JPH10242797A - Balanced type ultrathin plate multimode filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a balanced type ultrathin plate MCF that has high resistance to the noises by dividing a full electrode via a laser treatment at a position corresponding to a split electrode in regard to an ultrathin plate multimode filter which has the full electrode attached to its recessed side and the split electrode prepared on the surface opposite to the full electrode. SOLUTION: A balance type ultrathin plate MCF has a recessed part secured at a part of main surface of a piezoelectric substrate 1 using a parallel flat plate together with its bottom surface formed at a thin plate type ultrathin part 2 and a thick circular surrounding part 3 which supports the periphery of the part 2. The full electrodes 4a and 4b are formed on the MCF at the side of the recessed part (backside) with the electrodes 5 and 6 of the same size formed almost at the center of a vibration part 2 of the plane side (surface side) with a gap G1 secured between them. Then the electrodes 4a and 4b are cut separate from each other by means of a laser, etc., against and in parallel to the gap G1 set between the electrodes 5 and 6. A gap G2 is set bet between the electrodes 4a and 4b, and the pass band width can be controlled based on the gap G2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-mode piezoelectric filter (hereinafter, referred to as MCF) used for a portable radio device and the like, and particularly to an ultra-thin multi-mode filter having balanced inputs and outputs.

[0002]

2. Description of the Related Art Conventional MCFs have the advantages of small size, robustness and low cost, and have been widely used in portable radios. With the rapid spread and expansion of analog mobile phones and the like, the communication bandwidth has been narrowed to increase the communication capacity, the communication system has been digitized, and the carrier frequency has been increased. With these system changes, MC
The bandwidth of F has been required to be compressed, and the center frequency of the filter has been required to be higher with the higher frequency of the carrier. To realize high frequency using an AT-cut quartz substrate with good temperature characteristics, it is necessary to reduce the thickness of the substrate, but there is a limit to the thickness of the substrate due to mechanical processing or strength of the substrate. . In order to solve this thinning, there has been proposed an MCF in which a concave portion is provided in the center of the substrate and the concave portion is a vibrating portion.

However, the conventional method of connecting to a split electrode via a narrow lead electrode has a drawback that the lead electrode is easily cut at the step of the recess, so that the split electrode is connected to the substrate. It is provided on the flat surface side, and the concave side is used as the entire surface electrode to prevent the electrode from being cut by the step, thereby improving the manufacturing yield and the reliability of the high-frequency device. FIG. 4 is a diagram showing such a conventional ultra-thin plate MCF.
(A) is a perspective view of the plane side, (b) is A- of FIG.
FIG. 2A is a sectional view, and FIG. 2C is a perspective view on the concave surface side.
A conventional ultra-thin MCF is formed by forming a recess in a part of one main surface of a parallel-plate piezoelectric substrate 21, for example, an AT-cut quartz substrate, by means of etching or the like, and setting the bottom surface of the concave portion to the opposite surface. A parallel thin ultra-thin portion (vibrating portion) 22 is formed, and a thick annular surrounding portion 23 that supports the periphery of the ultra-thin portion 22 is integrally formed. As shown in FIG. 4C, the entire surface electrode 24 of the conductive film is formed on the concave side (referred to as the back side) by means of vapor deposition or the like, and a flat surface (referred to as the front side) opposed thereto. The electrodes 25 and 26 of the same size are arranged at the center of the vibrating part 22 with a gap G therebetween, and lead electrodes 27 and 28 are respectively provided from the electrodes toward the ends of the piezoelectric substrate and the bonding pads are provided on the respective tips. 29 and 30 are provided to form an ultra-thin MCF element E.

[0004] The ultra-thin sheet MCF element E formed as described above
5A, a conductive adhesive 32 is applied to the thick portion on the back side of the element E, and the ground electrode 33 is formed on the bottom of the package 31.
To the electrode 24 of the element E at the same time. The ground electrode 33 is hermetically connected to an external ground terminal of the package via a metal lead electrode. Furthermore, the electrodes 25 and 26 on the front surface and the input / output electrodes 34 and 35 provided on the package 31 are bonded to each other by using bonding wires 36 to form an ultra-thin piezoelectric filter. The input / output electrodes 34 and 35 are hermetically connected to external input / output terminals of the package via metal lead electrodes.

[0005] By arranging a full-surface electrode 24 on the back side of the vibrating part 22 of the ultra-thin plate and electrodes 25 and 26 on the front side with a gap G therebetween, vibration energy can be reduced.
By being confined in part 6 and acoustically coupled,
Two modes are strongly excited, and an ultra-thin MCF can be formed using the two modes.

[0006] The electrical equivalent circuit of the above ultra-thin plate MCF is:
As is well known, as shown in FIG. 6A, two resonance circuits are represented by an equivalent circuit connected in opposite phases, and by applying the bisecting theorem to this, the lattice type shown in FIG. It can be converted to a circuit. Thus the equivalent circuit thereof in sufficiently far frequency from the resonance frequency is balanced circuit due to electrostatic capacitance C _0. Usually, since the electrodes 25 and 26 are formed in the same shape, the capacitances C ₀ are equal to each other, and the feature is that a larger amount of blocking attenuation can be secured as the distance from the center frequency increases. Utilizing this transmission characteristic, it is widely used in portable radios and the like.

[0007]

However, in the above-mentioned conventional ultra-thin sheet MCF, the electrodes 24 are provided in the package 31.
So-called unbalanced ultra-thin sheet MC connected to earth electrode 33
F, and in the case of such an unbalanced filter, there is no means for removing the noise when noise or the like enters from the outside. Therefore, it is essential to perform sufficient shielding to shield external noise. As a result, there is a problem that the size of the wireless device is increased and the cost is increased. Recently, with the advance of IC technology, the IF peripheral circuit of a portable wireless device has a balanced configuration, and even if noise is input from outside, a differential amplifier is arranged after the IF filter to easily remove noise. A circuit configuration was developed. But,
As described above, in the conventional ultra-thin plate MCF, the electrode on the concave side has to be the entire surface electrode, and only the unbalanced filter can be configured inevitably, so that the advantage of the balanced filter cannot be enjoyed. was there. An object of the present invention is to provide a method for easily forming a balanced ultra-thin plate MCF without redesigning a conventional MCF having an electrode configuration.

[0008]

In order to achieve the above object, according to the present invention, a thin vibrating portion is formed by forming a recess in one main surface of a piezoelectric substrate. Ultra-thin plate multiple mode in which a thick annular surrounding portion for supporting the periphery of the portion is integrally formed, a full-surface electrode is attached to the concave side, and a split electrode is arranged on the other surface facing the concave portion. In the filter, there is provided a balanced ultrathin multi-mode filter, wherein the whole surface electrode is divided at a position corresponding to a divisional electrode facing the whole surface electrode. The invention according to claim 2 is the balanced ultra-thin plate multi-mode filter according to claim 1, wherein the entire surface electrode is divided by laser processing.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 is a view showing an embodiment of a balanced ultra-thin sheet MCF according to the present invention, wherein FIG.
Is a perspective view on a plane side, (b) is a cross-sectional view taken along the line AA in (a), and (c) is a perspective view on a concave side. In the balanced ultra-thin plate MCF according to the present invention, a concave portion is formed on a part of one main surface of a parallel-plate piezoelectric substrate 1, for example, an AT-cut quartz substrate, by etching or the like, and the bottom surface is formed in a thin plate-like shape. A thick annular surrounding portion 3 formed on the thin portion 2 and supporting the periphery of the ultra-thin portion 2 is integrally formed. The whole surface electrode 4 (4a, 4b) of a conductive film is formed on one of the concave portions (back surface side) on the ultra-thin plate substrate 1 holding the mechanical strength of the ultra-thin plate portion (vibrating portion) 2 by means such as vapor deposition. Are formed, and electrodes 5 and 6 having the same dimensions are arranged at the center of the vibrating portion 2 on the other flat surface side (front surface side) with a gap G1 therebetween. The electrode 5,
6 to the ends of the piezoelectric substrate, respectively.
Are arranged, and a bonding pad portion 9 is provided at each end.
10 is provided.

After that, the whole surface electrode 4 on the back surface is cut into electrodes 4a and 4b by using a laser or the like to face the gap G1 between the electrodes 5 and 6 on the front side and in parallel with the gap G1. G2. The relation between the gap G2 and the bandwidth of the ultra-thin plate MCF is such that when the gap G2 is increased, the coupling between the two modes is weakened and the pass bandwidth is narrowed, and when the gap G2 is narrowed, the coupling is strengthened and the bandwidth is widened. It is in. In addition, the laser sublimates and removes a substance such as a metal attached to the piezoelectric substrate with its energy, but a material such as a crystal transmits the laser and does not destroy the crystal.

FIG. 2 (a) shows a balanced ultra-thin MCF of the present invention.
FIG. 3 is a perspective view of a package 11 that accommodates an element E, and has four electrodes 12, 13, 15, 16 formed on the bottom surface thereof by printing or the like. The electrodes 4a and 4b facing each other across the gap G2 of the balanced ultra-thin plate MCF element E and one of the input / output terminals 12 and 13 of the package 11 are bonded and fixed using a conductive adhesive 14, respectively, and are simultaneously electrically connected. I do. Further, the bonding pad portions 9 and 10 provided on the front surface side of the element E and the other input / output terminals 15 and 16 of the package 11 are connected by wire bonding 17 respectively.
To form a balanced ultra-thin multi-mode filter.

The operation of the balanced ultra-thin plate MCF is the same as that of the unbalanced ultra-thin plate MCF. Vibration energy confined under the electrodes 5 and 6 is acoustically coupled to force the two modes. , And a bandpass filter is constructed using these two modes. The difference is that the pass band width of the conventional unbalanced ultra-thin MCF greatly depends on the gap G1 between the electrodes 5 and 6 and its film thickness.
The gap G2 between the electrodes 4a and 4b is also related to the pass bandwidth of the filter. The function of the electrode gap G2 is the same as that of G1, and the effect on the bandwidth is the same. Therefore, the pass band width can be controlled by the width of the electrode gap G2.

FIG. 3 shows a characteristic example of a prototype of a balanced ultra-thin plate MCF applied to the first IF filter for a terminal of a European digital telephone system (GSM) by applying the present invention. is there. A concave portion was formed in a part of the quartz piezoelectric substrate having a thickness of 80 μm by using an etching technique, and the frequency of the ultra-thin plate portion 2, that is, the vibrating portion was set to about 71 MHz (thickness: 23.5 μm). The dimensions of the electrodes 5 and 6 on the front side are the same, 0.7 mm × 0.35 mm, G1 = 2
8 μm, G2 = 15 μm, and the electrode film thickness was 1000 pm. FIG. 3A shows a pass band characteristic α and a group delay time characteristic β, and FIG. 3B shows an attenuation band characteristic, ± 5 MHz.
, And a characteristic β of ± 1 MHz. (C) is a measurement circuit when the data is measured.

Further, needless to say, a balanced ultra-thin sheet MCF having a steeper attenuation characteristic can be constituted by cascade-connecting a plurality of balanced ultra-thin sheet MCFs constructed by using the present invention. Alternatively, a filter in which the balanced ultra-thin plate MCF and the unbalanced ultra-thin plate MCF are cascade-connected may be configured as required. Also, not only two divisions,
You may apply to what is more than division. Further, the present invention relates to a piezoelectric material other than a quartz substrate, for example, LiTaO3, LiNbO.
3. It is obvious that the present invention can be applied to piezoelectric materials such as LBO and langasite.

[0015]

Since the present invention is constructed as described above, the back electrode is processed by a laser or the like and the package for accommodating the MCF is only slightly changed. The other steps are almost the same as the conventional manufacturing steps. The balanced ultra-thin plate MCF can be easily formed, and a remarkable effect that the advantage of the balanced type filter that is resistant to external noise can be enjoyed in the ultra-thin plate MCF is also exhibited.

[Brief description of the drawings]

FIG. 1A is a perspective view showing a front surface side of a balanced ultra-thin plate MCF according to one embodiment of the present invention, FIG. 1B is a cross-sectional view taken along AA, and FIG. FIG.

2A is a perspective view showing a package for accommodating a balanced ultra-thin plate MCF of the present invention, and FIG. 2B is a cross-sectional view when the balanced ultra-thin plate MCF of the present invention is mounted.

FIG. 3 is an actual measurement example of the balanced ultra-thin sheet MCF of the present invention,
(A) is a pass band characteristic α, a group delay time characteristic β, (b) is an attenuation band characteristic, α is a characteristic of ± 5 MHZ, β is a characteristic of ± 1 MHZ,
(C) is a measurement circuit of the balanced MCF.

4A is a perspective view showing the front side of a conventional ultra-thin sheet MCF, FIG. 4B is a cross-sectional view along AA, and FIG.
It is a perspective view showing the back side of CF.

FIG. 5A is a perspective view showing a conventional package for an ultra-thin MCF, and FIG. 5B is a cross-sectional view when a conventional ultra-thin MCF is mounted on the package.

6A is an electrical equivalent circuit of the MCF, and FIG. 6B is an equivalent circuit represented by a lattice type.

[Explanation of symbols]

 1. Quartz substrate 2. Ultra-thin portion (vibrating portion) 3. Annular surrounding portion 4a, 4b Back surface electrode 5, 6, Electrode 7, 8, Lead electrode 9, 10, Bonding pad Part 11: Package 12, 13, 15, 16, Output terminal 14: Adhesive 17: Bonding wire E: Balanced ultra-thin plate element G1, G2: Electrode gap

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 6, 1997

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (2)

[Claims] 1. A thin vibrating portion and a thick annular surrounding portion for supporting the periphery of the vibrating portion are integrally formed by forming a concave portion on one main surface of the piezoelectric substrate, and the concave portion is formed on the concave side. In an ultra-thin multi-mode filter configured by attaching a full-surface electrode and arranging a division electrode on the other surface opposite thereto, the full-surface electrode is divided at a position corresponding to the division electrode opposed thereto. Balanced ultra-thin multi-mode filter. 2. The multi-mode filter according to claim 1, wherein the whole surface electrode is divided by laser processing.