Re: [time-nuts] Etching of quartz crystals

[Bob kb8tq]

Hi

> On Feb 5, 2018, at 10:31 AM, jimlux  wrote:
> 
> On 2/5/18 5:54 AM, Attila Kinali wrote:
>> On Sun, 4 Feb 2018 09:21:54 -0500
>> Bob kb8tq  wrote:
 The images on this page gives a good impression about the current
 skill-level in that area:
 
https://www.azonano.com/article.aspx?ArticleID=2740 
 
>>> 
>>> The gotcha is shown in the pictures. First point is that they are etching 
>>> *very*
>>> small features. A 5 MHz 3rd overtone blank is way thicker than what they are
>>> playing with. The second issue is that even at small scale the walls are 
>>> going
>>> non-parallel.
>> That's exactly the issue here. While SAW resonators benefit quite a lot
>> from the processing skills learned from semiconductor fabrication, these
>> skills do not translate into BAW manufacturing. SAW resonators are built
>> etching or depositing small features ontop of a SiO2 wafer that is supposed
>> to be as flat as possible. On the other hand BAW oscillators are 3D 
>> structures
>> by themselves. They are lens shaped (thus not flat) to keep the oscillation
>> energy trapped in the center of the slap, thus allowing the edges to be used
>> for mounting/contacting, with minimal damping of the oscillation.
>> Yes, the shapes are simple. But not only because that's the only shapes
>> we know how to build, but also because these shapes allow us to calculate
>> how the crystal will oscialate and because the simpler the structure the
>> easier it is to build it with high precision and accuracy.
>> It would be possible to use edging of surface structures into the
>> crystal to form a Bragg reflector (instead of the lense shape).
>> But I have no idea how well it works. Considering that it is easier
>> to build a slap that is flat and then etching structures on it, than
>> to form a 3D structure, I wonder why I have not read about anyone
>> doing exactly that (beside for SAW structures).
> 
> 
> Follow the money - or lack thereof - Folks are happy with the existing 
> technology - If I'm flying a science mission that needs a space qualified 
> Ultra Stable Oscillator - I've already budgeted my several million dollars, 
> claiming that I'll just use what we already know how to build, and I spend no 
> more proposal pages talking about it.  I certainly am not going to say 
> "instead of spending $1M/oscillator for my 2 oscillators, I'm going to spend 
> $5M on an experimental process to change how the resonator is made, and by 
> the way, it might not work"
> 
> Would using ion milling and other modern fabrication techniques lead to an 
> oscillator with *significantly* better performance or *significantly* lower 
> cost?

Consider that a reasonable budget for just the gear to finish a precision 
resonator (not the fab side) is 
in the $3 to $5 million range these days. If you include the fab process, the 
question becomes “how 
far back” you go in that process. Do you start with growing the synthetic 
quartz? If so, the budget just
goot a *lot* bigger. 

People have indeed experimented a lot with alternative fab processes. There are 
alternatives out there.
So far, the precision end of things still *looks* a lot like it used to. If you 
scratch under the surface it’s
vastly different than it was 10 or 20 years ago. It’s nothing at all like it 
was in the 70’s, let alone back 
in the 50’. 

Bob


> 
> For those users for whom this is important, research focuses on looking for 
> another qualitatively different way to get there - That's sort of what the 
> CSAC and the Deep Space Atomic Clock (DSAC) are about - the ion trap clock 
> for DSAC gives you long term performance BETTER than a USO. Although probably 
> not at a lower cost, yet, there is potential for it to be so.
> The CSAC gives you "good accuracy at low power", compared to an OCXO - less 
> than 1/10th the power.
> 
> 
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Re: [time-nuts] Etching of quartz crystals

[jimlux]

On 2/5/18 5:54 AM, Attila Kinali wrote:

On Sun, 4 Feb 2018 09:21:54 -0500
Bob kb8tq  wrote:


The images on this page gives a good impression about the current
skill-level in that area:

https://www.azonano.com/article.aspx?ArticleID=2740 



The gotcha is shown in the pictures. First point is that they are etching *very*
small features. A 5 MHz 3rd overtone blank is way thicker than what they are
playing with. The second issue is that even at small scale the walls are going
non-parallel.


That's exactly the issue here. While SAW resonators benefit quite a lot
from the processing skills learned from semiconductor fabrication, these
skills do not translate into BAW manufacturing. SAW resonators are built
etching or depositing small features ontop of a SiO2 wafer that is supposed
to be as flat as possible. On the other hand BAW oscillators are 3D structures
by themselves. They are lens shaped (thus not flat) to keep the oscillation
energy trapped in the center of the slap, thus allowing the edges to be used
for mounting/contacting, with minimal damping of the oscillation.

Yes, the shapes are simple. But not only because that's the only shapes
we know how to build, but also because these shapes allow us to calculate
how the crystal will oscialate and because the simpler the structure the
easier it is to build it with high precision and accuracy.

It would be possible to use edging of surface structures into the
crystal to form a Bragg reflector (instead of the lense shape).
But I have no idea how well it works. Considering that it is easier
to build a slap that is flat and then etching structures on it, than
to form a 3D structure, I wonder why I have not read about anyone
doing exactly that (beside for SAW structures).



Follow the money - or lack thereof - Folks are happy with the existing 
technology - If I'm flying a science mission that needs a space 
qualified Ultra Stable Oscillator - I've already budgeted my several 
million dollars, claiming that I'll just use what we already know how to 
build, and I spend no more proposal pages talking about it.  I certainly 
am not going to say "instead of spending $1M/oscillator for my 2 
oscillators, I'm going to spend $5M on an experimental process to change 
how the resonator is made, and by the way, it might not work"


Would using ion milling and other modern fabrication techniques lead to 
an oscillator with *significantly* better performance or *significantly* 
lower cost?


For those users for whom this is important, research focuses on looking 
for another qualitatively different way to get there - That's sort of 
what the CSAC and the Deep Space Atomic Clock (DSAC) are about - the ion 
trap clock for DSAC gives you long term performance BETTER than a USO. 
Although probably not at a lower cost, yet, there is potential for it to 
be so.
The CSAC gives you "good accuracy at low power", compared to an OCXO - 
less than 1/10th the power.



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Re: [time-nuts] Etching of quartz crystals (was: Rakon HSO-14)

[Bob kb8tq]

Hi


> On Feb 5, 2018, at 8:54 AM, Attila Kinali  wrote:
> 
> On Sun, 4 Feb 2018 09:21:54 -0500
> Bob kb8tq  wrote:
> 
>>> The images on this page gives a good impression about the current
>>> skill-level in that area:
>>> 
>>> https://www.azonano.com/article.aspx?ArticleID=2740 
>>> 
>> 
>> The gotcha is shown in the pictures. First point is that they are etching 
>> *very*
>> small features. A 5 MHz 3rd overtone blank is way thicker than what they are 
>> playing with. The second issue is that even at small scale the walls are 
>> going 
>> non-parallel.
> 
> That's exactly the issue here. While SAW resonators benefit quite a lot
> from the processing skills learned from semiconductor fabrication, these
> skills do not translate into BAW manufacturing. SAW resonators are built
> etching or depositing small features ontop of a SiO2 wafer that is supposed
> to be as flat as possible. On the other hand BAW oscillators are 3D structures
> by themselves. They are lens shaped (thus not flat) to keep the oscillation
> energy trapped in the center of the slap, thus allowing the edges to be used
> for mounting/contacting, with minimal damping of the oscillation.
> 
> Yes, the shapes are simple. But not only because that's the only shapes
> we know how to build, but also because these shapes allow us to calculate
> how the crystal will oscialate and because the simpler the structure the
> easier it is to build it with high precision and accuracy.
> 
> It would be possible to use edging of surface structures into the
> crystal to form a Bragg reflector (instead of the lense shape).
> But I have no idea how well it works.

The typical quartz resonator is operating in a mode that involves 
more than a surface wave. Much of the effort involves not just that
mode but getting rid of the vast number of similar modes that can 
pop up. As you add structure complexity, you don’t just want to “improve”
the main mode. You also want to be sure you don’t encourage any 
others …..

That all said, there are indeed people out there who *do* understand how
this all works. There aren’t a lot of them, but they are out there. From what
I’ve seen, the supply of “those who know” actually exceeds the industrial 
demand for what they know. Like it or not, precision quartz resonators is
*not* a growth field. 

Bob


> Considering that it is easier
> to build a slap that is flat and then etching structures on it, than
> to form a 3D structure, I wonder why I have not read about anyone
> doing exactly that (beside for SAW structures). 
> 
> 
> 
>   Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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[time-nuts] Etching of quartz crystals (was: Rakon HSO-14)

[Attila Kinali]

On Sun, 4 Feb 2018 09:21:54 -0500
Bob kb8tq  wrote:

> > The images on this page gives a good impression about the current
> > skill-level in that area:
> > 
> > https://www.azonano.com/article.aspx?ArticleID=2740 
> > 
> 
> The gotcha is shown in the pictures. First point is that they are etching 
> *very*
> small features. A 5 MHz 3rd overtone blank is way thicker than what they are 
> playing with. The second issue is that even at small scale the walls are 
> going 
> non-parallel.

That's exactly the issue here. While SAW resonators benefit quite a lot
from the processing skills learned from semiconductor fabrication, these
skills do not translate into BAW manufacturing. SAW resonators are built
etching or depositing small features ontop of a SiO2 wafer that is supposed
to be as flat as possible. On the other hand BAW oscillators are 3D structures
by themselves. They are lens shaped (thus not flat) to keep the oscillation
energy trapped in the center of the slap, thus allowing the edges to be used
for mounting/contacting, with minimal damping of the oscillation.

Yes, the shapes are simple. But not only because that's the only shapes
we know how to build, but also because these shapes allow us to calculate
how the crystal will oscialate and because the simpler the structure the
easier it is to build it with high precision and accuracy.

It would be possible to use edging of surface structures into the
crystal to form a Bragg reflector (instead of the lense shape).
But I have no idea how well it works. Considering that it is easier
to build a slap that is flat and then etching structures on it, than
to form a 3D structure, I wonder why I have not read about anyone
doing exactly that (beside for SAW structures). 



Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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