JP7848635B2 - Monolithic quartz filter - Google Patents

Description

This invention relates to a monolithic quartz filter used in wireless communication equipment and the like.

Recent wireless communication equipment, such as professional-grade radios, requires monolithic crystal filters with various filter characteristics depending on their application and specifications. For example, there may be requirements for miniaturization, spurious signal suppression, relatively steep guaranteed attenuation characteristics, and wide or narrow passband widths. However, these filter characteristics also require reliability, including stability unaffected by external factors.

A monolithic quartz filter has an input electrode and an output electrode formed in parallel on the central portion of one main surface of an AT-cut quartz diaphragm, and a common electrode formed on the other main surface opposite the input and output electrodes. By applying an alternating electric field to the input and output electrodes, it functions as a quartz filter.

As is well known, the aforementioned monolithic quartz filter requires adjustment of several filter characteristics on the electrodes, such as frequency balance between electrodes and frequency band characteristics. For example, frequency balance between electrodes is achieved by adjusting the electrode thickness (thickness of the metal film) in the common electrode regions corresponding to the input and output electrodes on the back surface. Frequency band characteristics are adjusted by adjusting the electrode thickness (thickness of the metal film) in the regions corresponding to the input and output electrodes. Furthermore, the center frequency is adjusted by adjusting the electrode thickness across the entire common electrode surface.

However, in actual manufacturing processes, these filter characteristics are typically adjusted after the quartz diaphragm is mounted in the package (retainer). In practice, as mentioned above, the quartz diaphragm is held with the common electrode facing upwards in the package, and the above adjustments are made to the common electrode. However, for frequency balance and other parameters, it is necessary to accurately estimate the formation positions of the input and output electrodes, but the formation of the common electrode sometimes made it difficult to accurately estimate these positions.

Patent No. 3436251

As shown in paragraph 0009 of Patent Document 1, it is disclosed that various filter characteristics can be adjusted. However, as mentioned above, if the formation positions of the input and output electrodes are not properly estimated, the adjustment area relative to the common electrode may be misaligned, making it impossible to adjust the filter characteristics appropriately. As a result, the adjustment process can take a long time, significantly reducing productivity. Furthermore, unnecessary adjustments may be made, resulting in defective products being manufactured that could have been produced as good products with proper adjustments.

This invention has been made in view of the above problems, and aims to provide a monolithic quartz filter capable of high-precision adjustment of filter characteristics.

To achieve the above objective, the invention of claim 1 provides a translucent quartz diaphragm having an input electrode and an output electrode formed on one main surface, a common electrode directly opposite to the input electrode and the output electrode formed on the other main surface, and two connecting electrodes electrically connected independently to the input electrode and the output electrode, and one connecting electrode electrically connected to the common electrode ,
A monolithic quartz filter having an opening and a package that holds the quartz diaphragm and has two connection electrode pads which are conductively joined to the two connection electrodes, one connection electrode pad which is conductively joined to one connection electrode which is electrically connected to the common electrode, and a ground electrode pad which is grounded and separate from the two connection electrode pads and the one connection electrode pad, wherein the quartz diaphragm has one main surface facing the package and the two connection electrodes and the two connection electrode pads are conductively joined, the common electrode is positioned on the opening side of the package, one or more markers having positional information related to the formation positions of the input electrode and output electrode on the one main surface are formed on the one main surface, and when viewed in plan, the markers are formed on the quartz diaphragm outside the common electrode.

According to this configuration, a translucent quartz diaphragm is used, and one or more markers related to the formation positions of the input and output electrodes are formed on one main surface. When viewed in plan, the markers are formed on the quartz diaphragm outside the common electrode formed on the other main surface. Therefore, the position of the markers can be seen from the other main surface where the common electrode is formed. Since the markers have positional information related to the formation positions of the input and output electrodes, the positions of the markers can be used to identify the positions of the input and output electrodes on the opposite surface that are hidden by the common electrode.

Therefore, the formation positions of the input and output electrodes can be identified on the common electrode when viewed in a planar view, and multiple filter characteristic adjustments related to the formation positions of the input and output electrodes can be performed on the common electrode side, resulting in a monolithic quartz filter that allows for highly accurate filter characteristic adjustments.

The one or more markers associated with the formation positions of the input and output electrodes on one of the main surfaces described above may be one or two or more.

If a single marker is formed, the marker may be formed on the virtual midline between the input and output electrodes of one of the main surfaces, and on the quartz diaphragm outside the common electrode.

According to the above configuration, since the common electrode is formed on the midline between the input and output electrodes and outside the common electrode, it is possible to adjust the filter characteristics to the desired adjustment range without hindering vibrations during monolithic crystal filter operation, thereby obtaining a highly accurate monolithic crystal filter.

According to the present invention, a monolithic quartz filter capable of highly accurate filter characteristic adjustment can be obtained.

This is a plan view of one main surface of the electrode-formed quartz diaphragm according to this embodiment. This is a plan view of the other main surface of the electrode-formed quartz diaphragm according to this embodiment. This is a plan view of the package according to this embodiment. This is a plan view of the package according to this embodiment with a quartz diaphragm mounted on it. This is a cross-sectional view taken along line A-A of the package shown in Figure 4, sealed with a lid. This is a cross-sectional view along line B-B of the package shown in Figure 4, sealed with the lid. This is a plan view of one main surface of a quartz diaphragm with electrodes formed on it, showing another example of marker formation.

The embodiments of the present invention will be described in detail below with reference to the drawings.

First Embodiment A first embodiment of the present invention will be described with reference to Figures 1 to 6. Figure 1 is a plan view of one main surface of an electrode-formed quartz diaphragm showing this embodiment, and Figure 2 is a plan view of the other main surface of the electrode-formed quartz diaphragm. Figure 3 is a plan view showing a package that houses and holds the quartz diaphragm. Figure 4 is a plan view showing the state in which the quartz diaphragm is housed and held in the package, Figure 5 is a cross-sectional view taken along line A-A of Figure 4 in a state in which the package housing the quartz diaphragm and conductively bonded is hermetically sealed with a lid, and Figure 6 is a cross-sectional view taken along line B-B of Figure 4 in a similar state in which the package is hermetically sealed with a lid.

The monolithic quartz filter F has an overall rectangular parallelepiped shape and consists of a package 1 with a recessed opening at the top, a quartz diaphragm 2 which is a piezoelectric vibration element housed within the recess of the package 1, and a lid 3 which is joined to the opening of the package 1.

Package 1 is a ceramic package with metal film wiring formed on its interior and exterior. In cross-section, it has a concave shape, and includes a ridge (side wall) 10 around the concave shape and a circumferential metal seal portion 11 formed on the upper surface of the ridge. The metal seal portion 11 consists of a metallized layer made of tungsten or the like, and a metal film layer formed on the metallized layer. The metal film layer consists, for example, a nickel-plated layer in contact with the metallized layer and an extremely thin gold-plated layer formed on top of the nickel-plated layer. A welding metal ring, such as Kovar, may also be attached.

Inside the package 1, connection electrode pads 12a, 12b, and 12c are formed at the four corners, and a ground electrode pad 12d is also formed. These connection electrode pads and ground electrode pads are extended via conductive electrodes to the opposite side of the electrode pad formation surface, i.e., the external connection surface on the back of the package, which provides electrical connection to the outside, and are electrically connected to external connection terminals. Specifically, connection electrode pad 12a is electrically connected to external connection terminal 13a via conductive electrode 12a1, connection electrode pad 12b is electrically connected to external connection terminal 13b via conductive electrode 12b1, connection electrode pad 12c is electrically connected to external connection terminal 13c via conductive electrode 12c1, and ground electrode pad 12d is electrically connected to external connection terminal 13d via conductive electrode 12d1.

Furthermore, castellations 13a1, 13b1, 13c1, and 13d1 extending in the thickness direction are formed at the corners of the ceramic package, and castellations 13e1 and 13f1 are also formed on the side walls. Each of the castellations 13a1, 13b1, 13c1, and 13d1 is electrically connected to the external connection terminals 13a, 13b, 13c, and 13d, respectively. Although not shown in the figure, castellations 13e1 and 13f1 are connected to external connection terminals 13e and 13f formed on the back surface of the package, respectively.

These external connection terminals and castellar structures are constructed, for example, by applying nickel plating, gold plating, etc., to the top of a tungsten metallization layer.

The quartz diaphragm 2 is made of an AT-cut quartz plate and has a rectangular shape with a short side and a long side when viewed in plan. Electrodes constituting a monolithic quartz filter are formed on both the front and back surfaces of the quartz diaphragm 2. Specifically, on one main surface, a rectangular input electrode 21 and a rectangular output electrode 22 are formed in parallel with a predetermined spacing, while on the other main surface, a common electrode 23 corresponding to the input electrode 21 and output electrode 22 is formed. The common electrode 23 is also rectangular when viewed in plan and has an external size corresponding to the area formed in parallel by the input electrode 21 and output electrode 22.

From the input electrode 21 and output electrode 22, lead electrodes 21a and 22a extend in directions away from each other (long side direction), respectively. These lead electrodes 21a and 22a reach the ends (short side ends) of the quartz diaphragm 2, and then extend to diagonally opposite corners, forming connecting electrodes 21b and 22b at these corners.

An extension electrode 21c is formed on the opposite side (the other main surface) of the region where the connecting electrode 21b is formed. The extension electrode 21c extends along the short side, reaching near the other end of this short side. Similarly, an extension electrode 22c is formed on the opposite side (the other main surface) of the region where the connecting electrode 22b is formed. The extension electrode 22c extends along the long side, reaching near the other end of this long side. Furthermore, a portion of the connecting electrode and a portion of the extension electrode overlap at each corner. Although not shown, the connecting electrode 21b and extension electrode 21c of the input electrode 21, and the connecting electrode 22b and extension electrode 22c of the input electrode 22, may be electrically connected by side electrodes (metal thin films) formed on the side surface of the crystal diaphragm in the overlapping regions. In this case, the application of the conductive bonding material to the connecting electrode and the connecting electrode pad, as described later, can be omitted.

As shown in the upper right of Figure 2, the extension electrodes 21c and 22c are positioned close together at the corner of the quartz diaphragm, with the end faces of extension electrode 21c and extension electrode 22c facing each other with a gap t. This gap between the extension electrodes forms a bridging capacitance C. It is preferable that the end faces of the opposing extension electrodes 21c and 22c are positioned at a constant distance from each other. This facilitates the design of capacitance formation.

Furthermore, as shown in Figure 1, a marker M is formed on a virtual extension line L that passes midway between the input electrode 21 and the output electrode 22. This positional relationship allows the formation positions of the input electrode 21 and the output electrode 22 to be determined relative to the formation position of the marker M.

Marker M is, for example, circular and is formed independently between the common electrode formation region on the other main surface (opposite surface) of the quartz diaphragm and the extended electrode formation region, outside of that region. Since the quartz diaphragm is transparent, the marker can be seen from the other main surface, functioning as a positioning starting point during manufacturing and proving useful for identifying the adjustment region during characteristic adjustment, as described later.

Each of the aforementioned electrodes, namely the input/output electrodes, common electrode, lead electrode, connecting electrode, extension electrode, and marker, is made of a thin metal film. For example, a chromium (Cr) layer is used as the underlayer in contact with the quartz diaphragm, with gold (Au) or silver (Ag) formed on top of the underlayer. These thin metal films may be made of other metal materials; for example, a single-layer aluminum (Al) metal material may be used.

The dimensions of the electrodes and markers formed on the above-mentioned quartz diaphragm are exemplified below. The quartz diaphragm has a long side dimension of 1.55 mm and a short side dimension of 1.35 mm. Since an AT-cut quartz plate is used, the thickness is determined by the frequency. The input and output electrodes have a long side dimension of 0.3 mm, a short side dimension of 0.19 mm, and a thickness of approximately 600 angstroms. The common electrode corresponding to the input and output electrodes has a long side dimension of 0.66 mm, a short side dimension of 0.3 mm, and a thickness of approximately 1200-1500 angstroms. The marker is circular with a diameter of 0.1 mm and a thickness of approximately 600 angstroms. Note that the film thickness of the electrodes (metal thin films) is the film thickness before filter characteristic adjustment. As described later, the common electrode is adjusted by reducing its film thickness through ion milling; therefore, the film thickness after filter characteristic adjustment will be less than the above film thickness.

Figure 4 shows the crystal diaphragm 1 mounted flat on the package 1. The crystal diaphragm 2, with the electrodes formed on it, is mounted on the ceramic package so that one main surface, where the input and output electrodes are formed, faces the electrode pads 12a, 12b, 12c, and 12d of the package. It is then electrically and mechanically connected using a conductive bonding material S. Specifically, as shown in Figures 5 and 6, each connecting electrode and each connecting electrode pad are conductively bonded via the conductive bonding material S. For example, the conductive bonding material S is a resin bonding material with added conductive filler in paste form. The bonding material hardens due to thermoplasticity, and the crystal diaphragm 2 is conductively bonded to the package 1.

As a result, as shown in Figure 4, the common electrode 23 is positioned on the opening side of the package, the extended electrode 22c extends along the long side of the upper end of the quartz diaphragm, and the extended electrode 21c extends along the short side of the right end of the quartz diaphragm, with the components supported and fixed in this state. The conductive bonding material S is supplied to the connecting electrodes 21b, 22b, and 23b and their upper surfaces, as shown in Figures 1 and 4, thereby electrically bonding the connecting electrode 21b, the extended electrode 21c, and the connecting electrode pad 12c; the connecting electrode 22b, the extended electrode 22c, and the connecting electrode pad 12a; and the connecting electrode 23b and the connecting electrode pad 12b, respectively, independently.

Figure 5 shows a cross-sectional view along line A-A in Figure 4, where the conductive bonding material S conductively bonds the connecting electrode 23b and the connecting electrode pad 12b, and also conductively bonds the connecting electrode 22b, the extension electrode 22c, and the connecting electrode pad 12c.

Figure 6 shows a cross-sectional view along line B-B in Figure 4, where the conductive bonding material S conductively bonds the connecting electrode 21b, the extension electrode 21c, and the connecting electrode pad 12c. In the region of bridging capacitance C, the ground electrode pad is located directly below it, separated from the quartz diaphragm by a gap G. Here, the gap G is set to 0.01 mm to 0.08 mm. While a shorter gap G is preferable for improving characteristics such as suppressing external noise influence, since this is the free end portion, external impacts may cause contact between the quartz diaphragm and the ground electrode pad, potentially damaging the quartz diaphragm. Therefore, the above-mentioned gap G distance is preferable. Even more preferably, a gap G in the range of 0.02 mm to 0.06 mm is preferable, as this range further improves the stability of the filter characteristics against external noise and potential fluctuations, as well as improving shock resistance.

Furthermore, the extension electrode may be formed on the input electrode and output electrode formation side, and a bridging capacitance may be formed on one of the main surfaces. This configuration allows for a closer distance between the bridging capacitance formation region and the ground electrode pad, further improving the stability of the filter characteristics.

As shown in Figures 5 and 6, the quartz crystal diaphragm housing space is kept airtight by hermetically sealing package 1 with lid 3. This housing space may be filled with an inert gas or may be in a vacuum atmosphere.

Next, we will explain the method for adjusting the filter characteristics before hermetically sealing. Filter characteristics can be adjusted by increasing or decreasing the thickness of the electrode (metal thin film). For example, partial deposition is used to increase the thickness, while ion milling is used to decrease it. In actual manufacturing processes, adjustment is performed using either a method to increase or decrease the thickness.

This example demonstrates an adjustment method using ion milling to reduce the thickness of a metal thin film. When adjusting the frequency balance between electrodes on a common electrode 23 formed on the other main surface, the electrode thickness is reduced by irradiating the corresponding common electrode regions of the input electrode 21 and output electrode 22 on one main surface (opposite surface) with an ion beam. Similarly, when adjusting the frequency band characteristics, the electrode thickness is reduced by irradiating the common electrode region corresponding to the input electrode and output electrode with an ion beam.

It is desirable that the input electrode 21 and output electrode 22 formed on one main surface of the quartz diaphragm be directly opposite the common electrode 23 formed on the other main surface. However, during film formation using methods such as vacuum deposition or sputtering with a mask, a shift in the front and back surfaces may occur. In this case, the estimated position of the corresponding portions of the input electrode 21 and output electrode 23 on the common electrode 23 may be inaccurate. This is because the common electrode 23 covers the input electrode 21 and output electrode 22 formed on its opposite surface, causing the estimated positions of the input electrode 21 and output electrode 22 to be misaligned.

In this invention, markers M are formed on the same surface as the input electrode 21 and the output electrode 22. These input electrodes, output electrodes, and markers are formed using a mask means having openings for their formation. This ensures that the formation positions of the input and output electrodes are specified relative to the formation position of the marker M, eliminating any relative positional misalignment. The marker is formed in a manner that allows it to be visible through the transparent quartz diaphragm on one of the main surfaces. This visible marker M can be used as a reference to identify the adjustment region for the common electrode 23. In this embodiment, since the marker M is located midway between the input electrode 21 and the output electrode 22, the positions of the input electrode 21 and the output electrode 22 can be identified using it as a reference.

Furthermore, the center frequency is adjusted by changing the film thickness across the entire surface of the common electrode 23. The adjustment area is narrowed (limited) using a partial aperture mask with an opening in a metal plate. In Figure 4, the area indicated by the dashed line represents the partial aperture mask PW, which is used, for example, to reduce the film thickness across the entire surface of the common electrode where the center frequency is being adjusted. Note that, although not shown in the figure, adjustments to the input electrode area or the output electrode area of the common electrode are performed by setting a partial aperture mask with an opening only in that area and then performing ion milling.

Next, another embodiment using two markers will be described with reference to Figure 7. The example shown in Figure 7 has no extension electrodes or bridging capacitance. An input electrode 21 and an output electrode 22 are formed on one main surface of the quartz diaphragm 2, and a common electrode 23 is formed on the other main surface. A marker M1 corresponding to the input electrode and a marker M2 corresponding to the output electrode are formed. Marker M1 is formed in relation to the formation position of the input electrode, and marker M2 is formed in relation to the formation position of the output electrode. In this example, markers M1 and M2 are formed directly above the midpoint of the short-side direction of the input electrode and output electrode, respectively.

In this embodiment, the external size of the common electrode 23 is larger than the area where the input and output electrodes are arranged in parallel. Basically, when adjusting the filter characteristics of the common electrode from the other main surface, the exact positions of the input and output electrodes are unknown. However, the marker configuration described above allows for the precise identification of the formation positions of the input and output electrodes based on the positions of each marker. This enables accurate filter characteristic adjustment and allows for the acquisition of highly accurate filter characteristics.

In this embodiment, markers M1 and M2 are small squares. By identifying the corners of the squares, positional information can be obtained more accurately, contributing to the acquisition of high-precision filter characteristics.

Furthermore, in the above example, marker M2 may be formed below the output electrode, and markers M1 and M2 may be formed diagonally opposite each other. Three or more markers may also be formed, however, the weight of the markers themselves may affect the vibration of the crystal diaphragm. Therefore, when forming multiple markers, it is preferable to form them at a distance from the excitation region formed by the input electrode, output electrode, and common electrode.

Furthermore, the bridging capacitance C may be adjusted locally. For example, the bridging capacitance can be adjusted by partially removing electrodes near each extension electrode using laser or ion milling, or by adding electrodes (adding a thin metal film) by localized partial vacuum deposition, thereby changing the gap t or the electrode size.

Incidentally, when reducing the proximity distance or increasing the size of the extraction electrodes in the proximity region, electrode addition by partial deposition or the like is necessary. In this case, to facilitate electrode addition and stabilize film formation, an extremely thin metal film may be formed in advance in the area where the electrodes are to be added. This allows for adjustment of the bridging capacitance. The metal film should be made of, for example, chromium, with a thickness of several angstroms to several tens of angstroms, so that its resistance is high enough that it does not allow conductivity between the two extension electrodes. Furthermore, the intermediate portions of the closely facing extension electrodes may not have a metal film formed on them.

After completing the necessary adjustments described above, the electrode (metal film) is stabilized with an annealing treatment, and then hermetically sealed with lid 3. Lid 3 uses a metal plate with a base material made of a flat plate-shaped metal such as Kovar, and its surface is nickel-plated. Lid 3 is mounted on the metal seal portion 11, and in this state, the lid and the metal seal portion are melted and hermetically sealed by seam welding, laser beam welding, or brazing.

Although the above explanation uses a two-pole monolithic quartz filter as an example, the same principles can be applied to three-pole or four-pole quartz filters.

The embodiments disclosed herein are illustrative in all respects and are not intended to be restrictive. Therefore, the technical scope of the present invention is not construed solely by the embodiments described above, but is defined by the claims. This includes all modifications within the meaning and scope of the equivalents of the claims.

1 Package 10 Dam section 11 Metal seal section 2 Crystal diaphragm 3 Lid 12a, 12b, 12c Connecting electrode pads 12d Ground electrode pads 13a, 13b, 136c, 13d, 13e, 13f Castation C Bridge capacitance

Claims (2)

A translucent quartz diaphragm having input electrodes and output electrodes formed on one main surface, a common electrode directly opposite the input electrodes and output electrodes formed on the other main surface, two connecting electrodes electrically connected independently to the input electrodes and output electrodes , and one connecting electrode electrically connected to the common electrode ,
It has an opening and holds the crystal diaphragm, and comprises two connection electrode pads which are electrically joined to the two connection electrodes, and one connection electrode pad which is electrically joined to one connection electrode which is electrically connected to the common electrode,
A package having the two connecting electrode pads and a grounding electrode pad that is separate from the one connecting electrode pad,
A monolithic quartz filter having,
The quartz diaphragm is configured such that one main surface faces the package , the two connecting electrodes and the two connecting electrode pads are electrically bonded, and the common electrode is positioned on the opening side of the package.
A monolithic quartz filter characterized in that one or more markers having positional information related to the formation positions of the input electrode and output electrode on one of the main surfaces are formed on the one main surface, and when viewed in plan, the markers are formed on the quartz diaphragm outside the common electrode. The monolithic quartz filter according to claim 1, characterized in that the marker is formed on a virtual median line between the input electrode and the output electrode of one of the main surfaces.