MEMS acoustic transducer and method for fabricating the same

A MEMS acoustic transducer is provided, which includes a substrate, a MEMS chip, and a housing. The substrate has a first opening area and a lower electrode layer disposed over a surface of the substrate, wherein the first opening area includes at least one hole allowing acoustic pressure to enter the MEMS acoustic transducer. The MEMS chip is disposed over the surface of the substrate, including a second opening area and an upper electrode layer partially sealing the second opening area, wherein the upper electrode layer and the lower electrode layer, which are parallel to each other and have a gap therebetween, form an induction capacitor. The housing is disposed over the MEMS chip or the surface of the substrate creating a cavity with the MEMS chip or the substrate. In addition, a method for fabricating the above MEMS acoustic transducer is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of Taiwan Patent Application No. 100144117, filed on Dec. 1, 2011 and Taiwan Patent Application No. 101120613, filed on Jun. 8, 2012, the entirety of which is incorporated by reference herein.

TECHNICAL FIELD

The disclosure relates to a semiconductor device, and relates to a MEMS acoustic transducer and method of fabrication thereof.

BACKGROUND

With the increasing miniaturization of integrated circuits and the development of consumer electronic devices such as mobile phones, notebook and laptop computers, personal digital assistants, and digital cameras, the obvious market trend is toward making these devices lighter, thinner, and more compact. Thus, various electronic components should be manufactured and integrated into consumer electronic devices in such a way as to take up less space, yet provide more functions and improved performance. In the cell phone industry, smartphones in particular need to integrate various electronic components having a small volume, multi-functionality and low-cost properties in a specific volume, for example, integrating transmission mediums such as microphones with other communication devices.

Electric condenser microphones (hereinafter referred to as ECM), which are constructed using electret materials, are the most-often used microphones in consumer electronic devices. However, the ECM has been gradually replaced with a micro-electro-mechanical system acoustic transducer (hereinafter referred to as MEMS acoustic transducer). In general, both the ECM and the MEMS acoustic transducers detect sound by sensing the capacitance variation produced by acoustic pressure. In the ECM, a capacitor is formed of electret polymer membranes having eternal isolated charges for sensing the capacitance variation. In the MEMS acoustic transducer, there is a MEMS chip and an ASIC chip. The MEMS chip includes a capacitor formed of a membrane and a rigid through-hole back electrode on a silicon substrate for sensing the capacitance variation from the acoustic pressure, and the capacitance variation is processed by the ASIC chip. When comparing the ECM with the MEMS acoustic transducer, the latter may have a lot of advantages such as low cost, at least 30% of height reduction in its packaging structure, and resistance to degradation due to temperature, moisture, vibration, and general wear and tear. Moreover, the MEMS acoustic transducer is capable of being integrated with a band RF filter on ICs to reduce the interference produced by the RF, and the noise can be eliminated using arrays and algorithms. Thus, the MEMS acoustic transducer is especially suitable for RF applications such as cell phones and other devices that operate along similar principles, such as hearing aids, for example.

Thus, it is predicted that the MEMS acoustic transducer will largely replace the electret condenser microphones as the related technology continues to improve. Sensitivity is a key indicator of the MEMS acoustic transducer's effectiveness. Sensitivity is not only determined by a membrane in the MEMS chip, but is also determined by the volume of a back cavity. The volume of the back cavity is a closed volume behind the membrane and stands in contrast to the encountered acoustic pressure, which may provide a flexible recovery force to the membrane and can be used for tuning the acoustic resistive and response properties of the MEMS acoustic transducer. In addition, the fabrication process of the MEMS acoustic transducer is complicated, and therefore it is difficult to increase the sensitivity of the MEMS acoustic transducer while reducing production costs.

FIG. 1shows a MEMS acoustic transducer packaging structure. In order to increase the volume of the back cavity107in a limited space, an interior housing111is added. The MEMS acoustic transducer includes a cavity106surrounded by a packaging substrate102and a housing104. The housing104has a sound-opening112for receiving acoustic pressure. A MEMS acoustic transducer116and an application-specific integrated circuit (ASIC) chip126are disposed on the interior housing111within the cavity106. The MEMS acoustic transducer116includes a silicon substrate120, a membrane118(upper electrode), and a backplate (through-hole back electrode)114suspended below the membrane118. The interior housing111and the packaging substrate102create the back cavity107of the MEMS acoustic transducer116. Thus, the height of the back cavity107is similar to that of the MEMS acoustic transducer packaging structure when excluding of the height of the MEMS acoustic transducer116, and therefore the volume of the back cavity107can be increased. However, there is still some space inside the packaging structure that cannot be used efficiently. In addition, the membrane118and the backplate114of the MEMS acoustic transducer116are two thin films which are hard to fabricate and easy to stick to each other. Thus, the MEMS acoustic transducer, as shown inFIG. 1, still cannot meet requirements of future applications.

SUMMARY

An embodiment of the disclosure provides a MEMS acoustic transducer, including: a substrate having a first opening area and a lower electrode layer disposed over a surface of the substrate, wherein the first opening area includes at least one hole allowing acoustic pressure to enter the MEMS acoustic transducer; a MEMS chip disposed over the surface of the substrate, including a second opening area and an upper electrode layer partially sealing the second opening area, wherein the upper electrode layer and the lower electrode layer, which are parallel to each other and have a gap therebetween, form an induction capacitor; and a housing disposed over the MEMS chip or the surface of the substrate, creating a cavity with the MEMS chip or the substrate.

An embodiment of the disclosure provides a method for fabricating a MEMS acoustic transducer, including: providing a substrate having a first opening area and a lower electrode layer disposed over a surface of the substrate, wherein the first opening area includes at least one hole allowing acoustic pressure to enter the MEMS acoustic transducer; mounting a MEMS chip over the surface of the substrate; and mounting a housing over the MEMS chip or the surface of the substrate to create a cavity with the MEMS chip or the substrate. The MEMS chip includes a second opening area and an upper electrode layer partially sealing the second opening area, wherein the upper electrode layer and the lower electrode layer, which are parallel to each other and have a gap therebetween, form an induction capacitor.

Another embodiment of the disclosure provides a MEMS acoustic transducer, including: a substrate having a indentation depressed from a surface of the substrate; a lower electrode layer disposed on the substrate and partially sealing the indentation to create a cavity; a MEMS chip having an opening area disposed over the surface of the substrate, wherein the opening area comprises at least one sound port allowing sound pressure to enter the MEMS acoustic transducer; and an upper electrode layer disposed on the opening area of the MEMS chip without covering the sound port, wherein the upper electrode layer and the lower electrode layer which are parallel to each other and have a gap therebetween form an induction capacitor.

DETAILED DESCRIPTION

The following description is of the best-contemplated mode of carrying out the disclosure. This description is made for the purpose of illustrating the general principles of the disclosure and should not be taken in a limiting sense. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

A micro-electro-mechanical systems acoustic transducer (MEMS acoustic transducer) and a method of fabrication thereof according to an embodiment of the disclosure are illustrated in the following description. The MEMS acoustic transducer may comprise a substrate having a first opening area and a MEMS chip having a second opening area. A lower electrode layer and an upper electrode layer are formed on the substrate and the MEMS chip, respectively, such that an induction capacitor is formed for sensing the acoustic pressure entering into the acoustic transducer.

FIGS. 2 and 2Aillustrate a cross-sectional view and an exploded view, respectively, of a MEMS acoustic transducer according to an embodiment of the disclosure. The MEMS acoustic transducer200may comprise a substrate202and a housing204. The substrate202may be a porous packaging substrate. The substrate202may comprise a ceramic packaging substrate, a printed circuit board (PCB), a silicon substrate, or a plastic substrate having leadframes. The substrate202may comprise a plurality of conductive traces208electrically connected to outer circuits such as other PCBs or other large electronic devices or systems. The substrate202may comprise a first opening area210. In an embodiment, the first opening area210may have at least one sound port212, such as the plurality of sound ports as shown inFIGS. 2 and 2A. The sound port212may be a through hole through the substrate202for allowing the acoustic pressure outside the MEMS acoustic transducer to enter the MEMS acoustic transducer and be sensed. In an embodiment, the substrate202may have an aperture ratio of between about 30% and about 40%. The housing204may be disposed on a surface203of the substrate202to create a cavity206with the substrate202. The housing204may be formed of conductive materials such as metal or plastic plated with metal, or ceramic materials plated with metal. The housing204may perform the function of shielding electromagnetic interference (EMI) and RF. In an embodiment, an anti-infrared coating or an anti-visible-light coating may be further coated on the housing204.

The MEMS chip216may be disposed over the surface203of the substrate202. The MEMS chip216may comprise an upper electrode layer218, a semiconductor chip224and a dielectric layer226interposed therebetween. In one embodiment, two surfaces of the dielectric layer226are attached on a surface of the upper electrode layer218and a surface of the semiconductor layer224, respectively. In addition, the MEMS chip216may further comprise a second opening area220aligned to the first opening area210. The second opening area220may comprise at least one hole222through the semiconductor chip224and the dielectric layer226. In this embodiment, the upper electrode layer218may be a vibration membrane disposed over the semiconductor chip224and may partially seal the second opening area220. The vibration membrane may be a thin film comprised of polysilicon, metal, or other conductive materials, and may vibrate in response to the acoustic pressure. In an embodiment, the upper electrode layer218may be a porous membrane for reducing stress on itself. The semiconductor chip224may be a chip manufactured from a semiconductor wafer or a silicon-on-insulator (SOI) wafer. The dielectric layer226may comprise silicon oxide or other suitable dielectric materials.

The lower electrode layer214may be disposed on the surface203of the substrate202. The lower electrode layer214may be a patterned conductive layer, for example, having the pattern shown in theFIG. 2A. In an embodiment, the lower electrode layer214may have a pattern including corresponding to the shape of MEMS chip216and covering the first opening area210of the substrate202and other areas, and the lower electrode layer214attached the substrate202but without sealing the sound port212. In other words, the sound port212may penetrate through the substrate202and the lower electrode layer214. Furthermore, the lower electrode layer214may also have a pattern corresponding to the circuit design, such as being directly or indirectly electrically connected to outer circuits via the conductive traces208. The lower electrode layer214may comprise metal or any other conductive materials. In this embodiment, the lower electrode layer214may be a layer fixed on the surface203of the substrate202, but it would not vibrate with the acoustic pressure. Thus, the lower electrode layer214may function as the backplate of the MEMS acoustic transducer. In addition, the lower electrode layer214may be parallel to the MEMS chip216with a vertical gap215(rather than zero) therebetween. In other words, in this embodiment, the upper electrode layer218and the lower electrode layer214of the MEMS acoustic transducer200may form the inductor capacitor (by using air as the capacitor dielectric), and the capacitance of the inductor capacitor may be determined from the overlapping area between the upper electrode layer218and the lower electrode layer214and the length of the vertical gap215. In an embodiment, the capacitance of the inductor capacitor may also vary with the sizes and numbers of the sound port212.

In an embodiment, an isolation element230may be disposed between the MEMS chip216and the surface203of the substrate202for providing the vertical gap215between the upper electrode layer218and the lower electrode layer214. The isolation element230may be conductive glue. For example, the MEMS chip216may be electrically connected to the lower electrode layer214, the conductive traces208, and outer circuits via the conductive glue, or may electrically connect to conductive traces208and outer circuits via the conductive glue232A and232B under the ASIC chip234. In this embodiment, the thickness of the isolation element230may determine the length of the vertical gap215. The isolation element230may comprise a pattern surrounding the first opening area210, such as an enclosed ring.

In an embodiment, the application-specific integrated circuit (ASIC) chip234may be fixed on the substrate202by the conductive glue232A and232B, and the ASIC chip234may have a gap or distance with the MEMS chip216. For example, the ASIC chip234may be disposed on the substrate202and outside the first opening area210. The ASIC chip234may comprise a front-end amplifier chip, analog/digital conversion integrated circuit, or another chip having similar functions. The ASIC chip234may have one end electrically connected to the MEMS chip216via the conductive glue232A and the lower electrode layer214for receiving the capacitance variation detected by the MEMS chip216. In addition, the ASIC chip234may have another end electrically connected to the conductive traces208through the conductive glue232B. The isolation element230, the conductive glue232A and232B may comprise silver glue, solder ball, or other surface mounting technologies. The conductive glue232A and232B, and the isolation element230may have the same or different thickness.

In another embodiment, the ASIC chip234and the MEMS chip216may be fabricated together using CMOS processes. The ASIC chip234may be integrated into the semiconductor chip224of the MEMS chip216for forming system-on-chip (SOC). In other embodiments, the ASIC chip234may also be integrated into the substrate202. Thus, the total volume of the MEMS acoustic transducer200may be further reduced.

In an embodiment, the housing204may be fixed on the surface203of the substrate202and be electrically connected to the conductive trace208in the substrate202via a conductive glue236. The conductive glue236may comprise silver glue, solder ball, or other surface mounting technologies.

During the operation of the MEMS acoustic transducer200, the outside acoustic pressure may enter the cavity206of the MEMS acoustic transducer200via the sound port212of the first opening area210of the substrate202, and the upper electrode layer218of the MEMS chip216may have a responsive vibration such that the capacitance between the upper electrode layer218and the lower electrode layer214may vary with the vibration. The capacitance variation may be received and processed by the MEMS chip216and the ASIC chip234. When compared to the conventional MEMS acoustic transducer in which the membrane (upper electrode) and the backplate (lower electrode) of the conventional MEMS acoustic transducer are both formed in the MEMS chip, the lower electrode layer214of the MEMS acoustic transducer200is on the substrate202and directly functions as the backplate. Thus, it may be omitted conductive layer which can form the induction capacitor with the upper electrode layer218existing in the MEMS chip216of the MEMS acoustic transducer200. The capacitor configured to sense the acoustic pressure change is formed of the upper electrode layer218in the MEMS chip216and the lower electrode layer214on the substrate202. In addition, the vertical gap215between the upper electrode layer218and the lower electrode layer214may be adjusted to be large enough by means of the isolation element230, and the sticking problems may be therefore overcome.

FIG. 3shows a cross-sectional view of a MEMS acoustic transducer300according to another embodiment of the disclosure. In this embodiment, the same reference numeral represents the same or similar materials or forming methods described in the above embodiments. Thus, some features which have been described above will not be further discussed in the following. In this embodiment, the main difference from the above embodiment is that the housing is directly disposed on the MEMS chip.

Referring toFIG. 3, the MEMS acoustic transducer300may comprise a substrate202and a MEMS chip216disposed thereof. The MEMS chip216may comprise a semiconductor chip224, a dielectric layer226and an upper electrode layer218. The substrate202may have a lower electrode layer214disposed on the surface203of the substrate202, without sealing the sound port212. In this embodiment, the upper electrode layer218may be a vibration membrane which may vibrate in response to the acoustic pressure, and the lower electrode layer214may be a rigid layer fixed on the surface203of the substrate202. The upper electrode layer218and the lower electrode layer214may be parallel to each other and have a vertical gap215therebetween. The vertical gap215may have a cylindrical shape such that the acoustic pressure may force to the upper electrode layer218(vibration membrane) through the sound port212and the vertical gap215.

In this embodiment, the housing304may be directly disposed on a side of the semiconductor chip224opposite to another side of the semiconductor chip224facing the upper electrode layer218. The housing304may seal a side of the hole or holes222of the second opening area220opposite to another side of the hole or holes222of the second opening area220facing the upper electrode layer218. Thus, a cavity is created by the housing304, the MEMS chip216, and the upper electrode layer218. In other words, the hole or holes222in the MEMS chip216and the dielectric layer226may be the cavity which serves as the back cavity of the MEMS acoustic transducer300. In an embodiment, the housing304may be formed of polyimide.

In an embodiment, the ASIC chip (not shown) and the MEMS chip216may be fabricated together using CMOS processes. The ASIC chip may be integrated into the semiconductor chip224of the MEMS chip216for forming system-on-chip (SOC). In another embodiment, the ASIC chip also disposed in the substrate202.

It is understood that, in this embodiment, the acoustic pressure may enter the MEMS acoustic transducer300from the backside of the substrate202and through the sound port212of the first opening area210. In addition, since the housing304is directly disposed on the MEMS chip216, the at least one hole222may serve as the back cavity of the MEMS acoustic transducer300. Accordingly, the MEMS acoustic transducer300may have a reduced total thickness. The MEMS acoustic transducer300is not only in prone to the light-thinning trend, but also has a high sensitivity which would not be sacrificed with reduced volume. In addition, the volume of the back cavity is determined by the MEMS chip and would not be limited by the thickness of the substrate. Therefore, for the same structures or elements is not repeat again here.

FIG. 4shows a cross-sectional view of a MEMS acoustic transducer400according to another embodiment of the disclosure. In this embodiment, the same reference numeral represents the same or similar materials or forming methods described in the above embodiments. Thus, some features which have been described above will not be further discussed in the following. In this embodiment, the main difference from the above embodiment is that the isolation elements are provided by the substrate.

Referring toFIG. 4, the MEMS acoustic transducer400may comprise a substrate202and a MEMS chip216disposed thereon. An upper electrode layer218may be disposed on a lower side of the MEMS chip216. A lower electrode layer214may be disposed on a surface203of the substrate202, without sealing the sound port212of the first opening area210. In this embodiment, the upper electrode layer218may be a vibration membrane which may vibrate in response to the sound pressure, and the lower electrode layer214may be a rigid layer fixed on the surface203and the substrate202.

In this embodiment, an isolation element440may be formed on the substrate202. The isolation element440may have the same material with the substrate202, such as ceramic packaging materials, PCB materials or plastic materials having leadframes. The isolation element440and the substrate202may be fabricated by the same or different processes. For example, the isolation element440and the substrate202are an integrated unibody. In an embodiment, the ASIC chip (not shown) may also be integrated in the substrate202. Alternatively, the ASIC chip (not shown) and the MEMS chip216may be fabricated together using CMOS processes and the ASIC chip is integrated into the MEMS chip216with the semiconductor chip224for forming system-on-chip (SOC).

The isolation element440may have a height for providing the vertical gap215between the MEMS chip216and the substrate202. The vertical gap215may have a distance disposed between the upper electrode layer218of the MEMS chip216and the lower electrode layer214of the substrate202. Conductive glue230may be injected into the vertical gap215. In comparison to the above embodiments in which the height of the vertical gap215is achieved by using the conductive glue, controlling the vertical gap215by means of the isolation element440may be easier and more accurate. In addition, the overlapping area of a pattern of the lower electrode layer214and the upper electrode layer218may also vary by the horizontal disposition of the isolation element440. Thus, the MEMS acoustic transducer400may be fabricated by an easier process. As such, the capacitance of the inductor capacitor and the MEMS acoustic transducer400may have higher accuracy. In addition, the vertical gap215between the upper electrode layer218and the lower electrode layer214may be also tuned to be large enough by means of the isolation elements440, and sticking problems may be therefore overcome. The isolation element440may be an enclosed ring such that the acoustic pressure may force to the upper electrode layer218(vibration membrane) through the sound port212.

Moreover, the housing204may be directly attached on the upper side of the MEMS chip216, and the following embodiments may also vary with similar structures.

FIG. 5shows a cross-sectional view of a MEMS acoustic transducer according to a further embodiment of the disclosure. In this embodiment, the same reference numerals represent the same or similar materials or forming methods described in the above embodiments. Thus, some features which have been described above will not be further discussed in the following. In this embodiment, the main difference from the above embodiments is that the MEMS chip may have an extension portion for providing the vertical gap between the upper and lower electrode layers.

Referring toFIG. 5, the MEMS acoustic transducer500may include a substrate202and a MEMS chip216disposed thereon. The MEMS chip216may comprise an upper electrode layer218, a semiconductor chip and a dielectric layer226. The semiconductor chip may comprise a main portion224A and an extension portion224B extending outwardly from the main portion224A. The main portion224A and the extension portion224B of the semiconductor chip may be formed from a silicon substrate. For example, the main portion224A and the extension portion224B of the semiconductor chip may be formed from the same silicon substrate and have the desired shapes and thicknesses by using lithography processes. In an embodiment, the main portion224A and the extension portion224B of the semiconductor chip may be an integrated unibody. In other embodiments, the extension portion224B of the MEMS chip216may be a silicon oxide layer on the main portion224A formed by thermal oxide. The extension portion224B may have a ring shape. The upper electrode layer218may be formed on the main portion224A of the semiconductor chip224and be surrounded by the extension portion224B. A lower electrode layer214may be formed on a surface203of the substrate202, without sealing the sound ports212of a first opening area210. In this embodiment, the upper electrode layer218may be a vibration membrane which may vibrate in response to the sound pressure, and the lower electrode layer214may be a rigid layer fixed on the surface203of the substrate202. The upper electrode layer218and the lower electrode layer214may be parallel to each other and have a vertical gap215therebetween. In an embodiment, the ASIC chip (not shown) and the MEMS chip216may be formed together by using CMOS processes, and therefore the ASIC chip may be integrated into a semiconductor chip of the MEMS chip216for forming system-on-chip (SOC). In other embodiments, the ASIC chip may be integrated into the substrate202.

The extension portion224B of the MEMS chip216may have a height for providing the vertical gap215between the upper electrode layer218on the main portion224A of the semiconductor chip and the lower electrode layer214on the substrate202, when mounting the MEMS chip216onto the substrate202. Conductive glue230may be injected form the vertical gap215. In comparison to the above embodiments in which the height of the vertical gap is determined by using conductive glue, controlling the vertical gap215by means of the extension portion224B of the semiconductor chip may be easier and more accurate. In addition, the overlapping area of the lower electrode layer214and the upper electrode layer218may be also varied by the horizontal disposition of the extension portion224B of the MEMS chip216such that the capacitance may be tuned with high accuracy. As such, the accuracy of the MEMS acoustic transducer may be therefore improved. In addition, the MEMS acoustic transducer500may be fabricated by an easier process since the extension portion224B may be fabricated within the fabrication of the MEMS chip. The vertical gap215between the upper electrode layer218and the lower electrode layer214may be tuned to be large enough by means of the extension portion224B of the MEMS chip216, and sticking problems may be therefore avoided. Further, the housing204can also attach over an upper side of the MEMS chip216.

FIG. 6shows a cross-sectional view of a MEMS acoustic transducer600according to an alternative embodiment of the disclosure. In this embodiment, the same reference numeral represents the same or similar materials or forming methods described in the above embodiments. Thus, some features which have been described above will not be further discussed in the following.

The MEMS acoustic transducer600may comprise a substrate602and a housing604. The housing604may be disposed on the substrate602creating a cavity606with the substrate602. The substrate602may be a porous packaging substrate. The substrate602may comprise a ceramic packaging substrate, a printed circuit board, a silicon substrate, or a plastic substrate having leadframes. The substrate602may have a plurality of conductive traces608for electrically connecting to other PCBs or other larger electronic devices or systems. The substrate602may comprise a first opening area610. In an embodiment, the first opening area610may comprise at least one hole612. A lower electrode layer618may be disposed on the substrate602. The lower electrode layer618may be a porous vibration membrane which may vibrate in response to the sound pressure. The lower electrode layer618may have a plurality of holes613for reducing stress on itself and allowing outer sound pressure entering the MEMS acoustic transducer600. In an embodiment, the lower electrode layer618may be formed of polysilicon, metal or other conductive materials.

A MEMS chip616may be disposed on a surface603of the substrate602. The MEMS chip616may comprise a second opening area620substantially aligned to the first opening area610. The second opening area620may comprise a hollow portion623and at least one through hole622through the MEMS chip616. The hollow portion623may be extended from a surface of the MEMS chip616to an inter-level of the MEMS chip616, but does not penetrate through the MEMS chip616. The hollow portion623may provide more volume for the back cavity. The at least one through hole622may be extended from a bottom of a hollow portion623. The MEMS chip616may be fabricated from a semiconductor wafer or a silicon-on-insulator wafer. For example, the MEMS chip616may comprise a semiconductor chip having a main portion624A and an extension portion624B, a dielectric layer626and an upper electrode layer614. The dielectric layer626may be disposed between the upper electrode layer614and the main portion624A of the MEMS chip616. The main portion624A and the extension portion624B of the semiconductor chip may be formed from a silicon substrate. The extension portion624B of the semiconductor chip may be outwardly extended from the main portion624A such that a gap may be formed from the substrate602to the main portion624A of the semiconductor chip and the upper electrode layer614, when mounting the MEMS chip616onto the substrate602. In an embodiment, the main portion624A and the extension portion624B of the semiconductor chip may be formed together from the same silicon substrate using COMS processes. In other embodiments, the extension portion624B of the semiconductor chip may be a silicon oxide layer on the main portion of624A formed by thermal oxide. The dielectric layer626may comprise silicon oxide or other dielectric materials.

The upper electrode layer614may be disposed on the main portion624A of the semiconductor chip. For example, in this embodiment, the upper electrode layer614may be disposed on the main portion624A of the MEMS chip616, without sealing the through holes622. Note that, in this embodiment, the upper electrode layer614may be a rigid layer fixed on the surface of the MEMS chip616but that does not vibrate with the sound pressure, so that the upper electrode layer614may serve as the backplate of the MEMS acoustic transducer600.

The lower electrode layer618on the substrate602and the upper electrode layer614on the MEMS chip616may be parallel to each other and have a vertical gap615therebetween. Thus, the lower electrode layer618and the upper electrode layer614over the lower electrode layer618may form an induction capacitor (by using air as the capacitor dielectric), and the capacitance may be determined by the overlapping area of the upper and lower electrode layers and the length of the vertical gap615. In an embodiment, the length of the vertical gap615may be determined by the thickness of the extension portion624B of the MEMS chip616. In addition, the capacitance of the induction capacitor may also vary with the sizes and numbers of the through holes622.

In an embodiment, the ASIC chip (not shown) and the MEMS chip616may be formed together by using CMOS processes, and therefore the ASIC chip may be integrated into the main portion624A of semiconductor chip for forming system-on-chip (SOC). In other embodiments, the ASIC chip may be also integrated into the substrate602. Thus, the MEMS acoustic transducer600may have a reduced volume. In an embodiment, an conductive glue630may be injected into the vertical gap615between the upper electrode layer614and the substrate602for transmitting signals of the MEMS chip616to outer circuits. In an embodiment, the housing604may be mounted onto the surface603of the substrate602by the conductive glue636. The conductive glue630and636may comprise silver glue, solder balls, or other surface mount technologies. Furthermore, in an embodiment, the housing604may be directly disposed onto the MEMS chip616, similar with the housing304shown inFIG. 3.

In summary, during the operation of the MEMS acoustic transducer600, the sound pressure outside the cavity606may enter the cavity606of the MEMS acoustic transducer600via the holes612and613of the first opening area610of the substrate602. The lower electrode layer618may vibrate corresponding to the sound pressure, resulting in a capacitance variation between the upper electrode layer614and the lower electrode layer618. The capacitance variation may be received and processed by the MEMS chip616and the ASIC chip. Thus, there is no other conductive layer which can form the induction capacitor with the upper electrode layer614existing in the MEMS chip616of the MEMS acoustic transducer600according to the disclosure. The induction capacitor capable of sensing the changes of the sound pressure may be formed from the lower electrode layer618on the substrate602and the upper electrode layer614on the MEMS chip616.

FIG. 7shows a cross-sectional view of a MEMS acoustic transducer700according to another alternative embodiment of the disclosure. In this embodiment, the same reference numerals represent the same or similar materials or forming methods described in the above embodiments. Thus, some features which have been described above will not be further discussed in the following.

The MEMS acoustic transducer700may comprise a substrate702, such as a porous packaging substrate. The substrate702may comprise a ceramic packaging substrate, a printed circuit board substrate, a silicon substrate, or a plastic substrate having leadframes. The substrate702may have a plurality of conductive traces708for electrically connecting to PCB or other larger electronic devices or systems. The substrate702may comprise a indentation712depressed from a surface703of the substrate702.

A MEMS chip716may be disposed on the surface703of the substrate702. The MEMS chip716may comprise an opening area720substantially aligned to the indentation712. The opening area720may comprise at least one through hole722through the MEMS chip716. The through hole722may be a sound port allowing the outside sound pressure to enter the MEMS acoustic transducer700to be sensed. The MEMS chip716may be fabricated from a semiconductor wafer or a silicon-on-insulator wafer. For example, the MEMS chip716may comprise a semiconductor chip having a main portion724A and an extension portion724B, a dielectric layer726and an upper electrode layer714. The dielectric layer726may be disposed between the upper electrode layer714and the main portion724A. In an embodiment, the extension portion724B of the semiconductor chip may be outwardly extended from the main portion724A such that a gap may be formed from the substrate702to the main portion724A of the semiconductor chip and the upper electrode layer714. The main portion724A and the extension portion724B of the semiconductor chip may be fabricated together from the same silicon substrate using CMOS processes. In an embodiment, the extension portion724B of the semiconductor chip may be a silicon oxide layer on the main portion724A formed by thermal oxide. The dielectric layer726may comprise silicon oxide or other dielectric materials.

The upper electrode layer714may be disposed on a lower side of the main portion724A of the semiconductor chip. For example, in this embodiment, the upper electrode layer714and the dielectric layer726may be disposed on the main portion724A of the semiconductor chip. The upper electrode layer714and the dielectric layer726may have a portion located in the opening area720, without sealing the sound port. The upper electrode layer714may be a rigid layer fixed on the surface of the MEMS chip716but does not vibrate with the sound pressure, for serving as the backplate of the MEMS acoustic transducer700.

The lower electrode layer718may be disposed on the substrate702. For example, in this embodiment, the lower electrode layer718may be directly disposed on the substrate702and partially seal the opening of the indentation712. The lower electrode layer718may be a vibration membrane which may vibrate in response to the sound pressure that enters via the though holes722. In addition, the lower electrode layer718may have a plurality of holes713for reducing stress on itself. The lower electrode layer718may be formed of polysilicon, metal, and other conductive materials. Furthermore, the lower electrode layer718the upper electrode layer714may be parallel to each other and have a vertical gap715therebetween. Thus, the lower electrode layer718and the upper electrode layer714over the lower electrode layer718may form an induction capacitor (by using air as the capacitor dielectric), and the capacitance may be determined by the overlapping area of the upper and lower electrode layers and the length of the vertical gap715. The length of the vertical gap715may be determined by the thickness of the extension portion724B of the MEMS chip716. In this embodiment, the indentation712may serve as the back cavity of the MEMS acoustic transducer700. Therefore, the volume of the back cavity may be determined by the size of the indentation712.

In an embodiment, the ASIC chip (not shown) and the MEMS chip716may be formed together by using CMOS processes, and therefore the ASIC chip may be integrated into the main portion724A of the semiconductor chip for forming system-on-chip (SOC). In other embodiments, the ASIC chip may be integrated into the substrate702. Thus, the MEMS acoustic transducer700may have a reduced volume. In an embodiment, an conductive glue730, such as conductive glue, may be injected into the vertical gap715between the MEMS chip716and the substrate702for transmitting signals of the MEMS chip716to outer circuits.

In summary, during the operation of the MEMS acoustic transducer700, the outside sound pressure may enter the MEMS acoustic transducer700, such as entering the indentation712, via the though holes722of the opening area720of the MEMS chip716. Thus, a housing is unnecessary for the MEMS acoustic transducer700. The cavity created by the housing and the substrate in other embodiments may be directly replaced by the indentation712. The lower electrode layer718of the MEMS chip716may vibrate in response to the entered sound pressure resulting in a capacitance variation between the upper electrode layer714and the lower electrode layer718. The capacitance variation may be received and processed by the MEMS chip716and the ASIC chip. Thus, there is no conductive layer which can form the induction capacitor with the upper electrode layer714existing in the MEMS chip716of the MEMS acoustic transducer700according to the disclosure. The induction capacitor capable of sensing the changes of the sound pressure may be formed from the lower electrode layer718and the upper electrode layer714on the MEMS chip716.

FIGS. 8A˜8Cshow cross-sectional views of a method of fabricating a MEMS acoustic transducer at various stages according to an embodiment of the disclosure.FIGS. 8A˜8Cillustrate the method for fabricating the MEMS acoustic transducer200shown inFIG. 2, however, one skilled in the art can understand that similar concepts may also apply to other embodiments of the disclosure. In this embodiment, the same reference numerals represent the same or similar materials or forming methods described in the above embodiments.

Referring toFIG. 8A, a substrate202is provided first. The substrate202may comprise an opening area210. In an embodiment, the opening area210may comprise one or more sound port212. The sound port212may be formed by a CO2laser, UV-YAG laser, or other laser micro-drilling method. In addition, the substrate202may have a patterned lower electrode layer214disposed on a surface203of the substrate202. The substrate202may comprise a plurality of conductive traces208for electrically connecting to outer circuits. For example, the conductive traces208may be a through substrate via (TSV). As described above, the lower electrode layer214may have a pattern as shown inFIG. 2A, which comprises a pattern including corresponding to the shape of MEMS chip216and covering the opening area210of the substrate202and other areas, without sealing the sound port212.

Then, as shown inFIG. 8B, the MEMS chip216and the ASIC chip234are mounted on the substrate202. The MEMS chip216may be aligned to the first opening area210of the substrate202and mounted thereon using the conductive glue230. Thus, the MEMS chip216may be electrically connected to the lower electrode layer214via the conductive glue230. In an embodiment, the ASIC chip234and the MEMS chip216may be separately mounted on the substrate202. For example, the ASIC chip234may have one end electrically connected to the MEMS chip216via the conductive glue232A and the lower electrode layer214and have another end electrically connected to the conductive traces208in the substrate202via the conductive glue232B. In another embodiment, the ASIC chip234may be directly integrated to the MEMS chip for forming system-on-chip (SOC). In other embodiments, the ASIC chip may be integrated into the substrate202.

Finally, referring toFIG. 8C, a housing204is mounted on the surface203of the substrate202and a cavity206is accordingly formed. As such, the MEMS acoustic transducer200as shown inFIGS. 2 and 2Ais completed. The housing204may be fixed on the substrate202and electrically connected to the conductive traces208via the conductive glue236. The MEMS chip216and the ASIC chip234are both disposed in the cavity206.

FIGS. 8A˜8Cshow a method of fabricating the MEMS acoustic transducer according to an embodiment of the disclosure. For example, a substrate202having an opening area210is provided first, and then the MEMS chip216and the housing204are mounted. In addition, in the fabrication of the MEMS chip216, the dielectric layer226and the semiconductor chip224could be fabricated, rather than fabricating the backplate as shown inFIG. 1. Thus, the fabricating process can be further simplified, and the time and the cost can be also reduced.

In addition to the fabricating processes illustrated above, the fabricating processes may be also varied by one skilled in the art. For example, the housing may be directly mounted onto the MEMS chip; the conductive glue may be injected after the vertical gap is provided and controlled by the isolation element or the extension portion of the MEMS chip; the upper electrode layer may be mounted on the MEMS chip which is on the substrate after forming the lower electrode layer on the substrate; and/or forms a indentation within the substrate for instead of the cavity formed by the conductive housing and the substrate or MEMS chip.

The MEMS acoustic transducer described above may be applied to various electronic devices. For example, the electronic device may comprise a consumer electronic device, a part of the consumer electronic device, or electronic testing instruments. The consumer electronic device may comprise a cell phone, television, screen, computer, notebook or laptop computer, personal digital assistant, refrigerator, vehicle, stereo set, multimedia player, mp3 player, digital camera, washing machine, tumble, copier, scanner or watch.