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From: john larkin <JL@gct.com>
Newsgroups: sci.electronics.design
Subject: Re: BAW
Date: Wed, 22 Jan 2025 08:27:40 -0800
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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.