CN109911839B - Microelectrode capable of suppressing optical noise, circuit using same and preparation method thereof - Google Patents

Abstract

A microelectrode capable of suppressing optical noise, a circuit using the microelectrode and a preparation method thereof. In a microelectrode structure with silicon as the supporting material, the silicon as the substrate will generate non-equilibrium carriers due to illumination, which will then cause disturbance to the electrode signal on the upper layer. By doping the silicon substrate used as an electrode support, growing a metal layer, and carving a through hole in the insulating layer above it for grounding, the signal interference of the photogenerated carriers in the silicon substrate to the upper neural electrode can be greatly reduced or eliminated. It effectively solves the noise interference caused by light on silicon-based microelectrodes, especially lightly doped silicon substrates.

Description

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

Technical field

The present invention relates to the technical field of microsensors, and in particular to a microelectrode capable of suppressing optical noise, a circuit using the microelectrode and a preparation method thereof.

Background technique

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

Since the size of the microelectrode is very small, usually its lateral size is on the order of tens to hundreds of microns, the recorded signal is very weak. During the use of 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 as electrode optical noise when there is light. Very big. Silicon is currently one of the most mature materials for micromachining applications. Its mechanical strength is equivalent 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. Light is inevitably involved in the use of silicon-based microelectrodes. Preliminary research has shown that ordinary silicon electrodes used only for recording will produce optical 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 signal loss. In addition, as one of the tools for microelectrode stimulation, the research on photoelectrodes combined with optogenetics is particularly important. Silicon electrodes need to be used with various light sources to ensure stable stimulation and recording performance of photoelectrode devices. , it is very urgent to solve the optical noise problem of silicon-based microelectrodes.

Contents of the invention

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

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

The substrate is prepared from a semiconductor material that can generate photogenerated carriers under illumination conditions, preferably silicon, germanium, or gallium arsenide, and further preferably a silicon substrate;

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

Among them, the part where the substrate and the ground metal layer are combined has a doping concentration that can form a good ohmic contact with the metal;

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

Wherein, the ground metal layer is made of chromium, titanium, gold, titanium gold alloy, chromium gold alloy, graphene or amorphous carbon.

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

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. Form a heavily doped substrate structure with a surface doping concentration greater than 10 ¹⁸ cm ^-3 on a lightly doped substrate with a body doping concentration less than 10 ¹⁶ cm ^-3 ; the substrate is made of a material that can be used under light conditions. It is prepared from a semiconductor material that generates photogenerated carriers, preferably silicon, germanium, or gallium arsenide, and further preferably silicon;

B. Form a gridded ground layer on the substrate structure obtained in step A above;

C. Grow the lower insulating layer on the substrate structure obtained in step B above;

D. Use positive photoresist as a mask to align the overlay, and use dry etching to remove the lower insulation layer above the ground hole, expose the ground hole and remove the surface photoresist;

E. Form a metal line structure on the lower insulating layer obtained in the above step D through photolithography mark alignment photolithography;

F. Grow an insulating layer on the metal line structure obtained in step E above;

G. Use positive photoresist for alignment and overlay, then use the 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 Preparation of silicon-based microelectrodes capable of suppressing optical noise.

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

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

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

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

Preferably, the evaporated metal layer is Cr/Au/Cr, and the thicknesses are 12nm/150nm/12nm respectively.

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

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

Preferably, in step E, a negative photoresist is used to align the photolithography to form a blank metal line shape, and then evaporates to form a metal layer. The photoresist is peeled off in acetone and cleaned to form the metal lines. structure;

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

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

Among them, step H is also included:

H. Divide the prepared substrate according to the size of the electrode, then fix the electrode on the prepared PCB board, lead out the electrode pressure pad, and ground the ground layer on the substrate through a metal wire to achieve The purpose of reducing light noise.

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

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

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

(1) Using lightly doped silicon wafers as the substrate makes good use of the advantages of lightly doped silicon, such as its flexibility, ability to be integrated with CMOS circuits, and low cost;

(2) Considering the application scenarios of silicon electrodes used in combination with light, the signal-to-noise ratio of the photoelectrode recording signal can be improved by reducing the noise of the silicon electrode caused by light, and the stability of the electrode can be improved; the silicon liner used as the electrode support can be By doping and growing a metal layer on the bottom and carving a through hole on the insulating layer above it for grounding, the signal interference of the photogenerated carriers in the silicon substrate to the upper neural electrode can be greatly reduced or eliminated, effectively solving the problem of light on silicon Noise interference caused by microelectrodes, especially lightly doped silicon substrates;

(3) Due to the vertical structure of the silicon electrode for collecting signals and the fact that the electrode interface is in direct contact with the object being measured, it is unpackaged. On the basis of meeting this condition, the silicon electrode's ability to resist optical noise interference is enhanced;

(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 the promotion of various types of electrode structures based on planar processes.

Description of the drawings

Figure 1 is a schematic structural diagram of the silicon-based microelectrode with anti-light interference ability of the present invention;

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

Figure 3 is a flow chart of the method steps for preparing a silicon-based microelectrode that suppresses optical noise according to an embodiment of the present invention;

Figure 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 purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be noted that in the drawings or the description of the description, similar or identical parts use the same figure number. Implementations not shown or described in the drawings are known to those of ordinary skill in the art. Additionally, while the present invention may provide examples of parameters that include specific values, it should be understood that the parameters need not be exactly equal to the corresponding values, but may approximate the corresponding values 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 non-equilibrium minority carriers generated in the silicon substrate through the metal layer and then lead them away through the ground, thereby avoiding the impact on the upper electrode signal. The present invention has verified through experimental methods that the new silicon-based electrode structure can effectively suppress the generation of optical noise and improve the signal-to-noise ratio of the electrode collection signal.

The structure of the silicon-based microelectrode of the present invention that can suppress optical noise is shown in Figure 1. In a microelectrode structure with silicon as the supporting material, the silicon as the substrate will generate non-equilibrium carriers due to illumination, which will then cause disturbance to the electrode signal on the upper layer. By doping the silicon substrate as an electrode support, growing a metal layer, and carving via holes in the insulating layer above it to ground, the impact of light on silicon-based microelectrodes, especially lightly doped silicon substrates, can be greatly reduced or eliminated. causing noise interference.

Specifically, the present invention discloses a new type of electrode structure without encapsulation, which is directly based on the mature MEMS process and uses a lightly doped substrate to add a ground layer and lead out the ground to suppress the optical noise of silicon-based microelectrodes. , the test results are similar to the electrode optical noise characteristics of heavily doped substrates.

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

A. Select a silicon wafer and have high-concentration ions diffused or implanted on the surface. For example, choose an N-type lightly doped silicon wafer with a size of 4 inches, a thickness of 300 μm, and a resistivity of 1-10Ω·cm. In order to ensure good electrical contact characteristics between the substrate and the bottom layer, first diffuse a concentration of 1 on the surface of the substrate ×10 ¹⁸ cm ^-3 phosphorus, with a diffusion depth of 300nm, forming a heavily doped surface substrate structure;

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

C. PECVD growth lower insulation layer. Considering the compactness of the PECVD-grown insulating layer, the insulating layer type is a SiO ₂ / _Six N _y composite film with a thickness of 500nm;

D. Align the positive mask to overlay and etch the ground hole. Use positive glue AR-4620 to align the overlay, and then use dry etching to remove the composite film SiO ₂ / _Six N _y above the ground hole, expose the ground hole and remove the surface photoresist;

E. Align photolithography to form a metal line structure. First, use negative glue AR-4340 to align photolithography to form a blank metal line shape, then evaporate the metal layer Cr/Au/Cr = 12nm/150nm/12nm, soak it in acetone and peel it off, and then clean it to form an electrode line structure;

F.PECVD growth of the upper insulating layer. Due to the stress problem in the insulation layer grown by PECVD, SiO ₂ usually has compressive stress. The grown Si _x N _y can show either compressive stress or tensile stress depending on the properties, concentration, pressure and other conditions of the mixed gas. Therefore, in order to balance the stress problem between the films and based on the inventor's previous research results, the upper insulating layer adopts a composite film structure of SiO ₂ / _Six N _y /SiO ₂ =200nm/700nm/200nm.

G. Align the overlay with positive glue and dry-etch the electrode structure. Use positive glue AR-4620 for final alignment overlay, then use photoresist as a mask for dry etching to etch out the recording points and the PAD required for gold wire bonding. Finally, clean the photoresist to complete the entire process. Process preparation process for new electrodes on lightly doped substrates that reduce optical noise.

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

In one embodiment, the method for preparing a silicon-based microelectrode that suppresses optical noise includes the following steps: performing high-concentration ion diffusion on a lightly doped silicon substrate with a body doping concentration less than 10 ¹⁶ cm ^-3 to form a surface with low Resistivity silicon substrate; spin-coat photoresist on the substrate, expose the parts that require metal through photolithography; grow the metal layer, and then pattern the metal layer by stripping, being careful not to expose the metal layer to the electrode needles Body edge; grow an insulating layer on the pattern, spin-coat the photoresist, perform alignment overlaying, and then etch the insulating layer to expose the ground hole that needs to be led out; spin-coat the photoresist, form a line shape through photolithography, and grow the metal , peel off the electrode lines; grow the insulating layer and perform alignment overlaying. After cleaning the photoresist, a new electrode structure is formed. The electrode is packaged on the PCB board. The substrate ground point is led out through the pressure soldering point PAD and then connected to the amplifier. Ground connection, testing can obtain a silicon-based microelectrode structure that can suppress optical noise.

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

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 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 insulation 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 .

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 are only specific embodiments of the present invention and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent substitutions, improvements, etc. shall be included in the protection scope of the present invention.

Claims (8)

1. A microelectrode capable of suppressing optical noise, comprising a substrate, a grounding metal layer, a lower insulating layer, an electrode layer and an upper insulating layer, wherein:

the substrate is prepared from a semiconductor material capable of generating photo-generated carriers under the illumination condition, wherein the semiconductor material is selected from silicon, germanium and gallium arsenide materials;

the grounding metal layer is not electrically connected with the electrode layer;

the silicon substrate is grounded by doping, growing a grounding metal layer and etching a through hole on the lower insulating layer, and the grounding metal layer is connected with the ground of the amplifying circuit through the grounding through hole when in use.

2. The microelectrode capable of suppressing optical noise according to claim 1, wherein the region where the substrate is bonded to the grounded metal layer has a doping concentration capable of forming good ohmic contact with the metal;

the grounding metal layer is positioned on the front surface, the back surface or the inside of the substrate.

3. The microelectrode capable of suppressing optical noise according to claim 2, wherein the grounding metal layer is made of chromium, titanium, gold, titanium-gold alloy, chromium-gold alloy, graphene or amorphous carbon.

4. The preparation method of the microelectrode capable of inhibiting optical noise is characterized by comprising the following steps of:

A. a bulk doping concentration of less than 10 ¹⁶ cm ^-3 Forming a surface doping concentration of greater than 10 on a lightly doped substrate of (2) ¹⁸ cm ^-3 Is a heavily doped substrate structure; the substrate is prepared from a semiconductor material capable of generating photo-generated carriers under the condition of illumination, and the semiconductor material is selected from silicon, germanium and gallium arsenide materials;

B. forming a gridded ground layer on the substrate structure obtained in the step A;

C. growing a lower insulating layer on the substrate structure obtained in the step B;

D. adopting positive photoresist as mask alignment overlay, adopting a dry etching method to remove the lower insulating layer above the grounding hole, exposing the grounding hole and removing the surface photoresist;

E. forming a metal line structure on the lower insulating layer obtained in the step D through photoetching of photoetching marks alignment;

F. e, growing an upper insulating layer on the metal line structure obtained in the step;

G. aligning and overlaying by adopting positive photoresist, then carrying out dry etching by using the photoresist as a mask, etching out a recording point and a pad disc required by gold wire pressure welding, and finally cleaning the photoresist to finish the preparation of the microelectrode capable of inhibiting optical noise;

the lightly doped substrate is an N-type lightly doped substrate with resistivity of 1-10Ω & ltcm >

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

the surface of the substrate with the heavily doped surface has a diffusion concentration of 10 ¹⁸ cm ^-3 Is 300nm in diffusion depth;

in the step B, the step of forming the gridding grounding layer is to form a required blank gridding shape by photoetching negative photoresist on a substrate, vacuum evaporating a metal layer, and then removing the photoresist to obtain the gridding metal grounding layer;

the evaporated metal layer is Cr/Au/Cr, and the thickness is 12nm/150nm/12nm respectively.

5. The method of claim 4, wherein in the step C, the step of growing the lower insulating layer is performed by chemical vapor deposition PECVD;

the lower insulating layer is SiO ₂ /Si _x N _y The thickness of the composite film is 500nm;

in the step E, negative photoresist is adopted for alignment photoetching to form a blank metal line shape, then a metal layer is formed by evaporation, photoresist is stripped in acetone, and the metal line structure is formed after cleaning;

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

in the step F, the upper insulating layer is made of SiO ₂ /Si _x N _y /SiO ₂ Composite membrane structure =200 nm/700nm/200 nm.

6. The method of claim 4, further comprising the step of H:

H. scribing the prepared substrate according to the size of the electrode, fixing the electrode on a prepared PCB, leading out an electrode press welding point pad disc, and grounding a grounding layer on the substrate through a metal wire, thereby achieving the purpose of reducing optical noise.

7. A microelectrode capable of suppressing optical noise produced by the method for producing a microelectrode capable of suppressing optical noise as claimed in any one of claims 4 to 6.

8. A circuit employing the microelectrode capable of suppressing optical noise as claimed in any one of claims 1 to 3 and 7.