KR20020071656A - tunable bandpass filter and method for fabricating the same - Google Patents

Abstract

PURPOSE: A variable band pass filter and a method manufacturing for the same is provided to play an important role of improving a transmitting and receiving performance of a radio frequency (RF). CONSTITUTION: A variable band pass filter includes a substrate(1), a membrane(2) formed on the substrate(1), a thin film bulk acoustic resonator formed on the membrane(2) and a first and a second variable capacitors formed both sides of the thin film bulk acoustic resonator, respectively. The thin film bulk acoustic resonator is formed by forming a lower electrode(4) on the membrane(2) into a predetermined configuration, forming a piezoelectric material(5) on the lower electrode(4) and forming an upper electrode(6) on the piezoelectric material(5) into a preset configuration. The first and the second variable capacitors are obtained by lower electrodes(4a,4b) on the membrane(2) into a predetermined shape, forming a dielectric material(7) on the lower electrodes(4a,4b) and forming upper electrodes(6a,6b) on the dielectric material into a preset shape. The lower electrode(4a) of the first variable capacitor is electrically connected to the lower electrode(4) of the resonator and the lower electrode(4b) of the second variable capacitor is electrically connected to the upper electrode(6) of the resonator.

Description

Tunable bandpass filter and method for fabricating the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to components for wireless communications and high frequency communications, and more particularly to a variable bandpass filter and a method for manufacturing the same, which play an important role in improving the reception and transmission performance of RF signals.

Recently, with the rapid expansion of the mobile communication market, a breakthrough in information and communication technology has been made.

In particular, with the trend toward miniaturization of mobile communication terminals, miniaturization and high functionality of mobile communication information communication components are required.

The bandpass filter for high frequency transmission and reception uses a surface acoustic wave resonator method or a bulk acoustic wave resonator method instead of applying a conventional dielectric resonator method. Efforts have been made to apply.

The conventional dielectric resonator method has a disadvantage in that its volume is relatively large compared to other methods when viewed based on the same transmission frequency.

In addition, in the dielectric resonator method, in order to compensate for the center frequency (F _C ) error of the resonator, it is necessary to additionally mount the fine adjustment capacitor, so that the cost increases because the volume increases and the number of processes increases in mass production. The problem of a decrease in reliability arises.

As described above, since the dielectric resonator method has a limitation in reflecting the miniaturization trend of the mobile communication terminal, a study of an RF band duplexer using a surface acoustic wave resonator and a volume acoustic wave resonator has recently been conducted.

The surface acoustic wave resonator method has a manufacturing problem because the line width and spacing is too small when the pattern is formed in order to reach the frequency band of 2 GHz, and when the band is 2 GHz or more, the characteristics in the relatively low frequency band Compared to its characteristics.

Therefore, there is a limitation that the surface acoustic wave resonator cannot be applied to a bandpass filter having a center frequency of 2 GHz or more.

On the other hand, the volume acoustic wave resonator has an excellent center frequency and characteristics, and has the advantage of being able to be manufactured in a very small size using a silicon process.

However, the volume acoustic wave resonator has a difficult method of adjusting the center frequency.

Therefore, it is necessary to simultaneously solve the size and characteristic problems of the dielectric resonator, the characteristics problem at a relatively high frequency which is the problem of the surface acoustic wave resonator, and the fine tuning problem of the volume acoustic wave resonator.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a variable bandpass filter and a method of manufacturing the same, which can be miniaturized and have excellent frequency characteristics and reliability.

1 is a circuit diagram of a variable bandpass filter according to the present invention.

2 is a structural plan view showing a variable bandpass filter according to the present invention.

3 is a cross-sectional view of the structure according to II of FIG.

4A is a structural cross-sectional view showing a bias driven variable capacitor;

4b and 4c are structural cross-sectional views showing a variable capacitor of a mechanical tuning method;

5A through 5F are cross-sectional views illustrating a manufacturing process of a variable bandpass filter having a bias capacitor-type variable capacitor;

6A through 6F are cross-sectional views illustrating a manufacturing process of a variable bandpass filter having a variable capacitor of a mechanical driving method.

Explanation of symbols for main parts of the drawings

1: substrate 2: membrane

3: ground plate 4, 4a, 4b: lower electrode

5: piezoelectric 6, 6a, 6b: upper electrode

7 dielectric 10 sacrificial layer

The variable bandpass filter according to the present invention includes a substrate having a hole, a membrane film formed on the substrate, a resonator formed on the membrane film, and a first and second electrical connections to the resonator and electrically connected to the resonator. It consists of two variable capacitors.

In the substrate, first holes are formed in the resonator formation region, and second and third holes are formed in the first and second variable capacitor formation regions, respectively.

The resonator includes a lower electrode formed in a predetermined shape on the membrane film, a piezoelectric material formed on the lower electrode, and an upper electrode formed in a predetermined shape on the piezoelectric material.

The first and second variable capacitors include a lower electrode formed in a predetermined shape on the membrane film, a dielectric formed on the lower electrode, and an upper electrode formed in a predetermined shape on the dielectric. The lower electrode is electrically connected, and the lower electrode of the second capacitor is electrically connected to the upper electrode of the resonator.

At this time, the first and second variable capacitors are bias driving methods.

In addition, the first and second variable capacitors may be formed in a predetermined shape on the top of the dielectric so as to be released at a predetermined distance from the dielectric, and may also be formed in a mechanical driving manner to contact the dielectric according to an externally applied voltage. have.

Here, the upper electrode may be in the form of a cantilever that is fixed at one end and released from the dielectric or in the form of a bridge where both ends are fixed and released from the dielectric.

A method of manufacturing a variable bandpass filter according to the present invention includes a first step of forming a membrane film on a substrate, and forming and patterning a lower electrode material on the membrane film to form a lower electrode of the resonator and the first and second variable capacitors in a predetermined region. A second step of forming a lower electrode, a third step of forming a piezoelectric body on a part of the lower electrode of the resonator, and a third step of forming a dielectric on a part of the lower electrode of the first and second variable capacitors, and forming an upper electrode material on the front surface; Patterning to form an upper electrode of the resonator so as to extend over a portion of the lower electrode of the piezoelectric body and the second variable capacitor, and forming a top electrode of the first and second variable capacitors so as to extend over a portion of the dielectric; Etching the region to expose the resonator and the membrane film of the first and second variable capacitor forming regions. .

In order to fabricate a mechanically driven variable capacitor, an upper electrode of the resonator is formed to cover a portion of the lower electrode of the piezoelectric element and the second variable capacitor, a sacrificial layer is formed on the resonator and the first and second variable capacitor forming regions. Upper electrodes of the first and second variable capacitors are respectively formed on the sacrificial layer. Next, an upper electrode material is formed on the sacrificial layer, and the sacrificial layer is removed to form upper electrodes of the first and second variable capacitors released from the dielectric, respectively.

The variable bandpass filter of the present invention manufactured as described above combines the advantages of the thin film volume acoustic wave resonator with excellent center frequency characteristics and the variable capacitor finely adjusting the center frequency, thereby providing excellent frequency characteristics and reliability for various fields such as high frequency communication. Can be applied.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Referring to the accompanying drawings, preferred embodiments of the present invention having the features as described above are as follows.

1 is a circuit diagram of a variable bandpass filter according to the present invention, FIG. 2 is a structural plan view showing a variable bandpass filter according to the present invention, and FIG. 3 is a structural cross-sectional view according to I-I of FIG. 2.

1, 2, and 3, the present invention consists of thin film bulk acoustic resonators and on-chip variable capacitors.

Looking at the structure of the present invention in more detail, as shown in Figures 2 and 3, a membrane film (2) is formed on the substrate (1), a resonator is formed on the membrane film, and both sides of the resonator First and second variable capacitors are formed, respectively.

The ground plate 3 is formed around the resonator and the first and second variable capacitors.

Here, holes are formed in the region where the resonator is formed and the region where the first and second variable capacitors are formed.

Further, the resonator is a lower electrode 4 made of Au / Ti, Au / Cr, Pt / Ti, Pt / Cr, Ir / Ti, Ir / Cr, Ru / RuO ₂ , Ru / Ti, etc. on the membrane film 2. The piezoelectric body 5 is formed in a predetermined shape, and a piezoelectric body 5 made of ZnO, AlN, SiO ₂ , GaAs, PZT, PLT, etc. is formed on the lower electrode 4, and Au, Au / Cr, Pt, Pt is formed on the piezoelectric body 5. An upper electrode 6 made of / Cr, Ir, Ir / Cr, Ru, RuO _2, or the like is formed in a predetermined shape.

The first and second variable capacitors may be Au / Ti, Au / Cr, Pt / Ti, Pt / Cr, Ir / Ti, Ir / Cr, Ru / RuO ₂ , Ru / Ti, etc. on the membrane film 2. The lower electrodes 4a and 4b are formed in a predetermined shape, and a dielectric 7 made of STO and BSTO is formed on the lower electrodes 4a and 4b, and Au, Au / Cr, Pt, and Pt / Cr are formed on the dielectrics. And the upper electrodes 6a and 6b made of Ir, Ir / Cr, Ru, RuO ₂ , and the like are formed in a predetermined shape.

Here, the lower electrode 4a of the first variable capacitor is electrically connected to the lower electrode 4 of the resonator, and the lower electrode 4b of the second variable capacitor is electrically connected to the upper electrode 6 of the resonator. have.

In the present invention, the variable capacitor may be manufactured by a bias driven method as shown in FIG. 4A and a mechanical tuning method as shown in FIGS. 4B and 4C.

The bias driving method is as described above, and in the mechanical control method, a dielectric is formed on the lower electrode, and an upper electrode is formed in a predetermined shape so that the upper electrode is formed in a predetermined shape so as to be released at a predetermined interval away from the dielectric. It is a structure in contact with.

That is, the bias driving method has no mechanical movement, but the mechanical control method is different in that it is accompanied by physical displacement.

The mechanical control method is a cantilever type in which only one end of the upper electrode is fixed and the other end is released from the dielectric as shown in FIG. 4B, and a bridge in which both ends are fixed and the middle part is released from the dielectric as shown in FIG. 4C. ) Can be produced.

The dielectric constant of the variable capacitor manufactured by the bias driving method is configured to be controlled by applying a DC bias, but the variable capacitor manufactured by the mechanical control method is a method of controlling the thickness between electrodes rather than controlling the dielectric constant.

However, since the mechanical control method adjusts the thickness control between the electrodes through the DC bias, in the present invention, the mechanical control method may be regarded as a bias driving method.

The manufacturing method of this invention which has such a structure is as follows.

5A to 5F are cross-sectional views illustrating a manufacturing process of a variable bandpass filter according to the present invention, and a variable bandpass filter having a variable capacitor of a bias driving method.

First, as shown in FIG. 5A, a thermal oxide film, a nitride film, and an oxide film are sequentially deposited by chemical vapor deposition (CVD) on a (100) silicon substrate 1 having both surfaces polished. (2) is formed.

Here, the substrate 1 may be formed of GaAs, high resistance Si, or the like in addition to silicon.

Subsequently, an electrode material such as Au / Ti, Au / Cr, Pt / Ti, Pt / Cr, Ir / Ti, Ir / Cr, Ru / RuO ₂ , Ru / Ti, etc. is deposited and patterned on the membrane film 2. In the region, the lower electrode 4 of the resonator and the lower electrodes 4a and 4b of the variable capacitor are formed.

At this time, the lower electrode 4 of the resonator and the lower electrode 4a of the variable capacitor are electrically connected.

The deposition process of the lower electrode material may be DC sputtering, evaporation, chemical vapor deposition (CVD), etc., and the lower electrode patterning process may be wet etching, dry etching, or lift. A lift-off method or the like may be used.

As shown in FIG. 5B, the piezoelectric body 5 is formed on a part of the lower electrode 4 of the resonator.

Here, the deposition method of the piezoelectric body may be RF sputtering (RF sputtering), chemical vapor deposition, sol-gel (sol-gel), metal organic deposition (metal organic deposition) method and the like.

In the present invention, a piezoelectric material such as ZnO, AlN, SiO ₂ , GaAs, PZT, PLT, etc. is used. When forming a pattern of the ZnO piezoelectric material, an etchant of a solution made by mixing phosphoric acid, acetic acid, and DI is used. Use wet etching or lift-off.

Subsequently, as shown in FIG. 5C, a dielectric 7 is formed on a part of the lower electrodes 4a and 4b of the variable capacitor.

Here, the dielectric 7 is made of STO, BSTO, etc., and the deposition and patterning method uses the same method as the piezoelectric formation process.

Next, as shown in FIG. 5D, upper electrode materials such as Au, Au / Cr, Pt, Pt / Cr, Ir, Ir / Cr, Ru, and RuO ₂ are formed and patterned to form a piezoelectric body 5 and The upper electrode 6 of the resonator is formed so as to extend over a portion of the lower electrode 4b of the variable capacitor, and the upper electrodes 6a and 6b of the variable capacitor are formed so as to extend over a portion of the dielectric 7.

At this time, the upper electrode 6 of the resonator is electrically connected to the lower electrode 4b of the variable capacitor.

Like the lower electrode, the deposition process of the upper electrode material uses DC sputtering, evaporation, chemical vapor deposition (CVD), etc., and the upper electrode patterning process is wet etching, Dry etching, lift-off methods are used.

Subsequently, a photoresist is formed on the front surface of the substrate 1 to protect the resonator and the variable capacitor formed on the front surface of the substrate 1, as shown in FIG. Soak the oxide film on the back of the substrate.

Then, the predetermined region on the back side of the substrate is etched to expose the membrane film 2 in the region where the resonator is formed, and the membrane film 2 in the region where the variable capacitor is formed, as shown in FIG. 5F.

At this time, the etching of the substrate 1 uses a method such as wet etching, micro-machining (micro-machining).

Finally, although not shown, a pad electrode including a ground electrode is formed on the substrate 1 to complete the fabrication of the variable bandpass filter.

At this time, each electrode is produced using electroplating.

6A through 6F are cross-sectional views illustrating a manufacturing process of a variable bandpass filter according to the present invention, and a variable bandpass filter having a variable capacitor of a mechanical driving method.

6A to 6C are the same as the manufacturing process of FIGS. 5A to 5C described above, and thus a detailed description thereof will be omitted.

As shown in FIG. 6D, upper electrode materials such as Au, Au / Cr, Pt, Pt / Cr, Ir, Ir / Cr, Ru, and RuO ₂ are formed and patterned on the front surface of the piezoelectric body 5 and the variable capacitor. An upper electrode 6 of the resonator is formed to cover a portion of the lower electrode 4b, and the sacrificial layer 10 is formed in the resonator and the variable capacitor forming region.

Here, the sacrificial layer 10 may be formed of a polymer, a photoresist, a metal, or the like.

Subsequently, as shown in FIG. 6E, upper electrode materials are formed on the front surface and patterned to form upper electrodes 6a and 6b of the variable capacitor, respectively, to be disposed on a portion of the sacrificial layer 10.

At this time, the deposition process of the upper electrode material uses DC sputtering, evaporation, chemical vapor deposition (CVD), etc., like the lower electrode, and the upper electrode patterning process Wet etching, dry etching and lift-off methods are used.

Next, as shown in FIG. 6F, a photoresist is formed on the front surface of the substrate 1 to protect the resonator and the variable capacitor formed on the front surface of the substrate 1, and the substrate 1 is placed on a buffered oxide etchant (BOE) solution. Soak the oxide film on the back of the substrate.

Then, the predetermined region on the back side of the substrate is etched to expose the membrane film 2 in the region where the resonator is formed, and the membrane film 2 in the region where the variable capacitor is formed.

At this time, the etching of the substrate 1 uses a method such as wet etching, micro-machining (micro-machining).

Finally, although not shown, a pad electrode including a ground electrode is formed on the substrate 1 to complete the fabrication of the variable bandpass filter.

At this time, each electrode is produced using electroplating.

The variable bandpass filter of the present invention manufactured as described above combines the advantages of the thin film volume acoustic wave resonator with excellent center frequency characteristics and the variable capacitor finely adjusting the center frequency, thereby providing excellent frequency characteristics and reliability for various fields such as high frequency communication. There is an advantage that can be applied.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (15)

A substrate having holes; A membrane film formed on the substrate; A resonator formed on the membrane film; And, And a first variable variable capacitor and a second variable capacitor which are electrically connected to the resonator and are respectively formed on the membrane films on both sides of the resonator. The variable bandpass filter of claim 1, wherein a first hole is formed in the resonator formation region, and second and third holes are formed in the first and second variable capacitor formation regions, respectively. . The method of claim 1, wherein the resonator A lower electrode formed in a predetermined shape on the membrane film; A piezoelectric body formed on the lower electrode; And, Variable band pass filter, characterized in that consisting of the upper electrode formed in a predetermined shape on the piezoelectric body. The method of claim 1, wherein the first and second variable capacitor A lower electrode formed in a predetermined shape on the membrane film; A dielectric formed on the lower electrode; And, Variable band pass filter, characterized in that consisting of the upper electrode formed in a predetermined shape on the dielectric. The variable bandpass of claim 4, wherein the lower electrode of the first capacitor is electrically connected to the lower electrode of the resonator, and the lower electrode of the second capacitor is electrically connected to the upper electrode of the resonator. filter. The method of claim 1, wherein the first and second variable capacitor A lower electrode formed in a predetermined shape on the membrane film; A dielectric formed on the lower electrode; And, And an upper electrode formed in a predetermined shape on the dielectric so as to be released at a predetermined interval away from the dielectric, and configured to be in contact with the dielectric according to an externally applied voltage. The variable bandpass filter of claim 6, wherein the upper electrode has a cantilever shape in which only one end is fixed and released from the dielectric, or a bridge in which both ends are fixed and released from the dielectric. . The bottom electrode of claim 3, 4 or 6, wherein the lower electrode is formed of Au / Ti, Au / Cr, Pt / Ti, Pt / Cr, Ir / Ti, Ir / Cr, Ru / RuO ₂ , Ru. / Ti, any one of the piezoelectric material and the dielectric is made of any one of ZnO, AlN, SiO ₂ , GaAs, PZT, PLT, the upper electrode is Au, Au / Cr, Pt, Pt / Cr, Ir, Ir / Cr, Ru, RuO ₂ variable bandpass filter, characterized in that made of any one. In the method of manufacturing a variable bandpass filter having a resonator and a first, a second variable capacitor on a substrate, Forming a membrane film on the substrate; Forming and patterning a lower electrode material on the membrane layer to form a lower electrode of the resonator and a lower electrode of the first and second variable capacitors in a predetermined region; Forming a piezoelectric body on a portion of the lower electrode of the resonator and forming a dielectric on a portion of the lower electrode of the first and second variable capacitors, respectively; Forming and patterning an upper electrode material on the front surface to form an upper electrode of the resonator so as to cover the piezoelectric body and a portion of the lower electrode of the second variable capacitor, and an upper portion of the first and second variable capacitors so as to extend over the dielectric part. A fourth step of forming electrodes, respectively; And, And a fifth step of etching a predetermined region on the back side of the substrate to expose the resonator and the membrane film of the first and second variable capacitor forming regions. 10. The method of claim 9, wherein the first step is Forming a thermal oxide film on the substrate; Forming a nitride film on the thermal oxide film; And forming an oxide film on the nitride film. The method of claim 9, wherein in the second and fourth steps, The lower electrode and the upper electrode may be formed by any one of DC sputtering, evaporation, and chemical vapor deposition (CVD). . The method of claim 9, wherein in the third step, The piezoelectric material and the dielectric material are deposited by any one of RF sputtering, chemical vapor deposition (CVD), sol-gel, and metal organic deposition. A method of manufacturing a variable bandpass filter, characterized in that the patterning by any one of etching, dry etching, lift-off (lift-off) method. The method of claim 9, wherein in the second step, the lower electrode of the resonator and the lower electrode of the first variable capacitor are patterned to be electrically connected. In the fourth step, the upper electrode of the resonator and the lower electrode of the second variable capacitor are connected. Method for producing a variable bandpass filter, characterized in that the patterning to be electrically connected. In the method of manufacturing a variable bandpass filter having a resonator and a first, a second variable capacitor on a substrate, Forming a membrane film on the substrate; Forming and patterning a lower electrode material on the membrane layer to form a lower electrode of the resonator and a lower electrode of the first and second variable capacitors in a predetermined region; Forming a piezoelectric body on a portion of the lower electrode of the resonator and forming a dielectric on a portion of the lower electrode of the first and second variable capacitors, respectively; Forming and patterning an upper electrode material on the front surface to form an upper electrode of the resonator so as to extend over the piezoelectric body and a portion of the lower electrode of the second variable capacitor, and forming a sacrificial layer on the resonator and the first and second variable capacitor forming regions. Forming a fourth step; Forming a top electrode material on the front surface and patterning the top electrode material to form top electrodes of the first and second variable capacitors so as to extend over a portion of the sacrificial layer; A sixth step of removing the sacrificial layer; And, And a fifth step of etching a predetermined region on the back side of the substrate to expose the resonator and the membrane film of the first and second variable capacitor forming regions. The method of claim 14, wherein the sacrificial layer is any one of a polymer, a photoresist, and a metal.