Structure for protecting an integrated circuit against electrostatic discharges

1. A structure for protecting an integrated circuit against electrostatic discharges, comprising an assembly of identical cells, each of which is connected to a terminal forming a pad of the circuit, a first supply rail or a second supply rail, the cells forming between any two of said terminals an assembly of four alternated layers of different conductivity types wherein:

the cells are arranged in a matrix;

the cells of consecutive parallel diagonals are interconnected;

the consecutive diagonals of interconnected cells are connected to terminals forming, in the following order: the first supply rail ( 5 , VDD), a first pad ( 3 ), and the second supply rail ( 7 , VSS); and

the cells are formed in a layer of a first conductivity type of a first doping level, each cell comprising a well of a second conductivity type of a second doping level, containing on its surface side neighboring regions of doping levels greater than the first and second levels and of opposite conductivity types, in contact with a metallization connected to said terminal, wherein:

contact regions of the first conductivity type and of a doping level greater than the first level are arranged on the upper surface side of said layer and are capable of receiving a turn-on signal; and

the contact regions are connected to the output of a turn-on circuit capable of providing a control signal in case of an overvoltage between any two of said terminals, wherein the turn-on circuit comprises:

an overvoltage detector capable of providing a high output signal when the integrated circuit is supplied;

a first inverter having its input (A) connected to the output of the detector;

a second inverter having its input (B) connected to the output of the first inverter, the output (C) of the second inverter forming the output of the turn-on circuit;

at least one first diode forward-connected between the output (C) of the second inverter and the first supply rail; and

a thyristor forward-connected between the output (C) of the second inverter and a pad of the circuit, the anode and cathode gates of the thyristor being respectively connected to the output (C) of the second inverter and to the second supply rail.

2. The structure of claim 1 , wherein:

said detector is formed of a first P-channel MOS transistor and of a first N-channel MOS transistor, the source and the drain of the first P-channel transistor being respectively connected to the first supply rail and to the gate of the first N-channel transistor, the gate of the first P-channel transistor and the source and the drain of the first N-channel transistor being connected to the second supply rail;

the first inverter is formed of a second P-channel MOS transistor and of a second N-channel MOS transistor and is supplied by the first and second supply rails; and

the second inverter is formed of a third P-channel MOS transistor and of a third N-channel MOS transistor and is supplied by the first and second supply rails.

3. A structure for protecting an integrated circuit against electrostatic discharges, comprising an assembly of identical cells, each of which is connected to a terminal forming a pad of the circuit, a first supply rail or a second supply rail, the cells forming between any two of said terminals an assembly of four alternated layers of different conductivity types wherein:

the cells are arranged in a matrix;

the cells of consecutive parallel diagonals are interconnected;

the consecutive diagonals of interconnected cells are connected to terminals forming, in the following order: the first supply rail ( 5 , VDD), a first pad ( 3 ), and the second supply rail ( 7 , VSS); and

each pair of cells forms a triac between two of said terminals.