Ferroelectric thin film and method for manufacturing the same

Abstract

The application discloses a ferroelectric thin film and a preparation method thereof. (0.85‑x) Ca 0.15 Gd x ][Zr 0.2 Ti 0.8 ]O (3+0.5x) , wherein x=0.005-0.01. The ferroelectric thin film is prepared by using barium acetate as a barium source, calcium acetate and gadolinium acetate as doping sources, tetrabutyl titanate as a titanium source, zirconium n-butyrate as a zirconium source, acetic acid and glycol methyl ether as mixed solvents, and acetylacetone as an additive, and then uniformly and stably preparing a precursor solution through a sol-gel method, and then obtaining the ferroelectric thin film on a silicon substrate through spin coating, drying and calcining. The ferroelectric thin film has high crystallinity, low roughness and a nanocrystalline dense structure.

Description

TECHNICAL FIELD

[0001] The present application relates to a functional thin film and a preparation method thereof, in particular to a ferroelectric thin film and a preparation method thereof. BACKGROUND

[0002] Ferroelectric thin films are an important class of functional thin film materials, which have good ferroelectricity, piezoelectricity, pyroelectricity, dielectricity and nonlinear optical properties, and have wide application prospects in high-performance memory, micro-electro-mechanical systems, uncooled infrared detectors and other fields.

[0003] Ferroelectric thin films are currently mainly prepared by the following three methods: sol-gel method, magnetron sputtering method and pulsed laser deposition method (PLD). Among them, the sol-gel method is applied because of its advantages such as accurate control of ferroelectric thin film composition, simple equipment, low cost, good compatibility with semiconductor process, etc. However, obtaining a nanocrystalline ferroelectric thin film with uniform composition, high crystallinity, low roughness and density has always been one of the primary technical difficulties in the process of improving its functional characteristics. For example, the journal "Micro and Nano Electronics Technology", Vol. 55, No. 10, 2018, discloses a PbZr 0.3 Ti 0.7 O3 thin film prepared by a sol-gel process, and the well-crystallized PZT thin film has a root mean square roughness (RMS) value of 3.77 nm. The journal "Frontiers in materials", Vol. 8, No. 9, 2021, discloses a BaZr 0.3 Ti 0.7 O3 / PbZr 0.2 Ti 0.8 O3 / BaZr 0.52 Ti 0.48 O3 / BaZr 0.2 Ti 0.8 O3(BZT / PZT / BZT) multilayer ferroelectric thin film, and the surface root mean square roughness (RMS) value of the BZT / PZT / BZT ferroelectric thin film is 16.7 nm, and the grain size is about 1 μm. Patent CN200510021254.2 discloses a preparation method of a lead-based ferroelectric thin film, and the root mean square roughness (RMS) value of the lanthanum titanate lead (PLZT) ferroelectric thin film prepared by the magnetron sputtering method is 3.38 nm.

[0004] Therefore, there is an urgent need for a nanocrystalline dense ferroelectric film with high crystallinity and low roughness. SUMMARY

[0005] The purpose of the present application is to provide a nanocrystalline dense ferroelectric film with high crystallinity and low roughness; the second purpose of the present application is to provide a preparation method of the ferroelectric film.

[0006] Technical solution: The ferroelectric film provided by the present application has a chemical formula of [Ba (0.85-x) Ca 0.15 Gd x ][Zr 0.2 Ti 0.8 ]O (3+0.5x) , wherein x=0.005-0.01.

[0007] The preparation method of the ferroelectric film comprises the following steps:

[0008] (1) (CH3COO)2Ba, (CH3COO)2Ca, (CH3COO)3Gd.4H2O are dissolved in a mixed solvent of acetic acid and ethylene glycol methyl ether in a molar ratio of (0.85-x):0.15:x, and then heated and stirred to be clear to obtain a precursor solution A;

[0009] (2) CH 16 H 36 O4Zr, Ti(OC4H9)4 are dissolved in a mixed solvent of acetic acid and ethylene glycol methyl ether in a molar ratio, and acetylacetone is added, and then stirred to obtain a precursor solution B;

[0010] (3) The precursor A solution is slowly added to the precursor solution B, and stirred, placed and aged to obtain a precursor solution C;

[0011] (4) The precursor solution C is filtered and spin-coated on a substrate, and then dried and pre-crystallized on a hot plate, and repeated spin-coating, drying, calcination and crystallization to obtain a ferroelectric film.

[0012] In step (1), the volume ratio of acetic acid to ethylene glycol methyl ether in the mixed solvent is 2-2.4:1, and the heating temperature is 60-70°C.

[0013] In step (2), the volume ratio of acetic acid to ethylene glycol methyl ether in the mixed solvent is 1-1.2:1, and the stirring time is 30-60 min.

[0014] In step (2), the volume ratio of acetylacetone to the precursor solution B is 1:4-6.

[0015] In step (3), the concentration of the precursor solution C is 0.3-0.4 mol / L; and the aging time is 24-48 hours.

[0016] In step (4), the spin coating speed is 3500-4000 rpm, and the spin coating time is 25-35 seconds.

[0017] In step (4), the calcination process is carried out in an oxygen atmosphere, first heated to 400-450 DEG C at a heating rate of 1-3 DEG C / min for 5-10 min, and then heated to 700-800 DEG C at a heating rate of 8-10 DEG C / min for 15-45 min; and the oxygen flow rate is 130-170 ml / min.

[0018] In step (4), the drying and pre-crystallization process is carried out by heating the plate to 150 DEG C for 5-10 min, and then heating to 400 DEG C for 5-10 min; and the spin coating and drying process is repeated 5-7 times.

[0019] In step (4), the substrate is preferably a Si / SiO2 substrate.

[0020] Invention principle: Based on the barium titanate zirconate perovskite structure, the crystal cell structure is controlled by ion substitution, and the processes such as gelation, spin coating, and calcination are controlled, so that the high-crystallinity, low-roughness nanocrystalline dense ferroelectric film is prepared by the sol-gel method.

[0021] Beneficial effects: Compared with the prior art, the present application has the following remarkable effects: (1) the ferroelectric film has high crystallinity and low roughness RMS value; (2) the precursor solution is stable and can be stored at room temperature for 20-30 days; (3) the prepared ferroelectric film has uniform grain distribution and small average particle size. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 X-ray diffraction pattern of the ferroelectric film prepared in Example 2 of the present application;

[0023] Figure 2 Surface micro-morphology diagram of the ferroelectric film prepared in Example 2 of the present application;

[0024] Figure 3 Surface AFM two-dimensional diagram of the ferroelectric film prepared in Example 2 of the present application;

[0025] Figure 4 Surface AFM three-dimensional diagram of the ferroelectric film prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0026] The present application will be further described in detail below.

[0027] Example 1

[0028] A ferroelectric thin film with a chemical formula of: (Ba 0.845 Ca 0.15 Gd 0.005 )(Zr 0.2 Ti 0.8 )O 3.0025 , wherein x = 0.005. The preparation method of the thin film comprises the following steps:

[0029] (1) Dissolving (CH3COO)2Ba, (CH3COO)2Ca, (CH3COO)3Gd·4H2O in a molar ratio of 0.845:0.15:0.005 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 2:1, and then heating and stirring at 60°C until clear to obtain precursor solution A;

[0030] (2) Dissolving Ti(OC4H9)4, C 16 H 36 O4Zr in a molar ratio of 0.8:0.2 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 1:1, and adding acetylacetone, and then stirring at room temperature for 30 min to obtain precursor solution B, wherein the volume ratio of acetylacetone to precursor solution B is 1:5;

[0031] (3) Slowly adding precursor solution A to precursor solution B, mixing and stirring at room temperature, standing, and aging for 24 h to obtain a 0.3 mol / L precursor solution C;

[0032] (4) Using a spin coating method to spin coat the precursor solution C on a Si / SiO2 substrate, wherein the spin coating speed is 3500 rpm and the time is 30 s, and then placing it on a hot plate at 150°C for heating for 10 min, and then increasing the temperature to 400°C on the hot plate for heating for 5 min; repeating the spin coating and drying 7 times to obtain an amorphous thin film with a certain thickness; placing the amorphous thin film in a tube furnace, and introducing oxygen into the tube furnace at a flow rate of 150 ml / min, first heating at a rate of 1°C / min to 400°C and maintaining for 10 min, and then heating at a rate of 10°C / min to 700°C and maintaining for 30 min, and cooling to room temperature with the furnace to obtain a (Ba 0.845 Ca 0.15 Gd 0.005 )(Zr 0.2 Ti 0.8 )O 3.0025 nanocrystalline ferroelectric thin film with high crystallinity and low roughness.

[0033] The ferroelectric thin film prepared in this example has a crystallinity of 88.6%, a root mean square roughness (RMS) of 2.87 nm, and an average grain size of 43.6 nm.

[0034] Example 2

[0035] A ferroelectric thin film with the chemical formula: (Ba 0.8425 Ca 0.15 Gd 0.0075 (Zr) 0.2 Ti 0.8 )O 3.00375 Where x = 0.0075. The preparation method of this ferroelectric thin film includes the following steps:

[0036] (1) Dissolve (CH3COO)2Ba, (CH3COO)2Ca, and (CH3COO)3Gd·4H2O in a molar ratio of 0.8425:0.15:0.0075 in a mixed solvent of acetic acid and ethylene glycol methyl ether with a volume ratio of 2:1, and then heat and stir at 70°C until clear to obtain precursor solution A;

[0037] (2) Ti(OC4H9)4, C 16 H 36 O4Zr was dissolved in a mixture of acetic acid and ethylene glycol methyl ether in a molar ratio of 0.8:0.2 and a volume ratio of 1:1. Acetylacetone was added, and the mixture was stirred at room temperature for 45 min to obtain precursor solution B, wherein the volume ratio of acetylacetone to precursor solution B was 1:6.

[0038] (3) Slowly add precursor solution A to precursor solution B, mix and stir at room temperature, let stand and age for 24 hours to obtain 0.4 mol / L precursor solution C;

[0039] (4) The precursor solution C was spin-coated onto a Si / SiO2 substrate using a spin-coating method. The spin coating speed was 3800 rpm for 30 seconds. The substrate was then heated on a hot plate at 150°C for 5 minutes, followed by heating to 400°C for 10 minutes. This spin-coating and drying process was repeated 5 times to obtain an amorphous film of a certain thickness. The amorphous film was then placed in a tube furnace, with oxygen introduced at a flow rate of 150 ml / min. The temperature was first increased to 400°C at a rate of 2°C / min and held for 10 minutes, then increased to 800°C at a rate of 9°C / min and held for 30 minutes. The film was then cooled to room temperature with the furnace to obtain a (Ba) film with high crystallinity and low roughness. 0.8425 Ca 0.15 Gd 0.0075 (Zr) 0.2 Ti 0.8 )O 3.00375 Nanocrystalline ferroelectric thin films.

[0040] from Figure 1 It can be seen that the ferroelectric thin film prepared in this embodiment has a single-phase cubic perovskite structure with good crystallinity; calculations show that the crystallinity is as high as 90.4%. Figure 2, 3 It can be seen that the ferroelectric thin film is a dense nanocrystal with a uniform particle size distribution. Calculations show that its average grain size is only 58.4 nm. Figure 4 It can be seen that the surface roughness of the ferroelectric thin film is low, with a root mean square roughness (RMS) of 2.98 nm.

[0041] Example 3

[0042] A ferroelectric thin film with the chemical formula: (Ba 0.84 Ca 0.15 Gd 0.01 (Zr) 0.2 Ti 0.8 )O 3.005 Where x = 0.01. The preparation method of this ferroelectric thin film includes the following steps:

[0043] (1) Dissolve (CH3COO)2Ba, (CH3COO)2Ca, and (CH3COO)3Gd·4H2O in a mixed solvent of acetic acid and ethylene glycol methyl ether with a volume ratio of 2.4:1 in a molar ratio of 0.84:0.15:0.01, and then heat and stir at 70°C until clear to obtain precursor solution A;

[0044] (2) Ti(OC4H9)4, C 16 H 36 O4Zr was dissolved in a mixture of acetic acid and ethylene glycol methyl ether in a molar ratio of 0.8:0.2 and a volume ratio of 1.2:1. Acetylacetone was added, and the mixture was stirred at room temperature for 45 min to obtain precursor solution B, wherein the volume ratio of acetylacetone to precursor solution B was 1:5.

[0045] (3) Slowly add precursor solution A to precursor solution B, mix and stir at room temperature, let stand and age for 48 hours to obtain 0.35 mol / L precursor solution C;

[0046] (4) The precursor solution C was spin-coated onto a Si / SiO2 substrate using a spin-coating method. The spin coating speed was 4000 rpm for 35 seconds. The substrate was then heated on a 150°C hot plate for 10 minutes, followed by heating to 400°C for another 10 minutes. This spin-coating and drying process was repeated six times to obtain an amorphous film of a certain thickness. The amorphous film was then placed in a tube furnace, with oxygen introduced at a flow rate of 130 ml / min. The temperature was first increased to 450°C at a rate of 3°C / min and held for 5 minutes, then increased to 800°C at a rate of 10°C / min and held for 30 minutes. The film was then cooled to room temperature with the furnace to obtain a (Ba) film with high crystallinity and low roughness. 0.84 Ca 0.15 Gd 0.01 (Zr) 0.2 Ti 0.8 )O3.005 Nanocrystalline ferroelectric thin film

[0047] The ferroelectric thin film prepared in this example has a crystallinity of 91.2%, a root mean square roughness (RMS) of 3.07 nm, and an average grain size of 66.9 nm.

[0048] Example 4

[0049] A ferroelectric thin film has a chemical formula of: (Ba 0.845 Ca 0.15 Gd 0.005 )(Zr 0.2 Ti 0.8 )O 3.0025 wherein x = 0.005. The preparation method of the thin film comprises the following steps:

[0050] (1) Dissolve (CH3COO)2Ba, (CH3COO)2Ca, (CH3COO)3Gd·4H2O in a molar ratio of 0.845:0.15:0.005 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 2.2:1, and then heat and stir at 65°C until clear to obtain precursor solution A;

[0051] (2) Dissolve Ti(OC4H9)4, C 16 H 36 O4Zr in a molar ratio of 0.8:0.2 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 1:1, and add acetylacetone, and then stir at room temperature for 60 min to obtain precursor solution B, wherein the volume ratio of acetylacetone to precursor solution B is 1:4;

[0052] (3) Slowly add precursor solution A to precursor solution B, mix and stir at room temperature, stand, and age for 36 h to obtain a 0.3 mol / L precursor solution C;

[0053] (4) Spin coat the precursor solution C on a Si / SiO2 substrate by a spin coating method, wherein the spin coating speed is 4000 rpm and the time is 25 s, then place it on a hot plate at 150°C for 8 min, and then heat it to 400°C on a hot plate for 8 min; repeat the spin coating and drying 7 times to obtain an amorphous thin film of a certain thickness; place the amorphous thin film in a tube furnace, introduce oxygen into the tube furnace at a flow rate of 170 ml / min, first heat it to 420°C at a heating rate of 1°C / min and keep it at this temperature for 10 min, and then heat it to 750°C at a heating rate of 8°C / min and keep it at this temperature for 45 min, and then cool it to room temperature with the furnace to obtain a (Ba 0.845 Ca 0.15 Gd 0.005 )(Zr 0.2 Ti 0.8 )O3.0025 Nanocrystalline ferroelectric thin film

[0054] The ferroelectric thin film prepared in this example has a crystallinity of 89.6%, a root mean square roughness (RMS) of 2.96 nm, and an average grain size of 52.25 nm.

[0055] Example 5

[0056] A ferroelectric thin film has a chemical formula of: (Ba 0.84 Ca 0.15 Gd 0.01 )(Zr 0.2 Ti 0.8 )O 3.005 wherein x = 0.01. The preparation method of the thin film comprises the following steps:

[0057] (1) Dissolve (CH3COO)2Ba, (CH3COO)2Ca, (CH3COO)3Gd·4H2O in a molar ratio of 0.84:0.15:0.01 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 2:1, then heat and stir at 65°C until clear to obtain precursor solution A;

[0058] (2) Dissolve Ti(OC4H9)4, C 16 H 36 O4Zr in a molar ratio of 0.8:0.2 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 1.1:1, and add acetylacetone, then stir at room temperature for 45 min to obtain precursor solution B, wherein the volume ratio of acetylacetone to precursor solution B is 1:6;

[0059] (3) Slowly add precursor solution A to precursor solution B, mix and stir at room temperature, stand, and age for 24 h to obtain a 0.4 mol / L precursor solution C;

[0060] (4) Use a spin coating method to spin coat the precursor solution on a Si / SiO2 substrate, wherein the spin coating speed is 3750 rpm and the time is 30 s, then place it on a hot plate at 150°C for 10 min, then heat to 400°C on a hot plate for 8 min; repeat the spin coating, drying 5 times to obtain an amorphous thin film of a certain thickness; place the amorphous thin film in a tube furnace, pass oxygen into the tube furnace at a flow rate of 150 ml / min, first heat to 400°C at a heating rate of 2°C / min and keep for 8 min, then heat to 750°C at a heating rate of 9°C / min and keep for 15 min, and cool to room temperature with the furnace to obtain a (Ba 0.84 Ca 0.15 Gd 0.01 )(Zr 0.2 Ti 0.8 )O3.005 Nanocrystalline ferroelectric thin film

[0061] The ferroelectric thin film prepared in this example has a crystallinity of 89.4%, a root mean square roughness (RMS) of 3.07 nm, and an average grain size of 48.8 nm.

[0062] Comparative Example 1

[0063] A ferroelectric thin film having a chemical formula of: (Ba 0.8425 Ca 0.15 Gd 0.0075 )(Zr 0.2 Ti 0.8 )O 3.00375 wherein x = 0.0075. The preparation method of the ferroelectric thin film comprises the following steps:

[0064] (1) Dissolve (CH3COO)2Ba, (CH3COO)2Ca, (CH3COO)3Gd·4H2O in a molar ratio of 0.8425:0.15:0.0075 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 2:1, and then heat and stir at 70°C until clear to obtain precursor solution A;

[0065] (2) Dissolve Ti(OC4H9)4, C 16 H 36 O4Zr in a molar ratio of 0.8:0.2 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 1:1, and add acetylacetone, and then stir at room temperature for 45 min to obtain precursor solution B, wherein the volume ratio of acetylacetone to precursor solution B is 1:6;

[0066] (3) Slowly add precursor solution A to precursor solution B, mix and stir at room temperature, stand, and age for 24 h to obtain a precursor solution C of 0.4 mol / L;

[0067] (4) Spin coat the precursor solution C on a Si / SiO2 substrate by a spin coating method, wherein the spin coating speed is 3800 rpm and the time is 30 s, then place it on a hot plate at 150°C for 5 min, and then heat to 400°C on a hot plate for 10 min; repeat the spin coating and drying 5 times to obtain an amorphous thin film of a certain thickness; heat the amorphous thin film in a tube furnace, pass oxygen into the tube furnace at a flow rate of 150 ml / min, heat to 800°C at a heating rate of 5°C / min and keep for 30 min, and cool to room temperature with the furnace to obtain a (Ba 0.8425 Ca 0.15 Gd 0.0075 )(Zr 0.2 Ti 0.8 )O 3.00375 ferroelectric thin film.

[0068] The ferroelectric thin film prepared in this comparative example has a crystallinity of only 76.8%, a surface root mean square roughness (RMS) of 8.07 nm, and an average grain size of 85.2 nm.

[0069] Comparative Example 2

[0070] A ferroelectric thin film having the chemical formula: (Ba 0.8425 Ca 0.15 Gd 0.0075 )(Zr 0.2 Ti 0.8 )O 3.00375 wherein x = 0.0075. The method for preparing the ferroelectric thin film comprises the following steps:

[0071] (1) Dissolve (CH3COO)2Ba, (CH3COO)2Ca, (CH3COO)3Gd·4H2O in a molar ratio of 0.8425:0.15:0.0075 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 2:1, then heat and stir at 70°C until clear to obtain precursor solution A;

[0072] (2) Dissolve Ti(OC4H9)4, C 16 H 36 O4Zr in a molar ratio of 0.8:0.2 in a mixed solvent of acetic acid and ethylene glycol methyl ether in a volume ratio of 1:1, and add acetylacetone, then stir at room temperature for 45 min to obtain precursor solution B, wherein the volume ratio of acetylacetone to precursor solution B is 1:6;

[0073] (3) Slowly add precursor solution A to precursor solution B, mix and stir at room temperature, stand, and age for 24 h to obtain a 0.4 mol / L precursor solution C;

[0074] (4) Spin coat the precursor solution C on a Si / SiO2 substrate using a spin coating method, wherein the spin coating speed is 3800 rpm and the time is 30 s, then place it on a hot plate at 150°C for 5 min, then increase the temperature to 400°C on the hot plate for 10 min; repeat the spin coating and drying 5 times to obtain an amorphous thin film of a certain thickness; heat the amorphous thin film in a tube furnace in an air atmosphere at a heating rate of 2°C / min to 400°C for 10 min, then at a heating rate of 9°C / min to 800°C for 30 min, and cool to room temperature with the furnace to obtain a (Ba 0.8425 Ca 0.15 Gd 0.0075 )(Zr 0.2 Ti 0.8 )O 3.00375 ferroelectric thin film.

[0075] The ferroelectric thin film prepared in this comparative example has a crystallinity of 74.1%, a root mean square roughness (RMS) of 5.25 nm, and an average grain size of 57.8 nm.

Claims

1. A method for preparing a ferroelectric thin film, characterized in that, Includes the following steps: (1) Dissolve (CH3COO)2Ba, (CH3COO)2Ca, and (CH3COO)3Gd·4H2O in a mixed solvent of acetic acid and ethylene glycol methyl ether at a molar ratio of (0.85-x):0.15:x, and then heat and stir until clear to obtain precursor solution A; The x = 0.005~0.01; (2) C 16 H 36 O4Zr and Ti(OC4H9)4 were dissolved in a mixed solvent of acetic acid and ethylene glycol methyl ether in a molar ratio, and acetylacetone was added. The mixture was then stirred to obtain precursor solution B. (3) Slowly add precursor A solution to precursor B, stir, let stand, and age to obtain precursor solution C; (4) After the precursor solution C is filtered, it is spin-coated onto the substrate, and then dried and pre-crystallized on a heating plate. The spin-coating, drying, and calcination crystallization are repeated to obtain a ferroelectric thin film. The calcination crystallization is carried out in an oxygen atmosphere; the oxygen flow rate is 130-170 ml / min; the calcination crystallization is first heated to 400-450℃ at a heating rate of 1-3℃ / min and held for 5-10 min, and then heated to 700-800℃ at a heating rate of 8-10℃ / min and held for 15-45 min.

2. The method for preparing ferroelectric thin films according to claim 1, characterized in that, In step (2), the volume ratio of acetylacetone to precursor solution B is 1:4~6.

3. The method for preparing ferroelectric thin films according to claim 1, characterized in that, In step (3), the concentration of the precursor solution C is 0.3~0.4 mol / L.

4. The method for preparing ferroelectric thin films according to claim 1, characterized in that, In step (4), during the spin coating process, the spin coating speed is 3500~4000 rpm and the spin coating time is 25~35 seconds.

5. The method for preparing ferroelectric thin films according to claim 1, characterized in that, In step (4), during the drying and pre-crystallization process, the temperature on the heating plate is raised to 150°C and held for 5-10 minutes, and then raised to 400°C and held for 5-10 minutes.

6. The method for preparing ferroelectric thin films according to claim 1, characterized in that, In step (1), the volume ratio of acetic acid to ethylene glycol methyl ether in the mixed solvent is 2~2.4:1, and the heating temperature is 60~70℃; in step (2), the volume ratio of acetic acid to ethylene glycol methyl ether in the mixed solvent is 1~1.2:1, and the stirring time is 30~60min.

7. A ferroelectric thin film obtained by the method of claim 1, characterized in that, The chemical formula is [Ba (0.85-x) Ca 0.15 Gd x ][Zr 0.2 Ti 0.8 ]O (3+0.5x) , where x = 0.005~0.01.

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