Pressure sensor for detecting small pressure differences and low pressures

Abstract

A capacitive pressure sensor of substantially ceramic material comprises a thick base plate ( 100 ), a front plate ( 140 ) having the same thickness as the base plate and a movable diaphragm ( 120 ) located between the front plate and the base plate. Capacitor electrodes ( 121 b , 121 a ) are provided at the surface of the diaphragm facing the base plate and form a measurement capacitor. The diaphragm ( 120 ) is extremely thin and is produced by sintering a ceramic material such aluminium oxide. Owing to a pressing process used during the sintering a strong, very thin diaphragm is obtained having no mechanical stresses and fracture indications. It can be produced to have a very small thickness in order to provide pressure sensors having a high sensitivity, which can also for high-vacuum applications tolerate to be subjected to the atmospheric pressure. A shielding plate ( 110 ) can be inserted between the base plate ( 100 ) compensating the measurement capacitor. The shielding plate ( 110 ) can also be extremely thin, having a thickness down to a thickness corresponding to the thickness of a diaphragm ( 120 ).

What is claimed:  
     
         1 . A pressure sensor comprising: 
 an extremely thin diaphragm plate produced by sintering a ceramic material that is subjected to a pressing force during a portion of the sintering, the diaphragm plate having a movable portion, mounted for movement in response to a pressure to be measured;    said diaphragm plate including an electrode, the position of which can be electronically sensed; and    wherein diaphragm plate has a thickness smaller than 0.35% of the diameter of said movable portion thereof.    
     
     
         2 . A pressure sensor according to  claim 1  wherein said plate is made of a ceramic material.  
     
     
         3 . A pressure sensor according to  claim 1  wherein said ceramic material is aluminum oxide.  
     
     
         4 . A pressure sensor comprising: 
 a substantially rigid base plate;    a diaphragm plate, having at least a portion thereof which is movable in response to a pressure;    a first cavity formed between the base plate and the diaphragm plate, for forming a measurement electrode pair;    a shielding plate having a front surface, which forms a wall of the first cavity and is part of the measurement electrode pair, and a rear surface; and    a second cavity formed between the rear surface of the shielding plate and a surface of the base plate, the walls of the second cavity forming a reference electrode pair, for compensating measurement values captured by the measurement electrode.    
     
     
         5 . A pressure sensor according to  claim 4 , wherein said shielding plate has substantially the same thickness as said diaphragm plate.  
     
     
         6 . A pressure sensor according to  claim 4 , wherein said second cavity is connected to a reference pressure.  
     
     
         7 . A pressure sensor according to  claim 6  wherein the reference pressure is obtained by connecting the second cavity to a space containing a getter.  
     
     
         8 . A pressure sensor according to  claim 4 , wherein said movable portion of said diaphragm plate has a thickness smaller than 0.035% of the diameter of said movable portion.  
     
     
         9 . A pressure sensor according to  claim 5 , wherein said movable portion of said diaphragm plate has a thickness smaller than 0.35% of the diameter of said movable portion.  
     
     
         10 . A pressure sensor comprising: 
 a pressure housing assembly made of substantially ceramic materials comprising a substantially rigid base plate, a front plate, and an extremely thin diaphragm plate produced by sintering a film of ceramic material that is subjected to a variable pressing force during a portion of the sintering, the diaphragm plate being at least partly movable in response to a pressure;    said diaphragm plate being directly disposed between the base plate and the front plate to form a cavity between a side of the diaphragm plate and a side of the base plate, so that the walls of the cavity form a measurement electrode; and    wherein the base plate and the front plate have substantially the same thickness ane are made of substantially the same material    
     
     
         11 . A pressure sensor according to  claim 10 , wherein the front plate and the base plate have through-holes, the cross-sectional areas of which are small portions of the total area of the respective plate.