Mass sensor and mass sensor method

Abstract

A mass sensor including first and second connecting plates having a slit, an opening portion, and/or a thin-walled portion and a thick-walled portion formed therein; a first diaphragm joined with the first connecting plate at respective side surfaces thereof, and a second diaphragm joined with the second connecting plate at respective side surfaces thereof, between which connecting plates a first sensing plate to which a piezoelectric element is provided at least on a part of at least one surface is bridged; and a sensor substrate joined with the first and second connecting plates at respective side surfaces thereof so that the sensor substrate is positioned on a side opposite to the first diaphragm and the second diaphragm, wherein the diaphragms, connecting plates, sensing plate, and piezoelectric element form a resonating portion.

We claim:  
     
         1 . A mass sensor comprising: 
 a first connecting plate and a second connecting plate each having at least one of a slit, an opening portion, and a thin-walled portion and a thick-walled portion formed therein;    a first diaphragm joined with said first connecting plate at respective side surfaces thereof, and a second diaphragm joined with said second connecting plate at respective side surfaces thereof, between which connecting plates a first sensing plate to which a piezoelectric element is provided at least on a part of at least one surface is bridged; and    a sensor substrate joined with the first connecting plate and the second connecting plate at respective side surfaces thereof so that the sensor substrate is positioned on a side opposite to the first diaphragm and the second diaphragm,    wherein said diaphragms, said connecting plates, said sensing plate, and said piezoelectric element form a resonating portion.    
     
     
         2 . The mass sensor according to  claim 1 , wherein the first connecting plate is sandwiched by the first sensing plate and a second sensing plate, said second connecting plate is sandwiched by the first connecting plate and a third sensing plate, and said second sensing plate and said third sensing plate are joined so that both are joined with said sensor substrate in the joining direction at least with said connecting plate.  
     
     
         3 . The mass sensor according to  claim 2 , wherein a piezoelectric element is provided at least on one part of at least one surface of said second sensing plate and/or said third sensing plate, or one or more slit(s) are formed on said second sensing plate and/or said third sensing plate in a direction perpendicular to the joining direction of said first sensing plate and said first connecting plate.  
     
     
         4 . The mass sensor according to  claim 3 , wherein the direction of polarization of a piezoelectric film of piezoelectric elements which are provided on said first sensing plate and the direction of polarization of said piezoelectric film of piezoelectric elements which are provided on said second sensing plate and said third sensing plate are opposite.  
     
     
         5 . The mass sensor according to  claim 1 , wherein said connecting plates are formed by joining one thin plate and another plate or post-like spring plate having at least one of a slit and an opening portion formed therethrough.  
     
     
         6 . The mass sensor according to  claim 1 , wherein said diaphragms, said connecting plates, said sensing plate, and said sensor substrate are integrally formed.  
     
     
         7 . The mass sensor according to  claim 5 , wherein a portion of said connecting plates, said diaphragms, and said sensing plate are integrally formed from a vibrating plate, and another plate- or post-like spring plate forming said connecting plates is integrally formed from an intermediate plate, and said connecting plates are integrally formed by laminating said intermediate plate and said thin vibrating plate, and said sensor substrate is integrally formed by laminating said vibrating plate, said intermediate plate, and a base plate.  
     
     
         8 . The mass sensor according to  claim 1 , wherein the thickness of the thin-walled portion of said connecting plates is thicker than the thickness of one of said diaphragms and said sensing plate.  
     
     
         9 . The mass sensor according to  claim 8 , wherein the thickness of the thin-walled portion of said connecting plates includes the thickness of said sensing plate and of said piezoelectric element.  
     
     
         10 . The mass sensor according to  claim 1 , wherein said resonating portion is formed on each inner circumferential surface of at least one recessed portion or through hole formed through said sensor substrate.  
     
     
         11 . The mass sensor according to  claim 1 , wherein a catching substance reacting with and catching only a substance to be sensed is applied on at least one of said diaphragms, the resonant frequencies of said resonating portion are measured by said piezoelectric element in the state where said substance to be sensed has not been caught by said catching substance, and in the state after said substance to be sensed has been caught by said catching substance, and the mass of said substance to be sensed having been caught is measured from a change in the measured resonant frequencies.  
     
     
         12 . The mass sensor according to  claim 11 , wherein said mass sensor has at least a plurality of said diaphragms, and said catching substance is not applied to at least one of said diaphragms.  
     
     
         13 . The mass sensor according to  claim 11 , wherein said mass sensor comprises at least a plurality of diaphragms, and different types of catching substances are applied to each of said diaphragms.  
     
     
         14 . The mass sensor according to  claim 1 , wherein resonating portions are provided at least at two or more places on said sensor substrate so as to increase the dynamic range by integrating signals derived from said respective resonating portions.  
     
     
         15 . The mass sensor according to  claim 1 , wherein said piezoelectric element is divided into two, and one is used for driving and the other is used for sensing.  
     
     
         16 . The mass sensor according to  claim 1 , wherein two piezoelectric elements are provided at said resonating portion, and one of said piezoelectric elements is used for driving and the other of said piezoelectric elements is used for sensing.  
     
     
         17 . The mass sensor according to  claim 1 , wherein a piezoelectric element for sensing is provided on a surface of at least one of said connecting plates.  
     
     
         18 . The mass sensor according to  claim 1 , wherein a position sensor consisting of a pair of electrodes is provided on a middle position between said diaphragms and said piezoelectric element on said sensor substrate.  
     
     
         19 . The mass sensor according to  claim 1 , wherein said piezoelectric element, and electrode leads respectively connected to the electrode of said piezoelectric element are coated with a resin or glass insulation coating layer.  
     
     
         20 . The mass sensor according to  claim 19 , wherein said resin is fluorocarbon resin or silicone resin.  
     
     
         21 . The mass sensor according to  claim 19 , wherein a shield layer consisting of a conductive member is formed on at least a part of the surface of said insulation layer.  
     
     
         22 . The mass sensor according to  claim 1 , wherein said sensor substrate, said diaphragm, said connecting plates, and said sensing plate are fabricated using completely stabilized zirconia or partially stabilized zirconia.  
     
     
         23 . The mass sensor according to  claim 1 , wherein a piezoelectric film of said piezoelectric element is a material consisting mainly of lead zirconate, lead titanate, or lead magnesium niobate.  
     
     
         24 . The mass sensor according to  claim 1 , wherein the dimensional adjustment of the shape of at least one of said diaphragms, said connecting plates, and said sensing plate is performed by trimming using laser processing or machining.  
     
     
         25 . The mass sensor according to  claim 1 , wherein trimming using laser processing or machining is used for the dimensional adjustment of electrodes of said piezoelectric element, thereby the available electrode area of said piezoelectric element is adjusted.