Optical modulator using monocrystalline and polycrystalline silicon
Embodiments provide for an optical modulator, comprising: a lower guide, comprising: a lower hub, made of monocrystalline silicon; and a lower ridge, made of monocrystalline silicon that extends in a first direction from the lower hub; an upper guide, including: an upper hub; and an upper ridge, made of monocrystalline silicon that extends in a second direction, opposite of the first direction, from the upper hub and is aligned with the lower ridge; and a gate oxide layer separating the lower ridge from the upper ridge and defining a waveguide region with the lower guide and the upper guide.
1. A method of forming an optical modulator, comprising:
patterning a base component to impart:
a lower waveguide that is separated from a substrate of the base component by a first layer of an insulator;
an upper ridge for an upper waveguide that is located above the lower waveguide and is separated from the lower waveguide by a predefined height;
depositing a gate oxide layer on the lower waveguide;
depositing a second layer of the insulator on the gate oxide layer;
etching the second layer of the insulator to define a cavity of a predefined shape; and
forming polycrystalline silicon wings for the upper waveguide in the cavity.
2. The method of claim 1 , further comprising:
forming a first set of contacts through the second layer of the insulator to form a first electrical connection through the lower waveguide; and
forming a second set of contacts through the second layer of the insulator to form a second electrical connection through the upper waveguide.
3. The method of claim 1 , wherein the base component comprises:
the substrate;
the first layer of the insulator, formed on the substrate;
a Silicon-On-Insulator (SOI) layer, formed on the first layer of the insulator and doped to exhibit a first type of conductivity, wherein patterning the base component imparts the lower waveguide in the SOI layer;
a spacing layer, formed on the SOI layer; and
a second silicon layer, formed on the spacing layer and doped to exhibit a different type of conductivity than the SOI layer, wherein patterning the base component imparts the upper ridge in the second silicon layer.
4. The method of claim 3 , further comprising:
prior to patterning a base component, applying a cap layer to the second silicon layer; and
wherein patterning the base component further imparts a cap, made from the cap layer, extending upward from the upper ridge.
5. The method of claim 3 , further comprising:
patterning the base component to impart an optical source aligned along a light path with the upper waveguide and the lower waveguide.
6. The method of claim 3 , wherein the spacing layer is of the predefined height and made from a Silicon Germanium material; and
wherein patterning the base component further comprises:
applying an anchor material;
removing the spacing layer while the anchor material suspends the upper ridge above the lower waveguide;
wherein depositing the gate oxide layer on the lower waveguide fills a space previously occupied by the spacing layer between the upper ridge and the lower waveguide; and
in response to depositing the gate oxide layer, removing the anchor material.
7. The method of claim 6 , further comprising:
prior to removing the anchor material, applying an additional layer of the insulator on the gate oxide layer.
8. The method of claim 1 , wherein a portion of the upper ridge that extends upward for a first height into the cavity defines an upper hub, and wherein forming the polycrystalline silicon wings further comprises:
depositing a polycrystalline layer in the cavity;
etching a first wing of a first length and the first height into the polycrystalline layer on a first side of the upper hub;
etching a second wing of the first length and the first height into the polycrystalline layer on a second side of the upper hub;
etching a first interface of a second height greater than the first height into the polycrystalline layer on the first side of the first wing; and
etching a second interface of the second height into the polycrystalline layer on the second side of the second wing.
9. The method of claim 1 , wherein forming the polycrystalline silicon wings further comprises:
forming a single crystal silicon hub of a given height on the upper ridge;
forming, on a first side of the single crystal silicon hub, a first wing of the polycrystalline silicon wings at the given height;
forming on a second side of the single crystal silicon hub, a second wing of the polycrystalline silicon wings at the given height;
patterning the polycrystalline silicon wings to a given length; and
applying an additional layer of the insulator on the polycrystalline silicon wings and the single crystal silicon hub.
10. The method of claim 1 , wherein forming the polycrystalline silicon wings for the upper waveguide in the cavity aligns the polycrystalline silicon wings with a hub of the upper ridge.
11. The method of claim 1 , further comprising:
prior to forming the polycrystalline silicon wings, growing a hub as a single Silicon crystal on the upper ridge, wherein the polycrystalline silicon wings are aligned with the hub.