Abstract:
Measures are provided for increasing the resistance to compression of a component having a micromechanical microphone pattern. In particular, the robustness of the microphone pattern to highly dynamic pressure fluctuations is to be increased, without the microphone sensitivity, i.e. the microphone performance, being impaired. The microphone pattern of such a component is implemented in a layer construction on a semiconductor substrate and includes at least one acoustically active diaphragm, which spans a sound hole on the substrate backside, and a stationary acoustically penetrable counterelement having through hole openings, which is situated above/below the diaphragm in the layer construction. At least one outflow channel is developed which makes possible a rapid pressure equalization between the two sides of the diaphragm. In addition, at least one controllable closing element is provided, with which the at least one outflow channel is optionally able to be opened or closed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a component having at micromechanical microphone pattern, which is implemented in a layer construction on a semiconductor substrate. The microphone pattern includes an acoustically active diaphragm, which spans a sound hole on the backside of the substrate, and a stationary acoustically penetrable counterelement, having through hole openings, which is situated in the layer construction above or below the diaphragm. 
     BACKGROUND INFORMATION 
     The diaphragm&#39;s being acted upon by sound takes place via the sound hole in the substrate and/or via the through holes in the counterelement. The diaphragm deflections resulting from this, perpendicular to the layer planes, are able to be detected capacitively, for example. For this, the microphone pattern is equipped with a capacitor device which includes at least one deflectable electrode on the diaphragm and at least one stationary electrode on the counterelement. The volume directly in front of and behind the acoustically active diaphragm of the component under discussion should be as airtight as possible, in order to avoid an acoustical short circuit and to achieve a good microphone sensitivity. 
     The higher the pressure difference between the two sides of the diaphragm, the greater is the diaphragm deflection and, with that, also the mechanical stress of the diaphragm. The microphone diaphragm of the component being discussed is not normally designed for highly dynamic pressure fluctuations and high pressure differences. Such overload situations, which may even lead to damage in the microphone pattern, may not, however, be totally excluded either during the production process nor at the point of use of the component. Thus, during the production process, in “pick&#39;n place” assembly, very high suction pressures are used, and also at the place of use of the component, strong air blasts may occur, such as are caused by an air pistol, for example. 
     SUMMARY 
     The present invention provides measures for increasing the resistance to compression of a component named at the outset. In particular, the robustness of the microphone pattern to highly dynamic pressure fluctuations is to be increased, without the microphone sensitivity, i.e. the microphone performance, being impaired. 
     For this purpose, according to the present invention, at least one outflow channel is developed in the layer construction, which makes possible a rapid pressure equalization between the two sides of the diaphragm. Furthermore, according to the present invention, at least one controllable encrypting element is provided, with which the at least one outflow channel may optionally be opened or closed. 
     In normal operation, the active mode of the component, the outflow channel is to be held closed, in order not to impair the microphone sensitivity. Only when highly dynamic pressure fluctuations as of a specified magnitude occur, should the outflow channel be opened, so that the force of the corresponding pressure wave is conducted past the diaphragm or is weakened to such an extent that it does not lead to damage of the diaphragm. The closing element may simply be actuated as a function of the different operating modes of the component. In this case, the actuation of the closing element for closing the outflow channel may be connected to the actuation of the diaphragm. In the overload case, the outflow channel is opened automatically in the simplest case, i.e. by the acting pressure force or suction force. However, in the overload case, the closing element may also be actively actuated, for example, if the pressure conditions in the surroundings are monitored with the aid of a threshold value switch especially provided for this. 
     Basically there are different possibilities for implementing an outflow channel according to the present invention, having a controllable closing element. The construction of the microphone pattern has to be taken into account in this context. But the type of the overload situation that is to be avoided is also important, that is, whether an impact force or a suction force is to be reduced. As an impact force or an impact pressure, a force is designated in the following which presses the diaphragm away from the counterelement, while as a suction force a force is designated which presses or draws the diaphragm against the counterelement. The direction of the acting force must particularly be taken into account in the design of the closing element, since, in the case of an overload situation, the closing element should preferably be moved with, and not against the acting force, in order to open the outflow channel. 
     To compensate for impact pressure overload situations, the outflow channel may advantageously be implemented in the diaphragm range of the microphone pattern. In one preferred specific embodiment of the component according to the present invention, the outflow channel is developed at the edge of the diaphragm area, namely, in the form of a first pressure equalization opening in the edge region of the counterelement and of a second pressure equalization opening in the edge region of the diaphragm. The two pressure equalization openings communicate with each other by forming a flow connection between the two sides of the diaphragm, depending on the diaphragm position. Since the two pressure equalization openings are situated offset to each other, the diaphragm itself may be used as a controllable closing element. For this purpose, the diaphragm, in the active mode of the component, is drawn against the counterelement, the edge region of the counterelement functioning as a seat for the diaphragm edge. In this diaphragm position, both pressure equalization openings are closed. In response to the occurrence of an impact pressure, which presses the diaphragm away from the counterelement, the pressure equalization openings are automatically opened by the diaphragm motion, and thus make possible a rapid pressure equalization between the two sides of the diaphragm. In the layer construction at least one stop is advantageously developed for the diaphragm, which limits the diaphragm deflection during the opening of the outflow channel, and thus protects against damage from an overload. 
     In one particularly versatile usable refinement of this specific embodiment of the present invention, the diaphragm is not only able to be moved actively in the direction of the counterelement, in order to close the outflow channel, but also to be moved actively away from the counterelement, in orderly actively to open the outflow channel. This may be meaningful if the microphone function is not needed and/or highly dynamic pressure fluctuations are to be expected at clearly defined time periods. The actuation of the diaphragm preferably takes place electrostatically. In this case, the diaphragm is respectively pulled against a corresponding stop in the layer construction, which defines the closed position and the open position. 
     In one particularly advantageous specific embodiment of the component according to the present invention, which is able to be designed both for the case of an impact pressure-overload situation and also for the case of a suction pressure-overload situation, at least one outflow channel is developed laterally next to the diaphragm area and is connected to the backside of the diaphragm via a lateral access opening. The associated closing element is developed in at least one layer of the layer construction, in this case, so that it is movable perpendicular to the layer planes within the outflow channel. In this specific embodiment, the closing element is structurally independent of the diaphragm, and is also moved independently of it, in order to open or close the outflow channel. 
     The closed position of the closing element is preferably defined by a bottleneck in the outflow channel, which functions as an encircling stop or seat for the closing element, so that the outflow channel is closed as pressure-tightly as possible. It is important that the closing element be situated above this bottleneck, in the direction of the force occurring in the overload case, so that it is pressed out of its closed position by this force or together with this force, and the outflow channel is opened. Depending on the situation of the closing element with respect to the bottleneck in the outflow channel, the latter may thus be designed to dissipate a suction force or even an impact force. In each case it proves to be advantageous, even in this specific embodiment of the present invention, if, in the layer construction, at least one stop is developed which limits the deflection of the closing element in response to the opening of the outflow channel. 
     At this point, we should explicitly point out that a component, of the type under discussion, with the aid of the measures according to the present invention, is able to be designed both for impact force overload situations and for suction force overload situations. The component is advantageously equipped for this purpose with separate outflow channels and corresponding closing elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 a -1 c    show schematic sectional representations through the edge region of the microphone pattern of a first component  10  according to the present invention, in the passive operating mode ( FIG. 1 a   ) and the active operating mode ( FIG. 1 b   ) as well as in the case of an impact pressure overload situation ( FIG. 1 c   ). 
         FIGS. 2 a , 2 b    show schematic sectional representations through the edge region of the microphone pattern of a second component  20  according to the present invention, in the active operating mode ( FIG. 2 a   ) and in the case of an impact pressure overload situation ( FIG. 2 b   ). 
         FIGS. 3 a -3 c    show schematic sectional representations through the edge region of the microphone pattern of a third component  30  according to the present invention, in the passive operating mode ( FIG. 3 a   ) and the active operating mode ( FIG. 3 b   ) as well as in the case of an impact pressure overload situation ( FIG. 3 c   ). 
         FIGS. 4 a , 4 b    show schematic sectional representations through the edge region of the microphone pattern of a fourth component  40  according to the present invention, in the active operating mode ( FIG. 4 a   ) and in the case of a suction pressure overload situation ( FIG. 4 b   ). 
         FIGS. 5 a , 5 b    show schematic sectional representations through the edge region of the microphone pattern of a fifth component  50  according to the present invention, in the active operating mode ( FIG. 5 a   ) and in the case of a suction pressure overload situation ( FIG. 5 b   ). 
         FIGS. 6 a -6 c    show schematic sectional representations through the edge region of the microphone pattern of a sixth component  60  according to the present invention, in the active operating mode ( FIG. 6 a   ) in the case of an impact pressure overload situation ( FIG. 6 b   ) and in the case of a suction force overload situation ( FIG. 6 c   ). 
     
    
    
     DETAILED DESCRIPTION 
     The microphone patterns of components  10 ,  20  and  30  are each implemented in a layer construction on a semiconductor substrate  1 . They include an acoustically active diaphragm  11  which spans a sound hole  14  on the backside of the substrate. Moreover, the microphone patterns include a stationary acoustically penetrable counterelement  15  which, in the case of components  10  and  20 , is situated in the layer construction above diaphragm  11 , and in the case of component  30 , in the layer construction below diaphragm  11 . In particular, the sectional representations of  FIGS. 1 a  and 3 a   , the microphone patterns of components  10  and  30  in the passive operating mode show, illustrate that diaphragm  11  is in each case made up of an edge region  111 , a parallel-sided middle region  113  and a transitional region  112  between edge region  111  and middle region  113 , and that, between edge region  111  of diaphragm  11  and counterelement  15  there is a shorter distance than between parallel-sided middle region  113  of diaphragm  11  and counterelement  15 . In counterelement  15 , through hole openings are developed which are not shown here, however, since they are located over middle region  113  of diaphragm  11 . The signal detection takes place capacitively in each case with the aid of a capacitor device which includes at least one deflectable electrode on diaphragm  11  and at least one stationary electrode on counterelement  15 . 
     According to the present invention, in the layer construction of microphone components  10 , and  30 , in each case at least one outflow channel  17  is developed, which enables a rapid pressure equalization between the two sides of diaphragm  11 . For each outflow channel  17 , at least one controllable closing element  18  is provided, with which outflow channel  17  may optionally be opened or closed. 
     In the case of all three microphone components  10 ,  20  and  30 , outflow channel  17  is designed with closing element  18  to reduce an overload situation, in which diaphragm  11  is pushed away by counterelement  15 , which is designated as impact force overload situations. 
     Outflow channel  17  is in this instance, in each case, implemented in the form of a first pressure equalization opening  171  in the edge region of counterelement  15 , and a second pressure equalization opening  172  in the edge region of diaphragm  11 . These two pressure equalization openings  171  and  172  are situated in an offset manner to each other, so that, depending on the position of diaphragm  11 , they are closed or communicate with each other, that is, they make possible an air flow between the front side of the component and sound hole  14  and thus they make possible a pressure equalization between the two sides of diaphragm  11 . 
     Thus, accordingly, in all three cases diaphragm  11  itself, or rather edge region  111  of diaphragm  11 , functions as controllable closing element  18 , in that the two pressure equalization openings  171  and  172  are closed when edge region  111  of diaphragm  11  is draw against counterelement  15 . 
       FIGS. 1 a  through 1 c , 2 a , 2 b  and 3 a  through 3 c    illustrate the method of functioning of outflow channel  17  as a function of the operating mode of the respective microphone component  10 ,  20  and  30  and the diaphragm position corresponding to the operating mode. 
       FIG. 1 a    and  FIG. 3 a    show component  10  and component  30  in the so-called passive operating mode. The microphone function is not activated here. Accordingly, diaphragm  11  is in its at rest position, which comes about only based on the diaphragm pattern, the mechanical properties of the diaphragm and its integration into the layer construction. In this at rest position, edge region  111  of diaphragm  11  is at a distance from counterelement  15 , so that a flow connection exists between the two pressure equalization openings  171  and  172 . Outflow channel  17  is opened in this instance, so that the forces occurring in an impact pressure overload situation are reduced. 
       FIG. 1 b   ,  FIG. 2 a    and  FIG. 3 b    show components  10 ,  20  and  30  in the active operating mode, i.e. having the actuated diaphragm  11 . The actuation of diaphragm  11  for activating the microphone function may take place electrostatically, for example. In this context, diaphragm  11  is acted upon with a mechanical stress, in order to raise the microphone sensitivity. To do this, diaphragm  11  is drawn so far against counterelement  15  that edge region  111  of diaphragm  11  lies against counterelement  15 . In this diaphragm position, both pressure equalization openings  171  and  172  are closed, whereby an acoustical short circuit via outflow channel  17  is avoided and maximum microphone sensitivity is achieved. 
       FIG. 1 c   ,  FIG. 2 b    and  FIG. 3 c    show components  10 ,  20  and  30  in an impact pressure overload situations. In the case of components  10  and  20 , the forces occurring in this case act upon the components&#39; front side, while in component  30  they act upon the component&#39;s backside. In all three cases, diaphragm  11  is thereby pressed away from counterelement  15 . In the process, pressure equalization openings  171  and  172  are also opened in edge region  111  of diaphragm  11  and of counterelement  15 , so that a flow connection is created between the component front side and backside sound hole  14 . This outflow channel  17  enables a rapid pressure equalization between the two sides of diaphragm  11 , whereby the mechanical stress of the diaphragm is clearly weakened. 
     In the exemplary embodiment shown in  FIGS. 1 a  through 1 c   , microphone component  10 , substrate  1  in the edge region of sound hole  14  forms an encircling mechanical stop  19 , which limits the diaphragm motion during the opening of outflow channel  17 , and in this respect functions as overload protection for diaphragm  11  on the substrate side. 
     In the case of microphone component  20  shown in  FIGS. 2 a  and 2 b   , the edge region of sound hole  14  is also used as a stop for the diaphragm motion. However, in this case, in the region of outflow channel  17  a recess  141  has been developed, through which the opening cross section of outflow channel  17  to sound hole  14  is enlarged. 
     In microphone component  30  shown in  FIGS. 3 a  through 3 c   , in which diaphragm  11  is situated in the layer construction above counterelement  15 , a mechanical stop  39  is developed in the layer construction above diaphragm  11 , which limits the diaphragm motion during the opening of outflow channel  17 , and thus forms an overload protection against impact pressure overload situations. 
     At this place, let us point out again that all the abovementioned components  10 ,  20 ,  30  may also be equipped with means for actuating diaphragm  11 , which enable an active opening of outflow channel  17 . Because of that, the actuating of diaphragm  11  and the microphone function are able to be decoupled. This is particularly of advantage if the occurrence of impact pressure overload situations is detected even independently of the microphone pattern, such as with the aid of a dedicated sensor component. 
     The microphone pattern of capacitive microphone components  40  and  50  shown in  FIGS. 4 a , 4 b  and 5 a , 5 b    is also implemented in a layer construction on a semiconductor substrate  1 , and spans a sound hole  14  in the backside of the substrate. The microphone pattern includes an acoustically active diaphragm  11  having an edge region  111 , a middle region  113  offset in a manner that is parallel-sided to it and a transitional region  112  between edge region  111  and middle region  113 . In the layer construction above diaphragm  11 , a stationary acoustically penetrable counterelement  15  is situated. 
     According to the present invention, in these components  40  and  50 , there is also developed at least one outflow channel  47  in the layer construction, which enables a rapid pressure equalization between the two sides of diaphragm  11 . For each outflow channel  47 , at least one controllable closing element  48  is provided, with which outflow channel  47  may optionally be opened or closed. 
     In the case of microphone components  40  and  50  shown here, outflow channel  47  is designed with closing element  48  to reduce an overload situation, in which diaphragm  11  and particularly its middle region  113  is pulled against counterelement  15 , which is designated as suction force overload situations. 
     In this case, outflow channel  47  is situated laterally beside the diaphragm area and extends through the layer construction up to substrate  1 , where it is connected to the backside of diaphragm  11  via a lateral access opening  471 . In one layer of the layer construction, a bottleneck  472  is developed in outflow channel  47 . It functions as an encircling stop or seat for closing element  48 , which in this instance is also patterned out from the layer construction, namely, from a layer above bottleneck  472 . It is movable within outflow channel  47  perpendicular to the layer planes, in order to open or close outflow channel  47  in an optional manner. 
       FIGS. 4 a , 4 b  and 5 a , 5 b    illustrate the method of functioning outflow channel  47  as a function of the operating mode of the respective microphone component  40  or  50 . 
       FIG. 4 a    and  FIG. 5 a    show components  40  and  50  in the active operating mode, in which diaphragm  11  has been drawn against counterelement  15 , in order to act upon it with a mechanical stress. Outflow channel  47  is closed in order to avoid an acoustical short circuit and to achieve a maximum microphone sensitivity. For this purpose, closing element  48  was drawn against its seat  472  in outflow channel  47 . The actuation of closing element  48  required for this may take place electrostatically, for example. 
       FIG. 4 b    and  FIG. 5 b    show components  40  and  50  in a suction force overload situation. The forces occurring in this context, act upon the component front side, so that particularly middle region  113  of diaphragm  11  is drawn against counterelement  15 . In this context, however, closing element  48  is also drawn upwards, i.e. in the direction towards the front side of the component, whereby outflow channel  47  is opened. By this flow connection between the front side of the component and the sound hole  14  on the backside, the mechanical stress of diaphragm  11  is clearly weakened. 
     In both exemplary embodiments, in the layer construction above outflow channel  47 , a mechanical stop  49  is developed, which limits the motion of closing element  48  during the opening of outflow channel  47 , and thus forms an overload protection in suction force overload situations. 
     Both microphone components  40  and  50  described above may also be equipped with means for actuating closing element  48 , which enable an active opening of outflow channel  47 . 
     Closing elements  48  of the components under discussion, in this case, may also be used for the design of the microphone damping behavior, by providing them with suitable ventilating openings  56 , as in the case of microphone component  50 . 
     The microphone pattern of component  60  shown in  FIGS. 6 a  through 6 c    includes both an outflow channel  17  in the diaphragm area, which is designed for impact pressure overload situations, and an outflow channel  47 , having a closing element  48 , which is designed for suction force overload situations. These components of the microphone pattern were described thoroughly in connection with  FIGS. 1 a  through 1 c  and 4 a , 4 b   . Therefore, we shall subsequently only explain the manner of functioning of outflow channels  17  and  47 , with the aid of  FIGS. 6 a  through 6 c   , as a function of the operating mode of microphone component  60 . 
       FIG. 6 a    shows component  60  in the active operating mode, i.e. with an actuated diaphragm  11 . Diaphragm  11  was drawn so far against counterelement  15  that edge region  111  of diaphragm  11  lies against counterelement  15 . In this diaphragm position, both pressure equalization openings  171  and  172  are closed, whereby an acoustical short circuit via outflow channel  17  is avoided and maximum microphone sensitivity is achieved. Outflow channel  47  is also closed, so as to achieve maximum microphone sensitivity. For this purpose, closing element  48  was drawn against its seat  472  in outflow channel  47 . 
       FIG. 6 b    shows component  60  in an impact pressure overload situation, that is, in which diaphragm  11  is pressed away from counterelement  15 . In the process, pressure equalization openings  171  and  172  are also opened in edge region  111  of diaphragm  11  and of counterelement  15 , so that a flow connection is created between the component front side and backside sound hole  14 . This outflow channel  17  enables a rapid pressure equalization between the two sides of diaphragm  11 , whereby the mechanical stress of the diaphragm is clearly weakened. The position of closing element  48  on bottleneck  472  in outflow channel  47  does not change, since closing element  48  is additionally pressed against seat  472  by the impact pressure stress. 
       FIG. 6 c    shows component  60  in a suction force overload situation, in which, in particular, middle region  113  of diaphragm  11  is drawn against counterelement  15 . In this context, however, closing element  48  is also drawn upwards, i.e. in the direction towards the front side of the component, whereby outflow channel  47  is opened. By this flow connection between the front side of the component and the sound hole  14  on the backside, the mechanical stress of diaphragm  11  is clearly weakened. Pressure equalization openings  171  and  172  that are situated offset to each other remain closed, since diaphragm edge  111  is drawn against counterelement  15  in the case of a suction force acting upon the microphone pattern. 
     Microphone component  60  is proving itself both in impact pressure overload situations and in impact force overload situations as particularly stable to pressure, since the force of the respective pressure waves is guided past diaphragm  11 , via outflow channels  17  and  47 . The microphone sensitivity is not impaired thereby, since these outflow channels  17  and  47  are closed in the active operating mode of component  60 .