JP2019129437A - MEMS oscillator - Google Patents

Abstract

To provide a MEMS oscillator in which the influence of external stress is reduced as much as possible.SOLUTION: A MEMS oscillator includes: a base 6 having a housing recess 5; an IC chip 3 including an oscillator circuit; a MEMS element 2 including a MEMS resonator; and a lid 7 closing an opening of the housing recess 5. The housing recess 5 housing the IC chip 3 and the MEMS element 2 therein is hermetically sealed with the lid 7. At least the MEMS element 2 is exposed in a space S that has an outer peripheral surface formed by joining the housing recess 5 and the lid 7. The IC chip 3 with a substantially rectangular shape in plan view is housed such that the longitudinal direction of the IC chip is a direction orthogonal to the longitudinal direction of the base 6 with a substantially rectangular shape in plan view.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a MEMS oscillator provided with a MEMS resonator.

  In recent years, development of MEMS devices using MEMS (Micro Electro-Mechanical Systems) technology has been widely performed. The MEMS technology is a technology for realizing miniaturization of various mechanical elements by applying a technology in a semiconductor manufacturing process of silicon or the like, and may be called a micromachine.

  As a MEMS device manufactured using such a MEMS technology, for example, Patent Document 1 discloses a device in which a sensor chip manufactured using a MEMS technology and an IC chip are packaged with a resin. In Patent Document 1, as shown in FIG. 4, an IC chip to which a sensor chip is flip-chip bonded is assembled to a lead frame, and the entire sensor chip and IC chip are resin-molded.

JP 2005-528995 gazette

  In the MEMS device disclosed in Patent Document 1, since the sensor chip, which is a MEMS element manufactured using the MEMS technology, is completely covered with resin together with the IC chip, stress caused by expansion and contraction of the resin due to temperature change. And stress generated by the difference in linear expansion coefficient between single crystal silicon, which is the material of the sensor chip, and the resin, is applied to the sensor chip. It cannot be ignored.

  In particular, when the MEMS element is a MEMS resonator (MEMS resonator) that constitutes a MEMS oscillator, these stresses cause, for example, distortion in the MEMS resonator, and the oscillation frequency changes with temperature. So-called fluctuation of the so-called frequency temperature characteristics from the original characteristics or phenomena such as deterioration of the frequency hysteresis characteristics with respect to temperature occur.

  There is also the effect of external stresses from the circuit board on which the MEMS oscillator is mounted.

  The present invention has been made in view of the above points, and an object thereof is to provide a MEMS oscillator in which the influence of external stress is reduced as much as possible.

  The present invention is configured as follows to achieve the above object.

  That is, a MEMS oscillator according to the present invention includes a base having a housing recess, an integrated circuit element including an oscillation circuit, a MEMS element including a MEMS resonator, and a lid that closes an opening of the housing recess, and The housing recess in which the circuit element and the MEMS element are housed is hermetically sealed by the lid, and at least the MEMS element has a space formed by joining the housing recess and the lid to the outer peripheral surface. The base and the integrated circuit element are substantially rectangular in a plan view, and the integrated circuit element has the longitudinal direction perpendicular to the longitudinal direction of the base. It is stored in the storage recess.

  The MEMS device is preferably bonded to the integrated circuit device such that the active surface faces the active surface of the integrated circuit device.

  According to the MEMS oscillator of the present invention, the outer peripheral surface of the MEMS element including the MEMS resonator is exposed in the space formed by joining the housing recess and the lid, so that the outer peripheral surface of the MEMS element is It does not receive the stress by expansion and contraction of resin like the above-mentioned patent documents 1 covered with resin and not exposed in the space. As a result, the MEMS element is not distorted by the stress of the surrounding resin, and the variation of the frequency temperature characteristic of the MEMS oscillator and the frequency hysteresis characteristic with respect to the temperature can be improved.

  The base having a substantially rectangular shape in plan view that houses the integrated circuit element and the MEMS element is displaced due to deformation caused by a temperature change of the circuit board on which the MEMS oscillator is mounted. This displacement is smaller than the short side direction of the base. The longitudinal direction of the base, ie, the longitudinal direction of the base is larger.

  The integrated circuit device having a rectangular shape in plan view receives stress due to the displacement of the base in which the integrated circuit device is housed, but the stress is in the long side direction, ie, the integrated circuit as compared to the short side direction of the integrated circuit device. The longitudinal direction of the element is larger.

  In the present invention, the integrated circuit element receives a large stress from the base, and its longitudinal direction is not displaced by the deformation of the circuit board. Since the integrated circuit element is accommodated in the base in the direction of the short side of the base, the integrated circuit element is received from the base as compared to the case where the integrated circuit element is accommodated in the base with the longitudinal direction being the longitudinal direction of the base. Stress can be reduced.

  By reducing the stress that the integrated circuit element receives from the base in this way, the stress that acts on the MEMS element joined so as to face the active surface of the integrated circuit element can be relaxed.

  Preferably, the non-active surface opposite to the active surface of the integrated circuit element is bonded to the bottom surface of the housing recess via an adhesive.

  According to the above configuration, since the MEMS element can be bonded to the active surface of the integrated circuit element bonded to the bottom surface of the base recess, the integrated circuit element is interposed between the base and the MEMS element. become. By this, compared with the structure which joins a MEMS element to a base directly, the stress which acts on a MEMS element from a base can be reduced. Also, by using a resin adhesive as the adhesive, it is possible to relieve the stress acting on the integrated circuit element from the base, thus further increasing the stress acting on the MEMS element mounted on the integrated circuit element. Can be relaxed.

  The base is preferably made of a ceramic material having high hardness and excellent heat resistance and corrosion resistance.

  It is preferable that a stepped portion higher than the bottom surface of the storage recess is formed on the inner peripheral wall of the storage recess of the base.

  According to the above configuration, since the stepped portion is formed in the base, the thickness of the base is increased and the rigidity is enhanced. Thereby, it is possible to reduce stress from the outside of a circuit board or the like on which the MEMS oscillator is mounted, and it is possible to reduce stress acting on the MEMS element housed in the housing housing recess.

  According to the present invention, since the outer peripheral surface of the MEMS element including the MEMS resonator is exposed in the space formed by the junction of the storage recess of the base and the lid, the outer peripheral surface of the MEMS element is completely made of resin. As in the above-mentioned patent document 1 which is not exposed in the space, it does not receive stress due to expansion and contraction due to temperature change of the resin. As a result, the MEMS element is not distorted by the stress of the surrounding resin, and the variation of the frequency temperature characteristic of the MEMS oscillator and the frequency hysteresis characteristic with respect to the temperature can be improved.

  In addition, the integrated circuit device has a longitudinal direction that is orthogonal to the longitudinal direction of the base, not a longitudinal direction of the base where the displacement due to the deformation of the circuit board on which the MEMS oscillator is mounted increases. Since the integrated circuit device is accommodated in the base in the side direction, the stress received by the integrated circuit device from the base is reduced as compared to the case where the integrated circuit device is accommodated in the base in the longitudinal direction of the base. can do.

  By reducing the stress that the integrated circuit device receives from the base in this manner, it is possible to relieve the stress acting on the MEMS device bonded to the integrated circuit device.

FIG. 1 is a cross-sectional view of a MEMS oscillator according to an embodiment of the present invention. FIG. 2 is a plan view of the MEMS oscillator of FIG. 1 with the lid removed. FIG. 3 is a plan view corresponding to FIG. 2 of the comparative example. FIG. 4 is a cross-sectional view of a MEMS oscillator according to another embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view of a MEMS oscillator according to an embodiment of the present invention, and FIG. 2 is a plan view of the MEMS oscillator of FIG. 1 with a lid removed.

  The MEMS oscillator 1 according to this embodiment includes a MEMS element 2 including a MEMS resonator (MEMS resonator), an IC chip 3 as an integrated circuit element including an oscillation circuit, and a package 4 that houses these and hermetically seals them. It has.

  The package 4 has a storage recess 5 opened at the top, a base 6 for storing and holding the MEMS element 2 and the IC chip 3, and a lid closing the upper opening of the base 6 to hermetically seal the storage recess 5. And a seal ring 8 for joining the lid 7 to the base 6.

  The base 6 has a substantially rectangular shape in a plan view, is made of a ceramic material such as alumina, and is formed by laminating ceramic green sheets and integrally firing into a concave shape having an open top.

  The storage recess 5 of the base 6 has a substantially rectangular shape in plan view, and is closer to the inner peripheral walls at both ends in the long side direction (the left-right direction in FIGS. 1 and 2) than the bottom surface 5 a of the storage recess 5. High steps 5 b and 5 c are respectively provided along the short side direction (vertical direction in FIG. 2) of the base 6. The height from the bottom surface 5a of each stepped portion 5b, 5c is substantially equal, and on the upper surface of each stepped portion 5b, 5c, a plurality of connection electrodes 9b, 9c formed of a conductor wiring pattern for connecting IC chip 3 are formed. ing.

  As described above, since the stepped portions 5b and 5c higher than the bottom surface 5a are formed on the inner peripheral wall of the housing recessed portion 5 of the base 6 and the base 6 is thicker, the base is compared with the configuration in which the stepped portion is not formed. The rigidity of 6 increases. Thereby, the external stress from the circuit board on which the MEMS oscillator 1 is mounted can be reduced, and the external stress to the IC chip 3 and the MEMS element 2 stored in the housing recess 5 of the base 6 is reduced. Can do.

  The IC chip 3 is, for example, an application specific integrated circuit (ASIC), and constitutes an oscillation circuit together with the MEMS element 2. The IC chip 3 incorporates a PLL circuit, a temperature compensation circuit, and the like as needed. The IC chip 3 is substantially rectangular in plan view. The IC chip 3 has a non-active surface (lower surface) opposite to the active surface (upper surface) bonded to the bottom surface 5 a of the housing recess 5 of the base 6 by a resin-based conductive adhesive 10. As the resin-based conductive adhesive 10, for example, a polyimide-based, epoxy-based, or silicon-based conductive adhesive can be used.

  A solid ground wiring pattern (not shown) is formed on the bottom surface 5a of the housing recess 5 of the base 6, and the back surface of the IC chip 3 is connected to the ground wiring pattern via the conductive adhesive 10. The potential of the back surface of the IC chip 3 is fixed to the ground potential.

  On the active surface of the IC chip 3, a plurality of electrode pads 11 b and 11 c connected to the connection electrodes 9 b and 9 c of the base 6 are formed on the periphery thereof. Further, on the center side of the active surface of the IC chip 3, an electrode pad (not shown) for mounting the MEMS element 2 is formed.

  The electrode pads 11b and 11c of the IC chip 3 are electrically connected to the corresponding connection electrodes 9b and 9c formed on the stepped portions 5b and 5c of the base 6 by bonding wires 12b and 12c, respectively. As a material of the bonding wires 12b and 12c, Au is preferable from the viewpoint of reliability, but Cu or the like may be used.

  The MEMS element 2 is an element manufactured using the above-described MEMS technology, includes a Si resonator, and the movable portion is hermetically sealed. The MEMS element 2 of this embodiment is manufactured using an SOI (Silicon on Insulator) wafer which is a silicon wafer having a structure in which a silicon single crystal layer is formed on an oxide film.

  The MEMS element 2 is smaller than the outer shape of the IC chip 3 and is bonded to the IC chip 3 so that its active surface faces the active surface of the IC chip 3. That is, in the MEMS element 2, the electrode pads on the active surface thereof and the connection pads of the IC chip 3 are flip chip connected by the Au bumps 13 which are metal bumps. The metal bumps are not limited to Au bumps, but may be solder bumps or the like.

  The gap between the MEMS element 2 and the IC chip 3 may be filled with an underfill resin as a sealing resin in order to improve the mechanical bonding strength.

  The connection electrodes 9 b and 9 c of the base 6 are connected to external connection terminals (not shown) formed on the lower surface of the base by a conductor wiring pattern (not shown) formed inside the base 6.

  The lid 7 is made of, for example, a metal such as Kovar, and is a rectangular flat plate.

  The lid 7 is joined to the periphery of the opening of the base 6 by seam welding or the like by a rectangular annular seal ring 8 as a sealing material made of Kovar or the like, and an airtight space S is formed inside the package 4. . This bonding is performed in an inert gas atmosphere such as nitrogen gas or in a vacuum atmosphere, and the space S inside the package 4 is filled with an inert gas such as nitrogen gas or vacuum. Since the seal ring 8 is provided as described above, the package 4 is less likely to be deformed as compared with the configuration without the seal ring.

  In addition to the above-mentioned metal, ceramics, resin, glass, or the like can be used for the lid 7. For example, when a glass lid is used, a low melting point glass is used as a bonding material. A bonding material can be appropriately selected according to the material, and bonding between the base 6 and the lid 7 can be performed.

  According to this embodiment, the outer peripheral surface of the MEMS element 2, specifically, the outer peripheral surface other than the active surface of the MEMS element 2 is in the space S formed by the junction of the storage recess 5 of the base 6 and the lid 7. Is exposed.

  As described above, since the outer peripheral surface of the MEMS element 2 is exposed in the space S, the outer peripheral surface of the MEMS element is completely sealed with resin as in the above-mentioned Patent Document 1 which is not exposed in the space. The MEMS element 2 is not subjected to stress due to expansion or contraction of the resin due to temperature change or the like. As a result, it is possible to avoid a situation in which the MEMS element 2 is distorted by the stress of the surrounding resin, and it is possible to improve the variation of the frequency temperature characteristic of the MEMS oscillator 1 and the frequency hysteresis characteristic with respect to the temperature.

  In addition, since the MEMS element 2 is mounted on the IC chip 3 fixed to the housing recess 5 of the base 6, the IC chip 3 is interposed between the MEMS element 2 and the base 6. By this, compared with direct bonding of the MEMS element 2 to the base 6, the stress from the base 6 acting on the MEMS element 2 can be further reduced, and the characteristic variation of the MEMS element 2 can be reduced.

  Furthermore, since the IC chip 3 is bonded to the bottom surface 5 a of the housing recess 5 of the base 6 by the conductive adhesive 10 made of resin, stress from the base 6 can be relieved, and the IC chip 3 is bonded to the IC chip 3. The stress acting on the MEMS element 2 can be reduced.

  In this embodiment, since not only the MEMS element 2 but also the outer periphery of the IC chip 3 is exposed in the space S, the outer peripheral surface of the IC chip is completely sealed with resin and exposed to the space. As in the above-mentioned Patent Document 1, the IC chip 3 is not subjected to stress due to expansion and contraction of the resin due to temperature change and the like.

  Since the MEMS element 2 manufactured using the MEMS technology is very small, the MEMS oscillator 1 can be miniaturized.

  The MEMS oscillator 1 is mounted by soldering an external connection terminal (not shown) on the lower surface of the base 6 to a circuit board. When the circuit board is deformed due to a temperature change or the like, the base 6 is displaced. This displacement is in the long side direction, as compared with the short side direction (vertical direction in FIG. 2) of the base 6 substantially rectangular in plan view. That is, the longitudinal direction (left and right direction in FIGS. 1 and 2) of the base 6 becomes larger.

  The IC chip 3 housed in the base 6 is also substantially rectangular in plan view, and the stress received by the displacement of the base 6 is longer than the short side direction of the IC chip 3, ie, the longitudinal direction of the IC chip 3. Is bigger.

  In this embodiment, in order to reduce the stress applied to the IC chip 3 through the base 6 due to the deformation of the circuit board, and further to reduce the stress acting on the MEMS element 2 bonded to the IC chip 3, Like that.

  That is, as shown in FIG. 2, the IC chip 3 has a base direction so that its longitudinal direction (vertical direction in FIG. 2) is perpendicular to the longitudinal direction of the base 6 (horizontal direction in FIG. 2). It is stored in the storage recess 5 of 6.

  That is, the IC chip 3 receives stress from the base 6 and the longitudinal direction thereof is displaced by the deformation of the circuit board. The IC chip 3 is not the longitudinal direction of the base 6 but a direction orthogonal to the longitudinal direction. That is, the base 6 is accommodated so as to be in the direction of the short side of the base 6 (vertical direction in FIG. 2).

  Thus, for example, as shown in FIG. 3, when the IC chip 3 is stored in the base 6 so that the longitudinal direction thereof is (the left-right direction in FIG. 3) the longitudinal direction of the base 6 (the left-right direction in FIG. 3). In comparison with the above, the stress that the IC chip 3 receives from the base 6 can be reduced.

  Therefore, the stress acting on the MEMS element 2 bonded to the IC chip 3 can be reduced.

  As described above, the stress applied to the IC chip 3 from the base 6 can be reduced by storing the IC chip 3 so that the longitudinal direction thereof is perpendicular to the longitudinal direction of the base 6. The stress acting on the MEMS element 2 bonded to the IC chip 3 can be reduced. By this, it is possible to reduce the characteristic fluctuation of the MEMS element 2 and improve the fluctuation of the frequency temperature characteristic of the MEMS oscillator 1 and the frequency hysteresis characteristic with respect to the temperature.

Second Embodiment
Figure 4 is a cross-sectional view of a MEMS oscillator 1 ₁ of another embodiment of the present invention, the parts corresponding to the embodiments described above are denoted by the corresponding reference numerals.

MEMS oscillator 1 ₁ of this embodiment, the IC chip 3 _1, a plurality of connection electrodes (not shown) of the base _61, rather than connected by wire bonding, are to be connected by flip-chip.

Base 6 ₁ constituting the package 4 ₁ has a housing recess 5 ₁ for housing the MEMS device 2 and the IC chip 3 _1. The housing recess 5 _1, the entire circumference of the inner circumferential wall of the generally rectangular plan view, a high step portion 5 ₁ b is provided from the bottom surface 5 ₁ a of the housing recess 5 _1. The stepped portion 5 ₁ b is formed so as to surround a relatively narrow rectangular region corresponding to the MEMS device 2. That is, the stepped portion 5 ₁ b and the housing recess 5 ₁ of the bottom surface 5 ₁ a, space for housing the MEMS device 2 is partitioned. A plurality of connection electrodes made of a conductor wiring pattern are formed on the upper surface of the stepped portion 5 ₁ b.

IC chip 3 _1, the electrode pad of the peripheral edge of the active face is, the connection electrodes 9 ₁ on the step portion 5 ₁ b of the base ₆₁ is flip-chip connected by Au bumps 15 are metal bumps. The metal bumps are not limited to Au bumps, and may be solder bumps.

As in the above embodiment, the MEMS element 2 is bonded to the IC chip 3 ₁ so that the active surface thereof faces the active surface of the IC chip 3 ₁ . That, MEMS device 2, the electrode pads and the IC chip 3 ₁ of the connection pads of the active surface, are flip-chip connected by Au bumps 13 are metal bumps.

The gap between the MEMS device 2 and the IC chip 3 _1, may be filled with underfill resin as a sealing resin.

Electrode pads of the peripheral portion of the IC chip 3 _1, in a state that is flip-chip connected to the connection electrodes 9 ₁ on the step portion 5 ₁ b of the base 6 _1, MEMS element 2 bonded to the inboard IC chip 3 ₁ is located in the space S _2, which is defined by the side surface of the bottom surface 5 ₁ a of the housing recess 5 ₁ base 6 ₁ and the stepped portion 5 ₁ b. In this case, the active surface of the MEMS device 2 non-active surface of the opposite side, in a state of being separated from the bottom surface 5 ₁ a of the housing recess 5 ₁ base 6 _1, is opposed to the bottom surface 5 ₁ a.

Also in this embodiment, similarly to the embodiment shown in FIG. 1, IC chip 3 _1, so that its longitudinal direction is in a direction perpendicular to the base ₆₁ in the longitudinal direction (horizontal direction in FIG. 4) to, and is housed in the housing recess 5 _1.

  The other configuration is the same as that of the above embodiment.

According to this embodiment, the outer peripheral surface of the non-active surface of the MEMS device 2, the space S ₁ that is formed by the junction between housing recess 5 ₁ and the lid 7 of the base 6 _1, specifically, the base ₆₁ of the because exposed in the space S ₁ that is defined by a bottom surface 5 ₁ a of the stepped portion 5 ₁ b and the housing recess 5 _1, sealing completely resin outer peripheral surface of the MEMS device, exposed to the space The MEMS element 2 does not receive stress due to expansion and contraction of the resin due to a temperature change as in the above-mentioned Patent Document 1. By this, it is possible to prevent the MEMS element 2 from being distorted by the stress of the surrounding resin, and it is possible to improve the fluctuation of the frequency temperature characteristic of the MEMS oscillator 1 and the frequency hysteresis characteristic with respect to temperature.

Further, in this embodiment, the housing recess 5 higher step portion 5 ₁ b of the forming area is wider than the _first bottom surface 5 ₁ a, i.e., the region where the base ₆₁ is formed thick wide base ₆₁ of the further enhanced rigidity, it is possible to reduce the external stress from the circuit board to which the MEMS oscillator 1 ₁ is mounted. This makes it possible to reduce the external stress to the IC chip 3 ₁ and MEMS element 2 housed in the housing recess 5 ₁ of the base 6 _1.

Also in this embodiment, MEMS element 2, IC chip 3 ₁ is joined to the base ₆₁ of the housing recess 5 in ₁ in a state interposed, i.e., MEMS element 2 is bonded to the IC chip 3 _1, this IC chip 3 ₁ is joined to the base _61. Base Thus, between the MEMS device 2 and the base _61, which will be IC chip 3 ₁ is interposed, as compared to direct bonding of MEMS device 2 to the base _61, acting on the MEMS device 2 6 ₁ of the stress can be further reduced.

In the above embodiment, the bonding the entire surface of the non-active surface of the IC chip 3 on the bottom 5a of the housing recess 5 in the base 6, in this embodiment, the electrode pads of the active surface of the IC chip 3 _1, base 6 ₁ since flip-chip connected by Au bumps 15 to the connection electrode, the area of the junction is reduced, the thermal expansion coefficient towards the Au bumps to become smaller than the resin, applied from the base ₆₁ to the IC chip 3 ₁ stress Can be reduced. Thereby, the stress transmitted to the MEMS element 2 can be reduced, and the fluctuation of the frequency temperature characteristic of the MEMS oscillator 1 and the frequency hysteresis characteristic can be improved.

Further, the IC chip 3 _1, so that the longitudinal direction for housing such that the direction orthogonal to the longitudinal direction of the base _61, it is possible to reduce the stress applied from the base ₆₁ to the IC chip 3 _1, Thereby, the stress acting on the MEMS element 2 bonded to the IC chip 3 ₁ can be further reduced.

In the above embodiments, it stepped portions 5b, 5c, 5 ₁ b are provided one stage may be provided a plurality of stages.

1, 1 ₁ MEMS oscillator 2 MEMS element 3, 3 ₁ IC chip (integrated circuit element)
4, 4 ₁ package 5, 5 ₁ housing recess 6, 6 ₁ base 7 lid (lid)

Claims (5)

A base having a storage recess,
An integrated circuit element including an oscillation circuit;
A MEMS element including a MEMS resonator;
And a lid closing the opening of the storage recess,
The storage recess in which the integrated circuit element and the MEMS element are stored is hermetically sealed by the lid.
At least the outer peripheral surface of the MEMS element is exposed in a space formed by bonding of the storage recess and the lid.
The base and the integrated circuit device are substantially rectangular in plan view,
The integrated circuit element is housed in the housing recess such that the longitudinal direction thereof is perpendicular to the longitudinal direction of the base.
A MEMS oscillator characterized by The MEMS device is bonded to the integrated circuit device such that its active surface faces the active surface of the integrated circuit device.
The MEMS oscillator according to claim 1. A non-active surface opposite to the active surface of the integrated circuit element is bonded to the bottom surface of the housing recess via an adhesive.
The MEMS oscillator according to claim 2. The base is made of a ceramic material
The MEMS oscillator according to any one of claims 1 to 3. A stepped portion higher than the bottom surface of the storage recess is formed on the inner peripheral wall of the storage recess of the base.
The MEMS oscillator according to any one of claims 1 to 4.

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