JP4518877B2 - Surface acoustic wave device - 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 used as a duplexer in which both a transmission side filter and a reception side filter are arranged on the same piezoelectric substrate, and in particular, between a transmission side filter and a reception side filter. The present invention relates to a surface acoustic wave element having improved isolation characteristics and a communication apparatus using the surface acoustic wave element.

  In recent years, with the increase in the number of functions of communication device terminals, there is a demand for smaller and lighter mounting components. Among them, a duplexer that separates a signal in a transmission side frequency band (for example, a low frequency side frequency band) and a signal in a reception side frequency band (for example, a high frequency side frequency band) conventionally uses a dielectric. Have been used. However, the dielectric duplexer cannot be reduced in principle in the frequency band of the current communication standard, and the attenuation characteristic in the vicinity of the pass band cannot be steep, so that the transmission side frequency band and the reception side frequency band are close to each other. Satisfactory characteristics were not obtained with the communication standards.

Therefore, in recent years, an attempt has been made to use a filter using a surface acoustic wave element as a duplexer. Conventionally, a surface acoustic wave filter has been used as an interstage filter, but its power resistance is low for use as a duplexer. In recent years, however, this problem of power durability has been able to be solved by devising the electrode structure and electrode material of the excitation electrode, so that it is smaller than a dielectric duplexer and has good attenuation characteristics near the passband. Surface acoustic wave duplexers (hereinafter referred to as SAW-DPX) are beginning to appear.
JP-A-7-122291 WO99 / 54995 pamphlet Satoshi Matsuda, Yasuyuki Saito, Osamu Kawauchi, Akinori Miyamoto, "Improvement of SAW resonator characteristics by elastic wave observation", Proceedings of the 33rd EM Symposium, May 20, 2004, p.77-82

  In the conventional SAW filter used between the stages, the ratio of the entire filter on the mounting board has been reduced by forming filters of different frequency bands on the same piezoelectric substrate (hereinafter, such a SAW filter is referred to as a SAW filter). This is referred to as a Dual-SAW filter.) Similarly, in SAW-DPX, a transmission-side frequency band filter (hereinafter referred to as a Tx filter) and a reception-side frequency band filter (hereinafter referred to as an Rx filter) are formed on the same piezoelectric substrate. Therefore, the size can be reduced.

  However, when the Tx filter and the Rx filter are actually formed on the same piezoelectric substrate, there has been a problem that the isolation characteristics between the two filters cannot satisfy the required specifications in the communication terminal. This isolation characteristic is a characteristic of a signal leaking from one filter to the other filter, and it is necessary to suppress such signal leakage as small as possible. In particular, in a duplexer, if a transmission signal with high power amplified on the transmission side leaks from the Tx filter to the Rx filter and leaks to the reception side, a reception signal with low power cannot be received from the beginning. For this reason, the specification of the isolation characteristic required for the duplexer requires that the signal leakage be extremely small, which is much higher than the specification required for the Dual-SAW filter used between stages. It is getting strict.

  One of the causes of the deterioration of the isolation characteristic between the filters is considered to be surface acoustic wave leakage. In particular, in SAW-DPX, the surface acoustic wave excited by the excitation electrode forming the Tx filter cannot be sufficiently confined in the excitation electrode, and the surface acoustic wave leaking from the excitation electrode of the Tx filter is And is received by the excitation electrode forming the Rx filter, the signal leaks from the Tx filter to the Rx filter, and the isolation characteristic is considered to deteriorate. FIG. 9 is a top view showing the concept of the SAW-DPX surface acoustic wave element.

  In FIG. 9, reference numeral 1 denotes a surface acoustic wave element, which is provided with a Tx filter region 12 (indicated by a broken line) and an Rx filter region 13 (indicated by a broken line) on one main surface of the piezoelectric substrate 2. A surface acoustic wave filter including a plurality of excitation electrodes 3 and connection electrodes 4 connecting the excitation electrodes 3 is formed in each region. Reference numeral 5 denotes an input pad portion of the Tx filter, 6 denotes an output pad portion of the Tx filter connected to the antenna, 7 denotes an input pad portion of the Rx filter connected to the antenna, and 8 denotes an output pad portion of the Rx filter. Further, 9 is a ground electrode, and 10 is an annular conductor formed so as to individually surround the Tx filter region 12 and the Rx filter region 13.

  In the surface acoustic wave element 1, the Tx filter region 12 and the Rx filter region 13 are electrically separated by being individually surrounded by the annular conductor 10, but the excitation electrode 3 and the Rx filter region of the Tx filter region 12 are separated. Since the 13 excitation electrodes 3 are arranged so as to overlap the directions of the propagation paths of the respective surface acoustic waves, the excitation electrode 3 in the Tx filter region 12 is changed to the excitation electrode 3 in the Rx filter region 13 in FIG. As indicated by the arrows, surface acoustic wave leakage 14 occurs, which causes a problem that the isolation characteristics deteriorate.

  To solve this problem, the Tx filter region 12 and the Rx filter region 13 that have been formed on the same piezoelectric substrate 2 are formed on separate piezoelectric substrates and are separated, thereby causing surface acoustic wave leakage 14 to occur. Attempts have been made to improve the isolation characteristics by blocking propagation (see, for example, Non-Patent Document 1). However, such an attempt certainly improves the isolation characteristics, but the Tx filter region 12 and the Rx filter region 13 which were originally formed integrally are divided and formed on separate piezoelectric substrates. When the Rx filter is mounted on the mounting substrate, the area occupied by the branching filter is larger than when the Tx filter region 12 and the Rx filter region 13 are integrally formed on the same piezoelectric substrate 2. Therefore, there is a problem that it is impossible to meet the demand for downsizing.

  Therefore, the surface acoustic wave element shown in FIG. 10 is used so that the excitation electrodes 3 in the Tx filter region 12 and the Rx filter region 13 which are conventionally arranged as shown in FIG. If the Tx filter region 12 and the Rx filter region 13 are formed on the same piezoelectric substrate 2 without being divided into separate piezoelectric substrates, the isolation characteristics are improved while being reduced in size. It should be possible to make a small SAW-DPX. 10, the same parts as those in FIG. 9 are denoted by the same reference numerals. In the surface acoustic wave element shown in FIG. 10, the propagation of surface acoustic waves through the excitation electrodes 3 in the Tx filter region 12 and the Rx filter region 13 is performed. Since the paths are arranged in parallel, even if a surface acoustic wave leaks from the excitation electrode 3 in the Tx filter region 12, it is not received by the excitation electrode 3 in the Rx filter region 13. It does not deteriorate.

  However, when the inventors conducted detailed experiments, the isolation characteristics were not improved even with the arrangement of the excitation electrodes as shown in FIG. This means that the cause of deterioration of the isolation characteristics is not only the leakage of surface acoustic waves.

  Therefore, as a result of detailed studies by the present inventors, a cause that has not been known in the past regarding the deterioration of the isolation characteristic has been found, and the present invention has been devised as a solution.

  As described above, the present invention improves the isolation characteristic which is not a problem with the conventional Dual-SAW filter but is a problem with the SAW-DPX in which the Tx filter and the Rx filter are integrally formed on the same piezoelectric substrate. The object of the present invention is to provide a surface acoustic wave device that is small and has excellent isolation characteristics without dividing the Tx filter and the Rx filter into separate piezoelectric substrates. is there.

  Another object of the present invention is to provide a small surface acoustic wave device having excellent isolation characteristics that can be applied to a duplexer other than a duplexer in which a Tx filter and an Rx filter are integrated. There is to do.

  Based on detailed experiments and simulations, the present inventors have found that the input electrode of the Tx filter and the output electrode of the Rx filter formed on one main surface of the piezoelectric substrate are deteriorated in isolation characteristics. It has been found that this is caused by capacitive coupling through the back conductor layer formed over the entire main surface (hereinafter also referred to as the back surface). FIG. 11 shows a conceptual diagram of the simulation result and the circuit used for the simulation.

  11, (a) is a circuit diagram when there is no parasitic capacitance and a diagram showing an example of isolation characteristics, and (b) is a circuit diagram when there is a parasitic capacitance and lines showing examples of isolation characteristics. FIG. The parasitic capacitance shown in FIG. 11B is a parasitic capacitance existing between the input pad portion of the Tx filter and the output pad portion of the Rx filter, and is a very small parasitic capacitance of about 50 fF. From the results shown in FIG. 11, it can be seen that the isolation characteristic is deteriorated only by such a very small parasitic capacitance. That is, as can be seen from the comparison between FIGS. 11A and 11B, the signal intensity from 869 MHz to 894 MHz is −30 to −40 dB as shown in FIG. However, when there is no parasitic capacitance, it is −50 dB or less as shown in (a), and it can be seen that the isolation characteristic is greatly improved by the absence of parasitic capacitance.

  Such a parasitic capacitance of about 50 fF, for example, in the case of using a 250 μm-thick lithium tantalate single crystal substrate as the piezoelectric substrate, is calculated with a relative permittivity of 42.7. This corresponds to a capacitance formed when square electrodes of about 180 μm are opposed to each other. Usually, since the area of the input / output pad portion of the surface acoustic wave filter is about this level, it can be said that the value inserted as the parasitic capacitance in the simulation is a value that appropriately reflects the reality. Note that the parasitic capacitance between the input pad portion of the Tx filter and the output pad portion of the Rx filter described here has the most influence on the isolation characteristic, but the connection electrode that connects the excitation electrode of each filter. The parasitic capacitance generated between the input and output pad of each filter and between the connection electrode that connects the excitation electrode of one filter and the connection electrode that connects the excitation electrode of the other filter is similarly isolated. Deteriorate.

  A surface acoustic wave element is an element using comb-like excitation electrodes fabricated on a piezoelectric substrate. Usually, a piezoelectric body exhibits pyroelectricity due to a sudden temperature change, so when manufacturing a device using a piezoelectric substrate, if a process with a sudden temperature change is performed, a spark is generated due to the pyroelectricity of the piezoelectric substrate. As a result, the element is destroyed (pyroelectric breakdown). Therefore, in order to prevent electric charges from being accumulated in the piezoelectric substrate as much as possible, it is common to form a conductor layer over the entire back surface of the piezoelectric substrate. However, the present inventors have found that this back conductor layer is effective in preventing pyroelectric breakdown during the device fabrication process, but is harmful to the isolation characteristics of the surface acoustic wave device.

  By the way, by making this backside conductor layer conductive with the ground electrode of the mounting substrate, the capacitive coupling between the input / output pad portions of each filter can be reduced to some extent, but this measure is sufficient to improve the isolation characteristics. is not. Further, when the surface acoustic wave element is mounted with the back surface of the piezoelectric substrate (the surface on which the back conductor layer is formed) facing the main surface of the mounting substrate, a ground electrode may be provided on the main surface of the mounting substrate. In this case, however, it is necessary to protect the surface of the piezoelectric substrate by attaching a lid or cover in order to secure a vibration space on the surface side of the piezoelectric substrate and protect the excitation electrode from the outside. However, this requires a separate area for attaching the lid and cover, which is disadvantageous for downsizing the surface acoustic wave device. Further, when mounting (flip chip mounting) with the vibration space secured between the surface of the piezoelectric substrate (excitation electrode forming surface) and the main surface of the mounting substrate, it is advantageous for miniaturization. However, since the back conductor layer on the back surface of the piezoelectric substrate is spatially separated from the main surface of the mounting substrate where the ground potential can be obtained, to ground from the back conductor layer to the ground electrode on the main surface of the mounting substrate. Since an extra process is required, there is a problem that the manufacturing cost is increased.

  In addition, the surface acoustic wave excited by the SAW-DPX excitation electrode is partially converted into a bulk wave and propagates through the piezoelectric substrate, is reflected by the back surface of the piezoelectric substrate, and reaches the surface of the piezoelectric substrate again. Therefore, especially in a duplexer, when a bulk wave generated by a Tx filter leaks to a reception side after a transmission signal amplified by a transmission side has a large power, it receives a reception signal having a low power originally. Will not be able to. As described above, bulk waves may cause the isolation characteristics of the surface acoustic wave device to deteriorate.

  Therefore, in the present invention, the following surface acoustic wave device is used to solve the above-described problems.

  In the surface acoustic wave device of the present invention, (1) a transmission-side filter region and a reception-side filter region each having an excitation electrode, an input pad portion, and an output pad portion are formed on one main surface of the piezoelectric substrate, A surface acoustic wave element having a semiconductor layer formed on the other main surface is mounted on a mounting substrate with the one main surface facing each other.

  In the surface acoustic wave device according to the present invention, (2) in the configuration of (1), the semiconductor layer is composed mainly of at least one of silicon, germanium, titanium oxide, zinc oxide, and aluminum nitride. 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 in which the 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 configurations (1) to (3), the semiconductor layer covers the entire surface of the other main surface. is there.

  In the surface acoustic wave device according to the present invention, (5) in each of the configurations (1) to (3), the semiconductor layer has a non-formation region in a part of the other main surface. It is a feature.

  In the surface acoustic wave device according to the present invention, (6) in each of the constitutions (1) to (5), the piezoelectric substrate includes a piezoelectric material disposed on the one main surface side, and It is a composite substrate made of another material having a small relative dielectric constant.

  In the surface acoustic wave device according to the present invention, (7) in each of the configurations (1) to (6), the one main surface of the piezoelectric substrate surrounds the transmission-side filter region and the reception-side filter region. A conductor is formed, and this annular conductor is joined to a substrate-side annular conductor formed correspondingly on the mounting substrate.

  In the surface acoustic wave device according to the present invention, (8) in the configuration of (7), the excitation electrode is electrically connected to the annular conductor via a resistor, and the annular conductor has a ground potential. It is characterized by being.

  A communication apparatus according to the present invention is characterized in that the surface acoustic wave device according to the present invention having any one of the above configurations (1) to (8) is used as a duplexer.

  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 DC, but the frequency near the pass band of the filter formed on the surface acoustic wave element 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 element, so that the semiconductor has a frequency near the passband of the filter formed in the surface acoustic wave element. 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 isolation characteristics that have 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 pyroelectric breakdown well and the effect of preventing deterioration of isolation characteristics.

  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 thereof, 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.

  Further, according to the surface acoustic wave device of the present invention, when 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, Since the semiconductor layer composed of these can be manufactured by reducing the piezoelectric substrate before forming an electrode or the like on one main surface of the piezoelectric substrate, there is no need to change the manufacturing process of the surface acoustic wave element. .

  Further, according to the surface acoustic wave device of the present invention, when the semiconductor film covers the entire surface of the other main surface, it becomes possible to more efficiently release charges generated by a rapid temperature change in the manufacturing process, An effect of more reliably preventing damage to the electrode such as pyroelectric breakdown due to the pyroelectric property of the piezoelectric substrate can be obtained. Therefore, according to the surface acoustic wave device of the present invention, it is possible to obtain both an effect of preventing pyroelectric breakdown well and an effect of preventing deterioration of isolation characteristics.

  Further, according to the surface acoustic wave device of the present invention, when the semiconductor film has a non-formation region in a part of the other main surface and does not cover a part of the other main surface, the entire surface is covered. Since the formation area of the semiconductor layer is reduced by an amount corresponding to the non-formation region, the formation of parasitic capacitance can be prevented more reliably. In particular, this configuration is very effective when the carrier mobility of the semiconductor layer cannot be reduced sufficiently even by adjusting the formation conditions of the semiconductor layer. Therefore, it is possible to greatly improve the isolation characteristics that have been deteriorated due to the parasitic capacitance.

  Further, according to the surface acoustic wave device of the present invention, when the piezoelectric substrate is a composite substrate made of a piezoelectric material disposed on one main surface side and another material having a relative dielectric constant smaller than that of the piezoelectric material, Since the effective relative dielectric constant between the input pad portion and the output pad portion formed on one main surface of the semiconductor layer and the piezoelectric substrate can be reduced, the formation of parasitic capacitance can be prevented more reliably. In particular, this configuration is very effective when the carrier mobility of the semiconductor layer cannot be reduced sufficiently even by adjusting the formation conditions of the semiconductor layer. Therefore, it is possible to greatly improve the isolation characteristics that have been deteriorated due to the parasitic capacitance.

  Further, according to the surface acoustic wave device of the present invention, the annular conductor is formed on one main surface of the piezoelectric substrate so as to surround the transmission side filter region and the reception side filter region, and this annular conductor corresponds to the mounting substrate. When the substrate-side annular conductor is joined to the substrate-side annular conductor, the surface-acoustic wave element is firmly formed on the mounting substrate by joining the annular conductor and the substrate-side annular conductor, and the excitation electrode, the input pad portion, and Since the output pad portion can be mounted in an airtightly sealed state, when the surface acoustic wave element is mounted on the mounting base as described later, when processing the semiconductor layer on the other main surface of the piezoelectric substrate, Processing can be performed without damaging the excitation electrode formed on the one main surface of the piezoelectric substrate. The shape of the annular conductor may be a shape that individually surrounds the transmission-side filter region and the reception-side filter region or a shape that surrounds both.

  Further, according to the surface acoustic wave device of the present invention, the excitation electrode is electrically connected to the annular conductor via the resistor, and when the annular conductor is at the ground potential, the excitation electrode is DC-connected. Is connected to the ground potential, but in the frequency band in which the surface acoustic wave device is used, it can be isolated from the ground potential, so excitation without affecting the band-pass characteristics of the filter. Charges can be prevented from accumulating on the electrode. Therefore, pyroelectric breakdown of the surface acoustic wave device can be reliably prevented even if the semiconductor layer is not provided on the entire other main surface of the piezoelectric substrate.

  According to the communication device of the present invention, the above-described surface acoustic wave device of the present invention is used as a duplexer, thereby satisfying severe isolation characteristics required for the duplexer. In addition, since the surface acoustic wave device is a small-sized duplexer having good isolation characteristics, the mounting area of other components can be increased, and the range of component selection can be increased. Since it spreads, a highly functional communication apparatus can be realized.

  As described above, according to the present invention, it is possible to integrally form the transmission side filter and the reception side filter on the same piezoelectric substrate with greatly improved isolation characteristics. Therefore, a SAW-DPX that is smaller than the one in which the transmission side filter and the reception side filter are produced on separate piezoelectric substrates can be produced. In addition, since a large number of surface acoustic wave devices can be obtained from one piezoelectric substrate, it is possible to reduce the cost of the surface acoustic wave device. Further, even when mounting (flip chip mounting) is performed with one main surface (excitation electrode forming surface) of the piezoelectric substrate facing the main surface of the mounting substrate, the input electrode of the Tx filter and the output electrode of the Rx filter are not Since there is no capacitive coupling through the semiconductor layer on the other main surface, it is possible to obtain a surface acoustic wave device that is a small SAW-DPX but does not deteriorate the isolation characteristics. On the other hand, the pyroelectric breakdown of the surface acoustic wave element can be prevented even if there is no conductor layer on the entire main surface. Also, due to recent demands for miniaturization and low profile of parts, surface acoustic wave devices are also required to reduce the thickness of the piezoelectric substrate. However, the thinner the piezoelectric substrate, the one main surface of the piezoelectric substrate. The capacitance between the other electrode and the conductor layer on the other main surface becomes large, and therefore the deterioration of the isolation characteristic caused by capacitive coupling through the parasitic capacitance becomes more serious. By forming a semiconductor layer on the main surface, a thin surface acoustic wave device having good isolation characteristics can be obtained.

  The surface acoustic wave device according to the present invention is suitable as a duplexer that has a good isolation characteristic but is small in size. 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>
A top view showing one main surface of the surface acoustic wave element in Example 1 of the surface acoustic wave device according to the present invention is the same as FIG. 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. 9, on the piezoelectric substrate 2 of the surface acoustic wave element 1, a transmission side filter region 12 (shown surrounded by a broken line) and a reception side filter region 13 (shown surrounded by a broken line) are formed. Yes. In the transmission-side filter region 12, a plurality of excitation electrodes 3 constituting a resonator, a connection electrode 4 connecting these, and an excitation for connecting the surface acoustic wave element 1 and the mounting substrate (31 in FIG. 2). An input pad portion 5 and an output pad portion 6 that are electrically connected to the electrode 3 are formed. Similarly, a plurality of excitation electrodes 3 constituting a resonator, a connection electrode 4 connecting them, and an excitation electrode 3 for connecting the surface acoustic wave element 1 and the mounting substrate are electrically connected to the reception-side filter region 13. An input pad portion 7 and an output pad portion 8 that are connected to each other are formed.

  The annular conductor 10 is connected to a base-side annular conductor that also functions as a ground electrode, which is formed on the upper surface of the mounting base using solder or the like. In this example, the annular conductor 10 is integrally formed so as to individually surround the transmission-side filter region 12 and the reception-side filter region 13, and functions as a ground electrode for the Rx filter in the reception-side filter region 13 and is also piezoelectric. It serves to seal the transmission side filter region 12 and the reception side filter region 13 between the substrate 2 and the mounting substrate. In this example, the Tx filter in the transmission filter region 12 is grounded by connecting the ground electrode pad 11 to the ground electrode of the mounting substrate, and is connected to the annular conductor 10 on the piezoelectric substrate 2. Absent.

  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 these materials or these materials. And a laminated film of a layer made of a material such as titanium or chromium can be used. As a method for forming the conductor layer, 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 and photolithography is performed to open a desired pattern, and then a conductor layer is formed, and then the resist is formed on an unnecessary portion. A lift-off process for removing the entire conductor layer may be performed.

  Next, the semiconductor layer 22 is formed on the entire other main surface of the piezoelectric substrate 2. The semiconductor layer 22 can be made of at least one material selected from silicon, germanium, titanium oxide, zinc oxide, and aluminum nitride, or a material mainly containing at least one of these materials. 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 portions 5 and 7 and the output pad portions 6 and 8 to form input pads and output pads. This new conductor layer is for electrically and / or structurally connecting the surface acoustic wave element 1 and the mounting substrate with high reliability. For example, if solder is used for connection, It has a function of ensuring wettability and preventing diffusion, and if a gold bump is used for connection, it has a function of adjusting the hardness of the pad so that gold can be bonded using ultrasonic waves or the like. As a material and structure of such a new conductor layer, a laminated film of chromium / nickel / gold 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 portions 5, 7 and the output pad portions 6, 8 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 base 31 is a circuit board on which the surface acoustic wave element 1 is mounted on the upper surface, and input terminals corresponding to the input pad portions 5 and 7 and the output pad portions 6 and 8 are provided on the upper surface of the mounting base 31. An output terminal and a ground terminal (both not shown) and a base-side annular conductor 32 corresponding to the annular conductor 10 are formed.

  According to the example of the surface acoustic wave device using the surface acoustic wave element 1 and the mounting substrate 31, the transmission-side filter region 12 and the reception-side filter region are formed on one main surface of the piezoelectric substrate 2 of the surface acoustic wave element 1. An annular conductor 10 is formed so as to surround 13, and each pad of the surface acoustic wave element 1 is connected to each terminal of the mounting substrate 31 via a conductor bump, and this annular conductor 10 is connected to the mounting substrate 31. The surface acoustic wave element 1 is connected to the base-side annular conductor 32 formed on the upper surface corresponding to the base-side annular conductor 32 by using a brazing material 33 such as solder so as to be sealed in an annular shape. Therefore, the surface acoustic wave element 1 can be stably operated without being influenced by the exterior protective material and the operation can be stably performed for a long period of time. High reliability bullet It can be a surface acoustic wave device become.

  Further, by enclosing, for example, nitrogen gas, which is an inert gas, inside the annular conductor 10 and the base-side annular conductor 32 so as to be hermetically sealed, 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 of the present invention includes the excitation electrode 3, the input pad portions 5, 7 and the output pad portions 6, 8 on one main surface of the piezoelectric substrate 2, respectively. Since the transmission-side filter region 12 and the reception-side filter region 13 are formed, and the semiconductor layer 22 is formed on the other main surface of the piezoelectric substrate 2, the entire surface of the other main surface of the piezoelectric substrate is conventionally formed. Compared with the case where the conductor layer is formed, the carrier of the semiconductor layer 22 can be prevented from responding in the vicinity of the pass band of the filter formed in the surface acoustic wave element 1, so that the input of the transmission side filter region 12 can be prevented. The parasitic capacitance formed between the pad portion 5 and the output pad portion 8 in the reception-side filter region 13 can be significantly reduced, and deterioration of isolation characteristics due to the parasitic capacitance can be suppressed. Can be, it is possible to significantly improve the isolation characteristics.

  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 well and the deterioration of the isolation characteristic by preventing the carrier from responding at a frequency in the vicinity of the pass band of the filter formed in the surface acoustic wave element 1. Thus, it is possible to provide a surface acoustic wave element 1 having both of the effects of preventing the surface acoustic wave and a surface acoustic wave device using the same.

<Example 2 of embodiment>
The cross-sectional view and the top view of the second 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 2, since the piezoelectric substrate 2 itself has the semiconductor layer 22, it is not necessary to add a 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 3 of embodiment>
In the examples so far, the case where the semiconductor layer 22 is formed on the entire surface of the other main surface of the piezoelectric substrate 2 has been shown. However, when the carrier mobility of the semiconductor layer 22 cannot be sufficiently lowered, the semiconductor layer 22 It is effective to pattern 22 and provide a non-formation region of the semiconductor layer 22 on a part of the other main surface. As a pattern of the non-formation region effective for improving the isolation characteristics and preventing pyroelectric breakdown, for example, one main surface of the piezoelectric substrate 2 as shown in the top view of the other main surface in FIG. The other main surface regions 5a and 8a facing the input pad portion 5 and the output pad portion 8 are not formed, and the semiconductor layer 22 is not formed, or as shown in the same top view in FIG. A region not formed so as to separate the regions 5a and 8a from the surrounding semiconductor layer 22 or a Tx filter region 12 on one main surface of the piezoelectric substrate 2 as shown in a top view similar to FIG. The non-formation region is provided so as to divide the region 12a on the other main surface and the region 13a on the other main surface facing the Rx filter region 13, or as shown in the same top view in FIG. The other facing the Tx filter region 12 on one main surface of The semiconductor layer 22 is not provided with the main surface region 12a or the other main surface region 13a facing the Rx filter region 13 as a non-formation region, or as shown in a similar top view in FIG. An example is one in which a plurality of formation regions are scattered to reduce the area where the parasitic capacitance may be formed.

  As a method of patterning in order to provide a non-formation region in the semiconductor layer 22, there is a method of performing photolithography after the formation of the semiconductor layer 22 and then performing RIE (Reactive Ion Etching), wet etching, sand blasting, or the like. 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 through the inside of the piezoelectric substrate 2 from one filter region 12 (13), is reflected by the other main surface of the piezoelectric substrate 2, and is applied to the excitation electrode 3 formed in the other filter region 13 (12). The bulk waves that have been combined and have deteriorated isolation characteristics can be scattered at this portion of the other main surface of the piezoelectric substrate 2, and the isolation characteristics can be further improved.

<Example 4 of embodiment>
In Example 3, the isolation characteristics were improved by reducing the formation area of the semiconductor layer 22 that could form a parasitic capacitance. However, as the piezoelectric substrate 2, a piezoelectric material disposed on one main surface side, and the piezoelectric material When a composite substrate made of another material having a relative dielectric constant smaller than that of the material is used, the effective relative dielectric constant between the semiconductor layer 22 and the pad portions 5 to 8 formed on one main surface of the piezoelectric substrate 2 is reduced. As a result, parasitic capacitance can be reduced and isolation characteristics can be improved.

  Materials having 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), crystal (relative permittivity 3.8), glass Use a ceramic substrate such as a substrate (relative dielectric constant of about 3.8), alumina (relative dielectric constant of about 8.5), or a resin substrate such as polyimide or liquid crystal polymer (both have a dielectric constant of 10 or less). Can do.

  Also, a piezoelectric substrate 2 is bonded to a first substrate made of a piezoelectric material and a second substrate made of a material having a smaller coefficient of thermal expansion than that of a piezoelectric material such as silicon, glass, sapphire, quartz, crystal, or resin. In this case, it is possible to improve the frequency-temperature characteristics of the surface acoustic wave element 1 caused by distortion of the substrate 2 due to temperature change. Furthermore, when the piezoelectric substrate 2 is a composite substrate in which a second substrate made of a material having a higher thermal conductivity than the first substrate made of a piezoelectric material, such as sapphire, quartz, quartz, ceramics, is joined, Since the heat generated in the filter regions 12 and 13 can be efficiently released, the temperature rise of the piezoelectric substrate 2 itself can be suppressed, 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.

<Example 5 of embodiment>
In this example, the configuration on the one main surface side of the piezoelectric substrate 2 is the same as the example shown in FIG. 9, and the excitation electrode 3 that forms a resonator so that all the excitation electrodes 3 are in direct current conduction with the annular conductor 10. And the annular conductor 10 were connected via a resistor 15. A state in which the excitation electrode 3 is connected to the annular conductor 10 through the resistor 15 in this way is shown in FIG. Further, in this case, the annular electrode 10 is connected to the ground electrode of the mounting substrate to have a ground potential. In this way, the excitation electrode 3 is electrically connected to the annular conductor 10 via the resistor 15, and the annular conductor 10 is set to the ground potential. Since the electric charge can be released from the ground electrode to the ground electrode of the mounting substrate, pyroelectric breakdown of the surface acoustic wave device 1 can be more effectively prevented.

  The resistor 15 is selected so that it has a sufficiently high resistance in the frequency band in which the transmission side filter and the reception side filter are used, and has a resistance value that looks almost like an insulator. As the material of the resistor 15, 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.

<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 film thicknesses are 6 nm / 209 nm / 6 nm / 209 nm, respectively. Next, the conductive layer is patterned by photolithography and RIE to form a transmission side filter region 12 and a reception side filter region 13 having excitation electrodes 3, input pad portions 5, 7 and output pad portions 6, 8, respectively. A large number of surface acoustic wave element regions were formed. A mixed gas of BCl ₃ and Cl ₂ was used as an etching gas at this time. The line width of the comb-like electrode forming the excitation electrode 3 and the distance between adjacent comb-like electrodes 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 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 portions 5 and 7 and the output pad portions 6 and 8 to form input pads and output pads. 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.

  FIG. 13A is a diagram showing the isolation characteristics of the surface acoustic wave device 1 of the example manufactured as described above. Further, as a comparative example, a surface acoustic wave device is manufactured by forming an Al layer as a conductor layer instead of the semiconductor layer 22, and finally, the Al layer is removed by wet etching, and a parasitic capacitance is formed on the other main surface. A surface acoustic wave element without any layer that could be formed was produced. The step of removing the Al film after forming the Al film once is the step of removing the charge from the other main surface in the surface acoustic wave device manufacturing process, and the excitation electrode by pyroelectric breakdown. Or the piezoelectric substrate is stuck to the substrate stage of the film deposition system due to static electricity, and when performing automatic transfer, etc., the piezoelectric substrate itself may be damaged when the piezoelectric substrate is removed from the substrate stage with a push-up pin, etc. It is because it will do. FIG. 13B shows the isolation characteristics of the surface acoustic wave element of this comparative example as a diagram.

  These isolation characteristics were obtained by applying an RF signal to the input terminal of the Tx filter and measuring a signal from the output terminal of the Rx filter (note that the Tx filter is normally used when used as a duplexer). And the matching network inserted between the Rx filter and the Rx filter were measured without incorporation.) In the diagram of FIG. 13, the horizontal axis represents frequency (unit: MHz), the vertical axis represents isolation (unit: dB), and the characteristic curve represents the frequency characteristic of isolation.

  As can be seen from the results shown in FIG. 13, the surface acoustic wave device 1 of this example is different from the surface acoustic wave device of the comparative example in which no other layer that may form a parasitic capacitance is provided on the other main surface. Are substantially the same waveform and have very good isolation characteristics.

  After the measurement, the following steps were performed in order to complete the surface acoustic wave device 1 as a surface acoustic wave device.

  The surface acoustic wave device 1 was mounted on a mounting base made of a LTCC (Low Temperature Co-fired Ceramics) substrate with one main surface facing each other. Here, the LTCC substrate has a base-side annular conductor corresponding to the annular conductor 10 formed on one main surface of the piezoelectric substrate 2 and pad electrodes connected to the input / output pads of the surface acoustic wave element 1. Solder was printed on the base-side annular conductor 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. By doing so, the annular conductor 10 and the base-side annular conductor were connected, and the input / output pad and the pad electrode were connected. Thereby, the excitation electrode 3 and the input / output pad of the surface acoustic wave element 1 are completely hermetically sealed by the base-side annular conductor of the LTCC substrate and the annular conductor 10 connected thereto. The mounting process of the surface acoustic wave element 1 was performed in a nitrogen atmosphere.

  Next, the elastic surface of the present invention is formed by performing resin molding, protecting the other main surface (back surface) of the surface acoustic wave element 1 with an exterior resin, and finally dicing the mounting substrate between the surface acoustic wave elements. A wave device was obtained.

  The surface acoustic wave device according to the first embodiment of the present invention thus produced was suitable for a duplexer that had good isolation characteristics but was small.

<Second embodiment>
First, one main surface of the piezoelectric substrate 2 (substrate thickness is 250 μm) made of a 38.7 ° Y-cut X-propagating lithium tantalate single crystal substrate is protected with a photoresist, and then the other main surface is coated with a photoresist. Then, an opening corresponding to a region that does not become a surface acoustic wave element region was formed in a later step, and a semiconductor layer 22 made of silicon to which a small amount of boron was added was formed by sputtering. The film thickness is 200 nm. Thereafter, the resist was removed together with the semiconductor layer formed on the unnecessary portion, and the semiconductor layer 22 was formed only in a region corresponding to a region that does not become the surface acoustic wave element region in a later step. The pattern of the semiconductor layer 22 on the other main surface of the piezoelectric substrate 2 is the same as that shown in FIG.

  Next, four conductor layers made of Ti / Al-1 mass% Cu / Ti / Al-1 mass% Cu were formed on one main surface of the piezoelectric substrate 2 from the substrate side by sputtering. The film thicknesses are 6 nm / 209 nm / 6 nm / 209 nm, respectively.

Next, the conductor layer on the one main surface of the piezoelectric substrate 2 is patterned by photolithography and RIE, and the transmission side filter including the excitation electrode 3, the input pad portions 5, 7 and the output pad portions 6, 8 respectively. A number of surface acoustic wave element regions having the region 12 and the receiving filter region 13 were formed. BCl ₃ and Cl ₂ were used as etching gases in this RIE. Both the line width of the comb-like electrode that is the excitation electrode 3 and the distance between adjacent comb-like electrodes are about 1 μm.

  Next, a protective film 30 made of silica was formed on one main surface of the piezoelectric substrate 2 by plasma CVD. The film forming temperature is 300 ° C., and the film thickness is 20 nm.

  Next, a part of the protective film 30 is removed by photolithography and RIE, and a resistor 15 made of silicon to which a small amount of boron is added is formed on the part by sputtering, and the excitation electrode 3 is formed as the resistor. The annular conductor 10 was connected via 15.

  Next, a new conductor layer made of Cr / Ni / Au was laminated on the input pad portions 5 and 7 and the output pad portions 6 and 8 to form input pads and output pads. 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, and a large number of surface acoustic wave elements 1 were obtained. The subsequent mounting process is the same as in the first embodiment.

  In the second embodiment, in the first embodiment, the breakdown due to spark may occur during the mounting process, but by connecting the excitation electrode 3 to the ground potential in a DC manner by the resistor 15, No destruction occurred.

  The surface acoustic wave device according to the second embodiment of the present invention thus produced was also suitable as a duplexer that had good isolation characteristics but was small.

<Third embodiment>
A sectional view of the surface acoustic wave element 1 in the surface acoustic wave device of this example is shown in FIG. In this example, a composite substrate in which a lithium tantalate single crystal substrate 2a and a quartz substrate 21 are bonded to the piezoelectric substrate 2 was used. Here, one main surface of the quartz substrate 21 is a rough surface, the other main surface is a mirror surface, and a ZnO layer 22 is formed in advance on the other main surface by sputtering. The thickness of the ZnO layer 22 is 200 nm. On the other hand, one main surface of the lithium tantalate single crystal substrate 2a is a mirror surface (the surface on which the excitation electrode 3 and the annular conductor 10 are formed in a later step), and the other main surface is a rough surface and the lithium tantalate single crystal The other main surface of the substrate 2 a and the one main surface of the quartz substrate 21 were bonded using an adhesive layer 23. Other steps are the same as those in the first and second embodiments. By bonding the rough surfaces in this way, the excitation propagates from the one filter region 12 (13) to the inside of the piezoelectric substrate 2, is reflected at the bonding interface, and is formed in the other filter region 13 (12). It became possible to reliably scatter bulk waves that had been bonded to the electrode 3 and had deteriorated isolation characteristics. Further, since the rough surface has a large surface area, the bonding with the adhesive layer 23 is possible, and the surface acoustic wave device 1 having high reliability can be manufactured. In addition, although the ZnO layer 22 has a high crystallinity, the carrier mobility is large. However, the effective relative dielectric constant of the composite substrate is smaller than when the lithium tantalate single crystal substrate is used alone. Therefore, the isolation characteristics can be greatly improved compared to the conventional one.

  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 sets of duplexers may be provided on the same piezoelectric substrate, and other filters that do not affect the isolation characteristics of the duplexer 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.

  9 and the like show a case where a ladder type filter is used, the present invention does not limit the structure of the filter, and a DMS type or an IDT type filter may be used. Also, the arrangement of the input / output terminals is not limited to that shown in FIG. 9 and the like, and the terminals connected to the antenna may be located on the diagonal of the piezoelectric substrate. In this case, it is possible to reduce the deterioration of the isolation characteristics between the filters due to the surface acoustic wave leaked from the excitation electrode of the resonator.

  Further, the pattern of the non-formation region of the semiconductor layer 22 on the other main surface is not limited to that shown in FIG. 3 and the like, but changes in accordance with the shape of the filter formed on the one main surface.

  The semiconductor layer 22 may be formed using a CVD method, a laser ablation method, or the like.

It is sectional drawing which shows the surface acoustic wave element in Example 1 of Embodiment of the surface acoustic wave apparatus of this invention. It is sectional drawing of Example 1 of embodiment of the surface acoustic wave apparatus 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 3 of the surface acoustic wave apparatus 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 3 of the surface acoustic wave apparatus 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 3 of the surface acoustic wave apparatus 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 3 of the surface acoustic wave apparatus 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 3 of the surface acoustic wave apparatus of this invention. It is sectional drawing which shows the surface acoustic wave element in the 3rd Example of the surface acoustic wave apparatus of this invention. It is a top view which shows an example of the surface acoustic wave element of SAW-DPX which shows the concept of the cause of deterioration of an isolation characteristic. It is a top view which shows the other example of the SAW-DPX surface acoustic wave element. (A) is a circuit diagram when there is no parasitic capacitance and a diagram showing an example of isolation characteristics, and (b) is a diagram showing a circuit diagram when there is a parasitic capacitance and examples of isolation characteristics. It is a top view which shows the one main surface of the surface acoustic wave element in Example 5 of Embodiment of the surface acoustic wave apparatus of this invention. (A) And (b) is a diagram which shows the isolation characteristic of the surface acoustic wave apparatus produced in the 1st Example of this invention, respectively, and a comparative example, respectively.

Explanation of symbols

1: Surface acoustic wave element 2: Piezoelectric substrate 3: Excitation electrode 4: Connection electrode 5: Input pad portion of transmission side filter 6: Output pad portion of transmission side filter 7: Input pad portion of reception side filter 8: Reception side filter Output pad part 9: Ground electrode
10: Annular conductor
11: Ground electrode pad
12: Transmitter filter area
13: Receiving side filter area
14: Surface acoustic wave leakage
15: Resistor
21: A substrate made of a material having a relative dielectric constant smaller than that of a piezoelectric material
22: Semiconductor layer
23: Adhesive layer
30: Protective film
31: Substrate for mounting
32: Base side annular conductor
33: Brazing material
34: Exterior resin

Claims (7)

An elastic surface in which a transmission-side filter region and a reception-side filter region each having an excitation electrode, an input pad portion, and an output pad portion are formed on one main surface of the piezoelectric substrate, and a semiconductor layer is formed on the other main surface A surface acoustic wave device in which a wave element is mounted on a mounting substrate with the one main surface facing each other,
The semiconductor layer is provided with a non-formation region that separates a region facing the input pad portion of the transmission-side filter region and a region facing the output pad portion of the reception-side filter region from surrounding regions. A surface acoustic wave device. 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 any one of single crystals .   The surface acoustic wave device according to claim 1, wherein the semiconductor layer has a non-formation region in a part of the other main surface.   The piezoelectric substrate is a composite substrate comprising a piezoelectric material disposed on the one main surface side and another material having a relative dielectric constant smaller than that of the piezoelectric material. The surface acoustic wave device according to any one of the above.   An annular conductor is formed on the one main surface of the piezoelectric substrate so as to surround the transmission-side filter region and the reception-side filter region, and the annular conductor is formed correspondingly on the mounting substrate. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is bonded to the surface acoustic wave device.   6. The surface acoustic wave device according to claim 5, wherein the excitation electrode is electrically connected to the annular conductor via a resistor, and the annular conductor is at a ground potential. An elastic surface in which a transmission-side filter region and a reception-side filter region each having an excitation electrode, an input pad portion, and an output pad portion are formed on one main surface of the piezoelectric substrate, and a semiconductor layer is formed on the other main surface A surface acoustic wave device in which a wave element is mounted on a mounting substrate with the one main surface facing each other,
The surface acoustic wave device according to claim 1, wherein a non-formation region is provided in the semiconductor layer to divide a region facing the transmission filter region and a region facing the reception filter region .

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