High-precision interdigital electrode for sensing device and preparation method of high-precision interdigital electrode

Abstract

The invention belongs to the technical field of micro-nano manufacturing, and particularly relates to a high-precision interdigital electrode for a sensing device and a preparation method of the high-precision interdigital electrode. The method comprises the following steps: firstly, carrying out ultrasonic cleaning and plasma activation on a substrate; then, double-layer photoresist is adopted for coating, and a T-shaped structure is formed through high-precision mask alignment and exposure; vertical deposition of an aluminum electrode is achieved by combining an electron beam evaporation technology, and finally the high-precision interdigital electrode is obtained through ultrasonic-assisted stripping. Through cooperative matching of a double-layer glue structure and electron beam evaporation, it is ensured that the edge of the electrode is steep and free of lateral diffusion; the deposition rate and thickness can be accurately controlled; the line width deviation of the interdigital electrode is lt; the strain sensitivity reaches 138.8 Hz / mu epsilon, and the strain sensor is compatible with an MEMS sensor, a biological sensor and a wearable device. The electrode can detect + / -3000 mu epsilon wide-range strain in the flexible surface acoustic wave sensor, realizes temperature self-compensation through dual-mode resonance, and has the advantages of high efficiency, stable performance and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano manufacturing, and particularly relates to a high-precision interdigital electrode for sensor devices and a preparation method thereof. Background Art

[0002] Traditional interdigital electrode manufacturing technologies (such as thermal evaporation and magnetron sputtering) have the following defects:

[0003] (1) Thermal stress deformation: In the thermal evaporation process, the high temperature causes the photoresist layer to soften and deform, resulting in pattern shift.

[0004] (2) Poor thin film quality: The high sputtering rate in the sputtering process leads to poor densification of the thin film and significant edge burrs.

[0005] (3) Difficult process control: The wide-angle deposition in magnetron sputtering causes pattern size deviation, making it difficult to meet the sub-micron precision requirements.

[0006] (4) Low efficiency: The traditional thermal evaporation process has a low deposition rate and low processing efficiency for single-wafer processing.

[0007] Existing technologies (such as patent CN202211183990.8) all focus on the process improvement of double-layer photoresist, but its feasibility is difficult to achieve, and the problem of coordinated optimization of metal deposition and double-layer photoresist process has not been solved. Summary of the Invention

[0008] The purpose of the present invention is to provide an interdigital electrode for sensor devices with high precision, good stability and wide applicability, as well as a preparation method thereof, aiming at the problems of thermal stress deformation, poor thin film quality and low process precision existing in the traditional manufacture of interdigital electrodes.

[0009] The interdigital electrode for sensor devices provided by the present invention mainly consists of the following parts:

[0010] Substrate: Usually silicon, lithium niobate (LiNbO3), borosilicate glass or flexible materials (such as PI, PET) are selected.

[0011] Interdigital array: Composed of periodically alternating metal finger electrodes, including:

[0012] Positive electrodes: A group of parallel metal electrodes with a width of W and a spacing of S.

[0013] Negative electrodes: Interleaved with the positive electrodes, having the same width and spacing as the positive electrodes.

[0014] Lead electrodes: Located at both ends of the interdigital array for connecting to an external circuit.

[0015] Wherein:

[0016] The finger width (W) ranges from 0.5 μm to 50 μm, which directly affects the electric field distribution and sensing sensitivity.

[0017] The pitch (S) ranges from 0.5 μm to 50 μm, which together with the finger width determines the capacitive characteristics and signal response speed of the electrode.

[0018] The finger length (L) ranges from 100 μm to 5 mm, which affects the effective sensing area and current-carrying capacity of the electrode.

[0019] The layer thickness (T) (metal layer thickness) ranges from 50 nm to 500 nm, and it is necessary to satisfy the balance between conductivity and mechanical stability.

[0020] The working principle of the interdigital electrode:

[0021] The interdigital electrode forms a periodic electric field distribution through the staggered arrangement of positive and negative fingers. When the measured medium (such as gas, biomolecule or strain) acts on the electrode surface, the change in its dielectric constant or conductivity will cause a change in the capacitance or impedance between the electrodes, and then be converted into a detectable electrical signal through an external circuit. For example:

[0022] Surface acoustic wave sensor: The interdigital electrode excites and receives acoustic waves, and the medium perturbation changes the acoustic wave propagation characteristics.

[0023] Biosensor: The molecule to be measured adsorbs on the electrode surface, changing the double-layer capacitance or Faraday impedance.

[0024] The present invention also provides a preparation method for the above-mentioned interdigital electrode. First, the substrate is ultrasonically cleaned and plasma-activated; then a double-layer photoresist of LOR-10B and S1813 is coated, and a "T-shaped" structure is formed through high-precision mask alignment (±50 nm) and UV exposure (365 nm, 45 mJ / cm 2 ). The vertical deposition of the aluminum electrode is achieved by combining electron beam evaporation technology, and finally a high-precision interdigital electrode is obtained through ultrasonic-assisted stripping. The specific steps are as follows:

[0025] Step 1: Substrate pretreatment

[0026] (1) Cleaning:

[0027] The substrate (such as silicon, lithium niobate or flexible polymer) is placed in a mixed solution of acetone / isopropanol and ultrasonically cleaned; the ultrasonic frequency is from 40 kHz to 60 kHz, and the cleaning time is from 20 minutes to 40 minutes.

[0028] (2) Plasma activation:

[0029] Using a plasma cleaning device, the surface of the substrate is activated in an Ar / O2 mixed gas (mixing ratio 4:1 to 1:1) environment;

[0030] The activation power is 80 W to 120 W, and the processing time is 3 minutes to 8 minutes.

[0031] Step 2: Double-layer photoresist coating

[0032] (1) Bottom-layer resist coating:

[0033] Use LOR-10B photoresist and spin-coat it evenly on the substrate surface at a spin-coating speed of 3000 rpm to 5000 rpm.

[0034] Pre-bake at a temperature of 180°C - 200°C for 4 - 6 minutes, and the thickness of the resist layer is 0.8 μm to 1.2 μm.

[0035] (2) Top-layer resist coating:

[0036] Use S1813 positive photoresist and spin-coat it on top of the bottom-layer resist at a spin-coating speed of 2500 rpm to 3500 rpm.

[0037] Pre-bake at a temperature of 110°C to 120°C for 4 - 6 minutes, and the thickness of the resist layer is 0.8 μm to 1.2 μm.

[0038] Step 3: Patterning exposure;

[0039] (1) Mask alignment:

[0040] Precisely align the mask plate with the substrate coated with photoresist, and the alignment accuracy is 30 nm to 100 nm.

[0041] (2) Exposure:

[0042] Use a UV light source with a wavelength of 365 nm for exposure, and the exposure dose is 30 mJ / cm 2 to 60 mJ / cm 2 .

[0043] Step 4: Development and hard bake

[0044] (1) Development:

[0045] Immerse the exposed substrate in a 2.38% tetramethylammonium hydroxide (TMAH) developer for 30 - 60 seconds.

[0046] (2) Hard bake:

[0047] After development, place the substrate on a hot plate at 140°C to 160°C for hard baking for 8 - 12 minutes.

[0048] Step 5: Metal deposition

[0049] (1) Electron beam evaporation:

[0050] In a chamber with a vacuum degree of 1×10 -7 Pa to 5×10 -6 Pa, a metal layer is deposited using an electron beam evaporation equipment;

[0051] The electron beam energy is 10 keV to 15 keV, the deposition rate is 0.3 nm / s to 1.0 nm / s, and the thickness error is controlled within 0.3 nm to 1.0 nm.

[0052] (2) Target material selection:

[0053] The metal target material is aluminum, gold or platinum with a purity ≥ 99.999%, and it is selected according to the device application requirements.

[0054] Step 6: Stripping;

[0055] (1) Stripping treatment:

[0056] The substrate with the deposited metal is immersed in an N-methylpyrrolidone (NMP) or acetone stripping solution;

[0057] Ultrasonic-assisted stripping is applied, with the ultrasonic power being 40 W to 60 W and the treatment time being 20 minutes to 40 minutes.

[0058] (2) Final cleaning:

[0059] After the stripping is completed, the substrate is rinsed with deionized water and dried to obtain a device with high-precision interdigital electrodes.

[0060] The electrode prepared by the present invention: the electrode line width deviation < 5%, the strain sensitivity reaches 138.8 Hz / με, supports flexible substrates (such as PI, PET) and is compatible with MEMS sensors, biosensors and wearable devices. The examples show that this electrode can detect a wide range of strains of ±3000 με in a flexible surface acoustic wave sensor and achieve temperature self-compensation through dual-mode resonance, significantly superior to traditional processes. The present invention has the advantages of high process efficiency, wide application range, stable performance, etc.

[0061] Technical features and functional advantages of the present invention

[0062] (1) Process collaborative optimization: Adopting the collaborative matching of a double-layer resist structure and electron beam evaporation to ensure that the electrode edge is steep and there is no lateral diffusion;

[0063] (2) Parameter precise control: Through the dynamic feedback of electron beam energy - deposition rate - film thickness, precisely control the deposition rate and thickness (error ±0.5 nm);

[0064] (3) Material innovation: The combination of a high-adhesion photoresist and a low-defect metal target material.

[0065] (4) High purity of the thin film: In a high-vacuum chamber environment, high-purity particles are used for the target material. There is no need to introduce Ar (argon gas) into the chamber, and the thin film does not contain other elements.

[0066] (5) High dimensional accuracy of the thin film: Electron beam evaporation deposits vertically onto the substrate surface, hardly extending to both sides, with a small deviation in the electrode line width and precise control of the spacing.

[0067] (6) High deposition efficiency: The deposition rate reaches 0.5 nm / s, improving the production efficiency; the combination of high-purity target material and low-defect photoresist enhances the compactness of the thin film.

[0068] (7) Process compatibility: Supports new device substrate materials such as flexible substrates (PI, PET).

[0069] Interdigital electrodes are widely used in sensing devices: surface acoustic wave sensors, gas sensors, biosensors, flexible wearable devices, etc. Excellent devices are prepared by advanced process methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of the interdigital electrode structure of the present invention.

[0071] Figure 2 It is a schematic diagram of the process flow of the preparation method of the present invention.

[0072] Figure 3 It is a comparison diagram of the effects of electron beam (left) and magnetron sputtering deposition (right).

[0073] Figure 4 It is a SEM image of the typical "T"-shaped structure formed by the photoresist after development. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] The present invention will be further introduced below through embodiments.

[0075] Embodiment 1: Preparation and testing of interdigital electrodes for a flexible surface acoustic wave sensor.

[0076] 1. Substrate preparation and pretreatment

[0077] Substrate material: 128°Y-cut lithium niobate (LiNbO3) single crystal thin film with a thickness of 50 μm, prepared by a precision grinding process.

[0078] Grinding process:

[0079] (1) Bond a 3-inch original lithium niobate wafer with a thickness of 500 μm to a 130-μm UV protective film as a mechanical support.

[0080] (2) Use a diamond grinding wheel grinder (precision ±1 μm) for thinning, and finally control the thickness within 50 μm ±2 μm, with a surface roughness Ra <5 nm.

[0081] Cleaning and Activation:

[0082] Ultrasonic cleaning: Acetone / isopropanol mixed solution (volume ratio 1:1), frequency 40 kHz, time 30 minutes.

[0083] Plasma activation: Ar / O2 mixed gas (ratio 4:1), power 100 W, time 5 minutes, to enhance surface energy and photoresist adhesion.

[0084] 2. Interdigital Electrode (IDT) Fabrication

[0085] (1) Double-layer photoresist coating:

[0086] Bottom layer photoresist (LOR-10B): Spin coating speed 4000 rpm, pre-baking temperature 190 °C / 5 minutes, thickness 1.0 μm.

[0087] Top layer photoresist (S1813): Spin coating speed 3000 rpm, pre-baking temperature 115 °C / 5 minutes, thickness 1.0 μm.

[0088] (2) Patterning exposure:

[0089] Mask design: Interdigital electrode period λ = 20 μm, finger width W = 5 μm, spacing S = 5 μm, finger length L = 2 mm.

[0090] Alignment accuracy: ±50 nm (SUSS MA6 lithography machine), UV exposure wavelength 365 nm, dose 45 mJ / cm 2 .

[0091] (3) Development and hard baking:

[0092] Developer: 2.38% TMAH, development time 45 seconds, to form a "T-shaped" structure with vertical sidewalls.

[0093] Hard baking conditions: 150 °C / 10 minutes, to enhance the ability of the photoresist layer to resist metal deposition impact.

[0094] (4) Metal deposition:

[0095] Electron beam evaporation (DZS-500 equipment): Aluminum target (purity ≥99.999%), vacuum degree 5×10 -7 Pa, electron beam energy 12 keV, deposition rate 0.5 nm / s, total thickness 160 nm (error ±0.5 nm).

[0096] (5) Lift-off:

[0097] Lift-off solution: NMP (N-methylpyrrolidone), ultrasonic assistance (power 50 W, time 30 minutes), to completely remove the residual photoresist.

[0098] 3. Device Performance Verification

[0099] (1) Strain Sensitivity Test:

[0100] Experimental Setup: Bond the sensor to a steel tensile plate and attach a reference metal strain gauge (ASTM E251 standard) in parallel.

[0101] Signal Acquisition: Measure the Rayleigh mode resonance frequency shift (center frequency 195 MHz) using a network analyzer (Keysight N5221B).

[0102] Loading Conditions: Apply an axial strain range of ±3000 με with a step size of 500 με at a temperature environment of 25°C.

[0103] Results: The frequency shift has a linear relationship with strain (R 2 >0.99), and the sensitivity reaches 138.8 Hz / με, which is better than traditional rigid substrate sensors (<30 Hz / με).

[0104] (2) Temperature Stability Verification:

[0105] Temperature Range: 25°C – 100°C. The resonance frequencies of the dual modes (Rayleigh and thickness shear modes) shift synchronously, and the TCF ≈ -75 ppm / °C.

[0106] Adopt the beat frequency method (Δf b = f Rayleigh - n·f TSM ) to eliminate the interference of temperature on strain measurement.

[0107] 4. Technical Advantages and Innovations

[0108] (1) High-precision Manufacturing: The electron beam evaporation vertical deposition process enables sub-micron-level control of electrode size (line width deviation < ±5%).

[0109] (2) Dual-mode Sensing: The Rayleigh mode and thickness shear mode work together, supporting a wide strain range (±3000 με) and temperature self-compensation.

[0110] (3) Flexible Compatibility: The bending radius of the 50-μm lithium niobate thin film substrate < 10 mm, suitable for wearable devices and curved surface fitting scenarios.

[0111] 5. Application Scenarios

[0112] (1) Industrial Monitoring: Health monitoring of mechanical structures (such as bridges, aircraft skins).

[0113] (2) Biomedical: Implantable flexible sensors for real-time detection of tissue strain.

[0114] (3) Consumer Electronics: Flexible Screen Touch Feedback and Pressure Sensing.

[0115] Example 2: Preparation and Testing of Interdigitated Electrodes in Biosensors;

[0116] 1. Substrate Selection and Pretreatment;

[0117] Substrate Material: Borosilicate Glass Slide (Thickness: 1 mm, Optical Grade, Surface Roughness < 0.5 nm).

[0118] Pretreatment includes:

[0119] (1) Ultrasonic Cleaning: Immerse the glass slide in a mixed solution of acetone / isopropanol (volume ratio 1:1), and ultrasonically clean it at a frequency of 50 kHz for 30 minutes to remove surface organic contaminants.

[0120] (2) Plasma Activation: Treat it in an Ar / O2 mixed gas (ratio 3:1) environment at a power of 100 W for 5 minutes to enhance surface hydrophilicity and photoresist adhesion.

[0121] 2. Double-Layer Photoresist Coating and Patterning;

[0122] (1) Bottom Layer Resist (LOR-10B): Spin coating speed: 4000 rpm, pre-baking temperature 190 °C, time 5 minutes, resist layer thickness 1.0 μm.

[0123] (2) Top Layer Resist (S1813): Spin coating speed: 3000 rpm, pre-baking temperature 115 °C, time 5 minutes, resist layer thickness 1.0 μm.

[0124] (3) Patterned Exposure:

[0125] Mask Alignment Accuracy: ±50 nm, UV Exposure Wavelength 365 nm, Dose 50 mJ / cm 2 .

[0126] 3. Development and Hard Baking

[0127] (1) Developer: 2.38% TMAH Solution, Development Time 45 Seconds, to form a "T-shaped" photoresist structure.

[0128] (2) Hard Baking: Bake at 150 °C for 10 minutes to improve the mechanical stability of the resist layer.

[0129] 4. Metal Deposition and Lift-Off

[0130] (1) Electron Beam Evaporation:

[0131] Vacuum Degree: 3×10 -7Pa, electron beam energy 12 keV, aluminum target deposition rate 0.6 nm / s, total thickness 100 nm (error ±0.5 nm).

[0132] (2) Stripping:

[0133] Stripping solution: NMP (N-methylpyrrolidone), ultrasonic power 50 W, time 30 minutes, to completely remove the residual photoresist.

[0134] 5. Interdigitated electrode parameters and function verification

[0135] (1) Interdigitated structure: finger width W = 15 μm, spacing S = 10 μm, finger length L = 2 mm.

[0136] (2) Biosensing test:

[0137] Experimental design: Integrate the interdigitated electrode into a microfluidic chip and inject a culture solution containing cardiomyocytes (H9c2 cell line).

[0138] Signal detection: Real-time monitor the capacitance change caused by cell mechanical beating through an impedance analyzer (frequency range 100 Hz–10 MHz).

[0139] Result: The electrode shows a capacitance change rate ΔC / C0 = 1.8% during cell contraction, and the signal-to-noise ratio (SNR) > 20 dB, verifying its high-sensitivity response to biomechanical signals.

[0140] 6. Technical advantages

[0141] Compatibility: The borosilicate substrate meets the requirements of biocompatibility and has high light transmittance, facilitating microscopic observation.

[0142] Stability: The electron beam evaporation process ensures that the edges of the metal electrodes are steep and free of burrs, avoiding interference from cell adsorption.

[0143] Extended application: The electrode can be further modified with antibodies or DNA probes for specific biomolecule detection.

Claims

1. An interdigital electrode applicable to a sensor device, characterized in that, Composed of the following parts as follows: Substrate, selected from silicon, lithium niobate, borosilicate glass or flexible materials; Interdigital array, composed of periodically alternating metal finger electrodes, including: Positive fingers: A group of parallel metal electrodes with a width of W and a spacing of S; Negative fingers: Interleaved with the positive fingers, having the same width and spacing as the positive fingers; Lead electrodes: Located at both ends of the interdigital array for connecting to an external circuit; Wherein: the finger width W is 0.5 μm to 50 μm; the spacing S is 0.5 μm to 50 μm; the finger length L is 100 μm to 5 mm; the layer thickness T is 50 nm to 500 nm, meeting the balance of conductivity and mechanical stability.

2. The preparation method of the interdigital electrode according to claim 1, characterized in that; The specific steps are as follows: Step 1: Substrate pretreatment, including: (1) Cleaning: Place the substrate in an acetone / isopropanol mixed solution and perform ultrasonic cleaning; the ultrasonic frequency is 40 kHz to 60 kHz, and the cleaning time is 20 minutes to 40 minutes; (2) Plasma activation: Use a plasma cleaning device to activate the surface of the substrate in an Ar / O2 mixed gas environment; the activation power is 80 W to 120 W, and the processing time is 3 minutes to 8 minutes; Step 2: Double-layer photoresist coating; including: (1) Bottom layer resist coating: Use LOR-10B photoresist and spin-coat it evenly on the surface of the substrate at a spin-coating speed of 3000 rpm to 5000 rpm; perform pre-baking at a temperature of 180 °C - 200 °C for 4 - 6 minutes, and the thickness of the resist layer is 0.8 - 1.2 μm; (2) Top layer resist coating: Use S1813 positive photoresist and spin-coat it on top of the bottom layer resist at a spin-coating speed of 2500 - 3500 rpm; perform pre-baking at a temperature of 110 °C to 120 °C for 4 - 6 minutes, and the thickness of the resist layer is 0.8 - 1.2 μm; Step 3: Patterned exposure; (1) Mask alignment: Precisely align the mask with the substrate coated with photoresist, and the alignment accuracy is 30 nm to 100 nm; (2) Exposure: Perform exposure using an ultraviolet light source with a wavelength of 365 nm, and the exposure dose is 30 mJ / cm 2 to 60 mJ / cm 2 ; Step 4: Development and hard baking; (1) Development: Immerse the exposed substrate in a tetramethylammonium hydroxide developer for 30 - 60 seconds; (2) Hard baking: After development, place the substrate on a hot plate at 140 - 160 °C for hard baking for 8 - 12 minutes; Step 5, metal deposition; using electron beam evaporation: in a chamber with a vacuum degree of 1×10 -7 Pa to 5×10 -6 Pa, deposit a metal layer through an electron beam evaporation device; the electron beam energy is 10 keV to 15 keV, the deposition rate is 0.3 nm / s to 1.0 nm / s, and the thickness error is controlled within 0.3 nm to 1.0 nm; (2) Target material selection: The metal target material is aluminum, gold or platinum with a purity ≥ 99.999%, selected according to the device application requirements; Step 6, Lift-off; Immerse the substrate after depositing the metal in an N-methylpyrrolidone or acetone lift-off solution, apply ultrasonic waves for lift-off, the ultrasonic power is 40 W to 60 W, and the time is 20 minutes to 40 minutes; after lift-off is completed, rinse the substrate with deionized water and dry it to obtain an interdigital electrode with high precision.

3. A surface acoustic wave sensor or biosensor using the interdigital electrode as described in claim 1; in the surface acoustic wave sensor, the interdigital electrode excites and receives acoustic waves, and the medium perturbation changes the acoustic wave propagation characteristics; in the biosensor, the analyte molecules are adsorbed on the surface of the interdigital electrode, changing the double-layer capacitance or Faraday impedance.

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