JP2012019322A - Capacitor microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance broadband microphone with a narrow tolerance.SOLUTION: The microphone comprises capacitance type microphone dies 10a-10c each having a pair of counter electrodes, and a circuit die 20 in which an impedance conversion circuit performing impedance conversion of the output signal from the counter electrodes is formed. The counter electrodes of the plurality of microphone dies 10a-10c having the same shape are connected in parallel with each other, and contained in a package 30 together with the circuit die 20.

Description

  The present invention relates to a condenser microphone, and more particularly to a broadband microphone.

  Conventionally, there has been known a microphone that improves the S / N ratio by increasing the diameter of the diaphragm and obtains high-frequency characteristics using a diffraction effect due to the housing shape (for example, Non-Patent Documents 1 and 2). In addition, a technique is known in which MEMS microphones are arranged in an array, reflected ultrasonic waves from an object are received by each microphone, and the arrival direction of the reflected wave is detected by delay-adding the output signals of each microphone ( For example, Non-Patent Document 3). There is also known a configuration in which a plurality of pairs of counter electrodes are formed on one die and they are connected in parallel to improve the S / N ratio as one microphone.

Sanken Microphone: "Development of an ultra-wideband microphone for music recording", Journal of the Acoustical Society of Japan, Vol. 64, No. 11, 2008, pp.682-685 Kazuho Ono: “Broadband microphone”, Journal of the Acoustical Society of Japan, Vol. 64, No. 11, 2008, pp.656-660 Yoshifumi Watanabe (Panasonic Electric Works): "Ultrasonic sensor using MEMS and nanotechnology", Matsushita Electric Works Technical Report, Vol.53 No.2, 2005, pp.25-30

In Non-Patent Documents 1 and 2, since the area of the diaphragm is increased in order to increase sensitivity and improve the SN ratio, the outer dimensions of the microphone are increased. When the area of the diaphragm is increased, the resonance frequency of the diaphragm is shifted to a low frequency, and the sensitivity is rapidly decreased at a frequency higher than the resonance frequency. In order to improve this, it is necessary to apply a high tension to the diaphragm. However, the tension tends to decrease over time, and the sensitivity tends to decrease. Moreover, when the tension of the diaphragm is high, the vibration displacement with respect to a certain sound pressure becomes small. In a configuration in which a high bias voltage is supplied to increase sensitivity, versatility is reduced. Non-Patent Document 3 is a means for specifying the sound source direction, and is not a means for improving the SN ratio. Further, the array configuration is not specifically described. In a configuration in which a plurality of pairs of counter electrodes are formed on one die and they are connected in parallel, for example, depending on the performance of the individual counter electrodes, the characteristics of the microphone as a whole may vary.
It is an object of the present invention to provide a high-performance, narrow-tolerance broadband microphone.

  (1) A microphone for achieving the above object includes a capacitance type microphone die having a pair of counter electrodes, and a circuit die in which an impedance conversion circuit for impedance conversion of an output signal of the counter electrodes is formed. The counter electrodes of the plurality of microphone dies having the same shape are connected in parallel to each other and housed in a package together with the circuit die.

  According to the present invention, for each microphone die, the area of the diaphragm can be made small and light, so that the resonance frequency can be increased. Therefore, the microphone band can be widened. Further, the SN ratio can be improved by connecting in parallel a pair of counter electrodes formed on a plurality of microphone dies.

  In addition, although tolerance may occur in each microphone die, in the present invention, since a microphone die having a pair of counter electrodes is formed and then accommodated in the package, one package after the performance of each microphone die is inspected The combination of microphone dies accommodated in the can be determined. Therefore, the tolerance as a microphone can be kept small by the combination of the microphone dies. Specifically, for example, combining a microphone die with a higher value and a lower microphone die with respect to the median value indicating the performance of each microphone die reduces the tolerance of the microphones connected in parallel. Can do. For example, there is a large variation in performance between a microphone combined with only a microphone die higher than the median value and a microphone combined with only a microphone die lower than the median value. When a plurality of pairs of counter electrodes are formed on one die and they are connected in parallel, the combination of microphone dies cannot be freely changed as in the present invention, and thus the performance as one microphone can vary in this way. . However, according to the configuration of the present invention, since the combination can be changed according to the performance of the microphone die, the tolerance of the microphone can be narrowed.

  Further, in the present invention, the impedance conversion circuit is also housed in the same package together with a plurality of microphone dies, so that the influence of noise on the output signal can be reduced. Furthermore, since all the microphone dies have the same shape (joint), the manufacturing cost can be reduced. In addition, since all microphone dies have the same shape, the degree of freedom of design is high, such as the number of combinations of microphone dies to be housed in the package together with the impedance conversion circuit and the manner of arrangement.

  (2) In the microphone for achieving the above object, the shape of the microphone die in plan view may be a square shape. In this case, a bias for applying a bias voltage to one of the counter electrodes. Electrode pads are respectively disposed at corners at diagonal positions in the plan view of the microphone die, and an output side electrode pad connected to the other electrode of the counter electrodes is at least one remaining corner in the plan view. It may be arranged in the part.

  The microphone die of the present invention has a pair of counter electrodes, a vibrating electrode that vibrates by receiving sound waves and a stationary electrode that does not vibrate even when receiving sound waves, and the stationary electrodes of each microphone die are electrically connected to each other by a conductive wire. In addition, the counter electrodes are connected in parallel by electrically connecting the vibrating electrodes of the microphone dies with a conductive wire. A bias voltage is applied to one electrode side, and the other electrode is set as an output side. In this specification, viewing the microphone die from a direction perpendicular to the stationary electrode is referred to as a plan view.

  It is desirable that the conductive wire connecting the output side electrode pads be as short as possible in order to eliminate the influence of noise. It is desirable that the conductors connecting the bias electrode pads are short, but the conductors connecting the output electrode pads are more susceptible to noise than the conductors connecting the bias electrode pads, so the conductors connecting the output electrode pads are connected to each other. It is prioritized to be as short as possible. Therefore, if the corners provided with the output-side electrode pads are arranged so as to be close to the corners provided with the output-side electrode pads of the adjacent microphone dies (the direction of each microphone die is changed in plan view). ), The conductors connecting the output side electrode pads are shorter than when the corners where the output side electrode pads are provided are separated from each other (for example, when microphone dies are arranged in the same direction). can do.

  In addition, since the bias electrode pads are respectively provided at two corners having a diagonal relationship, even if the orientation of the microphone die in plan view is different by, for example, 90 °, one of the two is provided. These bias electrode pads and the bias electrode pad closer to the adjacent microphone die can be connected by a conductive wire. That is, in comparison with a configuration in which the bias electrode pads are provided only at one corner, or a configuration in which two bias electrode pads are provided at adjacent corners (a configuration not having a diagonal positional relationship), The length of the conducting wire to be connected can be shortened.

(3) In the microphone for achieving the above object, the shape of the microphone die in plan view may be a square.
When the configuration is such that bias electrode pads are provided at two corners in a diagonal relationship of a square microphone die in plan view, and output electrode pads are provided at at least one other corner, In addition to the effects described in (2), there are the following effects. That is, even if the orientation of the microphone die in plan view is different in units of 90 °, for example, the corner where one of the two bias electrode pads is provided is the bias of one of the adjacent microphone dies. It is always adjacent to the corner where the electrode pad is provided. For this reason, the bias electrode pads are connected to each other as compared with a configuration in which the bias electrode pads are provided only at one corner, or a configuration in which two bias electrode pads are provided at adjacent corners (a configuration not having a diagonal relationship). The length of the conducting wire can be shortened. Further, since the shape of the microphone die in plan view is square, the direction of the microphone die in plan view can be freely changed in units of 90 ° within a space limited in advance in plan view.

(1A) is a top view according to the first embodiment, and (1B) is a cross-sectional view thereof. Explanatory drawing about noise current. The top view concerning other embodiments of the present invention. The top view concerning other embodiments of the present invention.

  Hereinafter, embodiments of the present invention will be described in the following order with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.

1. First Embodiment FIG. 1 is a diagram showing a microphone 1 as an embodiment of the present invention. For convenience of description, orthogonal xyz axes are defined as shown in FIG. The microphone 1 includes a semiconductor package 30, a circuit LSI 20 (corresponding to a circuit die), and three microphone dies 10a to 10c. The semiconductor package 30 includes a box-shaped package body 31 and a lid 32. FIG. 1A is a top view of the microphone 1 with the lid 32 omitted, and FIG. 1B is a simplified cross-sectional view taken along the line 1B-1B in FIG. 1A. The lid 32 is formed with a plurality of mesh-like acoustic holes H1, which are through holes that connect the external space and the internal space of the package 30. A conductive material is used for at least a part of the lid 32 to provide a function as an electromagnetic shield. The lid 32 is water repellent. The microphone dies 10 a to 10 c and the circuit LSI 20 are accommodated in the semiconductor package 30. Each microphone die is a die formed by using a semiconductor device manufacturing process, and the bottom surface 101 of each die is fixed to the bottom of the package body 31 via an adhesive layer (not shown).

  The microphone dies 10a to 10c have the same shape, and the outer shape of the die in plan view, that is, the xy plane is a square. Each microphone die is formed with a plate P, a diaphragm D, an air chamber BC, and the like. The plate P is formed with a plurality of through holes H2 for propagating sound waves to the diaphragm D. Since the plate P is rigid enough not to vibrate in the acoustic space SS through which sound waves propagate, the plate P is formed thicker than the diaphragm D. The plate P is entirely made of a conductive material, and forms a stationary electrode. Only part of the plate P may form a stationary electrode. The spacer S is coupled to the edge of the diaphragm D and the edge of the plate P, and a gap is formed between the diaphragm D and the plate P. The spacer S has an insulating property and insulates the diaphragm D and the plate P from each other.

  The diaphragm D separates the acoustic space SS and the air chamber BC. The acoustic space SS and the air chamber BC may be airtightly separated by a diaphragm D, or may be connected by a passage such as a slit, trench, hole, or interlayer gap having high acoustic resistance. The diaphragm D needs to be flexible enough to bend and vibrate upon receiving a sound wave within the detection target range, so that the diaphragm D is formed thinner than the plate P. Since the entire diaphragm D is made of a conductive material, the diaphragm D forms a vibrating electrode together with a stationary electrode formed by the plate P. That is, each microphone die is formed with a pair of counter electrodes composed of a plate P and a diaphragm D. Only a part of the diaphragm D may form the vibrating electrode. The support part B supports the diaphragm D. An opening is formed in the support portion B. The air chamber BC is a space inside the opening, that is, a space surrounded by the diaphragm D, the support portion B, and the bottom portion of the package body 31.

  In the microphone die 10a, the plate P is electrically connected to the output-side electrode pad 12a by wiring. One output-side electrode pad 12a is formed on the support portion B, which is a corner portion of each microphone die whose outer plan view is square. Similarly, in the microphone die 10b, the plate P is connected to the output-side electrode pad 12b. The same applies to the microphone die 10c. In the microphone die 10a, the diaphragm D is electrically connected to the bias electrode pad 11a1 and the bias electrode pad 11a2 by wiring formed on the surface of the support portion B. The bias electrode pads 11a1 and 11a2 are formed at two corners on the support portion B, which are diagonal corners of the microphone die 10a in plan view. Bias electrode pads 11b1, 11b2, and 11c1 and 11c2 are similarly formed on the microphone dies 10b and 10c, and are connected to the diaphragm D of the microphone die on which each is formed.

  The circuit LSI 20 is formed with a charge pump circuit (not shown) for supplying a bias voltage and an impedance conversion circuit (not shown) for impedance conversion of the output voltage from the counter electrode of each microphone die. In addition, electrode pads 21 to 25 are formed on the circuit LSI 20. The electrode pad 21 is connected to GND, the electrode pad 22 is an output and connected to an external application circuit, and the electrode pad 23 is connected to a power source.

  The counter electrodes of each microphone die are connected in parallel to each other. That is, the electrode pad 24 and the bias electrode pad 11a1, the bias electrode pad 11a2 and the bias electrode pad 11b1, and the bias electrode pad 11b2 and the bias electrode pad 11c1 are connected by wire bonding, and a bias voltage is supplied from the electrode pad 24. . Further, the electrode pad 25 and the output side electrode pad 12a, the output side electrode pad 12a and the output side electrode pad 12b, and the output side electrode pad 12b and the output side electrode pad 12c are respectively connected by wire bonding and output to the electrode pad 25. The converted signal is impedance-converted by the impedance conversion circuit. Since the pair of counter electrodes formed on each microphone die are connected in parallel, the SN ratio of the output signal output from the microphone 1 can be improved.

  Further, in the present embodiment, as shown in FIG. 1A, in a plan view in units of 90 ° so that the corners of the microphone dies provided with the output-side electrode pads (12a, 12b, 12c) are closest to each other. The microphone die is placed in a different direction. Therefore, the conductors on the signal output side can be shortened as compared with the case where the microphone dies are arranged in the same direction, and the signal output side conductors can be made less susceptible to noise. Further, even if the orientation is changed by 90 ° so that the output-side electrode pads are closest to each other, the bias electrode pads are provided at two corners having a diagonal relationship in each microphone die. The corner where one of the two bias electrode pads is provided is necessarily adjacent to the corner where either bias electrode pad of the adjacent microphone die is provided. Therefore, the length of the conducting wire on the bias voltage side is also shortened as compared with a configuration in which the bias electrode pad has only one corner portion or a configuration in which two bias electrode pads are provided in adjacent corner portions (a configuration not having a diagonal positional relationship). be able to. Since the shape of each microphone die in plan view is square, the direction of the microphone die can be freely changed by 90 ° in plan view within a limited space in the package.

  When a noise current due to an external magnetic field is generated in a coil formed of a wire bonding conductor, for example, the noise current is canceled at the counter electrode portion, so that it is resistant to external noise. Specifically, for example, under the condition that a magnetic field from the diaphragm D toward the plate P is generated, a noise current due to the magnetic field is generated in the direction shown in FIG. 2 around the microphone die 10b. However, since the direction is reversed in the capacitor portion, the influence of noise is cancelled. Therefore, the configuration of the present embodiment is resistant to external noise.

  Further, when a configuration in which a plurality of microphone dies having a pair of counter electrodes are used and the counter electrodes of the microphone dies are connected in parallel as in the present embodiment, the area of each diaphragm D can be made small and light. Therefore, the resonance frequency can be increased for each microphone die. Therefore, a broadband microphone can be manufactured.

  In addition, although tolerance may occur in the microphone die, the tolerance as a microphone can be suppressed small by combining the microphone dies housed in one package. For example, when a high microphone die and a low microphone die are combined with respect to the median value indicating the performance of each microphone die, the tolerance as one microphone connecting them in parallel can be reduced.

  In the present embodiment, the circuit LSI 20 in which the impedance conversion circuit is formed is also housed in the same package together with the plurality of microphone dies, so that the influence of noise on the output signal can be reduced. Furthermore, since the plurality of microphone dies have the same shape (the shape in plan view is all square, and the positions of the bias electrode pad and the output electrode pad are the same in all microphone dies), the impedance conversion circuit is included in the package. The degree of freedom of design is high, such as the number of combinations of microphone dies to be stored and the way to arrange them.

2. Other Embodiments The technical scope of the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the configuration in which the wiring between the electrode pads is connected by wire bonding is described, but flip-chip connection may be used. In the case of flip chip connection, a sealing material is used to seal the gap to prevent sound waves from entering the air chamber from the gap between the bottom of the microphone die and the bottom of the package.

  3 and 4 show examples of the arrangement and connection of eight microphone dies and the circuit LSI 20. 3 and 4, each microphone die is provided with a bias electrode pad 13 at two corners having a diagonal relationship, and output side electrodes are provided at the other two corners having a diagonal relationship. A pad 14 is provided. For this reason, all the microphone dies are arranged in the same direction by changing the direction of the planar view between adjacent microphone dies in units of 90 ° so that the bias electrode pads 13 and the output side electrode pads 14 are adjacent to each other. Compared with the structure to perform, the length of each conducting wire can be shortened.

  The configuration of each microphone die and the configuration of the package for fixing the microphone die are not limited to the configuration shown in the above embodiment, for example. In the above embodiment, a bias voltage is applied to the diaphragm (vibrating electrode) and the plate (stationary electrode) is used as the output side. However, depending on the configuration of the support portion, diaphragm, and plate, they may be reversed. That is, a bias voltage may be applied to the plate and the diaphragm may be on the output side.

  In the above embodiment, the example in which the shape of the microphone die in plan view is square has been described, but the shape of the microphone die in plan view may be rectangular.

  1: microphone, 10a to 10c: microphone die, 11a1, 11a2: bias electrode pad, 11b1, 11b2: bias electrode pad, 11c1, 11c2: bias electrode pad, 12a: output electrode pad, 12b: output electrode pad, 12c : Output side electrode pad, 13: Bias electrode pad, 14: Output side electrode pad, 21-25: Electrode pad, 30: Semiconductor package, 31: Package body, 32: Lid, 101: Bottom, B: Support part, BC : Air chamber, D: Diaphragm, H1: Acoustic hole, H2: Through hole, 20: Circuit LSI, P: Plate, S: Spacer, SS: Acoustic space.

Claims (3)

A capacitive microphone die having a pair of counter electrodes;
A circuit die formed with an impedance conversion circuit for impedance conversion of the output signal of the counter electrode;
With
A microphone in which the counter electrodes of a plurality of microphone dies having the same shape are connected in parallel to each other and housed in a package together with the circuit die. The shape of the microphone die in plan view is a quadrangle,
Bias electrode pads for applying a bias voltage to one of the counter electrodes are respectively disposed at corners at diagonal positions in the plan view of the microphone die, and the other electrode of the counter electrodes. The output-side electrode pad connected to is disposed at at least one remaining corner in the plan view,
The microphone according to claim 1. The shape of the microphone die in plan view is a square,
The microphone according to claim 2.

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