KR100906679B1 - Band pass filter using thin film bulk acoustic wave resonator and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a band pass filter using a thin film bulk acoustic wave resonator (TFBAR) and a method of manufacturing the same. A conventional band pass filter using a thin film bulk acoustic wave resonator and a method of manufacturing the same are a limited number of thin films within a region allowed by the same membrane layer. Since volume acoustic wave resonators are mounted, performance between the resonators is severely deteriorated, and the number of resonators that can be formed in a single membrane layer is limited, and thus a multifunctional filter cannot be formed in the same membrane layer. In view of the above problems, the present invention provides a plurality of thin film molten acoustic wave resonators formed in accordance with a circuit of a band pass filter to be constructed; A membrane layer supporting the thin film volume acoustic wave resonators under the thin film volume acoustic wave resonator; An interference isolation frame configured in the form of a lattice to cross between regions in which the thin film volume acoustic wave resonators are located below the membrane layer; And a substrate in which a region of the membrane layer in which the thin film volume acoustic wave resonators are formed and a portion of the region is removed to float the interference isolation frame, wherein the interference isolation frame is formed by doping a portion of the substrate with boron ions. It is characterized by.

Description

BAND PASS FILTER USING THIN FILM BULK ACOUSTIC WAVE RESONATOR AND MANUFACTURING METHOD THEREOF

1 is a perspective view showing one embodiment of a typical volumetric microfabricated bulk acoustic wave resonator;

FIG. 2A is a photogram of a four series two parallel band pass filter using a microfabricated thin film acoustic wave resonator; FIG.

FIG. 2B is an illustration of a three series four parallel band pass filter using a microfabricated thin film volume acoustic wave resonator; FIG.

3 is an actual characteristic diagram of the three series four parallel band pass filter of FIG.

Fig. 4A is a configuration diagram of a resonator of a three series four parallel band pass filter.

4B is a graph showing the transmission characteristics of FIG. 4A.

Figure 5 is a plan view of a three series four parallel band pass filter applying an embodiment of the present invention.

6a to 6d is a cross-sectional view showing a process of manufacturing an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

10: Volumetric microfabrication TFBAR 11: Substrate

12: membrane layer 13: lower electrode                 

14: mechanism material 15: upper electrode

20: substrate 21: interference isolation frame

22: membrane layer 23: lower electrode

24: mechanism material 25: upper electrode

The present invention relates to a band pass filter using a thin film bulk acoustic wave resonator (TFBAR) and a method of manufacturing the same. In particular, the structural safety of the membrane layer is improved by forming an interference isolation frame under the membrane layer. The present invention relates to a band pass filter using a thin-film volume acoustic wave resonator and a method of manufacturing the same, which are suitable for increasing the maximum number of mounting and reliability of the same TFBAR and reducing interference between component resonators.

Bandpass filters (BPFs) and duplexers (DPXs), which are one of the key components used in telecommunication terminals including mobile phones, are devices that extract frequencies desired by users from many airwaves. I'm using a filter. However, due to limitations in size and high frequency band characteristics, studies are being conducted to apply FBAR filters to information communication terminals.

The FBAR filter has a wide frequency band, a small size, and a very small power consumption, which will contribute to miniaturization and low power of information and communication components. The FBAR thin film type resonator uses a mechanism material such as ZnO and AlN. The FBAR thin film resonator generates a resonance by connecting an electrode to a lower portion and an upper portion of the mechanism material to induce a bulk acoustic wave.

These FBARs can be miniaturized to less than one-hundreds of the size of dielectric and lumped constant (LC) filters. They also offer significantly lower insertion losses and greater usable power than surface acoustic wave devices. In addition, since it can be embedded in a MMIC (Monolithic Microwave Integrated Circuit), it is possible to implement a one-chip RF filter and to have high frequency characteristics, thereby being applied to a next-generation information communication terminal.

FIG. 1 is a perspective view showing the structure of a bulk micromachined TFBAR using a bulk micromachining technique. As shown in FIG. 1, a portion of the substrate 11 is etched to form a low stress membrane layer. Allow (12) to float and form TFBARs (13, 14, 15) on top.

As shown in the drawing, when the TFBAR is manufactured using the volumetric microfabrication method, since the substrate 11 is etched with an etching solution such as KOH, EDP, or TMAH, the angle formed between the substrate and the etching surface is inclined at 54.74 degrees. Therefore, the number of TFBARs that can be produced simultaneously on the membrane of such a structure is limited, and in order to manufacture a filter using the limited area, six to seven TFBARs are densely formed on the same membrane. When constructing a ladder filter, all the resonators used must be formed on the same membrane, and the smallest size band pass filter can be manufactured by connecting 6 to 7 TFBARs in series and in parallel. Due to the structural limitations of the membrane, no more than seven TFBARs are formed on the same membrane.

FIG. 2A is a photorealistic view of a four series two-parallel band pass filter using a microfabricated thin film volume acoustic wave resonator, and FIG. 2B is a photorealistic illustration of a three series four parallel type bandpass filter using a microfabricated thin film volume acoustic wave resonator. By placing six to seven TFBARs in the same confined membrane region, interference will inevitably occur because the series and parallel resonators are located on the same membrane. In particular, series and parallel resonators with different resonant frequencies have a large effect due to mutual interference, which degrades the performance of the band pass filter.

FIG. 3 is a graph showing the actual characteristics of the 3 series 4 parallel band pass filter shown in FIG. 2B. As shown in FIG. In other words, it can be seen that the poles are separated from the low frequency notch and the high frequency notch characteristics, and the roll-off characteristic is also greatly deteriorated. In addition, the insertion pressure loss in the band pass band also worsens like a slope. This problem occurs because the resonators constituting the band pass filter cross talk to vary the resonant frequency. In particular, it is a problem caused by mutual interference of each resonator formed on the same membrane.

As described above, a phenomenon in which the poles are separated from the low frequency and high frequency notches of the three-serial four-parallel band pass filter and the degradation of the roll-off characteristic due to the separation of the poles will be described with reference to FIGS. 4A to 4B. .

FIG. 4A illustrates a layout of TFBARs constituting a 3 series 4 parallel band pass filter, and is a ladder band pass filter including 4 TFBARs connected in parallel with 3 TFBARs connected in series as shown.

FIG. 4B is a graph showing transmission characteristics of the 3 series 4 parallel band pass filter shown in FIG. 4A. As shown, a low frequency notch is formed at the series resonance frequency fs (T2) of TFBAR2 resulting from the series resonance of TFBAR2, and is formed at the series resonance frequency fs (T1) of TFBAR1 connected in series with the parallel resonance frequency fp (T2) of TFBAR2. The insertion loss and ripple characteristics are determined in the band pass band. In addition, the high frequency notch characteristic is determined by the parallel resonance frequency fp (T1) of the series resonators. Here, if fs (T2), fp (T2), fs (T1), and fp (T1) of each individual resonator are different from each other, a very deteriorated band pass filter characteristic is shown as shown. The resonant frequency mismatch of each resonator may of course be caused by the non uniformity of the thin film thickness (bottom electrode, electromechanical material, upper electrode, membrane) in the manufacturing process, but is mainly caused by mutual coupling of peripheral resonators. . Since such mutual interference is well transmitted when the volume acoustic waves are on the same membrane, it is difficult to reduce mutual interference between resonators in the conventional construction and manufacturing method, and thus suffer a performance reduction.

As described above, a band pass filter using a thin film volume acoustic wave resonator and a method of manufacturing the same have a limited number of thin film volume acoustic wave resonators in a region allowed by the same membrane layer, so that interference between the resonators is severe and performance is degraded. Due to the limited number of resonators that can be formed in a single membrane layer, there is a problem in that a composite function filter cannot be configured in the same membrane layer.

In view of the above problems, the present invention is to form an interference isolation frame at the bottom of the membrane into a lattice to be suitable for the size of the volume acoustic wave resonator to be formed on the membrane, thereby reinforcing structural weakness of the membrane, An object of the present invention is to provide a band pass filter using a thin film volume acoustic wave resonator capable of increasing the number and reducing interference between resonators and a method of manufacturing the same.

The present invention for achieving the above object, a plurality of thin film molten acoustic wave resonator formed in accordance with the circuit of the band pass filter to be configured; A membrane layer supporting them below said thin film volume acoustic wave resonator; An interference isolation frame configured in the form of a lattice so as to traverse between regions in which the thin film volume acoustic wave resonators are located below the membrane layer; And a membrane layer region in which the thin film volume acoustic wave resonators are formed and a support substrate from which a portion of the region is removed to float the interference isolation frame.

The interference isolation frame is formed by doping boron ions in a portion of the substrate.

In addition, the present invention includes etching a portion of the area on the substrate by a photolithography method to form a pattern for interference hardened region frame; Doping a heterogeneous material to the formed pattern to form an interference benefit area frame made of an etch stop material within the substrate; Forming a membrane layer by forming a low stress thin film on the upper and lower portions of the substrate on which the interference-polished region frame is formed; Sequentially forming a lower electrode, a mechanism material, and an upper electrode on the membrane layer formed on the substrate to form a thin film volume acoustic wave resonator; And etching a portion of the membrane layer below the substrate and a portion of the substrate to expose the membrane layer of the thin film volume acoustic wave resonator forming region and the interference accounting region frame.

When described in detail with reference to the accompanying drawings an embodiment of the present invention configured as described above are as follows.

FIG. 5 is a plan view showing a structure of an embodiment of the present invention, in which thin-film volume acoustic wave resonators 23, 24, and 25 forming a three-series four-parallel band pass filter are disposed on a single membrane 22. As shown in FIG. Formed. In addition, an interference isolation frame 21, which is a feature of the present invention, is regularly formed in a lattice form under the membrane 22 between the respective resonators.

Since the interference isolation frame 21 evenly divides the membrane 22 in which the resonators are formed, the interference isolation frame 21 effectively reduces the interference of the resonators while compensating for the structural weakness of the low stress membrane 22.

Since the interference isolation frame 21 compensates for the structural weakness of the membrane 22, the interference isolation frame 21 relaxes the restriction on the number of resonators that can be simultaneously mounted due to the low stress. That is, since more than seven resonators can be simultaneously mounted on the same membrane 22, the transmission bandpass filter and the reception bandpass filter may be configured on the same membrane 22. This enables the TFBAR duplexer to be implemented on the same chip, dramatically reducing the size and manufacturing cost of the duplexer. That is, the application of the present invention can increase the number of TFBAR that can be formed on the same membrane, it is possible to realize an application circuit using a plurality of TFBAR.

In addition, since the interference between the respective resonators can be greatly alleviated by the interference isolation frame 21 passing between the respective resonators, the characteristics of the band pass filter can be greatly improved. This shows a great characteristic improvement effect when the frequencies of the resonators do not match.

Now, the method of forming the interference isolation frame 21 will be described in detail with reference to the manufacturing process of the embodiment of the present invention.

6A to 6C are cross-sectional views showing a process sequence of an embodiment of the present invention.

First, as shown in FIG. 6A, a photoresist pattern is formed on the silicon substrate 20, and a portion of the exposed silicon substrate 20 is etched to form an interference isolation frame pattern on the substrate. The pattern for the interference isolation frame is then in the form of a grating passing between the areas where TFBARs are to be formed. Naturally, it can be transformed into various forms, and it should form a closed curve covering the TFBAR to be formed later. The boron etch stop layer is formed by doping boron such that the pattern formed on the substrate 20 is p ++. The boron etch stop layer is formed as an interference isolation frame 21 supporting the membrane layer 22 to remain and be formed on the silicon substrate 20 even if the silicon substrate 20 is etched away.

Next, as shown in FIG. 6B, a low stress silicon nitride thin film is formed on the upper and lower portions of the structure by low power chemical vapor deposition to form the membrane 22. When the silicon nitride thin film is formed by a low power chemical vapor deposition method, a silicon nitride layer is simultaneously formed on the upper and lower portions of the substrate 20. The lower electrode 23 is formed by forming and patterning a first conductive layer on the membrane 22 formed on the substrate. The first conductive layer is a single material such as Pt, Mo, Au, Al, and the like, and may further form an adhesion improving material such as Ti, Ta, TiN, or the like below the first conductive layer in order to increase adhesion.

Next, as shown in FIG. 6C, the upper surface of the structure is formed by patterning and patterning a material material 24, and forming a top electrode 25 by forming and patterning a second conductive layer thereon. The mechanism material may be ZnO, ZlN, PZT, and the like, and the second conductive layer may be Pt, Mo, Au, Al, or the like.

Next, as shown in FIG. 6D, after patterning the silicon nitride layer 22 under the silicon substrate 20, the exposed silicon substrate 20 is wet-etched with a solution such as KOH, EDP, TMAH, and the like to make a volume fine. When processing, the etch stop occurs in the boron-doped interference isolation frame 21 and the membrane layer 22, so that a part of the silicon substrate 20 is removed leaving the corresponding portion. Since the interference isolation frame 21 is attached to the lower portion of the membrane layer 22, the structural strength of the membrane layer 22 is increased and the interference between the thin film volume acoustic wave resonators formed in the inner region of the frame 21 is reduced. do.

That is, in order to form the interference isolation frame 21 under the membrane 22, only the process of forming the interference isolation frame 21 is added without significantly changing the existing TFBAR bandpass filter manufacturing process. Application is possible.

As described above, the band pass filter using the thin film acoustic wave resonator of the present invention and a method of manufacturing the same have an interference isolation frame formed by forming a lattice so that the interference isolation frame below the membrane is suitable for the size of the volume acoustic wave resonator to be formed on the membrane. By simply adding the forming process to the existing process, the structural weakness of the membrane can be reinforced to increase the number of resonators mounted on the same membrane and thereby to configure the transmit / receive bandpass filter on the same chip. Since the interference between the resonators can be greatly reduced, the performance is improved.

Claims (6)

A plurality of thin film molten acoustic wave resonators formed in accordance with a circuit of a band pass filter to be constructed; A membrane layer supporting the thin film volume acoustic wave resonators under the thin film volume acoustic wave resonator; An interference isolation frame configured in the form of a lattice to cross between regions in which the thin film volume acoustic wave resonators are located below the membrane layer; And A membrane layer region in which the thin film volume acoustic wave resonators are formed and a substrate in which some regions are removed to float the interference isolation frame, The interference isolation frame, A band pass filter using a thin film bulk acoustic wave resonator, wherein a portion of the substrate is doped with boron ions. delete The band pass filter using the thin film volume acoustic wave resonator as set forth in claim 1, wherein at least seven thin film bulk acoustic wave resonators are formed on the same membrane. . Etching a portion of the region on the substrate by a photolithography method to form a pattern for the interference benefit region frame; Doping a heterogeneous material to the formed pattern to form an interference benefit area frame made of an etch stop material within the substrate; Forming a membrane layer by forming a low stress thin film on the upper and lower portions of the substrate on which the interference-polished region frame is formed; Sequentially forming a lower electrode, a mechanism material, and an upper electrode on the membrane layer formed on the substrate to form a thin film volume acoustic wave resonator; And Manufacturing a band pass filter using the thin film volume acoustic wave resonator by etching a portion of the membrane layer and a portion of the substrate under the substrate to expose the membrane layer of the thin film volume acoustic wave resonator forming region and the interference paying area frame. Way. The method of claim 4, wherein the forming of the interference benefit area frame in the substrate comprises: And forming a boron etch stop layer (p ++) by doping boron in the frame pattern formed on the substrate. The method of claim 4, wherein the substrate, A method for producing a band pass filter using a thin film volume acoustic wave resonator, characterized in that the silicon substrate.

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