KR20030073842A - Flim bulk acoustic resonator filter and manufacturing method for the same - Google Patents

Abstract

PURPOSE: A film bulk acoustic resonator(FBAR) filter and a fabrication method thereof are provided to improve band pass characteristics of the FBAR filter and to realize one chip integration by a MMIC(Monolithic Microwave Integrated Circuit) process without using an external individual device. CONSTITUTION: The first resonant part(61) is formed by connecting a number of film bulk acoustic resonators(FBAR)(61a,61b,61c) having the first resonant frequency serially. The second resonator part(62) is formed with a number of FBARs(62a,62b) connected in parallel with the FBARs of the first resonant part, and has the second resonant frequency. And the third resonant part(63) has the first resonant frequency, and is formed with a number of FBARs(63a,63b) connected in parallel with the FBARs of the first resonant part.

Description

Thin film bulk elastic resonator filter and its manufacturing method {Flim bulk acoustic resonator filter and manufacturing method for the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a thin film bulk elastic resonator (FBAR) filter for passing a signal in a desired frequency band, and in particular, to prevent passage of a signal in an undesired frequency band and to improve filter characteristics. By forming a function inside the FBAR filter, the size of the filter is reduced and the characteristics of the filter are improved.

In general, a band pass filter is an RF component that passes a signal of a desired frequency band. The band pass filter filters only signals necessary for transmitting and receiving signals through a base station or a terminal and removes unnecessary signals. .

SAW (Surface Acoustic Wave) filter, which is widely used as such a filter, can be mass-produced by using miniaturization and semiconductor process due to its small size, easy signal processing, and simple circuit, but it is difficult to use due to difficult power handling in high frequency band There is this.

FBAR filters, on the other hand, can be freely combined with RF active elements, making them extremely lightweight and ultra-thin, mass-produced using semiconductor processes, and improving the call quality of mobile communication terminals due to their stability and excellent signal-to-noise ratio. have.

As shown in FIGS. 1 to 3, general FBAR structures include a Membrane type, a solidly mounted resonator (SMR) type, and an air-gap type.

First, as shown in FIG. 1, the Membrane type forms the support layer 12 on the semiconductor substrate 11, and then positions the lower electrode 13, the piezoelectric layer 14, and the upper electrode 15, and mechanical vibration. A portion of the semiconductor substrate 11 is removed by backside etching to improve the efficiency.

In addition, as shown in FIG. 2, the solid-mounted resonator (SMR) type is formed by forming two layers 22 and 23 having a large difference in acoustic impedance on the semiconductor substrate 21 as a lower electrode. 24), the piezoelectric layer 25 and the upper electrode 26 are positioned to minimize the loss of sound waves through Bragg reflection.

Finally, as shown in FIG. 3, the air-gap type forms a sacrificial layer 31a between the semiconductor substrate 31 and the support layer 32 by using surface micromachining, and then the lower electrode 33 and the piezoelectric layer. As the structure in which the 34 and the upper electrode 35 are positioned, the backside etching process using bulk micro-machining is not required, and thus the process can be simplified.

The FBAR of the Membrane type, SMR (Solidly Mounted Resonator) type, and Air-Gap type has a frequency in which resonance characteristics of which impedance is almost infinite and “0” appear as the piezoelectric layers 14, 25, and 34 vibrate. Is generated, the frequency of the low impedance region is passed and the frequency of the remaining bands are cut off.

A plurality of FBARs formed of the Membrane type, SMR (Solidly Mounted Resonator) type, and Air-Gap type are connected in series and in parallel to form a FBAR filter capable of passing a signal having a desired pass frequency band.

4 is a block diagram showing the structure of a first FBAR filter according to the prior art.

As shown in FIG. 4, the first FBAR filter according to the related art includes a series resonator 41 having a first resonance characteristic by connecting a plurality of FBARs 41a, 41b, and 41c in series, and a second resonance characteristic. A parallel resonator 42 comprising a plurality of FBARs 42a, 42b, 42c, and 42d connected in parallel with the series filter unit 41, and the series resonator 41 and the parallel resonator 42. It is composed of a wiring 43 formed to transmit a signal through.

Here, the wiring 43 includes an input terminal 43a through which a signal is input from the outside, an output terminal 43b through which the signal is output to the outside, and a plurality of ground terminals 43c, 43d, 43e, which allow noise to be removed. 43f).

Impedance characteristics of the first FBAR filter according to the related art, which are configured as described above, are illustrated in FIG. 5 by the series resonator 41 and the parallel resonator 42, respectively. , 45, and the series and parallel impedance response curves 44 and 45 generate series resonance and parallel resonance 44a, 45a, 44b, and 45b at frequencies f1, f3, f2, and f4, respectively.

At this time, if the frequencies of f2 and f3 are matched, as shown in FIG. 6, band pass filter characteristics having center frequencies f2 and f3 and frequency passbands f1 to f4 appear.

However, since the first FBAR filter according to the related art has no loss in band pass characteristics in the case of an ideal FBAR filter, the band pass characteristics have a rectangular shape, but in actual cases, have a gentle slope. There is a problem that a signal in a frequency band that does not pass.

As shown in FIG. 7, the second FBAR filter structure according to the related art for solving the above problems includes a series resonator 51 including a plurality of series connected FBARs 51a, 51b, and 51c. A parallel resonator 52 comprising a plurality of FBARs 52a, 52b, 52c, and 52d connected in parallel with the series resonator 51, and a plurality of FBARs 52a, 52b, 52c, constituting the parallel resonator 52, And a plurality of inductors L1, L2, L3, L4 connected in series to 52d).

However, while the second FBAR filter according to the related art is filtered through the input terminal 53, the band pass characteristic of the external signal output through the output terminal 54 is improved, while individual elements such as inductors Since it must be added, there is a problem that the single chip of the filter by the MMIC (Monolithic Microwave Integrated Circuit) process is not easy.

The present invention has been made to solve the above problems of the prior art, the purpose of which is to improve the band pass characteristics of the FBAR filter and to use a separate device to the outside to enable a single chip by the MMIC (Monolithic Microwave Integrated Circuit) process Instead, it adds features to improve the bandpass characteristics inside the filter, reducing the size of the FBAR filter, reducing costs and simplifying the process.

1 to 3 are cross-sectional views showing the structure of a typical FBAR,

4 is a block diagram showing the structure of a first FBAR filter according to the prior art;

5 is a graph showing the impedance characteristics of the first FBAR filter according to the prior art;

6 is a graph illustrating bandpass characteristics of a first FBAR filter according to the related art;

7 is a circuit diagram showing the structure of a second FBAR filter according to the prior art;

8 is a block diagram showing the structure of an FBAR filter according to the present invention;

9 is a circuit diagram showing the structure of an FBAR filter according to the present invention;

10 is a graph showing the impedance characteristics of the FBAR filter according to the present invention;

11A to 11F show a first manufacturing method of the FBAR filter according to the present invention;

12A to 12G illustrate a second manufacturing method of the FBAR filter according to the present invention.

<Explanation of symbols on main parts of the drawings>

61: first resonator 61a, 61b, 61c: FBAR

62: second resonator 62a, 62b: FBAR

63: third resonator 63a, 63b: FBAR

64: wiring 64a: input terminal

64b: Output terminal 64c, 64d, 64e, 64f: Ground

According to a feature of the FBAR filter according to the present invention for solving the above problems, a plurality of FBAR is connected in series with a first resonator having a first resonance characteristics, and a plurality of FBARs connected in parallel with the first resonator And a third resonator including a second resonator having a second resonant characteristic, and a plurality of FBARs connected in parallel with the first resonator, and having a third resonant characteristic.

Further, according to another feature of the FBAR filter according to the present invention, the first step of forming a lower electrode on the semiconductor substrate on which the support layer is formed, and the first, second and third resonator in the lower electrode formed in the first step Forming the first, second and third piezoelectric layers to be used; and forming an upper electrode of a thickness and a material corresponding to the resonance frequencies of the first, second and third resonators. It consists of three steps formed in three piezoelectric layers.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

8 is a diagram showing the structure of an FBAR filter according to the present invention, and FIG. 9 is a circuit diagram showing an equivalent circuit of the structure of the FBAR filter according to the present invention.

As shown in FIG. 8 and FIG. 9, the FBAR filter according to the present invention includes a plurality of FBARs 61a, 61b, and 61c connected in series, and includes a first resonator 61 having a first resonance characteristic, A second resonator 62 formed of a plurality of FBARs 62a and 62b connected in parallel with the first resonator 61 and having a second resonant characteristic, and connected in parallel with the first resonator 61; It consists of a plurality of FBAR (63a, 63b) is composed of a third resonator (63) having a third resonance characteristic.

In this case, the first to third resonators 61, 62, and 63 may include the FBARs 61a, 61b, 61c, 62a, 62b, 63a, which form the first to third resonators 61, 62, and 63. 63b) forms different materials and thicknesses of the electrodes, whereby frequencies in which series and parallel resonance characteristics appear are determined. That is, the first to third resonators 61, 62, and 63 are formed of piezoelectric layers in which upper and lower electrodes are formed on upper and lower portions, and frequency in which series and parallel resonance characteristics appear depending on the thickness and material of the upper electrode. Will be determined.

In addition, the FBAR filter has a wire 64 formed to transmit a signal between the first to third resonators 61, 62, and 63, and the wire 64 has an input / output terminal 64a through which the signal is input and output. , 64b) and ground terminals 64c, 64d, 64e, and 64f for removing noise of the signal.

The impedance characteristic curve of the FBAR filter according to the present invention configured as described above is shown in Figure 10, the first resonator 61 is the first series resonance (65a) and f8 infinitely reduced impedance at the frequency of f7 The impedance characteristic curve 65 in which the first parallel resonance 65b is formed in which the impedance increases infinitely at the frequency of is shown.

Similarly to the first filter unit 61, the second and third resonators 62 and 63 may also have second and third series resonances 66a and 67a in which impedances are infinitely reduced at frequencies f5 and f9, respectively. Impedance characteristic curves 66 and 67 are formed in which second and third parallel resonances 66b and 67b are formed in which impedance increases infinitely at frequencies f6 and f10.

Here, the frequency pass band characteristics of the signal may be changed by adjusting the frequency at which the resonance characteristics appear in the impedance characteristic curves 65, 66, and 67.

Accordingly, the FBAR filter according to the present invention adjusts the frequency passband characteristics through the first to third resonators 61, 62, and 63 constituting the FBAR filter without forming a separate element outside. This reduces the size of the device and improves the frequency passband characteristics of the filter.

In the first manufacturing method of the FBAR filter according to the present invention configured as described above, first, as shown in FIGS. ).

The second step is to form the first to third resonators 61, 62, and 63 on the lower electrode 74 formed in the first step, as shown in FIG. 11C, respectively. Piezoelectric layers 75a, 75b, 75c are formed.

Step 3 includes a first upper portion on each of the first and second piezoelectric layers 75a and 76b, as shown in FIGS. 11D and 11E on the first and second piezoelectric layers 75a and 75b formed in the second step. After forming the electrode 76, a second upper electrode 77 is formed on the first and third piezoelectric layers 75b and 75c.

At this time, the second upper electrode 77 determines the resonant frequencies of the first and third resonators 61 and 62 by adjusting the thickness.

Accordingly, by forming different materials and thicknesses of the upper electrodes formed on the first to third piezoelectric layers 75a, 75b, and 75c, the frequency passband characteristics are determined by varying frequencies in which resonance characteristics appear. .

Finally, as shown in FIG. 11F, a portion of the bottom surface of the semiconductor substrate 71 is removed by etching to improve the mechanical vibration characteristics of the FBAR filter.

Meanwhile, in the second method of manufacturing the FBAR filter according to the present invention, as shown in FIGS. 12A to 12C in the first step, the lower electrode 84 is formed on the semiconductor substrate 81 having the support layers 82 and 83 formed on the upper and lower portions thereof. Next, first to third piezoelectric layers 85a, 85b, and 85c are formed to form the first to third resonators 61, 62, and 63.

12D and 12E, after forming the first upper electrode 86 on the first and second piezoelectric layers 85a and 85b formed in the first step, the second piezoelectric layer 85b is formed. ), A resonance frequency adjusting layer 87 is formed.

Step 3 forms a second upper electrode 88 on the third piezoelectric layer 85c, as shown in Fig. 12F.

Finally, as shown in FIG. 12G, by etching away a portion of the semiconductor substrate 81, the mechanical vibration of the FBAR filter is improved.

Accordingly, the thickness and the material of the upper electrodes are different in the first to third resonators 61, 62, and 63 so that the resonance frequency of the resonance characteristic is different, and the resonance frequency is adjusted to adjust the band pass characteristic of the filter. In addition to being easy to adjust, the band pass characteristic of the filter can be adjusted using a plurality of FBARs formed inside the filter, thereby reducing the size of the filter element.

The FBAR filter of the present invention configured as described above is composed of a plurality of FBAR series and parallel, and formed in the filter using a plurality of FBAR to improve the band pass characteristics, and can be manufactured at the same time in the semiconductor process MMIC (Monolithic Microwave Integrated Circuit) enables the reduction of the size of the filter element, which simplifies the process and reduces costs.

Claims (9)

A first resonator unit having a plurality of thin film bulk resonators (hereinafter referred to as FBARs) having a first resonant frequency in series; A second resonator having a second resonant frequency and comprising a plurality of FBARs connected in parallel with the plurality of FBARs of the first resonator; And a third resonator having a third resonant frequency and comprising a plurality of FBARs connected in parallel with a plurality of FBARs of the first resonator. According to claim 1, The FBAR filter has a wire formed to transmit a signal between the first to third resonators, and the wire includes an input / output terminal through which the signal is input and output and a ground terminal to remove noise of the signal. FBAR filter. In the manufacturing method of the FBAR filter, Forming a lower electrode on the semiconductor substrate; A second step of forming first, second and third piezoelectric layers on the lower electrode formed in the first step; A third step of forming an upper electrode in the first, second and third piezoelectric layers so that the resonant frequencies of the first, second and third piezoelectric layers formed in the second step are set differently; And a fourth step of partially removing the bottom surface of the semiconductor substrate through etching to improve mechanical vibration characteristics of the FBAR filter. The method of claim 3, wherein The third step may include a first process of forming a first upper electrode on the first and second piezoelectric layers; And a second process of forming a second upper electrode on the first and third piezoelectric layers. The method of claim 4, wherein And controlling the thickness of the second upper electrode to determine resonance frequencies of the first and third piezoelectric layers. In the FBAR filter manufacturing method, Forming a lower electrode on the semiconductor substrate; A second step of forming first, second and third piezoelectric layers on the lower electrode formed in the first step; A third step of forming an upper electrode and a resonance frequency adjusting layer in the first to third piezoelectric layers; And a fourth step of partially removing the bottom surface of the semiconductor substrate through etching to improve mechanical vibration of the semiconductor substrate. The method of claim 6, The third step may include a first process of forming a first upper electrode on the first and second piezoelectric layers; Forming a resonant frequency adjusting layer on the second piezoelectric layer; And a third process of forming a second upper electrode on the third piezoelectric layer. The method of claim 7, wherein The second piezoelectric layer is a FBAR filter manufacturing method characterized in that the resonance frequency is determined according to the thickness of the resonance frequency adjustment layer. The method according to claim 3 or 6, And a support layer is interposed between the semiconductor substrate and the lower electrode.