|
Packaging constitutes one of the most costly steps of MEMS/MOEMS manufacturing. The package protects the MEMS
devices and, in the case of MOEMS, it also provides light access to the device. In many cases, MEMS require a specific
atmosphere for their proper functioning. The atmosphere should be kept invariable during the lifetime of the package in
order to not degrade the performance of the device. Maintaining a constant atmosphere inside the package becomes more
challenging as the cavity volume is decreased to the microliter and nanoliter range. Other packaging requirements are
compatibility with wafer-level microfabrication techniques (cost reduction) and low temperature assembly in cases
where temperature sensitive devices are to be packaged.
In recent years, INO has performed a great amount of work towards the development of uncooled IR microbolometer
detectors using VOx technology. Different pixel designs have been optimized for different applications. The bolometer
pixels require a vacuum atmosphere below 10 mTorr to be maintained during the lifetime of the device in order to
operate at their highest sensitivity. INO's micropackaging technology has been demonstrated to provide base pressures
below 5 mTorr. An equivalent flow rate of 2.5×10-14 Torr.l/sec has been obtained for a device packaged without any
getter. The advantages of INO's micropackaging technology are the possibility of achieving very low base pressures, the
low temperatures required for the assembly (the package device is never exposed to a temperature above 150 °C) and its
compatibility with hybrid wafer-level packaging. The technology has been developed for the micropackaging of INO's
160×120 pixel uncooled microbolometer FPA, but it is compatible with any other kinds of MOEMS-MEMS devices
requiring vacuum hermetic packaging. In order to increase the lifetime of the package, knowledge of the gases
outgassing inside the package is crucial. A hybrid approach has been chosen as it permits packaging only known-good
dies and saving considerable quantities of IR window material. In INO's hybrid wafer-level packaging, dicing is
performed only through one of the wafers, therefore reducing the risk of perturbing the vacuum during the separation of
the different dies.
|
