Abstract:
A static electricity discharge circuit applied to a highly integrated semiconductor circuit includes a discharge unit connected with the input/output pad by a node and providing, in parallel to the node, a first discharge path connected with a power voltage line and a second discharge path connected with a ground voltage line, an electrostatic detection unit including a diode chain connected to the node and detecting a detection voltage corresponding to static electricity inputted to the node, and a clamp unit switching the discharge path between the power voltage line and the ground voltage line by the detection voltage of the electrostatic detection unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. 119(a) to Korean patent application number 10-2007-0091758 filed in the Korean Intellectual Property Office on Sep. 10, 2007, which is incorporated herein by reference in its entirety as if set forth in full. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The embodiments described herein relate to a static electricity discharge circuit, and more precisely, to a static electricity discharge circuit used to prevent defect in a semiconductor device due to a static electricity. 
         [0004]    2. Related Art 
         [0005]    In general, semiconductor devices are sensitive to the static electricity. When a high voltage is applied to an integrated circuit due to electrostatic discharge (hereinafter, referred to as ESD), thin insulation layers, channels and so on within the integrated circuit can be damaged by the high voltage and the chip becomes unable to operate normal. Therefore, in order to protect the integrated circuit from ESD, a conventional semiconductor integrated circuit has a built-in static electricity discharge circuit placed at an input/output pad. 
         [0006]    Such a static electricity discharge circuit is connected in parallel between an input/output pad or a power pad and ground within the integrated circuit of the chip to provide a discharge path. Therefore, the static electricity discharge circuit can discharge the static electricity and prevent the static electricity from damaging the integrated circuit. 
         [0007]    Recently, as the degree of integration increases, the size of semiconductor devices (e.g. MOS transistor) decreases, which can make the device more sensitive to static electricity. 
         [0008]    Conventional static electricity discharge circuits are shown in  FIGS. 1 and 2 . 
         [0009]    A static electricity discharge circuit  100  as illustrated in  FIG. 1  includes an ESD protection unit  130  and a grounded gate NMOS transistor (herein after, referred to as GGNMOS transistor) disposed in parallel between a power voltage line  150  and a ground voltage line  160 . The ESD protection unit  130  is connected between the power voltage line  150  and the ground voltage line  160  with respect to a node a between an input/output pad  110  and an internal circuit  120 . 
         [0010]    The power voltage line  150  is connected with the ESD protection unit  130  through a node (b 1 ) and the GGNMOS transistor  140  through a node (b 2 ). The ground voltage line  160  is connected with the ESD protection unit  130  through a node (c 1 ) and the GGNMOS transistor  140  through a node (c 2 ). 
         [0011]    The ESD protection unit  130  includes a diode  131  connected between the power voltage line  150  and the input/output pad  110  and a diode  132  connected between the input/output pad  110  and the ground voltage line  160 . 
         [0012]    When positive (+) static electricity is input into the static electricity discharge circuit of  FIG. 1 , the positive (+) static electricity is discharged to the ground voltage line  160  through the path of node (a)→node (b 1 )→node b 2 →node (c 2 ). 
         [0013]    The positive (+) static electricity causes the GGNMOS transistor to turn on and discharge the positive (+) static electricity to the ground voltage line  160  through node (c 2 ); however, the discharge circuit  100  has relatively long rising time, which delays the turn on of the GGNMOS transistor  140 . Therefore, the internal circuit  120  may be influenced by the static electricity, due to the delay in turning on the GGNMOS transistor. 
         [0014]    In order to solve the problem of the response speed in the static electricity discharge circuit  100  in  FIG. 1 , there has been suggested a RC trigger type static electricity discharge circuit  200  in  FIG. 2 . 
         [0015]    The static electricity discharge circuit  200  in  FIG. 2  is disposed between an input/output pad  210  and an internal circuit  220 , and includes an ESD protection unit  230  that provides a discharge path or static electricity applied from the input/output pad  210 , a trigger unit  240  that generates a trigger voltage related to the static electricity transferred from the ESD protection unit  230 , and a clamping unit  250  that is activated by the trigger voltage. The ESD protection unit  230 , the trigger unit  240 , and the clamping unit  250  are connected in parallel between a power voltage line  260  and a ground voltage line  270 . 
         [0016]    The power voltage line  260  is connected with the ESD protection unit  230  through a node (e 1 ), the trigger unit  240  through a node (e 2 ), and the clamping unit  250  through a node (e 3 ). The ground voltage line  270  is connected with the ESD protection unit  230  through a node (f 1 ), the trigger unit  240  through a node (f 2 ), and the clamping unit  250  through a node (f 3 ). 
         [0017]    The ESD protection unit  230  includes a diode  231  connected between the power voltage line  260  and the input/output pad  210  and a diode  232  connected between the input/output pad  210  and the ground voltage line  270 . 
         [0018]    The trigger unit is provided with a resistance component  241  and a capacitor  242 , and the clamping unit  250  is provided with a gate coupled NMOS transistor (hereinafter, referred to as GCNMOS transistor)  152  in which gate and drain thereof are coupled. 
         [0019]    In the static electricity discharge circuit  200  in  FIG. 2 , a positive (+) static electricity input through the input/output pad  210  is transferred to the nodes (e 2 ) and (e 3 ) through positively biased diode  231 , and the static electricity transferred to the node (e 3 ) is discharged to the ground voltage line  270  through the GCNMOS transistor  251  when the GCNMOS transistor  251  is turned on by the trigger voltage generated by the trigger unit  240 . 
         [0020]    The static electricity discharge circuit  200  has a response speed faster than that of the static electricity discharge circuit  100  in  FIG. 1  since it discharges the static electricity as the GCNMOS transistor  251  is turned on by the trigger voltage generated by the trigger unit  240 . 
         [0021]    In other words, since the ESD path of the static electricity discharge circuit  200  in  FIG. 2  is turned on by lower voltage than in the static electricity discharge circuit  100  in  FIG. 1 , the static electricity discharge circuit  200  in  FIG. 2  can better protect the internal circuit  220 . 
         [0022]    Sufficient current should be supplied to the gate of the GCNMOS transistor  251  to turn on the GCNMOS transistor  251 . This requires an increase in the area of the capacitor  242  to achieve a resultant increase in capacitance, which is needed to supply sufficient current. The increased area prevents higher integration of the semiconductor integrated circuit. 
       SUMMARY 
       [0023]    A static electricity discharge circuit in which an electrostatic discharge path is turned on by a low trigger voltage is described herein. A static electricity discharge circuit that has a fast response characteristic to static electricity is also described herein, as is a static electricity discharge circuit that can perform electrostatic discharge with small area. 
         [0024]    According to one aspect, there is provided a static electricity discharge circuit that discharges static electricity input from an input/output pad, which include: a discharge unit connected with the input/output pad by a node and providing, in parallel to the node, a first discharge path connected with a power voltage line and a second discharge path connected with a ground voltage line, an electrostatic detection unit including a diode chain connected to the node and detecting a detection voltage corresponding to static electricity inputted to the node, and a clamp unit switching the discharge path between the power voltage line and the ground voltage line by the detection voltage of the electrostatic detection unit. 
         [0025]    According to another aspect, there is provided a static electricity discharge circuit that discharges static electricity inputted into a node between an input/output pad and an internal circuit, which include: a discharge unit including at least one of a first discharge unit that provides a first discharge path between the node and a power voltage line and a second discharge path between the node and a ground voltage line, a diode chain connected with the node, wherein the diode chain has a turn-on voltage of higher level than that of a normal input signal of the node and detects a detection voltage corresponding to static electricity inputted to the node, and a MOS transistor connected between the power voltage line and the ground voltage line and switching the discharge path between the power voltage line and the ground voltage line by apply of the detection voltage of the diode chain to the gate of MOS transistor. 
         [0026]    These and other features, aspects, and embodiments are described below in the section entitled “Detailed Description.” 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0027]    Features, aspects, and embodiments are described in conjunction with the attached drawings, in which: 
           [0028]      FIG. 1  is a circuit diagram showing a conventional static electricity discharge circuit. 
           [0029]      FIG. 2  is a circuit diagram showing a conventional RC trigger type static electricity discharge circuit. 
           [0030]      FIG. 3  is a circuit diagram showing a static electricity discharge circuit according to one embodiment. 
           [0031]      FIG. 4  is a graph comparing trigger voltages for the circuit of  FIG. 3  and for the circuits of  FIG. 1  and  FIG. 2.conventional  art. 
           [0032]      FIG. 5  is a graph illustrating current and leakage current in static electricity discharge circuit of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION  
       [0033]    A static electricity discharge circuit according to the embodiments described herein can operate only when static electricity is applied without influence by an input signal, raise triggering speed, and reduce the circuit area by using a chain diode instead of a capacitor. 
         [0034]    As such, a static electricity discharge circuit according to the embodiments described herein can be applied to integrated circuit devices such as highly integrate semiconductor memory devices, micro processors, micro-electromechanical systems, opto-electronic devices and LCD driver ICs. 
         [0035]      FIG. 3  is a diagram illustrating a static electricity discharge circuit  300  according to one embodiment. As can be seen, circuit  300  can be connected between an input/output pad  310  that can be configured to send/receive external signals and an internal circuit  320  that can be configured to receive signals input through the input/output pad  310 , and provide a discharge path between a power voltage line  360  and a ground voltage line  370  to discharge static electricity. 
         [0036]    Specifically, the static electricity discharge circuit  300  can include a discharge unit  330  that can be configured to provide the discharge path for the static electricity applied from the input/output pad  310 , an electrostatic detection unit  340  that can comprise a diode chain and that can be configured to generate a detection voltage that corresponds to the static electricity applied from the input/output pad  310 , and a clamp unit  350  that can be configured to switch the discharge path between the power voltage line  360  and the ground voltage line  370  under control of the detection voltage from the electrostatic detection unit  340 . 
         [0037]    The discharge unit  330  can include a diode  331  connected between the power voltage line  360  and the input/output pad  310  and a diode  332  connected between the input/output pad  310  and the ground voltage line  370 . 
         [0038]    The electrostatic detection unit  340  can be connected to a node (g) between the input/output pad  310  and the clamp unit  350 , and the number of the diodes constituting the diode chain should be determined so as to have a turn-on voltage higher than the voltage of a normal input signal applied to the internal circuit  320 . 
         [0039]    The clamp unit  350  can be provided with a GCNMOS transistor  352  in which a gate and a bulk thereof are coupled and a resistance component  351  that applies a bias voltage to the GCNMOS transistor  352 . 
         [0040]    The power voltage line  360  can be connected with the discharge unit  330  through a node (h 1 ) and the clamp unit  350  through a node (h 2 ). Also, the ground voltage line  370  can be connected with the discharge unit  330  through a node (i 1 ) and the clamp unit  350  through a node (i 2 ). 
         [0041]    In the static electricity discharge circuit  300 , operation properties vary with the voltage level and transfer path of the static electricity applied from the outside. 
         [0042]    An operation of discharging positive (+) static electricity to the ground voltage line  370  when the positive (+) static electricity is applied to the static electricity discharge circuit  300  will now be described in detail. 
         [0043]    The positive (+) static electricity input through the input/output pad  310  turns on the electrostatic detection unit  340 . But if the positive static electricity has an insufficient voltage level, then the diode chain of detection unite  340  is not turned on. 
         [0044]    The electrostatic detection unit  340  can preferably be constructed so as to have a turn-on voltage larger than the voltage of the normal input signal. This way, the static electricity discharge circuit  300  is not influenced by the input signal and turns on, only when a static electricity having a voltage larger than the voltage of the normal input signal is applied to the detection unit  340 . 
         [0045]    The electrostatic detection unit  340 , therefore, can be a device that biases the voltage due to the static electricity to the GCNMOS transistor  352  using a diode chain, instead of the capacitor  242  of the conventional RC trigger type static electricity discharge circuit  200  as illustrated in  FIG. 2 . Moreover, the diode chain will occupy a smaller area as compared to the capacitor  242 . The triggering speed of unit  340  should also be relatively faster than that of the trigger circuit using the capacitor  242 . In other words, since the current flowing in the resistance device  351  is larger than the current flowing in, e.g., the resistance device  241 , the static electricity discharge circuit  300  can realize a relatively faster triggering speed than in circuits using the RC trigger circuit of  FIG. 2 . 
         [0046]    The positive (+) static electricity flowing to the first diode  331  through the input/output pad  310  is transferred from the node (g) to the node (h 1 ) through the positively biased first diode  331 , and then transferred to the node (h 2 ) through the power voltage line  360 . After that, the static electricity transferred to the node (h 2 ) is transferred to the node (i 2 ) through the clamp unit  350  and finally discharged to the ground voltage line  370 . 
         [0047]    In other words, the positive (+) static electricity input through the input/output pad  310  can be discharged through the path of nodes (g)→(h 1 ) &gt;(h 2 )→(i 2 ). 
         [0048]    As described above, since a diode chain is used, e.g., instead of a capacitor  242 , of the current flowing in the static electricity detection unit  340  and the clamp unit  350  ensures faster triggering speed of the clamp unit  350  than the current flowing, e.g., in the trigger unit  240  and the clamp unit  250  of the conventional RC trigger power clamp circuit  200  illustrated in  FIG. 20 . Therefore, the internal circuit  320  can be protected from static electricity faster due to the faster response speed. 
         [0049]    Also, since the diode chain is used instead of the capacitor, the area in a semiconductor chip occupied by the static electricity discharge circuit  300  is reduced. Therefore, it is more suitable to highly integrated circuit. 
         [0050]      FIG. 4  is a graph comparing trigger voltages of conventional static electricity discharge circuit  100 , conventional RC trigger type static electricity discharge circuit  200 , and the static electricity discharge circuit  300 . It can be appreciated that the static electricity discharge circuit  300  has the lowest voltage and shows the fastest triggering characteristic. 
         [0051]      FIG. 5  is a graph illustrating leakage current flowing through the electrostatic detection unit  340  when the static electricity is not applied to the static electricity discharge circuit  300 . This leakage current is illustrated by plot  502 . It can be appreciated that the leakage current does not have an influence on the suggested static electricity discharge circuit  300  since the leakage current flowing through the electrostatic detection unit  340  when the static electricity is not applied to the static electricity discharge circuit  300  is low current of 0.1 pA. This leakage current (plot  502 ) can be compared to that of a conventional circuit as illustrated in plot  504 . 
         [0052]    While certain embodiments have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the systems and methods described herein should not be limited based on the described embodiments. Rather, the systems and methods described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.