**1. Introduction**

Aluminum nitride (AlN) thin films have attracted much attention due to their excellent properties suitable for the manufacture of devices, which meet various applications [1–7]. In addition to their properties highlighted in **Figure 1**, these materials have been much investigated due to their high piezoelectricity and high surface acoustic velocity (v⊥ = 5600 m/s and v∥ = 11,000 m/s) [2, 3], suitable electromechanical coupling, chemical stability [3, 8–13] and good transparency in the region of the visible, infrared and ultraviolet [10, 13].

In recent years, AlN has been shown as an outstanding candidate for the development of micro-electro-mechanical systems (MEMS), particularly surface acoustic wave (SAW) devices operating in high frequency and in thermally and chemically harsh environments [3].

It has been observed that the thin film deposition technique influences the preferred orientation of the AlN film. Different techniques, such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE), and reactive sputtering (RF or DC, with or

**Figure 1.** *Some properties of AlN.*

without magnetron), have been used for the growth of AlN films [3, 12]. The advantages of RF magnetron sputtering technique are that besides the deposition parameters can be easily controlled, it uses low temperature (<400°C) and has compatibility with CMOS technology [3, 9]. Generally, the deposition vacuum systems used in industries have limitations due to the use of large vacuum chambers and of the laborious tasks of environment cleaning processes (chamber, substrates, and everything other system parts). In deposition systems used in microelectronics applications, there is also the possibility of incorporation of oxygen in the films due to the native oxygen on the silicon wafers and the residual relative to the background pressure 1.33 × 10−4 Pa (≈10−6 Torr). Thus, in these conditions, it is difficult to deposit crystalline and highly oriented textural AlN (100) films with low oxygen concentration in their structure, good stoichiometry Al/N (≈1∶1), and thickness close to 500 nm [14, 15].

In this chapter, an overview of the AlN thin film technology is presented. First, the structure and orientation of AlN material are described. Next, the incorporation of oxygen in this material is discussed. The largest section of the chapter is devoted to the growth of AlN films and their use as a buffer layer and sensing layer. Finally, some examples of SAW sensors based on AlN films are presented.
