JPH03220911A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To contrive miniaturization by providing an impedance matching circuit composed of plural film circuit elements on the inner and outer exposure faces of a package or between the layers of the ceramic package. CONSTITUTION:An impedance matching circuit composed of plural film circuit elements 5 is provided on the inner and outer exposure faces of the package 2 or between the layers of the ceramic package 2 to constitute this surface acoustic wave filter 10. Since the impedance matching circuit is integrated with the ceramic package 2 with the plural film circuit elements 5 provided between the layers of the ceramic package 2 or the inner and outer exposure faces of the package 2 in such a manner, it is not required to add another impedance matching circuit at the outside to constitute the filter circuit and the entire size of the filter circuit 10 is miniaturized.

Description

[Detailed Description of the Invention] [Summary] Regarding the structure of a surface acoustic wave filter, the purpose is to miniaturize a surface acoustic wave filter including an impedance matching circuit. In a surface acoustic wave filter formed by sealing a surface acoustic wave filter element with electrodes in a ceramic package, a plurality of membrane circuit elements are formed between the layers of the ceramic package or on the exposed inner and outer surfaces of the package. An impedance matching circuit is provided to configure a surface acoustic wave filter.

[Industrial application field]

The present invention relates to a surface acoustic wave filter, and particularly to a small filter structure in which an impedance matching circuit is incorporated in a ceramic package.

In recent years, demands for miniaturization and portability of information processing equipment and communication equipment have been increasing, and along with this, there has been a strong demand for miniaturization of signal processing filter circuits.

Generally, high frequency filter circuit (for example, 700MH
Dielectric resonator filters, which are often used in 2-band or higher filters, are large in size and heavy in weight, making them unsuitable for use in, for example, portable communication equipment.
There is a need for the development of filter devices that can significantly reduce the size of filter circuits.

[Conventional technology]

Recently, surface acoustic wave filters have attracted particular attention as small filter elements in high frequency bands.

A surface acoustic wave element, for example, a surface acoustic wave filter, is made of a piezoelectric substrate having a large electro-mechanical coupling coefficient and a relatively small frequency temperature coefficient, for example, a 36° rotation Y-cut to X-propagation LiTa03 (36° Y-X LiTa03
) It is a three-terminal or four-terminal device in which comb-shaped electrodes for input and output are provided on a single crystal substrate.

FIG. 8 is a diagram showing the configuration of a surface acoustic wave filter. In the figure, reference numeral 1 denotes a surface acoustic wave filter element, which is composed of a comb-shaped manual electrode 12 with comb-shaped electrode fingers made of AI or the like interposed therebetween and a comb-shaped output electrode 13 facing each other on a piezoelectric substrate 11. . The width of the electrode fingers (space), the pitch, the number of electrode fingers, the length of each electrode finger (the weighting is determined by the shape and the required filter characteristics.Due to their structure, these comb-shaped input/output electrodes always have parallel capacitance. Therefore, when connecting the surface acoustic wave filter element to another high frequency circuit, in order to prevent signal reflection, the impedance matching circuit 6 (6a and 6b) that cancels out the parallel capacitance is connected to the surface acoustic wave filter element. must be connected to the input/output terminals of

FIG. 9 is a diagram showing an equivalent circuit of a surface acoustic wave filter including a matching circuit. Figure (a) shows a parallel inductance type, with a parallel inductance Lp f l between the input terminals, and a parallel inductance LPo between the output terminals, while figure (b) shows a parallel capacitance type, with a series inductance Ls between the input and output terminals. Ls. are connected to each other, and parallel capacitors CPi + CPo are connected to the input and output terminals, and both have electrode capacitances CTi + CT. I'm trying to cancel it. In the figure, B and Bo are the radiation conductances of the comb-shaped manual electrode 12 and the comb-shaped output electrode 13, G, , G
. is also the radiation susceptance. The parallel capacitance type is suitable for circuits to which direct current is applied in order to avoid short-circuiting between terminals.

Figure 1O is a diagram showing an example of a conventional surface acoustic wave filter. Figure (A) is a perspective view with the lid removed to reveal the internal state, and Figure (B) is a perspective view of the product with the lid removed. The AA' cross-sectional view and the same figure (c) are the same<BB' cross-sectional views.

The ceramic package 2' is made of, for example, three layers of alumina ceramic, in which a second layer 22' and a first layer 21' having square holes of different sizes are laminated and fired on a plate-shaped third layer 23'. Between the first layer 21' and the second layer 22°, there are electrode terminal wiring parts 100°, 200', 300'.
, 400' metal pattern is formed, and further extends from the opening center part of the third layer 23' to the ground electrode terminal wiring part 300°.

Metal patterns 350° connected at 400° are integrally formed at the same time. The surface acoustic wave filter element 1 is die-bonded to the metal pattern 350' in the square hole of the central opening, for example, with a conductive adhesive, and the terminal pads of the element and the electrode terminal wiring parts 100', 200' are bonded.
. is formed.

In this example, from the side surface to the bottom surface of the ceramic package 2°, the electrode terminal wiring portions too', 200',
Since the 300° and 400° extensions are exposed to the outside as shown in the figure, surface mounting technology can be applied to connection with an external circuit. This is the case with a so-called leadless chip carrier (LCC) type package.

FIG. 11 is a diagram showing an example of a conventional impedance matching circuit formed on a printed circuit board. FIG. 11A shows a parallel inductance type circuit, and FIG. 11B shows a parallel capacitance type circuit.

For example, when mounting the surface acoustic wave filter 10° on the printed circuit board 500 to configure a filter circuit,
In the example of the same figure (a), the impedance matching circuit 6°a,
6' b as parallel inductance L.

L. is composed of a meander pattern formed at the same time as the conductor wiring pattern of the printed circuit board.In the example shown in the same figure (b), the series inductance LSi + LSo is formed as the impedance matching circuit 6''a, 6''b with the same conductor wiring pattern of the printed circuit board. It consists of a meander pattern formed simultaneously with the parallel capacitance Cp I+ Cp. For example, a chip controller is mounted and connected to each of the filter circuits using SMT technology to form a filter circuit.

[Problem to be solved by the invention]

However, in the configuration of the impedance matching circuit shown in the above conventional example, the surface acoustic wave filter lO.

Even if the impedance matching circuit 6' becomes smaller,
a, 6"b, 6"a, and 6"b occupy a large mounting area on the printed circuit board 500, impeding the miniaturization of the entire circuit, and causing damage to the meander pattern of the inductance element, resulting in problems in terms of reliability. This is a problem and requires a solution.

[Means to solve the problem]

The problem described above is that the comb-shaped input electrode 12 is placed on the piezoelectric substrate 11.
In a surface acoustic wave filter formed by sealing a surface acoustic wave filter element 1 in which a comb-shaped output electrode 13 is disposed in a ceramic package 2, a plurality of layers are formed between the layers of the ceramic package 2 or on the exposed inner and outer surfaces of the package. This problem can be solved by configuring a surface acoustic wave filter by providing an impedance matching circuit 6 formed from a membrane circuit element 5.

[Effect]

According to the present invention, the impedance matching circuit is formed integrally with the ceramic package 2 by a plurality of membrane circuit elements 5 between the layers of the ceramic package 2 that accommodates the surface acoustic wave filter element 1 or on the exposed inner and outer surfaces of the package. Therefore, there is no need to add a separate external impedance matching circuit to configure the filter circuit, and the entire filter circuit can be made smaller.

〔Example〕

FIG. 1 is a sectional view showing a first embodiment of the present invention, which is of a parallel inductance type. In the figure, l is a surface acoustic wave filter element, for example, made of a 36°Y-XLiTaO3 single crystal plate with a thickness of 0.5 mm and a size of 2 mm x 4 mm.
A comb-shaped manual electrode 12 with comb-shaped electrode fingers made of Af having a thickness of 200 nm and a comb-shaped output electrode 13 are disposed facing each other on a piezoelectric substrate 11, and the width of the electrode fingers is 9 intervals ( Space), pitch, number, length of each electrode finger (weighting is shape), etc. are determined by the required filter characteristics.
In this example, in order to obtain a center frequency of 800 MHz, the thickness of the electrode fingers is 1.2 μm, and the comb-shaped input and output electrodes are each 1.5 μm thick.
A pair of regular electrode fingers was used.

The external dimensions of the ceramic package 2 are 5 mm in height and 6 mm in size x 6 mm, and is made of, for example, four layers of alumina ceramic, with a square hole-sized hole formed on the plate-shaped fourth layer 24 and the third layer 23. Different second layers 22° and first layers 21 are laminated and fired, and electrode terminal wiring parts 100, 200, 300° 400 are formed between the first layer 21 and the second layer 22, and, for example, there are A thick film printed tungsten (W) with a thickness of 15 μm is formed, and a ground electrode terminal wiring portion 300.40 is formed at the center of the opening on the third layer 23 and from there.
Furthermore, a film circuit element 5 also made of W film is placed on the ceramic plate of the fourth layer 24, that is, between the third layer 23 and the metal pattern 350 made of W to be connected to the metal pattern 350. The whole is stacked in this order and fired at high temperature to form an integrated ceramic package.Finally, Ni is deposited on the W film exposed on the inner and outer surfaces of the ceramic package, and then a thick layer is applied on top of the W film. 1~2μ
The ceramic package 2 is completed by forming an external electrode metal pattern consisting of three layers plated with m of Au.

The above process involves applying thick film tungsten (
W) Layer the printed paste and fire it to form a body. This can be easily carried out by the so-called green sheet method.

A surface acoustic wave filter element l is placed in the square hole portion of the central opening.
For example, on the Au film of the metal pattern 350,
(g) Die bonding is performed using the conductive adhesive layer 450 or Au-3n eutectic between the terminal pad of the element and the electrode terminal wiring portion 100, 200, 300, and 400.

For example, AI! Alternatively, if the connection is made with a bonding wire 4 made of Au, and finally, the lid plate 3 made of, for example, a ceramic plate is hermetically sealed on the upper surface of the first layer 21 with, for example, an epoxy resin adhesive, the elasticity of the present invention can be improved. A surface wave filter IO is formed.

FIG. 2 is a diagram showing the main parts of the first embodiment of the present invention.
(A) is a matching circuit pattern diagram of the first embodiment, and (B) is a diagram of the bottom electrode pattern of the first embodiment. In the figure, 10
0 is the input terminal, 200 is the output terminal, 300 and 400
is a ground terminal connected to the Guihonding pad 350 of the surface acoustic wave filter element 1. 5I! is a membrane circuit element (a strip line is sandwiched between dielectrics; a so-called balanced microstrip line inductance element), and for example, as described above, the thickness is 15 μm.
A parallel inductance of 12 to 13 nH was obtained by forming a meander line with a width of about 130 μm and a length of about 13 mm.

External terminals 100, 200, 300.
400, it can be mounted, for example, on a predetermined wiring pad portion on the printed circuit board 500 by SMT technology.

The above embodiment is suitable for SMT packaging technology. So-called LC
Although we have shown an example in which the present invention is applied to a C package,
It goes without saying that the present invention is similarly applicable to ceramic packages with leads. Further, the package material is not limited to alumina ceramic, but other ceramic materials may also be used.

FIG. 3 shows a second embodiment of the present invention, in which (a) is a sectional view taken along the line xx' and (b) is a bottom view.

In this embodiment, the fourth layer 24 in the first embodiment is omitted,
In the case where a membrane circuit element 51 (in this case, an inductance element formed by an unbalanced microstrip line) is provided on the bottom surface of the third layer 23, it has a feature that is advantageous in terms of package formation, but mounting on a printed circuit board is difficult. At this time, since the membrane circuit element 51 (inductance element) is exposed outside the package, it is necessary to use it with care to avoid short circuits or changes in characteristics due to signal lines coming close together.

FIG. 4 shows a third embodiment of the present invention, in which (a) is a top view with the lid plate 3 removed, and (b) is a sectional view taken along line xx'. In this embodiment, the membrane circuit element 51C (inductance element) is formed between the first layer 21 and the second layer 22, so the package structure is simple and the second
Since the membrane circuit element 51 is not exposed outside the package as in the embodiment, there is no risk of interference from external circuits.

FIG. 5 shows a fourth embodiment of the present invention, in which (A) is a top view and (B) is a sectional view taken along line XX'.

In this embodiment, the second layer 2 inside the ceramic package 2
A membrane circuit element 51 (inductance element) is placed on the exposed part of 2.
For example, after assembling the surface acoustic wave filter element lO, adjust the parallel inductance.
For example, the width of the stripline can be laser trimmed to match the required impedance, and the configuration is suitable for improving performance or yield.

FIG. 6 shows a fifth embodiment of the present invention, in which (a) is a sectional view taken along the line xx', and (b) is a top view with the lid opened.

This embodiment shows an example of a parallel capacitance type, in which a membrane circuit element 51 (balanced microstrip This is an example in which an impedance matching circuit 6 is formed by forming a line inductance element) and a membrane circuit element 5c (parallel line type capacitance element). 500 and 60
0 is a connection conductor that connects the input/output terminal of the surface acoustic wave filter element l and one end of the membrane circuit element 51 (an inductance element using a balanced microstrip line).

Note that the same reference numerals are given to the same parts as those explained in the above countries, and the explanation of the same parts will be omitted.

FIG. 7 is a diagram showing the matching circuit pattern of the fifth embodiment of the present invention, and as shown, the membrane circuit element 5 in this embodiment
c (parallel line type capacitive element).

For example, line width 120μm, line gap 120μm
When the parallel line length was 3 mm, a parallel capacitance of about 2 to 5 pF was obtained.

The embodiments described above are just a few examples, and as long as they comply with the spirit of the present invention, preferred materials and configurations, combinations thereof, and modifications may be used as appropriate. Needless to say.

〔Effect of the invention〕

As described above, according to the present invention, the impedance matching circuit 6 is formed between the layers of the ceramic package 2 that houses the surface acoustic wave filter element 1, or by a plurality of membrane circuit elements 5 on the exposed inner and outer surfaces of the package. Since it is formed integrally with 2, there is no need to add a separate external impedance matching circuit to configure the filter circuit, and the entire filter circuit can be miniaturized.
It also increases reliability and greatly contributes to the miniaturization and improved functionality of surface acoustic wave filters.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a diagram showing main parts of the first embodiment of the present invention, and FIG. 3 is a cross-sectional view showing a second embodiment of the present invention.
FIG. 4 is a diagram showing a third embodiment of the present invention; FIG. 5 is a diagram showing a fourth embodiment of the present invention; FIG. 6 is a diagram showing a fifth embodiment of the present invention. , FIG. 7 is a diagram showing the matching circuit pattern of the fifth embodiment of the present invention, FIG. 8 is a diagram showing the configuration of the surface acoustic wave filter, and FIG. 9 is a diagram showing the equal film circuit of the surface acoustic wave filter including the matching circuit. FIG. 10 is a diagram showing a product example of a conventional surface acoustic wave filter, and FIG. 11 is a diagram showing an example of a conventional impedance matching circuit formed on a printed circuit board. In the figure, l is a surface acoustic wave filter element, 2 is a ceramic package, 3 is a lid plate, 4 is a bonding wire, 5 (!M, 5c) is a membrane circuit element, 6 (6a, 6b) is an impedance matching circuit, lO 1 is a surface acoustic wave filter, 11 is a piezoelectric substrate, 12 is a comb-shaped input electrode, and 13 is a comb-shaped output electrode.

Claims (1)

[Claims] A surface acoustic wave filter element (1) in which a comb-shaped input electrode (12) and a comb-shaped output electrode (13) are arranged on a piezoelectric substrate (11) is housed in a ceramic package (2). In the sealed surface acoustic wave filter, an impedance matching circuit (6) formed from a plurality of membrane circuit elements (5) is provided between the layers of the ceramic package (2) or on the exposed inner and outer surfaces of the package. A surface acoustic wave filter featuring