WO1996025792A1 - Elastic surface wave functional device and electronic circuit using the element - Google Patents

Abstract

An elastic surface wave functional device comprises a piezoelectric substrate or a multi-layered piezoelectric substrate (1) having a large electromechanical coupling factor, an active layer (3) of a semiconductor layer having large mobility and formed on the substrate (1), and a buffer layer (2) lattice matching the active layer. Futher, an input electrode (4) and an output electrode (5) are formed on both sides of the semiconductor layer. This elastic surface wave functional device generates a large degree of amplification at a low voltage. A transmission reception circuit of a high-frequency unit of a mobile communication equipment using this elastic surface wave functional device is obtained, too.

Description

Name of specification and invention Surface acoustic wave functional element and electronic device using the same II] Technical field The present invention relates to the interaction between a surface acoustic wave propagating through a piezoelectric substrate and a carrier in a semiconductor. The present invention relates to a surface acoustic wave functional element such as a surface acoustic wave amplifier and a surface acoustic wave convolver, and an electronic circuit such as a transmission / reception circuit of a mobile communication device using the functional element. 2. Description of the Related Art In recent years, as mobile communication devices such as mobile phones have become smaller, lower in voltage and lower in power consumption, monolithic devices mounted inside the mobile devices have been actively studied. However, among the high-frequency components, band-pass filters and transmission / reception duplexers have a large size, so there is almost no effect of monolithic integration with other components. Also, it is extremely difficult to make a power amplifier monolithic. Therefore, transmission / reception duplexers, power amplifiers, bandpass filters, and low-noise amplifiers placed before them have been developed and modularized as separate discrete elements. When these discrete elements are modularized, wiring for connecting a plurality of components and circuits for impedance matching are formed, and the unit has a very large size. On the other hand, there have been various attempts to amplify surface acoustic waves. It is known that a surface acoustic wave can be amplified by propagating the surface acoustic wave on a piezoelectric surface and coupling an electric field generated by the wave with a carrier in a semiconductor. Actual surface acoustic wave amplifiers are classified into three types: direct amplifiers (Fig. 3), separated amplifiers (Fig. 4), and monolithic amplifiers (Fig. 5), based on the combination of piezoelectric materials and semiconductors that transmit surface acoustic waves. You. As shown in FIG. 3, the first direct-type amplifier is provided with input / output electrodes 4 and 5 on a substrate 7 having both piezoelectricity and semiconductivity, such as CdS and GaAs. This is an amplifier having a structure in which a surface acoustic wave is amplified by using a configuration in which DC electric field application electrodes 6 are provided on both sides of 7. However, a piezoelectric semiconductor having both large piezoelectricity and large mobility has not been found so far. As shown in FIG. 4, the second separation type amplifier has a semiconductor layer 3 ′ having a high mobility disposed on a piezoelectric substrate 1 having a large piezoelectric property via a gap 8. This is an amplifier having a structure in which input / output electrodes 4 and 5 are provided on 1 and DC electric field application electrodes 6 are provided on both sides of the semiconductor layer 3 ′. This type of amplifier greatly affects the flatness of the surface of the semiconductor and the piezoelectric substrate, the size of the gap, and the degree of amplification. In order to obtain a practically usable amplification degree, the air gap must be kept as small as possible, and it must be kept constant over the entire operating range, which makes industrial production extremely difficult. On the other hand, in the third monolithic amplifier shown in FIG. 5, a semiconductor layer 3 ′ is formed on the piezoelectric substrate 1 via the dielectric film 9 without any gap, and the semiconductor layer 3 ′ is formed on the piezoelectric substrate 1. The amplifier has a structure in which input / output electrodes 4 and 5 are provided, and DC electric field application electrodes 6 are provided on both side surfaces of the semiconductor layer 3 ′. It is said that monolithic amplifiers can achieve high gain, can operate at high frequencies, and are suitable for mass production. However, there is no example of studying the application of these surface acoustic wave amplifiers to mobile communication devices such as mobile phones.

However, in order to realize a monolithic amplifier, a semiconductor with good electrical characteristics is formed on a piezoelectric substrate, and furthermore, a surface acoustic wave and a semiconductor carrier are formed. In order to efficiently interact with the rear, it is necessary to reduce the thickness of the semiconductor film. A study in the 1970s of Tohoku University Yamanouchi et al. (Yamanouchi K:..., Et al, Proceedings of the ffiEE, 75, P726 (1975)) According to the, the _{L i N b 0 3 S i} 0 on the substrate A structure in which an InSb thin film of 50 nm is deposited on top of a 30 nm coating, and a 1600 cm ² ZVs electron mobility of InSb is obtained. In the test, a DC voltage of 1100 V was applied, and a gain of 40 dB was obtained at a center frequency of 195 MHz. They also predicted from theoretical calculations that in a thin InSb thin film of 50 nm, the electron mobility was 3000 cm ² / Vs due to carrier surface scattering (Yamanouchi et al., IEICE Technical Report, US 78-17, CP M78-26, P19 (1978)). That is, the monolithic amplifier has a problem that it is extremely difficult to form a thin-film semiconductor layer having good electric characteristics on a piezoelectric substrate. Further, in the structure so far, a dielectric film such as S I_〇 was required explosion Gutame deterioration of degradation and L i Nb0 ₃ substrate surface I NSB by oxygen diffusion from the L iNb0 ₃ substrate. Furthermore, when a surface acoustic wave amplifier is used as the function of the amplifier and the bandpass filter in the high-frequency part of a portable device, it cannot be used unless the drive voltage of 3 to 6 V has an amplification effect. Conventional monolithic amplifiers require large voltages, and no surface acoustic wave amplifiers capable of low-voltage driving existed. In addition, similarly to the surface acoustic wave amplifier, the surface acoustic wave convolver using the interaction between surface acoustic waves and electrons also has a problem that the gain force ^s ' is insufficient.

 Generally, the gain G of a surface acoustic wave amplifier is given by the following equation.

G = AJC ² ^-(BV)

 ah

Here, A: constant, k ² : electromechanical coupling constant of the piezoelectric substrate, ε ρ: equivalent dielectric constant of the piezoelectric substrate, σ: conductivity, h: film thickness of the active layer, μ: electron mobility, Ε : Applied electric field, v: The velocity of the surface wave. In order to obtain a large amplification degree at a practical level of low voltage, 1) is formed as thin as possible semiconductor layer of high electron mobility in thickness, 2) k ² using only the large piezoelectric substrate possible to the is that .

Therefore, as a result of diligent studies, the inventors have found that an active layer having a thin film and excellent electric characteristics can be obtained by inserting a buffer layer between the piezoelectric substrate and the active layer. In addition, we have found that by using a multilayer piezoelectric thin film substrate with three or more layers as the piezoelectric substrate, it is possible to realize k ^{2 which} is much larger than that of bulk. Furthermore, a surface acoustic wave amplifier was manufactured using the semiconductor layer and the piezoelectric thin film substrate, and it was confirmed that a good amplification factor could be obtained at a practically low voltage. Thus, the present invention was completed. Moreover, the semiconductor layer having a buffer layer interposed between the piezoelectric substrate and the active layer of the present invention achieves an electron mobility of 500 cm ² ZVs or more in the active layer. That is, the present invention provides an input electrode, an output electrode, and a semiconductor layer between the input and output electrodes on a piezoelectric substrate, wherein the semiconductor layer lattice-matches the active layer with the active layer. This is a surface acoustic wave functional element characterized by comprising a layer. Here, the active layer is a layer that excites the propagated surface acoustic wave by the energy of a carrier in a semiconductor.

In the present invention, the very good electrical characteristics of the active layer were realized in the thin film because the crystallinity of the active layer could be improved by inserting a buffer layer between the piezoelectric substrate and the active layer. by. Furthermore, the crystallinity of the active layer can be further improved by making the lattice constant of the crystal constituting the active layer coincide with or close to the lattice constant of the crystal constituting the buffer layer. However, it has been found that the electrical characteristics of the active layer are dramatically improved even with a thin film. Furthermore, it has been found that even better electrical characteristics can be obtained by using a compound semiconductor containing Sb as the buffer layer of the present invention. Further, the buffer layer of the present invention is characterized in that it has a high resistance and the attenuation of surface acoustic waves in the buffer layer is small. The buffer layer of the present invention can be activated by oxygen from the piezoelectric substrate even if there is no dielectric film such as SiO on the piezoelectric substrate. It has an excellent feature that it can prevent the deterioration of the conductive layer and can be grown at a low temperature, so that the piezoelectric substrate does not deteriorate.

 The piezoelectric thin film substrate of the present invention is composed of three or more multilayer piezoelectric materials having at least two or more different electromechanical coupling constants on the piezoelectric substrate, and a piezoelectric film at the center of the multilayer of the multilayer piezoelectric material. Or * Having the largest electromechanical coupling constant makes it easier to efficiently concentrate surface acoustic wave energy s on the surface, far exceeding the electromechanical coupling constant of the piezoelectric material that constitutes each layer. A large electromechanical coupling constant can be realized.

 In the surface acoustic wave amplifier using the semiconductor layer of the present invention, an amplification effect was obtained only at a practically low voltage that can be used for portable equipment and the like. Further, with the multilayer piezoelectric body of the present invention, a higher amplification degree was realized.

 Further, in the surface acoustic wave convolver of the present invention, the interaction between the electrons and the convolved surface wave was enhanced by increasing the electron mobility of the semiconductor layer, and a larger gain was obtained than in the conventional structure.

 Further, the surface acoustic wave functional element having a large amplification degree at a practical low voltage according to the present invention may be used as a band-pass filter and a low-noise amplifier for a mobile communication device, or a band-pass filter and a power amplifier, or a band-pass filter and an amplifier and If it is used as a device for transmission / reception duplexers, it can exert a tremendous effect on miniaturization, thickness reduction, and weight reduction of mobile communication equipment. Therefore, in such transmission and reception circuits of mobile communication devices such as mobile phones and cordless phones, high-amplification elasticity is used as an amplifier and a bandpass filter, or as an amplifier and a bandpass filter and a transmission / reception duplexer. A transmission or reception circuit for a mobile communication device, which is configured by a surface acoustic wave functional element, is also included in the scope of the present invention.

Hereinafter, the present invention will be described in more detail. FIG. 1 shows a surface acoustic wave functional element that is the basis of the present invention. Figure 1A is a cross-sectional view of a surface acoustic wave functional element, and Figure 1B It is a perspective view of a surface acoustic wave functional element. 1 power ^s piezoelectric substrate, 2 is a buffer layer, 3 an active layer, 4 is an input electrode, 5 is an output electrode.

According to the present invention, the input electrode 4 and the output electrode 5 are arranged on the piezoelectric substrate 1 at intervals, and the active layer 3 is provided between the input / output electrodes 4 and 5 via the buffer layer 2. I have. -The piezoelectric body 1 according to the present invention may be a piezoelectric single crystal or a piezoelectric thin film substrate. Piezoelectric single crystal substrate is preferably an oxide-based piezoelectric substrate, for _{example, L iNb0 3, L i Ta0} 3 or L i ₂ B ₄ ◦ ₇ Hitoshiryoku ⁵ is preferably used. Further, 64 ° Y cut, 4 1 ° Y-cut, 128 ° Y cut, it is also preferable to use a substrate cutlet up surface such as a Y cut of L i Nb0 ₃ and 36 ° Y cut of L i Ta0 ₃ . Piezoelectric thin film substrate, which piezoelectric film is formed on a single crystal substrate such as sapphire or S i, for example as a pressure-collecting thin _{film, ZnO, L i NbO 3,} L i Ta0 3, PZT, such _{PbT i 0 3, BaT i 0} 3 or L i ₂ B ₄ 0 ₇ is preferably thin Takenawa charges used. The dielectric film such as S i 0 and S i 0 ₂ may be揷enter between the S i substrate and the piezoelectric thin film. Further, as the piezoelectric thin film substrate, a multilayer laminated film in which thin films of different types of the above piezoelectric thin films are alternately stacked may be formed on a single crystal substrate such as sapphire or Si.

 The piezoelectric substrate 1 of the present invention is composed of three or more multilayer piezoelectric materials having at least two or more kinds of different electromechanical coupling constants, and the piezoelectric film at the center of the multilayer of the multilayer piezoelectric material has the largest electrical conductivity. An extremely large electromechanical coupling constant can be realized by using a piezoelectric substrate characterized by being a piezoelectric film having a mechanical coupling constant.

An example of a three-layer structure of the multilayer piezoelectric substrate will be described below in detail with reference to FIG. The multilayer piezoelectric substrate 20 of the present invention has a structure in which a first piezoelectric film 22 is provided on a piezoelectric substrate 21 and a second piezoelectric film 23 is provided thereon. As the piezoelectric substrate 21, the same substrate as the above-mentioned piezoelectric substrate 1 can be used. However, the following conditions Needs to be satisfied. Each piezoelectric substrate 21, the electromechanical coupling constant of the first piezoelectric film 22 and the second pressure collector layer 23 in order, 1 ^, 1 ^ 1 Oyobi 1? _2, and further the piezoelectric substrate 21, a first turn V, and Vi and V ₂ the speed of the Rayleigh over wave of the piezoelectric film 22 and the second piezoelectric film 23. Further hi the thickness of the first piezoelectric film 22, the thickness of the second piezoelectric film 23 and h _2. Here, k 1 needs to be larger than k and k ₂ , preferably 1.2 times or more, and more preferably 2 times or more. Furthermore, when k is greater than k and k 2 and V i is greater than V and V 2, a larger electromechanical coupling constant is obtained. V ;! Is preferably larger than V and V ₂ by 10 OmZs or more, more preferably 25 OmZs or more. Hi is usually in the range of 30 nm or more and 2 O / m or less, more preferably 80 nm or more and 5 or less, and even more preferably 100 nm or more and 2 or less. Usually, h2 is 0.1 or more and 500 or less, preferably 0.15 or more and 50 or less, and more preferably 0.5 or more and 21 or less. Also, if the wavelength of the surface acoustic wave is s, usually h is less than 1 and h 2 / ska? 1 or less, preferably, h is 0.5 or less and h ₂ is 0.4 or less, and more preferably, hj / zl is 0.25 or less and h ₂ is 0.25 or less.

 The multilayer piezoelectric substrate 20 having a large electromechanical coupling constant according to the present invention can be used not only for a surface acoustic wave amplifier and a surface acoustic wave convolver but also for improving the characteristics of surface acoustic wave devices such as a surface acoustic wave filter and a surface acoustic wave resonator. Is also very preferably used.

As the active layer constituting the semiconductor layer of the present invention, one having high electron mobility is preferably used. Preferred examples of the active layer include GaAs, InSb, InAs, and PbTe. Further, not only binary systems but also ternary mixed crystals / quaternary mixed crystals combining these binary systems are preferably used. For example, I n _X G a丄 _{- x A s, I nAs y} Sb i_y> I nzGa i- z Sb such force ternary mixed _{crystal, I njjGa i-xA s y} S b E _ _y like are quaternary mixed crystal This is an example. Among these active layers, including In I I NAS and I n S b, because it has I nAs S b, I nGa S b, I nG aAs S b such force ^s very high electron mobility, is more preferably used. Further, the active layer may be formed as a multilayer laminated film in which semiconductor films having different compositions are laminated. The electron mobility of the active layer is preferably 5000 cm ² ZVs or more in order to increase the amplification of the surface acoustic wave amplifier.To obtain an extremely good amplification, the electron mobility of 10,000 cm ² ZVs or more is preferable. It is more preferred to have. In order to obtain this high electron mobility, as the composition of the active layer, _X of In X Gas can be 0≤χ ^ 1.0, but 0.5≤x 1.0 is preferable, and 0.8≤x≤1.0 is more preferable. This is a preferred range. Y of I nA s yS b can have high electron mobility in the range of 0≤y≤1.0, and more preferably 0.5≤y≤1.0. Z of InzG a —z S b is preferably 0.5 ≦ z ≦ 1.0, and more preferably 0.8 ≦ z ≦ 1.0.

When the thickness h of the active layer is 5 nm or less, the crystallinity of the active layer s is deteriorated, and high electron mobility cannot be obtained. On the other hand, when h exceeds 500 nm, the active layer has a low resistance, and the interaction efficiency between the surface acoustic wave and the carrier decreases. That is, in order to realize high electron mobility and efficiently perform the interaction between the surface acoustic wave and the carrier, the thickness h of the active layer needs to be 5 nm≤h≤500 nm, which is preferable. Is in the range of 10 nm≤h≤350 nm, and more preferably in the range of 12 nm≤h≤200 nm. Further, the surface resistance of the active layer, or the force ⁵ 'preferably 1 0 .OMEGA, more preferably not less than 50 Omega, more preferably Ah least 1 00Ω.

 The buffer layer formed on the piezoelectric substrate in the present invention is preferably insulative or semi-insulating, but any material having a high plate value according to these may be used. For example, the resistance value of the buffer layer may be at least 5 to 10 times higher than that of the active layer, preferably 100 times or more, more preferably 1000 times or more.

As a high resistance buffer layer, for example, G a S b, A l S b, Z nTe or C dT e Ternary system such as AIG a Sb, AlAs Sb, GaAs Sb, Alln Sb, etc., AIG aAs Sb, A1 InGaSb, A1 InAs S b, quaternary systems such as A1InPSb and A1GaPSb are preferred examples. Also, when determining the composition of these buffer layers, by adjusting the composition to have a value equal to or close to the lattice constant of the crystal constituting the active layer, a larger electron mobility of the active layer can be obtained. Can be realized. Here, the close lattice constant means that the difference between the lattice constant of the crystal forming the active layer and the lattice constant of the crystal forming the buffer layer is 7% or less, preferably 5% or less, more preferably ± 5%. It means 2% or less.

 In addition, in the step of actually forming the buffer layer 2 on the piezoelectric substrate 1, particularly, the buffer layer 2 containing Sb has a very fast lattice relaxation, so that even if the lattice irregularity with the piezoelectric substrate 1 is large, the buffer layer can be buffered. Lattice disorder is alleviated only by growing an ultra-thin film of layer 2, and growth begins with the unique lattice constant of the crystal constituting buffer layer 2. Immediately before the growth of the active layer 3, the surface condition of the buffer layer 2 becomes extremely good, and the crystallinity of the active layer 3 formed thereon can be greatly improved. Therefore, a compound semiconductor containing Sb is particularly preferably used as the buffer layer 2.

The thickness of the buffer layer 2 is better as it is thicker from the viewpoint of crystallinity, but is more preferable as it is thinner from the viewpoint of the interaction between the surface acoustic wave and the carrier. That is, the film thickness h ₃ of the buffer layer 2 is preferably _{1 0 nm≤h 3 ≤ 1 000 nm} , a more preferable range is 20 nm≤h ₃ 500 nm.

Further, since the buffer layer 2 of the present invention can be grown at a low temperature, the piezoelectric substrate 1 does not deteriorate due to oxygen bleeding and the like, and the active layer 3 formed on the buffer layer 2 also has a piezoelectric property. It is also a great feature that deterioration due to oxygen escaping from the substrate 1 can be prevented, and that it functions as a protective layer for the piezoelectric substrate 1 and the active layer 3. Therefore, the protective layer force ^s ′ using a dielectric film such as S i 0 or S i 0 ₂ which has been conventionally used becomes unnecessary. However, there is no problem even if a dielectric film is inserted between the piezoelectric substrate 1 and the buffer layer 2. The dielectric film, for example, S i 0, S i 0 2, silicon _{nitride, C e 0 2, CaF 2} , BaF 2, S rF 2, T i O 2, Y 2 0 3, Z r 0 2> MgO, A12〇3 etc. are used. The thickness of the dielectric film is preferably thin, but is preferably 100 nm or less, more preferably 50 nm or less. -Further, the buffer layer 2 of the present invention is compared with a dielectric film 9 such as Si0 inserted between the piezoelectric substrate 1 and the active layer 3 'of the conventional monolithic amplifier as shown in FIG. In addition, while being lattice-matched to the active layer and being a semiconductor, it has a large dielectric constant and a high resistance value. Therefore, the attenuation of the electric field of the surface acoustic wave in the buffer layer 2 of the present invention is small, and the interaction between the electric field of the surface acoustic wave and the carrier in the active layer 3 is more likely to occur more efficiently. It can be thicker than the body membrane 9.

 Further, a dielectric film or a semiconductor film may be laminated as a protective film on the active layer for the purpose of protecting the active layer 3. Is it necessary to use a dielectric film with the above composition? it can. A semiconductor film having the same composition as the buffer layer can be used.

 The buffer layer 2 and the active layer 3 can be generally formed by any method that can grow a thin film, such as a molecular beam epitaxy (MBE) method, an organometallic molecular beam epitaxy (MOMBE) method, and an organometallic chemical vapor deposition method. Phase growth (MOCVD) and atomic layer epitaxy (ALE) are particularly preferred methods.

Further, the input / output electrodes 4 and 5 on the piezoelectric substrate 1 of the present invention have an interdigital structure, and are used for a normal surface acoustic wave filter, such as an apodized electrode, a thinned electrode, a unidirectional electrode, a regular electrode, and the like. Is preferably used. Above all, the unidirectional electrode is particularly preferably used because the loss due to the bidirectionality of the surface acoustic wave can be reduced. There is no particular limitation on the material of the input / output electrodes 4 and 5, for example, A and Au, Pt, Cu, A1-Ti alloy, A1-Cu alloy, multilayer electrodes of A1 and Ti, etc. Is preferably used. When the buffer layer 2 is formed so as to cover the input / output electrodes 4 and 5 of the present invention, since the input / output electrodes 4 and 5 are formed first, there is no need to consider the unevenness of the semiconductor thin film. Contact exposure enables submicron electrode microfabrication.

 However, since the input / output electrodes 4 and 5 are embedded in the buffer layer 2, it is necessary to select an electrode material that is as small as possible such as deformation, melting, and diffusion while forming the buffer layer 2. For example, Pt, Au, Cu, A and Cr, Mo, Ni, Ta, Ti, W and the like are preferable. Further, multilayer electrodes such as Ti-Pt :, Ti-Al, Ti-Au, Cr-Au, and Cr-Pt are also preferably used.

 In the surface acoustic wave amplifier of the present invention, the material used for the electrode 6 for applying a DC electric field to the semiconductor layer is not particularly limited. For example, Al, Au, Ni / Au, Ti / AuCuZNiZAu, AuGeZNiZAu and the like are preferably used.

 When the surface acoustic wave function element of the present invention is used in a part requiring high power durability such as a power amplifier, the input electrode 4 and the output electrode 5 are electrodes capable of withstanding high power, for example, power of about several W. Materials must be used. For example, epitaxial A 1 film, A 1-Cu film, A 1 -C xx / CM / k 1-Cu laminated film, Ti added A 1 film, Cu added A 1 film, Pd added A 1 A high power electrode material such as a film is preferably used.

 In the surface acoustic wave amplifier according to the present invention, the semiconductor layer between the input / output electrodes 4 and 5 has two or more forces, and further has a structure for removing carriers moving in the direction opposite to the surface acoustic wave propagation direction. Alternatively, by forming a structure that removes the active layer 3 between the semiconductor layers, high amplification can be realized at low voltage. For example, as shown in FIG. 6, the semiconductor layer is separated by mesa etching, or a dielectric (not shown) is buried between the semiconductor layers after the mesa etching, so that carriers moving in the opposite direction due to a reverse electric field are removed. Can remove power s.

In the surface acoustic wave convolver of the present invention, the surface acoustic wave convolver is formed on the piezoelectric substrate. The electrodes are used as two input electrodes, and the convolved surface waves are extracted from extraction electrodes formed above the semiconductor layer and below the piezoelectric substrate. The electrode material of the extraction electrode is not particularly limited. For example, A, Au, Pt, and Cu are preferably used.

 In the RF section of a conventional mobile phone whose schematic diagram is shown in Fig. 7, a transmission / reception splitter 11 is connected to an antenna 10, and a reception amplifier 12 and a transmission amplifier 13 are connected to the transmission / reception splitter 11. The transmission and reception amplifiers 12 and 13 are connected to a bandpass filter 14 power, respectively. On the other hand, if the high-amplification surface acoustic wave functional element of the present invention is used, the receiving surface acoustic wave amplifier 15 and the transmitting surface acoustic wave amplifier 16 are connected to the antenna 10 as shown in FIG. Is only connected. Therefore, according to the present invention, the number of components in the RF section can be reduced, and further, each component can be reduced in size, weight, and thickness. That is, according to the present invention, it is possible to reduce the size, weight, and cost of a portable device terminal. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a cross-sectional view of a surface acoustic wave device according to one embodiment of the present invention. FIG. 1B is a perspective view of a surface acoustic wave device according to one embodiment of the present invention. FIG. 2 is a cross-sectional view of a multilayer piezoelectric substrate of the present invention.

 FIG. 3 is a cross-sectional view of a conventional direct amplifier.

 FIG. 4 is a cross-sectional view of a conventional separated amplifier.

 FIG. 5 is a cross-sectional view of a conventional monolithic amplifier.

 FIG. 6 is a sectional view of a semiconductor layer-separated surface acoustic wave amplifier according to one embodiment of the present invention.

Figure 7 is a schematic diagram of the RF section of a mobile phone. FIG. 8 is a schematic diagram of a transmission and reception circuit formed without using a transmission / reception splitter or a transmission / reception amplifier according to the present invention.

 Figure 9 is a cross-sectional view of a surface acoustic wave amplifier with input and output electrodes embedded in a buffer layer.

^ A o

 FIG. 10 is a cross-sectional view of a surface acoustic wave amplifier using a multilayer piezoelectric substrate.

 FIG. 11 is a sectional view of a surface acoustic wave convolver according to an embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below by way of specific examples.

 [Example 1]

After deposition of S i 0 ₂ 10 nm on the 64 ° Y cut L i Nb 0 ₃ single crystal substrate having a diameter of 3 Inchi, by MBE, as a buffer _{layer, A 1 0. 3 8 I} n 0. 62 After growing Sb by 150 nm and then growing InSb as an active layer by 50 nm, GaSb was grown by 2 nm as a protective layer to obtain a semiconductor layer. The electron mobility of this semiconductor layer was 32000 cm ² / Vs. Note that the electron mobility of the semiconductor layer was measured by the Vaner Pauw method.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 0.75 m, and the propagation length was 3 O O ^ m. Subsequently, an electrode for applying a DC electric field was formed on the active layer. The propagation length of the surface acoustic wave is preferably formed to be an integral multiple of the wavelength of the surface acoustic wave.

Next, the characteristics of the surface acoustic wave amplifier were measured. The amplification was evaluated using a network analyzer (Yokokawa Hewlett Packard, 8510B) based on the difference between the gain (or insertion loss) after applying the electric field and the insertion loss before applying the electric field. Surface acoustic wave enhancement of Example 1 As a result of evaluating the width gauge, the amplification degree was 22 dB at a DC applied voltage of 3 V and a center frequency of 150 MHz. This value is a good amplification factor when used in the low-noise amplifier and band-pass filter of the high-frequency part of a portable device, and because it is formed of a monolithic single element, the size of the portable device is small. And reduction of return loss due to wiring. From the above results, although the buffer layer exists between the active layer and the piezoelectric substrate with a thickness of 15 O nm, the attenuation of the electric field strength of the surface acoustic wave in the buffer layer is a problem on a practical level. There was no power s could be confirmed.

 [Example 2]

 Using the sample of Example 1, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed as input and output electrodes on the surface of the piezoelectric substrate by a lithography process. The electrodes were regular electrodes with a pitch of 1.4 m, and the propagation length was 280; / m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

 Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the amplification degree was performed in the same manner as in Example I. As a result of evaluating the surface acoustic wave amplifier of Example 2, the amplification was 12 dB at a DC applied voltage of 3 V and a center frequency of 80 OMHz. This value is a good amplification factor when used in the low-noise amplifier and band-pass filter of the high-frequency part of portable equipment.

 [Comparative Example 1]

Comparative Example 1 is shown as a comparison with Example 2. Was deposited S i 0 ₂ 1 0 nm on a 6 4 ° Y cut L i N b 0 ₃ single crystal substrate having a diameter of 3 Inchi. Further, InSb was grown as an active layer by 5 O nm by MBE, and then GaSb was grown by 2 nm as a protective layer. Then, the electrical characteristics of the laminated film were measured. In this comparative example, the active layer In Sb was formed directly on the piezoelectric substrate, so that the crystallinity of the active layer was poor and the electron mobility was low. It was only 1700 cm ² ZVs. Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 1.4 / m, and the propagation length was 28 Om. Continued after forming the electrode for DC electric field applied to the active layer, the force was measured surface acoustic wave amplifier characteristics in the same manner as in Example 2 ^s, amplification was not observed.

 [Embodiment 3]

After deposition of S i 0 ₂ 10 nm on the 64 ° Y Chikara' preparative L i Nb 0 ₃ single crystal substrate having a diameter of 3 Inchi, by MB E method, the _{A l o. 5 Gao. 5} Sb as the buffer layer After growing 200 nm, and then growing InAs0.5Sb0.5 as an active layer to 60 nm, GaSb was grown to 2 nm as a protective layer to obtain a semiconductor layer. The electron mobility of this semiconductor layer was 30,000 cm ² Vs.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 0.6 / m, and the propagation length was 240 / zm. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

 Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the degree of amplification was performed in the same manner as in Example 1. As a result of evaluation of the surface acoustic wave amplifier of Example 3, the amplification was 26 dB at a DC applied voltage of 3 V and a center frequency of 190 OMHz. This value is an extremely good amplification when used in the low-noise amplifier and band-pass filter of the high-frequency part of portable equipment.

 [Example 4]

After deposition of S i 0 ₂ 10 nm on the 64 ° Y cut L i Nb 0 ₃ single crystal substrate having a diameter of 3 Inchi, by MB E method, the _{A 1 0. 5 Ga 0.} 5 Sb as the buffer layer After growing it to 150 nm, and then growing InAs0.5Sb0.5 to 50 nm as an active layer, 2 nm of GaSb was grown as a protective layer to obtain a semiconductor layer. Of this semiconductor layer The electron mobility was 20900 cm ² ZVs.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 0.75, and the propagation length was 300 m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

 Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the amplification degree was performed in the same manner as in Example 1. As a result of evaluating the surface acoustic wave amplifier of Example 4, the amplification was 13 dB at a DC applied voltage of 3 V and a center frequency of 1530 MHz. This value is a good amplification factor when used for the low-noise amplifier and band-pass filter of the high-frequency part of portable equipment.

 [Example 5]

After deposition of S i 0 ₂ 10 nm on the 64 ° Y cutlet preparative L i Nb0 ₃ single crystal substrate having a diameter of 3 inches by MB E _{method, A l o. 5 Gao.} 5 Sb 10 0 as a buffer layer After growing 200 nm of InAs0.5Sb0.5 as an active layer, 200 nm of GaSb was grown as a protective layer to obtain a semiconductor layer. The electron mobility of this semiconductor layer was 32000 cm ² / Vs.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 0.75 m, and the propagation length was 300; m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

 Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the amplification degree was performed in the same manner as in Example 1. As a result of evaluating the surface acoustic wave amplifier of Example 5, the amplification was 6 dB at a DC applied voltage of 6 V and a center frequency of 1505 MHz. An amplification effect was obtained at a low voltage of 6V.

[Comparative Example 2] Comparative Example 2 is shown as a comparison with Example 4. After deposition of S i 0 ₂ 10 nm on the 64 ° Y cutlet preparative L i Nb0 ₃ single crystal substrate having a diameter of 3 inches by MB E method, the I n A s 0.5 S b 0.5 as the active layer 5 0 nm After the growth, G 351) was grown 211111 as a protective layer. The electrical characteristics of this laminated film were measured. In this comparative example, the active layer InAs 0.5 Sb 0.5 was formed directly on the piezoelectric substrate, so the crystallinity of the active layer was poor and the electron transfer The degree was only 1200 cm ² ZVs.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 0.75 m, and the propagation length was 300 / m. After the formation of ^ for applying a DC electric field to the active layer, the surface acoustic wave amplification characteristics were measured, but no amplification was observed.

 [Example 6]

After deposition of S i 0 ₂ 1 0 nm on a 64 degree Y-cut L i Nb 0 ₃ single crystal substrate having a diameter of 3 Inchi, by MB E method, A l o as a buffer layer. ₅ G a o. ₅ After growing Sb to 150 nm, and then growing InAs as an active layer to 350 nm, GaSb was grown to 2 nm as a protective layer to obtain a semiconductor layer. The electron mobility of this semiconductor layer was 22000 cn ^ ZVs.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 0.6, and the propagation length was 240 / m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the amplification degree was performed in the same manner as in Example 1. As a result of evaluating the surface acoustic wave amplifier of Example 6, the amplification was 2 dB at a DC applied voltage of 6 V and a center frequency of 150 OMHz. An amplification effect was obtained at a low voltage of 6 V. [Example 7]

After deposition of S i 0 ₂ 10 nm on the 64 ° Y Katsuhito L i Nb0 ₃ single crystal substrate having a diameter of 3 inches by MB E _{method, A 10.5 G a 0 .5 A} s ο.ι 2 as a buffer layer After growing Sb 0.88 to 150 nm and then growing InAs as an active layer to 50 nm, GaAs was grown to 2 nm as a protective layer to obtain a semiconductor layer. The electron mobility of this semiconductor layer is 13000

s.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes having a pitch of 1.4 / m, and the propagation length was 560 m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

 Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the amplification degree was performed in the same manner as in Example 1. As a result of evaluating the surface acoustic wave amplifier of Example 7, the amplification was 6 dB at a DC applied voltage of 5 V and a center frequency of 810 MHz. An amplification effect was obtained at a low voltage of 5 V.

 [Embodiment 8]

After deposition of S i 0 ₂ 1 0 nm on a 64 ° Y Katsuhito L i Nb 0 ₃ single crystal substrate having a diameter of 3 inches by MB E method, A 1 0.5 G a 0.5 A s 0- 1 as a buffer layer the 2 S b 0. _{8 8} grown 0.99 nm, then mixture was allowed I n a s is a 20 nm grown as the active layer, to obtain a semiconductor layer was G a S b is a 2 nm growth as a protective layer. The electron mobility of this semiconductor layer was 8000 cm ² ZVs.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 1.4 / m, and the propagation length was 560 / m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the amplification degree was the same as in Example 1. Was performed in the same manner. As a result of evaluating the surface acoustic wave amplifier of Example 8, the amplification was 3 dB at a DC applied voltage of 6 V and a center frequency of 835 MHz. An amplification effect was obtained at a low voltage of 6 V.

 [Embodiment 9]

After deposition of S i 0 ₂ 10 nm over the 64-degree Y-cut L i Nb 0 ₃ single crystal substrate having a diameter of 3 Inchi, by MB E _{method, A 1 o, 5 G a} 0 .5 A s As buffer layer ol 2 S b 0.8 ₈ was 0.99 nm growth, then mixture was allowed I n a s a is 10 nm grown as the active layer, to obtain a semiconductor layer is 2 nm grow G a Sb as a protective layer. The electron mobility of this semiconductor layer was 5000 cm ² ZVs.

 Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 0.75 / m, and the propagation length was 300 m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

 Next, the characteristics of the surface acoustic wave amplifier were measured. The evaluation of the amplification degree was performed in the same manner as in Example 1. As a result of evaluating the surface acoustic wave amplifier of Example 9, the amplification was 4 dB at a DC applied voltage of 6 V and a center frequency of 1560 MHz. An amplification effect was obtained at a low voltage of 6 V.

 [Comparative Example 3]

Comparative Example 3 is shown as a comparison with Example 7. After deposition of S i 0 ₂ 10 nm on the 64 ° Y cut L i Nb 0 ₃ single crystal substrate having a diameter of 3 Inchi, by MB E method, after the I n A s as the active layer was 50 nm grown As a protective layer, 2 nm of GaSb was grown to obtain a semiconductor layer. The electrical characteristics of this semiconductor layer were measured. In this comparative example, the active layer InAs was formed directly on the piezoelectric substrate, so the crystallinity of the active layer was poor and the electron mobility was 900 cm ² ZV s.

Next, the semiconductor layer at a predetermined position is removed by etching to expose the piezoelectric substrate. Was. Interdigital A1 electrodes were formed on the surface of the piezoelectric substrate as input and output electrodes by a lithography process. The electrodes were regular electrodes with a pitch of 1.4, and the propagation length was 56 Om. After successively forming an electrode for applying a DC electric field to the active layer, the force ^s for measuring the surface acoustic wave amplification characteristics, and no amplification was observed.

EXAMPLE 1 0] - on the 1 2 8 degrees Y cutlet preparative L i Nb 0 ₃ single crystal substrate having a diameter of 3 inches and more MB E method, A 1 0.5 G a 0.5 A sn S b 0.9 a buffer layer Was grown to 50 nm, and then InSb was grown to 400 nm as an active layer to obtain a semiconductor layer. The semiconductor layer had an electron mobility of 700 cm ² / Vs and a carrier concentration of 1 XI 0 ¹⁶ cm ⁻³ .

 Next, a surface acoustic wave amplifier was manufactured in the same manner as in Example 1. The electrodes were regular electrodes with a pitch of 0.75, and the propagation length was 300 μm.

As a result of measuring the characteristics of the surface acoustic wave amplifier, the amplification was 3 d 3 at a DC applied voltage of 5 V and a center frequency of 1500 1. An amplification effect was obtained at a low voltage of 5 V. Moreover even without the dielectric film, such as S i 0, degradation of L i N b 0 ₃ degradation of the substrate and _{L i Nb 0 3 I n S} b ¾14 layer due to oxygen diffusion from the substrate has failed observed. From the above results, it was confirmed that functions as a protective film of _{A 1 0.5 G a 0. 5} A s oj S b 0.9 buffer layer forces the piezoelectric substrate contact and the semiconductor active layer.

 [Comparative Example 4]

On the 6 4 ° Y Katsuhito L i Nb 0 ₃ single crystal substrate having a diameter of 3 inches and more MB E, direct, to obtain a semiconductor layer is 5 0 nm grow I n S b of the active layer. And since has been measured electrical characteristics of the semiconductor layer, which without forming a protective layer such as a dielectric film to L i Nb 0 ₃ on the substrate in this comparative example, the growth of the direct I n S b, L i Nb 0 Oxygen elimination from ₃ deteriorated the quality of the InSb film in the active layer, and the electron mobility could not be measured. Difficult case 1 1】

 A surface acoustic wave amplifier whose sectional structure is shown in FIG. 9 was manufactured.

First, ID-Pt electrodes, which are ID-shaped, are used as input / output electrodes 4 and 5 at regular positions on a 128-degree Y-cut L i NbO ₃ single-crystal substrate 1 with a 3-inch diameter. Formed by a lithodaraphy process by light exposure. Electrodes 4 and -5 were regular electrodes with a pitch of 1.4 m, and the propagation length was 364. Then, the MB E method, A 10.38 I n ₀ as a buffer layer 2 in a manner to embed the input and output interdigital transducers on said substrate. 6 ₂ S b was 0.99 nm growth, further I n S as an active layer 3 b was grown to 50 nm to obtain a semiconductor layer. The electron mobility of this semiconductor layer is 34000 cm ² ZVs.

 Next, after removing the active layer at a predetermined position by an ion milling method, an electrode 6 for applying a DC electric field was formed on the active layer 3 (FIG. 9 shows a cross-sectional structure). After that, a silicon nitride film for passivation was deposited, a window was opened, and the characteristics of the surface acoustic wave amplifier were measured. As a result, a large amplification of 17 dB was obtained at a DC applied voltage of 6 V and a center frequency of 809 MHz.

 [Example 12]

 A surface acoustic wave amplifier whose sectional structure is shown in FIG. 10 was manufactured.

By laser ablation method, on the Y cut L i T a 0 ₃ single crystal substrate 1, to grow L i Nb0 ₃ layer 17 having a thickness of 2.0 m, further L i T 30 _3-layer 18 of 0.1 thereon After growth, a multilayer piezoelectric substrate having a three-layer structure was formed. Results The grown thin film was analyzed by O one oxygenate electron spectroscopy, it was confirmed that L i Nb0 ₃ layer 17 with no deviation in Sutoikiome tree, L i T a 0 ₃ layer 18 is obtained. Also, by X-ray diffraction, (110) Li Nb0 ₃ layer 17 and (1 10) Li TaO 3 layer 18 are twin, domain-free and heteroepitaxially grown? In order to measure the electromechanical coupling constant of this multilayer piezoelectric substrate, an A1 comb-shaped electrode was formed by a normal lithography process so that the wavelength of the surface acoustic wave was 8 m. Then, when the electromechanical coupling constant was measured with a network analyzer, it showed a very large value of 20.0%.

 Further, using the multilayer piezoelectric substrate, a surface acoustic wave amplifier as shown in FIG. 10 was produced in the same manner as in Example 10. When the characteristics of the surface acoustic wave amplifier were measured, an increase of 12 dB was confirmed at a DC applied voltage of 5 V and a center frequency of 1500 MHz. It was confirmed that the multi-layer piezoelectric substrate having an extremely large electromechanical coupling constant of this embodiment has an effect of improving the amplification degree by about four times in the surface acoustic wave amplifier as compared with the tenth embodiment.

 [Comparative Example 5]

The electromechanical coupling constant of the multilayer piezoelectric substrate of Example 12 was compared with the electromechanical coupling constant of the material constituting each layer and the two-layer piezoelectric substrate. Measurement of the electromechanical coupling constant of the material itself constituting the layers in the same manner as in Example 12, a single crystal (110) L i N b 0 3 is 4.7%, the single crystal (1 10) L i T a 0 ₃ was 0.68%.

In addition, the electromechanical coupling constant when each constituent material had a two-layer structure was also measured. Immediate Chi, similarly grown Rezaabure one Chillon method was i Nb0 ₃ film and Y cut L i Ta0 ₃ Example 12 onto the substrate to measure the electromechanical coupling constant. As a result, the two-layer structure of _{L i Nb0 3 ZL i Ta03,} 3 · 0%, is lower than the single crystal _{(110) L i Nb 0 3} .

 Therefore, it can be seen that the electromechanical coupling constant is significantly improved only when the multilayer piezoelectric substrate of the present invention has a three-layer structure. In the twelfth embodiment, the improvement is about four times, which leads to an improvement in the amplification of the surface acoustic wave amplifier.

[Example 13] And growing a semiconductor layer in Example 1 0 the same manner as in 1 28 ° Y cutlet preparative L i Nb0 ₃ substrate. Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. On the surface of the piezoelectric substrate, an interdigitated A1-Cu / Cu / A1-1Cu laminated film electrode was formed by a lithography process as an input / output power-resistant electrode. The electrodes were regular electrodes with a pitch of 0.75 m, and the propagation length was 300 m. Subsequently, an electrode for applying a DC electric field was formed on the active layer.

 The characteristics of the surface acoustic wave amplifier were evaluated by applying an RF signal from a signal generator (Anritsu MG3670A) and measuring the amplification and transmission power using a power meter and a power sensor (Yokokawa Hewlett Packard, 437B, 8481H). The amplification factor is 22 dB at a DC applied voltage of 3 V and a center frequency of 152 OMHz, and the transmission power is 2.2 W. The surface acoustic wave amplifier of this embodiment has good power for high-frequency parts such as mobile communication equipment. It can be used as an amplifier, and can greatly contribute to downsizing of equipment.

 [Example 14]

And growing a semiconductor layer in Example 1 0 similarly to 1 28 ° Y cutlet preparative L i Nb 0 ₃ substrate. Next, a force for processing the semiconductor layer so as to be between input / output electrodes to be formed later was simultaneously etched so as to separate the semiconductor layer into three as shown in FIG. Then, interdigital A1 electrodes were formed as input / output electrodes on the exposed surface of the piezoelectric substrate. The electrode pitch and the propagation length are the same as in the tenth embodiment. Subsequently, an electrode for applying a DC electric field was formed on each of the separated active layers.

 The characteristics of the surface acoustic wave amplifier of this example were evaluated by applying a DC electric field to each active layer in parallel. As a result, the amplification was 8 dB at a DC applied voltage of 5 V and a center frequency of 1,500 MHz. It was confirmed that the amplification degree was improved about three times as compared with Example 10.

 [Example 15]

A surface acoustic wave convolver having a cross-sectional structure shown in FIG. 11 was manufactured. Was grown buffer layer 2 and the Do that semiconductor layer on Example 1 0 Similarly 1 28 ° Y cut and L i Nb0 ₃ substrate 1. Next, the semiconductor layer at a predetermined position was removed by etching to expose the piezoelectric substrate. On the surface of the piezoelectric substrate 1, two input electrodes 4, 4 were formed by a lithography process. Subsequently, as shown in FIG. 11, extraction electrodes 19 were formed on the upper surface of the semiconductor layer and the lower surface of the piezoelectric substrate, respectively, to produce a surface acoustic wave convolver.

 Next, using the surface acoustic wave convolver of the present embodiment, the amplification characteristics at a frequency of 1000 MHz were measured by a frequency analyzer, and a convolution output as a non-linear signal was obtained from the output electrode 19. Was.

 [Example 16]

Using the surface acoustic wave amplifier, the mixer, and the quadrature demodulator manufactured in Example 1, a receiving circuit of an RF unit of a mobile phone was manufactured. No special circuit is provided between the surface acoustic wave amplifier and the mixer for impedance matching. Normally, only the surface acoustic wave amplifier was used in the part composed of the low-noise amplifier and the high-frequency bandpass filter. The π / 4 QP SK modulated RF signal is supplied from the signal generator to the RF receiver circuit of the mobile phone fabricated as described above, and the IQ output signal after reception is received by a vector signal analyzer (Yokokawa Hewlett The demodulation error was measured using Parckard 89441 A). The maximum error vector was 16% rms when the input signal strength was -10 to 102 dBm. As a result of comparing the input data with the demodulated data, there was no error in the demodulated data. The noise figure and amplification of the surface acoustic wave amplifier were measured using a noise figure meter (Yokokawa Hewlett Parckard 8970B) and a noise source (Yokokawa Hewlett Packard 346B). As a result, the noise figure is 2.5 dB and the amplification is 14 dB at 810 MHz, and the noise figure is 3 dB, the amplification is 12 dB at 826 MHz, and the noise figure is 1.8 dB at 815 MHz. The degree was 16 dB. Also. Network attenuation characteristics outside the passband It was measured using an analyzer. The insertion loss was 35 dB at 94 OMHz and 40 dB at 956 MHz. From the above, it was confirmed that a receiving circuit using a surface acoustic wave amplifier instead of the low-noise amplifier and bandpass filter was possible. Further, by using the surface acoustic wave amplifier of the present embodiment, the high-frequency low-noise amplifier can be made monolithic, and the number of components of the receiving circuit can be reduced.

 [Example 17]

 Using a quadrature modulator, a mixer, a bandpass filter, and a surface acoustic wave amplifier, a transmitter circuit for the RF section of a mobile phone was fabricated. Usually, the surface acoustic wave amplifier of the present invention is used for a component constituted by a power amplifier. To this, an RF signal subjected to rZ4 QP SK modulation was supplied from a signal generator, and the output signal was measured for demodulation error using a vector signal analyzer. As a result, the magnitude of the error vector at a center frequency of 948 MHz was 5.5% rms. The transmission power at this time was 2.2 W. When the spectrum of the output signal was measured with a spectrum analyzer, it was confirmed that the system satisfies the Japanese digital car telephone system standard (RCR STD-27). From the above results, it was confirmed that the transmission circuit could be manufactured using a surface acoustic wave amplifier instead of the conventional power amplifier, and that the power embed unit could be reduced in size.

 [Example 18]

A transmission circuit of the RF section of the mobile phone similar to that in Example 17 was manufactured without using a bandpass filter. As a result, the magnitude of the error vector at a center frequency of 948 MHz was 4.0% rms. The transmission power at this time was 3.2 W, and it was confirmed that the transmission spectrum satisfied RCR STD-27. From the above results, a transmission circuit can be fabricated using a surface acoustic wave amplifier instead of the power amplifier module and bandpass filter of ί ^, and the power amplifier and bandpass filter can be made monolithic. ^That power was confirmed. [Example 19]

 A surface acoustic wave amplifier with a pass band of 810 to 826 MHz is used in place of the low noise amplifier and bandpass filter in the receiving circuit, and a surface acoustic wave amplifier with a pass band of 940 to 956 MHz is used as the power amplifier in the transmitting circuit. A transmission / reception circuit was fabricated using the filter instead of the bandpass filter. The same surface acoustic wave amplifier as that of the embodiment 16 was used for the receiving unit, and the same surface acoustic wave amplifier as that of the embodiment 17 was used for the transmitting unit. The antenna terminal and the transmission and reception circuits were connected by a microstrip line adjusted to have a characteristic impedance of 50 ohms without using a transmission / reception splitter. The reception characteristics and transmission characteristics of the transmission / reception circuit thus manufactured were measured in the same manner as in Examples 16 and 17. As a result of measuring the reception characteristics, the maximum error vector was 18% rms when the input signal strength was 110 to 102 dBm. Also, there was no error in the demodulated data at this time. As a result of measuring the transmission characteristics, the magnitude of the error vector at a center frequency of 948 MHz was 5.4% rms. At this time, the transmission power was 3.0 W, and it was confirmed that the transmission spectrum s' satisfied the RCR STD-27. From the above results, in the transmitting and receiving circuit of the RF section of the mobile phone, the surface acoustic wave was used as a substitute for the low noise amplifier and bandpass filter, as a substitute for the power amplifier module and bandpass filter, and as a substitute for the transmit / receive duplexer. It was confirmed that the circuit using the amplifier was usable. Therefore, the use of the transmission / reception circuit of the present embodiment enables a drastic reduction in the number of components in the RF section of conventional mobile communication devices, and dramatically reduces the size, weight, and cost of mobile device terminals. it can.

 [Comparative Example 6]

A typical size of a power amplifier module formed from a conventional GaAs FET or a capacitor is 2511111 1 2111111 3.7111111. On the other hand, the surface acoustic wave amplifier of Example 17 has a size of 5 mm × 5 mm × 2 mm. As a result, the size of the conventional power amplifier can be significantly reduced.

 By using the surface acoustic wave function element of the present invention, a significant improvement in the gain of the surface acoustic wave amplifier or an improvement in the efficiency of the surface acoustic wave convolver can be realized. Further, since the surface acoustic wave amplifier of the present invention can obtain a large amplification factor at a practically low voltage, it can be applied to a high-frequency unit such as a mobile communication device. Moreover,-amplifiers, bandpass filters, and transmission / reception duplexers, which have been used as discrete elements and were large in size, can be replaced with a single component. It can greatly contribute to weight reduction, thinning, and cost reduction.

Claims

The scope of the claims

1. A piezoelectric substrate, comprising: an input electrode and an output electrode on the piezoelectric substrate; and a semiconductor layer provided between the input electrode and the output electrode, wherein the semiconductor layer is an active layer and the active layer. A surface acoustic wave device comprising a buffer layer lattice-matched to the layer.

2. The surface acoustic wave device according to claim 1, wherein the buffer layer is a compound containing at least antimony.

3. The surface acoustic wave device according to claim 1, wherein the active layer is a compound containing at least indium.

4. The surface acoustic wave device according to claim 1, wherein the thickness of the active layer is 5 nm or more and 500 nm or less.

5. a piezoelectric substrate, comprising an input electrode and an output electrode on the piezoelectric substrate, wherein the piezoelectric substrate comprises at least two or more types of multilayer piezoelectric materials having three or more different electromechanical coupling constants; A surface acoustic wave functional element characterized in that a piezoelectric film at the center of a multilayer of a multilayer piezoelectric body has the largest electrical mechanical coupling constant.

6. The multilayer piezoelectric body consists of three layers, the piezoelectric film of the central portion is at L i N b 0 ₃ film, according to claim 5, wherein the other of the piezoelectric body is L i T a 0 ₃ An elastic surface wave functional element according to item 1.

7. The method according to claim 5, wherein a unidirectional converter is used as the input / output conversion. 7. A surface acoustic wave device according to claim 6.

8. The surface acoustic wave device according to claim 5, wherein a semiconductor layer is provided between the input / output electrodes.

9. The surface acoustic wave device according to claim 8, wherein the semiconductor layer comprises an active layer and a buffer layer lattice-matched to the active layer.

10. The surface acoustic wave function device according to claim 1, wherein a unidirectional converter is used as input / output conversion. 10.

11. The surface acoustic wave amplifier according to any one of claims 1 to 4, and 8 to 10, further comprising an electrode for applying a DC electric field to the semiconductor.

1 2. Between the input / output electrodes, two or more of the semiconductor layers are connected, and a structure in which carriers moving in the opposite direction are removed or a structure without an active layer between the semiconductor layers is provided. The surface acoustic wave amplifier according to claim 11, wherein:

1 3. The buffer layer in the form of input and output electrodes are embedded is formed, according to claim 1 1 surface acoustic wave amplifier as claimed in to that it is the layer ^forces? Formed on the buffer layer.

14. The surface acoustic wave amplifier according to claim 11, wherein the input / output electrode has a high power withstanding structure.

15. The piezoelectric device according to claim 1 to claim 4 and claim 8 to claim 10. A surface acoustic wave convolver, characterized in that two electrodes formed on a body substrate are both input electrodes, and uniform extraction electrodes are provided above the semiconductor layer and below the piezoelectric substrate.

16. The surface acoustic wave functional element according to claim 11 to claim 15 is configured as an amplifier and a bandpass filter or an amplifier and a bandpass filter and a transmission / reception duplexer in a transmission or reception circuit. A transmitting or receiving circuit.

17. The transmission or reception circuit of a mobile communication device according to claim 16, wherein the transmission or reception circuit is a transmission or reception circuit of a mobile communication device.