JP3702050B2 - Boundary acoustic wave device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a device in which two different solids are bonded to each other and an elastic boundary wave propagating to these boundary surfaces is applied. The elastic boundary wave using a piezoelectric material for one solid and a Si substrate for the other solid. Regarding devices.
[0002]
[Prior art]
A surface acoustic wave device (SAW device: Surface Acoustic Wave Device) is well known as one of devices to which an elastic wave is applied. This SAW device is, for example, various circuits in an apparatus for processing a radio signal in a frequency band of 45 MHz to 2 GHz, for example, a transmission band pass filter, a reception band pass filter, a local filter, an antenna duplexer, an IF filter, and an FM modulator. Used for etc.
[0003]
FIG. 14 shows the basic configuration of this SAW device. As shown in the figure, the SAW device is configured by providing interdigital transducers (IDT) 101 and 102 obtained by processing a metal material such as an Al thin film by etching or the like on a piezoelectric substrate 100 such as LiNbO _3. The When a high-frequency electric signal is applied to the IDT 101, the SAW 103 is excited on the surface of the piezoelectric substrate 100. The excited SAW 103 propagates on the surface of the piezoelectric substrate 100 and reaches the IDT 102, and is converted into an electric signal again in the IDT 102.
[0004]
[Problems to be solved by the invention]
By the way, in the SAW device, in order to use the boundary surface between the solid surface and the vacuum or gas, that is, the elastic wave propagating on the solid surface, the surface of the piezoelectric substrate as a propagation medium needs to be a free surface. Therefore, in a SAW device, for example, a chip cannot be covered with a plastic mold used for a semiconductor package, and it is necessary to provide a hollow portion for securing a free surface inside the package. However, the structure in which the hollow portion is provided inside the package has a problem that the device is relatively expensive and large.
[0005]
An object of the present invention is to address such a situation and to provide a boundary acoustic wave device that has functions equivalent to those of a SAW device and that can be easily reduced in size and cost.
[0006]
[Means for Solving the Problems]
In order to solve such a problem, the boundary acoustic wave device of the present invention is a substrate in which two substrates are bonded together, and an acoustic wave propagates to these boundary surfaces, one substrate being a Si substrate and the other substrate being LiNbO ₃ substrates were used, and these substrates were combined with the following cut surfaces and propagation directions.
[0007]
(1) Si substrate: [001] cut and <110> orientation propagation LiNbO ₃ : 175 ° rotation Y cut and X orientation propagation (2) Si substrate: [001] cut and <110> orientation propagation LiNbO ₃ : 125 ° rotation Y cut and X direction propagation (3) Si substrate: [001] cut and <100> direction propagation LiNbO ₃ : 133 ° rotation Y cut and X direction propagation (4) Si substrate: [001] cut and <100> direction propagation LiNbO ₃ : 175 ° rotation Y cut and X azimuth propagation (5) Si substrate: [110] cut and <110> azimuth propagation LiNbO ₃ : 19 ° rotation Y cut and X azimuth propagation, ie elastic boundary wave is between two kinds of solids The theoretical study on the existence of this boundary acoustic wave is, for example, “Propagating the boundary surface between ZnO and glass by Shimizu, Irino et al. That Theoretical Study of Stoneley Wave "ManabuShinron (C), J65-C, 11, are handled by Pp.883-890. In this paper, one of the two solids is handled as a combination of ZnO, which is a piezoelectric material, and the other is a combination of glass. In order to excite an elastic wave in at least one of the two solids, A boundary acoustic wave device can be realized if there is a wave that has piezoelectricity and propagates by concentrating the energy of the acoustic wave on the boundary surface between two kinds of solids.
[0008]
The inventors of the present invention have found that boundary acoustic waves exist at the interface where a Si substrate and a LiNbO ₃ substrate are newly bonded to each other, by means of elastic wave propagation analysis.
[0009]
The analysis results are shown in FIGS.
[0010]
In this analysis, using the [001] cut Si substrate, the cut orientation of the LiNbomikuron ₃ substrate case propagation direction of a boundary wave is Si to LiNbΟ ₃ Χ axis of the substrate and the <100> or <110> of the substrate matches the parameters The phase velocity, propagation loss, and electromechanical coupling coefficient (k ² : conversion efficiency from an electric signal to a boundary acoustic wave) were obtained by numerical analysis. 4 shows the phase velocity, FIG. 5 shows the propagation loss, and FIG. 6 shows the analysis result of the electromechanical coupling coefficient.
[0011]
From this analysis result, it can be seen that a boundary acoustic wave having a propagation loss of almost 0 and k ^{2 of} 11.6% can be obtained with the combination of Si [001] cut <110> propagation / 175 ° Y-Χ LiNbO ₃ .
[0012]
Further, Si [001] cut <110> propagation / 125 ° YX LiNbO ₃ , Si [001] cut <100> propagation / 133 ° Y-Χ LiNbO ₃ , Si [001] cut <100> propagation / 175 ° It was also found that the propagation loss was almost zero even with the combination of YX LiNbO ₃ .
[0013]
Furthermore, although not shown in the figure, a boundary acoustic wave having a phase velocity of 4.615 m / s, loss of approximately 0, and K ² of 9.8% with a combination of Si [111] cut <110> propagation / 19 ° YX LiNbO ₃ Was found to be obtained.
[0014]
The present invention makes it possible to propagate boundary acoustic waves on these boundary surfaces by using the combination of the Si substrate and LiNbO ₃ based on the analysis result. As a result, it has the same function as a SAW device, can directly cover the chip with a plastic mold, etc., can be manufactured by applying the semiconductor process as it is, and is equipped with other elements such as active elements. A boundary acoustic wave device that can also be realized.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
1 to 3 are diagrams showing a configuration of a boundary acoustic wave device according to an embodiment of the present invention. FIG. 1 is an exploded perspective view, FIG. 2 is a front view, and FIG. 3 is an arrow AA in FIG. FIG.
[0017]
As shown in these drawings, the boundary acoustic wave device 1 includes a dielectric film 4 having a comb-like groove 3 formed on the main surface of a Si substrate 2 and a conductive material embedded in the groove 3. Comb-like electrodes 5 are formed, and a LiNbO ₃ substrate 6 is laminated thereon.
[0018]
The Si substrate 2 is not intentionally reduced in specific resistance as n-type or p-type, as is normally used in semiconductor integrated circuits, and is 10 Ωcm in order to prevent DC leakage from the comb-like electrode 5. The above high resistance is preferable.
[0019]
The area of the main surface of the LiNbO ₃ substrate 6 is smaller than the area of the main surface of the Si substrate 2. For example, the main surface of the LiNbO ₃ substrate 6 may be attached only to an effective area necessary for propagation of boundary acoustic waves at the minimum. Thereby, it is possible to mount other elements such as an active element described later on the exposed surface 7 of the main surface of the Si substrate 2. In addition, since the LiNbO ₃ substrate 6 is relatively expensive compared to the Si substrate 2, the piezoelectric substrate material can be reduced and the cost can be reduced. However, the area of the main surface of the LiNbO ₃ substrate 6 and the area of the main surface of the Si substrate 2 can be made the same, and the area of the main surface of the LiNbO ₃ substrate 6 can be made equal to that of the main surface of the Si substrate 2. It is also possible to make it larger than the area.
[0020]
As described above, the Si substrate 2 and the LiNbO ₃ substrate 6 employ any one of the following combinations having a cut surface and a propagation direction.
[0021]
(1) Si substrate: [001] cut and <110> orientation propagation LiNbO ₃ : 175 ° rotation Y cut and X orientation propagation (2) Si substrate: [001] cut and <110> orientation propagation LiNbO ₃ : 125 ° rotation Y cut and X direction propagation (3) Si substrate: [001] cut and <100> direction propagation LiNbO ₃ : 133 ° rotation Y cut and X direction propagation (4) Si substrate: [001] cut and <100> direction propagation LiNbO ₃ : 175 ° rotation Y cut and X azimuth propagation (5) Si substrate: [110] cut and <110> azimuth propagation LiNbO ₃ : 19 ° rotation Y cut and X azimuth propagation dielectric film 4 is made of, for example, SiO ₂ Used. Thereby, SiO ₂ can be formed only by oxidizing the main surface of the Si substrate 2. However, another dielectric film 4 may be formed intentionally.
[0022]
For example, Al is used for the comb-like electrode 5. However, other conductive materials can be used. For example, the comb-like electrode 5 includes a pair of opposing comb-like electrodes 8 for excitation and a pair of opposing comb-like electrodes 9 for reception. However, a plurality of these electrodes may be provided. In addition to the comb-like electrode 5, for example, a reflective electrode may be provided so as to sandwich these electrodes. Furthermore, not only such electrodes but also a sound absorbing material may be formed so as to sandwich these electrodes, for example. In short, the boundary acoustic wave device according to the present invention is used in place of, for example, a conventional SAW device, that is, a filter, a delay line, a resonator, an oscillator, an analog signal processing circuit, an amplifier, a convolver memory, etc. However, the configuration of the comb-like electrode 5 and the like is appropriately changed in design according to these uses, specifications, and the like.
[0023]
Next, a method for manufacturing this boundary acoustic wave device will be described.
[0024]
FIG. 7 is a view for explaining an embodiment according to the manufacturing method.
[0025]
First, an SiO ₂ film 71 of about 0.1 to 2 μm is formed on the Si substrate 70 by, eg, thermal oxidation (FIG. 7A).
[0026]
Next, the comb-like groove 72 is patterned on the SiO ₂ film 71 by, for example, CD (Cemical Dry Ecthing) (FIG. 7B).
[0027]
Next, an Al film 73 is formed by sputtering, for example, so as to cover the SiO ₂ film 71 (FIG. 7C).
[0028]
Next, the surface of the silicon film 73 is polished until the SiO ₂ film appears (FIG. 7D).
[0029]
As a result, an electrode (comb-like electrode 74) in which Αl is embedded in the groove 72 of the SiO ₂ film 71 is formed.
[0030]
Next, by subjecting the main surface of the Si substrate 70 on which the SiO ₂ film 71 and the comb-like electrode 74 are formed and the main surface of the LiNbO ₃ substrate 75 to surface treatment with, for example, aqueous ammonia peroxide, both surfaces are hydroxylated. (FIG. 7 (e)).
[0031]
Next, the main surface of the Si substrate 70 and the main surface of the LiNbO ₃ substrate 75 are brought into contact with each other and heated at about 300 ° C. for about 1 to 2 hours (FIG. 7F).
[0032]
By such heat treatment, OH groups on the two kinds of substrate surfaces are bonded to each other to release H ₂ O, and the Si substrate 70 and the LiNbO ₃ substrate 75 which are different materials can be directly bonded. The heating temperature is preferably about 300 ° C, but can be between 100 and 1000 ° C. This is because the reaction of bonding OH groups does not occur at 100 ° C. or lower, and there is a possibility that the element member may be adversely affected by heat at 1000 ° C. or higher.
[0033]
Eda et al .: “Direct bonding of piezoelectric materials” IEICE Technical Report US95-24.ΕMD95-20, CPM95-32. (1995-07), pp.31 -38 is also reported. The Si substrate and the LiNbO ₃ substrate can be easily joined by a method other than the above as described in the report by Eda et al.
[0034]
In the boundary acoustic wave device formed through the above manufacturing process, the comb-tooth-shaped electrode 74 for exciting the boundary wave can be formed on the Si substrate 70, so that the normal semiconductor device manufacturing technique is directly used. be able to.
[0035]
In the above manufacturing method, the SiO ₂ film 71 and the comb-like electrode 74 are formed in advance on the Si substrate 70. However, the SiO ₂ film 71 and the comb-like electrode 74 are formed on the LiNbO ₃ substrate 75 in advance, A boundary acoustic wave device having a similar structure can also be manufactured by a method of directly attaching to the Si substrate 70.
[0036]
FIG. 8 shows another configuration method of the comb-shaped electrode in the boundary acoustic wave device of the present invention.
[0037]
First, comb-shaped grooves 81 of about 0.1 to 2 μm are formed on the Si substrate 80 by processing such as ion milling (FIG. 8A).
[0038]
Next, an Al film 82 is formed on the Si substrate 80 so as to cover the groove 81 by, eg, sputtering (FIG. 8B).
[0039]
Next, the surface of the Al film 82 is polished until the surface of the Si substrate 80 appears (FIG. 8C).
[0040]
As a result, an electrode (comb-like electrode 83) in which Αl is embedded in the groove 81 on the surface of the Si substrate 80 is formed.
[0041]
Next, an example in which another element such as an active element is mounted on the Si substrate will be described.
[0042]
FIG. 9 shows an example of this. A comb-like electrode (not shown) is formed in the first region 121 on the main surface of the Si substrate 120, and a LiNbO ₃ substrate 122 is bonded to cover this. Yes. An integrated circuit 124 is formed in the second region 123 that is an exposed region of the main surface of the Si substrate 120. As a result, for example, a functional device such as a programmable filter circuit element can be configured on one chip.
[0043]
10 and 11 show examples in which the boundary acoustic wave device shown in FIG. 9 is mounted on a printed wiring board.
[0044]
As shown in FIG. 10, a bonding pad 134 is formed in the second region 133 on the main surface of the Si substrate 132 of the boundary acoustic wave device 131. The boundary acoustic wave device 131 is mounted at a predetermined position on the printed wiring board 135, and a bonding pad 134 of the boundary acoustic wave device 131 and a bonding pad 136 provided at a predetermined position on the printed wiring board 135 are bonding wires. 137 is connected. A resin seal 138 is covered with polyimide, epoxy resin or the like so as to cover them.
[0045]
FIG. 11 shows another example. As shown in FIG. 11, a through hole 144 is formed in the Si substrate 142 of the boundary acoustic wave device 141 from the main surface circuit portion to the back surface pad 143. The boundary acoustic wave device 141 is mounted at a predetermined position on the printed wiring board 145, and the pad 143 of the boundary acoustic wave device 141 and the pad 146 provided at the predetermined position on the printed wiring board 145 are connected by the bump 147. Has been. A resin seal 148 is made of polyimide, epoxy resin or the like so as to cover them.
[0046]
The boundary acoustic wave device according to the present invention is used in, for example, a filter, a delay line, a resonator, an oscillator, an analog signal processing circuit, an amplifier, and a convolver memory. Filters, delay lines, resonators, and the like provided with these boundary acoustic wave devices are used for mobile phones, PHS, TVs, and the like.
[0047]
FIG. 12 is a block diagram showing the configuration of a mobile communication device such as a mobile phone or PHS. As shown in the figure, the received wave received via the antenna 151 is separated into a reception system by the antenna duplexer 152. The separated reception signal is amplified by the amplifier 153, and then a desired band is extracted by the reception band pass filter 154 and input to the mixer 155. The local signal generated by the PLL oscillator 156 is input to the mixer 155 via the local filter 157. The output of the mixer 155 is output as received sound from the speaker 160 via the IF filter 158 and the FM demodulator 159. On the other hand, the transmission sound input from the microphone 161 is input to the mixer 163 via the FM modulator 162. The local signal generated by the PLL oscillator 164 is input to the mixer 163. The output of the mixer 163 is output as a transmission wave from the antenna 151 via the transmission band-pass filter 165, the power amplifier 166, and the antenna duplexer 152.
[0048]
The boundary acoustic wave device according to the present invention can be used for each part of the mobile communication device. For example, the boundary acoustic wave device according to the present invention is used as an RF stage filter for the transmission band-pass filter 165, the reception band-pass filter 154, the local oscillation filter 157, and the antenna duplexer 152. In the IF filter 158, the boundary acoustic wave device according to the present invention is used as a narrow-band IF stage filter indispensable for channel selection. In the FM modulator 162, the boundary acoustic wave device according to the present invention is used as a resonator in sound FM modulation.
[0049]
The boundary acoustic wave device according to the present invention can also be used in an oscillation circuit of an RF modulator used in a VTR or CATV. The circuit configuration is shown in FIG. A comb-like electrode 167 is formed in the first region 121 of the main surface of the Si substrate 120 shown in FIG. 9, and a circuit portion 168 is formed in the second region 123, so that this oscillation circuit is configured by one chip. be able to.
[0050]
【The invention's effect】
As described in detail above, the boundary acoustic wave device of the present invention has the same function as the SAW device, can directly cover the chip with a plastic mold or the like, and is manufactured by applying the semiconductor process as it is. In addition, it is possible to mount other elements such as active elements, which facilitates downsizing and cost reduction.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing a configuration of a boundary acoustic wave device according to an embodiment of the present invention.
FIG. 2 is a front view of FIG. 1;
FIG. 3 is a plan view taken along arrow AA in FIG. 2;
FIG. 4 is a diagram showing the analysis result of the phase velocity of the boundary acoustic wave according to the present invention.
FIG. 5 is a diagram showing an analysis result of propagation loss of a boundary acoustic wave according to the present invention.
FIG. 6 is a diagram showing an analysis result of an electromechanical coupling coefficient of a boundary acoustic wave according to the present invention.
FIG. 7 is a process diagram for explaining an embodiment according to a method of manufacturing a boundary acoustic wave device of the present invention.
FIG. 8 is a process diagram showing another method of configuring a comb-shaped electrode in the boundary acoustic wave device of the present invention. It is a front view which shows other embodiment of the elastic boundary wave device of this invention.
FIG. 9 is a perspective view showing another embodiment of the boundary acoustic wave device of the present invention.
FIG. 10 is a front view showing an example in which the boundary acoustic wave device of the present invention is mounted on a printed wiring board.
FIG. 11 is a front view showing another example in which the boundary acoustic wave device of the present invention is mounted on a printed wiring board.
FIG. 12 is a block diagram showing a configuration of a mobile communication device in which the boundary acoustic wave device of the present invention is used.
FIG. 13 is a circuit diagram of an oscillation circuit of an RF modulator in which the boundary acoustic wave device of the present invention is used.
FIG. 14 is a perspective view showing a basic configuration of a SAW device.
[Explanation of symbols]
1 boundary acoustic wave device 2 first substrate 3 comb-shaped grooves 4 dielectric film 5 interdigital electrode 6 LiNbO ₃ substrate 7 exposed surface

Claims (5)

A boundary acoustic wave device in which two substrates are bonded to each other, and an elastic wave propagates to these boundary surfaces,
A boundary acoustic wave device characterized in that one substrate is a [001] cut and <110> azimuth propagation Si substrate, and the other substrate is a 175 ° rotated Y cut and X azimuth propagation LiNbO ₃ substrate. . A boundary acoustic wave device in which two substrates are bonded to each other, and an elastic wave propagates to these boundary surfaces,
A boundary acoustic wave device characterized in that one substrate is a [001] cut and <110> azimuth propagation Si substrate, and the other substrate is a 125 ° rotated Y cut and X azimuth propagation LiNbO ₃ substrate. . A boundary acoustic wave device in which two substrates are bonded to each other, and an elastic wave propagates to these boundary surfaces,
A boundary acoustic wave device characterized in that one substrate is a [001] cut and <100> azimuth propagation Si substrate, and the other substrate is a 133 ° rotated Y cut and X azimuth propagation LiNbO ₃ substrate. . A boundary acoustic wave device in which two substrates are bonded to each other, and an elastic wave propagates to these boundary surfaces,
A boundary acoustic wave device characterized in that one substrate is a [001] cut and <100> azimuth propagation Si substrate, and the other substrate is a 175 ° rotated Y cut and X azimuth propagation LiNbO ₃ substrate. . A boundary acoustic wave device in which two substrates are bonded to each other, and an elastic wave propagates to these boundary surfaces,
One substrate is a [110] cut and <110> azimuth propagation Si substrate, and the other substrate is a 19 ° rotation Y cut and X azimuth propagation LiNbO ₃ substrate. .

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