Wei-Tsai Chang

The liquid sensor using thin film bulk acoustic resonator with c-axis tilted AlN films

Dual-mode thin film bulk acoustic resonator (TFBAR) devices are fabricated with c-axis tilted AlN films. To fabricate dual-mode TFBAR devices, the off-axis RF magnetron sputtering method for the growth of tilted piezoelectric AlN thin films is adopted. In this report, the AlN thin films are deposited with tilting angles of 15° and 23°. The frequency response of the TFBAR device with 23° tilted AlN thin film is measured to reveal its ability to provide dual-mode resonance. The sensitivities of the longitudinal and shear modes tomass loading are calculated to be 2295 Hz cm2/ng and 1363 Hz cm2/ng with the mechanical quality factors of 480 and 287, respectively. The sensitivities of the longitudinal and shear modes are calculated to be 0 and 15Hz cm2/µg for liquid loading.

Design and fabrication of nanoscale IDTs using electron beam technology for high-frequency SAW devices

High-frequency Rayleigh-mode surface acoustic wave (SAW) devices were fabricated for 4G mobile telecommunications. The RF magnetron sputtering method was adopted to grow piezoelectric aluminum nitride (AlN) thin films on the Si3N4/Si substrates. The influence of sputtering parameters on the crystalline characteristics of AlN thin films was investigated. The interdigital transducer electrodes (IDTs) of aluminum (Al) were then fabricated onto the AlN surfaces by using the electron beam (e-beam) direct write lithography method to form the Al/AlN/Si3N4/Si structured SAW devices. The Al electrodes were adopted owing to its low resistivity, low cost, and low density of the material. For 4G applications in mobile telecommunications, the line widths of 937 nm, 750 nm, 562 nm, and 375 nm of IDTs were designed. Preferred orientation and crystalline properties of AlN thin films were determined by X-ray diffraction using a Siemens XRD-8 with CuKα radiation. Additionally, the cross-sectional images of AlN thin films were obtained by scanning electron microscope. Finally, the frequency responses of high-frequency SAW devices were measured using the E5071C network analyzer. The center frequencies of the high-frequency Rayleigh-mode SAW devices of 1.36 GHz, 1.81 GHz, 2.37 GHz, and 3.74 GHz are obtained. This study demonstrates that the proposed processing method significantly contributes to high-frequency SAW devices for wireless communications.

Study of deposition parameters on the RF magnetron sputtered ZnO films on Mo/SiN x /Si substrates

In this study, the high quality ZnO films deposited on Mo/SiNx/Si substrates were investigated. The Mo film was deposited on SiNx/Si substrates by DC sputtering. Then, the zinc oxide (ZnO) film was deposited onto the Mo film by radio frequency (RF) magnetron sputtering. The influence of sputtering power and sputtering pressure on the microstructures of ZnO films were investigated and discussed. The analysis of the crystalline structures and morphologies of the thin films was carried out using X-ray diffraction and field emission scanning electron microscope. The experimental results showed that the optimal ZnO films were obtained at sputtering power of 80W and sputtering pressure of 20 mTorr with epitaxial grain growth and a preferred (002) orientation.

Deposition of AlN thin films on LiTaO 3 substrates

In this study, the AlN thin films were deposited on LiTaO3 substrates by reactive radio frequency (RF) magnetron sputtering. The influence of sputtering power and sputtering pressure on the microstructures of AlN films were investigated and discussed. The analysis of the crystalline structures and morphologies of the thin films was carried out using X-ray diffraction (XRD), atomic force microscopic (AFM) and field emission scanning electron microscope (SEM). The experimental results showed that the AlN films with strongly c-axis orientated, low surface roughness and uniform surface morphologies were obtained at sputtering power of 270 W, sputtering pressure of 5 mtorr, substrate temperature of 300 °C and nitrogen fraction of 60%.

Fabrication of SAW Devices with Dual Mode Frequency Response Using AlN and ZnO Thin Films

In this study, surface acoustic wave (SAW) devices with dual mode frequency response are fabricated on Si3N4/Si substrate using double-layered piezoelectric thin films. Aluminum nitride (AlN) and zinc oxide (ZnO) are chosen as the piezoelectric thin films because the distinguished piezoelectricity of acoustic wave velocity and electromechanical coupling coefficient. The interdigital transducer electrodes (IDTs) of aluminum (Al) were then fabricated onto the piezoelectric layers by using the sputtering technology combined with photolithography to form the IDT/ZnO/AlN/Si3N4/Si SAW devices. For optimizing the characteristics of resonator and filter applications, the deposition conditions of AlN and ZnO thin films have been investigated. The SAW device shows the resonant frequency of 146.3 MHz (Rayleigh mode) and 265.7 MHz (Sezawa mode). The insertion loss Rayleigh mode and Sezawa mode are -14.2 dB and -17.4 dB, respectively.

Designing a Piezoelectric Vibration-Energy Harvester Used for a Rapid IgE Allergy Sensing System Platform

This investigation examines a novel means of integrating high-performance AlN piezoelectric thin films with a flexible stainless steel substrate (SUS304) to fabricate a double-sided piezoelectric transducer for wind-power generators. The double-sided piezoelectric transducer is constructed by depositing AlN piezoelectric thin films on both the front and the back sides of SUS304 substrate. The titanium (Ti) and platinum (Pt) layers were deposited using a dual-gun DC sputtering system between the AlN piezoelectric thin film and the back side of the SUS304 substrate. Scanning electron microscopy and X-ray diffraction of AlN piezoelectric films reveal a rigid surface structure and highly c-axis-preferred orientation. To fabricate a transducer with a resonant frequency of about 90 Hz, a cantilever length of 1 cm and a vibration area of 1 cm2 are designed, based on the cantilever vibration theory. The maximum open circuit voltage of the power transducer is approximately 14.6 V.

Investigation of acoustic properties and Raman scattering of AlN films for biosensor application

In this study, two approach of the molecular-level detection technique, acoustic-based and Raman-scattering-based detection, are adopted. The acoustic resonant signals are sensitive to the loading mass, such as nano particles and bio-molecules, while Raman scattering signals are highly surface sensitive to a wide range of adsorbate molecules. Aluminum nitride (AlN) thin film dominars both of the techniques. In the acoustic device, AlN acts as a piezoelectric layer to excite acoustic wave. In the Raman scattering experiment, the surface morphology of AlN give rise to a surface enhanced Raman signal. Thus, thin film bulk acoustic wave (TFBAW) properties as well as the surface enhanced Raman spectroscopy (SERS) signals of AlN are investigated. To obtain good piezoelectricity, a highly c-axis orientated AlN thin film is prepared by a reactive RF magnetron sputtering system. The c-axis orientated AlN possesses a pebble-like morphology, which is suitable for the SERS. Solidly-mounted resonators (SMR) are adopted to excite high frequency resonant signal, and the 1.5 GHz shear resonance signal is obtained. In the SERS measurement, the aqueous solution of Rhodamine 6G with concentration of 10−6 M added with 10 mM of sodium chloride was utilized to calibrate the enhancement factors.