JP4467403B2 - Surface acoustic wave element and communication apparatus - Google Patents

Description

  The present invention relates to a surface acoustic wave element and a communication device. More specifically, the present invention relates to a surface acoustic wave element having a face-down mounting structure, and more particularly to a surface acoustic wave element having improved attenuation outside the passband and a communication apparatus using the surface acoustic wave element.

  In recent years, surface acoustic wave filters that can be miniaturized and non-adjusted have come to be used in various communication devices, and are used as band-pass filters, etc., as communication devices increase in frequency and functionality. There is an increasing demand for increasing the attenuation outside the passband of a surface acoustic wave filter. For example, as a filter for a 900 MHz band cellular phone, a high-performance high attenuation filter that improves the attenuation outside the passband near the passband and also improves the attenuation outside the passband in the high frequency band of several GHz is desired. It is rare.

  FIG. 12 shows a schematic cross-sectional view of a surface acoustic wave element mounting structure in a conventional surface acoustic wave (hereinafter abbreviated as SAW) apparatus. In the surface acoustic wave device shown in FIG. 12, 51 is a piezoelectric substrate, 52 is a ground pad, 53 is an interdigital transducer (IDT) electrode (excitation electrode) formed on the piezoelectric substrate 51 for SAW elements, 54 Is a conductive pattern formed on the package 57, and 55 is a bump for connection. In the configuration shown in the figure, the ground pad 52 and the IDT electrode 53 are formed of, for example, an Al—Cu film, and the conductive pattern 54 and the ground pad 52 are joined and electrically connected by a bump 55 made of, for example, Au. Further, the lid 56 is sealed on the package 57 via a bonding layer 58 by seam welding or the like to maintain the airtightness inside the surface acoustic wave element.

The main causes of the deterioration of the out-of-band attenuation level in such a conventional surface-down surface acoustic wave device are, for example, electrodes such as the ground pad 52 of the surface acoustic wave element, the IDT electrode 53, and the conductive pattern 54 of the package 57. This is an electromagnetic coupling between the input and output due to an increase in electrical resistance or parasitic inductance or stray capacitance (parasitic capacitance). In particular, a filter region having an input pad portion such as a ground pad 52 and an output pad portion together with an IDT electrode 53 is formed on one main surface of the piezoelectric substrate 51, and a conductor layer (not shown) is formed on the other main surface. In the case of a surface acoustic wave device having a structure in which a surface acoustic wave element is mounted face-down, a conductor layer is formed on the other main surface of the piezoelectric substrate 51 in a region facing the input pad portion and output pad portion of the filter region. Therefore, there is a problem that capacitive coupling occurs between the input pad portion and the output pad portion, and the input and output are electromagnetically coupled, thereby deteriorating the attenuation outside the passband.
JP-A-4-313906

  A surface acoustic wave element is an element in which comb-like excitation electrodes (IDT electrodes) are formed on a piezoelectric substrate. Usually, since a piezoelectric body exhibits pyroelectricity due to a rapid temperature change, when a device having an excitation electrode on a piezoelectric substrate is manufactured, a process with a rapid temperature change is performed due to the pyroelectricity of the piezoelectric substrate. Sparks are generated between the electrodes, and the element is destroyed. Therefore, in order to prevent charges from being accumulated in the piezoelectric substrate as much as possible, it is a common practice to form a conductor layer over the entire back surface of the piezoelectric substrate. However, this backside conductor layer is effective in preventing pyroelectric breakdown during the device fabrication process, but for the reasons described above, it acts disadvantageously to improve the attenuation outside the passband due to the configuration of the device itself. (For example, refer to Patent Document 1).

  Also, using a surface acoustic wave element with an excitation electrode, an input pad portion and an output pad portion formed on the surface (one main surface) of the piezoelectric substrate, and a conductor layer formed on the back surface (the other main surface), face-up mounting In the case of a structure where the back side of the element is placed on the top surface of the package and grounded, capacitive coupling between the input pad portion on the front side and the output pad portion due to parasitic capacitance via the conductor layer on the back surface is Although there is no problem, in the case of face-down mounting, the back side conductor layer is not grounded, so capacitive coupling between the input pad part and the output pad part due to parasitic capacitance via this back side conductor layer becomes a problem, There is a problem that it is difficult to sufficiently secure the attenuation amount outside the passband of the filter by the surface acoustic wave element.

  Accordingly, an object of the present invention is to provide a surface acoustic wave device having a face-down mounting structure, which can improve the attenuation outside the passband of the filter, has good filter characteristics, and is excellent in reliability. It is to provide a communication apparatus using the same.

  In the surface acoustic wave device of the present invention, (1) a filter region including an excitation electrode, an input pad portion, and an output pad portion is formed on one main surface of a piezoelectric substrate, and a semiconductor layer is formed on the other main surface. It is characterized by this.

  In the surface acoustic wave device according to the present invention, (2) in the configuration of (1), the semiconductor layer has at least one of silicon, germanium, titanium oxide, zinc oxide, and aluminum nitride as a main component. It is characterized by being made of a material.

  In the surface acoustic wave device according to the present invention, (3) in the configuration of (1), the semiconductor layer has a lithium tantalate single crystal or a lithium niobate single crystal whose oxygen content is less than the stoichiometric composition. Or it consists of a lithium tetraborate single crystal.

  In the surface acoustic wave device according to the present invention, (4) in each of the above constitutions (1) to (3), the piezoelectric substrate has the one principal surface made of a piezoelectric material and the other principal surface is the piezoelectric material. It is characterized by being made of another material having a smaller relative dielectric constant.

  A communication apparatus according to the present invention includes at least one of a reception circuit and a transmission circuit having the surface acoustic wave element according to any one of the above configurations (1) to (4). .

  In the surface acoustic wave device of the present invention, the semiconductor layer formed on the other principal surface of the piezoelectric substrate is a conductor when viewed in terms of direct current, but the frequency near the pass band of the filter formed on the surface acoustic wave device is sufficient. It is a layer having a frequency characteristic of high resistance. Such frequency characteristics are mainly due to the frequency characteristics of carrier mobility in the semiconductor layer. The frequency characteristics of carrier mobility can be set to a desired value by adjusting the crystallinity, crystal grain size, impurity density, and the like of the semiconductor layer.

  According to the surface acoustic wave device of the present invention, the semiconductor layer is formed on the other main surface of the piezoelectric substrate of the surface acoustic wave device, so that the semiconductor has a frequency near the passband of the filter formed on the surface acoustic wave device. Since the mobility in the carrier in the layer can be made unresponsive, capacitive coupling is formed between the input pad portion and the output pad portion on one main surface of the piezoelectric substrate via the other main surface of the piezoelectric substrate. There is nothing to do. Therefore, it is possible to greatly improve the attenuation characteristic outside the passband, which has been deteriorated due to the parasitic capacitance. Furthermore, by forming a semiconductor layer that is a direct current conductor on the other main surface of the piezoelectric substrate, it is possible to efficiently release charges generated by a rapid temperature change in the manufacturing process. An effect of preventing damage to the electrode such as pyroelectric breakdown due to pyroelectricity can be obtained. Therefore, according to the surface acoustic wave device of the present invention, it is possible to obtain both the effect of preventing the pyroelectric breakdown well and the effect of preventing the deterioration of the attenuation characteristic outside the passband.

  Further, according to the surface acoustic wave device of the present invention, when the semiconductor layer is made of at least one of silicon, germanium, titanium oxide, zinc oxide, and aluminum nitride, or a material mainly composed of it, a sputtering method or a vapor deposition method. A semiconductor layer having an appropriate carrier mobility can be formed by appropriately adjusting film forming conditions such as a film forming pressure, a film forming speed, and a film forming temperature by a simple film forming method such as the above. Further, by adding an appropriate element or adjusting the composition ratio, it can be adjusted to have an appropriate conductivity in terms of direct current.

  According to the surface acoustic wave device of the present invention, the semiconductor layer is composed of a lithium tantalate single crystal, a lithium niobate single crystal, or a lithium tetraborate single crystal having an oxygen content less than the stoichiometric composition. Like the above-described silicon or the like, it has a property that it looks like a conductor in a direct current but almost looks like an insulator in a frequency band in which a surface acoustic wave device is used. Therefore, when a piezoelectric substrate made of a lithium tantalate single crystal, a lithium niobate single crystal, or a lithium tetraborate single crystal in which the oxygen content of at least the other main surface of the piezoelectric substrate is less than the stoichiometric composition is used in advance. It is possible to prevent electric charges from accumulating on the excitation electrode without affecting the band pass characteristics of the filter. Therefore, pyroelectric breakdown of the surface acoustic wave element can be more reliably prevented without forming a semiconductor layer such as silicon on the entire other main surface of the piezoelectric substrate. In addition, there is no need to increase the number of steps in the manufacturing process of the surface acoustic wave device in order to prevent pyroelectric breakdown.

  When the piezoelectric substrate is made of a piezoelectric material on one main surface side and the other main surface side is made of another material having a relative dielectric constant smaller than that of the piezoelectric material, it is provided between the input pad portion and the output pad portion of the filter. The effective dielectric constant of the filter can be reduced, and this can also reduce the parasitic capacitance (this corresponds to reducing the dielectric constant between the electrodes forming the parasitic capacitance). The external attenuation characteristic can be further improved. In particular, when this piezoelectric material is a lithium tantalate single crystal, a lithium niobate single crystal or a lithium tetraborate single crystal whose oxygen content is less than the stoichiometric composition, the effect of preventing pyroelectric breakdown well And the effect of reducing the effective dielectric constant can be obtained.

  According to the communication apparatus of the present invention, the above-described severe out-of-band attenuation, which has been conventionally required, is achieved by using the surface acoustic wave element of the present invention as described above for at least one of the reception circuit and the transmission circuit of the communication apparatus. In addition, the surface acoustic wave element having good out-of-band attenuation characteristics can be obtained while being small, so that the mounting area of other parts can be increased. Since the range of selection widens, a highly functional communication device can be realized.

  As described above, according to the present invention, even when the mounting (flip chip mounting) is performed with the excitation electrode forming surface of the piezoelectric substrate facing the main surface of the mounting substrate, the input pad portion and the output pad portion of the filter Is not capacitively coupled through the conductor layer on the other main surface, so that the attenuation outside the passband is not deteriorated even though the surface acoustic wave element is small. In addition, pyroelectric breakdown of the surface acoustic wave element can be prevented even if there is no conductor layer on the entire other main surface of the piezoelectric substrate in the manufacturing process. Also, due to recent demands for miniaturization and low profile of parts, surface acoustic wave elements are also required to have a thin piezoelectric substrate, but a conductor layer is formed on the other main surface of the piezoelectric substrate. In this case, the capacitance between the electrode on one main surface of the piezoelectric substrate and the conductor layer on the other main surface becomes large, and therefore, the attenuation of the out-of-pass band caused by the coupling of the parasitic capacitance between the input / output pad portions of the filter. Although the deterioration becomes more serious, a thin surface acoustic wave device having a good out-of-pass attenuation characteristic can be obtained by forming a semiconductor layer on the other main surface.

  Since the surface acoustic wave element of the present invention has a good out-of-pass band attenuation characteristic and is small in size, the receiving circuit having the surface acoustic wave element of the present invention and the surface acoustic wave element of the present invention According to the communication device of the present invention including at least one of the transmission circuits having high performance by realizing a large mounting area of other components while utilizing the good filter characteristics of the surface acoustic wave device of the present invention. A communication device that can be manufactured can be manufactured.

  Hereinafter, an example of an embodiment of a surface acoustic wave device of the present invention will be described in detail with reference to the drawings. In the drawings described below, the same portions are denoted by the same reference numerals. Further, the size of each electrode, the distance between the electrodes, the number of electrode fingers, the interval, and the like are schematically illustrated for explanation, and are not limited to these.

<Example 1 of embodiment>
FIG. 8 shows a top view of one main surface of the surface acoustic wave element in Example 1 of the surface acoustic wave element according to the present invention. A sectional view of the surface acoustic wave element in Example 1 is shown in FIG. FIG. 2 shows a cross-sectional view of a surface acoustic wave device in which the surface acoustic wave element of Example 1 is mounted.

  As shown in FIG. 8, a filter region 9 (shown surrounded by a broken line) is formed on the piezoelectric substrate 2 of the surface acoustic wave element 1. The filter region 9 is electrically connected to the plurality of excitation electrodes 3 constituting the resonator, the connection electrode 4 connecting them, and the excitation electrode 3 for connecting the surface acoustic wave element 1 and the mounting base 31. The input pad portion 5 and the output pad portion 6 are formed.

  The annular conductor 7 is connected to the base-side annular conductor 32 that also functions as a ground electrode formed on the upper surface of the mounting base 31 by using solder or the like. In this example, the annular conductor 7 is integrally formed so as to surround the filter region 9 and functions as a ground electrode of the filter in the filter region 9, and between the piezoelectric substrate 2 and the mounting substrate 31. 9 has a role of sealing.

  As shown in FIG. 1, a semiconductor layer 22 is formed on the entire other main surface of the piezoelectric substrate 2.

  Here, as the piezoelectric substrate 2, a lithium tantalate single crystal, a lithium niobate single crystal, a lithium tetraborate single crystal, or the like can be used.

  The excitation electrode 3 on one main surface of the piezoelectric substrate 2 is made of aluminum, an aluminum alloy, copper, a copper alloy, gold, a gold alloy, tantalum, a tantalum alloy, or a laminated film of layers made of these materials. A laminated film of a material and a layer made of a material such as titanium or chromium can be used. As a method for forming these laminated films, a sputtering method or an electron beam evaporation method can be used.

  As a method of patterning the excitation electrode 3, there is a method of performing photolithography after the formation of the excitation electrode 3, and then performing RIE (Reactive Ion Etching) or wet etching. Alternatively, before the excitation electrode 3 is formed, a resist is formed on one main surface of the piezoelectric substrate 2 and photolithography is performed to open a desired pattern, then a laminated film is formed, and then a resist is formed on an unnecessary portion. A lift-off process for removing the laminated film as a whole may be performed.

  Next, the semiconductor layer 22 is formed on the entire other main surface of the piezoelectric substrate 2. As the semiconductor layer 22, at least one material selected from silicon, germanium, titanium oxide, zinc oxide, and aluminum nitride, or a material containing at least one of them as a main component can be used. These materials may contain additives. As the film formation method, a sputtering method or an electron beam evaporation method can be used.

  Next, a protective film 30 for protecting the excitation electrode 3 is formed as shown in FIG. As a material of the protective film 30, silicon, silica, or the like can be used. As a film forming method, a sputtering method, a CVD (Chemical Vapor Deposition) method, an electron beam evaporation method, or the like can be used. In this protective film forming step, a temperature of about 50 to 300 ° C. may be necessary to obtain good film quality and adhesion. In such a case, the semiconductor layer 22 on the other main surface of the piezoelectric substrate 2 is used. Functions effectively to prevent pyroelectric breakdown.

  Next, a new conductor layer is laminated on the input pad portion 5 and the output pad portion 6 to form the input pad and the output pad. This new conductor layer is for electrically and / or structurally connecting the surface acoustic wave element 1 and the mounting substrate 31 with high reliability. For example, if solder is used for connection, In the case of using gold bumps for connection, the pad hardness is adjusted so that gold can be bonded using ultrasonic waves or the like. As the material and structure of such a new conductor layer, a laminated film of chromium / nickel / gold or chromium / aluminum or chromium / silver / gold, or a thick film of gold or aluminum can be used. As a film forming method, a sputtering method or an electron beam evaporation method can be used. In this new conductor layer forming step, a temperature of about 50 to 300 ° C. may be necessary to obtain good film quality and adhesion. In such a case, the other main surface of the piezoelectric substrate 2 is also required. The semiconductor layer 22 effectively functions to prevent pyroelectric breakdown.

  The pattern of the excitation electrode 3, the input pad portion 5, the output pad portion 6 and the like on one main surface of the piezoelectric substrate 2 manufactured through the steps so far is the same as that shown in FIG. However, the protective film 30 is not shown in FIG.

  Next, in the case where fabrication is performed by a so-called multi-cavity method in which a large number of surface acoustic wave element regions have been formed on a single piezoelectric substrate, the piezoelectric substrate is separated for each surface acoustic wave element region. A large number of surface acoustic wave elements 1 are obtained. As a separation method, for example, a dicing method using a dicing blade, a laser cutting method by laser processing, or the like can be used.

  Next, as shown in FIG. 2, the surface acoustic wave element 1 is mounted on the mounting base 31 with its one main surface facing.

  The mounting substrate 31 is a circuit board on which the surface acoustic wave element 1 is mounted on the upper surface. On the upper surface of the mounting substrate 31, input terminals and output terminals corresponding to the input pad portion 5 and the output pad portion 6 and grounding are provided. Terminals (both not shown) and a base-side annular conductor 32 corresponding to the annular conductor 7 are formed.

  According to the example of the surface acoustic wave device using the surface acoustic wave element 1 and the mounting base 31, the annular conductor 7 surrounds the filter region 9 on one main surface of the piezoelectric substrate 2 of the surface acoustic wave element 1. Each pad of the surface acoustic wave element 1 is connected to each terminal of the mounting substrate 31 via a conductor bump, and the annular conductor 7 is formed on the upper surface of the mounting substrate 31 correspondingly. The base-side annular conductor 32 is connected to the inner surface of the surface acoustic wave element 1 by using a brazing material 33 such as solder so that the inner side is sealed in an annular shape. Therefore, the surface acoustic wave element 1 can be stably operated without being affected by the exterior protective material or the like, and the operation can be stably performed over a long period of time. Can be a wave device It becomes.

  Further, the inside of the annular conductor 7 and the base-side annular conductor 32 is hermetically sealed in an annular shape, and further, for example, nitrogen gas, which is an inert gas, is sealed, so that each excitation electrode 3, each pad, each terminal Since deterioration due to oxidation or the like can be effectively prevented, higher reliability can be achieved.

  Then, as shown in FIG. 2, the surface acoustic wave element 1 mounted on the mounting base 31 is resin-molded using the exterior resin 34, and the mounting base 31 is packaged together with the exterior resin 34 for each surface acoustic wave element 1. A surface acoustic wave device using the surface acoustic wave element 1 of the present invention is obtained by dividing by dicing or the like. The exterior resin 34 may include a filler made of aluminum nitride, silver, nickel, or the like. By including such a filler, the thermal conductivity of the exterior resin 34 increases, thereby improving the heat dissipation of the surface acoustic wave element 1, and thus the power durability of the excitation electrode 3 is improved.

  As described above, the surface acoustic wave element 1 in the surface acoustic wave device according to the present invention has the filter region 9 including the excitation electrode 3, the input pad portion 5, and the output pad portion 6 on one main surface of the piezoelectric substrate 2, respectively. Since the semiconductor layer 22 is formed on the other main surface of the piezoelectric substrate 2 as compared with the case where the conductor layer is formed over the entire surface of the other main surface of the piezoelectric substrate as in the prior art, Since it is possible to prevent the carriers of the semiconductor layer 22 from responding in the vicinity of the pass band of the filter formed in the surface acoustic wave element 1, the gap between the input pad portion 5 of the filter region 9 and the output pad portion 6 of the filter region 9 The parasitic capacitance formed in the filter can be significantly reduced, the deterioration of the attenuation characteristic outside the passband due to the parasitic capacitance can be suppressed, and the attenuation characteristic outside the passband can be greatly improved. Can do.

  Further, in this example 1, since the semiconductor layer 22 is formed on the entire other main surface of the piezoelectric substrate 2, it is possible to efficiently release charges generated due to a rapid temperature change in the manufacturing process. An effect of preventing damage to the electrode such as pyroelectric breakdown due to the pyroelectric property of the substrate 2 can be obtained. Therefore, according to the first example, the effect of preventing pyroelectric breakdown satisfactorily and the amount of attenuation outside the pass band can be obtained by preventing the carrier from responding at a frequency near the pass band of the filter formed in the surface acoustic wave element 1. It is possible to provide a surface acoustic wave element 1 having both of the effects of preventing deterioration of characteristics and a surface acoustic wave device using the same.

<Example 2 of embodiment>
In Example 1, the case where the semiconductor layer 22 is formed on the entire other main surface of the piezoelectric substrate 2 is shown. However, when the carrier mobility of the semiconductor layer 22 cannot be lowered sufficiently, the semiconductor layer 22 is patterned. Thus, it is effective to provide a non-formation region of the semiconductor layer 22 in a part of the other main surface. As a pattern of the non-formation region effective for improving the attenuation characteristic outside the pass band and preventing pyroelectric breakdown, for example, one of the piezoelectric substrates 2 as shown in the top view of the other main surface in FIG. The semiconductor layer 22 is not formed with the other main surface regions 5a and 6a facing the input pad portion 5 and the output pad portion 6 on the main surface as non-forming regions, or as shown in the same top view in FIG. The non-formation region is provided so as to separate these regions 5a and 6a from the surrounding semiconductor layer 22, or the input of the filter region 9 on one main surface of the piezoelectric substrate 2 as shown in the same top view in FIG. The region 5b facing the whole of the portion connected from the pad portion 5 to the resonator excitation electrode 3 in a direct current and the output pad portion 6 of the filter region 9 to the resonator excitation electrode 3 are connected in a direct current. Excluding the region 6b facing the entire part As shown in a top view similar to that of a simple pattern or similar to FIG. 6, it faces the filter region 9 on one main surface of the piezoelectric substrate 2 in order to further suppress capacitive coupling via the parasitic capacitance. Except for the region 9a, a parasitic capacitance can be obtained by forming a semiconductor layer 22 on the other main surface of the piezoelectric substrate 2 or a plurality of non-formation regions of the semiconductor layer 22 as shown in the same top view in FIG. The area where there is a possibility of forming is small.

  As a method for patterning in order to provide a non-formation region in the semiconductor layer 22, there is a method in which photolithography is performed after the semiconductor layer 22 is formed, and then RIE, wet etching, sandblasting, or the like is performed. Alternatively, before the semiconductor layer 22 is formed, a resist is formed on one main surface of the piezoelectric substrate 2 and photolithography is performed to open a desired pattern. Then, the semiconductor layer 22 is formed, and then the resist is formed on unnecessary portions. A lift-off process for removing the entire semiconductor layer 22 may be performed. Alternatively, the non-formation region may be directly formed by removing the semiconductor layer 22 in a desired pattern using a router or the like without performing photolithography. At this time, if a method of etching and removing the semiconductor layer 22 mainly by a chemical action is used, the semiconductor layer 22 on the other main surface can be partially and reliably removed without damaging the piezoelectric substrate 2. it can. In addition, when a method of grinding and removing the semiconductor layer 22 mainly by a physical action is used, the semiconductor layer 22 can be removed and at the same time the other main surface of the piezoelectric substrate 2 can be made rougher than the original state. As a result, it propagates from the filter region 9 to the inside of the piezoelectric substrate 2, is reflected by the other main surface of the piezoelectric substrate 2, is coupled to the excitation electrode 3 formed in the filter region 9, and has an attenuation characteristic outside the passband. The deteriorated bulk wave can be scattered on this portion of the other main surface of the piezoelectric substrate 2, and the attenuation characteristic outside the passband can be improved.

  When the region 9a facing the filter region 9 on one main surface of the piezoelectric substrate 2 in the semiconductor layer 22 is excluded, the surface roughness of the region 9a where the semiconductor layer 22 on the other main surface of the piezoelectric substrate 2 is removed is set. Even when the surface roughness of the region where the semiconductor layer 22 is formed is larger than that of the region where the semiconductor layer 22 is formed, it is possible to increase the surface roughness in a wider area and more reliably suppress the propagation of the bulk wave, thereby reducing the out-of-passband attenuation. Of the deterioration of the quantity characteristic, the part deteriorated by the propagation of the bulk wave can be effectively reduced, which is advantageous for further greatly improving the out-of-passband attenuation quantity characteristic.

<Example 3 of embodiment>
FIG. 9 is a top view showing one main surface of the surface acoustic wave element in Example 3 of the embodiment of the surface acoustic wave element of the present invention. In this example, the configuration on the other main surface side of the piezoelectric substrate 2 is the same as the example shown in FIG. 8, and all the excitation electrodes 3 are in direct current conduction with the annular conductor 7 on the one main surface side of the piezoelectric substrate 2. The excitation electrode 3 forming the resonator and the annular conductor 7 were connected via a resistor 10. Further, the annular electrode 7 is connected to the substrate-side annular conductor 32 of the mounting substrate 31 to have a ground potential. In this way, the excitation electrode 3 is electrically connected to the annular conductor 7 via the resistor 10, and the annular conductor 7 is set to the ground potential, so that one main surface of the piezoelectric substrate 2 is provided. Since the electric charge can be released from the ground electrode to the ground electrode of the mounting substrate 31, pyroelectric breakdown of the surface acoustic wave element 1 can be effectively prevented.

  The resistor 10 is selected so that it has a sufficiently high resistance in the frequency band in which the filter is used and has a resistance value that looks almost like an insulator. As the material of the resistor 10, it is preferable to use a high-resistance semiconductor such as silicon or titanium oxide. These materials can control the resistance value to an appropriate value by adding a small amount of an element such as boron or adjusting the composition ratio.

<Example 4 of embodiment>
A cross-sectional view and a top view of the fourth example are the same as those of the first example, but the manufacturing method of the semiconductor layer 22 is different.

  In Example 1 of the embodiment, the semiconductor layer 22 is newly formed on the other main surface of the piezoelectric substrate 2 by film formation. However, the oxygen content is reduced from the stoichiometric composition by reducing the other main surface of the piezoelectric substrate 2. In such a state, the lithium tantalate single crystal, the lithium niobate single crystal, or the lithium tetraborate single crystal has conductivity in direct current, but is formed in the surface acoustic wave device 1. In the vicinity of the pass band of the filter, it has the property of almost appearing as an insulator. Therefore, a semiconductor layer having the same effect as the semiconductor layer 22 formed by film formation as described in Example 1 can be formed by reducing the other main surface of the piezoelectric substrate 2 in advance. In Example 4, since the piezoelectric substrate 2 itself has the semiconductor layer 22, it is not necessary to add the step of forming the semiconductor layer 22 to the step of forming the excitation electrode 3 such as an IDT electrode. Other steps are the same as in Example 1.

<Example 5 of embodiment>
In Example 2, the passband attenuation characteristic is improved by reducing the formation area of the semiconductor layer 22 that may form a parasitic capacitance. However, as the piezoelectric substrate 2, one main surface side is made of a piezoelectric material, and the other main layer side is formed. When a composite substrate made of another material whose surface has a relative dielectric constant smaller than that of the piezoelectric material is used, the effective relative dielectric constant between the semiconductor layer 22 and the pad portions 5 and 6 formed on one main surface of the piezoelectric substrate 2 is used. Since the rate can be reduced, the parasitic capacitance can be reduced and the attenuation characteristic outside the passband can be improved.

  Other materials with a relative dielectric constant smaller than that of the piezoelectric material of the piezoelectric substrate 2 are silicon (relative permittivity 3.4), sapphire (relative permittivity 9.4), quartz (relative permittivity 3.8), quartz (relative permittivity 3.8). , Ceramic substrates such as glass substrates (relative dielectric constant of about 3.8), alumina (relative dielectric constant of about 8.5), resin substrates such as polyimide and liquid crystal polymer (both have a dielectric constant of 10 or less) Can be used.

  Further, a composite in which the piezoelectric substrate 2 is joined to a first substrate made of a piezoelectric material and a second substrate made of another material having a smaller coefficient of thermal expansion than that of the piezoelectric material such as silicon, glass, sapphire, quartz, crystal, and resin. When the substrate is used, it is possible to improve the frequency-temperature characteristics of the surface acoustic wave element 1 caused by distortion of the piezoelectric substrate 2 due to temperature change. Furthermore, when the piezoelectric substrate 2 is a composite substrate in which a second substrate made of another material having a higher thermal conductivity than the first substrate made of a piezoelectric material, such as sapphire, quartz, quartz, or ceramic, is joined. Since heat generated in the filter region 9 can be efficiently released, it is possible to suppress the temperature rise of the piezoelectric substrate 2 itself, thereby improving the frequency temperature characteristics and accelerating according to the temperature. It is also possible to suppress the deterioration of the excitation electrode 3 to be performed.

  The surface acoustic wave element of the present invention can be applied to a communication device. That is, in a communication device including at least one of a receiving circuit and a transmitting circuit, the surface acoustic wave element of the present invention is used as a bandpass filter included in these circuits. For example, the transmission signal output from the transmission circuit is put on the carrier frequency by the mixer, the unnecessary signal is attenuated by the band pass filter, and then the transmission signal is amplified by the power amplifier and transmitted from the antenna through the duplexer. A communication device equipped with a transmission circuit that can perform reception, receives the received signal with an antenna, passes through a duplexer, amplifies the received signal with a low noise amplifier, attenuates unnecessary signals with a band-pass filter, and then uses a carrier frequency with a mixer The present invention can be applied to a communication apparatus having a receiving circuit that separates a signal from the signal and transmits the signal to a receiving circuit that extracts the signal. The surface acoustic wave device of the present invention is employed in at least one of the receiving circuit and the transmitting circuit. Thus, an excellent communication device of the present invention with improved transmission characteristics can be provided.

<First embodiment>
First, Ti / Al-1 mass% Cu / Ti / Al-1 is formed on one main surface of a piezoelectric substrate 2 (substrate thickness is 250 μm) made of a 38.7 ° Y-cut X-propagating lithium tantalate single crystal substrate from the substrate side by sputtering. Four conductor layers made of mass% Cu were formed. The layer thicknesses are 6 nm / 209 nm / 6 nm / 209 nm, respectively. Next, this conductor layer was patterned by photolithography and RIE to form a number of surface acoustic wave element regions each having a filter region 9 having an excitation electrode 3, an input pad portion 5, and an output pad portion 6, respectively. . A mixed gas of BCl ₃ and Cl ₂ was used as an etching gas at this time. The line width of the electrode fingers of the comb-like electrode forming the excitation electrode 3 and the distance between adjacent electrode fingers are both about 1 μm.

  Next, a semiconductor layer 22 made of silicon to which a small amount of boron was added was formed on the entire other main surface of the piezoelectric substrate 2 by sputtering. The thickness of the semiconductor layer 22 is 200 nm.

  Next, a new conductor layer made of Cr / Ni / Au was laminated on the input pad portion 5 and the output pad portion 6 to form an input pad and an output pad. The thicknesses of the new conductor layers are 6 nm / 1000 nm / 100 nm, respectively.

  Next, the piezoelectric substrate 2 was separated by dicing for each surface acoustic wave element region to obtain a large number of surface acoustic wave elements 1.

  Next, the surface acoustic wave element 1 was mounted on a mounting base 31 made of an LTCC (Low Temperature Co-fired Ceramics) substrate with one main surface facing each other. Here, the LTCC substrate has a base-side annular conductor 32 corresponding to the annular conductor 7 formed on one main surface of the piezoelectric substrate 2 and a pad electrode connected to the input / output pad of the surface acoustic wave element 1. Solder was printed on the base-side annular conductor 32 and the pad electrode. When the surface acoustic wave element 1 is mounted thereon, the surface acoustic wave element 1 is disposed so as to coincide with these solder patterns, temporarily fixed by applying ultrasonic waves, and then heated to melt the solder. Thus, the annular conductor 7 and the base-side annular conductor 32, and the input / output pad and the pad electrode were connected. As a result, the filter region 9 of the surface acoustic wave element 1 is completely hermetically sealed by the base-side annular conductor 32 of the LTCC substrate and the annular conductor 7 connected thereto. The mounting process of the surface acoustic wave element 1 was performed in a nitrogen atmosphere.

  Next, resin molding is performed, the other main surface (back surface) of the surface acoustic wave element 1 is protected by the exterior resin 34, and finally the mounting substrate 31 is diced between the surface acoustic wave elements 1 to thereby form the present invention. The surface acoustic wave device was obtained.

  As a comparative example, an elastic surface in which a filter region including an excitation electrode, an input pad portion, and an output pad portion is formed on one main surface of a piezoelectric substrate as in the prior art, and a conductor layer is formed on the entire other main surface. A surface acoustic wave device in which a wave element was mounted on a mounting substrate with one main surface facing each other was produced. The top view of this comparative example is the same as FIG.

  FIG. 10 is a diagram illustrating the frequency characteristics of the examples and comparative examples of the present invention thus manufactured. In the diagram of FIG. 10, the horizontal axis represents frequency (unit: MHz), the vertical axis represents attenuation (unit: dB), and the dotted characteristic curve shows a conductor layer formed on the entire other main surface of the LT substrate. The result of the comparative example is shown, and the solid characteristic curve shows the result of the example in which the semiconductor layer is formed on the entire other main surface of the LT substrate. As can be seen from the results shown in FIG. 10, the surface acoustic wave device according to the example of the present invention has a very good attenuation outside the passband as compared with the comparative example. In particular, the amount of attenuation outside the pass band in the vicinity of the pass band is greatly improved as compared with the comparative example.

  In addition, when the semiconductor layer 22 was patterned as shown in FIGS. 3 to 7 and the frequency characteristics were evaluated in the same manner as in the example, the attenuation outside the passband in the vicinity of the passband was greatly increased. It was confirmed that it was improved.

<Second embodiment>
In the present embodiment, the top view of the surface acoustic wave element 1 is the same as FIG. 8 except that the annular conductor 7 is not provided, but the sealing structure is different. In this embodiment, as shown in a cross-sectional view in FIG. 11, instead of using the annular conductor 7, a sealing structure comprising an annular insulator 41 and a cover member 42 for locally protecting the excitation electrode 3 is used. The excitation electrode 3 is protected, and the periphery thereof is protected by the exterior resin 34. A through hole is provided from the upper surface of the exterior resin 34 to reach the input pad portion 5, the output pad portion 6 and the ground electrode pad portion (not shown). A connection electrode was formed by filling the conductor pillars 43 therein. By adopting such a structure, the surface acoustic wave device 40 can be made smaller than when the annular conductor 7 is used.

  Here, the annular insulator 41 was formed using photosensitive polyimide and a normal photolithography process. Further, glass was used for the cover member 42, and the cover member 42 was bonded to the annular insulator 41 using a thermoplastic resin. The exterior resin 34 is photosensitive polyimide, and after forming a through hole by a photolithography process, a conductor column 43 is formed by plating to form a terminal electrode (connection electrode).

  Further, as a comparative example, a surface acoustic wave device using a surface acoustic wave element having a sealing structure similar to that of the present embodiment but not provided with the semiconductor layer 22 on the back surface was manufactured.

  As a result of comparing the yields of the examples and comparative examples of the present invention thus produced, about 2% of the whole of the comparative examples was defective due to the spark caused by the pyroelectric effect during the sealing process. However, in the examples of the present invention, no failure due to spark occurred, and no decrease in yield was observed before and after the sealing step.

  In addition, this invention is not limited to the example of the above embodiment, A various change may be added in the range which does not deviate from the summary of this invention. For example, two or more filter regions may be provided on the same piezoelectric substrate. In that case, the area occupied by the whole can be reduced compared with the case where a plurality of surface acoustic wave elements are separately manufactured.

  Moreover, although the example at the time of comprising a ladder type filter was shown in FIG. 8, etc., this invention does not limit the structure of a filter, You may use the filter of a DMS type or an IDT type. Further, the arrangement of the input / output pad portions is not limited to the example shown in FIG. 8 and the like, and the input / output pad portions may be disposed on the diagonal of the piezoelectric substrate.

  Further, the material of the excitation electrode is not limited to the materials mentioned in the embodiments, and a single layer of Al, Au, Ta, W, Mo, Ti, Cu or an alloy thereof may be used, or between these and the piezoelectric substrate. Alternatively, a structure in which an adhesion layer is inserted may be used.

  Moreover, although FIG. 2 etc. showed the example which carried out the flip chip mounting of the surface acoustic wave element of this invention to the base | substrate for mounting, you may carry out the flip chip mounting to the package which consists of ceramics or resin.

  In FIG. 11 and the like, the conductor pillar 43 is provided on the main surface of the surface acoustic wave element 1 to form a terminal electrode. However, a through hole is provided in the piezoelectric substrate 2 and a conductor layer is provided on the wall surface of the through hole. The terminal electrode may be formed by filling the through hole with a conductor. In this case, the mounting on the circuit board is face-up mounting, but since the surface acoustic wave element 1 itself is very small, the distance between the terminal electrodes is very small. When this is mounted on a circuit board using solder to connect terminal electrodes, when a ground electrode having an area capable of sufficiently preventing pyroelectric breakdown is formed on the back surface (the other main surface) of the surface acoustic wave element. Although the problem that the terminal electrode and the ground electrode are short-circuited occurs, it is possible to solve the pyroelectric breakdown and the short-circuit problem simultaneously by forming the semiconductor layer 22 as in the present invention. .

  Furthermore, in the above example, in the case where the non-formation region is provided in the semiconductor layer, it has been mainly explained that the semiconductor layer is once formed on the other main surface of the piezoelectric substrate and then the semiconductor layer in a desired region is removed. A region where a semiconductor layer is not formed may be set in advance, and a desired semiconductor non-formation region may be disposed so as to form a semiconductor layer in other regions.

It is sectional drawing which shows the surface acoustic wave element in Example 1 of Embodiment of the surface acoustic wave element of this invention. It is sectional drawing of Example 1 of embodiment of the surface acoustic wave element of this invention. It is a top view which shows the other main surface (pattern of the non-formation area | region of a semiconductor layer) of the piezoelectric substrate of the surface acoustic wave element in Example 2 of the surface acoustic wave element of this invention. It is a top view which shows the other main surface (pattern of the non-formation area | region of a semiconductor layer) of the piezoelectric substrate of the surface acoustic wave element in Example 2 of the surface acoustic wave element of this invention. It is a top view which shows the other main surface (pattern of the non-formation area | region of a semiconductor layer) of the piezoelectric substrate of the surface acoustic wave element in Example 2 of the surface acoustic wave element of this invention. It is a top view which shows the other main surface (pattern of the non-formation area | region of a semiconductor layer) of the piezoelectric substrate of the surface acoustic wave element in Example 2 of the surface acoustic wave element of this invention. It is a top view which shows the other main surface (pattern of the non-formation area | region of a semiconductor layer) of the piezoelectric substrate of the surface acoustic wave element in Example 2 of the surface acoustic wave element of this invention. 1 is a top view showing one main surface of a piezoelectric substrate of a surface acoustic wave element representing an example of a surface acoustic wave element of the present invention. It is a top view which shows one main surface of the piezoelectric substrate of the surface acoustic wave element showing the other example of the surface acoustic wave element of this invention. It is a diagram which shows the bandpass characteristic of the surface acoustic wave apparatus produced in the Example of this invention. It is sectional drawing of the 2nd Example of the surface acoustic wave element of this invention. It is sectional drawing which shows the mounting structure of the conventional surface acoustic wave apparatus typically.

Explanation of symbols

1: Surface acoustic wave element 2: Piezoelectric substrate 3: Excitation electrode 4: Connection electrode 5: Input pad portion 6: Output pad portion 7: Ring conductor 8: Ground electrode pad 9: Filter region
10: Resistor
22: Semiconductor layer
30: Protective film
31: Substrate for mounting
32: Base side annular conductor
33: Brazing material
34: Exterior resin
40: Surface acoustic wave device
41: Annular insulator
42: Cover member
43: Conductor pillar 5a: Region facing the input pad portion 5b: Region facing the DC connection portion from the input pad portion to the excitation electrode 6a: Region facing the output pad portion 6b: From the output pad portion Region facing the portion connected to the excitation electrode in a direct current manner 9a: Region facing the filter region

Claims (5)

A surface acoustic wave element in which a filter region including an excitation electrode, an input pad portion, and an output pad portion is formed on one main surface of a piezoelectric substrate, and a semiconductor layer is formed on the other main surface,
The surface acoustic wave device according to claim 1, wherein the semiconductor layer is formed excluding a region facing at least one of the input pad portion and the output pad portion . 2. The surface acoustic wave device according to claim 1, wherein the semiconductor layer is made of at least one of silicon, germanium, titanium oxide, zinc oxide, and aluminum nitride, or a material mainly composed thereof. The semiconductor layer is a lithium tantalate single crystal, lithium niobate single crystal, or lithium tetraborate in which the oxygen content is less than the stoichiometric composition by reducing the other main surface of the piezoelectric substrate. 2. The surface acoustic wave device according to claim 1, comprising a single crystal. 4. The piezoelectric substrate according to claim 1, wherein the one main surface side is made of a piezoelectric material, and the other main surface side is made of another material having a relative dielectric constant smaller than that of the piezoelectric material. The surface acoustic wave device described. A surface acoustic wave element in which a filter region including an excitation electrode, an input pad portion, and an output pad portion is formed on one main surface of a piezoelectric substrate, and a semiconductor layer is formed on the other main surface,
The surface acoustic wave device according to claim 1, wherein the semiconductor layer is formed except for a region facing the filter region.

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