Overview
SAW performance is heavily influenced by both the choice of substrate material and the choice of cut angle. OnScale enables designers to explore many non standard cut angles offering better control over RF performance and thermal stability.
Here we show a simple unit cell model to analyse the effect of cut angle on the electrical performance of two common SAW wafer materials; Lithium Niobate (LiNbO3) and Lithium Tantalate (LiTaO3).
Cut Orientation
Here we simulate the commonly utilized Y-cut of LiNbO3/LiTaO3. The direction of SAW propagation is in the X direction, and the cut will be rotated around the Y axis to modify device behaviour (beta rotation in Euler angles).
Model Setup
A simple unit cell model was used to provide a rapid assessment of potential performance. This model is described in full here.
Model setup was as follows:
|
Parameter |
Description |
Default Value |
|---|---|---|
|
subs_thk |
Thickness of substrate |
7.5 µm |
|
elec_thk |
Thickness of electrode |
200 nm |
|
fin_pitch |
SAW finger pitch |
1.3 µm |
|
aratio |
Metalization ratio |
0.5 |
|
nfing |
Number of finger pairs |
100 |
|
fin_len |
Finger length |
50 µm |
|
ncycles |
Simulation length in cycles |
2000 |
|
freqint |
Centre frequency |
1.5 GHz |
The design variable was the Y-cut angle in degrees. The orientation angle was swept from 0 to 180 degrees in 1 degree steps, for a total of 181 simulations. These were run in parallel.
LiNbO3 Results
Impedance results for the LiNbO3 sweep are as follows.
LiNbO3 Impedance Results
A top down view of this plot provides a clear illustration of the main modes of propagation.
LiNbO3 Impedance Results – Annotated
Non leaky and leaky SAW modes are clearly visible. The commonly used 128 degree Y-cut is highlighted.
LiTaO3 Results
Impedance results for the LiTaO3 sweep are as follows.
As with the previous results both non leaky and leaky SAW modes are clearly visible.
Simulation Statistics
|
Model size |
1026 elements |
|
Solve Time |
486 secs (2 CPUS) |
|
Number of Simulations |
181 |
|
Total Core Hours |
25 |
|
Memory Usage |
48 MB |