Ji-Hyuk Lim

6B-6 An Ultra Small SAW RF Filter using Wafer Level Packaging Technology

Since a multitude of surface acoustic wave (SAW) filters are the key components for wireless communications, they play an important role in todays mobile phone evolution. Increasing the levels of functional integration and size reduction are therefore the major driving forces in recent SAW radio frequency (RF) filter development. This paper presents a pioneering work for design and fabrication of ultra small SAW filter package. A novel wafer level packaging technology based on through-wafer interconnection and wafer-to-wafer bonding is designed to achieve highly miniaturized SAW RF filters. Based on this technology, SAW RF filters for mobile phone systems are developed in the worlds smallest size of 1.0 times 0.8 times 0.25 mm3. It is shown that our newly developed SAW RF filter offers equal frequency characteristics compared with the conventional chip-sized package. And the reliability test result of hermetically sealed SAW filter package will be presented to verify its application to mobile phones. As a result of these developments, wafer-level packaged SAW RF filters will offer considerable advantages over conventional chip-sized packages in many aspects of performance and production, including size, cost, and further integration

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.

Investigation of reliability problems in thermal inkjet printhead

This paper presents a failure analysis result for enhancing the reliability of thermal inkjet printhead. A novel inkjet printhead is fabricated using MEMS process, and we analyze the failure mechanism of inkjet head based on detailed experimental observations. The design modification of micro heater to avoid an early stage of failure yields the reliability enhancement of printhead.

Failure mechanisms in thermal inkjet printhead analyzed by experiments and numerical simulation

This paper presents a failure analysis result for enhancing the reliability of thermal inkjet printhead. A novel inkjet printhead is fabricated using MEMS process, and we analyze the failure mechanism of inkjet head based on detailed experimental observations and numerical simulations. The failures presented in this work showed three primary factors influencing the failure modes and lifetime of printhead; bubble cavitation damage, thermal fatigue, and electromigration of heater. The design modification of micro heater to avoid an early stage of failure by electromigration yields the reliability enhancement of thermal inkjet printhead.

Warpage Modeling and Characterization to Simulate the Fabrication Process of Wafer-Level Adhesive Bonding

Since the array of wafer-level packages formed by bonding of a cap wafer to a substrate wafer, how to well encapsulate the intricate sensor devices in wafer-level is the critical issue in the development of image sensor products. This paper presents an analytical model for design and fabrication of wafer-level adhesive bonding. A novel mechanical approach is proposed, which considers each layer in bonded wafer as a beam-type plate with effective material properties. Based on this mathematical modeling, the wafer warpage under thermal loading is predicted and compared to the experimental measurements. It is shown that our newly developed wafer warpage modeling offers simple and precise evaluation of wafer-level adhesive bonding process.

Visualization of bubbles generated by microheaters with various current density distributions

This work presents an experimental study to analyze the performance of thermal actuators to generate bubbles. The heaters are designed to have different current density distributions based on numerical analysis. The bubbles generated by heaters are compared to each other by visualization techniques. It is shown that the geometries and driving conditions of the heater strongly affect the bubble behaviors. The geometries like arc or trapezoid-shape induce nonuniform current densities and therefore change the driving conditions for generating bubbles. The experimental result reveals that the proper considerations on heater geometry are required to use the heater as a thermal actuator.