Moon-chul Lee

A low temperature, hermetic wafer level packaging method for RF MEMS switch

In this paper, a low temperature hermetic wafer level packaging (WLP) scheme for RF-MEMS devices such as micro-switches is presented. The real component with size 1mm/spl times/1mm is composed of two parts: cap substrate and device substrate, cap substrate has a via-in-cavity structure with cavity depth of 20/spl mu/m. High aspect ratio via hole is fabricated by inductive coupled plasma-reactive ion etching (ICP-RIE) and electroplated with Cu for electrical feed-through. Eutectic bonding is still the most commonly used packaging technology at present. For the purpose of hermetic sealing, Au-Sn multilayer metallization with a close square loop of 100/spl mu/m width have been sputtered onto cap wafer surface as soldering system. Deposition of cap wafer metallization should be finished in one high vacuum chamber process in order to prevent oxidation of Sn layer during producing process. And Ti-Ni-Au combination structure is deposited and patterned on device wafer in accordance with the sealing and interconnection areas in cap wafer. Bonding is performed in wafer level using eutectic bonder (TPS-2000A, BNP science) at a relative low temperature of 280/spl deg/C for heating in static N/sub 2/ ambience for a period of time. As-bonded wafers are then diced into pieces and subjected to a series of performance test for evaluation. Shear strength of two bonded interfaces are measured for sample cells by shear tester ROYCE 552 100K to evaluate mechanical property. RF characteristics insertion loss at 2GHz has measured by HP 8510C network analyzer probe station, a total packaging insertion loss less than 0.05DB could be achieved. For hermeticity test, specific test vehicles which have a large cavity of 0.5/spl times/0.5/spl times/0.05cm/sup 3/ are designed for helium leak test based on M1T-STD-883F since real device cavity has a tiny volume of only 600/spl times/600/spl times/30/spl mu/m/sup 3/, test vehicles indicate a maximum equivalent leak rate in air of 1.6/spl times/10/sup -8/ mbar.l/sec. Also residual gas analysis (RGA) test is performed for bonded device sample. Reliability tests like thermal shock and high temperature, high humidity storage test are also performed according to MIL-STD-883F. For samples before and after reliability tests, measurements also have been made for comparison to evaluate the quality and reliability of packaging structure.

Vertical MEMS gyroscope by horizontal driving

A vertical MEMS gyroscope by horizontal driving includes a substrate, a support layer fixed on an upper surface of an area of the substrate, a driving structure floating above the substrate and having a portion fixed to an upper surface of the support layer and another portion in parallel with the fixed portion, the driving structure having a predetermined area capable of vibrating in a predetermined direction parallel to the substrate, a detecting structure fixed to the driving structure on a same plane as the driving structure, and having a predetermined area capable of vibrating in a vertical direction with respect to the substrate, a cap wafer bonded with the substrate positioned above the driving structure and the detecting structure, and a fixed vertical displacement detection electrode formed at a predetermined location of an underside of the cap wafer, for detecting displacement of the detecting structure in the vertical direction.

Bulk acoustic wave resonators of low lateral energy leakage using air edge reflector

A novel bulk acoustic wave (BAW) resonator structure with air edge reflectors is proposed. The air reflectors provided at the border of the resonator suppress the acoustic wave leakage travelling in lateral direction. The difference of acoustic impedance at the air edge interface is so large that the reflectivity is almost unity which indicates perfect reflection. As a result of optimized lateral structure, the Q-factor at antiresonance frequency (Qa) is improved significantly to 2740. Furthermore, the effective electro-mechanical coupling coefficient (kt2) which is essential to achieve wide band-width of RF filters is increased considerably by 14%. We also perform multi-physics simulation and investigate the effect of the lateral wave leakage for the BAW structures.

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.