Measurements of the bulk, C-axis electromechanical coupling constant as a function of AlN film quality

Abstract

Piezoelectric thin film AlN has great potential for on-chip devices such as thin-film resonator (TFR)-based bandpass filters. The AlN electromechanical coupling constant, K(2), is an important material parameter that determines the maximum possible bandwidth for bandpass filters. Using a previously published extraction technique, the bulk c-axis electromechanical coupling constant was measured as a function of the AlN X-ray diffraction rocking curve [full width at half maximum (FWHM)]. For FWHM values of less than approximately 4 degrees , K (2) saturates at approximately 6.5%, equivalent to the value for epitaxial AlN. For FWHM values >4 degrees , K(2) gradually decreases to approximately 2.5% at a FWHM of 7.5 degrees . These results indicate that the maximum possible bandwidth for TFR-based bandpass filters using polycrystalline AlN is approximately 80 MHz and that, for 60-MHz bandwidth PCS applications, an AlN film quality of >5.5 degrees FWHM is required.

Research on the Piezoelectric Properties of AlN Thin Films for MEMS Applications

“…The full width of half maximum (FWHM) of the rocking curve was measured by X-ray diffraction (XRD) to assess, quantitatively, the preferred (002) orientation as shown in Figure 2. Generally, a (002)-oriented AlN film with the FWHM less than 4˝is the precondition of good piezoelectric property [14]. The FWHM of the rocking curve around (002) orientation for the AlN sample was about 1.9˝, which meant the AlN thin film has a good piezoelectric property.…”

Super-High-Frequency SAW Resonators on AlN/Diamond

“…Thus, K 2 is large, but v is limited by the smaller velocity value of the A1N overlayer. In addition to the intrinsic limitations imposed by the dispersion of the material system, the crystal quality and orientation of the sputtered A1N thin films, and thus their piezoelectricity, are limited by the film thickness [7], [8]. Moreover, the insulating character of A1N makes the e-beam patterning of the submicrometer IDTs more difficult.…”

Sputtered AlN Thin Films for Piezoelectric MEMS Devices - FBAR Resonators and Accelerometers

“…The AlN films were sputtered at various conditionssubstrate temperature from room temperature to 300°C, N 2 /Ar gas ratio of 9 to 1, pressure of 1 to 6mTorr, and power of 1 to 4kW -to obtain optimized films' properties. X-ray diffraction (XRD) rocking curve analysis was used to characterize the sputtered films since it has been shown that there is a correlation between the full width at half maximum (FWHM) of the XRD rocking curve and piezoelectric properties (Naik et al, 2000;Liaw & Hickernell, 1995). Fig.…”

“…Based on the initial sensor design (Gerfers et al, 2006), this chapter introduces the technique of stress concentration to improve the overall accelerometer SNR . In the first section, the deposition of highly c-axis oriented AlN films is described, since optimal piezoelectric and crystal properties of AlN films are essential for devices' performance (Ruby & Merchant, 1994;Naik et al, 2000). Furthermore, Section 2 discusses processing details and experimental results of the sputtered piezoelectric AlN films.…”