Kyu-dong Jung

Application of Au-Sn eutectic bonding in hermetic RF MEMS wafer level packaging

Recently the strong demands in wireless communication requires expanding development for the application of RF MEMS (Radio Frequency micro electro mechanical systems) sensing devices such as micro-switches, tunable capacitors because it offers lower power consumption, lower losses, higher linearity and higher Q factors compared with conventional communications components. To accelerate commercialization of RF MEMS products, development for packaging technologies is one of the most critical issues should be solved beforehand. Packaging for RF MEMS is more challenging compared with conventional IC (integrated Circuit) Packaging technologies because it has both electrical and mechanical component, a low temperature, and hermetic wafer level packaging technology is needed for RF MEMS device. Au-Sn metallization system has been successfully utilize for flip chip bonding in many applications such as optoelectronic packaging and microwave device because of their high strength, good wetting behaviors, and resistance for thermal fatigue compared with conventional Pb/Sn solder system. Au-Sn eutectic bonding is considered to be a promising low temperature, wafer level bonding technology. In this paper, Au-Sn eutectic bonding for RF MEMS application is presented, a closed square loop was designed for the bonding structure, test vehicle was prepared for DOE (Design of experiment) process for the optimization of bonding parameters, and bonding temperature and applied load are found to be the most critical parameters for the bonding result, bonding can be done at a relative low temperature below 300/spl deg/C. For bonded samples, shear strength, warpage, insertion loss and hermetic tests etc. are performed for the evaluation of bonding quality, AES (Auger Electron Spectrum) and SEM (Scanning Electron Microscopy) was also made to investigate the microstructure of bonded interface, and reliability test such as thermal shock and high temperature, high humidity storage test was performed for the evaluation of bonding quality.

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.

Zoom lens design using liquid lens for laparoscope

Traditional laparoscopic optical systems consisting of about 30 lenses have low optical magnification. To magnify tissue during surgical operations, one must change from one laparoscope to another or use a magnifying adapter between the laparoscope and the sensor. Our work focuses on how to change the sag of a liquid lens while zooming from 1 × zoom, to 2 × , and 4 × in an optical design for a laparoscope. The design includes several lenses and two liquid lenses with variable focal lengths. A pair of laparoscopes for 3-D stereoscopy is placed within a tube 11 mm in diameter. The predicted depth resolution of tissue is 0.5 mm without interpolation at 4 × zoom.

Microelectrofluidic iris for variable aperture

This paper presents a variable aperture design based on the microelectrofluidic technology which integrates electrowetting and microfluidics. The proposed microelectrofluidic iris (MEFI) consists of two immiscible fluids and two connected surface channels formed by three transparent plates and two spacers between them. In the initial state, the confined aqueous ring makes two fluidic interfaces, on which the Laplace pressure is same, in the hydrophobic surface channels. When a certain voltage is applied between the dielectric-coated control electrode beneath the three-phase contact line (TCL) and the reference electrode for grounding the aqueous, the contact angle changes on the activated control electrode. At high voltage over the threshold, the induced positive pressure difference makes the TCLs on the 1st channel advance to the center and the aperture narrow. If there is no potential difference between the control and reference electrodes, the pressure difference becomes negative. It makes the TCLs on the 1st channel recede and the aperture widen to the initial state. It is expected that the proposed MEFI is able to be widely used because of its fast response, circular aperture, digital operation, high aperture ratio, and possibility to be miniaturized for variable aperture.

A Wafer-Level Micro Mechanical Global Shutter for a Micro Camera

A novel wafer-level manufactured micro mechanical global shutter utilizing thin-film roll actuators is presented for a micro mobile camera. The aperture of the shutter is 2.2 mm in diameter and covered with 36 triangular roll actuators whose radius of curvature is designed to 235 ¿m. The stress induced rolling of thin composite layers and their pull-in behaviors are analyzed and experimented. A 0.8 mm-thick wafer-level shutter array is successfully implemented using batch processes. The fabricated shutter can follows 500 Hz-square wave signal of 30 V

Characterization and Reliability Verification of Wafer-Level Hermetic Package with Nano-Liter Cavity for RF-MEMS Applications

Wafer-level packaging (WLP) is a very promising candidate for RF-MEMS packaging, especially in the mobile applications, due to the lower cost and higher volume throughput relative to the component level packaging. However, the long-term reliability of WLP is still one of the critical concerns for the commercialization of RF-MEMS devices. In this paper, a wafer-level hermetic packaging scheme based on through-wafer interconnects and wafer-to-wafer bonding will be reviewed in terms of their construction, fabrication process, and electrical/mechanical performance. The film bulk acoustic resonators (FBARs) sealed with the wafer-level packaging scheme were also undergone through harsh environment tests, such as the pressure cooker test for 300 hours, the high humidity storage test at 85degC/85%RH for 1000 hours, the high temp storage test at 125degC for 1000 hours and the temperature cycling test (-55~125degC) for 1000 cycles, to investigate the long-term reliability of the packages. The performance evaluation and reliability results of the package will also be presented.

Variable aperture controlled by microelectrofluidic iris

This Letter presents an adaptive liquid iris based on microelectrofluidic technology with experimental results. In the microelectrofluidic iris (MEFI), the electrostatic force generated by electrowetting in a surface channel unbalances the Laplace pressure acting on two fluidic interfaces between air and a light-absorbing liquid in two connected surface channels in a chamber. Then, the changed net pressure makes the iris aperture of the liquid diaphragm adjustable. The present MEFI was designed to have a tunable range from 4.2 to 0.85 mm in diameter and a tuning ratio of 80%. The MEFI was fabricated with a transparent electrode patterned on three glass plates and two channel spacers. Concerning the optical and interfacial properties of the MEFI for its operation, an aqueous near-infrared dye used in optical coherence tomography (OCT) was forced into a ring shape as the driving liquid in the hydrophobic chamber. By switching the segmented concentric control electrodes in steps, digital operation of the MEFI was successfully observed with clear aperture stops. The measured turnaround speed was 80 mm/s, which is significantly higher than that for other comparable adaptive liquid irises. Due to a scalable aperture range with fast response, the concept of MEFI is expected to be widely applied in various optical systems that require high-quality imaging, as well as in real-time diagnostic OCT.

Wafer-level low temperature bonding with Au-In system

Wafer bonding at low temperature is an essential process for next generation MEMS & Sensor packaging. Optoelectronic devices, such as image sensor module and laser diode integrated circuit, need low bonding temperature, high re-melting temperature, high thermal conductivity, and stress-relaxed structure in many cases. Eutectic Au-In system was developed as a replacement of previous Au-Sn system for specific systems require bonding temperature lower than 200degC. Bonding temperature of developed Au-In system was set at 180degC, which was 100degC lower than that of Au-Sn system. Though polymer materials has been used for low temperature bonding, out-gassing and volume shrinkage during the bonding process often degraded bonding quality and accurate alignment between the wafers. Clean packaging with accurate alignment was achieved with eutectic Au-In bonding which also possessed high re-melting temperature over 450degC. Majority of the deposited metallizations to construct the system was converted to intermetallic compounds (AuIn & AuIn2) after bonding reaction. Peak temperature and duration time were varied to investigate optimum condition of wafer-level bonding and diced separate dies are used for X-ray inspection, microstructural observation of the cross-section, and shear test. The results showed that bonding parameters critically affected mechanical reliability of the bonded joint. Failure through the solder layer (unreacted pure In) resulted in higher shear strength, while clear separation between the wafer and under bump metallization (UBM) revealed low bond strength. Re-melting temperature of Au-In system was measured using TMA and the result showed that it was closely related with melting phenomena of pre-formed intermetallic compounds such as AuIn and gamma phases. The wafer-level bonding with Au-In system showed good feasibility for MEMS & sensor packagings that require low temperature bonding with high quality.

Low Temperature, Wafer Level Au-In Bonding for ISM Packaging

A low process temperature, hermetic and reliable wafer level packaging (WLP) technology is required for image sensor module (ISM) packaging. Eutectic bonding is regarded as one of the most common used methods for WLP. Au-Sn metallization system has been applied as a wafer level bonding technology in many applications, but it still has process temperature around 300degC which is not applicable for temperature sensitive materials contained device wafer like ISM. In this paper, a fluxless Au-In solder system with Au, In multilayer metallizations has been developed and fabrication process is also presented, the metallization is achieved using e-beam evaporation, test vehicle was then prepared for bonding quality evaluation. Bonding process is performed at 180degC with static force for a relatively long dwelling time of 30minutes in N2 ambience, finally a void free joint is formed. Microstructure observation reveals a combination of different Au-In intermetallic compounds AuIn2 and AuIn at the interface. Shear strength around 20MPa could be obtained for as-bonded samples, and a remelting temperature over 300degC is confirmed using thermomechanical analysis (TMA) test. Real time helium leak rate test are performed to check hermeticity of the package, samples are also subjected to pressure cooker test (PCT) for evaluation of bonding performance after reliability test