CN111575661B - Method for improving return loss and Q value of SMR device - Google Patents
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Abstract
The invention discloses a method for improving the return loss and Q value of an SMR device, which is a method for improving the acoustic impedance of a tungsten film of a high acoustic impedance layer in a Bragg layer by changing the magnetron sputtering power density so as to improve the acoustic impedance of the tungsten film and further improve the acoustic wave reflectivity of a Bragg layer reflector; in addition, the phase change of the tungsten film changes the stress level in the Bragg layer, and the (002) texture of the ZnO piezoelectric film grown on the Bragg layer is optimized through the stress transmission, so that an SMR device with excellent resonance characteristics is obtained, and the quality factor Q value of the SMR device is greatly improved. The method is expected to provide a new way for improving the performance of the SMR device. The preparation method is simple and convenient, easy to operate and low in cost.
Description
Technical Field
The invention relates to a preparation method of an SMR device, in particular to a method for improving the resonance performance of the SMR device, which is applied to the technical field of PVD vacuum coating and solid-attached resonator (SMR) device preparation.
Background
With the rapid development of the multi-functionalization of the wireless communication system, the radio frequency technology plays a great role in the fields of wireless communication and the like, and the requirements on miniaturization, low power consumption, low cost and high performance of radio frequency devices are higher and higher. The traditional radio frequency devices are mainly ceramic filters and Surface Acoustic Wave (SAW) filters, and the former cannot meet the miniaturization development of mobile terminals due to large volume; although the latter has small volume, the resonant frequency cannot be further improved due to the limitation of the photoetching process; therefore, both cannot meet the current communication requirements. Compared with a SAW device, the FBAR has the characteristics of small volume (mum level), high resonant frequency (GHz), high quality factor, low power consumption, stable performance and the like, has good adaptability to a wireless communication system, gradually replaces the traditional ceramic and SAW filters, and plays an increasingly important role in the field of wireless communication.
Based on thin film technology, FBAR devices are mainly classified into three categories: air gap type, back cavity type and solid-attached bulk acoustic wave resonators. The air gap type and the back cavity type are formed by etching air grooves or cavities through surface or integral micromachining, and the bottom electrode of the structure cannot be in direct contact with the substrate, so that the structure is extremely easy to damage under the action of external force. A solid-state resonator (SMR) was introduced in 1965 by neuell, in which a bragg layer reflector for reflecting sound waves, in addition to upper and lower electrodes and a piezoelectric film in a sandwich structure, was formed by alternately arranging high and low sound impedance materials having a thickness of one quarter wavelength (λ/4). Thin film tungsten is typically the material of the high acoustic impedance layers in bragg layer reflectors. The tungsten film has two distinct phases: metastable phase (beta-W) of A15 structure and stable phase (alpha-W) of body-centered cubic structure. There have been many studies on the preparation conditions, microstructures, resistivity and stress of two tungsten structures, but there have been few studies on the acoustic impedance of tungsten films of two different structures. alpha-W and beta-W have different crystal structures and oxygen contents and may have different acoustic impedances, and the two phases of tungsten films produced by magnetron sputtering should have different effects on SMR performance, a problem that has been overlooked in past studies, and this has caused unnecessary difficulties in the fabrication of SMR devices.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to overcome the defects in the prior art, provide a method for improving the return loss and the Q value of an SMR device, and solve the problems of low return loss and non-ideal Q value of the prior SMR in China. An alpha-W film is deposited by a magnetron sputtering coating technology with low power density and is applied to an SMR device process. The invention changes the phase structure of the tungsten film of the high acoustic impedance layer in the Bragg layer by changing the sputtering power density, thereby improving the resonance performance of the SMR device and being expected to provide a new way for improving the performance of the SMR device.
In order to achieve the purpose of the invention, the invention adopts the following inventive concept:
the invention changes the sputtering condition and the annealing condition to cause the tungsten film to generate phase change, and changes the acoustic impedance of the tungsten through the phase change; the (002) texture of the ZnO piezoelectric film deposited on the Bragg layer reflector is optimized by changing the phase structure of the high-acoustic-impedance layer tungsten film in the Bragg layer reflector; by changing the phase structure of the tungsten film in the Bragg layer reflector of the SMR device, the resonance characteristic of the SMR resonator is optimized, and the return loss and the quality factor Q value of the device are improved, so that the resonance performance of the SMR device is comprehensively improved.
According to the inventive concept, the invention adopts the following technical scheme:
a method of increasing the return loss and Q of an SMR device comprising the steps of:
a. cleaning a substrate:
sequentially putting a mirror polishing level single crystal Si (100) substrate into ethanol, acetone, ethanol and deionized water by adopting an ultrasonic cleaning 6-step method, wherein each ultrasonic cleaning step is not more than 10 minutes, then putting the silicon substrate into HF solution with the mass percentage concentration of not less than 5% for soaking for at least 1 minute, then putting the silicon substrate into deionized water for ultrasonic cleaning for at least 10 minutes, and finally, slowly blowing nitrogen from the center of the silicon substrate to the periphery until water beads on the surface of the substrate are completely blown out to obtain a clean and dry substrate;
b. preparing an alpha-W Bragg layer:
b, placing the substrate cleaned and dried in the step a into a vacuum chamber, and respectively using magnetron sputtering coating modes of DC and MF to coat tungsten and SiO 2 The thin films are alternately deposited on the surface of the cleaned silicon substrate; when the tungsten film layer is prepared, the sputtering power density of the tungsten film is controlled not to be higher than 1.5W/cm 2 (ii) a WhereinThe prepared tungsten thin film layer is a stable phase alpha-W with a body-centered cubic structure;
c. preparing a bottom electrode Ti by sputtering:
continuously depositing a Ti bottom electrode with the thickness not more than 120 nm;
d. preparing thin film ZnO by sputtering:
continuously sputtering a ZnO piezoelectric film on the Ti bottom electrode of the alpha-W Bragg layer, wherein the power density is not higher than 6.6W/cm 2 ；
e. Manufacturing an SMR device:
sputtering the top electrode Al film layer, and then performing subsequent MEMS processing to prepare the alpha-W SMR device.
In the step a, the substrate is cleaned for 40-60 minutes by an ultrasonic cleaning 6-step method, and then dried by a nitrogen gun.
In the step b, the substrate cleaned and dried in the step a is transferred into a vacuum chamber of a vacuum coating machine, a copper sheet is fixed on a sample rack, and the vacuum chamber is vacuumized until the vacuum in the chamber is not more than 5.0 multiplied by 10 -3 Pa; when preparing the tungsten film layer, argon is introduced into the cavity to ensure that the sputtering pressure is not higher than 0.52Pa, then a tungsten target power supply is started to ensure that the power density is not higher than 1.5W/cm 2 Controlling the revolution speed of the revolving frame to be not lower than 20r/min, and controlling the thickness of each tungsten film layer to be not lower than 570 nm; when SiO is carried out 2 When the film layer is prepared, argon and oxygen are simultaneously introduced into the cavity to enable the sputtering pressure to reach not less than 0.64Pa, the volume ratio of the argon to the nitrogen is 3:1, a silicon target power supply is started, the duty ratio is controlled to be 70%, and the power density is not less than 4.3W/cm 2 The revolution speed of the revolving frame is not lower than 20r/min, and each layer of SiO is prepared 2 The thickness of the film is not less than 660 nm; alternately depositing tungsten thin film layer and SiO 2 Film layer, up to at least the 6 th SiO layer 2 And finishing the preparation process of the alpha-W Bragg layer after the film deposition is finished.
As a preferred technical solution of the present invention, in the step b, when the tungsten thin film layer is prepared, the power density is controlled to be 1.0-1.5W/cm 2 The thickness of each tungsten film layer is prepared to be 570-580 nm.
As a preferred technical proposal of the invention, in the step b, SiO is carried out 2 When the thin film layer is prepared, each SiO layer is prepared 2 The film thickness is 660-690 nm.
As a preferred technical solution of the present invention, in the step d, the prepared ZnO piezoelectric thin film has a (002) texture.
As a preferred technical solution of the present invention, when the ZnO film is prepared in step d, the ZnO film is continuously prepared on the Ti bottom electrode on the α -W bragg layer reflector under the following preparation conditions: the bulk vacuum degree is not less than 5 x 10 -4 Pa, introducing argon to make the sputtering pressure not less than 0.96Pa, and adopting radio frequency power supply to make the power density not less than 6.6W/cm 2 And the thickness of the prepared ZnO film is not higher than 1.1 mu m.
In the step b, the sputtering condition and the annealing condition are changed to cause a phase change in the tungsten thin film, and the acoustic impedance of the tungsten thin film is changed by the phase change.
As a preferred technical solution of the present invention, in the step b, the oxygen content of the tungsten film is changed by adjusting the sputtering process, so that the tungsten film is subjected to phase change, thereby changing the acoustic impedance of the tungsten film.
As the preferred technical scheme of the invention, the internal stress level of the Bragg layer reflector is changed by regulating and controlling the phase change of the tungsten film in the Bragg layer and the amorphous SiO 2 And a Ti film for transferring stress to the ZnO piezoelectric film to regulate the (002) texture of ZnO.
Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. the method optimizes the resonance characteristic of the SMR resonator and improves the return loss and the quality factor Q value of the device by changing the phase structure of the tungsten film in the Bragg layer reflector of the SMR device, thereby comprehensively improving the resonance performance of the SMR device; the phase change rule of the tungsten film along with the change of the preparation conditions is explored, and the problem of poor device performance caused by improper preparation conditions in the SMR manufacturing process is solved;
2. the invention indirectly calculates the acoustic impedance of the tungsten films with two different phase structures by using a nano indentation method, and the acoustic impedance is not higher than 1.5W/cm 2 The power density sputtering of (a) increases the acoustic impedance value of the prepared alpha-W by at least 10% over that of beta-W; the method enables the ZnO piezoelectric film on the Bragg layer containing alpha-W to have better (002) texture; the method has the advantages that the return loss of the SMR device containing alpha-W is doubled compared with that of a beta-W SMR device, and the Q value is greatly improved;
3. the method is simple, low in cost, easy to realize and wide in application; the invention provides a novel method for optimizing the resonance characteristic of an SMR device through the phase change of a thin film in a Bragg layer, and the invention is expected to provide a novel way for improving the performance of the SMR device.
Drawings
FIG. 1 shows a magnetron sputtering system for preparing a Bragg layer, which is used in a method according to an embodiment of the invention.
Fig. 2 is a cross-sectional view of a bragg layer reflector and SMR device made in a method of an embodiment of the invention.
Fig. 3 is XRD patterns of two-phase tungsten films prepared by the method of the example of the present invention and the comparative example.
FIG. 4 is a graph comparing the nano-indentation (Young's modulus) of two tungsten films of different phases prepared by the method of the example of the present invention and the comparative example.
Fig. 5 is an XRD comparison pattern of ZnO grown on bragg layers of two different phases of tungsten prepared based on the method of example of the present invention and comparative example.
FIG. 6 is a graph of the Smith circles and the return loss for a β -W SMR prepared as a comparative example and a α -W SMR prepared as in one embodiment of the invention.
Detailed Description
In order to make the technical solutions better understood by those skilled in the art, the technical solutions in the embodiments of the present invention will be examined and completely described below with reference to the drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without any inventive step, shall fall within the scope of the present invention.
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:
the first embodiment is as follows:
in this embodiment, a method for increasing the return loss and Q value of an SMR device includes using a magnetron sputtering system for preparing a bragg layer as shown in fig. 1, and arranging a first tungsten target, a second tungsten target, a third silicon target, and a fourth silicon target around a sample holder in a vacuum chamber of a vacuum coater, where each target corresponds to an independent power supply. The steps of the method for improving the return loss and the Q value of the SMR device of the embodiment are as follows:
a. cleaning a substrate:
sequentially putting a 2-inch mirror polishing-level single crystal Si (100) substrate which is cleaned in advance into ethanol, acetone, ethanol and deionized water by adopting an ultrasonic cleaning 6-step method, performing ultrasonic cleaning for 10 minutes respectively, then putting the silicon substrate into an HF solution with the mass percentage concentration of 5% for soaking for 1 minute, putting the silicon substrate into the deionized water for ultrasonic cleaning for 10 minutes, and finally, blowing nitrogen from the center of the silicon substrate to the periphery slowly until water beads on the surface of the substrate are completely blown out to obtain a clean and dry substrate;
b. preparing an alpha-W Bragg layer:
transferring the silicon chip substrate cleaned and dried in the step a into a vacuum chamber of a vacuum coating machine, fixing the silicon chip substrate on a sample frame by using a copper sheet, and vacuumizing until the vacuum in the chamber is not more than 5.0 multiplied by 10 -3 Pa; alternately depositing a tungsten film layer and SiO on the surface of the cleaned silicon substrate by respectively using the magnetron sputtering coating modes of DC and MF 2 Thin film layer, SiO up to layer 6 2 Finishing the preparation process of the alpha-W Bragg layer after the film deposition is finished; the prepared tungsten thin film layer is a stable phase alpha-W with a body-centered cubic structure, as shown in figure 3;
when preparing the tungsten film layer, argon is introduced into the cavity to enable the sputtering pressure to reach 0.52Pa, then a tungsten target power supply is started, namely a direct-current first tungsten target power supply and a direct-current second tungsten target power supply are startedSource of power density not higher than 1.5W/cm 2 Controlling the revolution speed of the revolving frame to be 20r/min, and preparing the thickness of each tungsten film layer to be 570-580nm, as shown in FIG. 2; the tungsten film prepared by the method of the embodiment has the phase of alpha phase, the Young modulus of 204GPa and the acoustic impedance of 62kg/m 2 s, as shown in FIG. 4;
when SiO is carried out 2 When the film layer is prepared, argon and oxygen are simultaneously introduced into the cavity to enable the sputtering pressure to reach 0.64Pa, the volume ratio of the argon to the nitrogen is 3:1, a third silicon target power supply and a fourth silicon target power supply corresponding to the intermediate frequency power supply are started, the duty ratio is controlled to be 70%, and the power density is 4.3W/cm 2 The revolution speed of the revolving frame is 20r/min, and each layer of SiO is prepared 2 The film thickness is 660-690nm, as shown in FIG. 2;
c. preparing a bottom electrode Ti by sputtering:
continuously depositing a Ti bottom electrode with the thickness of 120 nm;
d. preparing thin film ZnO by sputtering:
continuously preparing a ZnO film on a Ti bottom electrode on the alpha-W Bragg layer reflector under the following preparation conditions: the bulk vacuum degree is 5 multiplied by 10 -4 Pa, introducing argon to make the sputtering pressure reach 0.96Pa, adopting a radio frequency power supply, and the power density is 6.6W/cm 2 The thickness of the prepared ZnO film is 1.05-1.1 μm, as shown in figure 2; the full width at half maximum of the (002) peak of the ZnO thin film deposited on the α -W bragg layer by the method of this example is 0.38 °, as shown in fig. 5, the ZnO piezoelectric thin film prepared by this example has a (002) texture;
e. manufacturing an SMR device:
sputtering a top electrode Al film layer, carrying out photoetching, developing and stripping, and then carrying out subsequent MEMS processing to prepare the alpha-W SMR device. The resonant frequency of the α -W SMR prepared by the method of this example was 2.78GHz, the return loss was 28.5dB, and the quality factor (Q) was 1390, as shown in FIG. 6. Fig. 6(a) and 6(b) are the smith chart and return loss plot of the β -W SMR prepared by the comparative example method, and fig. 6(c) and 6(d) are the smith chart and return loss plot of the α -W SMR prepared by the present example method.
Comparative example:
in this comparative example, a method for manufacturing an SMR device also employed a magnetron sputtering system for manufacturing a bragg layer as shown in fig. 1, and a first tungsten target, a second tungsten target, a third silicon target, and a fourth silicon target were disposed around a sample holder in a vacuum chamber of a vacuum coater, and corresponded to independent power supplies, respectively. The procedure for the preparation of the SMR device of this comparative example was as follows:
a. cleaning a substrate:
sequentially putting a 2-inch mirror polishing-level single crystal Si (100) substrate which is cleaned in advance into ethanol, acetone, ethanol and deionized water by adopting an ultrasonic cleaning 6-step method, performing ultrasonic cleaning for 10 minutes respectively, then putting the silicon substrate into an HF solution with the mass percentage concentration of 5% for soaking for 1 minute, putting the silicon substrate into the deionized water for ultrasonic cleaning for 10 minutes, and finally, blowing nitrogen from the center of the silicon substrate to the periphery slowly until water beads on the surface of the substrate are completely blown out to obtain a clean and dry substrate;
b. preparing a beta-W Bragg layer:
transferring the silicon chip substrate cleaned and dried in the step a into a vacuum chamber of a vacuum coating machine, fixing the silicon chip substrate on a sample frame by using a copper sheet, and vacuumizing until the vacuum in the chamber is not more than 5.0 multiplied by 10 -3 Pa; alternately depositing a tungsten film layer and SiO on the surface of the cleaned silicon substrate by respectively using the magnetron sputtering coating modes of DC and MF 2 Thin film layer, SiO up to layer 6 2 Finishing the preparation process of the beta-W Bragg layer after the film deposition is finished; the prepared tungsten thin film layer is metastable phase beta-W with A15 structure, as shown in FIG. 3;
when the tungsten film layer is prepared, argon is introduced into the cavity to enable the sputtering pressure to reach 0.52Pa, then a tungsten target power supply is started, namely a direct-current first tungsten target power supply and a direct-current second tungsten target power supply are started, so that the power density is higher than 5.0W/cm 2 Controlling the revolution speed of the revolving frame to be 20r/min, and preparing the thickness of each tungsten film layer to be 570 nm; the tungsten film prepared by the method of the comparative example has the phase of beta, the Young modulus of 170GPa and the acoustic impedance of 56kg/m 2 s, as shown in FIG. 4;
when SiO is carried out 2 When the film layer is prepared, argon and oxygen are simultaneously introduced into the cavity to sputter the air pressure to 0.64Pa, so that the volume ratio of the argon to the nitrogen is 3:1, turn on the intermediate frequencyThe third silicon target power supply and the fourth silicon target power supply corresponding to the power supplies control the duty ratio to be 70 percent and the power density to be 4.3W/cm 2 The revolution speed of the revolving frame is 20r/min, and each layer of SiO is prepared 2 The thickness of the film is 660 nm;
c. preparing a bottom electrode Ti by sputtering:
continuously depositing a Ti bottom electrode with the thickness of 120 nm;
d. preparing thin film ZnO by sputtering:
continuously preparing a ZnO film on a Ti bottom electrode on the beta-W Bragg layer reflector under the following preparation conditions: the bulk vacuum degree is 5 multiplied by 10 -4 Pa, introducing argon to make the sputtering pressure reach 0.96Pa, and adopting a radio frequency power supply with the power density of 6.6W/cm 2 The thickness of the prepared ZnO film is 1.1 mu m; the full width at half maximum of the ZnO film deposited on the beta-W bragg layer of this comparative example method was 0.58 deg., as shown in fig. 5;
e. manufacturing an SMR device:
sputtering a top electrode Al film layer, carrying out photoetching, developing and stripping, and then carrying out subsequent MEMS processing to prepare the beta-W SMR device. The β -W SMR prepared by the method of this comparative example produced a pronounced resonance at 2.40GHz with a return loss of 10.5dB and a quality factor (Q) of 338, as shown in FIG. 6.
In the first embodiment, a method for improving the return loss and the Q value of an SMR device adopts a low-power density deposition tungsten film to manufacture an alpha-W Bragg layer reflector; the preparation method of the comparative example SMR device adopts a tungsten film deposited with high power density to prepare the beta-W Bragg layer reflector. As can be seen from fig. 2 to 6, the method for improving the return loss and Q value of the SMR device in the embodiment utilizes the kinetic energy difference of sputtered ions or atoms caused by different sputtering power densities to cause the structural phase change of the tungsten thin film. Example methods to optimize SMR devices (002) texture of ZnO piezoelectric films deposited on bragg layer reflectors was optimized by changing the phase structure of the high acoustic impedance layer tungsten films in the bragg layer reflectors. Acoustic impedances of tungsten films with two different phase structures prepared in the first embodiment and the comparative example are indirectly calculated by a nano indentation method, and the acoustic impedance value of alpha-W is found to be improved by 10% compared with that of beta-W, return loss of an SMR device containing alpha-W in the first embodiment is improved by one time compared with that of a beta-W SMR device, and the Q value is greatly improved. The first embodiment and the comparative embodiment use the kinetic energy difference of sputtered ions or atoms caused by different sputtering power densities to cause the structural phase change of the tungsten film. Embodiments and methods optimize the resonance characteristics of an SMR resonator by changing the phase structure of a tungsten thin film in a bragg layer reflector of the SMR device, improving the return loss and quality factor Q value of the device. The embodiment has the advantages of simple method, low cost, easy realization and wide application.
Example two:
this embodiment is substantially the same as the first embodiment, and is characterized in that:
in this embodiment, the sputtering condition and the annealing condition are further changed to cause a phase change in the tungsten thin film, and the acoustic impedance of the tungsten thin film is changed by the phase change. In the embodiment, the phase change of the tungsten film of the high acoustic impedance layer in the Bragg layer is realized by changing the magnetron sputtering power density, so that the acoustic impedance of the tungsten film is improved, and the acoustic wave reflectivity of the Bragg layer reflector is further improved; this example optimizes the resonance characteristics of an SMR device by phase transformation of thin films in the bragg layer, which is expected to provide a new approach to improve SMR device performance.
Example three:
this embodiment is substantially the same as the previous embodiment, and is characterized in that:
in this embodiment, the oxygen content of the tungsten film is further changed by adjusting the sputtering process, so that the tungsten film undergoes a phase change, thereby changing the acoustic impedance of the tungsten film. In the embodiment, the phase structure of the tungsten film is regulated and controlled by adjusting the sputtering process, and the (002) texture of the ZnO piezoelectric film deposited on the Bragg layer reflector is optimized by changing the phase structure of the high-acoustic-impedance layer tungsten film in the Bragg layer reflector; and furthermore, the phase structure of a tungsten film in the Bragg layer reflector of the SMR device is changed, so that the resonance characteristic of the SMR resonator is optimized, and the return loss and the quality factor Q value of the device are improved.
Example four:
this embodiment is substantially the same as the previous embodiment, and is characterized in that:
in the bookIn the embodiment, the internal stress level of the Bragg layer reflector is changed by further regulating and controlling the phase change of the tungsten film in the Bragg layer and passing through amorphous SiO 2 And a Ti film for transferring stress to the ZnO piezoelectric film to regulate the (002) texture of ZnO. The phase change of the tungsten film changes the stress level in the Bragg layer, and the (002) texture of the ZnO piezoelectric film grown on the Bragg layer is optimized through the stress transmission, so that the SMR device with excellent resonance characteristics is obtained, and the quality factor Q value of the SMR device is greatly improved.
While the embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to the above embodiments, and various changes and modifications may be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be equivalent substitutions as long as the technical principle and inventive concept of the method for improving the return loss and Q value of an SMR device of the present invention are not departed from the technical principle and inventive concept of the method for improving the return loss and Q value of an SMR device.
Claims (10)
1. A method of increasing the return loss and Q of an SMR device, comprising the steps of:
a. cleaning a substrate:
sequentially putting a mirror polishing level single crystal Si (100) substrate into ethanol, acetone, ethanol and deionized water by adopting an ultrasonic cleaning 6-step method, wherein each ultrasonic cleaning step is not more than 10 minutes, then putting the silicon substrate into HF solution with the mass percentage concentration of not less than 5% for soaking for at least 1 minute, then putting the silicon substrate into deionized water for ultrasonic cleaning for at least 10 minutes, and finally, slowly blowing nitrogen from the center of the silicon substrate to the periphery until water beads on the surface of the substrate are completely blown out to obtain a clean and dry substrate;
b. preparing an alpha-W Bragg layer:
b, placing the substrate cleaned and dried in the step a into a vacuum chamber, and respectively using magnetron sputtering coating modes of DC and MF to coat tungsten and SiO 2 Alternately depositing the thin films on the surface of the cleaned silicon substrate; when the tungsten thin film layer is preparedControlling the sputtering power density of the tungsten film not to be higher than 1.5W/cm 2 (ii) a Wherein the prepared tungsten thin film layer is a stable phase alpha-W with a body-centered cubic structure;
c. preparing a bottom electrode Ti by sputtering:
continuously depositing a Ti bottom electrode with the thickness not more than 120 nm;
d. preparing thin film ZnO by sputtering:
continuously sputtering a ZnO piezoelectric film on the Ti bottom electrode of the alpha-W Bragg layer, wherein the power density is not higher than 6.6W/cm 2 ；
e. Manufacturing an SMR device:
sputtering a top electrode Al film layer, and then carrying out subsequent MEMS processing to prepare the alpha-W SMR device.
2. The method of improving the return loss and Q of an SMR device of claim 1, wherein: in the step a, the substrate is cleaned for 40-60 minutes by an ultrasonic cleaning 6-step method, and then dried by a nitrogen gun.
3. The method of improving the return loss and Q of an SMR device of claim 1, wherein: in the step b, the substrate cleaned and dried in the step a is transferred into a vacuum chamber of a vacuum coating machine, a copper sheet is fixed on a sample rack, and the vacuum chamber is vacuumized until the vacuum in the chamber is not more than 5.0 multiplied by 10 -3 Pa；
When preparing the tungsten film layer, argon is introduced into the cavity to ensure that the sputtering pressure is not higher than 0.52Pa, then a tungsten target power supply is started to ensure that the power density is not higher than 1.5W/cm 2 Controlling the revolution speed of the revolving frame to be not lower than 20r/min, and controlling the thickness of each tungsten film layer to be not lower than 570 nm;
when SiO is carried out 2 When the film layer is prepared, argon and oxygen are simultaneously introduced into the cavity to enable the sputtering pressure to reach not less than 0.64Pa, the volume ratio of the argon to the nitrogen is 3:1, a silicon target power supply is started, the duty ratio is controlled to be 70%, and the power density is not less than 4.3W/cm 2 The revolution speed of the revolving frame is not lower than 20r/min, and each layer of SiO is prepared 2 The thickness of the film is not less than 660 nm;
alternating deposition of tungsten filmsLayer and SiO 2 Film layer, up to at least the 6 th SiO layer 2 And finishing the preparation process of the alpha-W Bragg layer after the film deposition is finished.
4. The method of improving the return loss and Q of an SMR device of claim 3, wherein: in the step b, when the tungsten thin film layer is prepared, the power density is controlled to be 1.0-1.5W/cm 2 The thickness of each tungsten film layer is prepared to be 570-580 nm.
5. The method of improving the return loss and Q of an SMR device of claim 3, wherein: in the step b, SiO is carried out 2 When the thin film layer is prepared, each SiO layer is prepared 2 The film thickness is 660-690 nm.
6. The method of improving the return loss and Q of an SMR device of claim 1, wherein: in the step d, the prepared ZnO piezoelectric film has a (002) texture.
7. The method of improving the return loss and Q of an SMR device of claim 1, wherein: when the ZnO film is prepared in the step d, continuously preparing the ZnO film on the Ti bottom electrode on the alpha-W Bragg layer reflector under the following preparation conditions: the bulk vacuum degree is not less than 5 x 10 -4 Pa, introducing argon to make the sputtering pressure not less than 0.96Pa, and adopting radio frequency power supply to make the power density not less than 6.6W/cm 2 And the thickness of the prepared ZnO film is not higher than 1.1 mu m.
8. The method of improving the return loss and Q of an SMR device of claim 1, wherein: in the step b, the tungsten film is subjected to phase change by changing the sputtering condition and the annealing condition, and the acoustic impedance of the tungsten film is changed by the phase change.
9. The method of improving the return loss and Q of an SMR device of claim 1, wherein: in the step b, the oxygen content of the tungsten film is changed by adjusting the sputtering process, so that the tungsten film is subjected to phase change, and the acoustic impedance of the tungsten film is changed.
10. The method of improving the return loss and Q of an SMR device of claim 1, wherein: the internal stress level of the Bragg layer reflector is changed by regulating and controlling the phase change of the tungsten film in the Bragg layer, and the amorphous SiO 2 And a Ti film for transferring stress to the ZnO piezoelectric film to regulate the (002) texture of ZnO.
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