MICROPHONE ASSEMBLY AND PACKAGING METHODS FOR SIZE REDUCTION AND BACK VOLUME INCREASE

A piezoelectric microelectromechanical system microphone assembly comprises a carrier substrate including one of a through-hole or a recess, and a package including a microelectromechanical system die having a piezoelectric microelectromechanical system microphone mounted on a microphone substrate and a lid, at least a portion of the package disposed within the one of the through-hole or recess.

BACKGROUND

Technical Field

Embodiments disclosed herein relate to piezoelectric microelectromechanical system microphone packages and to devices including same.

Description of Related Technology

A microelectromechanical system (MEMS) microphone is a micro-machined electromechanical device to convert sound pressure (e.g., voice) into an electrical signal (e.g., voltage). MEMS microphones are widely used in mobile devices such as cellular telephones, headsets, smart speakers, and other voice-interface devices/systems. Capacitive MEMS microphones and piezoelectric MEMS microphones (PMMs) are both available in the market. PMMs requires no bias voltage for operation, therefore, they provide lower power consumption than capacitive MEMS microphones. The single membrane structure of PMMs enable them to generally provide more reliable performance than capacitive MEMS microphones in harsh environments. Existing PMMs are typically based on either cantilever MEMS structures or diaphragm MEMS structures.

Some of the important parameters to consider in the design of a PMM include performance parameters such as SNR (signal to noise ratio), bandwidth (related to frequency response flatness), size, and cost.

The performance of a PMM is largely affected by the size of the PMM, as a larger size may provide for a larger back volume to increase the SNR of the microphone. However, microphone size is becoming a more important design consideration as mobile devices or headsets in which such PMMs are utilized are shrinking and/or including additional functionality and related circuitry and less area is becoming available within the devices for PMMs. Performance of existing PMM designs is typically degraded as designers attempt to reduce the size of the PMMs to meet customer requirements.

SUMMARY

In accordance with one aspect, there is provided a piezoelectric microelectromechanical system microphone assembly. The piezoelectric microelectromechanical system microphone assembly comprises a carrier substrate including one of a through-hole or a recess, and a package including a microelectromechanical system die having a piezoelectric microelectromechanical system microphone mounted on a microphone substrate and a lid, at least a portion of the package disposed within the one of the through-hole or recess.

In some embodiments, the lid is a metal lid.

In some embodiments, the lid is at least partially disposed within the one of the through-hole or recess.

In some embodiments, the lid is fully disposed within the one of the through-hole or recess.

In some embodiments, an upper surface of the lid is substantially co-planar with a lower surface of the carrier substrate.

In some embodiments, the lid is formed over the microelectromechanical system die and, together with the microphone substrate, defines a back volume around the piezoelectric microelectromechanical system microphone.

In some embodiments, the package is a bottom-port package.

In some embodiments, a piezoelectric membrane of the piezoelectric microelectromechanical system microphone is disposed proximate the bottom port and between the bottom port and a support substrate for the piezoelectric membrane.

In some embodiments, the lid and microelectromechanical system die are disposed on opposite sides of the microphone substrate.

In some embodiments, the microelectromechanical system die is at least partially disposed within the one of the through-hole or the recess.

In some embodiments, the one of the through-hole or the recess is the recess, and the carrier substrate further includes an opening providing acoustic communication between the microelectromechanical system microphone and an environment outside of the package.

In some embodiments, the lid is at least partially disposed within the one of the through-hole or the recess.

In some embodiments, the one of the through-hole or the recess is the through-hole.

In some embodiments, the package is encapsulated by a conductive material.

In some embodiments, the assembly further comprises a mesh disposed over a piezoelectric membrane of the microelectromechanical system microphone.

In some embodiments, the mesh is conductive.

In some embodiments, the mesh is grounded.

In some embodiments, the assembly further comprises an application specific integrated circuit disposed within the package.

In some embodiments, the assembly is included in an electronics device module.

In some embodiments, the electronics device module is included in an electronic device.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Aspects and embodiments disclosed herein involve engineering of the packaging and assembly of a PMM to reduce the overall assembled package size without compromising performance of the PMM.

One example of a cantilever PMM is illustrated in a plan view inFIG.1Aand in a cross-sectional view inFIG.1B. The cantilever PMM includes six cantilevers and top, middle, and bottom sensing/active electrodes proximate the bases of the cantilevers. Cantilever MEMS microphone structures generate the maximum stress and piezoelectric charges near the edge of the anchor portion of the cantilever structure. Therefore, partial sensing electrodes near the anchor may be used for maximum output energy. The cantilevers are pie-piece shaped and together form a circular microphone structure with trenches (gaps) between adjacent cantilevers. It should be appreciated that in alternate embodiments, the cantilever structures could be shaped other than as illustrated, for example, as polygons with three or more straight or curved sides.

The cantilevers of a cantilever PMM as disclosed herein may have bases mounted on a support substrate including a SiO2layer on a Si substrate as illustrated inFIG.1B. The top, bottom, and middle sensing/active electrodes in the different cantilevers are connected in series between the bond pads, except for the cantilevers having electrical connection between the electrodes and bond pads. The top and bottom electrodes of each cantilever are electrically connected to the middle electrode in an adjacent cantilever. Vias to the middle electrode of one cantilever and to the top and bottom electrodes of an adjacent cantilever are used to provide electrical connection between the bond pads and cantilever electrodes. The electrodes are indicated inFIG.1Bas being Mo but could alternatively be Ru or any other suitable metal, alloy, or non-metallic conductive material.

In some embodiments, the layer of SiO2on the surface of the support substrate upon which the cantilevers are formed may have a thickness of from about 1 µm to about 5 µm. As illustrated inFIGS.1A and1B, the support substrate including the Si substrate and layer of SiO2typically extends outward beyond the periphery of the PMM piezoelectric material cantilevers. The layer of SiO2constrains the periphery of the PMM cantilevers.

An example of a diaphragm-type piezoelectric microelectromechanical system microphone (PMM) is illustrated in a plan view inFIG.2Aand in cross-sectional view inFIG.2B.

The diaphragm of the PMM may be formed of or include a film of piezoelectric material, for example, aluminum nitride (AlN), zinc oxide (ZnO), or PZT, (also referred to herein as a piezoelectric element) that generates a voltage difference across different portions of the diaphragm when the diaphragm deforms or vibrates due to the impingement of sound waves on the diaphragm. Although illustrated as circular inFIG.2A, the diaphragm may have a circular, rectangular, or polygonal shape. In the example ofFIGS.2A and2B, the diaphragm structure is fully clamped all around its perimeter by adhesion of the entire perimeter of the diaphragm to a layer of SiO2disposed on a Si substrate. To improve low-frequency roll-off control (f-3dBcontrol) one or more vent holes or apertures may be formed in the diaphragm structure that may be well defined by photolithography.

The diaphragm PMM ofFIGS.2A and2Bhas a circular diaphragm formed of two layers of piezoelectric material, for example, AlN, that is clamped at its periphery on layers of SiO2formed on a Si substrate with a cavity defined in the substrate below the diaphragm. The circular diaphragm PMM includes a plurality of pie-piece shaped sensing/active inner electrodes disposed in the central region of the diaphragm that are segmented and separated from one another by gaps. Outer sensing/active electrodes, segmented and separated circumferentially from one another by gaps, are positioned proximate a periphery of the diaphragm and extend inward from the clamped periphery a portion of the radius of the diaphragm toward the inner electrodes. Each outer sensing electrode is directly electrically connected to a corresponding inner sensing electrode by an electrical trace or conductor segment. Open areas that are free of sensing/active electrodes are defined between the inner electrodes and outer electrodes.

The inner electrodes and outer electrodes each include top or upper electrodes disposed on top of an upper layer of piezoelectric material of the diaphragm and bottom or lower electrodes disposed on the bottom of the lower layer of piezoelectric material of the diaphragm. In some embodiments, as illustrated inFIG.2Bthe inner electrodes and outer electrodes may further include middle electrodes disposed between the upper and lower layers of piezoelectric material. The multiple inner and outer electrodes are electrically connected in series between the two bond pads, except for inner and outer electrode segment pairs having electrical connection directly to the bond pads. The top and bottom electrodes of each inner and outer electrode segment pair are electrically connected to the middle electrode in an adjacent inner and outer electrode segment pair in embodiments including the middle electrodes. Vias to the middle electrode of one inner and outer electrode segment pair and to the top and bottom electrodes of an adjacent inner and outer electrode segment pair are used to provide electrical connection between the bond pads and electrodes. The electrodes are indicated as being Mo, but could alternatively be Ru, Pt, or any other suitable metal, alloy, or non-metallic conductive material.

Diaphragm structures generate maximum stress and piezoelectric charges in the center and near the edge of the diaphragm anchor. The charges in the center and edge have opposite polarities. Additionally, diaphragm structures generate piezoelectric charges at the top and the bottom surfaces and the charge polarities are opposite on the top and bottom surfaces in the same area. Partial sensing electrodes in the diaphragm center and near the anchor may be used for maximum output energy and sensitivity and to minimize parasitic capacitance.

A diaphragm PMM may include one, two, or multiple piezoelectric material film layers in the diaphragm. In embodiments including two piezoelectric material film layers, conductive layers forming sensing/active electrodes may be deposited on the top and the bottom of the diaphragm, as well as between the two piezoelectric material film layers, forming a bimorph diaphragm structure. Partial sensing electrodes may be employed. Inner electrodes may be placed in the center of diaphragm and outer electrodes may be placed near the anchor/perimeter of the diaphragm. Sensing/active electrodes may be placed on the bottom and top, and in the middle of the vertical extent of the multi-layer piezoelectric film forming the diaphragm. The size of the sensing/active electrodes may be selected to collect the maximum output energy (E=0.5*C*V2).

The packaging and assembly methods and structures disclosed herein may be utilized with either cantilever or diaphragm type PMMs.

One form of package for a PMM is a bottom-port package, an example of which is illustrated inFIG.3. The PMM is mounted on a printed circuit board (PCB), often along with an application specific integrated circuit (ASIC) with control circuitry for the PMM and covered by a lid that may be formed of metal. A sound hole is defined in the PCB for sound to reach the PMM.

Another form of package for a PMM is a top-port package, an example of which is illustrated inFIG.4A. The top-port package is similar to the bottom-port package, but the sound port is defined in the lid rather than in the PCB. A variation of a top-port package is shown inFIG.4B, in which the PMM and ASIC are mounted on the lid, which is formed of a laminate such as a PCB that is attached to a bottom PCB by walls also formed of laminate material.FIGS.5A and5Billustrate how a top-port and bottom-port PMM package, respectively, may be assembled onto the case of a device along with gaskets to minimize sound interference and sound holes in the device casing.

In many instances PMM packages are assembled on to carrier PCBs for ease of handling and for mechanical support. One example of a PMM assembly including a carrier substrate is illustrated inFIG.6in which examples of height dimensions in mm are shown. The carrier PCB (~0.7 mm) is typically much thicker than the microphone substrate PCB (~0.2 mm), therefore, a similar or larger back volume can be obtained by making a through hole (or a recess) on the carrier PCB and embedding at least a part of the PMM package, for example, at least a portion enclosed by the lid, into the through hole/recess, as shown inFIG.7A. If the carrier PCB is not thick enough, or larger microphone back volume (the space defined within the lid) is desired, a method as shown inFIG.7Bcan be utilized. In this method ofFIG.7Bthe thickness of microphone substrate PCB can be increased. A recess or through-hole is made in the carrier PCB in which the PMM package lid is embedded, thus providing a larger back volume than in the embodiment shown inFIG.7A. It can be seen that the assembly configurations illustrated inFIGS.7A and7Bhave heights reduced by about half as compared to the assembly configuration ofFIG.6. In a variation on the embodiment ofFIG.7B, in another embodiment illustrated inFIG.7Cthe MEMS die including the PMM may be flipped relative to its orientation inFIG.7B. In this way, the performance can be further improved as the back volume is increased and the front cavity volume is reduced.

In some embodiments, the MEMS die including the PMM can be placed on a different side of the microphone substrate PCB than the lid. The PMM package may be assembled into a carrier PCB having a through-hole or a recess. The PMM package can be mounted to the carrier PCB with the MEMS die fitted into the carrier PCB through-hole as illustrated inFIG.8A, or with the lid fitted into the carrier PCB through-hole as illustrated inFIG.8B. Even though the package size of PMM is larger in these embodiments than in previously described embodiments, the size will be reduced after assembly with the carrier PCB as the lid or PMM die is embedded into the carrier PCB.

To provide shielding against E-field, EM, or RF interference, the whole microphone package can be encapsulated by conductive materials by metal passing through a PCB via, through a silicon via, by a metal coating the outside of the package, etc., as illustrated in the examples ofFIGS.8A and8B.

A mesh can be added on top of the PMM to provide protection to the PMM membrane. The mesh can also be conductive to provide shielding against E-field, EM, or RF interferences. The conductive mesh can also be grounded to improve the shielding.

FIGS.9A and9Bshow a comparison of PMM assemblies as illustrated inFIGS.6and8Bin which example dimensions in mm are included. The PMM assembly illustrated inFIG.8Bas compared to that illustrated inFIG.6has height reduced from 1.1 mm to 0.6 mm, while back volume is increased by 71%.

In the various embodiments disclosed above, a through-hole is provided in the carrier substrate to house at least a portion of the PMM package. As illustrated in the comparison between the assemblies ofFIGS.10A and10B, instead of a through-hole, a recess may be provided in the carrier substrate to house at least a portion of the PMM package. If a recess on the carrier PCB is used instead of through-hole to house the MEMS die portion of the PMM package, then an opening may be formed from within the recess to the outside environment as illustrated in the comparison of embodiments inFIGS.11A and11B.

In various embodiments of the assembly structures disclosed herein, as illustrated inFIG.12, the areas of the MEMS die around the MEMS membrane can be extended to provide higher mechanical robustness which could be helpful for gasket mounting during the product assembly.

Any of the assembly structures disclosed herein may be modified to include an ASIC within the packaged structure, for example, on the MEMS die, as illustrated in the examples ofFIGS.13A and13B.

Examples of MEMS microphones and assembly structures including same as disclosed herein can be implemented in a variety of packaged modules and devices.FIG.14is a schematic block diagrams of an illustrative device100according to certain embodiments.

The wireless device100can be a cellular phone, smart phone, tablet, modem, communication network or any other portable or non-portable device configured for voice or data communication. The wireless device100can receive and transmit signals from the antenna110.

The wireless device100may include one or more microphones as disclosed herein. The one or more microphones may be included in an audio subsystem including, for example, an audio codec. The audio subsystem may be in electrical communication with an application processor and communication subsystem that is in electrical communication with the antenna110. As would be recognized to one of skill in the art, the wireless device would typically include a number of other circuit elements and features that are not illustrated, for example, a speaker, an RF transceiver, baseband sub-system, user interface, memory, battery, power management system, and other circuit elements.

The principles and advantages of the embodiments can be used for any systems or apparatus, such as any uplink wireless communication device, that could benefit from any of the embodiments described herein. The teachings herein are applicable to a variety of systems. Although this disclosure includes some example embodiments, the teachings described herein can be applied to a variety of structures. Any of the principles and advantages discussed herein can be implemented in association with RF circuits configured to process signals in a range from about 30 kHz to 10 GHz, such as in the X or Ku 5G frequency bands.

Aspects of this disclosure can be implemented in various electronic devices. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products such as packaged radio frequency modules, uplink wireless communication devices, wireless communication infrastructure, electronic test equipment, etc. Examples of the electronic devices can include, but are not limited to, a mobile phone such as a smart phone, a wearable computing device such as a smart watch or an ear piece, a telephone, a television, a computer monitor, a computer, a modem, a hand-held computer, a laptop computer, a tablet computer, a microwave, a refrigerator, a vehicular electronics system such as an automotive electronics system, a stereo system, a digital music player, a radio, a camera such as a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multifunctional peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products.

While certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. Any suitable combination of the elements and acts of the various embodiments described above can be combined to provide further embodiments. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.