JP6048218B2 - ESD protection device - Google Patents

Description

  The present invention relates to an ESD protection device for protecting an electronic circuit from electrostatic discharge.

  Various electronic devices are provided with ICs. In order to protect the IC from a surge caused by ESD (electrostatic discharge), an ESD protection device described in Patent Document 1, for example, is connected to the input / output unit of the IC. The protection device described in Patent Document 1 uses a bidirectional Zener diode constituted by two Zener diodes. By using a bidirectional Zener diode, the electronic circuit can be protected from both positive and negative ESD. Further, the ESD protection device described in Patent Document 1 can be mounted without limiting the mounting direction.

International Publication 2012/023394 Pamphlet

  However, since the on-resistance of the Zener diode is high, when two Zener diodes are connected in series as in Patent Document 1, there is a problem that the holding voltage (the voltage at both ends during ESD energization) becomes high.

  Therefore, an object of the present invention is to provide a bidirectional ESD protection device having a low holding voltage and excellent surge absorption characteristics.

  The present invention includes a Zener diode formed on a semiconductor substrate, a first diode formed on the semiconductor substrate, connected in series with the forward direction aligned, and connected in parallel with the Zener diode aligned in the forward direction, and A second diode, a third diode and a fourth diode formed on the semiconductor substrate, connected in series with the forward direction aligned, and connected in parallel with the Zener diode aligned in the forward direction; A first input / output terminal connected to a connection point of the first diode and the second diode, and a second input / output terminal connected to a connection point of the third diode and the fourth diode. In the ESD protection device, the first diode, the second diode, the third diode, and the fourth diode may be the first diode. The first input / output terminal is formed such that the Zener diode is interposed between the diode and the fourth diode, and between the second diode and the third diode. Is formed at a position closer to the Zener diode than the first diode and the second diode, and the second input / output terminal is positioned closer to the Zener diode than the third diode and the fourth diode. It is characterized by being formed.

  In this configuration, when a current due to ESD is input from the first input / output terminal, for example, the current flows through the first diode, the Zener diode, and the fourth diode to the second input / output terminal. On the other hand, when a current due to ESD is input from the second input / output terminal, the current flows through the third diode, the Zener diode, and the second diode to the first input / output terminal. As described above, only one Zener diode having a large on-resistance component is used, and since the forward drop voltage and the on-resistance value of the first to fourth diodes are low, both the holding voltage is low and the surge absorption characteristic is excellent. A directional ESD protection device can be realized.

  For example, when a current flows from the first input / output terminal, a loop formed by the first input / output terminal, the first diode and the Zener diode, and a second input / output terminal, the fourth diode and the Zener diode are formed. A closed magnetic circuit is formed by the loop to be performed. For this reason, it can suppress that the magnetic field which generate | occur | produces when an electric current flows leaks outside an ESD protection device.

  A redistribution layer is formed on the semiconductor substrate, and the redistribution layer is overlapped with a portion between the formation region of the first diode and the second diode and the formation region of the Zener diode. It is preferable to include a second electrode that overlaps with a first electrode to be formed, a region where the third diode and the fourth diode are formed, and a portion between the region where the Zener diode is formed.

  In this configuration, since the magnetic field generated when the current flows can be shielded by the first electrode and the second electrode, the magnetic field can be further suppressed from leaking outside the ESD protection device. Further, an eddy current is generated due to the proximity of the first electrode and the second electrode, and the inductance (ESL) of the line between the first input / output terminal and the second input / output terminal is suppressed. Thereby, reflection of surge current is suppressed and a low holding voltage can be maintained.

  Preferably, the first electrode is electrically connected to the first input terminal, and the second electrode is electrically connected to the second input terminal.

  In this configuration, since the first electrode and the second electrode can be used as terminal electrodes, it is not necessary to provide a separate electrode for shielding, and the ESD protection device can be downsized.

  Preferably, the first input / output terminal and the second input / output terminal are formed at symmetrical positions with respect to the formation position of the Zener diode.

  In this configuration, the magnitude of the magnetic field generated by the current flow is made substantially the same on the first diode (or second diode) side and the fourth diode (or third diode) side. Can do. For this reason, two magnetic fields are canceled and the magnetic field which leaks out of an ESD protection device can be suppressed.

  According to the present invention, a bidirectional ESD protection device having a low holding voltage and excellent surge absorption characteristics can be realized.

Front sectional view of an ESD protection device according to an embodiment The top view of each layer of the ESD protection device concerning an embodiment The figure which shows the ESD protection circuit formed in Si substrate The figure for demonstrating the positional relationship of the ESD protection circuit and terminal electrode of Si substrate (A) And (B) is a figure which shows the example of a connection of the ESD protection device which concerns on embodiment The figure for demonstrating the principle of operation of the ESD protection device which concerns on embodiment The figure for demonstrating the principle of operation of the ESD protection device which concerns on embodiment Diagram showing manufacturing process of ESD protection device The figure which shows the modification of the ESD protection device which changed the number of diodes The figure which shows the modification of the ESD protection device which changed the number of diodes The figure which shows the modification of the ESD protection device which changed the position of the pad

  FIG. 1 is a front sectional view of an ESD protection device 1 according to this embodiment. FIG. 2 is a plan view of each layer of the ESD protection device 1 according to this embodiment. The ESD protection device 1 is a CSP (Chip Size Package) type device, and a rewiring layer 20 including a plurality of resin layers and the like is formed on a Si substrate 10 on which an ESD protection circuit 10A including a diode and a Zener diode is formed. Has been. The Si substrate 10 corresponds to the semiconductor substrate according to the present invention, but the semiconductor substrate according to the present invention is not limited to the Si substrate, and may be a GaAs substrate or the like.

  FIG. 3 is a diagram showing an ESD protection circuit formed on the Si substrate 10. The Si substrate 10 will be described with reference to FIGS.

  Element formation regions 11, 12, and 13 are provided on the surface of the Si substrate 10. Specifically, a p epitaxial layer is formed on a p + type substrate, and an n well p well is formed in this p epitaxial layer in order, and the diode D1 is formed on the Si substrate 10 by these wells and the p diffusion layer or the n diffusion layer. , D2, D3, D4 and a Zener diode Dz are formed.

  The diodes D1 and D2 thus formed are connected in series with the forward direction aligned, and the diodes D3 and D4 are connected in series with the forward direction aligned. The diodes D1 and D2 and the diodes D3 and D4 connected in series are aligned in the forward direction and connected in parallel to the Zener diode Dz. Further, a Zener diode Dz is interposed between the formation positions of the diodes D1 and D4 and between the formation positions of the diodes D2 and D3.

  Al pads (hereinafter referred to as pads) P 1 and P 2 are formed on the Si substrate 10. The pad P1 is formed at a position drawn from the connection point of the diodes D1 and D2, and the pad P2 is formed at a position drawn from the connection point of the diodes D3 and D4. The pad P1 is formed at a position closer to the Zener diode Dz than the diodes D1 and D2, and the pad P2 is formed at a position closer to the Zener diode Dz than the diodes D3 and D4. Further, the pads P1 and P2 are formed at positions that are point-symmetric with respect to the formation position of the Zener diode Dz.

  Returning to FIG. 1, a SiN protective film 15 is formed on the surface of the Si substrate 10 so as to cover a part of the pads P1 and P2. The SiN protective film 15 is sputtered on the surface of the Si substrate 10 and an opening is formed by etching.

  The rewiring layer 20 includes a resin layer 41 formed on the Si substrate 10. The resin layer 41 is, for example, a low dielectric constant epoxy resin layer. In the resin layer 41, openings (contact holes) 21 and 22 (see FIG. 2) are formed at the positions of the openings formed in the SiN protective film 15. The pads P1 and P2 are exposed through the openings 21 and 22, and are electrically connected to the electrodes formed in the openings 21 and 22.

  The rewiring layer 20 includes terminal electrodes 31 and 32 formed on the resin layer 41. The terminal electrodes 31 and 32 are electrically connected to the pads P1 and P2 through the openings 21 and 22. The terminal electrodes 31 and 32 are composed of a layer made of Cu / Ni and a layer made of Au / Ni, and are terminal electrodes for input / output of the ESD protection device 1.

  The rewiring layer 20 includes a resin layer 42 further formed on the resin layer 41. The resin layer 42 is, for example, a low dielectric constant epoxy resin layer having a thickness of 10 μm. Rectangular openings 42 </ b> A and 42 </ b> B are formed in portions of the resin layer 42 that face part of the terminal electrodes 31 and 32. Solder bumps are formed in the openings 42A and 42B as necessary.

  Next, in the ESD protection device 1 formed as described above, the positional relationship between the ESD protection circuit 10A of the Si substrate 10 and the terminal electrodes 31 and 32 will be described. FIG. 4 is a diagram for explaining the positional relationship between the ESD protection circuit 10 </ b> A of the Si substrate 10 and the terminal electrodes 31 and 32. The terminal electrodes 31 and 32 are electrically connected to pads P1 and P2 formed on the Si substrate 10 through the openings 21 and 22. The terminal electrode 31 covers the formation regions of the diodes D1 and D2 and the pad P1 in the thickness direction of the ESD protection device 1, and the terminal electrode 32 covers the formation regions of the diodes D3 and D4 and the pad P2.

  Hereinafter, a connection example and an operation principle of the ESD protection device 1 according to the present embodiment will be described.

  FIG. 5A and FIG. 5B are diagrams showing a connection example of the ESD protection device 1 according to the present embodiment. The ESD protection device 1 is mounted on an electronic device. Examples of electronic devices include notebook PCs, tablet terminal devices, mobile phones, digital cameras, DVCs (Digital Video Cassettes), and portable music players.

  FIG. 5A shows an example in which the ESD protection device 1 is connected between the signal line connecting the I / O port 100 and the IC 101 to be protected and GND. The I / O port 100 is a port to which an antenna is connected, for example. The ESD protection device 1 according to the present embodiment is a bidirectional type, and either the first input / output terminal or the second input / output terminal may be on the input side. For example, when the first input / output terminal is the input side, the first input / output terminal is connected to the signal line, and the second input / output terminal is connected to the GND.

  FIG. 5B shows an example in which the ESD protection device 1 is connected between the signal line connecting the connector 102 and the IC 101 and the GND line. The signal line in this example is, for example, a high-speed transmission line (differential transmission line), and the ESD protection device 1 is connected between each of the plurality of signal lines and the GND line.

  6 and 7 are diagrams for explaining the operation principle of the ESD protection device 1 according to this embodiment.

  FIG. 6 is a diagram for explaining a case where a current flows from the pad P1 connected to the first input / output terminal (terminal electrode 31) to the pad P2 connected to the second input / output terminal (terminal electrode 32). When a surge voltage exceeding the Zener voltage of the Zener diode Dz is applied, the surge current that has entered from the first input terminal is routed from the pad P1 to the diode D1, the Zener diode Dz, and the diode D4, as indicated by the broken line in the figure. And discharged from the pad P2 to the ground. When a current flows through this path, a magnetic field is generated in the area A1 surrounded by the pad P1, the diode D1, and the Zener diode Dz, and the area surrounded by the pad P2, the diode D4, and the Zener diode Dz. In A2, a magnetic field is generated toward the front side of the page. That is, in the ESD protection device 1, a closed magnetic circuit is formed so that a magnetic flux loop indicated by a curved arrow in the figure is generated. Thereby, it can suppress that the magnetic field which generate | occur | produces by ESD is radiated | emitted outside the ESD protection device 1, and can suppress the influence by the leakage of the magnetic field to another element.

  Further, as shown in FIG. 4, in the thickness direction of the ESD protection device 1, parts of the regions A <b> 1 and A <b> 2 are covered with the terminal electrodes 31 and 32, so that when a magnetic field is generated in the regions A <b> 1 and A <b> 2, Eddy currents are induced in 31 and 32. This eddy current cancels a part of the magnetic field generated in the regions A1 and A2, and as a result, the inductance component (ESL) in the ESD protection device 1 is reduced. For this reason, reflection of surge current is suppressed and a low holding voltage can be maintained.

  FIG. 7 is a diagram for explaining a case where a current flows from the pad P2 connected to the second input / output terminal (terminal electrode 32) to the pad P1 connected to the first input / output terminal (terminal electrode 31). In this case, as indicated by a broken line in the figure, the surge current that has entered from the second input terminal flows from the pad P2 through the path of the diode D3, the Zener diode Dz, and the diode D2, and is discharged from the pad P1 to the ground. When current flows through this path, a magnetic field is generated in the area A3 surrounded by the pad P2, the diode D3, and the Zener diode Dz, and the area surrounded by the pad P1, the diode D2, and the Zener diode Dz. In A4, a magnetic field is generated toward the back of the page. That is, in the ESD protection device 1, a closed magnetic circuit is formed so that a magnetic flux loop indicated by a curved arrow in the figure is generated. Thereby, it can suppress that the magnetic field which generate | occur | produces by ESD is radiated | emitted outside the ESD protection device 1, and can suppress the influence by the leakage of the magnetic field to another element.

  Further, as in the case of FIG. 6, in the thickness direction of the ESD protection device 1, parts of the regions A3 and A4 are covered with the terminal electrodes 31 and 32, and thus when a magnetic field is generated in the regions A3 and A4, Eddy currents are induced in the electrodes 31 and 32. This eddy current cancels a part of the magnetic field generated in the regions A3 and A4. As a result, the inductance component (ESL) in the ESD protection device 1 is reduced. For this reason, reflection of surge current is suppressed and a low holding voltage can be maintained.

  As described above, the ESD protection device 1 according to this embodiment realizes the bidirectional ESD protection device 1 by using one Zener diode Dz and four diodes D1 to D4. In the ESD protection device 1, the forward voltage drop and the on-resistance value of the diodes D1 to D4 are lower than that of the Zener diode Dz, so that the holding voltage is lower than that in the case where two Zener diodes Dz are used, and the surge absorption characteristics are improved. An excellent bidirectional ESD protection device 1 can be realized.

  Further, by forming the Zener diode Dz and the diodes D1 to D4 in the positional relationship as shown in FIG. 3, it is possible to suppress the radiation of the magnetic field generated by the ESD to the outside of the ESD protection device 1, and other elements The influence by the leakage of the magnetic field to can be suppressed.

  Even if the electrodes that are not connected to the pads P1 and P2 (independent) cover the regions A1 and A2, the effect of the eddy current is produced. However, by connecting the terminal electrodes 31 and 32 and the pads P1 and P2, it is not necessary to separately provide a shielding electrode in the ESD protection device 1. For this reason, the ESD protection device 1 can be reduced in size.

  Below, the manufacturing process of the ESD protection device 1 is demonstrated.

  FIG. 8 is a diagram showing a manufacturing process of the ESD protection device 1. The ESD protection device 1 is manufactured by the following process.

(A) First, pads P1 and P2 that are electrically connected to the ESD protection circuit 10A are formed on the Si substrate 10 on which the ESD protection circuit 10A is formed by photolithography. Further, the SiN protective film 15 is sputtered on the substrate surface, and openings 15A and 15B are formed by etching.

  Note that, by reducing the area of the pads P1 and P2, the parasitic capacitance formed between the opposing substrates (ESD protection circuit 10A) can be reduced. By reducing the parasitic capacitance, it is possible to suppress the deviation of the impedance, and as a result, it is possible to reduce the loss in the signal line.

(B) Next, an epoxy solder girest is spin-coated on the Si substrate 10 to form a resin layer 41, and openings 41A and 41B are formed.

(C) The Cu / Ti electrode 23 is formed on the surface of the resin layer 41 by sputtering with a thickness of about 1.0 μm / 0.1 μm, and then the Au / Ni electrode 24 has a thickness of about 0.1 μm / 5.0 μm. The film is formed by sputtering. The Au / Ni electrode 24 is formed only in part by masking.

(D) Subsequently, the Cu / Ti electrode 23 is wet etched to form the terminal electrodes 31 and 32.

(E) Thereafter, an epoxy solder girest is formed on the surface of the resin layer 41 by spin coating to form the resin layer 42, and the openings 42A and 42B are formed.

  In the above-described embodiment, the first diode, the second diode, the third diode, and the fourth diode according to the present invention are represented as diodes D1, D2, D3, and D4. The number is not limited to this. 9 and 10 are diagrams showing modifications of the ESD protection device 1 having a different number of diodes. FIG. 9 shows an example in which two diodes connected in series are a first diode, a second diode, a third diode, and a fourth diode according to the present invention. FIG. 10 shows an example in which three diodes connected in parallel are replaced with a first diode, a second diode, a third diode, and a fourth diode according to the present invention.

  FIG. 11 is a diagram illustrating a modified example of the ESD protection device in which the positions of the pads P1 and P2 are changed. Also in the example shown in FIG. 11, pads P1 and P2 are formed at positions that are point-symmetric with respect to the Zener diode Dz. In this example, the loops (partial loops) of the current path constituting the regions A1 and A4 are reduced, but the sizes of the regions A1 and A4 and the regions A2 and A3 are the same. For this reason, the magnitudes of the magnetic fields generated by the current flow are the same in the regions A1 and A4, and the magnetic fields generated in the regions A1 and A4 are canceled. Further, the magnitudes of the magnetic fields generated in the areas A2 and A3 are the same, and the magnetic fields generated in the areas A2 and A3 are canceled out. As a result, the magnetic field leaking out of the ESD protection device can be suppressed.

1-ESD protection device 10-Si substrate (semiconductor substrate)
10A-ESD protection circuit 11, 12, 13-element formation region 15-SiN protective film 15A, 15B-opening 20-redistribution layer 21,22-opening 23-Cu / Ti electrode 24-Au / Ni electrode 31, 32- Terminal electrodes 41, 42-resin layers 41A, 41B-openings 42A, 42B-openings D1-diodes (first diodes)
D2-diode (second diode)
D3-diode (third diode)
D4-diode (fourth diode)
Dz-Zener diode P1-pad (first input / output terminal)
P2-pad (second input / output terminal)

Claims (3)

A Zener diode formed on a semiconductor substrate;
A first diode and a second diode formed on the semiconductor substrate, connected in series with the forward direction aligned, and connected in parallel with the Zener diode aligned in the forward direction;
A third diode and a fourth diode formed on the semiconductor substrate, connected in series with the forward direction aligned, and connected in parallel with the Zener diode aligned in the forward direction;
A first input / output terminal connected to a connection point of the first diode and the second diode;
A second input / output terminal connected to a connection point of the third diode and the fourth diode;
In an ESD protection device comprising:
The first diode, the second diode, the third diode, and the fourth diode are:
Formed between the first diode and the fourth diode and between the second diode and the third diode so that the Zener diode is interposed between them;
The first input / output terminal is
Formed at a position closer to the Zener diode than the first diode and the second diode;
The second input / output terminal is
Formed at a position closer to the Zener diode than the third diode and the fourth diode ;
A rewiring layer is formed on the semiconductor substrate;
In the rewiring layer,
A first electrode that overlaps with a portion between the formation region of the first diode and the second diode and the formation region of the Zener diode;
A second electrode that overlaps with a portion between the formation region of the third diode and the fourth diode and the formation region of the Zener diode;
An ESD protection device. Wherein the first electrode is electrically connected to the first input output terminal,
The second electrode is electrically connected to the second input output terminal,
The ESD protection device according to claim 1 . The ESD protection device according to claim 1, wherein the first input / output terminal and the second input / output terminal are formed at symmetrical positions with respect to a formation position of the Zener diode.

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