JP5818324B2 - Mechanical vibrator - Google Patents

Description

The present invention relates to micro-mechanical oscillator comprising a mechanical structure using a thin film.

  In order to realize mechanical parts such as waveguides, filters, and duplexers, a mechanism that can freely control the propagating mechanical vibration (phonon) is required. In the field of optical functional devices, in order to efficiently control propagating light (photons), photons are strongly confined in a minute region by multiple coupling of optical resonators, and the resulting non-linear effects are utilized. (See Non-Patent Document 1). On the other hand, the same applies to phonons. By combining and integrating vibrators, a strong confinement effect can be realized, and free control of phonons is expected. In order to construct an integrated mechanical system in which vibrators are coupled and integrated, it is important that the vibrator serving as a unit element has a mechanical structure suitable for coupling.

  In a structure in which micro mechanical vibrators are coupled, a mechanical vibrator having a cantilever structure or a double-supported beam structure has been used as a unit element so far. For example, the unit mechanical vibrators are mechanically coupled to each other through an overhang region below the support portion of the vibration portion generated in the manufacturing process between adjacent mechanical vibrators (see Non-Patent Document 2). There is also a technique for mechanically coupling unit mechanical vibrators through a bridged beam between a vibratory part of a mechanical vibrator and a vibratory part of an adjacent mechanical vibrator (see Non-Patent Document 3). . Furthermore, there is a technique of electrically coupling unit mechanical vibrators via electrodes and electric lines arranged in each mechanical vibrator (see Non-Patent Document 4).

M. Notomi, E. Kuramochi and T. Tanabe, "Large-scale arrays of ultrahigh-Q coupled nanocavities", Nature Photonics, vol.2, pp.741-747, 2008. M. Spletzer, A. Raman, H. Sumali, and J. P. Sullivan, "Highly sensitive mass detection and identification using vibration localization in coupled microcantilever arrays", Appl. Phys. Lett., Vol.92, 114102, 2008. M. Spletzer, A. Raman, H. Sumali, and J. P. Sullivan, "Highly sensitive mass detection and identification using vibration localization in coupled microcantilever arrays", Appl. Phys. Lett., Vol. 92, 114102, 2008. P. A. Truitt, J. B. Hertzberg, C. C. Huang, K. L. Ekinci, and K. C. Schwab, "Efficient and Sensitive Capacitive Readout of Nanomechanical Resonator Arrays", Nano Letter, vol.7, no.1, pp.120-126, 2007. K. Tamaru, K. Nonaka, M. Nagase, H. Yamaguchi, S. Warisawa and S. Ishihara, "Direct Actuation of GaAs Membrane with the Microprobe of Scanning Probe Microscopy", Jpn. J. Appl. Phys., Vol. 48, 06FG06, 2009.

  However, the mechanical structure or the coupling method of such mechanical vibrators lacks flexibility, and it is difficult to freely control the coupling of each unit mechanical vibrator. For example, in the mechanical coupling via overhang or cross-linking, the overhang region generated in the manufacturing process is determined by the width of the vibration part. For this reason, it is impossible to realize a coupling that is narrower than the width of the vibrating portion, that is, weak coupling. Further, the coupling direction is limited only to the direction perpendicular to the long axis of the vibrator.

  In contrast, in electrical coupling, integration can be realized two-dimensionally by the arrangement of electrodes and electrical lines, but advanced microfabrication technology is required for the installation of electrodes and electrical lines used for coupling, There was difficulty in the manufacturing method. Furthermore, in the electrical coupling, parasitic capacitance and parasitic resistance generated on the electrodes and the electric lines are signal loss sources (see Non-Patent Document 4).

  The present invention has been made to solve the above-described problems, and an object of the present invention is to arrange a plurality of unit mechanical vibrators two-dimensionally and to freely control their coupling. To do.

A mechanical vibrator according to the present invention includes a support layer formed on a substrate, a vibration film forming layer formed on the support layer, and a plurality of unit mechanical vibrators formed on the substrate. The unit mechanical vibrator is composed of a vibration film composed of a concave part formed in the support layer and a vibration film forming layer that hits the upper part of the concave part, and the concave part is oscillated through a hole formed in the vibration film. The support layer is formed by isotropically etching away the formation layer, and the recesses of the adjacent unit mechanical vibrators communicate with each other .

In the mechanical vibrator, the region of the unit mechanical vibrator is a shape of a part of a plane figure having rotational symmetry of three times or more in plan view, and a plurality of vibration films having a diameter smaller than one side of the plane shape. hole penetrating the is formed by equally spaced on the vibration film of the unit mechanical oscillator.

In addition, the vibration film forming layer should just be comprised from the piezoelectric material. Therefore, adjacent unit mechanical vibrators configured of the same vibration film forming layer are in a state where a part of the vibration film is shared.

The mechanical vibrator manufacturing method includes a first step of forming a support layer on a substrate, a second step of forming a vibration film formation layer on the support layer, and a plurality of holes in the vibration film formation layer. Forming a plurality of recesses in the support layer by selectively etching the support layer isotropically with respect to the vibration film forming layer through the hole, and forming the recesses and the recesses. and forming a plurality of unit mechanical oscillator comprising a vibrating membrane consisting of the vibrating membrane forming layer which corresponds to the upper parts at least comprises, the recess of the unit mechanical oscillator adjacent is formed is communicated, the unit mechanical vibrator This area is a shape of a part of a planar figure having a rotational symmetry of three times or more in a plan view, and a plurality of holes having a diameter smaller than one side of the planar shape are formed on the vibration film of the unit mechanical vibrator. They are arranged at intervals . Note that the vibration film forming layer may be made of a piezoelectric material. Therefore, adjacent unit mechanical vibrators configured of the same vibration film forming layer are formed in a state where a part of the vibration film is shared.

  As described above, according to the present invention, it is possible to obtain an excellent effect that a plurality of unit mechanical vibrators are two-dimensionally arranged and their coupling can be freely controlled.

FIG. 1 is a cross-sectional view (a) and a plan view (b) showing a configuration of a mechanical vibrator according to an embodiment of the present invention. FIG. 2A is a cross-sectional view showing a state in each step for explaining a method of manufacturing a mechanical vibrator in the embodiment of the present invention. FIG. 2B is a cross-sectional view showing a state in each step for explaining the method of manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 2C is a cross-sectional view showing a state in each step for explaining the method of manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 2D is a cross-sectional view showing a state in each step for explaining the method of manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 3 is an optical micrograph of a mechanical vibrator in which a plurality of unit mechanical vibrators are coupled. FIG. 4 is an explanatory diagram for explaining the control of the coupling strength of each unit mechanical vibrator in the mechanical vibrator. FIG. 5 is a photograph showing the state of the unit mechanical vibrator. FIG. 6 is a characteristic diagram showing the measurement result of the propagation phonon. FIG. 7A is a cross-sectional view schematically showing a state in each step for explaining the method of manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 7B is a cross-sectional view schematically showing a state in each step for explaining the method of manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 7C is a plan view schematically showing a state in each step for explaining the method of manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 7D is a cross sectional view schematically showing a state in each step for describing the method for manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 7E is a cross sectional view schematically showing a state in each step for describing the method for manufacturing the mechanical vibrator in the embodiment of the present invention. FIG. 7F is a plan view schematically showing a state in each step for explaining the method of manufacturing the mechanical vibrator in the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view (a) and a plan view (b) showing a configuration of a mechanical vibrator according to an embodiment of the present invention. The mechanical vibrator includes a support layer 102 formed on the substrate 101, a vibration film forming layer 103 formed on the support layer 102, and a plurality of unit mechanical vibrations formed on the substrate 101. And a child 104.

  The unit mechanical vibrator 104 includes a vibration film 106 including a concave part 105 formed in the support layer 102 and a vibration film forming layer 103 that hits the upper part of the concave part 105. Here, the recess 105 is formed by selectively and isotropically removing the support layer 102 with respect to the vibration film forming layer 103 through the hole 107 formed in the vibration film 106. is there. Further, the recessed portions 105 of the adjacent unit mechanical vibrators 104 communicate with each other. Therefore, adjacent unit mechanical vibrators 104 composed of the same vibration film forming layer 103 are in a state in which a part of each vibration film 106 is shared by a region where the recessed portion 105 communicates.

  In the mechanical vibrator according to the embodiment described with reference to FIG. 1, the recessed portion 105 is formed in a circular shape in plan view, and the hole portion 107 is a vibration film 106 in a circular region in a plan view above the recessed portion 105. It is formed in the central part. In this case, the vibration film 106 has a substantially circular shape in plan view. In addition, each vibration film 106 is provided with an electrode 111. If the vibration film forming layer 103 is made of a piezoelectric material, mechanical vibration can be locally induced (excited) and detected by the electrode 111. For example, when the vibration film forming layer 103 is made of a piezoelectric material having a three-layer structure of an n-type GaAs layer, AlGaAs layer, and GaAs layer, the vibration film 106 is locally excited by the locally formed electrode 111. be able to.

Next, a method for manufacturing a mechanical vibrator in the embodiment of the present invention will be described. First, as shown in FIG. 2A, a first semiconductor layer (support layer) 202 made of Al _0.65 Ga _0.35 As, a second semiconductor layer 203 made of GaAs doped with silicon, and Al _0.27 on a substrate 201 made of GaAs. A third semiconductor layer 204 made of Ga _0.73 As and a fourth semiconductor layer 205 made of GaAs are stacked. For example, the above-described layers may be epitaxially grown on the substrate 201 by a well-known metal organic chemical vapor deposition method or molecular beam epitaxy method.

  Next, for example, a resist pattern is formed by an electron beam lithography technique, and the fourth semiconductor layer 205, the third semiconductor layer 204, and the second semiconductor are formed by wet etching or reactive ion etching with phosphoric acid using the resist pattern as a mask. The layer 203 and a part of the first semiconductor layer 202 are patterned in the stacking direction to form a mesa structure as a base. After forming the mesa structure, the resist pattern is removed. The shape of this mesa structure is not shown.

  Next, as illustrated in FIG. 2B, the electrode 206 is formed on the fourth semiconductor layer 205. For example, a resist mask pattern having an opening is formed in a region to be the electrode 206, and an electrode material is formed thereon by a vacuum deposition method. Thereafter, the electrode 206 can be formed on the fourth semiconductor layer 205 by removing the resist mask pattern. This is a manufacturing method called a so-called lift-off method. The electrode 206 is used to induce and detect the mechanical vibration (phonon) of the mechanical vibrator by a piezoelectric effect. In addition, electrodes 206 are formed in each unit mechanical vibrator region 221.

  Next, as shown in FIG. 2C, a through hole (hole) 207 reaching the first semiconductor layer 202 is formed for each unit mechanical vibrator region 221. For example, a resist pattern having an opening corresponding to the through hole 207 may be formed by an electron beam lithography technique, and the through hole 207 may be formed by reactive ion etching using the resist pattern as a mask. Note that the resist pattern is removed after the through-hole 207 is formed.

  Next, the first semiconductor layer 202 is selectively and isotropic with respect to the fourth semiconductor layer 205, the third semiconductor layer 204, and the second semiconductor layer 203 through the through hole 207 using dilute hydrofluoric acid as an etchant. Etch away. By isotropic etching, the first semiconductor layer 202 is removed not only in the stacking direction but also in the planar direction of the first semiconductor layer 202. As a result, as shown in FIG. 2D, a recessed portion 208 is formed for each through-hole 207 (unit mechanical vibrator region 221). Further, a vibration film 209 is formed for each unit mechanical vibrator region 221 corresponding to each recessed portion 208 (see Non-Patent Document 5).

  Note that adjacent recesses 208 are formed in communication with each other by controlling the etching time. Thus, by forming the plurality of through holes 207, a plurality of unit mechanical vibrators composed of the plurality of vibration films 209 can be formed at a time in a coupled state. FIG. 3 is an optical micrograph of a mechanical vibrator in which a plurality of unit mechanical vibrators are manufactured as described above. FIG. 3 shows a state in which five unit mechanical vibrators are connected in series. In addition, the vibration part of each unit mechanical vibrator has a circular membrane structure. The radius r of the membrane is 15 μm, and the distance s between the centers of adjacent unit mechanical vibrators is 25 μm.

  Next, control of the coupling strength of each unit mechanical vibrator in the above-described mechanical vibrator will be described with reference to FIG. The mechanical vibrator described above includes a vibration part (membrane) having a circular shape in plan view. For this reason, the unit mechanical vibrators can be coupled from any direction in the plane direction because they only need to share the membranes. Further, as shown in FIG. 4, the coupling strength is determined by the radius r of the membrane and the distance s between the centers of adjacent unit mechanical vibrators.

  In the example described above, the recessed portion 208 is formed by selectively etching the first semiconductor layer 202, and the fourth semiconductor layer 205, the third semiconductor layer 204, and the second semiconductor layer in the region of the recessed portion 208 are formed. A membrane is constituted by 203 and becomes a vibration part (vibration film). For this reason, the diameter of the membrane (unit mechanical vibrator region) is determined by the etching time for forming the recessed portion 208. Further, the amount of the membrane entering the adjacent unit mechanical vibrator region is determined by the etching time. Therefore, the coupling strength between adjacent unit mechanical vibrators can be adjusted by the interval between the holes and the etching time.

  As shown in FIG. 4, the distance from the membrane center of the micro mechanical vibrator 401 to the center of the adjacent micro mechanical vibrator 402 is s, and the distance to the micro mechanical vibrator 403 is s ′. Let r be the radius of the membrane. As in the micro mechanical vibrator 401 and the micro mechanical vibrator 402, as s becomes shorter than 2r, the overlapping vibration part regions increase and the coupling becomes stronger. On the other hand, as s approaches 2r, the coupling is weakened. When s ′ is larger than 2r as in the micromechanical vibrator 401 and the micromechanical vibrator 403, the overlapping region is completely eliminated and the coupling disappears. .

  Further, as described above, since the resonance frequency of the membrane is uniformly determined by the etching time, all unit mechanical vibrators manufactured from the same type of through holes have the same frequency. However, the etching rate of the wet etching can be adjusted by changing the size of the through hole.

For example, when the first semiconductor layer 202 made of Al _0.65 Ga _0.35 As is etched for 33 minutes with dilute hydrofluoric acid having a concentration of 5% using a through hole 207 (design value 3 × 3 μm ² ) having a radius of 1.5 μm, The unit mechanical vibrator shown in the photograph of FIG. 5A is formed. When a through hole 207 having a radius of 0.2 μm (design value 0.5 × 0.5 μm ² ) is used and etching is performed with dilute hydrofluoric acid having a concentration of 5% for 20 minutes, a photograph shown in FIG. 5B is shown. A unit mechanical vibrator is formed. The etching rates of the first semiconductor layer 202 made of Al _0.65 Ga _0.35 As calculated from these results are 0.4 μm / min and 0.1 μm / min, respectively.

  As described above, since the resonance frequency can be determined for each vibrator of the unit micro mechanical vibrator by changing the hole diameter of the through hole, the distance between the unit mechanical vibrators described above and the unit mechanical vibrator In addition to the method of adjusting the membrane diameter, the coupling strength can be adjusted by changing the resonance frequencies of the unit mechanical vibrators to be combined with each other.

Next, a coupled mechanical vibrator (circular membrane diameter = 30 μm, distance between unit mechanical vibrators = 25 μm) in which five unit mechanical vibrators are connected in series was produced, and the vibration characteristics of the produced coupled mechanical vibrator were evaluated. The results will be described. In this evaluation, an AC voltage of 200 mV _rms was applied to the unit mechanical vibrator located at the left end to induce mechanical vibration (phonon), and this propagating phonon was measured (detected) by the right end unit mechanical vibrator. The result of the frequency response of the phonon in the 1.5-11.5 MHz band is shown in FIG.

  As shown in FIG. 6, in the frequency range of 3 to 3.5 MHz and 4 to 9 MHz, a plurality of peaks derived from mechanical vibration are observed, and phonons propagate through the coupled mechanical vibrator from one end to the other end. You can see the state. It is obvious that the frequency dependence of phonon propagation can be modulated by changing the radius r of the membrane of the unit mechanical oscillator, the distance s between the unit mechanical oscillators, and the resonance frequency of each unit mechanical oscillator. Also, the same modulation effect as described above can be obtained by electrically modulating the mechanical characteristics using the piezoelectric characteristics of the GaAs-based material.

  In the above description, the vibration film (membrane) has been described as having a substantially circular shape in plan view, but the present invention is not limited to this. The planar shape of the diaphragm defined by the unit mechanical vibrator region may be a planar figure having three or more rotational symmetries in plan view. For example, the planar shape of the diaphragm defined by the unit mechanical vibrator region may be a substantially equilateral triangle. This shape is formed by arranging a plurality of holes having a diameter smaller than one side of the planar shape at equal intervals in a region to be a vibration film of a unit mechanical vibrator, and a support layer is formed through these holes. It can be formed by selective and isotropic etching.

For example, as shown in FIG. 7A, first, a first semiconductor layer (support layer) 302 made of Al _0.65 Ga _0.35 As, a second semiconductor layer 303 made of GaAs doped with silicon, on a substrate 301 made of GaAs, A third semiconductor layer 304 made of Al _0.27 Ga _0.73 As and a fourth semiconductor layer 305 made of GaAs are stacked. For example, the above-described layers may be epitaxially grown on the substrate 301 by a well-known metal organic chemical vapor deposition method or molecular beam epitaxy method.

  Next, for example, a resist pattern is formed by an electron beam lithography technique, and the fourth semiconductor layer 305, the third semiconductor layer 304, and the second semiconductor are formed by wet etching or reactive ion etching with phosphoric acid using the resist pattern as a mask. The layer 303 and a part of the first semiconductor layer 302 are patterned in the stacking direction to form a mesa structure as a base. After forming the mesa structure, the resist pattern is removed. The shape of this mesa structure is not shown.

  Next, as illustrated in FIGS. 7B and 7C, a resist pattern 306 including a plurality of openings 307 is formed on the fourth semiconductor layer 305. The opening 307 has a hole diameter sufficiently smaller than the length a of one side of the equilateral triangle that defines the region 308 to be a unit mechanical vibrator. For example, in the plan view of FIG. 7C, a plurality of openings 307 having a hole diameter in a state where ten openings 307 are arranged on one side of the length a are arranged at equal intervals in a region to be a vibration film. It shows the state. FIG. 7B shows a cross section taken along line bb ′ of FIG. 7C. In the example shown in FIG. 7C, a case where four unit mechanical vibrators are formed is shown.

  Next, the fourth semiconductor layer 305, the third semiconductor layer 304, and the second semiconductor layer 303 are etched by reactive ion etching using the resist pattern 306 as a mask to reach the first semiconductor layer 302 as shown in FIG. 7D. A plurality of reaching through holes (holes) 309 are formed. FIG. 7D shows a state after the resist pattern 306 is removed.

  Next, the first semiconductor layer 302 is selectively and isotropic with respect to the fourth semiconductor layer 305, the third semiconductor layer 304, and the second semiconductor layer 303 through the through hole 309 using dilute hydrofluoric acid as an etchant. Etch away. Thereby, as shown in FIG. 7E and FIG. 7F, the recessed portion 310 is formed corresponding to the region where the through hole 309 is formed. Further, a substantially equilateral triangular diaphragm is formed for each unit mechanical vibrator region 308, and four unit mechanical vibrators are connected. Further, a region 308 serving as an adjacent unit mechanical vibrator constituted by the same vibration film forming layer including the fourth semiconductor layer 305, the third semiconductor layer 304, and the second semiconductor layer 303 is a part of each vibration film. Is shared by the connected areas. Even in this case, the recessed portion of each unit mechanical vibrator is in communication. FIG. 7E shows a cross section taken along line ee ′ of FIG. 7F.

  Here, an electrode may be formed in advance by avoiding the through hole forming portion and forming the recessed portion by the manufacturing method described above. In addition, with the electrode material layer formed on the vibrating membrane, a through hole is formed to form a recess, and then the electrode material layer is patterned to form an electrode corresponding to each unit mechanical vibrator. You may make it do. In the above description, the case of an equilateral triangle has been described. However, three or more unit mechanical vibrators having the same strength in three or more planes having the same rotational symmetry are connected by another regular polygon. You may do it.

  As described above, according to the present invention, the support layer formed under the vibration film is selectively and isotropic with respect to the vibration film forming layer through the hole formed in the vibration film. By removing the etching, a concave portion is formed in the support layer under the vibration membrane, so that the vibration membrane is configured by the support layer in the region of the concave portion, so that the following effects can be obtained. Become.

  First, for example, it is easy to mechanically overlap and arrange unit mechanical vibrators with a circular minute vibrating membrane (membrane), and according to the mechanical vibrator to which these unit mechanical vibrators are connected, It becomes possible to confine (phonon) and control it.

  Further, a coupled mechanical vibrator having an arbitrary coupling strength can be realized by changing the vibration part region shared by adjacent unit mechanical vibrators.

  Further, since the unit mechanical vibrator has an isotropic structure in a plan view, a two-dimensionally integrated mechanical system can be constructed. In addition, for example, non-centrosymmetric materials such as GaAs have a piezoelectric effect, so that on-chip vibration can be induced and detected, and in addition, mechanical properties can be modulated and electrically active. Machine system can be realized.

  As described above, by combining a plurality of unit mechanical vibrators, a strong confinement effect can be expected, and an artificial acoustic control substance such as a waveguide for guiding phonons or a phononic crystal can be expected. For this purpose, it is important to obtain two-dimensional integration of single unit mechanical vibrators and to obtain equal coupling strength in each coupling. Conventional bonding methods using overhangs and cross-linking are limited to one-dimensional bonding. On the other hand, according to the mechanical vibrator in which the unit mechanical vibrators are combined with a circular or polygonal vibration region (membrane), it is possible to construct a phonon control system such as the above-described waveguide or phononic crystal.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, each manufacturing technology such as lithography and etching is a combination of multiple existing microfabrication technologies such as electron beam lithography, photolithography, nanoimprint, dry / wet etching, deposition / sputtering / chemical vapor deposition, etc. However, the present invention is not limited to the method described in the above embodiment. Further, the vibration film forming layer (vibration film) is not limited to the piezoelectric material, and may be composed of other materials. In this case, the vibrating membrane may be excited by electrostatic force or the like. However, if the vibration film is made of a piezoelectric material, it is easy to excite locally by using an electrode.

  Moreover, although the example using GaAs, AlGaAs, etc. is shown in the above, it is needless to say that the present invention is not limited to this, and other materials may be used based on the gist of the present invention.

  DESCRIPTION OF SYMBOLS 101 ... Substrate, 102 ... Support layer, 103 ... Vibration film forming layer, 104 ... Unit mechanical vibrator, 105 ... Recessed part, 106 ... Vibration film, 107 ... Hole, 111 ... Electrode.

Claims (2)

A support layer formed on the substrate;
A vibration film forming layer formed on the support layer;
A plurality of unit mechanical vibrators formed on the substrate,
The unit mechanical vibrator is composed of a vibration film composed of a concave part formed in the support layer and the vibration film forming layer that hits the upper part of the concave part ,
The recessed portion of the adjacent Ri fit the unit mechanical oscillator is communicated,
The area of the unit mechanical vibrator is a shape of a part of a plane figure having a rotational symmetry of 3 or more in plan view,
A mechanical vibrator characterized in that holes penetrating through the plurality of vibrating membranes having a diameter smaller than one side of the planar shape are arranged at equal intervals in the vibrating membrane of the unit mechanical vibrator. . In claim 1 Symbol placement of mechanical oscillator,
The vibration film forming layer is made of a piezoelectric material, and is a mechanical vibrator.