Abstract:
In integrated circuit chips that are used for RFID, a method of calibrating an operation frequency that is generated in an operation frequency generator and a semiconductor wafer including a calibration circuit are provided. The method of calibrating an operation frequency of integrated circuit chips includes: supplying DC power to the integrated circuit chips; selecting an integrated circuit chip to perform calibration of an operation frequency; receiving an operation frequency that is generated in the selected integrated circuit chip; calculating a difference between a phase of the operation frequency and a phase of a calibration target frequency; generating a frequency calibration value of the operation frequency using the phase difference; transmitting a control signal including the frequency calibration value to the integrated circuit chip; and releasing a selection of the integrated circuit chip in which calibration of the operation frequency is complete.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0042305 filed in the Korean Intellectual Property Office on Apr. 23, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a method of auto-calibrating integrated circuit chips at a wafer level. More particularly, the present invention relates to a method of auto-calibrating integrated circuit chips in order to uniformly improve performance of integrated circuit chips that are used for radio frequency identification (referred to as an ‘RFID’) or an ubiquitous sensor network (referred to as an ‘USN’) at a wafer level using a phase-locked loop (PLL). 
     (b) Description of the Related Art 
     In general, RFID is technology that stores information at a tag that is formed in a form of integrated circuit chips or reads the stored information from the tag using a radio frequency. RFID technology may be used for identification, tracing, and management of vehicles, physical distribution, or animals according to a band of a radio frequency, or may be used for a traffic card. In this way, in order to apply RFID technology to a wide field, mass production technology of super-cheap tag chips is requested. For mass production of super-cheap tag chips, in a process of designing integrated circuit chips, an area of the chips should be minimized, and by decreasing an inferiority rate through performance calibration, a production cost should be lowered and a production time of the integrated circuit chips should be shortened. 
     In general, a chip that is formed with only a digital logic circuit is less influenced by a process change, but a radio frequency (RF)/analog chip including many passive elements is influenced by a process change and thus the radio frequency (RF)/analog chip does not have completely uniform performance. Particularly, in tag chips that are used for RFID, in an operation frequency generation circuit using a capacitor element or in a bias circuit using a resistor element, a failure occurrence probability is high. This is because many passive elements are included in the circuits, and a characteristic value of a resistor and a capacitor constituting the circuit may be changed by 10% or more according to a wafer. 
     Conventionally, in order to calibrate a performance change according to such a process change, laser trimming technology has been used, or a separate calibration circuit was added at the inside of integrated circuit chips. However, in laser trimming technology, time is additionally consumed, and when a calibration circuit is added, there is a drawback that an area of a chip increases and thus it is difficult to apply the above technology for mass production of super-cheap tag chips. 
     Further, at a wafer level, a method of testing an RFID tag chip with an on-wafer or a method of calibrating performance of a tag using a one-time programmable memory was suggested. However, the method of testing an RFID tag chip with an on-wafer is a method of verifying only whether a tag chip is defective, and in the method of calibrating performance of a tag using a one-time programmable memory, a relatively large amount of time is consumed in performance calibration of an individual tag chip and thus there is a problem that the production cost of the tag increases. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a method of auto-calibrating integrated circuit chips at a wafer level having advantages of rapidly calibrating performance of integrated circuit chips at a wafer level. In general, when adjusting performance of a circuit that outputs a digital value, performance of a plurality of integrated circuit chips can be rapidly calibrated, and an inferiority rate can be reduced. Therefore, by calibrating a frequency that is generated in an operation frequency generator that outputs a digital value rather than calibrating performance of a bias circuit that outputs an analog value, it is reasonable to calibrate the performance of all the integrated circuit chips. The present invention has been made in an effort to further provide a method of auto-calibrating integrated circuit chips at a wafer level having advantages of auto-calibrating an operation frequency of integrated circuit chips at a wafer level using a PLL. 
     An exemplary embodiment of the present invention provides a method of calibrating an operation frequency of integrated circuit chips. The method includes: supplying DC power to the integrated circuit chips; selecting an integrated circuit chip to perform calibration of an operation frequency; receiving an operation frequency that is generated in the selected integrated circuit chip; calculating a difference between a phase of the operation frequency and a phase of a calibration target frequency; generating a frequency calibration value of the operation frequency using the phase difference; transmitting a control signal including the frequency calibration value to the integrated circuit chip; and releasing a selection of the integrated circuit chip in which calibration of the operation frequency is complete. 
     The method may further include, after the transmitting of a control signal, calibrating the operation frequency according to the frequency calibration value that is included in the control signal, and storing the frequency calibration value at the integrated circuit chip according to the control signal. 
     Another embodiment of the present invention provides a semiconductor wafer for auto-calibrating an operation frequency of integrated circuit chips. The semiconductor wafer includes: an integrated circuit chip area; a probe area in which a calibration controller of an operation frequency is connected to the outside of the semiconductor wafer; a signal transmitting area that is connected to the probe area to transmit a signal of the integrated circuit chips to the calibration controller; and a buffer that relays a signal that is exchanged between the integrated circuit chips and the signal transmitting area. 
     The signal transmitting area may include: a chip selection bus that transmits a selection signal of the calibration controller for an integrated circuit chip to perform calibration of the operation frequency and a selection release signal for the integrated circuit chip in which calibration of the operation frequency is complete; an external power line that transmits DC power that is supplied to the integrated circuit chip; a frequency measurement line that transmits an operation frequency that is generated in the integrated circuit chip; and a calibration bus that transmits a control signal for calibrating the operation frequency, wherein the chip selection bus, the external power line, the frequency measurement line, and the calibration bus may be connected to the probe area. 
     The buffer may be positioned at an end portion of the chip selection bus and operate according to a selection signal and a selection release signal of the calibration controller, and when the buffer operates, a connection between the integrated circuit chip, the external power line, the frequency measurement line, and the calibration bus may be activated. 
     Yet another embodiment of the present invention provides a calibration controller for auto-calibrating an operation frequency of integrated circuit chips. The calibration controller generates an operation frequency calibration value using the phase difference, and includes a phase-locked loop that calculates a phase difference by comparing a phase of a calibration target frequency and a phase of the operation frequency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a tag chip auto-calibration system of a wafer level according to an exemplary embodiment of the present invention. 
         FIG. 2  is a diagram illustrating a semiconductor wafer according to an exemplary embodiment of the present invention. 
         FIG. 3  is a flowchart illustrating a method of auto-calibrating tag chips at a wafer level according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
     In addition, in the entire specification and claims, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     Hereinafter, a method of auto-calibrating integrated circuit chips of a wafer level according to an exemplary embodiment of the present invention will be described in detail with reference to the drawings. For convenience of description, tag chips as an example of an integrated circuit chip will be described. 
       FIG. 1  is a diagram illustrating a tag chip auto-calibration system of a wafer level according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , a tag chip auto-calibration system of a wafer level according to an exemplary embodiment of the present invention includes a calibration controller  100 , a probe pin  120 , and a semiconductor wafer including a plurality of tag chips  200 , buffers  210 , a signal transmitting area  220 , a plurality of signal lines  230 , and a probe area  240 . 
     The calibration controller  100  includes a PLL  110 , and electrically connects the semiconductor wafer and the calibration controller  100  by enabling the probe pin  120  to contact the probe area  240 , thereby performing frequency calibration of the tag chip  200 . 
     The probe pin  120  is connected to the calibration controller  100  that is positioned at the outside of the semiconductor wafer to contact the probe area  240  of the semiconductor wafer. 
     The plurality of tag chips  200  are integrated circuit chips that are formed on the semiconductor wafer. The plurality of tag chips  200  are each divided by a scribe line, and after a frequency calibration process according to an exemplary embodiment of the present invention is performed, the plurality of tag chips  200  are cut out along the scribe line to perform a function as a single chip. 
     The buffer  210  relays a signal that is exchanged between the tag chip  200  and the signal transmitting area  220 . When a specific tag chip  200  to perform a calibration process through the buffer  210  is selected, and when the buffer  210  operates, a signal exchange between the calibration controller  100  and the tag chip  200  may be performed. Further, the buffer  210  buffers a signal between the probe area  240  and the tag chip  200 . 
     The signal transmitting area  220  is formed in a scribe area within the semiconductor wafer and includes a plurality of signal lines  230 . 
     The buffer  210 , the signal transmitting area  220 , and the probe area  240  are included in a scribe area that is formed between the tag chips  200  and may be removed after the tag chips  200  are cut out. 
       FIG. 2  is a diagram illustrating a semiconductor wafer according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the signal transmitting area  220  that is formed in a scribe area includes a chip selection bus  231 , an external power line  232 , a frequency measurement line  233 , and a calibration bus  234 , while the tag chip  200  includes an analog part  250 , a digital part  260 , and a memory part  270 , and the buffer  210  is positioned between the tag chip  200  and the signal transmitting area  220 . 
     The analog part  250  of the tag chip  200  includes a voltage multiplier  251  and an operation frequency generator  252 , the digital part  260  includes a frequency regulator  261 , and the memory part  270  includes a user memory  271 . The voltage multiplier  251  performs a function of supplying DC power to the tag chip  200 , and in an exemplary embodiment of the present invention, calibration controller  100  distributes DC power that is supplied through the external power line  232  to each constituent element of the tag chip  200 , instead of the voltage multiplier  251 . 
     The operation frequency generator  252  generates an operation frequency necessary for operation of the tag chip  200 , and an operation frequency that is generated in the operation frequency generator  252  is transferred to the calibration controller  100  through the frequency measurement line  233  and is automatically calibrated according to an exemplary embodiment of the present invention. 
     The frequency regulator  261  is connected to the calibration bus  234  to receive a control signal for calibrating an operation frequency from the calibration controller  100 . Thereafter, the frequency regulator  261  reflects calibration contents of an operation frequency to the operation frequency generator  252  and stores a frequency value of the calibrated operation frequency at the user memory  271 . The user memory  271  is an area that is separately assigned in order to store a frequency value of an operation frequency and is included in a common memory part  270  of the tag chip  200 . 
     Hereinafter, an operation process of constituent elements of a system according to an exemplary embodiment of the present invention that is shown in  FIGS. 1 and 2  will be described with reference to  FIG. 3 . 
       FIG. 3  is a flowchart illustrating a method of auto-calibrating tag chips at a wafer level according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , when the calibration controller  100  selects the tag chip  200  to perform frequency calibration (S 10 ), an auto-calibration process of the tag chip  200  is started. A selection signal of the tag chip  200  that is transmitted by the calibration controller  100  is transmitted to the buffer  210  through the chip selection bus  231  (S 11 ), and thus the buffer  210  operates (S 12 ). 
     As the buffer  210  operates, a connection between the tag chip  200  and the external power line  232 , the frequency measurement line  233 , and the calibration bus  234  is activated and thus signals of the calibration controller  100  and the tag chip  200  can be exchanged. 
     Thereafter, the calibration controller  100  supplies DC power (S 13 ), and the calibration controller  100  transfers the DC power to each constituent element of the tag chip  200  through the external power line  232  (S 14 ) and thus the tag chip  200  operates (S 15 ). 
     In this case, as shown in  FIG. 3 , DC power may be supplied through the calibration controller  100 , but separate DC power may be directly supplied from the outside of a wafer. In this case, until a calibration process of all tag chips  200  is terminated, DC power may be continuously supplied to the semiconductor wafer, and power supply to each tag chip  200  may be determined according to whether the buffer  210  operates. 
     Thereafter, the operation frequency generator  252  generates an operation frequency (S 16 ), and the generated operation frequency is transferred to the calibration controller  100  through the frequency measurement line  233  (S 17 ). 
     The calibration controller  100  analyzes the received operation frequency and generates a frequency calibration value (S 18 ). 
     In more detail, the PLL  110  that is included in the calibration controller  100  compares a phase of the input calibration target frequency and a phase of the transmitted operation frequency. Thereafter, by reflecting a phase difference between the calibration target frequency and the operation frequency, the calibration controller  100  generates a frequency calibration value. 
     Further, the calibration controller  100  repeatedly performs a frequency calibration process, and when data are accumulated, the calibration controller  100  generates a calibration value appropriate for each wafer with reference to the data. 
     Thereafter, the calibration controller  100  includes a frequency calibration value that is generated by the above method in a control signal for calibrating a frequency, and transfers the control signal to the frequency regulator  261  through the calibration bus  234  (S 19  and S 20 ). 
     The frequency regulator  261 , having received the control signal for calibrating a frequency, stores a frequency calibration value according to the control signal at the user memory  271 , and changes an operation frequency that is generated by adjusting the operation frequency generator  252  according to the frequency calibration value (S 21 ). 
     Thereafter, the calibration controller  100  transfers a selection release signal of the tag chip  200  (S 22 ) and transfers the selection release signal to the buffer  210  through the chip selection bus  231  (S 23 ), and thus the buffer  210  terminates operation (S 24 ). 
     Finally, when operation of the buffer  210  is terminated, power that is supplied from the external power line  232  is intercepted and thus the tag chip  200  terminates operation (S 25 ). 
     However, after step S 22  is performed, power is no longer supplied to the tag chip  200 , and thus the tag chip  200  may not calibrate an operation frequency and store a frequency calibration value, and thus the calibration controller  100  transmits a control signal, when a random time has elapsed, and step S 22  may be performed. 
     Further, although not shown in  FIG. 3 , as the frequency regulator  261  performs a calibration/storage step of a frequency and transmits a completion message of the step to the calibration controller  100 , the tag chip selection release step S 22  of the calibration controller  100  may be performed. 
     According to an exemplary embodiment of the present invention, when performance of integrated circuit chips is calibrated at a wafer level, DC power is directly transmitted to the integrated circuit chips and thus a calibration operation can be performed more simply and efficiently than a case of receiving induction power. Further, by calibrating performance of an operation frequency generator that is sensitive to a production process change, calibration can be quickly performed, and thus a cost reduction effect can be obtained. 
     According to another exemplary embodiment of the present invention, by including a circuit for performing a calibration operation in a scribe area of a semiconductor wafer, a semiconductor wafer can be manufactured regardless of a yield of an integrated circuit chip, and by including a buffer to the circuit, an integrated circuit chip to calibrate can be easily selected, and by buffering a signal, even if a signal line is extended, calibration can be smoothly performed. 
     According to another exemplary embodiment of the present invention, by comparing and detecting a phase difference between a calibration target frequency and a frequency that is generated in an operation frequency generator using a calibration controller including a PLL, a frequency calibration value can be generated. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.