Edwin Jan Klein - Universiteit Twente

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Fabrication
To reduce this problem a built in misalignment, where the resonator is offset in one
direction with respect to the port waveguides, was introduced into the masks that were
used to create the vertically coupled resonator devices. The layout of these masks, of
which two types are shown in Figures 5.13 and 5.14, is similar to the layout used for
the laterally coupled devices with a standardized column width and device group size,
a central alignment bar with test structures, and dice lines. Instead of varying the gap
for the 6 device groups in a single column, however, a variation in the alignment error
is introduced. Within a single group the devices are all equal but for a variation of the
lateral distance between the resonator and port waveguides called the “symmetric
offset” which is also shown for reference in Figure 5.13b. In Figure 5.13a a mask is
shown that was used to create resonators that have port waveguides on opposing sides
as shown in Figure 5.13b. In this mask the alignment is varied in increments of 0.5
µm between -1.5 µm and 1.0 µm. Although this implies, by definition, that 5/6 th of the
devices will always be misaligned it also reduces the misalignment for one set of
devices in the column to 0.25 µm or better. However, due to the fact that there are
four columns in the mask and the small size of the resonators, meaning that many are
present in a single group, this can still lead to a substantial number of working
devices. The same approach of using built in misalignments is also used in the mask
layout of newer devices with port waveguides that are cross-coupled to the resonator
as shown in Figure 5.14b. Due to that fact that the waveguides are now susceptible to
alignment errors in the vertical as well as the horizontal direction, however, the
alignment has to be varied in two directions as shown in Figure 5.14a. This means
that although properly aligned devices can be fabricated these represent only 1/36 th of
the total number of fabricated devices.
a)
-1.5
-1.0
-0.5
Symmetric
offset
Figure 5.13. Mask layout a) for side coupled
resonators b). Also shown is the definition of
the symmetric offset of a resonator. This is
the distance between the center of the
resonator guide and the center of the port
waveguides.
0
0.5
1.0
-1.5 -1.0 -0.5 0 0.5
b) b)
Figure 5.14. Mask layout a) for cross coupled
resonators b).
a)
-1.5
-1.0
-0.5
0
0.5
1.0