GeBPSG top clad for a planar lightwave circuit
View Patent ↗A method of depositing a top clad layer for an optical waveguide of a planar lightwave circuit. A GeBPSG top clad layer for an optical waveguide structure of a planar lightwave circuit is fabricated such that the top clad layer comprises doped silica glass, wherein the dopant includes Ge (Germanium), P (Phosphorus), and B (Boron). In depositing a top clad layer for the optical waveguide, three separate doping gasses (e.g., GeH 4 , PH 3 , and B 2 H 6 ) are added during the PECVD (plasma enhanced chemical vapor deposition) process to make Ge, P and B doped silica glass (GeBPSG). The ratio of the Ge, P, and B dopants is configured to reduce the formation of crystallization areas within the top clad layer and maintain a constant refractive index within the top clad layer across an anneal temperature range. A thermal anneal process for the top clad layer can be a temperature within a range of 950 C to 1050 C. The GeBPSG top clad layer reduces the insertion loss of passive arrayed waveguide grating devices and active planar lightwave circuit devices.
1. A planar lightwave circuit comprising a first waveguide and a top clad layer, wherein the top clad layer comprises a doped silica glass that is doped with germanium, phosphorous and boron and wherein the doped silica glass has a germanium concentration from 0.93 percent by weight to 5 percent by weight and is free of crystals.
2. The planar lightwave circuit of claim 1 wherein the doped silica glass has a phosphorous concentration from 0.5 weight percent to 2.5 weight percent.
3. The planar lightwave circuit of claim 1 wherein the total concentration for phosphorous and boron is greater than 7.5 weight percent and the boron concentration is less than 7.0 weight percent.
4. The planar lightwave circuit of claim 1 wherein the total concentration for phosphorous and boron is from 7.5 weight percent to 9.0 weight percent.
5. The lightwave circuit of claim 1 wherein the doped silica glass has an anneal temperature from 900° C. to 1050° C.
6. The lightwave circuit of claim 1 further comprising a second waveguide that forms a gap between the first waveguide and the second waveguide.
7. The lightwave circuit of claim 1 wherein the first wave guide comprises a core of doped silica glass.
8. The lightwave circuit of claim 1 wherein the first waveguide partially covers a bottom cladding layer that comprises SiO 2 .
9. The lightwave circuit of claim 8 wherein the bottom cladding layer is on a silicon substrate.
10. The lightwave circuit of claim 1 wherein the top clad has a TE mode refractive index from 1.4445 to 1.4505.
11. The lightwave circuit of claim 1 wherein the top clad has a TE mode refractive index from 1.4455 to 1.4485.
12. The lightwave circuit of claim 6 wherein the gap is less than 6 microns.
13. The lightwave circuit of claim 6 wherein the gap is from 2 microns to 4 microns.
14. The lightwave circuit of claim 6 wherein the gap has an aspect ratio, defined as the height of the cores divided by the gap between the cores, between 2 and 3.