SAW Wafer Cut Angle Study

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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 um

 elec_thk

 Thickness of electrode

 200 nm

 fin_pitch

 SAW finger pitch

 1.3 um

 aratio

 Metalization ratio

 0.5

 nfing

 Number of finger pairs

 100

 fin_len

 Finger length

 50 um

 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.

im3.png

LiNbO3 Impedance Results

A top down view of this plot provides a clear illustration of the main modes of propagation.

im1.png

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.

im4.png

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

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