SAW Device with Improved Thermal Management

Abstract

The present invention focuses on minimizing hot spots on a filter chip by generating a thermal radiator using a mechanical acoustic structure and a connection circuitry. The relationship between the metal and the wafer is gradually increased to provide better heat dissipation and heat dissipation. Preferably, the shunt line of the stepped arrangement of SAW resonators (R S 1, R S 2, R S 3) includes a widened section (BS). Each two series resonators (R S 1, R S 2, R S 3) arranged successively with each other in the series signal line are connected via a common bus bar (BB CN ) extending over the entire length of the subsequent series resonator. The lateral extension of the common bus bar represents the first part of each corresponding shunt line. Each first shunt line section between the node and the parallel resonator (R S1 ) of the shunt line (SL P 1, R P 2) includes a widened section (BS) wider than the common bus bar. The widened section extends over the entire width of the parallel resonator (R P 1). The first reflector (REF1) of the parallel resonator facing the laterally adjacent series resonator is formed by the widened section (BS).

Description

Background Art

[0001] HPUE applications (HPUE = High Power User Equipment, a special category of user equipment for LTE cellular networks) and upcoming 5G implementations have high requirements for RF components in terms of high-power processing and reliability. HPUE is allowed to transmit with an output power of up to 31 dBm.

[0002] Acoustic filters for this type of mobile communication use SAW resonators with a ladder-type structure, and these SAW resonators can operate signals with higher power. The corresponding acoustic filter chips must handle power exceeding 1 W, and as a further obstacle, smaller chip sizes are currently required. High-power stage filters require thermal management, which enables the acoustic chips to avoid premature power compression at excessive power levels.

[0003] When the power is affected at the input of the filter / diplexer / multiplexer and observed at the output power, the ideal relationship between the input Pin and the output power Pout should be linear. This means the behavior should be as follows:

[0004] Pin = (alpha)*Pout,

[0005] where alpha is the constant loss of the passive filter device. However, when too much power is injected and the output power starts to saturate, this linear relationship fails. This power saturation results in very high local temperature gradients, and this local temperature gradient must be managed to prevent device failure. Summary of the Invention

[0006] Therefore, an object of the present invention is to provide a filter device with improved thermal management, which minimizes the risk of sudden thermal rise.

[0007] The SAW filter device according to the independent claims meets this object and other objects. Advantageous features and embodiments are given by the dependent claims.

[0008] The general idea is to solve the problem without any change in the acoustic characteristics, so only chip layout techniques are adopted without any impact on these characteristics. According to the present invention, there is provided a SAW filter device having SAW resonators with a ladder-type structure. This type of filter consists of a large number of resonators and many circuit systems between different resonators and between the resonators and the corresponding terminals. Therefore, there are many degrees of freedom for layout variations.

[0009] Thermal management of an acoustic chip (such as a SAW filter device) first requires a careful analysis of possible heat generation mechanisms. Three mechanisms can be found, including the first-order DC resistance of the connecting circuit system, RF resistance, and the coupling of mechanical and electrical energy with the piezoelectric material.

[0010] The present invention focuses on minimizing hot spots on a chip by creating a heat radiator using a mechanical acoustic structure and a connection circuit system. In the case of a filter, duplexer, or multiplexer, the relationship between the metal and the wafer is gradually increased to provide better heat dissipation and heat dissipation.

[0011] The SAW filter device has a ladder-type structure. Series signal lines connect the antenna terminal and the I / O terminals for input and output signals. In the series signal lines, a number of series resonators are arranged. Nodes are located in the series signal lines between every two series resonators. Shunt lines are respectively connected to their respective corresponding nodes, and parallel resonators are respectively arranged in the shunt lines.

[0012] Herein and hereinafter, the length of a resonator should be understood to mean the length measured along the longitudinal direction in accordance with the wave propagation direction. Similarly, the width of the resonator is measured along the transverse direction perpendicular to the longitudinal direction.

[0013] Every two series resonators arranged successively with each other in the series signal lines are connected via a metallized area called a common busbar that extends over the entire length of the two subsequent series resonators.

[0014] The lateral extensions of the common busbar respectively represent the first segments of the corresponding shunt lines. The first shunt line segment defined as the segment between the node and the corresponding parallel resonator includes a widened segment with a width ratio greater than the width of the common busbar. The widened segment is as wide as it extends over the entire width of the parallel resonator, thus almost filling the entire space between adjacent series resonators, signal lines, and parallel resonators. Advantageously, the first reflector of the parallel resonator facing the laterally adjacent series resonator is formed by the metallization of the widened segment.

[0015] Simply in this way, the metallized area on the surface of the filter chip (i.e., the surface of the SAW filter device) is significantly enhanced, thus providing an improved heat radiator without increasing the size of the SAW filter device.

[0016] To obtain better power resistance, those series resonators arranged between the first node and the last node in the series signal lines can be doubly cascaded by means of connection busbars inserted between the single resonators in cascade. The width of the connection busbar is greater than the width required for current conduction, and the width is at least 10 μm. Usually, this connection busbar between two cascaded resonators has a necessary width of about 2 μm or less.

[0017] According to one embodiment, laterally extending metallization of a common bus is used to form a first reflector, a first bus, and a second reflector of a respective parallel resonator in a respective shunt line. Also herein, the metallization area “around” the parallel resonator is maximized, and this metallization area is associated with respective improvements in heat dissipation and heat dissipation.

[0018] If the parallel resonator has a first reflector and a first bus formed by a first section of the shunt line, the respective second bus and second reflector may be formed by a second section of the shunt line.

[0019] According to one embodiment, those series resonators arranged between a first node and a last node in a series signal line are arranged in rows with one node below another on a line parallel to the lateral direction. Thus, the series signal line extends substantially parallel to the lateral direction. All shunt lines extend from the series signal line in a second direction consistent with the longitudinal direction. Reflectors of the series resonators arranged in rows facing away from the shunt line in a first direction are formed by strip-shaped metallization that extends over the entire length of the series resonators arranged in rows, has a width that is substantially constant when measured in the lateral direction, and a width that is at least equal to the width of the respective reflector formed in the strip-shaped metallization. The connection of the strip-shaped metallization to the ground terminal further improves heat dissipation and heat dissipation by providing another heat dissipation path.

[0020] In another embodiment, all series resonators arranged between a first node and a last node in a series signal line are cascaded, with each cascade including a series connection of two single resonators. In each series resonator cascade of these series resonator cascades, a second reflector facing the second direction is common to the two single resonators and extends over the total width of the two single resonators. These reflectors are connected to a respective common bus and are isolated from any other potential or ground terminal.

[0021] In all embodiments, the second reflector of the last series resonator facing the second direction, the second bus near the I / O terminal, and the I / O terminal are also formed of the same metallization and / or connected to the same potential. Further, this metallization may be elongated to extend away from the second bus along the longitudinal direction, where the length is longer than the width of the reflector.

[0022] Those series resonators arranged between a first node and a last node in a series signal line may be cascaded respectively by a series connection of two single resonators. Then, all first reflectors and second reflectors of the single resonators may be electrically isolated from each other and not connected to any line or external potential.

[0023] All second segments of the shunt line are connected to a common ground region, which has a width in the longitudinal direction that is at least the width of the second reflector of the parallel resonator.

[0024] The SAW filter device can be designed as a Tx filter, where the I / O terminals are Tx terminals. The last series resonator next to the Tx terminals is not cascaded, and its length is at least twice the length of the remaining series resonators.

[0025] The benefit of the new SAW filter device is that in the case of a rapid change in power, heat can be better diffused in the SAW filter chip, thereby eliminating hot spots that may damage the chip. To achieve this advantage, no new process is required, and the same package as the currently used SAW devices can be used. Compared with the same devices used previously, it has improved power compression performance and is slightly better for small signals. Description of the Drawings

[0026] The present invention will be explained in more detail below with reference to specific embodiments and the drawings. The drawings are only schematic and are drawn to scale. Therefore, exact relative or absolute measurements cannot be obtained from these drawings.

[0027] Figure 1 A SAW filter device is shown in which the first segment of the shunt line has a widened segment.

[0028] Figure 2 A cascade of two single resonators is shown that can replace the resonators in the ladder-type arrangement of the filter device.

[0029] Figure 3 Two representative SAW filter devices with different designs of the shunt line are shown, in which the first reflector and the second reflector of the parallel resonator are coupled to different busbars.

[0030] Figure 4 A SAW filter device is shown with strip-type metallization and reflectors for forming series resonators therein.

[0031] Figure 5 It is a block diagram of a TX SAW filter device.

[0032] Figure 6 The transfer curves of a control example and two embodiments are compared.

[0033] Figure 7 The reflectivity of the filter in the low stopband is shown.

[0034] Figure 8 The compression of the filter device measured at 50 °C and 915 MHz is shown.

[0035] Figure 9 Shows the compression of the filter device measured at 50 °C and 25 °C,

[0036] Figure 10 Shows the compression of the filter device measured at 25 °C, 50 °C and 85 °C when a continuous wave signal is applied at 912.5 MHz,

[0037] Figure 11 Shows a table with the threshold temperatures measured in examples at slight compression, severe compression and breakdown. Detailed Description

[0038] Figure 5 Shows a schematic block diagram of a TX SAW filter device using SAW resonators with a stepped arrangement. The shown filter consists of a large number of resonators and many circuitry systems between the different resonators and between the resonators and the respective terminals. Therefore, there are many degrees of freedom in the layout. A series signal line connects the antenna terminal AT and the I / O terminal IO for input and output signals, which is the terminal TX for inputting transmission signals in the example. A number of series resonators R S . Figure 5 The example has four series resonators R S 1 to R S 4. Nodes N1 to N3 are located in the series signal line between every two subsequent series resonators. Shunt lines SL are each connected to the respective node N, and parallel resonators R P are each arranged in the respective shunt line SL. The first section SL S1 of each shunt line SL connects the node N and the respective parallel resonator R P . The second section SL S2 of each shunt line SL connects this parallel resonator R P to the ground terminal GND. Preferably, all shunt lines are combined at the node NS on the chip to be commonly connected to the same ground terminal GND. However, according to the design requirements, one or more of the shunt lines SL can also be connected to individual ground terminals GND before being individually grounded.

[0039] The first three series resonators R S 1 to R S 3 are double - cascaded, each cascade including a series connection of two single resonators single resonators SR 1 , SR 2 , as Figure 2 shown. The fourth series resonator is not cascaded and has a greater extended length than the remaining three resonators.

[0040] Generally, as Figure 5All circuitry of the known filter shown is dimensioned according to requirements of effective conductivity and low ohmic losses. This design serves as a reference and is designated as the control example.

[0041] Figure 1 A schematic SAW filter structure according to the invention is shown. For simplicity, only two shunt lines SL are depicted, while three shunt lines and more according to the control example are also possible. For the series resonators R S the number thereof and their possible cascading or preferred cascading (not explicitly depicted in Figure 1 ), the same applies. Different from the control example, two subsequent series resonators are connected by a common bus bar BB CN which has a lateral extension forming the first section SL of the shunt line SL CN S1 Each such first section SL S1 has a widened section BS with a width greater than that of the common bus bar BB CN . The width is measured in the transverse direction TD indicated by the corresponding arrow in the figure.

[0042] In the widened section of each shunt line, a first reflector REF1 for the corresponding parallel resonator R P is formed. Generally, the reflector REF comprises a reflection grid embodied in a regular pattern of reflection metal strips. Each corresponding second reflector REF2 of the parallel resonator R P can also be connected to the first section of the shunt line. Alternatively, it can be electrically floating or preferably connected to the second bus bar of the resonator and the second section SL of the shunt line SL S2 .

[0043] Only the reflector REF of the series resonator is schematically shown. The reflector facing the second direction facing the shunt line is preferably floating and not connected to an external or fixed potential. Further, cascading of individual resonators SR can share the same reflector. The same applies to the reflector facing the first direction away from the shunt line.

[0044] Figure 2 Two cascaded individual resonators SR CC connected by a connection bus bar BB 1 , SR 2 are shown. In a preferred example (as in Examples 1 and 2 later), the width WBB of the connection bus bar BB CC is at least 10 μm. Two cascaded individual resonators SR can replace any or all of the series resonators R S , which is preferred.

[0045] Figure 3 is shown in connection with Figure 1 ​A filter device similar to the filter device. In this article, different possibilities of connecting and forming a second reflector REF2 as a reflector facing the second direction are shown. In the top part streamline, the second reflector of the parallel resonator is connected to the second bus bar, which is the top bus bar in the figure. Thus, the second section of the shunt line is connected to the second bus bar. In the bottom part streamline in the figure, the second reflector is formed by a laterally extending connecting bus bar and is thus connected to the first bus bar and the first section SL S1 .

[0046] Figure 4 Similar to Figure 1 and Figure 3 . In this article, the first reflector of the series resonator R S is formed by a strip-shaped metallization SM extending over the total length of the series resonator. For this purpose, those series resonators R S arranged between the first node and the last node N in the series signal line are arranged in rows one below the other on a line parallel to the transverse direction TD such that at least the first ends of the resonators are flush with each other. In the illustrated embodiment, the strip-shaped metallization SM is connected to the ground terminal GND.

[0047] Figure 6 Shows the signal transmission in the passband region of the Tx filter optimized for the frequency band 8. Curve 1 is consistent with the transmission of the control example using ordinary wires. Curve 2 is assigned to the first example with the strip-shaped metallization SM, as Figure 4 shown, while the second example according to curve 3 has a normal reflector on the first side of the series resonator and is separate for each series resonator. The results show that the three examples show similar transmission characteristics.

[0048] Figure 7 Shows the reflectivity of the above filter device in the lower stopband. The first example and the second example have higher reflections in the depicted frequency range due to lower ohmic losses compared to the control example.

[0049] Figure 8 Shows the corresponding compression measured at 50 °C and 915 MHz located at the upper right edge of the passband. The signal of the control example according to curve 1 starts to compress at the lowest input power Pin of about 28.5 dBm. The first example starts to compress at 29.5 dBm, and the first example starts to compress at about 0.3 dBm or lower. This is due to higher losses occurring in the control example.

[0050] Figure 9 Shows the corresponding compression measured at two different temperatures of 50 °C and 25 °C when a continuous wave signal of 915 MHz is applied. Figure 9 9A inFigure 9 9B in Figure 9 and 9C in

[0051] Figure 10 are in line with the first and second examples.

[0052] Figure 11 shows the corresponding compression of the same example measured at three different temperatures of 85°C, 50°C, and 25°C.

[0053] The present invention has been explained with reference to different individual features. However, without departing from the scope of the present invention, a real filter device may show one or more of the features implemented in different and arbitrary combinations.

[0054] List of reference numerals used

[0055] 1, 2, 3: Example numbers

[0056] AT: Antenna terminal

[0057] BB CN : Common bus

[0058] BB CC : Connecting bus

[0059] BS: Widened section of the first shunt line

[0060] GND: Ground terminal

[0061] IO: I / O terminal

[0062] LD: Longitudinal direction

[0063] N: Node

[0064] N1: First node of the series signal line next to the antenna

[0065] NS: Node connected to different shunt lines

[0066] REF: Reflector

[0067] REF1: First reflector of the parallel resonator

[0068] R P : Parallel resonator

[0069] R S : Series resonator

[0070] SL: Shunt line

[0071] SL S1 : The first shunt line segment

[0072] SM: Strip-shaped metallization

[0073] SR: Single resonator

[0074] TD: Transverse direction

[0075] WBB: Width of the bus bar

Claims

1. A SAW filter device having a stepped structure, comprising: - A series signal line connecting an antenna terminal and an I / O terminal; - Series resonators arranged on the series signal line; - Nodes located in the series signal line between two series resonators; - Shunt lines connected to corresponding nodes; - Parallel resonators, each parallel resonator being arranged in a corresponding shunt line; - Each resonator has a length measured along a longitudinal direction conforming to the wave propagation direction and a width measured along a transverse direction perpendicular to the longitudinal direction, wherein - Each two series resonators successively arranged in the series signal line are connected via a common busbar extending over the entire length of the subsequent series resonator, - The lateral extensions of the common busbar respectively represent the first shunt segments of the corresponding shunt lines; - Each first shunt segment between a node and the parallel resonator of the shunt line includes a widened segment wider than the common busbar; - The widened segment extends over the entire width of the parallel resonator; - The first reflector of the parallel resonator facing the laterally adjacent series resonator is formed by the widened segment.

2. The SAW filter device according to the preceding claim, wherein those series resonators arranged between the first node and the last node of the series signal line are doubly cascaded by means of a connection busbar, wherein the width of the connection busbar is at least 10 μm.

3. The SAW filter device according to one of the preceding claims, wherein the lateral extensions of the common busbar form the first reflector, the first busbar and the second busbar of the parallel resonator.

4. The SAW filter device according to claim 1 or 2, wherein the parallel resonator has a first reflector and a first busbar formed by the laterally extending first shunt segment, wherein the second busbar and the second reflector of the parallel resonator are formed by the second shunt segment of the shunt line.

5. The SAW filter device according to claim 1 or 2, - wherein those series resonators arranged between the first node and the last node in the series signal line are arranged in rows one below the other in a line parallel to the transverse direction; - wherein all shunt lines extend from the series signal line in the longitudinal direction; - wherein the reflectors of the series resonators arranged in rows facing away from the shunt lines are formed by strip metallization extending over the entire length of the series resonators arranged in rows, wherein the width measured along the transverse direction is at least the width of the corresponding reflector; - wherein the strip metallization is connected to a ground terminal.

6. The SAW filter device according to claim 1 or 2, wherein - those series resonators arranged between the first node and the last node in the series signal line are each cascaded by the series connection of two single resonators; - Among these series resonators, the second reflector located at one end facing the shunt line is common to the two single resonators and extends in the transverse direction over the total width of the two single resonators.

7. The SAW filter device according to claim 1 or 2, In the last series resonator beside the I / O terminal, the second reflector, the second bus bar, and the I / O terminal located at the end facing the corresponding shunt line are formed of the same metallization and / or connected to the same potential.

8. The SAW filter device according to claim 1 or 2, wherein - those series resonators arranged between the first node and the last node in the series signal line are each cascaded by a series connection of two single resonators; - all the first reflectors and the second reflectors of the single resonators are electrically isolated from each other and not connected to any line or external potential.

9. The SAW filter device according to claim 1 or 2, wherein all the second shunt segments of the shunt line are connected to a common ground area, and the width of the common ground area in the longitudinal direction is at least the width of the second reflector of the parallel resonator.

10. The SAW filter device according to claim 1 or 2, designed as a Tx filter, wherein the I / O terminal is the Tx terminal, and the last series resonator adjacent to the Tx terminal is not cascaded, and the length of the last series resonator is at least twice the length of each remaining series resonator.

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