Implantable deep brain broadband neural information detection electrode and preparation method thereof

Abstract

The invention discloses an implantable deep brain broadband neural information detection electrode and a preparation method thereof, and belongs to the field of biosensors and micromachining. The electrode comprises a microwave resonance magnetoelectric sensing assembly, a nerve electrophysiology recording site and a reference electrode, and a substrate adopts an SOI silicon wafer and is integrated through an MEMS technology. The microwave resonance magnetoelectric sensing assembly is composed of a FeGaB magnetostriction layer and an AlN piezoelectric layer, the resonance frequency is 0.2 GHz, and the microwave resonance magnetoelectric sensing assembly is used for detecting a megahertz-level high-frequency neural signal. The neural electrophysiology recording site and the reference electrode form a differential detection sensor, and the differential detection sensor covers the frequency band of 0.1 Hz to 10 kHz. By optimizing the material and structural design, the broadband, high sensitivity and long-term biocompatibility are realized. The preparation method is based on photoetching, sputtering and plasma etching processes, and is suitable for deep brain high-density implantation application.

Description

Technical Field

[0001] The present invention belongs to the field of biosensor design and micro-processing, and in particular relates to an implantable deep-brain broadband neural information detection electrode and a preparation method thereof. Background Art

[0002] Currently, the acquisition of neural signals within the brain is primarily limited to low-frequency signals within the kilohertz range, such as electroencephalogram (EEG) signals, field potentials, and action potentials. However, the discharge activity of nerve cells generates high-frequency electromagnetic fields in the microwave and even terahertz bands within their microenvironment. Due to the filtering effects of the skull and scalp, high-frequency neural signals cannot be collected using non-invasive devices. The demand for higher-frequency detection has driven the development of implantable neural detection electrodes.

[0003] The current mainstream method for neural signal detection is based on the capacitive coupling effect and can be used to collect low-frequency local field potentials and kilohertz action potentials. However, its sensitivity and signal conversion efficiency are insufficient at higher frequencies, making it difficult to effectively capture weaker microwave signals. Using antennas with specially sized structures can specifically detect signals in the microwave frequency range and is a technological direction for broadening the frequency range of neural information detection.

[0004] The shortcomings of the prior art are as follows:

[0005] (1) Limited high-frequency signal detection capabilities: Existing technologies mainly target low-frequency neural signals and cannot effectively detect high-frequency neural signals in the megahertz range.

[0006] (2) Size limitation: Traditional microwave antennas are large in size and difficult to integrate into micron-scale implantable neural electrodes.

[0007] (3) Insufficient signal conversion efficiency: The existing methods have low signal acquisition efficiency in the high-frequency band, making it difficult to stably obtain weak neural signals. Summary of the Invention

[0008] In order to solve the technical problems in the background technology, the present invention proposes an implantable deep-brain broadband neural information detection electrode and a preparation method thereof.

[0009] The technical solution of the present invention is as follows:

[0010] An implantable deep-brain broadband neural information detection electrode comprising:

[0011] The substrate is formed by back-etching silicon on insulator with a thickness of 25 μm and a 1200 nm Si3N4 insulating layer deposited on the surface;

[0012] A microwave resonant magnetoelectric sensing component is provided on a substrate and includes a magnetostrictive layer, a piezoelectric layer, a top electrode layer and a bottom electrode layer;

[0013] The magnetostrictive layer is made of FeGaB material with a thickness of 1 μm and is used to sense high-frequency magnetic fields;

[0014] The piezoelectric layer is made of AlN material with a thickness of 1 μm and converts mechanical strain into electrical signals;

[0015] The top electrode layer and the bottom electrode layer are made of Mo material with a thickness of 200 nm, forming a resonant cavity with a resonant frequency of 0.2 GHz;

[0016] The neuroelectrophysiological recording site is a circular Pt electrode with a diameter of 12 μm, which forms a differential detection sensor with the reference electrode to collect low-frequency field potential and kilohertz action potential signals;

[0017] The reference electrode is a Pt rectangular electrode with a size of 500 μm × 14 μm;

[0018] Leads, 4 μm wide, connect components to signal interfaces;

[0019] The insulating layer covers the leads and substrate, and is made of Si3N4 with a thickness of 2200 nm.

[0020] In the above technical solution, the resonant cavity of the microwave resonant magnetoelectric sensor component is formed by releasing the sacrificial layer SiO2 through HF vapor etching.

[0021] In the above technical solution, the sampling rate of the neuroelectrophysiological recording site is 30 kHz, covering the frequency band of 0.1 Hz to 10 kHz.

[0022] In the above technical solution, the longitudinal strain of the piezoelectric layer is generated by the high-frequency vibration of the magnetostrictive layer, and the resonant frequency range is 0.1-0.5 GHz.

[0023] In the above technical solution, the surface of the lead is covered with a Si3N4 insulating layer with a thickness of 2200 nm to shield external electromagnetic interference.

[0024] In the above technical solution, the Si3N4 layer of the substrate is processed by chemical mechanical polishing, and the surface roughness is ≤10nm.

[0025] In the above technical solution, the FeGaB material of the magnetostrictive layer is deposited by a sputtering process, with a thickness error of ±50 nm.

[0026] A method for preparing an implantable deep-brain broadband neural information detection electrode comprises the following steps:

[0027] a) The SOI wafer surface is cleaned, a 1 μm SiO2 sacrificial layer is deposited, and a cavity pattern is formed by photolithography.

[0028] b) Plasma chemical vapor deposition of a 1200 nm Si3N4 layer and polishing;

[0029] c) sequentially sputtering a Mo bottom electrode layer, an AlN piezoelectric layer, and a Mo top electrode layer;

[0030] d) Photolithography and sputtering of Pt to form neural electrophysiological recording sites, reference electrodes, and leads;

[0031] e) Deposit a 2200 nm Si3N4 insulating layer and selectively etch the electrodes using CF4 RIE;

[0032] f) Sputtering the FeGaB magnetostrictive layer and releasing the sacrificial SiO2 layer to form a resonant cavity.

[0033] In the above technical solution, concentrated sulfuric acid is used to treat the SOI surface to remove chemical impurities.

[0034] In the above technical solution, the HF vapor etching time is 60 seconds, and the cavity size accuracy is ±0.5 μm.

[0035] Beneficial effects:

[0036] (1) Broaden the detection frequency band: Compared with traditional capacitive coupling electrodes, the present invention can achieve wide-band neural signal acquisition from low frequency (<10 Hz) to megahertz (>1 MHz).

[0037] (2) Improve detection sensitivity: Through the design of a mechanically resonant magnetoelectric antenna, the ability to capture high-frequency neural signals is enhanced, thereby improving detection accuracy.

[0038] (3) High-integration design: Based on MEMS technology, high-density integration of micron-scale electrode arrays is achieved, which is suitable for deep brain implant applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of an implantable deep-brain broadband neural information detection electrode.

[0040] Figure 2 This is a cross-sectional view of an implantable deep-brain broadband neural information detection electrode.

[0041] Figure 3 It is a preparation process flow chart.

[0042] Among them, 1 is the microwave resonant magnetoelectric sensing component, 2 is the neuroelectrophysiological recording site, 3 is the reference electrode, 4 is the lead, 5 is the substrate, 6 is the insulating layer, 7 is the magnetostrictive layer, 8 is the piezoelectric layer, 9 is the top electrode layer, and 10 is the bottom electrode layer. DETAILED DESCRIPTION

[0043] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are intended only to explain the present invention, and the scope of protection of the present invention should include the entire contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement the entire contents of the claims of the present invention.

[0044] Example

[0045] Figure 1 This is a schematic diagram of the implantable deep-brain broadband neural information detection electrode, showing the electrode's overall shape and the planar layout of its internal sensing layer structure. It primarily comprises: a microwave resonant magnetoelectric sensor assembly 1, a neuroelectrophysiological recording site 2, a reference electrode 3, and a lead 4. The electrode has an overall width of 80 μm, and the microwave resonant magnetoelectric sensor structure measures 12 μm x 6 μm horizontally, sensing microwave signals. The neuroelectrophysiological recording site is circular with a diameter of 12 μm, similar to the size of a neuron. The reference electrode 3 is a rectangular electrode extending along the probe's axis, measuring 500 μm x 14 μm. Its larger size allows it to measure the average potential near that region, providing a reference potential for the neural electrical signals collected by the electrophysiological recording site 2. The neuroelectrophysiological recording site 2 and the reference electrode 3 form a differential detection sensor for neuroelectrophysiological signals, sampling at a 30 kHz rate. Its high-frequency components are kilohertz neuronal action potential signals, while its low-frequency components are local field potential signals. The lead 4 is connected to the microwave resonant magnetoelectric sensing component, the neuroelectrophysiological recording site 2, and the reference electrode 3. It has a width of 4 μm and the rear end is connected to the universal signal interface by welding to output microwave signals, low-frequency field potential signals, and kilohertz neuronal action potential signals.

[0046] Figure 2This is a cross-sectional view of the implantable deep-brain broadband neural information detection electrode, showing the structure of the microwave resonant magnetoelectric sensor component 1, the neuroelectrophysiological recording site 2, the reference electrode 3, the lead 4, the substrate 5, and the insulating layer 6. The microwave resonant magnetoelectric sensor component 1 comprises a magnetostrictive layer 7, a piezoelectric layer 8, a top electrode layer 9, and a bottom electrode layer 10. The magnetostrictive layer 7 is made of FeGaB material and is 1 μm thick. It senses changes in the external magnetic field and generates longitudinal strain, which is coupled to the piezoelectric layer 8. The piezoelectric layer 8 is made of AlN material and is 1 μm thick. The longitudinal strain generates a potential difference between its upper and lower sides, which is sensed by the top and bottom electrode layers 9 and 10. Both the top and bottom electrode layers 9 and 10 are made of Mo metal, which has good mechanical stability and is suitable for charge sensing under high-frequency vibration. They are 200 nm thick. A 12 μm × 6 μm × 1 μm cavity is located between the bottom electrode layer 10 and the substrate 5. This cavity reflects the longitudinal mechanical waves generated by the magnetostrictive layer 7 in response to the high-frequency magnetic field, thus generating resonance. Finite element analysis of the resonant structure revealed a resonant frequency of 0.2 GHz. This indicates that the microwave resonant magnetoelectric sensor assembly 1 can specifically detect microwave neural signals near this frequency and transmit them to the leads 4 connected to the top electrode layer 9 and the bottom electrode layer 10 for signal output. Leads 4, along with the neuroelectrophysiological recording sites 2 and the reference electrode 3, are all made of Pt metal, a material with high conductivity and biocompatibility. Leads 4 are covered with an insulating layer 6 made of Si₃N₄ to prevent external noise from entering and interfering with the microwave resonant magnetoelectric sensor assembly 1. The insulating layer is made of Si₃N₄. The substrate 5 is made of Si, specifically silicon-on-insulator (SiO2). A 25 μm thick top layer of Si is released through backside etching. Simultaneously, 1200 nm of Si₃N₄ is deposited on the upper surface 5 of the substrate for insulation and to provide space for the resonant cavity of the microwave resonant magnetoelectric sensor assembly 1.

[0047] The chip manufacturing process is based on MEMS technology, and the specific manufacturing process is as follows: Figure 3 As shown, the following steps are included:

[0048] a) Clean the surface of the SOI wafer and use the strong oxidizing property of concentrated sulfuric acid to eliminate chemical impurities on the surface to avoid affecting subsequent processes;

[0049] b) A 1μm thick SiO2 layer is deposited on the silicon wafer using thermal oxidation. A photolithography process is used to create a pattern that matches the resonant cavity and the remaining SiO2 is removed by etching, leaving the remaining SiO2 as a sacrificial layer.

[0050] c) Plasma chemical vapor deposition (PCVD) was used to deposit a 1200 nm layer of Si3N4 on the surface of the silicon wafer.

[0051] d) Chemical mechanical polishing of the Si3N4 surface;

[0052] e) forming a pattern of the bottom electrode layer 10 on the photoresist using a photolithography process, sputtering 200 nm of Mo, and stripping the Mo outside the electrode pattern;

[0053] f) Photolithography and sputtering of 1 μm thick AlN as the piezoelectric layer 8;

[0054] g) Photolithography and sputtering of 200 nm Mo as the top electrode layer 9;

[0055] h) Photolithography and sputtering of 300 nm Pt to create neuroelectrophysiological recording site 2, reference electrode 3, and lead 4;

[0056] i) depositing a 2200 nm thick Si3N4 layer as an insulating layer 6 on the surface using plasma chemical vapor deposition;

[0057] j) CF4 reactive ion etching (RIE) was used to selectively remove the Si3N4 layer above the top electrode layer 9, the neural electrophysiological recording site 2, the reference electrode 3, and the lead 4;

[0058] k) photolithography and sputtering of 1 μm thick FeGaB as the magnetostrictive layer 7;

[0059] l) Use HF vapor etching to release the sacrificial layer SiO2 to expose the resonant cavity.

[0060] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. An implantable deep-brain broadband neural information detection electrode, characterized in that: include: The substrate is formed by back-etching silicon on an insulator and depositing a Si3N4 insulating layer on the surface; A microwave resonant magnetoelectric sensing component is provided on a substrate and includes a magnetostrictive layer, a piezoelectric layer, a top electrode layer and a bottom electrode layer; The magnetostrictive layer is made of FeGaB material and is used to sense high-frequency magnetic fields; The piezoelectric layer is made of AlN material and converts mechanical strain into electrical signals; The top electrode layer and the bottom electrode layer are made of Mo material to form a resonant cavity; The neuroelectrophysiological recording site is a circular Pt electrode that forms a differential detection sensor with the reference electrode to collect low-frequency field potential and kilohertz action potential signals; The reference electrode is a Pt rectangular electrode; Leads, connecting each component to the signal interface; Insulation layer, covering the leads and substrate, made of Si3N4.

2. The electrode according to claim 1, characterized in that The resonant cavity of the microwave resonant magnetoelectric sensor component is formed by releasing the sacrificial layer SiO2 through HF vapor etching.

3. The electrode according to claim 1, characterized in that The sampling rate of the neuroelectrophysiological recording site is 30 kHz, covering the frequency band from 0.1 Hz to 10 kHz.

4. The electrode according to claim 1, characterized in that The longitudinal strain of the piezoelectric layer is generated by the high-frequency vibration of the magnetostrictive layer, and the resonance frequency range is 0.1-0.5 GHz.

5. The electrode according to claim 1, characterized in that The surface of the lead is covered with a Si3N4 insulating layer with a thickness of 2200nm, which is used to shield external electromagnetic interference.

6. The electrode according to claim 1, characterized in that The Si3N4 layer of the substrate is processed by chemical mechanical polishing, and the surface roughness is ≤10 nm.

7. The electrode according to claim 1, characterized in that The FeGaB material of the magnetostrictive layer is deposited by a sputtering process with a thickness error of ±50 nm.

8. A method for preparing an implantable deep-brain broadband neural information detection electrode, characterized in that: The following steps are involved: a) The SOI wafer surface is cleaned, a 1 μm SiO2 sacrificial layer is deposited, and a cavity pattern is formed by photolithography. b) Plasma chemical vapor deposition of a 1200 nm Si3N4 layer and polishing; c) sequentially sputtering a Mo bottom electrode layer, an AlN piezoelectric layer, and a Mo top electrode layer; d) Photolithography and sputtering of Pt to form neural electrophysiological recording sites, reference electrodes, and leads; e) Deposit a 2200 nm Si3N4 insulating layer and selectively etch the electrodes using CF4 RIE; f) Sputtering the FeGaB magnetostrictive layer and releasing the sacrificial SiO2 layer to form a resonant cavity.

9. The preparation method according to claim 8, characterized in that The SOI surface is treated with concentrated sulfuric acid to remove chemical impurities.

10. The preparation method according to claim 8, characterized in that The HF vapor etching time was 60 seconds, and the cavity size accuracy was ±0.5 μm.

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