Uncooled infrared imaging device

Abstract

An uncooled infrared imaging device according to an embodiment includes: reference pixels formed on a semiconductor substrate and arranged in at least one row; and infrared detection pixels arranged in the remaining rows and detecting incident infrared rays. Each of the reference pixels includes a first cell located above a first concave portion. The first cell includes a first thermoelectric conversion unit having a first infrared absorption film; and a first thermoelectric conversion element. Each of the infrared detection pixels includes a second cell located above a second concave portion, and having a larger area than the first cell. The second cell includes: a second thermoelectric converting unit located above the second concave portion; and first and second supporting structure units supporting the second thermoelectric converting unit above the second concave portion. The second thermoelectric converting unit includes: a second infrared absorption film; and a second thermoelectric conversion element.

What is claimed is: 
     
         1 . An uncooled infrared imaging device comprising:
 a semiconductor substrate;   an imaging region formed on the semiconductor substrate, a plurality of pixels being arranged in a matrix form in the imaging region,   the plurality of pixels including a plurality of reference pixels arranged in at least one row, and a plurality of infrared detection pixels arranged in the remaining rows, each of the infrared detection pixels being configured to detect an incident infrared ray,   each of the reference pixels including a first cell located above a first concave portion formed in a surface portion of the semiconductor substrate, the first cell including a first thermoelectric converting unit including a first infrared absorption film and a first thermoelectric conversion element, the first infrared absorption film being configured to absorb the incident infrared ray and convert the incident infrared ray into heat, the first thermoelectric conversion element being configured to convert the heat obtained by the first infrared absorption film into an electrical signal,   each of the infrared detection pixels including a second cell located above a second concave portion formed in a surface portion of the semiconductor substrate, the second cell including a second thermoelectric converting unit located above the second concave portion and first and second supporting structure units supporting the second thermoelectric converting unit above the second concave portion, the second thermoelectric converting unit including a second infrared absorption film and a second thermoelectric conversion element, the second infrared absorption film being configured to absorb the incident infrared ray and convert the incident infrared ray into heat, the second thermoelectric conversion element being configured to convert the heat obtained by the second infrared absorption film into an electrical signal, the first cell having a smaller area than the second cell when viewed from an incident direction of the infrared ray;   a plurality of row select lines formed in the imaging region, the plurality of row select lines corresponding to the rows of the plurality of pixels, each of the row select lines being connected to one end of the thermoelectric conversion element of each pixel of the corresponding one of the rows, each of the row select lines selecting the pixels of the corresponding one of the rows; and   a plurality of signal lines formed in the imaging region, the plurality of signal lines corresponding to columns of the plurality of pixels, each of the signal lines being connected to the other end of the thermoelectric conversion element of each pixel of the corresponding one of the columns, each of the signal lines being used for reading the electrical signal from each pixel of the corresponding one of the columns.   
     
     
         2 . The device according to  claim 1 , wherein, when G th     —     IMG  represents a heat conductance of each of the infrared detection pixels, C th     —     IMG  represents a heat capacity of each of the second cells, G th     —     TB  represents a heat conductance of each of the reference pixels, C th     —     TB  represents a heat capacity of each of the first cells, and tsel represents a duration of flowing of current to the infrared detection pixel and the reference pixels, the following equation is established, 
       
         
           
             
               
                 
                   1 
                   
                     G 
                     th_IMG 
                   
                 
                  
                 
                   { 
                   
                     1 
                     - 
                     
                       exp 
                        
                       
                         ( 
                         
                           - 
                           
                             tsel 
                             
                               
                                 C 
                                 th_IMG 
                               
                               / 
                               
                                 G 
                                 th_IMG 
                               
                             
                           
                         
                         ) 
                       
                     
                   
                   } 
                 
               
               = 
               
                 
                   1 
                   
                     G 
                     th_TB 
                   
                 
                  
                 
                   { 
                   
                     1 
                     - 
                     
                       exp 
                        
                       
                         ( 
                         
                           - 
                           
                             tsel 
                             
                               
                                 C 
                                 th_TB 
                               
                               / 
                               
                                 G 
                                 th_TB 
                               
                             
                           
                         
                         ) 
                       
                     
                   
                   } 
                 
               
             
           
         
         where one of the left-hand value and the right-hand value of the equation is 0.9 to 1.1 times larger than the other one of the left-hand value and the right-hand value. 
       
     
     
         3 . The device according to  claim 1 , further comprising
 a plurality of differential clamp circuits corresponding to the respective signal lines,   each of the differential clamp circuits including:   a coupling capacitor having one terminal connected to the corresponding one of the signal lines;   a differential amplifier having a positive-side input terminal connected to the other terminal of the coupling capacitor;   a feedback capacitor located between the positive-side input terminal of the differential amplifier and an output terminal of the differential amplifier; and   a feedback switch connected in parallel to the feedback capacitor.   
     
     
         4 . The device according to  claim 3 , further comprising
 a plurality of read transistors corresponding to the respective signal lines,   each of the read transistors having one of a source and a drain connected to the output terminal of the differential amplifier, each of the read transistors having the other one of the source and the drain connected to a read line, a gate of each of the read transistors receiving a select signal from a column select circuit.   
     
     
         5 . The device according to  claim 1 , further comprising
 a differential amplifier configured to amplify a difference between signal voltages obtained from the infrared detection pixels and the reference pixels.   
     
     
         6 . The device according to  claim 1 , wherein the first and second thermoelectric conversion elements are series-connected diodes. 
     
     
         7 . The device according to  claim 1 , wherein the first and second thermoelectric conversion elements are series-connected resistors.