CN109911839A - Microelectrode capable of suppressing optical noise, circuit using the same, and preparation method thereof - Google Patents

Abstract

A microelectrode capable of suppressing optical noise, a circuit using the same, and a preparation method thereof. In the micro-electrode structure with silicon as the supporting material, the silicon as the substrate will generate unbalanced carriers due to illumination, which will then disturb the electrode signal on the upper layer. By doping and growing the metal layer on the silicon substrate as the electrode support, and carving out through holes in the insulating layer above it, the grounding can greatly reduce or eliminate the signal interference of photogenerated carriers in the silicon substrate to the upper neural electrodes. The noise interference caused by light to silicon-based microelectrodes, especially lightly doped silicon substrates, is effectively solved.

Description

Microelectrode capable of suppressing optical noise, circuit using the same, and preparation method thereof

technical field

The invention relates to the technical field of micro-sensors, in particular to a micro-electrode capable of suppressing light noise, a circuit using the same and a preparation method thereof.

Background technique

Silicon-based microelectrodes are an important tool for neuroscience research. Silicon is usually used as a substrate to support the device. The upper layer is a traditional "sandwich" electrode structure with an insulating layer, a metal conductor, and an insulating layer. The silicon substrate and metal The electrodes are separated by an insulating layer, as shown in Figure 2.

Due to the small size of the microelectrodes, usually in the order of tens to hundreds of microns in lateral dimension, the recorded signals are very weak. In the process of using silicon-based microelectrodes, due to the sensitivity of the silicon substrate to light, the non-equilibrium carriers generated by light in the silicon substrate will affect the electrode signal, which is mainly manifested in the light noise of the electrode when there is light. Very big. Silicon is one of the most mature materials for micromachining applications. Its mechanical strength is comparable to that of stainless steel, and it can be integrated with circuits. It is the main research direction at present and even in the future. Silicon-based microelectrodes will inevitably involve light in the process of use. Preliminary studies have shown that ordinary silicon electrodes that are only used for recording will generate light noise under fluorescent lamps and even indoor light during the day, and the amplitude is very large. In some cases It will directly lead to the loss of signal. In addition, as one of the tools for microelectrode stimulation, the research on photoelectrodes combined with optogenetics is particularly important. Among them, silicon electrodes need to be used in conjunction with various light sources. In order to ensure the stable stimulation and recording performance of photoelectrode devices , it is very urgent to solve the optical noise problem of silicon-based microelectrodes.

SUMMARY OF THE INVENTION

In order to at least partially solve the optical noise problem of the above-mentioned silicon-based microelectrode, the present invention proposes a silicon-based microelectrode structure that can suppress the optical noise.

According to one aspect of the present invention, a microelectrode capable of suppressing optical noise is provided, which is characterized by comprising a substrate, a ground metal layer, a lower insulating layer, an electrode layer and an upper insulating layer, wherein:

The substrate is prepared by using a semiconductor material that can generate photogenerated carriers under illumination conditions, preferably silicon, germanium, and gallium arsenide materials, and more preferably a silicon substrate;

The ground metal layer and the electrode layer are not electrically connected.

Wherein, the part where the substrate is combined with the ground metal layer has a doping concentration that can form a good ohmic contact with the metal;

Preferably, the position of the ground metal layer is on the front side, the back side or the inside of the substrate.

Wherein, the ground metal layer is prepared by using chromium, titanium, gold, titanium-gold alloy, chromium-gold alloy, graphene or amorphous carbon.

Wherein, the ground metal layer is connected to the ground of the amplifying circuit through the ground through hole when in use.

According to another aspect of the present invention, a method for preparing a microelectrode capable of suppressing optical noise is provided, which is characterized in that it includes the following steps:

A. A heavily doped substrate structure with a surface doping concentration greater than 10 ¹⁸ cm ^-3 is formed on a lightly doped substrate with a bulk doping concentration less than 10 ¹⁶ cm ^-3 ; It is prepared from semiconductor materials that generate photogenerated carriers, preferably silicon, germanium, and gallium arsenide materials, and more preferably silicon;

B. A gridded ground layer is formed on the substrate structure obtained in the above step A;

C, grow lower insulating layer on the substrate structure obtained in above-mentioned step B;

D. Use positive photoresist as mask alignment overlay, and use dry etching to remove the lower insulating layer above the grounding hole, expose the grounding hole and remove the surface photoresist;

E, by photolithography mark alignment photolithography, form metal line structure on the lower insulating layer that above-mentioned step D obtains;

F, grow an upper insulating layer on the metal line structure obtained in above-mentioned step E;

G. Use positive photoresist for alignment overlay, then use photoresist as a mask for dry etching, etch out the pads required for recording points and gold wire bonding, and finally clean the photoresist to complete The preparation of the silicon-based microelectrode capable of suppressing optical noise.

Wherein, in the step A, the lightly doped substrate is an N-type lightly doped substrate with a resistivity of 1-10 Ω·cm;

In the step A, the step of forming the heavily doped substrate structure is realized by high-concentration ion diffusion or implantation;

Preferably, the surface of the heavily doped substrate has phosphorus with a diffusion concentration of 10 ¹⁸ cm ^-3 and a diffusion depth of 300 nm;

Preferably, in the step B, the step of forming a gridded ground layer is to perform photolithography on the substrate by using a negative photoresist to form a desired blank grid shape, vacuum evaporate the metal layer, and then remove the photoresist to obtain the gridded metal ground layer;

Preferably, the vapor-deposited metal layer is Cr/Au/Cr, and the thickness is 12 nm/150 nm/12 nm, respectively.

Wherein, in the step C, the step of growing the lower insulating layer is realized by chemical vapor deposition PECVD;

Preferably, the lower insulating layer is a composite film of SiO ₂ /Si _x N _y with a thickness of 500 nm;

Preferably, in the step E, a negative photoresist is used to align the photolithography to form a blank metal line morphology, and then a metal layer is formed by evaporation, the photoresist is peeled off in acetone, and the metal lines are formed after cleaning. structure;

Preferably, the metal layer formed by evaporation is Cr/Au/Cr, and the thickness is 12nm/150nm/12nm;

Preferably, in the step F, the upper insulating layer adopts a composite film structure of SiO ₂ /Si _x N _y /SiO ₂ =200nm/700nm/200nm.

Among them, it also includes step H:

H. Divide the prepared substrate according to the size of the electrodes, then fix the electrodes on the prepared PCB board, lead out the pads of the electrode pads, and ground the ground layer on the substrate through metal wires, so as to achieve The purpose of reducing optical noise.

According to yet another aspect of the present invention, there is also provided a microelectrode prepared by the above-mentioned preparation method of a microelectrode capable of suppressing optical noise.

According to still another aspect of the present invention, there is also provided a circuit using the microelectrode capable of suppressing optical noise as described above.

As can be seen from the above technical solutions, the method for preparing silicon-based microelectrodes of the present invention has the following beneficial effects:

(1) Lightly doped silicon wafer is used as the substrate, which makes good use of the advantages of lightly doped silicon, which is flexible, can be integrated with CMOS circuits, and has low cost;

(2) Considering the application scenario of the silicon electrode used in combination with light, the signal-to-noise ratio of the recording signal of the photoelectrode can be improved by reducing the noise of the silicon electrode caused by light, and the stability of the electrode can be improved; By doping and growing a metal layer at the bottom and engraving a through hole on the insulating layer on the bottom, it can greatly reduce or eliminate the signal interference of photogenerated carriers in the silicon substrate to the upper nerve electrode, effectively solving the problem of light to silicon Noise interference caused by base microelectrodes, especially lightly doped silicon substrates;

(3) Due to the vertical structure of the signal collected by the silicon electrode and the characteristics that the electrode interface is in direct contact with the object to be measured, it is unpackaged, and the ability of the silicon electrode to resist optical noise interference is enhanced on the basis of satisfying this condition;

(4) On the basis of the mature MEMS process, the purpose of reducing noise is achieved by improving the electrode structure, which is more conducive to promotion to various types of electrode structures based on planar technology.

Description of drawings

Fig. 1 is the structural representation of the silicon-based microelectrode with anti-light interference capability of the present invention;

2 is a schematic structural diagram of a silicon-based microelectrode in the prior art;

FIG. 3 is a flowchart showing the steps of a method for preparing a silicon-based microelectrode for suppressing optical noise according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a specific embodiment of the silicon-based microelectrode for suppressing optical noise of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be noted that, in the drawings or descriptions in the specification, similar or identical parts use the same reference numerals. Implementations not shown or described in the drawings are forms known to those of ordinary skill in the art. Additionally, while the present disclosure may provide demonstrations of parameters including specific values, it should be understood that the parameters need not be exactly equal to the corresponding values, but may be approximated within acceptable error tolerances or design constraints.

The electrode for suppressing optical noise of the present invention mainly uses the grounding "drainage" method to collect the unbalanced minority carriers generated in the silicon substrate through the metal layer and then lead them to the ground, thereby avoiding the influence on the upper electrode signal. The present invention verifies that the novel silicon-based electrode structure can effectively suppress the generation of optical noise and improve the signal-to-noise ratio of the signal collected by the electrode by comparing the experimental methods.

The silicon-based microelectrode structure capable of suppressing optical noise of the present invention is shown in FIG. 1 . In the micro-electrode structure with silicon as the supporting material, the silicon as the substrate will generate unbalanced carriers due to illumination, which will then disturb the electrode signal on the upper layer. The silicon substrate used as the electrode support is grounded by doping, growing a metal layer and carving through holes in the insulating layer on it, which can greatly reduce or eliminate light exposure to silicon-based microelectrodes, especially lightly doped silicon substrates. noise interference.

Specifically, the present invention discloses a new type of electrode structure without packaging, which is directly based on the mature MEMS process, and adopts a new type of electrode structure in which a ground layer is added on a lightly doped substrate and the ground is drawn out to suppress the optical noise of silicon-based microelectrodes. , the test effect is similar to the electrode light noise characteristics of heavily doped substrates.

In an exemplary embodiment of the present invention, a novel electrode structure preparation method for reducing optical noise is provided, as shown in FIG. 3 , and the specific experimental process structure is shown in FIG. 4 . The method in this embodiment includes:

A. Select silicon wafers with high concentration ion diffusion or implantation on the surface. For example, select an N-type lightly doped silicon wafer with a size of 4 inches, a thickness of 300 μm, and a resistivity of 1-10 Ω·cm. ×10 ¹⁸ cm ^-3 phosphorus with a diffusion depth of 300 nm, forming a heavily doped substrate structure on the surface;

B. Form a gridded ground plane. Use negative adhesive AR-4340 to do a photolithography on the substrate to form the required blank grid shape, vacuum evaporation metal layer Cr/Au/Cr=12nm/150nm/12nm, then soak and peel in acetone, after cleaning Form a grid-like metal layer;

C. PECVD grows the lower insulating layer. Considering the compactness of the insulating layer grown by PECVD, a composite film with an insulating layer type of SiO ₂ /Si _x N _y was set with a thickness of 500 nm;

D. The positive mask is aligned and etched and ground holes are etched. Align the overlay with positive adhesive AR-4620, and then use dry etching to remove the composite film SiO ₂ /Si _x N _y above the ground hole, expose the ground hole and remove the surface photoresist;

E. Align photolithography to form metal line structures. Firstly, the negative adhesive AR-4340 is used for aligning photolithography to form a blank metal line morphology, and then the metal layer Cr/Au/Cr=12nm/150nm/12nm is evaporated, soaked in acetone and peeled off, and cleaned to form an electrode line structure;

F. PECVD grows the upper insulating layer. Due to the stress problem of the insulating layer grown by PECVD, usually SiO ₂ is compressive stress, and the grown Si _x N _y can be expressed as either compressive stress or tensile stress according to the properties, concentration, gas pressure and other conditions of the mixed gas. Therefore, in order to balance the stress problem between thin films, and according to the previous research results of the present inventor, the upper insulating layer adopts a composite film structure of SiO ₂ /Si _x N _y /SiO ₂ =200nm/700nm/200nm.

G. Positive glue alignment overlay and dry-etched electrode structure. The positive adhesive AR-4620 is used for the final alignment overlay, and then the photoresist is used as a mask for dry etching, and the PAD required for the recording point and gold wire bonding is etched. Finally, the photoresist is cleaned to complete the whole process. A process flow for the fabrication of novel electrodes for lightly doped substrates with reduced optical noise.

H. Package after dicing. The prepared 4-inch piece is diced according to the size of the electrode, and then the electrode is fixed on the prepared PCB board, and the electrode pressure welding point PAD is drawn out. Pay special attention to the need to draw out the electrode PAD point corresponding to the grounding hole, and pass the metal wire during the test. The entire electrode substrate is grounded to reduce optical noise.

In one embodiment, the method for preparing a silicon-based microelectrode for suppressing optical noise includes the following steps: performing high-concentration ion diffusion on a lightly doped silicon substrate with a bulk doping concentration of less than 10 ¹⁶ cm ^-3 to form a surface with low Silicon substrate with resistivity; spin-coat photoresist on the substrate, expose the part that needs metal by photolithography; grow the metal layer, and then pattern the metal layer by stripping, taking care not to expose the metal layer on the electrode pins Body edge; grow an insulating layer on the pattern, spin-coat photoresist, perform alignment overlay, and then etch the insulating layer to expose the ground holes that need to be drawn out; spin-coat photoresist, form a line shape by photolithography, and grow metal , strip off the electrode lines; grow the insulating layer and perform alignment overlay, clean the photoresist to form a new electrode structure, package the electrodes on the PCB board, and lead out the grounding point of the substrate through the bonding point PAD and connect with the amplifier. Ground connection, the test can obtain a silicon-based microelectrode structure that can suppress optical noise.

So far, the description of this embodiment is completed. Based on the above description, those skilled in the art should have a clear understanding of the preparation of the silicon-based microelectrode structure for suppressing optical noise in the present invention.

In addition, it should be noted that the above definitions of each element are not limited to the various specific structures or shapes mentioned in the embodiments, and those of ordinary skill in the art can simply and familiarly replace them, for example:

(1) The type of the ground metal layer can be changed, and can be chromium, titanium, gold, titanium-gold alloy, chromium-gold alloy, graphene or amorphous carbon.

(2) The thickness of the ground metal layer can be changed and can be any thickness;

(3) The thickness of the lower insulating layer can be changed and can be any thickness;

(4) The doping concentration of the substrate can be changed, and can be any value greater than 10 ¹⁸ cm ^-3 or more.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned specific embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principle of the present invention, any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention.

Claims (10)

1. A micro-electrode capable of suppressing optical noise, comprising a substrate, a ground metal layer, a lower insulating layer, an electrode layer and an upper insulating layer, wherein: The substrate is prepared by using a semiconductor material that can generate photogenerated carriers under illumination conditions, preferably silicon, germanium, and gallium arsenide materials, and more preferably a silicon substrate; The ground metal layer and the electrode layer are not electrically connected. 2. The microelectrode capable of suppressing optical noise according to claim 1, wherein the part where the substrate is combined with the ground metal layer has a doping concentration that can form a good ohmic contact with the metal; Preferably, the position of the ground metal layer is on the front side, the back side or the inside of the substrate. 3 . The microelectrode capable of suppressing optical noise according to claim 2 , wherein the ground metal layer is made of chromium, titanium, gold, titanium-gold alloy, chromium-gold alloy, graphene or amorphous carbon. 4 . 4 . The microelectrode capable of suppressing optical noise according to claim 1 , wherein the ground metal layer is connected to the ground of the amplifier circuit through a ground through hole when in use. 5 . 5. A preparation method of a microelectrode capable of suppressing optical noise, comprising the following steps: A. A heavily doped substrate structure with a surface doping concentration greater than 10 ¹⁸ cm ^-3 is formed on a lightly doped substrate with a bulk doping concentration less than 10 ¹⁶ cm ^-3 ; It is prepared from semiconductor materials that generate photogenerated carriers, preferably silicon, germanium, and gallium arsenide materials, and more preferably silicon; B. A gridded ground layer is formed on the substrate structure obtained in the above step A; C, grow lower insulating layer on the substrate structure obtained in above-mentioned step B; D. Use positive photoresist as mask alignment overlay, and use dry etching to remove the lower insulating layer above the grounding hole, expose the grounding hole and remove the surface photoresist; E, by photolithography mark alignment photolithography, form metal line structure on the lower insulating layer that above-mentioned step D obtains; F, grow an upper insulating layer on the metal line structure obtained in above-mentioned step E; G. Use positive photoresist for alignment overlay, then use photoresist as a mask for dry etching, etch out the pads required for recording points and gold wire bonding, and finally clean the photoresist to complete The preparation of the silicon-based microelectrode capable of suppressing optical noise. 6. The preparation method according to claim 5, wherein in the step A, the lightly doped substrate is an N-type lightly doped substrate with a resistivity of 1-10 Ω·cm; In the step A, the step of forming the heavily doped substrate structure is realized by high-concentration ion diffusion or implantation; Preferably, the surface of the heavily doped substrate has phosphorus with a diffusion concentration of 10 ¹⁸ cm ^-3 and a diffusion depth of 300 nm; Preferably, in the step B, the step of forming a gridded ground layer is to perform photolithography on the substrate by using a negative photoresist to form a desired blank grid shape, vacuum evaporate the metal layer, and then remove the photoresist to obtain the gridded metal ground layer; Preferably, the vapor-deposited metal layer is Cr/Au/Cr, and the thickness is 12 nm/150 nm/12 nm, respectively. 7. The preparation method according to claim 5, wherein, in the step C, the step of growing the lower insulating layer is realized by chemical vapor deposition (PECVD); Preferably, the lower insulating layer is a composite film of SiO ₂ /Si _x N _y with a thickness of 500 nm; Preferably, in the step E, a negative photoresist is used to align the photolithography to form a blank metal line morphology, and then a metal layer is formed by evaporation, the photoresist is peeled off in acetone, and the metal lines are formed after cleaning. structure; Preferably, the metal layer formed by evaporation is Cr/Au/Cr, and the thickness is 12nm/150nm/12nm; Preferably, in the step F, the upper insulating layer adopts a composite film structure of SiO ₂ /Si _x N _y /SiO ₂ =200nm/700nm/200nm. 8. preparation method according to claim 5, is characterized in that, also comprises step H: H. Divide the prepared substrate according to the size of the electrodes, then fix the electrodes on the prepared PCB board, lead out the pads of the electrode pads, and ground the ground layer on the substrate through metal wires, so as to achieve The purpose of reducing optical noise. 9. A microelectrode prepared by the method for preparing a microelectrode capable of suppressing optical noise according to any one of claims 5 to 8. 10. A circuit using the microelectrode capable of suppressing optical noise as claimed in any one of claims 1 to 4 and 9.