Micromachined devices and MEMS have made significant progress during the past two decades with many prototype devices demonstrated for applications including pressure sensors, optical communication systems, and biomedical microsystems. While these applications require different devices and signal processing circuits, they all share the need for reliable, stable, and low-power packaging technologies. Traditional packages that contain cavities sealed in vacuum have utilized expensive ceramic containers that are manufactured in a serial process. In addition, packaging is applied to individual devices, typically at the end of the fabrication process after the devices are diced apart from their host wafer. This process requires individual handling of the final device, thereby increasing the chances of damage and resulting in low performance and higher cost.
Researchers at the University of Michigan have developed an improved method to package MEMS in vacuum on a wafer-level and to provide sealed feedthroughs to the outside world. The method is performed at low temperature, and includes forming a sacrificial spacer on a region of the substrate, and depositing a metal film to a desired thickness over the sacrificial spacer to encapsulate the sacrificial spacer. At least one fluid passageway is formed, allowing for communication of the sacrificial spacer with the ambient. The sacrificial spacer is then removed through the fluid passageway so that the metal film forms a metal diaphragm, which defines a microcavity.
Applications and Advantages
- Packaging of MEMS in vacuum on the wafer level
- Automotive and aerospace applications:-nl-accelerometers, gyroscopes, pressure sensors
- Communications systems: resonators for cell-nl-phones
- Reduced cost: batch process, no bonding of a-nl-second substrate required
- Flexibility: room temperature process, many-nl-feedthroughs can be incorporated