JP7119265B2 - Method for manufacturing dielectric film - Google Patents

Description

The present invention relates to a method for producing a void-free, dense dielectric film using a liquid composition containing at least Bi, K and Ti, but not containing Pb.

Conventionally, (1-x)Bi _0.5 Na _0.5 TiO ₃ -xBi _0.5 K _0.5 TiO ₃ [BNT-BKT] thin film is deposited on a substrate by a sol-gel method and rapid annealing in a method for synthesizing a lead-free ferroelectric thin film. is disclosed (see, for example, Non-Patent Document 1). In order to synthesize this ferroelectric thin film, a thin film (BNT-BKT) in which x of (1-x)Bi _0.5 Na _0.5 TiO ₃ -xBi _0.5 K _0.5 TiO ₃ varies from 0 to 0.2 was prepared by a sol-gel method. and synthesized by rapid annealing. Specifically, first, at 70° C. in air, 99.5% bismuth nitrate [Bi(NO ₃ ) _{3.5H 2} O], 99.5% sodium nitrate [NaNO ₃ ], 99% A precursor solution was prepared by dissolving an appropriate amount of potassium nitrate [KNO ₃ ] in acetic acid. Acetylacetone (99%) was then added to titanium isopropoxide [Ti( _OC3H7 ) ₄ ] ₍ 98%, Steam Chemicals) to form a stable solution to prevent hydrolysis due to moisture in the air. . A stoichiometric amount of titanium isopropoxide solution was then added to the nitrate solution at room temperature. The mixture was then stirred constantly until a clear, stable yellow precursor solution with a polar concentration of 0.25 mol/dm ³ was obtained. Furthermore, the above precursor solution was spin-coated on a Pt film formed on a Si substrate via a SiO ₂ film and a Ti film at a rotation speed of 3000 rpm for 20 seconds to form a coating film. After being dried on a hot plate at 250° C. for 5 minutes, it was rapidly annealed at 700° C. for 5 minutes in a rapid thermal processor (RTP) in an oxygen atmosphere. This process, ie spin coating, drying and rapid annealing, was repeated six times to obtain a thick film with a thickness of about 600 nm.

The ferroelectric thin films thus synthesized are well deposited on Pt electrodes and the morphotropic phase boundary (MPB) between Bi _0.5 Na _0.5 TiO ₃ and Bi _0.5 K _0.5 TiO ₃ is x=˜0. .15, and further near the MPB, the grain size of the thin film is maximized, the dielectric constant ε of the thin film has a maximum value of 360, and the polarization value Pr of the thin film has a maximum value of 13.8 μC/cm ² . .

T. Yu, K. W. Kwok, H. L. W. Chan, "The synthesis of lead-free ferroelectric Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 thin films by sol-gel method", material letters 61 (2007) 2117-2120

However, in the ferroelectric thin film synthesis method disclosed in the conventional non-patent document 1, since bismuth nitrate is used as the Bi raw material, the ferroelectric thin film is dense, but the wettability of the precursor solution is poor. Unfortunately, the ferroelectric thin film is prone to defects. Therefore, there is a problem that it is difficult to apply the precursor solution to a large-sized substrate by spin coating.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a dielectric film, in which the wettability of the liquid composition to the substrate is excellent, and a dense and defect-free dielectric film can be obtained.

The present inventors have found that when bismuth 2-ethylhexanoate is reacted with a potassium raw material, a liquid composition (sol-gel liquid) with poor thermal decomposition is formed. It was confirmed by infrared spectroscopy that carbonates are likely to form and carbon chains are difficult to remove when heated to around °C. These phenomena can be explained kinetically, and we presume that the main factor is the formation of carbonates and other heterogeneous phases that are stable and difficult to thermally decompose before the formation of the perovskite phase. When the liquid composition prepared using bismuth 2-ethylhexanoate was heated at a rate of less than 30 ° C./sec in the temperature range from 500 ° C. to 600 ° C. during firing, It was found that carbonate is formed in the dielectric film, leading to void formation and deterioration of crystallinity. In other words, having found that it is necessary to raise the temperature in the above temperature range at a rate of 30° C./second or more in order to obtain a dense dielectric film with good crystallinity using the above liquid composition, The inventors have completed the present invention.

A first aspect of the present invention is to prepare a calcined film by calcining a coating film obtained by applying a liquid composition containing at least Bi, K and Ti on a substrate, and calcining the calcined film to metal oxidation. Further containing Sr and Zr, Bi raw material is bismuth 2-ethylhexanoate, and the temperature is raised from 500° C. to 600° C. during firing of the calcined film. It is characterized by setting the speed to 30° C./second or more.

A second aspect of the present invention is an invention based on the first aspect, characterized in that it further contains Na.

A third aspect of the present invention is an invention based on the first or second aspect, wherein the liquid composition has the general formula: y(Bit K _s TiO ₃ )-(1- _y )(Sr _m Zr _n O ₃ ) or y(Bit (Na, K) _s TiO ₃ )-(1- _y ) (Sr _m Zr _n O ₃ ) (where 0.9≤y≤1, 0.4≤t≤0 .6, 0.4≤s≤0.6, 0.9≤m≤1.1, 0.9≤n≤1.1).

In the method for producing a dielectric film according to the first aspect of the present invention, bismuth 2-ethylhexanoate is used as the Bi raw material, so that the wettability of the liquid composition to the substrate is excellent. In addition, since the rate of temperature increase from 500° C. to 600° C. is set to 30° C./second or more during firing of the calcined film, carbonates that are stable and difficult to thermally decompose and other heterophases do not form before the perovskite phase is formed. . As a result, since carbonate is not formed in the dielectric film, voids are not generated in the dielectric film, the crystallinity of the dielectric film is improved, and a dense and defect-free dielectric film is obtained.
In addition, the method for manufacturing a dielectric film according to the first aspect of the present invention further contains Sr and Zr, so that it is possible to obtain higher piezoelectric properties.

In the method of manufacturing a dielectric film according to the second aspect of the present invention, since Na is further included, there is a feature that higher piezoelectric properties can be obtained.

In the method for producing a dielectric film according to the third aspect of the present invention, the liquid composition has the general formula: y(Bi _t K _s TiO ₃ )-(1-y)(Sr _m Zr _n O ₃ ) or y(Bi _t (Na, K) _s TiO ₃ )-(1-y)(Sr _m Zr _n O ₃ ) (where 0.9≦y≦1, 0.4≦t≦0.6, 0.4≦s ≤ 0.6, 0.9 ≤ m ≤ 1.1, 0.9 ≤ n ≤ 1.1). It has the advantage of light load.

Next, a mode for carrying out the present invention will be described. The liquid composition for manufacturing the dielectric film of this embodiment contains at least Bi, K and Ti. This liquid composition is preferably a compound represented by the general formula: Bi _x K _1-x TiO ₃ (0.4≦x≦0.6). Here, in the above general formula, x is limited to the range of 0.4 ≤ x ≤ 0.6. This is because if the value exceeds 0.6, sufficient electrical characteristics cannot be obtained. Further, Na may be further included in addition to the above metal elements. Furthermore, in addition to the above metal elements, it may further contain Sr and Zr together with Na, or may further contain Sr and Zr without containing Na. Further containing Na has the advantage of obtaining higher piezoelectric properties, and further containing Sr and Zr has the advantage of obtaining higher piezoelectric properties. The liquid composition further containing Na is represented by the general formula: Bix(NayK1 _{-y ) 1- xTiO3} ( _{0.4≤x≤0.6} , 0.1≤y≤0.9). It is preferably a compound that can be Here, the reason why x is limited to the range of 0.4≦x≦0.6 is that if it is less than 0.4, the deviation from the stoichiometric ratio is too large, and sufficient electrical characteristics cannot be obtained. This is because if it exceeds 6, sufficient electrical characteristics cannot be obtained. The reason why y is limited to the range of 0.1≦y≦0.9 is that if it is less than 0.1 or exceeds 0.9, sufficient piezoelectric characteristics cannot be obtained. On the other hand, the liquid composition further containing Sr and Zr together with Na has the general formula: y(Bi _t K _s TiO ₃ )-(1-y)(Sr _m Zr _n O ₃ ) or y(Bi _t (Na, K) _s TiO ₃ )-(1-y)(Sr _m Zr _n O ₃ ) (where 0.9≦y≦1, 0.4≦t≦0.6, 0.4≦s≦0.6 , 0.9≦m≦1.1, 0.9≦n≦1.1). Here, y, t, s, m, and n are 0.9≤y≤1, 0.4≤t≤0.6, 0.4≤s≤0.6, 0.9≤m≤1.1. , 0.9≦n≦1.1 because the film must be formed with a composition within this range in order to obtain a sufficient piezoelectric constant.

As a raw material for Bi, bismuth 2-ethylhexanoate is used. Here, the reason why bismuth 2-ethylhexanoate was used as the raw material of Bi is to improve the wettability of the liquid composition to the substrate. Raw materials for K include potassium acetate, potassium 2-ethylhexanoate, potassium ethoxide, potassium tertiary butoxide and the like. Ti raw materials include titanium tetraethoxide: Ti(OEt) ₄ , titanium tetraisopropoxide: Ti(OiPr) ₄ , titanium tetra-n-butoxide: Ti(OiBu) ₄ , titanium tetraisobutoxide: Ti(OiBu). ) ₄ , titanium tetra-t-butoxide: Ti(OtBu) ₄ , titanium dimethoxydiisopropoxide: Ti(OMe) ₂ (OiPr) ₂ and the like. Furthermore, Na raw materials include sodium methoxide: Na ₂ (OMe), sodium ethoxide: Na ₂ (OEt), sodium t-butoxide: Na ₂ (OtBu), and the like.

A method for preparing the liquid composition thus constituted will be described.
(1) When manufacturing a dielectric film containing Bi, K and Ti, or a dielectric film containing Bi, Na, K and Ti Dielectric film containing Bi, K and Ti, or Bi, Na, K and Ti In order to make a dielectric film containing . First, a Ti raw material and a solvent such as acetylacetone, ethanol, or 1-butanol are mixed at a predetermined ratio, and refluxed at 80° C. to 160° C. for 30 minutes to 180 minutes to prepare a first mixed solution. Next, a solvent such as ethanol, 1-butanol, or acetic acid, potassium acetate (K raw material), and sodium ethoxide (Na raw material) are mixed with this first mixed liquid, and the mixture is heated at 80° C. to 160° C. for 30 minutes to 180° C. Reflux for 1 minute to prepare a second mixture. Next, bismuth 2-ethylhexanoate (Bi raw material) is added to this second mixed liquid and refluxed at 80° C. to 160° C. for 30 minutes to 180 minutes to prepare a third mixed liquid. The pressure is reduced while heating the liquid at 80° C. to 160° C. to remove about half of the solvent in the third mixed liquid. Further, this third mixed solution is diluted with a solvent such as 1-propanol, ethanol, 1-butanol, etc. to obtain a liquid composition by diluting the oxide concentration to 5% by mass to 10% by mass. Here, the oxide concentration is the concentration when all metal elements contained in the liquid composition are assumed to be stable oxides. That is, it is the concentration when the metal elements Bi, Na, K and Ti present in the liquid composition are assumed to be Bi ₂ O ₃ , Na ₂ O, K ₂ O and TiO ₂ , respectively.

(2) In the case of producing a dielectric film further containing Sr and Zr in addition to Bi, Na, K and Ti First, Na raw materials such as sodium ethoxide and sodium tertiary butoxide, potassium ethoxide, potassium tertiary butoxide and the like are prepared. and a solvent such as ethanol or methanol are mixed in a predetermined ratio and stirred at room temperature for 30 to 60 minutes to prepare a suspension. Next, a Ti raw material such as tetratitanium isopropoxide and tetratitanium butoxide and a Zr raw material such as zirconium butoxide are added to this suspension, and refluxed for 30 to 60 minutes to prepare a first mixed liquid. . A Bi raw material such as bismuth 2-ethylhexanoate, an Sr raw material such as strontium acetate pentahydrate and strontium nitrate, and a diol such as propylene glycol and ethylene glycol are added to the first mixed solution, and the mixture is stirred for 30 minutes. Reflux for ~60 minutes to prepare a second mixture. Next, a stabilizing agent such as acetylacetone is added to the second mixture, and the mixture is refluxed for 30 to 60 minutes to prepare a third mixture. After desorbing the solvent from this third mixture to remove the solvent such as ethanol and the reaction by-products, a diol such as propylene glycol or ethylene glycol is added, and the content is reduced to 8% by mass to 12% by mass in terms of oxide. Dilute. Furthermore, a stabilizer such as 2-dimethylaminoethanol or 1-ethanolamine is added to the diluted solution so that the molar ratio of Ti:stabilizer is 1:1, followed by 1-butanol, After diluting the liquid with ethanol or the like to 4% by mass to 10% by mass in terms of oxides, the resulting liquid is filtered to remove dust to obtain a liquid composition.

On the other hand, for example, a silicon wafer with a Pt electrode is prepared in order to apply the liquid composition. Specifically, first, a thermal oxide film having a thickness of 100 nm to 500 nm is formed on the silicon wafer surface. Next, after forming a Ti film with a thickness of 10 nm to 30 nm on this thermal oxide film by a sputtering method, it is heated to a temperature of 700° C. to 800° C. for 1 minute to 3 minutes by an infrared rapid heating apparatus (RTA) in an oxygen atmosphere. A TiOx film is formed by holding and baking. Furthermore, a Pt electrode with a thickness of 100 nm to 200 nm is formed on the TiOx film to obtain a silicon wafer with a Pt electrode.

A method of forming a dielectric film on a silicon wafer with a Pt electrode using the liquid composition will be described. First, after the liquid composition is filtered through a membrane filter, the liquid composition is spin-coated at a speed of 2000 rpm to 3000 rpm to form a coating film on a wafer with a Pt electrode. Here, since bismuth 2-ethylhexanoate was used as a raw material of Bi in the liquid composition, the wettability of the liquid composition to the substrate is excellent. Next, this coating film is calcined by holding it at a temperature of 300° C. to 400° C. for 3 to 10 minutes using a heating device such as a hot plate to prepare a calcined film having a thickness of about 50 nm to 100 nm. This operation is repeated several times to obtain a calcined film with a thickness of 100 nm to 200 nm. Here, the reason why the calcination temperature of the coating film is limited to the range of 300° C. to 400° C. is that if it is less than 300° C., degreasing is insufficient and carbon tends to remain in the dielectric film, and if it exceeds 400° C. This is because it is difficult to obtain a homogeneous dielectric film due to the difficulty of proper temperature control. The reason why the temporary baking time of the coating film is limited to the range of 3 minutes to 10 minutes is that if it is less than 3 minutes, degreasing is insufficient and carbon tends to remain in the dielectric film, and if it exceeds 10 minutes, productivity is poor. It is from. The reason why the thickness of the calcined film formed by one calcination is limited to within the range of 50 nm to 100 nm is that if it is less than 50 nm, the productivity is poor, and if it exceeds 100 nm, cracks are likely to occur. be. Furthermore, the reason why the thickness of the calcined film after repeated calcinations is limited to within the range of 100 nm to 200 nm is that if it is less than 100 nm, the productivity is poor, and if it exceeds 200 nm, cracks occur. This is because there is a problem that it is easy to

Further, the wafer having the calcined film formed on its surface is heated to a predetermined temperature within the range of room temperature to 650° C. to 800° C. by RTA in an oxygen atmosphere, and held at this temperature for a predetermined period of time. Specifically, the temperature was raised from room temperature to 500° C. at a rate of 10° C./sec to 100° C./sec, and then from 500° C. to 600° C., which is the characteristic temperature range of the present invention, at a rate of 30° C./sec or more. After that, the temperature is raised from 600° C. to a predetermined temperature in the range of 650° C. to 800° C. at a rate of 10° C./second to 100° C./second, and the predetermined temperature in the range of 650° C. to 800° C. is reached for 1 minute to 10 minutes. A dielectric film is formed on the wafer surface by holding for a predetermined time within the range of . Here, the reason why the temperature increase rate from 500° C. to 600° C. is limited to 30° C./sec or more among the temperature increase rates during firing of the calcined film is that if the temperature is less than 30° C./sec, the kinetics of carbonate increases. This is because the generation becomes dominant and the dielectric film becomes porous. The faster the rate of temperature rise from 500° C. to 600° C., the better. However, RTA having an output of 100° C./second or more increases the equipment cost, so it is preferably 100° C./second or less. In addition, the rate of temperature increase from room temperature to 500°C is set widely within the range of 10°C/sec to 100°C/sec, and the rate of temperature increase from 600°C to a predetermined temperature within the range of 650°C to 800°C is set to 10°C. The reason why the temperature is set widely within the range of ° C./sec to 100 ° C./sec is that there is no need to limit it. to 600° C. is preferably the same. The firing temperature of the calcined film is limited to a predetermined temperature in the range of 650° C. to 800° C. The reason is that crystallization does not proceed sufficiently below 650° C., and the lower electrode deteriorates if it exceeds 800° C. Because it will be stored away. Furthermore, the reason why the firing time of the calcined film is limited to a predetermined time in the range of 3 minutes to 10 minutes is that if it is less than 3 minutes, sufficient degreasing cannot be performed and carbon tends to remain in the dielectric film. This is because if the time exceeds one minute, the productivity is poor.

In the dielectric film thus produced, since the rate of temperature increase from 500° C. to 600° C. was set to 30° C./second or more during firing of the pre-fired film, stable and hard to thermally decompose carbonates and other different phases were generated. , does not form before the formation of the perovskite phase. As a result, since carbonate is not formed in the dielectric film, voids are not generated in the dielectric film, the crystallinity of the dielectric film is improved, and a dense and defect-free dielectric film is obtained.

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

<Example 1>
In order to make a dielectric film containing Bi, Na, K and Ti, the volatiles in the process were compensated, i.e. 8% by weight of Bi and 16% by weight of Na and K were added in excess to obtain Bi _0.54 A liquid composition was synthesized so as to be (Na _0.8 K _0.2 ) _0.58 TiO ₃ . Specifically, first, titanium isopropoxide (Ti raw material) and acetylacetone were mixed at a molar ratio of 1:2, and refluxed at 150° C. for 30 minutes to prepare a first mixed solution. Next, ethanol, potassium acetate (K raw material) and sodium ethoxide (Na raw material) were mixed with this first mixed liquid, and refluxed at 150° C. for 30 minutes to prepare a second mixed liquid. Next, bismuth 2-ethylhexanoate (Bi raw material) is added to this second mixed liquid and refluxed at 150° C. for 30 minutes to prepare a third mixed liquid, and then this third mixed liquid is heated at 150° C. While reducing the pressure, half of the ethanol in the third mixture was removed. Furthermore, this third mixture was diluted with 1-propanol to an oxide concentration of 8% by mass to obtain a liquid composition. Here, the oxide concentration is the concentration when all metal elements contained in the liquid composition are assumed to be stable oxides. That is, it is the concentration when the metal elements Bi, Na, K and Ti present in the liquid composition are assumed to be Bi ₂ O ₃ , Na ₂ O, K ₂ O and TiO ₂ , respectively.

On the other hand, a silicon wafer with a Pt electrode was prepared for coating the liquid composition. Specifically, first, a thermal oxide film with a thickness of 500 nm was formed on the surface of a silicon wafer with a diameter of 4 inches. Next, after forming a Ti film with a thickness of 20 nm on this thermal oxide film by a sputtering method, the TiO film was fired by holding at a temperature of 700° C. for 1 minute in an oxygen atmosphere with an infrared rapid heating apparatus (RTA). ₂ films were formed. Furthermore, a Pt electrode with a thickness of 200 nm was formed on the TiO ₂ film to obtain a silicon wafer with a Pt electrode.

After the liquid composition was filtered through a membrane filter, the liquid composition was spin-coated at a speed of 3000 rpm to form a coating film on the wafer with the Pt electrode. The dropping time during spin coating was 30 seconds. Next, this coating film was calcined by holding it at a temperature of 350° C. for 5 minutes on a hot plate to prepare a calcined film having a thickness of about 67 nm. This operation was repeated three times to obtain a calcined film having a thickness of about 200 nm. Further, the wafer having the calcined film formed on its surface was heated from room temperature to 700° C. at a rate of 50° C./sec by RTA in an oxygen atmosphere, and then held at 700° C. for 1 minute to obtain a dielectric film on the wafer surface. A body membrane was prepared. This dielectric film was designated as Example 1.

<Examples 2 to 7 and Comparative Examples 1 to 5>
In Examples 2 to 7 and Comparative Examples 1 to 5, the raw materials shown in Table 1 were used as Bi raw materials, and each raw material was used so that the metal atomic ratios of Bi, Na, K, and Ti were the metal atomic ratios shown in Table 1. A dielectric film was produced in the same manner as in Example 1, except that the rate of temperature rise during firing of the calcined film was set to the value shown in Table 1.

<Example 8>
First, ethanol (solvent), sodium ethoxide (Na raw material), and potassium ethoxide (K raw material) were placed in a flask and stirred at room temperature for 30 minutes to obtain a reddish brown suspension. Next, tetratitanium isopropoxide (Ti raw material) and zirconium butoxide (Zr raw material) were added to this suspension, and the mixture was refluxed for 30 minutes to prepare a first mixed liquid. Bismuth 2-ethylhexanoate (Bi raw material), strontium acetate 0.5 hydrate (Sr raw material), and propylene glycol (diol) were added to the first mixed solution, and refluxed for 30 minutes. 2 mixtures were prepared. Next, acetylacetone (stabilizer) was added to this second mixed liquid and refluxed for 30 minutes to prepare a third mixed liquid. After desorbing the solvent from this third mixture to remove ethanol (solvent) and reaction by-products, propylene glycol (diol) was added to dilute to 15 mass % in terms of oxide. Furthermore, 2-dimethylaminoethanol as a stabilizer was added to this diluted solution so that the molar ratio of Ti: stabilizer was 1:1, and then the solution was diluted with 1-butanol to 8 in terms of oxide. After diluting to % by mass, the resulting liquid was filtered to remove dust, thereby obtaining a liquid composition. Then, a dielectric film was produced in the same manner as in Example 1 using this liquid composition. This dielectric film was designated as Example 8.

<Examples 9 to 12, Comparative Examples 6 and 7>
In Examples 9 to 12, Comparative Examples 6 and 7, raw materials were blended so that the metal atomic ratios shown in Table 1 were obtained to prepare liquid compositions (Examples 11 and 7). 12) Dielectrics were prepared in the same manner as in Example 1, except that the rate of temperature increase during firing of the calcined film was changed to the value shown in Table 1 (Examples 9 to 12, Comparative Examples 6 and 7). A membrane was prepared.

<Comparative test 1 and evaluation>
The dielectric films of Examples 1 to 12 and Comparative Examples 1 to 7 were examined for void ratio and presence or absence of pinholes. The above void ratio is obtained by observing the cross section of the dielectric film with a scanning electron microscope (SEM) and analyzing the image of the cross section to obtain the image area of the film portion and the image area of the void portion in the film. Then, the void ratio (%) was calculated by calculating [(image area of void portion)/(image area of film portion)]×100. In addition, the presence or absence of pinholes was determined by visually observing the surface of the dielectric film. If there were no pinholes, it was rated as "absent", and if there were one or more pinholes, it was rated as "yes". Table 1 shows the results. In the Bi raw material column of Table 1, "A" indicates bismuth 2-ethylhexanoate and "B" indicates bismuth nitrate pentahydrate. Table 2 shows the metal atomic ratios of Bi, Na, K, Ti, Sr and Zr in the dielectric film together with the metal atomic ratios of Bi, Na, K, Ti, Sr and Zr in the liquid composition. Furthermore, the metal atomic ratio of the dielectric film was measured with a fluorescent X-ray device (manufactured by Rigaku, model name: Primus III+).

As is clear from Table 1, the dielectric films of Comparative Examples 1 to 3, 6, and 7, which had a heating rate during firing of 10 to 25° C./sec, which was smaller than the appropriate range (30° C./sec or more), were not pinned. Although there were no holes, the void ratio increased to 19 to 32%, while the heating rate during firing was 30 to 100°C/sec, which was within an appropriate range (30°C/sec or more). In 1 to 12, there were no pinholes, and the void ratio was as small as 2 to 12%. Further, the metal atomic ratio of Bi, Na, K, Ti, Sr and Zr in the liquid composition is 0.54:0.464:0.116:1:0:0, and as the Bi raw material of the liquid composition In the dielectric films of Comparative Examples 4 and 5 using bismuth nitrate pentahydrate, the void ratio was as small as 8% and 9% regardless of the rate of temperature rise during firing, but pinholes were formed. Occurred. In contrast, the liquid composition has a metal atomic ratio of Bi, Na, K, Ti, Sr, and Zr of 0.54:0.464:0.116:1:0:0, and the liquid composition has a Bi In the dielectric films of Examples 1 to 3 using bismuth 2-ethylhexanoate as a raw material, when the temperature increase rate during firing is within an appropriate range of 30 to 100 ° C./sec (30 ° C./sec or more) Furthermore, there were no pinholes and the void ratio was as small as 4 to 12%. From these results, it was confirmed that a heating rate of 30° C./second or more is necessary for densification of the dielectric film only when the Bi raw material is bismuth diethylhexanoate.

In addition, the metal atomic ratio of Bi, Na, K, Ti, Sr, and Zr in the liquid composition was 0.54:0:0.58:1:0:0, and the heating rate during firing was 25°C. /sec, which is smaller than the appropriate range (30°C/sec or more), the dielectric film of Comparative Example 3 did not have pinholes, but had a high void ratio of 19%. The metal atomic ratio of Na, K, Ti, Sr, and Zr is 0.54:0:0.58:1:0:0, and the heating rate during firing is 50°C/sec, which is an appropriate range (30 °C/sec), there were no pinholes, and the void fraction was extremely small at 2%. From this, it was confirmed that the densification of the dielectric film did not proceed unless the temperature increase rate was 30° C./second or more.

Furthermore, as is clear from Tables 1 and 2, the liquid composition contains Sr and Zr, and the metal atomic ratio of Bi, Na, K, Ti, Sr and Zr in the liquid composition is 0.54:0.464. : 0.116: 0.975: 0.025: 0.025, and the temperature increase rate during firing is 25 ° C./sec, which is smaller than the appropriate range (30 ° C./sec or more). In the dielectric film, the metal atomic ratio of Bi in the dielectric film was 0.490 to 0.499, and the decrease rate from the metal atomic ratio of Bi in the liquid composition was 0.54. Sr and Zr are included, and the metal atomic ratio of Bi, Na, K, Ti, Sr and Zr in the liquid composition is 0.54:0.464:0.116:0.975:0.025:0.025 In the dielectric films of Examples 8 to 12, in which the rate of temperature rise during firing is within the appropriate range of 30° C./sec to 100° C./sec (30° C./sec or more), these dielectric films The metal atomic ratio of Bi was 0.502 to 0.508, and the rate of decrease from the metal atomic ratio of Bi of the liquid composition of 0.54 was small. The reason for this is thought to be that the addition of Sr and Zr increased the crystallization rate.

In addition, when firing the calcined films of Examples 1 to 12, the rate of temperature increase from room temperature to 500° C. was 15° C./sec, and the rate of temperature increase from 500° C. to 600° C. was set at the rate shown in Table 1. When the temperature rate is 15° C./sec from 600° C. to 700° C., the void fraction of the dielectric film is almost the same as the values of Examples 1 to 12 shown in Table 1. There were no pinholes.

The method for producing a dielectric film of the present invention can be used to produce dielectric films for MEMS (Microelectromechanical Systems) applications such as capacitors, inkjet heads, mirror devices, autofocus, gyro sensors, and micropumps.

Claims (3)

A coating film obtained by applying a liquid composition containing at least Bi, K and Ti on a substrate is calcined to prepare a calcined film, and the calcined film is calcined to manufacture a dielectric film made of a metal oxide. a method,
further comprising Sr and Zr;
The Bi raw material is bismuth 2-ethylhexanoate,
A method for producing a dielectric film, wherein a rate of temperature increase from 500° C. to 600° C. is set to 30° C./second or more during firing of the calcined film. 2. The method of manufacturing a dielectric film according to claim 1, further comprising Na. The liquid composition has the general formula: y(Bit K _s TiO ₃ )-(1- _y )(Sr _m Zr _n O ₃ ) or _y (Bit (Na, K) _s TiO ₃ )-(1-y ) (Sr _m Zr _n O ₃ ) (where 0.9 ≤ y ≤ 1, 0.4 ≤ t ≤ 0.6, 0.4 ≤ s ≤ 0.6, 0.9 ≤ m ≤ 1.1, 3. The method for producing a dielectric film according to claim 1, wherein the compound is represented by 0.9≤n≤1.1).