Abstract:
In a method for manufacturing a transversal surface acoustic wave filter device, measurement pads for use in probe measurement are formed on a wafer, and are shared by adjacent transversal surface acoustic wave filter devices. The number of measurement pads is reduced to about half the standard, thereby reducing the area occupied per device.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to transversal surface acoustic wave filter devices.  
         [0003]     2. Description of the Related Art  
         [0004]     In a method for manufacturing a transversal surface acoustic wave (SAW) filter, an aluminum thin film or an aluminum alloy thin film is formed on a wafer of single-crystal piezoelectric substrate material, such as lithium tantalate (LiTaO 3 ) or lithium niobate (LiNbO 3 ), using vacuum deposition or sputtering, and is patterned by photolithography, and multiple transversal SAW filter devices are closely formed in a grid pattern. Alternatively, an aluminum thin film or an aluminum alloy thin film is formed on a glass substrate using vacuum deposition or sputtering, and is patterned by photolithography, a piezoelectric thin film of zinc oxide (ZnO) or the like is formed on the patterned thin film, and multiple transversal SAW filter devices are closely formed in a grid pattern. After that, the wafer is cut into individual transversal SAW filter devices, and each of them is packaged. A transversal SAW filter is thus produced.  
         [0005]     In the manufacturing method described above, probe measurement is performed on each of the multiple transversal SAW filter devices on the piezoelectric substrate wafer using a wafer probe to test and measure the performance of the transversal SAW filter devices.  
         [0006]     With this on-wafer test step, the performance of the unpackaged transversal SAW filter devices can be verified in advance before they are packaged, leading to high yield and efficient production of transversal SAW filters.  
         [0007]     If probe measurement is performed using external-connection pads of the transversal SAW filter devices, probe marks are left on the external-connection pads, resulting in low bump connection reliability at the time of mounting using wire bonding.  
         [0008]     A first solution to such a problem is shown in  FIG. 5 . As shown in  FIG. 5 , measurement pads  24   a  to  24   f  and  25   a  to  25   f  and external-connection pads are separately constructed so that no probe marks are left on the external-connection pads and low bump connection reliability occurs. This invention is disclosed in Japanese Unexamined Patent Application Publication No. 2002-319841.  
         [0009]     Japanese Unexamined Patent Application Publication No. 2004-48098 discloses a manufacturing method in which the electrode pad forming step is performed again after the test step so as not to leave the probe marks.  
         [0010]     However, in a case where the multiple transversal SAW filter devices on the piezoelectric substrate wafer are individually provided with measurement electrode pads, each of the transversal SAW filter devices is large in size, and the integration density of the devices decreases. Therefore, the number of transversal SAW filter devices that can be formed on a single wafer is reduced.  
         [0011]     In a case where measurement electrode pads and external-connection pads are shared and the electrode pad forming step is performed again to delete the probe marks produced by the measurement, the cost and time loss of performing this step are required, and the overall cost increases.  
         [0012]     In a balanced-operation transversal SAW filter device, it is difficult to connect a shield electrode to a portion of an interdigital electrode of a transmitter or receiver, and an additional measurement pad for the shield electrode is therefore required. Therefore, the size of the transversal SAW filter device increases.  
       SUMMARY OF THE INVENTION  
       [0013]     In order to overcome the problems described above, preferred embodiments of the present invention provide a method for manufacturing a transversal surface acoustic wave filter device including a piezoelectric substrate for propagating surface acoustic waves, a pair of transmitter-side comb electrodes defined on the piezoelectric substrate for transmitting surface acoustic waves, and a pair of receiver-side comb electrodes defined on the piezoelectric substrate for receiving surface acoustic waves, the pair of transmitter-side comb electrodes including a pair of transmitter-side external-connection electrode pads and the pair of receiver-side comb electrodes including a pair of receiver-side external-connection electrode pads. The method includes an electrode forming step including the steps of forming pairs of the transmitter-side comb electrodes, pairs of the transmitter-side external-connection electrode pads, an electrode pattern for connecting the pairs of transmitter-side comb electrodes to the pairs of transmitter-side external-connection electrode pads, pairs of the receiver-side comb electrodes, pairs of the receiver-side external-connection electrode pads, and an electrode pattern for connecting the pairs of receiver-side comb electrodes to the pairs of receiver-side external-connection electrode pads on a wafer of piezoelectric substrate material so that a plurality of devices are formed in a grid pattern on the wafer. Then, forming a transmitter-side connection electrode pattern for connecting adjacent devices at an arbitrary position on the electrode pattern extending from the pairs of transmitter-side external-connection electrode pads to the pairs of transmitter-side comb electrodes and a receiver-side connection electrode pattern for connecting adjacent devices at an arbitrary position on the electrode pattern extending from the pairs of receiver-side external-connection electrode pads to the pairs of receiver-side comb electrodes so as to traverse tentative cutting lines on the wafer along which the wafer is cut into the devices, and forming one measurement pad for each of the transmitter-side connection electrode pattern and the receiver-side connection electrode pattern. The method further includes a quality determining step of measuring a high-frequency characteristic of the transversal surface acoustic wave filter device in an on-wafer state using the measurement pads to determine the quality of each of the devices on the wafer, and a device separating step of separating the devices from one another along the tentative cutting lines.  
         [0014]     According to this structure, therefore, since measurement pads are shared by adjacent transversal SAW filter devices formed on the wafer, the number of measurement pads can be reduced to about half of the measurement pads  24   a  to  24   f  and  25   a  to  25   f  of the related art shown in  FIG. 5 , and the space for each of them can be reduced. Thus, the transversal SAW filter devices can be reduced in size, and the integration density of the transversal SAW filter devices formed on the wafer can increase. The number of filters manufactured per wafer increases, resulting in low cost of the devices.  
         [0015]     In the above-described method, at least one of the measurement pads is defined on a tentative cutting line along which the wafer is cut into device chips.  
         [0016]     According to this structure, therefore, the measurement pads formed on tentative cutting line regions allow effective utilization of the area cut out by dicing, which corresponds to the width of a dicing blade used for dicing. Thus, the transversal SAW filter devices can further be reduced in size, and the integration density of the transversal SAW filter devices formed on the wafer can further increase. The number of filters manufactured per wafer further increases, resulting in a lower cost of the devices.  
         [0017]     According to another preferred embodiment of the present invention, there is provided a method for manufacturing a transversal surface acoustic wave filter device including a piezoelectric substrate for propagating surface acoustic waves, a pair of transmitter-side comb electrodes defined on the piezoelectric substrate for transmitting surface acoustic waves, a pair of receiver-side comb electrodes defined on the piezoelectric substrate for receiving surface acoustic waves, the pair of transmitter-side comb electrodes including a pair of transmitter-side external-connection electrode pads and the pair of receiver-side comb electrodes including a pair of receiver-side external-connection electrode pads, and a shield electrode separately and independently defined between the pair of transmitter-side comb electrodes and the pair of receiver-side comb electrodes, the shield electrode including a shield-electrode external-connection electrode pad. The method includes an electrode forming step including the steps of forming pairs of the transmitter-side comb electrodes, pairs of the transmitter-side external-connection electrode pads, an electrode pattern for connecting the pairs of transmitter-side comb electrodes to the pairs of transmitter-side external-connection electrode pads, pairs of the receiver-side comb electrodes, pairs of the receiver-side external-connection electrode pads, an electrode pattern for connecting the pairs of receiver-side comb electrodes to the pairs of receiver-side external-connection electrode pads, shield electrodes, and electrode patterns each for connecting the shield electrode to the shield-electrode external-connection electrode pad on a wafer of piezoelectric substrate material so that a plurality of devices are formed in a grid pattern on the wafer. Then, forming a transmitter-side connection electrode pattern for connecting adjacent devices at an arbitrary position on the electrode pattern extending from the pairs of transmitter-side external-connection electrode pads to the pairs of transmitter-side comb electrodes, a receiver-side connection electrode pattern for connecting adjacent devices at an arbitrary position on the electrode pattern extending from the pairs of receiver-side external-connection electrode pads to the pairs of receiver-side comb electrodes, and an electrode pattern for connecting the shield-electrode external-connection electrode pads to the transmitter-side connection electrode pattern or an electrode pattern for connecting the shield-electrode external-connection electrode pads to the receiver-side connection electrode pattern so as to traverse tentative cutting lines on the wafer along which the wafer is cut into the devices, and forming one measurement pad for each of the transmitter-side connection electrode pattern and the receiver-side connection electrode pattern. The method further includes a quality determining step of measuring a high-frequency characteristic of the transversal surface acoustic wave filter device in an on-wafer state using the measurement pads to determine the quality of each of the devices, and a device separating step of separating the devices from one another along the tentative cutting lines.  
         [0018]     According to this structure, therefore, in a balanced-operation transversal SAW filter device in which a shield electrode is not formed continuously to a portion of interdigital electrodes, it is only required to connect a shield electrode to a probe electrode pad connected to the interdigital electrode which is set to a ground potential at the time of probe measurement to perform probe measurement without an additional shield-electrode measurement pad. The probe electrode pad connected to the interdigital electrode and the shield electrode are electrically isolated at the time of dicing, thereby producing a transversal SAW filter device capable of operating with balanced input and output without increasing the size of the device.  
         [0019]     In the above-described method, at least one of the measurement pads is defined on a tentative cutting line along which the wafer is cut into device chips.  
         [0020]     According to this structure, therefore, the measurement pads formed on tentative cutting line regions allow effective utilization of the area cut out by dicing, which corresponds to the width of a dicing blade used for dicing. Thus, the transversal SAW filter devices can further be reduced in size, and the integration density of the transversal SAW filter devices formed on the wafer can further increase. The number of filters manufactured per wafer further increases, resulting in lower cost of the devices.  
         [0021]     Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a diagram illustrating a transversal SAW filter device according to a first preferred embodiment of the present invention.  
         [0023]      FIG. 2  is a diagram illustrating a transversal SAW filter device according to a second preferred embodiment of the present invention.  
         [0024]      FIG. 3  is a diagram illustrating a transversal SAW filter device according to a third preferred embodiment of the present invention.  
         [0025]      FIG. 4  is a diagram illustrating a transversal SAW filter device according to a fourth preferred embodiment of the present invention.  
         [0026]      FIG. 5  is a diagram illustrating a transversal SAW filter device of the related art.  
         [0027]      FIG. 6  is a diagram illustrating another transversal SAW filter device of the related art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     A first preferred embodiment of the present invention will now be described below with reference to  FIG. 1 . Referring to  FIG. 1 , multiple transversal SAW filter devices are formed in a grid pattern on a piezoelectric substrate  1 , and a portion of the transversal SAW filter devices, namely, three transversal SAW filter devices, is illustrated in an enlarged view in  FIG. 1 .  
         [0029]     Transmitters  3   a  to  3   c  each including a pair of comb electrodes and receivers  4   a  to  4   c  each including a pair of comb electrodes are defined on the piezoelectric substrate  1 . A pair of comb electrodes is referred to as an interdigital transducer (IDT).  
         [0030]     Each of shield electrodes  5   a  to  5   c  is formed continuously with one comb electrode of each of the receivers  4   a  to  4   c.  The shield electrodes  5   a  to  5   c  suppress unwanted spatial coupling between the transmitters  3   a  to  3   c  and the receivers  4   a  to  4   c  or direct radiation produced on the substrate  1 . While each of the shield electrodes  5   a  to  5   c  is formed continuously with one comb electrode of each of the receivers  4   a  to  4   c  in  FIG. 1 , the shield electrodes  5   a  to  5   c  may be formed continuously with one comb electrode of each of the transmitters  3   a  to  3   c.    
         [0031]     Dampers  6   a  to  6   c  are defined on the side of the transmitters  3   a  to  3   c  which does not face the receivers  4   a  to  4   c.  Dampers  7   a  to  7   c  are defined on the side of the receivers  4   a  to  4   c  which does not face the transmitters  3   a  to  3   c . The dampers  6   a  to  6   c  and  7   a  to  7   c  absorb the unwanted surface acoustic waves propagating from the transmitters  3   a  to  3   c  and the receivers  4   a  to  4   c.    
         [0032]     The transmitters  3   a  to  3   c  are provided with external-connection pads  8   a  to  8   c  and  9   a  to  9   c  via connection electrode patterns (not specifically identified by a reference numeral in the figure), and the receivers  4   a  to  4   c  are provided with external-connection pads  10   a  to  10   c  and  11   a  to  11   c  via connection electrode patterns (not specifically identified by a reference numeral in the figure). Connecting electrode patterns  12   a  to  12   d  and  13   a  to  13   d  for connecting between the external-connection pads of the adjacent transversal SAW filter devices are defined in the vicinity of the external-connection pads  8   a  to  8   c ,  9   a  to  9   c ,  10   a  to  10   c , and  11   a  to  11   c . The connecting electrode patterns  12   b  to  12   d  and  13   b  to  13   d  include larger portions, which serve as measurement pads  14   a  to  14   c  and  15   a  to  15   c.    
         [0033]     A transversal SAW filter device according to the first preferred embodiment will be described in the context of the middle filter device of the three filter devices illustrated in the enlarged view in  FIG. 1 . When signals are input from the external-connection pads  8   b  and  9   b , surface acoustic waves are excited and filtered by the transmitter  3   b , and are received by the receiver  4   b  and are output from the external-connection pads  10   b  and  11   b . The transversal SAW filter device functions in this way.  
         [0034]     Lines  16   a  to  16   f  indicated by one-dot chain lines are tentative cutting lines of the wafer. In consideration of regions to be cut out by dicing, the regions defined by two-dot chain lines  17   a  to  17   c  are tentative outer frames of the cut out transversal SAW filter devices.  
         [0035]     In the transversal SAW filter devices, input-signal probes are applied to the measurement pads  14   a  and  14   b , and output-signal probes are applied to the measurement pads  15   a  and  15   b , and the surface acoustic waves excited by the transmitter  3   b  are extracted from the receiver  4   b  so that frequency characteristics of the transversal SAW filter devices defined on the piezoelectric substrate  1  can be examined in the on-wafer state. Although the measurement pad  14   a  is also connected to the external-connection pad  9   a , the transmitter  3   a  does not operate because no voltage is applied to the external-connection pad  8   a . For the same reason, the transmitter  3   c  and the receivers  4   a  and  4   c  do not operate. Therefore, it is only required to selectively apply test probes to measurement probes to measure the frequency characteristics of the desired transversal SAW filter device in the on-wafer state to determine the quality of the desired transversal SAW filter device.  
         [0036]     Each of the measurement electrode pads  14   a  to  14   c  and  15   a  to  15   c  is shared by two adjacent devices. Thus, the area occupied by the transversal SAW filter devices on the wafer can be reduced compared with the structure of the related art shown in  FIG. 5 . The number of transversal SAW filter devices formed on the same wafer can therefore increase.  
         [0037]     A second preferred embodiment of the present invention will now be described below with reference to  FIG. 2 . Referring to  FIG. 2 , a glass substrate  2  is patterned in a similar manner to the substrate in the first preferred embodiment, and piezoelectric thin films  27   a  to  27   c  of zinc oxide (ZnO) or the like are formed so as to continuously cover transmitters  3   a  to  3   c , shield electrodes  5   a  to  5   c , and receivers  4   a  to  4   c . Dampers  6   a  to  6   c  are defined at the end of the piezoelectric thin films  27   a  to  27   c  on the side of the transmitters  3   a  to  3   c  which does not face the receivers  4   a  to  4   c . Dampers  7   a  to  7   c  are defined at the end of the piezoelectric thin films  27   a  to  27   c  on the side of the receivers  4   a  to  4   c  which does not face the transmitters  3   a  to  3   c.    
         [0038]     With the above-described structure, particularly in a case where the piezoelectric thin films  27   a  to  27   c  are made of zinc oxide (ZnO), the transversal SAW filter devices have the advantage of higher temperature stability than transversal SAW filter devices constructed so that electrodes are formed on a wafer of single-crystal piezoelectric substrate material, such as lithium tantalate (LiTaO 3 ) or lithium niobate (LiNbO 3 ). The electrode pattern configuration in the second preferred embodiment, which falls within the scope of the present invention, is similar to that in the first preferred embodiment, and similar advances are therefore achieved.  
         [0039]     A third preferred embodiment of the present invention will now be described below with reference to  FIG. 3 . As in  FIG. 1 , a portion of multiple transversal SAW filter devices defined on a piezoelectric substrate, namely, three transversal SAW filter devices, is illustrated in an enlarged view in  FIG. 3 .  
         [0040]     In the transversal SAW filter devices, the adjacent external-electrode connection pads are connected to each other via connecting electrode patterns  12   a  to  12   d  and  13   a  to  13   d . The connecting electrode patterns  12   a  to  12   d  and  13   a  to  13   d  include larger portions, which serve as measurement pads  18   a  to  18   d  and  19   a  to  19   d , and the measurement pads  18   a  to  18   d  and  19   a  to  19   d  are defined at the positions at which the connecting electrode patterns  12   a  to  12   d  and  13   a  to  13   d  intersect tentative cutting lines  16   c  to  16   f.    
         [0041]     According to the third preferred embodiment, the measurement pads  18   a  to  18   d  and  19   a  to  19   d  defined on the tentative cutting lines  16   c  to  16   f  allow effective utilization of the area cut out by dicing, which corresponds to the width of a dicing blade used for dicing. Therefore, the size of the transversal SAW filter devices can be reduced compared with the first preferred embodiment, and the integration density on the wafer and the number of transversal SAW filter devices manufactured per wafer increases.  
         [0042]     Also in the third preferred embodiment, as in the second preferred embodiment, the electrode pattern may be defined on a glass substrate and a piezoelectric thin film may be overlaid to form transversal SAW filter devices.  
         [0043]     A fourth preferred embodiment of the present invention will now be described below with reference to  FIG. 4 . As in  FIG. 1 , a portion of multiple transversal SAW filter devices defined on a piezoelectric substrate, namely, three transversal SAW filter devices, is illustrated in an enlarged view in  FIG. 4 .  
         [0044]     Shield electrodes  5   a  to  5   c  are defined separately from transmitters  3   a  to  3   c  and receivers  4   a  to  4   c . The shield electrodes  5   a  to  5   c  include external-connection electrode pads  22   a  to  22   c  that are connected to the shield electrodes via electrode patterns (not specifically identified by a reference numeral in the figure). The shield-electrode external-connection pads  22   a  to  22   c  are connected to measurement pads  21   b  to  21   d  via connecting electrode patterns  23   a  to  23   c . However, the shield-electrode external connections pads  22   a  to  22   c  may be connected to the measurement pads  20   b  to  20   d  for the transmitters  3   b  and  3   c.    
         [0045]     In the event of performing probe measurement in the on-wafer state, the measurement pads  21   a  to  21   d  are connected to the shield-electrode external-connection pads  22   a  to  22   c . The measurement pad  21   a  is set to a ground potential when the measurement is performed using the measurement pads  21   a  and  21   b , the measurement pad  21   b  is set to the ground potential when using the measurement pads  21   b  and  21   c , and the measurement pad  21   c  is set to the ground potential when using the measurement pads  21   c  and  21   d.    
         [0046]     When the transversal SAW filter devices are cut out along the tentative cutting lines  16   a  to  16   f , the connecting electrode patterns  23   a  to  23   c  are cut out, and the shield electrodes  5   a  to  5   c  are electrically isolated from the receivers  4   a  to  4   c , thereby manufacturing balanced-operation transversal SAW filter devices.  
         [0047]     According to the fourth preferred embodiment, shield-electrode measurement pads  26   a  to  26   c  of the related art shown in  FIG. 6  can be removed, and the number of measurement pads can be reduced. As in the third preferred embodiment, the measurement pads  20   a  to  20   d  and  21   a  to  21   d  defined on the tentative cutting lines  16   c  to  16   f  allow effective utilization of the area cut out by dicing, which corresponds to the width of a dicing blade used for dicing. Therefore, the size of the transversal SAW filter devices can be reduced compared with the related art shown in  FIG. 6 , and the integration density on the wafer and the number of transversal SAW filter devices manufactured per wafer increases.  
         [0048]     Also in the fourth preferred embodiment, as in the second preferred embodiment, the electrode pattern may be formed on a glass substrate and a piezoelectric thin film may be overlaid to form transversal SAW filter devices.  
         [0049]     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.