Compact and easily producible MEMS package with enhanced protection properties

Abstract

Preferably, the present application relates to a MEMS package with at least one layer for protecting a MEMS element, wherein the MEMS element has at least one MEMS interaction area on a substrate and a surface conformal coating of the MEMS element is applied with a dielectric layer. Particularly preferably, the present application relates to a MEMS transducer package, wherein a MEMS element, e.g. with a MEMS membrane and a processor, preferably an integrated circuit, is arranged on a substrate. For providing protection, a surface conformal coating of a dielectric is preferably first applied to the MEMS element, e.g. by spray coating, mist coating and / or vapor coating. Then, preferably, an electrically conductive layer is applied. Depending on the configuration, these layers can be removed in certain areas above the MEMS interaction area of the MEMS element, e.g. for a sound opening of the MEMS membrane.

Description

TECHNICAL FIELD

[0001] Preferably, the present application relates to a MEMS package having at least one layer for protecting a MEMS (microelectromechanical system) element, wherein the MEMS element has at least one MEMS interaction area on a substrate and a surface conformal coating of the MEMS element is applied with a dielectric layer. Particularly preferably, the present application relates to a MEMS transducer package, wherein a MEMS element, for example having a MEMS membrane and a processor, preferably an integrated circuit, is present on a substrate. For protection, a surface conformal coating of a dielectric is preferably first applied to the MEMS element, for example by spray coating, mist coating and / or vapor coating. Then, preferably, a layer of an electrical conductor is applied. Depending on the configuration, these layers can be removed in regions above the MEMS interaction area of the MEMS element, for example for sound ports of the MEMS membrane. BACKGROUND

[0002] Today, microsystem technology is used in many fields of application for the production of compact electromechanical devices. Microsystems (microelectromechanical systems, MEMS for short) that can be produced in this way are very compact (in the micrometer range), have excellent functionality and lower production costs.

[0003] Applications of MEMS technology include MEMS-based optical emitters or receivers, filters, electrochemical sensors, gas sensors, or even MEMS acoustic transducers.

[0004] The MEMS transducer is preferably a MEMS sound transducer and can be designed, for example, as a MEMS microphone or a MEMS loudspeaker. Both functions can also be implemented by one MEMS transducer. Such a MEMS transducer is used, for example, in modern smartphones.

[0005] The MEMS transducer preferably comprises a MEMS device (for example a MEMS chip) having a vibratable membrane, the vibration of which is generated and / or read out, for example, by piezoelectric or piezoresistive components on or at the membrane. Likewise, capacitive methods for generating and / or measuring the vibration of the membrane are known.

[0006] The MEMS transducers are usually arranged on a substrate together with an integrated circuit (IC) for controlling and / or evaluating the oscillation, and are in contact with these transducers via electrical connections, which are formed, for example, by wire bonds and / or are applied in the substrate, for example, by conductive tracks. The substrate serves, in particular, as a carrier and can be designed, for example, as a printed circuit board (PCB) or as a ceramic. In addition to the carrier function, the substrate can also preferably fulfill an electrical function, for example, to provide electrical connections for individual components.

[0007] The IC is preferably an electronic component, by means of which a control unit or a regulating unit is implemented. In particular, the IC is an electronic chip. For example, the IC can have an application-specific integrated circuit (ASIC), which is particularly suitable for mass production. However, the IC can also be a programmable logic device (PLD), for example, a field-programmable gate array (FPGA), in particular for individual applications.

[0008] The MEMS elements, such as the MEMS transducers, are most sensitive to external influences and are therefore protected by a so-called package.

[0009] In this respect, the package of the MEMS elements fulfills several tasks. These tasks include protecting the components from dust, moisture and liquids, and from ESD (electrostatic discharge). At the same time, however, the functional properties of the MEMS elements, for example, the acoustic properties of an acoustic MEMS transducer, should be preserved.

[0010] The package preferably fulfills the housing function of the MEMS elements. On the underside of the MEMS elements, the substrate itself can fulfill this function. In addition, it is also necessary to protect the components arranged on the substrate from above.

[0011] One or more MEMS devices can be conventionally arranged on the substrate, or in a so-called flip-chip assembly, whereby the chip is mounted with the active contact side facing downwards towards the substrate, without additional connecting wires. For this purpose, the substrate itself preferably has contact bumps. This advantageously leads to a small size of the housing and a short length of the electrical conductors.

[0012] The MEMS devices and / or the MEMS membrane can be present on the substrate in the MEMS acoustic transducer in various ways.

[0013] The volume to be measured and / or to generate acoustic waves as seen from the MEMS membrane is preferably referred to as front volume. The other side is preferably referred to as back volume. This back volume is preferably closed and has no direct connection to the front volume except possibly via an opening on the membrane. Depending on the arrangement, the back volume can be located for example between the membrane and the substrate. In this case, the front volume is located above the MEMS device and the substrate. The housing component (e.g. cover) located here closing the package at the top preferably has a sound port in this area.

[0014] However, the back volume can also be located between the membrane and a housing component arranged above the MEMS device and the substrate. This back volume is then preferably completely closed. Thus, the front volume is preferably located between the membrane and a sound port in the substrate. The dimensions and geometry of these volumes and the size ratio of these volumes influence the acoustic properties of the MEMS transducer. The MEMS membrane can preferably be present in both described constellations within the height of the MEMS device or arranged at the upper end or at the lower end towards the substrate.

[0015] In the case of a MEMS transducer, the electronic components of the MEMS device itself, for example the electrodes of a capacitive MEMS transducer, are preferably present in or arranged towards the back volume (for example on the side of the membrane oriented towards the back volume) in order to be able to measure certain liquids for example through the membrane without these components being short-circuited or contaminated. Preferably, this allows direct contact of the fluid with the membrane. In this way, a general protection against short-circuits caused by moisture is also achieved. However, a prerequisite for this is that the package can prevent moisture / liquid from entering other areas of the MEMS transducer via the sound port. Thus, the sound port in the package should only be an opening to the membrane and not to other areas of the MEMS transducer.

[0016] Prior art packages for MEMS transducers (see for example Dehé et al. 2013) have metal covers. These covers enclose a volume which is significantly larger than the volume required for the underlying components of the MEMS transducer. The main reason for this is to maintain a distance between the cover and the components, some of which are electrically conductive (for example wire bonds, electrodes of a capacitive MEMS transducer, etc.), in order to avoid short-circuits. At the same time, metal is desirable as the starting material for these covers, since metal is mechanically stable and impermeable to air and water, among other things. Impermeable to air and water in particular means impermeability under the usual operating conditions of the transducer, i.e. preferably also at pressures considerably above atmospheric pressure. In addition, sensitive components can also be electromagnetically shielded. In this way, negative effects and electrostatic discharges (ESD) can be avoided. However, these covers counteract the compact design of modern MEMS transducers.

[0017] The metal cover can be provided with openings for sound. Even so, however, direct contact of the MEMS membrane with the material to be measured (solid, gas, liquid) is difficult, since the openings are located at a distance above the membrane (see above) and this distance has to be overcome. Furthermore, since the cover and the openings are not flush with the transducer components, liquid can enter into the space between the cover and the MEMS device, which can lead to short circuits between the conductive areas of the MEMS device and facilitate the ingress of dirt and other harmful substances.

[0018] The sound port through the substrate (see also Dehe et al.) has in particular the disadvantage that due to the size of the aperture and the length of the aperture, which is predetermined at least by the thickness of the substrate, a low-pass filter of the sound frequency is produced, which particularly impedes the usability of an ultrasonic transducer.

[0019] The so-called flip-chip package (Feiertag et al., 2010) can reduce the height of the cover, since the flip-chip package no longer needs to be designed for wire bonds. However, the miniaturization effect here is also small.

[0020] Feiertag et al. also know the use of a metallized polymer film as an outer encapsulation layer. For this purpose, the polymer film is laminated onto the upper side of the MEMS transducer and then provided with a metal layer. However, this process is expensive. Furthermore, for this purpose, the film has to be heat deformed and / or heated by laser ablation during post-processing / structuring, which introduces temperatures into the MEMS transducer.

[0021] Heating makes thermoplastic plastics more easily formed, which is used in similar blow molding or thermoforming polymers. However, in all these processes, additional stresses are exerted on the components. This can introduce stresses into the components or cause other damage and unnecessary outgassing. It is also difficult to place the film flush and tightly on the MEMS transducer on all sides, so that leaks of the package environment can occur and affect the compact design.

[0022] US 6,956,283 B1 discloses a method for protecting components of a MEMS sensor from external influences in a "package first, release later" approach. A matrix array of micro-mirrors is placed on a silicon chip, which in turn is placed on a substrate. In the proposed method, a protective layer is applied to a large number of components of the sensor. Various methods can be used for the coating, such as spraying or vacuum coating. After deposition, the protective layer is removed on the active area. Finally, a cover is applied as a protective housing.

[0023] US 2019 / 0148566 A1 relates to a production method of a semiconductor sensor element, wherein the semiconductor sensor element can be a pressure sensor, a gas sensor or a capacitive sensor. The semiconductor sensor element comprises a substrate on the semiconductor element, which is connected to the substrate via a bond wire. A dielectric layer is deposited on the semiconductor sensor element via an evaporation process. A laser beam can be used to partially remove the dielectric layer. A cover is used to protect the semiconductor element from external forces.

[0024] US 2019 / 0311961 A1 discloses a semiconductor sensor comprising a substrate having a chip located on the substrate. A film layer is deposited on components of the semiconductor sensor to protect the semiconductor sensor, for example, from external gases, liquids, etc. The film layer is preferably applied via vapor deposition and is located over all components of the sensor positioned within a package. The housing comprises an opening and is used to protect and support the components of the semiconductor sensor.

[0025] It is not known in the prior art that a MEMS package can work without a rigid cover or package.

[0026] In view of the disadvantages of the prior art, there is a need for an alternative or improved package for packaging a MEMS element, in particular a MEMS transducer, and a production method. SUMMARY

[0027] Object of the present invention

[0028] It is an object of the present invention to provide a MEMS package and a method of producing such a MEMS package, which do not have the disadvantages of the prior art. In particular, it is an object of the present invention to provide a very compact MEMS package, while providing a MEMS element, for example a MEMS transducer, with a high level of protection against dust, moisture, liquids and ESD and ensuring the required functional properties, for example acoustic properties in the case of a MEMS transducer. Due to the fewer and simpler steps, the package is also considered to be particularly easy and cost-effective for production and suitable for mass production.

[0029] Content of the present invention

[0030] This object is solved by the production method of a MEMS package and the MEMS package provided by the present application.

[0031] The present invention preferably relates to a production method for a MEMS package having at least one layer for protecting a MEMS element, comprising the following steps:

[0032] - providing a MEMS element on a substrate, the MEMS element comprising at least one MEMS interaction area,

[0033] - providing a surface conformal coating of the MEMS element with a dielectric layer.

[0034] Preferably, the MEMS interaction area is a basic functional component of the MEMS element that preferably interacts with the medium in a desired way.

[0035] The surface conformal coating is in particular a coating that is in substantially direct and shape preserving close contact with the underlying structure.

[0036] Substantially direct and shape preserving preferably means that the majority of the coating is in direct contact, but includes volumes that are not filled by the component, for example under corner areas or line joints.

[0037] The surface conformal coating is preferably completely surface conformal. This in particular means that the coating is almost completely a close fit or surface conformal, and even the smallest structures can be coated in a close-fitting manner. The smallest structures are preferably structures having dimensions of the order of magnitude of at most 10 nanometers (nm), at most 100 nm, at most 1 micrometer (pm), at most 10 pm or at most 100 pm.

[0038] The dielectric layer preferably comprises at least one polymer. This is inexpensive and easy to process. Oxide layers or nitride layers can also be preferably applied as dielectric layers. For the surface conformal coating, physical or chemical vapor deposition (PVD and CVD) is particularly suitable for this purpose.

[0039] In a preferred embodiment, the polymer is a photo structural polymer, for example by means of a suitable mixture of photoactive components. In particular, the polymer is a photoresist.

[0040] Advantageously, the properties of the polymer can be adapted to the function of the MEMS element. For example, in the case of a MEMS transducer as a MEMS element, the relative permittivity cr of the polymer can be preferably adapted to the high-frequency application of the MEMS transducer. For example, cr can be chosen to attenuate high-frequency electromagnetic fields.

[0041] Such a functional coating with a dielectric is not possible in prior art processes and advantageously provides an extremely compact protective layer that provides electrical insulation and mechanical protection of the MEMS element.

[0042] In a preferred embodiment, the MEMS element is selected from the group consisting of an optical MEMS transducer, an acoustic MEMS transducer, a MEMS sensor, in particular a MEMS gas sensor, and / or a MEMS filter. The inventors realized that the proposed package can provide a reliable protection for many different MEMS elements by means of a dielectric coating, preferably with a polymer.

[0043] On the one hand, a hermetic, space-optimized protection layer can be applied very economically effective by a surface conformal coating, for example by means of a spray process with a polymer. On the other hand, a surface conformal coating, for example using a photostructured polymer, allows a high flexibility with respect to planned openings or recesses of the protection layer in the interaction region of the MEMS element.

[0044] The MEMS interaction region preferably refers to the functional part of the MEMS element that interacts with the external medium in the desired way. For example, in the case of an acoustic MEMS transducer, the MEMS interaction region is the MEMS membrane. For example, in the case of an optical MEMS transducer, the MEMS interaction region is the optical emitter.

[0045] In both cases, it is preferred that, on the one hand, the protection layer is not applied directly in the interaction region of the MEMS element, thereby reducing the interaction of the MEMS element with the environment (sound emission or reception, transmission or reception of optical signals), while ensuring the protection of sensitive electronic components. The method according to the application achieves this in a simple and efficient manner by means of a surface-form coating, preferably by applying a polymer.

[0046] In a preferred embodiment, the MEMS element is an optical MEMS transducer, wherein the MEMS interaction region comprises an optical emitter and / or an optical receiver.

[0047] The optical emitter can comprise, for example, a surface emitter or a VCSEL (vertical cavity surface emitting laser) or an LED. The optical receiver is, for example, a photodiode or an image sensor.

[0048] In a preferred embodiment, the optical emitter can be a modulatable MEMS emitter. For example, the modulation of the intensity of the optical emitter can be done using an aperture structure and a MEMS actuator, such as an electrostatic actuator, a piezoelectric actuator, an electromagnetic actuator and / or a thermal actuator.

[0049] In a preferred embodiment, the MEMS element is a MEMS acoustic transducer, wherein the MEMS interaction region comprises a MEMS membrane.

[0050] In a preferred embodiment, the MEMS transducer is a MEMS loudspeaker, a MEMS microphone and / or a MEMS ultrasonic transducer. Preferably, the MEMS membrane is vibratable. The membrane is preferably a thin planar structure, for example having a circumference in a substantially circular and / or polygonal configuration. The membrane is preferably regionally vibratable at least along one of the circumferences.

[0051] The terms such as substantially, approximately, about, etc. preferably describe a tolerance range of less than ± 20 %, preferably less than ± 10 %, even more preferably less than ± 5 %, and in particular less than ± 1 %. The indication of substantially, approximately, about, etc. also always discloses and includes the exact value mentioned.

[0052] A MEMS loudspeaker or a MEMS microphone preferably refers to a loudspeaker or microphone based on MEMS technology, and whose sound generating or sound receiving structure has at least partially dimensions in the micrometer range (1 pm to 1000 pm). Preferably, the width, height and / or thickness of the vibratable membrane can have dimensions in the range of less than 1000 pm.

[0053] The term MEMS transducer refers to a MEMS microphone and a MEMS loudspeaker. In general, a MEMS transducer refers to a transducer interacting with a volume flow of a fluid, which is based on MEMS technology, and whose structure interacting with the volume flow or receiving or generating pressure waves of the fluid has dimensions in the micrometer range (1 pm to 1000 pm). The fluid can be a gaseous fluid as well as a liquid fluid. The structure of the MEMS transducer, in particular the vibratable membrane, is designed to generate or receive pressure waves of the fluid.

[0054] For example, as in the case of a MEMS loudspeaker or a MEMS microphone, the pressure waves of the fluid can be sound pressure waves. However, the MEMS transducer can equally well be suitable as an actuator or sensor for other pressure waves. Thus, the MEMS transducer is preferably a device that transduces pressure waves (e.g. acoustic signals as sound pressure waves) into electrical signals or vice versa (transduces electrical signals into pressure waves, such as acoustic signals).

[0055] The MEMS transducer preferably comprises a MEMS device (e.g. a MEMS chip) having a vibratable membrane, the vibration of which is generated and / or read out, for example, by piezoelectric or piezoresistive components on or at the membrane.

[0056] In a preferred embodiment, the MEMS transducer is a piezoelectric MEMS transducer.

[0057] Similarly, capacitive methods for generating and / or measuring membrane vibrations are also known.

[0058] In a preferred embodiment, the MEMS transducer is a capacitive MEMS transducer.

[0059] In a preferred embodiment, the MEMS transducer can also be a MEMS ultrasonic transducer suitable for transmitting and / or receiving ultrasonic waves.

[0060] In particular, these sensors are capacitive micromachined ultrasonic transducers (CMUT), piezoelectric micromachined ultrasonic transducers (PMUT) or combined ultrasonic transducers (piezoelectric composite ultrasonic transducers, PC-MUT).

[0061] Ultrasonic waves cover frequencies from 1 kilohertz (kHz), usually mainly from 16 kHz. Applications of compact ultrasonic transducers include imaging methods, for example in medicine, but also measurements of other objects. For ultrasonic density measurements, for strength measurements of concrete, gypsum and cement, for level measurements of liquid and solid media of different consistencies and surface properties, or for applications of ultrasonic microscopes are also conceivable. Here, it is usually desirable that the membrane of the transducer, i.e. the membrane of the MEMS interaction region, is in direct contact with the object / liquid to be measured.

[0062] Using the method for surface conformal coating of a dielectric protective layer according to the application, it can be achieved advantageously without impairing the protective function. In contrast, in a simple manner, the dielectric protective layer in the interaction region can be removed in a targeted manner while the layer remains in close contact with the remaining structure. In particular with regard to acoustic MEMS transducers, such as MEMS microphones or MEMS loudspeakers, influences on the acoustic behavior can be avoided in this way and good detection or sound results can be obtained.

[0063] In another preferred embodiment, the MEMS element is a MEMS gas sensor, wherein the MEMS interaction region comprises a MEMS membrane and / or a MEMS electrochemical sensing region.

[0064] For example, the MEMS element can be a photoacoustic spectrometer with a MEMS sensor.

[0065] In photoacoustic spectroscopy, intensity-modulated infrared radiation is preferably used together with the frequencies in the absorption spectrum of the molecules to be detected in the gas. If this molecule is present in the beam path, a modulated absorption occurs, which leads to a heating process and a cooling process, the time scale of which reflects the modulation frequency of the radiation. The heating process and the cooling process lead to expansions and contractions of the gas, which in turn cause sound waves at the modulation frequency. These can be measured by sensors such as sound detectors or flow sensors.

[0066] Preferably, the power of the acoustic waves is directly proportional to the concentration of the absorbed gas. Thus, the photoacoustic spectrometer preferably comprises at least one emitter, a detector and a cell. In the MEMS gas sensor, the detector is preferably implemented as a MEMS sensor.

[0067] For example, the MEMS sensor can comprise a piezoelectric, a piezoresistive and / or a magneto-optic light beam and / or a capacitive, a piezoelectric and / or a piezoresistive microphone or membrane and / or an optical microphone or membrane, which is electrically or optically readable.

[0068] For the present invention, the MEMS sensor of the photoacoustic spectrometer can preferably be understood as the MEMS interaction area of the MEMS sensor, since this is preferably in direct contact with the medium.

[0069] In another preferred embodiment, the MEMS element is a MEMS filter, preferably a MEMS frequency filter, in particular a SAW filter or a BAW filter, wherein the MEMS interaction area comprises a MEMS filter structure, in particular a MEMS electrode and / or a MEMS bulk area.

[0070] The SAW filter is preferably an acoustic surface wave filter (also AOW filter), which is in particular a bandpass filter for electrical signals.

[0071] These are preferably based on the interference of signals of different transit times and preferably use the piezoelectric effect. Preferably, each piezoelectric single crystal comprises a pair of comb interlocking electrodes, which preferably form the interaction area.

[0072] The BAW filter (bulk acoustic wave) is preferably an electronic filter analogue with bandpass properties. However, compared to the SAW filter, the BAW filter preferably has a substrate (bulk) in which the propagation of the acoustic waves takes place. This substrate or bulk area preferably forms the MEMS interaction area.

[0073] In a preferred embodiment of the present invention, the surface conformal coating is performed by a dielectric coating process, wherein the coating process is selected from the group consisting of: spray coating, mist coating, electroplating and / or vapor coating.

[0074] Spraying preferably refers to a two-dimensional application of the dielectric layer, wherein the dielectric is preferably pressurized (e.g. above the current ambient pressure, e.g. at atmospheric pressure preferably more than 1 bar, more preferably more than 2 bar, in particular between 2 bar and 6 bar) before spraying, so that a fine particle / aerosol of the dielectric and / or a foam is formed. In this way, a particularly fine coating of all sprayed areas can be achieved, even if, for example, these areas have surfaces at an unfavorable angle to the spraying direction. Thus, even surfaces / areas that are angled with respect to each other can preferably be directly coated. Directly coating these areas without creating uncoated volumes is very difficult when using films like in the known prior art, due to, for example, the fact that the film is continuous and under tension.

[0075] Preferably, for the coating process, the liquid dielectric is atomized and applied on the surface at a greater pressure than the ambient.

[0076] The sprayed coating is preferably a paint coating.

[0077] The sprayed coating and / or the surface conformal coating can also be a vapor deposition, in particular if the dielectric layer comprises a polymer that can come from a vapor deposition and / or a liquid deposition, such as tetraethyl orthosilicate (TEOS) and / or p-xylene. In this way, a particularly tight-fitting or surface-conformal coating can be achieved on the transducer component.

[0078] The mist coating preferably comprises a coating consisting of fine droplets of the dielectric, which are finely dispersed in the atmosphere, preferably a gas. The mist coating preferably allows a completely surface-conformal coating to be achieved.

[0079] The vapor phase coating is preferably applied from a dielectric in the form of a gas phase or gas. For example, the vapor phase coating can comprise a PVD (physical vapor deposition) or a CVD (chemical vapor deposition). Vapor deposition advantageously enables a completely surface-conformal coating of the dielectric.

[0080] In a preferred embodiment, the surface-conformal coating is applied by depositing the dielectric layer using a physical vapor deposition (PVD) or a chemical vapor deposition (CVD) process.

[0081] In a preferred embodiment, the dielectric layer is an oxide or nitride layer, which is preferably deposited by physical or chemical vapor deposition (CVD).

[0082] For example, the oxide layer or the nitride layer can be a metal oxide layer or a semi-metal oxide layer, or a metal nitride layer or a semi-metal nitride layer.

[0083] In a preferred embodiment, the dielectric layer is a layer comprising aluminum nitride, silicon nitride, aluminum oxide, silicon dioxide, titanium dioxide and / or tantalum oxide. The galvanic coating can also be included in the surface conformal coating. Galvanic preferably refers to the electrochemical deposition of a coating on a substrate, in this case a MEMS element.

[0084] In a preferred embodiment, the surface conformal coating is provided by a coating which wets the MEMS element at least in certain regions.

[0085] Wetting preferably means complete wetting or substantially complete wetting. Complete wetting preferably means that a dielectric, preferably applied in liquid form, spreads over the surface in the form of a flat disc. In particular, there is no macroscopic contact angle. Preferably, it is a substantially monomolecular film with a contact angle of zero.

[0086] Preferably, the spreading parameter S describes the difference between the surface tension of the substrate (GS), the surface tension of the liquid (GL) and the interfacial tension between substrate and liquid (GSL). This can preferably be used to distinguish between complete wetting and partial wetting:

[0087]

[0088] If S > 0, the dielectric completely wets the substrate. The case S < 0 is characterized by partial wetting.

[0089] Preferably, complete wetting S > 0 is meant.

[0090] In a preferred embodiment, the dielectric of the MEMS element, the coating method and / or the surface are configured (at least regionally) for wetting the coating.

[0091] How exactly the material, the drop size of the dielectric, the roughness of the surface, etc. are chosen in order to obtain the desired wetting is known to the person skilled in the art. For example, the method of Härth et al. (2012) can be followed to calculate the relevant variables.

[0092] In a preferred embodiment, the surface conformal coating is performed by de-wetting the MEMS element at least in regions, which preferably include the MEMS interaction regions.

[0093] Particularly preferably, the surface conformal coating is carried out by means of a coating which wets the MEMS element at least in certain regions, wherein the wetting coating is applied in the MEMS interaction regions.

[0094] De-wetting preferably means that the dielectric shrinks on the surface to form a roughly spherical droplet and / or has a contact angle of more than 90°. With slight tilting of the surface, the droplet preferably slides down without any liquid residue, in particular liquid (dielectric) beads falling off. Preferably, the dielectric has a contact angle of substantially 180° when applied to the surface and the droplet only touches the solid at substantially one point. This makes it particularly easy to remove the dielectric from the MEMS interaction area after coating.

[0095] In a preferred embodiment of the present application, the dielectric of the MEMS element, the coating method and / or the area of the surface, preferably the MEMS interaction area, is configured for wetting the coated portion.

[0096] Preferably, the same considerations play the same role as in the case of wetting the coated portion. With regard to the selection of the droplet size of the dielectric, the surface roughness, etc., the person skilled in the art can be guided by methods known from the technical literature (cf. Härth et al. 2012).

[0097] In a preferred embodiment, the dielectric layer and / or the dielectric comprises a polymer or a polymer mixture.

[0098] A polymer preferably denotes a compound comprising chain molecules or branched molecules (macromolecules) composed of identical or similar units (so-called monomers).

[0099] Non-limiting examples of polymers are polymethyl methacrylate (PMMA), poly(methyl methacrylate-co-methyl methacrylate) (PMMA co MA), poly(a-methylstyrene-co-chloromethyl methacrylate) (PMS co Cl-MMA), polystyrene (PS), polyhydroxystyrene (PSOH), poly(hydroxystyrene-co-methyl methacrylate) (PSOH co MMA), phenol formaldehyde resin, in particular polyimide (PI) or poly-p-xylylene.

[0100] Polymers are particularly suitable for dielectric coating due to their ease of processing and form-fit coating capability.

[0101] In a preferred embodiment, the polymer used to coat the MEMS element with a dielectric layer is a photostructurable polymer or a photostructurable polymer blend. Photostructurable preferably means that the polymer can be structured by light, electron and / or ion irradiation.

[0102] The dielectric layer can be formed particularly easily by a polymer coating, preferably by means of a photostructurable polymer or a photostructurable polymer blend. Photostructurable polymer or polymer blend preferably means a coating which can be modified by exposure (irradiation with electromagnetic radiation) to obtain a structure by subsequently dissolving away certain regions in accordance with the irradiation which has taken place.

[0103] The polymer blend can retain the photostructure, for example by mixing of suitable photoactive components. Particularly preferably, the photostructurable polymer or photostructurable polymer blend is a photoresist.

[0104] This advantageously allows subsequent removal of the dielectric layer using optical methods, for example of the dielectric layer in the MEMS interaction region. If a photostructurable polymer is included in the dielectric layer and a photolithographic method is used, the removal of specific regions of the dielectric layer is particularly easy.

[0105] In a preferred embodiment of the application, the surface conformal coating of the MEMS element having a dielectric layer is carried out by a surface conformal coating having a photoresist.

[0106] Photoresists and photoresist compositions are well known to the person skilled in the art and are used in particular for photolithographic techniques.

[0107] The construction of a photoresist generally involves several steps, including exposure of the photoresist to a selected light source through a suitable mask to record the latent image of the mask, followed by development and removal of selected regions of the photoresist. In "positive" photoresists, the exposed regions are altered so that the regions are selectively removable; in "negative" photoresists, on the other hand, the exposed regions are stable, while the unexposed regions are removable.

[0108] Negative photoresists can preferably be polymerized by exposure and subsequent baking steps, so that the regions become insoluble in the photoresist developer. Thus, after one development, only the exposed regions remain. On the other hand, the unexposed regions are dissolved by the photoresist developer.

[0109] By contrast, positive photoresists are characterized in that the irradiated regions become soluble in the photoresist developer. On the other hand, the unexposed regions of the photoresist remain insoluble and thus remain present even after development.

[0110] A positive photoresist can comprise, for example, a polymeric resin (e.g. novolak) and a photoactive ingredient (e.g. a polymeric diazonium compound) and a solvent. The novolak is preferably a phenol-formaldehyde resin with a formaldehyde-phenol ratio of less than 1 :1, which can be obtained by acid condensation of cresol and phenol. After coating, the positive photoresist, which is preferably liquid, can be pre-baked. In this process, the solvent preferably escapes and the photoresist solidifies. When the photoresist is exposed to, for example, UV light, the photoresist can be structured by breaking the material bonds in the photoresist in the irradiated areas. The coating becomes dissolvable at the exposed areas. After exposure, these areas are washed away with a suitable photoresist developer solution, leaving the unexposed parts of the photoresist. The photoresist mask can be additionally stabilized by a further baking (hard-baking).

[0111] A polymeric resin material that can be activated, for example, by means of irradiation, is referred to as a photoresist.

[0112] The polymeric resin material typically comprises one or more polymers that are soluble in aqueous alkali (see the polymers described above, such as PMMA or PI). One example of a polymeric resin is novolak.

[0113] In order to obtain a photostructurability, a photosensitive ingredient such as naphthoquinone diazonium or a polymeric diazonium compound such as diazonaphthoquinone (DNQ) is preferably added to the photoresist.

[0114] The photoresist is processed as a solution, and suitable solvents are known to the person skilled in the art and can include, for example, 1 -methoxy-2-propyl acetate (PMA), ethyl lactate, butyrolactone ether, glycol ethers, aromatic hydrocarbons, ketones, esters and other similar solvents.

[0115] In addition, the photoresist can also comprise ingredients such as surfactants, bases, acid-forming substances or crosslinking agents. In particular, the structure of a negative photoresist is based on stabilizing the exposed areas using a crosslinking agent. Free-radical initiators, such as azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (DBDO), form reactive radicals by heating or irradiation (preferably short-wave light < 300 nm), which cause crosslinking of the polymer matrix due to the triggering of chain reactions.

[0116] This leads to a reduction in the solubility of the organic photoresist developer used (such as MIBK developer). As a result, the exposed areas remain after development. The acid-forming substance can be activated after crosslinking by reaction with an added amino ingredient (Cymel).

[0117] In a preferred embodiment, the photoresist can comprise a polymer and freely selected adjuvants to impart the desired functionality. Examples of optional adjuvants include photochemical acid generators, thermal acid generators, acid enhancers, photochemical base generators, thermal base generators, photo-degradable bases, surfactants, organic solvents, base plug agents, sensitizers, and combinations of the above adjuvants.

[0118] Such photoresists are well known in the prior art. However, according to the present application, it is recognized that a surface conformal coating as described is particularly suitable as a dielectric protective layer for a MEMS package.

[0119] In a preferred embodiment, the dielectric layer and / or the dielectric comprises polymethyl methacrylate, polyimide (PI), novolak, polymethyl glutarimide, a polymer that can be deposited from the gas phase and / or the liquid phase, in particular tetraethyl orthosilicate (TEOS) and / or p-xylene and / or an epoxy resin, in particular SU-8.

[0120] The use of a polymer to provide the dielectric protective layer by means of a coating process advantageously makes the coating conformal to the surface in particular and allows all components to be coated in a form-fit manner. For example, here spray deposition or vapor deposition can be used.

[0121] Advantageously, even the smallest structures of the MEMS element can be reliably covered hermetically. In the case of a conventional chip design, additional protection of, for example, bond wires can be omitted. Further processes to fill flip-chip components are also not required.

[0122] Furthermore, the polymer coating can be used to tailor the functionality of the dielectric layer to the MEMS element.

[0123] For example, the relative permittivity of the polymer can be adapted to the high-frequency application of the MEMS transducer, preferably. Here, the relative permittivity can be selected such that the high-frequency electromagnetic field is reliably attenuated, preferably.

[0124] It can also be preferred to deposit different polymers on top of one another, for example, to create a permittivity gradient of a high-frequency component or to optimize the dielectric layer with respect to optical properties, in particular if the MEMS device comprises or consists of micro-opto-electromechanical (MOEMS) components.

[0125] By means of a surface conformal coating process, in particular using a polymer, a powerful and extremely compact MEMS package can be easily provided while at the same time providing comprehensive protection for the sensitive structures of the MEMS element, for example, a MEMS transducer.

[0126] In a preferred embodiment, the production method additionally comprises the following steps:

[0127] The electrically conductive layer is applied to the dielectric layer at least in certain regions.

[0128] The application of the electrically conductive layer to the dielectric layer at least in certain regions has the advantage that the resulting layer system substantially fits tightly and protects the MEMS transducer from short circuits and electrostatic discharges and seals the MEMS transducer against the ingress of liquids and / or air. The mechanical protection is also preferably improved.

[0129] In particular, the electrically conductive layer is a metal, which provides mechanical protection for the MEMS element and prevents the penetration of air, moisture, liquids, dust into the interior of the package. In particular, the metal coating is air-tight.

[0130] By applying the electrically conductive layer, preferably a metal layer, on the dielectric layer, a mechanically stable closure can also be ensured, which not only resists the penetration of air, moisture and liquids, but also external forces. The layer system comprising the metal layer on the dielectric layer thus has a particularly effective housing function, so that a separate cover or housing can be dispensed with. Advantageously, the layer system also ensures a good acoustic seal and, in the case of use of a MEMS loudspeaker or a MEMS microphone, can lead to very good detection or sound results.

[0131] In a preferred embodiment, the electrically conductive layer comprises a metal, which is preferably aluminum and / or a noble metal, which is preferably gold, platinum, iridium, palladium, osmium, silver, rhodium and / or ruthenium.

[0132] The electrically conductive layer is preferably applied or deposited. The electrically conductive layer is preferably a metal layer, particularly preferably a metal film, in particular a metal thin film.

[0133] In a preferred embodiment, the electrically conductive layer is applied by a coating process, in particular by a PVD, CVD and / or sputtering process.

[0134] Preferably, the dielectric layer is superimposed at the outer edges of the dielectric layer. Such outer edges are located, for example, on the upper side of the substrate where the dielectric layer ends. There, the electrically conductive layer preferably covers the edge regions of all sides and extends onto the substrate. This superimposition can improve the impermeability of the package.

[0135] The layer system produced in this way is very compact and simple to produce, but provides comprehensive protection for the MEMS element, for example a MEMS transducer. A surface-conformal coating, for example a spray coating, can be used to achieve a tightly fitting coating on all sides, which contributes to the density and impermeability of the packaging environment.

[0136] This close fit cannot be achieved with a film. Furthermore, no additional and expensive steps are required compared to a film, which can also affect the MEMS element.

[0137] Advantageously, the electrically conductive layer can be applied directly to the dielectric layer. The layer system can be visually distinguished from a film package, for example by the fineness of the layer (measurable roughness) and the direct contact to the underlying components. Furthermore, the spray coating also allows the wire bond to be covered compared to a film-based package, since the spray layer advantageously simply covers the wire bond(s) without exerting any significant force on the wire bond which could destroy the wire bond.

[0138] In a preferred embodiment, the MEMS element comprises a MEMS device and a processor, preferably an integrated circuit, on a substrate, and / or comprises an electrical connection between the MEMS device and the processor, preferably an integrated circuit. Here, it is particularly preferred that the dielectric layer and optionally the electrically conductive layer, preferably a metal layer, extends over the MEMS element and the processor, and / or over the electrical connection between the MEMS device and the processor. Thus, the layer system can preferably simultaneously achieve full protection of both sensitive micromechanical components as well as electronic components or processors. No separate housing is required to enclose and protect the processor and the MEMS device.

[0139] For the purposes of the present application, the term processor preferably means a logic circuit capable of transmitting, receiving and processing data or electrical signals. Preferred processors include, but are not limited to, integrated circuits (ICs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), microprocessors, microcomputers, programmable logic controllers and / or other electronic, preferably programmable, circuits.

[0140] For example, the substrate can be selected from the group consisting of silicon, monocrystalline silicon, polycrystalline silicon, silicon dioxide, silicon carbide, germanium silicon, silicon nitride, silicon nitride, germanium, carbon, gallium arsenide, gallium nitride and / or indium phosphide.

[0141] In a preferred embodiment, the MEMS element and / or the processor are mounted in a flip-chip design, and preferably the electrical connection is made through the substrate, in particular through electrically conductive tracks in the substrate.

[0142] The surface-conformal coating can preferably be applied such that it encloses the MEMS element at least in certain regions between the MEMS element itself and the substrate, so that the MEMS element is preferably electrically insulated and / or chemically protected with the dielectric coating, but preferably at the same time the gap between the MEMS element (underneath the MEMS element) and the substrate is not filled with a dielectric having a high εr. This is particularly advantageous for high-frequency applications.

[0143] In a preferred embodiment of the application, the MEMS element and / or the processor, preferably an integrated circuit, are not mounted in a flip-chip design, and the electrical connections are preferably made via at least one wire bond.

[0144] Furthermore, unlike a film-based encapsulation, a surface-conformal coating, such as a spray coating with a polymer, also allows the wire bonds to be covered, since the coating is advantageously placed directly on the wire bond(s) without exerting any significant force on the wire bond that would destroy it.

[0145] On the other hand, a tensioned film often destroys the wire bonds, so that this type of encapsulation can usually only be used for flip-chip encapsulations. On the other hand, the encapsulation created by the process described here is form-fitting to the encapsulation structure without putting the encapsulation structure under significant tension. This is another way in which the encapsulation described here can be distinguished from other encapsulations when using wire bonds. For example, the wire bonds are still visible from the outside, although they are enclosed and protected by the layer system. In general, for these encapsulations, the structure of the MEMS element can also be seen from the outside through the encapsulation layers.

[0146] In a preferred embodiment of the application, the production method comprises the following steps:

[0147] - providing a MEMS element on a substrate, the MEMS element comprising a MEMS interaction region,

[0148] - providing a surface-conformal coating, in particular a spray coating, of the MEMS element, so that the MEMS element is completely enclosed between a dielectric layer and the substrate,

[0149] - preferably, applying an electrically conductive layer at least in certain regions on the dielectric layer, the electrically conductive layer preferably forming a layer system with the dielectric layer,

[0150] - optionally, arranging an opening above the interaction region by removing the dielectric layer and / or the layer system above the interaction region at least in certain regions.

[0151] In a preferred embodiment of the application, the arrangement of the dielectric layer, the layer system of the MEMS element and / or the MEMS interaction region is such that, after removal of the dielectric layer or the layer system, no electrically conductive region is in direct contact with the encapsulation environment. In particular, these are sealed against the ingress of air and / or liquids.

[0152] By removing the dielectric layer and / or the layer system comprising the dielectric layer and the electrically conductive layer in certain regions, the interaction of the interaction region with the desired medium, in particular with the encapsulation environment, can be improved.

[0153] For example, in the case of an acoustic MEMS transducer, the MEMS interaction region is the MEMS membrane which interacts with the packaging environment to pick up or generate acoustic pressure waves.

[0154] In the case of an optical MEMS transducer, the MEMS interaction region can for example be a light emitter or a light receiver which interacts with the packaging environment by emitting or receiving electromagnetic radiation.

[0155] In both cases, it is preferred that, first, no dielectric or electrically conductive layer reduces the interaction of the MEMS element with the environment (acoustic emission, light signal) directly in the interaction region of the MEMS element.

[0156] By removing the layer system and / or the dielectric layer in certain regions, for example using a photo-structured polymer, unhindered interaction of the MEMS element within its functional region can be achieved, while reliable protection of the entire electronic system can be ensured.

[0157] The MEMS element preferably comprises a MEMS device with a MEMS membrane for a MEMS transducer. The MEMS package produced in this way can also preferably be referred to as a MEMS transducer package. Preferred MEMS transducers are acoustic MEMS transducers, in particular PMUTs, CMUTs and / or PC-MUTs.

[0158] Preferably, the layer system is a conformal layer system with respect to the surfaces of the coated components of the MEMS element (for example: MEMS device, integrated circuit, and preferably integrated circuit of the electrical interconnects, in particular wire bonds).

[0159] The spray coating is preferably implemented such that the MEMS element is completely enclosed between the dielectric layer and the substrate. In particular, no electrically conductive and / or electrically functional regions of the MEMS element should be exposed to the packaging environment, in order to avoid short circuits in particular. All electronic components or electrically conductive components should preferably be covered.

[0160] In particular, the processor, preferably an integrated circuit (IC), exposed electrical wires, and electrically functional or conductive regions of the MEMS element should be covered. Such a dielectric layer advantageously provides a base for a subsequent electrically conductive layer. The dielectric layer can prevent the electrically conductive layer from causing short circuits on the MEMS element. In contrast, the electrically conductive layer itself provides an electrical shield for the MEMS element. Furthermore, the electrically conductive layer, if formed for example from metal, can provide additional mechanical protection and prevent air, moisture, liquids, dust from entering the interior of the package.

[0161] The layer system thus represents a particularly reliable barrier which, in addition to mechanical protection, can prevent the penetration of potentially harmful external influences such as water vapor, dust, etc.

[0162] The electrically conductive layer is preferably applied to the dielectric layer at least in certain regions. Preferably, the electrically conductive layer completely covers the dielectric layer. However, the electrically conductive layer can already be prestructured during the application, so that the regions where the sound port is to be created later are already recessed. Then, only the dielectric layer has to be removed later. If the dielectric layer comprises a photostructurable polymer and a photolithographic process is used, the removal of the dielectric layer is particularly easy.

[0163] For example, the electrically conductive layer, for example a metal layer, can be prestructured with a shadow mask and is preferably used as a hard mask for the subsequent photolithography, for example for creating the sound hole.

[0164] The application of the electrically conductive layer at least in certain regions on top of the dielectric layer advantageously means that the resulting layer system substantially fits tightly and protects the MEMS element from short circuits and electrostatic discharges and seals the layer system against the influence of liquids and / or air. Substantially tight fitting preferably means that most of the coating is in direct contact, but includes volumes that are not filled under components in certain regions, such as in corner regions or wire bonds. If the spray coating is a vapor deposition, at least the dielectric layer, preferably both layers, is completely tight or surface conformal.

[0165] Advantageously, the spray / or vapor deposition enables a form fit of the coating of the components. No further process for filling the flip chip components is necessary, nor is additional protection of, for example, wire bonds.

[0166] In a preferred embodiment of the application, the removal of the layer system or of the dielectric layer is carried out by a photolithographic process, in particular by a suitable exposure of a photostructurable polymer to prestructure the dielectric layer.

[0167] Preferably, photolithography, electron beam lithography and / or ion beam lithography can be carried out.

[0168] Preferably, this removal is carried out layer by layer. In particular for the dielectric layer, if a photostructurable polymer is contained, the process can be simplified.

[0169] The etching process can be carried out, for example, by wet etching or wet-chemical etching.

[0170] Such a process is particularly easy, fast and cost-effective.

[0171] In another preferred embodiment of the present application, the removal of the layer system is performed by a lift-off process, wherein the pre-structuring of the dielectric layer in particular is performed by a suitable exposure of a photo-structured polymer. In particular, a lift-off method is used to remove the entire layer system within the sound port area. For example, the layers can be pre-structured such that in one lift-off step the metal and polymer layers are removed, for example, if the lift-off coating (in particular the dielectric layer) is sufficiently thick or thicker than in other areas at the location to be removed.

[0172] In a preferred embodiment, the thickness of the dielectric layer is between 10 nm and 1 mm. Intermediate ranges of the above-mentioned ranges can also be preferred, such as 10 nm to 100 nm, 100 nm to 200 nm, 200 nm to 500 nm, 500 nm to 1 pm, 1 pm to 5 pm, 5 pm to 10 pm, 10 pm to 50 pm, 50 pm to 100 pm, 100 pm to 500 pm, even 500 pm to 1 mm. The skilled person will recognize that the above-mentioned range limits can also be combined to obtain other preferred ranges, such as 100 nm to 1 pm, 500 nm to 5 pm, or 200 nm to 10 pm.

[0173] In a preferred embodiment, the thickness of the electrically conductive layer is between 10 nm and 20 pm. Intermediate ranges of the above-mentioned ranges can also be preferred, such as 10 nm to 100 nm, 100 nm to 200 nm, 200 nm to 500 nm, 500 nm to 1 pm, 1 pm to 5 pm, 5 pm to 10 pm, even 10 pm to 20 pm. The skilled person will recognize that the above-mentioned range limits can also be combined to obtain other preferred ranges, such as 200 nm to 1 pm, 100 nm to 5 pm, or 500 nm to 10 pm.

[0174] The preferred thicknesses of the dielectric layer and the electrically conductive layer result in an excellent protection of the MEMS element while maintaining a compact design and strong functionality.

[0175] In a preferred embodiment, the present application relates to a production method for a MEMS transducer package having a layer system for protecting a MEMS transducer, the method comprising the following steps:

[0176] - providing a MEMS device on a substrate, the MEMS device comprising a MEMS membrane,

[0177] - providing an integrated circuit on the substrate, the integrated circuit having an electrical connection to the MEMS device,

[0178] - providing a spray-coated portion of the MEMS device, of the integrated circuit, preferably of the MEMS device, of the integrated circuit, and of the electrical interconnect, with the dielectric layer, such that the MEMS device, the integrated circuit, and the electrical interconnect are completely encapsulated between the dielectric layer and the substrate,

[0179] - applying the dielectric layer to the electrically conductive layer at least in certain regions.

[0180] The MEMS device having the MEMS membrane and the integrated circuit on the substrate and comprising the electrical connection preferably comprises a MEMS transducer. In particular, the MEMS transducer is a PMUT, a CMUT, or a PC-MUT. Preferably, the electrical connection is at least one wire bond.

[0181] The preferred embodiments and described advantages for the MEMS package apply likewise and in particular to the preferred MEMS transducer package.

[0182] The produced layer system comprising the dielectric layer and the electrically conductive layer is very compact and easy to produce and provides comprehensive protection of the MEMS transducer. It is particularly advantageous that the acoustic properties of the MEMS transducer are not reduced in the process.

[0183] In a preferred embodiment of the application, there is a back volume of the MEMS transducer arranged between the substrate and the MEMS membrane, and comprising the following steps:

[0184] - arranging a sound port above the membrane by removing the layer or layer system above the membrane at least in certain regions.

[0185] The removal can be achieved, for example, by an etching process that physically processes the layer(s).

[0186] If the electrically conductive layer is not initially applied in this region, only the dielectric layer has to be removed. Otherwise, the dielectric layer and the electrically conductive layer have to be removed at the same time. In particular, this is carried out such that the membrane is uncovered at least in certain regions in order to maintain the acoustic properties of the MEMS transducer, or there is a direct contact between the membrane and the sound medium at least in certain regions. Since the layer system is located directly flush on the MEMS transducer, a direct contact between the membrane and the sound medium can be established, while the sound medium cannot reach other regions of the MEMS transducer. Thus, comprehensive protection against moisture and liquids can be achieved while maintaining the acoustic properties. The flush sealing of the sound port and the membrane also improves the acoustic performance of the MEMS transducer.

[0187] It is particularly preferred that this step is carried out between the application of the spray coating and the application of the electrically conductive layer. For example, the spray coating can then be removed by means of a photolithographic process. If the electrically conductive layer, in particular the metal layer, is applied only after the removal of the dielectric layer, it can be ensured that the electrically conductive layer seals the edge region of the sound hole flush with the MEMS device, which means that the encapsulation can now be guaranteed to be impermeable, in particular to gases, in particular air, moisture and / or liquids.

[0188] In particular, the CMUT preferably comprises two MEMS membranes. In the present embodiment, with the sound port in the layer system, it can advantageously be sufficient if the lower membrane is hermetically sealed to the encapsulation environment.

[0189] In a preferred embodiment of the application, the arrangement of the dielectric layer, the layer system, the MEMS device and / or the MEMS membrane is such that, after removal of the layer or layer system, no electrically conductive region is in direct contact with the encapsulation environment. In particular, these are sealed against air and / or liquids.

[0190] In another preferred embodiment of the application, the electrodes of the capacitive MEMS transducer, in particular of the capacitive micro-machined ultrasonic transducer, are arranged within or face the back volume. For example, the electrodes are located on the side of the membrane facing the back volume. In this way, short circuits caused by moisture, liquids or contamination can be avoided.

[0191] In a preferred embodiment, the MEMS interaction region is only brought into a mobile state after the dielectric layer or layer system has been deposited or removed, preferably by means of a release process, in particular by means of removal of a sacrificial layer.

[0192] In particular, this ensures that the steps of the encapsulation method do not have a negative effect on the function of the mechanically sensitive and finely structured MEMS interaction region. Rather, the preferred release process of the MEMS interaction region takes place as one of the last process steps, only after the application of the dielectric layer or layer system, and, if necessary, with targeted removal of the MEMS interaction region.

[0193] In the case of a MEMS transducer as a MEMS element, an example of a mechanically sensitive and finely structured MEMS interaction region is a MEMS membrane.

[0194] In a preferred embodiment, the MEMS membrane is only brought into a vibrating state after the application or removal of the layer or layer system, preferably by means of a release process, in particular by means of removal of a sacrificial layer.

[0195] MEMS membranes are important components of MEMS transducers. At the same time, such membranes are particularly finely structured and sensitive in order to achieve the desired acoustic properties. Thus, the application of a layer system or the process of removing a layer or layer system for a sound port can influence or even destroy the membrane.

[0196] For this reason, the membrane is preferably only brought into a vibrating state afterwards, in particular by removing a suitably structured sacrificial layer, which is present, for example, between the membrane and other transducer components, thus blocking and protecting the membrane. This can be achieved by means of an etching process, preferably removing the excess material of the sacrificial layer from the package. Preferably, the sacrificial layer can be positioned opposite the membrane and towards the front volume. Then, the material can be removed through the sound port. If the sacrificial layer is present in the back volume, the material is preferably removed through a suitable small channel or opening. These can preferably be closed afterwards.

[0197] This release is particularly relevant for CMUTs, PMUTs and PC-MUTs. These advantages can likewise be transferred to other MEMS elements.

[0198] In another aspect, the present invention relates to a MEMS package producible or produced by the production method.

[0199] In particular, the present invention relates to a MEMS package comprising:

[0200] - a substrate,

[0201] - a MEMS element arranged on the substrate, the MEMS element comprising a MEMS interaction area,

[0202] - a dielectric layer for protecting the MEMS element, the dielectric layer being produced by a conformal coating of a surface of the MEMS element by means of a dielectric coating process.

[0203] The person skilled in the art recognizes that the technical features, definitions and advantages of the described preferred embodiments of the production method for a MEMS package apply likewise to the obtained MEMS package and vice versa.

[0204] Particularly preferred, as described before, is the application of the inventive package method to a MEMS transducer.

[0205] Thus, in a preferred embodiment, the present invention also relates to a MEMS package, which is a MEMS transducer package, the MEMS transducer package comprising:

[0206] - a substrate,

[0207] - a MEMS device arranged on a substrate, the MEMS device comprising a MEMS membrane, wherein a back volume of the MEMS transducer is preferably arranged between the substrate and the MEMS membrane,

[0208] - a processor, preferably an integrated circuit, arranged on the substrate, the processor having electrical connections to the MEMS device,

[0209] - a layer system for protecting the MEMS transducer, the layer system resulting from the following steps:

[0210] a. providing a surface conformal coating, preferably a spray coating, of the MEMS device, the processor, and preferably the electrical interconnects, with a dielectric layer, in particular an optical structured polymer, such that the MEMS device, the processor, preferably an integrated circuit, and the electrical interconnects are completely contained between the dielectric layer and the substrate,

[0211] b. applying an electrically conductive layer at least in regions on the dielectric layer,

[0212] c. optionally arranging a sound port above the MEMS membrane by removing the dielectric layer or layer system above the membrane in certain regions, in particular by a lithography and / or lift-off process.

[0213] Preferably, the arrangement of the layer system, the MEMS device, and / or the MEMS membrane can be such that, after removal of the dielectric layer or layer system, no electrically conductive region is in direct contact with the packaging environment and / or the back volume of the MEMS transducer and the electrically conductive region are sealed by air and / or a liquid, wherein the back volume of the MEMS transducer is preferably arranged between the substrate and the MEMS membrane and the MEMS transducer package has a sound port above the membrane. BRIEF DESCRIPTION OF DRAWINGS

[0214] The application will be explained below with reference to further drawings and examples. These examples and drawings serve to illustrate the preferred embodiments of the application without being limited to the described preferred embodiments.

[0215] Figures 1 to 4 A preferred embodiment of a production method of a MEMS package is shown using a MEMS transducer package 14 as an example. DETAILED DESCRIPTION

[0216] Figure 1 A MEMS transducer 1 without finished package 14 is shown. A MEMS device 2, also referred to as MEMS device, with a MEMS membrane 3 is present on a substrate 4. Likewise, an IC 5, here in the form of an ASIC, is arranged on the substrate 4. Here, the MEMS device 2 and the IC 5 are electrically connected via wire bonds 6.

[0217] Figure 2 The application of the coating system 16 to protect the MEMS transducer 1 is schematically shown. First, a surface conformal coating 7, for example a spray coating, is applied with a dielectric, which coats all components present on the substrate with a dielectric layer 8. This layer thus encloses these components, namely here the MEMS device 2, the IC 5 and the wire bond 6, between the layer itself and the substrate 4 and is essentially a tight fit. Next, a conductive layer 9 is applied to the dielectric layer 8, which also covers the outer edge region of the dielectric layer 8 and is preferably flush with the substrate 4 at the outer edge of the coating, in order to achieve a good seal at the outer edge of the coating.

[0218] Figure 3 A MEMS transducer package 14 is shown, which separates the MEMS transducer 1 from the packaging environment 17 and thus protects it. The MEMS device 2 is arranged such that the back volume 13 is located between the membrane 3 and the substrate 4. The sound port 11 is thus introduced into the layer system 16 above the membrane, wherein two layers 8, 9 are removed above the membrane 3, for example by means of a lithography process. The membrane 3 is present here as a non-released membrane, which is temporarily protected by the sacrificial layer 12.

[0219] In Figure 4 the released membrane 15 is created by removing the sacrificial layer 12.

[0220] Figure 5 A package is shown, which is preferably completely surface conformal, wherein a completely surface conformal coating system 18 is created by means of vapor deposition of a polymer, for example p-xylene. Figure 5 It is shown how tightly fitting the layer system created in this way is, wherein the structure of the wire bond 6 is preserved even after coating in the package 14.

[0221] List of reference signs

[0222] 1 MEMS element, for example a MEMS transducer

[0223] 2 MEMS device

[0224] 3 MEMS interaction area, for example a MEMS membrane

[0225] 4 Substrate

[0226] 5 Processor, preferably an integrated circuit (IC)

[0227] 6 Electrical connection, preferably a wire bond

[0228] 7 Surface conformal coating, for example a spray coating

[0229] 8 dielectric layer

[0230] 9 electrically conductive layer

[0231] 10 outer edge of the coating

[0232] 11 opening in the front of the MEMS interaction area, preferably a sound port

[0233] 12 sacrificial layer of the non-released interaction area, e.g. a sacrificial layer of an unexposed membrane

[0234] 13 back volume

[0235] 14 MEMS package, e.g. a MEMS transducer package

[0236] 15 released MEMS interaction area, e.g. a released MEMS membrane

[0237] 16 layer system

[0238] 17 packaging environment

[0239] 18 surface conformal layer system.

[0240] References

[0241] Alfons Dehe, Martin Wurzer, Marc Fϋldner and Ulrich Krumbein, The Infineon Silicon MEMS Microphone, AMA Conferences 2013 - SENSOR 2013, OPTO 2013, IRS 2 2013.

[0242] Gregor Feiertag, Wolfgang Pahl, Matthias Winter, Anton Leidl, Stefan Seitz, Christian Siegel, Andreas Beer, Flip chip MEMS microphone package with large acoustic reference volume, Proc. Eurosensors XXIV, September 5-8, 2010, Linz, Austria.

[0243] M. Härth, D. W. Schubert, Simple Approach for Spreading Dynamics of Polymeric Fluids. In: Macromol. Chem. Phys. 213, no. 6, March 2012, pp. 654-665.

Claims

1. A method for manufacturing a MEMS package (14), the MEMS package having at least one layer for protecting a MEMS element (1), the method comprising the following steps: - A MEMS element (1) is provided on a substrate (4), the MEMS element including at least one MEMS interaction region (3), wherein the MEMS element (1) includes a MEMS device (2) and a processor (5) on the substrate (4), and an electrical connection (6) is present between the MEMS device (2) and the processor (5). - A dielectric layer (8) is used to provide a conformal coating on the surface of the MEMS element (1). - An electrically conductive layer (9) is applied in at least a region on the dielectric layer (8), wherein the dielectric layer (8) and the electrically conductive layer (9) extend over the MEMS device (2) and the processor (5), the thickness of the dielectric layer (8) being between 10 nm and 1 mm, and the thickness of the electrically conductive layer (9) being between 10 nm and 20 µm, thereby providing electrical insulation and mechanical protection for the MEMS element (1) and realizing the housing function of the MEMS element (1).

2. The production method according to claim 1, Its features are, The MEMS element (1) is selected from: acoustic MEMS transducers, optical MEMS transducers, MEMS sensors, and / or MEMS filters.

3. The production method according to claim 2, wherein, The MEMS sensor is a MEMS gas sensor.

4. The production method according to any one of claims 1 to 3, wherein, The MEMS device is an acoustic MEMS transducer, and the electrically conductive layer (9) and the dielectric layer (8) ensure acoustic sealing.

5. The production method according to any one of claims 1 to 3, Its features are, The conformal coating is achieved by a dielectric coating process, which is selected from spray coating, mist coating, vapor phase coating and / or electroplating.

6. The production method according to any one of claims 1 to 3, Its features are, The conformal coating is achieved by a coating that wets the MEMS element (1) in the MEMS interaction region (3).

7. The production method according to any one of claims 1 to 3, Its features are, The dielectric layer (8) comprises a polymer.

8. The production method according to claim 7, wherein the polymer is a photostructured polymer, polymethyl methacrylate, polyimide, phenolic varnish, polymethylglutarimide, p-xylene, and / or epoxy resin.

9. The production method according to any one of claims 1 to 3, Its features are, The electrically conductive layer (9) comprises metal, and / or, The electrically conductive layer (9) is applied by a coating process.

10. The production method according to claim 9, characterized in that, The metal is aluminum and / or a precious metal.

11. The production method according to claim 10, characterized in that, The precious metals are gold, platinum, iridium, palladium, osmium, silver, rhodium and / or ruthenium.

12. The production method according to any one of claims 1 to 3, characterized in that, The electrically conductive layer (9) is applied by PVD and / or CVD.

13. The production method according to any one of claims 1 to 3, Its features are, The MEMS device (2) and / or the processor (5) are mounted in a flip-chip design, and the electrical connection (6) is formed via the substrate (4), and / or, The MEMS device (2) and / or the processor (5) are present in a conventional design but not in a flip-chip design, and the electrical connection (6) is made via at least one wire connection.

14. A manufacturing method according to any one of claims 1 to 3, the manufacturing method being used for a MEMS package (14), the MEMS package (14) having a layer system (16) for protecting the MEMS element (1), the MEMS element (1) including the MEMS device (2) and the processor (5), the manufacturing method comprising the following steps: - The MEMS device (2) is provided on the substrate (4), the MEMS element including a MEMS interaction region (3). - The processor (5) is provided on the substrate (4), the processor (5) having an electrical connection (6) for connection with the MEMS device (2). - The dielectric layer (8) is used to provide a conformal coating on the surface of the MEMS device (2), the processor (5), and the electrical connection (6), so that the MEMS device (2), the processor (5), and the electrical connection (6) are completely enclosed between the dielectric layer (8) and the substrate (4). - An electrically conductive layer (9) is applied in at least a region on the dielectric layer (8), the electrically conductive layer (9) forming a layer system (16) with the dielectric layer (8). - An opening (11) is arranged above the MEMS interaction region (3) by removing the dielectric layer (8) and / or the layer system (16) in at least some areas above the MEMS interaction region (3).

15. The production method according to claim 14, wherein, The conformal coating part is a spray coating part (7).

16. The production method according to claim 14, wherein, The MEMS device (2) is an acoustic MEMS transducer having a MEMS film on a substrate. The method includes the following steps: using the dielectric layer (8) to provide a conformal coating on the surface of the MEMS device (2), the processor (5) and the electrical connection (6), such that the MEMS device (2), the processor (5) and the electrical connection (6) are completely enclosed between the dielectric layer (8) and the substrate (4).

17. The production method according to claim 16, wherein, The back volume of the MEMS transducer is arranged between the substrate and the MEMS membrane, and a sound port is arranged above the membrane by removing the layer system (16) in at least some areas above the membrane.

18. The production method according to claim 14, Its features are, The removal of the dielectric layer (8) is performed by photolithography or stripping, wherein the dielectric layer (8) is formed of a photostructured polymer, and the pre-structuring of the dielectric layer (8) is performed by corresponding exposure of the photostructured polymer to light.

19. The production method according to claim 13, Its features are, The MEMS element (1) is an optical MEMS transducer, and the MEMS interaction region (3) includes an optical transmitter or an optical receiver, or The MEMS element (1) is an acoustic MEMS transducer, and the MEMS interaction region (3) includes a MEMS film, or The MEMS element (1) is a MEMS gas sensor, and the MEMS interaction region (3) includes a MEMS membrane or an electrochemical MEMS sensor region, or The MEMS element (1) is a MEMS filter, and the MEMS interaction region (3) includes a MEMS filter structure.

20. The production method according to claim 19, wherein, The MEMS filter is a MEMS frequency filter.

21. The production method according to claim 19, wherein, The MEMS filter is a SAW filter or a BAW filter.

22. The production method according to claim 13, wherein, The MEMS interaction region (3) includes MEMS electrodes and / or MEMS bulk regions.

23. The production method according to any one of claims 1 to 3, Its features are, The MEMS element (1) is a MEMS acoustic transducer, and the MEMS element (1) includes a MEMS device and a processor (5), and the manufacturing method includes the following steps: - The MEMS device (2) is provided on a substrate (4), the MEMS device comprising a MEMS film serving as the MEMS interaction region (3). - The processor (5) is provided on the substrate (4), the processor having an electrical connection (6) connected to the MEMS device (2). - The dielectric layer (8) is used to provide a conformal coating on the surface of the MEMS device (2), the processor (5), and the electrical connection (6), so that the MEMS device (2), the processor (5), and the electrical connection (6) are completely enclosed between the dielectric layer (8) and the substrate (4). - An electrically conductive layer (9) is applied in at least some regions on the dielectric layer (8), the electrically conductive layer (9) forming a layer system (16) with the dielectric layer (8). - A sound port is arranged above the MEMS membrane (3) by removing the dielectric layer (8) or the layer system (16) in at least some areas above the membrane (3).

24. A MEMS package (14) capable of being manufactured by a production method according to any one of claims 1 to 23.

25. A MEMS package (14), comprising: - Base (4) - MEMS element (1), the MEMS element (1) is disposed on the substrate (4), the MEMS element (1) includes a MEMS interaction region (3), wherein the MEMS element (1) includes a MEMS device (2) and a processor (5) on the substrate (4). - A dielectric layer (8) is used to protect the MEMS element (1). The dielectric layer is produced by a conformal coating process on the surface of the MEMS element (1). - An electrically conductive layer (9) is present at least in a region on the dielectric layer (8), wherein the dielectric layer (8) and the electrically conductive layer (9) extend over the MEMS device (2) and the processor (5), the thickness of the dielectric layer (8) is between 10 nm and 1 mm, and the thickness of the electrically conductive layer (9) is between 10 nm and 20 µm, thereby providing electrical insulation and mechanical protection for the MEMS element (1) and realizing the housing function of the MEMS element (1).

26. The MEMS package (14) according to claim 25, wherein, The MEMS device (2) is an acoustic MEMS transducer, and the electrically conductive layer (9) and the dielectric layer (8) ensure acoustic sealing.

27. The MEMS package (14) according to claim 26, wherein, The acoustic MEMS transducer includes a MEMS membrane located on a substrate, the back volume of the acoustic MEMS transducer being arranged between the substrate and the MEMS membrane, and an acoustic port being arranged above the membrane by removing the dielectric layer (8) and the electrically conductive layer (9) in at least some areas above the membrane.

Images