LSU ECE Seminar Announcement and Schedule

                                                                       
            Uncooled Semiconducting YBaCuO Infrared and Far-Infrared   
                                   Detectors                           
                                                                       
                                Mahmoud Almasri                        
            Postdoctoral Fellow at Georgia Institute of Technology,    
                                  Atlanta, GA                          
                                                                       
         Abstract--A new generation of microbolometers were designed,  
         fabricated and tested for the NASA CERES (Clouds and the      
         Earth's Radiant Energy System) instrument to measure the      
         radiation flux at the Earth's surface and the radiant energy  
         flow within the atmosphere. These detectors are designed to   
         measure the earth radiances in three spectral channels        
         consisting of a short wave channel of 0.3 to 5 micro m, a     
         wide-band channel of 0.3 to 100 micro m and a window channel  
         from 8 to 12 micro m each housing a l.5 x 1.5 mm^2            
         microbolometers or alternatively 400 x 400 micro m^2          
         microbolometers in a 1 x 4 array of detectors in each of the  
         three wavelength bands. The microbolometers were fabricated by
         radio frequency (RF) magnetron sputtering at ambient          
         temperature, using polyimide sacrificial layers and standard  
         micromachining techniques. A semiconducting YBaCuO thermometer
         was employed. A double micromirror structure with multiple    
         resonance cavities was designed to achieve a relatively       
         uniform absorption from 0.3 to 100 micro m wavelength. Surface
         micromachining techniques in conjunction with a polyinide     
         sacrificial layer were utilized to create a gap underneath the
         detector. The temperature coefficient of resistance (TCE) was 
         measured to be 2.8%/K. These devices have successfully        
         demonstrated voltage responsivities over 10^{3} V/W,          
         detectivities above 10^{8} cm Hz^{1/2}/W NEP less than 4 x    
         10^{-10}W/Hz^{1/2} and thermal time constant less than 15 ms. 
         The second part of the talk describes a new micromachined     
         microbolometer array structure that utilizes a self-supporting
         semiconducting YBaCuO thin film thermometer. The YBaCuO       
         thermometer is held above the substrate only by the electrode 
         arms without the need of any underlying supporting membrane.  
         This represents a significant improvement in the              
         state-of-the-art for microbolometers by eliminating the       
         thermal mass associated with the supporting membrane. The     
         reduced thermal mass permits lowering the thermal conductance 
         to the substrate to obtain increased responsivity or having a 
         shorter thermal time constant to allow for higher frame rate  
         camera. Devices were fabricated by growing YBaCuO films on a  
         conventional polyimide sacrificial layer mesa. Subsequent     
         etching of the sacrificial layer provides the air gap that    
         thermally isolates the microbolometer. The measured TCE was   
         3.1%/K at room temperature. The measured responsivity and     
         detectivity approached 10^{4} V/W and 10^{8} cm Hz /W. The    
         micromachining techniques employed are post-complementary     
         metal-oxide-semiconductor (CMOS) compatible, allowing for the 
         fabrication of focal plane arrays for IR cameras.             
                                                                       
         Thursday, 2 December 2004, 13:00 - 14:00                      
         Room 117 EE Building                                          
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Schedule as of 1 Dec 2004.  For updates visit http://www.ece.lsu.edu/seminar

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