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Impact of SAW device passivation on RF performance
B W Marks1, D W Sheddrick, S Jen
1RF Monolithics, Inc, Dallas, TX 75244, USA. marks@rfm.com
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
|September 26, 2001
Summary
Sputtered aluminum oxide (Al2O3) passivation layers on surface acoustic wave (SAW) devices slightly increase surface stiffness and insertion loss. These layers effectively reduce short circuits without significantly impacting reflectivity, aiding SAW device design.
Area of Science:
- Materials Science
- Electrical Engineering
- Acoustics
Background:
- Surface Acoustic Wave (SAW) devices are susceptible to short circuits.
- Passivation layers are crucial for device reliability and performance.
Purpose of the Study:
- To investigate the effects of sputtered aluminum oxide (Al2O3) passivation layers on SAW devices.
- To assess the impact of these layers on device performance, specifically shorts, velocity, attenuation, and reflectivity.
Main Methods:
- Deposition of Al2O3 passivation layers onto SAW devices.
- Utilizing a coupling-of-modes model for analysis.
- Testing one-port resonators, coupled resonator filters (CRF), and dedicated test structures.
Main Results:
- The Al2O3 layer increases surface stiffness, enhancing acoustic velocity proportionally to the layer thickness (tau) and wavelength (lambda).
- A slight increase in attenuation was observed, resulting in a 0.25-dB loss increase in one-port resonators at 314 MHz.
- The impact on reflectivity was found to be minimal.
Conclusions:
- Sputtered Al2O3 passivation effectively reduces shorts in SAW devices.
- The observed changes in velocity and attenuation are manageable and predictable.
- The minimal effect on reflectivity makes Al2O3 a viable passivation option for SAW device designers.