BIOLOGICAL-ELECTRODE PROTECTION MODULES, MEDICAL DEVICES AND BIOLOGICAL IMPLANTS, AND THEIR FABRICATION METHODS

Abstract

A biological-electrode protection module is a monolithic component including a capacitor and a voltage-limiting component integrated in a common substrate. The capacitor component is connected in the series path between the input and output terminals. The voltage-limiting component is connected between ground and a node in the series path. The voltage-limiting component has a low breakdown voltage no greater than 6 volts and may be a biphasic device operating in the punch-through mode. Moreover, the protection module is connected to or integrated with a set of biological electrodes at a distance no greater than 1 cm. The capacitor may be a 3D capacitor, and common fabrication processes may be used in forming the voltage-limiting component and the capacitor. A JFET may be integrated in the same substrate so that an electrical signal output from the monolithic protection device is already pre-amplified.

Claims

1. A biological-electrode protection module, comprising: input and output terminals, one of the input and output terminals comprising a set of ports to receive a set of one or more biological electrodes or to receive a set of leads connecting to said biological electrodes, and the other of the input and output terminals being configured to connect to an electrical-biosignal acquisition module; a series path between the input and output terminals; a node on said series path; a capacitor component connected in the series path between the input and output terminals; a voltage-limiting component connected between ground and said node in the series path; and a common substrate in which the voltage-limiting component and capacitor component are formed; wherein the voltage-limiting component has a breakdown voltage equal to or less than 6 volts.

2. The biological-electrode protection module according to claim 1, wherein the voltage-limiting component is a biphasic device.

3. The biological-electrode protection module according to claim 1, further comprising a pre-amplifier component integrated in said substrate.

4. The biological-electrode protection module according to claim 3, wherein the preamplifier component is a junction field effect transistor.

5. The biological-electrode protection module according to claim 1, wherein there is a distance equal to or less than 1 cm between the biological-electrode protection module and the set of biological electrodes.

6. The biological-electrode protection module according to claim 1, wherein the voltage-limiting component comprises an NPN or PNP structure that is configured to operate in a punch-through mode.

7. The biological-electrode protection module according to claim 1, wherein the capacitor component comprises one or more three-dimensional capacitors.

8. The biological-electrode protection module according to claim 7, wherein one or more isolation trenches comprising electrically-insulating material are disposed in the substrate and electrically-isolate the one or more three-dimensional capacitors and the voltage-limiting component.

9. A medical device comprising: a biological-electrode protection module according to claim 1, and said set of biological electrodes.

10. A biological implant comprising a biological-electrode protection module according to claim 1, wherein the voltage-limiting component has a breakdown voltage equal to or less than 3.3 volts.

11. The biological implant according to claim 10, further comprising said set of biological electrodes.

12. A method of fabricating a biological-electrode protection module, comprising: forming a capacitor component and a voltage-limiting component in a common substrate; and forming input and output terminals of the biological-electrode protection module, one of the input and output terminals comprising a set of ports to receive a set of one or more biological electrodes or to receive a set of leads connecting to said biological electrodes, and the other of the input and output terminals being configured to connect to an electrical-biosignal acquisition module; forming the capacitor component in a series path between the input and output terminals; and forming the voltage-limiting component in a path between ground and a node on said series path between the input and output terminals, wherein the voltage-limiting component has a breakdown voltage equal to or less than 6 volts.

13. The fabrication method according to claim 12, further comprising: forming a pre-amplifier component in the substrate; and using common masking and doping steps in forming the voltage-limiting component and pre-amplifier component.

14. The fabrication method according to claim 12, comprising: forming, by a common etching process, relief features in the substrate and forming in the substrate one or more isolation trenches interposed between passive components in the substrate; and providing electrically-insulating material in the one or more isolation trenches, wherein the forming of the capacitor comprises forming one or more three-dimensional capacitor including layers formed conformally over said relief features in the substrate.

15. The fabrication method according to claim 13, wherein: the forming of the voltage-limiting component comprises forming a bipolar structure that operates in punch-through mode; the forming of the pre-amplifier component comprises forming a junction field effect transistor; and a common set of process steps forms the voltage-limiting component, capacitor component and pre-amplifier component in the common substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further features and advantages of the present invention will become apparent from the following description of certain embodiments thereof, given by way of illustration only, not limitation, with reference to the accompanying drawings in which:

[0036] FIGS. 1A to 1E are block diagrams schematically representing known electrical-biosignal acquisition chains, in which:

[0037] FIG. 1A illustrates a first conventional approach using an ASIC,

[0038] FIG. 1B illustrates a variant of the conventional approach using an ASIC,

[0039] FIG. 1C illustrates an approach using an advanced ASIC,

[0040] FIG. 1D illustrates an approach using a SIP, and

[0041] FIG. 1E illustrates an approach using an advanced SIP;

[0042] FIGS. 2A and 2B are block diagrams schematically representing electrical-biosignal acquisition chains employing biological-electrode protection modules according to exemplary embodiments, in which:

[0043] FIG. 2A illustrates a first arrangement in which a monolithic biological-electrode protection module according to an exemplary embodiment is connected to a set of biological electrodes,

[0044] FIG. 2B illustrates a first arrangement in which a biological-electrode protection module according to an exemplary embodiment is integrated with a set of biological electrodes;

[0045] FIG. 3 is a diagram illustrating the structure of a biological-electrode protection module according to a first exemplary embodiment;

[0046] FIG. 4 is a diagram illustrating an equivalent circuit of the biological-electrode protection module of FIG. 3 connected to a downstream ASIC;

[0047] FIG. 5 is an enlarged representation of the biological-electrode protection module of FIG. 3;

[0048] FIG. 6 is a diagram illustrating the structure of a biological-electrode protection module according to a second exemplary embodiment;

[0049] FIG. 7 is a diagram illustrating the structure of a biological-electrode protection module according to a third exemplary embodiment;

[0050] FIGS. 8A to 8H are a series of views to illustrate stages in an example method of manufacturing the module of FIG. 7; and

[0051] FIG. 9 is a flow diagram of the manufacturing method of FIGS. 8A-8H.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0052] Exemplary embodiments of the present disclosure provide biological-electrode protection modules to provide electrical protection during electrical sensing and/or electrical stimulation practiced on the human or animal body. Principles of the present invention will become clear from the following description of certain example embodiments. The example embodiments describe functionality occurring during electrical sensing but the skilled person will readily understand that biological-electrode protection modules embodying the invention may also be applied in electrical stimulation systems or in systems which implement both biological sensing and stimulation.

[0053] FIGS. 2A and 2B illustrates the approach taken in the present invention, which is to provide a monolithic protection module that incorporates a capacitance component and a low-breakdown-voltage voltage-limiting component formed in a common substrate. The resultant protection module is compact. The surface area of a protection module according to the exemplary embodiment can be around 60 mm.sup.2 and the thickness of the protection module 20 can be very low (e.g. 150 μm).

[0054] As can be seen from FIGS. 2A and 2B, the protection module 20/30 according to the exemplary embodiment is connected between biological electrodes and an electrical-biosignal acquisition module 4 (which may comprise amplifiers, filters and sampling components as appropriate to the specific medical application). Thus, it is clear that the protection module 20/30 has input and output terminals, one of the input and output terminals comprising a set of ports (not shown) to receive the set of one or more biological electrodes or to receive a set of leads connecting to the biological electrodes, and the other of the input and output terminals is configured to connect to the electrical-biosignal acquisition module 4.

[0055] Accordingly, as illustrated in FIG. 2A, the protection module can be a discrete component 20 that can be positioned very close to the biological electrodes 1, notably less than 1 cm away. Indeed, typically, the biological-electrode protection module according to the exemplary embodiment can be positioned so close to the electrodes that the length of the connection wire between a given electrode and a terminal of the protection module can be less than 1 mm. Alternatively, as illustrated in FIG. 2B, the compact protection device can be implemented as a medical device, e.g. composite device 20a, which integrates the protection module with the electrodes (for example, the biological electrodes are formed directly on top of the die). The heavy border illustrated in FIG. 2B indicates schematically a housing for the biological-electrode protection module. In certain embodiments, the housing is made of biocompatible material, e.g. parylene or similar polymers or ceramics, notably so that the module is well-suited to being implanted.

[0056] Furthermore, in some embodiments the protection module 30/30a has a pre-amplifier component integrated into the same substrate as the capacitor component and low-breakdown-voltage voltage-limiting component. In such embodiments, an advantage of implementing direct amplification close to the sensing electrode is that the electrical signal output from the protection module 30/30a towards the rest of the signal acquisition electronics 4 has a level which provides better immunity against noise/unwanted parasitic signals. Accordingly, conventional off-the-shelf amplifiers and samplers can be used in the downstream portion of the signal acquisition chain. So, compared to the configurations illustrated in FIGS. 1A to 1E, the specialized amplifier and filter components in module 3 can be omitted.

[0057] The structure of a first embodiment of a discrete biological-electrode protection module 20 according to the exemplary embodiment is illustrated in a simplified manner in FIG. 3.

[0058] The biological-electrode protection module (20) of this embodiment comprises a capacitor component (22) and a voltage-limiting component (24) integrated in a common substrate (25). Input and output terminals (28) are also provided for interconnection of the biological-electrode protection module 20 to the set of electrodes 1 and to the downstream signal acquisition electronics 4.

[0059] FIG. 4 is a diagram illustrating an equivalent circuit to the configuration illustrated in FIG. 3.

[0060] As illustrated in FIG. 3, only a single voltage-limiting component 24 and capacitor component 22 can be seen in the biological-electrode protection module 20, but it is to be understood that multiple components may be provided depending on the application (and, in particular, depending on the connections that are to be made to the set of biological electrodes).

[0061] As can be seen from FIGS. 3 and 4, there is a series path between the input and output terminals of the protection module 20 and the capacitor component 22 is connected in the series path between the input and output terminals. Further, as can be seen from FIGS. 3 and 4, the voltage-limiting component 24 is connected between ground and a node N in the series path.

[0062] The number of input/output terminals of the biological-electrode protection module 20 depends on the application and, in particular, on the number of biological electrodes, whether they are operated for sensing or for stimulation or for both (e.g. with individual channels implementing sensing or stimulation in a time-division manner, or with sensing and stimulation performed simultaneously via different channels). In general, the protection module 20 is customized to the specific set of electrodes 1.

[0063] The capacitor component 22 used in the biological-electrode protection module 20 is advantageously implemented as a high-density capacitive element. In the example illustrated in FIG. 3, the capacitor component is implemented as a three-dimensional capacitor, notably a capacitor having electrode and dielectric layers formed conformally over relief features in the substrate 25. In the illustrated example the 3D capacitor 24 is formed in wells in the substrate 25, but other 3D capacitor structures may be used, for example the electrode and dielectric layers may be formed conformally over pillars/columns in the substrate. Use of 3D capacitors allows a relatively high capacitance value to be achieved in a small space. The high-density capacitors function as DC-blocking elements to prevent any continuous polarization being applied to the patient's body.

[0064] The voltage-limiting component 24 used in the biological-electrode protection module 20 is a low-breakdown-voltage voltage-limiting component, notably having a breakdown voltage equal to or less than 6 volts. In the example illustrated in FIG. 3, the voltage-limiting component 24 is implemented by exploiting an NPN or PNP transistor-type structure, employed here for its ability to block voltage pulses of both polarities (i.e. equating to a pair of back-to-back diodes which operate in a punch-through mode).

[0065] An advantage of implementing the voltage-limiting component 24 as an integrated component having an NPN or PNP structure is the ability to achieve a low voltage voltage-limiter using the punch through mode. This specific voltage-limiting structure has a low breakdown voltage (<3.6V) and can handle large surge current (biphasic pulses), making it particularly well adapted for use in a biological electrode protection module. Moreover, the technology and manufacturing processes needed to implement the PNP or NPN structure is compatible with the technology and manufacturing processes needed to implement the capacitor component, especially in the case of fabricating the capacitor component as one or more integrated 3D capacitors.

[0066] The voltage-limiting component 24 may be fabricated to have a particularly low breakdown voltage, e.g. equal to or less than 3.3 volts, so as to make the overall module 20 suitable for use as an implantable device. Voltage-limiting components having still lower breakdown voltages (e.g. equal to or less than 2.2 volts; equal to or less than 1.8 volts; etc.) may also be employed, depending upon the application in which the biological electrodes are used, i.e. in a pacemaker, in neurostimulation, etc. As the operating voltage is reduced the power consumption reduces and this, in turn, may extend the useful life of the product.

[0067] In the example illustrated in FIG. 3 deep isolation trenches 26 are provided in the substrate 25 extending substantially all the way through the substrate 25. These isolation trenches function to electrically isolate from one another the active and passive components that are integrated into the common substrate 25. Various techniques may be used to form and fill the isolation trenches. The Applicant's earlier patent application EP 18 306 164.7 describes certain isolation trenches and methods to manufacture the trenches. The properties and fabrication steps described in that application can be applied in the present embodiment, and the teaching of that document is incorporated herein by reference. Using the isolation structure proposed in application EP 18 306 164.7 makes it possible to provide high isolation between each channel, which may allow stimulation and sensing to be performed in the same operating phase.

[0068] In view of the description in the present document of the structure and function of biological-electrode protection modules embodying the invention and, in particular, the disclosure of which components and component technologies can be integrated together in a common substrate, the skilled person will readily understand how to construct biological-electrode protection modules embodying the principles described herein. Accordingly, the components will not be further described individually in detail.

[0069] It is noted that the exemplary embodiments are not particularly limited having regard to the choice of materials and layer thicknesses in the components illustrated in FIG. 3 and the skilled reader will readily understand that these parameters may be varied while still constructing an integrated device according to the present disclosure. Purely for the purposes of illustration, some example materials and values are provided below in relation to the enlarged view illustrated in FIG. 5. In the example illustrated in FIG. 5, the substrate 25 is a SOI (silicon on insulator) substrate provided on a multi-layer base consisting of an oxide layer 42 for example silicon oxide (SiO.sub.2). The substrate 25 has a high resistivity, typically >>4 Ohms.Math.cm, more particularity >100 Ohms.Math.cm even more particularity between 1K to 3K Ohm.Math.cm), achieved by doping to a corresponding doping concentration, e.g. of 10e14 atoms/cm.sup.3 (that is, 10.sup.14 atoms/cm.sup.3). A doped region 46 is provided in the substrate 25, and an epitaxial layer 50 is formed above the doped region 46 in the zone where the capacitor component is provided. The thickness of the epitaxial layer 50 is typically of the order of 500 nm to 2 μm. In the capacitor component 22 illustrated in FIG. 5, a dielectric layer 51 is formed conformally over wells in the doped region 50 and the substrate 25. As an example, the dielectric layer may advantageously be formed of a material having a relatively high dielectric constant such as silicon nitride, alumina (Al.sub.2O.sub.3), hafnium oxide, etc., and plural layers may be overlain to form the dielectric layer of the capacitor component. The remaining space in the wells is then filled with a conductive material 52 to serve as the capacitor top electrode. The conductive material may, for example, be formed of doped polysilicon, TiN, TaN, NiB, Ru, etc. Terminals 54 made of a conductive material are provided connected to the capacitor electrodes. The conductive material used for the terminals may be, for example, a metal such as Al, Cu, Ag, combined or not with barrier metals such as, for example, TiN or TaN, or made of other metals or alloys, a multi-layer structure containing plural metals and/or alloys, etc.

[0070] In the example illustrated in FIG. 5, the voltage-limiting component 24 is a punch-through bipolar structure that comprises an n-type region 50 having relatively low doping (typically in the range 10.sup.13 atoms/cm.sup.3 to 10.sup.15 atoms/cm.sup.3), a p-type region 61, i.e. a region of opposite polarity from the region 50, typically having a doping level in the range 10.sup.14 atoms/cm.sup.3 to 10.sup.16 atoms/cm.sup.3, and an n-type region 62 of the same polarity as the region 50 but considerably more heavily doped (typically in the range 10.sup.16 atoms/cm.sup.3 to 10.sup.20 atoms/cm.sup.3). This structure provides back-to-back NP and PN junctions. However, the exemplary embodiments of the present invention are not limited to that case; the polarity of each of the regions 50, 61 and 62 can be inverted so that the structure comprises back-to-back NP and PN junctions. Typically, the region 62 has a thickness in the range from 30 to 300 nm, and the layer 61 has a thickness in the range of 30 nm to 100 nm. A via filled with conductive material 64 provides a connection to one end of the voltage-limiting component and a conductive layer 56 provides a connection to the other end of the voltage-limiting component.

[0071] In the example illustrated in FIG. 5, the 3D capacitor 22 is formed in wells of a depth set in the range from about 50 μm to about 100 μm. Typically, the critical dimension of the well mouth (i.e. the diameter for a well of circular cross-section, or the narrow dimension for a well having an elongated cross-section) is of the order of 1 μm. Typically, the thickness of the dielectric layer is between 1 nm to 100 nm more specifically between 5 and 40 nm.

[0072] The skilled person will understand that the material, doping levels, thicknesses, etc. quoted above in regard to the example of FIG. 5 are purely illustrative and are not limitative of the present embodiment.

[0073] FIG. 6 illustrates a second exemplary embodiment of biological-electrode protection device 30. This embodiment incorporates a pre-amplifier 32 integrated into the same substrate as the voltage-limiting component and capacitor component. As mentioned above, when using biological-electrode protection modules 30 of this type, that include a pre-amplifier 32, conventional devices for amplification and sampling can be used in the signal acquisition stream downstream, it is not necessary to use advanced amplifiers or special filtering.

[0074] In the example illustrated in FIG. 6 the pre-amplifier is implemented as a JFET. This presents a number of advantages, notably in terms of simplifying the process required to fabricate the overall product. In particular, because of overlap in technologies: [0075] Common process steps can be used to form the JFET and to form the low voltage voltage-limiting component, [0076] Common process steps can be used to form the deep isolation trenches and the 3D capacitor structures, and [0077] Common process steps can be used to deposit a layer to form the dielectric layer of the capacitor and a layer in the JFET device (to form a MOSFET).

[0078] These overlaps in technology keep the fabrication process simple and fast, and may allow the use of just only 2 levels of interconnections.

[0079] In the embodiments illustrated in FIGS. 3-6 the substrate is a Sol substrate, but the exemplary embodiments of the present invention are not limited to use of such a substrate. In a similar way, in the example illustrated in FIGS. 3-6 the wells containing the layers of the 3D capacitor are shallower than the wells containing the deep trench isolation, but the invention is not limited to this configuration.

[0080] FIG. 7 illustrates a third exemplary embodiment of biological-electrode protection module. In the embodiment illustrated in FIG. 7, similarly to the second embodiment, a preamplifier component PA implemented as a JFET is provided as well as a voltage-limiting component VL in the form of an NPN structure, and a 3D capacitor C. Deep isolation trenches DI are also included in the architecture. However, in this embodiment the deep isolation trenches and the 3D capacitor wells all extend through the entire thickness of the substrate. Moreover, the substrate is a simple doped silicon substrate 75 rather than a Sol substrate, and a backside oxide layer 102 is provided on the rear of the substrate 75.

[0081] The skilled person will readily appreciate the process steps that may be used to fabricate a biological-electrode protection module having the voltage-limiting component, capacitor and, optionally, pre-amplifier components discussed above. Nevertheless, for the purposes of illustration, not limitation, a typical process flow for manufacturing the module illustrated in FIG. 7 will be described below with reference to FIGS. 8A-8H and FIG. 9.

[0082] In a first step S901 antimony is implanted into a P-type Si substrate having a resistivity of 1 kOhm.Math.cm, to form a layer 80 which will constitute a bottom gate of the JFET constituting the preamplifier, as illustrated in FIG. 8A.

[0083] Next, in a step S902, an epitaxial layer 85 is formed on the layer 80, as shown in FIG. 8B. This layer 85 is doped with As.

[0084] Next, boron is implanted into regions 87 and 97 which will form, respectively, the drain/source of the JFET and the base of the NPN structure, as shown in FIG. 8C.

[0085] Next, in a doping process S904, As is implanted into regions 88 and 98 which will form, respectively, the upper gate of the JFET and the emitter of the NPN structure, and P or B is implanted into regions 89 and 99 which will form contacts, as shown in FIG. 8D.

[0086] A common patterning and etching process S905 forms relatively broad wells 100a for use in creating the deep isolation trenches and somewhat narrower wells 100b for use in forming the 3D capacitor, as shown in FIG. 8E.

[0087] A common deposition process S906 deposits a dielectric layer 104 along the walls of the openings 100a and 100b, as illustrated in FIG. 8F. Then, a common deposition process S907 deposits a conductive material into the openings 100a and 100b to constitute filling 106 for the isolation trenches and a top electrode 107 for the 3D capacitor, as illustrated in FIG. 8G.

[0088] Next, in a stage S908 an insulator layer 110 is deposited on the top of the structure, patterning and deposition processes are implemented to form contacts 112-126 at the top of the module, and a backside oxide layer 102 is formed at the rear of the substrate 75, as illustrated in FIG. 8H. The contact 112 connects to the collector of the voltage-limiting NPN structure. The contact 114 connects to the emitter of the voltage-limiting NPN structure. The contact 116 connects to the base of the voltage-limiting NPN structure. The contact 118 connects to bottom gate of the JFET. The contact 120 connects to the source of the JFET. The contact 122 connects to the upper base of the JFET. The contact 124 connects to the drain of the JFET. The contact 126 connects to the top electrode of the 3D capacitor. The bottom electrode of the capacitor is not shown in the figures and may be implemented in different manners, as known by the skilled person, depending on whether it is desired to make contact to the capacitor top and bottom electrodes at the same side of the substrate (e.g. at the top) or at opposite sides of the substrate.

[0089] It will be understood that the above description is merely illustrative and numerous aspects of the manufacturing process may be varied. However, the above description is given to illustrate the fact that, when manufacturing a module of the types illustrated in FIGS. 6 and 7, which combine a preamplifier implemented as a JFET, a voltage-limiting component implemented using an NPN structure (or PNP structure) and a capacitor which is implemented as a 3D capacitor, common processes may be used to form aspects of more than one of the voltage-limiting component, pre-amplifier and 3D capacitor.

[0090] As mentioned above, because the protection modules according to exemplary embodiments of the invention are particularly compact, they can be laid down on the biological electrodes, or even integrated with the biological electrodes, for example by forming the biological electrodes on the top of the die. Thus, it is feasible to construct implantable devices incorporating biological-electrode protection modules according to certain embodiments of the invention.

[0091] Exemplary embodiments of the present invention can provide one or more of the following advantages: [0092] the same Si die can carry high-value capacitors, voltage-limiting structure specifically adapted to handle biphasic pulses and operating in the punch through mode (for low voltage) and thereby avoid the use of oversized active parts; [0093] because of overlap in technologies used to implement the components, common processes can be shared and used in forming the voltage-limiting component, capacitor component, isolation trenches and pre-amplifier, thus rendering manufacture of the biological-electrode protection module simpler and cheaper; [0094] the biological-electrode protection module has a high level of integration, producing a compact device capable of being laid down on the biological electrodes; [0095] the biological-electrode protection module can be customized to connect to multiple sensing/stimulation channels, enabling it to be used with a micro-electrode array [0096] in some embodiments, a bipolar transistor structure (implementing the voltage-limiting component), JFET transistor, deep isolation trenches, and deep-trench capacitors can be integrated in a common substrate (e.g. SOI) to produce a particularly compact structure [0097] the biological-electrode protection module is compatible with voltage-drive and current-drive architectures [0098] parasitics are reduced [0099] direct signal sampling is enabled (no need to shield, to filter, or use a differential approach in the signal acquisition chain downstream of the protection module) [0100] component matching between channels can be below 0.1%, providing high CMRR (>70 dB).

[0101] Although the exemplary embodiment of the present invention have been described above with reference to certain specific embodiments, it will be understood that the invention is not limited by the particularities of the specific embodiments. Numerous variations, modifications and developments may be made in the above-described embodiments within the scope of the appended claims.