Residual stress analysis of aluminum nitride piezoelectric micromachined ultrasonic transducers using Raman spectroscopy
Abstract
In this study, the Raman biaxial stress coefficients KII and strain-free phonon frequencies ω0 have been determined for the E2 (low), E2 (high), and A1 (LO) phonon modes of aluminum nitride, AlN, using both experimental and theoretical approaches. The E2 (high) mode of AlN is recommended for the residual stress analysis of AlN due to its high sensitivity and the largest signal-to-noise ratio among the studied modes. The E2 (high) Raman biaxial stress coefficient of −3.8 cm−1/GPa and strain-free phonon frequency of 656.68 cm−1 were then applied to perform both macroscopic and microscopic stress mappings. For macroscopic stress evaluation, the spatial variation of residual stress was measured across an AlN-on-Si wafer prepared by sputter deposition. A cross-wafer variation in residual stress of ∼150 MPa was observed regardless of the average stress state of the film. Microscopic stress evaluation was performed on AlN piezoelectric micromachined ultrasonic transducers (pMUTs) with submicrometer spatial resolution. These measurements were used to assess the effect of device fabrication on residual stress distribution in an individual pMUT and the effect of residual stress on the resonance frequency. At ∼20 μm directly outside the outer edge of the pMUT electrode, a large lateral spatial variation in residual stress of ∼100 MPa was measured, highlighting the impact of metallization structures on residual stress in the AlN film.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jul 23, 2021
- Source ID
- 10.1063/5.0056302
Entities
People
- Adam Edstrand
- Baxter Moody
- Benjamin A. Griffin
- E Douglas
- Elizabeth A. Moore
- Giovanni Esteves
- Jacob H. Leach
- James S Lundh
- Kathleen Coleman
- Sukwon Choi
- Susan Trolier-McKinstry
- Yiwen Song
- Ştefan C. Bǎdescu
Organizations
- Air Force Office of Scientific Research
- Air Force Research Laboratory
- Defense Advanced Research Projects Agency
- National Science Foundation
- Pennsylvania State University
- Sandia National Laboratories
- Wyle Laboratories