Silicon-on-sapphire RF switch from Peregrine

Peregrine Semiconductor has just released the PE42440 SP4T (single-pole four-throw) RF switch. They intend these parts for wireless base stations and general RF use. I am really taken by silicon-on-sapphire technology. Firstly, it makes for devices that are radiation hard. Because there is no silicon substrate, there is no place for cosmic and gamma rays to make free holes and electrons as the rays plow through the part. That keeps the devices working to specification in satellites and such. Silicon-on-sapphire (SOS) also has better thermal performance than glass (silicon dioxide) dielectric isolation, Crystal silicon is 10 times better than glass and SOS is 3 times better than glass. I touch on this in my recent article about the benefits of dis-integration, putting your system on multiple chips. Finally the wafers of SOS are just cool, they are clear so you can see through them where there is no metallization.

So SOS gives you all the benefits of dielectric isolation, plus better thermal performance. And you also get a nice well-understood CMOS process to lay down devices on the substrate. RF Micro Devices claims to equal or surpass the performance of SOS switches with their silicon switches. There are reports circulating that say the SOS is a disruptive technology so be on the lookout for it.

This SOS wafer from Sapphicon is clear. Check out their technology page with SOS videos and white papers.

I told analog guru and EDN contributing editor Jim Williams about Peregrine and he was most impressed that they manage to keep a controlled low 50 ohm impedance on their parts. Jim comments that it is hard to do that repeatably and accurately. That is coherent with what the Peregrine people tell me, that a lot of companies will talk about making SOS as long as a decade ago, but when you push them, the companies will admit they made maybe one wafer for military project. Peregrine is in high-volume production of their SOS process. What impresses me is that they make parts for cell-phones, the cheapest most cost brutal market, as well as satellites, a market where cost is not that important but specs are everything. I think these RF switches are aiming for the middle, the industrial scientific and medial markets as well as the booming wireless base station market that got such a boost from the iPhone and other smart phones. We need lots of new base stations to carry all the data you folks are using. The cool thing about the Peregrine parts is that they maintain the linearity of the signal, something critical in the new cell phone modulations since the information is carried in the RF envelope and not the zero crossings.

Regarding that RF switch, Peregrine says that it has:

• An IIP3 of +67 dBm and P1dB of 41.5 dBm (across the range);
• Insertion Loss of 0.45 dB; 
• Isolation of 34 dB (at 1 GHz);
• Broadband RF performance from 50 MHz up to 3 GHz

You can check out my article if you want to learn about analog switches in general, but I did not put too much emphasis on RF analog switchers. That may be a good topic for the next article.