RU2491684C2 - Multilayer ceramic heterostructure with magnetoelectric effect and method for production thereof - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to making magnetoelectric converters used as a base for magnetic field sensors, microwave electronic devices, for magnetoelectric information recording technology and for electromagnetic energy and vibration energy storages. The method involves forming a stack of alternating magnetostrictor and piezoceramic layers. Said stack is formed in three steps: first, electroconductive contacts are deposited on the entire surface of magnetostrictors; all surfaces of magnetostrictors and piezoceramic, except end surfaces, are coated with a layer of electroconductive epoxy adhesive, after which a stack of alternating magnetostrictor and piezoceramic layers is formed. The layers are joined by pressing at temperature of 60-100°C and excess pressure of (1.3-2.6)·10⁵ Pa. The multilayer ceramic heterostructure contains 9-11 magnetostrictor and piezoceramic layers. The piezoeceramic layer has thickness of 0.10-0.13 mm and the magnetostrictor layer has thickness of 0.25-0.30 mm.

EFFECT: low power consumption and high sensitivity.

2 cl, 2 tbl, 4 dwg

Description

The invention relates to electronic equipment, namely: to the field of creating magnetoelectric converters used as the basis for magnetic field sensors, microwave electronics devices, the basis for magnetoelectric information recording technology and for storage of electromagnetic energy and vibration energy.

The invention is illustrated in graphic materials (Figure 1 ÷ 4, Tables 1 ÷ 2).

Figure 1. Multilayer ceramic heterostructure with magnetoelectric effect.

1 - a layer of conductive glue; 2 - piezoceramics; 3 - magnetostrictor; 4 - conductive contact.

Figure 2. Dependences of the magnetoelectric response on the magnitude of the constant magnetic field at the frequency of one of the resonances.

Figure 3. The prototype of the claimed device. Permanent magnetic field sensors.

a) a single-element sensor; b) - two-element sensor with an extended measurement range of a constant magnetic field;

1 - conductive contact; 2 - piezoceramics; 3 - magnetostrictor; 4 - magnetizing coil.

Figure 4. Tubular furnace for connecting the elements of the package.

Table 1. Characteristics of a layered structure with a magnetoelectric effect obtained by the present method.

Table 2. The main parameters of conductive glue.

A known method for producing layered heterostructures with a magnetoelectric effect (Bichurin M.I., Petrov V.M., Petrov R.V. Ferroelectrics, 2002, v.280, p.199-202, prototype), including:

- the formation of a package of alternating layers of magnetostrictor and piezoceramics by slip casting;

- connection of the layers of the package by sintering at a temperature of 1200 ° C in a tubular or chamber furnace;

- polarization of ceramics by applying voltage in order to induce piezoelectric activity;

- cutting the bag into products of the required size.

Features of the known method:

- high energy costs for the formation of a package of alternating layers of magnetostrictor and piezoceramics by slip casting and sintering of the layers of the package;

- low sensitivity of the finished product to constant and variable magnetic fields.

The technical result of the proposed method is that it is characterized by low energy intensity and the ability to obtain a finished product with high sensitivity to constant and alternating magnetic fields.

The technical result is achieved in that the package is formed in three stages: first, conductive contacts are applied to the entire surface of the magnetostrictors, then all surfaces of the magnetostrictors and piezoceramics, except the end ones, are coated with a layer of electrically conductive epoxy adhesive, after which the package is formed by alternating layers of magnetostrictor and piezoceramics, the layers are pressed by pressing at a temperature of 60 ÷ 100 ° C and overpressure (1.3 ÷ 2.6) · 10 ⁵ Pa.

A study of the prior art found that methods for producing layered heterostructures with a magnetoelectric effect, comprising forming a packet in three stages: first, electrically conductive contacts are applied to the entire surface of the magnetostrictors, then all surfaces of the magnetostrictors and piezoceramics, except the end ones, are coated with a layer of electrically conductive epoxy adhesive, after which the packet is formed by alternating layers magnetostrictor and piezoceramics, the connection of the layers is carried out by pressing at a temperature of 60 ÷ 100 ° C and internal pressure (1,3 ÷ 2,6) · 10 ⁵ Pa, is not detected.

A known method for producing layered heterostructures with a magnetoelectric effect (Bichurin M.I., Petrov V.M., Petrov R.V. Ferroelectrics, 2002, V.280, p.199-202, prototype).

Distinctive features of the proposed method in comparison with the prototype:

- in the known method, the formation of a packet of alternating layers of magnetostrictor and piezoceramics is performed by slip casting, and in the claimed method, the formation of the packet occurs in three stages: first, conductive contacts are applied to the entire surface of the magnetostrictors, then all surfaces of the magnetostrictors and piezoceramics, except the end ones, are coated with a layer of electrically conductive epoxy glue, after which a packet is formed by alternating layers of magnetostrictor and piezoceramics, the layers are joined by pressing at a temperature of 60 ÷ 100 ° C and overpressure (1.3 ÷ 2.6) · 10 ⁵ Pa,

- in the known method, the layers of the package are connected by sintering at a temperature of 1200 ° C, and in the claimed method by pressing at a temperature of 50 ÷ 100 ° C and overpressure (1.3 ÷ 2.6) · 10 ⁵ Pa;

- the known method includes the stage of polarization of piezoceramics after the formation of the structure by applying voltage, in the inventive method, this stage is absent.

Known layered heterostructure with a magnetoelectric effect (patent for the invention No. 2244318, 2005, prototype), containing alternating layers of magnetostrictor and piezoceramics (Figure 3).

The known device contains an electrically conductive contact 1, a layer of piezoceramics 2, a magnetostrictor 3 and a magnetizing coil 4.

A disadvantage of the known device is its low sensitivity to constant and alternating magnetic fields.

The technical result of the claimed device is that the sensitivity of a layered heterostructure with a magnetoelectric effect to a constant magnetic field reaches 3.5 · 10 ^-6 T, to an alternating magnetic field - 80 · 10 ^-9 T. The maximum value of the coefficient of magnetoelectric conversion is 45 V / (cm · E) and is observed near the piezomechanical resonance at a frequency f = 144 kHz, the material is located near the magnetic saturation µ _o H _DC = 5 mT, simulating the field µ _o H _DC = 0.15 mT; there are no voltage drops on the dielectric layers of magnetostrictive ceramics due to the creation of a conductive layer on the surface of the ferrite plates; sensitivity for constant and alternating fields is 3.5 · 10 ^-6 T and 80 · 10 ^-9 T, respectively; the range of working constant fields is 0 ÷ 0.12 T, for a variable field - 0 ÷ 0.06 T.

The technical result is achieved by the fact that the device contains 9 ÷ 11 alternating layers of magnetostrictor and piezoceramics, the thickness of the layer of piezoceramics is 0.10 ÷ 0.13 mm, magnetostrictor is 0.25 ÷ 0.30 mm.

Distinctive features of the claimed device in comparison with the prototype:

- in the known device, the thickness of the layer of piezoceramics and magnetostrictor is less than 70 microns, and in the claimed thickness of the layer of piezoceramics is 0.10 ÷ 0.13 mm, magnetostrictor is 0.25 ÷ 0.30 mm (The generated voltage in the piezoelectric layers is proportional to the thickness, moreover the absolute deformation caused by magnetosriction is proportional to the thickness of the magnetoactive layer, both of which increase the output of the magnetoelectric signal, which simplifies its detection);

- the dielectric layers of the magnetically active material are electrically shorted due to the application of electrically conductive contacts to the surface of the magnetic ceramic. This eliminates the voltage drop across the dielectric layers of the magnetostrictor.

Description of the invention

A composite ceramic hetero structure can be considered as a battery of series-connected capacitors made of piezoelectric ceramics. Each piezoelectric element of the battery is mechanically rigidly connected to ceramic magnetically active materials - magnetostrictive ferrites. The layers of ferrite, in turn, are completely coated with electrically conductive contacts, which provides electrical contact between the layers of the piezoelectric material. The whole compositional heterostructure is mechanically monolithic.

When the magnetic field changes, ferrite sizes change due to magnetostriction, which causes mechanical effects on the piezoelectric elements, this leads to the appearance of a potential difference on each piezoelectric element and the total potential difference between the upper and lower metallization layers of the composite heterostructure as a whole; a change in the boundary conditions of the equations of state of piezoelectric ceramics in piezoelectric elements, this leads to a change in the dielectric constant and, accordingly, the capacitance of the heterostructure as a whole; a change in the elastic characteristics of the heterostructure and its dimensions, this leads to a change in the resonance and antiresonance frequencies of various vibration modes. With such a composite ceramic structure, one can measure:

- the potential difference arising between the upper and lower metallization layers of the composite heterostructure;

пьезокерамики и размерами пьезоэлементов;- the capacity of the heterostructure, which is determined mainly by the dielectric constant $${\epsilon }_{}^{}$$$${}_{33}^T/{\mathrm{<figure-callout\; id="0"\; label="\epsilon "\; filenames="00000005.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_0$$

piezoceramics and the size of the piezoelectric elements;

и антирезонанса $$f_a^i$$

, которые определяются, в основном, модами колебаний, размерами и упругими характеристиками композиционной гетероструктуры в целом.- resonance frequencies $$f_r^i$$

and antiresonance $$f_a^i$$

, which are determined mainly by vibration modes, sizes and elastic characteristics of the composite heterostructure as a whole.

An example of the method

A number of samples of magnetoelectric layered heterostructures were manufactured using the created technology.

The dimensions of the construction of multilayer composite ceramic hetero structures based on magneto and piezoelectric materials and the number of layers are selected taking into account the maximum magnitude of the magnetoelectric response from the heterostructure and the technical parameters required for magnetic field measurement sensors.

Size ranges are technologically convenient: - length L ~ (5-30) mm; - width W ~ (5 ÷ 30) mm; - height H ~ (0.15 ÷ 3) mm. The thickness of the ceramic layers of magnetostrictive ferrites t ₁ and piezoelectric elements t ₂ can vary in the range of ~ (30 ÷ 300) μm.

The package consisted of 11 alternating layers of the PZT-46 piezoelectric material and the magnetostrictive material of nickel-zinc ferrite of the composition Ni _0.8 Zn _0.2 Fe ₂ O ₄ .

The fabrication of packages of multilayer composite heterostructures was carried out by gluing layer-by-layer ferrite and piezoelectric layers, followed by under-pressing and low-temperature annealing.

As a material for the formation of a strong mechanical bond between the layers, TDS CW2460 conductive epoxy adhesive was used. The main parameters of the adhesive are presented below in Table 2.

To ensure electrical contact between the layers of piezoelectric ceramics, silver electrodes were deposited on the surface of the ferrite plates. The thickness of the layer of conductive material made of an alloy of silver with palladium is chosen technologically minimal - of the order of h ~ (1.5 ÷ 6.0) μm.

After gluing the layers, the bag was placed in a pressing device and annealed at a temperature of 60 ÷ 100 ° C in a TZF 15/610 three-zone tube furnace in an air atmosphere (Figure 4).

The magnitude of the magnetoelectric effect in planar structures is characterized by the ME conversion coefficient k. Another important indicator is the sensitivity of the sensor to constant and variable fields. To use this heterostructure as a magnetic field sensor, it is important to have a linear relationship between the external field and the voltage value taken from the plates of the composite.

The characteristics of the device obtained in this way are presented in Table 1.

The inventive method was tested in the laboratories of Tver State University with obtaining samples of a multilayer ceramic heterostructure with a magnetoelectric effect.

The inventive layered structure with a magnetoelectric effect can be used as the basis for a magnetoelectric transducer of constant and slowly varying alternating magnetic fields.

Table 1 ME conversion coefficient k, V / cm * E Sensitivity for a constant field, T Sensitivity by an alternating field, T Range of working constants, T Range of working variables, T The linearity range of the composite, T Max. value 45 V / cm * O. It is observed near the piezomechanical resonance Г = 144 kHz, the material is near magnetic saturation μ _o H _DC = 5 mT, the simulating field μ _o H _AC = 0.15 mT 3.5 * 10 ^-6 80 * 10 ^-9 0-0.12 0-1 0-0.005

table 2 Parameter Test method Value Minimum operating temperature, ° C -55 Maximum working temperature, ° C 150 Hardening time At 24 ° C, h 5 At 65 ° C, min fifteen Working time with the material at a temperature (22 ^V C), min 10 Ratio of components 1: 1 Volume resistivity at temperature (25 ° С), Ohm × cm ³ MIL-STD-883E NOTICE 3, method 5011.4 0,038 Tensile strength, kgf × cm ASTM-D-638-02A 70 Elongation,% ASTM-D-638-02A 0.3 The compressive strength, kgf × cm ² ASTM-D-638-02A 77.34 Bending force, kgf × cm ² ASTM-D-790-03 0.1758 Shear strength, kgf × cm ² ASTM-D-732-02 16.45 Impact strength of the sample with Izod notches, J × m ² ASTM-D256-02 1 819.59 Coefficient of thermal expansion, mm / mm ASTM-E-831-03 79.3 × 10 ⁶ Specific gravity, g / cm ³ ASTM-D-256-02 E1 2,34 Coefficient of thermal conductivity. W / (m × ° C) ASTM-C-518 0.578

Claims (2)

1. A method for producing multilayer ceramic heterostructures with a magnetoelectric effect, comprising forming a stack of alternating layers of magnetostrictor and piezoceramics, characterized in that the formation of the stack is carried out in three stages: first, conductive contacts are applied to the entire surface of the magnetostrictors, then all surfaces of the magnetostrictors and piezoceramics, except the end ones, covered with a layer of electrically conductive epoxy glue, after which a packet is formed by alternating 9 ÷ 11 layers of piezoceramic magnetoset ictor with thicknesses of 0.10 ÷ 0.13 mm and 0.25 ÷ 0.30 mm, respectively, the layers are joined by pressing at a temperature of 60 - 100 ° C and overpressure (1.3 ÷ 2.6) · 10 ⁵ Pa. 2. A multilayer ceramic heterostructure with a magnetoelectric effect, containing layers of piezoceramics and magnetostrictor, characterized in that the number of layers of piezoceramic magnetostrictor is 9 ÷ 11, the thickness of the layer of piezoceramics is 0.10 ÷ 0.13 mm, magnetostrictor 0.25 ÷ 0.30 mm .

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