Abstract:
A system for protecting a diaphragm of a microelectromechanical systems (MEMS) device includes a housing coupled to the MEMS device such that its sensing diaphragm is surrounded thereby. A perforated barrier in the housing is adjacent to the sensing diaphragm. A protection diaphragm in the housing has its first side exposed to an external environment of interest, and has its second side facing the perforated barrier and spaced apart therefrom. A fluid is disposed contiguously between the second side of the protection diaphragm and the sensing diaphragm.

Description:
ORIGIN OF THE INVENTION 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to microelectromechanical systems (MEMS) devices, and more particularly to a system that protects the diaphragm of a MEMS device from over pressurization. 
     BACKGROUND OF THE INVENTION 
     Microelectromechanical systems (MEMS) are miniaturized devices (i.e., micron to millimeter dimensions) that can be configured as actuators, sensors, and other mechanical structures. Many of these devices need to interact with outside stimuli such as temperature, flow, acceleration or pressure, and may be further designed to respond only when the particular stimulus is within a specific range. It is not uncommon for this range to be exceeded during the lifetime of the MEMS device. When the MEMS device uses a flexible diaphragm to detect changes in an outside pressure stimulus and the operational range of the sensing diaphragm is exceeded, the MEMS device may be irreparably damaged. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a system that protects a MEMS device&#39;s diaphragm from excessive loading. 
     Another object of the present invention is to provide a system that limits the pressure that acts on a MEMS device&#39;s diaphragm to a specified maximum pressure. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     In accordance with the present invention, a system for protecting a diaphragm of a MEMS device is provided. A housing is fixedly coupled to a MEMS device where the sensing diaphragm of the MEMS device is surrounded by the housing. A perforated barrier is fitted in the housing and is adjacent to the sensing diaphragm. A protection diaphragm is also fitted in the housing. More specifically, a first side of the protection diaphragm is exposed to an external environment of interest, while a second side of the protection diaphragm faces the perforated barrier and is spaced apart therefrom. A fluid is disposed contiguously between the second side of the protection diaphragm and the sensing diaphragm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the exemplary embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
         FIG. 1  is a schematic view of a system for protecting a MEMS device&#39;s diaphragm in accordance with the present invention; and 
         FIG. 2  is a cross-sectional view of a microchip embodiment of the system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to  FIG. 1 , a system for protecting the diaphragm  102  of a MEMS device  100  is shown and is referenced generally by numeral  10 . In general, MEMS device  100  is mounted on a support  200  (e.g., a printed circuit board) and has an exposed diaphragm  102  designed to flex up to a position indicated by defined lines  102 A. Such flexing of diaphragm  102  is generally brought about by some changing condition in an environment of interest that ultimately causes a pressure change acting on diaphragm  102 . The particular condition and/or environment are not limitations of the present invention. Accordingly, the particular construction of MEMS device  100  and its intended application are not limitations of the present invention. It is sufficient to say that if the condition changes by an amount that exceeds the designed operating range of diaphragm  102  (illustrated by dashed line  102 A), the effectiveness of MEMS device  100  may be jeopardized. 
     System  10  provides protection for MEMS device  100  as it protects diaphragm  102  from being over pressurized, i.e., flexed beyond its designed maximum allowed deflection limit defined by dashed line  102 A. To do this, system  10  includes an external housing  12  that is generally mounted to MEMS device  100 , support  200 , and/or some other type of support (not shown) such that diaphragm  102  is surrounded and enclosed by housing  12 . Mounted in housing  12  and spaced apart from diaphragm  102  is a barrier  14  having one or more holes  16  therethrough. Generally, barrier  14  is rigid for reasons that will become evident later herein. 
     A flexible diaphragm  18  is mounted in housing  12  and is adjacent to barrier  14  (e.g., abutting, spaced apart from barrier  14  as illustrated, etc.) such that a volume  20  is defined in housing  12  between one side of diaphragm  18  and one side of diaphragm  102 . Volume  20  is contiguous between diaphragms  18  and  102  owing to holes  16  in barrier  14 . That is, volume  20  includes the volume defined by holes  16 . Contiguous volume  20  is filled with a fluid  22  (e.g., a gas, an incompressible fluid, or any fluid medium that can flow through holes  16 ). The other side of diaphragm  18  is exposed to an external environment  300  that is subject to a changing condition for which MEMS device  100  is designed to sense. 
     In operation, when a changing condition in environment  300  causes diaphragm  18  to flex into volume  20 , fluid  22  is pushed through holes  16  towards diaphragm  102  thereby causing a corresponding flex in diaphragm  102 . Barrier  14  is placed such that diaphragm  18  is limited to flexing (under the force of the environmental condition) by an amount that corresponds with the maximum allowed deflection limit  102 A. Thus, system  10  forms an in-line protection system for diaphragm  102 . 
     Since MEMS device  100  is generally fabricated using microchip technology, an embodiment of the present invention could be fabricated using the same technology. For example,  FIG. 2  illustrates a microchip realization of the present invention where the microchip is referenced generally by numeral  50 . In the illustrated embodiment, microchip  50  is defined by three layers that may be fabricated and installed on MEMS device  100 , or could be fabricated sequentially directly on MEMS device  100 . Still further, microchip  50  could be fabricated as part of MEMS device  100  without departing from the scope of the present invention. 
     Microchip  50  includes a barrier layer  52  having an outer perimeter  52 A that is coupled and sealed to MEMS device  100  and that surrounds/encloses diaphragm  102 . Barrier layer  52  is generally rigid with multiple perforations  54  formed therethrough. 
     A volume defining layer  56  is coupled/sealed to barrier layer  52 . 
     More specifically, volume defining layer  56  has a solid annular perimeter  56 A that is coupled/sealed to outer perimeter  52 A. Solid annular perimeter  56 A encloses a volume  56 B that extends contiguously through perforations  54  and up to diaphragm  102 . A diaphragm layer  58  is coupled/sealed to volume defining layer  56 . 
     That is, a rigid annular perimeter  58 A is coupled/sealed to solid annular perimeter  56 A, and a flexible diaphragm  58 B is coupled to perimeter  58 A. One side of diaphragm  58 B faces volume  56 B while the other side of diaphragm  58 B is exposed to external environment  300 . Similar to system  10 , microchip  50  has a fluid  62  contiguously filling volume  56 B. Operation of the microchip  50  is essentially the same as described above for system  10 . 
     The advantages of the present invention are numerous. The in-line protection system for a MEMS device&#39;s diaphragm may be added to existing MEMS devices or incorporated into MEMS devices as they are being batch fabricated. The protection system may use the same fabrication technology and scale used for current MEMS devices. 
     Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described. 
     Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.