# US 8,786,989 B2 · Electronic device comprising a buffer and means for protecting against electrostatic discharges

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- Number: US 8,786,989 B2
- Document ID: US8786989B2
- Status: Granted
- Kind: B2
- Application number: 13/198,436
- Filed: 2011-08-04
- Published: 2012-03-01
- Granted: 2014-07-22
- Earliest claimed: 2010-08-26
- Assignees: STMicroelectronics S.r.l.
- Applicants: Philippe Galy; Jean Jimenez
- Inventors: Philippe Galy; Jean Jimenez
- Web page: https://patentgrep.com/patent/US8786989B2

## CPC

- H03K 19/00346: {Modifications for eliminating interference or parasitic voltages or currents}
- H10D 89/815: {involving a parasitic bipolar transistor triggered by the local electrical biasing of the layer acting as base region of said parasitic bipolar transistor}
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

The electronic device comprises a first terminal and a second terminal, a buffer connected between the first terminal and the second terminal and comprising a signal input, and means for protecting against electrostatic discharges likely to occur across at least a pair of nodes of the buffer. The device comprises at least one integrated structure connected between the two nodes and said signal input, containing at least one MOS transistor and forming both said protection means and at least a part of said buffer.

## Claims

### Claim 1

An integrated circuit comprising:
a first terminal;
a second terminal;
a signal terminal;
an integrated buffer and electrostatic discharge protection circuit connected between the first terminal and the second terminal, the integrated buffer and electrostatic discharge protection circuit comprising a MOS transistor configured to operate as part of both a buffer and an electrostatic discharge protection circuit; and
logic circuitry configured to receive a logic signal from the buffer and to be protected against electrostatic discharge by the electrostatic discharge protection circuit.

### Claim 2 (depends on 1)

The integrated circuit of claim 1, wherein the MOS transistor is configured to operate at least partially in a hybrid mode during an electrostatic discharge event occurring between the first terminal and the second terminal.

### Claim 3 (depends on 1)

The integrated circuit of claim 1, wherein the integrated buffer and electrostatic discharge protection circuit comprises;
the MOS transistor coupled between the first terminal and the second terminal;
a second MOS transistor coupled between the first terminal and a common node; and
a resistive element coupled between the common node and the second terminal.

### Claim 4 (depends on 3)

The integrated circuit of claim 3, further comprising an additional transistor coupled between a gate of the MOS transistor and the common node.

### Claim 5 (depends on 3)

The integrated circuit of claim 3, further comprising a second electrostatic discharge protection circuit coupled between the common node and the second terminal.

### Claim 6 (depends on 5)

The integrated circuit of claim 5, wherein the second electrostatic discharge protection circuit comprises a diode.

### Claim 7 (depends on 6)

The integrated circuit of claim 6, wherein the integrated buffer and electrostatic protection circuit comprises a CMOS buffer.

### Claim 8 (depends on 1)

The integrated circuit of claim 1, wherein the signal terminal is coupled to a gate of the MOS transistor.

### Claim 9 (depends on 1)

The integrated circuit of claim 1, wherein the first and second terminals are input/output pads of the integrated circuit.

### Claim 10 (depends on 1)

The integrated circuit of claim 1, further comprising a plurality of additional MOS transistors coupled in parallel with the MOS transistor between the first and second terminals.

### Claim 11 (depends on 1)

The integrated circuit of claim 1, wherein
the MOS transistor has a current path coupled between the first terminal and the second terminal, and wherein the MOS transistor has a control terminal coupled to the signal terminal, and
the integrated buffer further comprises a control circuit coupled to a substrate contact of the MOS transistor, the control circuit configured to control a substrate voltage of the MOS transistor.

### Claim 12 (depends on 11)

The integrated circuit of claim 11, wherein the control circuit comprises a second MOS transistor.

### Claim 13 (depends on 12)

The integrated circuit of claim 12, wherein the control circuit further comprises a third MOS transistor coupled between the first terminal and the substrate contact of the MOS transistor.

### Claim 14 (depends on 13)

The integrated circuit of claim 13, wherein a control terminal of the second MOS transistor is coupled to a substrate contact terminal of the second MOS transistor and a control terminal of the third MOS transistor is coupled to a substrate contact terminal of the third MOS transistor.

### Claim 15 (depends on 13)

The integrated circuit of claim 13, wherein each MOS transistor has a gate length of less than 1 micrometer.

### Claim 16 (depends on 11)

The integrated circuit of claim 11, wherein the MOS transistor is configured to operate at least transiently in a hybrid mode during an electrostatic discharge event between the first terminal and the second terminal, wherein the hybrid mode includes both a MOS transistor type current and a bipolar transistor type current.

### Claim 17 (depends on 11)

The integrated circuit of claim 11, wherein the MOS transistor comprises a plurality of MOS transistors of a same conductivity type connected in parallel.

### Claim 18

An integrated circuit comprising:
a first terminal;
a second terminal;
a signal terminal; and
an integrated buffer and electrostatic discharge protection circuit connected between the first terminal and the second terminal, comprising at least one MOS transistor configured to operate at least transiently in a hybrid mode during an electrostatic discharge event occurring between the first or the second terminal and another terminal, wherein the at least one MOS transistor comprises a plurality of MOS transistors coupled in parallel with one another.

### Claim 19

An integrated circuit comprising:
a first terminal;
a second terminal;
a signal terminal;
an integrated buffer and electrostatic discharge protection circuit connected between the first terminal and the second terminal, comprising at least one MOS transistor configured to operate at least transiently in a hybrid mode during an electrostatic discharge event occurring between the first or the second terminal and another terminal; and logic circuitry configured to receive a logic signal from the integrated buffer and to be protected against electrostatic discharge by the integrated electrostatic discharge protection circuit.

### Claim 20

An integrated circuit comprising:
a first terminal;
a second terminal;
a signal terminal;
an integrated buffer and electrostatic discharge protection circuit connected between the first terminal and the second terminal, the integrated buffer and electrostatic discharge protection circuit comprising:
a first MOS transistor having a current path coupled between the first terminal and the second terminal, wherein the first MOS transistor has a control terminal coupled to the signal terminal, and
a control circuit coupled to a substrate contact of the first MOS transistor, the control circuit configured to control a substrate voltage of the MOS transistor; and
a first additional MOS transistor of a conductivity type opposite from the first MOS transistor, the first additional MOS transistor having a current path coupled between the second terminal and a third terminal and having a control terminal coupled to the signal terminal.

### Claim 21 (depends on 20)

The integrated circuit of claim 20, wherein the first additional MOS transistor comprises a portion of the integrated buffer and electrostatic discharge protection circuit.

### Claim 22 (depends on 20)

The integrated circuit of claim 20, further comprising:
a second additional MOS transistor having a source/drain coupled to a substrate contact of the first additional MOS transistor;
a third additional MOS transistor having a source/drain coupled to the substrate contact of the first additional MOS transistor; and
a resistive element coupled between the substrate contact of the first additional MOS transistor and the third terminal.

### Claim 23 (depends on 20)

The integrated circuit of claim 20, further comprising a further electrostatic discharge protection circuit coupled between the second and third terminals and in parallel with the first additional MOS transistor.

### Claim 24

An integrated circuit comprising:
a first terminal;
a second terminal;
a third terminal;
a first MOS transistor having a current path coupled between the first terminal and the second terminal, having a control terminal coupled to the third terminal, and having a substrate contact;
a second MOS transistor having a current path coupled between the third terminal and the substrate contact of the first MOS transistor;
a first resistive element coupled between the second terminal and the substrate contact of the first MOS transistor;
a third MOS transistor coupled between the first terminal and the substrate contact of the first MOS transistor; and
a second resistive element coupled between the third terminal and a substrate contact of the second MOS transistor.

### Claim 25 (depends on 24)

The integrated circuit of claim 24, wherein a control terminal of the second MOS transistor is coupled to a substrate contact of the second MOS transistor and wherein a control terminal of the third MOS transistor is coupled to a substrate contact of the third MOS transistor.

### Claim 26 (depends on 24)

The integrated circuit of claim 24, further comprising a third resistive element coupled between the substrate contact of the first MOS transistor and a substrate contact of the third MOS transistor.

### Claim 27 (depends on 24)

The integrated circuit of claim 24, wherein the first MOS transistor comprises a plurality of MOS transistors of a same conductivity type connected in parallel.

### Claim 28 (depends on 24)

The integrated circuit of claim 24, wherein the integrated circuit comprises a buffer connected between the first terminal and a fourth terminal, and wherein the buffer comprises the first MOS transistor and an additional MOS transistor of a second conductivity type opposite that of the first MOS transistor, the additional MOS transistor having a current path coupled between the second terminal and the fourth terminal.

### Claim 29 (depends on 28)

The integrated circuit of claim 28, wherein the integrated circuit further comprises:
a second additional MOS transistor having a source/drain coupled to a substrate contact of the additional MOS transistor;
a third additional MOS transistor having a source/drain coupled to the substrate contact of the additional MOS transistor; and
a second resistive element coupled between the substrate contact of the additional MOS transistor and the fourth terminal.

### Claim 30

A method of operating a semiconductor device that includes an integrated buffer and electrostatic discharge protection circuit comprising a MOS transistor, wherein the method comprises:
during normal operation, buffering an input signal with the MOS transistor by:
receiving the input signal at a gate of the MOS transistor;
supplying a buffered output to an output terminal via a first source/drain terminal of the MOS transistor;
during an electrostatic discharge event, operating the MOS transistor at least transiently in a hybrid mode to provide a discharge current path, wherein operating in the hybrid mode comprises:
generating a MOS transistor type sub-threshold current in the MOS transistor; and
generating a bipolar transistor type current in the MOS transistor dependent on a source-substrate voltage applied to the MOS transistor.

### Claim 31 (depends on 30)

The method of claim 30, wherein the discharge path include the first source/drain terminal of the MOS transistor and a second source/drain second terminal of the MOS transistor.

### Claim 32 (depends on 30)

The method of claim 30, further comprising regulating a voltage on a substrate contact of the MOS transistor, wherein regulating the voltage on the substrate contact of the MOS transistor comprises, during the electrostatic discharge event, providing a positive voltage to the substrate contact operable to enable the bipolar transistor type current.

### Claim 33 (depends on 30)

The method of claim 30, further comprising operating a second MOS transistor coupled to a substrate of the MOS transistor and a third MOS transistor coupled to the substrate of the MOS transistor at least transiently in the hybrid mode during an electrostatic discharge event.