Focal plane array and method for manufacturing the same

Abstract

A method of forming a focal plane array by: preparing a first wafer having sensing material provided on a surface, which is covered by a sacrificial layer; preparing a second wafer including read-out integrated circuit and a contact pad, which is covered by another sacrificial layer into which are formed support legs in contact with the contact pad, the support legs being covered with a further sacrificial layer; bonding the sacrificial layers of the first and second wafers together such that the sensing material is transferred from the first wafer to the second wafer when a sacrificial bulk layer of the first wafer is removed; defining a pixel in the sensing material and forming a conductive via through the pixel for providing a connection between an uppermost surface of the pixel and the supporting legs; and removing the sacrificial layers to release the pixel, with the supporting legs underneath it.

1 . A method of forming a focal plane array comprising one or more pixels, the focal plane array being fabricated by:
 preparing a first wafer having sensing material provided on a surface, which is covered by a first sacrificial layer;   preparing a second wafer including read-out integrated circuit (ROIC) and a contact pad, which is covered by a second sacrificial layer into which are formed one or more support legs in contact with the contact pad, the support legs being covered with a further sacrificial layer;   bonding the sacrificial layers of the first and second wafers together such that the sensing material is transferred from the first wafer to the second wafer when a sacrificial bulk layer of the first wafer is removed;   defining a pixel in the sensing material above each of the one or more support legs and forming a conductive via through each pixel defined for providing a connection between an uppermost surface of the pixel and its support legs; and   removing the sacrificial layers to release the one or more pixel, each of the one or more pixels being defined such that its support legs are arranged to be completely beneath the sensing material of the pixel.   
     
     
         2 . The method of  claim 1 , further comprising the step of providing a reflector layer between the surface of the first wafer and the sensing material provided on its surface. 
     
     
         3 . The method of  claim 2 , further comprising the step of providing an absorber layer on the surface of the sensing material after the bulk layer is removed. 
     
     
         4 . The method of  claim 3 , wherein the sensing material is infrared (IR) sensitive. 
     
     
         5 . The method of  claim 4 , wherein the sensing material is a thermistor material and the pixel is a bolometer pixel. 
     
     
         6 . The method of  claim 5 , further comprising the step of encapsulating the at least one pixel beneath a cap that is sealed over the focal plane array. 
     
     
         7 . The method of  claim 6 , further comprising the step of forming at least one bonding member on the second wafer for the cap to be bonded to. 
     
     
         8 . The method of  claim 7 , wherein a plurality of focal plane arrays are provided on the second wafer, each focal plane array being defined by a plurality of bonding members, wherein the plurality of focal plane arrays are sealed by a single cap wafer following which they can be divided into individual focal plane arrays. 
     
     
         9 . A thermal imaging device comprising a focal plane array manufactured by the method of  claim 1 . 
     
     
         10 . A pixel assembly for a focal plane array, the pixel assembly comprising:
 a pixel comprising:
 a reflecting layer; and 
 a sensing layer comprising a sensing material formed on one side of the reflecting layer; 
   a support leg positioned entirely on a reverse side of the reflecting layer and arranged to support, in use, the pixel on a wafer and provide electrical connection between the pixel and the wafer,   wherein said support leg is completely beneath the sensing material when supporting the pixel on the wafer; and   a via associated with the support leg, each via providing electrical connection through the sensing layer from the support leg to the sensing material of the pixel.   
     
     
         11 . A pixel assembly according to  claim 10  formed as an infrared detector. 
     
     
         12 . A focal plane array formed from a plurality of pixels in accordance with  claim 10 . 
     
     
         13 . The method of  claim 1 , further comprising the step of providing an absorber layer on the surface of the sensing material after the bulk layer is removed. 
     
     
         14 . The method of  claim 13 , wherein the sensing material is infrared (IR) sensitive. 
     
     
         15 . The method of  claim 14 , wherein the sensing material is a thermistor material and the pixel is a bolometer pixel. 
     
     
         16 . The method of  claim 15 , further comprising the step of encapsulating the at least one pixel beneath a cap that is sealed over the focal plane array. 
     
     
         17 . The method of  claim 16 , further comprising the step of forming at least one bonding member on the second wafer for the cap to be bonded to. 
     
     
         18 . The method of  claim 17 , wherein a plurality of focal plane arrays are provided on the second wafer, each focal plane array being defined by a plurality of bonding members, wherein the plurality of focal plane arrays are sealed by a single cap wafer following which they can be divided into individual focal plane arrays. 
     
     
         19 . The method of  claim 1 , wherein the sensing material is infrared (IR) sensitive. 
     
     
         20 . The method of  claim 1 , further comprising the step of encapsulating the at least one pixel beneath a cap that is sealed over the focal plane array. 
     
     
         21 . The pixel assembly of  claim 10 , including a conductive contact that communicates electrically with the support leg and extends through the via to intersect the sensing material of the pixel. 
     
     
         22 . The pixel assembly of  claim 21 , wherein said support leg contacts the conductive contact. 
     
     
         23 . The pixel assembly of  claim 21 , wherein said support leg is elongated and projects laterally along the pixel and relative to the conductive contact. 
     
     
         24 . A pixel assembly for a focal plane array, the pixel assembly comprising:
 a pixel comprising:
 a reflecting layer; and 
 a sensing layer comprising a sensing material formed on one side of the reflecting layer; 
   a support leg positioned entirely on a reverse side of the reflecting layer and arranged to support, in use, the pixel on a wafer and provide electrical connection between the pixel and the wafer,   wherein said support leg is completely beneath the sensing material when supporting the pixel on the wafer;   a via associated with the support leg, each via providing electrical connection through the sensing layer from the support leg to the sensing material of the pixel; and   a conductive contact that communicates electrically with the support leg and extends through the via to intersect the sensing material of the pixel,   wherein said support leg is elongated and projects laterally along the pixel and relative to the conductive contact, and   wherein said support leg presents opposite leg ends spaced laterally from one another, with one of the leg ends being attached to the conductive contact and the other one of the leg ends operable to be in supporting engagement with the wafer.   
     
     
         25 . The pixel assembly of  claim 24 , wherein said support leg includes a thin film material that extends between the leg ends. 
     
     
         26 . The pixel assembly of  claim 24 , wherein said one leg end is spaced laterally outboard from said other leg end. 
     
     
         27 . The pixel assembly of  claim 10 , wherein said support leg is spaced below the reflecting layer. 
     
     
         28 . The pixel assembly of  claim 10 , wherein said sensing material presents a laterally outermost extent and said support leg is located entirely within the laterally outermost extent of the sensing material. 
     
     
         29 . The pixel assembly of  claim 10 , wherein said support leg includes a thin film material.