JP2004357101A - Thin film bulk acoustic resonator element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure an air gap (isolation) structure indispensable for obtaining a high Q value of a thin film bulk acoustic resonator element. <P>SOLUTION: The thin film bulk acoustic resonator element is configured such that a membrane layer is formed on a substrate, a first electrode, a piezoelectric layer, and a second electrode are sequentially formed on the membrane layer, and an air-gap is formed under the first electrode. An electrode forming part made of the same material as that of the first electrode is deposited on the membrane layer around the air-gap to form the air-gap. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thin film bulk acoustic resonator (FBAR), and more particularly, to a structure of a thin film bulk acoustic resonator for obtaining a structurally strong element.
[0002]
[Prior art]
In recent years, with the rapid development of communication technology, there has been a demand for the corresponding development of signal processing technology and radio frequency (RF) component technology. In particular, the high-frequency component technology on the hardware side has shifted to higher frequencies and higher densities, starting with mobile communication devices, and furthermore, there has been an active demand for miniaturization of various mobile communication devices.
[0003]
Mobile communication devices that have been covered by the specification characteristics in the passband of several hundred MHz to GHz, which is the passband of surface acoustic wave filters (SAWs), now use bulk acoustic waves with the increasing frequency of mobile communication devices. Research and development of thin film bulk acoustic resonator elements (FBAR elements) have been actively conducted. As the next generation of mobile phones, high-speed wireless LANs, and other high-bandwidth and high-frequency technologies, the carrier wave shifts to the 3 to 5 GHz band in the future. It is feared that the thinning of the line width causes a decrease in Q value (quality) due to a decrease in withstand power or an increase in resistance value.
[0004]
[Patent Document 1]
JP-A-2002-198758 [0005]
[Problems to be solved by the invention]
In general, an FBAR element is formed by forming a membrane layer on a substrate and forming a first electrode, a piezoelectric layer, and a second electrode on the membrane layer in that order. At this time, a high quality factor (high Q) is required. In order to maintain, when the electric field is applied through the first electrode and the second electrode, the substrate and the first electrode, the second electrode, and the piezoelectric layer are connected so that the acoustic wave generated in the piezoelectric layer is not affected by the substrate. An air gap structure for isolation is required. In the substrate, an air gap structure that isolates a resonance region including the first electrode, the piezoelectric layer, and the second electrode is an important condition that affects the performance of the FBAR element and the practical use of the FBAR element.
[0006]
Methods for separating the resonance region and the substrate are roughly classified into an air gap method using an etching cavity and a reflection film method using Bragg reflection.
[0007]
Here, as an example of the air gap method, ZnO is formed as a sacrificial layer at the position of the air gap on the substrate, a sacrificial layer is formed thereon, and a membrane layer is formed on the substrate. After laminating the layers and the second electrode sequentially, a resist film is formed on the piezoelectric layer, and the sacrificial layer is etched through the resist film through a via hole to form an air gap.
[0008]
Therefore, in the case of the above-described method, there is a problem that a step is formed in order to form the membrane layer on the sacrificial layer and the substrate, and there is a problem that mechanical strength and coating properties at the step may be deteriorated. .
[0009]
[Problems to be solved by the invention]
Therefore, in order to solve the above-mentioned problem, the present invention forms a membrane layer on a substrate, and sequentially forms a first electrode, a piezoelectric layer, and a second electrode thereon, and forms an air gap below the first electrode. The thin-film bulk acoustic resonator element according to claim 1, wherein an electrode forming portion made of the same material as the first electrode is arranged on the membrane layer around the air gap.
[0010]
In short, when the air gap method is used to secure the air gap portion of the vibrating portion of the thin film bulk acoustic resonator element, a step is formed to form the membrane layer on the sacrificial layer and the substrate, There is a possibility that the mechanical strength and the coating property at the step portion may be deteriorated. In the present invention, in order to improve the mechanical strength and the film property deterioration at the stepped portion, by providing an electrode forming portion in the air gap portion, it is possible to support the air bridge and prevent erosion from the etching solution. .
[0011]
Therefore, since the electrode forming portion of the same material as the first electrode formed on the membrane layer around the air gap is formed in the same manufacturing process as the first electrode due to the structure of the element, at least the first electrode and the first electrode are formed. The feature is that it is connected, and the problem is solved by the above-described structure for preventing erosion of the etchant around the via hole.
[0012]
【background】
With the recent increase in the frequency of mobile communication, research and development of thin film bulk acoustic resonator elements (FBARs) using bulk acoustic waves have been actively conducted. In the world, next-generation mobile phones, high-speed wireless LANs, and other high-bandwidth and high-frequency technologies are being promoted, and in the future, carrier waves will shift to the 3 to 5 GHz band. In this respect, the thin-film bulk acoustic resonator element can be made into a monolithic RF circuit.
[0013]
Agilent introduced the PCS duplexer in 1999 for the technology of thin-film bulk acoustic resonator elements, and has attracted worldwide attention. In the future, mass production will be developed for practical use. It is considered.
[0014]
The present invention relates to a thin-film bulk acoustic resonator element which is a main part of a thin-film bulk acoustic resonator element, in which a membrane layer is formed on a substrate and a first electrode, a piezoelectric layer, and a second electrode are formed thereon in this order. In order to obtain the Q value, attention is paid to the configuration and securing of an air gap portion for preventing acoustic waves generated in the piezoelectric layer when an electric field is applied to the electrodes from being affected by the substrate. The air gap (isolation) structure and the film quality of the piezoelectric layer are important factors for the performance and mass production of the resonator. As an example of a circuit using the thin-film bulk acoustic resonator element, a ladder-type filter is used as a basic configuration as shown in FIG.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, the same reference numeral indicates the same object. FIG. 1 is a plan view showing the thin-film bulk acoustic resonator element 7, FIG. 2 is a cross-sectional view of the thin-film bulk acoustic resonator element 7 shown in FIG. It is sectional drawing of the arrow BB part of the thin film bulk acoustic resonator element 7 shown by. Although the electrode forming portion 8 of the present invention is shown with a dotted line in FIG. 1, an enlarged view focusing on the electrode forming portion 8 is shown in FIG. Note that the resist film is not drawn in FIG.
[0016]
1, the ZnO film is formed on the entire surface of the substrate by RF magnetron sputtering, an air gap sacrificial layer is formed by acetic acid etching, and then a SiO ₂ layer (2,500 Å) is formed on the entire surface of the substrate by RF magnetron sputtering. ).
[0017]
Then, an electrode forming portion 8 is formed as a first electrode 2 on the Cr-Au electrode layer (1500 angstroms) below the thin film bulk acoustic resonator element 7 and on the membrane layer 11 around the air gap 5 by the EB vacuum deposition method. Then, a ZnO film (1000 Å) is formed on the entire surface of the substrate by an RF magnetron method, and then a second electrode 3 (AI-Cu electrode 1 pattern: 1500 Å) is formed by an EB vacuum evaporation method and a lift-off method. Thereafter, the SiO ₂ layer is penetrated by BHF, and finally, the sacrificial layer is etched by acetic acid to form an air gap to obtain the thin-film bulk acoustic resonator element 7. (The flow is shown in FIG. 6)
[0018]
FIG. 3 is an enlarged cross-sectional view taken along the line BB in FIG. 1. As can be seen from FIG. 3, the electrode is also formed on the membrane layer 11 around the air gap 5 at the position where the first electrode 2 is formed. By forming a metal material of the same material as that described above, erosion damage when etching the resist film around the air gap 5 is improved, the air gap 5 can be manufactured stably.
[0019]
FIG. 4 is a plan view focusing on an electrode forming portion 8 formed on the membrane layer 11 around the air gap 5 which is a main part of the present invention. In FIG. 4, the piezoelectric layer 4 and the second electrode 3 formed above the first electrode 2 are removed and formed on the membrane layer 11 around the air gap 5 in order to easily draw and express the features of the main parts. FIG. 3 is a diagram mainly illustrating an electrode forming unit 8. As shown in FIG. 4, the outer peripheral portion of the air gap 5 is formed so as to be continuous with the first electrode 2 so as to straddle the step (the boundary between the presence and absence of the sacrificial layer 10) of the membrane layer 11 of the element 7. The formation of the electrode forming portion 8 along the line is drawn. As shown in FIG. 4, the left side of the air gap 5 is connected to the first electrode 2 and the electrode forming portion 8, but the right side of the air gap 5 must not be connected to the first electrode 2. In FIG. 4, the area around the air gap 5 is drawn by a dotted line.
[0020]
Here, various conditions described in the present embodiment are based on the assumption that the air gap structure forms a cavity of the order of 100 μm width × 0.1 μm thickness in the device, and the sacrificial layer is etched later to form the air gap. It is made of an easy substance, and examples thereof include metal such as Al, Cu, and NiFe or ZnO which is an oxide thin film. These films are formed by sputtering or vapor deposition, but are not limited to this vapor deposition. Further, the membrane layer 11 is formed by evaporating a substance used in a conventional known technique, and the membrane layer 11 can be realized by SiO ₂ of several μm or the like.
[0021]
On the other hand, the first electrode 2, the second electrode, and the electrode forming portion 8 formed on the membrane layer 11 around the air gap 5 use a normal conductive material such as a metal. For example, it is preferable to select Al, W, Au, Pt and Mo. In addition, as a normal piezoelectric substance of the piezoelectric layer 4, aluminum nitride (AlN), ZnO, and zinc sulfide are preferable, but not limited thereto. In addition, the electrode forming part 8 arranged on the membrane layer 11 around the air gap can be selectively selected and combined with the above-described metal material of the first electrode 2.
[0022]
【The invention's effect】
As described above, when manufacturing a thin-film bulk acoustic resonator element according to the present invention, particularly by improving the accuracy of air gap formation, the oscillation Q value of the thin-film bulk acoustic resonator element can be maintained and improved. . As a result, it is possible to improve the yield and the quality in the manufacturing process of the thin film bulk acoustic resonator element, and reduce the manufacturing cost. Further, as can be seen from the description of the specification, the structure of the thin film bulk acoustic resonator element is very delicate, so that it is effective when mass-producing the element by the technique of the present invention.
[Brief description of the drawings]
FIG. 1 is a plan view showing a structure of a thin film bulk acoustic resonator element.
FIG. 2 is a sectional view of a section AA of the thin-film bulk acoustic resonator element shown in FIG. 1;
FIG. 3 is a partially enlarged view of an air gap portion (cross section BB in FIG. 1) showing a feature of the present invention.
FIG. 4 is an enlarged view of a main part of the present invention.
FIG. 5 is a basic configuration diagram of a ladder-type filter using a thin-film bulk acoustic resonator element.
FIG. 6 is a flowchart showing a manufacturing flow of the thin-film bulk acoustic resonator element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 1st electrode 3 2nd electrode 4 Piezoelectric layer 5 Air gap 6 Via hole 7 Thin film bulk acoustic resonator element 8 Electrode formation part

Claims (2)

In a thin film bulk acoustic resonator element having a membrane layer formed on a substrate, a first electrode, a piezoelectric layer, and a second electrode formed thereon in that order, and having an air gap below the first electrode,
A thin-film bulk acoustic resonator element, wherein an electrode forming portion made of the same material as the first electrode is arranged on the membrane layer around the air gap. The thin-film bulk acoustic resonator element according to claim 1, wherein an electrode forming portion formed on the membrane layer around the air gap is connected to at least the first electrode.

Images