Transmitting interdigital transducer structure for inhibiting clutter of surface acoustic wave filter

Abstract

The invention discloses a transmitting interdigital transducer structure for suppressing clutters of a surface acoustic wave filter, an IDT pattern is formed between two bus bars, the IDT pattern is formed by crosswise arranging a positive electrode pair and a negative electrode pair, and each electrode pair is at least composed of two electrodes with the same polarity; each electrode comprises a true finger and a false finger which are oppositely arranged, and all the true fingers and all the false fingers in any electrode pair are connected through inner connecting strips. The inline strip is connected with the tail ends of all true fingers and false fingers of the electrode pair in a penetrating mode, the thickness of the inline strip is larger than that of the electrode layer, the propagation speed of sound waves in the inline strip is equal to the propagation speed between the true fingers and the false fingers by reasonably setting the thickness of the inline strip, and therefore the clutter mode of the inline strip serving as effective electrode excitation is eliminated; a clutter mode generated in a sound wave propagation process is suppressed, and passband ripples and out-of-band suppression of the surface acoustic wave filter are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to an interdigital transducer, in particular to a transmitting interdigital transducer structure for suppressing spurious of a surface acoustic wave filter, and belongs to the technical field of surface acoustic wave devices. BACKGROUND

[0002] Surface acoustic wave (SAW) filters are widely used in the fields of national defense and mobile communication due to their small size, low cost and high reliability. A conventional transverse surface acoustic wave filter is usually composed of a transmitting interdigital transducer and a receiving interdigital transducer. The transmitting interdigital transducer has different finger sampling (referred to as sampling finger). Different frequency and shape filter curves are realized by the sampling finger weighting of the transmitting transducer and the apodization weighting of the receiving transducer. The advantage of this type of filter is that it has extremely steep rectangularity. In order to reduce the electrode resistance of the sampling finger weighting and thus reduce the insertion loss of the filter, the same polarity electrodes are usually connected by inline strips to reduce the electrode resistance, but this will bring additional spurious modes. Such spurious modes will reduce the out-of-band rejection, increase the in-band ripple, and easily lead to a decrease in the signal-to-noise ratio of the application system, thus causing signal distortion.

[0003] The current common suppression method is to suppress and compensate the receiving interdigital transducer, but this method will reduce the receiving efficiency of the receiving interdigital transducer. SUMMARY

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a transmitting interdigital transducer structure for suppressing spurious of a surface acoustic wave filter. The present application can suppress the spurious modes generated in the process of sound wave propagation and improve the passband ripple and out-of-band rejection of the surface acoustic wave filter.

[0005] In order to solve the above technical problems, the present application adopts the following technical solutions: The application discloses a structure of a transmitting interdigital transducer for suppressing spurious waves of a surface acoustic wave filter, which comprises a substrate and an electrode layer on the substrate, the electrode layer comprises two parallel bus bars, and an IDT pattern is formed by a plurality of electrodes between the two bus bars; the IDT pattern is composed of positive electrode pairs and negative electrode pairs arranged in a cross manner, each electrode pair is composed of at least two electrodes with the same polarity; the center distance between any two adjacent electrodes is equal and is p; each electrode comprises a real finger and a false finger arranged oppositely, the lengths of all the real fingers in the same electrode pair are equal and the real fingers are arranged on the same bus bar, the lengths of all the false fingers in the same electrode pair are equal and the false fingers are arranged on the other bus bar opposite to the real fingers; the real fingers of two adjacent electrode pairs are located on different bus bars; all the real fingers in any electrode pair are connected by a real finger interconnection, and all the false fingers in any electrode pair are connected by a false finger interconnection; each real finger interconnection is located at the end face of the real fingers of the electrode pair away from the bus bar and connects all the real fingers of the electrode pair in a penetrating manner; each false finger interconnection is located at the end face of the false fingers of the electrode pair away from the bus bar and connects all the false fingers of the electrode pair in a penetrating manner; the thicknesses of all the interconnections are equal and are higher than the thickness of the electrode layer, and the thickness of the interconnection is such that the propagation speed of the acoustic wave in the interconnection is equal to the propagation speed between the real finger and the false finger.

[0006] Further, the thicknesses of all the real fingers, the false fingers and the bus bars are equal, and the thickness is the thickness of the electrode layer.

[0007] Further, in each electrode, the interval distance between the real finger and the false finger is less than 1 um, and in all the electrodes, the interval distance between the real finger and the false finger is equal.

[0008] Compared with the prior art, the application has the beneficial effects that: The transmitting interdigital transducer structure provided by the application adopts the penetrating interconnection at the ends of the real finger and the false finger, the thickness of the interconnection is higher than the thickness of the electrode layer, the thickness of the interconnection is reasonably set so that the propagation speed of the acoustic wave in the interconnection is equal to the propagation speed between the real finger and the false finger, the spurious wave mode caused by the interconnection as an effective electrode is eliminated, the spurious wave mode generated in the process of acoustic wave propagation is suppressed, and the passband ripple and the out-of-band suppression of the surface acoustic wave filter are improved. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 It is a top view of the transmitting interdigital transducer structure of the application. Figure 2 It is a side view of the transmitting interdigital transducer structure of the application. Figure 3 It is a simulation admittance curve diagram of a conventional transmitting interdigital transducer. Figure 4 It is a simulation admittance curve diagram of the transmitting interdigital transducer of the application. Among them, 1-busbar; 2-false finger; 3-false finger inline bar; 4-true finger; 5-true finger inline bar; 6-substrate. Detailed Implementation

[0010] The present invention will now be described in further detail with reference to the accompanying drawings.

[0011] Please see Figure 1 and Figure 2 This invention discloses a transmitting interdigital transducer structure for suppressing surface acoustic wave (SAW) filter clutter, comprising a substrate 6 and an electrode layer on the substrate. The electrode layer includes two parallel busbars 1, with an IDT pattern formed between the two busbars 1 by a plurality of electrodes. The IDT pattern is composed of alternating positive and negative electrode pairs, each electrode pair consisting of at least two electrodes of the same polarity. The center-to-center distance between any two adjacent electrodes is equal and p. Each electrode includes a true finger 4 and a false finger 2 arranged opposite each other. All true fingers 4 in the same electrode pair are of equal length and located on the same busbar, and all false fingers 2 in the same electrode pair are of equal length and located on another busbar opposite the true finger. The true fingers of adjacent electrode pairs are located on different busbars. All true fingers 4 in any electrode pair are connected by true finger connecting strips 2, and all false fingers 2 in any electrode pair are connected by false finger connecting strips 3. Each true finger inline strip 5 is located on the end face of all true fingers of the electrode pair away from the busbar, and connects all true fingers of the electrode pair in a through manner; each false finger inline strip 3 is located on the end face of all false fingers of the electrode pair away from the busbar, and connects all false fingers of the electrode pair in a through manner; all inline strips have the same thickness and are higher than the electrode layer thickness, and the thickness of the inline strips makes the propagation speed of sound waves in the inline strips equal to the propagation speed between true and false fingers.

[0012] All true fingers 4, false fingers 2, and busbar 1 have the same thickness, which is the thickness of the electrode layer.

[0013] In each electrode, the distance between the true finger 4 and the false finger 2 is <1µm, and the distance between the true finger and the false finger is equal in all electrodes.

[0014] like Figure 3 , Figure 4As shown, simulated admittance curves for a transmitting interdigital transducer structure for suppressing surface acoustic wave filter clutter, provided in Embodiment 1 of the present invention, are presented respectively. Both structures use aluminum electrodes, with a 36°YX-quartz substrate. The period p in both structures is 2.835 μm, the busbar height is 4*p, the pseudo-finger height is 4*p and the width is 0.5*p; the true finger height is 170 μm and the width is 0.5*p; the inline bar height is 5.67 μm, and the electrode layer thickness is 108 nm. In Embodiment 1 of the present invention, the inline bar thickness is 308 nm, which is greater than the electrode layer thickness. In the conventional structure, the inline bar thickness and the electrode layer thickness are the same. (Comparison) Figure 3 and Figure 4 The simulation results clearly show that, after adopting the structure of this invention, the clutter modes of the interdigital transducer are significantly suppressed, and the amplitude of the dominant mode excitation is significantly improved. This indicates that the structure of this invention can both suppress the clutter modes of surface acoustic wave filtering and reduce the insertion loss of the filter. It should be noted that the height here refers to... Figure 1 Vertical dimension, width refers to Figure 1 Left and right dimensions, thickness refers to Figure 2 Dimensions in the vertical direction.

[0015] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made. All obvious changes derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A transmitting interdigital transducer structure for suppressing surface acoustic wave filter clutter, comprising a substrate and an electrode layer on the substrate, wherein the electrode layer includes two parallel busbars, and an IDT pattern is formed between the two busbars by a plurality of electrodes; the IDT pattern is composed of positive electrode pairs and negative electrode pairs arranged alternately, each electrode pair consisting of at least two electrodes of the same polarity; the center-to-center distance between any two adjacent electrodes is equal and p; each electrode includes a true finger and a false finger arranged opposite each other, all true fingers in the same electrode pair are of equal length and are disposed on the same busbar, and all false fingers in the same electrode pair are of equal length and are disposed on another busbar opposite to the true finger; the true fingers of adjacent electrode pairs are located on different busbars; all true fingers in any electrode pair are connected by true finger inline strips, and all false fingers in any electrode pair are connected by false finger inline strips; characterized in that: Each true finger inline strip is located on the end face of all true fingers of the electrode pair furthest from the busbar, and connects all true fingers of the electrode pair in a through manner; each false finger inline strip is located on the end face of all false fingers of the electrode pair furthest from the busbar, and connects all false fingers of the electrode pair in a through manner; all inline strips have the same thickness and are higher than the electrode layer thickness, and the thickness of the inline strips makes the propagation speed of sound waves in the inline strips equal to the propagation speed between true and false fingers.

2. The transmitting interdigital transducer structure for suppressing surface acoustic wave filter clutter according to claim 1, characterized in that: All true fingers, false fingers, and busbars have the same thickness, which is the electrode layer thickness.

3. The transmitting interdigital transducer structure for suppressing surface acoustic wave filter clutter according to claim 2, characterized in that: In each electrode, the distance between the real finger and the spur finger is <1µm, and the distance between the real finger and the spur finger is equal in all electrodes.

Images