Preparation method of single-crack sensor

Abstract

The invention discloses a preparation method of a single-crack sensor, and relates to the technical field of crack strain sensors, and the method comprises the following steps: 1, carrying out fluorination treatment on a silicon wafer in a closed container for 3 h to obtain a hydrophobic surface; 2, mixing the PMDS main agent and the curing agent according to the mass ratio of 10: 1, and then stirring the mixture by using a centrifugal mixer until the mixture is uniform; after the mixture is uniform, putting the mixture into a vacuum chamber to eliminate bubbles; carrying out spin coating on the fluorinated silicon wafer at a speed of 150r / min for 60s, and drying in a drying oven at 80 DEG C for 2h to obtain a PDMS film; 3, cutting the PDMS film into long strips with the length of 30mm and the width of 7mm, and attaching a pre-designed metal mask structure to the central position of the PDMS; according to the invention, by controlling a single crack in the conductive layer, cracks are prevented from being generated at other positions, the SWCNT conductive network on the crack provides a stable conductive channel, and the prepared crack strain sensor has better stability while maintaining high sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of crack strain sensors, and particularly relates to a preparation method of a single-crack sensor. Background Art

[0002] Metal crack sensors are widely used in the detection of various weak physiological signals due to their excellent sensitivity and stretchability. Their working principle is that when the external strain causes the substrate to deform, the cracks in the conductive layer open or close, resulting in a change in resistance.

[0003] Stability and sensitivity are crucial performance of metal crack sensors. The stability of metal crack sensors is usually poor. After applying strain for a period of time, there are significant changes in their initial resistance and relative resistance change, which is related to uncontrollable crack propagation. The sensitivity of metal crack sensors is related to the number and morphology of cracks. Although increasing the number of cracks and forming channel cracks can improve the sensitivity, the problem of uncontrollable propagation of multiple cracks still exists and will lead to a decrease in stability. A feasible method is to prepare a single-channel crack to avoid the uncontrollable propagation of most cracks. Therefore, the present invention proposes a preparation method of a single-crack sensor herein. Summary of the Invention

[0004] The purpose of the present invention is to solve the defects existing in the prior art, and a preparation method of a single-crack sensor is proposed.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A preparation method of a single-crack sensor, the method comprising the following steps: Step 1: Fluorinate the silicon wafer in a sealed container for 3 h to obtain a hydrophobic surface; Step 2: Mix the PMDS main agent and the curing agent in a mass ratio of 10:1, and then stir the mixture with a centrifugal mixer until it is uniform; after the mixture is uniform, place it in a vacuum chamber to remove air bubbles; spin-coat on the fluorinated silicon wafer at a speed of 150 r / min for 60 s, and dry it in an 80 °C oven for 2 h to obtain a PDMS film; Step 3: Cut the PDMS film into a strip with a length of 30 mm and a width of 7 mm, attach the pre-designed metal mask structure to the center position of the PDMS, and sequentially deposit a 5-nm Cr brittle induction layer and a 40-nm Au conductive layer by electron beam; Step 4: Use an alcohol droplet to infiltrate the contact surface between the metal mask and the flexible substrate, cooperate with tweezers to remove the metal mask, and dry it naturally for later use; Step 5: Fix the distance between the clamps of the sensor on the micron stretching stage at 20 mm, stretch the metal mask at a step of 1 um / S to control the formation of a single crack, and at the same time use liquid metal as the electrode to collect data. When the single crack penetrates and the resistance ≥ 10 6 orders of magnitude, stop stretching; Step 6: Keep the strain state of the stopped stretching, use a microliter syringe to drop 1 ul of 4 g / L SWCNT solution on the single crack, then dry it at 50 °C for 10 minutes, and cool it to room temperature to obtain the sensor.

[0006] Further, in the step 2, the mixture of the PMDS main agent and the curing agent is put into a vacuum chamber for degassing for 30 min after being fully mixed.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: By controlling a single crack in the conductive layer, the present invention avoids the generation of cracks in other positions, and the SWCNT conductive network on the crack provides a stable conductive channel. The prepared crack strain sensor has better stability while maintaining high sensitivity. Description of the Drawings

[0008] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0009] Figure 1 It is the sensitivity response curve graph of the single crack sensor prepared by the present invention; Figure 2 It is the stability dynamic response curve graph of the single crack sensor prepared by the present invention when the strain is below 2%; Figure 3 It is the stability dynamic response curve graph of the single crack sensor prepared by the present invention when the strain is 2.45%. Detailed Embodiments

[0010] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention; Referring to Figures 1 - 3 , a preparation method of a single crack sensor, the method includes the following steps: Step 1: Fluorinate the silicon wafer in a sealed container for 3 h to obtain a hydrophobic surface; Step 2: Mix the PMDS base agent and the curing agent at a mass ratio of 10:1, and then stir the mixture with a centrifugal mixer until it is uniform; after the mixture is uniform, place it in a vacuum chamber to eliminate air bubbles (in this embodiment, place it in a vacuum box and evacuate for 30 min), spin-coat on the fluorinated silicon wafer at a speed of 150 r / min for 60 s, and dry in an oven at 80 °C for 2 h to obtain a PDMS film; Step 3: Cut the PDMS film into strips with a length of 30 mm and a width of 7 mm, attach the pre-designed metal mask structure to the center position of the PDMS film, and sequentially deposit a 5-nm Cr brittle induction layer and a 40-nm Au sensing layer by electron beam; where the rate: Cr: 0.5 Å / S, Au: 1 Å / S, current: 1.2 A, 1.4 A; air pressure: 9.0x10 -4 Pa; Step 4: Use an alcohol droplet to infiltrate the contact surface between the metal mask and the flexible substrate, and then slowly remove the metal mask with tweezers to avoid premature crack generation, and set aside after natural drying; Step 5: Fix the distance between the clamps of the sensor on the micro-tensile stage to 20 mm, use a 1-μm / S stepwise stretch for the metal mask to control the formation of a single crack, and at the same time use liquid metal as an electrode to collect data. When the single crack penetrates and the resistance ≥ 10 6 order of magnitude, stop stretching; Step 6: Keep the strain state of the stopped stretching, use a microliter syringe to drop 1 μl of 4 g / L SWCNT solution onto the crack, dry at 50 °C for 10 minutes, and cool to room temperature to obtain the sensor.

[0011] Use the brittle intermediate layer Cr to induce cracks in the sensing layer; use Au as the intermediate sensing layer and CNT as the top sensing layer.

[0012] Deposit a metal layer using a metal mask, and construct a stress concentration structure in the metal layer. Its geometric feature is a pair of stress concentration notches to generate a single crack.

[0013] Figure 1 Shows the sensitivity of the sensor. The sensor shows high sensitivity within 2.5%, and is divided into three segments GF: 647588, 1233120, 6664549.

[0014] Figure 2 Is the detection limit (0.075%) of the sensor, and the cyclic characteristics: stable performance in 5 cycles at 0.5%, 1%, 1.5%, and 2% strain.

[0015] Figure 3For 600 cycles of the sensor under a large strain of 2.45%, it exhibits a stable ultra-large resistance change, and the high-resistance state is quite stable. This is because when the strain is released, the metal closes into a very low-resistance state; when strain is applied, the metal cracks separate, and the CNT network serves as the conductive path. Moreover, the conductive path gradually decreases under strain, and the CNT network film itself has a relatively large resistance, resulting in a cross-order-of-magnitude strain response. Also, due to the stress concentration effect, the deformation mainly occurs in the CNTs on a single crack. Therefore, different from the complex structure of multi-crack sensors, the resistance change of our single-crack sensor has good stability.

Claims

1. A method for preparing a single crack sensor, characterized in that: The method comprises the following steps: Step 1: The silicon wafer is subjected to fluorination treatment in a sealed container for 3 hours to obtain a hydrophobic surface; Step 2: Mix the PMDS main agent and the curing agent in a mass ratio of 10:1, and then stir the mixture with a centrifugal mixer until it is uniform; after the mixture is uniform, put it into a vacuum chamber to eliminate bubbles; spin coat it on the fluorinated silicon wafer at a speed of 150r / min for 60s, and dry it in an oven at 80℃ for 2h to obtain a PDMS film; Step 3: Cut the PDMS film into strips with a length of 30 mm and a width of 7 mm, attach the metal mask to the center of the PDMS, and deposit a 5 nm Cr brittle inducing layer and a 40 nm Au conductive layer in sequence by electron beam; Step 4: Use alcohol droplets to soak the contact surface of the metal mask and the flexible substrate, use tweezers to remove the metal mask, and dry it naturally for later use; Step 5: Fix the distance between the sensors on the micron stretching table to 20mm, use 1um / S step stretching for the metal mask to control the formation of a single crack, and use liquid metal as an electrode to collect data. When a single crack penetrates, the resistance is ≥10 6 Magnitude, stop stretching; Step 6: Keep the strain state of stopping stretching, use a microliter injector to drop 1ul of 4g / LSWCNT solution on the single crack, then dry at 50℃ for 10 minutes, and obtain the sensor after cooling to room temperature.

2. The method for preparing a single crack sensor according to claim 1, characterized in that In the step 2, the mixture of the PMDS main agent and the curing agent is fully mixed and placed in a vacuum box for degassing for 30 minutes.

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