KR20080072329A - Low voltage driven piezoelectric microspeaker and a method for producing the same - Google Patents

Abstract

A low voltage driven piezoelectric microspeaker and a method for producing the same are provided to generate large strain with the same applied voltage. A method of producing a low voltage driven piezoelectric microspeaker includes the steps of preparing a substrate(105) made of a silicon wafer and depositing a silicon nitride layer through a low pressure chemical vapor deposition method on upper and lower surfaces of the substrate to form a diaphragm(110) functioning as a vibration plate of the microspeaker(S110), forming a primary electrode(120) on the center part of upper surface of the diaphragm(S120), depositing a piezoelectric thin film(130) on the diaphragm(S130), forming secondary electrodes(140,145) on an upper region of the piezoelectric thin film corresponding to the first electrode(S140), and exposing the center part of a lower surface of the diaphragm by removing a lower surface of the substrate(S150).

Description

Low voltage driven piezoelectric microspeaker and a method of manufacturing the same {Low voltage driven piezoelectric microspeaker and a method for producing the same}

1 is a structural diagram of a piezoelectric microspeaker according to the prior art.

2 is a structural diagram of a low voltage driven piezoelectric microspeaker according to an exemplary embodiment of the present invention.

Figure 3 is a flow chart of a method of manufacturing a low voltage driven piezoelectric microspeaker according to an embodiment of the present invention.

4 is an explanatory view of the operation principle of the low-voltage driving piezoelectric microspeaker of the present invention.

5 is a prototype photograph of a low voltage driven piezoelectric microspeaker having a circular electrode according to an embodiment of the present invention.

6 is a prototype photograph of a low voltage driven piezoelectric microspeaker having a rectangular electrode according to an embodiment of the present invention.

7 is an output characteristic curve of the low voltage driven piezoelectric microspeakers of FIGS. 5 and 6 according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to piezoelectric microspeakers, and more particularly, to a low voltage driven piezoelectric microspeaker formed by using a microfabrication technique and a semiconductor thin film technique, and a manufacturing method thereof.

Recently, the technology related to the microspeaker manufactured by combining the microfabrication technology and the semiconductor thin film technology has been largely divided into three technical fields.

The first is to manufacture the existing electrodynamic type speaker in planar shape using MEMS (Micro-Electro-Mechanical-Systems) technology and the semiconductor process technology. The second is thin film by the voltage applied from the outside. Piezoelectric microspeakers using piezoelectric thin films, which induce mechanical strain on them, and third, speakers made by CMOS technology.

Conventional techniques for piezoelectric microspeakers related to the present invention include "Parylene-Diaphragm Piezoelectric Acoustic Transducers" by C.H. Han and EunSok Kim, Technical Digest of IEEE MEMS, pp. 148-152, 2000, there is a piezoelectric microspeaker of the configuration shown in FIG.

The piezoelectric microspeaker of FIG. 1 is manufactured by using a piezoelectric ZnO thin film 10 and a parylene diaphragm 20, and has one electrode 30 and 40 on the upper and lower portions of the piezoelectric ZnO thin film 10, respectively. ) Has the structure of a typical piezoelectric microspeaker formed.

In the conventional piezoelectric microspeaker, the strain is induced inside the piezoelectric thin film by the voltage applied through the electrodes 30 and 40, and the resulting diaphragm strain is compressed and stretched by the polarity of the applied voltage. The deflection of the diaphragm causes a negative pressure.

The reason for using the paraline diaphragm in the piezoelectric microspeaker of FIG. 1 is that the paraline has a very small residual stress (about 20 to 40 MPa), and as a kind of polymer, the elastic modulus is smaller than that of a silicon nitride film, which is a conventional diaphragm material. This is because relatively good sensitivity and deflection can be expected when used as a device.

The piezoelectric microspeaker of FIG. 1 was reported to exhibit an output sound pressure of about 600 mPa at a resonance frequency when measured at a distance of about 2 mm from the microspeaker at a driving voltage of 11 Vrms.

However, the prior art requires too high a driving voltage (i.e., greater than 5 Vrms) to be applied to various practical applications such as mobile phones, earphones, hearing aids, headsets, and the sound pressure is insufficient compared to the high driving voltage. For example, a typical mobile phone requires at least 60 dB of sound pressure generation at a frequency of 1 KHz when measured at a distance of about 3 cm, which is less than 5 V and the ear canal to the eardrum. Did not satisfy.

It is therefore an object of the present invention to provide a low voltage driven piezoelectric microspeaker capable of driving at low voltage while providing sufficient sound pressure.

It is also an object of the present invention to provide a low voltage driven piezoelectric microspeaker having an electrode structure for causing a large strain with the same applied voltage.

It is also an object of the present invention to provide a low voltage driven piezoelectric microspeaker which causes a large strain by changing the polarity of the voltage applied to the electrode.

According to an aspect of the present invention, there is provided a low-voltage driving piezoelectric microspeaker comprising: a semiconductor substrate having a central portion removed to form a diaphragm; A diaphragm formed on an upper surface of the semiconductor substrate; A primary electrode formed at the center of the upper surface of the diaphragm; A piezoelectric thin film formed on an upper surface of the primary electrode and an exposed upper surface of the diaphragm; And a secondary electrode formed in an electrically separated form of two or more in the upper region of the center portion of the piezoelectric thin film corresponding to the primary electrode.

In addition, the method of manufacturing a low voltage driven piezoelectric microspeaker of the present invention includes forming a diaphragm material on an upper surface of a semiconductor substrate; Forming a primary electrode on a central portion of an upper surface of the diaphragm; Forming a piezoelectric thin film on an upper surface of the primary electrode and an exposed upper surface of the diaphragm; Forming a secondary electrode having two or more electrically separated shapes in an upper region of the piezoelectric thin film corresponding to the primary electrode; And removing a lower surface of the semiconductor substrate to expose a central portion of the lower surface of the diaphragm.

In addition, the secondary electrode is formed of a secondary center electrode formed in the center of the center portion of the piezoelectric thin film and a secondary peripheral electrode formed around the center of the piezoelectric thin film so as to surround the secondary central electrode, and having a concentric shape with each other. It is formed in at least one of the concentric square shape, the shape is not limited to improve the speaker characteristics, the voltage of the opposite polarity is applied to the secondary center electrode and the secondary peripheral electrode is the secondary of the piezoelectric thin film The portion corresponding to the center electrode and the portion corresponding to the secondary peripheral electrode generate strain in opposite directions.

Hereinafter, the present invention will be described in detail with reference to an embodiment of the present invention shown in the accompanying drawings.

2 is a structural diagram of a low voltage driven piezoelectric microspeaker according to an exemplary embodiment of the present invention.

The microspeaker of FIG. 2 includes a semiconductor substrate 105, a diaphragm 110 and a diaphragm 110 formed on the semiconductor substrate 105 using a low stress non-chemically equivalent silicon nitride film (Si _x N _y ). The primary electrode 120 formed of Al or Mo / Ti on the upper center of the upper surface, the ZnO or AlN piezoelectric thin film 130 formed on the entire upper surface of the diaphragm 110 on which the primary electrode 120 is formed, and the primary electrode Secondary electrodes 140 and 145 formed using Al or Mo / Ti to be divided into a central electrode 140 and a peripheral electrode 145 in an upper region of the piezoelectric thin film 130 corresponding to 120, and Diaphragms 110 and terminals 142 and 147 electrically connected to the secondary electrode center electrode 140 and the secondary peripheral electrode 145 and formed using Al or Mo / Ti to apply a driving voltage. A support layer 150 formed by depositing a polymer, such as paraline, to impart mechanical stability to the It is rock configuration.

Since the material of each part is to illustrate those widely used in the semiconductor thin film process for the production of piezoelectric microspeakers, those skilled in the art will be able to manufacture the microspeakers of the present invention using a different type of materials than those exemplified The characteristics of the microspeaker of the present invention are in a structure of a secondary electrode formed to be separated into two or more so as to apply voltages of different polarities, and there is no particular limitation on the applied material.

Figure 3 is a flow chart of a method of manufacturing a low voltage driven piezoelectric microspeaker according to an embodiment of the present invention.

First, a substrate 105 made of a silicon wafer is prepared, and low pressure chemical vapor deposition (LPCVD) is formed on the upper and lower surfaces of the substrate 105 to form the diaphragm 110 serving as a shaking plate of the microspeaker. A low stress non-chemically equivalent silicon nitride film (eg, Si _x N _y ) is deposited (S110).

Alternatively, an oxide film (eg, SiO ₂ ) is grown to a predetermined thickness on the silicon wafer substrate 105, and a chemically equivalent silicon nitride film (eg, Si ₃ N ₄ ) is formed by LPCVD, and then LTO ( Low temperature oxide (eg, SiO _x ) may be deposited by LPCVD to form the diaphragm 110 having an oxide-nitride-oxide (ONO) structure.

Since the residual stress of each of the thin films such as the oxide film and the nitride film is known, those skilled in the art will be able to form a compressed or tensile diaphragm having a desired residual stress by forming each thin film from the above-described substrate with an appropriate thickness. Various thin film formation methods may be used.

Next, the primary electrode 120 is formed in the center of the upper surface of the diaphragm 110 (S120). The material of the primary electrode 120 may be appropriately selected according to the type of piezoelectric thin film to be formed thereon. For example, an Al electrode may be used for a ZnO piezoelectric thin film, and an Mo / Ti structure electrode may be used for an AlN piezoelectric thin film. However, the electrode material is not limited to improve the structural characteristics of the piezoelectric thin film.

Subsequently, the piezoelectric thin film 130 is deposited on the diaphragm 110 on which the primary electrode 120 is formed (S130). The method of forming the piezoelectric thin film 130 may vary depending on the type of piezoelectric material. For example, ZnO or AlN may be deposited by RF magnetron sputtering, or a polymer piezoelectric film such as PVDF (Polyvinylidene fluoride) may be coated. The piezoelectric thin film 130 can be formed.

 Next, secondary electrodes 140 and 145 are formed in an upper region of the piezoelectric thin film 130 corresponding to the primary electrode 120 (S140). The secondary electrode is formed so as to be divided into the center electrode 140 and the peripheral electrode 145 by patterning the same material, but there is no particular limitation on the shape of the electrode, but as shown in FIGS. 5 and 6 to improve the output sound pressure. It is preferable to be patterned to have a shape such as a concentric shape or a square.

Meanwhile, at the same time as the formation of the secondary electrode, using the same pattern, the terminal is electrically connected to the secondary center electrode 140 and the secondary peripheral electrode 145 at the edge of the microspeaker 100 to apply a driving voltage. Fields 142 and 147 may be formed.

Finally, in order to expose the diaphragm 110, the silicon nitride substrate under the silicon wafer substrate 105 and the silicon wafer substrate 105 under the region where the electrode is formed are etched to complete the microspeaker (S150).

Meanwhile, before removing the silicon wafer substrate 105 and the silicon nitride film under the silicon wafer substrate 105, the support layer 150 may be formed as shown in S150 of FIG. 4 to additionally provide mechanical stability to the diaphragm 110. . The support layer may be formed by using a polymer in various ways. For example, after depositing a polymer such as paraline on the upper front surface of the piezoelectric thin film 130, formation of holes for opening the driving voltage applying terminals 142 and 147 may be performed. For example, a method of forming a predetermined pattern and etching the patterned polymer by a method such as reactive ion etching (RIE) may be used.

4 is an explanatory view of the operation principle of the low-voltage driving piezoelectric microspeaker of the present invention.

Basically, the characteristics of the low-voltage driven piezoelectric microspeaker of the present invention that is capable of driving at low voltage while providing sufficient sound pressure are separated into two or more secondary electrodes 140 and 145 formed to apply different bias voltages. It is due to the structure of.

In FIG. 4, the secondary electrode is formed on the upper surface of the piezoelectric thin film 130 facing the primary electrode 120 while being separated into the secondary center electrode 140 and the secondary peripheral electrode 145. To apply bias voltages (ie, bias voltages having a phase difference of 180 °) to the secondary center electrode 140 and the secondary peripheral electrode 145 through the power supply terminals 142 and 147 formed at the edges of It is.

In FIG. 4, since a negative bias voltage is applied to the secondary center electrode 140 and a positive bias voltage is applied to the secondary peripheral electrode 145, the secondary center electrode 140 is thus applied. Positive charge is charged to the portion of the piezoelectric thin film 130 in contact with the negative electrode, and negative charge is induced to the portion of the piezoelectric thin film 130 in contact with the diaphragm 110.

Accordingly, the electric field (not shown) in the piezoelectric thin film 130 is formed in the direction of the diaphragm 110 from the secondary central electrode 140, and is formed on the secondary central electrode 140 by the piezoelectric phenomenon of the piezoelectric thin film 130. The portion of the piezoelectric thin film 130 that is in contact is mechanically expanded and the portion of the piezoelectric thin film 130 that is in contact with the diaphragm 110 is mechanically contracted.

In addition, the reverse process is performed in the portion of the piezoelectric thin film 130 that is in contact with the secondary peripheral electrode 145, so that the portion of the piezoelectric thin film 130 which is in contact with the secondary peripheral electrode 145 is mechanically shrunk and the diaphragm 110 is disposed. The portion of the piezoelectric thin film 130 that is in contact is mechanically expanded.

As a result, the strain of the piezoelectric thin film 130 is increased according to portions of the same piezoelectric thin film 130, and thus the size of the total strain generated in the piezoelectric thin film 130 is increased. 110 causes greater deflection in the direction perpendicular to the piezoelectric thin film.

Accordingly, when the same voltage is applied, a larger strain may be induced compared to the microspeaker of the related art, and even when a low voltage is applied, the bending characteristic of the diaphragm 110 is improved, so that a large output sound pressure is generated during low voltage driving. The piezoelectric microspeaker shown can be obtained.

On the other hand, the bias voltage is not applied to the primary electrode 120, but induces the generation of potential only by the induced charge, but because it is a metal plate on the same plane to form an equipotential surface, the polarity of the secondary electrodes 140 and 145 different from each other. When the voltage of is applied, the primary electrode 120 serves as an electrically floating zero potential (that is, an electrically grounded state), but grounding in the entire circuit may be applied in one way. have.

5 is a photograph of a prototype (# 17_J3) of a low voltage driven piezoelectric microspeaker having a circular electrode according to an embodiment of the present invention, Figure 6 is a low voltage driven piezoelectric having a square electrode according to an embodiment of the present invention. This is a picture of a microspeaker prototype (# 17_G5).

5 and 6 show a 6 inch silicon wafer substrate 105, a diaphragm 110 formed of an ONO film having a thickness of 0.6 / 0.3 / 0.2 μm and a residual stress of -60 MPa, and some compressive stress. A piezoelectric microspeaker 100 having a diaphragm having a size of 4m * 4m using a ZnO piezoelectric thin film 130 having a diameter is shown. In an actual process, the ONO film of the diaphragm may be etched into the KOH etchant for etching the silicon substrate in the final fabrication step and present as the ON film, where the final diaphragm will have tensile residual stress characteristics.

7 is an output characteristic curve of the low voltage driven piezoelectric microspeakers of FIGS. 5 and 6 according to an embodiment of the present invention.

7 is a curve measured at a distance of 3 mm from a sound source with a driving voltage of 5 V (peak-to-peak), and indicates that the lowest sound pressure generated in a piezoelectric microspeaker before packaging is in a range of 50 to 60 dB (based on a frequency of 1 KHz). Able to know. This can be seen that the sound pressure characteristic is sufficient to be practical, considering that the increase in the sound pressure increase according to the packaging of the microspeaker is about 20 ~ 30dB. In addition, it can be seen that the driving voltage is 5 V (peak-to-peak), which generates a better output sound pressure even at a much lower voltage than the piezoelectric microspeakers of the prior art.

According to the present invention, there is provided a low voltage driven piezoelectric microsphere that is capable of driving at low voltage while providing sufficient sound pressure.

According to the present invention, there is also provided a low voltage driven piezoelectric microspeaker having an electrode structure for causing a large strain with the same applied voltage.

According to the present invention, there is also provided a low voltage driven piezoelectric microspeaker which causes a large strain by changing the polarity of the voltage applied to the electrode.

Claims (14)

Forming a diaphragm on the upper surface of the semiconductor substrate; Forming a primary electrode on a central portion of an upper surface of the diaphragm; Forming a piezoelectric thin film on an upper surface of the primary electrode and an exposed upper surface of the diaphragm; Forming a secondary electrode having two or more electrically separated shapes in an upper region of the piezoelectric thin film corresponding to the primary electrode; And Removing the lower surface of the semiconductor substrate to expose a central portion of the lower surface of the diaphragm. According to claim 1, And forming a support layer on an upper surface of the secondary electrode and an exposed upper surface of the piezoelectric thin film. According to claim 1, Prior to forming the support layer, forming a driving voltage applying terminal electrically connected to the secondary electrode in the upper edge region of the piezoelectric thin film, the support layer for exposing the driving voltage applying terminal A low voltage driven piezoelectric microspeaker manufacturing method, characterized in that it is formed to have a hole. The method of claim 3, wherein The secondary electrode forming step is a step of forming a secondary peripheral electrode to form a secondary central electrode at the center of the center portion by patterning the same electrode material and surrounding the secondary central electrode, low voltage drive Type piezoelectric microspeaker manufacturing method. The method of claim 4, wherein The forming of the secondary electrode may include forming the secondary center electrode and the secondary peripheral electrode in at least one of a concentric circle shape and a concentric square shape. The method of claim 5, wherein The diaphragm forming step is a step of forming a diaphragm on the upper and lower surfaces of the semiconductor substrate, low voltage drive piezoelectric microspeaker manufacturing method. A low voltage driven piezoelectric microspeaker manufactured by the method of any one of claims 1 to 6. A semiconductor substrate with a center portion removed; A diaphragm formed on an upper surface of the semiconductor substrate; A primary electrode formed at the center of the upper surface of the diaphragm; A piezoelectric thin film formed on an upper surface of the primary electrode and an exposed upper surface of the diaphragm; And And a secondary electrode formed in an electrically separated form of two or more in the upper region of the center portion of the piezoelectric thin film corresponding to the primary electrode. The method of claim 8, The secondary electrode includes a secondary center electrode formed at the center of the center portion of the piezoelectric thin film and a secondary peripheral electrode formed around the center portion of the piezoelectric thin film so as to surround the secondary center electrode. Piezoelectric microspeakers. The method of claim 9, A voltage of opposite polarity is applied to the secondary center electrode and the secondary peripheral electrode, and a portion corresponding to the secondary center electrode of the piezoelectric thin film and a portion corresponding to the secondary peripheral electrode are mutually applied when the voltage is applied. A low voltage driven piezoelectric microspeaker, characterized by generating strain in the opposite direction. The method of claim 10, And the secondary center electrode and the secondary peripheral electrode are formed in at least one of a concentric circle shape and a concentric square shape. The method of claim 11, wherein And a support layer formed on an upper surface of the secondary electrode and an exposed upper surface of the piezoelectric thin film. The method of claim 12, And the primary electrode is grounded. The method according to any one of claims 8 to 13, The piezoelectric thin film is formed of one of ZnO, AlN, and PVDF, and the primary electrode and the secondary electrode are formed of one of Al and Mo / Ti, and the diaphragm has a low stress non-chemical equivalent. A low voltage driven piezoelectric micro speaker, which is formed of a material of one of a silicon nitride film and an ONO film, and wherein the support layer is formed of a parallel film.

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