AlN (aluminum nitride) is a covalent bond compound with a hexagonal wurtzite structure. Usually gray or grayish white in color, it has advantages such as high thermal conductivity, high-temperature insulation, good dielectric properties, high material strength at high temperatures, and low coefficient of thermal expansion. Due to the significant piezoelectric effect of AlN orientation along the c-axis, high-performance thin film bulk acoustic wave devices can be obtained by preparing AlN films with c-axis preferred orientation on electrode materials. AlN thin film is an ideal piezoelectric thin film material for radio frequency(RF) filters. PAM-XIAMEN’s Si based AlN thin film can be used to prepare SAW and FBAR filters. Please refer to the following table for specific parameters:
1. Specification of AlN Thin Film Depositionon Silicon Substrate
PAM221103-AOS
| Substrate | |
| Material | Si (111) |
| Diameter | 4~6inch |
| Epi layer | |
| Material | AlN |
| Thickness | 200nm |
| XRD FWHM(002) | ≤1500 arcsec |
| Bow | ≤30um |
| RMS（5x5um2） | ≤0.35nm |
| Edge crack | No |
| Scratch | No |
2. Characteristics of Piezoelectric AlN Epitaxial Thin Film
There are mainly two types of RF filters, surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters. FBAR is a type of BAW. The main piezoelectric materials available for selection include LiNbO3, LiTaO3, PZT, ZnO, and AlN. Among them, LiNbO3 and LiTaO3 are widely used in surface acoustic wave filters (SAW), and have absolute advantages in preparing SAW filters with lower frequencies (<3 GHz). But in higher frequency FBAR filters, piezoelectric materials such as PZT, ZnO, and AlN are mainly used.
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Characteristics of AlN, ZnO, PZT Piezoelectric Materials |
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| Material properties | AlN | ZnO | PZT |
| Kt2（%） | 6.5 | 7.5 | 8-15 |
| Dielectric constant | 9.5 | 9.2 | 80-400 |
| Longitudinal sound velocity (m/s) | 10400 | 6350 | 4000-6000 |
| Inherent material loss | very low | low | high |
| CMOS process compatibility | compatible | incompatible | incompatible |
| Sedimentation rate | high | medium | low |
| 1GHz attenuation (dB/m) | 800 | 2500 | very large |
In known filter piezoelectric materials, the sound wave propagation speed of epitaxial AlN thin films can reach 10400m/s (compared to traditional substrate materials below 4000m/s). Due to its excellent chemical and thermal stability, as well as high sensitivity to external environments such as pressure, temperature, stress, and gas, and compatibility with conventional silicon-based CMOS technology, piezoelectric aluminum nitride thin-film is the most ideal piezoelectric material in 5G high-frequency SAW/BAW filters and MEMS sensors. Especially, scandium doped AlN thin film piezoelectric effect can significantly increase their piezoelectric coefficient, thereby enhancing the electromechanical coupling coefficient of SAW/BAW, making them the core piezoelectric/substrate material for the new generation 5G RF SAW/BAW filtering.
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