Phase change switches

New for July 2019.  We created this page to try to tie together some new RF switch technologies that leverage material changes to change the conductance in an RF path.  Perhaps there is a better name that encompasses all of these switch techniques, let us know your suggestions!

None of these switch technologies have passed full qualification, and they are not ready for production, but each offers hope for a better technology compared to MEMS. As in all engineering, there are many tradeoffs to consider.

Click here to learn about chalcogenide switches

Chalcogenides are a type of material that can hold two different states at room temperture (amorphous and cystalline).  According to Wikipedia, the term "chalcogenide" is commonly reserved for sulfides, selenides, tellurides, and polonides.  In the microwave industry, the one chalcogenide switch to keep an eye on is germanium telluride as a lot of research money has been spent here. The two states of the switch are provided by carefully controlling a time-versus-temperature thermal profile.  Heating up to a specific temperature and "quenching" results in the amorphous, insulating state.  Heating up to a lower specific temperature for a longer time (annealing) and cooling results in the crystalline, conducting state.  Fortunately, the heat the energy required is very small for an individual device, and the time to accomplish either state is on the order of microseconds.

Click here to learn about metal-insulator-transition switches

MIT switches have two states which are controlled by temperature.  Rather than melting, an MIT switch remains solid but changes from a conductor to an insulator a specific temperature point. In the case of vanadium dixode, this occurs at 68C. If you instantly think "taht would make a great receiver protector", you're too late, it's already patented...

Click here to learn about liquid metal switches

Liquid metal switches might not belong in the class of "phase change" but we put them in here for now.  The original liquic metal switch used mercury, which poses an environmental nightmare. Modern liquid-metal switches use gallium, which is said to be nontoxic, but it is not exactly an accepted food additive or vitamin.




Author : Unknown Editor