Abstract:
A three-dimensional neural probe electrode array system is described. Planar probes are microfabricated and electrically connected to flexible micro-machined ribbon cables using a rivet bonding technique. The distal end of each cable is connected to a probe with the proximal end of the cable being customized for connection to a printed circuit board. Final assembly consists of combining multiple such assemblies into a single structure. Each of the two-dimensional neural probe arrays is positioned into a micro-machined platform that provides mechanical support and alignment for each array. Lastly, a micro-machined cap is placed on top of each neural electrode probe and cable assembly to protect them from damage during shipping and subsequent use. The cap provides a relatively planar surface for attachment of a computer controlled inserter for precise insertion into the tissue.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Application Ser. No. 61/901,783, filed on Nov. 8, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to the field of devices and methods used for neural interventions. 
         [0004]    2. Prior Art 
         [0005]    The conventional method used to interface the nervous system includes a multi-contact electrode array. Electrode arrays are designed to transmit signals into the tissue (“stimulation”) or extract signals from the tissue (“sense”). These electrode arrays are commonly used in neuroscience and neurophysiological research as well as in clinical therapeutic applications. Often, a precise volume of tissue in the peripheral nervous system or in the central nervous system is the target for placement of the electrode array. Additionally, it is desirable to interface with the targeted volume in three-dimensions. Commercially available electrode arrays are limited in their ability to position electrode contacts in a three-dimensional arrangement. Two examples are the planar silicon array, often referred to as the “Michigan Probe” and an alternative silicon-based technology referred to as the “Utah Array”. The Michigan Probe is limited to positioning electrode contacts in a two-dimensional arrangement, all within a single plane. The Utah Array is also limited to positioning electrode contacts in a two-dimensional plane. Moreover, electrode contacts in a Utah Array are limited to placement on the tip of each electrode shank. 
         [0006]    The present invention presents a method for creating a true three-dimensional arrangement of electrode contacts using two or more two-dimensional planar silicon microelectrode arrays. The planar electrode arrays are aligned in rows to provide a three-dimensional tissue interface. There is prior art where researchers have constructed three-dimensional microelectrode arrays using various methods, but the present invention is a novel approach using a multitude of planar neural electrode probes combined to make a customizable and scalable three-dimensional array. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a structure for stimulation and sensing of neurophysiological signals from an array of microelectrode contacts positioned in a three-dimensional arrangement. This provides a “richer” communication pathway to and from the neural circuit of interest. 
         [0008]    The primary advantage is that the present invention describes a method of creating a three-dimensional electrode tissue interface using multiple neural probe electrode arrays consisting of two or more planar probes arranged in side-by-side electrically connected to flexible ribbon cables. The multiple neural probe electrode arrays are supported by a pedestal to thereby provide a plurality of neural electrode probes in an “x” and “y” configuration, for example a 4×4 array of neural electrode probes. Additionally, each probe has a number of stimulation or sensing electrodes along its “z” length. This effectively provides a three-dimensional stimulation or sensing array. Any one of a number of neural electrode arrays can be designed for a desired application. In that respect, the present invention leverages a long standing history of a proven technology (i.e., planar neural electrode probes, but arranged into an x, y and z configuration) and is a method that is scalable and customizable with regards to the geometry, size and number of electrode contacts. 
         [0009]    A three dimensional electrode array configuration is important for many reasons. One example is when considering interfacing with the cortex where neurons are structured in an inhomogeneous manner that differs anatomically and physiologically across ventral/dorsal and medial/lateral directions. Neurons in the cortex are generally oriented vertically. Being able to arrange electrode contacts across depths provides more tolerance in positioning to help ensure that a richest signal can be obtained. This also allows positioning of electrode contacts at multiple points along a single neuron, for example spanning the distance from a particular neuron&#39;s cell body to its respective dendritic tree. Neurons in the cortex are organized in columns where cells within a specific column perform similar functions and these functions may differ between columns. Therefore, a three-dimensional arrangement (x, y and z) of contacts has the ability to span multiple neuronal columns. 
         [0010]    These and other objects will become apparent to one of ordinary skill in the art by reference to the following description and the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a neural probe electrode array system  10  according to the present invention. 
           [0012]      FIG. 1A  is a perspective view of the neural probe electrode array system  10  shown in  FIG. 1  mounted to a skull  150  adjacent to a craniotomy opening  202 . 
           [0013]      FIG. 2  is a perspective view of a skull mounting plate  12  of the neural probe system  10 . 
           [0014]      FIG. 3  is a perspective view showing an electronics housing  14  separated from the skull mounting plate  12  of the neural probe system  10 . 
           [0015]      FIG. 4  is a perspective view of an exemplary embodiment of a neural probe electrode assembly  18  according to the present invention. 
           [0016]      FIGS. 5 and 6  are front elevational views of exemplary neural probe electrode arrays  78 A and  92 , respectively. 
           [0017]      FIG. 7  is an exploded view of a 4×4 neural probe electrode assembly  18  according to the present invention. 
           [0018]      FIGS. 8 and 9  are photographs showing rivets connecting the bond pads of a neural electrode probe  100  to a ribbon cable  102 . 
           [0019]      FIG. 10  is a perspective view of a neural probe electrode assembly  18  according to the present invention. 
           [0020]      FIG. 11  is a perspective view of neural probe electrode array system  10  shown in  FIG. 1  just prior to removal of the electrode assembly  18  from its cradle  56  on the electronics housing  14 . 
           [0021]      FIG. 12  is a perspective view of the neural probe electrode array system  10  shown in  FIG. 11 , but with the electrode assembly  18  removed from cradle  56 . 
           [0022]      FIG. 13  is a perspective view of the neural probe electrode array system  10  shown in  FIG. 12  and with the electrode assembly  18  attached to an actuatable vacuum insertion tool  128 . 
           [0023]      FIG. 14  is a perspective view of the neural probe electrode array system  10  shown in  FIG. 13 , as the electrode assembly  18  would be positioned in body tissue. 
           [0024]      FIGS. 15 and 16  are perspective views of the neural probe system  10  shown in  FIG. 14 , but with the shipping cover  52  being removed and replaced by permanent cover  136 . 
           [0025]      FIGS. 17 to 21  illustrate of an exemplary process for manufacturing the platform  76  for the neural probe assembly  18 . 
           [0026]      FIGS. 22 to 26  illustrate an exemplary process for manufacturing a cover for the platform  76  shown in  FIGS. 4 ,  7  and  10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Turning now to the drawings,  FIG. 1  is a perspective view of a neural probe electrode array system  10  according to the present invention. The neural probe system  10  comprises a skull mounting plate  12  supporting an electronics housing  14 . A flexible ribbon cable  16  connects from electronics (see connectors  134 A to  134 D in  FIGS. 15 and 16 ) in the housing  14  to a neural probe electrode assembly  18 . A neural probe electrode assembly  18  according to the present invention includes at least one, and preferably a plurality of neural probe electrode arrays as exemplified in  FIGS. 5 and 6 . The housing  14  further includes wires  19  for grounding the subject. These wires not only ground the animal, but may be used as a reference when performing differential recording, or as a return path for current when stimulating. 
         [0028]      FIG. 2  illustrates the skull mounting plate  12  comprising a curved mount body  20  supporting a plurality of extending legs  22 . The curved body  20  is a dome-shaped member having a plurality of first, unthreaded openings  24  adjacent to a perimeter  26  thereof. Preferably the first openings  24  are at regularly spaced intervals. Legs  22  extend from the perimeter  26  and provide a number of second, unthreaded openings  28 . While not necessary, the second openings  28  are illustrated as being spaced at regular intervals along the length of each leg  22 . Seven legs  22  are shown, but that is not necessary. There can be more or less than that number of legs. 
         [0029]      FIG. 2  further illustrates that first screws  30  are received in the first unthreaded openings  24  in the dome-shaped body  20  and second screw  32  are received in the second unthreaded openings  28  in the legs  22 . Moreover, the second screws  32  can be positioned in any one of the three second openings  32  of each leg  22 . Leg  22 A shows screw  32 A positioned in a first leg opening  28 A adjacent to the mount body  20 , leg  22 B shows screw  32 B positioned in a second opening  28 B and leg  22 C shows screw  32 C positioned in a third, most distal opening  28 C. If desired, the legs  22  can be cut to shorten their lengths and thereby eliminate some or all of the leg openings  28  as desired for a particular surgical procedure.  FIG. 1  shows an exemplary embodiment where the skull mounting plate is devoid of any legs  22 . The legs  22  can also be bent to match the curvature of a skull. 
         [0030]    It is noted that the length of first screws  30  is desirably somewhat longer than that of the second screws  32 . The first screws  30  are of a sufficient length to provide first threads screwed into the skull or cranium bone to accommodate for the offset distance of the mount body  20  from a skull as a result of its dome shape. That is in comparison to the legs  22 , which are relatively closely spaced to the skull. In any event, screws  30 ,  32  have threads that are configured for threading into the skull  150  ( FIG. 1A ). In one embodiment according to the present invention, the first screws  30  are 2.4 mm wide×6 mm long and the second screws  32  are 2 mm wide×4 mm long. The screws  30 ,  32  are preferably titanium. 
         [0031]    The skull mounting plate  12  has a cylindrical-shaped pedestal  34  extending upwardly from the dome-shaped mount body  20 . A U-shaped yoke  36  is supported on an upper face of the pedestal  34 . A threaded opening  38  is provided into the depth of each arm  36 A,  36 B of the yoke. There is also a threaded opening  40  extending into the depth of each arm  36 A,  36 B adjacent to the pedestal  34 . Preferably, the threaded openings  38  and  40  do not intersect each other. 
         [0032]      FIG. 3  illustrates the electronics housing  14  just prior to being mounted to the skull mounting plate  12 . In one embodiment according to the present invention, the electronics housing  14  is a rectangular-shaped member of a biocompatible metal, such as titanium. As those of skill in the art will readily understand, the shape of electronics housing  14  illustrated in the drawings is exemplary and should not limit the scope of the present invention. Other shapes for the electronics housing  14  may be desired for a particular surgical procedure or application. 
         [0033]    In the illustrated embodiment, the electronics housing  14  comprises right and left sidewalls  42  and  44  meeting front and back sidewall  46  and  48 , all extending to a bottom wall  50  and a top wall  51  ( FIGS. 15 and 16 ). A shipping cover plate  52  is temporarily secured to the upper edges of the right, left, front and back sidewalls using screws  54  threaded into receptacles therein. 
         [0034]    The shipping cover plate  52  supports a cradle  56  for the neural probe assembly  18 . The cradle  56  comprises spaced apart webs  58  and  60  that are aligned perpendicular to the front sidewall  46 . Enlarged portions of the webs  58 ,  60  extending out past the front sidewall  46  support a guard bar  62  received in openings in the webs  58 ,  60 . The guard bar  62  has an L-shaped end  62 A that nests in a recess  58 A of web  58  ( FIG. 11 ). The L-shaped end  62 A acts as a stop so that the guard bar  62  cannot be moved completely through the web openings. 
         [0035]    A shaped secondary cover  64  is supported on the cradle  56  by screws  66  threaded into the shipping cover plate  52 . With the secondary cover  64  mounted to the shipping cover plate  52  over cradle  56 , there is a forwardly facing opening  68  underneath guard bar  62 . The significance of opening  68  will be described in detail hereinafter. 
         [0036]      FIG. 3  further illustrates the electronics housing  14  just prior to it being mounted on the cylindrical pedestal  34  of the skull mounting plate  12 . The bottom wall  50  of the electronics housing  14  has an opening (not shown) configured to receive the yoke  36 . With the electronics housing  14  supported on the skull mounting plate  12 , screws  70  are received through oversized openings  70 A ( FIGS. 11 to 14 ) in the cover plate  52  and threaded into openings  38  in the yoke arms  36 A,  36 B adjacent to the cylindrical pedestal  34 . That way, the cover plate  52  can be removed from the housing  14  without having to disconnect the electronics housing from the skull mounting plate  12 . 
         [0037]    Those skilled in the art will readily understand that the electronics housing  14  can be secured to the skull mounting plate  12  by means other than screws  70  threaded into the yoke  36 . For example, the yoke could be replaced with a threaded post and the housing could have a matching opening in its bottom wall for threadingly connecting the housing  14  to the mounting plate  12 . A ball and detent connection can also be used. 
         [0038]    A silicone gasket  72  is disposed between the electronics housing and the skull mounting plate. That is for the purpose of providing a fluid barrier as well as cushioned connection between the housing  14  and pedestal  34 . The gasket  72  also serves as a barrier when skin is cinched up against the pedestal  34 , but underneath the electronics housing  14  during a surgical procedure. 
         [0039]      FIG. 4  is an enlarged view of the ribbon cable  16  connected to a neural probe electrode assembly  18 . The ribbon cable is designed to be flexible so that the neural probe electrode assembly is virtually untethered from the electronics housing. This allows the neural probe electrode assembly to “float” with the brain during brain pulsation or brain shift. The ribbon cable may be a thin-film based cable like those made from polyimde, parylene, or silicone with embedded conductors (e.g., gold, platinum, etc.). 
         [0040]    The neural probe electrode assembly  18  comprises a probe platform  76  supporting a plurality of neural probe electrode arrays. Four neural probe electrode arrays  78 A,  78 B,  78 C and  78 D are shown with each array having four neural probes  80 A,  80 B,  80 C and  80 D. 
         [0041]      FIG. 5  shows that the exemplary thin-film neural probe electrode array  78 A comprises a proximal bond pad plate  82  (e.g., titanium/gold stack) connected to buried conductive traces that run along each shank  90 A,  90 B,  90 C and  90 D (e.g., titanium/gold/platinum stack) to connect to the electrode contacts  88  (e.g., titanium/gold/platinum stack). 
         [0042]    The bond pad plate has an upper edge  82 A spaced from a lower edge  82 B, both the upper and lower edges meeting spaced apart right and left edges  82 C and  82 D. A step  84 A resides where the right edge  82 C meets the lower edge  82 B. An opposed step  84 B resides where the left edge  82 D meets the lower edge  82 B. Plate  82  supports a plurality of bond pads  86  that are electrically connected to a respective one of the plurality of electrodes  88  supported on a shank by buried conductive traces. The exemplary neural probe electrode array  78 A has four equally spaced apart shanks  90 A,  90 B,  90 C and  90 D extending distally from the plate  82 . The shanks are of equal lengths. 
         [0043]    While not shown in the drawing, each thin-film neural probe electrode array according to the present invention is comprised of multiple metal traces and electrode sites. As many as 100 conductive traces and electrode sites can be realized on an array that is as narrow as 30 microns and as thin as 6 microns. In order to be strong enough to be inserted into tissue, these neural probe electrode arrays must be either integrated during fabrication on a carrier that provides strength, or attached to a strengthening carrier post-fabrication. If the strengthening carrier is stiff, the electrode array can be inserted into tissue along a desired axial direction of a guiding element. Moreover, the electrode array shanks have pointed tips, which help reduce the tissue resistance to insertion. 
         [0044]      FIG. 6  illustrates another embodiment of a neural probe electrode array  92  comprising a bond plate  94  supporting bond pads  96 . Four equally spaced apart electrode shanks  98 A,  98 B,  98 C and  98 D depend from the bond plate. In this exemplary array, the shanks are of unequal lengths. Those skilled in the art will readily understand that a neural probe array according to the present invention can have more or less than four electrode shanks. If there are two or more shanks, but not one, they can be of the same or different lengths. If there are three or more electrode shanks, but not two or one, they can be equally or unequally spaced apart from each other. Moreover, any one shank can support more or less electrodes  88  than another shank. 
         [0045]      FIG. 7  is an exploded view illustrating a 4×4 neural probe electrode assembly  18  (four neural probes having four electrode shanks each). The first neural probe array  100  has four electrode shanks  100 A extending from bond plate  100 B. Bond plate  100 B supports bonds pads  100 C which are physically and electrically connected to cable bond pads  102 A at a distal end of a first flexible ribbon cable  102 . The second neural probe array  104  has four electrode shanks  104 A extending from bond plate  104 B. Bond pads  104 C supported on plate  104 B are physically and electrically connected to cable bond pads  106 A at a distal end of a second flexible ribbon cable  106 . The third neural probe array  108  has four electrode shanks  108 A extending from bond plate  108 B. Bond pads  108 C supported on plate  108 B are physically and electrically connected to cable bond pads  110 A at a distal end of a third flexible ribbon cable  110 . Finally, the fourth neural probe array  112  has four electrode shanks  112 A extending from bond plate  112 B. Bond pads  112 C supported on plate  112 B are physically and electrically connected to cable bond pads  114 A at a distal end of a fourth flexible ribbon cable  114 . 
         [0046]    Referring back to  FIG. 4 , the probe platform  76  of the neural probe electrode assembly  18  comprises right and left sidewalls  76 A and  76 B extending to distal and proximal sidewalls  76 C and  76 D. The sidewalls  76 A,  76 B,  76 C and  76 D extend to an upper face wall  76 E and a lower face wall  76 F. There are four slots  116 ,  118 ,  120  and  122  extending through the thickness of the platform from the upper face wall  76 E to the lower face wall  76 F thereof. The slots are aligned parallel to each other and to the distal and proximal sidewalls  76 C,  76 D. The four slots extend to, but do not meet the right and left sidewalls  76 A,  76 B. While four slots are shown, that is by way of example. Moreover, the slots need not be parallel to each other. Instead, they can be aligned at an angle other than 180° with respect to each other. 
         [0047]    Slot  116  is exemplary of the other slots. It comprises a proximal slot portion  116 A of a width extending toward the right and left sidewalls  76 A,  76 B that is longer than the width of a distal slot portion  116 B. However the proximal slot portion  116  is of a lesser depth measured along axis A-A intersecting the distal and proximal sidewalls  76 C,  76 D than the depth of distal slot portion  116 B. 
         [0048]    With reference to the exemplary schematic shown in  FIG. 7 ,  FIGS. 8 and 9  are photographs showing rivets connecting the bond pads  100 C on bond plate  100 B of neural electrode probe array  100  to the cable bond pads  102 A at the distal end of ribbon cable  102 . The increased width of the distal slot portion  116 B accommodates these rivet connections when the neural probe array  100  is seated into slot  116 . Moreover, the distal slot portion  116  extends completely through the thickness of the platform, but the proximal slot portion  116 A does not. The steps  84 A,  84 B of bond plate  82  ( FIG. 8 ) register where the proximal and distal slot portions  116 A,  116 B meet inside the platform  76 . In this position, the neural probe array  100  is aligned perpendicular to axis A-A. With the first to fourth neural probes  78 A,  78 B,  78 C and  78 D received in the respective first, second, third and fourth slots  116 ,  118 ,  120  and  122  in platform  76 , the respective neural probe flexible ribbon cables  102 ,  106 ,  110  and  112  lay over the upper pedestal wall  78 E. 
         [0049]    Referring to  FIG. 11 , locating slots (not shown) are provided in the webs  58 ,  60  of the cradle  56 . Spaced apart locating ears  124 A and  124 B are supported on the left and right sidewalls  76 A,  76 B of the pedestal  76 . A cover  126  is mounted on the upper cover wall  78 E to protect the connection between bond plates  100 B,  106 B,  110 B and  114 B and their respective ribbon cables  102 ,  106 ,  110  and  114 . 
         [0050]      FIG. 12  illustrates the neural probe electrode array system  10  at the beginning of a surgical procedure. The flexible ribbon cable  16  has its proximal end  16 A extending through the face wall  46  to physically and electrically connect to electronic circuits in the housing  14 . The distal end of ribbon cable  16  physically and electrically connects to the respective neural probe electrode arrays  100 ,  104 ,  108  and  112 . Prior to implanting the neural probe electrode assembly  18  into brain tissue, the electrode assembly is nested in the cradle  56  between the spaced apart webs  58 ,  60 . The guard bar  62  blocks the neural probe electrode assembly  18  from inadvertently falling out of the cradle  56  while the secondary cover  64  prevents the array from being damaged during shipping and subsequent assembly of the electronics housing  14  to the skull mounting plate  12 . 
         [0051]    As shown in  FIG. 1A , the mounting plate  12  is secured to the skull  150  adjacent to the access opening  202 . That is done using screws  30  and  32  received into the unthreaded openings  24  and  28  of the respective dome-shaped mount body and legs  20 ,  22 . The screws are then threaded into the skull  150 . As previously described, the electronics housing  14  is secured to the skull mounting plate  12  with screws  70  received through oversized openings  70 A in the cover plate  52  and threaded into openings  38  in the yoke arms  36 A,  36 B. 
         [0052]    With the electronics housing  14  fixedly secured to the mounting plate  12 , the neural probe electrode array  18  is ready for implantation into the brain. The secondary cover  64  is removed from the electronics housing  14  by unthreading screws  66  from the housing cover plate  52 . The guard bar  62  is manipulated in a direction to remove the L-shaped end  62 A from recess  58 A in web  58  until the bar is clear of the opening  68  between the webs  58 ,  60 . A pair of tweezers or a similar type tool is used to grab the ribbon cable  16  adjacent to the neural probe electrode assembly  18  and move the cable and electrode assembly out of the cradle  56 . The neural probe electrode assembly  18  is turned upside down to access the back face of a pedestal  76  for the assembly. 
         [0053]      FIG. 1A  is a schematic view of the neural probe electrode array system  10  mounted to a skull  150  adjacent to a craniotomy opening  202  during a surgical procedure. 
         [0054]    An actuatable vacuum insertion tool  128  is maneuvered to grab onto the cove  126  of the platform  76 . The insertion tool  128  is a computer-controlled, microsite machine that provides for accurate and controlled insertion of the neural array  18  into the brain tissue. The motor for the insertion tool  128  is designed for fifty millimeters of movement with step depths as small as 0.5 μm. The insertion speed and acceleration are also adjustable. 
         [0055]      FIG. 14  shows the neural probe electrode assembly  18  as it will appear once insertion into brain tissue is complete. The durotomy and craniotomy are then closed using conventional techniques. Cinching and suturing of skin are performed over the dome-shaped mount body  20  and around the pedestal  34  and underneath gasket  72 . A cable guard  130  is secured to the electronic housing  14  using screws  132  extending through openings  132 A in face wall  46  and threaded into openings  40  in the arms  36 A,  36 B of yoke  36 . 
         [0056]      FIG. 15  illustrates the electronics housing  14 , but with the shipping cover plate  52  removed. That is done by unthreading screws  54  from receptacles in the upper edges of the right, left, front and back sidewalls  42 ,  44 ,  46  and  48 . Four connector assemblies  134 A,  134 B,  134 C and  134 D are shown housed inside the housing  14 . These connector assemblies serve as interfaces from the respective neural probe electrode assemblies  78 A,  78 B,  78 C and  78 D to any one of a number of external devices. Suitable external device include, but are not limited to, a printed circuit board with or without on-board integrated circuits and/or on-chip circuitry for signal conditioning and/or stimulus generation, an Application Specific Integrated Circuit (ASIC), a multiplexer chip, a buffer amplifier, an electronics interface, an implantable rechargeable battery, integrated electronics for either real-time signal processing of the input (recorded) or output (stimulation) signals, integrated electronics for control of a fluidic component, integrated electronics for control of a light source for delivery of light for optogenetic applications, or any other suitable electrical subsystem, or any combination thereof. 
         [0057]    Since there is no longer a need to cradle the electrode assembly  18 , the shipping cover  52  including its cradle  56  is no longer needed.  FIG. 16  shows that the shipping cover  52  is replaced with a top cover  136 . The top cover  136  is used throughout the surgical procedure. 
         [0058]    Upon completion of the surgical procedure, the skull mounting plate  12  can be removed from the skull or left in place, affixed to the skull. The latter might be desirable if it is determined that a different electronics housing  14  including the flexible cable  16  connected to a different neural probe assembly  18  is desired. For example, that could be for the purpose of using a different neural stimulation protocol or a different configuration for the neural probe arrays comprising the neural probe assembly  18 . 
         [0059]      FIGS. 17 to 21  illustrate of an exemplary process for manufacturing the platform  76  for the neural probe assembly  18 . The process begins with an SOI (silicon-on-insulator) wafer  200 , preferably about 500 μm thick. A photo mask (not shown) having interior outlines of the shapes of the respective slots  116 ,  118 ,  120  and  122  and their relative orientation to each other is first provided on the upper and lower surfaces of the wafer  200 . Wafer  200  consists of a first silicon layer  202 , preferably about 100 μm thick, supported on a buried oxide layer  204 . The oxide layer  304  is from about 0.5 to 1 μm thick and is sandwiched between the first layer  202  and a second silicon layer  206 , which is preferably about 400 μm thick ( FIG. 17 ). 
         [0060]      FIG. 18  shows that the first silicon layer  202  has undergone a reactive ion etch (dry etch) to remove portions of the dielectric material, leaving the buried oxide layer  204  exposed between the spaced apart silicon portions  202 A and  202 B. 
         [0061]    In  FIG. 19 , the patterned silicon layer  202  supported on the oxide layer  204  is turned upside down and temporarily supported on a carrier wafer  208 . In  FIG. 20 , the second silicon layer  206  and the oxide layer  204  are subjected to a further reactive ion etch process. This serves to pattern the second silicon layer into sections  206 A,  206 B and the oxide layer into corresponding sections  204 A,  204 B. Relatively thin oxide layers  204 A,  204 B are supported on the first silicon layers  202 A,  202 B. As shown, the outer edges of the respective first silicon layer  202 , oxide layer  204  and second silicon layer  206  are aligned with each other. This defines previously described the right and left sidewalls  76 A,  76 B for the platform. Moreover, the inner edges of the first silicon layer and the oxide layer are aligned, but spaced from the inner edge of the second silicon layer. This serves to define where the steps  84 A,  84 B of the bond pad plate  82  for the exemplary neural probe array  78 A reside in the finished neural assembly  18 . 
         [0062]      FIG. 21  is a cross-sectional view along line  21 - 21  of  FIG. 4  that shows the finished platform section  210  comprising the shaped first silicon layer  202 , oxide layer  204  and second silicon layer  206  after having been released from the carrier  208 . That is done by dissolving the carrier in a suitable solvent. The resulting open area designated  116  is the slot shown in  FIG. 4 . The other slots  118 ,  120  and  122  are manufactured at the same time from the SOI wafer  200 .  FIG. 21  further illustrates the exemplary thin-film neural probe electrode array  78 A in phantom as it would be positioned in slot  116 . 
         [0063]      FIGS. 22 to 26  illustrate an exemplary process for manufacturing another embodiment of a cover for the platform  76  shown in  FIGS. 4 ,  7  and  10 . The process is similar to that described with respect to  FIGS. 17 to 21  for manufacturing the platform  76  and begins with an SOI (silicon-on-insulator) wafer  300 , preferably about 500 μm thick. The wafer  300  consists of a first silicon layer  302 , preferably about 100 μm thick, supported on an oxide layer  304 . The oxide layer  304  is from about 0.5 to 1 μm thick. The oxide layer is sandwiched between the first layer  302  and a second silicon layer  306 , preferably about 400 μm thick ( FIG. 22 ). 
         [0064]      FIG. 23  shows the first silicon layer  302  after having been subjected to a reactive ion etch (dry etch) to remove selected portions thereof. Oxide layer portions  304 A and  304 B are exposed on opposite sides of a central portion  302 . The exposed oxide surfaces  304 A,  304 B extend to respective edges  306 A and  306 B of the second silicon layer  306 . 
         [0065]      FIG. 24  shows that the wafer consisting of the patterned first silicon layer  302  intermediate the oxide layer  304  after having been turned upside down and supported on a carrier wafer  308 . 
         [0066]    In  FIG. 25 , the second silicon layer  306  and the oxide layer  304  are subjected to a further reactive ion etch process. This defines upstanding protrusions  306 A and  306 B supported on oxide layers  304 A and  304 B. These structures serve as sidewalls for the cover. The carrier wafer  308  is released from the first silicon layer  302  to thereby provide the product cover. If desired, the upstanding protrusions  306 A,  306 B and their supporting oxide layers  304 A,  304 B can be eliminated. In that case, a cover similar to that designated as  126  in  FIGS. 7 and 10  is the result. 
         [0067]    Thus, a three-dimensional neural probe electrode array system is provided. The system consists of an electronics housing that can be detachably mounted to a skull mounting plate affixed to a skull adjacent to a craniotomy. A neural probe assembly connected to the housing consists of a platform supporting a plurality of planar neural probe arrays. When a plurality of two-dimensional neural probe arrays are supported in the platform, the result is a three-dimensional configuration of stimulation and recording electrodes that can be configured for a particular application or surgical procedure. The detachable electronics housing means that, if desired, one neural probe assembly can be changed out for another. 
         [0068]    While this invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variations that fall within the broad scope of the appended claims.