Ceramic heater and method of securing a thermocouple thereto

Abstract

A ceramic heater is provided that includes a thermocouple having a hot or measuring junction in a form of a bead directly bonded to a ceramic substrate by an active brazing material. Alternatively, a metallized layer is provided on the ceramic substrate and the bead of the thermocouple is directly bonded to the metallized layer by an ordinary brazing material. Due to the direct bonding of the bead to a ceramic substrate, the temperature of the bead reflects the temperature of the ceramic heater almost instantaneously so that the thermocouple can more accurately measure the temperature of the ceramic heater.

1 . A ceramic heater comprising: 
 a ceramic substrate; and    at least one thermocouple for measuring a temperature of the ceramic substrate, the at least one thermocouple comprising a junction directly bonded to the ceramic substrate.    
   
   
       2 . The ceramic heater according to  claim 1 , wherein the junction is bonded to the ceramic substrate by an active brazing material.  
   
   
       3 . The ceramic heater according to  claim 2 , wherein the active brazing material is selected from a group consisting of Au—Cu—Ti alloy, Ag—Ti alloy, Au—Ni—Ti alloy and Au—Ti alloy.  
   
   
       4 . The ceramic heater according to  claim 1 , wherein the ceramic substrate is made of a material selected from a group consisting of aluminum nitride (AlN), alumina (Al 2 O 3 ), and silicon nitride (Si 3 N 4 ).  
   
   
       5 . The ceramic heater according to  claim 1 , wherein the at least one thermocouple is selected from a group consisting of a K-type, J-type, T-type, R-type, C-type, and B-type thermocouple.  
   
   
       6 . The ceramic heater according to  claim 1 , wherein the ceramic substrate defines a recess in which the junction of the at least one thermocouple is disposed.  
   
   
       7 . The ceramic heater according to  claim 6 , wherein the recess of the ceramic substrate is substantially filled with an active brazing material.  
   
   
       8 . The ceramic heater according to  claim 1 , wherein the at least one thermocouple includes a pair of wires defining a distal end portion, the junction being disposed proximate the distal end portion.  
   
   
       9 . The ceramic heater according to  claim 8 , wherein the distal ends portions are joined to form a bead, the bead being in contact with an active brazing material disposed on the ceramic substrate, thereby bonding the thermocouple to the ceramic substrate.  
   
   
       10 . The ceramic heater according to  claim 8 , wherein at least a portion of the pair of wires is surrounded by insulation.  
   
   
       11 . The ceramic heater according to  claim 10 , wherein the insulation comprises a pair of ceramic sleeves disposed over the pair of wires.  
   
   
       12 . The ceramic heater according to  claim 1 , further comprising a metallized layer in contact with the ceramic substrate and the junction is bonded to the metallized layer.  
   
   
       13 . The ceramic heater according to  claim 12 , wherein the metallized layer comprises a first layer made from a mixture of Mo, MnO, glass frit and organic bonder.  
   
   
       14 . The ceramic heater according to  claim 13 , wherein the metallized layer further comprises a second layer made of a material selected from a group consisting of Ni, Cu, and Au.  
   
   
       15 . The ceramic heater according to  claim 12 , wherein the metallized layer is a Ti layer.  
   
   
       16 . The ceramic heater according to  claim 12 , wherein the junction is bonded to the metallized layer by a brazing material.  
   
   
       17 . The ceramic heater according to  claim 16 , wherein the brazing material is selected from a group consisting of Ag—Cu alloy and Au—Ni alloy.  
   
   
       18 . A ceramic heater comprising: 
 a ceramic substrate defining at least one recess;    a resistive heating element embedded within the ceramic substrate;    at least one thermocouple including a pair of wires defining a distal end portion and a junction disposed proximate the distal end portion, the junction being disposed within the recess; and    an active brazing material disposed within the recess and the junction of the at least one thermocouple being in contact with the active brazing material.    
   
   
       19 . A method of securing a thermocouple including a pair of wires that define a junction to a ceramic substrate, the method comprising directly bonding the junction of the thermocouple to the ceramic substrate.  
   
   
       20 . The method according to  claim 19 , wherein the directly bonding is achieved by using an active brazing material.  
   
   
       21 . The method according to  claim 20 , further comprising applying the active brazing material in the form of a paste to the ceramic substrate and placing the junction of the thermocouple on the active brazing material paste.  
   
   
       22 . The method according to  claim 21 , further comprising heating the active brazing material on which the junction of the thermocouple is disposed to about 950° C. to about 1080° C. and maintaining the temperature for about 5 to 60 minutes.  
   
   
       23 . The method according to  claim 22 , wherein the heating is performed in a vacuum chamber of less than 5×10 −6  torr.  
   
   
       24 . The method according to  claim 20 , wherein the active brazing material is filled in a recess of the ceramic substrate.  
   
   
       25 . The method according to  claim 20 , wherein the active brazing material is applied to an exterior surface of the ceramic substrate.  
   
   
       26 . The method according to  claim 19 , wherein the junction is formed by welding the wires at distal end portions of the wires.  
   
   
       27 . The method according to  claim 19 , wherein the directly bonding comprises providing a metallized layer on the ceramic substrate and bonding the junction to the metallized layer by a brazing material.  
   
   
       28 . The method according to  claim 27 , wherein providing a metallized layer comprises applying a mixture of Mo, MnO, glass frit, organic bonder and solvent on the ceramic substrate to form a first layer, and applying a material selected from a group consisting of Ni, Cu and Au to form a second layer.  
   
   
       29 . The method according to  claim 27 , wherein providing a metallized layer comprises providing a Ti layer on the ceramic substrate.  
   
   
       30 . A method of securing a thermocouple comprising a pair of wires to a ceramic substrate comprising: 
 welding the wires of the thermocouple to form a junction;    cleaning a surface of the ceramic substrate;    applying an active brazing material onto the surface of the ceramic substrate;    placing the junction on the active brazing material;    drying the active brazing material;    heating the active brazing material in a vacuum chamber;    maintaining the active brazing material at a predetermined temperature and time in the vacuum chamber; and    cooling the active brazing material to room temperature.    
   
   
       31 . The method according to  claim 30 , wherein the active brazing material is in a form selected from a group consisting of foil and paste.