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.

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Thin-film piezoelectric materials such as ZnO and AlN have great potential for on-chip devices such as filters, actuators and sensors. The electromechanical coupling constant is an important material parameter which determines the piezoelectric response of these films. This paper presents a technique based on the Butterworth Van-Dyke (BVD) model which, together with a simple one-mask over-moded resonator, can be used to extract the bulk, one-dimensional electromechanical coupling constant K(2) of any piezoelectrically active thin-film. The BVD model is used to explicitly define the series resonance, parallel resonance, and quality factor Q of any given resonating mode. Common methods of defining the series resonance, parallel resonance, and Q are shown to be inaccurate for low coupling, lossy resonators such as the over-moded resonator. Specifically, an electromechanical coupling constant K(2) of (2.6+/-0.1)% was measured for an (002) c-axis textured AlN film with an X-ray diffraction rocking curve of 7.5 degrees using the BVD based extraction technique.

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Very large scale integration (VLSI), complementary metal on oxide semiconductor (CMOS) compatible piezoelectric materials such as AlN have great potential for applications as miniature bandpass filters. The AlN film quality strongly determines the figures of merit for such devices. For device integration into a VLSI CMOS process with Al electrodes, a low‐temperature deposition technique is necessary. A direct current (dc) magnetron sputtering system was reconstructed to deposit high‐quality, polycrystalline AlN films on Si and Al substrates at temperatures of approximately 150°C. X‐ray diffraction rocking curves of 2.3° on Si substrates and 5.7° on thin‐film Al substrates were achieved. Due to the relatively low deposition rates and the required low deposition temperature, the AlN film quality was found to be limited by the oxygen content within the film. For a deposition rate of 1 μm/h and a deposition temperature of 150°C, the partial pressure of oxygen‐containing species must be less than approximately 5×10−10 Torr for such narrow rocking curve material. The amount of oxygen contamination is dependent on various system‐ and process‐related factors such as the deposition rate, deposition temperature, base pressure, oxygen and moisture partial pressure, target purity, and gas purity. Therefore, the AlN film quality is strongly system dependent. All films were tensile in nature, with stresses of 300–600 MPa for 1 μm films on either substrate. Minimal stress control was possible with the dc magnetron source. © 1999 The Electrochemical Society. All rights reserved.