SAW COM-parameter extraction in AlN/diamond layered structures

Prior research has shown that piezoelectric materials like aluminum nitride (AlN) are suitable for surface acoustic wave (SAW) devices. However, achieving high c-axis orientation in AlN films at low temperatures remains a challenge. Earlier studies focused on high-temperature deposition methods, which limit compatibility with certain substrates. This gap motivated the investigation of low-temperature deposition techniques for AlN films. The need for precise SAW parameter extraction in layered structures is well established. Yet, no prior work had resolved how to effectively extract coupling parameters from SAW resonators on diamond substrates. The use of diamond as a substrate is novel in this context. This study aims to address the technical limitations of traditional deposition methods. It also explores the feasibility of using diamond as a substrate for SAW devices.

The aim of this study was to investigate the feasibility of depositing highly c-axis oriented AlN films on diamond substrates at low temperatures. The researchers sought to determine whether such films could support SAW resonators with measurable performance. They also aimed to extract key SAW parameters from these devices. The motivation was to expand the range of substrates available for SAW applications. The study focused on evaluating the structural and acoustic properties of AlN/diamond layers. It also aimed to compare measured SAW velocities with theoretical dispersion curves. The researchers wanted to assess the effectiveness of curve fitting for parameter extraction. This work contributes to the development of low-temperature SAW device fabrication.

The study used pulsed direct current (DC) magnetron reactive sputter-deposition to grow AlN films on diamond substrates. The deposition occurred at room temperature, below 50 degrees Celsius. The orientation of the AlN films was analyzed using rocking curve measurements. The full width at half maximum (FWHM) of the AlN-002-peak was measured. One-port SAW resonators were designed and fabricated on the AlN films. SAW phase velocities were measured experimentally. The researchers compared these velocities with calculated dispersion curves. Coupling parameters were extracted from S11 measurements using curve fitting techniques.

The AlN films showed a typical FWHM of 2.1 degrees for the AlN-002-peak. This indicates high c-axis orientation of the films. SAW resonators on these films supported multiple SAW modes. Measured phase velocities reached up to 11,800 m/s. These values aligned with theoretical dispersion curves for the AlN/diamond structure. The first SAW mode was analyzed using curve fitting of S11 measurements. The extracted coupling parameter K2 was 0.91%. The quality factor (Q) was approximately 600 at 1050 MHz.

The study demonstrates that AlN films can be deposited on diamond substrates at low temperatures. The films exhibit high c-axis orientation, as indicated by the FWHM measurement. SAW resonators on these films support multiple modes with measurable velocities. The measured phase velocities agree with theoretical predictions. The researchers successfully extracted coupling parameters using S11 measurements. The K2 value of 0.91% and Q factor of 600 were obtained for the first SAW mode. These findings suggest that diamond substrates are viable for SAW devices. The results support the use of low-temperature deposition methods for AlN films.