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SYMMICTM is a software package for design-stage thermal analysis of high-power radio frequency (RF) components. The easy-to-use simulator facilitates detailed analysis of heating in Field Effect Transistors (FETs) and Monolithic Microwave Integrated Circuits (MMICs). Packaging of MMICs into radar and communication systems can be further analyzed to determine the impact of design choices on peak junction temperatures within individual FETs. SYMMIC is a transformative tool enabling transistor, circuit and packaging designers to obtain optimal performance and reliability in RF systems.
SYMMIC is a multi-hierarchy thermal simulator that facilitates top-down analysis of RF systems. Analysis begins with configuration of the basic devices, such as transistors and resistors. These can be then assembled to form MMIC models; a number of MMICs can be assembled to form a module, and a number of modules can be configured to create a more complex subsystem. Thermal analysis can be performed at each level of the hierarchy, with user-supplied boundary conditions or with boundary conditions extracted from analysis of a higher level of the hierarchy.
Thermal simulations are generated from template files that describe the geometry and operating conditions of a device or circuit. The template file contains a set of parameters that allow the thermal analysis to be rapidly reconfigured to evaluate the consequences of a wide variety of design choices within a device family. To perform a thermal analysis of a particular device, both a template describing the device and the SYMMIC software for processing the template are required. Templates created by CapeSym, Inc. are designed to ensure an accurate thermal analysis over a range of parameter settings. Layouts of multiple devices can be created to allow thermal analysis of larger structures. This process of making and analyzing layouts can be continued hierarchically to study the thermal behavior of entire subsystems.
Figure 1 describes a possible work flow for using SYMMIC to analyze a subsystem of a radar, the Line Replaceable Unit (LRU). Step 1 begins with configuring the basic device templates to match the geometry and materials of the power-dissipating devices, the FET and the resistor, used in the subsystem. A thermal analysis can be done on each device independently, but the backside thermal boundary conditions must be estimated and this approach fails to capture the thermal cross-coupling between devices in a MMIC. In Step 2, a MMIC is modeled by assembling a number of basic devices in a layout. The MMIC can be analyzed at this stage, with the understanding that the boundary conditions on the backside of the MMIC are still unknown and can only be estimated. In Step 3, the MMIC layout is exported to a device representation for incorporation in a module. This reduces the thermal model to the essential features necessary to represent the MMIC's contribution to heating of the module. In Step 4, several such module devices are assembled to form the whole Transmit/Receive (T/R) module. Again, thermal analysis can be performed at the T/R module level, but the goal is to find out how well the cold plate attachment to the front of the LRU cools the MMIC. So in Step 5, the T/R module is exported to an LRU device and several such LRU devices are assembled in a layout to form the complete LRU (Step 6). In Step 7 the thermal analysis of the entire LRU is performed to compute the temperature distributions on the boundaries of all the lower level components of the LRU, including the backside boundary conditions for the T/R module, the MMIC, and the basic devices (FETs and resisitors). These boundary conditions can now be used to analyze those layouts. Step 8 shows one approach where the boundary condition obtained from the LRU is used to modify the MMIC boundary condition and analyze the MMIC. With these boundary conditions in place, the MMIC thermal analysis (Step 9) accurately resolves the peak temperatures in every active region in every device of the MMIC.
Figure 1. Top-down work flow for SYMMIC
The SYMMIC software consists of a Graphical User Interface (GUI) and a solver for finite element analysis of thermal problems. The GUI displays the device template and layout geometry as shaded, 3D renderings that can be rotated, sliced, and zoomed. The GUI allows device dimensions and materials to be quickly modified. Thermal analysis consists of automated finite element mesh generation, setting of boundary conditions, and solution of the heat transfer equations. The GUI then displays the solution, which can also be rotated, sliced, and zoomed. Temperatures can be plotted for any location within the device, and solutions and plots can be animated through time. The finite element solution can also be exported in formats compatible with other software such as Tecplot.
To familiarize yourself with SYMMIC, open one of the template files that was installed with the application, such as QuarterFET.xml. Loading a template will produce a 3D rendering of the device in the window. Before modifying any parameters, try running a simulation with the default parameter settings by selecting Run simulation from the Solve menu. After the simulation is complete, the temperature solution will replace the template in the window. Select the temperature scale menu item from the Results menu to view the range of temperatures in the solution. Next, try plotting the maximum temperatures from the Results menu and taking a snapshot of the plot by selecting the Snapshot... menu item. This creates an HTML file that provides a detailed description of the currently displayed template and solution. Thermal analysis of a device is just that easy with SYMMIC.
A set of video tutorials that demonstrate how to use SYMMIC are available online at: www.symmic.biz For a complete understanding of the capabilities of the software, please read through the rest of the manual. The chapter on Top-Down Analysis describes some basic device templates and shows how these templates may be used to conduct the types of analyses sketched in Figure 1. It may also be helpful to work step-by-step through the MMIC, T/R Module, and LRU modeling examples using the templates in the \examples folder on the installation CD.
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