Substrates in EMDS

A substrate definition describes the media where a circuit exists. An example is the substrate of a multilayer circuit board which consists of layers of metal traces, insulating material, ground planes, vias that connect traces, and the air that surrounds the board. A substrate definition enables you to specify properties such as the number of layers in the substrate, the dielectric constant, and the height of each layer for your circuit.

A substrate definition is made up of substrate layers and metallization layers. Substrate layers define the dielectric media, ground planes, covers, air or other layered material. Metallization layers are the conductive layers in between the substrate layers, and they are used in conjunction with the layout layers. By mapping layout layers to metallization layers, you can position the layout layers that your circuit is drawn on within the substrate. An example of a substrate is shown below. It contains four substrate layers and two microstrips with a via.

Substrate definitions can be saved and used with other circuits. A variety of predefined substrates are included with Advanced Design System, which can be used "as is", or modified to your design specifications.

The steps for defining a substrate include:

Details on how to work with existing substrate definitions and create new ones follow.

Selecting a Predefined Substrate

EMDS for ADS includes a number of predefined substrate definitions, so it may not be necessary to create a substrate from scratch. Substrate files end with the extension .slm.

To open a predefined substrate:

  1. In the layout window, select EMDS > Substrate > Open.
  2. If you want to open a supplied substrate, click Yes. A list of supplied substrate files appears.
    If you want to open a substrate that has been saved as part of the project, click No. A list of substrate files that are saved as part of the project appear.
    For more information on locating substrate files, refer to To save a named file, choose EMDS > Substrate > Save. Identifying Where Substrates are Saved.
  3. Select the substrate file, then click OK.

Creating/Modifying a Substrate

This section provides information about creating, modifying and editing a substrate. For information on metallization layers, refer to Defining Metallization Layers.

Defining Substrate Layers

You can define a substrate from scratch or edit an existing one. A substrate must have, at the minimum, a top plane and a bottom plane.

Note
Do not use substrate components that might appear on layout component palettes. You must use the dialog box under EMDS > Substrate > Create/Modify to create or edit substrate definitions.

To define substrate layers:

  1. Choose EMDS > Substrate > Create/Modify.
  2. If this is a new definition, three default layers appear in the Substrate Layers Field:
    • Free_space (top plane)
    • Alumina (dielectric)
    • GND (bottom plane)
      These layers represent a basic substrate definition that includes the three types of substrate layers in EMDS for ADS.
    • Free_Space represents the top plane of the substrate. In this definition, it is defined as an open boundary.
    • Alumina represents a dielectric layer of finite thickness. These layers are also referred to as interface layers.
    • GND represents the bottom plane of the substrate. GND defines a closed boundary. Closed boundaries define ground planes or other closed boundaries, such as the lid or bottom of an enclosure.
      For an existing substrate definition, you may see more layers with different names, but they will all be one of these three basic types of layer, and the substrate will have a top and bottom plane. A substrate definition must have a top plane and a bottom plane, and these planes can be defined either as open boundaries or closed boundaries.
  3. Select the layer of interest.
  4. To create a substrate, you will edit these layers, rename them, and add to them as desired. More information on how to perform these tasks is detailed in the following sections.
  5. When you are finished defining the substrate, click OK to dismiss the dialog box.

Defining an Open Boundary

An open boundary represents a layer of infinite thickness, such as air. An open boundary can be used to define other gases or infinitely-thick materials by editing the relative permeability and permittivity values of the boundary.

To define an open boundary:

  1. Select the Free_Space layer or another open boundary layer.
  2. Select Open from the Boundary list.
  3. From the Permittivity (Er) listbox, select a format for the relative permittivity of the boundary. You can enter the components of relative permittivity as:
    • Real and imaginary
    • Real and loss tangent
    • Real and conductivity, conductivity in Siemens/meter
      The real portion of the relative permittivity, , is a dimensionless quantity and is identical to the material's relative dielectric constant, . For more information on this parameter, refer to Dielectric Permittivity.
      To represent a dielectric that dissipates the power of a high-frequency electric field, enter the dielectric loss tangent, , of the material in the Loss Tangent field. The smaller the loss tangent, the less lossy the material. For more information on this parameter, refer to Dielectric Loss Tangent.
      Enter the components of the relative permittivity in the fields below the listbox.
  4. From the Permeability (MUr) listbox, select a format for the relative permeability of the boundary. You can enter the components of relative permeability as:
    • Real and imaginary
    • Real and loss tangent
      The real portion of the relative permeability, , is a dimensionless quantity and is identical to the material's relative permeability constant. For more information on this parameter refer to Dielectric Relative Permeability.
      To represent a dielectric that dissipates the power of a high-frequency magnetic field, enter the magnetic loss tangent, , of the material in the Permeability Loss Tangent field. The smaller the loss tangent, the less lossy the material. For more information on this parameter, refer to Dielectric Magnetic Loss Tangent.
      Enter the components of the relative permeability in the fields below the listbox.
  5. Click Apply to accept the open boundary definition.
    Hint
    You can create a ground plane from a open boundary layer by selecting the layer and choosing Close from the Boundary list.

Defining an Interface Layer

Interface layers have finite thickness, and they can be characterized using relative permittivity and permeability values. The thickness of a layer can be an arbitrary value, with these considerations:

To edit an interface layer:

  1. Select the Alumina layer or other interface layer of interest.
  2. Enter the thickness of the layer in the Thickness field and select the appropriate units in the adjacent listbox.
  3. From the Permittivity (Er) listbox, select a format for the relative permittivity of the boundary. You can enter the components of relative permittivity as:
    • Real and imaginary
    • Real and loss tangent
    • Real and conductivity, conductivity in Siemens/meter
      The real portion of the relative permittivity, , is a dimensionless quantity and is identical to the material's relative dielectric constant, . For more information on this parameter, refer to Dielectric Permittivity.
      To represent a dielectric that dissipates the power of a high-frequency electric field, enter the dielectric loss tangent, , of the material in the Loss Tangent field. The smaller the loss tangent, the less lossy the material. For more information on this parameter, refer to Dielectric Loss Tangent.
      Enter the components of the relative permittivity in the fields below the listbox.
  4. From the Permeability (MUr) listbox, select a format for the relative permeability of the boundary. You can enter the components of relative permeability as:
    • Real and imaginary
    • Real and loss tangent
      The real portion of the relative permeability, , is a dimensionless quantity. For more information on this parameter refer to Dielectric Relative Permeability.
      To represent a dielectric that dissipates the power of a high-frequency magnetic field, enter the magnetic loss tangent, , of the material in the Permeability Loss Tangent field. The smaller the loss tangent, the less lossy the material. For more information on this parameter, refer to Dielectric Magnetic Loss Tangent.
      Enter the relative permeability components in the fields below the listbox.
  5. Click Apply to accept the layer definition.

Defining a Closed Boundary Layer

A closed boundary represents a plane, such as a ground plane. It is a layer with zero thickness. It can be defined as a perfect conductor, or you can specify bulk conductivity or sheet impedance to characterize it as a lossy conductor.

To edit a ground plane:

  1. Select the ///GND/// layer of interest.
  2. Select Closed from the Boundary list.
  3. From the Plane listbox, select a format for the ground plane. You can specify the ground plane using these parameters:
    • Perfect conductor
    • Bulk conductivity in Siemens/meter
    • Sheet impedance in Ohms/square
      Conductivity is entered as a real number. Impedance is entered as the real and imaginary components of a complex value.
      Enter the ground plane parameters in the field below the listbox.
  4. Click Apply to accept the closed boundary definition.
    Hint
    You can create an open boundary layer from a ground plane by selecting the ground plane and choosing Open from the Boundary list.

Renaming a Layer

To rename a layer:

  1. Select a substrate in the Substrate Layers list.
  2. The name appears in the Substrate Layer Name field. Edit the name as desired.
  3. Click Apply.
    Note
    A ground plane is identified as ///GND/// and its name cannot be changed.

Deleting, Adding, and Moving Layers

To organize your substrate layers in the correct order, you can delete, add, and move layers.

To delete a substrate layer:

  1. Select a substrate layer in the Substrate Layers list.
  2. Click Cut. The layer definition is deleted.

To add a substrate layer:

  1. Select a substrate layer in the Substrate Layers list that has the same basic property (open boundary, closed boundary, or finite thickness) as the layer you are adding.
  2. Click Add .
  3. The new layer is highlighted. To rename the new layer, edit the Substrate Layer Name field.

To move a substrate layer:

  1. Select the substrate layer that you want to move from the Substrate Layers list.
  2. Click Cut.
  3. Select the substrate layer that you want positioned below the substrate that you are moving.
  4. Click Paste.

Defining Silicon Substrate Layers

The electrical behavior of Silicon material is usually specified using the dielectric constant and a resistivity (or conductivity value).

For the dielectric constant, a value for of 11.8 (11.9 is usually used).
Resistivity () values are normally specified in ohm cm, and a typical value is 10.

In EMDS for ADS, you can specify the conductivity () in S/m (inverse of the resistivity).

For more information, see Dielectric Conductivity.

Calculating Conductivity from Resistivity

Conductivity is simply the inverse of resistivity. Make certain that the units of resistivity are ohms m before inverting.

Example:

  1. = 10 ohm cm
  2. = 10 ohm cm = 0.1 ohm m
  3. = 1/rho = 10 S/m

Defining Conductivity

To define conductivity for silicon substrates:

  1. Choose EMDS > Substrate > Create/Modify.
  2. In the Create/Modify dialogue box, select RE, Conductivity under Permittivity ER).
  3. Specify the substrate dielectric constant and conductivity (S/m).
  4. When you are finished, click OK to dismiss the dialog box.

Defining Metallization Layers

Metallization layers enable you to:

In order to identify which areas of a layout layer are conductive, a layer can be specified as:

Some examples of using strips and slots include:

Note that a layout can have many other layers that are not part of the actual circuit, such as text or error reporting layers. For the purposes of an EMDS for ADS simulation, they are ignored. If layout layers containing parts of the circuit are not mapped to metallization layers, they are ignored as well.

The steps for defining metallization layers are:

Details for performing these steps are presented in the following sections.

Applying and Drawing Vias in Layout

EMDS for ADS creates a via by extruding the object that is mapped as via through the substrate layer it is applied to. Vias are drawn as lines or closed polygons. A simple line segment via is the simplest and most practical way of drawing a via. Vias drawn as lines are often called sheet vias because, when the line is extruded through the substrate, it is treated as a horizontal metal sheet. For vias of other shapes, you draw a closed polygon. So, for example, for a cylinder via you draw a circle. When the shape is mapped to a via metallization layer in EMDS for ADS, another dimension is added to the object in order for the shape to cut through the substrate. Thus a line becomes a sheet, a circle becomes a cylinder.

Regardless of how you draw vias, avoid having them extend over the sides of the objects that they connect to. Vias must be on the edge or inside the object. Any portion of the via outside of the object boundaries will not be taken into account during the simulation. The figure below illustrates various vias connecting two strips.

Vias are treated in the following manner:

Vias through Multiple Substrate Layers

Vias can be applied to multiple layers so that they cut through one or more layers.

When drawing vias that cut through multiple substrate layers, each via must be drawn once on a single layout layer. This layout layer must then be mapped as Via to each substrate layer that the via cuts through (using the Metallization tab) to assign the via layer to all substrate layers.

Mapping a Layout Layer

Layout layers that contain any shapes or components that are part of the circuit must be mapped to metallization layers. If layout layers are not mapped to metallization layers, they will not be included in the simulation.

To map a layout layer:

  1. Choose EMDS > Substrate > Create/Modify.
  2. Click the Metallization Layers tab.
  3. Select a layer from the Layout Layers list box. Note that the layout layer default cannot be mapped to a metallization layer, the first valid layer is cond.
  4. To map the layer as a slot or strip, select from the Substrate Layers list a dashed line to position the slot or strip in between two substrate layers, then click Strip or Slot.
    If you make a mistake, click Unmap, then click the correct choice.
    • A Strip defines the objects on the layout layer as conductive, the area surrounding the objects is not.
    • A Slot is the inverse of a strip, it defines the objects on the layout layer as not conductive, but the area of this layer surrounding the objects is conductive. When simulated, EMDS for ADS considers the electric field distribution (the equivalent magnetic current flow) in the slot.
      Note
      Conductivity in slot metallization is ignored and perfect metallization is assumed.
  5. To map the layer as a via, select the substrate layer that you want the via to cut through, then click Via.
    If you want the via to cut through more than one layer, select the next layer, then click Via again.
    • A Via defines the objects on the layout layer as conductive and they vertically cut through one or more substrate layers.
  6. To define the conductivity characteristics of this layer, refer to Defining Conductivity.
  7. If you have or suspect that you have overlapping layers, you need to set overlap precedence. Refer to Setting Overlap Precedence.
  8. Click the Apply button.

Unmapping a Layer

If you want to change the location of a layer or remove one from the substrate definition, use Unmap.
To unmap a layer:

  1. Choose EMDS > Substrate > Create/Modify.
  2. Click the Metallization Layers tab.
  3. In the Substrate Layers list, select the substrate layer or the interface where the layout layer is mapped.
  4. Click Unmap . This removes all layout layers assigned to this position.
  5. To remap a layer, refer to the steps in Mapping a Layout Layer.

Via Simulation Models

EMDS for ADS only supports 3D Distributed via models. For information about 2D Distributed and Lumped via models in Momentum, refer to the Via Simulation Models section in Chapter 3:Substrates of the Momentum documentation.

EMDS for ADS Layer Mapping GUI

The EMDS for ADS layer mapping dialog has been enhanced to accommodate the new via models. The following changes are implemented:

Sheet (No Expansion)

Thick (Expansion Up)

Thick (Expansion Down)

Unmapped Layer

Layered Mapped as STRIP

Layer Mapped as SLOT

Layout Layer Mapped as VIA

Selection of Via Model

Selection of Material

Defining Conductivity

You can define a layout layer as a conductor or a resistor. If the layout layer is defined as a strip or via, you define the conductivity of the strip or via. However, if the layout layer is defined as a slot, it is not possible to define the conductivity of the metal around the slot. This is because a slot is assumed to be surrounded by a perfect conductor.

To define conductivity:

  1. Choose EMDS > Substrate > Create/Modify.
  2. Choose the Metallization Layers tab.
  3. Select a mapped layout layer from the Layout Mapping list.
  4. Select the conductor type from Type list in the Layout Layers section. Choose Sheet Conductor , Thick Conductor (up) or Thick Conductor (down).
  5. Set the Thickness.
  6. Select the conductivity definition from the Conductivity list:
    • Perfect conductor
    • Sigma (Re, Im)
    • Impedance (Re, Im)
      Perfect Conductor means the strip, via, or metal around the slot is a perfect conductor and is lossless. No further definition is required.
      Sigma (Re, Im, thickness) specifies bulk conductivity as a complex number. Enter bulk conductivity's real and imaginary value in the respective fields below the Conductivity list, in Siemens/meter or Siemens/centimeter. The imaginary value is important for super-conductivity applications. Enter the metal thickness in the Thickness field above the Conductivity list and select the appropriate units. These values will be used to calculate the dc and high frequency loss mechanisms when determining the equivalent surface impedance. For example, the bulk conductivity of gold is 41,000,410 Siemens per meter with any arbitrary thickness. The equivalent DC sheet impedance that will be used when conductivity and thickness are specified is:

      where σ r is the real part of the conductivity (S/m) and t is the thickness of the conductor (m).
      At high frequencies, the equivalent sheet impedance will be equivalent to:

      where δ is the skin depth given by:

      with f as the frequency (Hz) and µ0 the free space permeability. This high frequency loss specification corresponds to a single sheet skin-effect loss model, meaning that it assumes the current at high frequency is assumed to be concentrated on one side of the finite thickness conductor.
      Impedance (Re, Im,) specifies conductivity in terms of sheet impedance, in Ohms/square. Enter the real and imaginary component of the value in the Real and Imaginary fields, respectively.

      Note
      EMDS for ADS treats such metal layer definitions as a constant, frequency independent loss model. The thickness entered in UI is ignored in this case.
  7. When you are finished with the definition, click Apply.
  8. Repeat these steps for the remaining mapped layout layers.
  9. When you are finished, click OK to dismiss the dialog box.

Defining Finite Dielectrics

You can also define a layout layer as a dielectric. This enables you to define finite dielectric regions such as finite substrates, dielectric resonators, or implant regions inside semiconducting substrates.

Note
Dielectric mask regions are only supported in EMDS for ADS. Any layout layer that is given a dielectric material property will be ignored during Momentum simulations.

If the layout layer is defined as a strip or via, you define dielectric properties of the strip or via. However, if the layout layer is defined as a slot, it is not possible to define the dielectric properties of the slot. This is because a slot is assumed to be surrounded by a perfect conductor.

To define a dielectric region (as a thick strip):

  1. Choose EMDS > Substrate > Create/Modify.
  2. Choose the Metallization Layers tab.
  3. Select a mapped layout layer from the Layout Mapping list.
  4. Select the model type from Model list in the Layout Layers section. Choose Thick Conductor (up) or Thick Conductor (down).
  5. Set the Thickness.
  6. Select the material definition from the Material list:
    • Dielectric (Eps)
    • Dielectric (Eps LossTan)
    • Dielectric (Eps Sigma)
      Dielectric (Eps) specifies the material property as a complex relative permeability. Enter the real and imaginary relative permeability values in the respective fields below the Material list.
      Dielectric (Eps, LossTan) specifies the material property as a real relative permeability and a loss tangent. Enter the real relative permeability values in the Eps field and the loss tangent in the Loss Tan field.
      Dielectric (Eps, Sigma) specifies the material property as a real relative permeability and a conductivity. Enter the real relative permeability values in the Eps field and the conductivity (in Siemens/m) in the Sigma field.
  7. When you are finished with the definition, click Apply.
  8. Repeat these steps for the remaining mapped layout layers.
  9. When you are finished, click OK to dismiss the dialog box.

Automatic 3-D Expansion for Thick Conductors

Conductors with finite thickness can be modeled in EMDS for ADS using the 3D metal expansion feature. This feature will automatically expand the mask of a conductor with finite thickness in the direction orthogonal to the layered medium, using the specified thickness of this conductor.

Automated 3D expansion is activated by selecting either the Thick Conductor (up) or Thick Conductor (down) expansion. In both cases, an extra dielectric layer is included in the internal EMDS for ADS substrate model. This is done for each metal layer that is expanded. The thickness values of the dielectric layers in between the metal layers are not changed, which will preserve the capacitance value between two conductors lying on top of each other in the substrates.

To select the automated 3-D Metal Expansion Substrate items:

  1. Choose EMDS > Substrate > Create/Modify .
  2. Click the Metallization Layers tab.
  3. In the Substrate Layers list, select the substrate layer or the interface where the layout layer is mapped.
  4. Select the Type drop-down list from the Layout Layer dialog box.
  5. Choose either Thick Conductor (up) or Thick Conductor (down)

Simulations with automatic expansion require more simulation time and memory, but result in more accurate simulation results. Typically, when the height/thickness aspect ratio is smaller than a factor of 5, the effect of accounting for the finite thickness of the conductors will need to be allowed for in EMDS for ADS simulations.

The following figure illustrates the internal substrate model when using an "up" and "down" expansion for a conductor. In both cases, an extra dielectric layer is inserted (indicated with [new] in the figure), which in the case of an "up" expansion has the dielectric properties of the layer above the metal layer. In the case of a "down" expansion, the new layer has the material properties of the layer below the metal layer.

Note
Extra internal metallization layers are automatically added in EMDS for ADS to model the currents on all four sides of the finite thickness conductor.

Setting Overlap Precedence

Overlap precedence specifies which layout layer has precedence over another if two or more layout layers are assigned to the same metallization layer and objects on the metallization layer overlap. Precedence is used by the mesh maker so that objects on the layer with the greatest precedence number are meshed and any overlap with objects on layers with lesser numbers is logically subtracted from the circuit. If you do not set the precedence, and there are overlapping objects, a mesh will automatically and arbitrarily be created, with no errors reported. Resistive layers generated from schematics are automatically set to the highest precedence.

In some cases, you may be designing with an intentional overlap because of manufacturing layout guidelines. In this case, assign a precedence number to the layout layers that overlap with precedence order in reverse numerical order (largest to smallest). The system will draw the boundary at the edge of the higher numbered layer without returning an error.

Precedence affects only how the mesh is created, it does not affect or alter the layout layers in your design.

To specify overlap precedence:

  1. Choose EMDS > Substrate > Create/Modify.
  2. Choose the Metallization Layers tab.
  3. Select one of the overlapping layout layers from the list of Substrate Layers in the Layer Mapping section.
  4. Assign its order of precedence in the Overlap Precedence field. Either type a value directly into the field or use the arrow keys to select a value.
  5. Click Apply.
  6. Repeat these steps for the remaining overlapping layers.
  7. When you are finished, click OK to dismiss the dialog box.

About Dielectric Parameters

The sections below give additional detail about the following dielectric parameters:

Dielectric Permittivity

The relative permittivity of all dielectrics is assumed to be complex:

which can also be expressed as:

where is the real portion of and is the dielectric loss tangent.

Examples of materials and their typical permittivity are shown in the following table:

Material Relative Permittivity
Alumina 9.8
Sapphire 9.3 - 11.7
Berrylia 6.0
Rutile 100.0
GaAs 12.9
Note
The values listed in the table are for illustrative purposes only; use values specifically measured for the materials that you are using.

Dielectric Loss Tangent

Material <th
Alumina .0002
Glass .002
Berrylia .0001
Rutile .0004
GaAs .0016
Note
These values are listed for illustrative purposes only. Use values specifically measured for the materials that you are using.

Dielectric Conductivity

For some materials (for example, Silicon), the substrate loss effects are better described using the combination (, = conductivity) instead of (, loss tangent). The complex dielectric constant is related to (, conductivity) using the following formula:

where:

= 2 frequency

= 8.85e-12 F/m (absolute dielectric constant free space)

Often, resistivity () is specified instead of conductivity. The relationship between resistivity and conductivity is:

Resistivity is usually specified in cm, conductivity is specified in S/m.

Example:

A typical value for resistivity of a Silicon material is

= 10 cm

which corresponds to a conductivity value of:

= 10 S/m.

Dielectric Relative Permeability

The relative permeability of all dielectrics is assumed to be complex:

which can also be expressed as:

where is the real portion of and is the magnetic loss tangent.

Examples of relative permeabilities are shown in Materials and Relative Permeability.

Material Relative Permeability
Gold .99996
Air 1
Aluminum 1.00002
Nickel 250
Iron 4000

Note
The values listed above are for illustrative purposes only. Use values specifically measured for the materials that you are using.

Dielectric Magnetic Loss Tangent

The magnetic loss tangent associated with a material is a function of frequency. An example of a material with a magnetic loss tangent is polyiron which, at 30 GHz, has a loss tangent of 0.0208.

Reading a Substrate Definition from a Schematic

Choose EMDS > Substrate > Update From Schematic to update a substrate under the following conditions:

In order to retrieve the new substrate information, you must use EMDS > Substrate > Update From Schematic . Using Layout > Generate/Update Layout will not transfer the new substrate information to the layout.

To update a substrate definition from a schematic:

  1. Choose EMDS > Substrate > Update From Schematic. The substrate on the correct schematic is read and the new information is entered in the EMDS for ADS substrate definition.

Saving a Substrate

A substrate definition can be saved to a file. This enables you to store the definition outside of the current project, making it easier to use the substrate definition in other designs.

To save a substrate:

  1. Choose EMDS > Substrate > Save As.
  2. Type a name for the file and click OK . Substrate files end with the extension .slm
    To save a named file, choose EMDS > Substrate > Save. Identifying Where Substrates are Saved
    Substrates are saved in one of two locations:

Reusing Substrate Calculations

Substrate definitions and substrate computations can be reused for other designs, if the substrate database is accessible. If you are unsure about access to the database, consult your system administrator.

Before a calculation begins, several folders are searched to determine if a solution has already been generated.

The folders searched, in order, are:

Deleting a Substrate

This command erases the substrate file (.slm) that you select. If the substrate has been precomputed, the calculations remain in the database.
To delete a file:

  1. Choose EMDS > Substrate > Delete .
  2. Select the name of the file that you want to delete.
  3. Click OK.

Substrate Examples

Use the following examples to help you set up your own circuits:

Substrate for Radiating Antennas

To define a substrate for an antenna that radiates into air, you can set up the following substrate definition:

Both layers are defined as open boundaries with the characteristics of air (for permittivity and permeability, Real = 1, Loss Tangent = 0). The antenna design is positioned on the metallization layer in between the two layers of air.

377 Ohm Terminations and Radiation Patterns

It is possible to define the top and bottom layers of a design with 377 ohm terminations, then calculate radiation patterns for these structures after simulation. For such applications, note the following considerations:

Substrate for Designs with Air Bridges

In order to designing a substrate definition for a design that contains an air bridge, you need to first identify components of the air bridge and their placement on layout layers. Refer to the illustration that follows.

A basic air bridge between two components consists of the follow items:

The layout must be drawn on at least three independent layers:

No two items that comprise the air bridge (except for the vias) can be on the same layer. For this illustration, the components that are connected by the air bridge are on the same layer.

The substrate definition would consist of the following items:

You map the layout layers to the substrate as follows:

It is not required for the components that the bridge connects to be on the same layout layer or mapped to the same metallization layer. Nor do the vias need to be on the same layout layer. Just be sure that the substrate definition has the correct number of substrate layers and that the components, vias, and bridge are mapped to the appropriate metallization layers.

Drawing Air Bridges in Layout

If you are simulating an air bridge, you will have to create a layout and a substrate definition that will support the geometry. This means adding an air layer (height equal to the air bridge) which the vias will cut through. For example, you would have some geometry (like a spiral) on a dielectric layer. Then a via would rise vertically cutting through the air layer, where it would connect to a metal bridge. Then another via would connect from the bridge, down to the previous layer, and onto another path.

Silicon Substrate

The following is an example of a silicon substrate used in a EMDS for ADS simulation (this example is taken from examples > Momentum > Microwave > SPIRAL_prj ):

Free space

--------------- strip2

Layer3 (Eps=3.9) | via

--------------- spiral (strip)

Layer2 (Eps=3.9)
Layer1 (Eps=11.9 ; cond=12.5 S/m)
GND

Silicon Substrate with 3D Expansion

The following is an example of a silicon substrate used with automatic expansion of a thick conductor:
Free space

-----------------Strip thick conductor up (thickness 4 mil conductivity

Sigma Re: 5e+6 S/m)
Alumina (Eps=9.6 ; Thickness=25 mil)
GND

With the Thick conductor up selected, the substrate used for the simulation will become:
Free space

-----------------Strip

air | via (substrate layer thickness 4 mil ; Eps =1 )

-----------------Strip

Alumina (Eps=9.6 ; Thickness=25 mil)
GND

For more information on automatic 3-D expansion for thick conductors, refer to Automatic 3-D Expansion for Thick Conductors.

 

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