FBAR 2D Design Study

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It is useful to use parametric simulation when designing FBARs because the structure of the device effects many performance aspects. Performing a design study aids designers in optimising their design for frequency range, quality factor and many other key performance characteristics.

In this design study, we simulate a 2D FBAR to analyse the effect of top electrode and AlN thickness on the electrical performance.

Model Description

This 2D FBAR model provides a simple starting structure consisting of a piezoelectric active layer (Aluminum Nitride), Molybdenum electrodes and silicon substrate material at the sides of the air cavity.

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Download and Open the Model

Download: FBAR 2D Model

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 

We are going to run a sweep of AlN thickness and Top Electrode thickness. This is done in the Cloud Scheduler. To open the Cloud Scheduler select the Run on Cloud button in the Home tab of the application and follow these steps:

  1. Set End Value of aln_thk to 8.5e-7
  2. Set number of Simulations of aln_thk to 10
  3. Set End Value of elec_top to 5e-7
  4. Set number of Simulations of elec_top to 10
  5. Select Estimate
  6. Select Run

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 Note: To sweep variables on the cloud, they must be defined as symbx variables in the input file.

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: fbar_2D-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 'fbar_2D.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 2e9 and Maximum to 2.15e9
  9. In Plot Controls, set yAxis Minimum to 0.2 and Maximum to 966
  10. Click on plot legend and name the curves
    1. aln_thk=800 nm
    2. aln_thk = 806 nm
    3. aln_thk = 811 nm
    4. aln_thk = 816 nm

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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  fbar_2D-YYYYMMDD-HHMMSS directory where all of the simulation folders are
  4. Open KPIs.m in MATLAB
  5. Select Run

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

What's Next?

Simulate a Full 3D FBAR

 

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