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SAW Metallization Study

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Chloe Allison
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SAW metallization presents the designer with a great deal of variables. OnScale can be used to clearly present the design trade offs which exist, allowing the optimum design to be reached quickly.

In this design study, we simulate a Unit Cell SAW to analyse the effect of both the aspect ratio of the SAW electrode fingers and the electrode thickness on the electrical performance.

What is symbol?: Check out these articles to get more familiar with OnScale's scripting language symbol.

Model Description

This simple unit cell model of a single port Surface Acoustic Wave (SAW) filter allows rapid simulation of device performance. The model comprises a pair aluminum electrodes on a piezoelectric substrate. The substrate can either be Lithium Tantalate (LiTaO3) or Lithium Niobate (LiNbO3). The model is set up to simulate a Y-cut, which can be rotated to the desired angle. The base design generates an SH mode at 1.5 GHz using a finger pitch of 1.3 µm.

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Download and Open the Model

Download: SAW Unit Cell

OnScale Input Files have the file extension *.flxinp. To open the downloaded file:

  1. Open OnScale 
  2. Select Analyst Mode
  3. Select the Menu button in the top left of the application
  4. Select Open
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Preview Model

Preview model is used to view the geometry dimensions and material assignment of a model to ensure the script is correct. To preview a model, select the Preview Model icon in the Home tab of the application ribbon.

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Note: Preview model will display data from any grph commands that come before the prcs command. If you have more than one grph command, you can cycle through the graphics by continuously selecting Preview Model. To close the preview, select Stop Preview.

Run Model on Cloud 

To run the model on the cloud, select the Run on Cloud button in the Home tab of the application and follow these steps:

  1. Set Start Value and End Value of aratio to 0.4 and 0.6 respectively
  2. Set number of Simulations of aratio to 10
  3. Set Start Value and End Value of elec_thk to 180e-9 and 220e-9 respectively
  4. Set number of Simulations of elec_thk to 10
  5. Select Estimate
  6. Select Run
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Download Results

  1. From the Home tab, select the Storage icon
  2. Select the Refresh icon to refresh storage
  3. Select the Job Name from the dropdown menu
  4. Select all Simulation folders using SHFT + Select
  5. Right click on a Simulation folder and select Download Selection By Type > .flxhst
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Choose a directory to download the results to. These results will be stored in the folder: saw_unit_3D-YYYYMMDD-HHMMSS\X where YYYYMMDD-HHMMSS is the current date and time and X is the simulation number.

Switch to Post Processor

Post Processor is a suite of tools used to visualise and analyse output data generated from OnScale simulations. Switch to Post Post Processor.

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What kind of analysis can I do in Post Processor? Find out here.

Analyse Results

Post-Processor

To plot the impedance of some of the simulations, follow these steps:

  1. In File Explorer, navigate to the download directory, expand folder Simulation 10 and double click the file 'saw_unit_3D.flxhst' to open it
  2. Repeat Step 1 for files in Simulation 20, 30 and 40
  3. In Results Manager, select the first voltage time history 'pize top:Voltage' by left clicking it
  4. From the Home tab of the ribbon, select the Impedance icon to calculate impedance
  5. In the Frequency History section of the Results Manager, double click the first 'Impd:top.amp' to plot impedance amplitude
  6. Repeat Steps 3-5 for the second, third and fourth curves
  7. In Plot Controls, tick Log yAxis
  8. In Plot Controls, set xAxis Minimum to 1.45e9 and Maximum to 1.66e9
  9. In Plot Controls, set yAxis Minimum to 0.3 and Maximum to 5.2e3
  10. Click on plot legend and name the curves
    1. aratio= 0.4
    2. aratio= 0.4222
    3. aratio= 0.444
    4. aratio= 0.4667

out.png

Batch Post-Processing

Dealing with large data-sets is usually easier in a code based processing package such as MATLAB. This is why we have created a MATLAB script which calculates Fs, Fp and Q for all of the 100 simulations.

Download: MATLAB Files

  1. Navigate to the directory which the MATLAB Files where downloaded to
  2. Right click the MATLAB Files folder and select Extract All > Extract
  3. Open the MATLAB Files folder and copy the contents into the  saw_unit_3D-YYYYMMDD-HHMMSS directory where all of the simulation folders are
  4. Open KPIs.m in MATLAB
  5. Select Run

out_proper.jpg

Note: If you don't have MATLAB, similar results can be displayed using Octave, Python etc.

What's Next?

Simulate a Full 3D SAW

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