WO2024001157A1

WO2024001157A1 - Fbar filter and multi-ladder filter

Info

Publication number: WO2024001157A1
Application number: PCT/CN2023/071388
Authority: WO
Inventors: 李国强
Original assignee: 河源市艾佛光通科技有限公司
Priority date: 2022-06-29
Filing date: 2023-01-09
Publication date: 2024-01-04
Also published as: CN115242216A

Abstract

The present application discloses an FBAR filter and a multi-ladder filter. The FBAR filter comprises a series resonator, a parallel resonator, a first inductor, and a second inductor; the series resonator and the parallel resonator are cascaded; two ends of the series resonator are connected in parallel to the first inductor; and one end of the parallel resonator is connected to the second inductor, and the other end of parallel resonator is grounded. The multi-ladder filter comprises a plurality of FBAR filters, and the plurality of FBAR filters are connected in series. The present application is suitable for existing resonators, the design of an ultra-wideband film bulk acoustic wave filter is achieved, and the market requirements of existing ultra-wideband filters are satisfied.

Description

An FBAR filter and a multi-step filter

This application claims priority to the Chinese patent application submitted to the China Patent Office on June 29, 2022, with application number 202210785076.4, and the invention title is "an FBAR filter and a multi-step filter", the entire content of which is incorporated by reference. in this application.

Technical field

The present application relates to the field of filter technology, and more specifically, to an FBAR filter and a multi-ladder filter.

Background technique

RF front-end filters, duplexers, and multiplexers based on thin film bulk acoustic wave devices are widely used in smartphones, communication terminals, and communication base stations because of their small size, low insertion loss, fast roll-off, and low power consumption. According to Shannon's channel theorem, the upper limit of the channel information transmission rate is related to the channel signal-to-noise ratio and bandwidth. As the bandwidth increases, the transmission rate increases, the power decreases, and confidentiality is enhanced. Therefore, the development of ultra-wideband filters is of great application value.

A typical thin film bulk acoustic wave filter is composed of thin film bulk acoustic wave resonators connected in series and parallel. In the passband, the series thin film bulk acoustic wave resonators show low resistance characteristics, and the parallel thin film bulk acoustic wave resonators show high resistance characteristics, so the pass band Low loss. Outside the passband, the series thin film bulk acoustic resonator exhibits high resistance characteristics, and the parallel thin film bulk acoustic wave resonator exhibits low resistance characteristics, achieving out-of-band suppression. The electromechanical coupling coefficient of AlN and ZnO piezoelectric materials used in traditional thin film bulk acoustic resonators is below 8%. The electromechanical coupling coefficient of the device of the realized resonator is below 9%. The 3dB relative bandwidth of the realized filter will also be only It can reach 9%, and ultra-wideband filtering cannot be achieved.

Contents of the invention

In order to overcome the shortcomings of the existing technology, the purpose of this application is to provide an FBAR filter and a multi-step filter, which are suitable for existing resonators and realize the design of ultra-wideband thin film bulk acoustic wave filters to meet the current needs of ultra-wideband filters. Filter market demand.

One of the purposes of this application is achieved using the following technical solutions:

An FBAR filter includes a series resonator and a parallel resonator, a first inductor, and a second inductor. The series resonator and the parallel resonator are cascaded; the first inductor is connected in parallel at both ends of the series resonator, and the parallel resonator is connected in parallel with the first inductor. One end of the resonator is connected to the second inductor, and the other end of the parallel resonator is connected to ground.

The third purpose of this application is achieved using the following technical solutions:

A multi-ladder type filter includes a plurality of FBAR filters as described above, and a plurality of the FBAR filters are connected in series.

Compared with the existing technology, the beneficial effects of this application are:

This application provides an FBAR filter and a multi-step filter, which are provided with a series resonator, a parallel resonator, a first inductor, and a second inductor. The series resonator and the parallel resonator are cascaded; the series resonance A first inductor is connected in parallel at both ends of the parallel resonator, one end of the parallel resonator is connected to a second inductor, and the other end of the parallel resonator is grounded. It can be applied to existing filters and can achieve a relative bandwidth exceeding 8% to 40%. Broadband thin film bulk acoustic wave filter design to meet the current market demand for ultra-wideband filters.

Description of drawings

Figure 1 is a circuit structure diagram of the FBAR filter provided in this application;

Figure 2 is the impedance curve of the traditional series and parallel thin film bulk acoustic resonators provided by this application;

Figure 3 is an impedance curve diagram of a series structure of a series thin film bulk acoustic wave resonator with an inductor and a capacitor in parallel provided by this application;

Figure 4 is an impedance curve diagram of a parallel thin-film bulk acoustic wave resonator provided by the present application and a series structure of an inductor and a capacitor in parallel;

Figure 5 is a circuit diagram of the multi-stage ladder type FABR filter provided by this application;

Figure 6 is a passband frequency response curve diagram of the multi-stage ladder type FABR filter provided by this application.

Detailed ways

Below, the present application will be further described with reference to the accompanying drawings and specific embodiments. It should be noted that, on the premise that there is no conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments. .

As shown in Figures 1 to 6, this application provides an FBAR filter that is suitable for existing resonators to realize the design of ultra-wideband thin film bulk acoustic wave filters and meet the current market demand for ultra-wideband filters.

Specifically, the FBAR filter includes a series resonator and a parallel resonator, a first inductor, and a second inductor. The series resonator and the parallel resonator are cascaded; the first inductor is connected in parallel at both ends of the series resonator, so One end of the parallel resonator is connected to the second inductor, and the other end of the parallel resonator is connected to ground. Both the series resonator and the parallel resonator include a substrate with grooves on the upper surface, a bottom electrode layer located on the substrate, a piezoelectric layer located on the bottom electrode layer, and a top electrode layer located on the piezoelectric layer. . In this application, series thin film bulk acoustic wave resonators and parallel thin film bulk acoustic wave resonators are connected together to form a first-order ladder-shaped filter.

This filter is a thin film bulk acoustic wave filter N77 frequency band used in 5G communications. The passband frequency of the filter is 3.3GHz ~ 3.8GHz, the center frequency is 3.55GHz, and the relative bandwidth is 14%. The suppression of the 3.2GHz frequency point on the left side of the passband exceeds -40dB, and the suppression of the 3.92GHz frequency point on the right side of the passband exceeds -40dB.

Specifically, by changing the bottom electrode thickness, piezoelectric layer thickness or top electrode thickness of the series resonator, its parallel resonance frequency is slightly higher than the passband frequency of the filter, and the position is located at 1.05 times of the filter. By changing the bottom electrode thickness, piezoelectric layer thickness or top electrode thickness of the parallel resonator, its parallel resonant frequency is located at the center frequency of the filter. That is, by adjusting the bottom electrode layer or top electrode layer of the series resonator, or the thickness of the piezoelectric layer, the parallel resonance frequency of the series resonator is located at 3.92GHz, that is, the suppression degree on the right side of the passband exceeds 40dB.

By adjusting the thickness of the bottom electrode layer or the top electrode layer or the piezoelectric layer of the parallel resonator, the series resonance frequency of the parallel resonator is located at 3.2GHz, that is, the suppression degree on the left side of the passband exceeds 40dB. As shown in Figure 2, the comparison chart of the series resonator impedance curve a and the parallel resonator impedance curve b. The series resonator in this embodiment is a series thin film bulk acoustic wave resonator; the parallel resonator is a parallel thin film bulk acoustic wave resonator. The series resonator and the parallel resonator have a substrate, a bottom electrode layer, a piezoelectric layer, and a top electrode layer distributed in order from bottom to top; and the upper surface of the substrate is provided with grooves.

As shown in Figure 3, it is a comparison diagram of the impedance curve m1 after the inductor is connected in parallel with the series thin film bulk acoustic resonator, and the impedance curve m2 of the single series thin film bulk acoustic resonator. Due to the introduction of the inductor branch, the series resonator and parallel resonance frequencies shift to high frequencies, which is equivalent to increasing the electromechanical coupling coefficient of the equivalent device of the thin film bulk acoustic wave resonator. By adjusting the thickness of the thin film bulk acoustic resonator, the frequency position of the parallel resonance point can be changed. Change the thickness of the series resonator so that the parallel resonance frequency of this filter is slightly higher than the upper band, ensuring that the zero point of the filter is outside the band, thereby determining the inductance value of the first inductor in parallel with the series resonator to be 0.4nH.

As shown in Figure 4, the impedance curve m1 of the inductor connected in series with the parallel thin film bulk acoustic resonator is compared with the impedance curve m2 of the independent parallel thin film bulk acoustic resonator. Due to the introduction of the inductor branch, the series resonance frequency of the parallel thin film bulk acoustic resonator shifts to low frequency, which means the equivalent device electromechanical coupling coefficient of the thin film bulk acoustic resonator is increased. By adjusting the thickness of the thin film bulk acoustic resonator, the frequency position of the parallel resonance point can be changed. Change the thickness of the parallel thin film bulk acoustic resonator so that the series resonance frequency of the broadband basic unit is slightly lower than the left band, ensuring that the zero point of the filter is outside the band, thereby determining the inductance value of the second inductor in series with the parallel resonator. In the range of 0.1~0.2nH, 0.15nH is taken in this application.

Based on the same inventive concept, this application also provides another filter, including an FBAR filter as described above, and a plurality of the FBAR filters are connected in series. The FBAR filter is a ladder-shaped filter, and multiple ladder-shaped filters are connected in series to form a high-step ladder filter. The FBAR filter includes a series resonator and a parallel resonator, and the parallel resonator of each FBAR filter is connected to the series resonator of another FBAR filter.

As shown in Figure 5, it is a schematic diagram of a three-ladder filter, which includes three one-ladder filters. Each one-step filter is a cascade of series resonators and parallel resonators. The series resonators are connected in parallel with a first inductor, and the parallel resonators are connected in series with a second inductor. Three first-order ladder filters are cascaded to form a third-order ladder filter. The number of echelon filters in the higher echelon filter is not limited here.

Figure 6 shows the passband response curve of the N77 filter applied to the multi-step filter in this application. The solid line is the insertion loss, and the dotted line is the standing wave. The insertion loss, standing wave, and suppression of the filter all meet the 5G communication N77 frequency band requirements.

The above-mentioned embodiments are only preferred embodiments of the present application and cannot be used to limit the scope of protection of the present application. Any non-substantive changes and substitutions made by those skilled in the art on the basis of the present application shall fall within the scope of the present application. Scope of protection claimed.

Claims

An FBAR filter includes a series resonator and a parallel resonator, a first inductor, and a second inductor. The series resonator and the parallel resonator are cascaded; the first inductor is connected in parallel at both ends of the series resonator, and the parallel resonator is connected in parallel with the first inductor. One end of the resonator is connected to the second inductor, and the other end of the parallel resonator is connected to ground.
An FBAR filter as claimed in claim 1, wherein the series resonators and parallel resonators are arranged in a substrate, a bottom electrode layer, a piezoelectric layer, and a top electrode layer from bottom to top; and the substrate Grooves are provided on the upper surface.
An FBAR filter as claimed in claim 1, wherein the parallel resonance frequency of the series resonator is located at 3.92 GHz by adjusting the thickness of the bottom electrode layer, top electrode layer or piezoelectric layer of the series resonator.
An FBAR filter as claimed in claim 1, wherein the parallel resonance frequency of the series resonator is higher than the passband frequency of the filter composed of a cascade of series and parallel resonators.
An FBAR filter as claimed in claim 1, wherein the parallel resonant frequency of the parallel resonator is located at the center frequency of the filter composed of a cascade of series and parallel resonators.
An FBAR filter as claimed in claim 1, wherein the difference between the resonant frequency of the branch where the inductor is located and the series resonant frequency of the corresponding parallel resonator is less than 1%.
An FBAR filter as claimed in claim 1, wherein the first inductor and the second inductor are bonding wire inductors, planar spiral inductors, chip inductors or TSV inductors.
An FBAR filter as claimed in claim 1, wherein the inductance value of the second inductor is 0.1~0.2nH.
An FBAR filter as claimed in claim 1, wherein the passband frequency of the filter is 3.3GHz to 3.8GHz, the center frequency is 3.55GHz, and the relative bandwidth is 14%.
An FBAR filter as claimed in claim 1, wherein the series resonance frequency of the parallel resonator is located at 3.2 GHz.
An FBAR filter as claimed in claim 1, wherein the inductance value of the first inductor is 0.4nH.
A multi-ladder type filter includes a plurality of FBAR filters according to any one of claims 1 to 11, and a plurality of said FBAR filters are connected in series.
A multi-step filter as claimed in claim 12, wherein the FBAR filter includes a series resonator and a parallel resonator, and the parallel resonator of each FBAR filter is connected to the series resonator of another FBAR filter. .