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Low-Cost Wafer-Level Vacuum Packaging for MEMS Roland Gooch and Thomas Schimert Abstract Vacuum packaging of high-performance surface-micromachined uncooled microbolometer detectors and focal-plane arrays (FPAs) for infrared imaging and nonimaging applications, inertial MEMS (microelectromechanical systems) accelerometers and gyroscopes, and rf MEMS resonators is a key issue in the technology development path to low-cost, high-volume MEMS production. In this article, two approaches to vacuum packaging for MEMS will be discussed. The first is component-level vacuum packaging, a die-level approach that involves packaging individual die in a ceramic package using either a silicon or germanium lid. The second approach is wafer-level vacuum packaging, in which the vacuum-packaging process is carried out at the wafer level prior to dicing the wafer into individual die. We focus the discussion of MEMS vacuum packaging on surface-micromachined uncooled amorphous silicon infrared microbolometer detectors and FPAs for which both component-level and wafer-level vacuum packaging have found widespread application and system insertion. We first discuss the requirement for vacuum packaging of uncooled a-Si microbolometers and FPAs. Second, we discuss the details of the component-level and wafer-level vacuum-packaging approaches. Finally, we discuss the system insertion of wafer-level vacuum packaging into the Raytheon 2000AS uncooled infrared imaging camera product line that employs a wafer-level-packaged 160
120 pixel a-Si infrared FPA. Keywords: infrared microbolometers, microelectromechanical systems (MEMS), microelectronics packaging and integration, wafer-level vacuum packaging.

Introduction Vacuum packaging of high-performance surface-micromachined uncooled microbolometer detectors and focal-plane arrays (FPAs) for infrared nonimaging1–3 and imaging applications,4–7 inertial MEMS (microelectromechanical systems) accelerometers and gyroscopes,8–13 and rf MEMS resonators is a key issue in the technology development path to low-cost, highvolume MEMS production. Vacuum packaging is a cost driver in these applications. For MEMS to become useful in these applications, a low-cost approach to highvolume vacuum packaging is essential. Two approaches have been developed for MEMS vacuum packaging, as shown in Figure 1. The first is component-level vacuum packaging, a die-level approach (Figure 1a), while the second is waferlevel vacuum packaging (Figure 1b). In

MRS BULLETIN/JANUARY 2003

this article, we will contrast these two approaches to vacuum packaging for MEMS. Component-level vacuum packaging is a die-level approach that involves packaging individual die in a ceramic package using either a silicon or germanium lid. In this approach, the die are mounted in a ceramic package, usually with a solder preform attachment. The package and lid are placed in a vacuum chamber and vacuumbaked at elevated temperature to outgas the package and lid prior to sealing the package. Once outgassing is complete, the lid is sealed to the packag