TWI676611B - Ferroelectric film and method of producing same - Google Patents

Abstract

The present invention provides a ferroelectric thin film with excellent life reliability and a method for manufacturing the same. The ferroelectric thin film is a ferroelectric thin film made of a plurality of fired films, and is made of a metal oxide with a perovskite structure containing Pb, Zr, and Ti. The total content of Li, Na, and K It is 3 mass ppm or less, and the total content of Li, Na, and K on one side of each of the fired films constituting the plurality of fired films is more than 5 times the total content of Li, Na, and K on the other side.

Description

Ferroelectric thin film and manufacturing method thereof

The present invention relates to a ferroelectric thin film with improved lifetime reliability and a method for manufacturing the same.

This application claims priority based on Japanese Patent Application No. 2015-064152 filed in Japan on March 26, 2015 and Japanese Patent Application No. 2016-054836 filed in Japan on March 18, 2016, the contents of which are incorporated herein by reference.

As a ferroelectric thin film used in infrared sensors, piezoelectric filters, vibrators, laser modulators, optical shutters, capacitor films, non-volatile memories, etc., it contains Pb, La, Zr And Ti perovskite structure PLZT film. For example, Patent Document 1 discloses a PLZT thin film in which the contents of Li, Na, and K are reduced and the leakage current is suppressed.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 2956356 (B)

As described in Patent Document 1, if the contents of Li, Na, and K are reduced, the leakage current of the PLZT film can be reduced, but from the viewpoint of lifetime reliability, sufficient characteristics may not be obtained.

An object of the present invention is to provide a ferroelectric thin film with improved lifetime reliability and a method for manufacturing the same.

The first aspect of the present invention is a ferroelectric thin film, which is characterized by a ferroelectric thin film formed of a plurality of fired films and a metal oxide composed of a perovskite containing Pb, Zr, and Ti. The total content of Li, Na, and K is 3 mass ppm or less, and the total content of Li, Na, and K on one side of each of the fired films constituting the plurality of fired films is equal to that of Li, Na, and K on the other side. More than 5 times the total content.

In the above-mentioned ferroelectric thin film, in each of the fired films, the total content of Li, Na, and K between the one side and the other side may form a constant concentration gradient in the film thickness direction.

In addition, in the plurality of fired films, when any adjacent pair of fired films is set as the first fired film and the second fired film, the other surface (the concentration of Li or the like) of the first fired film is The surface on the lower side) may be adjacent to the surface on the second fired film (the surface on the side with a higher concentration of Li and the like).

Furthermore, the total content of Li, Na, and K on the one side of the second fired film (the side with the higher concentration of Li and the like) is the other side of the first fired film (the concentration of Li and the like is low) Side surface) of the total content of Li, Na and K is 5 times or more.

The second aspect of the present invention is a method for manufacturing a ferroelectric thin film, which is characterized in that the following steps are performed at least once respectively: coating a liquid composition for forming a ferroelectric thin film containing Pb, Zr, and Ti A coating step of forming a precursor film on a substrate, heating the precursor film to convert it into a composite oxide, forming a calcined film, and calcining the calcined film to form a sintered film. The firing step of the thin film, and the total composition of the above-mentioned liquid composition for forming a ferroelectric thin film containing Li, Na, and K is 3 mass ppm or more and 10 mass ppm or less. The air velocity is set to be not less than 0.1 m / s and not more than 1.0 m / s.

A third aspect of the present invention is an electronic component having the ferroelectric thin film based on the first aspect.

Since the total content of Li, Na, and K of the ferroelectric thin film of the first state of the present invention is 3 mass ppm or less, the total of Li, Na, and K on one side of each of the fired films constituting the plurality of fired films described above The content is more than 5 times the total content of Li, Na, and K on the other side, so it has excellent life reliability. That is, in such a ferroelectric thin film of the present invention, each of the fired films contains a specific amount of Li, Na, and K, and At the interface of the sintered film adjacent to the sintered film, the contents of Li, Na, and K drastically changed to produce a concentration gradient. The abrupt change in the content of Li and the like at the interface of the fired film suppresses the movement of oxygen defects toward the film thickness, which contributes to the improvement of the life of the ferroelectric film.

According to the method for manufacturing a ferroelectric thin film according to the second aspect of the present invention, since a liquid composition for forming a ferroelectric thin film (hereinafter referred to as a liquid composition hereinafter) is used, the total amount of Li and the like is 3 mass ppm to 10 mass ppm. And the carrier gas wind speed at a height of 10 mm from the upper surface of the substrate is set to 0.1 m / sec or more and 1.0 m / sec or less in the calcination step, so that Li is contained at a specific content and the concentration is gradient, thereby obtaining Strong dielectric film with better life reliability.

The electronic component in the third aspect of the present invention has the above-mentioned ferroelectric thin film, and therefore has excellent life reliability.

10‧‧‧ Ferroelectric Thin Film

10a‧‧‧ precursor film

10b‧‧‧fired film

11‧‧‧Lower electrode

12‧‧‧ substrate

15‧‧‧Heating plate device

16‧‧‧ chamber

16a‧‧‧Supply

16b‧‧‧Exhaust

17‧‧‧ base

18‧‧‧ heater

G‧‧‧ carrier gas

FIG. 1 is a schematic cross-sectional view of a ferroelectric thin film according to an embodiment of the present invention.

FIG. 2 is a graph showing changes in the concentration of Li and the like in the thickness direction of the ferroelectric thin film according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view of an important part of a heating plate device used in a calcining method according to an embodiment of the present invention.

Next, the form for implementing this invention is demonstrated based on drawing. However, the present invention is not limited to the configuration of this embodiment.

[Ferroelectric Thin Film]

As shown in FIG. 1, the ferroelectric thin film 10 of this embodiment is formed by a five-layer fired film 101 formed on the lower electrode 11 of the substrate having the lower electrode 11. The ferroelectric thin film 10 is made of a metal oxide having a perovskite structure containing Pb, Zr, and Ti, and the total content of Li, Na, and K is 3 mass ppm or less. Further, as shown in FIG. 2, the total content of Li, Na, and K (hereinafter referred to as Li, etc.) on one side of each of the fired films 101 is more than 5 times the total content of Li, Na, and K on the other side. The ferroelectric thin film 10 may contain La in addition to Pb, Zr, and Ti.

(1) Total content of Li etc.

Since the total content of Li and the like in the ferroelectric thin film 10 is 3 mass ppm or less, impurities at the grain boundaries in the film are less segregated, and leakage current is less likely to occur. Therefore, even if time passes, insulation breakdown is less likely to occur, and life stability is excellent. When the total content of Li and the like is less than 0.3 mass ppm, since it is difficult to obtain a preferable concentration gradient of Li and the like, the total content of Li and the like is preferably 0.3 mass ppm or more. When the total content of Li, Na, and K exceeds 3 mass ppm, the leakage current becomes too large, resulting in shortened life. In addition, when the total content of Li and the like on one side of each of the fired films is less than 5 times the total content of Li and the like on the other side, the The concentration gradient is small, the change in the content of Li and the like at the interface of the sintered film is small, and the function of suppressing the movement of oxygen defects is insufficient to shorten the life. The total content of Li and the like is more preferably 0.5 mass ppm or more and 3 mass ppm or less, and still more preferably 1 mass ppm or more and 3 mass ppm or less.

(2) Concentration gradient in the firing film of Li and the like

The total content of Li and the like on one side of each of the fired films 101 is more than 5 times the total content of Li and the like on the other side. Therefore, the concentration gradient of Li and the like in the thickness direction of the fired film is sufficient. The content of Li and the like change abruptly, and the movement of oxygen defects at the interface of the fired film is suppressed. As a result, the ferroelectric thin film of this embodiment has excellent life stability. In addition, in order to increase the concentration gradient of Li and the like, it is necessary to increase the total content of Li and the like. For the reasons described above, the total content of Li and the like must be 3 mass ppm or less. Therefore, the concentration gradient in the fired film of Li or the like is preferably set to 12 times or less. The concentration gradient is more preferably 5 times to 10 times, more preferably 5 times to 9 times.

The concentration gradient is preferably a constant concentration gradient from a maximum value to a minimum value. However, if the tendency of concentration change is kept in one direction (decreasing direction or increasing direction), the ideal fixed concentration gradient (mass ppm / nm) can be locally deviated by about 20%.

(3) Number of layers of fired film

The ferroelectric thin film 10 is preferably made of two or more and 23 or less fired films 101. By laminating a plurality of fired films 101 to the ferroelectric An interface is introduced into the film 10. This interface plays a role as a trapping agent for suppressing the movement of oxygen defects and contributes to the reduction of the mobility of oxygen defects. As a result, the lifetime reliability of the ferroelectric thin film 10 can be further improved. The reason why the number of layers of the fired film 101 is 2 or more and 23 or less is because the interface is not introduced into the ferroelectric thin film 10 when the lower limit is not reached, so further improvement in life reliability cannot be achieved. Making the upper limit takes time. The number of layers of the fired film 101 is more preferably 2 or more and 6 or less, and even more preferably 2 or more and 3 or less.

When the laminated fired film 101 is laminated, an arbitrary adjacent pair of fired films is defined as the first fired film and the second fired film on the other side of the first fired film (Li The surface on the side where the concentration is low) is laminated in a direction adjacent to one surface (the surface on the side where the concentration of Li and the like is high) of the second fired film. Thereby, the content of Li or the like can be rapidly changed at the interface of the fired film.

The total content of Li and the like on one side of the second fired film (the side with a high concentration of Li and the like) is preferably set to the Li and the other side of the first fired film (the side with a low concentration of Li and the like). More than 5 times the total content. The rapid change in the total content of Li and the like at the interface of the fired film is preferably 5 times to 10 times, more preferably 5 times to 9 times. However, the present invention is not particularly limited to these preferable ranges.

(4) Film thickness of fired film

The film thickness t of each fired thin film 101 is preferably in a range of 45 nm to 500 nm. Because it is not easy to obtain a uniform continuous thin film when the lower limit is not reached When the film exceeds the upper limit, cracks may occur. The film thickness t is more preferably 45 nm or more and 135 nm or less, and still more preferably 60 nm or more and 120 nm or less. The film thickness T of the ferroelectric thin film 10 is preferably in a range of 150 nm to 5000 nm. If it does not reach the lower limit, it will become a thin film with poor productivity, and defects may occur on the characteristic surface such as a higher leakage current density. On the other hand, cracks may occur when the upper limit is exceeded. The film thickness T is more preferably 200 nm to 4000 nm, and more preferably 250 nm to 3000 nm.

(5) Metal atom ratio

The ferroelectric thin film 10 preferably has a metal atomic ratio Pb: La: Zr: Ti of (0.95 to 1.25): (0 to 0.05): (0.40 to 0.55): (0.45 to 0.60). The reason for such a metal atomic ratio is that it has a higher specific permittivity and has excellent characteristics as a ferroelectric. The metal atomic ratio is more preferably (1.00 ~ 1.15): (0 ~ 0.03): (0.50 ~ 0.55): (0.45 ~ 0.50), and more preferably (1.05 ~ 1.10): (0.01 ~ 0.03): (0.51 ~ 0.53): (0.47 ~ 0.49).

(6) Substrate and lower electrode of ferroelectric thin film

As the substrate 12 on which the ferroelectric thin film 10 is formed, a heat-resistant substrate such as a silicon substrate, a SiO ₂ / Si substrate, or a sapphire substrate is used. The lower electrode 11 is made of silicon, such as Pt, Ir, or Ru, which has conductivity and does not react with the ferroelectric thin film 10.

[Liquid composition for forming ferroelectric thin film]

The liquid composition for forming a ferroelectric thin film (hereinafter referred to as a liquid composition) is a raw material solution for forming the ferroelectric thin film 10, and it is expected that a precursor of a metal oxide for constituting a perovskite structure is desired. The ratio is dissolved in a solvent and adjusted to a concentration suitable for coating.

(1) Total content of Li etc.

The liquid composition contains Li and the like in a total of 3 mass ppm to 10 mass ppm. Since the total content of Li and the like is 3 mass ppm or more, a fired film 101 having a sufficient concentration gradient can be obtained, and since it is 10 mass ppm or less, the total of Li and the like contained in the obtained ferroelectric thin film 10 can be suppressed. Reduced concentration. The total content of Li and the like is more preferably 3 mass ppm to 5 mass ppm. The total content of Li and the like in the liquid composition can be adjusted by a method described in Patent Document 1 in which each metal component is repeatedly evaporated, sublimated, recrystallized, or a combination of these in the form of a metal organic compound.

(2) precursor

As the precursor to be prepared in the liquid composition, an organometallic compound that bonds an organic group through its oxygen or nitrogen atom to each metal element of Pb, La, Zr, or Ti can be used. For example, metal alkoxides, partial hydrolysates thereof, metal diol complexes, metal triol complexes, metal carboxylates, metal beta-diketone complexes, metal beta-diketone complexes can be used. Group, metal β-imine ketone complex, and metal amine complex More than that. Particularly preferred compounds are metal alkoxides, partial hydrolysates thereof, and metal carboxylates.

These precursors are contained in the liquid composition to obtain the desired metal atomic ratio.

For example, the metal atomic ratio Pb: La: Zr: Ti is preferably a ratio of (0.95 to 1.25): (0 to 0.05): (0.40 to 0.55): (0.45 to 0.60). Thereby, a ferroelectric thin film 10 having a preferable metal atomic ratio as described above can be obtained. Among them, the metal atom ratio is more preferably (1.00 to 1.15) than (Pb: La: Zr: Ti): (0 to 0.03): (0.50 to 0.55): (0.45 to 0.50), and more preferably (1.05 to 1.10): ( 0.01 ~ 0.03): (0.51 ~ 0.53): (0.47 ~ 0.49).

The proportion of the precursor in 100% by mass of the liquid composition is calculated in terms of oxides, and is preferably 10% by mass or more and 35% by mass or less. When the lower limit is not reached, it is not easy to obtain a sufficient film thickness in one coating. If the upper limit is exceeded, the ferroelectric thin film may crack. The proportion of the precursor is more preferably from 10% by mass to 20% by mass, and even more preferably from 12% by mass to 17% by mass. The ratio in terms of oxides refers to the ratio of the metal oxides to 100% by mass of the liquid composition when all metal elements contained in the liquid composition are oxides.

(3) Solvent

The solvent used for the preparation of the liquid composition is appropriately determined according to the raw materials used. For example, carboxylic acids, alcohols, esters, ketones, ethers, naphthenes, aromatics, other tetrahydrofurans, or a mixture of two or more of these solvents can be used.

(4) Polymer compounds

In addition, the liquid composition may contain a polymer compound such as polyvinylpyrrolidone (PVP) or polyethylene glycol in order to adjust the liquid viscosity. The proportion of the polymer compound is preferably in the range of 0.15 mol to 0.50 mol in terms of monomers for 1 mol of the precursor. If the lower limit is not reached, cracks may occur, and if the upper limit is exceeded, holes may occur.

(5) stabilizer

Also, as a stabilizer, (the number of stabilizer molecules) / (the number of metal atoms) may be 0.2 or more and 3 or less. Β-diketones, β-keto acids, β-keto esters, oxo acids, and the like may be added. Low oxo acids and alkyl esters, oxy ketones, glycols, triols, higher carboxylic acids, alkanolamines, polyamines, etc. It is particularly preferable to add β-diketones and polyols. Acetylacetone as a β-diketone and propylene glycol as a polyhydric alcohol are preferably added.

[Manufacturing method of liquid composition]

When preparing a liquid composition, the precursor is first weighed to obtain a desired metal atomic ratio. The precursor and the solvent are put into a reaction container and mixed, and the reaction is preferably refluxed in a nitrogen atmosphere at a temperature of 150 ° C or higher and 160 ° C or lower for 30 minutes or longer and 3 hours or shorter. Then, the solvent is removed by a method such as distillation or evaporation. When adding a stabilizing agent such as acetoacetone, the stabilizing agent is added to the synthesized solution after desolvation, and refluxed again under the same conditions as before. Furthermore, the solvent was added to dilute it, and the liquid composition was The concentration of each component is adjusted to the desired concentration. If necessary, the polymer compound is added in a specific ratio, and it is preferable to stir and disperse uniformly at a temperature near room temperature for 30 minutes to 3 hours. Thereby, a liquid composition is obtained.

[Manufacturing method of ferroelectric thin film]

The manufacturing method of the ferroelectric thin film of this embodiment uses the above-mentioned liquid composition containing Li and the like in a total amount of 3 mass ppm to 10 mass ppm to set a carrier gas wind speed at a height of 10 mm from the upper surface of the substrate in the firing step. 0.1m / s or more and 1.0m / s or less. Thereby, the ferroelectric thin film of this embodiment containing Li and the like can be obtained with a specific content and concentration gradient.

As the carrier gas, air, water vapor, or nitrogen containing water vapor can be used.

The wind speed of the carrier gas means the wind speed on the outermost precursor film 10a in a direction parallel to the outermost precursor film 10a and at a point 10 mm above the substrate 12 (point P in FIG. 3).

Here, if Li and the like contained in the liquid composition are less than 3 ppm, a fired film having a sufficient concentration gradient cannot be obtained, and when it exceeds 10 mass ppm, the total concentration of Li and the like contained in the obtained ferroelectric thin film is excessive. Larger is not good. In addition, when the carrier gas wind speed is less than 0.1 m / sec, the volatilization of Li and the like during heat treatment is insufficient, so that the total concentration of Li and the like remaining in the film is too large, and a fired film having an appropriate concentration gradient cannot be obtained. 1.0m / sec, the material removal speed from the precursor film is too fast, and cracks are generated in the resulting fired film, which is not good.

As shown in FIG. 3, the ferroelectric thin film 10 of this embodiment In the manufacturing method, the following steps are performed at least once respectively: coating a liquid composition for forming a ferroelectric thin film containing Pb, Zr and Ti and optionally La on a substrate 12 to form a coating of a precursor film 10a The firing step is a firing step of heating the precursor film 10a to convert it into a composite oxide to form a fired film 10b, and a firing step of firing the fired film 10b to form a fired film 101. When the firing film 101 is provided in a plurality of layers, the coating step, the firing step, and the firing step are appropriately repeated.

(1) Coating step

The coating step is as shown in FIG. 3, and the liquid composition is applied on the surface of the substrate 12 to form a lower electrode 11 (see FIG. 1) to form a precursor film 10a. The lower electrode is not shown in FIG. 3. The coating amount of the liquid composition at this time is set as described above so that the film thickness of the fired thin film 101 after firing becomes 45 nm to 500 nm. The coating method is not particularly limited, and examples thereof include spin coating, dip coating, LSMCD (Liquid Source Misted Chemical Deposition) method, and spin spray method.

(2) drying step

After the coating step, a drying step of heating the precursor film 10a may be performed in order to remove a low boiling point solvent or adsorbed water molecules. The heating temperature varies depending on the type of the solvent, but it is usually about 50 ° C to 200 ° C, and more preferably 65 ° C to 75 ° C. However, in the heating and heating in the following calcination step, the low boiling point solvent can be removed, so the drying is omitted. In the step and the calcination step, low-boiling solvents and the like may be removed.

(3) Calcination step

The calcination step is performed by heating the precursor film 10a into a composite oxide to form a calcined film 10b. The calcination step and the drying step are performed using, for example, a heating plate device 15 shown in FIG. 3. The heating plate device 15 includes a chamber 16, a base 17 having a horizontal upper surface, and a heater 18 embedded in the base. A supply port 16a for supplying a carrier gas G into the heating plate device is provided at the center of the upper portion of the chamber 16, and discharge ports 16b for discharging the carrier gas G are provided on both sides of the lower base 17. The heater 18 is connected to a heater power supply device with a temperature control mechanism (not shown). A substrate 12 having a precursor film 10 a is mounted on the upper surface of the base 17. In this heating plate device 15, after the carrier gas G introduced from the supply port 16a of the chamber 16 is directed toward the center of the substrate 11, it flows along the upper surface of the substrate 11 and is discharged from the lower discharge port 16b of the chamber 16. The wind speed of the carrier gas G can be controlled by adjusting an exhaust mechanism (not shown).

In the calcination step, the substrate 12 is placed on the base 17 and heated while flowing into the carrier gas G in the heating plate device 15. Here, the wind speed of the carrier gas G at a point P at a height h of 10 mm from the upper surface of the substrate 12 is set to 0.1 m / s or more and 1.0 m / s or less. The flow of the carrier gas G removes impurities such as Li contained in the precursor film 10a together with solvents or decomposition products of the precursor. However, since the wind speed is set to be 0.1 m / sec or more, the The amount of impurities is greater than the amount of impurities removed from the bottom surface side of the precursor film 10a, and a fired film 101 having a sufficient concentration gradient can be obtained. Due to wind speed When it is set to 1.0 m / sec or less, the material removal rate from the precursor film 10a will be too fast, so that cracking of the fired film 101 can be prevented. The wind speed is more preferably 0.4 m / s or more and 0.6 m / s or less. The reason why the observation point of the wind speed is set to a height h of 10 mm from the upper surface of the substrate 12 is to accurately grasp the effect on the removal of the material on the self-fired film 10 b.

The calcination step is preferably performed under conditions of, for example, 150 ° C to 450 ° C, and 1 minute to 10 minutes. The calcination temperature is more preferably 200 ° C to 400 ° C, and more preferably 300 ° C to 375 ° C. The calcination time is preferably 2 minutes to 5 minutes. The calcination step is performed in order to remove the solvent and thermally decompose or hydrolyze the precursor to convert it into a composite oxide. Therefore, the calcination step is preferably performed in air, an oxidizing atmosphere, or a water vapor atmosphere. Therefore, as the carrier gas G, for example, air, water vapor, nitrogen containing water vapor, or the like can be used. The coating step and the calcination step may be performed once, but in order to make the calcined film 10b a desired film thickness, after repeating the coating step and the calcination step several times, the subsequent calcination step may be performed. .

(4) firing step

The firing step involves firing and crystallizing the calcined film 10b to form a fired film 101. The firing conditions are preferably, for example, 600 ° C. to 800 ° C., and 1 minute to 5 minutes, and the firing time is more preferably 650 ° C. to 750 ° C. The firing can be performed by using a rapid thermal annealing (RTA) device and rapid temperature rise and fall heat treatment (RTA treatment) heated by an infrared lamp. When sintering with RTA, the heating rate is faster than For example, it is preferably 2.5 ° C / second or more and 100 ° C / second or less, and more preferably 20 ° C / second or more and 100 ° C / second or less. The firing atmosphere is preferably, for example, oxygen, nitrogen, or a mixed gas thereof. By performing the above-mentioned coating step, calcination step, and firing step at least twice, the ferroelectric thin film 10 made of a plurality of fired films 101 is obtained.

〔Electronic parts〕

The electronic parts of this embodiment are, for example, a thin film battery, a capacitor, an IPD, a DRAM memory battery, a multilayer battery, a gate insulator of a transistor, a nonvolatile memory, a pyroelectric infrared detection element, a piezoelectric element, or electro-optic. Electronic components such as components, actuators, resonators, ultrasonic motors, electrical switches, optical switches, or composite electronic components of LC noise filter elements, and having the above-mentioned ferroelectric thin film 10. Since these electronic components have the above-mentioned ferroelectric thin film 10, they have excellent lifetime reliability.

[Example]

Next, examples and comparative examples of the present invention will be described in detail.

<Example 1>

The method described in Patent Document 1 is applied to the test reagent special grade of lead acetate trihydrate (Pb source), lanthanum acetate (La source), titanium tetraisopropoxide (Ti source), and tetrabutyl zirconia (Zr source). , Recrystallized from ultrapure water twice to obtain high purity, and made precursor. The precursors were individually weighed so that the metal atomic ratio Pb / La / Zr / Ti became 110/3/52/48. The propylene glycol added to the reaction container prepares a synthetic liquid. After the synthetic solution was refluxed in a nitrogen atmosphere at a temperature of 150 ° C. for 60 minutes, the solvent was removed by distillation. Subsequently, ethylacetoacetone as a stabilizer was added and refluxed at 150 ° C for 60 minutes.

Next, propylene glycol was added to the synthetic solution, and the total concentration of the precursors diluted to propylene glycol was 35% by mass in terms of oxides. Further, ethanol was added and diluted to a total concentration of the precursors to 25% by mass in terms of oxides. Next, polyvinylpyrrolidone (k value = 30) was added so that 1 mole of the precursor became 0.025 mole, and stirred at room temperature for 24 hours, thereby obtaining a liquid composition for forming a ferroelectric film. The concentration of Li, Na, and K in the liquid composition was measured by ICP (manufactured by Thermal Fisher Scientific), and the total concentration was 10 mass ppm.

Then, a coating step is performed. A liquid composition was dropped on a Pt / TiO ₂ / SiO ₂ / Si substrate provided on a spin coater, and spin-coated at a rotation speed of 3000 rpm for 30 seconds to form a precursor film on the substrate. The rotation speed and time of the spin coater are set such that the film thickness of the fired film obtained in one firing step is 90 nm.

Next, a calcination step is performed. The substrate with the precursor film was placed on the base of the heating plate device, and the carrier gas (dry air) was flowed so that the wind speed at a height of 10 mm from the upper surface of the substrate was set to 1 m / sec, and kept at 300 ° C for 5 minutes. , And the precursor is converted into a composite oxide to form a calcined film. The wind speed was measured by a hot-wire anemometer (CUSTOM, model CW-60).

Next, a firing step is performed. Using RTA device, every time In an atmosphere of 2 liters of flowing oxygen for 2 minutes, the temperature was raised to 700 ° C at a temperature increase rate of 30 ° C / second and held for 1 minute. Thereby, a fired film having a film thickness of 90 nm was formed on the lower electrode of the substrate. By repeating the process from the coating step to the firing step three times, a ferroelectric thin film having a film thickness of 270 nm formed from three layers of the fired thin film 101 was obtained. The film thickness was measured with a scanning electron microscope (HITACHI s4300). The metal atomic ratio Pb: La: Zr: Ti of the ferroelectric thin film was measured by ICP (manufactured by Thermal Fisher Scientific), and the result was 103/3/52/48.

<Examples 2 to 9, Comparative Examples 1 to 4>

A ferroelectric thin film was formed in the same manner as in Example 1 except that various conditions were changed as described in Table 1. Specifically, for some examples, the spin coater rotation speed and time were adjusted to change the film thickness of the fired film. For some examples, the number of repetitions (the number of firing steps) and the film thickness of the ferroelectric thin film were changed. For some examples and comparative examples, liquid compositions having different concentrations of Li and the like were used by changing the number of high-purification times of recrystallization. For some comparative examples, the wind speed in the calcination step was changed. For Example 9, the metal atom ratio Pb / La / Zr / Ti of the precursor was set to 110/0/52/48.

<Evaluation>

Regarding the ferroelectric thin films formed in the examples and comparative examples, the total concentration, concentration gradient, and lifetime reliability of Li and the like in the films were evaluated by the following methods. These results are shown in Table 1 below.

(1) Total concentration of Li etc.

The total concentration of Li and the like was measured using ICP (manufactured by Thermal Fisher Scientific).

(2) Li concentration concentration gradient

The concentration gradient of Li and the like was measured using AES (manufactured by ULVAC) in the concentration distribution of Li and the like in the film thickness direction shown in FIG. 2. A concentration gradient was obtained by dividing the concentration of Li and the like on one side of each of the fired films by the concentration of Li and the like on the other side. Table 1 shows the average values of the concentration gradients of all the fired films.

(3) Life reliability

The evaluation of the life characteristics is performed by an accelerated test (HALT: highly-accelerated life testing) under exposure to a higher load (high temperature / high voltage) environment than the conditions generally used. On the ferroelectric thin film of each of Examples and Comparative Examples, a platinum thin film (area: 3.5 × 10 ^-2 mm ² ) was formed into a thin film by sputtering to form an upper Pt electrode, and a plurality of Pt electrodes were formed on the same substrate. After the capacitor was structured, it was heated at 700 ° C. for an additional minute in an oxygen atmosphere to obtain an evaluation sample.

The upper Pt electrode and the lower Pt electrode of the film capacitor are electrically connected, and a voltage of 10 to 20 V is applied in a state where the film capacitor is heated to 125 to 205 ° C, and the voltage application time and the leakage current value flowing through each capacitor are measured. In order to confirm that the capacitors deteriorate with time, If the edge breaks and the leakage current increases sharply, the time from the reading of the measurement data to the insulation breakdown of each capacitor (TDDB (time-dependent dielectric breakdown) evaluation). Specifically, when the leakage current value exceeds 100 μA, it is considered to cause insulation damage. The Weibull distribution analysis is used to statistically process the data of multiple insulation damage times. The average damage time is 63.2% of the total capacitor damage time. (mean time to failure; hereinafter referred to as MTF). The bulk capacitor is known as the following empirical formula (1).

Here t is the MTF, T is the test temperature, V is the DC applied voltage, E _a is the activation energy, N is the voltage acceleration coefficient, and K _B is the Bozman constant. Any condition. From the above formula (1), it is determined that the temperature T and the applied voltage V influence the life time of the capacitor. This time, the relationship is applied to a film capacitor. When the voltage V in the above formula (1) is fixed (V ₁ = V ₂ ), it becomes

(Here K _v is a constant with respect to temperature), the inverse number of temperature and the logarithm of MTF have a linear relationship. Using this, the activation energy E _a for the acceleration factor of temperature can also be estimated. Similarly, when the temperature T is fixed (T ₁ = T ₂ ) in the above formula (1), it becomes

(Here, K _T is a constant for the applied voltage). The voltage acceleration coefficient N for the voltage acceleration factor can also be estimated. Using the values of the two acceleration factors E _a , N, extrapolate the MTF in the state of 5V voltage heated to 85 ° C, and this value can be estimated as the predicted life. The results obtained are shown in Table 1 below.

From Table 1, it can be seen that the ferroelectric thin film of the embodiment having a total concentration and concentration gradient of Li and the like in a specific range formed within the range of the manufacturing method of the present invention has a long predicted life and excellent life reliability. The ferroelectric thin film of Comparative Example 1 using a liquid composition with a low total concentration of Li and the like has a small concentration gradient and a shorter life expectancy compared to the examples. In the ferroelectric thin film of Comparative Example 2 where the wind speed in the calcination step is small, the total concentration of Li and the like is high, the concentration gradient is large, and the predicted life is short compared with the examples. The ferroelectric thin film of Comparative Example 3 having a large wind speed in the calcination step was visually cracked. The total concentration of Li and the like in the ferroelectric thin film of Comparative Example 4 using a liquid composition having a high total and concentration of Li and the like was high, and the lifetime was predicted compared with the examples. Life is short.

[Industrial availability]

The ferroelectric thin film of the present invention can be used in thin film storage batteries, capacitors, IPD, DRAM memory storage batteries, laminated storage batteries, gate insulators of transistors, non-volatile memory, pyroelectric infrared detection elements, and piezoelectric elements Electronic components such as electro-optical components, actuators, resonators, ultrasonic motors, electrical switches, optical switches or composite electronic components of LC noise filter components.

Claims (6)

A ferroelectric thin film characterized by a ferroelectric thin film made of a plurality of fired films and made of a metal oxide of a perovskite structure containing Pb, Zr and Ti, Li, Na and K The total content is 3 mass ppm or less, and the total content of Li, Na, and K on one side of each of the fired films constituting the plurality of fired films is more than 5 times the total content of Li, Na, and K on the other side. For example, the ferroelectric thin film of claim 1, wherein in each of the foregoing fired films, the total content of Li, Na, and K forms a constant concentration gradient in the film thickness direction between the one side and the other side. For example, in the ferroelectric thin film of claim 2, wherein among the plurality of fired films, any adjacent pair of fired films is defined as the first fired film and the second fired film. The other side is adjacent to the one side of the second fired film. For example, the ferroelectric thin film of claim 3, wherein the total content of Li, Na, and K on the first side of the second fired film is the total content of Li, Na, and K on the other side of the first fired film. 5 times or more. A method for manufacturing a ferroelectric thin film, which is characterized in that the following steps are performed at least once respectively: a liquid composition for forming a ferroelectric thin film containing Pb, Zr, and Ti is coated on a substrate to form a precursor thin film; A coating step, a calcination step of heating the precursor film to convert it into a composite oxide to form a calcined film, and a calcination step of calcining the calcined film to form a calcined film, and The liquid composition for forming a ferroelectric thin film contains Li, Na, and K in a total amount of 3 mass ppm or more and 10 mass ppm or less. In the calcination step, a wind speed of a carrier gas at a height of 10 mm from the upper surface of the substrate is set to 0.1 m Above 1.0 m / sec. An electronic component having a ferroelectric thin film as claimed in claim 1.