Marco Amiotti

Getters for flat-panel displays

Getters play a crucial role in solution of the main technical issues on the way to commercial exploitation of new flat-panel technologies: packaging, reliability and lifetime. The production steps of flat-panel displays (FPDs) often include a long baking and exhaust process to minimize the impurity content prior to the final sealing, which dramatically increases the manufacturing costs up to a level that might be incompatible with mass production requirements. These problems can be tackled and solved by the introduction of a specific getter device that can permanently remove the undesirable species by the formation of irreversible chemical bonds. In this paper we will focus on long-studied FPD technologies such as vacuum-fluorescent displays, field-emission displays, and plasma display panels, showing how proper getter solutions based on special metal alloys can increase their lifetime and reliability and, in particular cases, also improve the manufacturing process conditions.

New getter configuration at wafer level for assuring long-term stability of MEMS

The evolution from ceramic packages to wafer to wafer hermetic sealing poses tremendous technical challenges to integrate a proper getter inside the MEMs to assure a long term stability and reliability of the devices. The state of the art solution to integrate a getter inside the MEMs of the last generation consists in patterning the getter material with a specific geometry onto the Si cap wafer. The practical implementation of this solution consists in a 4” or 6” Si wafers with grooves or particular incisures, where the getter material is placed in form of a thick film. The typical thickness of these thick films is in the range of few microns, depending on the gas load to be handled during the lifetime of the device. The structure of the thick getter film is highly porous in order to improve sorption performances, but at the same time there are no loose particles thanks to a proprietary manufacturing method. The getter thick film is composed of a Zr special alloy with a proper composition to optimize the sorption performances. The getter thick film can be placed selectively into grooves without affecting the lateral regions, surrounding the grooves where the hermetic sealing is performed.

Chemical treatment of getter films on wafers prior to vacuum packaging

The patterned getter film at wafer level has been proven to be the viable technical solution to integrate a getter film in vacuum packaged MEMS. The different MEMS vacuum bonding technologies such as eutectic, direct fusion and anodic bonding guarantee a suitable combination of time and temperature to properly activate the getter film. However, before any MEMS vacuum bonding process it has been discovered that a caustic chemical treatment of the getter film both cleans the film and enhances its performance without measurable degradation of its structural integrity. For example, caustic chemical treatment with SC1 with NH4OH and SC2 with HCl did not affect the morphology and the sorption capacities of the getter film and significantly increased the sorption capacity. The getter film at wafer level can withstand also treatment with a highly aggressive HNO3 process. Therefore, we demonstrated the full compatibility of the getter film towards both temperature and chemical treatment with regards to the activation and capacity of the getter film.

B-DRY®: Edge sealant for sensitive photovoltaic modules

Moisture permeation inside modules is one of the major issues accounting for the degradation of different components in the photovoltaic technology. B-Dry®i is a new edge sealant able to block the moisture penetration both in damp heat accelerated tests and in real operative conditions. Moreover, mechanical resistance and adhesion must be ensured beyond the regulation requirement. B-Dry® has been developed to respect hard aging tests such as Miami UV, damp heat and thermal cycling also for the structural property.

Patterned gas absorbing films for assuring long-term reliability and improving performances of mems and omems

Microsensor packaging is one of the most important and challenging technology areas. Many microelectro-mechanical systems (MEMS) and optical MEMS (OMEMS) need to be protected from outside environment stresses: therefore the package must provide an interior environment compatible with the device operation, performances, reliability and lifetime. In addition some MEMS need a specific gas or pressure environment within the package to operate as specified: in particular, OMEMS should be protected against moisture related failures

Development of thin film getters for assuring high reliability and long lifetime to crystal oscillators

The shrinkage of hermetic packages for crystal oscillators poses tremendous challenges to keep constant the pressure during the lifetime of the device because of the considerable effect of surface outgassing and gas permeation. Getters have been used over tens of years in the vacuum tube industry to keep constant vacuum inside sealed devices. To provide a suitable getter solution to miniaturized hermetic packages, a few micron thick getter film has been developed and placed on the lid of the hermetic packages. This technical solution, the getter thin film on the lid, assures a long lifetime and stability to hermetically packaged oscillating structures.

Outgassing and Gettering

Outgassing is an unavoidable issue and although the cleaning process and long baking are carried out, the effect can be limited only by using the getter technology. This technology absorbs the residual gases trapped in the device during the process and maintains the pressure at a very low level for the required lifetime, limiting the gas flux. It has been described that there are gases remaining inside MEMS devices that need a vacuum or other stable pressure to operate properly. The MEMS packaging technology moved from hermetic vacuum discrete packages to vacuum wafer-level packages. Conventional packaging of microelectronic and optoelectronic devices is usually stable and not affected by the external environment except for a few specific cases. Vacuum wafer-level packaging is a very effective technique to produce low-cost, hermetically sealed packages for micromachined sensors and actuators. The main contamination source is the leakage and outgassing phenomena. The leakage is mainly caused by defects in the bonding frame and can be solved by a suitable improvement of the technology or accepting a limited yield in the MEMS production. In the case of outgassing a technically viable solution to assure a long lifetime and high reliability to MEMS device is the integration of a getter film. This has also been explained in detail.

Chapter Forty – Outgassing and Gettering

Publisher Summary Outgassing is an unavoidable issue and although the cleaning process and long baking are carried out, the effect can be limited only by using the getter technology. This technology absorbs the residual gases trapped into the device during the process and maintains the pressure at very low level for the required lifetime, limiting the gas flux. It has been clearly described that there are gasses remaining inside MEMS devices that need a vacuum or other stable pressure to operate properly. The MEMS packaging technology moved from hermetic vacuum discrete packages to vacuum wafer-level pack- ages. Conventional packaging of microelectronic and optoelectronic devices is usually stable and not affected by the external environment except for a few specific cases. Hydrogen Vacuum wafer-level packaging is a very effective technique to produce low-cost, hermetically sealed packages for micromachined sensors and actuators. The MEMS devices requiring a vacuum to operate properly are shown in pressure level is a key parameter for the quality of the MEMS devices. The main contamination source is the leakage in the bonding and outgassing phenomena. The leakage is mainly caused by defects in the bonding and can be solved by a suitable improvement of the technology or accepting a limited yield in the MEMS production. A technically viable solution to assure a long lifetime and high reliability to MEMS device is the possibility to integrate a getter film. This has also been explained in detail.

Novel edge sealing getter tape: ultra long breakthrough time and high mechanical properties at high temperature

Moisture permeation is widely recognized as one of the most important causes of degradation in time of the performances of photovoltaic modules, especially thin film ones. B-Dry®i is a newly developed edge sealant tape which is able to block moisture penetration into PV modules for thousands of hours in Damp Heat Test (DHT) conditions, thanks to the presence of a getter material. Visco-elastic behavior, even at relatively high temperatures, makes B-Dry® especially suitable to guarantee mechanical stability of PV modules operating in hot and humid climates.