EP3042509B1 - Digital acoustic device with increased sound power - Google Patents

Description

TECHNICAL FIELD AND PRIOR ART

The present invention relates to a digital acoustic device with increased sound power, for example a digital speaker or an acoustic photo imaging system.

The speakers are present in a large number of devices such as mobile phones, flat screens ... and their miniaturization is sought. MEMS technologies can provide ultrafine speakers.

MEMS technology is particularly suitable for making digital loudspeakers, for which the large membrane of the analogue loudspeaker is replaced by several unitary membranes or more generally by several ultrafine acoustic transducers, called speaklets, of small sizes, making it possible to reconstitute the his.

In the case of the digital speaker, each speaklet is operated individually according to the sound to be reconstructed, in a high position, or in a low position.

The digital speakers nevertheless offer a low noise level.

Solutions have been proposed to increase the sound pressure of a microphone. For example the document US 2011/0075867 describes a loudspeaker comprising a membrane provided at its center with a mass having the effect of reducing the resonant frequency of the membrane and thus increasing the sound pressure. The document US 2011/0051985 describes a loudspeaker comprising a membrane provided with a piston fixed on the membrane.

The document US 2012/148071 describes a digital speaker of electrostatic type, the diaphragm, in operation, is moved to contact with each other two front and rear frames.

STATEMENT OF THE INVENTION

It is therefore an object of the present invention to provide a digital acoustic device, for example a speaker with increased acoustic power.

The previously stated goal is achieved by a digital acoustic device comprising at least one suspended membrane, at least one actuator associated with the membrane to move it upwards or downwards, and means interrupting the displacement of the membrane following the activation of the actuator associated with the membrane. The interruption means are dimensioned so that the displacement of the membrane is interrupted when it has a non-zero speed.

Preferably, the speed at which the upward or downward movement due to the use of the associated actuator is stopped is the maximum or substantially maximum speed that the membrane can have. The greater the deceleration of the membrane, the greater the acoustic pressure generated by the displacement of the membrane.

In other words, in the digital acoustic device according to the invention the displacement of the membrane is deliberately interrupted, preferably when it has a high or even maximum speed to obtain a sudden deceleration of the membrane and thus generate an acoustic pressure high. These stop elements are sized to interrupt the movement of the membrane before it reaches the end of its course.

Advantageously, the means for stopping the membrane during its displacement are carried by a substrate facing the membrane they form one or more elements projecting from the substrate in the direction of the membrane and are sized to come into contact with the membrane when it has a non-zero speed, preferably a high speed and more preferably a maximum speed. Preferably, the distance between the free end of the stop element (s) and the membrane at rest is between 50% and 75% of the theoretical maximum stroke of the membrane.

Alternatively, the means for stopping the membrane during its displacement are carried by the membrane they form one or more projecting elements and are dimensioned to come into contact with the substrate facing the membrane when it has a non-zero speed, preferably a high speed and more preferably a maximum speed. Preferably, the distance between the free end of the stop element (s) and the support when the membrane is at rest is between 50% and 75% of the theoretical maximum stroke of the membrane.

The digital acoustic device may be a digital speaker or an acoustic photo imaging system.

The subject of the present invention is therefore a digital acoustic device comprising at least one membrane suspended facing a support and at least one actuator associated with said membrane, said associated actuator being intended to move said membrane away from and / or towards said support, said device also comprising stop means for interrupting the displacement of said membrane following the activation of said actuator when the membrane has a non-zero speed, the stop means being dimensioned so as to interrupt the movement of the membrane when the displacement of the membrane is greater than or equal to 50% of the theoretical maximum stroke of the membrane and less than or equal to 75% of the theoretical maximum stroke of the membrane.

Preferably, the stop means are dimensioned so as to interrupt the displacement of the membrane when the displacement of the membrane is between 50% and 60% of the theoretical maximum stroke of the membrane.

Advantageously, the stop means are dimensioned so as to interrupt the displacement of the membrane when it moves to its maximum speed or at a speed close to its maximum speed, ie at a speed greater than or equal to 75% of its maximum speed.

The stop means may comprise at least one stop element projecting from the support in the direction of the membrane and / or protruding from the membrane towards the support, and having a free end separated by a non-zero distance respectively from the membrane and / or support in the rest state.

The stop element may be located opposite a central zone of the membrane or may be fixed in a central zone of the membrane.

Advantageously, the distance separating the free end of the stop element and the membrane or the free end of the stop element and the support is between 50% and 75% of the theoretical maximum stroke of the membrane. .

Advantageously, the digital acoustic device comprises a plurality of stop elements.

Preferably, the stop elements are distributed over an area corresponding to a surface representing between 10% and 50% of the surface of the membrane.

In an exemplary embodiment, the digital acoustic device comprises a gaseous fluid between the membrane and the support, the device comprising at least one passage in the support for the flow of the gaseous fluid so as to reduce the viscous damping. The passage can be formed between two stop elements.

For example, the stop element (s) have a cross-section, circular, square, ellipsoidal or trapezoidal column shape.

The stop element (s) can be in one piece with the support and / or the membrane.

According to an additional characteristic, the stop element or elements are formed of one or more layers of materials added to the substrate and / or the membrane.

The actuator may be carried by the membrane and is opposite the free end of the stop element, said device comprising a protective layer deposited on the actuator so as to protect it from contact with the free end. of the stop element.

At least one actuator may be formed by a piezoelectric actuator.

The digital acoustic device may comprise a first actuator in contact with the membrane intended to exert a force on the membrane in a first direction, a second actuator in contact with the membrane intended to exert a force on the membrane in a second direction opposite to the first .

The first and second actuators may comprise a ferroelectric piezoelectric material, each of the first and second actuators being intended to deform the membrane in an opposite direction.

In an exemplary embodiment, the first actuator borders the outer periphery of the membrane and the second actuator is located substantially in a central zone of the membrane.

The digital acoustic device may comprise a second support facing the membrane opposite the first support, said second support having stop means for interrupting the movement of said membrane following activation of said second actuator.

Preferably, the digital acoustic device comprises a plurality of membranes and actuators associated with each of the membranes.

1. a) réalisation de la membrane et de l'actionneur,
2. b) réalisation des moyens d'arrêt sur le support et/ou sur la membrane,
3. c) assemblage de la membrane et de l'actionneur avec le support de sorte que les moyens d'arrêt soient en regard respectivement de la membrane et/ou du support, à une distance donnée lorsque la membrane est au repos.

The present invention also relates to a method for producing a digital acoustic device according to the invention,

1. a) realization of the membrane and the actuator,
2. b) realization of the stop means on the support and / or on the membrane,
3. c) assembly of the membrane and the actuator with the support so that the stop means are respectively facing the membrane and / or the support at a given distance when the membrane is at rest.

The stop element can advantageously be realized simultaneously with at least one electrical connection of the actuator, between the support and the actuator,
In an exemplary embodiment, prior to the production of the stop element and the electrical connection, an electrical line can be made, the electrical connection being formed on said electrical line, so that the height of the connection assembly electrical line is greater than that of the stop element.

In another embodiment, prior to the production of the stop element, a recess can be made in an area of the support where the stop element is formed so that the height of the support and connection assembly electrical power is greater than that of the support assembly and stop element.

The stop element is for example made in said substrate and / or the membrane by etching.

For example, the assembly between the support and the membrane is not thermocompression and / or bonding, for example by molecular bonding ...

Steps a) and b) are advantageously carried out by microelectronic techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1A est une vue de dessus d'un exemple d'une membrane munie d'actionneur pour un haut-parleur digital de l'invention,
• les figures 1B et 1C sont des vues de côté de la membrane de la figure 1A dans deux états différents,
• la figure 2 est une vue de côté d'un exemple de réalisation d'haut-parleur selon l'invention,
• la figure 3 est une vue de côté d'un autre exemple de réalisation d'un haut-parleur selon l'invention,
• la figure 4 est une représentation graphique de l'accélération de la membrane en fonction du temps t pour un système de l'état de la technique et un haut-parleur selon l'invention,
• les figures 5A à 5R sont des représentations schématiques d'étapes de réalisation d'une membrane et des actionneurs d'un haut parleur selon un exemple de procédé de réalisation,
• les figures 6A à 6D sont des représentations schématiques d'étapes de réalisation d'un support muni de moyens d'arrêt selon l'invention selon un exemple de procédé de réalisation,
• la figure 7 est une représentation schématique d'une variante du procédé des figures 6A à 6D,
• les figures 8A à 8C sont des représentations schématiques d'étapes de réalisation d'un support muni de moyens d'arrêt selon l'invention selon un autre exemple de procédé de réalisation,
• la figure 9 est une représentation schématique d'un haut-parleur comportant des moyens d'arrêt en regard de chacune des faces de la membrane.

The present invention will be better understood with the aid of the description which follows and the drawings in appendices in which:

• the Figure 1A is a top view of an example of a membrane provided with an actuator for a digital loudspeaker of the invention,
• the Figures 1B and 1C are side views of the membrane of the Figure 1A in two different states,
• the figure 2 is a side view of an exemplary embodiment of loudspeaker according to the invention,
• the figure 3 is a side view of another embodiment of a loudspeaker according to the invention,
• the figure 4 is a graphical representation of the acceleration of the membrane as a function of time t for a system of the state of the art and a loudspeaker according to the invention,
• the Figures 5A to 5R are diagrammatic representations of steps for producing a diaphragm and actuators for a loudspeaker according to an exemplary embodiment method,
• the Figures 6A to 6D are schematic representations of steps for producing a support provided with stop means according to the invention according to an exemplary embodiment method,
• the figure 7 is a schematic representation of a variant of the method of Figures 6A to 6D ,
• the Figures 8A to 8C are schematic representations of steps for producing a support provided with stop means according to the invention according to another exemplary embodiment method,
• the figure 9 is a schematic representation of a loudspeaker having stop means facing each of the faces of the membrane.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

In the description which follows, the invention will be described by considering a digital speaker but it will be understood that the invention also on an acoustic photo imaging system, and more generally on a digital acoustic device.

A digital speaker has a plurality of acoustic transducers or speaklets individually controlled. The sound to be reproduced is reconstructed by the principle of the additivity of the elemental sounds of the speaklets in the air. In the description that follows, we will consider an elementary speaker with a speaklet.

On the Figures 1A to 1C and 2 a particularly advantageous example of a piezoelectric actuated elementary loudspeaker can be seen. On the Figures 1A to 1C only the diaphragm is shown with the actuators. On the figure 2 the digital loudspeaker comprising a diaphragm 2 in the form of a disk suspended on a support 4 can be seen, a piezoelectric material element 6 in the shape of a ring situated on an upper face of the membrane 2 and on the outer edge of the membrane 2.

The outer periphery of the ring 6 is on the support 4 and the inner periphery is on the membrane 2. The ring is connected to a source of voltage or current 8 as is schematized on the Figures 1C and 1B so that it forms a first actuator adapted to set the membrane 2 in motion. For this, an electrode is provided on the upper face and the lower face of the ring 6 to ensure its connection to the voltage source 8.

In the example shown and advantageously, the membrane device also comprises a second element of piezoelectric material 10 in disk form in the example shown, and located in a central portion of the upper face of the membrane 2. The disk 10 is also connected to a voltage or current source 12 as is schematized on the Figures 1C and 1B so that it forms a second actuator adapted to move the membrane 2. An electrode is provided on each face of the disk to ensure its connection to the voltage source 8.

In another variant, the membrane may have a square or rectangular shape, in this case the actuator may have a shape similar to that of the membrane but with a different surface.

It should be noted that the second actuator has no part of its surface anchored on the support part.

The first and second actuators may be made of the same piezoelectric materials or with different piezoelectric materials.

In an exemplary embodiment, the actuators are made from ferroelectric piezoelectric materials such as PZT. The movements of the membrane obtained thanks to these actuators are those represented on the Figures 1B and 1C .

Indeed, whatever the sign of the applied voltage, if it is greater in absolute value to the coercive field of the ferroelectric piezoelectric material, then this one expands in the thickness and contracts radially. Therefore, the upward or downward movements of the diaphragm are caused by the shape and position of the actuator on the diaphragm and not by the sign of the control voltage.

In the example shown, the application of a voltage on the first actuator 6 causes a displacement of the membrane 2 upwards, it then has a convex shape relative to the support 4. The application of a voltage on the second actuator 10 causes a displacement of the membrane 2 downwards which then has a concave shape with respect to the support 4.

In another embodiment, the actuators are made from piezoelectric materials such as AIN, ZnO, etc. A positive voltage causes the piezoelectric material to expand while a negative voltage will induce its contraction. Thus the upward and downward movements can be obtained using a single actuator.

The amplitude of the displacement of the membrane is proportional to the voltage applied across the actuators.

The use of two actuators has the advantage of being able to move the membrane upwards and downwards, which makes it easier to produce a loudspeaker with a fine reproduction of the sound.

But a speaker with a single actuator is not beyond the scope of the present invention. Furthermore, the digital acoustic device according to the invention may comprise other types of actuator that piezoelectric actuators, it may be electrostatic actuators, magnetic, thermal ... which are well known to the man of the job.

According to an exemplary embodiment of the invention, and as is more particularly visible on the figure 2 protruding elements are provided on a substrate facing the membrane and towards the membrane so as to form stop elements of the displacement of the membrane as it moves at a non-zero speed. The height of the stop elements 14 is chosen so that their free end 14.1 comes into contact with the substrate while the membrane has a non-zero speed. The distance between the membrane at rest and the free end 14.1 of the stop elements is designated h. Preferably, the height of the stop elements is such that the free end of the stop elements comes into contact with the membrane while the membrane has its maximum or substantially maximum speed. Alternatively, the projecting elements may be located below the membrane in the representation of the figure 2 .

Advantageously, the distance h is between 50% and 75% of the theoretical maximum stroke of the membrane.

Preferably, the height of the stop elements is a function of the deformation of the membrane.

In the case of stop elements having all the same height, the stop elements located closer to the center of the membrane will enter contact with the membrane first. The membrane, due to the inertia generated by its movement will continue to deform for a short time, and stops further periphery will come into contact in turn.

Preferably, the stop elements are located facing a central zone of the membrane having the largest deformed it is also the area with the highest speed. The central portion has for example half the diameter of the membrane. The stop elements are distributed over a portion of the surface of the membrane so as not to risk damaging or breaking the membrane.

The distance between the free end of at least one stop element 14 and the membrane at rest is then less than the theoretical maximum stroke of the membrane, so as to ensure contact between the free end 14.1 of the element stop and the membrane before it has zero velocity.

Putting the stop elements opposite this zone makes it possible to cause a significant deceleration and therefore the generation of a high acoustic pressure.

A single stop element 14 up to several tens or even hundreds of stop elements can be provided.

Preferably the stop element or elements are distributed over an area having a surface corresponding to between 10% and 50% of the surface of the membrane.

The stop elements may have any shape, for example have a cylindrical shape with circular section, ellipsoidal, a form of pavement right ...

The section of the stop elements is determined according to the number of stop elements, and / or the surface of the membrane and / or the rigidity of the membrane. The section of the stop elements may for example be between a few tens of μm ² to a few mm ² .

The distance between the stop elements is also chosen according to the surface of the membrane and / or the rigidity of the membrane. For example, the more flexible the membrane, the more the stop elements will be close to each other to limit or even avoid parasitic deformations of the membrane. This distance is preferably between a few tens of μm and a few mm, this distance also making it possible to reduce the gaseous damping that can be induced by the presence of these stop elements.

Advantageously, at least one passage 16 is provided in the substrate facing the membrane in the substrate in order to limit the appearance of viscous damping when the membrane approaches the stop elements, this passage allowing the air or other gaseous fluid to flow and not to dampen the movement of the membrane. In the example shown, passages 16 are made between the stop elements.

Advantageously, a protective layer is formed at least on the central actuator 10 so that the contact between the stop elements and the actuator does not damage it.

In other actuator embodiments, preferably the stop members are arranged with respect to the actuator or actuators so as not to contact the actuator. For example in the configuration of the actuators 6 and 10 of the figure 1 , the stop elements are arranged between the actuators 10 and 6. Considering a membrane having a small surface, the arrangement of the stop elements only on a ring is sufficient to stop the membrane and not induce excessive deformation of the center of it.

The distance between the rest position of the membrane and the free end 14.1 of the stop element is determined as a function of the dimension of the membrane and of these materials forming it, in particular the mechanical properties thereof, defined in particular by the Young's module, the density and Poisson's ratio, these parameters setting the maximum stroke of the membrane.

Avec : $$p_3=\frac{\pi g_{31}{E}_{1}V\left(3t_1-2t_3\right)}{\left(1-{\mu }_1\right)\overline{{\beta }_{33}}}$$

$$E_1=\frac{1}{S_{11}^D},\mathrm{}{\mu }_1=-\frac{S_{12}^D}{S_{11}^D},\mathrm{}\overline{{\beta }_{33}}={\beta }_{33}+\frac{2g_{31}^2{E}_1}{1-{\mu }_1}$$

$${\lambda }_1=1+{\mu }_1,\mathrm{}{\lambda }_2=6+2{\mu }_1,\mathrm{}{\lambda }_3=5+{\mu }_1$$

$$\begin{array}{l}{M}_1=8P_1{\displaystyle {\int }_0^a{H}_1\left(r\right)\mathit{rdr}+}8P_2{\displaystyle {\int }_0^b{H}_2\left(r\right)\mathit{rdr}+16P_4{\displaystyle {\int }_0^b{H}_3\left(r\right)\mathit{rdr}}}\\ -\left\{\pi t_2{\rho }_m{\omega }^2{\displaystyle {\int }_0^a{H}_4\left(r\right)\mathit{rdr}+2\pi t_1{\rho }_p{\omega }^2{\displaystyle {\int }_0^b{H}_4\left(r\right)\mathit{rdr}}}\right\}\end{array}$$

$$H_1\left(r\right)=20{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4+{\mu }_2\left(12{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4\right)$$

$$H_2\left(r\right)=20{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4+{\mu }_1\left(12{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4\right)$$

$$H_3\left(r\right)={\left(4{\lambda }_1{r}^2-{\lambda }_1{b}^2\right)}^2$$

$$H_4\left(r\right)={\left({\lambda }_1{r}^4-{\lambda }_2{b}^2{r}^2+{\lambda }_3{b}^4\right)}^2$$

$$H_5\left(r\right)=4{\lambda }_1{r}^2-{\lambda }_2{b}^2$$

To determine the maximum stroke of the membrane, the displacement of the membrane is calculated. This can be calculated by finite element software such as ANSYS, COVENTOR ... or analytically as in the following equation giving the dynamic displacement of the membrane: $$w=\frac{-4P_{3}V\left({\lambda }_1{r}^4-{\lambda }_2{b}^2{r}^2+{\lambda }_3{b}^4\right){\displaystyle {\int }_0^b{H}_5\left(r\right)\mathit{rDR}}}{M_1},$$

With: $$p_3=\frac{\pi {\mathrm{boy\; Wut}}_{31}{E}_{1}V\left(3t_1-2t_3\right)}{\left(1-{\mu }_1\right)\widetilde{{\beta }_{33}}}$$

$$E_1=\frac{1}{S_{11}^D},\mathrm{}{\mu }_1=-\frac{S_{12}^D}{S_{11}^D},\mathrm{}\widetilde{{\beta }_{33}}={\beta }_{33}+\frac{2{\mathrm{boy\; Wut}}_{31}^2{E}_1}{1-{\mu }_1}$$

$${\lambda }_1=1+{\mu }_1,\mathrm{}{\lambda }_2=6+2{\mu }_1,\mathrm{}{\lambda }_3=5+{\mu }_1$$

$$\begin{array}{l}{M}_1=8P_1{\displaystyle {\int }_0^{\mathrm{at}}{H}_1\left(r\right)\mathit{rDR}+}8P_2{\displaystyle {\int }_0^b{H}_2\left(r\right)\mathit{rDR}+16P_4{\displaystyle {\int }_0^b{H}_3\left(r\right)\mathit{rDR}}}\\ -\left\{\pi t_2{\rho }_m{\omega }^2{\displaystyle {\int }_0^{\mathrm{at}}{H}_4\left(r\right)\mathit{rDR}+2\pi t_1{\rho }_p{\omega }^2{\displaystyle {\int }_0^b{H}_4\left(r\right)\mathit{rDR}}}\right\}\end{array}$$

$$H_1\left(r\right)=20{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4+{\mu }_2\left(12{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4\right)$$

$$H_2\left(r\right)=20{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4+{\mu }_1\left(12{\lambda }_1^2{r}^4-8{\lambda }_1{\lambda }_2{b}^2{r}^2+{\lambda }_2^2{b}^4\right)$$

$$H_3\left(r\right)={\left(4{\lambda }_1{r}^2-{\lambda }_1{b}^2\right)}^2$$

$$H_4\left(r\right)={\left({\lambda }_1{r}^4-{\lambda }_2{b}^2{r}^2+{\lambda }_3{b}^4\right)}^2$$

$$H_5\left(r\right)=4{\lambda }_1{r}^2-{\lambda }_2{b}^2$$

g ₃₁ is the piezoelectric coefficient which connects the applied electric field out of plane (direction 3) and the stress in the plane (direction 1), V denotes the applied voltage. S ₁₁ ^D and S ₁₂ ^D are respectively the relative deformations in the plane (direction 1 and 2) obtained in response to a stress applied in direction 1. The exponent D means "constant load". b is the radius of the piezoelectric layer. This equation is by example explained in the document Li, "Theoretical modeling of a circular piezoelectric actuator for micro systems", ICINA 2010 . The distance between the membrane at rest and the free end 14.1 of the stop element 14 is then determined.

This distance is chosen sufficient to allow the membrane to reach a high speed, preferably its maximum speed. Preferably, the contact between the membrane and the free end of the stop member takes place before the membrane decelerates. A distance will preferably be chosen between the membrane at rest and the free end of the stop element between 50% to 75% of the maximum stroke of the membrane, preferably between 50% and 60%.

By way of example, for a membrane with a radius of 500 μm, for example, the deflection of the membrane will be of the order of 3 μm. If h is chosen so as to be at 50% of the maximum stroke, then h will be 1.5 μm.

On the figure 3 we can see another embodiment, in which the stop elements are carried by the membrane. In this case, the distance h 'between the free ends 14.1' of the stop elements 14 'and the substrate is set when the membrane is at rest between 50% and 75% preferably of the theoretical maximum stroke of the membrane.

The characteristics of the stop elements carried by the substrate, such as the section, the spacing ... described for the stop elements 14 also apply to the stop elements 14 '.

On the figure 4 it is possible to see, as a function of time, the variation of the acceleration a of a diaphragm of a loudspeaker according to the invention (curve designated I) and the variation of the acceleration of a diaphragm a loudspeaker of the state of the art without a stop element (designated curve II).

The areas of the two curves are identical, but the peak designated p due to the deceleration of the membrane is more abrupt than that of the peak of curve II and its amplitude is greater than that of the peak of curve II at acceleration. A denotes the contact between the stop element (s) and the membrane in the realization of the figure 2 .

However, the acoustic pressure caused by a speaklet and thus the capacity of the digital speaker to reconstruct an audible sound of the desired sound level, depends on the speed (acceleration a) of the speaklet membrane and its ability not to cause parasite , ie its ability not to present parasitic oscillations.

Ou bien $$P\left(r,t\right)=\frac{{\rho }_0.a^2}{r}\mathit{Acc}\left(t\right)$$

ou bien $$P\left(r,t\right)=\frac{{\rho }_0.S}{\pi \cdot r}\mathit{Acc}\left(t\right)$$

Avec

• p0 : masse volumique de l'air
• a : rayon de l'élément mobile
• S : surface de l'élément mobile
• r : distance d'écoute
• V : vitesse de l'élément mobile
• Acc : accélération de l'élément mobile

The sound pressure according to the acceleration is written: $$P\left(r,t\right)=\frac{{\rho }_0.{\mathrm{at}}^2}{r}\frac{\mathit{dV}\left(t\right)}{\mathit{dt}}$$

Or $$P\left(r,t\right)=\frac{{\rho }_0.{\mathrm{at}}^2}{r}\mathit{Acc}\left(t\right)$$

or $$P\left(r,t\right)=\frac{{\rho }_0.S}{\pi \cdot r}\mathit{Acc}\left(t\right)$$

With

• p0: density of the air
• a: radius of the moving element
• S: surface of the moving element
• r: listening distance
• V: speed of the moving element
• Acc: acceleration of the moving element

If a increases, the sound pressure will increase. The above equation also applies with deceleration. According to the present invention, we increase the deceleration. By increasing it, the sound pressure is also increased.

We will now describe a particularly advantageous example of a method of producing a loudspeaker according to the invention.

The steps are schematically represented on the Figures 5A to 5R .

For example, a silicon substrate 100 represented on the Figure 5A , having for example a thickness of 725 microns and a diameter of 200 mm in diameter.

In a first step, the substrate is subjected to thermal oxidation so as to form an oxide layer 102 on all the substrate surfaces with a thickness of 2 μm, for example. The element thus obtained is represented on the Figure 5B .

Then, an oxide hard mask 104 is made on the rear face of the substrate. This mask has for example a thickness of 7 microns. the mask is made by inverting the substrate; depending on the chosen deposition composition; it is possible to remove the mask only on this face. It may be for example a PVD type deposit (Physical Vapor Deposition). The element thus obtained is represented on the Figure 5C .

A lithography is then carried out on the rear face so as to reach the silicon. The element thus obtained is represented on the figure 5D .

In a next step, the hard mask is etched, for example by reactive ion etching (RIE), so as to reach the rear face of the substrate 100. The element thus obtained is represented on the figure 5E .

In a next step, the oxide layer is removed on the front face, for example by deoxidation or chemical etching. The element thus obtained is represented on the figure 5F .

In a next step, an oxide layer 106 is formed on the front face. Advantageously, a densification annealing takes place for example at a temperature of the order of 800 ° C. The element thus obtained is represented on the figure 5G .

In a next step, a layer 108 is formed on the front face intended to form the membrane 2, and a layer 110 on the rear face. Preferably, these layers are for example polysilicon, SiC or SiO ₂ . The thickness of the layers 108, 110 is for example between a few hundred nm to several μm, or even several tens of μm.

The layers 108, 110 are for example made by chemical vapor deposition (or CVD for Chemical Vapor Deposition in English terminology) or by epitaxial growth. Preferably, the stresses of the layers 108, 110 are controlled.

The layers 108, 110 can be formed in several times. For example, for a thickness of 4 microns, two layers of 1.5 microns thick and 1 layer of 1 micron thick are made successively.

Advantageously, an annealing step then takes place. The element thus obtained is represented on the figure 5H .

In a next step, a layer 112 is formed on the layer 108, for example SiO ₂ or SiN, having for example a thickness between a few hundred nm and several μm. The layer 112 is formed for example by thermal oxidation or by CVD deposition. Advantageously, a densification annealing takes place for example at a temperature of the order of 800 ° C.

The element thus obtained is represented on the figure 5I .

In a next step, the first and second actuators are made.

For this purpose, a layer 114 is firstly made for forming the lower electrodes of the actuators, for example in Pt, Mo. layer 114 is made for example by deposition on the layer 112. The layer 114 has for example a thickness between a few tens of nm to a few hundred nm. The element thus obtained is represented on the figure 5J .

A layer of piezoelectric material 116 is then formed on the layer 114, for example PZT, AlN, ZnO, LNO whose thickness is for example between a few hundred nm to a few microns.

The upper electrode is then produced by forming a layer 118 on the piezoelectric material 116, for example in Ru or Au for example having a thickness of between a few tens of nm and a few hundred nm. The element thus obtained is represented on the figure 5K .

Then there are etching steps.

First, the layer 118 is etched so as to delimit the annular actuator 8 and the disc-shaped actuator 10.

Then, the layer 116 of piezoelectric material is etched.

The element thus obtained is represented on the figure 5L .

Then, the remaining layer portions 118 are etched again so that they are recessed with respect to the layer portions 116.

The layer 114 is then etched, as well as the oxide layer 112. The element thus obtained is represented on the figure 5M .

Preferably, a staircase profile is produced. This is obtained because all the layers are deposited and etched from the top layer, using different photolithography masks, the second mask being wider than the first, etc. This allows to leave safety margins to avoid layer overlap, which may appear due to the uncertainty of the positioning of the masks. This avoids any short electrical circuit between the electrodes. The element thus obtained is represented on the figure 5N .

In the following steps, contact pickup pads 120 are formed. Preliminary, a layer 122 of dielectric material, for example SiO _{2, is formed} on the edges of the stacks formed by the lower, upper and piezoelectric electrodes, this layer being etched so as to partially disengage the lower and upper electrodes. The element thus obtained is represented on the figure 50 .

Then, for example, a layer of AISi or TiAu is formed and is etched, thus forming contact pads at the regions where the electrodes have been released. The element thus obtained is represented on the figure 5P .

Advantageously, in a subsequent step, a protective layer 124 is formed on the actuators, for example an oxide layer, in order to protect the actuators from contact with the stop elements. The thickness of this layer may be between a few hundred nm to a few μm, for example 500 nm.

In a next step, the layer 124 is etched to access the contacts.

The element thus obtained is represented on the figure 5Q .

Preferably, during a following step, the actuators are protected, for example by the deposition of a dry film 126. Next, the rear face is etched in order to release the membrane 2.

The membrane is released by deep etching of the substrate through the backside until it reaches the membrane.

The element thus obtained is represented on the figure 5R .

The realization of the stop elements will now be described, in this example, they are made on a substrate type "interposer", ie having electrical connections and / or electronic circuits (control, sensors ... ). In the example shown and very advantageously, the stop elements are made simultaneously with the connections Electrical 18, also referred to as microbumps or copper pillar. Thus the production process is faster. The stop elements therefore have a structure similar to that of the electrical connections. The electrical connections are intended to route the signal of the speaklets to pads at the periphery of the substrate 200 or to the electronics if it is made on the substrate 20. In the example described, a single stop element is formed, but it will be understood that several stop elements can be formed simultaneously.

For this, we start for example with a silicon substrate 200 ( Figure 6A ).

In a first step, lines are made to bring the signal of the speaklet to contact pads (not shown) at the periphery of the substrate 200, it is for example copper lines. A layer of, for example, TiCu 2 O 2 is then formed on one side. Resin zones are then defined by means of a resin for the formation of thick copper layers. The copper layers 204 are then formed for example by growth. Then the resin is removed and the TiCu layer is etched.

The element thus obtained is represented on the Figure 6B . The copper lines are present only in line with the contact pads connected to the electrodes. The area of the substrate 200 at least vertically above the central zone of the membrane, does not yet comprise any layer.

In a next step, a layer of TiCu 206 is again deposited at the places where it is desired to make the electrical connections and the abutments, then Cu growth zones are defined and the copper portions 208 are grown. During this step, the microbumps are produced on the two copper lines and in the region of the substrate 200 in line with the central zone of the membrane.

SnAg 210 layers are then formed on the three portions of copper 208 and SnAg 210. The resin is removed and the TiCu layer is etched. The portions 208 and 210 have a reduced section relative to that of the portions 204.

Advantageously, in a next step, passages 16 may be made in the substrate between the electrical connections and the stop element 14 for example by etching; these passages being intended to reduce the viscous damping as has been described above.

The element thus obtained is represented on the Figure 6C .

Then the membrane 2 and the actuators 6, 10 represented on the figure 5R and the substrate provided with the electrical connections and the stop member 14 of the Figure 6C are assembled. The electrical connections 18 are aligned with the contact pads, then brought into contact with the contact pads. The assembly is done for example by thermocompression. The speaker is represented on the Figure 6D . In practice, the dry film is removed after assembling the two substrates.

In this example, the height of the stop element is identical to that of the electrical connections, on the other hand the stop element being made directly on the substrate 200, are free end 14.1 does not come into contact with the membrane resting. The distance between the free end 14.1 and the membrane designated h is thus determined in this embodiment by the thickness of the portions of the connection lines. To determine h, we consider the membrane carrying the actuators. On the Figure 6D , h is the distance between the free end 14.1 and the actioneur6. In the case of a loudspeaker comprising another type of actuator, it would not necessarily be taken into account in the calculation of the distance h.

The distance h between the free end 14.1 of the stop element and the membrane is chosen to be less than the theoretical maximum stroke of the membrane, preferably h is between 50% of the theoretical maximum stroke and 75 % of the theoretical maximum stroke of the membrane. The Maximum deformation of the membrane is determined from the dimensions of the membrane.

In an exemplary embodiment in which a single actuator is used, the method of producing the stop elements and the connection or connections is similar to that described above.

On the figure 7 , we can see an alternative embodiment of the stop elements, in the case where the control electronics is made on the substrate 200. In this case, the copper tracks are not required to set the height h of the elements of stop but only to route the signal to pads or to the electronics. Electrical connections can be made directly to the substrate by depositing a Ti / Cu layer and thick copper growth. The distance h between the free end 14.1 of the stop element and the membrane is then obtained by making a recess 20 in the electronic substrate 200 at the future location of the element or the stop elements prior to the making the electrical connections and the stop element. This recess has a depth h. This recess is an example made partially etching the electronic substrate 200. The stop element at the same height as the microbumps but, because of the presence of the depth recess h, the free end 14.1 of the substrate is at a distance h from the membrane at rest.

On the Figures 8A to 8C we can see another embodiment of the stop elements. In this case, the substrate is of the "packaging" type, ie the substrate serves to cover the membrane in order to encapsulate it.

We start from a substrate 300, for example made of silicon ( figure 8A ).

Then, a layer 302 is formed which is sealed with the membrane, for example gold or oxide.

The sealing layer is then etched to leave this layer only on the periphery of the substrate. The substrate is then structured, for example by partial etching, to produce the stop element 14. The depth the etching is chosen so as to obtain the desired distance h between the free end 14.1 of the stop element and the membrane The depth of the etching takes into account the thickness induced by the assembly, for example by gold-gold bonding or molecular bonding, this involves taking into account the thickness of the sealing layer.

The element thus obtained is represented on the Figure 8B . The stop element is in one piece with the substrate type "packaging".

This element is then sealed with the membrane of the figure 5Q , for example by gold-gold bonding, by molecular assembly ( Figure 8C ).

It should be noted that it would be possible to produce on the "packaging" type substrate the stop element by adding material, as in the example of FIG. figure 7 . And conversely, it could be envisaged in the case of an interposed substrate to make one or more stop elements in one piece with the interposing substrate.

On the figure 9 , we can see an alternative embodiment in which the loudspeaker comprises stop elements of the membrane opposite its two faces. This achievement is particularly adapted to the speaklet of Figures 1A to 1C which comprises two actuators able to move the membrane upwards and downwards in the representation of the Figure 8C . As indicated above, actuation of the membrane in both directions makes it possible to reproduce the sound more finely.

The speaker of the figure 9 is for example realized as has been described in connection with the Figures 8A and 8B , but this is not limiting.

Then, a second substrate such as that of the Figure 8B .

The support substrate of the membrane is then thinned so as to make its thickness less than the maximum stroke of the membrane. It can be envisaged to completely remove the support substrate.

The substrate 300 is then assembled facing the face of the membrane opposite to that carrying the actuators.

In the example shown, the stop elements 14 on either side of the membrane 2 have the same height but one could predict that they have different heights, for example depending on the level of thinning of the substrate membrane support.

In addition, one could plan to assemble on the subset of the Figure 6C and to assemble a substrate of the Figure 8B .

In the embodiment where the stop elements would be carried by the membrane, their production would for example be obtained by deposition of material after the step shown in FIG. figure 5P or that represented on the figure 5Q . For example; the stop elements would be made by retaining a portion of the original substrate 100. The substrate would then be thinned to the thickness of the desired stop elements, then the membrane would be released by etching the substrate, it would then be possible to leave the stop elements.

The digital acoustic device according to the invention offers increased sound power with a relatively simple structure. In addition, the production method is not very complex compared to the production of digital acoustic devices of the state of the art, in particular in the case of microbumps realization.

It is particularly suitable for the realization of digital speakers having a plurality of speaklets.

Claims (15)

1. A digital acoustic device comprising at least one suspended diaphragm (2) facing a support (4) and at least one piezoelectric actuator (6, 10) associated with said diaphragm, said associated actuator (6, 10) being configured to move said diaphragm (2) away from and/or closer to said support (4), said device also comprising stop means (14) configured to interrupt the movement of said diaphragm (2) further to activating said actuator (6, 10) when the diaphragm has a non-zero speed, the stop means (14) being sized so as to interrupt the movement of the diaphragm (2) when the movement of the diaphragm is greater than or equal to 50% of the theoretical maximum stroke of the diaphragm and lower than or equal to 75% of the theoretical maximum stroke of the diaphragm.
2. The digital acoustic device according to claim 1, wherein the stop means are sized so as to interrupt the movement of the diaphragm when the movement of the diaphragm is between 50% and 60% the theoretical maximum stroke of the diaphragm.
3. The digital acoustic device according to claim 1 or 2, wherein the stop means are sized so as to interrupt the movement of the diaphragm when it moves at its maximum speed or at a speed close to its maximum speed.
4. The digital acoustic device according to one of claims 1 to 3, wherein the stop means comprise at least one stop member (14) protruding from the support (4) towards the diaphragm (2) and/or protruding from the diaphragm (2) towards the support (4), and having a free end (14.1) separated by a non-zero distance from the diaphragm (2) and/or the support at rest, respectively, the stop member being optionally located facing a central area of the diaphragm or is fixed in a central area of the diaphragm.
5. The digital acoustic device according to claim 4, wherein the distance separating the free end (14.1) from the stop member (14) and the diaphragm (2) or the free end (14.1') from the stop member (14') and the support (4) is between 50% and 75% of the theoretical maximum stroke of the diaphragm.
6. The digital acoustic device according to one of claims 1 to 5, wherein the stop means comprise a plurality of stop members (14, 14') protruding from the support (4) towards the diaphragm (2) and/or protruding from the diaphragm (2) towards the support (4), and having a free end (14.1) separated by a non-zero distance from the diaphragm (2) and/or the support at rest, respectively, the stop members (14, 14') being optionnaly distributed on an area corresponding to a surface representing between 10% and 50% of the diaphragm surface and the stop member(s) (14; 14') being optionally in the shape of a column with a circular, square, ellipsoidal or trapezoidal cross-section.
7. The digital acoustic device according to one of claims 4 to 6, wherein the stop member(s) (14) are integral with the support and/or the diaphragm, or wherein the stop member(s) (14) are formed by one or more layers of materials inserted on a substrate and/or the diaphragm.
8. The digital acoustic device according to one of claims 4 to 7, wherein the actuator (6, 10) is carried by the diaphragm (2) and is facing the free end (14.1) of the stop member (14), said device comprising a protective layer deposited on the actuator (6, 10) so as to protect it from the contact with the free end (14.1) of the stop member (14).
9. The digital acoustic device according to one of claims 1 to 8, comprising a gaseous fluid between the diaphragm and the support, the device comprising at least one passageway (16) in the support (4) for the flow of the gaseous fluid so as to reduce the viscous damping, said passageway (16) being optionally formed between two stop members (14, 14').
10. The digital acoustic device according to one of claims 1 to 9, comprising a first actuator (6, 6') in contact with the diaphragm (2) configured to exert a strain on the diaphragm (2) along a first direction, a second actuator (10, 10') in contact with the diaphragm (2) configured to exert a strain on the diaphragm (2) along a second direction opposite to the first direction, the first and second actuators optionally comprising a ferroelectric piezoelectric material, each of the first (6) and second (10) actuators being configured to deform the diaphragm (2) in an opposite direction.
11. The digital acoustic device according to claim 10, wherein the first actuator (6) bounds the outer periphery of the diaphragm (2) and the second actuator (10) is substantially located in a central area of the diaphragm (2) and/or wherein the digital acoustic device comprises a second support facing the diaphragm opposite to the first support, said second support comprising stop means configured to interrupt the movement of said diaphragm further to activating said second actuator.
12. The digital acoustic device according to one of claims 1 to 11, comprising a plurality of diaphragms and actuators associated with each of the diaphragms.
13. The digital acoustic device according to one of claims 1 to 12, forming a digital loudspeaker.
14. A method for manufacturing a digital acoustic device according to one of claims 1 to 13, comprising the steps of:

    a) creating the diaphragm and the actuator, on the substrate and/or the diaphragm, advantageously by etching.

    b) creating the stop means on the support and/or on the diaphragm,

    c) assembling the diaphragm and the actuator with the support so that the stop means are facing the diaphragm and/or the support respectively, at a given distance (h) when the diaphragm is at rest, assembling the support to the diaphragm being optionnally made by thermocompression and/or gluing, for example by molecular gluing.
15. The manufacturing method according to claim 14, wherein the stop member is created simultaneously to at least one electric connection of the actuator, between the support and the actuator, optionally, prior to creating the stop member and the electric connection, an electric line is created, the electric connection being formed on said electric line, so that the height of the electric line connection assembly is greater than the one of the stop member, or prior to creating the stop member, a recess is created in an area of the support where the stop member is formed so that the height of the support and electric connection assembly is greater than the one of the support and stop member assembly.

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