Abstract:
The present invention relates to a fuse option circuit of an integrated circuit and a method thereof. More particularly it concerns a fuse option circuit comprising: a first fuse formed on a chip, which is cut by providing a larger electric current than a set value; a second fuse formed on the chip identically with the first fuse; a fuse cutting means providing a cutting current loop to the first fuse in response to a fuse cutting signal; and an option signal generating means which produces a fuse option signal by comparing resistance values of the first and second fuses. Accordingly, even if the first use is abnormally cut, the fuse option can be precisely provided by comparing the first fuse having a changed resistance after cutting process with the second fuse keeping an initial resistance value. Therefore, the reliability of a fuse option of an integrated circuit can be improved.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fuse option circuit of an integrated circuit and a method thereof. More particularly, it concerns a fuse option circuit for detecting precisely if a fuse is cut or not through comparing resistance values of a cut fuse and a fuse kept without a cutting process which are formed on a chip of an integrated circuit, in order to generate more reliable fuse option signaling. 
     DESCRIPTION OF THE PRIOR ART 
     IC products of a semiconductor use an option operating method in order to change an operational mode of a device, product or system. This conventional method is divided into a bonding option, a metal option or a fuse option Particularly, a fuse option is widely used as a repairing method for replacing an abnormal memory cell, generated during manufacturing process of a semiconductor device, with a normal memory cell. A fuse option is divided to a laser cutting method and electrical cutting method. A laser-cutting method is to radiate a laser beam to cut a fuse, as shown in FIG.  1 A. An electrical cutting method is to charge an excessive electric current in order to cut a fuse, as shown in FIG.  1 B. 
     An electrical cutting method doesn&#39;t have to use a special cutting device for conventing a mode and repairing a memory cell, and its algorithm is very simple. Also, this method can convert a mode and repair a memory cell at the same time of test, and has an advantage that it can be also used at a package level. But the electrical cutting method is not as precise as the laser cutting method. Accordingly, there is much probability of failure in the case of the electrical cutting method and there is a disadvantage that a fuse may be linked again after cutting. Thus, the electrical cut fuse option circuit has been unreliable as compared with the laser fuse option circuit. 
     FIG. 2 illustrates the conventional fuse option circuit using an electrical cutting method. The fuse option circuit includes a cutting circuit  10 , a fuse  12  and an output circuit of a fuse option signal  14 . When an enable signal(VCCH) is applied thereto, the fuse option circuit charges or flows the file  12  with a cutting current for a predetermined time so as to cat electrically the fuse  12 . Accordingly, an electric potential of a node N is changed from high level to low level by the fuse cutting in the output circuit of the fuse option signal  14 , and then this low state is latched to output a fuse option signal OUT of a high state. 
     In the conventional fuse option circuit, a non-zero fuse resistance produces an output error in case that a fuse is not cut normally, i.e. one that is cut imprecisely as shown in FIG. 1 b.  And even if an error is not made, an electric current flows through a fuse that is incompletely cut as shown in FIG. 1 b.  Accordingly, there is the added disadvantage in prior art fuse option circuits of consuming an excessive electric power. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to provide a reliable fuse option circuit of an integrated circuit and a method thereof through generating a precise fuse option signal by comparing resistance values of a fuse after cutting and a reference fuse in order to overcome disadvantages of the conventional technology. 
     Another aspect of the present invention is to provide a fuse option circuit and method thereof for reducing power consumption generated by a fuse that is incompletely cut. 
     According to the present invention, a circuit comprises: a first fuse, which is formed on a chip and cut when a larger electric current is charged thereto than a set value; a second fuse formed on the chip identically with the first fuse; a fuse cutting means which provides the first fuse with a current loop in response to a fuse cutting signal; and a fuse option signal generating means which produces a fuse option signal, comparing resistance values of the first fuse and the second fuse. It is preferred that the option signal generating means is one chosen from among a CMOS inverter, a latch circuit composed of a CMOS inverter, a differential amplifier, a latch amplifier or a sense amplifier. 
     A fuse option method according to the present invention comprises the following steps of: arranging a first and second fuses on a chip; cutting the first fuse through charging a cutting current thereto; comparing resistance values of the first and the second fuses; and generating a fuse option signal in response to a result of comparing the resistance values. 
    
    
     BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS 
     FIG. 1 illustrates a state of cutting in the conventional electrical fuse. 
     FIG. 2 is a circuit diagram of the conventional fuse option circuit. 
     FIG. 3 is a circuit diagram of a fuse option circuit according to a first embodiment of the present invention. 
     FIG. 4 is a circuit diagram of a fuse option circuit according to a second embodiment of the present invention. 
     FIG. 5 is a circuit diagram of a fuse option circuit according to a third embodiment of the present invention. 
     FIG. 6 is a circuit diagram of a fuse option circuit according to a fourth embodiment of the present invention. 
     FIG. 7 is a circuit diagram of a fuse option circuit according to a fifth embodiment of the present invention. 
     FIG. 8 is a circuit diagram of a fuse option circuit according to a sixth embodiment of the present invention. 
     FIG. 9 is a circuit diagram of a fuse option circuit according to a seventh embodiment of the present invention. 
     FIG. 10 is a circuit diagram of a fuse option circuit according to a eighth embodiment of the present invention. 
    
    
     Further objects and advantages of the invention can be more fully understood from the following embodiments taken in conjunction with the accompanying drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 is a circuit diagram of a fuse option circuit according to tie first embodiment of the present invention. 
     According to the first embodiment, a fuse option circuit comprises a first fuse F 1 , a second fuse F 2 , a fuse cutting means  20 , an option signal generating means  30  and an output means  40 . 
     The first and second fuses F 1 , F 2  are made of a polysilicon which is used for forming a bit line, a storage, a gate or a plate, or metal. 
     The first fuse F 1  is electrically cut by the fuse cutting means  20 . The second fuse F 2  is a reference fuse that maintains an initial resistance value before and after the cutting of fuse F 1 . The fuse cutting means  20  comprises MOS transistor NM 5 , that is a fifth switching means, whose drain is connected to one end of the first fuse and whose source is grounded. A fuse cutting signal (PCUT) is applied to its gate. 
     The option signal generating means  30  comprises a first through fourth switching means, i.e. MOS transistors (NM 1 -NM 4 ). 
     A first switching means is the MOS transistor NM 1  whose source and drain are connected respectively to the other end of the first fuse F 1  and a power supply voltage (VCC), while an enable signal (PEFE) is applied to its gate. 
     A second switching means is the MOS transistor NM 2  whose source and drain are connected respectively to the other end of the second fuse F 2  and the power supply voltage (VCC), while an enable signal (PEFE) is applied to its gate. 
     A third switching means is the MOS transistor NM 3  whose source and drain are connected respectively to one end of the first fuse F 1  and a ground voltage, while its gate is connected to a second node N 2 . 
     A fourth switching means is the MOS transistor NM 4  whose source and drain are connected respectively to one end of the second use F 2  and a ground voltage, while its gate is connected to a first node N 1 . The output means  40  is an inverter INV 1  for generating a fuse option signal (POUT) by inverting a signal of the second node N 2 . The current-driving ability of the MOS transistor NM 5  is much greater than those of the MOS transistors NM 3  and NM 4 , ad great enough to supply the first fuse F 1  with a sufficient cutting current. 
     Accordingly, in a high level wherein the enable signal (PEFE) is in an active state, the option signal generating means  30  is enabled. When the fuse cutting signal (PCUT) is in a high level and the option signal generating means  30  is enabled, the MOS transistor NM 5  is turned on to flow a cutting current through the first fuse F 1 . Consequently, the first fuse F 1  is cut. 
     When the first fuse F 1  is cut and the enable signal (PEFE) is in a high level of an active state, the second node N 2  is in a high state via application of a power supply voltage through the second fuse (F 2 ), which turns on MOS transistor NM 3 . In response to the high level gate input from node N 2 , NM 3  turns on and the first node N 1  goes low toward a ground voltage. Accordingly, the first node N 1  is latched as a low state, and the second node N 2  is latched as a high state. Therefore, a low signal is outputted as the fuse option signal (POUT) through the inverter INV 1 . 
     Even if the first fuse F 1  is not precisely cut, a resistance value of the first fuse F 1  is increased to some appreciable extent by the cutting process, as compared with a resistance value of the second fuse F 2 , which is identically formed but has not been cut at all. So, much more current is provided to the second node N 2  through the second fuse F 2  maintaining its initial higher resistance value so that the second node N 2  goes to a high voltage state more rapidly than the first node N 1 . Accordingly, the MOS transistor NM 3  is turned on prior to the MOS transistor NM 4 , and then the second node N 2  is latched as a high level. 
     That is, according to the first embodiment of the present invention, the fuse option signal (POUT) is precisely generated by the difference of the resistance values of two fuses (F 1 , F 2 ). 
     FIG. 4 is a circuit diagram of a fuse option circuit according to the second embodiment of the present invention. A circuit of the second embodiment comprises a first fuse F 1 , a second fuse F 2 , a fuse cutting means  20 , an option signal generating means  60  and an output means  40 . Accordingly, all of the components are identical with the first embodiment except the option signal generating means  60  and the output means  40 . 
     In the second embodiment, the option signal generating means  60  includes three MOS transistors (NM 3 , NM 4 , NM 16 ) and an inverter (INV 6 ). The MOS transistors NM 3  and NM 4  are connected to each other in the same latch configuration as in the first embodiment, and the MOS transistor NM 16  is connected between a common source and a ground of two transistors (NM 3 , NM 4 ). An enable signal (VCCH) is applied to a gate of the MOS transistor NM 16  through the inverter INV 6 . One end of each of the first and second fuses (F 1 , F 2 ) are commonly connected to power supply voltage (VCC). The output means  40  includes two inverters (INV 1 , INV 2 ) connected in a latch configuration. 
     Accordingly, the first fuse F 1  is cut by providing the first fuse F 1  with a cutting current in response to a high signal of the fuse cuting signal (PCUT). 
     In case that the first fuse F 1  is cut, the option signal generating means  60  is enabled in a low state of the enable signal (VCCH). And a low state of the first node N 1  is latched at the output means  40  to output the fuse option signal (POUT) as a high state. 
     FIG. 5 is a circuit diagram of a fuse option circuit according to the third embodiment of the present invention. All components are identical with the first embodiment except an output means  40  composed of a latch. Other same components appear with the same references without detailed description. 
     The output means  40  of the third embodiment further comprises an inverter INV 2  whose input end is connected to an output end of an inverter INV 1 , and whose output end is connected to an input end of the inverter INV 1 . 
     FIG. 6 is a circuit diagram of a fuse option circuit according to the fourth embodiment of the present invention. All components are identical with the first embodiment except an output means  40  composed of a differential amplifier  42 . Other same components appear with the same references without detailed description. 
     The differential amplifier  42  comprises two PMOS transistors (PM 1 , PM 2 ) and three NMOS transistors (NM 6 , NM 7 , NM 8 ), A gate of the MOS transistor NM 6  is connected with a first node N 1 , and a gate of the MOS transistor NM 7  is connected with a second node N 2 . And a gate of the MOS transistor NM 8  is connected with an enable signal (PEFE). Accordingly, in the differential amplifier  42 , an inverted output terminal N 3  is maintained in a low state by an electric potential difference between the first node N 1  and the second node N 2 . Therefore, a fuse option signal (POUT) is outputted as a low signal through the inverter INV 3  and the latch (INV 4 , INV 5 ). 
     FIG.  7  and FIG. 8 are circuit diagrams of a fuse option circuit according to the fifth and sixth embodiment of the present invention respectively. In the fifth and sixth embodiments, an option signal generating means  50  is an amplifier. 
     A circuit of the fifth embodiment comprises a first fuse F 1 , a second fuse F 2 , a fuse cutting means  20  and an option signal generating means  50 . The option signal generating means  50  comprises a first input means  52 , a second input means  54  and a differential amplifier  56 . The first input means  52  is a MOS transistor NM 9  whose gate and drain are connected to a first node N 1  and whose source is grounded. The second input means  54  is a MOS transistor NM 10  whose gate and drain are connected to a second node N 2  and whose source is grounded. The differential amplifier  56  includes two PMOS transistors (PM 3 , PM 4 ) and three NMOS transistors (NM 11 -NM 13 ). A gate of the MOS transistor NM 11  is connected with the first node N 1 , a gate of the MOS transistor NM 12  is connected with the second node N 2 . A gate of the MOS transistor NM 13  is connected with an enable signal (PEFE). 
     Accordingly, the differential amplifier outputs a fuse option signal (POUT) of a low state on an inverted output terminal by amplifying an electric potential difference between the first and second node. 
     All components of the sixth embodiment shown in FIG. 8 are identical with the first embodiment except the differential amplifier  58  is a latch amplifier. Other same components appear with the same references without detailed description. 
     The latch amplifier  58  includes two PMOS transistors (PM 3 , PM 4 ) and five NMOS transistors (NM 3 , NM 11 -NM 14 ). The MOS transistors (PM 3 , NM 13 ) and the MOS transistors (PM 4 , NM 14 ) are connected respectively as a CMOS transistor construction, and two inverters are connected to each other in a latch configuration. Accordingly, a latched output is provided based upon a differential input from fuses F 1 , F 2 . 
     FIG. 9 is a circuit diagram of a fuse option circuit according to the seventh embodiment of the present invention. FIG. 10 is a circuit diagram of a fuse option circuit according to the eighth embodiment of the present invention. 
     A circuit of the seventh embodiment comprises a first fuse F 1 , a second fuse F 2 , a fuse cutting means  20 , an option signal generating means  60  and an output means  70 . The option signal generating means  60  includes three MOS transistors (NM 3 , NM 4 , NM 16 ) and an inverter (INV 6 ). The MOS transistors (NM 3 , NM 4 ) are connected to each other in the same latch construction as described in the first embodiment. And the MOS transistor (NM 16 ) is connected between a common source of two transistors (NM 3 , NM 4 ) and a ground. An enable signal (VCCH) is applied to a gate of the MOS transistor (NM 16 ) through the inverter (INV 6 ). 
     The output means  70  includes two inverters (INV 1 , INV 2 ) connected to each other in a latch configuration, and a PMOS transistor (PM 5 ). An input terminal of the latch construction is connected to a first node N 1 , and an enable signal (VCCH) is applied to a gate of the MOS transistor (PM 5 ) whose drain is connected to the first node N 1 . 
     Accordingly, the first fuse F 1  is cut by providing a cutting current thereto in response to a high signal of a fuse cutting signal (PCUT). 
     In case that the first fuse F 1  is cut, the option signal generating means  60  and the output means  70  are enabled in a low state of the enable signal (VCCH). And the low state is latched to the first node N 1  to output the fuse option signal (POUT) as a high state. 
     All components of the eighth embodiment shown in FIG. 10 are identical with the seventh embodiment shown in FIG. 9 except for an option signal generating means  80  having a PMOS transistor (PM 6 ) to be turned on by an enable signal (VCCH). Other same components appear with the same references without detailed description. 
     A source and drain of the MOS transistor (PM 6 ) are connected between a power supply voltage (VCC) and a point of contact of a first fuse F 1  and a second fuse F 2 , an enable signal (VCCH) is applied to a gate of the MOS transistor (PM 6 ). 
     The circuits of the seventh and eighth embodiments operate only when they are enabled by the enable signal (VCCH), so that there is no electrical current consumption in a standby state 
     As described above, an integrated circuit provides a pair of a fuse to be cut and a reference fuse on a chip, compares resistance values of the cut fuse and the reference fuse, and then generates a fuse option signal as result of the comparison. Accordingly, even if the fuse is not precisely cut or the fuse is linked again, power consumption can be reduced since any current that flows through the fuse is slight. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.