Appendix

Appendix#

Besides the files that are included in the formatting guidelines accompanying the submission flow, the PDK folders also contains the files below for the Wavephotonics (WP) validator to function:

  • process_overview.yaml

  • drc_rules.lydrc

  • materials\*.csv

  • floorplans\floorplans.yaml

  • CHANGELOG.md

  • layerstack.png

  • layers.lyp

Changes within these files, and components/processes that require such changes will not pass the Submission pre-acceptance checks as they are not compatible with the services provided by CORNERSTONE.

Below, we explain the function of these files for the curious and interested.

Process overview file (process_overview.yaml)#

This file provides metadata about the fabrication process flow, as well as the functional layers. Let’s take a look at SiN_300nm/process_overview.yaml:

process_name: SiN_300nm
foundry: CORNERSTONE
description: SiN platform with heaters
material: SiN
is_public: true
gds_type: only_real_gds
includes_heaters: true
includes_rf_layers: false
has_a_no_metals_option: true

Leaving aside the self-explanatory fields, we have:

  • process_name: Name of the process platform, must be identical to the name of the containing folder

  • material: Material platform used within the process, must be listed within the list of allowed material platforms

  • gds_type: Describes type of components supplied (black-boxed, full component, black-boxed with real component swap at tapeout). CORNERSTONE will always use only_real_gds.

  • includes_heaters, includes_rf_layers: Logical fields for the existence of heaters and RF layers within the platform.

  • has_a_no_metals_option: Logical field that specifies if the platform is offered without heater/metal layer for a reduced price. See Access Charges.

The GDS layer information is then described within gds_layers field. For each element, we describe the layer information, depth tolerance, DRC rules assigned to the layer, and any aliases to use within the file later on. Practically, the information within the platform design guidelines (see Design Rules) are described within this section in YAML format.

gds_layers:
  - name: SiN_Etch1_LF_300nm
    layer: [203, 0]
    description: Full SiN etch to BOX (light) for waveguides, layer will be protected. No max feature length @0.35um features.
    drc: 
    - { min_feature_size: 0.25, min_gap: 0.25, max_feature_length: 20.0 }
    - { min_feature_size: 0.35, min_gap: 0.25}
    alias: wg_lf
  - name: SiN_Etch1_DF_300nm
    layer: [204, 0]
    description: Full SiN etch to BOX (dark) for waveguides, layer will be etched. No max feature length @0.35um gaps
    drc: 
    - { min_feature_size: 0.25, min_gap: 0.25, max_feature_length: 20.0 }
    - { min_feature_size: 0.25, min_gap: 0.35}
    alias: wg_df
  - name: Heat_Fil_LF
    layer: [39, 0]
    description: Heater filaments (light), layer will become metal.
    drc: { min_feature_size: 0.6, min_gap: 10.0 }
  - name: Heat_CP_LF
    layer: [41, 0]
    description: Heater contact pads (light), layer will become metal.
    drc: { min_feature_size: 2.0, min_gap: 10.0 }
  - name: Clad_Open_DF
    layer: [22, 0]
    description: Area for oxide etching (dark), layer will be etched. 
    drc: { min_feature_size: 20.0, min_gap: 20.0 }
  - name: Floorplan
    layer: [99, 0]
    is_info_only: true
    description: Cell outline
  - name: Label_Etch_DF
    layer: [100, 0]
    description: Labels (dark), will be etched, will not be checked in DRC
    drc: { min_feature_size: 0.25, min_gap: 0.25 }

Continuing, we have layer_stack, which is designed to assist WP in simulating and exporting the platform components:

layer_stack:
  - name: BOX
    description: BOX - buried oxide
    material: SiO2
    thickness: { value: 3.0 }
    gds_layer: null
  - name: Waveguide
    description: Full thickness SiN layer
    material: SiN
    thickness: { value: 0.3, tol: 0.015 }
    gds_layer: wg_lf or not wg_df
  - name: TOX
    description: Top cladding layer
    material: SiO2
    thickness: { value: 2.0, tol: 0.2 }
    gds_layer: not Clad_Open_DF
  - name: Heater_filament
    description: Heater filament layer (TiN)
    material: metal1
    is_metal_layer: true
    thickness: { value: 0.15, tol: 0.01}
    gds_layer: Heat_Fil_LF
  - name: Contact_pads
    description: Al layer for contact pads and electrical routing
    material: metal2
    is_metal_layer: true
    thickness: { value: 0.22, tol: 0.01}
    gds_layer: Heat_CP_LF

Here, we are using the alias as described within the gds_layers to simplify the categorisation of functional regions. As an example, from the desciption of TOX layer stack, we can see that everywhere on the design file has silicon dioxide as cladding except the regions defined by the Clad_Open_DF, which corresponds to the [22/0] layer in the GDS files. By defining layer_stack field, we combine the 2-D information given to us by the GDS file with the depth information, constructing the physical devices for simulations.

DRC file (drc_rules.lydrc)#

This is a file that describes the DRC rules to be performed by KLayout as part of pre-submission design checks. Each platform folder contains a drc_rules.lydrc file that is identical in the information content to the DRC script provided within Design Rules.

Material refractive index files (materials/*.csv)#

Material refractive index values across a wavelength range is required for accurate modeling of the components. We provide the refractive index values within a broad spectrum for the materials used in respective platforms in CSV format. These files are located within materials folder in each platform folder, with file names corresponding to the material subfield of layer_stack elements within process_overview.yaml for the platform.

Floorplans (floorplans/floorplans.yaml)#

The floorplans folder contains the allowed design area specification for the individual platforms in both YAML and GDS formats. These design area specifications can be found within Access Charges or in the Design Guidelines document of the MPW call in Design Rules.

Layer formatting file (layers.lyp)#

We provide the colour, pattern, border and animation information of the layers to declutter the design window in KLayout. The layer properties follow from the layer numbers and names from the gds_layers field of the process_overview.yaml file.

Others#

We also provide layerstack.png as a visual representation of the cross-section of the supported waveguides of the platform, and CHANGELOG.md to keep track of the cumulative changes between consecutive stable release versions of the platforms.

image