is believed that accelerated corrosion, for example if the enclosure is subjected to an NaCl solution in water, is caused by electrochemical processes between the material of the coating and the material of the conductive rod.

Accordingly, it is preferred to form the electrically conductive coating without any gaps such that the entire material of the conductive rod(s) which is exposed to the outside of the enclosure is covered and thus shielded from the environment. In order to achieve a gapless and complete coverage of the exposed surfaces of the metal rod(s), it is preferred to extend the electrically conductive coating to an area of the glass substrate surface adjacent to the respective conductive rod. This adjacent area preferably extends beyond the edge of the conductive rod for a distance of at least <NUM>, more preferred at least <NUM>, more preferred at least <NUM>, more preferred at least <NUM> and most preferred at least <NUM>. Since the accuracy of the patterning equipment also limits how well one can align and center the coating steps with respect to the conductive rods, it is preferred to choose the diameter of the contact pad dp greater than the diameter of the via dv; so dp = dv + Δd, with Δd > <NUM>, more preferred <NUM>, most preferred <NUM> or more. Without loss of generality, cylindrical conduction rods and conductive contact pads are assumed. In case those cross sections are not circular, dv= 2rmax, with rmax the maximum radius measured from the center of the via cross section and dp=2rmin, with rmin the minimum distance measured from the center of the of the contact pad cross section.

In addition to application of the electrically conductive coating to an outward facing side, it is possible to also arrange the electrically conductive coating on an inside facing side of the conductive rods. Further, it is possible to extend the electrically conductive coating over a part of a surface of the substrate in order to form electrically conductive structures. In cases where the electrically conductive coating is applied on an inside facing side of the substate and/or the conductive rods, it is preferred that said coating covers the entire inside facing side of the conductive rod, but it is also possible to cover only a part of the conductive rod's front surface with the coating.

The corrosion resistant contact layer provides both protection of the conductive rods from environmental influence and at the same time provides a reliable electrical contact surface for establishing an electrical connection. By means of this corrosion resistant contact layer, the hermetic enclosure may be used in corrosive environments including the animal and human body.

The corrosion resistant contact layer provides a contact surface which may be used to establish permanent electrical connections, for example by means of soldering a wire to the contact surface. The contact surface may also be used as part of a connector or receptacle for establishing a disconnectable electrical connection.

In case a solder connection is desired, the electrically conductive coating may be configured such that solder pads are formed.

The electrical feedthrough comprises a depression in or an elevation on an outside facing surface of the glass substrate and/or on an inside facing surface of the glass substrate, wherein the recess or elevation surrounds the electrically conductive rod, and wherein the recess or elevation is preferably flush with a front surface of the conductive rod, and wherein a depths of the depression or a height of the elevation is preferably at least <NUM> and/or less than <NUM>, preferably less than <NUM>, more preferably less than <NUM>.

Choosing the depths/height of the depression/elevation and the lengths of the conductive rod such that the conductive rod's front surface is flush with the depression/elevation, allows for a flat and homogenous surface wherein the corrosion resistant conductive coating may extend seamlessly from the front surface of the conductive rod to a part of the surface of the glass substrate. A contact pad or solder pad formed by the coating may then be chosen to have a larger surface than the size of the front surface of the conductive rod, making it easier to establish an electrical connection.

Preferably, the depths/height and/or shape of the recess or elevation are configured such that the recess or elevation serves as a flow boundary for solder. The depression or recess forms a boundary which influences and limits the flow of a solder material. If, for example, the entire area of the elevation or depression is covered with the electrically conductive coating, then the solder is only in contact with the formed solder pad and does not touch the glass substrate.

The structuring of the glass substrate provided by the recess or elevation may also serve as anchor for the coating and may thus improve adhesion of the coating.

Preferably, the electrically conductive coating is also arranged on at least a part of the glass substrate, wherein the electrically conductive coating forms a contact pad having a pad diameter dp which is larger than a via diameter dv of the conductive rod to which to contact pad is electrically connected.

The electrically conductive coating may additionally or alternatively be configured to form at least one conductive trace. Such conductive traces may form electrical connections between one or more of the electrical feedthroughs, between an electrical feedthrough and a contact pad, or between two contact pads arranged on a surface of the glass substrate. A conductive trace may also be configured to form an antenna and/or coil structure. Such a structure may be arranged on an inside facing surface and/or an outside facing surface of a substrate of the enclosure.

The electrically conductive coating is a multilayer structure having at least two layers. As the multilayer structure is electrically conductive, each of the layers is selected from an electrically conductive material.

The corrosion resistant layer is preferably configured as a diffusion barrier layer and/or a corrosion resistant contact layer. It is possible that the electrically conductive coating comprises both a diffusion barrier layer and a corrosion resistant contact layer.

Preferably, the multilayer structure of the electrically conductive coating comprises in this order the adhesion layer in direct contact with the conductive rod, at least one diffusion barrier layer, and the corrosion resistant contact layer.

The adhesive layer is chosen such that it has good adhesion on the conductive rod's material and/or on the material of the glass substrate. Suitable adhesive layers are, for example, made from or comprise Ti, Ta, Cr, Ni, NiCr, TiAl and combinations thereof.

A thickness of the adhesion layer is preferably in the range of from <NUM> to <NUM>, more preferably from <NUM> to <NUM> and most preferably from <NUM> to <NUM>.

The diffusion barrier layer is chosen such that diffusion of materials from the corrosion resistant contact layer or substances from outside of the hermetic enclosure cannot diffuse or propagate towards the conductive rods and vice versa. In particular, the diffusion barrier layer is chosen such that materials contained in a solder material or an adhesive material as well as oxygen from the environment cannot damage the conductive rods of the electrical feedthroughs. Further the material of the diffusion barrier layer is preferably chosen to be biocompatible. Biocompatible materials are non-toxic and have not injurious effects on biological systems.

Preferably, the diffusion barrier layer is made from or comprises platinum (Pt), titan-nitride (TiN) and combinations thereof. If the diffusion barrier layer is the outermost layer of the multilayer structure, the material of the diffusion barrier layer is preferably chosen from a biocompatible material.

A thickness of the diffusion barrier layer is preferably in the range of from <NUM> to <NUM>, more preferably from <NUM> to <NUM> and most preferably from <NUM> to <NUM>.

The corrosion resistant contact layer is preferably not only resistant to corrosive environments but is preferably also a material with good electrical conductivity and good wettability for solder materials in order to enable high quality electrical connections. Still further, as the corrosion resistant contact layer preferably forms the outermost layer of the electrically conductive coating, the corrosion resistant contact layer is preferably chosen from a biocompatible material.

Preferably, the corrosion resistant contact layer is made from or comprises gold (Au).

A thickness of the corrosion resistant contact layer is preferably in the range of from <NUM> to <NUM>, more preferably from <NUM> to <NUM> and most preferably from <NUM> to <NUM>.

The electrically conductive coating may in principle be applied to the surface of the conductive rods and optionally to a part of the glass substrate's surface by means of any suitable coating method. Preferably, at least one of the layers of the electrically conductive coating is obtained by means of electroplating, electroless plating, physical vapor deposition (PVD, e.g., sputtering or evaporation, in particular resistive evaporation), electron beam deposition and/or atomic layer deposition (ALD).

Preferably, the corrosion resistant contact layer is a gold layer obtained by electroless plating. Such a process may employ the use of a seed layer to start an autocatalytic deposition of gold. Preferably, the adhesive layer or, if present, the diffusion barrier layer is chosen such that said layer serves as seed layer so that no additional seed layer is required.

Preferably, the material of the glass substrate and/or the electrically conductive coating are selected such that said materials are resistant to exposure to an NaCl solution in water, in particular to a solution of <NUM>/l NaCl. The enclosure may, for example, be immersed in such a solution for seven days at a temperature of <NUM> and may then be examined visually for signs of corrosion. Further, it is possible to assess the corrosion resistance by determining a loss of mass. A material may then be considered to be corrosion resistant if the loss of mass is less than <NUM>%, preferably less than <NUM>% and most preferably less than <NUM>%. The total mass of the electrically conductive coating is a small quantity so that a loss of mass of the material of the electrically conducting coating is hard to measure. However, if the coating is not resistant, it will develop gaps after exposure with a corrosive environment and said gaps will lead to an exposure of the conductive rods to the NaCl solution. Accordingly, the material of the electrically conductive coating is in particular considered to be corrosion resistant, if the conductive rods remain protected and thus an overall mass loss of the material of the conductive rods after exposure of the enclosure to an NaCl solution in water with <NUM>/l NaCl at a temperature of <NUM> for <NUM> days, is preferably less than <NUM>%, more preferably less than <NUM>% and most preferred less than <NUM>%. Further, for the material of the glass substrate it is preferred that the mass loss of the material of the glass substrate is less than <NUM>%, preferably less than <NUM>% and more preferably less than <NUM>%.

As the loss of mass of a conductive rod is a small quantity, it is preferred to use an ensemble of several enclosures to test for corrosion resistance. For example, if the enclosure has V conductive rods of mass mr, an ensemble of N enclosures is used so that the total mass of the conduction rods is larger than <NUM>: <MAT>.

The measurement may then be performed by first drying the samples, for example in in a drying cabinet using IR-drying at <NUM> for <NUM>. After drying, the initial weight M<NUM> of the dry ensemble is determined, for example by means of an analytical balance (e.g., VWRI <NUM>-<NUM> / LA314i from Avantor). The ensemble of enclosures is then immersed in NaCl -solution (<NUM>/l) for seven days at <NUM>. After the testing period, the samples are rinsed with de-ionzed water and then dried, for example in a drying cabinet (IR-drying, <NUM> for <NUM>). After drying, the weight M<NUM> of the dry ensemble is determined, for example by means of an analytical balance (e.g., VWRI <NUM>-<NUM> / LA314i from Avantor).

Hence, ΔM = M0 - M1 and ΔM/Mr < <NUM>%, < <NUM>%, most preferred less than <NUM>%.

In order to discriminate, whether the loss in mass results from loss of mass of the conductive rods or from a corrosion of the glass (which should also be avoided), the test may be repeated on a matching ensemble using the same method with glass enclosures of the same spatial dimensions and of the same glass but with no though glass vias and thus without conductive rods. A difference in the determined mass losses ΔM between these two measurements yields the mass loss of the material of the conductive rods.

The structure of the electrically conductive coating is summarized in table <NUM>.

Examples for suitable coatings applied to a glass substrate having through glass vias are given in table <NUM> below.

The enclosure may comprise more than one substrate made from a glass and having at least one through glass via. For example, not only the base substrate, but also the cover substrate may be configured as a glass substrate having feedthroughs protected by the electrically conductive coating having a corrosion resistant layer.

A further aspect of the invention can be seen in providing a method for producing the hermetic enclosure described herein. The method comprises providing a glass substrate having at least one electrical feedthrough configured as a through glass via and subsequent coating of a surface of the glass substrate with an electrically conductive coating. After the coating, an optional step of selectively removing the electrically conductive coating in areas between two or more through glass vias to form contact pads or to structure conductive traces may be performed.

The glass substrate is hermetically bonded to a further substrate, preferably by means of laser bonding wherein at least one bond line is formed in which material of the glass substrate and the further substrate has been melted and mixed. For laser bonding, at least one laser weld line is preferably made using an ultrashort pulse laser. Typical pulse widths are in the range of <NUM> fs to <NUM> ps. A method for carrying out such a laser bond with one or more laser welding lines is known, for example, from <CIT>.

The steps of coating and hermetic bonding can be performed in any order.

The hermetic enclosure described herein is in particular suitable for use as a housing for medical implants. Accordingly, a medical implant is provided comprising one of the hermetic enclosures described herein.

It is understood that the above-mentioned features and those to be explained below can be used not only in the respective combination as shown, but also in other combinations or on their own, without leaving the scope of the present invention.

Preferred embodiments of the invention are shown in the figures and will be explained in more detail in the following description, wherein identical reference numerals refer to identical or similar components or elements.

<FIG> shows a hermetic enclosure <NUM> with through glass vias <NUM> in a schematic side view. The enclosure <NUM> is formed by a glass substrate <NUM> comprising the through glass vias <NUM> and further substrates <NUM>.

In the example depicted in <FIG>, the base glass substrate <NUM> forms the bottom of the enclosure <NUM>. A spacer substrate <NUM> as a first further substrate <NUM> forms side walls of the enclosure <NUM> and a cover substrate <NUM> as second further substrate <NUM> forms a top wall of the enclosure <NUM>. The enclosure <NUM> defines a cavity or function area <NUM>.

In order to ensure that the function area <NUM> is hermetically enclosed, the glass substrate <NUM> is hermetically bonded to the spacer substrate <NUM> and the spacer substrate <NUM> is hermetically bonded to the cover substrate <NUM> by means of a laser bonding process. In said laser bonding process, the material at the interface of the two respective substrates <NUM>, <NUM>, <NUM> is melted and mixed in order to form bond lines <NUM>. The weld lines <NUM> preferably completely surround the function area <NUM>.

In the example shown in <FIG>, an electrical device <NUM> is located in the function area <NUM> and is thus enclosed by the enclosure <NUM>. In order to establish an electrical connection to the outside of the enclosure <NUM>, the electrical device <NUM> is arranged over the through glass vias <NUM> and is electrically connected to said through glass vias <NUM> by means of a solder connection formed by solder drops <NUM>. It is of course also possible to use other means to connect the electrical device <NUM> to the through glass vias <NUM>. For example, the electrical device <NUM> may be located next to the through glass vias <NUM> on the glass substrate <NUM> and bond wires may be used to connect the electrical device <NUM> to the through glass vias <NUM>.

For corrosion protection, an electrically conductive coating <NUM> configured as contact pads <NUM> is arranged on the outside facing side of the through glass vias <NUM>. The detailed structure of the through glass vias <NUM> and the coating <NUM> is further described with respect to <FIG>.

<FIG> shows an enlarged cross-section side view of a through glass via <NUM> of the hermetic enclosure <NUM> shown in <FIG>. The through glass via <NUM> comprises a metal rod as electrically conductive rod <NUM> which is arranged such that a front surface of the conductive rod <NUM> is flush with an inside facing surface of the glass substrate <NUM>. A further front surface of the conductive rod <NUM> is flush with an outside facing surface of the glass substrate <NUM>. This allows the conductive rod <NUM> to provide an electrically conductive connection from the inside of the enclosure <NUM> to the outside.

For corrosion protection of the through glass via <NUM> and in particular for corrosion protection of the conductive rod <NUM>, the electrically conductive coating <NUM> is arranged on the outside facing front side of the conductive rod <NUM> and a part of the outside facing surface of the glass substrate <NUM>.

The electrically conductive coating <NUM> is in the depicted embodiment configured as a layer structure having in this order an adhesion layer <NUM>, a diffusion barrier layer <NUM> and a corrosion resistant contact layer <NUM>. The coating <NUM> is structured to form a contact pad <NUM> having a diameter dp which is larger than a diameter dv of the conductive rod <NUM> of the through glass via <NUM>. The material of the corrosion resistant contact layer <NUM> is in this example a material with good wettability for solder materials such as gold (Au).

In the layer structure of the example depicted in <FIG>, the outermost layer is the corrosion resistant contact layer <NUM>. The material of said corrosion resistant contact layer <NUM> is selected such that it can withstand a defined corrosive environment, such as a NaCl solution.

In an alternative embodiment, where no solder connection is required, the diffusion barrier layer can be selected from a corrosion resistant electrically conductive material and may thus serve as outermost layer.

The diffusion barrier layer is selected from a material such as platinum (Pt) which prevents diffusion of substances from the outside environment into the material of the conductive rod <NUM> and vice versa. In particular, the diffusion barrier layer is chosen such that it prevents diffusion of oxygen into the material of the conductive rods <NUM>.

In this embodiment, the electrically conductive coating <NUM> is both arranged on the outside facing side as well as on the inside facing side of the glass substrate <NUM>.

The electrically conductive coating <NUM> on the inside facing side serves as a contact pad <NUM> for the solder drop <NUM> which electrically connects the electrical device <NUM>, see <FIG>, to the through glass via <NUM>.

In further embodiments, a part of the surface of the glass substrate <NUM> surrounding the conductive rod <NUM> could be raised or lowered compared to the remaining surface of the glass substrate <NUM> to form an elevation or depression surrounding the conductive rod <NUM>. The raised or lowered area is preferably flush with the end surface of the conductive rod <NUM>. Preferably, the electrically conductive coating <NUM> forming the contact pad <NUM> covers the entire area of said elevation or depression. Such an elevation or depression may be applied to control the flow of a solder material, wherein preferably said solder material would be confined to the elevation or depression.

The corrosion-resistant properties of the electrically conductive coating <NUM> are not required on the inside facing surface as the enclosure <NUM> protects the enclosed function area <NUM> from any corrosive influence from the outside. However, having the same electrically conductive coating <NUM> on both surfaces allows the use of the same coating process and results in a symmetrical glass substrate <NUM> so that any of the two sides may face towards the spacer substrate <NUM>.

<FIG> shows a cross-section view of an enclosure <NUM> formed by the glass substrate <NUM>, the spacer substrate <NUM> and the cover substate <NUM>. The three substrates <NUM>, <NUM>, <NUM> are bonded together via bond lines <NUM>. The enclosure <NUM> hermetically encloses the function area <NUM> which receives the electrical device <NUM>. Further the three substrates <NUM>, <NUM> and <NUM> define a connector receptacle area <NUM> which allows the insertion of a suitable connector.

Said connector receptacle area <NUM> is in electrical contact with the electrical device <NUM> by means of through glass vias <NUM> and conductive traces <NUM>. The traces <NUM> are defined by structuring the electrically conductive coating <NUM> arranged on the respective outside facing surfaces of the glass substrate <NUM> and the cover substrate <NUM>.

As it is not intended to form a solder connection to the conductive traces <NUM>, the electrically conductive coating <NUM> arranged on the outside facing surfaces of the glass substrate <NUM> and the cover substrate <NUM> may be configured as a two-layer structure comprising the adhesion layer (<NUM>) and the barrier layer (<NUM>) as corrosion resistant layer.

Within the connector receptacle area <NUM>, an upper contact <NUM> and a lower contact <NUM> are defined by structuring of the electrically conductive coating <NUM> arranged on the inside facing surfaces of the glass substrate <NUM> and the cover substrate <NUM>. Further, for mechanically securing of a connector, connector notches <NUM> are formed in the glass substrate <NUM> and the cover substrate <NUM>. The connector notches <NUM> are configured to receive latching elements of the connector.

<FIG> shows another enclosure <NUM>, similar to the enclosure described with respect to <FIG>. In contrast to the embodiment of <FIG>, the substrates <NUM>, <NUM>, <NUM> are configured to form a clamp <NUM> designed to receive and hold a nerve <NUM>.

Within the clamp <NUM>, the electrically conductive coating <NUM> is structured to form a contact pad <NUM> for electrically contacting the clamped nerve <NUM>. This allows, for example, the nerve <NUM> to be in electrical contact with the electrical device <NUM> and to stimulate the nerve <NUM> by electrical pulses from the electrical device <NUM>.

<FIG> shows another enclosure <NUM>, where electrical contacts <NUM> are provided on the upper surface of the glass substrate <NUM> on either side of the enclosed function area <NUM>. The two electrical contact pads <NUM> are obtained by structuring the electrically conductive coating <NUM>. The respective electrical contact pads <NUM> are connected to the back side of the glass substrate <NUM> by through glass vias <NUM> and the electrical devices <NUM> is likewise connected to through glass vias <NUM>. Conductive traces <NUM> formed on the outside facing surface of the glass substrate <NUM> by structuring of the electrically conductive coating <NUM> establish an electrical connection between two of the through glass vias <NUM>. The electrically conductive coating <NUM> is structured such that the exposed surfaces of the conductive rods <NUM> of the through glass vias <NUM>, see <FIG>, are covered by the coating <NUM>.

The arrangement shown in <FIG> allows the spacer substrate <NUM> as well as the cover substrate <NUM> to remain free from electrical contacts and through glass vias <NUM> while still providing access to the contact pads <NUM> from an upper side of the enclosure <NUM> via a free space <NUM> located above the contact pads <NUM>. Thus, optical properties of the spacer substrate <NUM> and the cover substrate <NUM> are not impaired.

Claim 1:
Hermetic enclosure (<NUM>) comprising at least one glass substrate (<NUM>) having at least one electrical feedthrough configured as a through glass via (<NUM>), the through glass via (<NUM>) comprising a conductive rod (<NUM>) electrically connecting the inside of the hermetic enclosure (<NUM>) to the outside through the glass substrate (<NUM>), wherein the part of the conductive rod's (<NUM>) surface facing towards the outside of the hermetic enclosure (<NUM>) is completely covered with an electrically conductive coating (<NUM>), wherein the electrically conductive coating (<NUM>) is a multilayer structure comprising at least an adhesion layer (<NUM>) in direct contact with the conductive rod (<NUM>) and a corrosion resistant layer, characterized in that the electrical feedthrough comprises a depression in or an elevation on an outside facing surface of the glass substrate (<NUM>) and/or on an inside facing surface of the glass substrate (<NUM>), wherein the recess or elevation surrounds the conductive rod (<NUM>).