Re: BAW

On Wed, 22 Jan 2025 10:36:06 +0100, Jeroen Belleman
<jeroen@nospam.please> wrote:

On 1/22/25 09:38, John R Walliker wrote:

On 22/01/2025 04:30, Bill Sloman wrote:

On 22/01/2025 10:52 am, Buzz McCool wrote:

On 1/21/2025 10:56 AM, john larkin wrote:

>
This has got to crush the XO business. It looks like it's a single
chip that's encapsulated like any other IC. XOs are complex and need
hermetic cans.

>
XOs used to use handmounted crystals. There's nothing all that
complicated about them, but low volume manufacture tends to be a bit
knife and fork.
>

Looking through this BAW app note
https://www.ti.com/lit/an/snaa362/snaa362.pdf, I couldn't tell BAW
devices would work at high altitude or in a vacuum. I have to ask
because the "acoustic" in the name makes me want to make sure that
some sort of atmosphere isn't needed.

>
As far as I can see these are surface acoustic wave devices.
Integrated circuits are pretty well encapsulated. This one probably
dumps any heat it generates into the board it is mounted on, which
might run a bit warmer in a vacuum, but that would be the only risk I
can see.
>

 
It does look more like bulk acoustic waves - hence the name!  There
is no cavity inside, so they should be immune to the effects of
helium, unlike the  oscillators that use MEMS resonators where it
appears that helium can diffuse through the silicon to clog up
the vacuum cavity.
Phase noise performance looks excellent as is the temperature
stability.
John
 

>
You can look up the patent:
<https://patents.google.com/patent/US20070285191A1/en>.
>
Apparently the resonator is built up layer by layer, first
the multi-layer Bragg reflector, then the bottom resonator
electrode, the resonator material itself, and finally the
top electrode. The patent does not mention a top reflector,
so such a resonator would need a bit of free space above.
>
The patent text is voluntarily vague about the materials
used for the reflector and resonator layers. They mention
lots of examples, without clearly saying what they really
used. I'd expect that most examples don't work.
>
Jeroen Belleman

The next step might be to have BAWs on uPs or FPGAs or watch circuits
or something, super accurate clocks instead of external XOs or bad RC
oscillators.