Patent Publication Number: US-2023136979-A1

Title: Electrostatic protection circuit for chip

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2021/138502 filed on Dec. 15, 2021, which claims priority to Chinese Patent Application No. 202111300465.5 filed on Nov. 4, 2021. The disclosures of these applications are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Electro-Static discharge (ESD) is one of the unavoidable phenomena for a device such as a chip containing a large-scale integrated circuit. In order to reduce the effect of ESD on the device, it is necessary to design an effective electrostatic protection circuit in the manufacturing process of the chip. However, with the development of the large-scale integrated circuit, the requirements for high integration are constantly increasing, and devices become increasingly sophisticated, which poses a great challenge to the design of the electrostatic protection circuit. 
     SUMMARY 
     Embodiments of the present disclosure relate to semiconductor manufacturing technologies, and relate to, but are not limited to, an electrostatic protection circuit for a chip. 
     In view of the above, embodiments of the present disclosure provide an electrostatic protection circuit for a chip including a power supply pad and a ground pad, where the electrostatic protection circuit includes: a monitoring assembly, configured to generate a trigger signal when an electrostatic pulse is present on the power pad; a discharge transistor, connected between the power pad and the ground pad and configured to be turned on under control of the trigger signal to discharge electrostatic charges to the ground pad; and a control circuit, connected to the monitoring assembly and configured to control a duration of the trigger signal generated by the monitoring assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings herein are incorporated in and constitute a part of this specification, illustrate embodiments conforming to the present disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG.  1    is a first schematic structural diagram of an electrostatic protection circuit according to an embodiment of the present disclosure; 
         FIG.  2    is a second schematic structural diagram of an electrostatic protection circuit according to an embodiment of the present disclosure; 
         FIG.  3    is a third schematic structural diagram of an electrostatic protection circuit according to an embodiment of the present disclosure; 
         FIG.  4    is a fourth schematic structural diagram of an electrostatic protection circuit according to an embodiment of the present disclosure; 
         FIG.  5    is a fifth schematic structural diagram of an electrostatic protection circuit according to an embodiment of the present disclosure. 
     
    
    
     Specific embodiments of the present disclosure have been shown by the above drawings, and will be described in more detail hereinafter. These drawings and textual descriptions are not intended to limit the scope of the inventions of the present disclosure in any way, but rather to illustrate the concepts of the present disclosure by reference to specific embodiments by those skilled in the art. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the present disclosure. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the invention as recited in the appended claims. 
     Other embodiments of the present disclosure will be readily contemplated by those skilled in the art after considering the specification and practicing the invention disclosed herein. The present application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include well-known common sense or customary technical means in the art that are not disclosed in the present disclosure. The specification and embodiments are considered exemplary only, and the true scope and spirit of the present disclosure are indicated by the following claims. The technical solution of the present disclosure is further described in detail below in conjunction with the accompanying drawings and embodiments. 
       FIG.  1    shows an electrostatic protection circuit for a chip according to an embodiment of the present disclosure. As shown in  FIG.  1   , the chip includes: a power supply pad VDD and a ground pad VSS; and the electrostatic protection circuit  100  includes: a monitoring assembly  110  configured to generate a trigger signal when an electrostatic pulse is present on the power pad VDD; a discharge transistor  120  connected between the power pad VDD and the ground pad VSS, and configured to be turned on under control of the trigger signal to discharge electrostatic charges to the ground pad; and a control circuit  130  connected to the monitoring assembly  110 , and configured to control a duration of the trigger signal generated by the monitoring assembly  110 . 
     In the embodiment of the present disclosure, under the influence of electrostatic charges, the monitoring assembly  110  may trigger the discharge transistor  120  to discharge the electrostatic charges. That is to say, when an electrostatic pulse is present on the power supply pad VDD, the electrostatic pulse is transferred to the monitoring assembly  110  to generate a trigger signal. The trigger signal is generated only when the electrostatic pulse is present, so that the discharge transistor  120  is turned on to form a discharge path between the power supply pad VDD and the ground pad VSS. Therefore, it is possible to facilitate discharging the electrostatic pulses through the discharge path, so as to achieve the function of protecting the chip  10 . 
     In the absence of an electrostatic pulse in the normal operation of the chip, the monitoring assembly  110  does not generate the trigger signal, and therefore does not trigger turning on of the discharge transistor  120 . 
     Since the duration of the trigger signal generated by the monitoring assembly  110  affects the discharge duration of the discharge transistor  120 , and further affects the electrostatic discharge effect, it is necessary to adjust the discharge duration by adjusting the duration of the trigger signal generated by the monitoring assembly  110 , so as to determine the duration that satisfies the electrostatic protection requirement. 
     Exemplarily, the number or combination of elements operating in the monitoring assembly  110  may affect the duration. Therefore, in the embodiment of the present disclosure, the control circuit is configured to flexibly adjust the duration of the trigger signal generated by the monitoring assembly  110 . For example, the duration is adjusted by adjusting the number of connected components, so as to achieve the purpose of testing the discharge effect of the electrostatic protection circuit, and further determine the electrostatic protection circuit meeting the requirement. 
     In some embodiments, as shown in  FIG.  2   , the monitoring assembly  110  includes a primary monitoring unit  111  and at least one secondary monitoring unit  112 .The primary monitoring unit  111  is connected between the power supply pad VDD and the ground pad VSS; the primary monitoring unit  111  and the secondary monitoring unit are connected to a control terminal  121  of the discharge transistor  120 , and output signals of the primary monitoring unit and the secondary monitoring unit are together applied to the control terminal of the discharge transistor; and the secondary monitoring unit  112  is connected to the control circuit  130 . 
     In the embodiment of the present disclosure, the primary monitoring unit  111  of the monitoring assembly  100  is connected to the control terminal of the discharge transistor  120 , so that the output signal of the primary monitoring unit  111  can be used as the trigger signal to trigger the turning on of the discharge transistor  120 . 
     The secondary monitoring unit  112  is connected to the control circuit  130 , and the secondary monitoring unit  112  is also connected to the control terminal. In this way, the signal output by the secondary monitoring unit and the trigger signal output by the primary monitoring unit  111  are together applied to the control terminal, so that the duration of the trigger signal can be controlled by adjusting the operation state of the secondary monitoring unit. 
     In the embodiment of the present disclosure, the secondary monitoring unit  112  is connected to the control circuit  130 . The control circuit  130  may adjust the secondary monitoring unit  112  to output different signals, and the different signals and the trigger signal output from the primary monitoring unit  111  are together applied to the discharge transistor, so that the trigger signal has different durations. Exemplarily, multiple secondary monitoring units  112  may be connected to the primary monitoring unit  111 , and the number of secondary monitoring units  112  may affect the duration of the trigger signal. Therefore, the number of secondary monitoring units  112  connected to the primary monitoring unit  111  can be changed by the control circuit  130 , so that the effect of controlling the duration of the trigger signal output from the monitoring assembly  110  is achieved. 
     In some embodiments, the control circuit  130  includes: at least one first control unit  131  and at least one second control unit  132 , a number of the at least one first control unit  131  being identical to a number of the at least one second control unit  132 , and being identical to a number of the at least one secondary monitoring unit  112 , where the first control unit is connected between the secondary monitoring unit  112  and the power supply pad VDD, and the first control unit is configured to control an operation state of the secondary monitoring unit by a power supply voltage supplied from the power supply pad; and the second control unit  132  is connected between the secondary monitoring unit  112  and the ground pad VSS, and the second control unit is configured to control the operation state of the secondary monitoring unit by a ground voltage supplied from the ground pad. 
     In the embodiment of the present disclosure, both the first control unit  131  and the second control unit  132  in the control circuit  130  are elements having switching characteristics, and may function to turn on or turn off a specified signal path. Exemplarily, the first control unit  131  and the second control unit  132  may be implemented by a three-terminal device such as an MOS transistor, a bipolar junction transistor, or the like. 
     The number of the first control unit  131  may be identical to the number of the second control unit  132  and the number of the secondary monitoring unit  112 , that is to say, each secondary monitoring unit  112  may be respectively connected to one first control unit  131  and one second control unit  132 . The first control unit  131  is connected between the secondary monitoring unit  112  and the power supply pad VDD. Therefore, when the first control unit  131  is turned on and the second control unit  132  is turned off, the voltage of the power supply pad VDD is applied to the secondary monitoring unit  112 ; and when the second control unit  132  is turned on and the first control unit  131  is turned off, the voltage of the ground pad VSS is applied to the secondary monitoring unit  112 . By applying different voltages to the secondary monitoring unit, the functions of the secondary monitoring unit  112  in the monitoring assembly  110 , such as voltage division, shunting, increasing current and increasing voltage, can be changed, and thus, the duration of the trigger signal generated by the monitoring assembly  110  can be adjusted. 
     In the embodiment of the present disclosure, since the monitoring assembly  110  includes multiple secondary monitoring units  112 , the monitoring assembly  110  can output multiple trigger signals having different durations by combinations of the turning one and turning off of the first control unit  131  and the second control unit  132  corresponding to the multiple secondary monitoring units  112 . In practical applications, it is possible to determine, through experiments, one of these trigger signals having different durations that can bring a better electrostatic protection effect, and the combination corresponding to a determined trigger signal can be taken as a structure in an actual product for mass production. 
     In some embodiments, as shown in  FIG.  4   , the secondary monitoring unit  112  includes a monitoring capacitor C 1  having a first end connected to the first control unit  131 ; and a monitoring resistor R 1  having a first end connected to a second end of the monitoring capacitor C 1  and the control terminal  121  of the discharge transistor  120 , and having a second end connected to the second control unit  132 . 
     The secondary monitoring unit  112  is constituted by an resistor-capacitor (RC) circuit, and one end of the RC circuit, that is, the first end of the monitoring capacitor C 1  is connected to the power supply pad VDD through the first control unit  131 ; and the other end of the RC circuit, that is, the second end of the monitoring resistor R 1  is connected to the ground pad VSS through the second control unit  132 . In addition, the connection terminal of the monitoring capacitor C 1  and the monitoring resistor R 1  in the RC circuit is also connected to the control terminal of the discharge transistor  120 . That is to say, both the secondary monitoring unit  112  and the primary monitoring unit  111  may be connected to the discharge transistor  120 , to work together to output the trigger signal. Since the electrostatic protection circuit may include multiple secondary monitoring units, two secondary monitoring units are shown in  FIG.  4   , where the monitoring resistors of the secondary monitoring units are denoted by R 1  and R 2 , respectively, and the monitoring capacitors of the secondary monitoring units are denoted by C 1  and C 2 , respectively. 
     The multiple secondary monitoring units  112  are all connected to the control terminal of the discharge transistor  120 , and the number of connected monitoring resistors and monitoring capacitors can be changed by switching the on states of the first control unit  131  and the second control unit  132 . The smaller the total resistance R in the monitoring assembly, the shorter the duration of the trigger signal; and the larger the total capacitance C, the longer the corresponding duration of the trigger signal. 
     In some embodiments, as shown in  FIG.  4   , the primary monitoring unit  111  includes a primary monitoring capacitor CO having a first end connected to the power supply pad VDD; and a primary monitoring resistor RO having a first end connected to the primary monitoring capacitor CO and the control terminal of the discharge transistor  120 , and having a second end connected to the ground pad VSS. 
     Since at least one monitoring unit is required in the monitoring assembly  110 , the primary monitoring unit  111  may be directly connected between the power supply pad VDD and the ground pad VSS without requiring the control units to switch their on state. 
     It can be seen that when both the first control unit  131  and the second control unit  132  connected to the secondary monitoring unit  112  are in the on state, the structure of the secondary monitoring unit  112  is substantially identical to the structure of the primary monitoring unit  111 , and the secondary monitoring unit  112  and the primary monitoring unit  111  are connected in parallel between the power supply pad VDD and the ground pad VSS. Each of the RC circuits is connected to the control terminal of the discharge transistor  120 , which means that all the capacitors respectively in the secondary monitoring unit  112  and the primary monitoring unit  111  are connected in parallel with each other, and all the resistors respectively in the secondary monitoring unit  112  and the primary monitoring unit  111  are connected in parallel with each other. Therefore, the more the secondary monitoring units  112  that are turned on in the monitoring assembly, the more the parallel capacitors and resistors, the larger the total capacitance C, and the smaller the total resistance R. Certainly, the capacitance values of the capacitors in respective monitoring units  112  may be different from each other, and the resistance values of the resistors in respective secondary monitoring units  112  may be different from each other, so that various combinations of capacitance values and resistance values can be implemented, and thus flexible and precise adjustment can be realized. 
     In some embodiments, the control circuit  130  further includes a first switch assembly configured to switch an operation state of the first control unit  131 ; and a second switch assembly configured to switch an operation state of the second control unit  132 . 
     In some embodiments, as shown in  FIG.  5   , the first switch assembly includes a first switch K 1  and a second switch K 2 , the control terminal of the first control unit  131  being connected to the power supply pad VDD through the first switch K 1  and being connected to the ground pad VSS through the second switch K; and the second switch assembly includes a third switch K 3  and a fourth switch K 4 , the control terminal of the second control unit  132  being connected to the power supply pad VDD through the third switch K 3  and being connected to the ground pad VSS through the fourth switch K 4 . 
     In the embodiment of the present disclosure, the on states of the first control unit  131  and the second control unit  132  may be switched by two switches. Each of the first switch K 1  to the fourth switch K 4  has a first end and a second end. 
     The first end of the first switch K 1  is connected to the control terminal of the first control unit  131 , and the second end of the first switch K 11  is connected to a power supply, which may be configured to provide the power supply voltage VDD equal to a potential of the power supply pad. The first switch K 1  is configured to switch from a closed state to an open state or from the open state to the closed state under the control of the control signal, so as to determine whether the power supply voltage VDD is supplied to the control terminal of the first control unit  131 . 
     The first end of the second switch K 2  is connected to the control terminal of the first control unit  131 , and the second end of the second switch K 2  is grounded or a low potential, that is, a low voltage VSS having an equal potential to the ground pad. The second switch K 2  is configured to switch from the closed state to the open state or from the open state to the closed state under the control of the control signal, so as to determine whether the ground voltage VSS is supplied to the control terminal of the first control unit  131 . 
     The first switch K 1  and the second switch K 2  have the characteristic that they cannot be turned on or turned off at the same time, but the first switch K 1  may be turned on and the second switch K 2  may be turned off, so that the potential of the control terminal of the first control unit  131  reaches the power supply voltage VDD, or the second switch K 2  may be turned on and the first switch K 1  may be turned off, so that the potential of the control terminal of the first control unit  131  reaches the low voltage VSS. In this way, switching of the on state of the first control unit  131  can be implemented. 
     Similarly to the first control unit  131 , the control terminal of the second control unit  132  is also connected to two switches, i.e., the third switch K 3  and the fourth switch K 4 , respectively. The switching of the on state of the second control unit  132  can be implemented by the switching states of the third switch K 3  and the fourth switch K 4 . 
     In some embodiments, the first control unit  131  is configured to switch, according to switching states of the first switch K 1  and the second switch K 2 , from a cutoff state to an on state to increase a total capacitance of the monitoring assembly  110 , or from the on state to the off state to reduce the total capacitance of the monitoring assembly  110 , where the switching state of the first switch is different from the switching state of the second switch. 
     The total capacitance of the monitoring assembly  110  can be determined by whether each first control unit  131  is turned on, and the total resistance of the monitoring assembly  110  can be determined by whether each second control unit  132  is turned on. Therefore, it is possible to adjust the total capacitance or total resistance as a whole with the monitoring assembly  110  by changing the switching states of the switches as described above, rather than merely changing the number of secondary monitoring units. 
     Herein, the total capacitance of the monitoring assembly  110  is adjusted by switching the states of the first switch K 1  and the second switch K 2  in each secondary monitoring unit. 
     In some embodiments, the states of the first switch K 1  and the second switch K 2  may include the on state or the off state, when the switch is in the on state, the circuit where the switch is located is turned on, and the potentials at two ends of the switch are the same; when the switch is in the off state, the circuit where the switch is located is turned off, and the potentials at two ends of the switch are different. 
     Specifically, in some embodiments, the first control unit  131  is an N-type transistor; when the first switch K 1  is in the on state and the second switch K 2  is in the off state, the first control unit  131  is in the on state; and when the first switch K 1  is in the off state and the second switch K 2  is in the on state, the first control unit  131  is in the cutoff state. 
     In some embodiments, the first control unit  131  is a P-type transistor. when the first switch K 1  is in the on state and the second switch K 2  is in the off state, the first control unit  131  is in the cutoff state; and when the first switch K 1  is in the off state and the second switch K 2  is in the on state, the first control unit  131  is in the on state. 
     Similarly to the first control unit  131 , the state of the second control unit  132  is controlled by the third switch K 3  and the fourth switch K 4 . Specifically, in some embodiments, the second control unit  132  is configured to switch, according to the switching states of the third switch K 3  and the fourth switch K 4 , from an cutoff state to an on state to reduce a total resistance of the monitoring assembly  110 , or from the on state to the cutoff state to increase the total resistance of the monitoring assembly  110 . 
     That is to say, by individually controlling the switching states of the third switch K 3  and the fourth switch K 4  in each secondary monitoring unit, the total resistance of the monitoring assembly  110  can be adjusted. 
     Herein, the states of the third switch K 3  and the fourth switch K 4  include an on state or an off state. When the switch is in the on state, the circuit where the switch is located is turned on, and the potentials at both ends of the switch are the same; when the switch is in the off state, the circuit where the switch is located is turned off, and the potential at both ends of the switch are different. 
     Specifically, in some embodiments, the second control unit  132  is an N-type transistor. When the third switch K 3  is in the on state and the fourth switch K 4  is in the off state, the second control unit  132  is in the on state; and when the third switch K 3  is in the off state and the fourth switch K 4  is in the on state, the second control unit  132  is in the cutoff state. 
     In some embodiments, the second control unit  132  is a P-type transistor. When the third switch K 3  is in the on state and the fourth switch K 4  is in the off state, the second control unit  132  is in the cutoff state; and when the third switch K 3  is in the off state and the fourth switch K 4  is in the on state, the second control unit  132  is in the on state. 
     In some embodiments, the first switch, the second switch, the third switch and the fourth switch are one-time-programmable (OTP) memories. 
     By programming control of the OTP memories, switching of the switching states of the first switch K 1  to the fourth switch K 4  can be implemented, and thus the control of the first control unit  131  and the second control unit  132  is implemented. 
     Since electrostatic breakdown typically occurs in a power-off state, the solution of controlling the switch to close or open through a control signal generated by a circuit cannot be applied to the case where the chip is in the power-off state. The adjustment of the electrostatic protection capability of the electrostatic protection circuit by switching the operating states of the first control unit  131  and the second control unit  132  through the programming control of the disposable programmable device can be implemented without requiring that the chip is in a power-on state, so that the chip having the electrostatic protection circuit with different structures can be obtained according to the test requirements, and then the chip is is tested for the electrostatic protection capability. 
     In some embodiments, the first switch, the second switch, the third switch and the fourth switch are laser fuse devices. 
     The laser fuse device is an OTP device. The laser fuse device connected to the first control unit  131  and the second control unit  132  is irradiated with laser light, so that the first control unit  131  and the second control unit  132  can be switched between the on state and the off state. In this way, the electrostatic protection capability of the chip can be set according to the test requirements. 
     It should be understood that reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic associated with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of &amp; “in one embodiment” or “in an embodiment” in various places throughout the specification do not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It is to be understood that, in the various embodiments of the present disclosure, the magnitude of the sequence numbers of the processes described above is not meant to mean the order of execution, and the order of execution of the processes should be determined by their function and intrinsic logic, and should not be construed as any limitation on the implementation of the embodiments of the present disclosure. The numbers of the embodiments of the present disclosure are for description only and do not represent that one embodiment is superior to another embodiment. 
     It is to be noted that, in this disclosure, the terms “includes”, “including” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or device that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or device. Without more limitations, an element is defined by the statement “including a . . . ” that does not rule out there are additional identical elements in a process, method, article, or apparatus that includes the element. 
     In several embodiments provided by the present disclosure, it should be understood that the disclosed devices and methods can be realized in other ways. For example, the embodiment of the device described above is only schematic. For example, the division of the unit is only a logical function division, and there can be another division method in actual implementation, for example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not implemented. On the other hand, the mutual coupling or direct coupling or communication connection illustrated or discussed can be indirect coupling or communication connection through some interfaces, devices or units, and can be electric, mechanical or other forms. 
     The unit described as a separation part may or may not be physically separated, and the unit displayed as a unit may or may not be a physical unit, that is, it may be located in one place, or it may be distributed to multiple network units. Some or all of the units can be selected according to the actual needs to achieve the purpose of the embodiment. 
     In addition, each functional unit in each embodiment of the present disclosure may be integrated in one processing unit, each unit may exist physically alone, or two or more units may be integrated in one unit; the integrated unit may be implemented in the form of hardware or in the form of the combination of the hardware and software functional units. 
     The above is only the specific embodiments of the disclosure, but the scope of protection of the disclosure is not limited to this. Any person skilled in the technical field who can easily think of change or replacement within the technical scope of the disclosure shall be covered in the scope of protection of the disclosure. Therefore, the protection scope of the disclosure shall be subject to the protection scope of the claims. 
     The electrostatic protection circuit provided by the technical solutions of the embodiments of the present disclosure has a discharge transistor and a monitoring assembly, and also has a control circuit configured to control a duration of the trigger signal generated by the monitoring assembly. In this way, the adjustment and test can be performed by the control circuit to determine an electrostatic protection circuit meeting requirements on the electrostatic protection capability, without the need for multiple tape-outs, it is thus possible to reduce the cost of designing and testing the electrostatic protection circuit, and optimize the protection capability of the electrostatic protection circuit.