Abstract:
Measures are described which simplify the functional testing of a component having an MEMS element provided with a pressure-sensitive sensor diaphragm, and which allow a self-calibration of the component even after it is already in place, i.e., following the end of the production process. The component has a housing, in which are situated at least one MEMS element having a pressure-sensitive sensor diaphragm and a switching arrangement for detecting the diaphragm deflections as measuring signals; an arrangement for analyzing the measuring signals; and an arrangement for the defined excitation of the sensor diaphragm. The housing has at least one pressure connection port. The arrangement for exciting the sensor diaphragm includes at least one selectively actuable actuator component for generating defined pressure pulses that act on the sensor diaphragm.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a component part having a housing, in which at least one MEMS element having a pressure-sensitive sensor diaphragm and a switching arrangement for detecting the diaphragm deflections as measuring signals is situated, as well as means for analyzing the measuring signals, and an arrangement for the defined excitation of the sensor diaphragm. The housing of the component part is provided with at least one pressure-port opening. 
     In addition, the present invention relates to a method for testing such a component part. The component part preferably is a microphone element or also a pressure sensor component. 
     BACKGROUND INFORMATION 
     As a rule, such microphone elements are subjected to a final acoustics measurement at the end of production, during which compliance with specifications is checked, e.g., the sensitivity, noise, frequency response characteristic and current consumption. A test for the correct functioning of the individual components parts, especially the MEMS and ASIC elements at the wafer level, which is relatively cost-effective, is insufficient in this case since the microphone packaging, i.e., the physical layout and connection technology and the component housing, has an important influence on the microphone performance. The testing costs represent a significant portion of the total cost of the component part. 
     German Published Patent Application No. 101 54 867 describes one possibility for testing the sensor properties of a micromechanical pressure sensor element. This pressure sensor element includes a sensor diaphragm, which spans a sealed cavity in the semiconductor substrate of the structural element. An electrode, which forms a capacitor together with an electrode on the diaphragm, is situated on the cavity bottom. This capacitor is used not only for the capacitive signal acquisition, but also the selective excitation of the diaphragm. To do so, a defined, i.e., temporally varying, voltage is applied to the capacitor in order to induce vibrations in the sensor diaphragm. The resulting diaphragm deflections are then recorded in terms of quantity and quality with the aid of the capacitor. When the measuring signals obtained in this manner are analyzed, it is possible to draw conclusions regarding the height and extension of the cavity, as well as the mobility and thickness of the diaphragm, its maximum deflectability and its elastic modulus. 
     SUMMARY 
     The present invention provides measures that simplify the functional testing of a component part of the type discussed here; they additionally allow a self-calibration of the component part even after it is already in place, i.e., after completion of the production process. 
     According to the present invention, the component part is provided with at least one selectively actuable actuator component for generating defined pressure pulses that act on the sensor diaphragm. 
     The operativeness of such an actuator component is able to be checked at the wafer level, in the same way as the operativeness of the other components of the component part. The expense this entails is relatively low. With the aid of the actuator component, the final testing of the component part, during which the influence of the packaging then comes to bear as well, is able to be performed separately for each component part. Since this final testing does not require a special testing environment, the related expense remains reasonable, so that the overall testing costs for the component part according to the present invention are relatively low. 
     In addition, the measures of the present invention allow a functional test under authentic testing conditions, which contributes to the meaningfulness of the test results. For the sensor diaphragm is not actively deflected in such a case, but incited using a test signal that corresponds to the type of measured quantity and which also ranges within the framework of the expected signal level. The actuator component generates a corresponding pressure signal for this purpose, which impinges on the sensor diaphragm in the manner of a measuring pressure or a sound wave. The diaphragm deflections that come about as a result are acquired in the way of measuring signals. Only the analysis of the signals acquired in testing mode differs from the analysis of the measured signals acquired in standard operation. 
     The component part according to the present invention is characterized by low fault susceptibility, because the functions of the individual component parts are clearly separated from each other. For example, the sensor component is used exclusively for the acquisition of signals. The actuator component is actuated exclusively in test mode, to apply a defined pressure signal to the sensor diaphragm. Only the analysis of the measuring signals depends on the operating mode of the component part. 
     In general, there are different possibilities for realizing a component part according to the present invention, in particular as far as the actuator component of the component part is concerned. 
     In order to decouple the individual component parts not only with regard to function, but also from the aspect of their manufacture, the actuator component may be implemented in a stand-alone component installed inside the component housing, independently of the MEMS component having the sensor diaphragm. This could be an additional MEMS element. However, a different technology may be used to realize the actuator component. In an advantageous manner, the arrangement for actuating the actuator component and the arrangement for analyzing the measured signals of the sensor component are situated on a shared ASIC element, because these processes are executed in coordinated manner, as previously elucidated. 
     In one preferred specific embodiment of the present invention, the actuator component is at least partially integrated into the structural element configuration of the MEMS element. In this case, the pressure pulses are generated with the aid of a micromechanical structure, which is able to be actuated independently of the sensor structure of the MEMS element. 
     In this specific embodiment, the actuator structure and the type of sensor structure are advantageously adapted to one another. For one, this makes it possible to optimize the layout of the MEMS element and for another, the actuator structure and sensor structure are then able to be produced jointly in the layer structure of the MEMS element, in a single production process. Therefore, the actuator component advantageously includes at least one actuator diaphragm which is developed on the side, next to the sensor diaphragm. In addition, a switching arrangement is provided to allow the actuator diaphragm to be actuated and deflected independently of the sensor diaphragm. This makes it possible to selectively generate defined pressure pulses that act on the sensor diaphragm. The switching arrangement, for example, may be piezoelectric layers featuring selective actuation, which preferably are disposed in the edge region of the actuator diaphragm. In this way it is possible to cause relatively large deflections of the actuator diaphragm, and thus to also generate relatively large pressure pulses. 
     However, the actuator diaphragm may also be actuated in capacitive manner. This variant is especially suitable for capacitive microphone elements having a microphone diaphragm and a stationary counter element, on which the electrodes of a microphone capacitor are situated. In this case, the actuator diaphragm, too, is provided with at least one electrode, which forms a selectively actuable actuator capacitor in combination with at least one electrode on the stationary counter element. 
     In view of a uniform excitation of the sensor diaphragm, it is advantageous if the actuator diaphragm is developed in the form of a ring and placed concentrically with respect to the sensor diaphragm. 
     As already mentioned, the actuator component of the component part of the present invention is used for generating defined pressure pulses inside the component housing in order to thereby deflect the sensor diaphragm or to excite it to vibrations for testing purposes. Toward this end, for example, the diaphragm of the actuator component may be selectively deflected as far as a stop in the actuator structure. Since the actuator travel is defined in such a case, the resulting pressure pulse is defined as well. A corresponding analysis of the measuring signal obtained in this manner allows the functional properties of the component part to be evaluated. Components may thus be declared to be in good order or to be defective at the end of the production process, so that defective parts may be identified and discarded. The analysis of the measuring signals caused by the defined pressure pulses also allows a calibration of the component, in which the electrical sensor parameters, especially the polarization voltage and the mechanical prestressing of the sensor diaphragm, are adapted as a function of the result of the analysis in order to obtain the desired sensor specification. 
     Since the actuator component is an element of the component part, the sensor characteristics of the component part are thus able to be checked and adjusted again and again across its entire service life, so that drift of the sensor properties is counteracted. Such a function check with a subsequent adaptation of the electrical sensor parameters may be initiated automatically, i.e., at regular time intervals, for instance, or otherwise also be activated from the outside. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a schematic sectional view through a microphone element  100  according to the present invention. 
         FIG. 2  shows a schematic sectional view through MEMS element  20  of a component part according to the present invention. 
         FIG. 3 a, b    show schematic sectional views through MEMS element  30  of a component part according to the present invention, with an activated actuator component. and 
         FIG. 4  shows a flow chart of the method of the present invention for testing a component part of the type under discussion. 
     
    
    
     DETAILED DESCRIPTION 
     Component part  100  shown in  FIG. 1  is a microphone component part having an MEMS microphone element  10 . The microphone structure is realized in a layer construction on a semiconductor substrate  1  and includes a microphone diaphragm  2 , which spans a cavity  3  in the rear side of the substrate. A stationary counter element  4  provided with through holes  5  is situated in the layer construction above microphone diaphragm  2 . Microphone element  10  is mounted on a support  101  via the substrate rear side, so that support  101  seals cavity  3  underneath microphone diaphragm  2  in pressure-tight manner. Support  101  forms the housing of component part  100 , together with a cover part  102 . A pressure connection port  103  is situated in cover part  102 . Sound is applied to microphone diaphragm  2  via this pressure connection port  103  in the component housing, and via through holes  5  in counter element  4  of microphone element  10 . Sealed cavity  3  is used as rear volume. The deflections of microphone diaphragm  2  are detected in capacitive manner. Toward this end, microphone diaphragm  2  and counter element  4  each have at least one electrode which jointly form a microphone capacitor. The microphone signal obtained in this manner is analyzed with the aid of an ASIC element  11 , which is situated next to microphone element  10  on support  101  inside the component housing. 
     According to the present invention, component part  100  furthermore includes a selectively actuable actuator component  12 , which may be used to generate defined pressure pulses inside the housing. These pressure pulses act on microphone diaphragm  2  and excite it to vibrations, which are detected with the aid of the microphone capacitor and analyzed with the aid of ASIC element  11 . 
     In the exemplary embodiment shown here, actuator component  12  is realized in the form of a stand-alone element  12 , which is likewise installed on support  101  inside the component housing. Like microphone element  10 , actuator element  12  is electrically connected to ASIC element  11  via bond wires  13  as well. The ASIC element in this case coordinates the activation of actuator component  12  and the analysis of the measuring signals detected by the microphone capacitor in test mode. 
     Bond wires  13  also connect ASIC element  11  to support  101 , by way of which the external contacting takes place in the second-level installation of component  100 . 
       FIG. 2  shows an MEMS element  20 , which is specifically configured for use in a component part according to the present invention. Here, too, this is a microphone element  20  having a microphone diaphragm  22  and a stationary counter element  24 , each being equipped with at least one electrode of a microphone capacitor. Microphone diaphragm  22  and counter element  24  are realized in a layer configuration on a semiconductor substrate  1 , so that microphone diaphragm  22  spans a cavity  23  in the rear side of the substrate. Counter element  24  is situated above microphone diaphragm  22  in the layer construction and has through holes  251  above the diaphragm region. 
     In addition to this microphone structure, MEMS element  20  includes an actuator structure by which the microphone diaphragm is able to be selectively incited for the function test of the component part. This actuator structure includes a ring diaphragm  26 , which is disposed concentrically to microphone diaphragm  22  and formed in the same layer of the layer construction. Through holes  252  in stationary counter element  24  are formed above ring diaphragm  26  as well. Like microphone diaphragm  22  and the opposite-lying region of counter element  24 , ring diaphragm  26  and the region of counter element  24  lying opposite it are provided with at least one electrode of a capacitor system in each case. In contrast to the microphone capacitor, which is used for signal acquisition, the capacitor system in the region of ring diaphragm  26  is used for the selective actuation of ring diaphragm  26 , i.e., for the generation of defined pressure pulses that act on microphone diaphragm  22 . The vibrations of microphone diaphragm  22  induced in this manner are detected with the aid of the microphone capacitor and may then be analyzed in the sense of a function test of the component part. 
     Microphone element  20  shown in  FIG. 2  may be installed on the element support of a component housing, just like microphone element  20  shown in  FIG. 2 , so that rear-side cavity  23  as rear side volume is sealed in pressure-tight manner. Because of the concentric placement of microphone diaphragm  22  and actuator ring diaphragm  26  above rear-side cavity  23 , microphone element  20  has a greater rear-side volume than microphone element  10  shown in  FIG. 1 , which has a positive effect on the microphone properties of a component part realized in this manner. 
     MEMS microphone element  20  shown in  FIGS. 3 a  and 3 b   , is also configured specifically for use in a component part according to the present invention and, in addition to the capacitive microphone structure, has been provided with an actuator structure which is actuable in capacitive manner. As in the case of microphone element  20 , both the microphone structure and the actuator structure are realized in a layer construction on a semiconductor substrate  1 . The microphone structure includes a microphone diaphragm  32  and a stationary counter element  34  having through holes  351  in the region above microphone diaphragm  32 . The actuator structure also includes a diaphragm  36 , which in this case is disposed on the side next to microphone diaphragm  32  and formed in the same layer of the layer construction. Through holes  352  in stationary counter element  34  are situated in the region above this actuator diaphragm  36 . Like microphone diaphragm  32  and the region of counter element  34  lying opposite it, actuator diaphragm  36  and the opposite-lying region of counter element  34  are each provided with at least one electrode of a capacitor system. The microphone capacitor is used for signal detection, while the capacitor system in the region of actuator diaphragm  36  is used for the selective actuation of actuator diaphragm  36 . 
     In contrast to microphone element  20 , only microphone diaphragm  32  extends above cavity  33  in the rear side of the substrate in this particular case. Actuator diaphragm  36  is situated along the side thereof and exposed only within the layer construction on substrate  1 . Another stationary electrode of the capacitor system of the actuator construction is situated on substrate  1 , underneath actuator diaphragm  36 . This electrode may be realized in the form of suitable substrate doping or also in the form of conductive coating that is electrically insulated with respect to the substrate.  FIGS. 3 a  and 3 b    illustrate that actuator diaphragm  36  is selectively deflectable with the aid of this capacitor system, both in the direction of counter element  34  and in the direction of substrate  1 . Because of the greater diaphragm excursion of actuator diaphragm  36  in comparison to microphone element  20 , it is therefore possible to generate greater pressure pulses for the excitation of microphone diaphragm  32 . 
     Like microphone element  10  shown in  FIG. 1 , microphone element  30  is preferably installed on the component support of a component housing, so that rear-side cavity  33  as rear-side volume is sealed in pressure-tight manner. 
     In this context it should be noted once again that it is not absolutely necessary to provide a separate ASIC element for the arrangement for signal analysis and actuation of the actuator component. A corresponding switching arrangement could also be integrated into the MEMS element of the component part of the present invention. 
     The method according to the present invention for the purely electrical testing, characterization and adaptation of the sensor properties of a microphone component part having a microphone element as illustrated in  FIGS. 2 and 3  will be explained in the following text with reference to  FIG. 4 . The component part is operated in test mode for this functional test. In a first step  41 , the capacitor system of the actuator component is actuated by applying a defined test voltage V test . This causes a defined deflection of the actuator diaphragm. In the next step  42 , the test voltage is switched off, so that the actuator diaphragm is released and vibrates. The pressure pulses induced in this manner impinge upon the microphone diaphragm and excite it to vibrations as well. These deflections of the microphone diaphragm are detected in step  43  with the aid of the microphone capacitor and analyzed according to the test mode. Since the measuring signal obtained in this manner contains all the information of the acoustic properties of the housed microphone element, it will then be possible in step  44  to adapt the electrical sensor parameters appropriately, such as the polarization voltage and the mechanical diaphragm prestressing, for instance. The test process may then be repeated in order to ascertain whether the performed adaptations of the sensor parameters have had the desired effect on the acoustic properties of the microphone element. In a final method step  45 , the component is classified either as good part or as reject part, depending on the determined acoustic characteristics.