CN111446943A - Single crystal film bulk acoustic resonator filter optimized by radio frequency inductor and preparation method thereof - Google Patents

Abstract

The invention discloses a single crystal film bulk acoustic resonator filter optimized by radio frequency inductance and a preparation method thereof. The filter comprises an epitaxial substrate, a bottom electrode, a piezoelectric film, a top electrode, a protective layer, an electrical connection through hole, an electrode connection microstrip line and a radio frequency inductance plane metal line segment. The filter comprises a resonator unit with a sandwich structure and a radio frequency inductance component. The resonator unit is a silicon back etching type FBAR resonator, the single crystal AlN piezoelectric layer is used as an acoustic oscillation layer, the FBAR filter obtained by the preparation method effectively improves out-of-band rejection, reduces in-band ripples, simplifies the preparation process of the FBAR filter, reduces the preparation cost of devices and improves the product performance.

Description

An optimized single crystal thin film bulk acoustic wave resonator filter using radio frequency inductance and its fabrication backup method

technical field

The invention relates to the technical field of thin-film bulk acoustic wave resonators and the field of MEMS micromachining, in particular to a single-crystal thin-film bulk acoustic wave resonator filter optimized by radio frequency inductance and a preparation method thereof.

Background technique

With the popularization and development of 5G technology, the communication field has ushered in another period of rapid growth. Corresponding technology upgrades and device replacements also follow. Following the mainstream SAW surface acoustic wave devices in the 4G era, BAW bulk acoustic wave devices have gradually entered people's attention. As a key component of RF signal front-end processing, FBAR is called a thin-film bulk acoustic wave device, and is currently the most widely used and promising member of BAW devices. FBAR BAW filter components have the advantages of high applicable frequency, high quality factor and relatively low processing difficulty.

At present, the mainstream FBAR BAW filter devices are mainly divided into three structures: silicon back etching type, air cavity type and solid assembly type. Among them, the silicon back etching type has the advantages of low processing difficulty and high quality factor, and will play an important role in the future 5G filtering field.

The mainstream FBAR filter preparation method is to connect multiple FBAR resonators in series and parallel to form a topology structure, but this method has problems such as large insertion loss and poor out-of-band suppression when preparing high-frequency filter devices, especially when the frequency is above 5GHz. . How to coordinate the relationship between in-band insertion loss and out-of-band rejection through easily fabricated RF inductor components is the key to preparing FBAR filters with superior performance.

The existing research on the preparation of high-performance AlN bulk acoustic wave filter by MBVD model simulation (Li Li, Zheng Shengling, Wang Shengfu, Li Feng, Li Hongjun. Research on high-performance AlN thin film bulk acoustic wave resonator [J]. Semiconductor Technology, 2013,38( 06):448-452.). In the present invention, the out-of-band suppression performance of the bulk acoustic wave filter is enhanced by the radio frequency inductance.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an optimized single crystal thin film bulk acoustic wave resonator filter using radio frequency inductance and a preparation method thereof.

The object of the present invention is achieved by at least one of the following technical solutions.

Based on this, the purpose of the present invention is to propose an optimized single crystal thin film bulk acoustic wave resonator filter using radio frequency inductance and a preparation method thereof. Compared with the traditional FBAR preparation process, the FBAR using this preparation method can improve the out-of-band suppression of the FBAR filter and reduce the in-band insertion loss at the same time. In the fourth-order FBAR filter, the in-band insertion loss is not affected. increase the out-of-band rejection by 10dB.

The object of the present invention is achieved by one of the following technical solutions.

The single crystal thin film bulk acoustic wave resonator filter optimized by using radio frequency inductance provided by the present invention includes a substrate, a piezoelectric bulk acoustic wave resonator, a radio frequency coupling inductance element and a peripheral compensation circuit. The piezoelectric bulk acoustic resonator includes two single crystal thin film bulk acoustic resonators in series and the two parallel single crystal thin film bulk acoustic resonators. The radio frequency coupling inductance element is connected to the bulk acoustic wave resonator, and the radio frequency inductance is located between the parallel bulk acoustic wave resonator and the electrical ground plane. The radio frequency coupling inductance element includes a first radio frequency inductance element and a second radio frequency inductance element; the first radio frequency inductance element includes an on-chip spiral inductance structure, and the spiral inductance structure includes the inductance electrode and the first parallel connection The single crystal thin film bulk acoustic wave resonator top electrode, the flat metal spiral wire and the surrounding medium. The first radio frequency inductive element includes an inductive element path; the inductive element path includes that the upper electrode is connected to the top electrode of the second parallel single crystal thin film bulk acoustic wave resonator, the flat metal spiral wire layer and the related media.

The invention provides a single crystal thin film bulk acoustic wave resonator filter optimized by using radio frequency inductance, which includes an epitaxial substrate, a bottom electrode, a piezoelectric film, a top electrode, a protective layer, an electrical connection through hole, an electrode connection microstrip line and a RF inductor plane metal line segment; the epitaxial substrate is connected to the bottom electrode; the bottom electrode is connected to the piezoelectric film; the piezoelectric film is connected to the top electrode; the top electrode is connected to the protective layer; An electrical connection through hole is provided; the electrical connection through hole is connected with the top electrode; the radio frequency inductor plane metal line segment is connected with the electrical connection through hole through the electrode connection microstrip line; the bottom surface of the epitaxial substrate is recessed inward and exposed Out of the middle of the bottom electrode.

Further, the epitaxial substrate is a single crystal silicon wafer or a GaN polished wafer.

Further, the thickness of the bottom electrode is 30 nm to 1 μm; the bottom electrode is one of Mo, Ti, Cu, Al, Au, and Ag; the number of the bottom electrodes is 2; The bottom electrode is a pentagon whose sides are not parallel to each other.

Further, the piezoelectric film is an AlN piezoelectric layer; the thickness of the piezoelectric film is 100 nm-2 μm; the piezoelectric film separates the two bottom electrodes.

Preferably, a planar helical radio frequency inductor metal line segment is prepared in the non-working area of the piezoelectric film (the area other than the top electrode).

Further, the top electrode is a metal electrode; the top electrode is one of Mo, Ti, Cu, Al, Au, and Ag; the thickness of the top electrode is 30 nm to 1 μm; the number of the top electrodes is 2.

Further, the protective layer is SiO ₂ ; the thickness of the protective layer is 0.3 μm-3 μm.

Preferably, the thickness of the protective layer is 2.3 μm.

Further, the protective layer is provided with two electrical connection through holes; the two electrical connection through holes are respectively connected with two top electrodes; the radio frequency inductance plane metal line segment is provided with two; the two radio frequency inductance plane The metal line segments are respectively connected to the two top electrodes through the electrode connecting microstrip line, and the interval between the two radio frequency inductor plane metal line segments is 50 nm-3 μm.

Further, the planar metal line segment of the radio frequency inductor is a metal spiral wire; the planar metal line segment of the radio frequency inductor is one of Mo, Pt, Ti, and Au; the thickness of the planar metal line segment of the radio frequency inductor is 100 nm-2 μm; The width of the planar metal line segment of the radio frequency inductor is 30nm-1μm.

Preferably, the thickness of the protective layer is 0.3 μm-3 μm; the thickness of the top electrode and the bottom electrode is 30 nm-1 μm.

The present invention provides a method for preparing the single-crystal thin-film bulk acoustic wave resonator filter optimized by using radio frequency inductance, which specifically includes the following steps:

(1) Make the substrate surface smooth by standard pickling and organic cleaning;

(2) On the substrate described in step (1), use evaporation, PVD magnetron sputtering, ALD and other processes to deposit Mo, Ti, Cu, Al, Au, Ag and other metals with a thickness of 30 nm to 1 μm as the bottom electrode (BAW resonator bottom electrode);

(3) Using MEMS patterning technology on the wafer to prepare the bottom electrode with the special pentagon shape whose sides are not parallel to each other; on the bottom electrode and the substrate by PECVD or PLD or ALD or PVD, etc. A piezoelectric thin film (AlN piezoelectric layer) with a thickness of 100nm-2μm is deposited; wherein the AlN piezoelectric layer can improve its piezoelectric coupling coefficient by doping and ion implantation;

(4) Sputtering or evaporating the top electrode (the metal top electrode of the bulk acoustic wave resonator) on the piezoelectric film (AlN piezoelectric layer) described in step (3); using photolithography, wet or dry etching methods The top electrode of the bulk acoustic wave resonator is patterned to obtain the top electrode of the special pattern;

(5) A protective layer (SiO ₂ protective layer) is grown on the piezoelectric film and the top electrode (the metal top electrode of the bulk acoustic wave resonator) using methods such as PECVD;

(6) performing deep silicon etching on the bottom surface of the substrate, removing the substrate under the bottom electrode (bulk acoustic wave resonator metal electrode), and exposing the middle of the bottom electrode;

(7) Use photolithography technology and dry etching method to etch electrical connection through holes on the protective layer (there are two in total, one is the connection through hole between the first radio frequency inductor electrode and the top electrode of the first parallel bulk acoustic wave resonator, The other is the connection through hole between the second radio frequency inductor electrode and the top electrode of the second parallel bulk acoustic wave resonator), and the through hole can be dry etched by ICP process; the electrical connection through hole is connected with the top electrode;

(8) Prepare the RF inductor plane metal line segment on the protective layer (there are two in total, namely the first plane spiral RF inductor metal line segment and the second plane spiral RF inductor metal line segment); then pass the RF inductor plane metal line segment through the electrode The microstrip line is connected to the top electrode to obtain the single crystal thin film bulk acoustic wave resonator filter optimized by using the radio frequency inductance.

Further, in step (2), the method for depositing the bottom electrode includes magnetron sputtering; in step (3), the method for depositing piezoelectric thin film includes more than one of PVD, MOCVD, PLD, and ALD; in step (4) , the method of sputtering the top electrode includes magnetron sputtering; in step (5), the method of growing the protective layer includes the method of plasma enhanced chemical vapor deposition (PECVD); in step (8), the method of preparing the radio frequency inductor plane metal line segment is as follows One or more of vapor deposition and PVD.

Preferably, in step (3), the method for depositing the piezoelectric thin film is PLD, and the single crystal AlN piezoelectric layer is epitaxially grown.

Preferably, in step (8), the method of preparing the planar metal wire segment of the radio frequency inductor is PVD magnetron sputtering.

The invention provides a single-crystal thin-film bulk acoustic wave resonator filter optimized by radio frequency inductance. The resonator includes a substrate layer, a bottom electrode layer, a piezoelectric crystal layer, a top electrode layer, and a SiO2 protection layer sequentially distributed from bottom to top. Layer and the plane spiral RF inductor above, the protective layer is grown by PECVD, the backside Si substrate is etched by RIE or ICP for deep silicon, and the top electrode, piezoelectric film and bottom electrode form the sandwich of the piezoelectric oscillator stack. structure.

The filter includes a resonator unit having a sandwich structure, and a radio frequency inductance part. The resonator unit is a silicon back-etched FBAR resonator, and a single crystal AlN piezoelectric layer is used as an acoustic oscillation layer. The FBAR filter using the preparation method effectively improves out-of-band suppression, reduces in-band ripple, and simplifies The FBAR filter preparation process can reduce the device preparation cost and improve the product performance.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) In the preparation method provided by the present invention, by preparing a radio frequency inductor, the out-of-band suppression characteristics of the bulk acoustic wave filter can be significantly enhanced, and the in-band ripple and insertion loss properties corresponding to the FBAR thin-film bulk acoustic wave filter can be reduced at the same time;

(2) The preparation method provided by the present invention innovatively integrates the planar spiral RF inductor and the FBAR bulk acoustic wave filter into the third-generation semiconductor process, which can reduce the performance loss introduced by the external circuit;

(3) The single crystal thin film bulk acoustic wave resonator filter optimized by the use of radio frequency inductance provided by the present invention adopts a single crystal piezoelectric thin film, which is more suitable for the 5G frequency band.

Description of drawings

1 is a cross-sectional view of preparing a bottom electrode metal layer on an epitaxial substrate 1 in Example 1;

2 is a cross-sectional view of sputtering or depositing a piezoelectric thin film on an epitaxial substrate 1 in Example 1;

FIG. 3 is a cross-sectional view of preparing protective layer SiO and backside Si etching on the basis of FIG. 2 of Example 1;

Fig. 4 is the top view of preparing radio frequency planar spiral inductor metal line segment in embodiment 1;

5 is a cross-sectional view of preparing a radio frequency planar inductor by evaporation or PVD sputtering on the epitaxial substrate 1 of Example 1;

6 is a schematic diagram of a single-crystal thin-film bulk acoustic resonator filter optimized by using a radio frequency inductance provided in Embodiment 1;

7 is a topological representation diagram of a single resonator connected to an inductor in Embodiment 1;

Fig. 8 is the S21 parameter comparison schematic diagram of the common FBAR bulk acoustic wave resonator with the same structural parameters and the single crystal thin film bulk acoustic wave resonator filter optimized by using the radio frequency inductance provided by embodiment 1;

The figure includes: epitaxial substrate 101 , bottom electrode 102 , piezoelectric film 103 , top electrode 104 , protective layer 105 , electrical connection vias 106 , electrode connection microstrip line 107 , and RF inductor planar metal line segment 108 .

Detailed ways

The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatus and/or systems described herein. However, various changes, modifications and equivalents of the methods, apparatus and/or systems described herein will be apparent after understanding the disclosure of the present application. For example, the order of operations described herein is merely an example and is not limited to the order set forth herein, but rather than operations that must occur in a particular order, may be made that will become apparent upon understanding the disclosure of the present application change. Also, descriptions of features known in the art may be omitted for increased clarity and conciseness. The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein have been provided only to illustrate some of the many possible ways of implementing the methods, devices and/or systems described herein that will be apparent after an understanding of the disclosure of the present application.

Example 1

This embodiment provides a single crystal thin film bulk acoustic wave resonator filter optimized by radio frequency inductance. As shown in FIG. 6 , the resonator includes an epitaxial substrate 101 , a bottom electrode 102 , a piezoelectric The film 103, the top electrode 104, the protective layer 105, the electrical connection vias 106, the electrode connection microstrip line 107, and the RF inductor planar metal line segment 108, wherein the top electrode 104, the piezoelectric film 103, and the bottom electrode 102 together form a sandwich structure.

The transfer substrate 101 is single crystal Si; the protective layer 105 is SiO ₂ ; the piezoelectric film 103 is AlN with a thickness of 2 μm; the bottom electrode and the top electrode are both metal electrode layers, the thickness of the electrode layer is 40 nm, and the electrode metal is Mo .

The thickness of the protective layer is 2.3um; the spacing between the metal segments of the planar spiral inductor is 50nm~3um; the thickness of the metal spiral is 100nm~2μm, and the metal width of the radio frequency inductor is 30nm~1um;

This embodiment also provides a method for preparing the above-mentioned optimized single-crystal thin-film bulk acoustic resonator filter using radio frequency inductance, including the following steps:

(1) Select the (100) crystal orientation Si substrate as the epitaxial substrate 101, carry out pickling and organic cleaning of the epitaxial substrate to make the surface of the substrate clean, and use the photolithography process and the PVD magnetron sputtering process to deposit the Mo metal bottom Electrode, use photolithography and wet or dry etching process to pattern the bottom electrode, and obtain the patterned bottom electrode as shown in Figure 1;

(2) On the basis of the (100) crystal-oriented Si substrate in step (1), a piezoelectric film (such as AlN) is deposited by PLD and MOCVD, as shown in FIG. 2 . ;

(3) Mo metal top electrode is prepared on the piezoelectric film (such as AlN) prepared on the basis of step (2) by evaporation and sputtering processes, and photolithography and wet or dry etching are also used to pattern the above-mentioned Top electrode, continue to use PEVCD to grow a layer of SiO ₂ protective layer on the top electrode. The backside etching of the Si substrate by RIE or ICP is shown in Figure 3;

(4) Electrode connection through holes are prepared on the SiO ₂ protective layer, and the RF inductor planar spiral metal line segment is prepared by PVD magnetron sputtering or evaporation, as shown in Figure 4 and Figure 5;

(5) Finally, on the basis of step (4), the electrical connection metal line segment for connecting the planar RF inductor and the FBAR bulk acoustic wave parallel resonance unit is evaporated as shown in Figure 6;

(6) Test the prepared FBAR bulk acoustic wave filter, connect the filter chip to the vector network analyzer through the probe station (as shown in Figure 7), and optimize the scattering parameter S21 of the FBAR device with two-port capacitors. Comparison with ordinary FBAR measurements of the same structure size is shown in Figure 8. The solid line in FIG. 8 represents the S(2,1) parameter of the device after capacitance optimization is performed, and the dashed line represents the S(2,1) parameter of the device without capacitance optimization. The out-of-band suppression of the FBAR filter prepared in Example 1 is obviously optimized, and the out-of-band suppression is improved by 5-10 dB compared with the common FBAR filter. In-band ripple and insertion loss are significantly reduced.

The above examples are only preferred embodiments of the present invention, and are only used to explain the present invention, but not to limit the present invention. Changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention shall belong to the present invention. the scope of protection of the invention.

Claims (10)

1. A single crystal film bulk acoustic resonator filter optimized by radio frequency inductance is characterized by comprising an epitaxial substrate (101), a bottom electrode (102), a piezoelectric film (103), a top electrode (104), a protective layer (105), an electrical connection through hole (106), an electrode connection microstrip line (107) and a radio frequency inductance plane metal line segment (108); the epitaxial substrate (101) is connected with a bottom electrode (102); the bottom electrode (102) is connected with the piezoelectric film (103); the piezoelectric film (103) is connected with the top electrode (104); the top electrode (104) is connected with the protective layer (105); an electrical connection through hole (106) is formed in the protective layer (105); the electrical connection via (106) is connected with the top electrode (104); the radio frequency inductance plane metal line segment (108) is connected with the electrical connection through hole (106) through an electrode connection microstrip line (107); the bottom surface of the epitaxial substrate (101) is recessed inwards, and the middle part of the bottom electrode (102) is exposed.

2. The single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to claim 1, characterized in that the epitaxial substrate (101) is a single crystal silicon wafer or a GaN polished wafer.

3. The single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to claim 1, characterized in that the thickness of the bottom electrode (102) is 30nm-1 μ ι η; the bottom electrode (102) is one of Mo, Ti, Cu, Al, Au and Ag; the number of the bottom electrodes (102) is 2; the bottom electrode (102) is a pentagon whose sides are not parallel to each other in a plan view.

4. The single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to claim 1, characterized in that the piezoelectric thin film (103) is an AlN piezoelectric layer; the thickness of the piezoelectric film (103) is 100nm-2 mu m; the piezoelectric film (103) separates the two bottom electrodes (102).

5. The single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to claim 1, characterized in that the top electrode (104) is a metal electrode; the top electrode (104) is one of Mo, Ti, Cu, Al, Au and Ag; the thickness of the top electrode (104) is 30nm-1 mu m; the number of the top electrodes (102) is 2.

6. The single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to claim 1, characterized in that the protective layer (105) is SiO₂(ii) a The thickness of the protective layer (105) is 0.3-3 μm.

7. The single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to claim 1, characterized in that the protective layer (105) is provided with 2 electrical connection vias (106); the two electrical connection through holes (106) are respectively connected with the two top electrodes (104); two planar metal wire sections (108) of the radio frequency inductor are arranged; the two radio frequency inductance plane metal line segments (108) are respectively connected with the two top electrodes (104) through electrode connecting microstrip lines (107), and the interval between the two radio frequency inductance plane metal line segments is 50nm-3 mu m.

8. The single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to claim 1, characterized in that the radio frequency inductance planar metal line segment (108) is a metal spiral wire; the radio frequency inductor planar metal line segment (108) is one of Mo, Pt, Ti and Au; the thickness of the radio frequency inductance plane metal line segment (108) is 100nm-2 mu m; the width of the radio frequency inductance plane metal line segment (108) is 30nm-1 μm.

9. A method of manufacturing a single crystal thin film bulk acoustic resonator filter optimized with radio frequency inductance according to any one of claims 1 to 8, comprising the steps of:

(1) the surface of the substrate is smooth through standard acid washing and organic cleaning;

(2) depositing a bottom electrode (102) on the substrate of step (1);

(3) depositing a piezoelectric film (103) on the bottom electrode (102) and the substrate;

(4) sputtering or evaporating a top electrode (104) on the piezoelectric film (103) in the step (3);

(5) growing a protective layer (105) on the piezoelectric film (103) and the top electrode (104);

(6) performing deep silicon etching on the bottom surface of the substrate, and removing the substrate below the bottom electrode (102) to expose the middle part of the bottom electrode (102);

(7) etching an electrical connection via (106) on the protective layer (105); connecting the electrical connection via (106) with the top electrode (104);

(8) preparing a radio frequency inductance plane metal wire section (108) on the protective layer (105); and then connecting the radio frequency inductance plane metal line segment (108) with the top electrode (104) through the electrode connecting microstrip line (107) to obtain the single crystal film bulk acoustic wave resonator filter optimized by the radio frequency inductance.

10. The method for preparing the single crystal film bulk acoustic resonator filter optimized by the radio frequency inductance is characterized in that in the step (2), the method for depositing the bottom electrode (102) comprises magnetron sputtering, in the step (3), the method for depositing the piezoelectric film (103) comprises more than one of PVD, MOCVD and P L D, A L D, in the step (4), the method for sputtering the top electrode (104) comprises magnetron sputtering, in the step (5), the method for growing the protective layer (105) comprises a PECVD method of plasma enhanced chemical vapor deposition, and in the step (8), the method for preparing the radio frequency inductance plane metal line segment (108) comprises more than one of evaporation and PVD.

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