Patent Publication Number: US-2011049663-A1

Title: Structure of photodiode array

Description:
FIELD OF THE INVENTION 
     The present invention relates to a structure of photodiode array, and in particular to a structure of photodiode array that allows for accurate detection of light current and improving cross-talking between adjacent diodes. 
     BACKGROUND OF THE INVENTION 
     Photodiode arrays have been widely applied in electronic products.  FIG. 5  of the attached drawings shows the structure of a conventional photodiode array. The conventional photodiode array structure, which is generally designated at  200 , comprises a cathode  210  and a plurality of anodes  220 . The anodes  220  are arranged in an array on the cathode  210 . In this arrangement, the result of test of the light current through a single photodiode cell is susceptible to the influence caused by the light current through adjacent photodiode cells and this often causes an increase of the light current of the photodiode cell to be tested, affecting the accuracy of test. 
     In view of the problem, the present invention aims to provide a structure of a photodiode array that provides accurate test result so as to reduce the costs and enhance the performance. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a structure of photodiode array, which allows for accurate detection of light current and improving cross-talking between adjacent diodes. 
     To realize the above objective, the present invention provides a structure of photodiode structure that comprises a first electrode; a plurality of second electrodes, which is arranged on the first electrode in a spaced manner to form an array; and a plurality of isolation sections, which is each formed between adjacent second electrodes to block light diffusion current flowing therethrough. With such an arrangement, accurate detection of the light currents can be realized to improve cross-talking between adjacent dodoes, so as to effectively suppress interference of noise and alleviate the problem of low S/N (signal to noise) ratio, enhancing accuracy of devices and stability of function, and reducing flaw rate of product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following description of a preferred embodiment thereof with reference to the drawings, in which: 
         FIG. 1  is a perspective view of a structure of photodiode array in accordance with the present invention; 
         FIG. 2  is a top plan view of the structure of photodiode array in accordance with the present-invention; 
         FIG. 3  is a cross-sectional view of the structure of photodiode array in accordance with the present invention; 
         FIG. 4  show curves of light current obtained with the photodiode array structures of the present invention and a structure of a conventional photodiode array, in which L 1  indicates Comparison Example 1 of the conventional structure; and L 2 , L 3 , and L 4  respectively indicate Embodiments 1, 2, and 3, all being embodiments of the present invention; and 
         FIG. 5  is a schematic view of a structure of a conventional photodiode array. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the drawings and in particular to  FIGS. 1-3 , which show, respectively a perspective view, a top plan view, and a cross-sectional view of a structure of photodiode array in accordance with the present invention, the structure of photodiode array in accordance with the present invention, generally designated with reference numeral  100 , comprises a first electrode  110 , a plurality of second electrodes  120 , and a plurality of isolation sections  130  for realizing correct detection of light current in the test of light current. 
     The second electrodes  120  are arranged on the first electrode  1  in a spaced manner and forming an array. In an embodiment, the first electrode  110  serves as a cathode and the second electrodes  120  are anodes. In an alternative embodiment, the first electrode  110  serves as an anode and the second electrodes  120  are cathodes. In the embodiment illustrated in the drawings, the first electrode  110  is taken as a cathode. 
     Each isolation section  130 , which is formed as a notch having a predetermined depth in the first electrode  110 , is arranged between adjacent second electrodes  120 , whereby the light diffusion current induced in the test of light current of the photodiode array structure  100  is blocked by a barrier formed by the isolation section  130  so as to provide correct result of detection of the light current and alleviate cross-talking between adjacent diodes. The depth of the isolation sections  130  is set to be greater than a depth of the second electrodes and preferably ranges from 5 to 550 micrometers. 
     Referring to  FIG. 4 , curves of light current obtained with the photodiode array structure of the present invention are shown, which are obtained with dices containing photodiode array structures made with the same process and subjected to half cutting as indicated in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Embodiment 
                   
                   
                 Comparison 
               
               
                   
                 1 
                 Embodiment 2 
                 Embodiment 3 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Depth 
                 50 
                 100 
                 150 
                 0 
               
               
                 (micron) 
               
               
                   
               
            
           
         
       
     
     Tests of light current are then carried out on the above provided dices that are subjected to half cutting and contain photodiode array structures and the results of the tests are listed in Tables 2-5. The curves of  FIG. 4  are plotted in accordance with the data listed in Tables 2-5, in which L 1  indicates Comparison Example 1 of the conventional structure, L 2  indicates Embodiment 1 of the present invention, L 3  indicates Embodiment 2 of the present invention, and L 4  indicates Embodiment 3 of the present invention. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Comparison Example 1 
               
            
           
           
               
               
               
            
               
                   
                 Cell 
                 Light Current (μA) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                  1 
                 264.5 
               
               
                   
                  2 
                 287.5 
               
               
                   
                  3 
                 308.7 
               
               
                   
                  4 
                 315.2 
               
               
                   
                  5 
                 322.5 
               
               
                   
                  6 
                 325.5 
               
               
                   
                  7 
                 322.0 
               
               
                   
                  8 
                 319.0 
               
               
                   
                  9 
                 322.0 
               
               
                   
                 10 
                 321.0 
               
               
                   
                 11 
                 316.0 
               
               
                   
                 12 
                 312.0 
               
               
                   
                 13 
                 315.7 
               
               
                   
                 14 
                 318.9 
               
               
                   
                 15 
                 321.5 
               
               
                   
                 16 
                 320.9 
               
               
                   
                 17 
                 322.2 
               
               
                   
                 18 
                 320.0 
               
               
                   
                 19 
                 318.9 
               
               
                   
                 20 
                 316.8 
               
               
                   
                 21 
                 312.7 
               
               
                   
                 22 
                 308.7 
               
               
                   
                 23 
                 300.0 
               
               
                   
                 24 
                 248.0 
               
               
                   
                 Average 
                 310.84 
               
               
                   
                 Standard Deviation 
                 18.89 
               
               
                   
                 Percentage 
                 6.1% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Embodiment 1 
               
            
           
           
               
               
               
            
               
                   
                 Cell 
                 Light Current (μA) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                  1 
                 225.5 
               
               
                   
                  2 
                 249.0 
               
               
                   
                  3 
                 249.0 
               
               
                   
                  4 
                 248.5 
               
               
                   
                  5 
                 247.5 
               
               
                   
                  6 
                 246.5 
               
               
                   
                  7 
                 246.5 
               
               
                   
                  8 
                 247.0 
               
               
                   
                  9 
                 246.0 
               
               
                   
                 10 
                 245.0 
               
               
                   
                 11 
                 245.0 
               
               
                   
                 12 
                 246.5 
               
               
                   
                 13 
                 245.5 
               
               
                   
                 14 
                 244.0 
               
               
                   
                 15 
                 244.0 
               
               
                   
                 16 
                 243.5 
               
               
                   
                 17 
                 244.0 
               
               
                   
                 18 
                 246.5 
               
               
                   
                 19 
                 246.5 
               
               
                   
                 20 
                 246.5 
               
               
                   
                 21 
                 246.0 
               
               
                   
                 22 
                 244.5 
               
               
                   
                 23 
                 245.0 
               
               
                   
                 24 
                 222.0 
               
               
                   
                 Average 
                 244.17 
               
               
                   
                 Standard Deviation 
                 6.49 
               
               
                   
                 Percentage 
                 2.7% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Embodiment 2 
               
            
           
           
               
               
               
            
               
                   
                 Cell 
                 Light Current (μA) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                  1 
                 213.0 
               
               
                   
                  2 
                 228.5 
               
               
                   
                  3 
                 228.5 
               
               
                   
                  4 
                 229.0 
               
               
                   
                  5 
                 229.0 
               
               
                   
                  6 
                 229.0 
               
               
                   
                  7 
                 228.5 
               
               
                   
                  8 
                 226.5 
               
               
                   
                  9 
                 225.5 
               
               
                   
                 10 
                 227.0 
               
               
                   
                 11 
                 227.5 
               
               
                   
                 12 
                 226.5 
               
               
                   
                 13 
                 226.5 
               
               
                   
                 14 
                 226.0 
               
               
                   
                 15 
                 226.5 
               
               
                   
                 16 
                 226.5 
               
               
                   
                 17 
                 226.0 
               
               
                   
                 18 
                 226.5 
               
               
                   
                 19 
                 228.0 
               
               
                   
                 20 
                 228.0 
               
               
                   
                 21 
                 226.0 
               
               
                   
                 22 
                 226.0 
               
               
                   
                 23 
                 226.0 
               
               
                   
                 24 
                 212.5 
               
               
                   
                 Average 
                 225.98 
               
               
                   
                 Standard Deviation 
                 4.22 
               
               
                   
                 Percentage 
                 1.9% 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Embodiment 3 
               
            
           
           
               
               
               
            
               
                   
                 Cell 
                 Light Current (μA) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                  1 
                 206.5 
               
               
                   
                  2 
                 212.5 
               
               
                   
                  3 
                 212.0 
               
               
                   
                  4 
                 212.5 
               
               
                   
                  5 
                 212.5 
               
               
                   
                  6 
                 212.5 
               
               
                   
                  7 
                 212.5 
               
               
                   
                  8 
                 212.5 
               
               
                   
                  9 
                 212.5 
               
               
                   
                 10 
                 212.5 
               
               
                   
                 11 
                 212.0 
               
               
                   
                 12 
                 212.0 
               
               
                   
                 13 
                 213.0 
               
               
                   
                 14 
                 213.5 
               
               
                   
                 15 
                 213.0 
               
               
                   
                 16 
                 212.5 
               
               
                   
                 17 
                 212.0 
               
               
                   
                 18 
                 212.0 
               
               
                   
                 19 
                 212.0 
               
               
                   
                 20 
                 212.0 
               
               
                   
                 21 
                 213.5 
               
               
                   
                 22 
                 213.5 
               
               
                   
                 23 
                 212.0 
               
               
                   
                 24 
                 203.5 
               
               
                   
                 Average 
                 211.88 
               
               
                   
                 Standard Deviation 
                 2.22 
               
               
                   
                 Percentage 
                 1.0% 
               
               
                   
                   
               
            
           
         
       
     
     The results of tests shown in Tables 2-5 and  FIG. 4  indicate that the light current detected with the photodiode array structure in accordance with the present invention have a lower value of standard deviation as compared to the light current obtained with a photodiode array structure that is not provided with the isolation sections, and the standard deviation of the light current obtained with a photodiode array structure having isolation sections of a great depth is lower than the light current obtained with a photodiode array structure having isolation sections of a small depth. In other words, when the second electrodes of the photodiode array structure are used as an active area, the isolation sections arranged between adjacent second electrodes may function as barriers for blocking light, whereby in receiving light with the photodiode array structure, the light diffusion current induced can be blocked by the barriers formed by the isolation sections thereby providing the photodiode array structure with more stabilized detection of the current. 
     To summarize, the structure of photodiode array in accordance with the present invention comprises a first electrode on which a plurality of second electrodes is arranged in a spaced manner forming an array and a plurality of isolation sections, which is each formed between adjacent ones of the spaced and arrayed second electrodes, whereby in carrying out tests of light currents, accurate detection of the light currents can be realized to improve cross-talking between adjacent dodoes, effectively suppress interference of noise, and thus alleviates the problem of low S/N (signal to noise) ratio, enhances accuracy of devices and stability of function, reduces flaw rate of product, and eliminates the concern about probability of matching a light source, so as to simplify the test process and reduce the cost of test. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.