WO2007010421A2

WO2007010421A2 - Mems microphone and package

Info

Publication number: WO2007010421A2
Application number: PCT/IB2006/052262
Authority: WO
Inventors: Langereis Geert
Original assignee: Koninklijke Philips Electronics N. V.
Priority date: 2005-07-18
Filing date: 2006-07-05
Publication date: 2007-01-25
Also published as: TW200711510A; WO2007010421A3

Abstract

A microphone package has a first die (10), a microphone (15) formed on the first die, one or more passive components (20) formed on the first die, and an integrated circuit (25) on a second die (30), mounted on the first die and electrically coupled to the microphone or passive components. Compared to integrating the microphone on the same die as an integrated circuit, the first die can use fewer layers, and fewer processing steps. An integrated capacitive microphone has a diaphragm (70, 230) and a backplate (120, 190) for the microphone made of Al or AlCu on a substrate (40). These materials are more conductive and therefore the associated circuitry can be more sensitive or use less power. Forming the diaphragm and backplate by evaporation or sputtering of Al or AlCu on a substrate is more cost effective.

Description

MEMS microphone and package

This invention relates to MEMS devices especially to pressure sensors in general and to pressure sensors with an optimized frequency range such as microphones and to packages having pressure sensors optimised for a certain frequency range such as microphones, and methods of manufacturing such devices.

In many systems having microphones, such as mobile phones, there is demand to reduce size and manufacturing costs. Electronics associated with the microphone may comprise pre- amplifiers (for the high-impedance capacitive transducer), biasing circuit (for non-electret type microphones at least), A/D converters and signal processing. PCB mounting is often preferred by mobile phone manufacturers; to conform with existing high speed assembly lines. The commonly used electret microphones do not have the desired form factor for integration with their associated electronics and cannot be soldered because the electrical charge would be lost due to heating. It is known to use Miniaturised ElectroMechanical Systems (referred to as "MEMS") type microphones, as discussed in "The top ten reason for using MEMS in cell phones" In-Stat MDR, September 2003. One advantage is that such MEMS type microphones can be less sensitive to damage by heating during soldering operations.

It is known from US 5,870,482 that miniature silicon condenser microphones which can be integrated with CMOS circuitry require a number of trade-offs to achieve high sensitivity and low noise in the smallest volume. Typically a condenser microphone system consists of four elements; a fixed, perforated backplate, a highly compliant, moveable diaphragm (which together form the two plates of a variable air-gap capacitor), a voltage bias source, and a buffer amplifier. The diaphragm must be highly compliant and precisely positioned relative to the backplate, while the backplate must remain stationary and present a minimum of resistance to the flow of air through it. Achieving all of these characteristics in microphones below 1 mm in size using integrated circuit materials has been challenging. Typical stress levels in integrated circuit thin films, if not relieved in the finished diaphragm, are many times greater than the levels at which the diaphragm becomes unusable due to over- stiffening or buckling. Compliance tends to decrease very rapidly with decreasing size for a given diaphragm material and thickness. The known system proposes providing an alternative diaphragm and backplate construction in which the form of the diaphragm is based on a cantilever and in which alternate configurations for venting the backplate, appropriate for sub-mm-size microphones are used.

MEMS microphone principles are explained further in: P.R. Scheeper, A.G.H. van deer Donk, W. Olthuis and P. Bergveld, Fabrication of silicon condenser microphones using single wafer technology, Journal of Microelectromechanical Systems, Vol. I, No.3, September 1992, M. Pedersen, W. Olthuis and P. Bergveld, An Integrated silicon capacitive microphone with frequency-modulated digital output, Sensors and Actuators A69 (1998), pp. 267-275 and JJ. Neumann Jr. and KJ. Gabriel, CMOS MEMS membrane for audiofrequency acoustic actuation, Sensors and Actuators A95 (2002), pp. 175-182

It is known from US patent application 2005/0018864 to build microphone elements on the surface of a silicon die. To protect the transducer from outside interferences while having an acoustic pressure reference, the silicon die must be shielded. For instance, insulated metal cans or discs have been provided, or DIPs and small outline integrated circuit (SOIC) packages have been utilized. To improve lead time, cost, and tooling, this patent application proposes a silicon condenser microphone package that allows acoustic energy to contact a transducer disposed within a housing. The housing provides the necessary pressure reference while at the same time protects the transducer from light, electromagnetic interference, and physical damage. The substrate may have an upper surface with a recess formed therein allowing the transducer to be attached to the upper surface and to overlap at least a portion of the recess thus forming a back volume. The cover is placed over the transducer and includes an aperture adapted for allowing sound waves to reach the transducer. An environmental barrier over or within the aperture for protecting the transducer unit from environmental elements such as sunlight, moisture, oil, dirt, and/or dust is typically a polymeric material formed as a film, such as a polytetrafluoroethylene (PTFE) or a sintered metal. The environmental barrier layer may be secured between layers of conductive material thereby permitting the layers of conductive material to act as a capacitor (with electrodes defined by the metal) that can be used to filter input and output signals or the input power. The environmental barrier layer may further serve as a dielectric protective layer when in contact with the conductive layers in the event that the conductive layers also contain thin film passive devices such as resistors and capacitors. A known microphone and amplifier package made by Knowles has a MEMS microphone packaged with a CMOS integrated circuit and RF filtering capacitors. Another known arrangement, the Sonion MEMS/Microtronic "SiMic" has an Si substrate on which is mounted a microphone chip and an ASIC, referred to in Udo Klein, Matthias Mullenborn and Primin Rombach, "The advent of silicon microphones in high- volume applications", MSTnews 021/1, pp. 40-41, and in patent application WO2004057909.

An object of the invention is to provide improved MEMS devices such as pressure sensors in general and especially to improved pressure sensors optimized for a certain frequency range such as microphones, and to packages having such sensors, e.g. microphones, and methods of manufacturing such devices. The present invention can provide a pressure sensor optimised for a certain frequency range such as a microphone, for example in the range 10Hz to 10kHz. According to a first aspect, the invention provides:

A pressure sensor package such as a microphone package having a first die, a pressure sensor such as the microphone formed on the first die, one or more passive components formed on the first die, and at least one other component electrically coupled to the pressure sensor, e.g. the microphone or passive components. Compared to integrating the microphone on the same die as an integrated circuit, the first die can be made more simply and cost effectively, typically with fewer layers, and fewer processing steps. Yet by integrating the passive components with the microphone, the package size and/or number of manufacturing/assembly steps can be reduced, compared to using discrete passive components. Thus, in this unusual case, the overall cost of the two dies can be lower than the overall cost of a single more highly integrated die.

Another feature of some embodiments is the other component comprising an integrated circuit formed on a second die.

Having separate dies means each can be made more cost effectively, to keep the cost of the package lower, while reducing the amount of circuitry external to the package and so reducing overall part count or assembly costs associated with such external circuitry. The first aspect is intended to encompass alternatives such as the other components being formed on the first die, or off the first die, on a common substrate. The substrate may be a semiconductor substrate, for example. Another feature of some or all of the embodiments is the first or the second die being mounted on the other of the dies, and having an electrical connection between the dies using the contacts. This can help reduce the space required, and can ease assembly if connecting wires can be shortened or removed. Again, the first aspect is intended to encompass other alternatives such as the second die being mounted off the first die, on a common substrate.

Another feature of some embodiments is the microphone having an etched structure in a semiconductor substrate, e.g. silicon. This is a feature of MEMS devices which can follow established manufacturing techniques. Another feature of some embodiments is the microphone having two parallel electrodes forming a capacitor, whose capacitance varies according to received sound waves.

Another feature of some embodiments is one of the electrodes comprising a compliant microphone diaphragm formed of metal, e.g. Al or aluminium alloys such as AlCu. Aluminium or its alloys has the advantage of having a low mass and being highly conductive. The electrical resistance of the metal, e.g. Al layer is much lower than when using doped polysilicon or a thin Cr/ Au/ Al film on silicon nitride. The square resistance can be lower by a factor of over 1000, which improves the performance over other MEMS techniques.

Another feature of some embodiments is another of the electrodes being a backplate formed of metal e.g. aluminium or an aluminium alloy such as AlCu. The electrical resistances of the AlCu layer is much lower than when using doped polysilicon or a Cr/ Au/ Al film on silicon nitride. The square resistance can be lower by a factor of over 1000, which improves the performance over other MEMS techniques. Optimisation of the frequency range of the pressure sensitive device can be done by the acoustical design: the positioning of holes in the backplate and selecting the air-gap thickness.

Another such additional feature is the package being suitable for soldering to a circuit board. This can be commercially important to facilitate use with existing assembly equipment. That is the device has means suitable for soldering, e.g. a ball grid array or by means of wave soldering. Another aspect of the invention provides a device having a first and a second die, one mounted on the other, the first or second die having a first surface suitable for mounting on a circuit board, and having a second surface for mounting the other of the dies, facing away from the circuit board when mounted, the first die having an integrated MEMS device, and one or more integrated passive components, the second die having an integrated circuit.

This can enable corresponding advantages as discussed above. An additional feature of some embodiments is the integrated passive components being located under the second die. This can help reduce the size of the first die, for a more compact device.

Another additional feature is the first die being substantially planar, the first and second surfaces being the major surfaces, and the MEMS device comprising a microphone extending through the first die. Alternatives such as the first and second surfaces not being parallel are intended to be encompassed.

Another aspect of the invention provides:

A method of manufacturing a package having two or more dies, one of the dies having an integrated MEMS device and one or more integrated passive components, a second of the dies having integrated circuits, the method having the step of mounting either of the first or second dies on the other.

This can help enable a more compact package with a smaller footprint than if the dies are mounted separately. Yet, compared to integrating all on a single die, having a separate die for the MEMS and passives can reduce the cost for the following reasons. A simpler, cheaper integration technology can be used for the first die having the MEMS, compared to that needed for the integrated circuit. This can help reduce the cost of the die used for the MEMS. Furthermore, the size of the more expensive second die is much reduced if the relatively large MEMS and passive devices are removed. Thus, in this unusual case, the overall cost of the two dies can be lower than the overall cost of a single more highly integrated die. By integrating the passive components with the MEMS, the size and/or number of manufacturing/assembly steps can be reduced, compared to using discrete passive components. As MEMS devices are relatively tolerant to soldering, it is relatively easy to make the package suitable for assembly by conventional soldering techniques on conventional assembly lines.

The use of MEMS technology can have the advantage of providing the possibility of making small air gaps which require much lower biasing voltages than the conventional miniature microphones. The low bias voltage allows avoidance of the electret and to work with an DC voltage for biasing. If electret is not used, the device can be optimised for soldering. An additional feature of some embodiments is the method having the step of forming a diaphragm or a backplate for the microphone component by evaporation or sputtering.

Another aspect provides an integrated capacitive microphone having a diaphragm and a backplate for the microphone made of a metal such as Al or an aluminium alloy such as AlCu on a substrate.

Another aspect of the invention provides a method of manufacturing a capacitive pressure sensor such as a microphone having the steps of forming a diaphragm and a backplate for the pressure sensor, e.g. the microphone by evaporation or sputtering of metals such as Al or an aluminium alloy such as AlCu on a substrate. The advantage of aluminium or its alloys is the combination of low weight and high conductivity. Addition of other metals in an alloy such as by adding Cu, can control the stress.

A variety of substrates can be used especially those which can be etched easily, e.g. silicon, using an anisotropic etching with KOH. Although the semiconductor property of the silicon substrate is not an essential aspect of the present invention.

The method can be more cost effective than the conventional materials and methods for integrated microphones. Also the materials are more conductive and therefore the associated circuitry can be more sensitive or use less power for example. Another additional feature of some embodiments is etching away the substrate underneath the diaphragm after the diaphragm is formed. This leaves the diaphragm suspended and movable, and is not done in a conventional PASSI type process.

An additional feature of some embodiments is forming a first insulating layer on a semiconductor substrate, e.g. a silicon substrate, before forming the diaphragm. Another such additional feature is forming a second insulating layer over the diaphragm.

Another such additional feature is forming a sacrificial layer over the second insulating layer, to define a gap between the diaphragm and the backplate.

Another such additional feature is the step of forming the backplate over the sacrificial layer.

Another such additional feature is the step of forming holes to reach the sacrificial layer, then etching away the sacrificial layer

Any of the additional features can be combined together and combined with any of the aspects. Other advantages will be apparent to those skilled in the art, especially over other prior art. Numerous variations and modifications can be made without departing from the claims of the present invention. Therefore, it should be clearly understood that the form of the present invention is illustrative only and is not intended to limit the scope of the present invention.

How the present invention may be put into effect will now be described by way of example with reference to the appended drawings, in which:

Fig 1 shows a cross section of an embodiment having microphone and passives in one die and the electronics in a second die,

Figs 2 to 16 show steps in a manufacturing process according to an embodiment,

Fig 17 shows a cross sectional view of an embodiment of the microphone,

Fig 18 shows a perspective view of an embodiment of the microphone, Fig 19 shows a plan view of another embodiment of the microphone, and

Fig 20 shows a cross section of another embodiment of the microphone.

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. Any reference signs in the claims shall not be construed as limiting the scope. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun e.g. "a" or "an", "the", this includes a plural of that noun unless something else is specifically stated.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

The term "MEMS device" relates to any batch processable micromechanical system.

The embodiments show examples including integrating a MEMS microphone with passive components into a single die which can act as the base-plate for mounting an active CMOS chip. The processing may be based on standard silicon processing but the present invention is not limited thereto. An example of a suitable manufacturing implementation is based on the passive integration in silicon (PASSI™) platform which is known for integrating resistors, coils and capacitors. This is cost effective as it is based on an existing silicon process flow. An integrated microphone with associated electronics usually has a MEMS microphone chip, a CMOS chip and some external passive components in a single package. The electronics may comprise a selection from for example: a pre-amplifier; a voltage multiplier; an AID converter and digital signal processing circuitry, depending on the application. The external passive components can be used for the voltage multiplier or for decoupling purposes for example. If the microphone were integrated on the same die as the CMOS electronics as has been suggested, the present inventors have appreciated that this involves combining expensive/small- surface CMOS technology with a cheaper/large-surface MEMS microphone, so the result is a microphone at the higher costs of a CMOS die. The embodiments are based on the realisation that a separate CMOS- die and a separate dedicated MEMS-chip in the same package can be more cost effective.

The embodiments show examples in which the MEMS device (such as a microphone, or other sensor or device) and the external passive components are integrated into a single die which can act as the base -plate for mounting the CMOS chip. The CMOS chip can have electronics associated with the MEMS sensor or microphone, or can have other circuitry not associated with the MEMS. One example is a capacitive MEMS microphone manufactured by a new process based on known PASSI™- technology Fig 1, embodiment with two dies.

According to first embodiment of the invention, fig 1 shows a first die 10 comprising a semiconductor material, e.g. silicon in this example, and a second die 30, also of a semiconductor material, e.g. silicon in this example. In embodiments of the present invention, the term "substrate" may include any material or materials that may be used to form MEMS devices thereon. For integration purposes the substrate may be such that a device, a circuit or an epitaxial layer may be formed thereon. In embodiments, this "substrate" may include an insulating material or a conductive material or a semiconductor substrate such as e.g. doped silicon, a gallium arsenide (GaAs), a gallium arsenide phosphide (GaAsP), an indium phosphide (InP), a germanium (Ge), or a silicon germanium (SiGe) substrate. The "substrate" may include for example, an insulating layer such as a SiO₂ or a silicon-nitride layer in addition to a semiconductor substrate portion. Thus, the term substrate also includes silicon-on-glass, silicon-on sapphire substrates. The term "substrate" is thus used to define generally the elements for layers that underlie a layer or portions of interest. Also, the "substrate" may be any other base on which a layer is formed, for example a glass or metal layer.

Integrated in the first die is a microphone 15, and passive components 20, in this case capacitors and resistors which can be formed using established techniques which need not be described in detail here. The microphone extends through the substantially planar first die in this case. The passives are preferably on a lower surface facing the second die 30, though they can be located elsewhere. The second die is mounted by soldering or gluing or other means for example, onto mounting pads on the first die, again using established techniques as desired, e.g. by means of flip-chipping techniques as is a known method for skilled persons. Electronics as described above are integrated on the second die, on the surface facing the first die, or on another surface. The two dies can be suitable for mounting on a circuit board by soldering on a top (second) surface of the first die, or a bottom (second) surface of the first die for example, or the two dies can be mounted on a further base or substrate if appropriate, to facilitate mounting and making electrical connections to the circuit board, or for thermal dissipation for example. Another alternative is to mount the dies separately on a common substrate with electrical connections between them such as conventional wire bonds. Figs 2 to 18, embodiment of manufacturing of first die

This embodiment is based on "passive integration platforms" similar to the known manufacturing processes of the applicant, called PASSI™. These provide a process flow in which passive components like coils, bulk-capacitors and resistors, MEMS switches and tuneable capacitors for mobile phone applications for example.

The difference between MEMS or RF-MEMS with standard PASSI™ is a sacrificial layer etching step in order to create surface-micromachined free -hanging structures. A further difference from making RF-MEMS to making a MEMS microphone is an additional anisotropic etch through the silicon wafer, as will be described by way of example in more detail below.

This embodiment is based on the known MEMS PASSI process, and more details of this can be found in J.T.M. van Beek et al., "High-Q integrated RF passives and RF-MEMS on silicon: Materials, integration and packaging issues for high-frequency devices", Symp. Boston 2003, ed. by P. Muralt et al. MRS FaIl meeting. Vol. 783. Warrendale, MRS Materials Research Soc, 97-108, 2004; T.G.S. Rijks et ai, "MEMS tunable capacitors and switches for RF applications", MIEL 2004, Ms, Serbia, 24h Int. Conf Microelectronics, Conference proceedings.

Fig 2 shows a starting point of a silicon wafer 40 with a silicon <100> structure. In one example, a 100 mm wafer with low resistance, e.g. 525μm thickness and standard wafer cleaning is used. In fig 3, an insulating layer such as an SiO₂ layer e.g. 300nm thick followed by an implant such as an Ar implant 50, is created on the silicon. Fig 4 shows a deposition step such as a chemical vapour deposition step, e.g. a PECVD (Pressure Enhanced Chemical Vapour Deposition) process, to create an insulating layer, e.g. a nitride layer 60. Fig 5 shows forming a metal, e.g. Al or aluminium alloy such as AlCu - layer 70 of e.g. 500nm thickness an etch step to pattern this layer to create one of the capacitor electrodes for the microphone. Various patterns are possible, examples are shown below in figures 18 and 19. Fig 6 shows a PECVD step for depositing a further Nitride layer 80 of thickness of e.g. 425nm.

Fig 7 shows forming an insulating layer 90 of thickness e.g. 3μm on the further nitride layer, followed by an etch step to pattern this layer. Fig 8 shows a PECVD step for oxide deposition 100 to a thickness of e.g. 200nm over the previous layer. Fig 9 shows an etch step to form contact holes 110 for the Al electrode. An optional additional step, not illustrated, is backside preprocessing such as grinding and polishing to reduce the substrate thickness, e.g. semiconductor such as Si substrate thickness, to make subsequent backside etching easier. Fig 10 shows deposition of a back-plate conductor layer 120 to form a backplate, which forms the other electrode of the capacitor of the microphone. An etch step is used to pattern holes in the backplate.

A MEMS microphone usually has holes in the backplate to access the acoustical back-chamber. Typically an optimised pattern or size of holes is used based on the acoustic design of the microphone, so a dedicated mask is used. Holes are typically 10 to 30μm for a microphone.

Fig 11 shows a PECVD step for oxide deposition 130, as is done for RF MEMS devices, in this case to a thickness of e.g. 200nm. Fig 12 shows a sacrificial later etch step for creating holes 140 in the oxide of the backplate, for subsequent sacrificial layer etching. Again this is similar to the process for RF MEMS devices. Up to this stage, the process is similar to a standard PASSI™ processing.

Fig 13 shows an additional step involving an anisotropic etch, e.g. a wet etch step, e.g. a KOH etch step of the backside, to create an opening 150 in the silicon for the microphone, and to remove support from the Al layer electrode so that it is free to be moved by the pressure of sound waves. Potassium-hydroxide KOH etch is one way of etching crystalline silicon anisotropically. Another commonly used etching liquid is TMAH (tetramethyl ammonium hydroxide). Yet a further alternative is to use reactive ion etching (RIE). Fig 14 shows removing oxide on the backside in the opening 160, to expose the underside of the first nitride layer. This step is optional and could be skipped and the oxide removed later by the step shown in Fig 16. Fig 15 shows a step of sacrificial layer etch of layer 170 between the electrodes. Fig 16 shows an oxide etch step for removing oxide 180 on the upper and lower surfaces of the backplate forming the upper electrode. A final and conventional step is dicing the wafer to isolate each device from the wafer.

Even for embodiments having no passive components integrated, the modified PASSI process described above is useful, compared to a traditional polysilicon and silicon- nitride based MEMS microphone. These advantages are also applicable to RF- MEMS: [1] The electrical resistances of the AL or aluminium alloy layers such as AlCu used for PASSI are much lower than when using doped polysilicon or a Cr/Au/Al film on silicon nitride. The square resistance is over a factor 1000 lower. This improves the performance of the PASSI devices over other silicon MEMS. [2] The PASSI process is said to be cheaper than the polysilicon and silicon-nitride equivalences. The reason is that evaporation/sputtering of Al and AlCu is cheaper than the CVD and PECVD processes for pSi and SiN.

Fig 17 shows a view of the device showing a metal, e.g. the AlCu backplate 190, having its contact electrode 200 for connecting to sensing electronics for converting the capacitance changes into a signal representing sound. The other capacitor electrode formed by the metal, e.g. Al diaphragm 230 below air gap 220, has its contact electrode 210. Compared to a MEMS switch, where the holes in the upper electrode are made large enough to allow movement up or down, to open or close the switch, in this example of the microphone, the upper electrode is made more rigid, by thicker layers, or smaller holes, and the lower electrode is allowed to move.

The resulting structure is a typical capacitive microphone. Vibrations in the diaphragm can be sensed as changes in the electrical capacitance between the two conducting plates. Fig 18 shows a perspective view of an example of the backplate with small holes 260. A dotted line shows where the cross section views of figs 2 to 17 are taken. Contact areas 250 are provided at either side of the electrodes, one for each electrode. Other patterns are conceivable. The holes in the back-plate are needed to reduce the influence of the air resistance in the air gap. In one example, the air gap can be 3μm, the diaphragm is 0.5μm and the backplate is 5μm thick.

Figs 19-20, alternative embodiments

If the stress in the Al layer after manufacture is too high to make a sufficiently sensitive microphone, e.g. tens of nanometers per Pascal, then a structured membrane can be used. This involves making the pattern of the diaphragm such that a number of thin bendable beams are provided at the periphery, and the major central part is suspended by these beams. For example, eight beams 270, 280 are shown in the example illustrated in plan view in fig 19 and cross section in fig 20. In that case, the compliance of the membrane is no longer determined by the two dimensional stress stretching the membrane, but by the one dimensional bending of the supporting beams, governed by Young's modulus of the beams. This can be controlled more easily by the pattern of the beams and is less susceptible to unrelieved stresses following manufacturing.

The sensitivity of a capacitive microphone is proportional to (and mainly determined by) the compliance of the membrane. The compliance is the flexibility of the membrane. A very flexible membrane gives a high sensitivity, so sound pressure can activate the membrane easily. A drum-type membrane without beams has a cosine-shaped bending profile, meaning the deflection is determined by the stress or by the Young's modulus, depending on which is dominant.

An alternative is to pattern the diaphragm to form beams which are more flexible than the main body of the diaphragm because the beams are patterned to be relatively thin in plan view. Another example could have four radial, flexible beams. In this case, the compliance is completely determined by the beams and the plate deflects uniformly. For acoustical applications, it is preferable to avoid large gaps between the beams, to avoid an acoustical shortcut. Therefore, the beams are placed tightly along the diaphragm, or in Y - shapes For a "large" microphone of 2x2 mm², or greater, the membrane will be flexible enough, depending on the thickness of the membrane. However, in smaller sizes such as 0.5x0.5mm², or less, beams may become more worthwhile to achieve greater sensitivity if desired.

Concluding remarks

Besides mobile phones, miniature microphones can be applied in PDA's, headsets, hearing aids, etc. In the future more microphones in a single application are likely in order add functionality like directional control. Above has been described integrating a MEMS microphone and external passive components into a single die. The integration can be carried out using a PASSI™-like process. The MEMS microphone packages described, comprising a MEMS microphone, a CMOS integrated circuit and separate passive components (like capacitors and resistors) can be smaller and less bulky than e.g. the known packages. They can use less space than the known concepts which still require additional passive components. The integrated MEMS microphone with the external components can easily act as the base -plate for mounting the CMOS chip to save space. Compared to integrating a MEMS microphone with the CMOS chip, cost can be reduced since CMOS is much more expensive than MEMS technology per surface area. Typically CMOS can require 30 masks (expensive), with low yield, and small size MEMS typically uses 4-6 masks (less expensive), higher yield, and uses significant chip area. So the combination of MEMS with CMOS gives an expensive low yield chip with a relatively large chip area. The embodiments can thus provide a better balance of component cost, size and assembly cost.

Claims

CLAIMS:

1. A pressure sensor package having a first die (10), a pressure sensor (15) formed on the first die (10), one or more passive components (20) formed on the first die (10), and at least one other component (25) electrically coupled to the pressure sensor (15) or to the one or more passive components (20).

2. A pressure sensor package according to claim 1, the other component comprising an integrated circuit formed on a second die (30).

3. A pressure sensor package according to any previous claim, wherein the first or the second die (10, 30) is mounted on the other of the dies (30, 10), and there is an electrical connection between the dies (10, 30) using the contacts.

4. A pressure sensor package according to any previous claim wherein the pressure sensor has two parallel electrodes (70, 120; 190, 230) forming a capacitor, whose capacitance varies according to received pressure waves.

5. A pressure sensor package according to claim 4, wherein one of the electrodes (70, 120; 190, 230) comprises a compliant diaphragm (230) formed of a metal.

6. A pressure sensor package according to claim 5, wherein another of the electrodes (70, 120; 190, 230) is a backplate (190) formed of a metal.

7. A pressure sensor package wherein the package has means for soldering to a circuit board.

8. A pressure sensor package according to any previous claim wherein the pressure sensor (15) is a microphone.

9. A device having a first and a second die (10, 30), one mounted on the other, the first or second die (10, 30) having a first surface suitable for mounting on a circuit board, and having a second surface for mounting the other of the dies, facing away from the circuit board when mounted, the first die (10) having an integrated MEMS device (15), and one or more integrated passive components (20), the second die (30) having an integrated circuit.

10. The device of claim 9, wherein the integrated passive components (20) are located under the second die (30).

11. The device according to claim 9 or 10, wherein the first die (10) is substantially planar, the first and second surfaces being the major surfaces, and the MEMS device (15) comprises a microphone extending through the first die (10).

12. A method of manufacturing a package having two or more dies (10, 30), one of the dies (10, 30) having an integrated MEMS device (15) and one or more integrated passive components (20), a second (30, 10) of the dies having integrated circuits, the method having the step of mounting either of the first or second dies on the other.

13. The method of claim 12, further comprising forming a diaphragm (230) or a backplate (190) for a pressure sensor component (15) by evaporation or sputtering.

14. An integrated capacitive microphone having a diaphragm (230) and a backplate (190) for the microphone (15) made of Al or AlCu on a substrate (40).

15. A method of manufacturing a capacitive microphone (15) having the steps of forming a diaphragm (230) and a backplate (190) for the microphone by evaporation or sputtering of Al or AlCu on a substrate (40).

16. The method of claim 15, further comprising etching away the substrate (40) underneath the diaphragm (230) after the diaphragm is formed.

17. The method according to claim 15 or 16, further comprising a first insulating layer (50, 60) on the substrate, before forming the diaphragm (230).

18. The method according to any of the claims 15 to 17 further comprising forming a second insulating layer (80, 90, 100) over the diaphragm (230).

19. The method according to claim 18, further comprising forming a sacrificial layer (170) over the second insulating layer (80, 90, 100), to define a gap between the diaphragm (230) and the backplate (190).

20. The method of claim 19, further comprising forming the backplate (190) over the sacrificial layer (170).

21. The method according to claim 19 or 20, further comprising forming holes (140) in the backplate (190) to reach the sacrificial layer (170), then etching away the sacrificial layer.