CN102393264A - Pressure sensor based on nano-piezoelectric fiber - Google Patents

Abstract

The invention discloses a pressure sensor based on nano-piezoelectric fiber, relates to a pressure sensor, and provides the pressure sensor which is based on the nano-piezoelectric fiber and has higher sensitivity. The pressure sensor is provided with a silicone substrate, a boron dopped layer, a silicon dioxide thin film, two metal electrodes and the PVDF (Polyvinylidene Fluoride) nano-piezoelectric fiber, wherein the boron dopped layer is arranged on the upper surface of the silicone substrate and connected with the silicone substrate into a whole; a cavity is arranged in the silicone substrate; the silicon dioxide thin film grows on the non-cavity side of the silicone substrate; the metal electrodes are fixed the silicon dioxide thin film; the PVDF nano-piezoelectric fiber is arranged between the metal electrodes directly; and the PVDF nano-piezoelectric fiber are in ohmic contact with and the metal electrodes.

Description

A Pressure Sensor Based on Nano Piezoelectric Fiber

technical field

The invention relates to a pressure sensor, in particular to a pressure sensor based on direct-writing electrospun nano piezoelectric fibers.

Background technique

Piezoelectric sensor is a kind of self-generating sensor. It is based on the piezoelectric effect of certain dielectrics. Under the action of external force, charges are generated on the surface of the dielectric, so as to achieve the purpose of non-electrical measurement. Piezoelectric sensing element is a force sensitive element, which can measure those non-electric physical quantities that can be transformed into force, such as dynamic force, dynamic pressure, vibration acceleration, etc. Piezoelectric sensors have the characteristics of small size, light weight, high frequency response, and high signal-to-noise ratio. Since it has no moving parts, it has a solid structure, high reliability and stability.

Based on the above advantages, piezoelectric sensors have received a lot of attention. For example, piezoelectric acceleration sensors used in computer hard disk anti-drop protection, automatic adjustment of camera focus, automotive airbags, anti-lock braking systems and traction control systems; in recent years, they have been widely used in dynamic pressure measurement. The applied piezoelectric pressure sensor has good dynamic response (high frequency up to 400kHz), and has the advantages of high mechanical strength, fatigue resistance, vibration resistance, high temperature resistance, small size and long life; piezoelectric immune sensor, piezoelectric DNA sensors are used in biomedical measurement to achieve the purpose of immune analysis and DNA recognition.

At present, the most widely used materials for piezoelectric sensors are piezoelectric crystals and piezoelectric ceramics. Among them, piezoelectric crystals are mainly quartz crystals, water-soluble piezoelectric crystals and lithium niobate crystals. Quartz crystals have low sensitivity and no pyroelectricity. Effect (the effect of charge release due to temperature changes), mainly used to measure the force of a large number of values or used in occasions requiring high accuracy and stability and used to make standard sensors; water-soluble piezoelectric crystals are prone to moisture and low mechanical strength , the resistivity is also low, so it is limited to use at room temperature and low humidity environment; lithium niobate has obvious anisotropic mechanical properties, compared with quartz crystal, it is very fragile, and its thermal shock resistance is very poor, so it can be used in processing Care must be taken during assembly and use to avoid excessive force, rapid cooling and rapid heating. Piezoelectric sensors made of piezoelectric ceramics have high sensitivity, but their temperature stability and mechanical strength are not as good as quartz, and they require a higher operating temperature.

The development of piezoelectric polymers has a history of 30 to 40 years. Peterlin et al. observed the ε value of rolled polyvinylidene fluoride (PVDF) in 1967 and confirmed its piezoelectricity. PVDF piezoelectric film has strong piezoelectric properties, its charge piezoelectric constant d is more than 10 times higher than that of quartz, and the value of voltage piezoelectric constant g is about 20 times higher than that of PZT (piezoelectric ceramics). Electrical properties, flexibility, chemical stability, biocompatibility, low acoustic impedance, high bandwidth, easy processing, light weight and low cost, etc., are used in sonar, biomedicine, acoustics, pneumatics and hydraulics Systems, MEMS and MEMS-based fields..

Some scholars have manufactured sensors for different applications based on PVDF. Shrinov et al. manufactured pressure sensors by encapsulating PVDF films on PVDF materials. PVDF pressure sensors manufactured by Gonzalez et al. were used in biomedicine. Jingang et al. simulated and successfully tested PVDF-based deformation and motion sensors.

The piezoelectric properties of PVDF are mainly determined by the content of β-phase PVDF. At present, the methods for preparing β-phase PVDF mainly include high-voltage crystallization, electric field polarization and uniaxial thermal stretching. The first two methods have strict requirements on experimental conditions and equipment, while the latter method is prone to defects. Bhoopesh P. Mahale et al. used the method of spin coating to prepare β-phase PVDF. It is necessary to optimally control the rotation speed and time to obtain a PVDF film of ideal thickness and β-phase.

The manufacturing process of the above PVDF film is complicated, and conditions such as temperature and polarization voltage need to be strictly controlled.

Chinese patent CN1250158 discloses a piezoelectric pressure sensor and two pressure sensors. Both use piezoelectric composite materials consisting of amorphous chlorinated polyethylene, crystalline chlorinated polyethylene and piezoelectric ceramic powder. The first is a piezoelectric cable, which includes an inner conductor composed of a metal helical wire and insulating fine polymer fibers filled therebetween, a piezoelectric composite layer that surrounds the inner conductor, and a metal film attached to a polymer film. constitute the outer conductor. The metal thin film is in contact with the piezoelectric composite layer but separated from the inner conductor, and the protective cover. The second type is a planar pressure sensor. It consists of a planar piezoelectric composite layer sandwiched between two metal film conductors on two polymer films. The metal thin film is in contact with the composite layer, but separated from each other.

Chinese patent CN101573600 discloses a pressure sensor, which includes a fiber Bragg grating (FBG) strain sensor arranged in an optical fiber, a fiber optic strain sensor bearing rod and a pressure enhancing sleeve. The load bar is formed from a first fiberglass epoxy composite having a first stiffness/modulus of elasticity in a strain sensing direction. The sleeve is formed from a second composite material having a lower axial stiffness in the strain sensing direction than the axial stiffness of the load rod in the strain sensing direction. Under an applied hydrostatic load, the sleeve applies an axial compressive load to the portion of the rod on the sleeve. The axial compressive strain to which the rod is subjected is thus increased in the region inside the sleeve compared to the axial compressive strain that would have occurred in the rod if the sleeve were not present.

Contents of the invention

The object of the present invention is to provide a pressure sensor based on nano piezoelectric fiber with high sensitivity in order to overcome the problems of complex PVDF piezoelectric film process and strict manufacturing conditions in the prior art.

The invention is provided with a silicon substrate, a boron-doped layer, a silicon dioxide film, a metal electrode and a PVDF nano-piezoelectric fiber; the boron-doped layer is arranged on the upper surface of the silicon substrate, and the boron-doped layer is integrated with the silicon substrate , there is a cavity in the silicon substrate, the silicon dioxide film is grown on the side of the silicon substrate without the cavity, two metal electrodes are fixed on the silicon dioxide film, and PVDF nano-piezoelectric fibers are directly written between the two metal electrodes , Form ohmic contacts between PVDF nanopiezoelectric fibers and metal electrodes.

The upper surface of the silicon substrate may have a square structure.

The cavity may be a stepped cavity.

The thickness of the silicon dioxide film may be 0.5-1.5 μm.

The metal electrode is fixed on the silicon dioxide film, and the metal electrode can be fixed on the silicon dioxide film by sputtering; the thickness of the metal electrode can be 0.3-0.6 μm.

The PVDF nano-piezoelectric fiber is directly written between two metal electrodes, and the PVDF nano-piezoelectric fiber can be directly written between two metal electrodes through an electrospinning device; the nano-piezoelectric fiber The diameter can be 60-800nm.

The silicon dioxide film serves as an insulating layer. The function of the boron-doped layer is mainly to obtain a pressure-sensitive film with an ideal thickness during the self-stop corrosion process. Two metal electrodes are arranged on the silicon dioxide film, and the metal electrodes are fixed on the silicon dioxide film. PVDF nano piezoelectric fibers are directly written between the two metal electrodes in a direct writing manner through an electrospinning device. When external pressure is applied to the pressure-sensitive membrane of the sensor, the PVDF nano-piezoelectric fiber is deformed due to the force, and due to the piezoelectric effect, a polarization phenomenon occurs inside it, and at the same time, positive and negative opposites appear on the two ends of the nano-piezoelectric fiber. charge. Through the charge amplifier and the measurement circuit, the charge between the two metal electrodes is amplified and measured successively, and then the pressure is calculated.

The sensitive element of the present invention is PVDF nano-piezoelectric fiber. Compared with the traditional PVDF film manufacturing process, the present invention has the advantages of simple process and low cost; the preparation of the material has no strict requirements on the experimental conditions, and can be made at room temperature. conduct. And its shape is fiber, the specific surface area is much larger than the general PVDF film, which can effectively improve the sensitivity of the sensor.

The piezoelectric material used in the present invention is also PVDF, but its form is a fiber with a diameter of nanoscale. Sensitivity is an important index in the sensor, and the sensitivity of the sensing membrane is directly proportional to the surface area of the membrane per unit mass. Since the electrospun nanopiezoelectric fibers have a much larger specific surface area than general-purpose membranes, the sensitivity of the sensor can be improved. The electrospinning device can directly write PVDF nano-piezoelectric fibers between the electrodes. The electrospinning device is mainly composed of four parts: capillary nozzle, fiber collecting plate (device), polymer fluid supply system and high-voltage generating device. The equipment is simple. ; There is no strict requirement on the experimental conditions, it can be carried out at room temperature.

Description of drawings

Fig. 1 is a schematic structural diagram of a pressure sensor based on nano piezoelectric fibers of the present invention.

Fig. 2 is a structural schematic diagram of the silicon dioxide film, metal electrodes and PVDF nano piezoelectric fiber of the pressure sensor based on the nano piezoelectric fiber of the present invention.

FIG. 3 is a cross-sectional view along line A-A of FIG. 2 .

In Figures 1 to 3, each mark is: 1. Silicon substrate 2. Boron doped layer 3. Silicon dioxide film 4. Metal electrode 5. PVDF nano piezoelectric fiber.

Detailed ways

Referring to Figures 1 to 3, the embodiment of the present invention is provided with a silicon substrate 1, a boron-doped layer 2, a silicon dioxide film 3, a metal electrode 4 and a PVDF nano-piezoelectric fiber 5; the boron-doped layer 2 is arranged on a silicon substrate 1, the boron-doped layer 2 is integrated with the silicon substrate 1, a cavity is provided in the silicon substrate 1, a silicon dioxide film 3 is grown on the side of the silicon substrate 1 without the cavity, and two metal electrodes 4 are fixed On the silicon dioxide film 3 , the PVDF nano piezoelectric fiber 5 is directly written between two metal electrodes 4 , and the PVDF nano piezoelectric fiber 5 and the metal electrode 4 form an ohmic contact.

The upper surface of the silicon substrate 1 is a square structure. The cavity is a trapezoidal cavity.

The thickness of the silicon dioxide film 3 is 0.5-1.5 μm.

The metal electrode 4 is fixed on the silicon dioxide film 3, and the metal electrode 4 is fixed on the silicon dioxide film 3 by sputtering; the thickness of the metal electrode 4 may be 0.3-0.6 μm.

The PVDF nano piezoelectric fiber 5 is directly written between the two metal electrodes 4, and the PVDF nano piezoelectric fiber 5 is directly written between the two metal electrodes 4 through an electrospinning device; The diameter of the piezoelectric fiber is 60-800nm.

During the process, the silicon substrate 1 is first subjected to double-sided oxidation, photolithography and other steps to obtain a silicon dioxide film, which acts as a mask layer for blocking boron diffusion. Next, windowize the silicon dioxide film and do boron doping on the silicon substrate 1 to obtain a boron-doped layer 2 with a thickness of 6 μm to 30 μm. The function of the boron-doped layer 2 is mainly to obtain an ideal thickness during the self-stop corrosion process pressure-sensitive membrane. The silicon substrate 1 and the boron-doped layer 2 are integrated, and the inside of the silicon substrate 1 is etched into a stepped cavity by using a self-stop etching technique. Then grow a layer of silicon dioxide film on the side without the cavity, with a film thickness of 0.5-1.5 μm, and finally fix the metal electrode 4 on the silicon dioxide film 3 by sputtering, with a thickness of 0.3-0.6 μm. μm. The magnitude of the pressure is calculated by amplifying and measuring the charge between the two metal electrodes 4 . The PVDF nano-piezoelectric fiber 5 is directly written between two metal electrodes 4 through an electrospinning device, and the fiber diameter is 60-800nm to form a good ohmic contact between the nano-piezoelectric fiber and the metal electrode.

The working process of the present invention is: when external pressure is applied to the pressure-sensitive membrane of the pressure sensor, the PVDF nano-piezoelectric fiber is deformed, and due to the piezoelectric effect of this material, polarization occurs inside it, and at the same time, in the fiber Opposite positive and negative charges appear on the two end faces. The charge between the two metal electrodes 4 is respectively amplified and measured by the charge amplifier and the measuring circuit, and the change of the measurement result indirectly reflects the change of the external pressure, and then the pressure is calculated.

Claims (8)

1. the pressure transducer based on the nanometer piezoelectric fabric is characterized in that being provided with silicon base, boron-dopped layer, silica membrane, metal electrode and PVDF nanometer piezoelectric fabric; Said boron-dopped layer is located at the upper surface of silicon base; Boron-dopped layer and silicon base are connected as a single entity; Be provided with cavity in the silicon base, silicon dioxide film growth does not have a side of cavity in silicon base, and 2 metal electrodes are fixed on the silica membrane; PVDF nanometer piezoelectric fabric directly writes between 2 metal electrodes, forms Ohmic contact between PVDF nanometer piezoelectric fabric and the metal electrode.

2. a kind of pressure transducer based on the nanometer piezoelectric fabric as claimed in claim 1, the upper surface that it is characterized in that said silicon base is a square structure.

3. a kind of pressure transducer based on the nanometer piezoelectric fabric as claimed in claim 1 is characterized in that said cavity is the trapezoidal shape cavity.

4. a kind of pressure transducer based on the nanometer piezoelectric fabric as claimed in claim 1, the thickness that it is characterized in that said silica membrane are 0.5～1.5 μ m.

5. a kind of pressure transducer based on the nanometer piezoelectric fabric as claimed in claim 1 is characterized in that said metal electrode is fixed on the silica membrane, is to adopt the method for sputter that metal electrode is fixed on the silica membrane.

6. a kind of pressure transducer based on the nanometer piezoelectric fabric as claimed in claim 1, the thickness that it is characterized in that said metal electrode are 0.3～0.6 μ m.

7. a kind of pressure transducer as claimed in claim 1 based on the nanometer piezoelectric fabric; It is characterized in that said PVDF nanometer piezoelectric fabric directly writes between 2 metal electrodes, be with the mode of directly writing PVDF nanometer piezoelectric fabric directly to be write between 2 metal electrodes through electrostatic spinning apparatus.

8. a kind of pressure transducer based on the nanometer piezoelectric fabric as claimed in claim 1, the diameter that it is characterized in that said nanometer piezoelectric fabric is 60～800nm.

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