KR100791084B1 - Piezoelectric microspeaker with corrugated diaphragm - Google Patents

Abstract

The present invention relates to a piezoelectric micro speaker and a method for manufacturing the same, and an object of the present invention is to provide a method for manufacturing a piezoelectric micro speaker with improved output performance and a speaker made by the method.

To this end, the present invention provides a method for improving the performance of the speaker by providing artificial irregularities to the compressive thin film of the diaphragm of the piezoelectric micro speaker and installing a package structure on the diaphragm, and a speaker made by the method.

The piezoelectric micro speaker according to the present invention has the effect that the displacement of the membrane is increased and the output of the micro speaker is improved by amplifying the sound pressure by the package.

Description

Piezoelectric micro speaker and its manufacturing method {PIEZOELECTRIC MICROSPEAKER WITH CORRUGATED DIAPHRAGM}

The present invention relates to a piezoelectric micro speaker and a method of manufacturing the same. More particularly, the present invention relates to a method for improving speaker performance by providing an unevenness to a diaphragm of a piezoelectric micro speaker and installing a package structure on the diaphragm. It is about.

The use of personal cellular terminals (cellular phones) is rapidly increasing due to the convenience of personal cellular communication or data transmission, and many developments have been made to provide high quality services with miniaturization and light weight.

BACKGROUND OF THE INVENTION Microphones and speakers for personal digital assistants have been developed in the direction of miniaturization and integrated devices that can include the functions of microphones, speakers and buzzers. However, miniaturizing the microphone and the miniature speaker without degrading its operating characteristics has many difficulties, and its application area is limited.

That is, in the case of a micro speaker that is currently commercialized, its application in a place requiring a micro acoustic device such as a hearing aid is limited.

This problem occurs equally in various fields in which a small speaker can be used, such as a toy field including a laptop computer and various entertainment devices, a toy field including voice-generated toys, and a variety of card playing field.

On the other hand, in recent years, a technique for miniaturizing a microphone and a speaker on a silicon wafer using a micro electro mechanical systems (MEMS) technology has been disclosed.

The method of manufacturing acoustic transducers on silicon wafers using this MEMS technology can be manufactured by a semiconductor batch process, which can reduce costs and integrate multiple transducers and amplifiers in a single chip. There are many advantages compared to the conventional method, such as the miniaturization of the acoustic device including the signal processor.

Generally, piezoelectric thin films are mainly used for the production of speakers and microphones using MEMS technology. The piezoelectric thin film transducers require permanent magnets and drive coils, which are required in conventional electro-dynamic speakers. Because it is not necessary, the microphone is easier to manufacture than the condenser type, there is no need for polarization voltage, and has the advantage of having a wider operating range.

However, the conventional acoustic transducer using MEMS technology has a non-stoichiometric Nitride membrane having a compressive residual stress, and thus has a relatively low sensitivity in a microphone and a low output in a speaker.

That is, in the case of a micro speaker using a non-chemical equivalent nitride film having only compressive residual stress, 1) the tone is not uniform due to uneven wrinkles, and 2) it is not easy to deposit a non-chemical equivalent nitride film with compressive stress, 3) Because only wrinkles are used, the generation of volume is limited because deflection is not easy when driving the piezoelectric thin film. 4) There is no package structure to amplify sound pressure, so sound pressure generated under the same voltage is higher than that of conventional commercial dynamic speakers. There is a problem of being small.

Disclosure of the Invention

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a piezoelectric micro speaker and a method of manufacturing the same.

In order to achieve the above object, the present invention provides a method for providing irregularities to the diaphragm of a piezoelectric micro speaker and installing a package structure on the diaphragm.

1A to 1L are cross-sectional views of each manufacturing step of one embodiment of the piezoelectric micro speaker manufacturing method according to the present invention.

Figure 2 is a process diagram of one embodiment of a piezoelectric micro speaker manufacturing method according to the present invention

* Description of symbols on the main parts of the drawings *

100: silicon substrate 102, 102 ': oxide film

104: unevenness 106: compressible thin film

108, 108 ': lower electrode 110: piezoelectric thin film

112: lower insulating film 114, 114 ': upper electrode

116: upper insulating film 118: anchor region

120 thick film photosensitive film 122 seed film thin film

124: upper photosensitive film 126: electroless nickel layer

128: void

Piezoelectric micro-speaker manufacturing method according to the present invention comprises the steps of forming an uneven portion on the substrate by etching the outer side of one surface of the silicon substrate; Forming a compressive thin film on both sides of the substrate; Forming a lower electrode on a central portion of the substrate surface surrounded by the unevenness and a part of the outer unevenness; Forming a piezoelectric thin film covering the lower electrode formed at the center portion of the substrate; Forming an insulating film on the entire surface of the substrate; Forming an upper electrode at a position not overlapping with an insulating lower side electrode on the insulating film in the center portion of the substrate; Forming an insulating film on the entire surface of the substrate; And removing the silicon substrate under the central portion and the uneven portion.

In addition, the method for manufacturing a piezoelectric micro speaker according to the present invention comprises the steps of: forming an anchor region by removing an insulating film on a part of the outer surface of the substrate surface on which the piezoelectric micro speaker is formed; Forming a thick photoresist layer on the surface of the substrate except for the anchor region; Forming a seed thin film on the entire surface of the substrate; Forming an upper photoresist layer on an outer side of the anchor region and a portion of the center portion of the substrate; Growing an electroless nickel layer on the entire surface of the substrate except for the upper photoresist layer; And removing the upper photoresist layer, the seed film and the thick film photoresist layer in contact with the upper photoresist layer.

Piezoelectric micro speaker according to another embodiment of the present invention,

1) film cleaning step for initial cleaning and wafer backside protection and artificial corrugation structure as a step of cleaning and oxide film growth (about 1 micrometer) of the wafer; 2) patterning and front side Si etching to form surface corrugation; 3) growing or depositing an oxide etch and compressive membrane deposition (about 1 micron) step into a compressive membrane (ie, a non-chemical equivalent nitride, oxide / membrane, or nitride / oxide / nitride) structure; 4) depositing and patterning a lower electrode (Al: about 0.5 micrometer) such that the lower aluminum electrode is positioned inside the uneven structure during patterning; 5) dry etching or using the chemicals described in the applicant's published paper to prevent damage to the lower electrode as a deposition (within about 0.5 micrometer) and etching step of the piezoelectric thin film (ZnO, AlN, etc.); 6) Insulating film is deposited (Parlin-C or Parlin-D, within about 0.2 micrometer) and patterning step to deposit an insulating film to prevent electrical short between the lower electrode and the porous piezoelectric material, and stable contact of the contact of the upper electrode material Patterning to ensure a; 7) Upper electrode (Al or Au / Cr bilayer: within about 0.5 micrometer) As the deposition and patterning step, the upper electrode is also located inside the uneven structure, and the upper electrode is slightly smaller than the lower electrode, thereby preventing the electrical short between the upper and lower electrodes. Preventing; 8) Thick film (approximately 1 micron) Paraline-C or paraline-D deposition and patterning step, in which a thick film is deposited and Ni / N in order to increase mechanical strength or control stress at the end of the membrane when cutting with the last single chip. Patterning to secure an anchor region for securing adhesion of the Cr seed layer; 9) Patterning and etching of the backside compressive thin film to determine the size of the membrane, and then patterning to form a membrane by etching silicon in anisotropic etching solution (KOH solution) and then patterning in a reactive ion etching system Performing etching of the compressive thin film; 10) Application of thick film photoresistor, patterning and deposition of Ni / Cr seed film by applying a thick film photosensitive film to secure the cavity area and patterning to define the seed layer to adhere to silicon only where desired. To prevent deterioration during deposition of the Ni / Cr differential layer, the thick film photoresist is cured for about 30 minutes at a high temperature of about 150 degrees, and the Ni / Cr seed layer is formed to a thickness of 0.1 micrometer or less by thermal deposition or sputtering. Depositing; 11) Thin photoresist coating, patterning and electroless nickel plating steps, after the electroless nickel plating to apply a thin photoresist to define the lift-off and the sound outlet part, and to form the package structure at low temperature Depositing a metal thin film having a thickness of about 5 micrometers by electroless nickel plating under the process conditions set forth in the applicant's paper for the purpose; 12) Photosensitive film removal and backside silicon removal step, in order to form voids after electroless (or electrolytic) plating, the thin film and thick film photoresist under the surface and nickel film were subjected to ultrasonic cleaning process in acetone solution for about 10 seconds. After removing the internal and external photoresist film completely by standing in the acetone solution for a predetermined time, using a silicon etching device to protect the processed device on the front surface and to form a membrane by controlling the silicon for a predetermined time in the anisotropic etching solution ; And 13) chip cutting and wire bonding, comprising: separating the silicon into each single element after silicon anisotropic etching and electrically connecting each electrode portion with a predetermined contact portion.

The piezoelectric micro speaker according to the present invention is characterized by being manufactured by the above method.

Hereinafter, the present invention will be described with reference to the accompanying drawings. 1A to 11 are cross-sectional views of each manufacturing step of one embodiment of the piezoelectric micro speaker manufacturing method according to the present invention. That is, FIG. 11 is a final cross-sectional view of a speaker manufactured by the method of manufacturing a piezoelectric micro speaker according to the present invention.

2 is an embodiment of a method of manufacturing a piezoelectric micro speaker according to the present invention.

The silicon substrate 100 is cleaned and the oxide films 102 and 102 ′ having a thickness of 1 μm are grown (200). The outer side of one surface of the silicon substrate 100 is etched to form the unevenness 104 on the substrate (202). The uneven 104 is formed in a shape surrounding the membrane on which the compressive thin film is to be deposited. The etching of the silicon 100 for forming the unevenness 104 may be performed by patterning the oxide film 102.

The oxide film 102 on both sides of the substrate 100 is removed by a wet etching method and formed by depositing a compressive thin film 106 having a thickness of 1 μm (204). The compressive thin film 106 is selected from a nonchemically equivalent nitride film, a double film of an oxide film and a nitride film, and a triple film of a nitride film, an oxide film, and a nitride film. Since the compressive thin film 106 uses a film having a compressive residual stress, when silicon is removed, wrinkles are formed around the membrane so that the vertical movement of the membrane is easier than that of the film having a tensile residual stress.

The lower electrodes 108 and 108 ′ are formed by depositing and patterning Al having a thickness of 0.5 μm on a central portion of the substrate surface and a part of the outer side of the unevenness (206). The lower electrode 108 in the center is positioned inside the unevenness.

A piezoelectric thin film 110 covering the lower electrode 108 formed in the center of the substrate is formed (208). The piezoelectric thin film 110 is selected from ZnO or AlN and is deposited and etched after calculating the thickness in consideration of the residual stress of the entire thin film. In this case, dry etching may be used to minimize damage to the lower electrode 108. Further, in order to insulate the upper and lower electrodes of the piezoelectric thin film, the pattern is etched so as to completely cover the side surface of the lower electrode 108.

The lower insulating layer 112 is formed on the entire substrate surface (210). The lower insulating film 112 is selected from Parylene-C and Parylene-D and is deposited to 0.2 μm. The lower insulating layer 112 is deposited to prevent an electrical short between the lower electrode and the porous piezoelectric body.

The upper electrodes 114 and 114 'are formed at positions not overlapping with the lower insulating film 112 and the uneven outer lower electrode 108' at the center of the substrate (212). The upper electrodes 114, 114 'are deposited and patterned at 0.5 mu m with an Au / Cr bilayer of a predetermined thickness considering Al or residual stress within 0.5 mu m. The upper electrode 114 of the center part is also located inside the uneven structure and slightly smaller than the lower electrode 108, thereby preventing electrical short circuit and coupling between the upper and lower electrodes as much as possible.

At this time, the upper electrode forms an electrode part divided into one or two parts to maximize the deformation of the piezoelectric thin film. That is, when two upper electrodes use voltage as an application terminal, the lower electrode is used as a common electrode.

An upper insulating film 116 is formed on the entire substrate surface (214). At this time, Parylene-C or Parylene-D is deposited to a thickness of 1㎛. The film 116 is deposited to increase mechanical strength and control stress at the membrane tip when cutting into the last single chip.

Anchor regions are formed by removing the insulating layers 112 and 116 of a portion outside the substrate surface (216). This is to secure the adhesion of the seed layer 122. The compressive thin film 102 'on the backside of the substrate is patterned and removed (218). This defines the final area of the membrane. After the patterning, the etching of the compressive thin film 102 'proceeds in a reactive ion etching system.

A thick photoresistor 120 is formed on the substrate surface excluding the anchor region (220). The thick film photoresist 120 is applied to secure a cavity 128 between the membrane and the package using the electroless nickel thin film. At this time, the thick film photoresist 120 is cured for 30 minutes at 150 ℃ in order to minimize the deterioration generated during the deposition of the seed film, and to prevent micro cracks.

The seed thin film 122 is formed on the entire substrate surface (222). The seed film 122 is deposited with a nickel chromium alloy to a thickness of 0.1 μm by thermal evaporation or sputtering.

An upper photoresist layer 124 layer is formed on an outer side of the anchor region 118 and a portion of the center portion of the substrate (224). The application of the thin photosensitive film 124 is to form an electroless nickel layer in the region excluding the acoustic discharge port, and to define and remove unnecessary portions on the element region after the electroless nickel plating.

An electroless nickel layer 126 is formed on the entire surface of the substrate except for the upper photoresist layer 124 (226). The electroless nickel plating 126 is for forming a package structure at a low temperature of 100 ° C. or lower, and deposits a metal thin film having a thickness of 5 μm to 10 μm by the electroless plating method. At this time, the residual stress of the plated nickel is manufactured by adjusting the composition, temperature and acidity (pH) of the plating solution, as shown in FIG.

In order to form the pores 128, the thin film 124 and the thick film photoresist 120 under the surface and the nickel film undergo an ultrasonic cleaning process in acetone solution for several seconds to remove the photoresist films 120 and 124. In this case, when the upper photoresist layer 124 is removed, the seed layer 122 of the lower portion of the photoresist layer is also removed, whereby the acetone is removed along with the thick film photoresist layer 120 under the seed layer through the formed sound discharge port.

The membrane is formed by etching the silicon substrate 100 in the central portion and the lower portion of the unevenness in an aqueous potassium hydroxide solution (KOH SOLUTION) (230). In this case, a silicon is formed by protecting a device fabricated on the entire surface of the substrate using a silicon etching apparatus, and etching the silicon 100 for a predetermined time in the anisotropic etching solution.

The chip is cut and wire bonded (232). After the anisotropic etching of the silicon substrate, the device is completed by separating into elements and electrically connecting each electrode part with a predetermined contact part.

In the piezoelectric micro speaker according to the present invention, the operation principle is as follows. Electrodes (Al or lower Al and upper Au / Cr structure or upper and lower secondary electrodes, where the lower electrode is used as a common electrode) are arranged on the upper and lower parts of the piezoelectric thin film to form a sandwich plate having a sandwich structure. When an AC voltage is applied at, the piezoelectric thin film contracts and expands according to the polarity change of the applied voltage. This contraction and expansion according to the applied voltage causes the vertical motion of the membrane deposited on the silicon substrate, thereby moving the upper and lower air layers of the membrane.

At this time, due to the inherent properties of the membrane membrane manufactured to have compressive residual stress, artificial uneven structure, and the residual stress of the overall regulated membrane, the membrane easily causes a vibration having a large amplitude according to the alternating voltage. In other words, the combination of the intrinsic properties of the membrane membrane itself with the artificial uneven structure generates vibrations of greater amplitude more easily than a speaker without the artificial uneven structure.

At this time, the vibration of the membrane causes a change in the pressure of the air layer located above the membrane, thereby generating a negative pressure. The issued sound pressure is amplified by a package structure having pores located at the top of the membrane, and the amplified sound pressure is transferred to the air through the formed sound pressure discharge port of the package portion, thereby serving as a micro speaker having a larger sound pressure.

The piezoelectric micro speaker according to the present invention is easy to manufacture, but the operation performance of the speaker membrane is improved by the unevenness, and the output of the speaker is improved by the package. In addition, the combination of a large amplitude membrane membrane structure and an artificial concave-convex structure increases the sound pressure generated, and a package structure with air gaps provides a compact speaker that structurally amplifies the sound pressure and protects the membrane from mechanical shock. do.

It is apparent to those skilled in the art that such a speaker of the present invention can be used for a wide variety of applications, such as a voice generator in medical fields, a medical ultra-compact hearing aid, a voice generator for toys, a thin film speaker used for a sound reproduction type postal card, and the like.

The present invention has been described above as an embodiment, but the present invention is not limited to the above-described embodiments, and those skilled in the art without departing from the gist of the present invention claimed in the claims. Anyone can make a variety of variations. As set forth in the claims appended hereto, at least 1) a speaker structure having a membrane composed of a nitride film, nitride film / oxide film or nitride film / oxide film / nitride film to form a membrane having compressive residual stress, 2) unevenness ( corrugation) micro speaker and 3) micro speaker using the combination of 1) and 2) above, 4) micromachining to amplify the volume in the structure of 1), 2) and 3) above. 5) Ultrasonic speaker containing a package having a pore structure manufactured by 5) Ultrasonic speaker made by using electrolytic or electroless plating technology in the case of a metal, forming a package having a void, 6) Ultra small consisting of all the above terms As a speaker, a micro speaker using a piezoelectric thin film such as ZnO or AlN to drive the speaker is included in the scope of the present invention.

Claims (7)

1) etching the outer side of one surface of the silicon substrate to form irregularities on the substrate; 2) forming a compressive thin film on both sides of the substrate; 3) forming a lower electrode on a central portion of the substrate surface surrounded by the unevenness and a part of the outer side of the unevenness; 4) forming a piezoelectric thin film covering the lower electrode formed at the center portion of the substrate; 5) forming a lower insulating film on the entire surface of the substrate; 6) forming an upper electrode on a lower insulating layer on the center portion of the substrate and on a position not overlapping with an outer lower electrode of the unevenness; 7) forming an upper insulating film on the entire surface of the substrate; And 8) A piezoelectric micro speaker manufacturing method comprising the step of removing the silicon substrate of the central portion and the uneven portion. delete The method of claim 1, wherein the piezoelectric thin film of step 4) is one of ZnO and AlN. The method of claim 1, wherein the lower and upper insulating films are one of Parylene-C and Parylene-D. The method of claim 1, wherein the lower electrode is a common electrode, and the upper electrode is divided into two. delete delete

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