diff --git a/cspdk/si220/__init__.py b/cspdk/si220/__init__.py
index c55245a..45b5634 100644
--- a/cspdk/si220/__init__.py
+++ b/cspdk/si220/__init__.py
@@ -24,12 +24,12 @@ def get_pdk() -> Pdk:
     """Return Cornerstone PDK."""
     return Pdk(
         name="cornerstone_si220",
-        cells=_cells,
+        cells=_cells,  # layout parametric cells
         cross_sections=_cross_sections,  # type: ignore
         layers=LAYER,
         layer_stack=LAYER_STACK,
         layer_views=LAYER_VIEWS,
-        models=_models,
+        models=_models,  # models for simulation
         routing_strategies=routing_strategies,
     )
 
diff --git a/cspdk/si220/cells/primitives.py b/cspdk/si220/cells/primitives.py
index 6bc5e1c..d52f3f6 100644
--- a/cspdk/si220/cells/primitives.py
+++ b/cspdk/si220/cells/primitives.py
@@ -614,6 +614,52 @@ def mzi(
 )
 
 
+@gf.cell
+def mzi_lattice_sc(
+    delta_length: float = 10.0,
+    bend="bend_euler_sc",
+    straight="straight_sc",
+    splitter="mmi1x2_sc",
+    combiner="mmi2x2_sc",
+    cross_section: CrossSectionSpec = "xs_sc",
+) -> gf.Component:
+    """A Mach-Zehnder Interferometer.
+
+    Args:
+        delta_length: the difference in length between the upper and lower arms of the mzi
+        bend: the name of the default bend of the mzi
+        straight: the name of the default straight of the mzi
+        splitter: the name of the default splitter of the mzi
+        combiner: the name of the default combiner of the mzi
+        cross_section: a cross section or its name or a function generating a cross section.
+    """
+    return gf.c.mzi(
+        delta_length=delta_length,
+        length_y=1.0,
+        length_x=0.1,
+        straight_y=None,
+        straight_x_top=None,
+        straight_x_bot=None,
+        with_splitter=True,
+        port_e1_splitter="o2",
+        port_e0_splitter="o3",
+        port_e1_combiner="o3",
+        port_e0_combiner="o4",
+        nbends=2,
+        cross_section=cross_section,
+        cross_section_x_top=None,
+        cross_section_x_bot=None,
+        mirror_bot=False,
+        add_optical_ports_arms=False,
+        min_length=10e-3,
+        auto_rename_ports=True,
+        bend=bend,
+        straight=straight,
+        splitter=splitter,
+        combiner=combiner,
+    )
+
+
 @gf.cell
 def coupler_ring_sc(
     gap: float = 0.2,
diff --git a/cspdk/si220/models.py b/cspdk/si220/models.py
index 8c55335..39a7f5d 100644
--- a/cspdk/si220/models.py
+++ b/cspdk/si220/models.py
@@ -257,9 +257,9 @@ def coupler_symmetric() -> sax.SDict:
     raise NotImplementedError("No model for 'coupler_symmetric'")
 
 
-coupler_sc = partial(sm.mmi2x2, wl0=1.55, fwhm=0.2)
+coupler_sc = partial(sm.coupler, wl0=1.55, fwhm=0.2)
 coupler_rc = coupler_sc
-coupler_so = partial(sm.mmi2x2, wl0=1.31, fwhm=0.2)
+coupler_so = partial(sm.coupler, wl0=1.31, fwhm=0.2)
 coupler_ro = coupler_so
 
 coupler_ring_sc = partial(sm.coupler, wl0=1.55)
diff --git a/cspdk/si220/samples/circuit_lattice.py b/cspdk/si220/samples/circuit_lattice.py
new file mode 100644
index 0000000..59be04b
--- /dev/null
+++ b/cspdk/si220/samples/circuit_lattice.py
@@ -0,0 +1,29 @@
+"""Circuit simulation with routes."""
+
+import gdsfactory as gf
+import jax.numpy as jnp
+import matplotlib.pyplot as plt
+import sax
+
+from cspdk.si220 import PDK, cells
+
+def lattice_filter():
+
+if __name__ == "__main__":
+    c = gf.Component()
+    mzi_lattice = cells.mzi_lattice(delta_length=10)
+
+    netlist = c.get_netlist(recursive=True)
+    c.plot_netlist(recursive=True)
+    models = PDK.models
+    circuit, _ = sax.circuit(netlist, models=models)  # type: ignore
+    wl = jnp.linspace(1.5, 1.6, 256)
+
+    S = circuit(wl=wl)
+    plt.figure(figsize=(14, 4))
+    plt.title("MZI")
+    plt.plot(1e3 * wl, jnp.abs(S["o1", "o2"]) ** 2)  # type: ignore
+    plt.xlabel("λ [nm]")
+    plt.ylabel("T")
+    plt.grid(True)
+    plt.show()
diff --git a/cspdk/si220/samples/circuit_simulations_sc.py b/cspdk/si220/samples/circuit_simulations_sc.py
index b6c3c6c..de2ac40 100644
--- a/cspdk/si220/samples/circuit_simulations_sc.py
+++ b/cspdk/si220/samples/circuit_simulations_sc.py
@@ -7,8 +7,11 @@
 from cspdk.si220 import PDK, cells
 
 if __name__ == "__main__":
-    c = cells.mzi_sc(delta_length=12)
-    c.show()
+    # Layout definition
+    c = cells.mzi_sc(delta_length=12 * 2)
+    c.show()  # show the layout in Klayout
+
+    # Circuit simulation
     netlist = c.get_netlist()
     c.plot_netlist()
     models = PDK.models