Thermal Conductivity of Aluminum Scandium Nitride for 5G Mobile Applications and Beyond

Abstract

Radio frequency (RF) microelectromechanical systems (MEMS) based on Al1–x Sc x N are replacing AlN-based devices because of their higher achievable bandwidths, suitable for the fifth-generation (5G) mobile network. However, overheating of Al1–x Sc x N film bulk acoustic resonators (FBARs) used in RF MEMS filters limits power handling and thus the phone’s ability to operate in an increasingly congested RF environment while maintaining its maximum data transmission rate. In this work, the ramifications of tailoring of the piezoelectric response and microstructure of Al1–x Sc x N films on the thermal transport have been studied. The thermal conductivity of Al1–x Sc x N films (3–8 W m–1 K–1) grown by reactive sputter deposition was found to be orders of magnitude lower than that for c-axis-textured AlN films due to alloying effects. The film thickness dependence of the thermal conductivity suggests that higher frequency FBAR structures may suffer from limited power handling due to exacerbated overheating concerns. The reduction of the abnormally oriented grain (AOG) density was found to have a modest effect on the measured thermal conductivity. However, the use of low AOG density films resulted in lower insertion loss and thus less power dissipated within the resonator, which will lead to an overall enhancement of the device thermal performance.

Thermal Conductivity of β-Phase Ga2O3 and (AlxGa1–x)2O3 Heteroepitaxial Thin Films

“…In contrast, the thermal conductivity of the β-(Al 0.27 Ga 0.73 ) 2 O 3 film is relatively invariant across this temperature range. A similar trend was previously observed in solid solutions Al 1– x Ga x N and Al x Sc 1– x N . The tested temperature range reaches up to the Debye temperatures of the two constitutive materials (α-Al 2 O 3 and β-Ga 2 O 3 .…”

“…53 In contrast, the thermal conductivity of the β-(Al 0.27 Ga 0.73 ) 2 O 3 film is relatively invariant across this temperature range. A similar trend was previously observed in solid solutions Al 1−x Ga x N 51 and Al x Sc 1−x N. 54 The tested temperature range reaches up to the Debye temperatures of the two constitutive materials (α-Al 3) peak flattens and cannot be identified. The peak position (P (cm −1 )) of the A g (3) Raman peak can be roughly correlated with the Al composition (x) up to 27% as P (cm −1 ) = 201.382 + 0.107 x; however, it should be noted that not only the Al composition but also the strain in the films will influence the Raman peak position.…”

“…TDTR is an optical pump–probe technique that allows us to measure the thermophysical properties of thin films based on heat diffusion from ultrafast femtosecond laser pulses . The details of the setup for TDTR measurements used in this study can be found in our previous work . The radii of the focused pump and probe beams were characterized using a scanning slit optical beam profiler (Thorlabs BP209-VIS) and were 7.0 and 4.5 μm, respectively.…”

“…FDTR is an optical pump–probe technique that extracts the thermal properties of thin films from the phase response of a thermal wave over a range of modulation frequencies . The details of the FDTR setup used in this study can be found in our previous work . The radii of the focused pump and probe beams were 13.4 and 13.1 μm, respectively.…”

“…47 The details of the setup for TDTR measurements used in this study can be found in our previous work. 54 The radii of the focused pump and probe beams were characterized using a scanning slit optical beam profiler (Thorlabs BP209-VIS) and were 7.0 and 4.5 μm, respectively. It should be noted that TDTR and FDTR measurements require a relatively smooth sample surface; 31 in this study, only samples with a reflected probe signal intensity greater than 40% of that for a smooth Au/Si calibration sample were included, which is expected to have a RMS surface roughness less than 30 nm.…”