Dongkyu Chai

Effects of thermal annealing of W/SiO2 multilayer Bragg reflectors on resonance characteristics of film bulk acoustic resonator devices with cobalt electrodes

In this article, we present the thermal annealing effects of the W/SiO2 multilayer reflectors in ZnO-based film bulk acoustic resonator (FBAR) devices with cobalt (Co) electrodes in comparison with those with aluminum (Al) electrodes. Various thermal annealing conditions have been implemented on the W/SiO2 multilayer reflectors formed on p-type (100) silicon substrates. The resonance characteristics could be significantly improved due to the thermal annealing and were observed to depend strongly on the annealing conditions applied to the reflectors. Particularly, the FBAR devices with the W/SiO2 multilayer reflectors annealed at 400 °C/30 min have shown superior resonance characteristics in terms of return loss and quality factor. In addition, the use of Co electrodes has resulted in the further improvement of the resonance characteristics as compared with the Al electrodes. As a result, the combined use of both the thermal annealing and Co electrodes seems very useful to more effectively improve the reso...

Improved Resonance Characteristics by Thermal Annealing of W/SiO2 Multi-Layers in Film Bulk Acoustic Wave Resonator Devices

In this paper, we, for the first time, present the effects of the thermal annealing of the W/SiO2 multi-layer Bragg reflectors on the resonance characteristics of the ZnO-based film bulk acoustic wave resonator (FBAR) devices. In order to improve the resonance characteristics of the FBAR devices, we employed a thermal annealing process after the Bragg reflectors were formed on a silicon substrate using a radio frequency (RF) magnetron sputtering technique. As a result, the resonance characteristics of the FBAR devices were observed to strongly depend on the annealing conditions applied to the Bragg reflectors. The FBAR devices with the Bragg reflectors annealed at 400°C/30 min showed excellent resonance characteristics as compared to those with the non-annealed (as-deposited) Bragg reflectors. The newly proposed simple thermal annealing process will be very useful to more effectively improve the resonance characteristics of the future FBAR devices with multi-layer Bragg reflectors.

ZnO film deposition on Al film and effects of deposition temperature on ZnO film growth characteristics

The effects of the deposition temperature on the growth characteristics of the ZnO films were studied for film bulk acoustic wave resonator (FBAR) device applications. All films were deposited using a radio frequency magnetron sputtering technique. It was found that the growth characteristics of ZnO films have a strong dependence on the deposition temperature from 25 to 350 °C. ZnO films deposited below 200 °C exhibited reasonably good columnar grain structures with highly preferred c-axis orientation while those above 200 °C showed very poor columnar grain structures with mixed-axis orientation. This study seems very useful for future FBAR device applications.

Optimization of film bulk acoustic wave resonator (FBAR) for RF filter applications

In this paper, we present the effects of the thermal annealing of the W/SiO/sub 2/ multi-layer Bragg reflectors on the resonance characteristics of the ZnO-based film bulk acoustic resonator (FBAR) devices and the use of the cobalt (Co) electrodes instead of the aluminum (Al) electrodes to optimize the FBAR for RF filter applications. The resonance characteristics could be significantly improved by the thermal annealing and using the Co as the electrodes in FBAR devices. The FBAR devices with the Bragg reflectors annealed at 400/spl deg/C/30 min show excellent resonance characteristics in term of the return loss and Q-factor.

BSTO/MgO microstrip line 45/spl deg/ phase shifter with wide tuning range and low insertion loss

The design of a 7-coupled microstrip line 45/spl deg/ phase shifter is proposed in this paper. Tunability was achieved by utilizing the characteristic that the relative dielectric constant of ferroelectrics depends on the applied bias voltage. To obtain a large tuning range of the phase shifter, we added many couplings within the allowable loss range. In terms of control voltage, we applied 0 V and 150 V respectively to inspect the variance of phase shift. At 16 GHz and 0 V, DPS (differential phase shift) is 45/spl deg/. But at the same frequency and 150 V, DPS is 126/spl deg/. Thus, the tuning range of the phase shifter reaches 81/spl deg/. Our frequency band of interest is from 15 GHz to 16.8 GHz. As a result of simulations, RL (return loss) is larger than 19 dB and IL (insertion loss) is less than 2.7 dB with both 0 V and 150 V in this frequency range. The size of the tunable phase shifter is 7.4 mm /spl times/ 2.2 mm /spl times/ 0.5 mm.