The present invention relates to the field of biological sensing/stimulation electronics. More particularly, the invention relates to biological-electrode protection modules and to methods of fabricating such modules, as well as to medical devices and biological implants incorporating such modules.
Various technologies have been developed to sense electrical biosignals in living beings. Thus, for example, various devices have been developed to measure electrical biosignals such as EECs (electroencephalograms), EMGs (electromyograms), ECGs (electrocardiograms), etc. Moreover, various devices have been developed to apply electrical signals to various body parts, for instance to perform deep brain stimulation, to stimulate cells in the spinal cord as a clinical therapy, etc. In general, biological electrodes are applied to the body so to enable the sensing/stimulation to be performed. In some applications it is desirable to be able to implant one or more biological electrodes within the body.
Typically, very small electrical signals (mV or μV) are measured using biological electrodes, and the measurement channel has high impedance (100 KOhms, or even MOhms). Accordingly, the electrical signals output by biological electrodes tend to be extremely sensitive to interference and can easily be degraded by noise. The design of the signal acquisition electronics can have an impact on the accuracy with which the electrical biosignal can be measured.
The electrical signals from biological electrodes are generally handled using a small acquisition chain containing the following elements:
electrode->protection module->instrumentation amplifier (preamplifier)->filtering module->amplifiers->sampling module->software analysis module
Various known electrical biosignal acquisition chains are illustrated in
Biological electrodes come in various sizes and shapes and are made from various materials. These electrodes are internal to the body (i.e. in contact with tissues, organs, cell systems, etc.) or external to the body (notably in contact with the skin). The electrodes 1 are made of biocompatible material. The characteristics of the electrodes are highly significant to the design of the acquisition chain. The electrical characteristic of interest (e.g. representing the sensed parameter, or the target characteristic of the stimulation signal) may be current, voltage, frequency and/or a specific waveform. The biological electrodes 1 are often provided as a set of electrodes on a cable or braid.
The electronics modules on the circuit board 10 include a protection module 1, a combined pre-amplifier and filtering module 2, and an ASIC (Application Specific Integrated Circuit) 5 combining components 4 for further amplification, filtering and sampling.
The protection module 2 contains discrete passive components, such as resistors, capacitors (nF range) and diodes. These elements are combined to form analogue filtering functions or security functions, for instance diodes are used as over-stress voltage suppressors to protect sensitive electronics from external unwanted electrical surges such as may arise in the case where the patient undergoes an MRI or is being operated on using an electrosurgical device. Capacitors are used as a DC blocking component to prevent any continuous voltage being applied to the body.
In the configuration illustrated in
In configurations such as those of
Furthermore, typically the ASIC has to perform impedance conversion between a high-impedance environment on the side of the biological electrodes and a low-impedance environment on the side of the software analysis module. This induces some limitations in terms of signal treatment, and signal acquisition will not be optimum. Therefore, the size and the power consumption of the ASIC increases, as well as the price.
Other proposals have been made to employ a SIP (System-in-Package) in the acquisition chain of biological electrical signals, in which various dies are assembled together in a common package.
A disadvantage of the SIP configurations, in addition to the fact that they tend to be expensive, is that manufacture of the SIP generally requires assembling together components that have been manufactured according to different technologies. This means that a large number of manufacturing steps are involved in producing the overall SIP. Moreover, as each technology type has its own failure modes, the concatenation of different technologies results in a large number of potential sources of failure. Furthermore, additional potential sources of failure result from the interconnections that must be made between the various SIP components.
In view of the above-noted problems, an exemplary embodiment of a biological-electrode protection module is provided that includes 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 (22) 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; a common substrate (25) in which the voltage-limiting component (24) and capacitor component are formed; wherein the voltage-limiting component has a breakdown voltage equal to or less than 6 volts.
By integrating the capacitor component and the low-breakdown-voltage voltage-limiting component in a common substrate, the protection device can be compact and thus it becomes easier to locate the protection module close to the biological electrodes, e.g. at a distance of 1 cm or less, or even to integrate the protection module with the biological electrodes as a kind of biological interface. In contrast to configurations that use ASIC technology, this platform is cost-effective and not area consuming.
In the present description, the breakdown voltage may be a reversible breakdown voltage.
In the biological-electrode protection module the voltage-limiting component may be a biphasic device. In this way, the voltage-limiting component provides protection irrespective of the polarity of a voltage surge that may occur in the patient's body.
In some embodiments of biological-electrode protection modules disclosed herein, a pre-amplifier component is integrated into the same substrate as the capacitor component and the voltage-limiting component. Accordingly, the electrical signal output by the module has a larger amplitude and is less susceptible to degradation by noise/interference. This makes it possible to dispense with the need for advanced amplification and filtering components in the downstream part of the signal acquisition chain.
Such a preamplifier component may be implemented as a junction field effect transistor in the same substrate as the capacitor component and voltage-limiting component. The voltage-limiting component may be designed to operate in a punch-through mode (e.g. by being configured as a preferentially vertical bipolar structure of either type PNP or NPN).
The capacitor component may be a three-dimensional capacitor (i.e. a capacitor in which the electrodes and dielectric are contoured, for example by being formed conformally in wells in the substrate or conformally over columns/pillars in the substrate). This enables common technologies and process steps to be used during fabrication of the capacitor component, voltage-limiting component and pre-amplifier, reducing the cost of manufacture and reducing potential failure modes of the finished product.
The capacitor component may comprise plural individual capacitors that are electrically isolated from one another, for example, one capacitor for each biological electrode to which the protection module is to be connected bearing in mind that each biological electrode may correspond to a separate sensing and/or stimulation channel.
There may be isolation trenches, filled with electrically-insulating material, provided in the substrate to electrically isolate from each other the various electrical components formed in the substrate. In some embodiments the isolation trenches may be deep trenches (e.g. extending through substantially the whole thickness of the substrate) and may be formed in a common process with relief features (wells or columns/pillars) over which capacitor layers are to be formed. Moreover, an integrated biological-electrode protection module is disclosed herein that incorporates such isolation trenches, provides excellent isolation between the sensing/stimulation channels. Moreover, in the case where the protection module incorporates a pre-amplifier component as well as the capacitor and voltage-limiting components, there can be superior rejection between adjacent channels in the cable interconnecting the protection module to the rest of the signal acquisition electronics. These two effects may make it possible to increase the overall number of channels included in the sensing/stimulation system and/or may allow the use of sensing and stimulation signals in very closely-spaced channels.
In another exemplary embodiment, a medical device is provided that includes a biological-electrode protection module as disclosed in the present document, and a set of biological electrodes.
In another exemplary embodiment a biological implant is provided that includes a biological-electrode protection module as disclosed in the present document, wherein the voltage-limiting component has a breakdown voltage equal to or less than 3.3 volts.
A biological implant incorporating a biological-electrode protection module according to the present disclosure can have a small size and yet provide sufficient protection to the body in which the device is implanted, especially in the case where the capacitor component is implemented as one or more three-dimensional capacitors (which can provide a large capacitance value in a small space). Moreover, by incorporating a voltage-limiting component having a low breakdown voltage, an adequate degree of protection can be assured for electronics modules connected to the implant.
In yet another exemplary embodiment, a method is provided of fabricating a biological-electrode protection module, with the method including 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; wherein the capacitor component is formed in a series path between the input and output terminals; wherein the voltage-limiting component is formed in a path between ground and a node on said series path between the input and output terminals; and wherein the voltage-limiting component has a breakdown voltage equal to or less than 6 volts.
The fabrication method may include forming a pre-amplifier component in the substrate and common masking and doping steps may be used during the formation of the voltage-limiting component and the pre-amplifier component.
In the above-mentioned method a common process, such as an etching process, may form relief features (e.g. wells/holes/trenches or pillars/columns) in the substrate and may form one or more isolation trenches in the substrate to isolate the voltage-limiting and capacitor components (and pre-amplifier, if present) in the substrate from one another. The method may then further include providing electrically-insulating material in the isolation trench (es).
In the above-described fabrication method the forming of the voltage-limiting component may comprise forming a bipolar structure (preferably NPN) to create a voltage-limiting component that operates in punch-through mode, and the forming of the pre-amplifier component may comprises forming a junction field effect transistor. In this case a common set of process steps may be used in the formation of the voltage-limiting component, capacitor component and pre-amplifier component in the common substrate, avoiding the need for specific assembly steps to bring the components together. This reduces the potential failure modes of the finished module, leading to improved manufacturing yield.
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:
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.
As can be seen from
Accordingly, as illustrated in
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
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
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.
As illustrated in
As can be seen from
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.
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
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
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.
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.
In the example illustrated in
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.
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
In the example illustrated in
In the example illustrated in
The skilled person will understand that the material, doping levels, thicknesses, etc. quoted above in regard to the example of
In the example illustrated in
These overlaps in technology keep the fabrication process simple and fast, and may allow the use of just only 2 levels of interconnections.
In the embodiments illustrated in
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
In a first step S901 antimony is implanted into a P-type Si substrate having a resistivity of 1 kOhm·cm, to form a layer 80 which will constitute a bottom gate of the JFET constituting the preamplifier, as illustrated in
Next, in a step S902, an epitaxial layer 85 is formed on the layer 80, as shown in
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
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
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
A common deposition process S906 deposits a dielectric layer 104 along the walls of the openings 100a and 100b, as illustrated in
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
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
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.
Exemplary embodiments of the present invention can provide one or more of the following advantages:
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.
Number | Date | Country | Kind |
---|---|---|---|
20305073.7 | Jan 2020 | EP | regional |
This application is a continuation of PCT Application No. PCT/IB2021/050655, filed Jan. 28, 2021, which claims priority to European Patent Application No. 20305073.7, filed Jan. 28, 2020, the entire contents of each of which are hereby incorporated in their entirety.
Number | Date | Country | |
---|---|---|---|
Parent | PCT/IB2021/050655 | Jan 2021 | US |
Child | 17874668 | US |