A thermoacoustic chip includes a shell having a hole and a speaker located in the shell. The speaker includes a substrate having a surface, a sound wave generator located on the surface of the substrate and opposite to the hole of the shell, and, a first electrode and a second electrode. The first electrode and the second electrode are spaced from each other and electrically connected to the sound wave generator.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201210471054.7, filed on Nov. 20, 2012 in the China Intellectual Property Office.

BACKGROUND

1. Technical Field

The present disclosure relates to a thermoacoustic chip, especially a thermoacoustic chip based on carbon nanotubes.

2. Description of Related Art

In traditional speakers, sounds are produced by mechanical movement of one or more diaphragms.

In one article, entitled “The thermophone as a precision source of sound” by H. D. Arnold and I. B. Crandall, Phys. Rev. 10, pp22-38 (1917), a thermophone based on the thermoacoustic effect is disclosed. The thermophone in the article includes a platinum strip used as sound wave generator and two terminal clamps. The two terminal clamps are located apart from each other, and are electrically connected to the platinum strip. The platinum strip has a thickness of 0.7 micrometers. Frequency response range and sound pressure of sound wave are closely related to the heat capacity per unit area of the platinum strip. The higher the heat capacity per unit area, the narrower the frequency response range and the weaker the sound pressure. An extremely thin metal strip such as a platinum strip is difficult to produce. For example, the platinum strip has a heat capacity per unit area higher than 2×10−4J/cm2*K. The highest frequency response of the platinum strip is only 4×103Hz, and the sound pressure produced by the platinum strip is also too weak and is difficult to be heard by human.

In another article, entitled “Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers” by Fan et al., Nano Letters, Vol. 8 (12), 4539-4545 (2008), a carbon nanotube speaker is disclosed. The carbon nanotube speaker includes a sound wave generator. The sound wave generator is a carbon nanotube film. The carbon nanotube speaker can produce a sound that can be heard because of a large specific surface area and small heat capacity per unit area of the carbon nanotube film. The frequency response range of the carbon nanotube speaker can range from about 100 Hz to about 100 KHz. However, carbon nanotube speakers are not convenient for use.

What is needed, therefore, is to provide a carbon nanotube speaker which is convenient for use.

DETAILED DESCRIPTION

References will now be made to the drawings to describe, in detail, various embodiments of the thermoacoustic chips.

Referring toFIG. 1, a thermoacoustic chip10A of a first embodiment is shown. The thermoacoustic chip10includes a speaker100and a shell200. The shell200defines a space to accommodate and protect the speaker100.

The speaker100includes a substrate102, a first electrode104, a second electrode106, and a sound wave generator108. The substrate102has a first surface101and a second surface103opposite to the first surface101. The first electrode104and the second electrode106are spaced from each other and electrically connected to the sound wave generator108. If the substrate102is insulative, the first electrode104and the second electrode106can be located on the first surface101of the substrate102directly. The sound wave generator108can be in contact with the first surface101of the substrate102or spaced from the first surface101of the substrate102with the first electrode104and the second electrode106. That is, part of the sound wave generator108is suspended by the first electrode104and the second electrode106and free of contact with any other surface.

The shape of the substrate102is not limited, such as round, square, or rectangle. The first surface and the second surface of the substrate102can be flat or curved. The size of the substrate102can be selected according to need. The area of the substrate102can be in a range from about 25 square millimeters to about 100 square millimeters, such as about 40 square millimeters, about 60 square millimeters, or about 80 square millimeters. The thickness of the substrate102can be in a range from about 0.2 millimeters to about 0.8 millimeters. Thus, the speaker100can meet the demand for miniaturization of the electronic devices, such as mobile phones, computers, headsets, or walkman. The material of the substrate102is not limited and can be made of flexible materials or rigid materials. In one embodiment, the resistance of the substrate102is greater than the resistance of the sound wave generator108. If the sound wave generator108is in contact with the first surface of the substrate102, the substrate102should be made of material with a certain heat-insulating property so that the heat produced by the sound wave generator108will not be absorbed by the substrate102too quickly. The material of the substrate102can be glass, ceramic, quartz, diamond, polymer, silicon oxide, metal oxide, or wood. In one embodiment, the substrate102is a square glass plate with a thickness of about 0.6 millimeters and a side length of about 0.8 millimeters. The first surface can be flat.

The sound wave generator108has a very small heat capacity per unit area. The heat capacity per unit area of the sound wave generator108is less than 2×10−4J/cm2*K. The sound wave generator108can be a conductive structure with a small heat capacity per unit area and a small thickness. The sound wave generator108can have a large specific surface area for generating pressure oscillation in the surrounding medium by the temperature waves generated by the sound wave generator108. The term “surrounding medium” means the medium outside of the sound wave generator108, and does not include the medium inside the sound wave generator108. If the sound wave generator108includes carbon nanotubes, the “surrounding medium” does not include the medium inside each carbon nanotube. The sound wave generator108can be a free-standing structure. The term “free-standing” includes, but is not limited to, a structure that does not have to be supported by a substrate and can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. The suspended part of the sound wave generator108will have more sufficient contact with the surrounding medium (e.g., air) to have heat exchange with the surrounding medium from both sides of the sound wave generator108. The sound wave generator108is a thermoacoustic film.

The sound wave generator108can be or include a free-standing carbon nanotube structure. The thickness of the carbon nanotube structure may range from about 0.5 nanometers to about 1 millimeter. If the thickness of the carbon nanotube structure is less than 10 micrometers, the carbon nanotube structure has good light transparency. The carbon nanotubes in the carbon nanotube structure are combined by van der Waals attractive force therebetween so that the carbon nanotube structure is free standing and can have at least a part be suspended. The carbon nanotube structure has a large specific surface area (e.g., above 30 m2/g). The larger the specific surface area of the carbon nanotube structure, the smaller the heat capacity per unit area will be. The smaller the heat capacity per unit area, the higher the sound pressure level of the sound produced by the sound wave generator108.

The carbon nanotube structure can include at least one carbon nanotube film, a plurality of carbon nanotube wires, or a combination of carbon nanotube film and the plurality of carbon nanotube wires. The carbon nanotube film can be a drawn carbon nanotube film formed by drawing a film from a carbon nanotube array that is capable of having a film drawn therefrom. The heat capacity per unit area of the drawn carbon nanotube film can be less than or equal to about 1.7×10−6J/cm2*K. The drawn carbon nanotube film can have a large specific surface area (e.g., above 100 m2/g). In one embodiment, the drawn carbon nanotube film has a specific surface area in the range of about 200 m2/g to about 2600 m2/g. In one embodiment, the drawn carbon nanotube film is a pure carbon nanotube structure consisting of a plurality of carbon nanotubes, and has a specific weight of about 0.05 g/m2.

The thickness of the drawn carbon nanotube film can be in a range from about 0.5 nanometers to about 100 nanometers. If the thickness of the drawn carbon nanotube film is small enough (e.g., smaller than 10 μm), the drawn carbon nanotube film is substantially transparent.

Referring toFIG. 2, the drawn carbon nanotube film includes a plurality of successive and oriented carbon nanotubes joined end-to-end by van der Waals attractive force therebetween. The carbon nanotubes in the drawn carbon nanotube film can be substantially oriented along a single direction and substantially parallel to the surface of the carbon nanotube film. Furthermore, an angle β can exist between the oriented direction of the carbon nanotubes in the drawn carbon nanotube film and the extending direction of the plurality of grooves1222, with 0≦β≦90°. As can be seen inFIG. 2, some variations can occur in the drawn carbon nanotube film. The drawn carbon nanotube film is a free-standing film. The drawn carbon nanotube film can be formed by drawing a film from a carbon nanotube array that is capable of having a carbon nanotube film drawn therefrom.

The carbon nanotube structure can include more than one carbon nanotube film. The carbon nanotube films in the carbon nanotube structure can be coplanar and/or stacked. Coplanar carbon nanotube films can also be stacked one upon other coplanar films. Additionally, an angle can exist between the orientation of carbon nanotubes in adjacent films, stacked and/or coplanar. Adjacent carbon nanotube films can be combined by only the van der Waals attractive force therebetween without the need of an additional adhesive. The number of the layers of the carbon nanotube films is not limited. However, as the stacked number of the carbon nanotube films increases, the specific surface area of the carbon nanotube structure will decrease. A large enough specific surface area (e.g., above 30 m2/g) must be maintained to achieve an acceptable acoustic volume. An angle θ between the aligned directions of the carbon nanotubes in the two adjacent drawn carbon nanotube films can range from about 0 degrees to about 90 degrees. Spaces are defined between two adjacent carbon nanotubes in the drawn carbon nanotube film. If the angle θ between the aligned directions of the carbon nanotubes in adjacent drawn carbon nanotube films is larger than 0 degrees, a microporous structure is defined by the carbon nanotubes in the sound wave generator108. The carbon nanotube structure in an embodiment employing these films will have a plurality of micropores. Stacking the carbon nanotube films will add to the structural integrity of the carbon nanotube structure.

In one embodiment, the sound wave generator108is a single drawn carbon nanotube film drawn from the carbon nanotube array and suspended by the first electrode104and the second electrode106. The drawn carbon nanotube film can be attached on the first electrode104and the second electrode106by the inherent adhesive nature of the drawn carbon nanotube film or by a conductive bonder. The carbon nanotubes of the drawn carbon nanotube film substantially extend from the first electrode104to the second electrode106. The drawn carbon nanotube film has a thickness of about 50 nanometers, and has a transmittance of visible light in a range from 67% to 95%.

The carbon nanotube wire can be untwisted or twisted. Treating the drawn carbon nanotube film with a volatile organic solvent can form the untwisted carbon nanotube wire. Specifically, the organic solvent, such as ethanol, methanol, acetone, ethylene dichloride, or chloroform is applied to soak the entire surface of the drawn carbon nanotube film. During the soaking, adjacent parallel carbon nanotubes in the drawn carbon nanotube film will bundle together, caused by the surface tension of the organic solvent as it volatilizes, and thus, the drawn carbon nanotube film will be shrunk into untwisted carbon nanotube wire. Referring toFIG. 3, the untwisted carbon nanotube wire includes a plurality of carbon nanotubes substantially oriented along one direction (i.e., a direction along the length of the untwisted carbon nanotube wire). The carbon nanotubes are substantially parallel to the axis of the untwisted carbon nanotube wire. More specifically, the untwisted carbon nanotube wire includes a plurality of successive carbon nanotube segments joined end to end by van der Waals attractive force therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes substantially parallel to each other, and combined by van der Waals attractive force therebetween. The carbon nanotube segments can vary in width, thickness, uniformity, and shape. Length of the untwisted carbon nanotube wire can be arbitrarily set as desired. A diameter of the untwisted carbon nanotube wire ranges from about 0.5 nm to about 100 μm.

The twisted carbon nanotube wire can be formed by twisting a drawn carbon nanotube film using a mechanical force to turn the two ends of the drawn carbon nanotube film in opposite directions. Referring toFIG. 4, the twisted carbon nanotube wire includes a plurality of carbon nanotubes helically oriented around an axial direction of the twisted carbon nanotube wire. More specifically, the twisted carbon nanotube wire includes a plurality of successive carbon nanotube segments joined end to end by van der Waals attractive force therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes substantially parallel to each other, and combined by van der Waals attractive force therebetween. A length of the carbon nanotube wire can be set as desired. A diameter of the twisted carbon nanotube wire can be from about 0.5 nm to about 100 μm. Further, the twisted carbon nanotube wire can be treated with a volatile organic solvent after being twisted. After being soaked by the organic solvent, the adjacent paralleled carbon nanotubes in the twisted carbon nanotube wire will bundle together, caused by the surface tension of the organic solvent when the organic solvent volatilizes. The specific surface area of the twisted carbon nanotube wire will decrease, while the density and strength of the twisted carbon nanotube wire will increase. The deformation of the sound wave generator110can be avoided during operation, and the degree of distortion of the sound wave can be reduced.

The first electrode104and the second electrode106are electrically connected to the sound wave generator108and used to input audio signal to the sound wave generator108. The audio signal is inputted into the carbon nanotube structure through the first electrode104and the second electrode106. The first electrode104and the second electrode106can be located on the first surface of the substrate102or on two supports (not shown) on the substrate102. The first electrode104and the second electrode106are made of conductive material. The shape of the first electrode104or the second electrode106is not limited and can be lamellar, rod, wire, and block, among other shapes. A material of the first electrode104or the second electrode106can be metals, conductive paste, conductive adhesives, carbon nanotubes, and indium tin oxides, among other conductive materials. The first electrode104and the second electrode106can be metal wire or conductive material layers, such as metal layers formed by a sputtering method, or conductive paste layers formed by a method of screen-printing. In one embodiment, the first electrode104and the second electrode106are two substantially parallel conductive paste layers.

The shell200is used to protect the speaker100so that the carbon nanotube structure would not be damaged because the strength of the carbon nanotube film is relatively low. The shape and size of the shell200is not limited. The shell200defines at lease one hole210allowing the sounds produced by the speaker100to transmit outside of the shell200. In one embodiment, the shell200includes a planar plate202and a housing204located on a surface of the plate202. The speaker100is located on the plate202and in the housing204. The carbon nanotube structure sound wave generator108is located between the substrate102and the hole210, and the sound wave generator108has a surface opposite to the hole210.

The plate202can be a glass plate, a ceramic plate, a printed circuit board (PCB), a polymer plate, or a wood plate. The plate202is used to support and fix the speaker100. The shape and size of the plate202is not limited. The size of the plate202is greater than the size of the speaker100. The area of the plate202can be in a range from about 36 square millimeters to about 150 square millimeters, such as 49 square millimeters, 64 square millimeters, 81 square millimeters, or 100 square millimeters. The thickness of the plate202can be in a range from about 0.5 millimeters to about 5 millimeters, such as 1 millimeter, 2 millimeters, 3 millimeters, or 4 millimeters. The housing204has a side wall206and a bottom wall208connected to the side wall206. The side wall206is curved to form a hollow structure with a cross section in various shapes such as round, square, or rectangle. The bottom wall208defines a plurality of holes210. The shape and size of the housing204can be selected according to need. The size of the housing204is a little greater than the size of the speaker100. The housing204can be fixed on the plate202with an adhesive, or installed on the plate202with a fastener. The material of the housing204can be glass, ceramic, polymer, or metal. In one embodiment, the plate202is a PCB, and the housing204is a metal bucket with a plurality of holes210on the bottom wall208. The housing204is spaced from the speaker100.

The shell200can further includes two connectors212on the side wall206or plate202. The two connectors212can be located on the same side or a different side of the shell200. One of the two connectors212is electrically connected to the first electrode104and the other one is electrically connected to the second electrode106. When the two connectors212are pins, the pins can be inserted into the holes of the PCB of the electronic device using the thermoacoustic chip10A to electrically connect the speaker100to an external circuit. If the two connectors212are pads, the pads can be welded with the pads of the PCB of the electronic device using the thermoacoustic chip10A to electrically connect the speaker100to an external circuit. In one embodiment, the two connectors212are pins and located on the bottom surface of the plate202and electrically connected to the first electrode104and the second electrode106via wires110.

Referring toFIG. 5, a thermoacoustic chip10B of a second embodiment is shown. The thermoacoustic chip10B includes a plurality of speakers100and a shell200. The shell200defines a plurality of spaces to accommodate and protect the plurality of speakers100.

The thermoacoustic chip10B is similar to the thermoacoustic chip10A above except that the shell200includes a common plate202and a plurality of housings204located on a surface of the plate202, the plurality of speakers100are located on the plate202, and each of the plurality of speakers100is located in one of the plurality of housings204.

Furthermore, the shell200includes a plurality of connectors212. Each two of the plurality of connectors212are located corresponding to one of the plurality of speakers100and electrically connected to the first electrode104and the second electrode106of the corresponding one of the plurality of speakers100. The plurality of speakers100can be controlled by a controlling circuit to produce sound simultaneously or according to a phase difference. If the plurality of speakers100are electrically connected in parallel or in series with the PCB plate202, the plurality of speakers100can use only two connectors212.

Referring toFIG. 6, a thermoacoustic chip10C of a third embodiment is shown. The thermoacoustic chip10C includes a plurality of speakers100and a shell200. The shell200defines a space to accommodate and protect the plurality of speakers100. The thermoacoustic chip10C is similar to the thermoacoustic chip10A above except that the plurality of speakers100are located together on the plate202and in the same housing204.

Referring toFIG. 7, a thermoacoustic chip20A of a fourth embodiment is shown. The thermoacoustic chip20A includes a speaker100and a shell200. The shell200defines a space to accommodate and protect the speaker100.

The thermoacoustic chip20A is similar to the thermoacoustic chip10A above except that the shell200includes the plate202defining a first recess214and a cover216covering the first recess214, and the speaker100is located in the first recess214. The cover216has a plurality of holes210. The cover216can be a metal mesh, fiber net, or a metal plate with a plurality of through holes, a glass plate with a plurality of through holes, a polymer plate with a plurality of through holes, or a ceramic plate with a plurality of through holes. The first recess214can be formed by punching, etching, or stamping. In one embodiment, the plate202is a PCB, and the cover216is a metal mesh suspended above the first recess214. Two connectors212can be located on the side surface or bottom surface of the plate202.

Referring toFIG. 8, a thermoacoustic chip20B of a fifth embodiment is shown. The thermoacoustic chip20B includes a plurality of speakers100and a shell200. The shell200defines a plurality of spaces to accommodate and protect the plurality of speakers100.

The thermoacoustic chip20B is similar to the thermoacoustic chip20A above except that the plate202defines a plurality of first recesses214on the same surface of the plate202, and each of the plurality of speakers100is located in one of the plurality of first recesses214, and the plurality of first recesses214are covered by a common cover216.

Referring toFIG. 9, a thermoacoustic chip20C of a sixth embodiment is shown. The thermoacoustic chip20C includes a plurality of speakers100and a shell200. The shell200defines a space to accommodate and protect the plurality of speakers100. The thermoacoustic chip20C is similar to the thermoacoustic chip20A above except that the plurality of speakers100are located in the same first recesses214.

Referring toFIG. 10, a thermoacoustic chip30A of a seventh embodiment is shown. The thermoacoustic chip30A includes a speaker100D and a shell200. The shell200defines a space to accommodate and protect the speaker100D. <Change100A to100D inFIG. 10. This is different than speaker100because100has a substrate102><Ok, done!>

The thermoacoustic chip30A is similar to the thermoacoustic chip10A above except that the speaker100D only includes a first electrode104, a second electrode106, and a sound wave generator108, and the two connectors212are located on two different side of the shell200. In one embodiment, the first electrode104and the second electrode106are located on the surface of the plate202directly, and the sound wave generator108is suspended over the first electrode104and the second electrode106. That is, the speaker100D omits the substrate102and has a simple structure. The plate202is insulated. If the plate202is electrically conductive, an insulative layer would need to be coated on the plate202.

Referring toFIG. 11, a thermoacoustic chip30B of an eighth embodiment is shown. The thermoacoustic chip30B includes a speaker100A and a shell200. The shell200defines a space to accommodate and protect the speaker100A.

The thermoacoustic chip30B is similar to the thermoacoustic chip20A above except that the speaker100A only includes a first electrode104, a second electrode106, and a sound wave generator108, and the two connectors212are located on two different corners of the plate202. In one embodiment, a depression2142is formed on the bottom surface of the first recess214, and the sound wave generator108is suspended over the depression2142. The first electrode104and the second electrode106are located on the surface of the sound wave generator108. That is, two ends of the sound wave generator108are sandwiched between the electrode104,106and the bottom surface of the first recess214.

Referring toFIG. 12, a thermoacoustic chip40A of a ninth embodiment is shown. The thermoacoustic chip40A includes a speaker100B, a shell200, and an integrated circuit (IC) chip120. The shell200defines a space to accommodate and protect the speaker100B and the IC chip120.

The thermoacoustic chip40A is similar to the thermoacoustic chip20A above except that it further includes the IC chip120located in the shell200and electrically connected to the speaker100B. In one embodiment, the substrate102defines a second recess114on the first surface101and a third recess116on the second surface103. The sound wave generator108is suspended over the second recess114, and the IC chip120located in the third recess116. The shell200can further include four connectors212. Two of the four connectors212are electrically connected to the IC chip120and used to supply driving voltage, and the other two of the four connectors212are electrically connected to the first electrode104and the second electrode10via the IC chip120and used to input audio signal.

The IC chip120can be located on any surface of the substrate102or embedded inside the substrate102. The IC chip120can be fixed on the substrate102with an adhesive, or installed on the substrate102with a fastener. The IC chip120includes a power amplification circuit for amplifying audio signal and a direct current (DC) bias circuit. Thus, the IC chip120can amplify the audio signal and input the amplified audio signal to the sound wave generator108. Simultaneously, the IC chip120can bias the DC electric signal. The shape and size of the IC chip120can be selected according to need. The internal structure of the IC chip120is simple because the IC chip120only has the functions of power amplification and DC bias. The area of the IC chip120is less than 1 square centimeters, such as 49 square millimeters, 25 square millimeters, or 9 square millimeters, to meet the demand for miniaturization of the thermoacoustic chip40A.

In one embodiment, the IC chip120is a packaged IC chip having a plurality of connectors, such as pins or pads. The IC chip120can be installed on the substrate102with the plurality of connectors or fixed on the substrate102by adhesive. The IC chip120is electrically connected to the first electrode104and the second electrode106via conductive wires (not shown) through holes on the substrate102. If the substrate102is conductive, the conductive wires should be coated with an insulative layer. In operation of the thermoacoustic chip40A, the IC chip120inputs an audio signal to the sound wave generator108and the sound wave generator108heats the surrounding medium intermittently according to the input signal to produce a sound by expansion and contraction of the surrounding medium.

Referring toFIGS. 13-14, a thermoacoustic chip40B of an tenth embodiment is shown. The thermoacoustic chip40B includes a speaker100C, a shell200, and an integrated circuit (IC) chip120. The shell200defines a space to accommodate and protect the speaker100C and the IC chip120.

The thermoacoustic chip40B is similar to the thermoacoustic chip40A above except that the substrate102is a silicon wafer, the IC chip120is directly integrated onto the substrate102, the substrate102has a concave-convex structure122on the first surface101, and the sound wave generator108is suspended over the concave-convex structure122. The speaker100C includes a plurality of first electrodes104and a plurality of second electrodes106.

The material of the substrate102can be monocrystalline silicon or polycrystalline silicon. Thus, the IC chip120can be formed on the substrate102by microelectronics processes, such as epitaxial process, diffusion process, ion implantation technology, oxidation process, lithography, etching, or thin film deposition. Thus, the size of the speaker100C can be smaller to meet the demand for miniaturization and integration of the electronic devices. The concave-convex structure122allows the heat produced by the IC chip120and the sound wave generator108to dissipate quickly and in time. The substrate102is near the second surface103. The concave-convex structure122can be formed by etching after the IC chip120is made on the substrate102. Then, the carbon nanotubes structure is placed on the concave-convex structure122. The first electrodes104and the second electrodes106are formed on the carbon nanotubes structure. Because the process of placing the carbon nanotubes structure and forming the first electrodes104and the second electrodes106do not involve a high temperature process, the IC chip120would not be damaged.

The concave-convex structure122defines a plurality of grooves1222and a plurality of bulges1220alternately located. The carbon nanotube structure has a first portion located on the top surface of the plurality of bulges1220and a second portion suspended above the plurality of grooves1222. The plurality of first electrodes104and the plurality of second electrodes106are alternately located on the top surface of the plurality of bulges1220. The plurality of first electrodes104and the plurality of second electrodes106can be located between the carbon nanotube structure and the plurality of bulges1220, or the carbon nanotube structure can be located between the plurality of bulges1220and the plurality of electrodes104,106. The plurality of first electrodes104are electrically connected to each other to form a comb-shaped first electrode, and the plurality of second electrodes106are electrically connected to each other to form a comb-shaped second electrode. As shown inFIG. 16, the tooth of the comb-shaped first electrode and the tooth of the comb-shaped second electrode are alternately located. Thus, the plurality of first electrodes104, the plurality of second electrodes106, and the sound wave generator108can form a plurality of thermoacoustic units electrically connected to each other in parallel, and the driving voltage of the sound wave generator108can be decreased.

The plurality of grooves1122can be substantially parallel with each other and extend substantially along the same direction. The length of the plurality of grooves1122can be smaller than or equal to the side length of the substrate102. The depth of the plurality of grooves1122can be in a range from about 100 micrometers to about 200 micrometers. The range of depth, the sound wave generator108having a certain distance away from the bottom surface of the groove1122, prevent the heat produced by the sound wave generator108from being absorbed by the substrate102too quickly, and simultaneously produce good sound at different frequencies. The cross section of each of the plurality of grooves1122along the extending direction can be V-shaped, rectangular, or trapezoid. The width (maximum span of the cross section) of each of the plurality of grooves1122can be in a range from about 0.2 millimeters to about 1 millimeter. The distance d1between adjacent grooves1122can range from about 20 micrometers to about 200 micrometers. Thus the first electrodes104and the second electrodes106can be printed on the plurality of bulges1120by screen printing. Thus sound wave generator108can be protected. Furthermore, a driven voltage of the sound wave generator108can be reduced to lower than 12V. In one embodiment, the driven voltage of the sound wave generator108is lower than or equal to 5V.

In one embodiment, the substrate102is a square monocrystalline silicon wafer with a side length of about 8 millimeters and a thickness of about 0.6 millimeters. The shape of the groove1122is a trapezoid. An angle α is defined between the sidewall and the bottom surface of the groove1122, is equal to the crystal plane angle of the substrate102. The width of the groove1122is about 0.6 millimeters, the depth of the groove1122is about 150 micrometers, the distance d1between adjacent grooves1122is about 100 micrometers, and the angle α is about 54.7 degrees.

Furthermore, an insulating layer118can be located on the first surface101of the substrate102. The insulating layer118can be a single-layer structure or a multi-layer structure. In one embodiment, the insulating layer118can be merely located on the top surfaces of the plurality of bulges1220. In another embodiment, the insulating layer118is a continuous structure, and attached on the entire first surface101. That is, the insulating layer118is located on the top surfaces of the plurality of bulges1220, and the side wall and bottom surface of the plurality of grooves1222. The insulating layer118covers the plurality of grooves1222and the plurality of bulges1220. The sound wave generator108is insulated from the substrate102by the insulating layer118. In one embodiment, the insulating layer118is a single-layer structure and covers the entire first surface101. The material of the insulating layer118can be SiO2, Si3N4, or a combination of them. The material of the insulating layer118can also be other insulating materials. The thickness of the insulating layer118can range from about 10 nanometers to about 2 micrometers, such as about 50 nanometers, about 90 nanometers, and about 1 micrometer. In one embodiment, the thickness of the insulating layer is a single SiO2layer with a thickness of about 1.2 micrometers.

In one embodiment, the sound wave generator108includes a plurality of carbon nanotube wires substantially parallel with and spaced from each other. The extending direction of the plurality of carbon nanotube wires and the extending direction of the plurality of grooves1222are substantially perpendicular with each other. Each of the plurality of carbon nanotube wire includes a plurality of carbon nanotubes substantially oriented along a direction along the length of the carbon nanotube wire. Part of the plurality of carbon nanotube wires are suspended over the plurality of grooves1222. That is, the suspended parts of the plurality of carbon nanotube wires are free of contact with any other surface. The distance between adjacent carbon nanotube wires can be in a range from about 1 micrometer to about 200 micrometers. In one embodiment, the distance between adjacent carbon nanotube wires is in a range from about 50 micrometers to about 150 micrometers. In one embodiment, the distance between adjacent carbon nanotube wires is about 120 micrometers, and the diameter of the plurality of carbon nanotube wires is about 1 micrometer.

In one embodiment, the plurality of carbon nanotube wires can be made by the following steps:

step (10), laying a carbon nanotube film on the first electrode104and the second electrode106, wherein the carbon nanotubes of the carbon nanotube film extend substantially along a direction perpendicular with the extending direction of the first electrode104and the second electrode106;

step (12), forming a plurality of carbon nanotube belts in parallel with and spaced from each other by cutting the carbon nanotube film along the extending direction of the carbon nanotubes of the carbon nanotube film by a laser; and

step (13), shrinking the plurality of carbon nanotube belts by treating with organic solvent, wherein the organic solvent can be dripped on the plurality of carbon nanotube belts.

In step (12), the width of the carbon nanotube belt is in a range from about 20 micrometers to about 50 micrometers so that the carbon nanotube belt can be shrunk into carbon nanotube wire completely. If the width of the carbon nanotube belt is too great, after the shrinking process, the carbon nanotube wire will have rips therebetween which will affect the sound produced by the carbon nanotube wire. If the width of the carbon nanotube belt is too small, the strength of the carbon nanotube wire will be too small which will affect the life span of the carbon nanotube wire.

In step (13), the plurality of carbon nanotube belts is shrunk to form the plurality of carbon nanotube wires (the dark portion is the substrate102, and the white portions are the first electrode104and the second electrode106) as shown inFIG. 15. The two opposite ends of the plurality of carbon nanotube wires are electrically connected to the first electrode104and the second electrode106. The diameter of the carbon nanotube wires ranges from about 0.5 micrometers to about 3 micrometers. In one embodiment, the width of the carbon nanotube belt is about 30 micrometers, the diameter of the carbon nanotube wire is about 1 micrometer, and the distance between adjacent carbon nanotube wires is about 120 micrometers.

After treating the carbon nanotube belts, the driven voltage between the first electrode104and the second electrode106can be reduced. During the shrinking process, a part of the plurality of carbon nanotube belts attached on the plurality of bulges1220will not be shrunk by the organic solvent so that the plurality of carbon nanotube wires have a greater contact surface with the first electrode104and the second electrode106. Thus after being shrunk, this part of the plurality of carbon nanotube wires can be firmly fixed on the bulges104, and electrically connected to the first electrode106and the second electrode116. Furthermore, after the shrinking process, the suspended part of the carbon nanotube wires are tightened and can prevent the sound produced by the carbon nanotube wire from being distorted.

Referring toFIGS. 17-18, the sound effect of the speaker100C of the thermoacoustic chip40B is related to the depth of the plurality of grooves1222. In one embodiment, the depth of the plurality of grooves1222ranges from about 100 micrometers to about 200 micrometers. Thus, in the frequency band for which the human can hear, the thermoacoustic chip60have excellent thermal wavelength. Therefore, the thermoacoustic chip60still has good sound effects depsite its small size.

In use, the thermoacoustic chip can be located inside of the electronic devices directly, such as mobile phones, computers, headsets or walkman, and electrically connected to the circuit of the electronic devices easily.

It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. The above-described embodiments illustrate the disclosure but do not restrict the scope of the disclosure.