The sensitive electrode of a silicon conductive four-electrode electrochemical angular vibration sensor and its manufacturing method

Abstract

This invention provides a silicon conductive four-electrode electrochemical angular vibration sensor sensitive electrode and its manufacturing method. The sensitive electrode includes a silicon substrate, an insulating layer, an anode, a flow hole, a cathode, and an anode-cathode gap. The sensitive electrode structure is a four-electrode structure consisting of anode-cathode-cathode-anode from top to bottom. The silicon substrate is formed by bonding or bonding two wafers together using SU-8 adhesive. The manufacturing method includes the following steps: (1) cleaning the silicon wafer by boiling it in acid and water, and growing single-sided silicon oxide by plasma-enhanced chemical vapor deposition (PECVD); (2) treating the surface of the silicon wafer without an oxide layer with oxygen plasma to increase adhesion; (3) spin-coating the surface without an oxide layer with SU-8 negative photoresist to obtain an SU-8 adhesive layer; (4) bonding and aligning another silicon wafer with the coated silicon wafer, and applying stable pressure to initially press it; (5) pressing the film and heating to dry; (6) checking the bonding strength after confirming that the SU-8 adhesive has been completely cured, and further checking it with a microscope; and obtaining the raw silicon wafer.

Description

Technical Field

[0001] This invention relates to the fields of MEMS sensor technology, angular vibration measurement technology, fluid mechanics technology, and electrochemical reaction technology, and particularly to the structural design and fabrication method of the sensitive element of a low-frequency angular vibration sensor. Background Technology

[0002] Against the backdrop of my country's rapid scientific and technological development, the demand and requirements for precision measurement are constantly increasing. Angular vibration sensors are a typical type of inertial sensor, characterized by angular velocity or angular acceleration. They convert angular vibration signals from the external environment into electrical signals through a specific conversion law, and then process, store, and display these signals through a measurement system. In recent years, researchers have discovered that low-frequency angular acceleration signals contain more valuable information in areas such as seismic wave propagation and urban building structural design.

[0003] The development of angular vibration sensors has led to the emergence of many sensor types based on different transduction principles. Compared to piezoelectric and fiber optic sensors, electrochemical angular vibration sensors operate in the low-pass stage, possessing a high electromechanical conversion coefficient and excellent low-frequency characteristics. The reactions between liquid ions endow them with tiltability, high sensitivity, and strong noise immunity. As sensor technology has evolved, miniaturization, intelligence, and integration are essential for upgrades. Compared to traditional platinum mesh electrode sensors, electrochemical angular vibration sensors incorporating MEMS technology achieve miniaturization, integration, and mass production, thus better meeting the practical testing needs of related fields.

[0004] Since the advent of electrochemical gainers and molecular electronic sensors, vibration sensors based on electrochemical principles have been proposed and implemented. The electrolyte system is an aqueous solution composed of I₂ and KI at a specific concentration. The electrode structure consists of two pairs of electrodes arranged in an ACCA (anodide-cathode-cathode-anodide) configuration. The electrode chip is immersed in the electrolyte system. After a set input voltage is applied, oxidation occurs at the anode, resulting in the loss of electrons, while reduction occurs at the cathode, resulting in the gain of electrons. When the sensor detects an external angular vibration signal, the inertial mass of the liquid causes relative motion between the electrolyte system and the electrode chip. This leads to an increase and decrease in the concentration of active ions near the two cathodes, respectively. This results in current changes of the same magnitude but opposite directions at the two pairs of electrodes. The differential output, after circuit processing, yields the angular vibration information.

[0005] Regarding the structural design of electrode chips, the improvement directions for the electrode structure design of the sensing unit of MEMS-based angular vibration electrochemical sensors are as follows: 1. From multi-layer to double-layer, and finally to single-layer; with the exploration of MEMS processes and the improvement of equipment, single-layer chips, compared to multi-layer chips, do not require complex assembly and manual alignment. They simplify manual operations through a clear process flow, resulting in smaller size, higher reliability, and higher utilization of on-chip and sidewall area. 2. Four-electrode differential structure, which has complete depletion and insulation regions. The symmetrical structure design provides stable output in the static state and good symmetry in the detection state, with a short stabilization time. 3. Silicon conductivity; heavily doped low-resistivity silicon eliminates complex lead-making methods through silicon conductivity, achieving a lead-free structural design. The above improvements are made in terms of silicon wafer selection, electrode division, lead design, and insulation layer design. Simultaneously, the MEMS process is simplified, achieving a controllable process flow and a higher success rate. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a silicon-conductive integrated four-electrode structure for a MEMS electrochemical angular vibration sensor, along with its manufacturing method. The electrode chip comprises thousands of through-holes to allow electrolyte flow, with Pt electrodes uniformly distributed on the sidewalls of the through-holes and the chip surface. This monolithic integrated four-electrode structure possesses a complete insulating layer between the cathodes and an active ion depletion layer. Silicon conductivity simplifies process design while increasing the effective electrode area.

[0007] The present invention adopts the following technical solution:

[0008] A silicon conductive four-electrode electrochemical angular vibration sensor has a sensitive electrode comprising a silicon substrate, an insulating layer, an anode, flow holes, a cathode, and an anode-cathode gap. The sensitive electrode structure, from top to bottom, is a four-electrode structure consisting of an anode-cathode-cathode-anode. The silicon substrate is formed by bonding or bonding two wafers together using SU-8 adhesive.

[0009] The insulating layer material is silicon oxide or silicon nitride;

[0010] The insulating layer is located on the upper and lower surfaces of the silicon substrate; the anode is formed on the insulating layer, which is used to isolate the anode from the silicon substrate for insulation; the flow hole penetrates the silicon substrate and the insulating layer; the cathode is formed on the sidewall inside the flow hole, and the cathode electrode is led out through the silicon substrate for conduction; there is an anode-cathode gap between adjacent anodes and cathodes, and the gap between the anode and cathode is used to achieve insulation between the anode and cathode; two adjacent cathodes in the double-sided flow hole of the silicon substrate are insulated.

[0011] Furthermore, the anode pads extending from the upper and lower surfaces of the sensitive electrode are directly connected to the anode on the surface.

[0012] Furthermore, the conductive cathode pads on the silicon substrate are made conductive by etching through-holes and then sputtering metal.

[0013] Furthermore, each side of the sensitive electrode is designed with two pads for the same electrode, and the upper and lower sides contain a total of eight pads, from which four electrodes are led out.

[0014] Furthermore, the sensitive electrode is connected to the lead wire of the signal acquisition system circuit by gold wire bonding, and then encapsulated for testing.

[0015] The method for manufacturing a sensitive electrode as described in any of the preceding claims includes the following steps: (i) wafer-level bonding based on SU-8 and (ii) fabrication of a silicon conductive through-type integrated quad electrode.

[0016] Furthermore, the SU-8-based wafer-level bonding includes the following steps:

[0017] (1) The silicon wafer is boiled in acid and water for cleaning, and then single-sided silicon oxide is grown by plasma-enhanced chemical vapor deposition (PECVD).

[0018] (2) Apply surface oxygen plasma treatment to the silicon wafer without an oxide layer to increase adhesion;

[0019] (3) SU-8 negative photoresist was spin-coated onto the surface without an oxide layer to obtain an SU-8 photoresist layer;

[0020] (4) Bond and align the other silicon wafer with the silicon wafer after the adhesive has been homogenized, and apply stable pressure to initially press it down;

[0021] (5) Press the film and heat to dry;

[0022] (6) After confirming that the SU-8 adhesive has been completely cured, check the bonding strength and conduct further inspection using a microscope; obtain the raw silicon wafer.

[0023] Furthermore, the fabrication of the silicon conductive through-type integrated quad electrode includes the following steps:

[0024] a. Using the raw silicon wafer as a substrate, clean it;

[0025] b. Oxygen plasma treatment, pre-baking, double-sided spin coating of AZ1500, pre-baking, photolithography, development to create a photoresist mask for sputtering;

[0026] c. A Ti layer is first sputtered on both sides of the silicon wafer, and then a Pt layer is sputtered on the Ti layer. The metal pattern obtained after the stripping is acetone-alcohol-water and is used as the anode of the electrode chip.

[0027] d. Oxygen plasma treatment, pre-baking, spin coating of AZ4620 on the front side, pre-baking, photolithography, and development to create a photoresist mask for front side etching;

[0028] e. Use reactive ion etching (RIE) equipment to etch the front silicon oxide layer, and use deep reactive ion etching (DRIE) equipment to etch the silicon substrate;

[0029] f. Spin-coating AZ4620 on the back side, pre-baking, photolithography, and development to create a mask for back-side etching;

[0030] g. Use a RIE device to etch the back silicon oxide layer and a DRIE device to etch the silicon substrate;

[0031] h. Use RIE equipment to introduce CF4 / O2, etch the intermediate SU-8 adhesive layer, and create a fully penetrating electrode chip flow hole;

[0032] i. SD220 dry film photoresist was used for double-sided attachment to fabricate a photoresist mask for the sputtering flow hole sidewall electrode;

[0033] j. A Ti layer is first sputtered onto the inner sidewalls of the double-sided flow holes, and then a Pt layer is sputtered onto the Ti layer. The metal pattern obtained by acetone-alcohol-water stripping is used as the cathode of the electrode chip; thus, the sensitive electrode is obtained.

[0034] Furthermore, the insulating layer material includes, but is not limited to, silicon oxide, silicon nitride, etc.

[0035] Furthermore, the shape of the flow hole includes, but is not limited to, square, circular, triangular, etc.;

[0036] Furthermore, the assembly method of the two silicon wafers is not limited to SU-8 bonding, and the thickness of the interlayer is not fixed. The two chips can also be assembled together using silicon-silicon bonding.

[0037] Furthermore, the electrolyte system of potassium iodide and iodine can be replaced by other electrolyte systems that can undergo reversible redox reactions, including bromide-bromine, ferricyanide-ferrocyanide, etc.

[0038] Furthermore, the choice of anode and cathode materials is not limited to Pt; other materials with excellent conductivity and corrosion resistance can also be used.

[0039] The beneficial effects of this invention are:

[0040] (1) The integrated design and manufacturing significantly reduces assembly difficulty and significantly improves assembly efficiency.

[0041] (2) The SU-8 process achieves wafer-level bonding, ensuring the consistency of multiple devices;

[0042] (3) All parameters of the electrode structure are controllable, which greatly reduces the distance between the two cathodes;

[0043] (4) Omit electrode leads to increase effective electrode area and improve sensitivity;

[0044] (4) The upper and lower laminar flow holes are perfectly aligned, and there is no hole offset. Attached Figure Description

[0045] Figure 1 This is a cross-sectional view of an electrochemically sensitive electrode chip;

[0046] Figure 2 A three-dimensional schematic diagram of the electrochemically sensitive electrode chip (100);

[0047] Figure 3 This is a wafer-level bonding diagram based on SU-8;

[0048] Figure 4 A flowchart illustrating the fabrication process of a silicon conductive through-type integrated quad electrode.

[0049] In the figure, 100: Sensitive electrode chip; 101: Silicon substrate; 102: Silicon oxide insulating layer; 103: SU-8; 104: Anode; 105: Flow hole; 106: Cathode; 107: Anode-cathode gap; 108: Anode pad; 109: Cathode pad. Detailed Implementation

[0050] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0051] Figure 1 This is a cross-sectional view of an electrochemically sensitive electrode chip 100, which includes a silicon substrate 101, a silicon oxide insulating layer 102, a SU-81 03, an anode 104, a flow hole 105, a cathode 106, and an anode-cathode gap 107. The electrode structure, from top to bottom, is a four-electrode structure consisting of anode-cathode-cathode-anode. The silicon oxide insulating layer 102 is located on the upper and lower surfaces of the silicon substrate 101; the anode 104 is formed on the silicon oxide insulating layer 102, which is used to isolate the anode 104 from the silicon substrate 101 for insulation; the flow hole 105 penetrates the silicon substrate 101 and the silicon oxide insulating layer 102; the cathode is formed on the sidewall inside the flow hole 105, and the cathode 106 electrode is led out through the conductivity of the silicon substrate 101; there is an anode-cathode gap 107 between adjacent anodes 104 and cathodes 106, which is used to achieve insulation between the anode and cathode; two adjacent cathodes 106 are insulated within the double-sided flow holes of the silicon substrate 101.

[0052] The cathode electrode is led out through the conductive silicon substrate 101. With a substrate resistance of less than 0.0015 Ω / cm, the electrode leads are omitted, and the area is converted into an effective on-chip electrode area, increasing the utilization rate of the chip structure and improving device sensitivity. A silicon oxide insulating layer 102 is used to isolate the anode from the silicon substrate. An inter-cathode gap 107 is used to achieve insulation between the anode and cathode. Two wafers are bonded together using SU-8103. The bond strength allows for subsequent processing and achieves insulation between the silicon substrates. Simultaneously, a certain degree of side drilling is used to isolate metal during double-sided sputtering of electrodes within the sputtering apertures 105, preventing the two cathodes 106 from conducting due to sputtering.

[0053] Figure 2 This is a 3D schematic diagram of the electrochemical sensitive electrode chip 100. The top image shows the assembled sensitive electrode chip, and the bottom image is its cross-sectional view. The anode pads 108 leading out from the top and bottom surfaces of the chip are directly connected to the anode 104 on the surface. The cathode pads 109 leading out from the conductive silicon substrate 101 are made conductive by etching through-holes and sputtering metal. The anode and cathode are insulated by silicon oxide. Two pads with the same electrode are designed on each side, with a total of eight pads on the top and bottom surfaces, leading out four electrodes. The pads are connected to the lead wires of the signal acquisition system circuit by gold wire bonding, and the chip can be tested after encapsulation. Since the bonding between silicon wafers is completed at the wafer stage, SU-8103 exists as an intermediate layer around each single hole. This fabrication method does not require insulation treatment of the contact layer between silicon wafers. It is achieved through standardized operations of MEMS process. Compared with manual bonding after chip fabrication, it has many improvements, simplifies the operation, significantly reduces and makes controllable cathode spacing, has better wafer-level bonding insulation effect, higher strength, and can complete a large number of devices in one go.

[0054] Figure 3 Wafer-level bonding diagram based on SU-8:

[0055] (1) The silicon wafer is boiled in acid and water for cleaning, and 1µm single-sided silicon oxide is grown by PECVD;

[0056] (2) Non-oxidizing surface oxygen plasma treatment for 3 mins to increase adhesion;

[0057] (3) SU-8 negative photoresist was spin-coated on the surface without oxide layer. The spin coating speed was 2000 rpm / min and the spin coating time was 30 s to obtain a SU-8 photoresist layer of less than 5 μm.

[0058] (4) Bond and align the other low-resistivity silicon wafer with the silicon wafer after homogenization, and apply stable pressure to initially press it together;

[0059] (5) Press the film twice at 95°C on the film press machine, and then dry it on a 95°C hot plate for 1 hour.

[0060] (6) After confirming that the SU-8 adhesive has been completely cured, check the bonding strength and conduct further inspection using a microscope; obtain the raw silicon wafer.

[0061] Figure 4 Fabrication process flow diagram for silicon conductive through-type integrated quad electrode:

[0062] j. Clean the raw silicon wafers and select raw silicon wafers that meet the bonding requirements as the substrate;

[0063] k. Oxygen plasma treatment, pre-baking, double-sided spin coating of AZ1500, pre-baking, photolithography, development to prepare a photoresist mask for sputtering;

[0064] l. Both sides of the silicon wafer are sputtered with Ti / Pt ( First, a Ti layer is sputtered, and then a Pt layer is sputtered on the Ti layer. The alloy is then stripped using acetone-alcohol-water. The resulting metal pattern is used as the anode of the electrode chip.

[0065] m. Oxygen plasma treatment, pre-baking, spin coating of AZ4620 on the front side, pre-baking, photolithography, development to create a photoresist mask for front etching;

[0066] n. Use reactive ion etching (RIE) equipment to etch the front silicon oxide layer, and use deep reactive ion etching (DRIE) equipment to etch the silicon substrate;

[0067] o. Spin coat AZ4620 on the back side, using the same procedure as on the front side, to create a mask for back-side etching;

[0068] p. Use a RIE device to etch the back silicon oxide layer, and a DRIE device to etch the silicon substrate;

[0069] q. Using a RIE device to pass through CF4 / O2 (in CF4 / O2, the volume ratio of CF4 to O2 is 1 / 4), 600W power and 1mins time are used to etch the intermediate SU-8 bonding layer to create a fully penetrating electrode chip flow hole;

[0070] r. SD220 dry film photoresist was used for double-sided attachment to fabricate a photoresist mask for the sputtering flow hole sidewall electrode;

[0071] s. Both sides of the flow hole sidewalls are sputtered with Ti / Pt ( First, a Ti layer is sputtered, then a Pt layer is sputtered on the Ti layer. The metal pattern obtained by acetone-alcohol-water stripping is used as the cathode of the electrode chip; the chip fabrication is complete.

[0072] In some embodiments of the present invention, the insulating layer material includes, but is not limited to, silicon oxide, silicon nitride, etc.;

[0073] In some embodiments of the present invention, the shape of the flow hole includes, but is not limited to, square, circular, triangular, etc.

[0074] In some embodiments of the present invention, the assembly method of the two silicon wafers is not limited to SU-8 bonding, the thickness of the interlayer is not fixed, and the two chips can also be assembled together by silicon-silicon bonding.

[0075] In some embodiments of the present invention, the electrolyte system of liquid potassium iodide and iodine can be replaced by other electrolyte systems capable of reversible redox reactions, including bromide-bromine, ferricyanide-ferrocyanide, etc.

[0076] In some embodiments of the present invention, the anode and cathode materials are not limited to Pt; other materials with excellent conductivity and corrosion resistance can also be used.

[0077] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the invention, and do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A method for manufacturing the sensitive electrode of a silicon conductive four-electrode electrochemical angular vibration sensor, characterized in that, The sensitive electrode includes a silicon substrate, an insulating layer, an anode, flow holes, a cathode, and an anode-cathode gap; the sensitive electrode structure is a four-electrode structure consisting of anode-cathode-cathode-anode from top to bottom; the silicon substrate is formed by bonding two wafers together using SU-8 adhesive. An insulating layer is located on the upper and lower surfaces of the silicon substrate; an anode is formed on the insulating layer, which is used to isolate the anode from the silicon substrate for insulation; flow holes penetrate the silicon substrate and the insulating layer; The cathode is formed on the sidewall inside the flow hole, and the cathode electrode is led out through the silicon substrate. There is an anode-cathode gap between adjacent anodes and cathodes, and the gap between the anode and cathode is used to achieve insulation between the anode and cathode. The two adjacent cathodes in the double-sided flow hole of the silicon substrate are insulated. The cathode pads led out from the silicon substrate are made conductive by etching through holes and sputtering metal. The manufacturing method includes: (a) Steps for wafer-level bonding based on SU-8: (1) The silicon wafer is boiled in acid and water for cleaning, and then single-sided silicon oxide is grown by PECVD; (2) Treat the silicon wafer with surface oxygen plasma without oxide layer; (3) SU-8 negative photoresist is spin-coated onto the surface without an oxide layer to obtain an SU-8 photoresist layer; (4) Bond and align the other silicon wafer with the silicon wafer after the adhesive has been homogenized, and apply stable pressure to initially press it together; (5) Press the film and heat to dry; (6) After the SU-8 adhesive is fully cured, the raw silicon wafer is obtained; (II) Steps for fabricating a silicon conductive through-type integrated quad electrode: a. Using the raw silicon wafer as a substrate, clean it; b. Oxygen plasma treatment, pre-baking, double-sided spin coating of AZ1500, pre-baking, photolithography, development to create a photoresist mask for sputtering; c. A Ti layer is first sputtered on both sides of the silicon wafer, followed by a Pt layer. The wafer is then stripped using acetone-alcohol-water. The resulting metal pattern is used as the anode of the electrode chip. d. Oxygen plasma treatment, pre-baking, spin coating of AZ4620 on the front side, pre-baking, photolithography, and development to create a photoresist mask for front side etching; e. Use RIE equipment to etch the front silicon oxide layer, and use deep reactive ion etching equipment to etch the silicon substrate; f. Spin-coating AZ4620 on the back side, pre-baking, photolithography, and development to create a mask for back-side etching; g. Use a RIE device to etch the back silicon oxide layer and a DRIE device to etch the silicon substrate; h. Use RIE equipment to introduce CF4 / O2, etch the intermediate SU-8 adhesive layer, and create a fully penetrating electrode chip flow hole; i. SD220 dry film photoresist was used for double-sided attachment to fabricate a photoresist mask for the sputtering flow hole sidewall electrode; j. A Ti layer is first sputtered onto the inner wall of each of the two flow holes, followed by a Pt layer. The metal pattern obtained by acetone-alcohol-water stripping is used as the cathode of the electrode chip to obtain the sensitive electrode.

2. The manufacturing method according to claim 1, characterized in that, The anode pads extending from the upper and lower surfaces of the sensitive electrode are directly connected to the anode on the surface.

3. The manufacturing method according to claim 1, characterized in that, Each side of the sensitive electrode is designed with two pads for the same electrode, and the upper and lower sides contain a total of eight pads, from which four electrodes are led out.

4. The manufacturing method according to claim 1, characterized in that, The sensitive electrode is connected to the lead wire of the signal acquisition system circuit by gold wire bonding, and is then encapsulated for testing.

5. The manufacturing method according to claim 1, characterized in that, The insulating layer material is silicon oxide or silicon nitride.

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