CN100419346C - Ferroelectric ceramic microrefrigerator and preparation method thereof - Google Patents

Abstract

A ferroelectric ceramic micro-refrigerator and a preparation method thereof. It is characterized in that the micro-refrigerator adopts a "double-stage cascade" refrigeration structure, and the preparation of the micro-refrigerator of the present invention adopts the relaxivity Pb(Mg _1/3 Nb _2/3 ) O ₃ and PbTiO ₃ solid solution wet sol-gel preparation method, and adopt a new physical and chemical thinning method and electric heating performance detection means. The wet sol-gel preparation method of the present invention can effectively inhibit the formation of the pyrochlore phase in the subsequent sintering process, and solve the problem of component segregation caused by uneven mixing and the introduction of metal ion impurities in the dry ceramic mixing process of the prior art. The problem is that the conditions for forming porcelain are lower than those of the conventional PMNT ceramic preparation process. The ferroelectric ceramic microrefrigerator of the present invention is light in weight, small in size, noiseless, pollution-free, and simple in structure, and can be refrigerated directly by applying an electric field without using a refrigerant; the refrigerating start-up is fast, and the refrigerating efficiency is high, especially suitable for micro-scale devices low power refrigeration.

Description

Ferroelectric ceramic microrefrigerator and preparation method thereof

technical field

The invention relates to a micro-refrigerator and a preparation method thereof, in particular to a ferroelectric ceramic micro-refrigerator and a preparation method thereof.

Background technique

At present, various refrigeration methods widely used in micro-refrigerators, such as mechanical compression of working fluid materials and application of electric and magnetic fields, are mainly based on the following three principles:

1) Semiconductor bismuth telluride-based pn junction refrigeration originates from the Peltier effect, but in the final analysis is due to the change of the barrier height during the carrier transition process;

2) Phase change refrigeration, derived from the latent heat change of the phase change of substances under induced conditions, such as ice-salt phase change cooling, dry ice phase change cooling, liquid evaporative cooling and other solid sublimation cooling, etc. Freon, which was eliminated in the 1990s (CFC) refrigeration and lithium bromide refrigeration commonly used at present are typical gas-liquid phase change refrigeration;

3) Entropy-change refrigeration is derived from the adiabatic entropy-change effect of matter under induced conditions, such as magnetic refrigeration is a typical entropy-change refrigeration. Strictly speaking, phase change refrigeration should also belong to entropy change refrigeration, which is a form of entropy change in which the form of matter changes.

Some other refrigeration methods such as throttling refrigeration, pulse tube refrigeration, radiation refrigeration and thermoacoustic refrigeration have not been widely used due to their application in some more extreme conditions.

In order to seek a new way of refrigeration applied in the room temperature range, adiabatic demagnetization refrigeration appeared in the 1980s and became popular for a time. The United States, France and Japan have mastered relatively mature technologies in the field of low-temperature (mK to 20K) magnetic refrigeration research and manufactured refrigeration devices. They are currently seeking suitable magnetic refrigeration materials to improve their refrigeration capacity and efficiency. However, the difficulty in obtaining high-intensity magnetic fields in magnetic refrigeration technology and the high cost of rare earth magnetic working materials also limit the development and application of room temperature magnetic refrigeration. Since high electric fields are easier to obtain than high magnetic fields, and the equipment is simple, coupled with the low cost of ferroelectric materials, the ferroelectric depolarization refrigeration effect is more suitable for room temperature refrigeration than magnetic refrigeration. In the 1990s, researchers considered the entropy cooling of relaxor ferroelectrics, that is, the effect of changing the temperature of ferroelectric materials when an external electric field is applied to them under adiabatic conditions. This effect is also called the reverse pyroelectric effect. Or the electrothermal (EC) effect. Such as literature 1. Shebanov L A, Bornman K J. The application of Ferroelectric and PiezoelectricMaterials. Ferroelectrics, Vol.127, 1992: 143; 2. Xiao D Q, Zhu J G, Yang B, et al. Ferroelectric refrigeratory materials and their application. Piezoelectric and Acoustoptics, Vol.16(8), 1994: 31-35, etc., Russia and other countries reported the use of relaxive Pb(Sc _1/2 Nb _1/2 )O ₃ , Pb(Mg _1/3 Nb _{2/ 3} ) O ₃ (abbreviated as PST, PMN) ferroelectric solid solution realizes adiabatic depolarization refrigeration near room temperature. This research has laid a technical foundation for worldwide ferroelectric refrigeration research.

However, there are some technical problems in the development of ferroelectric refrigerators from prototypes to practical devices, especially in order to meet the needs of modern micro-heating devices and systems with increasingly high integration and high energy density, the refrigerator itself must also be miniaturized . It is undoubtedly the best choice to use microelectromechanical systems (MEMS) technology monolithic integration and compatible microfabrication of ferroelectric materials and heating devices on Si substrates, but this requires depositing high-quality iron materials with a thickness of more than 10 μm on Si substrates. Electrical thick film materials, the technology is still in the exploratory stage.

In order to meet the requirements of miniaturization, the thickness of the ferroelectric ceramic working medium sheet as a ferroelectric refrigeration device must be in the range of 50 μm to 700 μm, and must be uniform. The prior art adopts a hybrid patch method to assemble the ferroelectric refrigeration device and the refrigerator to be cooled together, but it has the following defects in the key steps of the assembly structure of the refrigerator and the preparation of the ferroelectric ceramic and its working medium sheet:

1) Single-layer refrigeration assembly structure, which requires a high driving voltage of about 1500V, and cannot adjust the refrigeration capacity. Therefore, it is necessary to design a multi-layer refrigerator to reduce the driving voltage under the same thickness and enhance the selectivity of the refrigeration cycle.

2) In the traditional dry ceramic preparation process, there are problems such as uneven mixing of materials, causing component segregation and introducing metal ion impurities.

3) It is difficult to obtain ferroelectric ceramic thin slices with a thickness of less than 200 μm and a uniformity of more than 90% by using a grinding machine, and the high-precision crystal slicer cannot prepare large-area thin slices because of the expensive equipment, which is not conducive to ferroelectric ceramics. Popularization and application of electric refrigerators.

4) It is more sensitive to test the EC effect of bulk ceramics by thermocouple contact under traditional silicone oil immersion, but the ferroelectric refrigeration capacity decreases after the working fluid material is miniaturized, and it is difficult for a thermocouple with a sensitivity of about 0.1°C to detect the tiny EC of the working fluid sheet. effect, so a temperature detection method with higher sensitivity must be used.

Contents of the invention

In order to overcome the shortcomings of the prior art, the invention proposes a new ferroelectric ceramic micro-refrigerator and a preparation method thereof. The ferroelectric ceramic microrefrigerator of the present invention adopts a two-stage cascaded refrigeration structure, and adopts relaxant Pb(Mg _1/3 Nb _2/3 )O ₃ and PbTiO ₃ (PT) (PMNT for short) with high EC effect ) solid solution sol-gel (Sol-Gel) wet preparation method, and a new physical and chemical thinning method and electrothermal (EC) performance detection means.

The ferroelectric ceramic microrefrigerator of the present invention is light in weight, small in size, noiseless, pollution-free, simple in structure, can be refrigerated directly by applying an electric field, and does not need to use a refrigerant; the refrigerating start is fast, and the refrigerating/heat conversion is conveniently performed; High refrigeration efficiency and low cost, especially suitable for low-power refrigeration of micro-scale devices.

The technical scheme adopted in the present invention:

The ferroelectric ceramic microrefrigerator of the present invention adopts a "double-stage cascade" refrigeration structure. The feature of this structure is: the double-layer ferroelectric ceramic sheet composed of two single-layer ferroelectric ceramic sheets is coupled through low-temperature eutectic ceramic technology to form the so-called "double-stage" structure in the working state, and then the two "double-stage "The structure is superimposed on the front and back sides of the heat-collecting mica sheet and the mica sheet to form a so-called "cascade" structure. In this "double-stage cascade" refrigeration structure, the upper and lower surfaces of each layer of ferroelectric ceramic sheets are covered with Sn/Ag electrodes, and the "double-stage" structure shares a layer of Sn/Ag electrodes. Between the underlying Sn/Ag electrode coated on the mica sheet and the mica sheet, it accelerates heat conduction; the two "double-stage" structures correspond to the front and back of the mica sheet.

The ferroelectric ceramic micro-refrigerator with double-stage cascade structure of the present invention adopts the working principle of cooling when the ferroelectric is depolarized, so its working state must include adding positive electric field polarization and adding reverse electric field depolarization. process. The specific working process is: take (0-16) kV/cm as the forward electric field, start from zero field strength and increase the field strength at a rate of 4kV/(cm.min) to 16kV/cm, and complete the polarization process; then switch the input The polarity of the electrodes also uses (0-16) kV/cm as the reverse electric field, and the field strength starts from 16kV/cm at a rate of 8kV/(cm.min) to stop at zero field strength to complete the depolarization process. Using this slow polarization and fast depolarization working method can effectively increase the net cooling capacity of the single cycle process; the double-stage cascade structure can double the driving voltage under the same total thickness, and through a certain refrigeration The on-off control of the electric field of the chip enhances the selectivity of the refrigeration cycle and obtains refrigeration capacity at all levels. For example, for a two-stage cascade structure with a total thickness of 1mm, including four refrigerating sheets each with a thickness of 200μm, only a voltage of 320V can be applied to make the applied field strength reach 16kV/cm, and if a single-layer refrigerating sheet with a thickness of 800μm is adopted , it is necessary to apply a voltage of 1280V to make the applied field strength reach 16kV/cm, and this single-layer refrigeration sheet has only one set of electric field on-off options, and only one refrigeration capacity can be obtained.

The method and process steps of preparing ferroelectric ceramic micro-cooler of the present invention are as follows:

1. Preparation of relaxant Pb(Mg _1/3 Nb _2/3 )O ₃ and PbTiO ₃ solid solution referred to as PMNT

Domestic analytical pure Pb(C ₂ H ₃ O ₂ ) ₂ powder, chemically pure Ti(OC ₄ H ₉ ) ₄ solvent, Mg(C ₂ H ₃ O ₂ ) ₂ and electronically pure Nb ₂ O ₅ powder were used as the Raw materials, according to the formula of Pb(Mg _1/3 Nb _2/3 )O ₃ (referred to as PMN) and PbTiO ₃ (referred to as PT) with a molar ratio of 85/15, and the excess of Mg in the sample is 4-6 mol%, Pb The excess of ingredients is 5-8 mol%.

1) Firstly, the above-mentioned raw materials conforming to the stoichiometric ratio are miscible in an organic solvent of ethylene glycol ether to obtain a white sol (Sol).

2) Putting the sol (Sol) into a ball milling tank and fully ball milling for 8-10 hours, at this time, the components of the raw materials are mixed at the molecular level to obtain the PMNT precursor.

3) Put the PMNT precursor into an infrared oven to fully dry and gel at 120-180°C, then put it into a resistance furnace and pre-fire it at 450-490°C and 750-800°C for 2 hours respectively to obtain PMNT pre-crystallized powder material.

4) The PMNT pre-crystallized powder is pressed into a green body with a mold at a pressure of 120-180Mpa; finally, a 1-3mm thick PMNT ceramic solid solution is prepared according to the conventional ceramic sintering process. Hour.

The technical feature of the wet sol-gel preparation method of the present invention is that the raw materials are mixed at the molecular level in a solid/liquid mixed state, that is, the raw materials have had intermolecular interactions before sintering, and the branched chain structure in the sol Interpenetration, entanglement, aggregation or rearrangement occur to form highly cross-linked polymer units. This polymerization process can effectively inhibit the formation of the pyrochlore phase in the subsequent sintering process, and solve the problem of uneven mixing in the dry ceramic mixing process of the prior art. Both cause problems such as component segregation and the introduction of metal ion impurities, and because the raw materials are fully mixed, the activation free energy required in the sintering process is reduced, which leads to the porcelain-forming conditions of this preparation technology being lower than the conventional PMNT ceramic preparation process.

2. Thinning PMNT ceramic working material and detecting electrothermal (EC) effect

(1) After the relaxation PMNT ceramic is made, it is thinned by a grinding machine combined with an ion milling process

1) Thin the PMNT ceramic sample with a thickness of 1-3mm with a grinding machine first, and reserve a thickness of 50 μm before reaching the required thickness.

2) Then use ion milling to the required thickness (the thickness depends on the cooling capacity requirement). The process parameters of ion milling and etching are: plate spacing 20mm, high-frequency power 500W at 10MHz, vacuum degree 0.13Pa, etching gas SF6, gas flow rate 30-40mL/min, etching time 20-25min.

3) The etching residue on the surface of the sheet is removed by ultrasonic cleaning in water medium, and a uniform and smooth PMNT ceramic sheet can be obtained.

After the ion milling process is completed, part of the etching residue will adhere to the surface of the sheet, affecting the smoothness of the sheet and thus affecting the stability of the subsequent electrode plating process. However, the mechanical polishing process is easy to damage thin slices below 100 μm. Therefore, the present invention adopts an aqueous medium ultrasonic cleaning method to remove etching residues and obtain uniform and smooth PMNT ceramic thin slices. The invention adopts the ion milling process, which can ensure the uniformity of the thickness of the ceramic sheet and the uniformity and stability of the applied electric field intensity.

(2) Thinning by chemical etching process

1) Polishing the PMNT ceramic sheet obtained in the previous process step, and coating polymethyl methacrylate (PMMA) photoresist on the edge of the ceramic sheet by dip coating.

2) After three times of 160-190°C/30min hot plate pre-baking process and one time of fixing with isopropanol (IPA) fixer, the PMMA photoresist will reach a thickness of about 100-150nm.

3) Use a mixed solution with the optimal mol ratio of HCl/HF/NH ₄ F = 1:3:15-20 as the etching solution to obtain ceramic sheets without undercutting on the surface, and finally rinse with acetone to obtain smooth ceramics Flakes.

Experiments show that the above process range can ensure good compactness of the photoresist, and under this premise, the main factor affecting the thinning effect is the etching solution. The present invention obtains the optimum mol ratio of etching solution through experiments as HCl/HF/NH ₄ F = 1:3:15-20, the surface of the ceramic sheet thus obtained is smooth and free from undercutting, and the etching rate is 3-5 μm /min, and finally rinsed with acetone to obtain smooth ceramic flakes. During the grinding and etching process of the ceramic sheet, the thickness above about 100 μm is directly measured with a spiral micrometer, and the etching depth and thickness are obtained by the quasi-focus method of an optical microscope for the sheet below about 100 μm.

The above-mentioned thinning process of PMNT ceramic working fluid materials adopts non-mechanical polishing treatment to prepare ferroelectric ceramic working medium sheets with a thickness in the range of 50 μm to 700 μm, smooth surface and uniform thickness, and the smoothness and uniformity of thickness can be guaranteed. Electrode stability and uniformity of applied electric field strength.

(3) Detection of electrothermal (EC) effects

The invention uses an infrared temperature detector (or an infrared camera) to test the EC effect of the ferroelectric ceramic sheet in real time in a non-contact manner. The basic steps are: first put the ferroelectric ceramic sheet into the plexiglass cover, then lead out the lead wire, connect to the terminal of the DZ2670A withstand voltage tester, and finally apply a field strength to it through the withstand voltage tester, and detect the iron by the infrared probe. The temperature change of the electric ceramic sheet, and the temperature value is displayed by the infrared temperature detector (or the temperature distribution map is displayed by the infrared camera). In this test structure, the following measures are taken to improve the test accuracy:

1) Use a plexiglass cover to prevent air circulation in the test environment, thereby reducing convective heat loss;

2) Using 1/2 spatial resolution infrared probe, the temperature measurement accuracy is 0.02°C, which is much smaller than the 0.1°C resolution of thermocouples;

3) Use heat insulation support and heat insulation pad to reduce the energy exchange between the sample and the base;

4) Adopt high-precision DZ2670A withstand voltage tester to provide DC high voltage applied to the sample;

5) Use φ200μm Al/Cu alloy wire as lead wire to reduce heat conduction loss and Joule heat loss.

Since there is no semiconducting doping element, the resistivity of the ceramic sample is at the TΩ level, and the leakage current intensity is at the nA level. The Joule heat of the sample itself should be less than 0.001°C, which is below the temperature detection sensitivity of this experiment. Therefore, when the ambient temperature is maintained well, the tested temperature change should come from the EC effect. Due to the reduction of ferroelectric refrigeration capacity after miniaturization, the present invention uses a high-precision infrared temperature detector to test the EC effect of the working medium in a real-time non-contact manner, which is more convenient than the traditional thermocouple contact test method under silicone oil immersion.

3. The low-temperature eutectic ceramic technology is used to make a double-stage cascade refrigeration structure

1) First divide the PMNT ceramic sheet into equal-area square pieces; then evenly coat the Sn-containing silver paste with low melting point on both sides of the square piece, and the coating range is slightly smaller than the square piece area;

2) Superimpose the square sheets and sandwich Al/Cu alloy wires with a diameter of 150-200 μm on the upper and lower surfaces and between them as leads;

3) Then put the laminated sheet in the clamped state into a resistance furnace for pre-sintering at 300-400°C for 10-15 minutes; then place it at 750-800°C for 25-30 minutes to fully wet the Sn-containing silver paste Coated and penetrated into the ceramic interface layer.

4) grinding the edge of the multilayer refrigeration structure made by 3) to prevent short circuit; grinding the oxide layer of the electrode lead wire and coating flux thereon;

5) The surface of the upper and lower Sn-containing silver electrodes is coated with a PMMA photoresist with a thickness of about 100 nm by a spin coating process to eliminate electric sparks.

6) Finally, the obtained cooling structure is welded on the dual in-line socket to form a ferroelectric ceramic micro-refrigerator.

So far, the preparation of the ferroelectric ceramic microrefrigerator of the present invention is completed.

Description of drawings

Fig. 1. the structural representation of specific embodiment of ferroelectric ceramic microrefrigerator of the present invention, in the figure: 1Sn/Ag electrode, 2 PMNT ferroelectric ceramic sheet, 3 heat-conducting silicone greases, 4 heat-collecting mica sheets.

Figure 2. X-ray diffraction analysis (XRD) patterns of PMNT ceramics.

Fig. 3. PMNT ferroelectric ceramics EC effect detection device schematic diagram, in the figure: 11 plexiglass cover; 12 infrared temperature probes; 13 ceramic samples, 14 heat insulation supports, 15 electrodes, 16 insulating heat insulating pads, 17 separate infrared thermometers , 18 Hipot tester.

Fig. 4. Refrigeration of 100 μm thick PMNT ceramic flakes under different conditions.

Detailed ways

The ferroelectric ceramic microrefrigerator of the present invention adopts a "double-stage cascade" refrigeration structure. As shown in Figure 1, in this "two-stage cascade" cooling structure, the upper and lower surfaces of each layer of ferroelectric ceramic sheet 2 are covered with Sn/Ag electrodes 1 (the "two-stage" structure shares a layer of Sn/Ag electrodes ), the heat-conducting silicone grease 3 is located between the bottom Sn/Ag electrode coated by the ferroelectric ceramic sheet and the heat-collecting mica sheet 4, which accelerates heat conduction, and the two "double-stage" structures correspond to the front and back of the mica sheet.

Example 1: Analytical pure Pb (C ₂ H ₃ O ₂ ) ₂ powder, chemically pure Ti (OC ₄ H ₉ ) ₄ solvent and Mg (C ₂ H ₃ O ₂ ) ₂ and electronically pure Nb ₂ O ₅ powder Material, etc. are used as raw materials, according to the formula of Pb(Mg _1/3 Nb _2/3 )O ₃ and PbTiO ₃ mol ratio of 85/15, and the excess of Mg component is 4 mol%, and the excess of Pb component is 5 mol%. First, the above-mentioned PMNT raw materials meeting the stoichiometric ratio are miscible in an organic solvent of ethylene glycol ether to obtain a white sol. The sol is put into a ball mill jar and fully ball milled for 8 hours. At this time, various raw material components are mixed at a molecular level to obtain a PMNT precursor. The PMNT precursor was placed in an infrared oven to fully dry and gel at 120°C, and then placed in a resistance furnace for pre-calcination at 450°C and 750°C for 2 hours respectively to obtain PMNT pre-crystallized powder. The PMNT pre-crystallized powder is pressed into a green body with a mold at 120Mpa; finally, a 1-3mm thick PMNT ceramic solid solution is prepared according to the conventional ceramic sintering process.

Example 2: Analytical pure Pb (C ₂ H ₃ O ₂ ) ₂ powder, chemically pure Ti (OC ₄ H ₉ ) ₄ solvent and Mg (C ₂ H ₃ O ₂ ) ₂ and electronically pure Nb ₂ O ₅ powder Mg _1/3 Nb _2/3 )O ₃ to PbTiO ₃ mol ratio is 85/15, and the excess of Mg is 6 mol%, and the excess of Pb is 8 mol%. First, the above-mentioned PMNT raw materials meeting the stoichiometric ratio are miscible in an organic solvent of ethylene glycol ether to obtain a white sol. The sol is put into a ball mill jar, and is fully ball milled for 10 hours. At this time, each raw material component is mixed at a molecular level to obtain a PMNT precursor. The PMNT precursor was placed in an infrared oven to fully dry and gel at 180°C, and then placed in a resistance furnace for pre-calcination at 490°C and 800°C for 2 hours respectively to obtain PMNT pre-crystallized powder. The PMNT pre-crystallized powder is pressed into a green body with a mold at 160Mpa; finally, a 1-3mm thick PMNT ceramic solid solution is prepared according to the conventional ceramic sintering process, and the sample sintering temperature is 1250°C and kept for 2 hours.

Example 3: Analytical pure Pb (C ₂ H ₃ O ₂ ) ₂ powder, chemically pure Ti (OC ₄ H ₉ ) ₄ solvent and Mg (C ₂ H ₃ O ₂ ) ₂ and electronically pure Nb ₂ O ₅ powder Mg _1/3 Nb _2/3 )O ₃ to PbTiO ₃ mol ratio is 85/15, and the excess of Mg is 5 mol%, and the excess of Pb is 7 mol%. First, the above-mentioned PMNT raw materials meeting the stoichiometric ratio are miscible in an organic solvent of ethylene glycol ether to obtain a white sol. The sol is put into a ball mill jar and fully ball milled for 9 hours. At this time, each raw material component is mixed at a molecular level to obtain a PMNT precursor. Put the PMNT precursor into an infrared oven to fully dry and gel at 160°C, then put it into a resistance furnace and pre-fire it at 470°C and 800°C for 2 hours respectively to obtain PMNT pre-crystallized powder. The PMNT pre-crystallized powder is pressed into a green body with a mold at 140Mpa; finally, a 1-3mm thick PMNT ceramic solid solution is prepared according to the conventional ceramic sintering process.

Auger electron spectroscopy and X-ray diffraction analysis (XRD) were used to determine the porcelain formation of the PMNT solid solution obtained in Example 3. The results show that the obtained PMNT ceramics have diffraction peaks of pure perovskite phase structure, no miscellaneous peaks exist, and the ceramic composition conforms to the predetermined stoichiometric ratio. Fig. 2 is the XRD spectrum of the PMNT ceramics obtained in Example 3. It can be seen from the figure that the Sol-Gel preparation technology effectively inhibits the formation of the pyrochlore phase, and the porcelain-forming conditions of this preparation technology are lower than those of the conventional PMNT ceramic preparation process.

Thinning by chemical etching process with photoresist protection on ceramic edges. Firstly, the PMNT ceramics are polished, and the edge is dip-coated with polymethyl methacrylate (PMMA) photoresist, after three times of 160-190°C/30min hot plate pre-baking process and one time of isopropyl alcohol (IPA) fixer After fixing, the PMMA photoresist is about 100-150nm thick. Experiments show that the above process range can ensure good compactness of PMMA photoresist, and under this premise, the main factor affecting the thinning effect is the etching solution. The present invention adopts the optimum molar ratio of etching solution as HCl/HF/ _NH4F =1:3:15-20, so that the surface of the ceramic sheet obtained by this method is smooth and free from undercutting phenomenon, and the etching rate is 3-5 μm/min , and finally rinsed with acetone to obtain smooth ceramic flakes. During the grinding and etching process of the ceramic sheet, the thickness above about 100 μm is directly measured with a spiral micrometer, and the etching depth and thickness are obtained by the quasi-focus method of an optical microscope for the sheet below about 100 μm.

For the smooth and uniform ceramic sheet obtained by the above-mentioned ceramic preparation process and thinning process, an infrared temperature detector is used to test its EC effect in real time. As shown in Figure 3, put the ceramic sample 13 into the plexiglass cover 11, use the heat insulation support 14 and the insulation pad 16 as the thermal insulation structure with the base, and then lead the lead wire out through the electrode 15, and connect it to the DZ2670A withstand voltage tester 18 binding posts, the field strength is applied by the DZ2670A withstand voltage tester, the temperature change of the ferroelectric ceramic sheet is detected by the infrared temperature probe 12, and the temperature value is displayed by the SCIT separate infrared temperature detector 17.

Through experiments, the main parameters and performance indicators that the ferroelectric ceramic micro-cooler of the present invention reaches are as follows:

Heat absorption efficiency: 109mJcm ^-3 ;

430μm thick 5cm ² PMNT ceramic sheet single-stage refrigeration capacity: θ ₀ =4.7mW;

(The existing technologies for the above indicators are respectively μJcm ^-3 and μW levels);

Cooling power: 2×10 ^-5 Wmm ^-3 ;

Working temperature zone: 260-320K;

Energy conversion efficiency: >85%.

Figure 4 is the cooling situation of 100 μm thick PMNT ceramic flakes under different conditions. It can be seen from Figure 4 that the maximum linear electrothermal (EC) effect EC _max δT is 1.71°C (single-stage single cycle, at 18°C and 16kV/cm reverse depolarization process).

The low-temperature eutectic ceramic technology is used to make a double-stage cascaded refrigeration structure.

1) First divide the PMNT ceramic sheet into equal-area square pieces; then evenly coat the Sn-containing silver paste with low melting point on both sides of the square piece, and the coating range is slightly smaller than the square piece area;

2) Superimpose the square sheets and sandwich Al/Cu alloy wires with a diameter of 150-200 μm on the upper and lower surfaces and between them as leads;

3) Then put the laminated sheet in the clamped state into a resistance furnace, and pre-fire it at 300-400°C for 10-15min; Wetting the coating and penetrating into the ceramic interface layer;

4) grinding the edge of the multilayer refrigeration structure obtained in 3) to prevent short circuit; grinding the oxide layer of the electrode lead wire and coating flux thereon;

5) Coating about 100nm thick polymethyl methacrylate (PMMA) photoresist on the surface of the upper and lower Sn-containing silver electrodes by spin coating process to eliminate electric sparks;

6) Finally, the obtained refrigeration structure is welded on the dual in-line socket to form a ferroelectric ceramic microrefrigerator.

So far, the preparation of the ferroelectric ceramic micro-cooler according to the embodiment of the present invention is completed.

The ferroelectric ceramic micro-cooler of the present invention can be widely used in the refrigeration of devices and systems with small size and general heat dissipation power, such as microelectronic devices, instruments and meters, and micro-small low temperature or thermostats in medical equipment, especially Cooling of components and equipment such as large-scale integrated circuits (ULSI), photosensitive devices, power devices, high-frequency transistors, MEMS and micro-opto-electromechanical systems (MOEMS).

Claims (2)

1. little refrigerator of ferroelectric ceramics, the double-layer ferro-electricity potsherd (2) that it is characterized in that being made up of two individual layer ferroelectric ceramics sheets is by the coupling of low-temperature eutectic ceramic process, form " twin-stage " structure, the ferroelectric ceramics sheet (2) of two " twin-stage " structures is superimposed at thermal-arrest mica sheet (4) tow sides and mica sheet, each layer ferroelectric ceramics sheet (2) upper and lower surface is all draped over one's shoulders Sn/Ag (1) electrode, the shared one deck Sn/Ag of " twin-stage " structure electrode; Heat-conducting silicone grease is positioned between the coated bottom Sn/Ag of ferroelectric ceramics sheet electrode (1) and the mica sheet (4); Two " twin-stage " structures are corresponding in mica sheet (4) positive and negative position.

2. method for preparing the little refrigerator of ferroelectric ceramics is characterized in that its processing step is as follows:

1) preparation abbreviates the relaxation property Pb (Mg of PMNT as _1/3Nb _2/3) O ₃With PbTiO ₃Solid solution;

To analyze pure Pb (C ₂H ₃O ₂) ₂Powder, chemical pure Ti (OC ₄H ₉) ₄Solvent and Mg (C ₂H ₃O ₂) ₂And the pure Nb of electronics ₂O ₅Powders etc. are raw material, press Pb (Mg _1/3Nb _2/3) O ₃With PbTiO ₃Mol ratio is 85/15 prescription, and makes the excessive 4～6mol% of Mg composition, Pb composition excessive (5～8) mol% in sample;

(1) it is miscible in the ethylene glycol ethyl ether organic solvent to meet the above-mentioned raw materials of stoichiometric proportion earlier, obtains leucosol;

(2) colloidal sol is inserted in the ball grinder, the abundant ball milling through 8～10 hours, and each material component obtains the PMNT presoma with the molecular level immixture at this moment;

(3) the PMNT presoma is inserted in the IR bake at 120～180 ℃ down after the abundant dry gelling, put into resistance furnace and distinguish pre-burning 2 hours down, obtain the pre-crystallization powder of PMNT at 450～490 ℃ and 750～800 ℃;

(4) the pre-crystallization powder of PMNT is adopted mould compacting green compact, mold pressing 120～180Mpa; Prepare the thick PMNT pottery of 1～3mm solid solution according to conventional ceramic sintering process at last, the sample sintering temperature is 1180～1250 ℃, is incubated 1～2 hour;

2) adopt wafer lapping machine coupled ion grinding process and chemical etching technology attenuate PMNT potter's material and detection electricity to give birth to fuel factor;

(1) after relaxation property PMNT ceramics sample was made, elder generation with the thick PMNT pottery of 1～3mm solid solution attenuate, reserved the thick surplus of 50 μ m with wafer lapping machine before reaching desired thickness;

(2) adopt the ion mill to be etched to desired thickness then; Ion mill etching technics parameter is: polar plate spacing 20mm, high frequency power 500W under the 10MHz, vacuum 0.13Pa, etching gas SF ₆, gas flow 30～40mL/min, etch period 20～25min;

(3) remove sheet surface etching residue with aqueous medium ultrasonic cleaning mode, can obtain even bright and clean PMNT ceramic sheet;

(4) will go up the PMNT ceramic sheet polishing that a processing step makes, coat the polymethyl methacrylate photoresist with the dip-coating mode at the ceramic sheet edge;

(5) before 3 160～190 ℃/30min hot plates after baking technology and the photographic fixing of 1 isopropyl alcohol fixing solution, it is thick that the polymethyl methacrylate photoresist reaches 100～150nm approximately;

(6) adopting best mol proportioning is HCl/HF/NH ₄F=1: 3: 15～20 mixed liquor obtains the ceramic sheet of the no undercutting phenomenon in surface as etching liquid, adopts the acetone rinsing at last, obtains bright and clean ceramic sheet;

(7) will go up the ceramics sample (13) that a processing step makes inserts in the plexiglass tent (11), adopt heat insulation support (14) and insulation and thermal insulation pad (16) as with the thermal insulation structure of base, by electrode (15) lead-in wire is drawn again, connect DZ2670A Hi-pot Tester (18) binding post, apply field intensity by the DZ2670A Hi-pot Tester, by the variations in temperature of infrared temperature probe (12) detection ferroelectric ceramics sheet, and by SCIT separate infrared hygrosensor displays temperature value;

3) the low-temperature eutectic ceramic process is made refrigeration structure;

(1) will go up the square sheet that PMNT ceramic sheet that a processing step makes divides homalographic into earlier; Evenly apply low-melting Sn silver slurry, the coating scope side of being slightly smaller than sheet area of containing again on square sheet two sides;

(2) folded to be incorporated in upper and lower surface and to fold up diameter between the two be 150～200 with square sheet) the Al/Cu alloy silk of μ m goes between;

(3) lamination layer that will be in then under the clamp position is inserted 300～400 ℃ of following pre-burning 10～15min in the resistance furnace; Insert 750～800 ℃ of following sintering 25～30min again, make to contain the abundant wetting coating of Sn silver slurry, and infiltrate ceramic interfacial layers;

(4) the multilayer refrigeration structure edge that makes of the last processing step of polishing is to prevent short circuit; The oxide layer of polishing electrode outlet line reaches prefluxing thereon;

(5) containing the thick polymethyl methacrylate photoresist of the about 100nm of Sn silver electrode surface employing spin coating proceeding coating up and down to eliminate electric spark;

(6) on the dual-in-line base, weld prepared refrigeration structure at last and form the little refrigerator of ferroelectric ceramics.

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