ELECTRO-ACOUSTIC TRANSDUCER

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from Korean Patent Application No. 10-2013-0141752, filed on Nov. 20, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field

The present disclosure relates to an electro-acoustic transducer, and more particularly, to a micro-machined electro-acoustic transducer.

2. Description of the Related Art

An electro-acoustic transducer is a device that converts electric energy into acoustic energy or vice versa, and may include an ultrasonic transducer, a microphone, and the like. A micro-machined electro-acoustic transducer includes a micro-electro-mechanical system (MEMS), and a typical example thereof is a micro-machined ultrasonic transducer (MUT). The MUT is a device that converts electric signals into ultrasonic signals or vice versa, and may be classified into a piezoelectric MUT (pMUT), a capacitive MUT (cMUT), a magnetic MUT (mMUT), and the like, according to a converting method of the MUT. Generally, the pMUT has been mainly used, but recently, as the cMUT has been developed, cMUT applications have increased. The cMUT is advantageous in terms of the transmission and reception of broadband signals, integrated manufacturing by using semiconductor processing, and integration with electric circuits. The cMUT is preferred to manufacture medical diagnostic imaging devices and sensors.

Recently, ultrasound devices having broadband characteristics have been actively developed due to an increased demand for various methods of obtaining ultrasound images, such as B-mode imaging, Doppler imaging, harmonic imaging, photoacoustic imaging, and the like. Such ultrasound devices are also necessary for diagnosing organs having different sizes and depth, such as the abdomen, heart, and thyroid. Although the cMUT may transmit and receive signals of a broader frequency band than a general pMUT, the cMUT may not be capable of receiving signals in the entire frequency band. Therefore, methods of combining cells with different resonant frequencies to manufacture electro-acoustic transducers with broadband characteristics are under development.

SUMMARY

Exemplary embodiments may address at least the above problems and/or disadvantages and other disadvantages not described above. Also, the exemplary embodiments are not required to overcome the disadvantages described above, and an exemplary embodiment may not overcome any of the problems described above.

One or more of exemplary embodiments provide a micro-machined electro-acoustic transducer.

According to an exemplary embodiment, an electro-acoustic transducer includes a plurality of elements. Each of the plurality of elements includes a plurality of cells, and the plurality of cells include at least two membranes that have different thicknesses.

Respective frequency bands of the plurality of elements may be broader than respective frequency bands of the plurality of cells of the plurality of elements.

The plurality of cells may each include a substrate, a support that has a cavity and is provided on the substrate, a membrane provided to cover the cavity, and an electrode provided on a top surface of the membrane.

The substrate may include a conductive material. For example, the substrate may include low resistivity silicon having a specific electrical resistance of 0.01 Ωcm or less. An insulating layer may be further provided on the substrate. The membrane may include, for example, silicon.

The plurality of elements and the plurality of cells may be two-dimensionally arrayed. The plurality of cells may have the same size. The electro-acoustic transducer may include a capacitive micro-machined ultrasound transducer (cMUT).

According to an exemplary embodiment, an element of an electro-acoustic transducer, the element includes a plurality of cells, and the plurality of cells may include at least two membranes that have different thicknesses.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become more apparent by describing certain exemplary embodiments, with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a transducer chip of an electro-acoustic transducer according to an exemplary embodiment;

FIG. 2 is a plan view of an element illustrated in FIG. 1;

FIG. 3 is a cross-sectional view of the element that is cut along the line III-III′ of FIG. 2;

FIG. 4 is a perspective view of membranes illustrated in FIG. 3;

FIG. 5 is a graph for comparing a frequency characteristic of an electro-acoustic transducer that is configured of cells including membranes that have the same thickness, and an electro-acoustic transducer having two types of cells including membranes that have different thickness;

FIG. 6 is a plan view of a modified example of the element illustrated in FIG. 2;

FIG. 7 is a perspective view of membranes that configure cells illustrated in FIG. 6; and

FIG. 8 is a cross-sectional view of the element of the electro-acoustic transducer, according to an exemplary embodiment.

DETAILED DESCRIPTION

Certain exemplary embodiments are described in greater detail below with reference to the accompanying drawings.

In the following description, the same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of exemplary embodiments. Thus, it is apparent that exemplary embodiments can be carried out without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure exemplary embodiments with unnecessary detail.

It will be understood that when a predetermined material layer is referred to as being “formed on” a substrate or another layer, the predetermined material layer can be directly or indirectly formed on the substrate or the other layer. That is, an intervening layer may be present between the predetermined layer and the substrate or the other layer. It will be understood that respective materials consisting layers of the embodiments described below are merely provided as examples, and accordingly, other materials may be used.

Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

FIG. 1 is a plan view of a transducer chip 100 of an electro-acoustic transducer according to an exemplary embodiment of the present invention. The electro-acoustic transducer may include a plurality of transducer chips 100. FIG. 1 illustrates the transducer chip 100 among the plurality of transducer chips 100 that are included in the electro-acoustic transducer. The electro-acoustic transducer may be, for example, a capacitive micro-machined ultrasound transducer (cMUT). Referring to FIG. 1, the transducer chip 100 may include a plurality of elements 118 that are arrayed two-dimensionally. The elements 118 may be driven independently. The elements 118 may have the same frequency characteristic, but an exemplary embodiment is not limited to, and at least some of the elements 118 may have different frequency characteristics. Also, each of the elements 118 includes a plurality of cells 111 that are arrayed two-dimensionally. The cells 111 may have the same size.

FIG. 2 is a plan view of one of the elements 118 illustrated in FIG. 1.

Referring to FIG. 2, an element 110 includes the plurality of cells 111 that are arrayed two-dimensionally. FIG. 2 illustrates a case where the element 110 includes nine cells 111 that are arrayed to form a square. However, this case is merely provided as an example, and the number and an array shape of the cells 111 may be modified in various ways. The element 110 may include at least one first cell 111a and at least one second cell 111b which have different frequency characteristics (i.e., resonant frequency). FIG. 2 illustrates a case where the element 110 includes six first cells 111a and three second cells 111b. The first and second cells 111a and 111b are alternately arrayed in the X-direction. However, this case is merely an example, and the number and an array form of the first and second cells 111a and 111b may be modified in various ways. As described below, the first and second cells 111a and 111b may respectively include first and second membranes 115a and 115b which have different thicknesses. Accordingly, when the element 110 of the electro-acoustic transducer is configured by using the first and second cells 111a and 111b which respectively include the first and second membranes 115a and 115b having different thicknesses, a frequency band of the element 110 may be broader than respective frequency bands of the first and second cells 111a and 111b. Sizes of the first and second cells 111a and 111b configuring the element 110 may be the same, i.e., as seen in a top view of FIG. 2. That is, respective radiuses of the first and second cells 111a and 111b may be the same.

FIG. 3 is a cross-sectional view of the element 110 that is cut along the line III-III′ of FIG. 2. FIG. 4 is a perspective view of the first and second membranes 115a and 115b illustrated in FIG. 3.

Referring to FIGS. 3 and 4, the first cell 111a includes a substrate 112, a support 114 provided on the substrate 112, the first membrane 115a provided on the support 114, and an electrode 116 provided on the first membrane 115a. The substrate 112 may function as a lower electrode. Therefore, the substrate 112 may include a conductive material. For example, the substrate 112 may include, but is not limited to, low resistivity silicon having a specific electrical resistance of about 0.01 Ωcm or less. An insulating layer 113 formed of, for example, silicon oxide, may be further provided on a top surface of the substrate 112.

The support 114 including a cavity 120 is provided on the insulating layer 113. The support 114 may include, but is not limited to, silicon oxide. The first membrane 115a is provided on the support 114 to cover the cavity 120. The first membrane 115a may include, but is not limited to, silicon. In this case, the first membrane 115a may have a first thickness t1 that differs from a second thickness t2 of the second membrane 115b that is described below. Also, the electrode 116 is provided on a top surface of the first membrane 115a. The electrode 116 functions as an upper electrode, and may include, but is not limited to, metal.

The second cell 111b includes the substrate 112, the support 114 that includes the cavity 120 and is provided on the substrate 112, the second membrane 115b provided on the support 114 to cover the cavity 120, and the electrode 116 provided on the second membrane 115b. Since the substrate 112, the support 114, and the electrode 116 are described above, descriptions thereof will be omitted. The second membrane 115b has the second thickness t2 that differs from the first thickness t1 of the first membrane 115a. FIG. 3 illustrates a case where the second thickness t2 of the second membrane 115b is less than the first thickness t1 of the first membrane 115a. The second membrane 115b may include the same material as the first membrane 115a, such as silicon. FIG. 4 illustrates a case where the first and second membranes 115a and 115b having different thicknesses are alternately arrayed in the X-direction.

As described above, the element 110 of the electro-acoustic transducer is configured by using the at least one first cell 111a and the at least one second cell 111b which have different frequency characteristics. In this case, the first and second cells 111a and 111b respectively include the first and second membranes 115a and 115b which have different thicknesses. Therefore, the electro-acoustic transducer has a broadband frequency characteristic.

In general, a resonant frequency fc of a cell in a cMUT is defined by Equation 1.

$\begin{matrix} f_{c} = \frac{{(2.4)}^{2}}{2 π} \sqrt{\frac{Y_{o}}{12 ρ (1 - δ^{2})}} \frac{t_{n}}{a^{2}} & [Equation 1] \end{matrix}$

- where Y₀, ρ, and δ respectively indicate a Young's modulus, a density, and a Poisson's ratio of a membrane. Also, t_nand a respectively indicate a thickness of the membrane and a radius of the cell.

Referring to Equation 1, it may be understood that the resonant frequency f_cof the cell may be modified by changing the radius of the cell. Accordingly, an element of the electro-acoustic transducer having a broadband property may be manufactured by combining cells that have different resonant frequencies by changing the radius of the cell. In this case, however, not only it is difficult to uniformly dispose various sized cells in a limited area, but also, the cells may not be efficiently disposed. In an exemplary embodiment, the electro-acoustic transducer is manufactured by combining the first and second cells 111a and 111b that have different frequency characteristics by changing the respective thicknesses of the membranes. Accordingly, the electro-acoustic transducer has broadband frequency characteristics.

FIG. 5 is a graph for comparing a frequency characteristic of an electro-acoustic transducer having cells including membranes that have the same thickness and an electro-acoustic transducer having two types of cells including membranes that have different thickness. In FIG. 5, A1 is a line showing a frequency characteristic of an element having cells including membranes that have the first thickness t1, A2 is a line showing a frequency characteristic of an element having cells including membranes that have the second thickness t2 (<t1). It may be understood that a resonant frequency of the element including the cells including the membranes that have the first thickness t1 is higher than that of the element including the cells including the membranes that have the second thickness t2 (<t1). In addition, B is a line showing a frequency characteristic of an element that is manufactured by combining the cells including the membranes that have the first thickness t1 and the cells including the membranes that have the second thickness t2. When an element is manufactured by combining two cells having different resonant frequencies, frequency bands of the two cells overlap, and thus, the element has a frequency characteristic in a frequency band broader than respective frequency bands of the two cells. Accordingly, in an exemplary embodiment, the electro-acoustic transducer having a broadband frequency characteristic is manufactured by combining the at least one first cell 111a and the at least one second cell 111b that have different frequency properties by changing respective thicknesses of the membranes.

FIG. 2 illustrates a case where the first and second cells 111a and 111b which have different frequency properties and configure the element 110 of the electro-acoustic transducer are alternately arrayed in the X-direction. However, the embodiments of the present invention are not limited thereto, and the number and array form of the first and second cells 111a and 111b may be modified in various ways.

FIG. 6 is a plan view of an element 110′ which is a modified example of the element 110 illustrated in FIG. 2. FIG. 7 is a perspective view of first and second membranes 115′a and 115′b that configure a plurality of cells 111′ illustrated in FIG. 6.

Referring to FIGS. 6 and 7, the element 110′ of the electro-acoustic transducer includes the plurality of cells 111′ that are two-dimensionally arrayed. In this case, the element 110′ may include at least one first cell 111′a and at least one second cell 111′b that have different frequency characteristics. FIG. 6 illustrates a case where the element 110′ has five first cells 111′a and four second cells 111′b, which are alternately respectively arrayed in the X-direction and the Y-direction. The first cell 111′a includes the first membrane 115′a that has a first thickness t1, and the second cell 111′b includes the second membrane 115′b that has the second thickness t2. Accordingly, when the element 110′ of the electro-acoustic transducer is manufactured by combining the first and second cells 111′a and 111′b which have different frequency characteristics, a broadband frequency characteristic may be obtained as described above. The number and array shape of the first and second cells 111′a and 111′b are merely provided as an example in the description above, and the number and array shape may be modified in various ways.

FIG. 8 is a cross-sectional view of an element 210 of the electro-acoustic transducer, according to an exemplary embodiment. FIG. 8 illustrates a case where the element 210 includes first, second, and third cells 211a, 211b, and 211c which have different thicknesses. The element 210 may be one of a plurality of elements of the electro-acoustic transducer 100.

Referring to FIG. 8, the element 210 includes a plurality of cells 211 that are two-dimensionally arrayed. The number and array shape of the plurality of cells 211 in the element 210 may be modified in various ways. The element 210 may include at least one first cell 211a, at least one second cell 211b, and at least one third cell 211c which have different frequency characteristics (i.e., resonant frequency). The number and arrays of the first, second, and third cells 211a, 211b, and 211c may be modified in various ways.

The first, second, and third cells 211a, 211b, and 211c respectively include first, second, and third membranes 215a, 215b, and 215c which have different thicknesses. When the element 210 of the electro-acoustic transducer is configured of the first, second, and third cells 211a, 211b, and 211c which respectively include the first, second, and third membranes 215a, 215b, and 215c which have different thicknesses, a frequency band of the element 210 may be broader than respective frequency bands of the first, second, and third cells 211a, 211b, and 211c. Sizes of the first, second, and third cells 211a, 211b, and 211c that configure the element 210 may be the same. That is, respective radiuses of the first, second, and third cells 211a, 211b, and 211c may be the same.

The first cell 211a includes a substrate 212, a support 214 provided on the substrate 212, the first membrane 215a provided on the support 214, and an electrode 216 provided on the first membrane 215a. The substrate 212 may function as a lower electrode, and therefore, the substrate 112 may include a conductive material. For example, the substrate 212 may include, but is not limited to, low resistivity silicon having a specific electrical resistance of about 0.01 Ωcm or less. An insulating layer 213, which is formed of, for example, silicon oxide, may be further provided on a top surface of the substrate 212.

The support 214 including a cavity is provided on the insulating layer 213. The support 214 may include, but is not limited to, silicon oxide. The first membrane 215a is provided on the support 214 to cover the cavity 220. The first membrane 215a may include, but is not limited to, silicon. In this case, the first membrane 215a may have a first thickness t1 that differs from second and third thicknesses t2 and t3 of the second and third membranes 215b and 215c. Also, the electrode 216 is provided on a top surface of the first membrane 215a. The electrode 216 functions as an upper electrode, and may include, but is not limited to, metal.

The second cell 211b includes the substrate 212, the support 214 that includes the cavity 220 and is provided on the substrate 212, the second membrane 215b provided on the support 214 to cover the cavity 220, and the electrode 216 provided on the second membrane 215b. Since the substrate 212, the support 214, and the electrode 216 are described above, descriptions thereof will be omitted. The second membrane 215b has the second thickness t2 that differs from the first and third thicknesses t1 and t3 of the first and third membranes 215a and 215c. FIG. 8 illustrates a case where the second thickness t2 of the second membrane 215b is less than the first thickness t1 of the first membrane 215a. The second membrane 215b may include the same material as the first membrane 215a, such as silicon.

The third cell 211c includes the substrate 212, the support 214 that includes the cavity 220 and is provided on the substrate 212, the third membrane 215c that is provided on the support 214 to cover the cavity 220, and the electrode 216 provided on the third membrane 215c. Since the substrate 212, the support 214, and the electrode 216 are described above, descriptions thereof will be omitted. The third membrane 215c has the third thickness t3 that differs from the first and second thicknesses t1 and t2 of the first and second membranes 215a and 215b. FIG. 8 illustrates a case where the third thickness t3 of the third membrane 215c is less than the second thickness t2 of the second membrane 215b. The third membrane 215c may include the same material as the first and second membranes 215a and 215b, such as silicon.

As described above, in an exemplary embodiment, the element 210 of the electro-acoustic transducer is configured by using the first, second, and third cells 211a, 211b, and 211c which have different frequency characteristics. In this case, the first, second, and third cells 211a, 211b, and 211c respectively include the first, second, and third membranes 215a, 215b, and 215c which have different thicknesses. Therefore, when the element 210 of the electro-acoustic transducer is manufactured by combining the first, second, and third cells 211a, 211b, and 211c which have different frequency properties, a broadband frequency characteristic may be obtained, as described above. Although in the embodiment described above, the element 210 includes the first, second, and third cells 211a, 211b, and 211c which have different frequency characteristics, the embodiments of the present invention are not limited thereto and an element may include four or more cells that have different frequency characteristics

As described above, according to the one or more of the above embodiments of the present invention, when an electro-acoustic transducer is manufactured, a thickness of a membrane may be changed to manufacture cells that have different frequency characteristics, and then, the cells may be combined to manufacture an element having a broadband frequency characteristic. The electro-acoustic transducer that includes elements having broadband frequency characteristics may be used in ultrasound devices for obtaining ultrasound images by using various methods, such as B-mode imaging, Doppler imaging, harmonic imaging, photoacoustic imaging, and the like, and for diagnosing organs having different sizes and depth, such as the abdomen, heart, and thyroid.

It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.

The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.

ELECTRO-ACOUSTIC TRANSDUCER

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