Design and fabrication of aluminum nitride thin film bulk acoustic wave devices

• Main Authors: Kuan-Hsun Chiu, 邱冠勳
• Other Authors: Ruey-Shing Huang
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/56238313719318909558

博士 === 國立清華大學 === 電子工程研究所 === 95 === Film bulk acoustic wave devices show considerable promise as an integrated solution for RF bandpass filter, duplexer and sensor. This thesis is devoted to the analysis, design, and fabrication of film bulk acoustic wave devices, which are targeted for RF front-end in communication devices and sensors. The film bulk acoustic wave device uses c-axis oriented aluminum nitride (AlN) thin film as its piezoelectric layer. Comprehensive studies on the relationships between the key deposition process parameters and the properties of sputter deposited c-axis oriented AlN thin films are presented. These AlN films were deposited on Pt electrode by reactive magnetron sputtering under various deposition conditions. A polycrystalline AlN film with highly c axis-preferred orientation was achieved. The XRD rocking curve shows a narrow peak measured was 2.7°. This thesis also covers the description of the studies on developed a dry backside silicon etching process to fabricate a number of devices including a membrane type film bulk acoustic wave resonator (FBAR), a ladder type bandpass filter, a FBAR duplexer and FBAR based sensors. The membrane type thin film FBAR was fabricated by high aspect ratio silicon etching process. The quality factor of this FBAR is estimated to be 974 and the electromechanical coupling constant is 0.063. The resonance and anti-resonance frequencies are 1.888 GHz and 1.940 GHz, respectively. This FBAR is a high Q device and is suitable for making a ladder type filter. A ladder type bandpass FBAR filter was fabricated based on our membrane type FBAR. This thesis also developed a 1.9 GHz RF transmitter (Tx) filter. This FBAR based filter has potential of simple process to achieve high yield and hence low cost. The measured in-band insertion loss, return loss and the broadband rejection of the Tx filter were 2 dB, 9 dB and 25 dB, respectively. The filter has band pass of 60 MHz bandwidth from 1850 to 1910 MHz. A duplexer was also fabricated based on our FBAR technology. The duplexer has transmitted and received band pass of 60 MHz bandwidth from 1850 to 1910 MHz and 1930 to 1990 MHz, respectively. A FBAR-based sensor for the simultaneous measurement of temperature and pressure with high sensitivity was fabricated and characterized. Temperature or pressure sensing is determined by the change in the series resonant frequency of the FBAR device when exposed to a measurement environment. For temperature sensing, measurement results show a sensitivity of 25.02 ppm/℃, a nonlinearity less than ±0.005 % over the measurement range of 10 to 80 ℃, and a hysteresis within ±0.005 % in one temperature cycle. In pressure sensing, measured results show a sensitivity of 336.2 ppm/bar, a nonlinearity less than ±0.004 % over the measurement pressure range of 0 to 2.07 bar, and a hysteresis within ±0.007 % in one pressure cycle.