JP2006020134A - Surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve electric power resistance in a surface acoustic wave element in which an electrode 2 to be an interdigital transducer is formed on a piezoelectric substrate 1. <P>SOLUTION: In this surface acoustic wave element, the electrode 2 on the piezoelectric substrate 1 is configured by sequentially laminating a lower part Ti layer 3, an intermediate metal layer 4 made of Mo, W or alloy composed of these metal, an upper part Ti layer 5 and an upper part conductive layer 6 made of Al or an Al alloy. In such a case, the thickness A of the lower part Ti layer is ≥10 and ≤30 nm, the thickness B of the intermediate metal layer 4 is ≥35 and ≤65 nm, and the thickness C of the upper part Ti layer 5 is ≥10 and ≤30 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface acoustic wave element in which an electrode serving as an interdigital transducer is formed on a piezoelectric substrate.

  Conventionally, in communication devices such as mobile phones, surface acoustic wave elements are used as circuit elements such as resonator filters and duplexers. For example, in the surface acoustic wave element shown in FIG. 16, two interdigital transducers (52) each made of a pair of aluminum-made electrodes (52a) (52a) are provided on the surface of the piezoelectric substrate (51). At the same time, reflectors (53) and (53) made of grid-like electrodes are disposed on both sides of the interdigital transducers (52) and (52). A pair of input pads (54) and (54) and a pair of output pads (55) and (55) are connected to the interdigital transducers (52) and (52), respectively.

  In recent years, with the increase in frequency of communication devices, the operating frequency of surface acoustic wave elements has been increased, and higher output has been required. In order to increase the operating frequency, it is necessary to reduce the line width of each electrode (52a). For example, when the operating frequency is a gigahertz band, the line width of the electrode (52a) is less than 1 μm. When a voltage is applied to the surface acoustic wave element having such a small line width electrode, a stress is repeatedly applied to the electrode (52a) by the surface acoustic wave generated on the surface of the piezoelectric substrate (51). If the stress exceeds the critical stress inherent to the material of the electrode (52a), stress migration occurs. In addition, electromigration occurs as the electron flow through the electrode (52a) increases in density. As a result, voids (voids) and protrusions (hillocks) are formed in the electrode (52a), and the electrode (52a) is destroyed due to deterioration of power durability, leading to an electrical short circuit and an increase in insertion loss. .

  Therefore, in contrast to a conventional general surface acoustic wave element in which an electrode (7) made of an Al—Cu alloy is formed on a piezoelectric substrate (1) as shown in FIG. 3, the piezoelectric substrate (1) as shown in FIG. The electrode (8) includes a lower Ti layer (9), an intermediate metal layer (10) made of an Al—Cu alloy, an upper Ti layer (11), and an upper conductive layer (12) made of an Al—Cu alloy. An elastic surface element formed by stacking has been proposed (see Patent Document 1).

Further, as shown in FIG. 5, the electrode (13) on the piezoelectric substrate (1) is formed by laminating a base metal layer (14) made of a Ti—Mo alloy and an upper conductive layer (15) made of an Al—Cu alloy. As shown in FIG. 6, the electrode (16) on the piezoelectric substrate (1) is composed of a base metal layer (17) made of Mo and an upper conductive layer (18) made of an Al-Cu alloy. A surface acoustic wave element configured as described above has been proposed (see Patent Document 2).
Japanese Patent Application No. 2004-41175 JP 2001-94382 A JP-A-9-135143 JP 2002-368568 A JP 2002-353767 A JP 2002-135070 A

  In the surface acoustic wave device including the AlCu single layer electrode (7) shown in FIG. 3, for example, the thickness of the electrode (7) is 430 nm, and the interdigital transducers (52) (52) and the reflectors (53) (53) ) Is optimally designed, the filter characteristic indicated by the solid line (a) in FIG. 8 is obtained.

  The surface acoustic wave device including the electrode (8) having the laminated structure shown in FIG. 4 includes an intermediate metal layer (10) of AlCu interposed between the lower Ti layer (9) and the upper Ti layer (11). In addition to increasing the thickness of the base consisting of three layers, for example, as shown in the figure, the lower Ti layer (9) is 80 nm, the intermediate metal layer (10) is 20 nm, and the upper Ti layer (11) is 20 nm. However, as shown by the broken line (b) in FIG. 8, in the band of 835 MHz or less in the band of the single-layer electrode structure (solid line (a)), the filter characteristics are improved. However, although the insertion loss decreases, the insertion loss increases in the frequency band of 835 MHz or higher, and it cannot be said that sufficient filter characteristics are still realized.

  Further, in the surface acoustic wave device in which the electrode (13) includes a TiMo base metal layer (14) as shown in FIG. 5, the power durability is maximized when the thickness of the base metal layer (14) is 80 nm. However, as shown by the broken line (d) in FIG. 9, the insertion loss is larger than that in the case of the single-layer electrode structure (solid line (a)). As a result, the heat generation amount increases and the power durability decreases. There is a problem that invites.

  As shown in FIG. 6, in the surface acoustic wave device in which the electrode (16) includes the Mo base metal layer (17), the power durability is maximized when the thickness of the base metal layer (17) is 95 nm. However, as shown by the broken line (e) in FIG. 10, the insertion loss is remarkably increased as compared with the case of the single-layer electrode structure (solid line (a)). There is a problem that causes a drop. There is also a problem that the diffusion of Mo into the upper conductive layer (18) of the base metal layer (17) becomes significant.

As described above, any of the conventional surface acoustic wave devices has a large insertion loss in the pass band, and cannot achieve high power durability.
SUMMARY OF THE INVENTION An object of the present invention is to provide a surface acoustic wave device that can sufficiently reduce the insertion loss in the passband and obtain higher power durability than the conventional one.

  The surface acoustic wave device according to the present invention is obtained by forming an electrode to be an interdigital transducer on a piezoelectric substrate, and the electrode has a first layer made of Ti, Mo or W, or these on the surface of the piezoelectric substrate. A second layer made of an alloy of the above metal, a third layer made of Ti, and a fourth layer made of Al or an Al alloy are sequentially laminated, and the thickness A of the first layer is 10 nm or more and 30 nm or less. And the thickness B of the second layer is 35 nm or more and 65 nm or less, and the thickness C of the third layer is 10 nm or more and 30 nm or less.

In the present invention, the composition of the intermediate metal layer in the electrode structure shown in FIG. 4, that is, the laminated structure in which the intermediate metal layer is interposed in the Ti layer effective in suppressing the stress migration, instead of the conventional Al or Al alloy, Mo or W or an alloy of these metals is adopted.
The present inventors have experimentally found that such an electrode laminated structure can reduce insertion loss in the passband and obtain higher power durability, and have completed the present invention. .

  In the surface acoustic wave device according to the present invention, the thickness A of the first layer is set to 10 nm or more and 30 nm or less, the thickness B of the second layer is set to 35 nm or more and 65 nm or less, and the thickness C of the third layer is set. By setting the thickness to 10 nm or more and 30 nm or less, it is possible to reduce the insertion loss, thereby suppressing the amount of heat generated and obtaining high power durability.

  Specifically, the second layer is made of Mo, and the thickness B of the second layer is 40 nm or more and 60 nm or less. According to the specific configuration, the insertion loss can be further reduced.

  According to the surface acoustic wave device according to the present invention, the in-band insertion loss can be reduced as compared with the prior art, and high power durability can be obtained.

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.
As shown in FIG. 1, the surface acoustic wave device according to the present invention is configured by forming an electrode (2) to be an interdigital transducer on a piezoelectric substrate (1). The lower Ti layer (3), the intermediate metal layer (4) made of Mo or W or an alloy of these metals, the upper Ti layer (5), and the upper conductive layer (6) made of an Al alloy are laminated in this order from the side. It is a thing.

  The intermediate metal layer (4) constituting the electrode (2) is formed of Mo, and the thicknesses of the lower Ti layer (3), the intermediate metal layer (4), and the upper Ti layer (5) are variously changed. The surface acoustic wave elements of the surface acoustic wave elements were manufactured as prototypes, the lifetimes of these surface acoustic wave elements were estimated due to the reduced power durability, and the insertion loss in the filter passband was measured. Based on the results, the lower Ti layer (3 ), The thickness of the intermediate metal layer (4) and the upper Ti layer (5) were optimized.

  In the production of the surface acoustic wave element, the upper conductive layer (6) made of an Al—Cu (0.5 wt%) alloy and both Ti layers (3) and (5) are used as the film forming conditions by the DC sputtering apparatus. Set a power of 1 kW and an Ar gas atmosphere of 0.32 Pa. For the intermediate metal layer (4) made of Mo, a power of 1 kW and an Ar gas atmosphere of 0.7 Pa were set. Further, as the piezoelectric substrate (1), a 36 ° Y-cut lithium tantalate substrate (thickness 350 nm) was adopted, and the electrode was processed using RIE. Then, an 800 MHz band ladder type filter was constructed, and the insertion loss in the filter pass band was measured.

  11 to 15 show the thickness of the intermediate metal layer (4) on the horizontal axis for five types of surface acoustic wave devices in which the thickness C of the upper Ti layer (5) is 5 nm, 10 nm, 20 nm, 30 nm, and 40 nm, respectively. B is taken, and the average insertion loss in the passband when the thickness A of the lower Ti layer (3) is changed to 5 nm, 10 nm, 20 nm, 30 nm, and 40 nm, taking the average insertion loss in the passband on the vertical axis. It represents a change. The average insertion loss in the pass band means the average value of the insertion loss in the pass band of 824 MHz to 849 MHz.

As shown in FIG. 11, when the thickness C of the upper Ti layer (5) is 5 nm, it is within the passband regardless of the thickness A of the lower Ti layer (3) and the thickness B of the intermediate metal layer (4). The average insertion loss showed a high value around 1.55 dB.
On the other hand, when the thickness C of the upper Ti layer (5) is 10 nm as shown in FIG. 12, when the thickness A of the lower Ti layer (3) is 5 nm and 40 nm, the thickness of the intermediate metal layer (4). Regardless of B, the average insertion loss in the passband showed a high value of around 1.55 dB, but the thickness A of the lower Ti layer (3) was in the range of 10 nm to 30 nm, and the intermediate metal layer (4 ) In the range of 35 nm to 65 nm, the average insertion loss in the pass band rapidly decreases to 1.4 dB or less, and in the range of the thickness B of the intermediate metal layer (4) in the range of 40 nm to 60 nm, The average insertion loss is below 1.3 dB.

  Further, even when the thickness C of the upper Ti layer (5) is 20 nm as shown in FIG. 13, when the thickness A of the lower Ti layer (3) is 5 nm and 40 nm, the thickness B of the intermediate metal layer (4). Regardless, the average insertion loss in the passband showed a high value of around 1.55 dB, but the thickness A of the lower Ti layer (3) was in the range of 10 nm to 30 nm, and the intermediate metal layer (4) When the thickness B of the intermediate metal layer (4) is in the range of 40 nm to 60 nm, the average insertion loss in the pass band rapidly decreases to 1.4 dB or less. The insertion loss is below 1.3 dB.

  Further, even when the thickness C of the upper Ti layer (5) is 30 nm as shown in FIG. 14, when the thickness A of the lower Ti layer (3) is 5 nm and 40 nm, the thickness B of the intermediate metal layer (4). Regardless, the average insertion loss in the passband showed a high value of around 1.55 dB, but the thickness A of the lower Ti layer (3) was in the range of 10 nm to 30 nm, and the intermediate metal layer (4) When the thickness B of the intermediate metal layer (4) is in the range of 40 nm to 60 nm, the average insertion loss in the pass band rapidly decreases to 1.4 dB or less. The insertion loss is below 1.3 dB.

  However, as shown in FIG. 15, when the thickness C of the upper Ti layer (5) is 40 nm, regardless of the thickness A of the lower Ti layer (3) and the thickness B of the intermediate metal layer (4), the passband The inner average insertion loss showed a high value exceeding 1.55 dB.

  From the above results, the thickness A of the lower Ti layer (3) constituting the electrode (2) is preferably 10 nm or more and 30 nm or less, and the thickness B of the intermediate metal layer (4) is 35 nm or more and 65 nm or less. Preferably, it can be said that the thickness C of the upper Ti layer (5) is preferably 10 nm or more and 30 nm or less. Furthermore, it can be said that the thickness B of the intermediate metal layer (4) is more preferably 40 nm or more and 60 nm or less.

  In the surface acoustic wave device shown in FIG. 2, the electrode (2) on the piezoelectric substrate (1) has a lower Ti layer (3) having a thickness of 20 nm, an intermediate metal layer (4) of Mo having a thickness of 40 nm, and a thickness. The upper Ti layer (5) having a thickness of 15 nm and the upper conductive layer (6) made of an Al—Cu alloy having a thickness of 295 nm, each of the layers (3), (4) and (5) having the above-mentioned preferable thicknesses. is doing.

  When the filter characteristics of the surface acoustic wave device were measured, the result shown by the broken line (c) in FIG. 7 was obtained. As shown in the figure, the insertion loss is reduced in the wide band of 815 MHz to 855 MHz than in the case of the single-layer electrode structure (solid line (a)), and it can be seen that sufficient filter characteristics are realized.

Table 1 below shows five types of surface acoustic wave devices (FIGS. 3, 4, 2, and 5) having the filter characteristics (a), (b), (c), (d), and (e) shown in FIGS. 6), the minimum value (Top IL; top loss) of the insertion loss in the passband, the average insertion loss in the passband, and the estimated lifetime are shown.
The minimum value (Top IL) of the insertion loss in the pass band means the minimum value of the insertion loss in the pass band of 824 MHz to 849 MHz, and the estimated lifetime is a reduction amount of the insertion loss at 849 MHz of 0.5 dB. It means a value converted to a lifetime at 1.2 W and 50 degrees Celsius by extrapolation calculation of the Arrhenius plot obtained by the acceleration test, with the time exceeding the lifetime.

表１から明らかな様に、図２に示す本発明の弾性表面波素子(特性(ｃ))において最も通過帯域内挿入損失の最小値(Ｔｏｐ ＩＬ)及び通過帯域内平均挿入損失が低くなっており、然も最も長い推定寿命が得られている。

As apparent from Table 1, in the surface acoustic wave device of the present invention shown in FIG. 2 (characteristic (c)), the minimum value (Top IL) of the insertion loss in the passband and the average insertion loss in the passband are the lowest. However, the longest estimated life is obtained.

In the surface acoustic wave element shown in FIG. 2, Mo is adopted as the material of the intermediate metal layer (4), but W can also be adopted as the material of the intermediate metal layer (4).
As shown in Table 2 below, W, like Mo, has a specific gravity greater than that of Al or Ti, has a low resistivity, and has a high Young's modulus, and therefore can exhibit the same function as Mo.

そこで、電極(２)を構成する中間金属層(４)の材質としてＷを採用した弾性表面波素子を試作して、通過帯域内挿入損失の最小値(Ｔｏｐ ＩＬ)、通過帯域内平均挿入損失、及び推定寿命を測定した。その結果を下記表３に示す。
尚、弾性表面波素子の製造においては、ＤＣスパッタ装置による成膜条件として、Ｗからなる中間金属層(４)については、１ｋＷのパワー、１.２ＰａのＡｒガス雰囲気を設定したことを除き、他は同じ条件を設定した。

Therefore, a surface acoustic wave device employing W as the material of the intermediate metal layer (4) constituting the electrode (2) was prototyped, and the minimum value of the insertion loss in the passband (Top IL), the average insertion loss in the passband. , And estimated lifetime. The results are shown in Table 3 below.
In the production of the surface acoustic wave element, as the film forming conditions by the DC sputtering apparatus, for the intermediate metal layer (4) made of W, 1 kW power and 1.2 Pa Ar gas atmosphere were set. Others set the same conditions.

表３から明らかな様に、下部Ｔｉ層(３)、中間金属層(４)及び上部Ｔｉ層(５)の厚さＡ、Ｂ、Ｃが異なる２種類の弾性表面波素子において、通過帯域内挿入損失の最小値(Ｔｏｐ ＩＬ)、通過帯域内平均挿入損失、及び推定寿命の何れの点でも、中間金属層(４)がＭｏの場合と同等の高い性能が得られている。
従って、電極(２)を構成する中間金属層(４)をＷから形成した弾性表面波素子においても、下部Ｔｉ層(３)の厚さＡを１０ｎｍ以上、３０ｎｍ以下とし、中間金属層(４)の厚さＢを３５ｎｍ以上、６５ｎｍ以下とし、上部Ｔｉ層(５)の厚さＣを１０ｎｍ以上、３０ｎｍ以下とすることによって、従来よりも高い耐電力性を得ることが出来る。

As can be seen from Table 3, in the surface acoustic wave devices having different thicknesses A, B and C of the lower Ti layer (3), the intermediate metal layer (4) and the upper Ti layer (5) In terms of any of the minimum value of insertion loss (Top IL), the average insertion loss in the passband, and the estimated lifetime, high performance equivalent to that in the case where the intermediate metal layer (4) is Mo is obtained.
Therefore, even in the surface acoustic wave device in which the intermediate metal layer (4) constituting the electrode (2) is formed of W, the thickness A of the lower Ti layer (3) is set to 10 nm or more and 30 nm or less, and the intermediate metal layer (4 ) Thickness B is 35 nm or more and 65 nm or less, and the thickness C of the upper Ti layer (5) is 10 nm or more and 30 nm or less.

  In addition, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim. For example, the material of the upper conductive layer (6) constituting the electrode (2) is not limited to a binary Al alloy in which Cu is added to Al, but in addition to Cu, V, Mg or the like is added to Al. It is also possible to employ an original alloy.

It is sectional drawing which shows the electrode laminated structure of the surface acoustic wave element which concerns on this invention. It is sectional drawing which shows the specific example of this electrode laminated structure. It is sectional drawing which shows the electrode laminated structure of the conventional surface acoustic wave element. It is sectional drawing which shows the other conventional electrode laminated structure. It is sectional drawing which shows the other conventional electrode laminated structure. It is sectional drawing which shows other conventional electrode laminated structures. It is the graph which compared the filter characteristic in the surface acoustic wave element of the present invention with the conventional filter characteristic. It is a graph which shows the filter characteristic of the conventional surface acoustic wave element. It is a graph which shows the filter characteristic of the other conventional surface acoustic wave element. It is a graph which shows the filter characteristic of other conventional surface acoustic wave elements. It is a graph which shows the change of the insertion loss by the difference in the thickness of each layer which comprises an electrode. It is another graph same as the above. It is another graph same as the above. It is another graph same as the above. It is another graph same as the above. It is a top view which shows the electrode pattern of the conventional surface acoustic wave element.

Explanation of symbols

(1) Piezoelectric substrate
(2) Electrode
(3) Lower Ti layer
(4) Intermediate metal layer
(5) Upper Ti layer
(6) Upper conductive layer

Claims (2)

  In the surface acoustic wave element in which an electrode serving as an interdigital transducer is formed on a piezoelectric substrate, the electrode has a first layer made of Ti, Mo or W, or an alloy of these metals formed on the surface of the piezoelectric substrate. Two layers, a third layer made of Ti, and a fourth layer made of Al or an Al alloy are sequentially laminated, and the thickness A of the first layer is 10 nm or more and 30 nm or less, and the thickness of the second layer A surface acoustic wave device, wherein the thickness B is 35 nm or more and 65 nm or less, and the thickness C of the third layer is 10 nm or more and 30 nm or less.   2. The surface acoustic wave device according to claim 1, wherein the second layer is made of Mo, and the thickness B of the second layer is not less than 40 nm and not more than 60 nm.

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