Drain-extended MOS ESD protection structure
A protection structure ( 30; 30′; 30″ ) for safely conducting charge from electrostatic discharge (ESD) at a terminal (IN) is disclosed. The protection structure ( 30; 30′; 30″ ) includes a pair of drain-extended metal-oxide-semiconductor (MOS) transistors ( 32, 34 ). In a pump transistors ( 32 ), t...
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| Main Authors | , , |
|---|---|
| Format | Patent |
| Language | English |
| Published |
12.02.2004
|
| Online Access | Get full text |
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| Summary: | A protection structure (
30; 30′; 30″
) for safely conducting charge from electrostatic discharge (ESD) at a terminal (IN) is disclosed. The protection structure (
30; 30′; 30″
) includes a pair of drain-extended metal-oxide-semiconductor (MOS) transistors (
32, 34
). In a pump transistors (
32
), the gate electrode (
45
) overlaps a portion of a well (
42
) in which the drain (
44
) is disposed, to provide a significant gate-to-drain capacitance. The drains of the transistors (
32, 34
) are connected together and to the terminal (IN), while the gates of the transistors (
32, 34
) are connected together. The source of one transistor (
32
) is connected to a guard ring (
50
), of the same conductivity type as the substrate (
40
) within which the channel region of the other transistors (
34
) is disposed. An ESD event received at the terminal (IN) is thus coupled to the gate of the transistors (
32, 34
), causing conduction to the substrate (
40
) via the guard ring (
50
), and turning on a parasitic bipolar transistor at the other transistor (
34
), safely conducting the ESD current. One alternative structure (
30′
) includes a junction capacitor (
65
) coupled between the terminal (IN) and the gates of the transistors (
32, 34
) to improve the coupling. Another alternative structure (
30″
) includes a clamping diode (
92
) that also presents a parasitic bipolar transistor (
95
) enhancing the current conducted to the substrate (
40
). |
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