DE102017203912A1 - Micromechanical membrane device for a loudspeaker - Google Patents

Abstract

A micromechanical membrane device (100) for a loudspeaker, comprising: - a frame element (10); - A membrane element (20) having a spring element (30), wherein the membrane element (20) by means of the spring element (30) is connected to the frame element (10); - A cover member (60) adapted to provide a closed back volume (50) between the membrane element (20) with the spring element (30) and the cover member (60); and - an airtight sealing element (40) which is formed with the membrane element (20) and with the spring element (30) contacting.

Description

The invention relates to a micromechanical membrane device for a loudspeaker. The invention further relates to a method for producing a micromechanical membrane device for a loudspeaker.

State of the art

Speakers are transducers that convert an input electrical signal into mechanical vibrations perceived as sound. Speakers are usually used to generate sound for the reproduction of speech and music for humans with a typical working range of about 20 Hz to about 20 kHz. The size varies between millimeter-sized forms that can be worn in the ear (so-called "in-ear headphones") up to several meters for the sound of concerts.

To convert electrical signals into sound waves, a medium is set into mechanical vibrations by electrical energy. This function is handled by a membrane. A loudspeaker therefore consists in most cases of three component groups: the diaphragm, the drive unit and their connecting elements.

In classical speakers, the electrodynamic drive is preferably used. This is based on a freely moving, current-carrying coil, which is located in the field of a fixed, external magnet. A current flow through the coil in the surrounding magnetic field causes a force (the so-called Lorentz force) on the freely movable coil in the vertical direction. Due to the vertical mechanical movement of the coil, the tethered membrane is excited to vibrate, which in turn emits sound waves directly into the surrounding air.

In piezoelectric loudspeakers, the deflection of the membrane takes place via a thin piezoelectric layer. By applying a sound frequency electrical voltage to the electrodes on the piezoelectric material, this begins to deform at the frequency. This mechanical vibration is transmitted to the membrane, which emits sound waves directly into the surrounding air.

Capacitive or electrostatic loudspeakers, in turn, work with a highly transformed signal, which acts via stators on a membrane under constant electrical tension.

If a loudspeaker is freely suspended in the room without partition wall or housing, the sound waves radiated from both sides of the membrane can overlap so that the resulting pressure on the front of the membrane and the negative pressure on the back of the membrane almost cancel each other out 1 shown speaker with a membrane element 20 and a drive device 70 is indicated. As a result, the sound pressure drops sharply, so that a listener at a distance greater than the wavelength no longer perceives sound. This reduction of the sound radiation due to the direct pressure equalization is called "acoustic short circuit".

The simplest remedies to the acoustic short circuit are a sealed enclosure or baffle that separates the radiated sound waves on the front and back of the membrane so that a direct acoustic short can no longer occur. This is in the 2 and 3 is shown, which is a speaker with a membrane element 20 , a drive device 70 and a sealing element 40 demonstrate.

In addition to the enclosed housing or the dividing wall, the membrane itself serves for the separation between the air on the front and rear side. Smallest openings (e.g., slits or tears) in the membrane could cause the radiated back sound to pass through the membrane to the front, causing an acoustic short. Therefore, an air-impermeable membrane is essential for avoiding an acoustic short circuit.

The trend towards microelectronic components and microsystems with integrated sensors and actuators is unstoppable, at least since the significant increase in mobile devices. Many of the components required for mobile devices have already been miniaturized and integrated using MEMS technology. Electrodynamically operating miniature loudspeakers known in many mobile terminals today, such as e.g. Smartphones, tablets, laptops, etc. are to be found.

Disadvantages of these miniature speakers are an unsatisfactory sound quality and too large dimensions. An unsatisfactory sound quality results from the fact that the loudspeakers are overdriven from a certain electrical input voltage. Then the uniform movement of the loudspeaker diaphragm changes and deformations (nonlinearity) of the deflection signal occur. The result is a so-called clinking on the speaker and thus a deterioration of the sound quality. The smaller the speaker, the faster this overdrive is achieved.

Further problems of conventional loudspeakers are that their classical construction of the miniaturization physical and production limits are set and whose production requires a variety of materials and assembly steps. In addition, the processing on the motherboards of terminals is very difficult and the speakers are subject to undesirable quality variations.

The fabrication of the speakers on Si wafers (MEMS technology) brings significant advantages, such as: higher accuracy and reproducibility, as well as lower cost manufacturing and packaging processes compared to current manufacturing technology.

4 shows a perspective view of a conventional electrodynamically driven MEMS speaker. The silicon-made loudspeaker consists of a silicon membrane 20 passing through silicon springs 30 is suspended freely on the edge. On the membrane 20 is a drive device 70 applied in the form of a copper coil with leads, with a permanent magnet at the edge of the membrane 20 is placed. On the current-carrying coil in the magnetic field acts the Lorentz force, the membrane 20 stimulates mechanical vibrations.

Five possible different design variants of spring structures which can be manufactured using MEMS technology are shown in FIGS. A) to e) of FIG 5 ,

Also known are electrodynamically driven MEMS speakers in which a thin layer of metallic glass is used as the membrane. In conjunction with a dispensed magnetic paste and a microcoil while a copper technology for the MEMS speaker is realized (not shown).

Also known are piezoelectrically driven MEMS membrane devices, which in 6 is shown and which can be used for mobile communication devices, such as tablets, laptops and headphones. Visible is a membrane element 20 to which spring elements 30 are arranged.

Also known is a capacitive MEMS speaker, which has a membrane made of graphene, which is a very light and strong material and is also still electrically conductive. Deflection of the membrane is effected electrostatically by perforated silicon plates above and below it (not shown).

Disclosure of the invention

It is an object of the present invention to provide an improved membrane device for a MEMS speaker.

• – ein Rahmenelement;
• – ein Membranelement mit einem Federelement, wobei das Membranelement mittels des Federelements an das Rahmenelement angebunden ist;
• – ein Abdeckelement, das ausgebildet ist, ein abgeschlossenes Rückvolumen zwischen dem Membranelement mit dem Federelement und dem Abdeckelement bereitzustellen; und
• – ein luftdichtes Dichtelement, welches mit dem Membranelement und mit dem Federelement kontaktierend ausgebildet ist.

According to a first aspect, the object is achieved with a micromechanical membrane device for a loudspeaker, comprising:

• A frame element;
• - A membrane element with a spring element, wherein the membrane element is connected by means of the spring element to the frame member;
• A cover member configured to provide a closed back volume between the diaphragm member with the spring member and the cover member; and
• - An airtight sealing element which is formed with the membrane element and the spring element contacting.

By means of the airtight sealing element, an acoustic short circuit is prevented, because air can not flow. In this way, an improved operating characteristic for the micromechanical membrane device of the loudspeaker is provided.

• – Bereitstellen eines Rahmenelements;
• – Bereitstellen eines Membranelements mit einem Federelement, wobei das Membranelement mittels des Federelements an das Rahmenelement angebunden wird;
• – Bereitstellen eines Abdeckelements, das ausgebildet ist, ein abgeschlossenes Rückvolumen zwischen dem Membranelement mit dem Federelement und dem Abdeckelement bereitzustellen; und
• – Bereitstellen eines luftdichten Dichtelements, welches mit dem Membranelement und mit dem Federelement kontaktierend ausgebildet wird.

According to a second aspect, the object is achieved with a method for producing a micromechanical membrane device for a loudspeaker, comprising the steps:

• - providing a frame element;
• - Providing a membrane element with a spring element, wherein the membrane element is connected by means of the spring element to the frame member;
• Providing a cover member configured to provide a closed back volume between the diaphragm member with the spring member and the cover member; and
• - Providing an airtight sealing element, which is formed with the membrane element and the spring element contacting.

Advantageous developments of the micromechanical membrane device are the subject of dependent claims.

An advantageous development of the membrane device is characterized in that the airtight sealing element is a polymer layer. Thereby, a flexible, airtight sealing element is provided, which is easy to apply.

A further advantageous development of the membrane device provides that the airtight sealing element is a graphene layer. To this This provides an alternative realization possibility for a flexible, airtight sealing element.

Further advantageous developments of the membrane device provide that the airtight sealing element is arranged above or below the membrane element with the spring element. In this way, two different positioning possibilities for the airtight sealing element are advantageously provided.

Further advantageous developments of the membrane device provide that the cover element is a wafer or a packaging element. In this way, different possibilities for the training of the completed return volume are provided.

The invention will be described below with further features and advantages with reference to several figures in detail. In this case, all features, regardless of their representation in the description and in the figures, as well as regardless of their dependency in the claims, the subject of the present invention. The figures are primarily intended to illustrate the principles essential to the invention and are not necessarily drawn to scale. Same or functionally identical elements have the same reference numerals.

Disclosed method features are analogous to corresponding disclosed device features and vice versa. This means, in particular, that features, technical advantages and embodiments relating to the micromechanical membrane device result analogously from corresponding embodiments, features and advantages of the method for producing a micromechanical membrane device and vice versa.

In the figures shows:

1 a representation of a conventional speaker for explaining an acoustic short circuit;

2 . 3 Representations of a conventional speaker with means for preventing the acoustic short circuit;

4 a perspective view of a conventional MEMS speaker;

5 Views of Spring Elements for a MEMS Speaker;

6 a representation of a conventional MEMS speaker with piezo drive;

7 a plan view of an embodiment of a proposed membrane device;

8th a cross-sectional view of an embodiment of a proposed membrane device; and

9 a sequence of a method for producing a micromechanical membrane device for a MEMS speaker.

Description of embodiments

A basic idea of the invention is, in particular, to provide an improved membrane device for a MEMS loudspeaker. As already explained above, MEMS loudspeakers usually consist of a membrane (or a plate), which is clamped by freely movable springs in a frame. Using silicon technology, membrane and springs can be made from a wafer. In order to make membrane and springs freely movable in the vertical direction, it is essential that the springs are exposed at the edge by means of a Tiefenätzprozesses.

The resulting small air gaps at the spring edges, as in the 4 to 6 In fact, because of the air gaps, there is a separation between the air on the front and back of the membrane element 20 not given anymore. Sound waves radiated from the back can pass through the etched-off air gaps onto the front side of the membrane element 20 penetrate and cause an acoustic short circuit in this way. Due to the resulting direct pressure equalization the sound radiation of the speaker is greatly reduced and its full functionality is no longer guaranteed.

The invention proposes a structure of an airtight MEMS-based loudspeaker device which is suspended on freestanding springs on an outer frame. In order to avoid the mentioned acoustic short circuit, the springs and the membrane are sealed by means of a flexible, airtight layer towards the ambient air.

Requirements for the flexible, airtight layer are on the one hand a low mass and a low spring stiffness, in order not to influence the membrane vibration and on the other hand to provide a high tensile strength and robustness against deflections. Suitable materials for the realization of the flexible, airtight layer are e.g. Polymers or graphene.

Advantageously, by using the flexible, airtight layer, an acoustic short circuit in MEMS-based speaker devices can be avoided. The functions of the membrane, springs and the airtight layer are advantageously clearly separated from each other and assigned to these components. This advantageously allows separate optimization of the flexible springs, the light and rigid membrane and the airtight, flexible layer.

This also supports a high flexibility of the arrangement and the design of the springs, the membrane and the airtight layer. In addition, this advantageously results in the high precision and reproducibility of the manufactured geometries by using MEMS technology for producing the loudspeaker diaphragm, the springs and the airtight layer, resulting in a good and reproducible sound quality of the MEMS loudspeakers equipped therewith.

7 shows a plan view of a realizable by MEMS technology speaker membrane element 20 , at the edge by freely movable spring elements 30 in an outer frame element 10 fixed or "clamped" is. The membrane element 20 , the spring element 30 and the outer frame member 10 can be made from a single silicon wafer. The spring elements 30 at the edge of the membrane element 20 can be structured by known standard methods of semiconductor technology. For this purpose, trenches are etched into the material to the edge of the spring elements 30 define. Both the membrane element 20 as well as the spring elements 30 are freestanding. This can be realized by means of a deep etching process, in which the Si wafer from the back to the desired thickness of the membrane element 20 is etched away.

8th shows a cross-sectional view of in 7 illustrated arrangement with the undercut membrane element 20 and the structure of the spring elements 30 , A completed back volume 50 Under the membrane-spring structure can be achieved by a suitable cover 60 which is formed, for example, as a packaging element or as another wafer which is bonded to the back side of the device.

To create an acoustic short between the front of the membrane and the back volume 50 To avoid, the membrane spring structure with a flexible, airtight, ie air-impermeable, layer-shaped sealing element 40 sealed. The sealing element 40 can either on the top or on the underside of the membrane element 20 with the spring elements 30 be applied contacting. Suitable materials for the flexible, airtight, layered sealing element 40 are for example polymers or graphene.

As a result, the micromechanical membrane device thus provided has 100 a high degree of flexibility with regard to the design of the membrane 20 and the spring elements 30 on. For example, the in 5 illustrated designs of the spring structures are used.

9 1 shows a sequence of a method for producing a micromechanical membrane device for a loudspeaker:

In one step 200 becomes a provision of a frame element 10 carried out.

In one step 210 becomes a provision of a membrane element 20 with a spring element 30 performed, wherein the membrane element 20 by means of the spring element 30 to the frame element 10 is connected.

In one step 220 becomes a provision of a cover member 60 performed, which is formed, a closed back volume 50 between the membrane element 20 with the spring element 30 and the cover member 60 provide.

In one step 230 becomes a provision of an airtight sealing element 40 performed, which with the membrane element 20 and with the spring element 30 is formed contacting.

In summary, the present invention provides a micromechanical membrane device for a loudspeaker with which advantageously an acoustic short circuit can be prevented or at least greatly reduced.

Although the invention has been described above by means of concrete examples of application, the person skilled in the art can realize previously or only partially disclosed embodiments, without departing from the gist of the invention.

Claims (11)

Micromechanical membrane device ( 100 ) for a loudspeaker, comprising: - a frame element ( 10 ); A membrane element ( 20 ) with a spring element ( 30 ), wherein the membrane element ( 20 ) by means of the spring element ( 30 ) to the frame element ( 10 ) is connected; A cover element ( 60 ), which is designed to have a closed back volume ( 50 ) between the membrane element ( 20 ) with the spring element ( 30 ) and the cover element ( 60 ) to provide; and An airtight sealing element ( 40 ), which with the membrane element ( 20 ) and with the spring element ( 30 ) is formed contacting. Micromechanical membrane device ( 100 ) according to claim 1, characterized in that the airtight sealing element ( 40 ) is a polymer layer. Micromechanical membrane device ( 100 ) according to claim 1, characterized in that the airtight sealing element ( 40 ) is a graphene layer. Micromechanical membrane device ( 100 ) according to claim 1 or 2, characterized in that the airtight sealing element ( 40 ) above or below the membrane element ( 20 ) with the spring element ( 30 ) is arranged. Micromechanical membrane device ( 100 ) according to one of the preceding claims, characterized in that the cover element ( 60 ) is a wafer. Micromechanical membrane device ( 100 ) according to one of claims 1 to 4, characterized in that the cover element ( 60 ) is a packaging element. Loudspeaker comprising a micromechanical membrane device ( 100 ) according to one of claims 1 to 6. Method for producing a micromechanical membrane device ( 100 ) for a loudspeaker, comprising the steps: - providing a frame element ( 10 ); Providing a membrane element ( 20 ) with a spring element ( 30 ), wherein the membrane element ( 20 ) by means of the spring element ( 30 ) to the frame element ( 10 ) is connected; Providing a cover element ( 60 ), which is designed to have a closed back volume ( 50 ) between the membrane element ( 20 ) with the spring element ( 30 ) and the cover element ( 60 ) to provide; and - providing an airtight sealing element ( 40 ), which with the membrane element ( 20 ) and with the spring element ( 30 ) is formed contacting. Method according to claim 8, wherein the airtight sealing element ( 40 ) above or below the membrane element ( 20 ) with the spring element ( 30 ) is arranged. A method according to claim 8 or 9, wherein as an airtight sealing element ( 40 ) a graphene layer or a polymer layer is used. Use of a micromechanical membrane device ( 100 ) according to one of claims 1 to 6 in a loudspeaker.

Images