CN1513809A - Preparation method of high performance lead zirconate titanate film - Google Patents

Abstract

The invention relates to a method for preparing a high-performance lead zirconate titanate thin film, which belongs to a method for preparing ferroelectric functional ceramic materials, and in particular relates to a method for preparing a lead zirconate titanate (PZT) ferroelectric thin film. The preparation process is as follows: ① prepare the precursor solution by sol-gel method; ② make the substrate with PZT crystal seed layer; ③ atomize and accelerate the precursor solution to deposit on the substrate to form a thin film; The bottom and the film are heat treated; or: when the thickness of the atomized coating is 0.5 to 1 micron, a layer of PZT film is coated on it by the spin coating method. Compared with the traditional sol-gel method, the present invention has outstanding advantages, not only inheriting the advantages of accurate composition, easy control, and preferred orientation of the obtained film; moreover, the film growth speed is fast, and the single-layer film thickness can reach 0.5-2 microns; The precursor solution has less waste and high utilization rate; the device has simple structure, low cost, and is compatible with commonly used micro-electro-mechanical system processing technology. The PZT ferroelectric film prepared by the invention can simultaneously obtain large film thickness and excellent piezoelectric and dielectric properties.

Description

Preparation method of high performance lead zirconate titanate film

Technical field:

The invention belongs to a preparation method of a ferroelectric functional ceramic material, in particular to a preparation method of a lead zirconate titanate ferroelectric thin film.

Background technique:

Lead zirconate titanate (molecular formula is Pb(Zr _x Ti _1-x )O ₃ , referred to as PZT), as a ferroelectric material with excellent performance, has been widely used in microelectronics technology, such as the manufacture of non-volatile dynamic random access memory (FRAM). In recent years, with the development of microsystem technology, the advantages of high piezoelectric constant and high dielectric constant of PZT are very suitable for making microsensors and microdrivers in microsystems, and are considered to be the most promising in the field of microsystems. One of the sensing and driving materials. The PZT ferroelectric thin film used in the production of micro-drivers should have excellent piezoelectric properties and a film thickness of more than 2 microns to provide sufficient power for the device. In the commonly used preparation methods of PZT ferroelectric thin films, the thin films prepared by the sol-gel method have excellent piezoelectric and dielectric properties, but during the heat treatment process of the wet film, due to the large shrinkage of the film volume, As a result, a large internal stress is generated inside the film and between the film and the substrate, resulting in a maximum non-cracking single-layer film thickness of only 0.1-0.2 microns, and when there are too many layers of the film, the heat treatment time will be too long, resulting in Pt The bottom electrode diffuses into the PZT, so it is difficult to obtain a PZT ferroelectric film with a thickness of more than 2 microns; other preparation methods, such as: magnetron sputtering, laser pulse deposition, hydrothermal method, chemical vapor deposition, etc., although PZT ferroelectric films with a thickness of more than 2 microns can be produced, but the equipment is complicated, the cost is high, and it is difficult to obtain excellent piezoelectric properties (poor preferred orientation).

Invention content:

The purpose of the present invention is to provide a preparation method capable of obtaining a large film thickness on the premise of ensuring the excellent performance of the PZT ferroelectric film.

Technical solution of the present invention is as follows:

The preparation process of the thin film is as follows: ① Prepare the precursor solution by sol-gel method; ② Make the substrate with the PZT crystal seed layer; ③ Atomize and accelerate the precursor solution to deposit it on the substrate to form a thin film; The substrate and thin film are heat treated.

Or: ① Prepare the precursor solution by sol-gel method; ② Make the substrate with PZT crystal seed layer; ③ Atomize and accelerate the precursor solution to deposit it on the substrate to form a thin film, each coating 0.5 ~ 1 micron When the thickness is thick, a layer of PZT film is coated on it by the spin coating method; and the substrate and the film are heat treated.

The preparation process of the substrate is as follows: a PZT wet film is coated on the Pt/Ti/SiO ₂ /Si substrate by the spin coating method, and the wet film is baked at 350-400°C for 40 minutes, and then baked at 600°C Bake for 15 minutes to form a PZT ferroelectric thin film strongly oriented along the (100) crystal direction as a crystallization seed layer.

The atomization process is as follows: the precursor solution is put into the container of the electro-atomization device, the substrate is placed on the grounded heating plate under the nozzle, and the precursor solution is ejected from the nozzle under the action of a high-voltage electric field to form Under the acceleration of the electric field, the droplets move towards the substrate at high speed and finally deposit on the substrate to form a PZT film.

The heat treatment process is as follows: heating the substrate during the atomization process and keeping the substrate temperature greater than or equal to 20°C and less than 300°C; baking the substrate and film at 300-400°C for 40-40°C when the coating thickness is 0.5-1 micron. 60 minutes, then bake at 600°C for 15-20 minutes; anneal the substrate and the film with the required thickness in a PbO saturated atmosphere at 600°C for 2-4 hours. Alternatively, heat the substrate during the atomization process and keep the substrate temperature greater than or equal to 300°C and less than 400°C; bake the substrate and film at 600°C for 15 to 20 minutes for each coating thickness of 1 to 2 microns; And the thin film that reaches the desired thickness is annealed at 600° C. for 2 to 4 hours in a PbO saturated atmosphere.

That is to say, the present invention improves the sol-gel method and forms a new sol-electrospray method: first, the sol-gel method is used to prepare the precursor solution; Electricity overcomes the surface tension of the liquid, so that the precursor solution forms uniformly sized charged droplets, and the droplets move toward the substrate at high speed under the acceleration of the electric field, thereby forming a film on the surface of the substrate. The specific method is as follows:

① Preparation of lead zirconate titanate precursor solution by conventional sol-gel method: the salts of lead, zirconium and titanium used should be made of volatile solvents, among which lead acetate, zirconium propoxide and titanium isopropoxide are preferred. Dissolve anhydrous lead acetate in acetic acid first, and then follow the molar concentration ratio of lead, zirconium and titanium as Pb:Zr:Ti=1:X:(1-X) (where 0<X<1) in sequence Zirconium propoxide and titanium isopropoxide are added. After the solution is stirred evenly by ultrasonic vibration, a mixed solution of deionized water, acetic acid and isopropanol is added in a volume ratio of deionized water: acetic acid: isopropanol = 3:5:10. After ultrasonic vibration and stirring the solution evenly, a PZT precursor solution with a concentration of 0.4-0.5 mol/liter is finally obtained (if the concentration is inappropriate, the solution can also be adjusted appropriately with acetic acid and isopropanol). The formed precursor solution is a colorless and transparent liquid.

② Substrate fabrication: Prepare a single-layer (about 80-120 nm thick) PZT ferroelectric thin film on a commonly used Pt/Ti/SiO ₂ /Si substrate by spin coating method, and bake the wet film at 350-400 °C Bake for 40 minutes, and then bake at 600°C for 15 minutes to make it strongly oriented along the (100) crystal direction. It can be used as a crystallization seed layer when the film grows in the subsequent process, so that the atomized deposited PZT ferroelectric film can also be strongly oriented along the (100) crystal direction.

③ Atomize the precursor solution to deposit it on the substrate to form a thin film: the atomization device can use a conventional electrospray device. It includes precursor solution supply system, DC high-voltage power supply system, temperature control system, etc. (as shown in Figure 1). Add the PZT precursor solution into the container of the electro-atomization device, which is propelled by a DC motor; the substrate is placed on the heating plate under the nozzle, and the heating plate can be grounded to be used as a ground electrode; the atomization nozzle is tubular, with an inner diameter of less than 1 mm; Under DC high voltage of thousands of volts (about 4000-7000 volts), the precursor solution is atomized at the outlet of the nozzle into charged droplets with a diameter of micron (0.5-2 microns) (see Figure 2). In the range of 70-90° divergence angle, the size and velocity of the droplets are uniform, forming a uniform fog field. The droplets move towards the substrate at high speed under the acceleration of the electric field, and deposit on the Pt/Ti/SiO ₂ /Si substrate with the crystallization seed layer to form a wet film. The distance between the nozzle and the substrate should be determined according to the divergence angle of the uniform fog field and the area of the PZT ferroelectric film to be prepared (for a substrate with a diameter of 2 to 3 inches, the distance between the nozzle and the substrate Generally 5-8 cm); the solution flow depends on the inner diameter of the nozzle and the voltage between the nozzle and the substrate (generally 0.4-1 ml/hour); the voltage depends on the conductivity of the precursor solution and the nozzle and the substrate. depends on the distance between the substrates.

Heat treatment of the substrate and film: Under the action of substrate heating, the solvent in the wet film can be continuously volatilized, which helps to form a continuous stress-free film. Substrate heating can be achieved by a heating plate. If the temperature of the substrate is controlled at 20-100°C (greater than or equal to 20°C, less than 100°C), when the thickness of each coating film is about 0.5 microns, put the substrate and film into a resistance furnace and bake at 300-400°C for 40-60 Minutes (to completely volatilize the residual organic solvent), and then bake at about 600°C for 15 to 20 minutes (to promote the crystallization of the prepared film along the (100) crystal direction to ensure the preferred orientation); if the substrate temperature is controlled to When the temperature is 100-300°C (greater than or equal to 100°C, less than 300°C), the above-mentioned baking is carried out when the thickness of each coating is about 1 micron; Baking directly at 600°C for 15 to 20 minutes when the thickness of each coating is about 2 microns. Finally, anneal the substrate and the film with the required thickness in a PbO saturated atmosphere at 600° C. for 2 to 4 hours to prepare a thick PZT ferroelectric film strongly oriented along the (100) crystal direction.

In summary, the sol-electrospray method used in the present invention prepares PZT ferroelectric thin films, compared with the traditional sol-gel method, has outstanding advantages: 1. inherits the composition of the sol-gel method, which is accurate and easy to control , simple device, low cost, and the preferred orientation of the obtained film; ②The substrate temperature can be arbitrarily set to a suitable temperature according to the needs during the preparation process. Since the formation of the wet film is a continuous process, the effect of the substrate temperature Under high temperature conditions, the internal stress caused by the volume shrinkage of the wet film will be gradually released, so the film growth rate is fast, and the single-layer film thickness at 25 ° C, 100 ° C and 350 ° C can reach 0.5 microns, 1 microns, and 2 microns respectively. ③Because the waste of the precursor solution in the atomization process is very little, the solution utilization rate is high; ④The device structure is simple, the cost is very low, and it is compatible with the commonly used micro-electromechanical system processing technology, which is conducive to the intervention of micro-sensors or micro-drivers on the production line. The PZT ferroelectric film prepared by the invention can simultaneously obtain large film thickness and excellent film properties (and have excellent piezoelectric and dielectric properties), and can basically meet the needs of micro sensors and micro drivers in microsystems.

Description of drawings:

Figure 1 is a schematic diagram of the electrospray process and device. Figure 2 shows an example of a photo of the formation of droplet atomization at the outlet of the nozzle. Fig. 3 shows the XRD spectrum of the PZT ferroelectric thin film prepared when the substrate temperature is 25°C (Example 1). The thin film forms a single perovskite phase and is strongly oriented along the (100) crystal direction. Fig. 4 shows the atomic force micrograph of the PZT ferroelectric thin film prepared when the substrate temperature is 100°C (Example 2), the crystal grain size is uniform, about 0.2 micron. Shown in Fig. 5 is the optical micrograph of the PZT ferroelectric thin film that (example 3) makes when substrate temperature is 350 ℃, and surface is smooth without crack; Fig. 6 shows that when substrate temperature is 25 ℃ (example 4) The hysteresis loop of the prepared PZT ferroelectric thin film shows that the remnant polarization of the thin film is 12.5 μc/cm ² and the coercive field strength is 32 kV/cm.

Detailed ways:

The substantive characteristics and remarkable progress of the present invention are further illustrated below by examples, but the present invention is by no means limited to the described examples.

Example 1

Anhydrous lead acetate is dissolved in acetic acid, and then zirconium propoxide and titanium isopropoxide are sequentially added according to the molar concentration ratio of lead, zirconium and titanium in the ratio of Pb:Zr:Ti=1:0.53:0.47. After stirring evenly with ultrasonic vibration, add a mixed solution of deionized water, acetic acid and isopropanol in a volume ratio of deionized water: acetic acid: isopropanol = 3:5:10. After being uniformly stirred by ultrasonic vibration, the solution was diluted to 0.4 mol/L with acetic acid and isopropanol. The prepared precursor solution was added to the electroatomization device, the flow rate was controlled at 0.6 ml/hour, the inner diameter of the atomization nozzle was 0.25 mm, the distance between the nozzle and the substrate was 5 cm, and a DC voltage of 4500 volts was applied. The substrate used is: prepare _SiO2 film on Si substrate according to the previous thermal oxidation method, prepare Ti film and Pt film by sputtering method, and then use spin coating method on the Pt/Ti/ _SiO2 /Si substrate to prepare A single layer of 100nm-thick PZT crystalline seed layer was prepared, and the wet film was baked at 350°C for 40 minutes, and then baked at 600°C for 15 minutes to make it strongly oriented along the (100) crystal direction. The temperature of the substrate is set at 25°C, and the coating time is 20 minutes, wherein the substrate and film are placed in a resistance furnace for 5 minutes (about 0.5 micron thick) and baked at 350°C for 60 minutes, and then baked at 600°C. ℃ for 20 minutes, and then anneal the substrate and the film with the required thickness in a PbO saturated atmosphere at 600 ℃ for 4 hours to obtain a completely perovskite phase and a thickness of 2 microns that is strongly oriented along the (100) crystal direction. PZT ferroelectric thin film.

Example 2

Other conditions are the same as Example 1, the control flow rate is 0.8 ml/hour, the inner diameter of the atomizing nozzle is 0.4 mm, the distance between the nozzle and the substrate is 6 cm, and a DC voltage of 4800 volts is added. The substrate temperature is set at 100°C, and the coating time is 20 minutes. For every 10 minutes of coating (about 1 micron thick), the substrate and film are placed in a resistance furnace and baked at 350°C for 40 minutes, and then baked at 600°C. Baking for 20 minutes, and then annealing the substrate and the film with the desired thickness in a PbO saturated atmosphere at 600°C for 4 hours to obtain a PZT iron with a thickness of 2 microns that is completely perovskite and strongly oriented along the (100) crystal direction. Electric film.

Example 3

Other conditions are the same as Example 1, the control flow rate is 1 ml/hour, the inner diameter of the atomizing nozzle is 0.6 mm, the distance between the nozzle and the substrate is 7 cm, and a DC voltage of 5500 volts is added. The substrate temperature is set at 350°C, and the coating time is 40 minutes, among which the substrate and film are placed in a resistance furnace for 20 minutes (about 2 microns thick) and baked at 600°C for 15 minutes, and then the substrate and The film with the desired thickness was annealed in a PbO saturated atmosphere at 600°C for 2 hours to obtain a PZT ferroelectric film with a thickness of 4 microns that was completely perovskite and preferentially oriented along the (100) crystal direction.

Example 4

All the other conditions are the same as example 1, the substrate temperature is set at 25 ℃, and the coating time is 20 minutes, and after every coating 5 minutes, after the same heat treatment, use the spin coating method to coat a layer of PZT film (about 100 nanometers thick), to strengthen The compactness and preferred orientation of the film, the PZT film prepared by the spin coating method needs to be heat-treated, baked at 350°C for 40 minutes, and then baked at 600°C for 15 minutes to obtain a 2-micron thick PZT ferroelectric film. The perovskite phase is strongly oriented along the (100) crystal direction. The relative permittivity of the film is 960, the remnant polarization is 12.5μc/cm ² , and the coercive field strength is 32kV/cm.

Claims (11)

1, a kind of preparation method of high-performance lead zirconate titanate thin film is characterized in that: preparation process is: 1. prepare precursor solution with sol-gel method; 2. make the substrate with PZT crystallization seed layer; 3. make precursor solution Atomize and accelerate to deposit on the substrate to form a thin film; and heat treat the substrate and thin film. 2, a kind of preparation method of high-performance lead zirconate titanate film, it is characterized in that: preparation process is: 1. prepare precursor solution with sol-gel method; 2 make the substrate with PZT crystallization seed layer; 3 make precursor solution Atomize and accelerate to deposit on the substrate to form a thin film, and then use the spin coating method to coat a layer of PZT film on it when the thickness of each coating is 0.5 to 1 micron; and heat treat the substrate and the film. 3. The preparation method according to claim 1 or 2, characterized in that: the preparation process of the substrate is: using the spin coating method to coat a PZT wet film on the Pt/Ti/SiO ₂ /Si substrate, and The wet film is baked at 350-400°C for 40 minutes, and then baked at 600°C for 15 minutes to form a PZT ferroelectric film strongly oriented along the (100) crystal direction as a crystallization seed layer; the thickness of the crystallization seed layer is controlled at 80-120 nanometers. 4. The preparation method according to claim 1 or 2, characterized in that: the atomization process is: put the precursor solution into the container of the electric atomization device, place the substrate on a grounded heating plate under the nozzle, Under the action of a high-voltage electric field, the precursor solution is ejected from the nozzle to form uniformly charged droplets with a diameter in the order of microns. Under the acceleration of the electric field, the droplets move to the substrate at high speed and finally deposit on the substrate to form a PZT film. 5. The preparation method according to claim 3, characterized in that: the atomization process is as follows: the precursor solution is put into the container of the electric atomization device, the substrate is placed on a grounded heating plate under the nozzle, and the Under the action of the electric field, the precursor solution is ejected from the nozzle to form uniformly charged droplets with a diameter of micron scale. Under the acceleration of the electric field, the droplets move to the substrate at high speed and finally deposit on the substrate to form a PZT film. 6. The preparation method according to claim 1, 2 or 5, characterized in that: the heat treatment process is: heating the substrate during the atomization process and keeping the substrate temperature greater than or equal to 20°C and less than 300°C; When the thickness is 0.5-1 micron, bake the substrate and film at 300-400°C for 40-60 minutes, and then bake at 600°C for 15-20 minutes; put the substrate and the film with the required thickness in a PbO saturated atmosphere for 600 ℃ annealing for 2 to 4 hours. 7. The preparation method according to claim 3, characterized in that: the heat treatment process is: heating the substrate during the atomization process and keeping the substrate temperature greater than or equal to 20°C and less than 300°C; When the thickness is determined, bake the substrate and film at 300-400°C for 40-60 minutes, and then bake at 600°C for 15-20 minutes; 4 hours. 8. The preparation method according to claim 4, characterized in that: the heat treatment process is: heating the substrate during the atomization process and keeping the substrate temperature greater than or equal to 20°C and less than 300°C; When the thickness is determined, bake the substrate and film at 300-400°C for 40-60 minutes, and then bake at 600°C for 15-20 minutes; 4 hours. 9. The preparation method according to claim 1, 2 or 5, characterized in that: the heat treatment process is: heating the substrate during the atomization process and keeping the substrate temperature greater than or equal to 300°C and less than 400°C; When the thickness is 1-2 microns, the substrate and the film are baked at 600° C. for 15-20 minutes; the substrate and the film with the required thickness are annealed at 600° C. for 2-4 hours in a PbO saturated atmosphere. 10. The preparation method according to claim 3, characterized in that: the heat treatment process is: heating the substrate during the atomization process and keeping the substrate temperature greater than or equal to 300°C and less than 400°C; The substrate and film are baked at 600°C for 15-20 minutes according to the thickness; the substrate and the film with the required thickness are annealed at 600°C for 2-4 hours in a PbO saturated atmosphere. 11. The preparation method according to claim 4, characterized in that: the heat treatment process is: heating the substrate during the atomization process and keeping the substrate temperature greater than or equal to 300°C and less than 400°C; The substrate and film are baked at 600°C for 15-20 minutes according to the thickness; the substrate and the film with the required thickness are annealed at 600°C for 2-4 hours in a PbO saturated atmosphere.

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