WO2022183491A1

WO2022183491A1 - Quartz crystal resonator and processing method therefor, and electronic device

Info

Publication number: WO2022183491A1
Application number: PCT/CN2021/079334
Authority: WO
Inventors: 张孟伦; 庞慰
Original assignee: 天津大学
Priority date: 2021-03-05
Filing date: 2021-03-05
Publication date: 2022-09-09

Abstract

Provided are a quartz crystal resonator (501), which can both satisfy the requirement of high resonant frequency, and satisfy the requirements of stability and reliability for resistance to external stress and resistance to mechanical shock, and a processing method therefor, and an electronic device. The quartz crystal resonator (501) comprises, from bottom to top, a substrate (300), a piezoelectric stack structure, a mechanical reinforcement structure (200) and a cap structure (406). The piezoelectric stack structure and the mechanical reinforcement structure (200) are connected to each other at a first abutment position, and the piezoelectric stack structure and the substrate (300) are connected to each other at a second abutment position. The first abutment position is located in a non-resonant active region of a device, and the first abutment position is located above the second abutment position.

Description

Quartz thin-film bulk acoustic resonator, its processing method, and electronic equipment

technical field

The invention relates to the technical field of resonators, in particular to a quartz thin-film bulk acoustic wave resonator, a processing method thereof, and electronic equipment.

Background technique

Quartz Thin Film Bulk Acoustic Resonator (Quartz Crystal Resonator) is a kind of electronic components that use the piezoelectric effect of quartz crystals. It is a key component in electronic equipment such as oscillators and filters. It has outstanding advantages and wide application. Current trends require quartz resonators to have higher resonant frequencies (eg, greater than 40 MHz) and better stability and reliability against mechanical shocks. On the one hand, it is difficult to form a thinner quartz resonant region by etching the quartz substrate by traditional methods, which has reached a higher target resonant frequency. Using MEMS technology to fabricate a quartz film is more conducive to fabricating high-frequency quartz resonators. On the other hand, when the quartz film is thinner, the external stress (such as the stress from the substrate) is more easily transmitted to the resonance region of the quartz film and thus affects the frequency stability of the resonator; at the same time, when the quartz film is thinner, the resonator is easier to Affected by mechanical shock and environmental vibration, its reliability is further deteriorated compared to low frequency quartz resonators.

There is an urgent need to find a structural design and fabrication method, which can meet the requirements of high resonant frequency of quartz resonators on the one hand, and can meet the requirements of external stress resistance, mechanical shock resistance stability and reliability on the other hand.

SUMMARY OF THE INVENTION

In view of this, the present invention proposes a quartz thin-film bulk acoustic wave resonator that can not only meet the high resonant frequency requirements of the quartz resonator, but also meet the requirements of resistance to external stress, mechanical shock resistance, stability and reliability, as well as a processing method and an electronic device. equipment. The present invention provides the following technical solutions:

A quartz thin-film bulk acoustic wave resonator, comprising in order from bottom to top: a substrate, a piezoelectric stack structure, a mechanical reinforcement structure, and a cap structure, wherein the piezoelectric stack structure and the mechanical reinforcement structure are mutually adjacent at a first adjoining position. connected, the piezoelectric stack and the substrate are interconnected at a second abutment location, wherein the first abutment location is located within a non-resonant active region of the device, and the first abutment location is located at the second abutment location above the location.

Optionally, the mechanical reinforcement structure is a cap-shaped mechanical reinforcement structure, the cap-shaped mechanical reinforcement structure covers the piezoelectric stack structure, and there is air between the cap-shaped mechanical reinforcement structure and the piezoelectric stack structure. cavity.

Optionally, the piezoelectric stack structure includes a bottom electrode, a top electrode lead-out structure, a quartz piezoelectric layer, and a top electrode, and the mechanical reinforcement structure is directly bonded to the quartz piezoelectric layer.

Optionally, the material of the mechanical reinforcement structure is silicon or quartz.

Optionally, the bottom electrode and the top electrode lead-out structure are connected to the substrate through an electrode bonding layer.

Optionally, the thickness of the quartz piezoelectric layer is 0.1 to 50 microns.

Optionally, the signal lead-out terminals of the top electrode and the bottom electrode are located on two sides or the same side of the device.

Optionally, the cap structure is connected to the substrate through a hermetic bonding layer.

Optionally, the cap structure is provided with electrical signal lead-out through holes and the cap structure is provided with test pads or electrode pins, or the base is provided with electrical signal lead-out through holes and below the substrate. With test pads or electrode pins.

Optionally, the material of the substrate or the cap structure is silicon.

An electronic device includes the quartz thin-film bulk acoustic wave resonator of the present invention.

A method for processing a quartz film bulk acoustic wave resonator, comprising: forming a top electrode on a quartz piezoelectric layer; etching an acoustic mirror on the top of a silicon wafer; inverting the quartz piezoelectric layer and the top electrode post-bonding to the silicon wafer and having the top electrode located inside the acoustic mirror; etching a through hole in the quartz piezoelectric layer; at the through hole and the quartz piezoelectric A top electrode lead-out structure is formed on the layer, and a bottom electrode is formed on the quartz piezoelectric layer; a first electrode bonding layer is formed on the top electrode lead-out structure and the bottom electrode, wherein the first electrode bonding layer is formed. An electrode bonding layer is located within the non-resonant active region of the device; the current semiconductor structure is inverted and then bonded onto a second electrode bonding layer on top of the substrate, wherein the second electrode bonding layer is connected to the first electrode The bonding layers are aligned; a cap structure is formed over the substrate.

Optionally, the material of the substrate or the cap structure is silicon.

According to the technical scheme of the present invention, the high-frequency quartz thin-film bulk acoustic wave resonator manufactured by the MEMS process is used to thin the quartz wafer as a whole through MEMS processes such as grinding, chemical mechanical polishing, dry etching, etc., so that the quartz resonant area has reached the target. The thickness (that is, the target frequency), and at the same time, a structure with stronger mechanical stability is configured in the non-resonant region (especially the bonding position with the substrate), the device is insensitive to external stress, mechanical shock and environmental vibration, and has a higher reliability and frequency stability.

Description of drawings

For purposes of illustration and not limitation, the present invention will now be described in accordance with preferred embodiments thereof, particularly with reference to the accompanying drawings, wherein:

1a to 1k are schematic diagrams of the manufacturing process of the quartz thin-film bulk acoustic resonator according to the first embodiment of the present invention;

2 is a top view of the quartz thin-film bulk acoustic resonator according to the first embodiment of the present invention;

3 is a schematic cross-sectional view of a quartz thin-film bulk acoustic wave resonator according to a second embodiment of the present invention.

Fig. 4a is a top view of a quartz thin-film bulk acoustic resonator according to a third embodiment of the present invention, and Fig. 4b is a schematic cross-sectional view taken along the line D-D' of Fig. 4a.

Detailed ways

The quartz thin-film bulk acoustic wave resonator in the embodiment of the present invention includes, from bottom to top, a substrate, a piezoelectric stack structure, a mechanical reinforcement structure, and a cap structure. Wherein, the piezoelectric stack structure at least includes a bottom electrode, a quartz piezoelectric layer and a top electrode which are stacked in sequence. The piezoelectric stack and the mechanical reinforcement are interconnected at a first abutment location, and the piezoelectric stack and the substrate are interconnected at a second abutment location. The first abutment location is located within the non-resonant active region of the device, and the first abutment location is located above the second abutment location.

On the one hand, because the first abutting position is located in the non-resonant effective region, which means that the mechanical reinforcement structure does not hinder the normal operation of the resonant effective region, the device can achieve the target frequency; on the other hand, because the first abutting position is located in the second abutting position. Above, this means that the mechanical reinforcement structure can smoothly undertake the external stress transmitted from the substrate, and enhance the stability of the device against mechanical shock. Therefore, the quartz thin film bulk acoustic wave resonator of the embodiment of the present invention can not only meet the requirements of high resonance frequency of the quartz resonator, but also meet the requirements of resistance to external stress, mechanical shock resistance, stability and reliability.

The mechanical reinforcement structure may be a cap-shaped mechanical reinforcement structure covering the piezoelectric stack structure and having an air cavity between the cap-shaped mechanical reinforcement structure and the piezoelectric stack structure. The piezoelectric stack structure includes a bottom electrode, a top electrode lead-out structure, a quartz piezoelectric layer and a top electrode, and the mechanically enhanced structure is directly bonded and connected to the quartz piezoelectric layer. The material of the mechanical reinforcement structure can be silicon or quartz. When the mechanical reinforcement structure is selected from silicon or quartz, the mechanical reinforcement structure and the quartz piezoelectric layer are relatively easy to bond. The thickness of the quartz piezoelectric layer may be 0.1 to 50 microns. The thinner the thickness of the quartz piezoelectric layer, the higher the resonant frequency of the device.

The bottom electrode and the top electrode lead-out structure and the substrate may be connected through the first bonding layer. Specifically, the first electrode bonding layer can be provided on the bottom electrode and the top electrode lead-out structure first, and the second electrode bonding layer can be provided on the substrate, and then the first electrode bonding layer and the second electrode bonding layer can be aligned After bonding. The signal terminals of the top electrode and the bottom electrode can be located on both sides of the device or on the same side.

The cap structure and the substrate may be connected by a hermetic bonding layer. Specifically, the first sealing bonding layer may be disposed on the cap structure, and the second sealing bonding layer may be disposed on the substrate, and then the first sealing bonding layer and the second sealing bonding layer may be aligned and then bonded. . The cap structure is provided with electrical signal lead-out through holes and the cap structure is provided with test pads, or the base is provided with electrical signal lead-out through holes and the test pads are provided under the substrate.

The quartz thin-film bulk acoustic wave resonator and the processing method thereof according to the embodiments of the present invention will be described below with reference to specific examples.

1a to 1k are schematic diagrams of the manufacturing process of the quartz thin-film bulk acoustic resonator according to the first embodiment of the present invention. FIG. 2 is a top view of the quartz thin-film bulk acoustic resonator according to the first embodiment of the present invention. The schematic cross-sectional view taken along A-A' in Fig. 2 is exactly Fig. 1k.

Four wafers were prepared as shown in Figure 1a. Quartz wafer 100 used as a quartz piezoelectric layer, a quartz wafer or silicon wafer 200 used as a mechanical reinforcement structure, a silicon wafer 300 used as a base, and a silicon wafer 400 used as a cap.

As shown in FIG. 1 b , a top electrode 101 is deposited and patterned on the quartz wafer 100 .

As shown in FIG. 1 c , an acoustic mirror 201 is etched on a quartz wafer or a silicon wafer 200 to provide space required for the device to vibrate.

As shown in FIG. 1 d , the structure shown in FIG. 1 b is inverted, and then directly bonded to the quartz wafer or silicon wafer 200 .

As shown in FIG. 1e, the quartz wafer 100 is thinned to a desired thickness through processes such as grinding, chemical mechanical polishing, dry etching, etc. At this time, the quartz wafer 100 becomes the quartz piezoelectric layer 102, and its thickness is in the range of Between 0.1 microns and 50 microns.

As shown in FIG. 1 f , through holes 103 are etched on the surface of the quartz piezoelectric layer 102 through a dry etching process, so that the electrical signals of the subsequent top electrodes can be extracted.

As shown in Figure 1g, a bottom electrode 104 and a top electrode extraction structure 105 are deposited and patterned.

As shown in FIG. 1 h , a first electrode bonding layer 106 is formed on the bottom electrode 104 and the top electrode lead-out structure 105 . The current semiconductor structure is referred to as the active structure 107 . At this time, the quartz wafer or silicon wafer 200 becomes the cap-shaped mechanical reinforcement structure 200 .

As shown in FIG. 1i , firstly, the second electrode bonding layer 302 and the second sealing bonding layer 301 are formed on the substrate 300 . The single effective structure 107 is then inverted, and the first electrode bonding layer 106 and the second electrode bonding layer 302 in the effective structure 107 are aligned and bonded. Denote the current semiconductor structure as 303 . As can be seen from the figure, B is defined as the bonding area between the effective structure 107 and the second electrode bonding layer 302 , and the quartz piezoelectric layer 102 and the cap-shaped mechanical reinforcement structure 200 are jointly stressed during the bonding process. In the absence of the cap-shaped mechanical reinforcement structure 200 and only the quartz piezoelectric layer as the bonding point, the film structure is easily damaged after being mechanically impacted, and the resonant frequency of the resonator is also easily affected by the stress conducted from the outside (such as the substrate). Influence, resulting in a decrease in the firmness and stability of the resonator. In this embodiment, the bonding point is placed under the cap-shaped mechanical reinforcement structure 200, which helps to avoid the influence of mechanical vibration on the firmness and frequency of the device, thereby obtaining higher mechanical strength and frequency stability of the quartz film.

As shown in FIG. 1 j , a deep cavity 401 is fabricated on a silicon wafer 400 to provide a sealed space for the effective structure 107 . Vias 402 are prepared and metallized on the silicon wafer 400 for the extraction of electrical signals. The first sealing bonding layer 404 , the electrode lead-out bonding layer 403 , and the test pad 405 are prepared. The current semiconductor structure is referred to as cap structure 406 . It should be noted that the manufacturing process of the cap structure is not fixed, for example, the test pad 405 can be manufactured after bonding.

As shown in FIG. 1k , the cap structure 406 is turned upside down and thermocompression bonded to the device 303 . After dicing along the C-C' line, the fabrication of a single quartz thin-film bulk acoustic resonator 501 can be completed.

The quartz thin-film bulk acoustic wave resonator of the embodiment of the present invention completely adopts the MEMS process flow and the wafer-level packaging process, which helps to realize mass production and low cost production, and the produced devices have high precision and good consistency.

3 is a schematic cross-sectional view of a quartz thin-film bulk acoustic wave resonator according to a second embodiment of the present invention. The embodiment shown in FIG. 3 is similar to the single quartz thin-film BAW resonator 501 in FIG. 1k , except that the through holes 304 and the test pads 305 for drawing out electrical signals are located on the substrate 300 .

Fig. 4a is a top view of a quartz thin-film bulk acoustic resonator according to a third embodiment of the present invention, and Fig. 4b is a schematic cross-sectional view taken along the line D-D' of Fig. 4a. In this embodiment, the signal terminals 405 of the top electrode 101 and the bottom electrode 104 are located on the same side of the device.

According to the technical solution of the embodiment of the present invention, the high-frequency quartz thin-film bulk acoustic wave resonator manufactured by the MEMS process is used to thin the quartz wafer as a whole through MEMS processes such as grinding, chemical mechanical polishing, dry etching, etc., so that the quartz resonant area has To the target thickness (that is, the target frequency), and at the same time, a structure with stronger mechanical stability is configured in the non-resonant region (especially the bonding position with the substrate), and the device is insensitive to external stress, mechanical shock and environmental vibration, and has more advantages. High reliability and frequency stability.

The above-mentioned specific embodiments do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

A quartz thin-film bulk acoustic wave resonator is characterized in that, from bottom to top, it comprises: a substrate, a piezoelectric stack structure, a mechanical reinforcement structure, and a cap structure, wherein,

The piezoelectric stack and the mechanical reinforcement are interconnected at a first abutment location, and the piezoelectric stack and the substrate are interconnected at a second abutment location, wherein the first abutment location is at a non-contact position of the device. within the effective area of resonance, and the first abutment location is located above the second abutment location.
The quartz thin-film bulk acoustic wave resonator according to claim 1, wherein the mechanical reinforcement structure is a cap-shaped mechanical reinforcement structure, the cap-shaped mechanical reinforcement structure covers the piezoelectric stack structure, and the cap-shaped mechanical reinforcement structure There is an air cavity between the mechanical reinforcement structure and the piezoelectric stack structure.
The quartz thin-film bulk acoustic wave resonator according to claim 1 or 2, wherein the piezoelectric stack structure comprises a bottom electrode, a top electrode lead-out structure, a quartz piezoelectric layer and a top electrode, and the mechanical reinforcement structure is the same as the The quartz piezoelectric layer is directly bonded and connected.
The quartz thin-film bulk acoustic wave resonator according to claim 3, wherein the material of the mechanical reinforcement structure is silicon or quartz.
The quartz thin-film bulk acoustic wave resonator according to claim 3, wherein the bottom electrode and the top electrode lead-out structure are connected to the substrate through an electrode bonding layer.
The quartz thin film bulk acoustic wave resonator according to claim 3, wherein the thickness of the quartz piezoelectric layer is 0.1 to 50 microns.
The quartz thin-film bulk acoustic wave resonator according to claim 3, wherein the signal lead-out ends of the top electrode and the bottom electrode are located on two sides or the same side of the device.
The quartz thin-film bulk acoustic wave resonator according to claim 1 or 2, wherein the cap structure is connected with the substrate through a hermetic bonding layer.
The quartz thin-film bulk acoustic wave resonator according to claim 1 or 2, wherein the cap structure is provided with electrical signal lead-out through holes and the cap structure is provided with test pads or electrode pins, or the cap structure is provided with test pads or electrode pins. The base is provided with electrical signal lead-out through holes and the base is provided with test pads or electrode pins.
The quartz thin-film bulk acoustic resonator according to claim 1 or 2, wherein the material of the base or the cap structure is silicon.
An electronic device, characterized by comprising the quartz thin-film bulk acoustic wave resonator according to any one of claims 1 to 10.
A method for processing a quartz thin-film bulk acoustic wave resonator, comprising:

forming a top electrode on the quartz piezoelectric layer;

The acoustic mirror is etched on top of the silicon wafer;

Inverting the quartz piezoelectric layer and the top electrode and bonding them to the silicon wafer and making the top electrode located inside the acoustic mirror;

etching through holes in the quartz piezoelectric layer;

forming a top electrode lead-out structure at the through hole and on the quartz piezoelectric layer, and forming a bottom electrode on the quartz piezoelectric layer;

A first electrode bonding layer is formed on the top electrode lead-out structure and the bottom electrode, wherein the first electrode bonding layer is located in the non-resonant effective area of the device;

inverting the current semiconductor structure, and then bonding onto the second electrode bonding layer on top of the substrate, wherein the second electrode bonding layer is aligned with the first electrode bonding layer;

A cap structure is formed over the substrate.
The method according to claim 12, wherein the material of the substrate or the cap structure is silicon.