JP2009254892A - Thin-film fabrication technology for implantation electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an electrode assembly using photolithographic technology. <P>SOLUTION: A long and thin implantation electrode assembly (50) includes a set of electrode pads (12 and 14) placed in a predetermined pattern, and a plurality of electric wires (34 and 36) extending in a longitudinal direction each wire being connected to at least one pad. The electrode assembly can be formed using photolithographic technology by: firstly depositing the pads (12 and 14) on a sacrifice layer (10), secondly attaching the electric wires (34 and 36) to the pads (12 and 14), thirdly implanting the pads and electric wires in a carrier (46), and finally removing the sacrifice layer (10). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method of forming an electrode suitable for implantation in an organ utilizing thin film technology commonly used in the manufacture of integrated circuits.

  The implantable electrode assembly made according to the method of the present invention can be used in a transplant cochlear stimulator.

A neurostimulation or recording microelectrode system consists of a series of conductive pads placed close to the nerve of interest. These pads are connected to each other and to recording or stimulation electronics via conductors that are insulated from the surrounding medium. One example of such an electrode array that is in widespread use today is the Cochlear Implant I 22M, Australia, New South Wells.
Manufactured by Cochlear Limited of South Wales, Lane Cove. This device typically consists of a number of platinum rings or spheres arranged along a flexible insulating carrier formed of silicon rubber.

Although some attempts have been made to produce the electrodes using thin film processing techniques, it has not been possible to produce reliable electrodes suitable for use in the human body. For example, the electrode may be composed of a silicon substrate. Such a micromachine type device would be suitable as an electrode for a transplanted cochlear stimulator. Sensors and Actuators 1994 A45, 47-55: "Development of micromachine type device using polyimide substrate" (Development
See of micromachined devices using polyimide-based processes, Frazier AB, Ahn CH, Allen MG. However, the electrodes are extremely thin (5-15 μm) in order to be flexible enough to be inserted into the cochlea. Because of these extremely small dimensions, such electrodes are extremely fragile and difficult to handle.

  In general, thin film technology is not applicable to the commercial production of transplanted cochlear stimulators, or other neural electrodes, both for processing techniques and for the tissues where micromachined devices must be used. It is difficult to select a suitable material. The choice of conductor is limited to noble metals such as platinum or iridium.

Although the selection of insulating materials is wide, the following characteristics must be maintained.
1. 1. Biocompatibility 2. Stability to the process used to make the metallization pattern Flexibility and mechanical compatibility with the organ of interest So far, even materials that adequately meet the requirements of items 1 and 2 above do not have the mechanical properties required by item 3. Therefore, it is clear that there is a need for improved technology for commercial production of electrodes that take advantage of photolithography technology and can be used relatively inexpensively and efficiently, such as transplanted cochlear stimulators.

  In view of the above, it is an object of the present invention to provide an implantable electrode system using thin film technology or a method of manufacturing an array.

According to one aspect of the invention,
Prepare the sacrificial layer,
Forming a plurality of pads on the sacrificial layer, the pads being made from a conductive biocompatible material;
Forming a plurality of wires, the wires connected to at least one of the pads;
An assembly is formed by embedding the pad and the electric wire in a non-conductive material,
Removing the sacrificial layer from the assembly;
A method of manufacturing an elongated implantable electrode assembly comprising each stage is provided.

According to another feature of the invention, a method of forming an electrode assembly having a plurality of electrodes and a plurality of electrical wires extending in the longitudinal direction of the electrode assembly and connected to the electrodes,
Forming the wire,
Forming a carrier around the wire and pad, the carrier being formed of a flexible non-conductive material;
Removing the sacrificial layer;
Said method comprising the steps is provided.

  Employing thin film technology is a clear advantage over the cumbersome and time consuming manual assembly method. The use of thin film lithographic technology allows for faster fabrication of smaller structures with high density electrodes than those that can be fabricated by manual assembly.

  According to the present invention, the conductor can be formed by photolithography. Next, an elastomeric insulator is added to the self-supporting conductor pattern thus formed. Since the polymerization is a low energy process, the technique of the present invention has the additional advantage that the metal-polymer adhesion can be optimized relatively easily. Obtaining the desired adhesion between the metal membrane and the polymer support ensures the mechanical integrity of the device. Most metal deposition processes require inherently high energy levels. For example, thermal evaporation or sputtering uses metal atoms that have a high energy level when impacting the polymer surface. The chemical rearrangement that occurs as a result of such a collision reduces the adhesion between the metal and the polymer. The solution proposed here is to add the polymer to the metal, unlike the other existing methods. The following relates to a process based on standard thin film technology that enables the above. Although this technique is a description of a transplanted cochlear stimulator electrode, other nerve stimulation electrodes or recording electrodes can be produced by a similar method.

  Briefly, in accordance with an embodiment of the present invention, an electrode array suitable for implantation in a patient's body is an elongated carrier made of a relatively hard non-conductive material, arranged in a preselected pattern. Consists of a plurality of pads embedded therein. The carrier must be stiff enough to smoothly insert the electrode assembly into the patient's body through an incision made for the above purpose, or through a natural cavity or opening. To ensure that only a small incision or opening is required and does not interfere with the patient's tissue during implantation, the carrier is preferably of minimal cross-section. The carrier includes a distal portion adjacent to at least some electrode pads to be disposed and a base. The plurality of connecting wires extend from the pad to the base in the carrier body. These wires are connected at the base by coupling means to the electrical circuit for sending and / or receiving electrical signals from the pads.

  The photolithographic process is used to produce an electrode assembly that uses a sacrificial layer as the initial substrate. More specifically, first, pads are formed on the substrate in a preselected pattern. Next, a pad connector is attached to the pad. The third stage consists of forming a wire extending from this pad connector to the base. The wires, connectors, and pads are then embedded or encapsulated in the plastic sheath forming the carrier, after which the substrate is removed.

  If necessary, a strain relief zone configured and arranged so as to be a flexible electric wire that does not break in the process of manufacturing or implantation is formed in the electric wire. Such a zone is advantageous because it also provides a strong bond with the encapsulated sheath.

1A to 1I show perspective views of respective manufacturing stages of an electrode assembly according to the present invention. 2A to F show cross-sectional views of the electrode assembly side surface at several stages of FIG. FIG. 3 shows a flowchart of the subject method. 4A to 4C show a mask used to make an electrode assembly according to the first embodiment of the present invention. FIGS. 5A to I show a mask used to make an electrode assembly according to the second embodiment, and FIG. 5J shows a cross-sectional view of an electrode assembly configured using the masks of FIGS. 5A to I. Show. FIG. 6 shows a cross-sectional view of another embodiment of the present invention.

  In one embodiment of the present invention, electrode fabrication is performed on a sacrificial layer made of a material selected to withstand all conditions of the processing stage but can be removed by melting, peeling, or heating. .

The electrode pads, electrodes, and wires are formed by plating with platinum or other suitable metal with a photolithographic technique, primarily with a polyimide mask. This process relies on a combination of three basic technologies.
1. 1. Evaporation of platinum by heat or electron beam 2. Masking and etching Thickening by Electrolyte Deposition The platinum can also be deposited directly on the copper substrate by electroplating using a desired mask.

  Each electric wire is attached to the electrode pad by a connector. The connector is positioned so that the wires are free-standing in the air when the polyimide mask is removed. The wire should be formed with a step or flexible zone etched in polyamide to improve the longitudinal flexibility of the electrode and facilitate encapsulation of the structure at the corners. Is preferred.

  The polyimide in the structure can be removed by plasma etching or chemical etching.

  The polymer support, parylene, or silicone rubber is then added in two steps to the free standing electrode structure. Initially, an electrode support is formed, after which the sacrificial layer (eg, copper substrate) is removed. If the sacrificial layer is a material that can be etched, the polymer can probably be added in only one step. This is realized by forming a groove in the substrate material by simple undercut etching.

Referring to the drawings, a sacrificial layer 10 made of, for example, polished copper (step 100) is first prepared (FIGS. 1A, 2A, and 3) according to this embodiment of the present invention to make an electrode assembly (FIGS. 1A, 2A, and 3). . The sacrificial layer must have a thickness selected to be strong enough to withstand the chemistry of other processing steps required to produce the electrode assembly.
Next, a plurality of electrode pads 12, 14 are formed on layer 10 (step 102). The pad is preferably made of a highly conductive biocompatible material, such as platinum, iridium, or other similar material. As mentioned above, the pads are preferably formed on layer 10 using thin film techniques well known in the art of integrated circuit manufacturing. More particularly, as shown in FIGS. 1B-1D, stage 102 comprises a number of sub-stages. First, (FIG. 1B) layer 10 is covered with a thin layer 16 of photopolymerizable polymer (PR) material, for example by spinning.
Photolithographic techniques are then used to create openings 18, 20 in the layer 16 having the dimensions of the pads 12, 14. Photolithographic technology attaches a mask (not shown) to layer 16, exposes the mask and layer 16 to light having a specific wavelength, removes the mask, and dissolves the light-sensitized portion. Developing layer 16 to form openings 18, 20. These steps are well known and need not be described in further detail here.
Next, platinum is added to the layer 16 to form the pads 12, 14 in the holes 18, 20 by, for example, sputtering or heated electron beam evaporation.
Eventually, layer 16 is dissolved leaving pads 12, 14 as shown in FIGS. 1D and 2B.

  Alternatively, the pads 12 and 14 can be formed by attaching a mask on the layer 10, electroplating with platinum through the opening of the mask, and then removing the mask.

In the next step 104, pad contacts are attached. This step 104 is substantially performed by repeating the substeps used to form the pads 12,14. As shown in FIG. 1E, a PR layer 22 is first applied to both layer 10 and pads 12, 14. Next, two round openings 24, 26 are formed in the layer 22 on the top surface of the pads 12, 14. A third opening 28 is also formed in the layer 10 over the location between the pads 12, 14, as shown in FIG. 1E. Next, platinum is deposited on the openings 24, 26, for example by vacuum or electroplating, to make the contacts 30, 32 (FIG. 1F). The structure thus formed is shown in FIG. 2C.
Next, as indicated by step 106, in addition to the flexible zone 38, the wires 34, 36 for the pads 12, 14 are formed.
For this purpose, the grooves 40 and 42 are etched using another mask (not shown). The groove 40 leads from the contact 30 to the base of the assembly (not shown), and the groove 42 also leads from the contact 32 to the base. Next, platinum is introduced into the grooves 40 and 42, for example, by electroplating. Eventually, layer 22 is removed, leaving a structure as shown in FIGS. 1H and 2D. Importantly, the wire 34 sags down toward the layer 10 and includes a step back, as best seen in FIG. 2D, thereby providing a reinforcement zone, Alternatively, the flexible zone 38 is formed. This step extends through the air above the pad 14 and reinforces the substantially self-supporting wire 34.

In each of the above stages, the PR could be removed by either plasma etching or chemical etching.
Next, an insulating material 46, for example made of parylene or silicone rubber, is added to evenly embed the pads 12, 14, contacts 30, 32 and the wires 34, 36, and a tight elongated body. 48 is formed (step 108, FIG. 2E).

  Finally (step 110), the sacrificial layer 10 is removed, leaving the completed electrode assembly 50 (FIGS. 1I, 2F). The insulating material 46 may be further shaped into a preselected shape or laminated.

  1 and 2 illustrate the steps of making an electrode assembly at a microscopic level. 4A-C and FIGS. 5A-J show two different outlines for making electrode assemblies at a macroscopic level.

  More particularly, FIGS. 4A-C show several masks used to form the openings of FIGS. 1 and 2 and the relationship of each opening. FIG. 4A shows a mask 160 having a square zone 161. This mask is attached to layer 16 (FIG. 1B) to form openings 18,20.

  FIG. 4B shows a mask 162 having a plurality of rod-like zones 164. In the peripheral part, the mask 162 has a round part 166 formed therein. This mask is used to form the openings 24, 26 and 28 of FIG. 1E, which will be the contacts 30, 32 and step 38, respectively. Each zone 164 forms a step 38.

  FIG. 4C shows a mask 168 used to form longitudinal openings 40, 42 (FIG. 1G) for forming electrical wires 34, 36 (FIG. 1H). As seen in FIG. 4C, the mask includes several dark lines 170 that are substantially parallel. Each wire 170 includes a base 172 for connection to an external terminal (not shown) and a distal portion 174 electrically coupled to a connector such as 30. In this manner, each pad is connected to an electric wire extending corresponding to the length of the electrode system 50.

  The process described above will be used for the production of electrode assemblies with a very large number of electrodes. For example, in FIGS. 4A-4C, the mask can create an assembly with 22 electrodes. And in this aggregate | assembly, all the electric wires are arranged in the one common layer substantially.

  However, a multilayering method is necessary for an assembly with a very large number of electrodes and / or if the electrode assembly has to be in a limited cross-sectional area. . 5A to 5J show a mask for forming 22 electrode assemblies in three layers. 5A-5C and 5D-5F each show a layer for 8 electrodes, whereas FIGS. 5G-5I show a mask for 6 additional electrodes. Yes. As shown in the cross-sectional view of FIG. 5J of the electrode assembly formed using the masks of FIGS. 5A-I, the mask substrate of FIGS. 5B, 5E, and 5H is such that the steps formed on the wires overlap. Are preferably arranged in a line.

  In this embodiment, the electrodes are formed in three different sets, denoted as 212A, 212B, and 212C in the drawing, and by using the techniques described in the embodiments of FIGS. Each has its own connector pads and wires. After the three sets were completed, they were placed in parallel positions and sandwiched as shown in FIG. 5J. Thereafter, an exterior 246 is added to form the electrode carrier.

  In another embodiment of the present invention, the sacrificial layer 310 shown in FIG. 6 was formed of an etchable material so that two grooves 302 and 304 were formed therein before the electrode assembly was formed. . The electrode assembly includes all of the electrode 312, the connector 330, and the electric wire 334 disposed in the exterior or carrier 346. Since the carrier 346 is formed so as to surround the electrode, the connector, and the electric wire, the carrier 346 flows into the grooves 302 and 304. A similar groove is formed and fills with insulating material under the flexible zone 38 (FIGS. 1H and 2D) of the wire. After the carrier is cured, the entire electrode assembly 350 can be peeled from the sheet 310 in one step.

Current electrode manufacturing techniques rely on cumbersome and costly manual assembly techniques. The photolithographic techniques disclosed herein provide several obvious advantages.
1. 1. Low cost and increased processing capacity of the device. 2. A higher density electrode can be formed. 3. Costly rigorous manual labor (mold work, etc.) can be eliminated. A flexible and quick design cycle.
Although the invention has been described with reference to a few specific embodiments, it is to be understood that these embodiments are merely illustrative of the application of the principles of the invention. Accordingly, the described embodiments are not to be considered as limiting but are to be considered as examples with respect to the following claims.

Claims (9)

A method for producing an implantable electrode assembly that can be inserted into an organ,
Prepare the sacrificial layer,
Forming a plurality of pads on the sacrificial layer, the pads being made of a conductive biocompatible material;
Forming a plurality of wires, the wires connected to at least one of the pads;
The pad and the electric wire are embedded in a non-conductive material to form an assembly,
Removing the sacrificial layer from the assembly;
A manufacturing method of an elongated implantable electrode assembly comprising each step, wherein the pad and the electric wire are made of platinum and formed by photolithography. Prepare the sacrificial layer,
Forming a plurality of pads on the sacrificial layer, the pads being made of a conductive biocompatible material;
Forming a plurality of wires, the wires connected to at least one of the pads;
The pad and the electric wire are embedded in a non-conductive material to form an assembly,
The pad and the electric wire are made of platinum, and formed by a photolithographic technique, a method for producing an implantable electrode assembly,
A method for producing an elongated implantable electrode assembly comprising the step of forming a contact point of a pad between the electric wire and a corresponding pad. A method of forming the electrode assembly having a plurality of electrodes and a plurality of electric wires extending in a longitudinal direction of the electrode assembly and coupled to the electrode;
Prepare the sacrificial layer,
Forming the electrodes in a preselected pattern on the sacrificial layer;
Forming the electrical wire, the electrical wire connected to at least one of the electrodes;
Forming a carrier around the wire, the carrier being formed of a flexible non-conductive material;
Removing the sacrificial layer;
A method of forming an electrode assembly comprising each step, wherein the electrode and the electric wire are formed by a photolithographic technique.   The method of claim 4, wherein the plurality of electrodes are formed substantially simultaneously.   The plurality of electrodes are divided into a number of sets, and the method includes separately forming sets of electrodes, each set having a unique wire, and then assembling the set. Item 4. The method according to Item 3.   The method according to claim 3, wherein the electric wire is formed by forming a zone for reinforcement at a predetermined position of the electric wire. A method for producing an elongated implantable electrode assembly,
Prepare the sacrificial layer,
Forming a plurality of pads on the sacrificial layer, the pads being made of a conductive biocompatible material;
Forming a plurality of wires, the wires connected to at least one of the pads;
The pad and the wire are embedded in a non-conductive material to form an assembly,
Removing the sacrificial layer from the assembly;
A method of manufacturing an elongated implantable electrode assembly comprising the steps, wherein the pad and the electric wire are formed of a material selected from platinum and iridium and are formed by a photolithographic technique. A method for producing an elongated implantable electrode assembly,
Prepare the sacrificial layer,
Forming a plurality of pads on the sacrificial layer, the pads being made of a conductive biocompatible material;
Forming multiple wires,
Forming a plurality of pad contacts, each wire being connected to at least one of the pads by the pad contacts;
The pad and the wire are embedded in a non-conductive material to form an assembly,
Removing the sacrificial layer from the assembly;
A manufacturing method of an elongated implantable electrode assembly comprising each step, wherein the pad and the electric wire are formed by a photolithographic technique. A method for producing an elongated implantable electrode assembly,
Prepare the sacrificial layer,
Forming a plurality of pads on the sacrificial layer, the pads being made of a conductive biocompatible material;
The pad and the wire are embedded in a non-conductive material to form an assembly,
Removing the sacrificial layer from the assembly;
A method of manufacturing an elongated implantable electrode assembly comprising the steps, wherein the pad and the electric wire are formed by photolithography and at least some of the electric wires are formed with zones for reinforcement.

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