Patent Publication Number: US-2023139130-A1

Title: Complementary metal oxide semiconductor circuit of memory device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2021/126779 filed on Oct. 27, 2021, which claims the benefit of priority to Chinese Application No. 202011336570.X, filed on Nov. 25, 2020. The entire contents of each of these two applications are expressly incorporated herein by reference. 
    
    
     BACKGROUND 
     In recent years, the development of flash memories has been particularly rapid. Flash memories have a main feature that stored information can be maintained for a long time without power on, and have the advantages of high integration, fast access speed, easy erasing and rewriting, etc. Flash memories have been widely used in many fields such as microcomputers and automation control. In order to further increase the bit density of flash memories and reduce the bit cost, three-dimensional flash memory (3D NAND) technology has been rapidly developed. 
     In a CMOS circuit of the 3D NAND, some functional circuits (such as a switching circuit and a level translation circuit) usually operate under a high voltage, resulting in the deterioration of the hot carrier injection effect of a Metal Oxide Semiconductor (MOS) device due to an excessive drain-source voltage in the rising stage of output voltage, resulting in the reliability risk of such high-voltage functional circuits. In the related art, in order to solve this technical problem, Metal Oxide Semiconductor (MOS) devices with higher performance of high-voltage resistance are usually used to design such high-voltage functional circuits, resulting in such high-voltage functional circuits having a larger area and a smaller current. 
     SUMMARY 
     The disclosure relates to the field of integrated circuit design, and particularly to a Complementary Metal Oxide Semiconductor (CMOS) circuit of a memory device, including a high-voltage functional circuit, and an auxiliary clamping circuit. 
     The high-voltage functional circuit includes at least one MOS transistor. One of a source terminal and a drain terminal of one of the at least one MOS transistor is coupled to an input high-voltage. The high-voltage functional circuit has an output voltage that, when an enable signal is valid, gradually increases and reaches a maximum value. 
     The auxiliary clamping circuit is arranged between the input high-voltage and the one of the source terminal and the drain terminal of the MOS transistor, and is configured to clamp the voltage input to the one of the source terminal and the drain terminal of the MOS transistor during a rising phase of the output voltage, so that a clamping voltage is smaller than the input high-voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a schematic diagram of a CMOS circuit of a memory device according to a first implementation of the disclosure. 
         FIG.  2    illustrates a schematic structural diagram of an existing high-voltage functional circuit. 
       In  FIG.  3   , (a) illustrates waveform diagrams of an enable signal (EN) and its phase-inverted signal; (b) illustrates a waveform diagram of an output voltage of the existing high-voltage functional circuit under the enable signal and a waveform diagram of a voltage input to a MOS transistor during a rising phase of the output voltage of the existing high-voltage functional circuit; and (c) illustrates a waveform diagram of an output voltage of the CMOS circuit of the memory device in the first implementation under the enable signal and a waveform diagram of a voltage input to the MOS transistor during a rising phase of the output voltage of the CMOS circuit of the memory device in the first implementation. 
         FIG.  4    illustrates a schematic structural diagram of the CMOS circuit of the memory device according to a second implementation of the disclosure. 
     
    
    
     DESCRIPTION OF COMPONENT SIGNS 
       100  High-voltage functional circuit 
       200  Auxiliary clamping circuit 
     DETAILED DESCRIPTION 
     Hereinafter, specific examples are used to illustrate the implementation of the disclosure, and those in the art may easily understand other advantages and effects of the disclosure from the contents disclosed in this specification. The disclosure may also be implemented or applied through other different implementations, and various details in this specification may also be modified or changed based on different viewpoints and applications without departing from the spirit of the disclosure. 
     Please refer to  FIGS.  1  to  4   . It should be noted that the drawings provided in this implementation only illustrate the basic idea of the disclosure in a schematic manner, although the drawings only illustrate components related to the disclosure, rather than drawn according to the number, shape, and size of components in actual implementation, the morphology, number, and proportion of components may be changed at will during actual implementation, and its component layout may also be more complicated. 
     First Implementation 
     As illustrated in  FIG.  1   , this implementation provides a CMOS circuit of a memory device, including a high-voltage functional circuit  100  and an auxiliary clamping circuit  200 . 
     The high-voltage functional circuit  100  includes at least one MOS transistor. One of a source terminal and a drain terminal of a MOS transistor M 1  is coupled to an input high-voltage HV The high-voltage functional circuit  100  has an output voltage that, when an enable signal is valid, gradually increases and reaches a maximum value HV. 
     The auxiliary clamping circuit  200  is arranged between the input high-voltage HV and the one of the source terminal and the drain terminal of the MOS transistor M 1 . The auxiliary clamping circuit  200  is configured to clamp, during a rising phase of the output voltage, a voltage input to the one of the source terminal and the drain terminal of the MOS transistor M 1 . In this way, a clamping voltage HV_clamp is smaller than the input high-voltage HV. 
     As an example, the high-voltage functional circuit  100  includes a switching circuit or a level translation circuit. In some examples, the high-voltage functional circuit  100  is a level translation circuit. In the example, the level translation circuit only includes three MOS transistors M 1 -M 3  and the drain terminal of the MOS transistor M 1  is coupled to the input high-voltage HV (as illustrated in  FIG.  1   ). In some implementations, level translation circuits of other composition structures are also applicable. 
     In an implementation, the MOS transistors in the high-voltage functional circuit  100  may be MOS transistors (that is, non-high-voltage MOS transistors) or high-voltage MOS transistors. In the case of MOS transistors, by the design of the auxiliary clamping circuit  200 , the CMOS circuit of the memory device described in this implementation can be applicable for high-voltage application scenarios. In the case of high-voltage MOS transistors, by the design of the auxiliary clamping circuit  200 , the CMOS circuit of the memory device described in this implementation can be applicable for application scenarios of a higher voltage. 
     As an example, as illustrated in  FIG.  1   , the auxiliary clamping circuit  200  includes a first depletion-type high-voltage N-type metal oxide semiconductor (NMOS) transistor and a second depletion-type high-voltage NMOS transistor MN 2 . A first connection terminal of the first depletion-type high-voltage NMOS transistor MN 1  is connected to a first connection terminal of the second depletion-type high-voltage NMOS transistor MN 2  and is coupled to the input high-voltage HV. A second connection terminal of the first depletion-type high-voltage NMOS transistor MN 1  is connected to a second connection terminal of the second depletion-type high-voltage NMOS transistor MN 2  and is connected to the one of the source terminal and the drain terminal of the MOS transistor M 1 . A gate terminal of the first depletion-type high-voltage NMOS transistor MN 1  is coupled to a preset voltage HV 1 . Agate terminal of the second depletion-type high-voltage NMOS transistor MN 2  is connected to an output terminal of the high-voltage functional circuit  100 . The preset voltage HV 1  is less than the input high-voltage HV. A threshold voltage of the second depletion-type high-voltage NMOS transistor MN 1  is less than zero. In practical applications, the first connection terminal of the first depletion-type high-voltage NMOS transistor MN 1  and the first connection terminal of the second depletion-type high-voltage NMOS transistor MN 2  may be drain terminals, and the second connection terminal of the first depletion-type high-voltage NMOS transistor MN 1  and the second connection terminal of the second depletion-type high-voltage NMOS transistor MN 2  may be source terminals. 
     In an implementation, the preset voltage HV 1  is equal to half of the input high-voltage HV, so that the CMOS circuit of the memory device of the disclosure satisfies its own circuit function while having reliability improved as much as possible. Thus, the CMOS circuit of the memory device with such settings may satisfy most of the existing application requirements. In actual applications, the value of the prose voltage HV 1  can be set according to specific application scenarios, especially for some special application scenarios. In such cases, the value of the preset voltage HV 1  may be greater than half of the input high-voltage HV, or may be less than half of the input high-voltage HV. 
     In an implementation, the threshold voltage of the first depletion-type high-voltage NMOS transistor MN 1  is less than 0, so that the first depletion-type high-voltage NMOS transistor MN 1  and the second depletion-type high-voltage NMOS transistor MN 2  are completely the same. Thus, the two transistors may be arranged closely in the layout design, which is conducive to reducing the circuit area and facilitating the model selection of devices. 
     Referring to  FIGS.  1  to  3   , the performance of the CMOS circuit of the memory device of this implementation is in combination with an existing high-voltage functional circuit. 
     As illustrated in  FIG.  2    as well as parts (a) and (b) in  FIG.  3   , for an existing level translation circuit, when the enable signal EN is valid (that is, the enable signal EN changes from a low level to a high level), the output voltage Vout gradually increases and reaches the maximum value HV. However, during the rising phase of the output voltage Vout, since a voltage Vin input to the drain terminal of the MOS transistor M 1  is HV, a maximum drain-source voltage Vds of the MOS transistor M 1  is (HV-Vth_M 1 ). Vth_M 1  is the threshold voltage of the MOS transistor M 1 . It may be seen that during the rising phase of the output voltage Vout, since the drain-source voltage Vds of the MOS transistor M 1  is relatively large, there is a relatively serious hot carrier injection effect, which causes a reliability problem with the level translation circuit. It should he noted that as the output voltage Vout continues to increase, the drain-source voltage Vds of the MOS transistor M 1  will continue to decrease; so the circuit reliability problems caused by the hot carrier injection effect mainly occur in the first half time of the rising phase of the output voltage Vout, that is, the initial phase when the enable signal is valid. 
     As illustrated in  FIG.  1    as well as parts (a) and (c) in  FIG.  3   . with respect to the CMOS circuit of the memory device of the disclosure, when the enable signal EN is valid (that is, the enable signal EN changes from a low level to a high level), the output voltage Vout gradually increases and reaches the maximum value HV. During the rising phase of the output voltage Vout, due to the design of the auxiliary clamping circuit  200  of the disclosure, the voltage Vin input to the drain terminal of the MOS transistor M 1  is clamped to the clamping voltage HV_clamp. Therefore, the maximum drain-source voltage Vds of the MOS transistor M 1  in such a case is (HV_clamp-Vth_M 1 ). In an implementation, in the first half time of the rising phase of the output voltage Vout, since the output voltage Vout is relatively small, the first depletion-type high-voltage NMOS transistor M 1  in the auxiliary clamping circuit  200  plays a clamping function at this time, and clamps the voltage input to the drain terminal of the MOS transistor M 1  to be (HV 1 -Vth_MN 1 ). During the second half time of the rising phase of the output voltage Vout, that is, when the output voltage Vout is close to the preset voltage HV 1 , the second depletion-type high-voltage NMOS transistor MN 2  in the auxiliary clamping circuit  200  plays a clamping function and clamps the voltage input to the drain terminal of the MOS transistor M 1  to be (Vout-Vt_MN 2 ); at this time, the clamping voltage HV_clamp changes following the output voltage Vout. However, since the auxiliary clamping circuit  200  is controlled by the input high-voltage HV, its maximum clamping voltage will not exceed the input high-voltage HV, that is, HV_clamp=min (HV, Vout-Vth_MN 2 ), Vth_MN 2 &lt;0. Vth_MN 1  is the threshold voltage of the first depletion-type high-voltage NMOS transistor MN 1 , and Vth_MN 2  is the threshold voltage of the second depletion-type high-voltage NMOS transistor MN 2 . It may be seen that during the rising phase of the output voltage Vout, the auxiliary clamping circuit  200  clamps the voltage input to the drain terminal of the MOS transistor M 1  to be a clamping voltage HV_clamp that is less than the input high-voltage HV, thereby reducing the drain-source voltage Vds of the MOS transistor M 1 , reducing its hot carrier injection effect, improving the high-voltage resistance performance of the circuit, improving the reliability of the circuit with a smaller area cost, and making the circuit of the disclosure applicable to an environment of a higher operating voltage. It should be noted that when the output voltage Vout of the high-voltage functional circuit  100  reaches the maximum value HV, the drain-source voltage Vds of the corresponding MOS transistor M 1  is very small, and the auxiliary clamping circuit  200  may be regarded as having no voltage loss at this time. That is, during the rising phase of the output voltage Vout, the auxiliary clamping circuit  200  of the disclosure clamps the voltage input to the MOS transistor M 1 , and after the output voltage Vout reaches the maximum value HV, there is no voltage loss. Moreover, since the auxiliary clamping circuit  200  of the disclosure only functions during the rising phase of the output voltage Vout, the delay caused to the high-voltage functional circuit  100  is very small and may be ignored, that is, the auxiliary clamping circuit has almost no influence on the performance of the high-voltage functional circuit. 
     Second Implementation 
     As illustrated in  FIG.  4   , the difference between this implementation and the First 
     Implementation is that the auxiliary clamping circuit  200  of this implementation further includes at least one third depletion-type high-voltage NMOS transistor MN 3 . A first connection terminal of the third depletion-type high-voltage NMOS transistor MN 3  is connected to the first connection terminal of the first depletion-type high-voltage NMOS transistor MN 1 , and a second connection terminal of the third depletion-type high-voltage NMOS transistor MN 3  is connected to the second connection terminal of the first depletion-type high-voltage NMOS transistor MN 1 . Agate terminal of the third depletion-type high-voltage NMOS transistor MN 3  is coupled to another preset voltage HV 2 . The another preset voltage HV 2  coupled to the gate terminal of the third depletion-type high-voltage NMOS transistor MN 3  is less than the preset voltage HV 1  coupled to the gate terminal of the first depletion-type high-voltage NMOS transistor MN 1 . 
     As an example, as illustrated in  FIG.  4   , the at least one third depletion-type high-voltage NMOS transistor includes multiple third depletion-type high-voltage NMOS transistors MN 3 . First connection terminals of the multiple third depletion-type high-voltage NMOS transistors MN 3  are connected to the first connection terminal of the first depletion-type high-voltage NMOS transistor MN 1 . Second connection terminals of the multiple third depletion-type high-voltage NMOS transistors MN 3  are connected to the second connection terminal of the first depletion-type high-voltage NMOS transistor MN 1 . Gate terminals of the multiple third depletion-type high-voltage NMOS transistors MN 3  are coupled to preset voltages (HV 2 -HVn) respectively. Values of the preset voltages (HV 2 -HVn) successively increase, and the preset voltage HVn with the largest value is less than the preset voltage HV 1  coupled to the gate terminal of the first depletion-type high-voltage NMOS transistor MN 1 . In practical applications, the first connection terminal of the first depletion-type high-voltage NMOS transistor MN 1 , the first connection terminal of the second depletion-type high-voltage NMOS transistor MN 2 , and the first connection terminals of the third depletion-type high-voltage NMOS transistors MN 3  may be drain terminals; and the second connection terminal of the first depletion-type high-voltage NMOS transistor MN 1 , the second connection terminal of the second depletion-type high-voltage NMOS transistor MN 2 , and the second connection terminals of the third depletion-type high-voltage NMOS transistors MN 3  may he source terminals. In the disclosure by the design of at least one third depletion-type high-voltage NMOS transistor MN 3 , the objective of accurately controlling the clamping voltage HV_clamp may be achieved. The greater the number of third depletion-type high-voltage NMOS transistors MN 3  in the design, the more accurate the control of the clamping voltage HV_clamp is, that is, the closer the clamping voltage HV_clamp is to the real value. 
     In an implementation, the preset voltage HV 1  coupled to the gate terminal of the first depletion-type high-voltage NMOS transistor MN 1  is equal to half of the input high-voltage HV, so that the CMOS circuit of the memory device of the disclosure satisfies its own circuit function while having the reliability improved as much as possible, so that the CMOS circuit of the memory device with such settings may satisfy most of the existing application requirements. In actual applications, the value of the preset voltage HV 1  needs to be set according to specific application scenarios, especially for some special application scenarios. In such cases, the value of the preset voltage HV 1  may be greater than half of the input high-voltage HV, or may be less than half of the input high-voltage HV. 
     In an implementation, the threshold voltage of the first depletion-type high-voltage NMOS transistor MN 1  is less than 0, and the threshold voltage of the third depletion-type high-voltage NMOS transistor MN 3  is less than 0, so that the first depletion-type high-voltage NMOS transistor MN 1 , the second depletion-type high-voltage NMOS transistor MN 2  and the third depletion-type high-voltage NMOS transistors MN 3  are exactly the same. In this way, these transistors may be arranged closely in the layout design, which is conducive to reducing the circuit area and facilitating the model selection of devices. 
     In summary, in the CMOS circuit of the memory device of the disclosure, without modifying the existing high-voltage functional circuit, only by adding an auxiliary clamping circuit at the high-voltage input terminal of the existing high-voltage functional circuit, the voltage input to the MOS transistor in the high-voltage functional circuit is clamped to a clamping voltage less than the input high-voltage in the rising stage of the output voltage. The drain-source voltage of the MOS transistor is reduced, and the hot carrier injection effect is reduced. The performance of the high-voltage resistance of the circuit is improved. The objective of improving the reliability of the circuit at a small area cost is realized, and the performance of the memory device is improved. Therefore, various shortcomings in the related art have been effectively overcome in the disclosure, so the disclosure has a high industrial value in use. 
     The above implementations only exemplarily illustrate the principles and effects of the disclosure, and are not used to limit the disclosure. Anyone familiar with this technology can modify or change the above implementations without departing from the spirit and scope of the disclosure. Therefore, all equivalent modifications or changes made by persons with ordinary knowledge in the art without departing from the spirit and technical ideas disclosed in the disclosure should still be covered by the claims of the disclosure.