Import an EMX process file¶

Some foundries deliver their RF back-end stack only as an EMX process file (.proc). load_emx_proc reads the nominal stack from such a file and returns a gsim LayerStack, so the file can be used without a PDK package:

from gsim.common.stack.emx import load_emx_proc
from gsim.palace import DrivenSim

stack = load_emx_proc("my_process.proc")

sim = DrivenSim()
sim.set_geometry(component)
sim.set_stack(stack)
sim.set_airbox(margin_x=50, margin_y=50, z_above=100)
sim.add_cpw_port("o1", layer="M3", s_width=10, gap_width=6)

The substrate of an RF process is often several hundred um thick. Use substrate_thickness_um to simulate a thinner (or thicker) wafer than the one declared in the file:

stack = load_emx_proc("my_process.proc", substrate_thickness_um=100)

What is imported¶

In the `.proc` file	In the gsim stack
`define NAME = expr` (numbers, `+ - * /`, other defines)	Evaluated; a table-valued define contributes its first (reference) entry
`layer <thickness> <er> [name N]`	A region of `stack.dielectrics` with permittivity `er`
`layer <thickness> <er> [name N] <rho> ohm-cm`	The substrate region, with conductivity `100 / rho` S/m
`layer infinity <er>`	Dropped; use `set_airbox()` for the surrounding air
`conductor <thickness> <rs or value S/m> NAME`	A `Layer` of type `conductor` named `NAME` (upper case)
`offset <value>` before a conductor	Shifts that conductor from the bottom of the preceding layer
`define NAME = l<L>t<D>`	The GDS layer `(L, D)` of the conductor or via `NAME`
`via FROM TO { ... <value> S/m ... } NAME`	A `Layer` of type `via` between conductors `FROM` and `TO`

Conventions of the resulting stack:

Lengths are in um. Layers are read from the bottom to the top of the file. z = 0 is the top of the substrate, so the substrate occupies [-thickness, 0].
An embedded conductor starts at the bottom of the layer that precedes it in the file, plus its optional offset. It does not move the layer interface.
A via spans from the top of the lower conductor it connects to the bottom of the upper one. The connectivity is stored in stack.simulation["emx"]["via_connectivity"], for example {"V1": ["M1", "M2"]}.
A conductor given as a sheet resistance Rs (ohm/sq) and thickness t gets the conductivity 1 / (Rs * t) in S/m, with t in m. A conductor given in S/m keeps its nominal value.
Material names start with emx_. Names that match the built-in gsim material database would otherwise be replaced by the database values.

What is ignored¶

Only the nominal stack is imported. For each of the following features that appears in the file, an EmxImportWarning is emitted and the feature is skipped:

geometry bias,
fill and slotting (optional fill streams are not mapped),
via merge operations,
temperature dependence (only the part of a conductivity expression before the first * is used, evaluated at the reference temperature).

Other limits:

A sheet resistance that depends on width and spacing is reduced to the first table entry.
A conductor or via drawn on several GDS streams uses the first stream. A conductor or via without a direct GDS stream is left out, with a warning.
gsim matches shapes to stack layers by GDS layer number only. Two layers that share a layer number with different datatypes therefore see the same shapes; this is reported as a warning.
Dielectric layers have no loss tangent in the file, so none is set. Add one to the material entry if needed, for example stack.materials["emx_dielectric_er_3p9"]["loss_tangent"] = 0.001.
The file must list layers from the bottom to the top. If the substrate is not the first layer, a warning points at a possible top-to-bottom listing.
Layer and conductor thicknesses and permittivities must be single tokens (a number or the name of a define), not expressions with spaces. An offset line may contain a spaced expression.

Portable JSON¶

parse_emx_proc(path) returns the parsed process as a plain dictionary (schema portable-em-stackup-v1) that can be saved with json.dump. load_portable_stackup_json(path) builds the same stack from such a file.