Method for improving electro-optic coefficient of PZT or PLZT film

Abstract

The method for improving the electro-optic coefficient of the PZT or PLZT thin film comprises the following steps: S1, attaching an electrode to the PZT or PLZT thin film; and S2, an external electric field is applied to the PZT or PLZT thin film through the electrode, the applied external electric field is larger than the internal coercive field, an electric domain in the PZT or PLZT thin film is turned, and effective polarization is achieved. According to the method for improving the electro-optic coefficient of the PZT or PLZT thin film, an original device structure does not need to be damaged, the electro-optic coefficient of the prepared PZT or PLZT thin film is improved through a polarization method, and the performance of the PZT or PLZT thin film in application of sensors, actuators, memories and the like is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electro-optical modulation, and particularly relates to a method for improving the electro-optic coefficient of a PZT or PLZT thin film applied to the field of electro-optical modulators. BACKGROUND

[0002] Optical fiber communication technology uses optical fibers as transmission media, converts electricity into light through photoelectric conversion, and transmits information through light. The transmission system mainly includes three main parts: optical transmitting end, photoelectric conversion end and optical receiving end. As the core device of the photoelectric conversion end, the electro-optical modulator is the conversion engine of electrical and optical signals, and is one of the keys to realizing large capacity, high bandwidth and low power consumption information transmission. Currently, electro-optical modulators are mainly based on the following three mechanisms to achieve optical modulation: a) Stark effect; b) plasmonic dispersion effect; c) Pockels effect. Compared with the first two effects, Pockels effect is a linear electro-optic effect, which can break through the modulation bandwidth limit and ensure high-quality transmission of high-speed signals. Pockels effect often exists in crystal materials that lack inversion symmetry, such as lithium niobate, lithium tantalate, PZT, PLZT, etc. Among them, PZT / PLZT thin film crystal has multiple excellent properties: 1) The electro-optic coefficient is as high as 130 pm / V or more; 2) The electro-optic thin film crystal can be prepared on various types of substrates, with excellent compatibility; 3) The thin film crystal can be prepared by liquid deposition method, with low preparation cost; 4) It has a wide transparent spectral range of 0.6~2.5 μm; 5) It has isotropic electro-optic effect. Its electro-optic effect mainly depends on the polarization process. Therefore, improving its electro-optic coefficient is crucial to improving its application performance in electro-optical devices.

[0003] In the prior art, methods for improving the electro-optic effect of PZT or PLZT thin film involve multiple aspects, including optimizing process conditions, selecting suitable substrate and electrode materials, controlling chemical composition and doping, and applying external enhancement means:

[0004] First, optimize the process conditions:

[0005] Annealing atmosphere control: By adjusting the oxygen atmosphere during annealing, the microstructure and optical properties of the PLZT thin film can be affected. A proper oxygen atmosphere helps to improve the uniformity and transparency of the thin film, thereby improving its electro-optic effect.

[0006] Annealing temperature: Annealing is an important step in optimizing the performance of the thin film. Studies have found that PZT / PLZT thin films annealed at 650℃ for 20 minutes can effectively crystallize and exhibit effective electro-optic properties.

[0007] Soaking time: Proper soaking time helps the growth and recombination of grains in the thin film, thereby improving its electro-optic properties.

[0008] Second, choose the right substrate and electrode material: choose a substrate that matches the lattice constant of PZT or PLZT film, such as ITO / quartz glass substrate, which can promote the oriented growth of the film and enhance the crystalline quality.

[0009] Electrode material: use high-conductivity and chemically stable electrode materials such as various metals such as gold, platinum, copper, aluminum, etc. or indium tin oxide ITO, which can reduce charge accumulation and current leakage, thereby improving the electro-optic response of the film.

[0010] Third, control the chemical composition: by adjusting the ratio of zirconium and titanium in PZT or PLZT, the electro-optic coefficient of the film can be optimized. For example, appropriate increase of lanthanum content can improve the transparency and electro-optic performance of PLZT film.

[0011] Doping modification: introducing appropriate amount of dopants such as lanthanum or magnesium can significantly change the electro-optic properties of the material. Doping not only improves the response speed, but also improves the thermal stability and laser intensity of the material.

[0012] The existing technology focuses on improving the crystalline quality of PZT / PLZT film by improving the preparation process such as annealing temperature, atmosphere control, etc. to provide a good foundation for high electro-optic properties. However, these methods are not suitable for already prepared films, and they all improve the crystalline quality of the film, but cannot directly improve the electro-optic coefficient of the already prepared PZT / PLZT film. How to change the chaotic domain state inside the existing film crystal, which shows a small electro-optic coefficient. How to achieve higher electro-optic effect for PZT or PLZT film with high crystalline quality is a technical problem that needs to be solved by those skilled in the art. SUMMARY

[0013] The purpose of the present application is to provide a method for improving the electro-optic coefficient of PZT or PLZT film.

[0014] To this end, the above-mentioned purpose of the present application is achieved by the following technical solution:

[0015] A method for improving the electro-optic coefficient of PZT or PLZT film, comprising the following steps:

[0016] S1, attaching electrodes to the PZT or PLZT film;

[0017] S2, by applying an external electric field to the PZT or PLZT film through the electrode, the internal domain of the PZT or PLZT film is turned to realize effective polarization, wherein the polarization electric field strength applied is:

[0018] 2. Ec(T_pol) < E_pol < S·Eb(T_pol),

[0019] Wherein, E_pol is the polarization electric field intensity, Ec(T_pol) is the coercive field intensity measured at the polarization temperature T_pol, Eb(T_pol) is the breakdown field intensity statistically estimated at the polarization temperature T_pol, and S is the safety factor.

[0020] In addition to the above technical solutions, the present application can also adopt or combine the following technical solutions:

[0021] As a preferred technical solution of the present application: the electrode is selected from gold, platinum, silver, copper or aluminum, and is prepared by metal stripping or electroplating process, and is uniformly attached to the PZT or PLZT thin film with a thickness greater than 200 nm to avoid breakdown.

[0022] As a preferred technical solution of the present application: in step S2, the polarization time of the applied external electric field is one hour, and the polarization process is completed.

[0023] As a preferred technical solution of the present application: the intensity, frequency and duration of the external electric field, as well as the change of the external environment, can be adjusted according to specific needs. The electric field is provided by an external source to overcome the internal coercive field to complete polarization according to the above conditions. After polarization, the electro-optic coefficient of the PZT / PLZT thin film is tested, and when the improvement of the electro-optic coefficient cannot meet the expectation, the polarization is carried out by increasing the electric field intensity, frequency or time to achieve a higher electro-optic coefficient.

[0024] As a preferred technical solution of the present application: a dielectric material is added to the electrode and the surface of the thin film crystal as a protective layer.

[0025] As a preferred technical solution of the present application: the external electric field is provided by a source table, and the applied electric field is a direct current electric field or an alternating current electric field.

[0026] As a preferred technical solution of the present application: in the polarization of the PZT or PLZT thin film, ultraviolet light is applied to enhance the polarization effect.

[0027] Compared with the prior art, the method for improving the electro-optic coefficient of the PZT or PLZT thin film has the following beneficial effects: under the action of an external electric field, the electric domains of the prepared PZT or PLZT thin film tend to be consistent with the direction of the external electric field, all the electric domain directions are unified, the spontaneous polarization directions of all the electric domains are the same, the symmetry of the crystal material in the thin film is improved, the disorder of the internal charge distribution is reduced, the regularly arranged polarization regions formed in the internal can more effectively change the refractive index distribution of the crystal, the electro-optic response ability and the nonlinear optical characteristics of the material are significantly enhanced, the electro-optic activity is significantly enhanced, and the electro-optic coefficient of the PZT or PLZT thin film is improved. In the application, the electro-optic coefficient of the prepared PZT / PLZT thin film is improved by using the polarization method without damaging the original device structure, the performance of the PZT / PLZT thin film in the applications such as sensors, actuators and memories is improved, and the problem that the two types of materials are limited in the applications in the fields of electro-optic and acousto-optic is solved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 To test the half-wave voltage of the PZT-based electro-optic modulator. DETAILED DESCRIPTION

[0029] The application will be further described in detail with reference to the drawings and specific examples.

[0030] The method for improving the electro-optic coefficient of the PZT or PLZT thin film provides a simple and effective method, and the electric domains in the PZT / PLZT thin film are oriented in the same direction by polarization, so that the electro-optic coefficient is improved. The polarization structure includes a PZT / PLZT thin film crystal and electrodes on both sides of the polarization region.

[0031] The method for improving the electro-optic coefficient of the PZT or PLZT thin film includes the following steps:

[0032] S1, attaching an electrode to the PZT or PLZT thin film;

[0033] S2, turning the electric domains in the PZT or PLZT thin film by applying an external electric field to the PZT or PLZT thin film through the electrode to achieve effective polarization, wherein

[0034] 2·Ec(T_pol)<E_pol<S·Eb(T_pol),

[0035] Wherein, E_pol is the polarization electric field intensity to be determined, Ec(T_pol) is the coercive field strength measured at the polarization temperature T_pol, Eb(T_pol) is the statistical estimated breakdown field strength at the polarization temperature T_pol, and S is a safety factor. Usually 0.7 ~ 0.8.

[0036] When an electric field is applied to PZT or PLZT, the internal domains are turned to the direction of the electric field, and as the electric field increases, more and more domains are turned to the direction of the electric field, and the turning and expanding speed of the domains are accelerated. The domains with the same direction as the electric field or with a small angle with the electric field are gradually expanded and stabilized, while the domains with the opposite direction or with a large angle with the electric field are gradually reduced. With the extension of the electric field, most of the domains are turned to the direction of the electric field, so that the material as a whole shows polarization in the direction of the electric field. Within a certain temperature range, the increase of temperature makes the domain movement and turning relatively easy, and the coercive field strength and the saturation field strength decrease with the increase of temperature, and when the polarization temperature is high, a higher efficiency of polarization effect can be achieved.

[0037] The PZT / PLZT thin film can be prepared on a silicon-based, quartz, sapphire or metal substrate.

[0038] The PZT / PLZT polarization region needs to have a conductive material as an electrode to apply an electric field, and the electrode material can be gold, silver, copper, aluminum or other materials with superconductivity or good conductivity.

[0039] A dielectric material can be added as a protective layer on the polarization electrode and the surface of the thin film crystal.

[0040] The source of the applied voltage is connected to the electrode of the device through a probe, and the polarization voltage and time information are controlled by software.

[0041] The applied electric field can be a direct current or an alternating current. The electrode is a driving electrode of an electro-optic modulator, and no additional electrode needs to be prepared.

[0042] The polarization effect can be affected by changing the temperature during the application of the electric field.

[0043] In step S2, the polarization time of the applied external electric field is one hour, and the polarization process is judged to be completed. The distribution of the domains can be observed by a laser interference piezoelectric force microscope to judge the polarization result.

[0044] The half-wave voltage of the modulator can be measured to judge. If the domain direction is not turned or the direction is not uniform, the material does not have electro-optic properties macroscopically, and the modulator cannot work. If it is uniform, the material has electro-optic properties macroscopically, and the modulator can work, and electro-optic modulation can be achieved and a smaller half-wave voltage can be measured.

[0045] The polarization effect can be affected by applying ultraviolet light or the like during the application of the electric field.

[0046] The application of the electric field can be continuous or intermittent.

[0047] The applied electric field can be in the form of direct current, alternating current, or pulse, or a combination of various forms.

[0048] The external electric field is provided by a source table, and the probe is pressed on the metal electrode, and a pulse voltage is applied on the electrode by using the contact polarization method, the pulse period is 1 second, and the duty cycle is 0.5. Compared with direct current polarization, pulse polarization can make the reversal of the domain more uniform, avoid the polarization insufficient phenomenon caused by the polarization current, effectively improve the polarization effect, and shorten the polarization time and improve the polarization efficiency.

[0049] The polarization time is determined according to the device structure.

[0050] The electrode material can be various metal materials or superconducting materials with strong conductivity.

[0051] The upper protective layer can be inorganic or organic material.

[0052] Embodiment 1

[0053] A method for improving the electro-optic coefficient of a PZT or PLZT thin film, comprising the following steps:

[0054] Thin film preparation: first, prepare a PZT / PLZT thin film on a substrate, which can be prepared by common methods such as solution method, laser deposition method, and physical vapor deposition method.

[0055] Waveguide preparation: PZT / PLZT optical waveguide is obtained by photoetching and etching on the prepared PZT / PLZT thin film for transmitting optical signals.

[0056] Electrode preparation: prepare an electrode on the prepared thin film or device structure for subsequent thin film polarization.

[0057] External field polarization: after the thin film is prepared, an external electric field is applied on the PZT / PLZT thin film through the electrode to make it polarize.

[0058] Polarization treatment: while applying the external electric field, the temperature, time, and voltage size are controlled to make the PZT / PLZT thin film polarize under the action of the external electric field.

[0059] In order to test the electro-optic coefficient of the obtained PZT / PLZT thin film crystal material, a Mach-Zehnder (MZ) electro-optic modulator is prepared on the PZT / PLZT thin film crystal, and the electro-optic coefficient of the electro-optic film is calculated by testing the half-wave voltage (Vπ) of the MZ-type electro-optic modulator. The Vπ of the MZ-type electro-optic modulator can be represented as:

[0060] (1)

[0061] where λ is wavelength, G is the gap between the two electrodes of the electro-optic modulator, n is the effective refractive index of the optical waveguide, is the electro-optic overlap factor, is the electro-optic coefficient of the PZT / PLZT thin film crystal material, and L is the electrode length.

[0062] The electro-optic coefficient of the PZT / PLZT thin film crystal material can be calculated from formula 1 :

[0063] (2)

[0064] The parameters of the electro-optic modulator tested are as follows: wavelength λ is 1550 nm, the gap between the two electrodes is 6 μm, the effective refractive index of the optical waveguide is 1.91, the electro-optic overlap factor is 0.4, and the electrode length is 2 mm, and its Vπ is 7.046 V, and the test results are shown in Figure 1 The electro-optic coefficient of the PZT electro-optic thin film crystal calculated from the above data is 120 pm / V.

[0065] The above specific embodiments are used to explain and illustrate the present application, and are only preferred embodiments of the present application, but not limit the present application, and any modification, equivalent replacement, improvement, etc. made to the present application falls within the protection scope of the present application.

Claims

1. A method for improving the electro-optic coefficient of PZT or PLZT thin film, comprising the steps of: S1. Attaching electrodes to the PZT or PLZT thin film; S2. Turning the internal domains of the PZT or PLZT thin film by applying an external electric field through the electrodes, to achieve effective polarization, wherein the applied polarization electric field strength is: 2·Ec(T_pol) < E_pol < S·Eb(T_pol), wherein E_pol is the polarization electric field strength, Ec(T_pol) is the coercive field strength measured at the polarization temperature T_pol, Eb(T_pol) is the statistical estimated breakdown field strength at the polarization temperature T_pol, and S is the safety factor.

2. The method of increasing the electro-optic coefficient of a PZT or PLZT thin film according to claim 1, wherein: The electrodes are made of gold, silver, copper or aluminum, prepared by metal stripping or electroplating process, uniformly attached to the PZT or PLZT thin film, and the electrode thickness is greater than 200 nm to avoid breakdown.

3. The method of increasing electro-optic coefficient of PZT or PLZT thin film according to claim 1, wherein: In step S2, the polarization time of the applied external electric field is one hour, and the polarization process is judged to be completed.

4. The method of increasing the electro-optic coefficient of a PZT or PLZT thin film of claim 1, wherein: The electrode and the thin film crystal surface are increased with dielectric material as a protective layer.

5. The method of increasing the electro-optic coefficient of a PZT or PLZT thin film of claim 1, wherein: The external electric field is provided by the source table, the probe is pressed on the metal electrode, and the pulsed voltage is applied on the electrode by the contact polarization method, the pulse period is 1 second, and the duty cycle is 0.

5.

6. The method of increasing the electro-optic coefficient of a PZT or PLZT thin film of claim 1, wherein: In the polarization of PZT or PLZT thin film, ultraviolet light is applied to enhance the polarization effect.

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