Transient voltage suppressor
A transient voltage suppressor includes a substrate, a first well, a second well, a third well, a first electrode, a second electrode and a doped region. The first well is formed in the substrate and near a surface of the substrate. The second well is formed in the first well and near the surface. The third well is formed in the first well and near the surface. There is a gap between the second well and the third well. The first electrode and second electrode are formed in the second well and near the surface respectively. The first well and first electrode have a first electrical property. The second well, third well and second electrode have a second electrical property. The doped region is formed between the first electrode and second electrode and near the surface and electrically connected with the first well and third well.
1. A transient voltage suppressor, comprising:
a substrate having a surface;
a first well, formed in the substrate and near the surface of the substrate, having a first electrical property;
a second well, formed in the first well and near the surface of the substrate, having a second electrical property;
a third well, formed in the first well and near the surface of the substrate, having the second electrical property;
a first electrode, formed in the second well and near the surface of the substrate, having the first electrical property;
a second electrode, formed in the first well and near the surface of the substrate, having the second electrical property;
a doped region, formed between the first electrode and the second electrode and near the surface of the substrate, electrically connected with the first well and the third well;
a fourth well, formed in the substrate and near the surface of the substrate, being outside the first well;
a third electrode, formed in the fourth well and near the surface of the substrate, having the first electrical property; and
a fourth electrode, formed in the fourth well and near the surface of the substrate, having the second electrical property,
wherein there is a gap between the second well and the third well, and the second well and the third well are diffused to connect each other to be conducted in the gap; the third electrode is electrically connected with an input/output terminal, and the fourth electrode is electrically connected with the first electrode.
2. The transient voltage suppressor of claim 1 , further comprising:
a heavily-doped region, formed under the doped region, having the same electrical property with the doped region and having a doping concentration higher than that of the doped region.
3. The transient voltage suppressor of claim 2 , wherein the heavily-doped region and the doped region both have the first electrical property.
4. The transient voltage suppressor of claim 2 , wherein the heavily-doped region and the doped region both have the second electrical property.
5. The transient voltage suppressor of claim 2 , wherein the third well and the second well are divided by the first well to form the gap between the third well and the second well; the second well and the third well are diffused to connect each other to be conducted through a drive-in process to form the diffusion-connected second well and third well, so that a first current path formed from the first electrode, the diffusion-connected second well and third well, the heavily-doped region, the first well to the second electrode is conducted.
6. The transient voltage suppressor of claim 2 , wherein when an electrostatic discharge (ESD) event occurs, not only a first current path formed from the first electrode, the diffusion-connected second well and third well, the heavily-doped region, the first well to the second electrode is conducted, but also a second current path formed from the first electrode, the second well, the first well to the second electrode is also conducted to reduce an overall resistance of the transient voltage suppressor.
7. The transient voltage suppressor of claim 2 , wherein a trigger voltage of the transient voltage suppressor is related to a doping concentration of the heavily-doped region.
8. The transient voltage suppressor of claim 1 , wherein the doped region is located on an edge of the third well and adjacent to the first well.
9. The transient voltage suppressor of claim 1 , wherein the first electrode and the second electrode are electrically connected with an anode and a cathode respectively.
10. The transient voltage suppressor of claim 1 , wherein the doped region is floating.
11. The transient voltage suppressor of claim 1 , wherein the diffusion-connected second well and third well forms a gourd-like well.
12. The transient voltage suppressor of claim 1 , wherein an on-resistance of the transient voltage suppressor is related to a size of the gap, a doping concentration of the second well and a doping concentration of the third well.
13. The transient voltage suppressor of claim 1 , wherein a doping concentration of the doped region is higher than doping concentrations of the first well, the second well and the third well.