KR20010069463A - Microphone and speaker made of polyvinylidene fluoride (pvdf) piezoelectric film having surface electrodes - Google Patents

Abstract

PURPOSE: A PVDF(PolyVinyliDene Fluoride) piezoelectric film type microphone and flat speaker with both-sided electrode are provided to form a microphone and a speaker having a vibration plate function and a signal conversion function by using piezoelectricity of a PVDF film. CONSTITUTION: A metal electrode with a thickness of 200 to 1080 angstrom is deposited on both sides of a PVDF piezoelectric film(20). A piezoelectric film type microphone of a flat structure or a curve structure is formed by using the PVDF piezoelectric film(20) with the metal electrode. The piezoelectric film type microphone has a size of 3cmx 2cm. A flat speaker and the microphone are formed with one unit by using a structure of the PVDF piezoelectric film(20).

Description

MICROPHONE AND SPEAKER MADE OF POLYVINYLIDENE FLUORIDE (PVDF) PIEZOELECTRIC FILM HAVING SURFACE ELECTRODES

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of ultra-thin microphones and speakers, and more particularly to piezoelectric thin film fabricated using polyvinylidene fluoride (hereinafter referred to as PVDF) of a double-sided electrode suitable for use in mobile communication devices and computer devices. A microphone / flat speaker.

Acoustic waves are waves of elastic vibration that travel through the gas, liquid, and solids around us. They are also called a combination of audible sound waves propagated in the air and ultrasonic waves of about 20 kHz or more. A microphone is used as a method of converting vibration of a diaphragm into an electric signal in a conventional microphone, such as coin type (dynamic type), electrostatic type (condenser type), carbon type (carbon type), and the like. Piezoelectric and the like. Coin-type conversion method is a way that the coil vibrating with the diaphragm detects the signal due to the displacement of the magnet, carbon-type conversion method is to detect the change of carbon resistance according to the displacement of the diaphragm, the electrostatic conversion method is The fixed electrode is installed on the rear surface of the conductive diaphragm to sense the change of capacitance between the anodes.

Small microphones currently used in many mobile communication devices and computer devices mainly use electret condenser microphones, and as shown in FIG. 1, the electret condenser microphone 10 has an electret diaphragm in which polarization remains in the dielectric material. (1) is assembled into an insulating plate (3), a back electrode (2), an insulating rear protective plate (6) and a front protective plate (5) and placed in the case (7) to have a structure of signal sensing through the connection of a resistor R _o . The electret condenser microphone of such a structure has a disadvantage in that a bias power source is required in a circuit, and has a disadvantage in that it is made of many components and has a high assembly cost and is difficult to manufacture with an ultra-thin microphone of less than 1 mm.

On the other hand, although the piezoelectric conversion method in which the piezoelectric ceramic is attached to the diaphragm and the vibration is transmitted to the piezoelectric to be converted into an electric signal has a simple structure, defects occur in firmly bonding the heavy ceramic piezoelectric body to the vibrating plate and the size is reduced. It is difficult and not suitable for small microphones due to the disadvantages of ceramics' easily cracking properties.

Contrary to the principle of the microphone, a speaker that converts an electrical signal into sound waves is a magnetic drive system mainly composed of magnetic diaphragms and coils. In order to reduce the thickness and simplify the light weight and manufacturing process, if the thickness of the magnet is reduced to 2 mm or less, the magnetic field is reduced. Its size shrinks with it, limiting its shrinkage. The piezoelectric speaker, which is a non-driven method for improving the problem, has been mainly made of ceramic piezoelectric material, but requires a strong bonding method with a diaphragm for signal conversion. Examples of piezoelectric speaker manufacturing methods are Korean Patent Publication No. 1986-005216, "Piezoelectric Speaker", Korean Patent Application Publication No. 1988-003534, "Double Diaphragm Piezoelectric Speaker", Korean Patent Publication No. 1992-014335 "Piezoelectric Ceramic -A method for producing a polymer composite speaker ", and" Piezoelectric speaker "in US Pat. No. 5,736,808.

On the other hand, a flat speaker that allows the diaphragm and the signal conversion to be performed at the same time is called a flat speaker, the flat speaker can be significantly reduced the weight, thickness and manufacturing cost of the speaker in a non-automatic manner. A method for applying a flat panel speaker to a flat panel video monitor is described in US Pat. No. 5,796,854, "Thin film speaker apparatus for use in a thin film video monitor device."

In particular, the European Telecommunications Standard Specification of the European Telecommunications Standards Institute (secretariat@etsi.fr), which certifies Digital cellular telecommunications system, Global System for Mobile Communication (GSM), etc. for the performance of wireless terminals for use in mobile communications. ETS 300 607-1 (1996. 3) must be satisfied. Here, the frequency sensitivity (Sensitivity / Frequency Response) of the speaker described in pp.1056-1071 of this standard is a sound pressure level (0 to 0 ~) which is generally constant in the sound reproduction band 300 Hz to 3.5 kHz in frequency versus sensitivity (dB) characteristics. -12 dB) is required.

Also, in general, wired / wireless communication terminals, especially mobile communication terminals such as cellular phones, adopt components that can extend talk time and minimize weight and size under a certain capacity of a rechargeable battery in pursuing light and small size. That's the trend. In today's mobile phones, the size of the battery, the keypad, the speaker, and the microphone must be provided. In particular, the speaker and the microphone is a thin thickness of less than 1mm, the situation is urgently needed devices that operate at low power.

The inventors of the present invention have a material that meets the trend of miniaturization and lightening of electronic components because the production cost is increased by using many kinds of ultra-small components when manufacturing the above-mentioned electret condenser microphone or a speaker of a self-drive type speaker. The company has sought ways to manufacture flat-panel microphones and speakers with a simple structure that can be used and reduce assembly costs.

Accordingly, an object of the present invention is to provide a microphone and a flat panel speaker capable of simultaneously acting as a diaphragm and a signal conversion by using the piezoelectricity of a polymer PVDF film.

Applications for known PVDF films include a 25 cm x 17.5 cm PVDF film printed on both sides by screen printing with silver (Ag) electrodes thicker than a few microns, mounted on a balloon, making it possible to operate as a speaker and microphone using piezoelectric properties. , "The interactive balloon: Sensing, actuation, and behavior in a common object," IBM SYSTEMS JOURNAL, VOL 35, NOS 3 & 4, pp. It was attempted in 473-487 (1996).

However, when the silver (Ag) electrode thick film used here is reduced to a size sufficient to be used in a mobile communication terminal, there is no consideration as to whether the microphone and the speaker are practically used.

The present invention provides a method of fabricating a simple microphone having a flat or curved structure having a size of about 3 cm x 2 cm and supporting only its edges using PVDF piezoelectric film material deposited on both sides of a thin film of thousands of micrometers. .

Preferably, the PVDF film has a thickness of 12 ~ 110 ㎛, preferably 12 ㎛, the thickness of the metal electrode deposited on the PVDF film is 200 kPa to 1080 kPa, the metal electrode using an ion beam deposition method or the like Is formed.

In addition, it is known that the piezoelectricity of PVDF film can be used as a speaker and a microphone. Therefore, by using the PVDF film structure jointly, the functions of the flat panel speaker and the microphone are configured as a single unit, thereby reducing the occupying area of the mobile communication terminal and reducing the cost. It provides a way to save money.

The method of separating input and output signals into a single unit is described in the above paper, which describes a solution by connecting two diodes of opposite polarity, "The interactiveballoon: Sensing, actuation, and behavior in a common object," IBM SYSTEMS JOURNAL, VOL 35, NOS 3 & 4, pp. 473-487 (1996).

In addition, the use of the piezoelectric film according to the present invention enables two-dimensional array type microphone input, thereby providing an arrangement method applicable to digital microphone / speaker development.

The use of the polymer PVDF piezoelectric thin film according to the present invention can reduce the number of parts in the production of electret condenser microphones and solve the technical problem of bonding the diaphragm and the piezoceramic in the ceramic piezoelectric conversion method. Simultaneously plays the role of signal conversion, making it possible to manufacture ultra-thin microphones with a thickness of less than 1mm.

In addition, the PVDF piezoelectric membrane type speaker that plays a role of signal conversion with the diaphragm removes the thick and heavy magnets required in the magnetic driving method, and is suitable for the frequency sensitivity standard for mobile communication, and it is possible to manufacture an ultra-thin speaker having a thickness of 1 mm or less.

1 is a cross-sectional view showing the structure of a conventional electret microphone.

2 is a block diagram of a PVDF piezoelectric thin film having a double-sided electrode used in the present invention.

3A and 3B are electron microscope surface and cross-sectional photographs of a PVDF piezoelectric thin film in which a platinum double-sided electrode used in the present invention is deposited by ion beam deposition;

4 is a block diagram of a PVDF piezoelectric thin film microphone and a flat panel speaker having a double-sided electrode used in the embodiment of the present invention.

5 is a spectrogram of a signal uttering "Hello" using a PVDF piezoelectric thin film microphone according to the present invention and recorded through a computer sound card.

FIG. 6 is a spectrogram of a signal recorded through a computer sound card uttering "hello" with a commercially available condenser microphone for comparison with FIG.

7 is a diagram illustrating a fast Fourier transform (FFT) analysis result for determining the shape of noise in a spectrogram of a signal recorded by the piezoelectric thin film microphone of FIG. 5.

Figure 8 is a schematic diagram showing the installation state of the piezoelectric thin film microphone and the flat panel speaker to a mobile communication terminal preferred to be applied to the present invention.

FIG. 9 is a graph showing an analysis result of sound pressure level according to a wavelength of a flat panel speaker having a size of about 3 cm x 2 cm mounted in FIG.

10 is a schematic diagram of an electrode pattern to be used in a multi-channel piezoelectric thin film microphone and a flat panel speaker.

FIG. 11 is a circuit diagram illustrating an example of a signal processing circuit for the multi-channel microphone of FIG. 10. FIG.

12 is a view showing an example of a driving circuit for a flat panel speaker according to the present invention.

As is known, polyvinylidene fluoride (PVDF) usually has a high dipole moment in the-(CH ₂ -CF ₂ -CH ₂ -CF _2- ) _n -structure. When the external electric field is applied by the electric reaction between the dipoles in the two polymer chains, the intermolecular distance is reduced by the dipole attraction, which results in a piezoelectric effect that reduces the total thickness of the PVDF thin film. PVDF thin films have many applications because of changes in temperature that lead to changes between dipoles and have pyroelectricity that results in changes in voltage (charge) (Gabor Harsanyi, "Polymer Films in Sensor Applications", Technomic Publishing Co. Lancaster USA 1995).

Features of PVDF piezoelectric film include low cost, flexible wear resistance, suitable for harsh conditions, good moldability, wide band (0.001 Hz to 10 ⁹ Hz), high sensitivity (10 ^-8 to 10 ⁶ psi), high efficiency, piezoceramic compared to piezoelectric ceramics Compared with 10 times higher voltage operation, less than 0.02% moisture absorption, and strong resistance to compounds, and suitable for electronic circuits.The disadvantages include poor operation at low frequencies, operation under 100 ℃, and blocking of electromagnetic waves. There is this.

Typical applications for the application of the piezoelectric effect of PVDF are pressure sensors (e.g. US Patent No. 4,990,815 "Robot gripper control system using PVDF piezoelectric sensors", US Patent No. 5,760,530 "Piezoelectric tactile sensor", US Patent No. 5,797,623). "Smart skin sensor for real-time side impact detection and off-line diagnostics"), the present invention contributes to the light and thin shortening of the sensor, that is, the microphone that converts sound waves into electrical signals using the same.

The configuration of a PVDF piezoelectric thin film having a double-sided electrode used in the present invention is schematically shown in FIG.

In order to simultaneously perform the roles of the diaphragm and the signal conversion, as shown in FIG. 2, appropriate electrodes 24-1 and 24-2 are deposited on both sides of the PVDF film 22 to form the signal lines 26-1 and 26-2. It must be connected to the electrode.

Screen printing method, which is widely used as a conventional double-sided electrode deposition method, is suitable for forming an electrode having a thickness of several μm or more, and the electrode deposition by this method applies a load to the diaphragm, so that a vacuum deposition method for forming a thinner metal electrode is used. It is advantageous. Although it is preferable to deposit a metal electrode at several thousand micrometers by vacuum deposition, PVDF material is difficult to deposit and form a composite because it does not have adhesion with other metal materials. Methods for improving the adhesion of fluorinated resins to metallic materials are disclosed in Korean Patent Application Publication No. 1999-081865, "Methods for Attaching Fluorinated Resins to Metals" and the United States of America, which is an invention for improving adhesion strength through modification of the surface of a polymer. Patent 5,783,641 describes "Process for modifying surfaces of polymers, and polymers having surfaces modified by such process."

(Example)

Platinum (Pt) was deposited on a 40 µm thick PVDF thin film using ion beam deposition (IBAD), Ar 5.6 sccm, total pressure 6.0 x 10 ^-5 torr, Ion gun discharge 470V, 400mA, Plug current 5mA, Ion beam The deposition was performed for 25 minutes under the condition of voltage 1100V, 44mA, 400V Accelerator 400V, 7mA without the surface modification process for adhesion improvement. Accordingly, electron microscope surface and cross-sectional photographs of the PVDF thin film deposited with platinum (Pt) are shown in FIGS. 3A and 3B.

As shown in the cross-sectional photograph of FIG. 3B (corresponding to FIG. 2), when the platinum thin film has a thickness of 1080 Å, severe cracks are not seen on the surface, and thus it can be used for manufacturing the microphone. Although not listed in this embodiment, metals such as gold, silver, copper, aluminum, and indium-tin-oxide (ITO), conductive polymer polyaniline, conductive polymer polypyrrol, The same applies to depositing and using a metallic material such as a conductive polymer polythiophene.

According to the surface photograph of FIG. 3A, micro-pin pinholes are not formed, and thus it may be used as a microphone. In addition, the thickness is not limited to 1080 kW, the sheet resistance available to the microphone is in the range of 1 ~ 10 Ω / □ but not limited to 200 kΩ. In this embodiment, the electrode deposition method using the IBAD is used, but not limited to this, all general thin film deposition methods can be used. Attachment strength used in the present embodiment was enough to manufacture the microphone, so the use of the invention to improve the adhesion is separate.

FIG. 4 is an assembly diagram of a microphone / speaker operation test apparatus using the PVDF piezoelectric film manufactured and described in FIG. 3.

The front electrode lead 26-1 and the back electrode lead using the conductive tape or conductive copper tape made by 3M (R) company for the double-sided electrodes 24-1 and 24-2 of the PVDF film 20 (refer FIG. 2). (26-2) is bonded. However, the method of adhering the electrode is not limited to the above method and includes all methods capable of forming the electrode. Since the PVDF film 20 has anisotropic piezoelectricity, when the PVDF film is bent in the stretching direction of the PVDF film, unlike the isotropic piezoelectric ceramics, the signal strength is large. Therefore, in FIG. 4, the front support plate 30A and the rear support plate 30B of the acrylic material having a hole having a size of 10 cm x 10 cm in the front and rear surfaces of the film 20 were bent at a curvature radius of about 15 cm. Holes are formed in the corner portions of the front and rear support plates 30A and 30B and the film 20, respectively, and the PVDF film 20 is placed between the front support plate 30A and the rear support plate 30B and bolts 32 and nuts The piezoelectric microphone device is completed by fastening at 34.

In FIG. 5, the signal line from the electrode of the PVDF piezoelectric thin film microphone manufactured as shown in FIG. 4 is connected to a sound card microphone input terminal of a personal computer, and a spectrogram of a signal file in which the word “Hello” is spoken is recorded. ) Is the result of analysis. The analysis was conducted by Kay Elemetrics Corp. Using the CSL 4300B, the analysis conditions are Window Weighting: Hamming, Pre-Emphasis Level: 0.8, 100 points, Band pass filter: 323 Hz. The upper waveform of FIG. 5 is a waveform of amplitude magnitude according to time of the recorded signal file, and a signal corresponding to each syllable of “in”, “yin”, “low”, “three”, and “yo” is detected. It became.

The lower waveform of FIG. 5 shows a distribution of frequencies (0 to 4470 Hz) over time. These spectrograms can only be used as microphones to distinguish vocal cord vibrations. In order to confirm this, a result of analyzing a signal file recorded through a computer sound card using a commercially available electret condenser microphone and saying "Hello" in the same way as described above is shown in FIG. Assay conditions are the same as in FIG. 5).

In comparison of the two results, it can be seen that the vocal cord vibration corresponding to each syllable of "not", "good", "ha", "three", and "yo" is equally detected. It can be seen that the conventional electret condenser microphone can be easily replaced.

In the above embodiment, a piezoelectric thin film having a size of 10 cm x 10 cm was used, but the same signal was detected even at a size of 5 cm x 5 cm. Therefore, the size of the piezoelectric thin film is not limited, and when a small size is used, the anisotropic piezoelectricity of the PVDF piezoelectric film may be used by bending the edge as in the diaphragm of the existing dynamic speaker.

In the spectrogram of FIG. 5, noise remained even when there was no vocal cord vibration. To confirm this, Fourier transform analysis (FFT) as shown in FIG. 7 was performed. In the upper graph of FIG. 7, a signal of a time corresponding to a vertical line is analyzed by FFT 4096 points and Window Weight: Hamming. In this graph, noise equivalent to an integer multiple of 60 Hz was detected, which is presumed to have detected AC power noise caused by poor grounding of the microphone. However, it will be appreciated by those skilled in the art that such noise can be sufficiently eliminated in the manufacture of the actual device.

In the above embodiment, an operation example of a square microphone such as 10 cm x 10 cm, 5 cm x 5 cm, etc. has been discussed, but the same applies to the case where it is reduced to 2 cm x 3 cm as shown in FIG. 8 for use for a mobile communication terminal. Characteristics can be obtained. In FIG. 8, even when the PVDF piezoelectric film 20 'having a size of 2 cm x 3 cm according to the present invention is attached to the rear of the display window 110 of the terminal 100 through the support 30B', Can be used. Preferably, the piezoelectric film 20 'is obtained by depositing a transparent metal ITO according to the present invention on both sides of transparent PVDF film material, and functions as a microphone without interfering with the function of the display when attached to the back of the display window 110. Can be performed. However, if a small size film is used, it may be necessary to attach an amplifier due to the weak signal strength. Reference numeral 115 denotes a keypad on the surface of the terminal.

In addition, since the piezoelectric film 20 'can be simultaneously operated as a speaker and a microphone, it has already been confirmed in the aforementioned paper by JA Paradiso. The piezoelectric microphone used in this embodiment is used as a speaker for a mobile communication device. It can be used as a PVDF piezoelectric thin film element applied to the integrated microphone.

In FIG. 9, when the PVDF piezoelectric film is attached to the display window of the terminal as shown in FIG. 8, it is attached to an artificial ear in an anechoic chamber (f _o 80 Hz) to analyze frequency (dB sensitivity). The analysis was performed using a Bruel and Kjaer (B & K) Type B & K 4191 microphone, a B & K 2716C preamplifier and a B & K 2012 heterodyne-analyzer. Analytical conditions increased the output level of the preamplifier by 1 volt interval and measured wavelength-to-sensitivity from 1 to 5 volts, but no significant change was observed.

According to the graph of Fig. 9, since a constant sound pressure level is generally detected in the sound reproduction band 300 Hz to 3.5 kHz, it can be used in a mobile phone terminal that satisfies the above-described ETSI standard. However, since the sensitivity of the 85 kHz band is significantly reduced by the mounting method of the film, it may be improved by adjusting the degree of tension when the film is mounted. Although not listed in the present embodiment, when analyzing the speaker having the structure of FIG. 4, no significant decrease in sensitivity of the 85 kHz band is observed, and shows good sensitivity over the audio frequency band.

Although the installation schematic diagram of the piezoelectric thin film microphone / flat speaker for a mobile communication terminal which is preferable in the present invention is shown in FIG. 8, a specific application method is not limited thereto. For reference, an example of a driving circuit for the flat panel speaker according to the present invention is shown in FIG. In FIG. 12, the output level of the amplifier is controlled by the variable resistor R1 provided at the audio signal input terminal of the amplifier OP1, and the output transformer T1 is filtered after the resistor R2 and the capacitors C1 and C2 are filtered. Audio outputs are supplied to the speaker terminals P1 and P2, which are connected to the metal electrode leads of the piezoelectric film 20 '.

As in the above embodiment, the PVDF piezoelectric thin film microphone / speaker utilizes a characteristic capable of simultaneously acting as a diaphragm and a signal conversion, but the present invention is not limited thereto. Technically permissible dimensions for the same PVDF piezoelectric thin film 22, the front side is (1,2,3 .... n) rows of electrodes 24 ₁ to 24 _n and the rear side is vertically (A, _A piezoelectric film patterned with electrodes 24 _A to 24 _{Z of} B, C, D, .... Z columns can be used as a microphone / speaker.

10 is a block diagram of an electrode pattern to be used in a multi-channel piezoelectric thin film microphone / speaker according to the present invention. Preferably, the widths of the electrodes 24 ₁ to 24 _n and 24 _a to 24 _z disposed on the front and rear surfaces are 3 mm and the intervals between the electrodes are 1 mm. However, the present invention is not limited thereto.

Such an electrode pattern is a small piezoelectric element, each of which intersects the front and rear electrodes, serves as a multi-channel array type microphone / speaker with respect to frequency, and thus can be extended to a digital microphone / speaker as a multi-channel type recognition function.

The patterned multi-channel microphone of the array microphone 200 composed of small piezoelectric elements 20 ₁ , 20 ₂ ,..., 20 _n , which are the portions where the electrodes on the front and rear surfaces intersect, as shown in FIG. 11. The combination of a switching circuit 50 for distributing the output signals of each channel to the amplification circuit 60 can be used as a digital microphone for mobile communication, and the microphone / speaker integrated device array described above. Can be extended to However, in order to use as an array speaker, since the direction of signal transmission is reversed, the configuration of the amplifying circuit must be changed to be suitable for the speaker operation. Signal processing circuits for the multichannel microphones / speakers are well known to those skilled in the art, and various circuit configurations are possible.

According to the present invention, by manufacturing a microphone and a flat panel speaker using a polymer PVDF piezoelectric film to simultaneously play a role of a diaphragm and signal conversion, it is possible to reduce the assembly cost of an ultra-thin microphone / speaker, and to use the microphone in a mobile communication terminal or a portable computer. There is an advantage in that the space required for using the speaker can be reduced.

On the other hand, since the PVDF piezoelectric film of the present invention is expected to have an effect such as expansion to a multi-channel type recognition function and a microphone-speaker integrated device, the specific embodiments have been described above, but various modifications and changes within the scope of the present invention are provided. Modifications may be possible.

Claims (8)

A polyvinylidene fluoride (PVDF) film having metal electrodes deposited on both sides with a predetermined thickness, Piezoelectric thin film microphone and flat panel speaker including a support for fixing the PVDF film in a flat or curved form. The method of claim 1, wherein the PVDF film has a thickness of 12 ~ 110 ㎛, the thickness of the metal electrode deposited on the PVDF film is 200 kPa to 1080 kPa, the metal electrode using a thin film deposition method such as ion beam deposition method Piezoelectric thin film microphone and flat panel speaker, characterized in that formed by. The method of claim 1, wherein the metal electrode is platinum, gold, silver, copper, aluminum, ITO (indium-tin-oxide), conductive polymer polyaniline, conductive polymer polypyrrol, conductive polymer polythiophene Piezoelectric thin film microphone and flat panel speaker, characterized in that formed by a metallic material selected from the group consisting of). The piezoelectric thin film microphone and flat panel speaker of claim 1, wherein the PVDF film has a size of about 3 cm x 2 cm, and only an edge portion of the PVDF film is fixed to the support. 5. The piezoelectric thin film microphone and flat panel speaker of claim 1 or 4, wherein the support has a radius of curvature of about 15 cm. The method of claim 1, wherein the metal electrode deposited on the front and rear of the PVDF film comprises electrodes patterned in a plurality of rows horizontally on the front surface, and electrodes patterned in a plurality of columns vertically on the rear surface. Piezoelectric thin microphones and flat panel speakers. The piezoelectric thin film microphone and flat panel speaker of claim 6, wherein each of the plurality of rows and columns of the patterned electrodes has a width of 3 mm and an inter-electrode spacing of 1 mm. A mobile communication terminal in which piezoelectric thin film microphones and flat panel speakers as described in claims 1 to 7 are attached to predetermined portions therein.