Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2001-03-30
2003-05-20
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S195000, C310S31300R, C310S31300R, C029S025350
Reexamination Certificate
active
06566980
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to die layouts for electronic circuits, and, more specifically, to die layouts for surface-acoustic-wave devices.
2. Description of Related Art
SAW devices typically comprise interdigitated conductive electrode patterns (transducers) and conductive electrode grating patterns on a surface of piezoelectric materials. When an alternating-polarity electrical signal is applied to the transducer of these devices, a surface acoustic wave is launched at the surface of the piezoelectric material. The electrode grating regions of the device serve to reflect the surface wave due to mechanical and electrical effects. The interdigitated conductive electrode patterns of the transducer have electrode regions and bus-bar regions. The transducer electrode regions serve to stress the piezoelectric and generate an acoustic wave when signals of alternating polarity are applied, while the bus-bar regions serve to electrically connect the individual electrodes in the electrode region to one polarity or the other, and to transmit the applied voltage to the electrodes. The conductive bus-bar regions that are connected to device electrical terminals to which voltage is applied are usually called bond pads, while the conductive bus-bar regions that are electrically connected to ground are generally called ground pads.
The gratings also have electrode regions and bus-bar regions. The electrode regions serve to reflect the surface acoustic wave, while the bus-bar regions serve to electrically connect the individual electrodes in the electrode region to one polarity.
SAW device types known as coupled resonator filters (CRFs) utilize multiple resonant regions coupled acoustically and electrically in configurations designed to achieve a desired frequency response. A typical CRF structure comprises two parallel tracks, each consisting of a central transducer with two bus bars and bond pads, two additional interdigitated transducer regions on either side of the central transducer, and two reflective gratings at the outer ends of this transducer structure. The “hot” bond pads for the transducers are isolated. The outer transducers do not have bond pads, but rather one bus bar polarity is connected with the ground pads of the adjacent gratings, and the other polarity bus bar is connected electrically to the bus bar of the similar transducer in the second track. Thus these transducers are electrically connected, and the nongrounded sides of these transducers are “floating” relative to the electric potential of the central transducers. Within each track, a resonance is established when the central transducer launches an acoustic wave. The series-connected floating transducers serve to couple the signal between the two tracks. A typical CRF layout
10
with isolated central transducers
11
,
12
is shown by way of example in FIG.
1
. It should be noted that all the figures presented herein have been simplified and enlarged to show the details of the device layout. Typical devices would have many more electrodes than illustrated.
Traditionally, for CRF devices the electrode regions have been oriented perpendicular to the direction of surface-wave propagation and parallel to the “ends”
13
,
14
of the SAW device die
10
. In this traditional configuration, the bus bars are generally parallel to the other set of die edges (the “sides”
15
,
16
of the die). This type of layout
10
is shown in FIG.
1
. Electrical performance requirements make it essential for the isolated “hot” bond pads
17
,
18
to be placed in close proximity to, and in good electrical contact with, the central transducer bus bar
19
,
20
. Manufacturing requirements dictate minimum sizes for bond pads, and that certain blank regions of crystal be left between the edge of the die and any metallized region, be it electrode or bus bar. This is particularly important for devices that are mounted using flip-chip technology, where the bumps formed on the bond pads can be torn off at the time the dies are singulated if the bond pads are not set far enough back from the die edge.
It can be seen from
FIG. 1
that the bus-bar and bond pad sizes and bare die regions add to the overall size of the die
10
. The choice of package size is dependent on how small the die can be made for a given level of electrical performance. Customers typically have requirements for electrical performance and desire as small a package size as possible. Thus improvements in die layout that result in a reduction in die size for a given electrical performance allow for an overall reduction in package and device size. In this case, reduction in the length of the die will result in package size reduction.
Historically, the die edges nominally perpendicular to the direction of surface-wave propagation have been called the “ends”
13
,
14
of the die
10
, and the spatial extent of the die perpendicular to these ends
13
,
14
has been called the die width
21
. The die edges parallel to the direction of surface-wave propagation have been called the “sides”
15
,
16
of the die. We will retain this terminology of die ends, sides, length, and width, even though the CRF devices under consideration often have aspect ratios such that the width may exceed the length. Generally CRF devices are small enough in the length dimension to fit into the small packages desired by the customer, but the problem arises in the width of the die required. In order to fit multiple transducer apertures and multiple (often 3 or more) bus bars and bond pads across the width of a die, the die width must be made substantially larger than necessary for the active electrode region alone. Specifically, the need to maintain the isolated hot bond pads
17
,
18
for the two central transducers
11
,
12
in close proximity to, and in good electrical contact with, the central transducers' bus bars
19
,
20
dictates that the largest dimension on the die electrode layout be the length
22
from the outer edge of one central transducer's
11
hot bond pad
17
to the outer edge of the other central transducer's
12
hot bond pad
18
. This dimension can be reduced as much as possible within manufacturing tolerances, but even when reduced as much as possible (while maintaining electrical performance and impedance characteristics), this dimension is the limiting factor in reducing die size further.
Further features of the prior art die
10
include four gratings
23
, two surrounding each central transducer
11
,
12
, and four bond pads
24
leading thereto. Generally square bond pads
17
,
18
,
24
are in this design generally collinear and are adjacent the sides
15
,
16
of the die
10
, with their outer edges generally parallel the sides
15
,
16
, and their top and bottom edges generally parallel the ends
13
,
14
. In such an embodiment the width
21
is smaller than the length
22
of the die
10
.
Whereas in
FIG. 1
, the two bond pads
25
,
26
between the transducer/grating array are separate and in spaced relation to each other,
FIG. 2
illustrates another prior art embodiment
10
′ in which the two bond pads
25
′,
26
′ have been joined, reducing the die width
21
′ and length
22
′ slightly.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a die layout that reduces die width.
It is another object to provide such a die layout that increases efficiency.
It is a further object to provide such a die layout that reduces package size.
It is an additional object to provide such a die layout that results in a reduced device size.
These and other objects are achieved by the present invention, a surface-acoustic-wave device. The device comprises a generally rectangular die that comprises a piezoelectric material. A surface-acoustic-wave electrode pattern is positioned atop the die. The pattern has a generally rectangular footprint, and the footprint has a top edge that is positioned at an acute, nonzero angle to a top end of the die. Th
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Sawtek Inc.
Summons Barbara
LandOfFree
Die layout for SAW devices and associated methods does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Die layout for SAW devices and associated methods, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Die layout for SAW devices and associated methods will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3003893