Contact method to allow benign failure in ceramic capacitor having self-clearing feature
View Patent ↗A capacitor exhibiting a benign failure mode has a first electrode layer, a first ceramic dielectric layer deposited on a surface of the first electrode, and a second electrode layer disposed on the ceramic dielectric layer, wherein selected areas of the ceramic dielectric layer have additional dielectric material of sufficient thickness to exhibit a higher dielectric breakdown voltage than the remaining majority of the dielectric layer. The added thickness of the dielectric layer in selected areas allows lead connections to be made at the selected areas of greater dielectric thickness while substantially eliminating a risk of dielectric breakdown and failure at the lead connections, whereby the benign failure mode is preserved.
1. A capacitor exhibiting a benign failure mode, comprising:
a first electrode layer;
a first dielectric layer disposed on a surface of the first electrode layer;
a second dielectric layer overlaying a portion of the first dielectric layer, said second dielectric layer exhibiting a higher dielectric breakdown voltage than the first dielectric layer;
a second electrode layer disposed over the first dielectric layer and the second dielectric layer, the second electrode layer being sufficiently thin to facilitate self-clearing of electrode material in the event of a failure; and
a first contact pad in electrical contact with the second electrode layer and overlaying only the portion of the first dielectric layer covered by the second dielectric layer.
2. The capacitor of claim 1 , in which the first dielectric layer is comprised of PLZT.
3. The capacitor of claim 1 , further comprising a buffer layer between the first electrode layer and the first dielectric layer, wherein the buffer layer is of a material selected from lanthanum nickel oxide (LNO) and organic solderable preservative (OSP).
4. The capacitor of claim 1 , in which the first electrode layer is of a material selected from the group consisting of nickel, copper, stainless steel and aluminum.
5. The capacitor of claim 1 , in which the first dielectric layer is comprised of barium titanate.
6. The capacitor of claim 1 , in which the first dielectric layer has a thickness of from 0.1 to 4 micrometers.
7. The capacitor of claim 1 , in which the second dielectric layer is an insulative oxide or glass material.
8. The capacitor of claim 1 , in which the second electrode layer has a thickness of about 0.01 to 0.1 micrometers.
9. The capacitor of claim 1 , in which the second electrode layer is comprised of a material selected from aluminum, platinum, copper, zinc, silver, gold and combinations of these materials.
10. The capacitor of claim 1 , further comprising a first electrical lead connected to the first contact pad.
11. The capacitor of claim 1 , further comprising a third dielectric layer disposed on a surface of the first electrode opposite the side on which the first dielectric layer is disposed;
a fourth dielectric layer overlaying a portion of the third dielectric layer, said fourth dielectric layer exhibiting a higher dielectric breakdown voltage than the third dielectric layer;
a third electrode layer disposed over the third dielectric layer and the fourth dielectric layer, the third electrode layer being sufficiently thin to facilitate self-clearing of the third electrode in the event of a failure; and
a second contact pad in electrical contact with the third electrode layer and overlaying only the portion of the third dielectric layer covered by the fourth dielectric layer.
12. The capacitor of claim 11 , further comprising a buffer layer between the third electrode layer and the third dielectric layer, wherein the buffer layer is of a material selected from lead lanthium zirconium titante (PLZT) or OSP.
13. The capacitor of claim 11 , in which the third dielectric layer is comprised of PLZT.
14. The capacitor of claim 11 , in which the third dielectric layer is comprised of barium titanate.
15. The capacitor of claim 11 , in which the third dielectric layer has a thickness of from 0.1 to 4 micrometers.
16. The capacitor of claim 11 , in which the fourth dielectric layer is an insulative oxide or glass material.
17. The capacitor of claim 11 , in which the third electrode layer has a thickness of from 0.01 to 0.1 micrometers.
18. The capacitor of claim 11 , in which the third electrode layer is comprised of a material selected from aluminum, platinum, copper, zinc, silver, gold and combinations of these materials.
19. The capacitor of claim 11 , in which the third electrode layer is aluminum having a thickness of from 0.2 to 0.3 micrometers.
20. The capacitor of claim 11 , further comprising a first electrical lead connected to the first contact pad; and
a second electrical lead connected to the second contact pad.