KR101066102B1 - Micro speaker and method for forming thereof - Google Patents

Abstract

The present invention relates to a piezoelectric micro speaker, comprising: a cantilever passing through a substrate, a piezoelectric layer formed on the substrate, an upper electrode formed on the piezoelectric layer, and the piezoelectric layer and the upper electrode. A polymer diaphragm using a piezoelectric cantilever or a similar structure is embedded in the polymer diaphragm, which fills a hole defining an area. In order to lower the pressure and increase the generation of sound pressure, a material having a small Young's modulus, that is, a polymer, may be used to generate sound pressure up to the low frequency region.

Piezoelectric microspeakers, cantilevers, Parylene-C, electrodes.

Description

Micro speaker and manufacturing method thereof

The present invention relates to a micro speaker and a method of manufacturing the same. In particular, the present invention relates to a piezoelectric micro speaker and a method of manufacturing the same.

The present invention is derived from the research conducted as part of the IT source technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunications Research and Development [Task Management No .: 2006-S-006-03, Task name: Parts / modules for ubiquitous terminals].

The present invention relates to a micro speaker having a diaphragm capable of increasing sound pressure by adopting a structure similar to a voice coil driving a cone and a cone applied in a loudspeaker in manufacturing a micro speaker using a piezoelectric thin film.

Background Art A technique for miniaturizing a microphone and a microspeaker on a silicon wafer using a Micro Electro Mechanical Systems (MEMS) technique has been disclosed. This method of manufacturing an acoustic transducer on a silicon wafer can be manufactured by batch processing, thereby reducing costs, and miniaturization is possible because multiple transducers and amplifiers can be integrated in a single chip. There are many advantages compared to.

Generally, a transducer using a condenser type micro system (MEMS) is used more than a transducer using a piezoelectric type micro system (MEMS), but a converter using a piezoelectric micro system (MEMS) is easier to manufacture than a condenser type. It does not require a polarization voltage and has a wider operating range.

However, piezoelectric transducers manufactured by MEMS have relatively low sensitivity in the microphone due to tensile residual stress in the transducer diaphragm, and show low output in the micro speaker.

This problem can be solved by using the compressive stress of the diaphragm, but there is a problem that wrinkles are formed in the diaphragm. Such wrinkles of the diaphragm make it difficult to control the repeatability of the speaker operation, and harmonic distortion. There is a problem that is difficult to minimize.

In general, a method of minimizing such tensile stress, in addition to the use of a compressible diaphragm, the most widely used method includes a method of using a wrinkle or hinge structure. However, there is an additional cost to fabricate wrinkles or hinge structures in microsystems using semiconductor processes.

Diaphragms that make up a microsystem structure can be roughly divided into cantilevers, bridges, and membranes. The cantilever is used to increase the displacement, or the diaphragm material is mainly changed.

In the case of the cantilever structure, the largest displacement among the three diaphragms can be obtained, but the sound pressure in the low frequency region is not generated when used in the acoustic transducer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric micro speaker having a polymer diaphragm which is easy to manufacture and can increase the output sound pressure of the micro speaker and a piezoelectric cantilever for driving the diaphragm.

The piezoelectric micro speaker according to the present invention defines a cantilever region through a substrate, a piezoelectric layer formed on the substrate, an upper electrode formed on the piezoelectric layer, and passing through the piezoelectric layer and the upper electrode. It includes a polymer diaphragm which is buried in the hole and formed on the upper electrode.

The piezoelectric layer may include ZnO, AlN, PZT, PMN-PT, PVDF, PZN-PT, PYN-PT or PIN-PT.

The substrate may have an opening from the hole of the piezoelectric layer to the lower surface of the substrate.

The piezoelectric micro speaker further includes an insulating film formed on the upper and lower surfaces of the substrate, and a lower electrode formed between the insulating film on the upper surface of the substrate and the piezoelectric layer, wherein the lower electrode, the piezoelectric layer, and the upper electrode form an IDE electrode. Can be formed.

The open portion of the substrate may have a rectangular or trapezoidal structure in the longitudinal direction in order to maximize the displacement of the piezoelectric layer.

The opening of the substrate may have a circular or rectangular cross section in the horizontal direction to maximize the displacement of the piezoelectric layer, and the IDE electrode may occupy an area of 50 to 70% with respect to the polymer diaphragm.

A method of manufacturing a piezoelectric micro-speaker according to the present invention comprises the steps of forming an insulating film on the upper and lower surfaces of the substrate, forming a piezoelectric layer on the insulating film on the upper surface of the substrate, forming an upper electrode on the piezoelectric layer, Etching the upper electrode and the piezoelectric layer to expose a top surface, and forming a hole, and filling the hole and forming a polymer diaphragm on the upper electrode.

The method may further include forming a lower electrode under the piezoelectric layer.

The piezoelectric layer may be formed by stacking ZnO, AlN, PZT, PMN-PT, PVDF, PZN-PT, PYN-PT or PIN-PT.

The method may further include forming an opening from the hole to which the upper surface is exposed by etching the substrate.

The opening may be etched such that the longitudinal section has a square or trapezoid.

The opening may be etched such that the cross section in the horizontal direction has a circle or a rectangle.

The polymer diaphragm micro speaker using the piezoelectric cantilever or the like structure of the present invention lowers the resonance frequency for the generation of music and sound, and uses a material having a small Young's modulus, that is, a polymer or the like, to increase the sound pressure to the low frequency region. May occur.

In order to enable the generation of the maximum sound pressure, the IDE system is adopted to use the d33 piezoelectric constant to increase the displacement of the piezoelectric material by adopting the cantilever structure having the largest displacement in the same dimension or the similar structure among the micro system structures.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. .

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

1 is a plan view of a micro speaker according to the present invention, Figure 2 is a cross-sectional view of the micro speaker of FIG.

Referring to FIG. 1, the micro speaker 100 according to the present invention includes a polymer diaphragm corresponding to a cone, similar to a loudspeaker, and includes a plurality of piezoelectric cantilevers 110 and piezoelectric elements corresponding to a voice coil for driving the cone. It includes an electrode 130 for transmitting a voltage to the cantilever 110.

That is, the micro speaker 100 is composed of four cantilever 110, the electrode 130 on the cantilever 110 for applying a voltage, the space between the cantilever 110 and the cantilever 110, and the electrode ( 130) The structure covered by the polymer diaphragm can be seen above. Since the actual electrode is very thin (having a thickness of a few um or less), the polymer diaphragm is covered in the entire space between the cantilever 110 and the micro speaker 100.

Referring to FIG. 2, in the micro speaker including the cantilever 110 and the polymer diaphragm, the silicon substrate 200 and a portion of the silicon substrate 200 are etched in the thickness direction, and the piezoelectric layer is formed on the etched silicon substrate 200. A 500 is formed to form a piezoelectric cantilever, and a polymer 700 is deposited on the piezoelectric cantilever, and a portion of the polymer 700 is etched to connect with an electrode to apply a voltage.

In detail, the plurality of insulating layers 300, the first electrode 400, the piezoelectric layer 500, and the second electrode 600 are stacked on the upper surface of the substrate 200 such as silicon. A portion of the second electrode 600 is patterned to maximize the amount of change from the piezoelectric layer (using the piezoelectric constant d33, d33> d31), and the insulating film 300, the first electrode 400, and the piezoelectric layer 500. And a hole 650 formed in the second electrode 600, and a polymer diaphragm 700 is formed on the second electrode 600.

In addition, a pad insulating film 800 is formed on the polymer diaphragm 700, and a contact hole 850 exposing the second electrode 600 penetrates the pad insulating film 800 and the polymer diaphragm 700. Formed.

Meanwhile, a plurality of insulating films 220 and a pad insulating film 820 are formed on the lower surface of the substrate 200, and the plurality of insulating films 220 and the pad insulating film 820 expose holes on the upper surface of the substrate 200. Has a diameter of greater than 650.

The substrate 200 includes an opening 250 inclined from the hole of the lower insulating film 220 to the upper insulating film 300 and etched to have a trapezoidal cross section. However, the cross section of the opening 250 of the substrate 200 may be rectangular.

The diaphragm 700 used in the micro-speaker is a material used as the cone of the loudspeaker, and the elastic modulus of the material is most suitable for use in the acoustic transducer. Use materials that are relatively small and have high hearing recognition. As the diaphragm 700, an elastic material having a low Young's modulus such as Parylene-C is used.

In addition, the micro speaker of the present invention has a fine cantilever as a cantilever or a similar structure capable of maximizing driving displacement for driving the diaphragm 700.

In addition, the current diameter of a typical micro speaker is more than 10mm because it is proportional to the area of the output sound pressure is emitted, and changes depending on the displacement and frequency that the structure can produce. Therefore, in the present invention, the micro speaker can be miniaturized by adjusting the emission area and displacement of the sound pressure.

In addition, in the piezoelectric layer 500, a d31 coefficient and a d33 coefficient exist due to a voltage-strain relationship, and generally a d33> 2 * d31 relation is established. In this case, in order to achieve the maximum displacement, it is preferable to use the d33 coefficient. Therefore, in the present invention, the first electrode 400 and the second electrode 600 form a capacitor using the IDE electrode structure, that is, the piezoelectric layer 500 as a dielectric. It has a structure.

Hereinafter, a method of manufacturing the micro speaker of FIG. 2 will be described with reference to FIGS. 3 to 10.

3 to 10 are cross-sectional views showing the manufacturing steps of the micro-speaker according to the present invention.

First, as shown in FIG. 3, the silicon substrate 200 is thermally oxidized to form silicon oxide films 300 and 220 on upper and lower portions of the substrate 200, and the silicon nitride film 300 is disposed on the upper and lower silicon oxide films 300 and 220. Vapor deposition is performed by low pressure chemical vapor deposition (LPCVD). In this case, the oxide film 300 may be further formed on the silicon nitride film 300 on the substrate 200 through PECVD.

The first electrode 400 may be formed by stacking a metal layer, for example, fluorium and titanium, or depositing a ZrO 2 (or Al 2 O 3) dielectric layer on the silicon nitride layer 300 on the substrate 200. A piezoelectric layer 500 such as ZnO, AlN, PZT (completely solid solution of PbZrO3 and PbTiO3), PMN-PT, PVDF, PZN-PT, PYN-PT, or PIN-PT is formed on 400).

Next, as shown in FIG. 4, the second electrode 600 is deposited to form the first electrode 400, the piezoelectric layer 500, and the IDE electrode on the piezoelectric layer 500. The second electrode 600 may be formed by stacking gold and chromium, and a capacitor structure of the first electrode 400, the piezoelectric layer 500, and the second electrode 600 forms an IDE electrode.

In this case, the first electrode 400 and the second electrode 600 are about 150 nm, and the piezoelectric layer 500 has a thickness of about 500 nm.

Next, as shown in FIG. 5, when the positive electrode photoresist is applied and etched to pattern the second electrode 600, as shown in FIG. 6, the positive electrode photoresist is applied and the substrate 200 is exposed to have a fine cantilever shape. The hole 650 is formed by etching the second electrode 600, the piezoelectric layer 500, the first electrode 400, the oxide film, and the nitride film 300.

In this case, etching may be performed by reactive ion etching (RIE).

Next, as shown in FIG. 7, the polymer 700 is deposited to fill the hole 650 and cover the upper portion of the second electrode 600. In this case, the polymer 700 may use Parylene-C, and the second electrode ( 600) is deposited to have a thickness of about 1um.

Next, as shown in FIG. 8, photoresist 800 and 820 are applied to upper and lower portions of the substrate 200, and the holes are formed by etching the substrate 200 to expose the lower portion of the substrate 200.

In addition, as illustrated in FIG. 9, the polymer 700 is etched to connect an electrode pad for applying a voltage to the piezoelectric layer 500 with the second electrode 600, as shown in FIG. 9, to the second electrode 600. To form a hole 850.

Finally, as shown in FIG. 10, the silicon substrate 200 is anisotropically etched to form an opening 250 that connects the hole 650 of the upper insulating layer 300 to the lower insulating layer 220. At this time, the anisotropic etching may be performed using a KOH solution.

In order to maximize the displacement of the piezoelectric layer 500, the opening part 250 may have a quadrangular or trapezoidal structure in the longitudinal direction, and may have a circular or rectangular cross section in the horizontal direction.

The IDE electrodes 400, 500, and 600 of the piezoelectric cantilever may occupy about 50 to 70% of the area of the polymer diaphragm 700.

In a typical piezoelectric micro speaker, the sound pressure level decreases as it is lowered into the low frequency region. This is because, in the case of a diaphragm using a metal or the like, not only the minimum resonant frequency is influenced, but also the diaphragm having the same dimension has the highest resonant frequency.

Therefore, in order to increase the sound pressure in the low frequency region, the minimum resonant frequency should be lowered. In the case of using the cantilever, the sound leaks due to the gap required for the fabrication of the cantilever, and the inverted phase sound waves generated on each side of the diaphragm Interfering with each other, the low frequency characteristics are significantly degraded, resulting in a decrease in sound pressure in the low frequency region.

However, by forming the polymer diaphragm 700 to fill the gap of the cantilever or similar structure as in the present invention, it is possible to isolate both sides of the diaphragm to prevent the interference of sound waves.

In addition, the polymer diaphragm 700 has a Young's modulus that is much lower than the diaphragm of silicon or silicon nitride / oxide, for example, about 100 times lower.

Diaphragms with low Young's modulus have little residual stress and can increase the displacement of movement.

In addition, by using an IDE electrode and depositing a polymer after etching the piezoelectric layer 500, an additional manufacturing process is not required as compared with a conventional parallel plate type structure.

In addition, by forming the diaphragm as a metal film, a high resonance peak value is generated in the metal film, and an additional insulating film or the like to reduce the frequency is not flattened, and a problem of generating strong harmonic distortion can be prevented. have.

That is, piezoelectric ceramic elements are formed by adhering a piezoelectric ceramic disk on a membrane made of a material, a synthetic material, or a polymer that dampens acoustic vibration, and has a flat frequency, and has a low harmonic distortion of 3% on average between 100 Hz and 20 kHz. Piezoelectric reproducing elements having a quality sufficient for music and sound reproduction for industrial applications can be implemented.

The resonance frequency of such a micro speaker can be represented by the following equation.

[Equation]

Where t = polymer film thickness, S = surface of membrane, y = Young's modulus, r = Poisson's ratio, K = assembly element, b = length of cantilever, D4 = diameter of polymer diaphragm, S1 = surface of free moving part , D1 = distance between the moving part of the polymer diaphragm and the wall.

S1 and D1 are determined by the packaging of the micro speaker element.

As a result, in the present invention, it can be seen that the minimum resonant frequency of the micro speaker is determined by the length and packaging of the cantilever. In the case of the piezoelectric driven cantilever, since it is made of a thin film, residual stress exists. Resonant frequency is increased by this residual stress, and if the cantilever structure is made in trapezoid shape to compensate for this, the moving displacement is hardly affected, and it is also possible to apply a structure that can further reduce the resonance frequency.

In the above resonance frequency equation, it can be seen that the resonance frequency is lowered by using a diaphragm material having a low Young's modulus.

The present invention uses a polymeric material similar to the Young's modulus of the cone used in loudspeakers for this purpose.

The embodiments of the present invention described above are not only implemented by the apparatus and method but may be implemented through a program for realizing the function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded, The embodiments can be easily implemented by those skilled in the art from the description of the embodiments described above.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a plan view of a piezoelectric micro speaker according to the present invention.

FIG. 2 is a cross-sectional view of the piezoelectric micro speaker of FIG. 1.

3 to 10 are cross-sectional views illustrating steps of manufacturing the piezoelectric micro speaker of FIG. 2.

Claims (12)

Board, A piezoelectric layer formed on the substrate, An upper electrode formed on the piezoelectric layer, Holes formed by etching the piezoelectric layer and the upper electrode such that the piezoelectric layer and the upper electrode have a cantilever shape, and A polymer diaphragm formed on the upper electrode while filling the hole passing through the piezoelectric layer and the upper electrode Piezoelectric micro speaker comprising a. The method of claim 1, The piezoelectric layer includes ZnO, AlN, PZT, PMN-PT, PVDF, PZN-PT, PYN-PT or PIN-PT Piezoelectric micro speaker. The method of claim 1, The substrate has an opening from the hole of the piezoelectric layer to the lower surface of the substrate. Piezoelectric micro speaker. The method of claim 1, The piezoelectric micro speaker, An insulating film formed on the upper and lower surfaces of the substrate, and A lower electrode formed between the insulating film on the upper surface of the substrate and the piezoelectric layer More, The lower electrode, the piezoelectric layer and the upper electrode to form an IDE electrode Piezoelectric micro speaker. The method of claim 3, The opening of the substrate has a square or trapezoidal structure in the longitudinal section in order to maximize the displacement of the piezoelectric layer. Piezoelectric micro speaker. 5. The method of claim 4, The opening of the substrate has a circular or rectangular cross section in the horizontal direction to maximize the displacement of the piezoelectric layer, and the IDE electrode occupies an area of 50 to 70% with respect to the polymer diaphragm. Piezoelectric micro speaker. Forming an insulating film on the upper and lower surfaces of the substrate, Forming a piezoelectric layer on the insulating film on the upper surface of the substrate, Forming an upper electrode on the piezoelectric layer, Etching the upper electrode and the piezoelectric layer to expose the top surface of the substrate to form holes; and Filling the hole and forming a polymer diaphragm on the upper electrode Method of manufacturing a piezoelectric micro speaker comprising a. The method of claim 7, wherein The method may further include forming a lower electrode under the piezoelectric layer. Method of manufacturing piezoelectric micro speakers. The method of claim 7, wherein The piezoelectric layer is formed by stacking ZnO, AlN, PZT, PMN-PT, PVDF, PZN-PT, PYN-PT or PIN-PT. Method of manufacturing piezoelectric micro speakers. The method of claim 7, wherein Etching the substrate to form an opening from a hole through which a top surface is exposed to a bottom surface; Method of manufacturing piezoelectric micro speakers. The method of claim 10, The opening may be etched so that the longitudinal cross section has a square or trapezoid. Method of manufacturing piezoelectric micro speakers. The method of claim 10, The opening portion may be etched so that the cross section in the horizontal direction has a circular or square shape. Method of manufacturing piezoelectric micro speakers.

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