Jea-Shik Shin

Nonlinear characteristics in radio frequency nanoelectromechanical resonators

The nonlinear oscillations of nanoelectromechanical resonators have previously been studied both experimentally and analytically. Nanoresonators have achieved superior sensitivity and high quality factors in many applications. However, the linear operating range of nanoresonators is significantly limited because of the small dimensions and thus the linear regime of nanoresonators may be required to expand performance in various conditions. In order to increase the linear operating range, we proposed that proper adjustments of simultaneous application of drive and electrothermal power can be used to optimize the resonance performance, providing a wider linear range as well as to tune the resonance frequency. For a nanoresonator operated by simultaneous drive and electrothermal power, experimental data are theoretically supported using nonlinear damping and spring terms. In the transition between linearity and nonlinearity by proper combinations of ac drive and dc electrothermal power, the experimental data can be better fitted, by theoretical study, with newly derived nonlinear damping terms. We believe that better understanding of these effects with different ac/dc combinations on radio frequency oscillation is crucial for utilizing nanoresonators for various applications such as sensors, oscillators and filters.

Resonance Properties of 3C-SiC Nanoelectromechanical Resonator in Room-Temperature Magnetomotive Transduction

We demonstrate the effect of nanoresonator geometry on the resonance property using a magnetomotive transduction technique for SiC nanoresonators in moderate conditions of pressure, temperature, and magnetic intensity. These trials were performed in conditions similar to those useful for practical applications to assist in the deployment of SiC-based nanoelectromechanical system prototype devices. This letter confirms that the resonant properties of a nanoscaled electromechanical resonator in moderate conditions are similar to those found during tests in ideal conditions. The resonance characteristics were analyzed based on the geometrical changes of the nanoresonator. The radio-frequency performance parameters such as the critical amplitude and dynamic range, which are crucial in the determination of linear operation range of nanoresonators, were maintained at a level comparable to those found under laboratory conditions. This letter brings this technology closer to practical applications in sensors, filters, and the oscillation of nanoscaled electromechanical devices.

Newly Developed High Q FBAR with Mesa-Shaped Membrane

In this paper, the authors present the newly developed high Q film bulk acoustic resonator (FBAR) which has the piezoelectric AlN film sandwiched between two electrode films and mesa-shaped membrane structure by utilizing poly-Si and XeF2 as a sacrificial layer and dry release gas, respectively. By controlling the etching profile of bottom electrode and sacrificial layer, the poor formation of AlN in the edge region of mesa-shaped membrane could be eliminated. In addition, by reducing the parasitic overlap which both of the electrodes and the piezoelectric layer resides directly on the substrate, the authors improve the characteristics of resonator and filter. When we compare with the typical surface micromachined FBAR, such as resonator having its own Bragg reflector or cavity, we could greatly reduce the needs for tight control of chemical mechanical polishing (CMP) of the layer underneath the resonator. The measured Q value and effective electromechanical coupling coefficient of the resonator with the area of 120times120 mum2 were 1450 and 6.43%. The peak insertion loss (IL) and bandwidth of filter were 0.60 dB and 70 MHz, respectively

A new BAWR (bulk acoustic wave resonator) structure for near zero TCF (temperature coefficient of frequency)

A BAWR (bulk acoustic wave resonator) is an essential component of RF filters and duplexers in wireless communication devices. The BAWR consists of a piezoelectric layer sandwiched between bottom and top electrodes. Its resonance frequency shifts as an environment temperature changes, normally ranging −25∼−30 ppm/°C, which is referred to TCF (temperature coefficient of frequency). A large TCF value reduces the gap between adjacent bands and gives rise to interference in their operation. To overcome this problem, a low TCF value is required as keeping carrier bandwidth, high Q, and high kt². In this work, a new BAWR structure with SiO<inf>2</inf>/SiN layers enabled TCF −0.3∼−7.8 ppm/°C, Q 2400, and kt² 5.4%, respectively. This BAWR has been applied to LTE Band-7 and Band-25 filters.

Novel Bulk acoustic wave resonator structure for reducing electrical loss of electrodes

A Bulk acoustic wave (BAW) resonator is an essential component in the RF filter and duplexer of mobile devices. The BAW resonator consists of a piezoelectric layer sandwiched between a top electrode and a bottom electrode. In this paper, a novel BAW resonator structure is presented to reduce the electrical loss of electrodes and thereby lower insertion loss which is important to achieve low loss RF filter and duplexer. For that, the resonator is designed to have a gold band of 12 um wide and 2 um high on its perimeter in which half region is connected to the top electrode and the other half the bottom electrode near the perimeter, respectively. As results, insertion loss of the resonator is reduced from -0.05dB to -0.03dB at resonance frequency. Q-factor and electrode resistance are also improved from 995 to 1360 and 1.07Ω to 0.81Ω, respectively.

Improved bulk acoustic wave resonator using edge method for high performance

We investigate the performance of aluminum nitride (AlN) resonator based bulk acoustic wave (BAW) structure made with air edge reflector and gold (Au) edge electrode. BAW Resonators have been fabricated, some devices using a thick film of e-beam evaporated gold as edge electrodes at the border of the resonator on bottom, top electrode. The air reflectors provided at the border of the resonator suppress the acoustic wave leakage through lateral direction. We have developed the simulation and measurement for the improving of resonator quality. The influence of the frame width on resonator surface after applied the air edge reflector and the gold edge electrode in the performance of the BAW resonators is analyzed. The Qa (Q-factor at anti-resonance frequency) and the effective electro-mechanical coupling coefficient (kt2) which is essential to achieve low loss and wide band-width of RF filters is increased by 19 % and 3.4 %, respectively. Also, Insertion loss at S21 parameter is improved significantly from -0.095 dB to -0.041 dB.