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New for July 2019. Content was moved from our microwave switches technology page, and then updated...
Chalgogenide is emerging as an excellent switch technology, for the following reasons
- Switch figure of merit beyond any other technology, including MEMS. The off-state capacitance is basically the capacitance in the microstrip gap that is left when the conductivity of the of the chalcogenide disappears.
- Ability to latch. Once you switch it, it consumes zero power to stay in either state. Point your phased array, then forget about it.
- Ability to combine with CMOS. Built-in drivers, serial interface, LNAs can all be right on-board.
- Ability to process on large wafers. If your switch technology is on four-inch wafers, you're never going to realise the PESA promise of low-cost.
The downsides that must be considered are:
- Switching speed is microseconds. This is not a big deal for many applications, but radar phased array people always ask about it...But, if you use chalcogenide switches in a PESA, you won't need to switch states between transmit and receive, as the array stays focussed. So get over it.
- power handling is on the order of 500 mW, with failure (or self switching) at 1W
- It is still not a released process anywhere, but it has established reliabilty.
A recent GeTe switch paper is:
https://ieeexplore.ieee.org/abstract/document/8059098
Pavel Borodulin, Nabil El-Hinnawy, Carlos R Padilla, Andy Ezis, Matthew R King, Daniel R Johnson, Doyle T Nichols, Robert M Young, "Recent advances in fabrication and characterization of GeTe-based phase-change RF switches and MMICs" 2017 IEEE MTT-S International Microwave Symposium (IMS), pp.285-288, June 2017.
Below is our original content on the topic, dating back to 2013:
At CSICS 2013 the following paper was presented:
"A 7.3 GHz cutoff Frequency, In-line, Chalcogenide Phase-Change RF switch using an Independent Resistive Heater for Activation", by Nabil El-Hinnawy et al, Northrop Grumman Electronic Systems.
Chalcogenide switches use phase-change technology which was originally developed for non-volatile memory for computers. The chalcogenide material has two states: in amorphous state, it has very high resistivity, in conducting state it acts like a metal. The two states are activated thermally. If the heat pulse is quick (amorphizing heat profile), the high loss state is provided, if it is longer and lower temperature (crystallizing heat profile), the metallic state occurs. The heat pulse for either state can be shorter than one nanosecond, making chalcogenide switches faster than MEMS switches. Chalcogenide switches are not technically "solid-state" but have no moving parts, which are the cause of the MEMS Tree of Woe.
The NG switch was partially funded by the Darpa RF-FPGA program. It is amazing how far the technology has come in just one year, and we expect it will continue to improve and set some new benchmarks for low-loss and high frequency response. If you can't think of a dozen ways to use this new technology, you aren't trying very hard. How about a new stab at passive ESAs? Tunable filters? Self-healing SSPAs? Let's move out on this!
The Unknown Editor tweeted that this was the best conference paper, even though he was co-author on a paper in the same session...
More to come.... just remember where you heard about this first!