Ceramic substrate for light emitting diode where the substrate incorporates ESD protection
View Patent ↗A metal oxide varistor comprising one or more zinc oxide layers is formed integral to a ceramic substrate to provide ESD protection of a semiconductor device mounted to the substrate. The portion of the ceramic substrate not forming the varistor may be aluminum oxide, aluminum nitride, silicon carbide, or boron nitride. The varistor portion may form any part of the ceramic substrate, including all of the ceramic substrate.
1. A device comprising:
a ceramic substrate having a top surface and a bottom surface, the ceramic substrate providing electrostatic discharge (ESD) protection of a semiconductor device mounted over the top surface,
the ceramic substrate comprising a first layer containing a first metal oxide, a first surface of the first layer being the top surface of the ceramic substrate, the first layer forming a metal oxide varistor that provides electrostatic discharge (ESD) protection of the semiconductor device mounted over the first surface of the first layer,
the ceramic substrate also comprising a second layer containing a ceramic second material that does not contain any first metal oxide, the second layer not forming a varistor, a second surface of the second layer forming the bottom surface of the ceramic substrate;
a first metal layer overlying a portion of the first surface of the first layer;
a second metal layer in contact with the first layer between the first layer and the second layer;
a first electrode area electrically coupled to the first metal layer to which a first electrode of the semiconductor device is electrically connected when mounted over the first surface;
a second electrode area electrically coupled to the second metal layer to which a second electrode of the semiconductor device is electrically connected when mounted over the first surface,
whereby the first metal layer, the first layer, and the second metal layer form a low resistance path between the first electrode area and the second electrode area when a voltage between the first electrode area and the second electrode area exceeds a threshold.
2. The device of claim 1 wherein the first metal oxide-comprises zinc oxide, and wherein the second material comprises one of aluminum oxide, aluminum nitride, silicon carbide, or boron nitride.
3. The device of claim 1 wherein the first metal layer and the second metal layer overlap with the first layer therebetween.
4. The device of claim 1 further comprising a third electrode area electrically connected to the first electrode area, the third electrode area formed on the bottom surface of the ceramic substrate for connection to a power source.
5. The device of claim 4 further comprising a fourth electrode area electrically connected to the second electrode area, the fourth electrode area formed on the bottom surface of the ceramic substrate for connection to the power source.
6. The device of claim 5 further comprising a first metal portion along a side of the ceramic substrate coupling the first electrode area to the third electrode area, and further comprising a second metal portion along another side of the ceramic substrate coupling the second electrode area to the fourth electrode area.
7. The device of claim 1 wherein there is only a single layer containing the first metal oxide.
8. The device of claim 1 wherein the varistor comprises ceramic grains at least partially sandwiched between the first metal layer and the second metal layer.
9. The device of claim 1 further comprising a light emitting diode (LED) chip mounted on the top surface of the ceramic substrate and being protected from ESD by the varistor.
10. The device of claim 1 wherein the varistor forms part of a heat conduction path between the semiconductor device and a printed circuit board over which the ceramic substrate is mounted.