Patent Publication Number: US-10783979-B2

Title: Built-in self-test (BIST) circuit, memory device including the same, and method of operating the BIST circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 15/262,027, filed Sep. 12, 2016, which claims the benefit of priority under 35 USC § 119 to Korean Patent Application No. 10-2015-0172660, filed on Dec. 4, 2015, in the Korean Intellectual Property Office, the disclosure of each of which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     The example embodiments relate to a built-in self-test (BIST) circuit, and more particularly, to a BIST circuit, a memory device including the BIST circuit, and a method of operating the BIST circuit. 
     As semiconductor manufacturing technology develops, integration of semiconductor devices increases and simultaneously a possibility of failure of the semiconductor device may further increase. Thus, a process of catching a problem of a semiconductor manufacturing process is desired and may be performed by analyzing a failure that occurs in the semiconductor device. 
     For example, a memory device has been tested by using external dedicated equipment. However, significant changes have occurred with respect to a method of testing the memory device due to the advent of system on chip (SoC) technology that forms a system in a single chip. An SoC uses a plurality of built-in memory devices having a large width data I/O for improving performance. It may be inefficient to test such built-in memory devices by using the existing dedicated test equipment due to a lack of channel numbers, a limitation of a high speed test, and low accessibility to the built-in memory devices. 
     As an alternative to handling the problem, a method of including a BIST circuit in an SoC has been developed. The method is often used in the high speed test compared to the method using external dedicated equipment, and thus research has been carried out thereon. At present, a BIST method is widely used as a method of testing a built-in memory device currently included in the SoC. 
     SUMMARY 
     The example embodiments provide a built-in self-test (BIST) circuit capable of reducing a test time with respect to a memory core according to diverse environments using a memory device and tuning a memory characteristic of, for example, the memory core in accordance with a variable operating environment. 
     According to an aspect of the inventive concept, there is provided a method of operating a built-in self-test (BIST) circuit configured to generate a test pattern based on a plurality of test parameters including a first test parameter and a second test parameter and perform a test on at least one memory core, the method including setting a sweep range including a sweep start point of the first test parameter and a sweep end point of the first test parameter; generating a first test pattern corresponding to each sweep point of the sweep range from the sweep start point of the first test parameter and the sweep end point of the first test parameter and providing the first test pattern to the at least one memory core; receiving output data corresponding to first test pattern from the at least memory core and comparing the output data and a predetermined reference data; and generating first test result information based on results of the comparing. 
     According to another aspect of the inventive concept, there is provided a method of operating a BIST circuit configured to repeatedly perform a plurality of test loops for performing a sweep test on at least one memory chip, the method comprising: generating a test pattern by sweeping at least one test parameter based on a sweep range corresponding to at least one of a plurality of test parameters, wherein at least one of the plurality of test loops performs the step of generating said test pattern; generating test result information by testing the at least one memory chip by using the test pattern, wherein at least one of the plurality of test loops performs the step of generating said test result information; and tuning a memory characteristic of the at least one memory chip based on a plurality of pieces of test result information generated through the plurality of test loops, wherein at least one of the plurality of test loops performs the step of tuning said memory characteristic. 
     According to another aspect of the inventive concept, there is provided a built-in self-test (BIST) circuit configured to generate a test pattern based on a plurality of test parameters including a first test parameter and a second test parameter and perform a test on at least one memory core. The BIST circuit includes: a control circuit configured to set a sweep range comprising a sweep start point of the first test parameter and a sweep end point of the first test parameter; a pattern generating circuit configured to generate a first test pattern corresponding to each sweep point of the sweep range from the sweep start point of the first test parameter and the sweep end point of the first test parameter and configured to provide the first test pattern to the at least one memory core; a comparing circuit configured to receive output data corresponding to the first test pattern from the at least one memory core and configured to compare the output data received from the at least one memory core and a predetermined reference data received from the pattern generating circuit in order to generate a comparison result; and a storage circuit configured to generate first test result information based on the comparison result received from the comparing circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram of a built-in self-test (BIST) circuit according to an exemplary embodiment; 
         FIG. 2  is a block diagram of a BIST control logic according to an exemplary embodiment; 
         FIG. 3  is a diagram of sweep parameter information for describing an operation of a BIST control logic according to an exemplary embodiment; 
         FIG. 4  is a block diagram of a BIST control logic according to another exemplary embodiment; 
         FIGS. 5A and 5B  are diagrams for describing test result information generated through a sweep test according to an exemplary embodiment; 
         FIG. 6  is a block diagram of a test result storing unit according to an exemplary embodiment; 
         FIG. 7  is a block diagram of a BIST circuit according to another exemplary embodiment; 
         FIG. 8  is a block diagram of a tuning control unit according to an exemplary embodiment; 
         FIG. 9  is a block diagram of a memory system according to an exemplary embodiment; 
         FIGS. 10A and 10B  are diagrams of a stack memory device according to another exemplary embodiment; 
         FIG. 11  is a flowchart for describing a method of operating a BIST circuit according to an exemplary embodiment; 
         FIG. 12  is a detailed flowchart for describing a method of operating a BIST circuit according to another exemplary embodiment; 
         FIG. 13  is a flowchart of a method of operating a BIST circuit related to a stack memory device according to an exemplary embodiment; 
         FIG. 14  is a diagram of a memory card according to an exemplary embodiment; and 
         FIG. 15  is a block diagram of a computing system including a memory system according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which various embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. These example embodiments are just that—examples—and many implementations and variations are possible that do not require the details provided herein. It should also be emphasized that the disclosure provides details of alternative examples, but such listing of alternatives is not exhaustive. Furthermore, any consistency of detail between various examples should not be interpreted as requiring such detail—it is impracticable to list every possible variation for every feature described herein. The language of the claims should be referenced in determining the requirements of the invention. 
     Although the figures described herein may be referred to using language such as “one embodiment,” or “certain embodiments,” these figures, and their corresponding descriptions are not intended to be mutually exclusive from other figures or descriptions, unless the context so indicates. Therefore, certain aspects from certain figures may be the same as certain features in other figures, and/or certain figures may be different representations or different portions of a particular exemplary embodiment. 
     As is traditional in the field of the inventive concepts, embodiments are described, and illustrated in the drawings, in terms of functional blocks, units and/or modules. Those skilled in the art will appreciate that these blocks, units and/or modules are physically implemented by electronic (or optical) circuits such as logic circuits, discrete components, microprocessors, hard-wired circuits, memory elements, wiring connections, and the like, which may be formed using semiconductor-based fabrication techniques or other manufacturing technologies. In the case of the blocks, units and/or modules being implemented by microprocessors or similar, they may be programmed using software (e.g., microcode) to perform various functions discussed herein and may optionally be driven by firmware and/or software. Alternatively, each block, unit and/or module may be implemented by dedicated hardware, or as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions. Also, each block, unit and/or module of the embodiments may be physically separated into two or more interacting and discrete blocks, units and/or modules without departing from the scope of the inventive concepts. Further, the blocks, units and/or modules of the embodiments may be physically combined into more complex blocks, units and/or modules without departing from the scope of the inventive concepts. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. Unless the context indicates otherwise, these terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section, for example as a naming convention. Thus, a first element, component, region, layer or section discussed below in one section of the specification could be termed a second element, component, region, layer or section in another section of the specification or in the claims without departing from the teachings of the present invention. In addition, in certain cases, even if a term is not described using “first,” “second,” etc., in the specification, it may still be referred to as “first” or “second” in a claim in order to distinguish different claimed elements from each other. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. 
       FIG. 1  is a block diagram of a built-in self-test (BIST) circuit  100  according to an exemplary embodiment. 
     As shown in  FIG. 1 , the BIST circuit  100  may include a BIST control logic  110  (e.g., a control circuit), a test pattern generating unit  120  (e.g., a test pattern generating circuit), a comparing unit  130  (e.g., a comparing circuit), and a test result storing unit  140  (e.g., a test result storing circuit). The BIST circuit  100  may be built in a memory device and may test a memory core MC included in the memory device. The BIST circuit  100  may be a circuit implementing a memory test algorithm for testing the memory core MC. The BIST circuit  100  may test memory cells of the memory core MC capable of repairing a built-in defect of the memory core MC, may analyze a defect phenomenon, and may extract information for recovery. Defective memory cells of the memory core MC may be recovered based on the information. The memory core MC may be at least one of a non-volatile memory, a volatile memory, and a memory including both the non-volatile memory and the volatile memory. 
     In this exemplary embodiment, the BIST circuit  100  may include the BIST control logic  110 , the test pattern generating unit  120 , the comparing unit  130 , and the test result storing unit  140 . The BIST control logic  110  may receive a BIST enable signal BIST_EN from outside of the BIST circuit  100  and may control a test on the memory core MC in response to the BIST enable signal BIST_EN. According to an exemplary embodiment, the BIST control logic  110  may include a parameter sweep control unit  115  (e.g., a parameter sweep controller or a parameter sweep control circuit). The parameter sweep control unit  115  may set a sweep range of a plurality of test parameters. For example, the sweep range of each test parameter may include a sweep start point, a sweep end point, and a sweep offset point. A test parameter refers to an operation timing parameter of the memory core MC when the memory core MC is being tested. A test pattern Test_P may be generated by the test pattern generating unit  120  based on the test parameter. For example, when the memory core MC is a DRAM, the test parameter may be one of tRC (Row cycle time), tRAS (Rowactive time), tRP (Row precharge time), tRRD (Row active to Row active delay), tRCD (/RAS to /CAS delay), tCK (test Clock), VRef (Voltage Reference), Temp (Temperature), etc. According to an embodiment, the test pattern generating unit  120  may generate the test pattern Test_P in accordance with test parameters such as tRC (Row cycle time), tRAS (Rowactive time), etc. According to an embodiment, the test pattern generating unit  120  may generate a test pattern by using March C-algorithm. The test pattern Test_P may include reference data REF_DATA (e.g., a predetermined reference data), a test address, a test command, etc. 
     The BIST control logic  110  may control the test by repeatedly performing a plurality of test loops to sweep each test parameter. Such a test is referred to as a sweep test in an exemplary embodiment. 
     According to an exemplary embodiment, an nth test loop that performs the sweep test using an nth test parameter will now be described. The BIST control logic  110  may control the test pattern generating unit  120  to generate the test pattern Test_P based on the nth test parameter when the nth test parameter has the sweep start point. In this regard, test parameters other than the nth test parameter may be fixed to have a preset reference point during the nth test loop. However, the embodiment that the test parameters other than the nth test parameter are fixed to have the preset reference point is merely an exemplary embodiment. At least one of the test parameters other than the nth test parameter may be swept simultaneously with the nth test parameter to perform the sweep test. The nth test loop may be performed several times by changing the reference point of the test parameters other than the nth test parameter. For example, when an n+1th test parameter has a fixed first reference point, a comparison result may be generated by performing the nth test loop using the nth test parameter and another comparison result may be generated by performing the nth test loop again by changing the n+1th test parameter to have a fixed second reference point. 
     The test pattern generating unit  120  may provide the test pattern Test_P to the memory core MC. The comparing unit  130  may receive output data Dout corresponding to the nth test parameter of the sweep start point from the memory core MC and may compare the output data Dout and reference data REF_DATA received from the test pattern generating unit  120 . The comparing unit  130  may generate a comparison result CR of the output data Dout and reference data REF_DATA and may provide the comparison result CR to the test result storing unit  140 . 
     Thereafter, the BIST control logic  110  may control the test pattern generating unit  120  to generate the test pattern Test_P based on the nth test parameter when the nth test parameter has a sweep point next the sweep start point. The comparing unit  130  may generate another comparison result by using the generated test pattern Test_P and provide the comparison result to the test result storing unit  140 . The BIST control logic  110  may repeat the nth test loop until the nth test parameter has the sweep end point and may store a plurality of comparison results generated through the nth test loop in the test result storing unit  140 . 
     The BIST control logic  110  may control an n+1th test loop that performs the sweep test by using the n+1th test parameter after ending the nth test loop. 
     The test result storing unit  140  may receive test condition information TCI including test parameters selected from the BIST control logic  110 , a sweep range of each test parameter, and sweep test progress status information, etc. The test result storing unit  140  may match the test condition information TCI and a stored comparison result to generate test result information TRI. For example, the test result storing unit  140  may match comparison results generated by performing the nth test loop and sweep points of the nth test parameter to generate nth test result information. 
     The test result storing unit  140  may provide a plurality of pieces of test result information TRI generated through a plurality of test loops to the outside (e.g., to a processor and a memory controller) and the BIST control logic  110 . The BIST control logic  110  may control the sweep test on the memory core MC based on the test result information TRI. According to an embodiment, the parameter sweep control unit  115  may reset a sweep range of each test parameter based on the test result information TRI. The BIST control logic  110  may control the sweep test based on the reset sweep range. 
     The BIST circuit  100  according to one embodiment may automatically sweep test parameters to perform a sweep test, thereby promptly obtaining a plurality of pieces of test result information according to a point of each test parameter. The plurality of pieces of test result information may be used to set a sweep test priority when a next sweep test is performed on test parameters. 
       FIG. 2  is a block diagram of a BIST control logic  200   a  according to an exemplary embodiment.  FIG. 3  is a diagram of sweep parameter information SPI for describing an operation of the BIST control logic  200   a  according to an exemplary embodiment. 
     As shown in  FIG. 2 , the BIST control logic  200   a  may include a parameter sweep control unit (e.g., a parameter sweep control circuit)  210   a  and a test loop control unit (e.g., a test loop control circuit)  230   a . The parameter sweep control unit  210   a  may include a sweep target parameter selecting unit (e.g., a sweep target parameter selecting circuit)  212   a  and a parameter sweep range setting unit (e.g., a parameter sweep range setting circuit)  214   a . The sweep target parameter selecting unit  212   a  may select at least one test parameter that is a sweep target from among a plurality of test parameters. The sweep target parameter selecting unit  212   a  may provide information Sel_PI regarding selected test parameters to the parameter sweep range setting unit  214   a . The parameter sweep range setting unit  214   a  may set a sweep range of the selected test parameters. The parameter sweep range setting unit  214   a  may provide the sweep parameter information SPI including the sweep range of the selected test parameters to the test loop control unit  230   a . The test loop control unit  230   a  may include a sweep priority setting unit (e.g., a sweep priority setting circuit)  235   a . The sweep priority setting unit  235   a  may set a sweep test priority of the selected test parameters based on the sweep parameter information SPI. The test loop control unit  230   a  may control a sweep test using the selected test parameters based on the sweep test priority. An embodiment in this regard will now be described in detail below. 
     As shown in  FIGS. 2 and 3 , the sweep target parameter selecting unit  212   a  may select first through fourth test parameters that are sweep targets from among the plurality of test parameters. The parameter sweep range setting unit  214   a  may set a sweep range of each of the selected first through fourth test parameters. The first test parameter may have a sweep range of 5-10 clock units. The second test parameter may have a sweep range of 10-20 clock units. The third test parameter may have a sweep range of 20-25 clock units. The fourth test parameter may have a sweep range of 10-15 clock units. A clock unit may correspond to an internal test clock unit of the BIST circuit  100  of  FIG. 1 . A sweep start point of the first test parameter may correspond to 5 and a sweep end point thereof may correspond to 10. The parameter sweep range setting unit  214   a  may set sweep offset points of the first through fourth test parameters as 1. Thus, the first test parameter may be swept in an order of sweep points of 5, 6, 7, 8, 9, and 10. However, this is merely an exemplary embodiment. Sweep offset points may be variously set according to each test parameter. However, this is merely an exemplary embodiment and the inventive concept is not limited to the above embodiment. Various sweep ranges may be set by selecting various test parameters. For example, in some embodiments, the parameter sweep range setting unit  214   a  may set sweep offset points of the first through fourth test parameters as 2. In one exemplary embodiment, the second test parameter, for example, may be swept in an order of sweep points of 10, 12, 14, 16, 18, and 20. 
     The sweep priority setting unit  235   a  may set the sweep test priority in order of the first test parameter, the second test parameter, the third test parameter, and the fourth test parameter with respect to the selected first through fourth test parameters. The test loop control unit  230   a  may control to firstly perform a first test loop Loop 1 that performs a sweep test using the first test parameter and lastly perform a fourth test loop Loop 4 that performs a sweep test using the fourth test parameter based on the sweep test priority. 
     According to the embodiment, only some of a plurality of test parameters may be selected as sweep targets, and thus a memory core may be more promptly tested, and a sweep test priority may be set with respect to test parameters when a sweep test is performed, thereby firstly sweeping an important test parameter and performing the sweep test. 
       FIG. 4  is a block diagram of a BIST control logic  200   b  according to another exemplary embodiment.  FIGS. 5A and 5B  are diagrams for describing the test result information TRI generated through a sweep test according to an exemplary embodiment. 
     As shown in  FIG. 4 , the BIST control logic  200   b  may include an interrupt signal generating unit (e.g., an interrupt signal generating circuit)  220   b  and a test loop control unit (e.g., a test loop control circuit)  230   b . The interrupt signal generating unit  220   b  may generate an interrupt signal IS that stops performing a test loop of the test loop control unit  230   b . The interrupt signal generating unit  220   b  may include a test result based signal generating unit (e.g., a test result based signal generating circuit)  222   b  and a memory temperature based signal generating unit (a memory temperature based signal generating circuit)  224   b.    
     The test result based signal generating unit  222   b  may receive the comparison result CR from the comparing unit  130  of  FIG. 1  or may receive the plurality of test result information TRI from the test result storing unit  140  to generate the interrupt signal IS based on the comparison result CR or the test result information TRI. According to an embodiment, if the test loop control unit  230   b  performs the nth test loop using the nth test parameter, when a generated comparison result is changed from fail Fail to pass Pass, the test result based signal generating unit  222   b  may provide the interrupt signal IS to the test loop control unit  230   b  and control to stop performing the nth test loop. Thereafter, the test loop control unit  230   b  may control to instantaneously perform another test loop using another test parameter. 
     For example, as a result of performing a second test loop using a second test parameter SP_ 2  of  FIG. 5A , when a comparison result firstly passes, the test result based signal generating unit  222   b  may control the test loop control unit  230   b  to stop performing the second test loop. Thereafter, the test loop control unit  230   b  may control to perform a third test loop using a third test parameter SP_ 3 . 
     The memory temperature based signal generating unit  224   b  may receive temperature information TempI of a memory device including the BIST circuit  200   b , may provide the interrupt signal IS to the test loop control unit  230   b  based on the temperature information TempI of the memory device, and may stop performing the test loop of the test loop control unit  230   b . According to an embodiment, the memory temperature based signal generating unit  224   b  may compare the temperature information TempI of the memory device and reference temperature information, and, when the temperature information TempI of the memory device exceeds the reference temperature information, may stop performing the test loop of the test loop control unit  230   b.    
     According to this exemplary embodiment, the BIST circuit  200   b  may instantly stop performing a test loop when it is difficult to perform the test loop since a temperature of a memory device exceeds a reference temperature, and when a desired comparison result or test result information is received by performing a test loop using a specific test parameter, may stop performing the specific test loop and may perform a test loop using a next test parameter, thereby performing an efficient sweep test. 
     Referring to  FIGS. 3 and 5A , the first test parameter SP_ 1  may be used to perform a first test loop and generate first test result information TRI 1 . The first test result information TRI 1  may include first through sixth comparison results 1 st  RC-6 th  RC. The 1 st  through 6 th  comparison results 1 st  RC-6 th  RC may respectively match sweep points of the first test parameter SP_ 1 . For example, the first comparison result 1 st  RC may match a 5 th  sweep point of the first test parameter SP_ 1 , the second comparison result 2 nd  RC may match a 6 th  sweep point of the first test parameter SP_ 1 , the sixth comparison result 6 th  RC may match a 10 th  sweep point of the first test parameter SP_ 1 , etc. Furthermore, the first test result information TRI 1  may separately include tag information regarding a sweep point of the first test parameter SP_ 1  matching each comparison result. The first test result information TRI 1  may include first margin information M 1  regarding the first test parameter SP_ 1 . Margin information may be information indicating sweep points of a test parameter matching a section in which a comparison result generated by performing a sweep test using a test parameter corresponds to the pass Pass. For example, the first margin information M 1  may be information indicating a 2 nd  sweep point through a 10 th  sweep point of the first test parameter SP_ 1  matching the second through sixth comparison results 2 nd  RC-6 th  RC. 
     The second test result information TRI 2  may include 1 st  through 11 th  comparison results 1 st  RC-11 th  RC. The second through 11 th  comparison results 1 st  RC-6 th  RC may respectively match sweep points of the second test parameter SP_ 2 . For example, the first comparison result 1 st  RC may match a 10 th  sweep point of the second test parameter SP_ 2 , the second comparison result 2 nd  RC may match a 11 th  sweep point of the second test parameter SP_ 2 , the third comparison result 3 rd  RC may match a 12 th  sweep point of the second test parameter SP_ 2 , the ninth comparison result 9 th  RC may match a 18 th  sweep point of the second test parameter SP_ 2 , etc. The second test result information TRI 2  may include second margin information M 2  indicating a 12 th  sweep point through a 20 th  sweep point of the second test parameter SP_ 2 . 
     The third test result information TRI 3  may include the first through sixth comparison results 1 st  RC-11 th  RC. The first through sixth comparison results 1 st  RC-6 th  RC may respectively match sweep points of the third test parameter SP_ 3 . For example, the first comparison result 1 st RC may match a 20 th  sweep point of the third test parameter SP_ 3 , the second comparison result 2 nd  RC may match a 21 st  sweep point of the third test parameter SP_ 3 , the sixth comparison result 6 th  RC may match a 25 th  sweep point of the third test parameter SP_ 3 , etc. The third test result information TRI 3  may include third margin information M 3  indicating a 24 th  sweep point through a 25 th  sweep point of the third test parameter SP_ 3 . 
     The fourth test result information TRI 4  may include the first through sixth comparison results 1 st  RC-11 th  RC. The first through sixth comparison results 1 st  RC-6 th  RC may respectively match sweep points of the fourth test parameter SP_ 4 . For example, the first comparison result 1 st  RC may match a 10 th  sweep point of the fourth test parameter SP_ 4 , the second comparison result 2 nd  RC may match a 11 th  sweep point of the fourth test parameter SP_ 4 , the sixth comparison result 6 th  RC may match a 15 th  sweep point of the fourth test parameter SP_ 4 , etc. The fourth test result information TRI 4  may not include fourth margin information M 4  since all the first through sixth comparison results 1 st  RC-6 th  RC fail Fail. 
     According to an exemplary embodiment, the parameter sweep control unit  115  of  FIG. 1  may receive the first through fourth test result information TRI 1 -TRI 4  and may reset a sweep range of the fourth test parameter SP 4  based on the first through fourth test result information TRI 1 -TRI 4 . For example, the parameter sweep control unit  115  may reset a sweep start point of the fourth test parameter SP 4  as 16 and a sweep end point thereof as 21. The BIST control logic  110  may re-perform the fourth test loop Loop 4  by using the fourth test parameter SP_ 4  based on the reset sweep range, thereby generating the fourth test result information TRI 4  including the fourth margin information M 4 . 
       FIG. 5B  is a diagram for generating a data format indicating test correlations between test parameters by using a plurality of pieces of test result information according to another exemplary embodiment. The test result storing unit  140  of  FIG. 1  may generate the data format indicating the test correlations between the test parameters based on the plurality of pieces of test result information. According to this exemplary embodiment, the data format may correspond to a Shmoo data format. 
     Referring to  FIG. 5B , a test correlation between the first test parameter SP_ 1  and the second test parameter SP_ 2  is illustrated. In some embodiments, the first test parameter SP_ 1  and the second test parameter SP_ 2  may refer to different types of measurements. For example, the first test parameter SP_ 1  may refer to temperature measurements and the second test parameter SP_ 2  may refer to voltage measurements when the memory core MC is being tested. In some embodiments, the first test parameter SP_ 1  and the second test parameter SP_ 2  may refer to different values of same type of measurement. For example, as discussed above, a test parameter refers to an operation timing parameter of the memory core MC when the memory core MC is being tested. Thus, the first test parameter SP_ 1  may refer to a first operation timing of the memory core MC when the memory core MC is being tested and the second test parameter SP_ 2  may refer to a second operation timing of the memory core MC when the memory core MC is being tested. A sweep range of the first test parameter SP_ 1  may be set as X 1 -X 4 . A sweep range of the second test parameter SP_ 2  may be set as Y 1 -Y 4 . The test result storing unit  140  of  FIG. 1  may generate a data format indicating the test correlation between the first test parameter SP_ 1  and the second test parameter SP_ 2  based on first test result information generated by performing a first test loop using the first test parameter SP_ 1  and second test result information generated by performing a second test loop using the second test parameter SP_ 2 . Accordingly, a test comparison result may be determined according to a sweep point of the first test parameter SP_ 1  and a sweep point of the second test parameter SP_ 2 . Furthermore, the BIST control logic  110  of  FIG. 1  may receive a data format indicating test correlations from the test result storing unit  140 , may divide a fail area FA and a pass area PA through the data format, and may discover sweep points of ideal test parameters during a sweep test. 
       FIG. 6  is a block diagram of a test result storing unit (e.g., a test result storing circuit)  300  according to an exemplary embodiment. 
     As shown in  FIG. 6 , the test result storing unit  300  may include a test result matching unit (e.g., a test result matching circuit)  310 , a first monitoring unit (e.g., a first monitoring circuit)  320 , and a second monitoring unit (e.g., a second monitoring circuit)  330 . The test result storing unit  300  may receive the test condition information TCI from a BIST control logic BIST_CL and may receive a comparing result from a comparing unit (e.g., a comparing circuit) COMP. The test condition information TCI may include related information such as a test parameter selected as a sweep target, a sweep range of each test parameter, a sweep test progress status, etc. 
     The first monitoring unit  320  may include a monitoring line connected to a BIST interface BIST_IF to provide the test condition information TCI received from the BIST control logic BIST_CL to the BIST interface BIST_IF in real time. The second monitoring unit  330  may include a monitoring line connected to the comparing unit COMP to provide the comparison result CR received from the comparing unit COMP to the BIST interface BIST_IF in real time. The test result storing unit  300  may provide the test condition information TCI and the comparison result CR to the outside (a memory controller, a processor, etc.) in real time through the BIST interface BIST_IF. 
     The test result matching unit  310  may match the test condition information TCI and the comparison result CR to generate test result information. For example, the test result matching unit  310  may match the comparison results CR generated by performing an nth test loop and sweep points of the nth test parameter included in the test condition information TCI to generate nth test result information. The test result matching unit  310  may store the test result information generated by matching the test condition information TCI and the comparison result CR in the test result storing unit  300  and may provide the test result information to the BIST interface BIST_IF. The test result storing unit  300  may provide the test result information to the outside (e.g., to a memory controller, a processor, etc.) through the BIST interface BIST_IF. 
       FIG. 7  is a block diagram of a BIST circuit  400  according to another exemplary embodiment. 
     As shown in  FIG. 7 , the BIST circuit  400  may correspond to the BIST circuit  100  of  FIG. 1 , except that the BIST circuit  400  further includes a tuning control unit (e.g., a tuning control circuit)  450 . The tuning control unit  450  included in the BIST circuit  400  will now be described below. 
     The tuning control unit  450  may receive the plurality of pieces of test result information TRI from a test result storing unit  40 . The tuning control unit  450  may provide a tuning control signal Tune_CS to the memory core MC based on the plurality of pieces of test result information TRI and may tune a memory characteristic of the memory core MC. The memory characteristic may include an operating timing characteristic of the memory core MC, input and output characteristics, and a voltage characteristic of the memory core MC. The tuning control unit  450  may tune at least one of the operating timing characteristic of the memory core MC, the input and output characteristics, and the voltage characteristic of the memory core MC. However, for convenience of description, the tuning control signal Tune_CS is provided to the memory core MC but the inventive concept is not limited thereto. The tuning control signal Tune_CS may be provided to a control logic capable of tuning the memory characteristic or a fuse area including a plurality of fuses, etc. 
     Methods of tuning the memory characteristic of the memory core MC will now be described below. According to an exemplary embodiment, a memory device including the BIST circuit  400  and the memory core MC may further include the fuse area including the plurality of fuses determining the memory characteristic of the memory core MC or a control logic capable of setting a mode register set. The tuning control unit  450  may select and self-fuse some fuses of the fuse area, thereby tuning the memory characteristic of the memory core MC. The tuning control unit  450  may set the mode register set corresponding to the memory characteristic of the memory core MC in the control logic to allow the memory core MC to operate based on the mode register set, thereby tuning the memory characteristic of the memory core MC. 
     Therefore, the BIST circuit  400  may not only test an operation of the memory core MC but also efficiently tune the memory characteristic of the memory core MC based on a test parameter corresponding to each test result. 
       FIG. 8  is a block diagram of a tuning control unit  500  according to an exemplary embodiment. 
     As shown in  FIG. 8 , the tuning control unit  500  may include a memory parameter tuning unit  510 , a memory input and output characteristic tuning unit  530 , a memory voltage characteristic tuning unit  550 , and a tuning target selecting unit  570 . 
     The memory parameter tuning unit  510  may tune an operating timing parameter of the memory core MC of  FIG. 7  based on test result information. When the memory core MC is DRAM, the operating timing parameter may correspond to one of tRC (Row cycle time), tRAS (Row active time), tRP (Row precharge time), tRRD (Row active to Row active delay), tRCD (/RAS to /CAS delay), tCK (test Clock), VRef (Voltage Reference), Temp (Temperature), etc. According to an embodiment, the memory parameter tuning unit  510  may tune points of the operating timing parameter of the memory core MC of  FIG. 7  in the same way as points of a test parameter when all comparison results pass based on the test result information. 
     The memory input and output characteristic tuning unit  530  may tune a size of an input and output driver of the memory core MC of  FIG. 7  based on the test result information or may tune a level of a reference voltage provided to the memory core MC based on the test result information, thereby tuning the input and output characteristics of the memory core MC. The memory voltage characteristic tuning unit  550  may tune a level of an external voltage applied to the memory device including the memory core MC based on the test result information, thereby tuning voltage characteristic of the memory core MC. However, this is an exemplary embodiment and the inventive concept is not limited thereto. The tuning control unit  500  may tune the memory characteristic of the memory core MC in various ways. 
     The tuning target selecting unit  570  may select a method of tuning the memory characteristic of the memory core MC. The tuning target selecting unit  570  may select at least one of the memory parameter tuning unit  510 , the memory input and output characteristic tuning unit  530 , and the memory voltage characteristic tuning unit  550  to tune the memory characteristic of the memory core MC. 
       FIG. 9  is a block diagram of a memory system  1000  according to an exemplary embodiment. 
     As shown in  FIG. 9 , the memory system  1000  may include a memory controller  1100  and a memory device  1200 . The memory device  1200  may include a BIST circuit  1210  and a memory core  1280 . The BIST circuit  1210  may include a BIST interface  1211 , a BIST control logic  1212 , a test pattern generating unit  1213 , a comparing unit  1214 , and a test result storing unit  1215 . As described above, the BIST circuit  1210  may perform a sweep test on the memory core  1280 . A plurality of pieces of test result information generated by performing the sweep test may be provided to the memory controller  1100  through the BIST interface  1211 . According to an embodiment, the BIST interface  1211  may be a general interface interfacing with a processor and may be configured as a standard interface such as the JTAG (Joint Test Action Group), IEEE 1500, etc. 
     The memory controller  1100  may include a tuning control unit  1150 . The tuning control unit  1150  may correspond to the tuning control unit  450  of  FIG. 7  or the tuning control unit  500  of  FIG. 8 . The tuning control unit  1150  may provide the tuning control signal Tune_CS to the memory core  1280  based on the plurality of pieces of test result information and may tune a memory characteristic of the memory core  1280 . However, this is an exemplary embodiment. The tuning control unit  1150  may be a separate device that is not included in the memory controller  1100  and is controlled by the memory controller  1100 . In this case, the memory controller  1100  may control the tuning control unit  1150  based on the plurality of pieces of test result information received from the BIST circuit  1210  to tune the memory characteristic of the memory core  1280 . The memory characteristic of the memory core  1280  may be tuned according to various embodiments in which the memory characteristic of the memory core  1280  is tuned through the BIST interface  1211 . 
     Methods of tuning the memory characteristic of the memory core  1280  will now be described below. According to an exemplary embodiment, the memory device  1200  may further include a fuse area including a plurality of fuses determining the memory characteristic of the memory core  1280  or a control logic capable of setting a mode register set. Under control of the memory controller  1100 , the tuning control unit  1150  may select and self-fuse some fuses of the fuse area, thereby tuning the memory characteristic of the memory core  1280 . The tuning control unit  1150  may set the mode register set corresponding to the memory characteristic of the memory core  1280  in the control logic to allow the memory core  1280  to operate based on the mode register set, thereby tuning the memory characteristic of the memory core  1280 . 
       FIGS. 10A and 10B  are diagrams of a stack memory device  2000   a  according to another exemplary embodiment. 
     As shown in  FIG. 10A , the stack memory device  2000   a  may include a system chip  2400   a  stacked on a substrate  2500   a  and a plurality of memory chips  2300   a  stacked on the system chip  2400   a . According to an embodiment, the plurality of memory chips  2300   a  may include a first memory chip  2310   a , a second memory chip  2320   a , and a third memory chip  2330   a . However, this is an exemplary embodiment and the inventive concept is not limited thereto. Various numbers of stacked memory chips may be included in the stack memory device  2000   a . The system chip  2400   a  may provide various commands, addresses, and data signals to each of the memory chips  2310   a - 2330   a  through a plurality of through silicon vias (TSVs) to control each of the memory chips  2310   a - 2330   a.    
     The system chip  2400   a  may include a memory controller  2420   a  and a BIST circuit  2410   a . The memory controller  2420   a  may enable the BIST circuit  2410   a  to perform a sweep test on the plurality of memory chips  2300   a . According to an exemplary embodiment, the BIST circuit  2410   a  may perform the sweep test on the first through third memory chips  2310   a - 2330   a . Accordingly, the BIST circuit  2410   a  may generate test result information of each of the first through third memory chips  2310   a - 2330   a . The BIST circuit  2410   a  may tune a memory characteristic of the first memory chip  2310   a  based on the test result information of the first memory chip  2310   a , tune a memory characteristic of the second memory chip  2320   a  based on the test result information of the second memory chip  2320   a , and tune a memory characteristic of the third memory chip  2330   a  based on the test result information of the third memory chip  2330   a.    
     According to an exemplary embodiment, the BIST circuit  2410   a  may tune at least one of an operating timing parameter of each of the first through third memory chips  2310   a - 2330   a , input and output characteristics thereof, and a voltage characteristic thereof based on the plurality of pieces of test result information in order to tune the memory characteristic of each of the first through third memory chips  2310   a - 2330   a . The BIST circuit  2410   a  may tune the memory characteristic of each of the first through third memory chips  2310   a - 2330   a  based on the test result information of each of the first through third memory chips  2310   a - 2330   a . According to an exemplary embodiment, the BIST circuit  2410   a  may detect an operating status deterioration degree of each of the plurality of memory chips  2300   a . For example, the BIST circuit  2410   a  may detect a memory chip (hereinafter referred to as the first memory chip  2310   a ) having a most deteriorated operating status from among the first through third memory chips  2310   a - 2330   a . The BIST circuit  2410   a  may tune the memory characteristic of the detected first memory chip  2310   a  based on the test result information of each of the first through third memory chips  2310   a - 2330   a  and may tune the memory characteristics of the second and third memory chips  2320   a  and  2330   a  in the same way as the memory characteristic of the detected first memory chip  2310   a.    
     Furthermore, the BIST circuit  2410   a  may select at least one of the plurality of memory chips  2300   a  and may perform a sweep test only on the selected memory chip. According to an embodiment, the BIST circuit  2410   a  may select the first memory chip  2310   a  most adjacent to the substrate  2500   a  and may perform the sweep test on the first memory chip  2310   a . The BIST circuit  2410   a  may generate the test result information of the first memory chip  2310   a  and may tune the memory characteristics of the second and third memory chips  2320   a  and  2330   a  in the same way as the memory characteristics of the first through third memory chips  2310   a - 2330   a  based on the test result information of the first memory chip  2310   a.    
     However, this is an exemplary embodiment. As described above, the memory controller  2420   a  may receive the test result information from the BIST circuit  2410   a  and may tune the memory characteristic of each of the plurality of memory chips  2300   a . In addition, various methods may be applied. 
     As shown in  FIG. 10B , the stack memory device  2300   b  may include a system chip  2400   b  and a plurality of memory chips  2300   b . Unlike  FIG. 10A , the system chip  2400   b  and the plurality of memory chips  2300   b  may be separately stacked on the substrate  2500   b . However, operations of elements are the same as described above, and thus detailed descriptions thereof are omitted. 
       FIG. 11  is a flowchart for describing a method of operating a BIST circuit according to an exemplary embodiment. 
     Referring to  FIG. 11 , the BIST circuit may set a sweep range of each of a plurality of test parameters (operation S 110 ). The BIST circuit may individually sweep each of the plurality of test parameters based on the set sweep range and may generate test patterns (operation S 120 ). The BIST circuit may test a memory core by using the test patterns to generate a plurality of pieces of test result information (operation S 130 ). The BIST circuit may provide the plurality of pieces of test result information to a memory controller, a processor, etc. through a BIST interface. 
       FIG. 12  is a detailed flowchart for describing a method of operating a BIST circuit according to another exemplary embodiment. 
     Referring to  FIG. 12 , the BIST circuit may generate a test pattern at a kth sweep point of an nth test parameter (operation S 210 ). The BIST circuit may provide the test pattern to a memory core and may receive output data corresponding to the test pattern from the memory core (operation S 220 ). The BIST circuit may perform a test of comparing the output data and reference data and may generate a comparison result (operation S 230 ). The BIST circuit may determine whether the kth sweep point is a sweep end point (operation S 240 ). When the kth sweep point is not the sweep end point (operation S 240 , NO), the BIST circuit may perform operations S 210  through S 230  by using the nth test parameter having a k+1th test point next to the kth sweep point. When the kth sweep point is the sweep end point (operation S 240 , YES), the BIST circuit may determine whether the nth test parameter is a last test parameter on which the sweep test is performed (operation S 250 ). When the nth test parameter is not the last test parameter (operation S 250 , NO), the BIST circuit may perform operations S 210  through S 240  by using an n+1th test parameter next to the nth test parameter. When the nth test parameter is the last test parameter (operation S 250 , YES), the BIST circuit may generate and store a plurality of pieces of test result information by using generated comparison results (operation S 260 ). The BIST circuit may tune a memory characteristic of the memory core based on the plurality of pieces of test result information (operation S 270 ). 
       FIG. 13  is a flowchart for describing a method of operating a BIST circuit relating to a stack memory device according to an exemplary embodiment. 
     The BIST circuit may select at least one memory chips that are sweep test targets from among a plurality of memory chips of the stack memory device (operation S 310 ). The BIST circuit may perform a sweep test on the selected memory chip to generate test result information (operation S 320 ). The BIST circuit may tune a memory characteristic of each of the plurality of memory chips based on the test result information (operation S 320 ). Furthermore, the BIST circuit may tune the memory characteristic of each of the plurality of memory chips in the same way. 
       FIG. 14  is a diagram of a memory card  3000  according to an embodiment. 
     Referring to  FIG. 14 , the memory card  3000  may be a portable storage device that may be used by being connected to an electronic device such as mobile device or a desk top computer. As shown in  FIG. 14 , the memory card  3000  may include a memory controller  3100 , a memory device  3200 , and a port area  3300 . 
     The memory card  3000  may communicate with an external host (not shown) through the port area  3300 . The memory controller  3100  may control the memory device  3200 . The memory controller  3100  may read and execute a program from a ROM (not shown) storing the program. The memory device  3200  may include the BIST circuit described with reference to  FIGS. 1 through 13  and may perform a sweep test on a memory core of the memory device  3200  or memory chips thereof. 
       FIG. 15  is a block diagram of a computing system  4000  including a storage system  4500  according to an exemplary embodiment. 
     Referring to  FIG. 15 , the computing system  4000  may be a mobile device or a desk top computer and may include a host  4100  including a CPU, etc., a RAM  4200 , a user interface  4300 , and a device driver  4400 . These elements may be electrically connected to a bus  4600 . The storage system  4500  may be connected to the device driver  4400 . 
     The host  4100  may control the computing system  4000  and may perform an arithmetic operation corresponding to a user command that is input through the user interface  4300 . The RAM  4200  may function as a data memory of the host  4100 . The host  4100  may record or read user data to or from the storage system  4500  through the device driver  4400 . The memory device included in the storage system  4500  may include the BIST circuit described with reference to  FIGS. 1 through 13  and may perform a sweep test on a memory core of the memory device or memory chips thereof. 
     While the inventive concept has been particularly shown and described with reference to embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.