JP2005192146A - Mems resonator and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a MEMS resonator and its manufacturing method in which the resonator having a desired resonant frequency can be accurately obtained. <P>SOLUTION: A group 25 of MEMS resonators having a beam structure and a plurality of kinds of resonant frequencies is formed, and a strong signal is input to the group 25 of MEMS resonators to destroy resonators 222 other than resonators 221, 223 having a desired frequency, thereby obtaining a MEMS resonator 20 in which only the resonators 221, 223 of the desired frequency are selected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a MEMS resonator and a manufacturing method thereof.

  With the development of information technology, the number of devices using a network has increased dramatically in recent years, and the demand for wireless network technology is increasing from the viewpoint of usability. The high-frequency front-end module used in wireless communication includes relatively large sizes such as surface acoustic wave (SAW) filters and dielectric filters for high-frequency (RF) filters and intermediate-frequency (IF) filters in addition to semiconductor chips. There are large parts. Their existence has hindered miniaturization and cost reduction of high-frequency front-end modules. It is currently required to incorporate these filter functions into a semiconductor chip.

  Beam-type MEMS (Micro Electro Mechanical Systems) resonators formed using a semiconductor process have a small device footprint, a high Q value, and can be integrated with other semiconductor devices. In the wireless communication device, use as an intermediate frequency (IF) filter and a high frequency (RF) filter has been proposed from research periods including the University of Michigan (see Non-Patent Document 1).

  FIG. 14 shows an outline of a MEMS resonator constituting the high-frequency filter described in Non-Patent Document 1. In the MEMS resonator 1, an input-side wiring layer 4 and an output electrode 5 made of, for example, polycrystalline silicon are formed on a semiconductor substrate 2 with an insulating film 3 interposed therebetween. A beam (so-called beam-type vibrating electrode) 7 that can be vibrated by polycrystalline silicon is formed. The beam 7 is connected to the input side wiring layer 4 across the output electrode 5 in a bridge shape so as to be supported by anchor portions (support portions) 8 [8A, 8B] at both ends. The beam 7 becomes an input electrode. For example, a gold (Au) film 9 is formed at the end of the input side wiring layer 4. In the MEMS resonator 1, the input terminal t 1 is derived from the gold (Au) film 9 of the input side wiring layer 4, and the output terminal t 2 is derived from the output electrode 5.

  In the MEMS resonator 1, a high frequency signal is supplied to the beam 7 through the input terminal t1 in a state where a DC bias voltage is applied between the beam 7 and the ground. That is, an input signal in which a DC bias voltage and a high frequency signal are superimposed is supplied from the input terminal t1. When a high frequency signal having a target frequency is input, the beam 7 having a natural frequency determined by the length L of the beam vibrates with an electrostatic force generated between the output electrode 5 and the beam 7. Due to this vibration, a high-frequency signal corresponding to the time change of the capacitance C0 between the output electrode 5 and the beam 7 and the DC bias voltage is output to the output electrode 5 (and hence the output terminal t2). The high frequency filter outputs a signal corresponding to the natural frequency (resonance frequency) of the beam 7.

C. T. T. et al. -Nguyen, "Micromechanical components for miniaturized low-power communications, (invited plenary)," proceedings, 1999 IEEE MTT-S International Microswing. 48-77.

  By the way, when a plurality of MEMS resonators are manufactured, there is a problem in that the length of the beam and the thickness of the beam vary due to variations in the semiconductor process, and the MEMS resonator deviates from a desired frequency. On the other hand, when a resonator group having a plurality of resonance frequencies is manufactured, a plurality of types of exposure masks are required depending on the combination of the resonance frequencies, and the manufacturing may be complicated.

In view of the above-described points, the present invention provides a MEMS resonator and a method for manufacturing the same that can improve characteristics at a desired resonance frequency even when there are variations in semiconductor processes, for example.
In addition, the present invention provides a MEMS resonator capable of combining any resonance frequency and a manufacturing method thereof.

  The MEMS resonator according to the present invention has a configuration in which a resonator other than a resonator having a desired frequency is destroyed by inputting a strong signal among resonator groups having a beam structure and a plurality of types of resonance frequencies.

  In the MEMS resonator of the present invention, a resonator other than the desired resonance frequency is destroyed by the input of a strong signal among the resonator group having a plurality of types of resonance frequencies, so that the MEMS having only the desired resonance frequency is used. It becomes a resonator.

  The method for manufacturing a MEMS resonator according to the present invention forms a MEMS resonator group having a plurality of types of resonance frequencies having a beam structure, and inputs a strong signal to the MEMS resonator group to obtain a device other than a resonator having a desired frequency. It is characterized by destroying the resonator.

  In the method for manufacturing a MEMS resonator according to the present invention, by inputting a strong signal to a group of MEMS resonators having a plurality of types of resonance frequencies, only the resonator having a desired resonance frequency is selected and remains, and other resonances are generated. The frequency resonator is eliminated. Thereby, a MEMS resonator having a desired resonance frequency is manufactured.

According to the MEMS resonator of the present invention, only a resonator having a desired resonance frequency is selected from the resonator group having a plurality of types of resonance frequencies, and the resonators having other resonance frequencies are removed. The Thereby, among the resonators having variations in the resonance frequency, the resonator having a large deviation from the desired resonance frequency can be removed, and the characteristics of the MEMS resonator can be improved. Therefore, even if there are variations in the semiconductor process, the characteristics of the MEMS resonator can be improved to a desired resonance frequency.
A MEMS resonator group in which resonators having arbitrary resonance frequencies are combined can be easily provided.

According to the method for manufacturing a MEMS resonator according to the present invention, a resonator having a large deviation from a desired resonance frequency is removed from resonators having variations in the resonance frequency, and only a resonator having a desired resonance frequency is left. As a result, a MEMS resonator with improved characteristics having only a desired resonance frequency can be manufactured.
A resonator group having an arbitrary resonance frequency can be manufactured without preparing a plurality of types of exposure masks. For example, a MEMS resonator group having a combination of arbitrary resonance frequencies can be manufactured by manufacturing resonators of 90 MHz to 110 MHz and removing some of them.

  Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show an embodiment of a MEMS resonator and a manufacturing method thereof according to the present invention.
In the present embodiment, as shown in FIG. 1, a plurality of MEMS resonator elements having a beam structure on a common substrate 21, that is, MEMS resonator elements 22 [221, 222, 223] having a plurality of types of resonance frequencies. Are formed in parallel, the input electrodes 23 are connected in parallel, and the output electrodes 24 are connected in parallel to produce a MEMS resonator group 25.
In this example, a resonator group 25 comprising three resonator elements of a 99 MHz MEMS resonator element 221, a 100 MHz MEMS resonator element 222, and a 101 MHz MEMS resonator element 223 is formed.

  Each MEMS resonator element 22 [221, 222, 223] is formed by branching an input electrode 23 and an output electrode 24 into three on the same plane of the substrate 21, as shown in FIGS. Then, beams (so-called beam-type vibrating electrodes) 27 [271, 272, 273] are formed to be independent diaphragms across the space 26 facing the branched input / output electrodes 23, 24. Configured. In the present embodiment, the MEMS resonator group 25 is configured as one device by connecting the plurality of MEMS resonator elements 22 in parallel.

Each beam 27 [271, 272, 273] spans the input / output electrodes 23, 24 in a bridge shape and is connected to a wiring layer 28 arranged outside the input / output electrodes 23, 24 at both ends with support portions ( A so-called anchor part) 29 [19A, 29B] is integrally supported. The beam 27 has a double-supported beam structure.
As the substrate 21, for example, a substrate in which an insulating film is formed on a semiconductor substrate such as silicon (Si) or gallium arsenide (GaAs), an insulating substrate such as a quartz substrate or a glass substrate, or the like is used. In this example, a substrate in which a silicon nitride film is formed on a silicon substrate is used. The input electrode 23, the output electrode 24, and the wiring layer 28 can be formed of the same conductive material, for example, a polycrystalline silicon film, a metal film such as aluminum (Al), and further formed by introducing impurities into a semiconductor substrate. An impurity semiconductor layer or the like can be used. The beam 27 can be formed of, for example, a polycrystalline silicon film or a metal film such as aluminum (Al).

  In the present embodiment, in the MEMS resonator group 25, the resonator elements having a specific resonance frequency are removed, and the resonator elements having other resonance frequencies are left. That is, in this example, only the resonator element 22 2 having a resonance frequency of 100 MHz is removed, and the target MEMS resonator 20 is manufactured while leaving the resonator elements 22 1 and 22 3 having other resonance frequencies.

  For this reason, the input electrode 23 of the MEMS resonator group 25 has a peak at 100 MHz as shown in FIG. 2 and is larger than the power for operating as a normal resonator, that is, the limit power at which the MEMS resonator element is not destroyed. A strong high-frequency signal S1 having a large power P2 exceeding P1 is input. When this high-frequency signal S1 is inputted, the beam 272 of the resonator element 222 of 100 MHz vibrates vigorously, the beam 272 is broken beyond the elastic limit, or the support 29 is broken. As a result, the 100 MHz resonator element 22 2 does not operate as a resonator, and as shown in FIG. 3, only the 100 MHz resonator element 22 2 is destroyed. In this way, only the 100 MHz resonator element 22 2 is removed from the MEMS resonator group 25 and the other 99 MHz and 101 MHz resonator elements 22 1, 223 are left, ie, the MEMS resonator group 20. Complete.

  The normal operation of the MEMS resonator element 22 is as follows. The required DC bias voltage of the beam 27 is applied. When a high frequency signal having a target frequency is input to the input electrode 23, the beam 27 resonates in a secondary vibration mode due to an electrostatic force generated between the beam 27 and the input electrode 23. The resonance of the beam 27 outputs a high frequency signal having a target frequency from the output electrode 24. When a number of other signals are input, the beam 27 does not resonate and no signal is output from the output electrode 24.

4 to 6 show another embodiment of the MEMS resonator and the manufacturing method thereof according to the present invention. In the present embodiment, as shown in FIG. 4, a plurality of MEMS resonator elements having a beam structure on a common substrate 21, that is, MEMS resonator elements 22 [221, 222, 223] having a plurality of types of resonance frequencies. Are formed in parallel, the input electrodes 23 are connected in parallel, and the output electrodes 24 are connected in parallel to produce a MEMS resonator group 25.
In this example, similarly to the above, a resonator group 25 including three resonator elements of a 99 MHz MEMS resonator element 221, a 100 MHz MEMS resonator element 222, and a 101 MHz MEMS resonator element 223 is formed.

  In the present embodiment, in the MEMS resonator group 25, only the resonator elements having a specific resonance frequency are left, and the resonator elements having other resonance frequencies are removed. In this example, only the resonator element 22 2 having a resonance frequency of 100 MHz is left, and the resonator elements 22 1 and 22 3 having other resonance frequencies are removed to produce the target MEMS resonator 30.

  For this reason, the power P2 of other frequencies except for 100 MHz as shown in FIG. 5 is larger than the power to operate as a normal resonator, that is, the MEMS element is destroyed at the input electrode 23 of the MEMS resonator group 25. A strong high-frequency signal S2 having a large power exceeding the limit power P1 that is not received is input. When this high-frequency signal S2 is input, the 99 MHz and 101 MHz resonator elements 221 and 223 vibrate violently, exceeding the elastic limit, the beams 271 and 273 are broken, or the support portions 29 of the beams 271 and 273 are broken. . As a result, the 99 MHz and 101 MHz resonator elements 22 1 and 223 do not operate as a resonator, and the 99 MHz resonator element 22 1 and the 101 MHz resonator element 223 are destroyed as shown in FIG. . In this way, only the 100 MHz resonator element 22 2 remains from the MEMS resonator group 25 and the other resonator elements 22 1, 22 3 of the other frequencies are removed, that is, the MEMS resonator group 30 is completed. To do.

  In the above example, only the resonator element having the required resonance frequency is left from the MEMS resonator group 25 having the three resonator elements 221 to 223 having the three types of resonance frequencies, and the other resonator elements are removed to achieve the target. Although the MEMS resonators 20 and 30 are configured, a MEMS resonator group including a plurality of resonator elements having two or three or more types of resonance frequencies is manufactured, and only an arbitrary resonator element is left. It is possible to configure a MEMS resonator by removing other resonator elements.

  According to the above-described embodiment, a strong signal is input to the MEMS resonator group 25 having a plurality of resonance frequencies, and only the resonator element having a desired resonance frequency is selected from the MEMS resonator group 25. By removing the other resonator elements, the MEMS resonators 20 and 30 having a desired resonance frequency can be configured. Further, even when the length and thickness of the beam 27 vary due to variations in the semiconductor process, for example, a resonator element having a large deviation from a desired resonance frequency can be removed, and the characteristics as a MEMS resonator can be obtained. Can be improved.

7 to 10 show still another embodiment of the MEMS resonator and the manufacturing method thereof according to the present invention. In this embodiment, a plurality of MEMS resonator elements 32 [321, 322, 323] having a plurality of types of resonance frequencies previously determined on the common substrate 21 and having beams 271, 272, 273, 274, 275, respectively. 324, 325] are formed in parallel, the input electrode 23 is connected in parallel, and the output electrode 24 is connected in parallel to produce a MEMS resonator group 33.
In this example, the five resonator elements are a 99 MHz MEMS resonator element 22 1, a 100 MHz MEMS resonator element 22 2, a 101 MHz MEMS resonator element 223, a 102 MHz MEMS resonator element 224, and a 103 MHz MEMS resonator element 225. A resonator group 33 is formed.

In the present embodiment, this MEMS resonator group 33 is used to produce a MEMS resonator group having an arbitrary combination of resonance frequencies.
Therefore, when configuring the first combination of MEMS resonator groups, for example, only the resonator elements 22 1, 22 2, and 22 4 are left on the input electrode 23 of the MEMS resonator group 33, and the other resonator elements 223 are used. A strong high frequency signal that destroys 225 is input. As a result, a MEMS resonator group 37 in which a 99 MHz resonator element 221, a 100 MHz resonator element 222, and a 102 MHz resonator element 224 are combined as shown in FIG.
When configuring the second MEMS resonator group, for example, only the resonator elements 222, 223 and 225 are left on the input electrode 23 of the MEMS resonator group 33, and the other resonator elements 221, 222 are destroyed. Input such a strong high-frequency signal. As a result, a MEMS resonator group 38 in which a 100 MHz resonator element 22 2, a 101 MHz resonator element 223 and a 103 MHz resonator element 22 5 are combined as shown in FIG. 9 is obtained.
When configuring the third MEMS resonator group, for example, only the resonator elements 221, 224 and 225 are left on the input electrode 23 of the MEMS resonator group 33, and the other resonator elements 222, 223 are destroyed. Input such a strong high-frequency signal. As a result, a MEMS resonator group 39 in which a 99 MHz resonator element 22 1, a 102 MHz resonator element 224 and a 103 MHz resonator element 225 are combined as shown in FIG. 10 is obtained.

  According to the present embodiment, a resonator in which resonator elements of any frequency are combined with only an exposure mask necessary for forming the MEMS resonator group 33 of FIG. 7 without producing a plurality of types of exposure masks. Groups 37, 38, 39 can be created. In this case, the semiconductor process of the resonator group having an arbitrary frequency is only performed once, and the manufacture becomes easy.

Next, a method for manufacturing the MEMS resonator groups 25 and 33 according to the present embodiment will be described with reference to FIGS. In the figure, the cross-sectional structure of the main part of the MEMS resonator element is shown.
In the present embodiment, first, as shown in FIG. 12A, a substrate 22 is prepared in which an insulating film 52 having a required film pressure is formed on the upper surface of a silicon substrate 51. In this example, a substrate 22 is formed by forming a silicon nitride film (SiN) film 52 having a thickness of 1 μm on a silicon substrate 51.

Next, as shown in FIG. 12B, a conductive film 53 having a required film thickness to be a lower electrode, that is, an input / output electrode, is formed on the insulating film 52 of the substrate 22. In this example, a polycrystalline silicon film 53 having a thickness of 0.5 μm is formed on the silicon nitride film 52 by vapor deposition.
Next, as shown in FIG. 12C, the polycrystalline silicon film 53 is patterned by selective etching to form an input electrode 23 and an output electrode 24 that serve as lower electrodes, and a wiring layer 28. The patterns of the input / output electrodes 23 and 24 and the wiring layer 28 are formed in a pattern corresponding to the above-described FIG. 1, FIG. 4, and FIG.

Next, as shown in FIG. 12D, a sacrificial layer 54 having a required film thickness is formed on the entire surface of the substrate 22 including the upper surfaces of the input / output electrodes 23 and 24 and the wiring layer 28. In this example, a silicon participation (SiO ₂ ) film 54 having a thickness of 0.5 μm serving as a sacrificial layer is formed by vapor deposition.
Next, as shown in FIG. 12E, the sacrificial layer 54 is planarized, and the thickness of the sacrificial layer 54 on the input / output electrodes 24 and 25 is set to a required thickness. The thickness of the sacrificial layer 54 corresponds to the height of the space 26 between the beam 27 and the input / output electrodes 23 and 24 described above. In this example, the silicon oxide film 54 as a sacrificial layer is flattened by using a CMP (Chemical Mechanical Polishing) method so that the silicon oxide film 54 is left on the input / output electrodes 23 and 24 to a thickness of 0.1 μm.

Next, as shown in FIG. 13F, a part of the sacrifice layer 54 is selectively etched to form a contact hole 55 in which a part of the wiring layer 28 is exposed.
Next, as shown in FIG. 13G, a conductive film 56 having a required film thickness to be a beam is formed on the sacrificial layer 54. At this time, a part of the conductive film 56 is connected to the wiring layer 28 through the contact hole 55. In this example, a polycrystalline silicon film 56 having a film thickness of 0.5 μm to be a beam is formed by vapor deposition.
The polycrystalline silicon films 53 and 56 and the silicon oxide film 54 can be formed by a chemical vapor deposition (CVD) method, but can also be formed by a physical vapor deposition method. .

  Next, as shown in FIG. 13H, the polycrystalline silicon film 56 which is a conductive film is patterned to form the beam 27. The pattern of the beam 27 is formed in a pattern corresponding to the above-described FIG. 1, FIG. 4, and FIG.

  Next, as shown in FIG. 13I, the sacrificial layer 54 is selectively removed. In this example, the silicon oxide film 54 which is a sacrificial layer is removed with hydrofluoric acid. As a result, the MEMS resonator group 25 or 33 shown in FIG. 1, FIG. 4, or FIG. 7 in which the beam 27 is disposed with the required space 26 interposed between the input electrode 23 and the output electrode 24 is obtained.

It is a block diagram which shows 1st Embodiment of the MEMS resonator group applied to preparation of the MEMS resonator which concerns on this invention. It is a signal waveform diagram which shows the example of the strong signal input into the MEMS resonator group of 1st Embodiment. It is a block diagram which shows one Embodiment of the MEMS resonator which concerns on this invention obtained from the MEMS resonator group of 1st Embodiment. It is a block diagram which shows 2nd Embodiment of the MEMS resonator group applied to preparation of the MEMS resonator which concerns on this invention. It is a signal waveform diagram which shows the example of the strong signal input into the MEMS resonator group of 2nd Embodiment. It is a block diagram which shows one Embodiment of the MEMS resonator which concerns on this invention obtained from the MEMS resonator group of 2nd Embodiment. It is a block diagram which shows 3rd Embodiment of the MEMS resonator group applied to preparation of the MEMS resonator which concerns on this invention. It is a block diagram which shows one Embodiment of the MEMS resonator which concerns on this invention obtained from the MEMS resonator group of 3rd Embodiment. It is a block diagram which shows other embodiment of the MEMS resonator which concerns on this invention obtained from the MEMS resonator group of 3rd Embodiment. It is a block diagram which shows other embodiment of the MEMS resonator which concerns on this invention obtained from the MEMS resonator group of 3rd Embodiment. A is a cross-sectional view of a MEMS resonator element according to the present invention. B is a plan view of a MEMS resonator element according to the present invention. FIG. A to E are manufacturing process diagrams (part 1) illustrating an embodiment of a method for manufacturing a MEMS resonator group according to the present invention. F to I are manufacturing process diagrams (part 2) illustrating an embodiment of a method for manufacturing a MEMS resonator group according to the present invention. It is sectional drawing of the conventional MEMS resonator.

Explanation of symbols

  20, 30, 37, 38, 39 .. MEMS resonator, 21 .. Substrate, 22 [221, 222, 223, 224, 225] .. MEMS resonator element, 23 .. Input electrode, 24 .. Output electrode , 25, 33 .. MEMS resonator group, 27 [271, 272, 273, 274, 275] .. Beam, S1, S2 .. Strong input signal

Claims (4)

A MEMS resonator, wherein a resonator other than a resonator having a desired frequency is destroyed by inputting a strong signal from a group of resonators having a beam structure and having a plurality of types of resonance frequencies. The MEMS resonator according to claim 1, wherein the resonator group includes a plurality of types of resonators connected in parallel. Forming a MEMS resonator group having a plurality of types of resonance frequencies having a beam structure;
A method for manufacturing a MEMS resonator, comprising: inputting a strong signal to the MEMS resonator group to destroy resonators other than a resonator having a desired frequency. The method of manufacturing a MEMS resonator according to claim 3, wherein the MEMS resonator group is a resonator group in which resonators having a plurality of types of resonance frequencies are connected in parallel.

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