Relative and absolute pressure sensor combined on chip

Abstract

A method for manufacturing a system in a wafer for measuring an absolute and a relative pressure includes etching a shallow and a deep cavity in the wafer. A top wafer is applied and the top wafer is thinned for forming a first respectively second membrane over the shallow respectively deep cavity, and for forming in the top wafer first respectively second bondpads at the first respectively second membrane resulting in a first respectively second sensor. Back grinding the wafer results in an opened deep cavity and a still closed shallow cavity. The first bondpads of the first sensor measure an absolute pressure and the second bondpads of the second sensor measure a relative pressure. The etching in the first step defines the edges of the first membrane and of the second membrane in respectively the sensors formed from the shallow and the deep cavity.

1 . A pressure measurement system for measuring both an absolute and a relative pressure, the system comprising:
 a base wafer comprising a closed shallow cavity with a first membrane over the shallow cavity forming an absolute pressure sensor, and   on the same base wafer, an open deep cavity, with and a second membrane over the deep cavity forming a relative second pressure sensor,   
       wherein the edge of the first membrane respectively second membrane is determined by the shallow cavity respectively the open deep cavity forming the sensors. 
     
     
         2 . A pressure measurement system according to  claim 1 , wherein the edges of the shallow cavity and of the deep cavity have an angle of between 80° and 100° with the vertical axis. 
     
     
         3 . A pressure measurement system according to  claim 1 , wherein the horizontal cross-section of the shallow and deep cavities is circular. 
     
     
         4 . A pressure measurement system according to  claim 1 , wherein the shallow cavity has a bottom and the deep cavity comprises at least one pillar, wherein the top of the pillar has the same height as the bottom of the shallow cavity. 
     
     
         5 . A pressure measurement system according to  claim 1 , wherein the area of the horizontal cross-section of the deep cavity has a different size than the area of the horizontal cross-section of the shallow cavity. 
     
     
         6 . A pressure measurement system according to  claim 1 , the relative and absolute pressure sensors comprising bondpads, wherein the bondpads are substantially made of platinum, copper, aluminium or gold. 
     
     
         7 . A flow meter for measuring a gas flow, the flow meter comprising a housing for housing a pressure measurement system according to  claim 1 ,
 wherein the housing comprises:
 a tube having a first opening and a second opening 
 a cavity in communication with the first opening and the second opening 
   wherein the system can be positioned such that
 the cavity is separated in a first part in communication with the first opening and a second part in communication with the second opening, 
 one side of the second membrane of the relative pressure sensor of the system is in the first part of the cavity, the other side of the second membrane of the relative pressure sensor being in the second part of the cavity. 
   
     
     
         8 . A flow meter according to  claim 7 , wherein the first membrane of the absolute pressure sensor is in the first part of the cavity.