Patent Publication Number: US-2006010981-A1

Title: Vibration type pressure sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2004-209290, filed on Jul. 16, 2004, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a resonant type pressure sensor in which compression strain due to a static pressure is improved and the static pressure effect is improved.  
      2. Description of the Related Art  
      JP-UM-A-63-63737 (page 2, FIG. 3) is referred to as a related art of a resonant type pressure sensor.  
       FIG. 12  is a sectional view of main portions of a related pressure sensor. Such a pressure sensor is disclosed in, for example, JP-UM-A-63-63737.  
      In the figure, the reference number  1  is a semiconductor chip.  
      In this case, silicon is used.  
      The reference numeral  2  is a dint which is formed in the semiconductor chip  1  and which fabricates a sensing diaphragm forming a pressure sensor.  
      The reference numeral  4  is a semiconductor pressure sensing element embedded in the strain sensitive portion  3  of the semiconductor chip  1 .  
      In this case, a silicon resonator is used.  
      The reference numeral  5  is a supporting base plate in which one face is connected to the semiconductor chip  1 , and which is made of an insulating material. A pressure introducing chamber  6  is comprised of the dint  2  and a piecing hole  7 .  
      In this case, Pyrex (registered trademark) glass is used, and the whole face of the glass is directly bonded to the semiconductor chip  1 .  
      In this case, the semiconductor chip  1  is anodically bonded to the supporting base plate  5 .  
      The reference numeral  7  is the piecing hole which is formed in the glass supporting substrate  5 , and which introduces the lower pressure PL to the pressure introducing chamber  6 .  
      In the above-described configuration, when a lower pressure PL is introduced into the pressure introducing chamber  6  and a higher pressure PH is applied from the other side to the diaphragm  3 , the diaphragm  3  is displaced by a pressure difference of (the higher pressure PH)—(the lower pressure PL).  
      This displacement is electrically transformed by using the semiconductor pressure sensing element  4 , so that an electric signal output corresponding to the pressure difference is obtained.  
      However, such an apparatus have the following problems.  
      When a static pressure is applied, the difference between the Young&#39;s modulus of the semiconductor chip  1  and the supporting base plate  5  causes compression strain which is larger than that of the semiconductor chip  1  itself. The larger compression strain is applied to the semiconductor pressure sensing element  4 .  
      In this case, the Young&#39;s modulus of the semiconductor chip  1  made of silicon is E=135 GPa, and that of the supporting base plate  5  made of Pyrex (registered trademark) glass is E=80 GPa. This means that the supporting base plate  5  is larger in bulk compressibility than the semiconductor chip  1 .  
      Therefore, compression strain which is larger (approximately 1.5 to 2 times) than that of the semiconductor chip  1  itself made of silicon is applied to the semiconductor pressure sensing element  4 .  
      As a result, the operational strain range of the semiconductor pressure sensing element  4  is limited, and the normal operation range and withstanding pressure performance of the semiconductor pressure sensor are restricted.  
      At present, therefore, the sensor sensitivity is restricted (the performance is lowered), or that the normal operation range is also restricted (the withstanding pressure performance is lowered) is inevitably taken.  
     SUMMARY OF THE INVENTION  
      The object of the invention is to provide a resonant type pressure sensor in which the withstanding pressure performance can be improved, the sensitivity can be enhanced, the range ability is widened, and the output ripple can be reduced.  
      The invention provides a resonant type pressure sensor having: a diaphragm to which a measuring pressure is to be applied; a vibrating beam which is embedded on the diaphragm; and orthogonal supporting portions which are provided at sides of both ends of the vibrating beam, wherein one end of each orthogonal supporting portion is substantially perpendicular to the vibrating beam, and another end of each orthogonal supporting portion is substantially perpendicular to a face of the diaphragm.  
      In the resonant type pressure sensor, a correction value of a static pressure effect is adjusted by adjusting mounting location of the supporting portions.  
      According to the resonant type pressure sensor, since compression strain of the vibrating beam due to static pressure strain is relaxed or reduced by applying of tension strain, the operation range of the vibrating beam can be widened.  
      Therefore, the withstanding pressure performance can be improved, and the sensitivity of the vibrating beam can be enhanced. As a result, a resonant type pressure sensor having the wide range ability and the small output ripple can be achieved.  
      Further, since the correction value of a static pressure effect can be adjusted by adjusting a mounting position of the supporting portions, it is possible to provide a resonant type pressure sensor in which the withstanding pressure performance can be further improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram illustrating the configuration of main portions of an embodiment of the invention;  
       FIG. 2  is a plan view of  FIG. 1 ;  
       FIG. 3  is a diagram illustrating the configuration of main portions of  FIG. 1 ;  
       FIG. 4  is a diagram illustrating fabrication process of  FIG. 1 ;  
       FIG. 5  is a diagram illustrating fabrication process of  FIG. 1 ;  
       FIG. 6  is a diagram illustrating fabrication process of  FIG. 1 ;  
       FIG. 7  is a diagram illustrating fabrication process of  FIG. 1 ;  
       FIG. 8  is a diagram illustrating fabrication process of  FIG. 1 ;  
       FIG. 9  is a diagram illustrating fabrication process of  FIG. 1 ;  
       FIG. 10  is a diagram illustrating fabrication process of  FIG. 1 ;  
       FIG. 11  is a diagram illustrating fabrication process of  FIG. 1 ; and  
       FIG. 12  is a diagram illustrating the configuration of main portions of a related pressure sensor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An embodiment of the invention will be described in detail with reference to the accompanying drawings.  
       FIG. 1  is a diagram illustrating the configuration of main portions of an embodiment of the invention,  FIG. 2  is a plan view of  FIG. 1 , and  FIG. 3  is a diagram illustrating the configuration of main portions of  FIG. 1 .  
      First and second orthogonal supporting portions  11 ,  12  are fabricated at sides of both ends of a vibrating beam  10 . One ends of the first and second orthogonal supporting portions  11 ,  12  are substantially perpendicular to the ends of the vibrating beam  10 , and other ends of the first and second orthogonal supporting portions  11 ,  12  are substantially perpendicular to a face of the diaphragm  3 .  
      The mounting positions (attachment position) of the supporting portions  11 ,  12  are adjustable, so that the correction value of a static pressure effect can be adjusted.  
      In the above-described configuration, when a static pressure F 1  is applied, compression strain F 2  is generated in the fixed ends of the vibrating beam  10 , so that tension strains F 3  in the directions of the arrows ← and → are produced in the portion of the vibrating beam  10 .  
      The thus configured apparatus is fabricated as shown in FIGS.  4  to  11 .  
      Referring to  FIG. 4 , a silicon dioxide film  101  is formed in the surface of the semiconductor chip  1 , and a portion corresponding to a gap below the vibrating beam  10  is then formed by using a photolithography process.  
      Electrode lead portions  102  are formed by P +  diffusion process.  
      Referring to  FIG. 5 , after the silicon dioxide film  101  is removed away, another silicon dioxide film  103  is formed, and holes for the first and second supporting portions  11 ,  12  are then formed by a photolithography process.  
      Referring to  FIG. 6 , a polysilicon film  104  corresponding to the portion of the vibrating beam  10  is grown. Thereafter, P ++  diffusion using boron B is implemented.  
      Referring to  FIG. 7 , the portion of the vibrating beam  10  is formed by an RIE etching process.  
      Referring to  FIG. 8 , a silicon dioxide film  105  is grown by CVD, and then a polysilicon film  106  is formed.  
      Referring to  FIG. 9 , channels for etching of the silicon dioxide films  103 ,  105  are formed in the polysilicon film  106 , and then the silicon dioxide films  103 ,  105  are removed away.  
      Referring to  FIG. 10 , a polysilicon film  107  is grown, and vacuum sealing is then completed.  
      As a result, the compression strain F 2  of the vibrating beam  10  due to the static pressure F 1  is relaxed or reduced by applying the tension strains F 3 , and hence the operation range of the vibrating beam  10  can be widened.  
      Therefore, the withstanding pressure performance can be improved, and the sensitivity of the vibrating beam  10  can be enhanced. As a result, it is possible to obtain a resonant type pressure sensor having the wide range ability is widened, and the small output ripple.  
      The above description shows only a specific preferred embodiment for the purposes of illustration and exemplification of the invention.  
      Therefore, the invention is not limited to the embodiment, and includes further changes and modifications without departing the spirit of the invention.