Bulk acoustic wave resonator with periodic void structure, method of fabrication, and bulk acoustic wave filter

Abstract

A bulk acoustic wave resonator with a periodic gap structure, its fabrication method, and a bulk acoustic wave filter are disclosed. The bulk acoustic wave resonator comprises, from bottom to top, a bottom electrode, a piezoelectric thin film, and a top electrode. The piezoelectric thin film has a periodically distributed gap structure, making its lateral and longitudinal dimensions of the piezoelectric thin film of the same order of magnitude, thereby increasing the lateral piezoelectric coefficient d of the piezoelectric material. 31 and longitudinal piezoelectric coefficient d 33 It is coupled and utilized to achieve an effective electromechanical coupling coefficient of over 7%.

Description

Technical Field

[0001] This invention relates to the field of resonator technology, and in particular to a bulk acoustic resonator with a periodic gap structure, its fabrication method, and a bulk acoustic filter. Background Technology

[0002] With the rapid development of wireless communication applications, people's demand for broadband and high-speed data transmission has increased, and the utilization rate of spectrum resources and the use of complex communication protocols have also increased accordingly, which has promoted the improvement of the transmission rate and data transmission capability of 5G networks, and the key components in the radio frequency front end have also been greatly developed.

[0003] The radio frequency front end is an important part of the wireless communication module, mainly including multiple components such as power amplifiers (PA), filters, low noise amplifiers (LNA), and switches.

[0004] As a basic component of filters, resonators play a role in generating resonant frequencies, providing stability, and suppressing interference. Currently, the main types of radio frequency resonators are surface acoustic wave (SAW) resonators and film bulk acoustic wave (FBAR) resonators.

[0005] Effective electromechanical coupling coefficient (k) 2 eff ) is a coefficient used to quantify the energy conversion efficiency of a resonator. Its definition is related to the series resonant frequency and the parallel resonant frequency of the resonator. k 2 eff The effective electromechanical coupling coefficient is directly proportional to the difference between the two and inversely proportional to the parallel resonant frequency. It is largely influenced by the piezoelectric material properties and, to some extent, by the resonator design.

[0006] Existing SAW resonators primarily operate in the lower frequency band below 2.5 GHz, making them unsuitable for high-frequency applications. Existing FBAR resonators, on the other hand, have gained widespread acceptance due to their utilization of longitudinal waves in the thickness direction to achieve high operating frequencies (above 2.5 GHz). They mainly consist of upper and lower electrode layers and an intermediate piezoelectric layer. The upper and lower electrode layers can be made of conductive materials with high acoustic impedance, low resistivity, and low density, while the intermediate piezoelectric layer can be fabricated using piezoelectric thin films such as AlN thin films through processes like magnetron sputtering. However, FBAR only utilizes the piezoelectric coefficient d in the thickness direction of the piezoelectric material. 33Furthermore, the resonant frequency of existing FBAR resonators is determined by the physical thickness of the piezoelectric film. During the manufacturing process, only FBARs with the same piezoelectric film thickness can be produced on the same wafer, meaning only resonators with the same resonant frequency can be produced, and resonators with different resonant frequencies cannot be produced. Therefore, the structure of FBARs prevents them from being flexibly tuned through photolithography during the manufacturing process. Summary of the Invention

[0007] In view of the shortcomings of the prior art, such as the inability of SAW to be used in the high-frequency range and the inability of FBAR to be tuned through photolithography, the technical problem to be solved by the present invention is to enable the use of resonators in the high-frequency range (above 3GHz), so that the resonators have a high effective electromechanical coupling coefficient (more than 10%), and through structural innovation, to enable the resonant frequency of the resonator to be adjustable in production using photolithography, that is, to realize the production of resonators with different resonant frequencies on the same wafer.

[0008] The technical solution of the present invention is as follows:

[0009] On one hand, the present invention provides a bulk acoustic resonator with a periodic gap structure, which includes a bottom electrode, a piezoelectric thin film and a top electrode from bottom to top. The feature is that the piezoelectric thin film has a periodicly distributed gap structure.

[0010] The period is the sum of the width of the piezoelectric film and the width of the void structure.

[0011] The width-to-thickness ratio of the piezoelectric film is in the range of 0.5-2.0.

[0012] The thickness ratio of the bottom electrode and the top electrode to the thickness of the piezoelectric film is between 0.05 and 0.2.

[0013] The void structure is a rectangular cavity that divides the piezoelectric film into equal parts, making the transverse and longitudinal dimensions of the piezoelectric film of the same order of magnitude, thereby increasing the transverse piezoelectric coefficient d of the piezoelectric material. 31 and longitudinal piezoelectric coefficient d 33 It is coupled and utilized to achieve an effective electromechanical coupling coefficient of over 7%.

[0014] The width of the void structure can be adjusted by photolithography.

[0015] An alternating current (AC) signal of opposite polarity is applied to the bottom and top electrodes.

[0016] The piezoelectric film is made of one of the following materials: aluminum nitride, zinc oxide, aluminum oxide alloy, gallium nitride, lithium titanate, lithium niobate, lead zirconate titanate, or lead magnesium niobate.

[0017] The bottom electrode and top electrode are made of one or more of the following materials: molybdenum, aluminum, ruthenium, tungsten, platinum, iridium, magnesium, gold, chromium, cobalt, titanium, copper, and beryllium.

[0018] On the other hand, the present invention also provides a method for fabricating a bulk acoustic resonator, characterized in that it includes:

[0019] Provide piezoelectric thin films;

[0020] A top electrode is formed on the upper layer of the piezoelectric thin film;

[0021] A bottom electrode is formed in the lower layer of the piezoelectric thin film;

[0022] A periodically distributed void structure is formed in the middle of the piezoelectric film.

[0023] Furthermore, the present invention also provides a bulk acoustic wave filter containing the above-mentioned bulk acoustic wave resonator. Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1) By arranging periodic void structures at equal intervals in the piezoelectric thin film, the transverse piezoelectric coefficient d of the piezoelectric material is increased. 31 and longitudinal piezoelectric coefficient d 33 Simultaneously coupled and utilized, this bulk acoustic resonator can achieve high frequency (above 3 GHz) and high effective electromechanical coupling coefficient (over 10%).

[0025] 2) Due to the periodic distribution of the void structure in the piezoelectric thin film, the resonant frequency of the resonator can be adjusted in the photolithography process, that is, resonators with different resonant frequencies can be produced on the same wafer. Attached Figure Description

[0026] Figure 1 This is a cross-sectional schematic diagram of the bulk acoustic resonator with a periodic gap structure according to the present invention;

[0027] Figure 2 This is the impedance-frequency curve of the resonator in Example 1;

[0028] Figure 3 This is a graph showing the change in resonant frequency when the width of the gap structure is adjusted in Example 1;

[0029] Figure 4 This is the impedance-frequency curve of the resonator in Example 2;

[0030] Figure 5 This is a graph showing the change in resonant frequency when the width of the gap structure is adjusted in Example 2.

[0031] In the figure: bottom electrode 100, void structure 200, piezoelectric film 300, top electrode 400. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of the present invention.

[0033] Please see Figure 1 , Figure 1 This is a cross-sectional schematic diagram of the bulk acoustic resonator with a periodic gap structure according to the present invention, as shown below. Figure 1 As shown, from bottom to top, it includes a bottom electrode 100, a piezoelectric thin film 300, and a top electrode 400. The void structure 200 is periodically distributed in the piezoelectric thin film, and the period is the sum of the width of the piezoelectric thin film 300 and the width of the void structure 200. The ratio of the width to the thickness of the piezoelectric thin film 300 is in the range of 0.5-2.0, and the ratio of the thickness of the electrodes 100 and 400 to the thickness of the piezoelectric thin film 300 is between 0.05-0.2. The width of the void structure 200 can be adjusted by photolithography. An alternating current (AC) signal of opposite polarity is applied to the bottom electrode 100 and the top electrode 400.

[0034] The material for the piezoelectric thin film can be selected from one of the following: aluminum nitride, zinc oxide, aluminum oxide alloy, gallium nitride, lithium titanate, lithium niobate, lead zirconate titanate, or lead magnesium niobate. The electrode material can be selected from one or more of the following: molybdenum, aluminum, ruthenium, tungsten, platinum, iridium, magnesium, gold, chromium, cobalt, titanium, copper, and beryllium.

[0035] Example 1

[0036] Both the top and bottom electrodes are made of molybdenum with a thickness of 0.1 μm; the piezoelectric thin film is made of aluminum nitride with a thickness of 1 μm and a width of 1.2 μm; the width of the void structure can be adjusted by photolithography. When the width of the piezoelectric thin film is 2.55 times the width of the void structure, that is, when the width of the void structure is 0.47 μm, the resonator can achieve a good performance with an effective electromechanical coupling coefficient of 11.0%.

[0037] Figure 2 The impedance-frequency curve (simulation) for Example 1 shows that the resonator can achieve high frequencies (above 3 GHz), and the effective electromechanical coupling coefficient of the resonator can reach 11.0%. When the width of the gap structure is adjusted using photolithography, such as... Figure 3 As shown, the design of this resonator allows the width of the gap structure to be adjusted through photolithography during the manufacturing process, ultimately enabling the production of resonators with different resonant frequencies on the same wafer, thus achieving adjustable resonant frequencies.

[0038] To investigate the resonant frequency (f) under different design parameters s ) and effective coupling coefficient (k 2 eff ). k 2 eff The calculation equation is as follows:

[0039]

[0040] Where f s It is the series resonant frequency, f p It is the parallel resonant frequency.

[0041] Example 2

[0042] Both the top and bottom electrodes are made of molybdenum with a thickness of 0.1 μm; the piezoelectric thin film is made of aluminum nitride with a thickness of 1 μm and a width of 0.8 μm; the width of the void structure can be adjusted by photolithography. When the width of the piezoelectric thin film is 1.74 times the width of the void structure, that is, when the width of the void structure is 0.46 μm, the resonator can achieve a good performance with an effective electromechanical coupling coefficient of 10.3%.

[0043] Figure 4 The impedance-frequency curve (simulation) for Example 2 shows that the resonator can achieve high frequencies (above 3 GHz), and the effective electromechanical coupling coefficient of the resonator can reach 10.3%. When the width of the gap structure is adjusted using photolithography, such as... Figure 5 As shown, the design of this resonator allows the width of the gap structure to be adjusted through photolithography during the manufacturing process, ultimately enabling the production of resonators with different resonant frequencies on the same wafer, thus achieving adjustable resonant frequencies.

Claims

1. A bulk acoustic wave resonator having a periodic gap structure, comprising, in order from bottom to top, a bottom electrode, a piezoelectric thin film, and a top electrode, characterized by, The piezoelectric film has periodically distributed void structures; the void structures are rectangular cavities that divide the piezoelectric film into equal parts, so that the transverse and longitudinal dimensions of the piezoelectric film are of the same order of magnitude, thereby allowing the transverse piezoelectric coefficient d31 and the longitudinal piezoelectric coefficient d33 of the piezoelectric material to be coupled and utilized, achieving an effective electromechanical coupling coefficient of more than 7%. The resonant frequency of the bulk acoustic resonator can be adjusted by adjusting the width of the gap structure, which can be adjusted by photolithography. The period is the sum of the width of the piezoelectric film and the width of the void structure.

2. The bulk acoustic resonator with a periodic gap structure according to claim 1, characterized in that, The width-to-thickness ratio of the piezoelectric film is in the range of 0.5-2.

0.

3. The bulk acoustic resonator with a periodic gap structure according to claim 1, characterized in that, The thickness ratio of the bottom electrode and the top electrode to the thickness of the piezoelectric film is between 0.05 and 0.

2.

4. The bulk acoustic resonator with a periodic gap structure according to claim 1, characterized in that, The rectangular cavity extends through the longitudinal direction of the piezoelectric film.

5. The bulk acoustic resonator with a periodic gap structure according to claim 1, characterized in that, An alternating voltage signal is applied between the bottom electrode and the top electrode to excite the bulk acoustic resonator to vibrate.

6. The bulk acoustic resonator with a periodic gap structure according to claim 1, characterized in that, The piezoelectric film is made of one of the following materials: aluminum nitride, zinc oxide, aluminum oxide alloy, gallium nitride, lithium titanate, lithium niobate, lead zirconate titanate, or lead magnesium niobate.

7. The bulk acoustic resonator with a periodic gap structure according to claim 1, characterized in that, The bottom electrode and top electrode are made of one or more of the following materials: molybdenum, aluminum, ruthenium, tungsten, platinum, iridium, magnesium, gold, chromium, cobalt, titanium, copper, and beryllium.

8. The method for fabricating the bulk acoustic resonator according to any one of claims 1-7, characterized in that, include: Provide piezoelectric thin films; A top electrode is formed on the upper layer of the piezoelectric thin film; A bottom electrode is formed in the lower layer of the piezoelectric thin film; A periodically distributed void structure is formed in the middle of the piezoelectric film.

9. A bulk acoustic wave filter, characterized in that, Includes the bulk acoustic resonator according to any one of claims 1-7.

Images