The packaging of implanted devices is crucial if high reliability is to be achieved with an intended operating lifetime of decades. The traditional approach with a welded metal enclosure is too large for many of the new devices that are being developed. Wafer bonding, which allows for simultaneously packaging of all the small devices on a wafer, is becoming a cost effective key technology for packaging of microelectromechanical systems (MEMS) and chip scale devices. A number of bond processes exist that have been utilized for packaging applications. However, these packaging methods are usually application specific. This thesis explores a method, which has the potential to become a standard MEMS/CMOS packaging technology. A gold-silicon bond process was developed to bond cap wafers to device wafers. The process, initially applied on experimental wafers, was designed in such a way that it can be applied, without modification, on CMOS processed wafers. The key steps in this technique are post-processing of device wafer, to define gold seal rings around the device area, fabrication of the cap wafer with corresponding silicon seal rings, and finally bonding these two wafers together according to the developed bond process. Various characterization techniques were employed to quantify and qualify the bonds, including reliability and accelerated aging. This thesis discusses the fabrication process for the developed technique and the challenges associated with all the steps of wafer fabrication and bonding. The result of this study indicated that the developed process can be employed for micropackaging of chip scale devices including MEMS and biomedical implants. An important feature is the ability to incorporate a humidity sensor as part of the active device. Thus, a thin film humidity sensor was also designed, fabricated and characterized as part of this research work. The sensor allows the internal humidity to be measured after the sealed device is implanted thus avoiding the danger of using the device if moisture gets in. Careful attention was paid to the effect of processing steps, in particular etching process, on the sensor performance. A set of experiments was designed to investigate the modifications in physical and chemical characteristics of the moisture sensing film when subjected to wet and dry etching.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:625900 |
| Date | January 2012 |
| Creators | Saeidi, N. |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1357936/ |
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