PROTECTION DEVICE AGAINST ELECTROSTATIC DISCHARGES

Description

Technical field

[0001] This description relates generally to electronic devices, and more particularly to devices for protection against electrostatic discharges. Prior art

[0002] Electrostatic discharges can produce harmful effects in integrated circuits or electronic components that are subjected to them, which may cause irreversible deterioration of all or part of their constituent elements. An integrated circuit or electronic component may thus suffer significant malfunctions or even be rendered completely inoperable following an electrostatic discharge. If necessary, replacement of the defective circuit or component may prove necessary, thus harming the reliability of electronic devices incorporating such circuits or components.

[0003] To protect against the harmful effects of electrostatic discharges, integrated circuits and electronic components may include protective devices. However, existing electrostatic discharge protection devices suffer from various drawbacks. In particular, the presence of a protective device may impede the operation of other circuits or components adjacent to the device.

[0004] US 2021 / 0242195 A1, US 2014 / 0198417 A1 and EP 0 148 577 A1 describe devices for protection against electrostatic discharges. Summary of the invention

[0005] There is a need to improve existing electrostatic discharge protection devices. In particular, there is a need to reduce disturbances caused by the presence of an electrostatic discharge protection device in an electronic device.

[0006] For this, claim 1 of the invention provides a pseudo-bidirectional device for protection against electrostatic discharges, comprising: first and second diodes respectively connecting first and second terminals to the same internal node of the device; and a third diode connecting the internal node to a third terminal for applying a reference potential, in which the third diode has a capacitance greater than that of the first and second diodes, the device further comprising first and second capacitive elements respectively connected in parallel with the first and second diodes.

[0007] According to one embodiment: the first diode comprises anode and cathode electrodes connected respectively to the internal node and the first terminal; and the second diode comprises anode and cathode electrodes connected respectively to the internal node and the second terminal.

[0008] According to one embodiment, the third diode comprises anode and cathode electrodes connected respectively to the internal node and to the third terminal.

[0009] According to one embodiment, the first and second capacitive elements are capacitors.

[0010] According to one embodiment, the device has a monolithic structure.

[0011] According to one embodiment, the first and second capacitive elements are MIM capacitors.

[0012] According to one embodiment, the device further comprises: third and fourth capacitive elements, distinct from the first and second capacitive elements, respectively connecting the first and second terminals to the third terminal; and first and second resistive elements respectively connecting the first and second terminals to fourth and fifth terminals.

[0013] According to one embodiment: the third and fourth capacitive elements each have a capacitance equal to about 55 pF; and the first and second resistive elements each have a resistance equal to about 50 Ω.

[0014] According to one embodiment, the first, second and third diodes are Zener diodes or transient voltage suppression diodes.

[0015] According to one embodiment, the first and second capacitive elements have capacities that are substantially identical to each other.

[0016] According to one embodiment, the first and second capacitive elements each have a capacitance equal to approximately 10 pF.

[0017] According to one embodiment, the third diode has a capacity at least twice as high, preferably at least five times as high, more preferably approximately ten times as high as those of the first and second diodes.

[0018] According to one embodiment: the first and second diodes each have a capacitance equal to about 4.5 pF; and the third diode has a capacitance equal to about 38 pF.

[0019] According to one embodiment, the first and second terminals are input and / or output terminals of an integrated circuit.

[0020] According to one embodiment, the internal node corresponds to a semiconductor substrate in and on which the device is formed. Brief description of the drawings

[0021] These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which: there figure 1 is an electrical diagram illustrating an example of a standard device for protection against electrostatic discharges; the figure 2 is an electrical diagram illustrating an example of an electrostatic discharge protection device according to one embodiment; and the figure 3 is an electrical diagram illustrating another example of an electrostatic discharge protection device according to one embodiment. Description of the embodiments

[0022] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0023] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the components or integrated circuits capable of being protected against electrostatic discharges by the devices of the present description will not be detailed, the described embodiments being compatible with the components or integrated circuits usually protected against electrostatic discharges.

[0024] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0025] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0026] Unless otherwise specified, the expressions “about”, “approximately”, “substantially”, and “in the order of” mean to within 10%, preferably to within 5%.

[0027] There figure 1 is an electrical diagram illustrating an example of a standard device 100 for protection against electrostatic discharges.

[0028] In the example shown, the device 100 comprises several diodes 101-1, 101-2, ... 101-n respectively connecting terminals 103-1, 103-2, ... 103-n to the same internal node 105. More precisely, in the example illustrated in figure 1 , each diode 101-1, 101-2, ... 101-n comprises an anode electrode or terminal connected to the internal node 105, and a cathode electrode or terminal connected to the corresponding terminal 103-1, 103-2, ... 103-n.

[0029] The terminals 103-1, 103-2, ... 103-n are, for example, input terminals, output terminals or input-output terminals of an integrated circuit or an electronic component to be protected against electrostatic discharges. Each terminal 103-1, 103-2, ... 103-n is, for example, adapted to receive or transmit a digital or analog signal, for example an analog signal having a frequency lower than 10 or 20 MHz. For example, the terminals 103-1, 103-2, ... 103-n are, in nominal operation, subjected to a potential of the order of 3.3 V, of the order of 5 V or of the order of 15 V.

[0030] Generally, the device 100 comprises n branches each comprising a terminal 103 connected to the node 105 by a diode 101, with n an integer greater than or equal to two. The number n is for example equal to the number of external terminals 103 of an integrated circuit to be protected against electrostatic discharges.

[0031] In the example shown, the electrostatic discharge protection device 100 further comprises another diode 107 connecting the internal node 105 to another terminal 109 for applying a reference potential, for example ground. More precisely, in the example illustrated in figure 1 , the diode 107 comprises an anode electrode or terminal connected to the internal node 105, and a cathode electrode or terminal connected to the reference potential application terminal 109.

[0032] The device 100 for protection against electrostatic discharges has a so-called “pseudo-bidirectional” architecture. This is reflected in particular by the fact that the diodes 101-1, 101-2, ... 101-n connected to the terminals 103-1, 103-2, ... 103-n have their anodes connected to the same node 105 and by the fact that a single diode 107 connects the anodes of the diodes 101-1, 101-2, ... 101-n to the terminal 109 for applying the reference potential.

[0033] The diode 107 of the device 100 has a strictly higher capacitance, for example at least twice higher, for example at least five times higher, for example approximately ten times higher than the capacitance of each diode 101-1, 101-2, ... 101-n. This makes it possible to reduce crosstalk phenomena between the terminals 103-1, 103-2, ... 103-n. The capacitance of each diode 101-1, 101-2, ... 101-n is for example of the order of a few picofarads, and the capacitance of the diode 107 is for example of the order of a few tens of picofarads. The diodes 101-1, 101-2, ... 101-n of the device 100 have for example capacitances that are substantially equal to each other, apart from manufacturing variations. For example, each diode 101-1, 101-2, ... 101-n has a capacitance equal to about 4.5 pF, and diode 107 has a capacitance equal to about 38 pF.

[0034] In the illustrated example, the diodes 101-1, 101-2, ... 101-n and 107 of the device 100 are Zener diodes. This example is not, however, limiting, each diode 101-1, 101-2, ... 101-n, 107 of the device 100 may, as a variant, be a transient voltage suppression diode (TVS).

[0035] In the event of electrostatic discharge, a positive or negative overvoltage may appear between one of the terminals 103-1, 103-2, ... 103-n and the terminal 109 for applying the reference potential. For example, in a case where each terminal 103-1, 103-2, ... 103-n is adapted to be polarized by a nominal voltage equal to approximately 3.3 V, a positive overvoltage may correspond to the application, between one of the terminals 103-1, 103-2, ... 103-n and the terminal 109, of a voltage of the order of +10 V and a negative overvoltage may correspond to the application, between one of the terminals 103-1, 103-2, ... 103-n and the terminal 109, of a voltage of the order of -10 V.

[0036] In the event of a positive overvoltage between one of the terminals 103-1, 103-2, ... 103-n and terminal 109 of the device 100, the diode 101-1, 101-2, ... 101-n connected to this terminal is reverse-biased by a voltage greater than its breakdown or avalanche voltage, and the diode 107 is forward-biased by a voltage greater than its threshold voltage. The diode 101-1, 101-2, ... 101-n then allows a reverse current to flow, and the diode 107 allows a forward current to flow. The current resulting from the electrostatic discharge is thus discharged from the terminal 103-1, 103-2, ... 103-n to the terminal 109.

[0037] In the event of a negative overvoltage between one of the terminals 103-1, 103-2, ... 103-n and terminal 109 of the device 100, the diode 101-1, 101-2, ... 101-n connected to this terminal is forward biased by a voltage greater than its threshold voltage, and the diode 107 is reverse biased by a voltage greater than its breakdown or avalanche voltage. The diode 101-1, 101-2, ... 101-n then allows a forward current to pass, and the diode 107 allows a reverse current to pass. The current resulting from the electrostatic discharge is thus discharged from terminal 109 to terminal 103-1, 103-2, ... 103-n.

[0038] A disadvantage of the device 100 for protection against electrostatic discharges is that its presence generates harmonics on the terminals 103-1, 103-2, ... 103-n, in particular second and third harmonics.

[0039] In order to reduce the production of harmonics, one solution could be to replace the pseudo-bidirectional device 100 with an electrostatic discharge protection device having a fully bidirectional structure. In such a device, the anodes of the n diodes 101-1, 101-2, ... 101-n are for example respectively connected to anodes of n other diodes whose cathodes are connected to the terminal 109 for applying the reference potential. In other words, a fully bidirectional device comprises as many diodes 101 whose cathodes are respectively connected to the terminals 103 as there are diodes whose cathodes are connected to the terminal 109, each terminal 103 thus being connected to the terminal 109 by a series connection of two diodes interconnected by their cathodes. A fully bidirectional device, however, would have greater bulk and cost than the 100 pseudo-bidirectional device.

[0040] There figure 2 is an electrical diagram illustrating an example of an electrostatic discharge protection device 200 according to one embodiment.

[0041] Device 200 of the figure 2 includes elements in common with device 100 of the figure 1 . These common elements will not be detailed again below. Device 200 of the figure 2 differs from device 100 of the figure 1 in that the device 200 of the figure 2 comprises n capacitive elements 201-1, 201-2, ... 201-n connected respectively in parallel with n diodes 101-1, 101-2, ... 101-n.

[0042] Each capacitive element 201-1, 201-2, ... 201-n is more precisely a capacitor comprising two electrically conductive electrodes or armatures, for example two metal electrodes parallel to each other, separated from each other by a dielectric material. For example, the device 200 may have a monolithic structure, each capacitive element 201-1, 201-2, ... 201-n then being for example a MIM type capacitor (from the English "Metal Insulator Metal") formed in a stack of electrically conductive levels, for example metal layers, separated from each other by electrically insulating levels, for example dielectric layers. Furthermore, in the case where the device 200 is monolithic, the node 105 corresponds for example to a substrate, for example a semiconductor substrate, in and on which the device 200 is formed.This example is not, however, limiting, the device 200 being able, as a variant, to be produced from discrete components.

[0043] The capacitive elements 201-1, 201-2, ... 201-n of the pseudo-bidirectional device for protection against electrostatic discharges 200 have, for example, capacities that are substantially equal to each other, apart from manufacturing variations. For example, the capacities of the capacitive elements 201-1, 201-2, ... 201-n are determined, as a function of one or more excitation frequencies of signals that may be applied to the device 200 by coupling, by simulation tools so as to minimize the harmonics produced by the device 200 at this or these frequencies.

[0044] An advantage of the pseudo-bidirectional device 200 for protection against electrostatic discharges is that the presence of the capacitive elements 201-1, 201-2, ... 201-n makes it possible, compared to the device 100, to reduce the power of the harmonics.

[0045] For example, in a case where each diode 101-1, 101-2, ... 101-n has a capacitance equal to approximately 4.5 pF, where the diode 107 has a capacitance equal to approximately 38 pF and where each capacitive element 201-1, 201-2, ... 201-n has a capacitance equal to approximately 10 pF, power reductions of the second harmonics of approximately -26 dB, for an excitation frequency of the order of 900 MHz, of approximately -33 dB, for an excitation frequency of the order of 1.75 GHz, and of approximately -37 dB, for an excitation frequency of the order of 2.55 GHz, are for example obtained thanks to the device 200 compared to the case where the device 100 is used.

[0046] Furthermore, power reductions of the third harmonics of approximately -18 dB, for an excitation frequency of the order of 900 MHz, of approximately -23 dB, for an excitation frequency of the order of 1.75 GHz, and of approximately -25 dB, for an excitation frequency of the order of 2.55 GHz, are for example obtained thanks to the device 200 compared to the device 100.

[0047] There figure 3 is an electrical diagram illustrating another example of an electrostatic discharge protection device 300 according to one embodiment.

[0048] Device 300 of the figure 3 includes elements in common with the device 200 of the figure 2 . These common elements will not be detailed again below. Device 300 of the figure 3 differs from the device 200 of the figure 2 in that the device 300 of the figure 3comprises n other capacitive elements 301-1, 301-2, ... 301-n respectively connecting terminals 103-1, 103-2, ... 103-n to terminal 109 for applying the reference potential. More precisely, in the example illustrated in figure 2 , each capacitive element 301-1, 301-2, ... 301-n comprises a first electrode or terminal connected to the terminal 109 for applying the reference potential, and a second electrode or terminal connected to the corresponding terminal 103-1, 103-2, ... 103-n. The capacitive elements 301-1, 301-2, ... 301-n are distinct from the capacitive elements 201-1, 201-2, ... 201-n.

[0049] The device 300 further comprises n resistive elements 303-1, 303-2, ... 303-n respectively connecting the terminals 103-1, 103-2, ... 103-n to terminals 305-1, 305-2, ... 305-n. The resistive elements 303-1, 303-2, ... 303-n are for example resistors each comprising two conductive electrodes, for example metal electrodes, connected by a resistive material. By way of example, the device 300 may have a monolithic structure, each resistive element 303-1, 303-2, ... 303-n then being for example formed in an electrically conductive level, for example a metal layer, of the structure. This example is not, however, limiting, the device 300 being able, as a variant, to be produced from discrete components.

[0050] The resistive elements 303-1, 303-2, ... 303-n of the pseudo-bidirectional device for protection against electrostatic discharges 300 have, for example, capacities that are substantially equal to each other, apart from manufacturing variations.

[0051] The terminals 305-1, 305-2, ... 305-n are, for example, input terminals, output terminals or input-output terminals of an integrated circuit or an electronic component to be protected against electrostatic discharges. Each terminal 305-1, 305-2, ... 305-n is, for example, adapted to receive or transmit a digital or analog signal, for example an analog signal having a frequency lower than 10 or 20 MHz. For example, the terminals 305-1, 305-2, ... 305-n are, in nominal operation, subjected to a potential of the order of 3.3 V, of the order of 5 V or of the order of 15 V.

[0052] Generally, the device 300 comprises n branches (with n being an integer greater than or equal to two) each comprising a diode 101 connecting terminal 103 to node 105, a capacitive element 201 connected in parallel with the diode 101, another capacitive element 301 connecting terminal 103 to terminal 109, and a resistive element 303 connecting terminal 103 to terminal 305. In each branch of the device 300, the resistive element 303 and the capacitive element 301 form an RC filter, for example a low-pass filter.

[0053] The capacitive elements 301-1, 301-2, ... 301-n of the pseudo-bidirectional electrostatic discharge protection device 300 have, for example, substantially equal capacitances, apart from manufacturing variations. For example, the capacitances of the capacitive elements 201-1, 201-2, ... 201-n and of the capacitive elements 301-1, 301-2, ... 301-n are determined, for example using digital simulation tools, so that the device 300 has an impedance equivalent to that of a device similar to the device 300 but which would be devoid of the capacitive elements 201-1, 201-2, ... 201-n, while obtaining a maximum reduction of the harmonics.

[0054] An advantage of the pseudo-bidirectional device 300 for protection against electrostatic discharges lies in the fact that the presence of the capacitive elements 201-1, 201-2, ... 201-n makes it possible, compared to a device similar to the device 300 but without the capacitive elements 201-1, 201-2, ... 201-n, to reduce the power of the harmonics produced.

[0055] For example, in a case where each diode 101-1, 101-2, ... 101-n has a capacitance equal to about 4.5 pF, where the diode 107 has a capacitance equal to about 38 pF, or each capacitive element 201-1, 201-2, ... 201-n has a capacitance equal to about 35 pF, where each capacitive element 301-1, 301-2, ... 301-n has a capacitance equal to about 55 pF and where each resistive element 303-1, 303-2, ... 303-n has a resistance equal to about 50 Ω, power reductions of the second harmonics of about -42 dB, for an excitation frequency of the order of 900 MHz, of about -38 dB, for an excitation frequency of the order of 1.75 GHz, and approximately -38 dB, for an excitation frequency of the order of 2.55 GHz, are for example obtained thanks to the device 300 compared to the case where a similar device, of the same impedance but without the capacitive elements 201-1, 201-2, ... 201-n, is used.

[0056] Furthermore, power reductions of the third harmonics of approximately -9 dB, for an excitation frequency of the order of 900 MHz, of approximately -11 dB, for an excitation frequency of the order of 1.75 GHz, and of approximately -11 dB, for an excitation frequency of the order of 2.55 GHz, are for example obtained thanks to the device 300 compared to a similar device, of the same impedance, but without the capacitive elements 201-1, 201-2, ... 201-n.

[0057] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, although the figure 3illustrates an example of an application in which the pseudo-bidirectional device 300 for protection against electrostatic discharges implements filtering functions, the embodiments are not limited to this type of application but can more generally be implemented in any type of integrated circuit or electronic component capable of benefiting from the presence of protection against electrostatic discharges.

[0058] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above. In particular, the person skilled in the art is able to determine the values ​​of the intrinsic capacitances of the diodes 101-1, 101-2, ... 101-n and 107, of the capacitances of the capacitive elements 201-1, 201-2, ... 201-n, of the capacitances of the capacitive elements 301-1, 301-2, ... 301-n and of the resistances of the resistive elements 303-1, 303-2, ... 303-n depending on the application, for example using digital simulation tools, in order to optimize the reduction of the harmonics produced by the pseudo-bidirectional device 200 or 300 for protection against electrostatic discharges while making it possible to ensure functions identical or similar to those of a similar device which would be devoid of the capacitive elements 201-1, 201-2, ... 201-n.

Claims

1. Pseudo-bidirectional device (200; 300) of protection against electrostatic discharges, comprising: - first and second diodes (101-1, 101-2) respectively coupling first and second terminals (103-1, 103-2) to a same inner node (105) of the device; and - a third diode (107) coupling the inner node (105) to a third terminal (109) of application of a reference potential, characterized in that the third diode (107) has a capacitance greater than that of the first and second diodes (101-1, 101-2), the device further comprising first and second capacitive elements (201-1, 201-2) respectively connected in parallel with the first and second diodes (101-1, 101-2).

2. Device (200; 300) according to claim 1, wherein: - the first diode (101-1) comprises anode and cathode electrodes respectively connected to the inner node (105) and to the first terminal (103-1); and - the second diode (101-2) comprises anode and cathode electrodes respectively connected to the inner node (105) and to the second terminal (103-2).

3. Device (200; 300) according to claim 1 or 2, wherein the third diode (107) comprises anode and cathode electrodes respectively connected to the inner node (105) and to the third terminal (109).

4. Device (200; 300) according to any of claims 1 to 3, wherein the first and second capacitive elements (201-1, 201-2) are capacitors.

5. Device (200; 300) according to any of claims 1 to 4, wherein the device has a monolithic structure.

6. Device (200; 300) according to claim 5, as dependent on claim 4, wherein the first and second capacitive elements (201-1, 201-2) are MIM capacitors.

7. Device (300) according to any of claims 1 to 6, further comprising: - third and fourth capacitive elements (301-1, 301-2), distinct from the first and second capacitive elements (201-1, 201-2), respectively coupling the first and second terminals (103-1, 103-2) to the third terminal (109); and - first and second resistive elements (303-1, 303-2) respectively coupling the first and second terminals (103-1, 103-2) to fourth and fifth terminals (305-1, 305-2) .

8. Device (300) according to claim 7, wherein: - the third and fourth capacitive elements (301-1, 301-2) each have capacitances equal to approximately 55 pF; and - the first and second resistive elements (303-1, 303-2) each have resistances equal to approximately 50 Ω.

9. Device (200; 300) according to any of claims 1 to 8, wherein the first, second, and third diodes (101-1, 101-2, 107) are Zener diodes or transient voltage suppression diodes.

10. Device (200; 300) according to any of claims 1 to 9, wherein the first and second capacitive elements (201-1, 201-2) have capacitances substantially identical to one another.

11. Device (200; 300) according to any of claims 1 to 10, wherein the first and second capacitive elements (201-1, 201-2) each have a capacitance equal to approximately 10 pF.

12. Device (200; 300) according to any of claims 1 to 11, wherein the third diode (107) has a capacitance at least twice greater, preferably at least five times greater, more preferably approximately ten times greater, than those of the first and second diodes (101-1, 101-2).

13. Device (200; 300) according to any of claims 1 to 12, wherein: - the first and second diodes (101-1, 101-2) each have a capacitance equal to approximately 4,5 pF; and - the third diode (107) has a capacitance equal to approximately 38 pF.

14. Device (200; 300) according to any of claims 1 to 13, wherein the first and second terminals (103-1, 103-2) are input and / or output terminals of an integrated circuit.

15. Device (200; 300) according to any of claims 1 to 14, wherein the inner node (105) corresponds to a semiconductor substrate inside and on top of which is formed the device.