Passive Components

Microfabrication processes allow geometries in the micron regime, as well as tolerances within a few hundreds of nanometers. This precision is very high compared to conventional mechanical manufacturing processes, and can be used for the benefit of macroscopic structures, too.

Hermetic Packaging

Hermetic packaging is used for the encapsulation of MEMS structures in order to protect them from environmental effects. Aging effects on sensors and actuators are thereby reduced and slowed down. The housing cavity is typically filled with an inert gas (e.g. Nitrogen). Using appropriate measurement techniques, we can determine the leak rate for a given gas, and extrapolate the theoretical lifetime of the system.

Setup

The hermetically packaged cavity sits between a silicon substrate and a glass substrate. Through dry etching (DRIE), cavities and vias are built into the silicon substrate. The cavity is sealed using a thermo-compressive low temperature bonding process. To this end, two microstructured gold thin films are pressed against each other at a temperature of 300 °C, and thus bonded. In the same process, vertical electrical feed-throughs are realized. These feed-throughs are the electrical contacts between the meander structures inside the cavity, and the devices on the outside.

Typical Values

  • Contact resistance of the vias: 0.4 ± 0.05 Ω
  • Standard leak rate: 4.3x10-10atm cm3/s
  • Cavity dimensions: 10 x 10 mm
  • Cavity depth: 200 µm
  • Via radius: 500 µm
  • Aspect ratio of the vias: 1
Hermetic package, consisting of a DRIE-etched silicon substrate and a glass substrate. The two substrates are joined by a gold-gold thermo-compressive bonding process. The image is the view over the silicon substrate.
SEM-image of the vertical electrical feed-throughs (Vias)
Backside of the package, with view of the glass substrate. The meander is contacted through the Vias.

Themoelectric Generators

Thermoelectric generators (TEGs) convert heat into electrical energy. A good example of their application is as power sources for sensors in difficult-to-reach locations.

 

Setup

A TEG consist of many thermoelements in series. Electrical conductor pairs that show as high a thermoelectric effect as possible are needed for this purpose. Various metals and semiconductors come into consideration as materials to build the thermoelectric matrices. Materials that are easy to structure and that have low thermal conductivity are preferred for TEGs. As a result of previous studies at the Institute MNT, we often use the materials SU8, FR4 and polyimide.

At the Instiute MNT, TEGs are investigated under student thesis work and development projects

 

Typical Values

  • Substrate thickness: 0.2 – 0.51 mm
  • Substrate geometry: up to 4“ square
  • Number of thermoelements: up to 1300
  • Tmax: 200 °C
  • Pmax: 1000 µW
FR4-TEG with packaging
Detailed image of the SU8-TEG