JP2004289442A - Thin-film element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin-film element dealing with a high frequency and a large power, which is provided with a piezoelectric substrate, a first electrode layer formed on the piezoelectric substrate and a second electrode layer constituted of Al on the first electrode layer, and to provide a manufacturing method thereof. <P>SOLUTION: The piezoelectric substrate 1 is provided with an IDT electrode 4 having a first electrode layer 2 and a second electrode layer 3. The film thickness of the first electrode layer 2 forming the IDT electrode 4 is 50 nm-100 nm. Also, the second electrode film 3 is constituted of Al. According to this thin-film element and the manufacturing method thereof, the first electrode layer for controlling transmission of exciting energy of the piezoelectric substrate 1 with respect to the second electrode layer as a main electrode. With this configuration, deterioration at the time of using the element is reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a thin-film element, particularly a high-frequency, high-power thin-film element comprising a first electrode layer formed on a piezoelectric substrate and a second electrode layer formed of Al formed thereon, and a thin-film element therefor. It relates to a manufacturing method.
[0002]
[Prior art]
In recent years, with the development of mobile phones and mobile communications, thin film elements having a desired electrode pattern formed on a piezoelectric substrate have been actively used as surface acoustic wave filters and surface acoustic wave resonators. For the electrode film of this thin film element, Al is used from the beginning because of its low specific gravity and low electric resistance. In order to cope with higher frequencies in a thin film element, it is necessary to make the electrode film thinner and to make the electrode pattern finer. On the other hand, a repetitive stress corresponding to the frequency to be used is applied to the electrode film in the operating state of the thin film element using the piezoelectric substrate. As the operating power increases and the frequency increases, the stress applied to the electrodes formed on the thin film element increases. The Al electrode film has a problem that due to the stress applied to the Al electrode film, migration of Al atoms occurs, a defect occurs in the electrode film, and characteristics of the thin film element are largely deteriorated. For this reason, it is required to improve the power durability of the electrodes of the thin film element used.
[0003]
Conventionally, measures for controlling the crystallinity of the Al film and increasing the orientation have been known to improve the power durability and reliability of the electrode film. Since these are greatly affected by the state of the substrate to be used, they have a problem that they lack stability. In addition, there is a problem that it is not possible to sufficiently cope with a further increase in frequency or an increase in operating power.
[0004]
Therefore, a surface acoustic wave element including a piezoelectric substrate, an IDT electrode formed on the piezoelectric substrate, a Ti underlayer provided on the piezoelectric substrate with a thickness of 100 to 200 nm, and a Ti underlayer laminated on the Ti underlayer. There has been proposed a surface acoustic wave device including an Al alloy film as described above (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP 2002-368568 A
[Problems to be solved by the invention]
However, the above-described conventional surface acoustic wave device has the following problems.
[0007]
In Patent Literature 1, the thickness of a Ti film used as a base film is set to 100 to 200 nm. Further, an Al alloy film is formed as an upper base film laminated on the Ti base film. As described above, it is generally known that an electrode film as a surface acoustic wave element is required to have a small specific gravity and a small electric resistance value. This is because the specific gravity and the electric resistance of the electrode film significantly affect characteristics such as insertion loss of the surface acoustic wave element. The Al alloy film of the upper base film used as the main electrode has a larger electric resistance value than Al. This has a problem that the original characteristics of the piezoelectric substrate cannot be sufficiently brought out. Further, the Ti film used as the base film also affects the electric resistance value of the electrode film. The setting of the thickness of Ti used as a base film in Patent Literature 1 may degrade the peak-cross value and the band width, which are important characteristics as a surface acoustic wave element, due to the electrical resistance and the like. Since the electric resistance of Ti is 48 μΩcm, which is very large as compared with 2.7 μΩcm of Al, an increase in the Ti film thickness results in an increase in the resistance value as an electrode, which degrades the characteristics. This has a problem that it cannot be used as an elastic thin film element requiring high quality.
[0008]
[Means for Solving the Problems]
In order to solve the above problem, the thin film element of the present invention includes a piezoelectric substrate, a first electrode layer formed on the piezoelectric substrate, and a second electrode layer made of Al on the first electrode. A thin film element, wherein the thickness of the first electrode layer is not less than 50 nm and less than 100 nm. Also. The first electrode layer is made of a metal containing any one of Ti, Ni, and Cr as a main component. Further, the piezoelectric substrate is a LiNbO ₃ substrate or a LiTaO ₃ substrate. Further, the LiNbO ₃ substrate or the LiTaO ₃ substrate is characterized in that it is a θ rotation Y cut X propagation substrate.
[0009]
A thin-film element comprising: a step of preparing a piezoelectric substrate; a step of forming a first electrode layer on the piezoelectric substrate; and a step of forming a second electrode layer made of Al on the first electrode layer. Wherein the thickness of the first electrode layer is 50 nm or more and less than 100 nm.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, without deteriorating the inherent characteristics of a piezoelectric substrate, having excellent power durability, and achieving high accuracy and high performance corresponding to the high performance of electronic devices. Provide a reliable thin film element.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0012]
FIG. 1 is a schematic sectional view of one embodiment of the thin film element of the present invention.
[0013]
The thin-film element shown in FIG. 1 has a piezoelectric substrate 1, a first electrode layer 2 on the piezoelectric substrate 1, and a second electrode layer 3 on the first electrode layer 2.
[0014]
As the piezoelectric substrate 1, for example, a θ rotation Y-cut X-propagation LiNbO ₃ substrate or LiTaO ₃ substrate is used. Since the cut angle of the piezoelectric substrate 1 affects the state of a film formed thereon, an appropriate angle corresponding to the piezoelectric substrate 1 to be used is set. The first electrode layer is made of a metal containing any one of Ti, Ni, and Cr as a main component, and has a thickness of 50 nm or more and less than 100 nm. Further, the second electrode layer is composed of an Al electrode film. This Al electrode film is preferably made of pure Al.
[0015]
Hereinafter, a method for manufacturing a thin film element of the present invention will be described.
[0016]
First, an IDT electrode 4 is formed on a piezoelectric substrate 1, for example, a 38.5 ° rotation Y-cut X-propagation LiTaO ₃ substrate 1 using a photolithography technique. To form the IDT electrode 4, first, the piezoelectric substrate 1 is set in a vapor deposition apparatus having a crucible compatible with multi-source.
[0017]
Next, the inside of the evaporation apparatus is evacuated by a vacuum pump. At this time, it is preferable to evacuate the inside of the vapor deposition apparatus to a pressure of the order of 10 ⁻⁵ Pa using a high vacuum pump.
[0018]
Next, 80 nm of Ti is formed as a first electrode layer on the piezoelectric substrate 1 by an electron beam evaporation method. Next, in order to cool the crucible which has been heated by the electron beam irradiation, the crucible is left standing for about 15 minutes to be cooled. Subsequently, the crucible is rotated to form Al to a thickness of 150 nm as a second electrode layer. These formations are preferably formed continuously without breaking vacuum. At this time, it is preferable to revolve the piezoelectric substrate 1 at a speed of 5 rpm so as to obtain a uniform film thickness distribution. Further, a shutter is provided on the upper part of the crucible, and its opening and closing are controlled so as to have a predetermined film thickness. Further, none of the piezoelectric substrates 1 during the film formation is particularly heated.
[0019]
This film formation method is not limited to the electron beam evaporation method, and a sputtering method or the like may be used.
[0020]
Next, a predetermined thickness of a resist is applied to the formed electrode layer using a spin coater or the like, and the resist is exposed through a photolithographic mask having a predetermined pattern formed thereon. Subsequently, the IDT electrode 4 is formed by performing a developing process and an etching process. This pattern forming method is not limited to the photolithography technique, and a dry etching technique may be used.
[0021]
The formed IDT electrode 4 has a pattern shape for a required function, for example, a comb shape with a line and space of 0.5 μm. Further, lead electrodes, pad electrodes, and the like are formed as necessary. Thereafter, a thin film element is obtained through steps such as dicing and packaging.
[0022]
The grounds for limiting the thickness of the first electrode layer in the present invention will be described below.
[0023]
FIG. 2 shows the relationship between the film thickness of Ti used for the first electrode layer 2 and the lifetime of the thin film element and the peak-cross value when a surface acoustic wave element is formed. FIG. 2 shows an experimental result obtained by an acceleration test in which the applied power was 1.4 W and the use atmosphere temperature was 150 ° C. The result of conversion into a value is shown. The conversion used the acceleration coefficient obtained from another experiment. The acceleration coefficient used is a power 7 law and a temperature 12 ° C. 2 times law.
[0024]
From FIG. 2, it can be confirmed that when the Ti film thickness is 50 nm or more, the life of the thin film element is sharply improved. In the result of the peak-cross value, a slight increase can be confirmed with an increase in the Ti film thickness, but it can be determined that the level is not a problem in use.
[0025]
The improvement of the life of the thin film element of the present invention is achieved by reducing the excitation energy from the piezoelectric substrate to the Al film of the second electrode layer as the main electrode when the Ti film thickness as the first electrode layer exceeds 50 nm. It is considered that the transmission is a result of being suppressed by the first electrode layer, Ti.
[0026]
The point where the effect of the Ti film thickness clearly appears was set as the lower limit of the film thickness of the first electrode layer.
[0027]
Next, FIG. 3 shows the relationship between the film thickness of Ti used for the first electrode layer 2 and the peak-cross value and the bandwidth (BW) at 3 dB.
[0028]
FIG. 3 shows that when the Ti film thickness becomes 100 nm or more, the peak-cross value and 3 dB-B. W. Can be confirmed to deteriorate rapidly. This can be determined to be deterioration due to the influence on the electric resistance value due to the increase in the thickness of the Ti film. As described above, the influence on the electrical resistance value and the specific gravity, which are the physical property values of the electrodes in the thin film element, depends on the peak-cross value and 3 dB-B. W. You can check at. The upper limit of the first electrode layer was set based on this result as a value having no problem in use as a thin film element.
[0029]
In the above embodiment, the LiTaO ₃ substrate of 38.5 ° rotation Y-cut X propagation is used as the piezoelectric substrate 1. However, the present invention can be applied to any substrate having piezoelectricity by the above setting. Similar effects can be obtained. Further, although Ti is used as the material of the first electrode layer 2, a metal mainly containing any of Ti, Ni, and Cr may be used.
[0030]
In the thin film element of the present invention, transmission of excitation energy to the Al film of the second electrode layer 3 is suppressed by the Ti film of the first electrode layer 2, and as a result, the life of the thin film element is prolonged. It is thought that it was. In addition, by setting the Ti film thickness within a range that does not show the characteristic deterioration tendency, a thin film element excellent in other characteristics can be obtained.
[0031]
【The invention's effect】
According to the thin film element of the present invention as described above, transmission of excitation energy to the Al film of the main electrode film is suppressed, and it is possible to provide an electrode film having high reliability.
[0032]
Therefore, it is possible to provide a high-precision and high-reliability thin-film element which is excellent in power resistance and does not deteriorate the inherent characteristics of the piezoelectric substrate, and is compatible with high performance of electronic devices.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing one embodiment of a thin film element of the present invention.
FIG. 2 is a graph showing the relationship between the life of the thin film element and the peak-cross value depending on the Ti film thickness in one embodiment of the thin film element of the present invention.
FIG. 3 is a graph showing the peak-to-peak and 3 dB-B. 6 is a graph showing a relationship with W.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2 ... 1st electrode layer 3 ... 2nd electrode layer 4 ... IDT electrode

Claims (5)

Piezoelectric substrate, a first electrode layer formed on the piezoelectric substrate, a thin film element including a second electrode layer made of Al on the first electrode layer,
The film thickness of the first electrode layer is 50 nm or more and less than 100 nm. The thin film element according to claim 1, wherein the first electrode layer is made of a metal containing any one of Ti, Ni, and Cr as a main component. The thin film element according to claim 1, wherein the piezoelectric substrate is a LiNbO ₃ substrate or a LiTaO ₃ substrate. 4. The thin film device according to claim 3, wherein the LiNbO ₃ substrate or the LiTaO ₃ substrate is a θ-rotation Y-cut X propagation substrate. A step of preparing a piezoelectric substrate, a step of forming a first electrode layer having a thickness of 50 nm or more and less than 100 nm on the piezoelectric substrate, and a second electrode layer made of Al on the first electrode layer Forming a thin film element.

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