please refer to fig5 . fig5 is a top view of an embodiment of the efuse bar code structure according to the present invention . the efuse bar code structure 20 comprises a substrate 22 and a plurality of efuse elements 24 disposed on substrate 22 . the substrate 22 may be a semiconductor substrate for facilitating the production of the efuse elements . the efuse elements 24 may be one - dimensionally , two - dimensionally or three - dimensionally ( i . e . multi - layer ) arranged in a form of an array . fig5 illustrates an example of two - dimensional arrangement . the efuse bar code structure 20 may further comprise a plurality of electric circuits for separately electrically connecting the efuse elements to an external circuit . for example , in the case of reading process , it may be electrically connected to row decoder 26 and column decoder 28 for decoding . it may be connected to a signal amplifier for amplifying signals . fig6 illustrates the a section of the efuse bar code structure in fig5 and the section view along line i - i ′. this is an example of the efuse element structure only , but the present invention is not limited to this example , and other efuse structures can be used . the efuse elements 24 are deposited on the substrate 22 and comprise a polysilicon layer 32 and a polycide layer 34 stacked on the polysilicon layer 32 . polysilicon is a material of low resistance . polycide is a material of high resistance . the stacking shape of polysilicon layer 32 and polycide layer 34 is narrow in the middle and wide at both ends . consequently , when the two ends of the polycide layer 34 serve as cathode and anode and a voltage is applied on the polycide layer 34 , strong electric current is continuously passing through the polycide layer 34 . the narrower the passage , the higher the electric current density . due to the electro - migration effect , the atoms in the polycide layer migrate along the lattice in the direction of electron flow . this makes the efuse elements 24 break off in the middle region to form two separate end segments without electric connection . fig7 is a schematic view of a blown efuse element 24 in fig6 after a voltage is applied . furthermore , a protection layer , such as a thin silicon oxide layer , may be applied on the polycide layer to protect it . when a plurality of efuse elements are arranged one - dimensionally , they resemble a one - dimensional bar code . when efuse elements are arranged two - dimensionally , they resemble a two - dimensional bar code . in addition to being electrically encoded and optically decoded , the efuse bar code structure of the present invention may be electrically encoded and decoded as well . they can also be arranged three - dimensionally without any difficulty in structure and for use . the efuse bar code structure according to the present invention may be patterned by blowing a fuse in the corresponding efuse elements with respect to a piece of information according to a bar code encoding method to form a bar pattern corresponding to the information . for example , fig8 is a schematic view after use . some fuses in the efuse elements 24 are blown to form a bar pattern . the pattern variations of the bar code structure may be referred to the conventional bar code encoding methods . for example , fig9 is a method of encoding bc412 disclosed in u . s . pat . no . 6 , 179 , 207 , regulating that a number or a letter may be represented by the existence or absence of seven lines . the encoding method of the efuse bar code structure of the present invention may be bc412 method . for example , the first row in fig8 represents number “ 7 ,” the second row for letter “ y ” and the third row for letter “ z .” the forth and the fifth rows are not in use at present . the efuse bar code structure according to the present invention may be arranged three - dimensionally . fig1 illustrates an embodiment in a three - dimensional arrangement . for example , after a layer of efuse elements and the necessary circuits are formed on the substrate , an insulation layer 36 of dielectric material , such as silicon oxide layer , may be deposited thereon as the substrate of the efuse elements on the next higher layer to continue the production of the efuse elements . a protection layer may be further deposited on the top layer of the efuse elements . there are many methods to “ break ” the fuse in the corresponding efuse elements . for example , the method may be carried out by connecting the efuse elements to an external circuit for applying a voltage on the fuse , i . e . applying a proper voltage to “ break ” the efuse . subsequently , a bar pattern is formed on the bar code structure . to break an efuse , in plain words , is to have an efuse “ blown ” by means of electro - migration effect . the term “ blown ” used herein is not particularly construed as “ having a fuse broken by means of heat ”. to do decoding is to read the fuse in the efuse elements to determine if the fuse is blown or not , so as to obtain the corresponding information . to determine if the fuse is blown or not may be carried out by connecting the efuse elements to an external circuit for reading electric signals . different electric signals help to determine if the fuse is blown or not because blown or unblown fuses represent different electric signals . it may also be possible to optically determine if the fuse is blown or not by optically scanning the bar pattern formed by blown or unblown fuses . this resembles the traditional way to scan the bar codes to obtain information . the efuse bar code structure according to the present invention may be applied in many aspects . it may be useful in recording information comprising process information of a product , test information before , during or after production , quality information or identification information , etc . the bar code structure in accordance with the present invention uses efuses as a bar pattern . they can be manufactured by semiconductor process . the advantages are the small and compact size and the ability to store a lot of information in a unit volume and batch information . the efuse bar code structure according to the present invention is especially useful in semiconductor processes and keeping track of product records . for example , the bar code structure may be built on the semiconductor substrates of each die in accordance with the production process to keep tracking of production , qc and logistic record after production . because the bar code structure is small , compact , information - concentrated and stable , information such as batch number , die number , test number and results , packing number and test results can be recorded successively . it can also be used to identify each die . accordingly , the efuse bar code structure of the present invention may be conveniently applied to other products . for example , the efuse bar code structure may be attached onto a product ( agricultural or electronic products , for example ) during or after production or onto its package to record the information successively . the so - called action of “ to record the information successively ” means to form another bar pattern according to a bar code encoding method with respect to another piece of information after a period of time by blowing a corresponding fuse which has not been used for forming the bar code pattern ( the forth and the fifth rows in fig8 , for example ) in the efuse elements . therefore , it is another feature of the present invention that information can be added to the same bar code structure successively . for example , an efuse bar code structure of the present invention may be formed on a proper place of a certain die during the production to record the batch number and the die number . later , the information such as production conditions , test number and test results , etc . may be recorded in the same bar code structure utilizing the region which has not been used after preliminary tests . then , the test results after packaging test can be successively recorded . all information in the same bar code structure facilitates the complete track record of a product . the advantages are essentially based on the large capacity of the efuse bar code structure and the principle of the efuse . a single bar code structure provides all information since production without having to be constantly replaced like conventional bar codes . it is therefore environment - friendly as well . the efuse bar code structure in accordance with the present invention can be manufactured by semiconductor processes . the advantages are the small and compact size compared to the conventional one . for example , the distance between each line can be shorter than 1 μm . so 1 mm 2 area may contain about 10 6 lines . accordingly , a lot of information can be stored in a unit volume . moreover , batch information is possible . in other words , information can be added to the same efuse bar code structure successively . all combinations and sub - combinations of the above - described features also belong to the present invention . those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention . accordingly , the above disclosure should be construed as limited only by the metes and bounds of the appended claims .