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Long-term Stability of VAcuum-encapsulated MEMS Devices using Eutectic Wafer BONDing

Objective

The proposed project aims at the development of improved wafer-to-wafer bonding techniques which allow long-term vacuum encapsulation especially for those micro-electro-mechanical systems (MEMS) requiring high-vacuum cavities to ensure a good performance and to improve the life expectancy and reliability. The vacuum wafer bonding will be optimised using eutecting bonding in combination with getter materials inside the device cavity. Furthermore, a hermetic feed through technology will be developed enabling vertical electrical visa through the cap wafer.

In the technology integration and validation phase the new technologies for high-vacuum encapsulation of MEMS devices will be applied to industrial demonstrators:
- RF-switch and HF resonator for telecommunication and consumer applications;
- Pressure sensor for high-reel avionics and industrial applications.

Objectives:
As many MEMS devices require a vacuum or controlled atmosphere operation, the main objective of the proposed project is to provide a high-vacuum encapsulation technology for MEMS devices working on wafer-level. The detailed objectives are:
- develop a vacuum wafer bonding technology using eutectic bonding in combination with getter materials inside the cavities enabling a stable vacuum (10-4 mbar, 10 years)
- develop a getter technology covering materials and processes which is compatible to Si-based MEMS technology;
- provide industrial processes and equipment for the vacuum wafer bonding in combination with getters;
- develop a vertical feed through technology enabling low stress, high density interconnect performance and excellent RF properties;
- develop in-situ measurement techniques for the internal pressure for the high-vacuum and the low-vacuum range, as well as for in-situ moisture detection;
- reliable demonstrators employing the new high-vacuum encapsulation technology.

Work description:
The project starts with a concept phase in which the technology specifications as well as the specifications of the demonstrators are compiled and agreed.
Then passive test structures are designed and realized which are needed for the subsequent process developments of the technologies for wafer-level, high-vacuum encapsulation of MEMS: eutectic wafer bonding; getter deposition, structuring and activation; electrical feed throughs realized as vertical vias through the cap wafer.
In the next step the characterization of the single technologies and of the test assemblies as well as the reliability analysis is performed.
Therefore, in-situ measurement techniques for measuring the internal pressure and moisture content in the device cavity are evaluated, the corresponding test structures are designed and realized. The vacuum-bonded test structures are used for in-situ measurements to characterize the test assemblies and analyse the long term stability of the internal pressure, humidity and other reliability relevant parameters related to the cavity atmosphere.
In the next workpackage (technology integration and validation) the technologies for high-vacuum encapsulation of MEMS devices are applied to the previously defined and specified demonstrators. Demonstrator assemblies are realized and tested according to the systems specifications.
Finally, dissemination and exploitation of the results from the project are performed.

Milestones:
The final result: the demonstrators realized using the new vacuum encapsulation technology and tested against the specifications. Important milestones on that way are:
- eutectic wafer bonding is hermetically tight according to MIL-STD-883D
- selection of getter materials and getter patterning technique;
- vertical electrical feed through processed on wafer-level are hermetically tight and work electrically and mechanically (stress).

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

FRAUNHOFER GESELLSCHAFT ZUR FOERDERUNG DER ANGEWANDTEN FORSCHUNG E.V.
Address
Hansastrasse 27C
80686 Muenchen
Germany

Participants (5)

E V GROUP E. THALLNER GMBH
Austria
Address
Gewerbegebiet
4780 St. Florian
SAES GETTERS S.P.A.
Italy
Address
Viale Italia 77
20151 Lainate (Mi)
STMICROELECTRONICS S.R.L.
Italy
Address
Via Olivetti 2
20041 Agrate Brianza
THALES AVIONICS SA
France
Address
1 Avenue Carnot
91883 Massy
UNIVERSITA DEGLI STUDI DI PAVIA
Italy
Address
Strada Nuova 65
27100 Pavia