CN1466268A

CN1466268A - Substrate charge circuit for input/output electrostatic discharge protection and protection method thereof

Info

Publication number: CN1466268A
Application number: CNA021412138A
Authority: CN
Inventors: 赖纯祥; 刘孟煌; 苏醒; 卢道政
Original assignee: Macronix International Co Ltd
Current assignee: Macronix International Co Ltd
Priority date: 2002-07-03
Filing date: 2002-07-03
Publication date: 2004-01-07
Anticipated expiration: 2022-07-03
Also published as: CN1225792C

Abstract

This invention relates to a base plate charge circuit and its protection method for input/output static discharge protection, in which, the static discharge protection includes connection points between MOS finger structure connecting input/output pads and internal circuit, the said charge circuit includes connection points between the said input/output pad and internal circuit connected by a MOS device and a base plate starting when the input/output pad is pressed by static discharge controlled by a switch to conduct a circuit to pass through a base plate resistance to make the voltage increase at the MOS structure to reduce its trigger voltage.

Description

Be used for the substrate charging circuit and the guard method of I/O electrostatic discharge (ESD) protection

Technical field

The present invention relates to the static discharge (Electro-StaticDischarge of a kind of integrated circuit (IC); ESD) protection is meant a kind of substrate charging (substratepump) circuit and guard method thereof that is used for I/O (I/O) esd protection especially.

Background technology

CMOS (Complementary Metal Oxide Semiconductor) (CMOS) integrated circuit (IC) apparatus is subject to that ESD triggers fault and impaired, especially for improving thin gate oxide, jitty and shallow junction structure and lightly doped drain (LDD) and self-aligned metal silicate (salicide) technology that the aggregation degree is used, the ability of the MOS element of more decaying opposing ESD.Had many technology to be used to self-protection output buffer or I/O node (node) to resist the ESD fault, wherein comprised the diode strangulation, laterally puncture element and retaining ring around joint sheet (pad), these circuit provide the effect of some degree.

The esd protection structure typically is divided into two classes, comprises the structure of protecting input buffer and the structure of protecting output buffer and I/O node.The protection of input buffer is considerably simple, because not conducting of the grid electric current of CMOS, therefore, special protection structure is implemented on the input buffer, and the grid voltage of its limit transistor is to maximum collapse (breakdown) voltage.Under the contrast, another kind of output buffer and I/O node contain feels bad the structure of protection, and its difficult origin cause of formation is because output buffer may the conducting electric current during ESD compressing (stress), thereby may be impaired.Protection structure must be designed and layout makes under ESD compressing situation, and this protection structure discharges the ESD compressing and not self-destruction, but output buffer conducting one minimum current only.The known esd protection structure that is used roughly utilizes the transistor of protective circuit to open mechanism and transistor returns two kinds of (snapback) mechanism suddenly, and the former is its feature with the conductive channel limit voltage, and the latter is its feature with the transistor breakdown voltage then.The rapid mechanism of returning that is widely used adds the esd protection structure on the contact between I/O pad and the internal circuit, for example nmos pass transistor when esd event takes place, utilizes the built-in transistorized bypass of parasitic two-carrier with the protection internal circuit.Allow a large amount of ESD electric currents for making nmos pass transistor; but avoid the vertical wide long of gate configuration; finger-like (finger) structure is used; unfortunately, because the textural born difference that finger caused, the finger of nmos pass transistor is difficult for as one man being opened; make the ESD electric current burn device because concentrate on the zonule; therefore, even if having very big esd protection element, its performance performance still can't be accepted.In the solution that other are suggested, the substrate charging circuit can reduce triggering (triggering) voltage of NMOS finger, to strengthen the consistency that it is unlocked.For substrate is boosted; charging circuit should be unlocked than esd protection circuit is more Zao during esd event; yet; if the width of charging transistor is too little; it may be damaged by the ESD electric current, and therefore, charging transistor must be even as big as bearing the ESD electric current; but thus, the substrate charging circuit just consumes very big chip area.So it is to be the institute Ji that a kind of undersized substrate charging circuit is used for the I/O esd protection.

Summary of the invention

Purpose of the present invention promptly is to propose a kind of substrate charging circuit and guard method of the I/O of being used for esd protection; it utilizes the PMOS finger that is not used in the integrated circuit as charging circuit; when taking place, esd event is unlocked and conducting one electric current process substrate resistance; make the substrate voltage at the contiguous place of NMOS finger be raised, thereby reduce the trigger voltage of this NMOS finger.

According to a preferred embodiment of the present invention; be the I/O pad of the NMOS finger connecting wafer of esd protection and the contact between the internal circuit; the base of this NMOS finger (base) is through substrate resistance ground connection; the source electrode of one PMOS finger connects the contact between this I/O pad and the internal circuit; its drain electrode connects the base of this NMOS finger; one switch connects the grid of this PMOS finger; during normal running; this PMOS finger is closed by this switch; and when esd event causes the voltage fast rise of I/O pad; this PMOS finger is unlocked to draw a little ESD electric current to this substrate charging, makes this NMOS finger as one man be opened and discharges most ESD electric current.

Particularly, the present invention is a kind of substrate charging circuit that is used for the I/O electrostatic discharge (ESD) protection, this electrostatic discharge (ESD) protection contains metal-oxide-semiconductor's finger that the I/o pad on substrate connects, this charging circuit comprises: a resistance is connected between the base and earth terminal of this metal-oxide-semiconductor's finger; One charger connects the base of this metal-oxide-semiconductor's finger; And a switch, make this charger of control during esd event conducting one charging current through this resistance.

The present invention also comprises a kind of method that is used for the I/O electrostatic discharge (ESD) protection, this electrostatic discharge (ESD) protection contains metal-oxide-semiconductor's finger that the I/o pad on substrate connects, and this method comprises the following steps: to connect resistance between the base and earth terminal of this metal-oxide-semiconductor's finger; And conducting one charging current is passed through this resistance during esd event.

Description of drawings

For the personage who has the knack of this skill, cooperate follow graphic from following being described in detail, the present invention can more clearly be understood, and its above-mentioned and other purpose and advantage will become more obvious, wherein:

Fig. 1: according to a preferred embodiment of the present invention;

Fig. 2: in four kinds of element connections of I/O pad;

Fig. 3: the current-voltage of esd protection element (I-V) curve chart;

The element of Fig. 4: Fig. 2 current-voltage curve separately; And

Fig. 5: the exemplary circuit of the switch among Fig. 1.

The figure number table of comparisons:

10 esd protection circuits

11 I/O pads

12 output drivers

13 ESD fingers

14 power ends

15 earth terminals

16 earth terminals

17 PMOS fingers

18 switches

19 NMOS fingers

20 NMOS fingers

The 21 PMOS transistors of closing

The 22 PMOS transistors of opening

The nmos pass transistor of 23 grounded-grids

The nmos pass transistor of 24 suspension joint grids

The I-V curve of 31 PMOS 21

The I-V curve of 32 PMOS 22

The I-V curve of 33 NMOS 23

The I-V curve of 34 NMOS 24

41 PMOS transistors

42 switching circuits

43 resistance

44 electric capacity

45 switching circuits

46 diode strings

Embodiment

Fig. 1 is according to a preferred embodiment of the present invention; esd protection circuit 10 contains contact and the power end 14 and earth terminal 15 between output driver (output driver) 12 and ESD finger 13 connection I/O pads 11 and the internal circuit; make during esd event to discharge the ESD electric current from I/O pad 11, NMOS finger 19 in output driver 12 and the

ESD finger

13 and 20 base are through substrate resistance R _SubBe grounded to earth terminal 16, the source electrode of the PMOS finger 17 that is not used connects the contact between I/O pad 11 and the internal circuit, and its drain electrode connects substrate resistance R _SubAnd the contact between the base of

NMOS finger

19 and 20, and its grid is connected to node A, switch 18 connected node A provide PMOS finger 17 voltages and control PMOS finger 17 with decision.

When I/O pad 11 is subjected to the positive current compressing in esd event, the voltage of I/O pad 11 will rise apace, make the voltage of node A will be lower than the voltage of I/O pad 11, the pressure difference of the two is that the source electrode of PMOS finger 17 differs from Vsg to the grid electricity, therefore, PMOS finger device 17 will at first be unlocked to grid pressure reduction Vsg＞Vt because of its source electrode, thereby conducting one electric current is through substrate resistance R _SubTo earth terminal 16, consequently promote the voltage at contiguous NMOS finger 19 of substrate and 20 places, thereby reduce the trigger voltage of

NMOS finger

19 and 20.

For ease of understanding four kinds of element connections of Fig. 2 illustration at the I/O pad.The PMOS transistor of in Fig. 2 (A), closing (" off " PMOS) 21, its drain electrode connects low pressure, and grid is connected high pressure in the lump with source electrode.Fig. 2 (B) shows the PMOS transistor of opening (" on " PMOS) 22, and its drain electrode connects low pressure, and source electrode connects high pressure, and grid connects another low pressure.The nmos pass transistor (grounded-gate NMOS) 23 of grounded-grid among Fig. 2 (C), its source electrode is connected low pressure with grid, and drain electrode connects high pressure.The nmos pass transistor (floating-gate NMOS) 24 of suspension joint grid among Fig. 2 (D), its source electrode is connected low pressure and high pressure respectively with drain electrode, and grid is suspension joint then.

Before further specifying the element operation characteristic of Fig. 2, please consult the rapid return characteristic current-voltage curve of element shown in Figure 3 figure earlier, when voltage when V1 rises gradually, electric current also increases thereupon, up to arriving its trigger voltage Vtrig, then voltage descends rapidly, and the variation of electric current is little, this trend drops to up to voltage to be kept (holding) voltage Vhold and just changes, and this after-current is being followed voltage again and up and apace increased.During the EDS incident, trigger voltage Vtrig is more little, and then this element more early is triggered.

Fig. 4 is four kinds of each self-corresponding current-voltage curve figure of device of Fig. 2, wherein curve 31 is the current-voltage curve of the PMOS transistor 21 of closing shown in Fig. 2 (A), the PMOS transistor 22 of the unlatching of curve 32 corresponding diagram 2 (B), curve 33 is current-voltage curves of nmos pass transistor 23 of the grounded-grid of Fig. 2 (C), and curve 34 is characteristic curves of the nmos pass transistor 24 of suspension joint grid shown in Fig. 2 (D).During esd event, curve from Fig. 4 as can be known, nmos pass transistor 34 its trigger voltages of suspension joint grid are lower than the trigger voltage of the nmos pass transistor 33 of grounded-grid, so, the NMOS finger that has used its grid during esd event draws most ESD electric current as suspension joint with being unlocked earlier, then because its grid of NMOS finger that is not used is being difficult to open of ground connection and just being damaged than low level rank (level).From other known technology, the similar rank, trigger voltage position of trigger voltage to that the substrate charging can reduce the NMOS finger that is used and is not used more as one man are unlocked them, thereby improve the ESD performance performance of I/O pad.

As shown in fig. 1, the substrate charging circuit comprises PMOS transistor 17 and switch 18, the latter will supply high pressure to close PMOS transistor 17 during normal running, and during esd event, supply low pressure to open PMOS transistor 17, so, the substrate charging circuit for cutting out, is unlatching during esd event during normal running.As shown in Figure 4, PMOS transistor 31 its trigger voltages of closing are higher than the trigger voltage of nmos pass transistor 33/34, therefore, during normal running, PMOS transistor 17 can not be unlocked, yet, during esd event, switch 18 will relatively reduce the grid voltage of PMOS transistor 17, with its unlatching, and then the ESD electric current that causes PMOS transistor 17 to draw part charges this charging current process substrate resistance R to substrate _SubTo earth terminal 16, the trigger voltage that is higher than nmos pass transistor up to the conducting voltage of PMOS transistor 17, owing to the increase along with the ESD electric current of the conducting voltage of PMOS transistor 17 increases, be high enough to trigger the NMOS finger at last, in case the NMOS finger is triggered, most ESD electric current is just drawn by the NMOS finger, therefore, PMOS transistor 17 will can not be subjected to the ESD current destroying, because most ESD electric current is by the NMOS finger.Also know that from the curve 32 of Fig. 4 arrive its trigger voltage and before being unlocked, PMOS transistor 32 can keep its opening at nmos pass transistor 33/34, therefore, the PMOS transistor 17 in Fig. 1 can guarantee its effect, and the situation that can not take place not open.

The circuit of the switch 18 among two Fig. 1 of Fig. 5 illustration, the PMOS transistor 17 in PMOS transistor 41 presentation graphs 1 among the figure.In Fig. 5 (A), the drain electrode of PMOS transistor 41 is connected low pressure and high pressure respectively with source electrode, switch 42 comprises between the resistance 43 of series connection and the supply voltage I/O Vdd2 14 and low pressure that electric capacity 44 is connected the I/O pad, and the high pressure that PMOS transistor 17 connects is connected to I/O Vdd2 14 by diode 48, the grid of PMOS transistor 41 connects the contact between resistance 43 and the electric capacity 44, when normal running since I/O Vdd2 14 through 43 pairs of electric capacity of resistance 44 charging, make the grid of PMOS transistor 41 be maintained at high pressure, therefore PMOS transistor 41 is closed, when the source voltage of PMOS transistor 41 rises apace because the time delay of resistance capacitance, grid potential has little time to rise, and the pressure reduction between its grid and the source electrode will rise and cause PMOS transistor 41 to be unlocked.In Fig. 5 (B), the drain electrode of PMOS transistor 41 is connected low pressure and high pressure respectively with source electrode, and its grid connects core (core) supply voltage Vdd, switch 45 comprises between the grid that diode string 46 is connected high pressure and PMOS transistor 41, therefore, PMOS transistor 41 is held closes, and only rises to its limit voltage at the source voltage of PMOS transistor 41 and is overcome, and 41 beginnings of PMOS transistor are unlocked.Though as example, can keep the PMOS transistor and close, and other circuit of opening after its source voltage rises all can be used as the circuit of implementing switch 18, the personage who has the knack of this described skill should readily understand and correct.In other varying circuit,, and all can be applicable among the present invention at the switch of esd event unlatching PMOS transistor 17 as long as can during normal running, close PMOS transistor 17.

According to the present invention, as long as a undersized MOS transistor can provide enough charging circuits, the preferably utilizes the PMOS finger that is not used in the integrated circuit, and, because it has high maintenance voltage, therefore can not damaged by the ESD electric current.

More than be stated as the purpose of illustrating for what preferred embodiment of the present invention was done, accurately be disclosed form and be not intended to limit the present invention, based on above instruction or to make an amendment or change from embodiments of the invention study be possible, embodiment has the knack of this described operator and utilizes the present invention to select in practical application with various embodiment and narrate for explaining orally principle of the present invention and allowing, and technological thought attempt of the present invention is decided by claims scope and equalization thereof.

Claims

1. substrate charging circuit that is used for the I/O electrostatic discharge (ESD) protection is characterized in that: this electrostatic discharge (ESD) protection contains metal-oxide-semiconductor's finger that the I/o pad on substrate connects, and this charging circuit comprises:

One resistance is connected between the base and earth terminal of this metal-oxide-semiconductor's finger;

One charger connects the base of this metal-oxide-semiconductor's finger; And

One switch makes this charger of control this resistance of conducting one charging current process during esd event.

2. substrate charging circuit as claimed in claim 1 is characterized in that: this resistance is substrate resistance.

3. substrate charging circuit as claimed in claim 1 is characterized in that: this charger is the PMOS transistor.

4. substrate charging circuit as claimed in claim 3 is characterized in that: this PMOS transistor is a finger.

5. substrate charging circuit as claimed in claim 3 is characterized in that: this PMOS transistor has source electrode and connects this I/o pad, and drain electrode connects the base of this metal-oxide-semiconductor's finger, and grid connects this switch.

6. substrate charging circuit as claimed in claim 1 is characterized in that: this switch is the resistance-capacitance circuit.

7. substrate charging circuit as claimed in claim 1 is characterized in that: this switch is the diode serial connection.

8. method that is used for the I/O electrostatic discharge (ESD) protection is characterized in that: this electrostatic discharge (ESD) protection contains metal-oxide-semiconductor's finger that the I/o pad on substrate connects, and this method comprises the following steps:

Connect resistance between the base and earth terminal of this metal-oxide-semiconductor's finger; And

Conducting one charging current is through this resistance during esd event.

9. method as claimed in claim 8 is characterized in that: this resistance is to utilize substrate resistance.

10. method as claimed in claim 8 is characterized in that: more comprise and open metal-oxide-semiconductor's device for should charging current.

11. method as claimed in claim 10 is characterized in that: this metal-oxide-semiconductor's device is the PMOS transistor.

12. method as claimed in claim 11 is characterized in that: this PMOS transistor is a finger.

13. method as claimed in claim 11 is characterized in that: more comprise connecting the transistorized source electrode of this PMOS, and drain electrode is to the base of this metal-oxide-semiconductor's finger to this I/o pad.

14. method as claimed in claim 8 is characterized in that: more comprise connecting switch to control this charging current.

15. method as claimed in claim 8 is characterized in that: this charging current is in the preceding conducting that is triggered of this metal-oxide-semiconductor's finger.