Planar inductors with cores on ICs

[Joerg]

Folks,

In order to achieve much higher inductance than the usual few
nanohenries on RF chips I am looking at MEMS structures, deposited core
materials and such. It's been done at labs quite a while ago, for example:

http://www.mems.gatech.edu/msma/pub...s on Silicon Wafers for MEMS Applications.pdf

I am especially curious about the spiral inductor with core in figure 1.
If you need very little in current handling and can exclude any DC
current it should be possible to achieve a higher inductance in a given
space than here. We'd have maybe 1/4th to 1/3rd of the real estate they
had but tens of ohms in DC resistance would be ok. If needed one could
also consider more metal layers. We'd probably have to run it at
13.56MHz. Also at a much lower frequency but there the inductance could
collapse or be whatever it wants to be.

Did anybody ever see this in real life? Experiences? Foundry?

 

[Joerg]

Intel is now building synchronous buck switchers on-chip, and they use
some sort of magnetics. There are papers around on that. They use
massive polyphase switching to keep the ripple voltage down.

That is done since a while. For example, Enpirion specializes in
converter chips with integrated magnetics:

http://www.enpirion.com/products-ep5357xui.htm

However, there are often inductors in the <1uH range and for high power.
I need the opposite, lots of inductance, low power, must work at 13.56MHz.

 

[RobertMacy]

Folks,

In order to achieve much higher inductance than the usual few
nanohenries on RF chips I am looking at MEMS structures, deposited core
materials and such. It's been done at labs quite a while ago, for
example:

http://www.mems.gatech.edu/msma/pub...s on Silicon Wafers for MEMS Applications.pdf

I am especially curious about the spiral inductor with core in figure 1.
If you need very little in current handling and can exclude any DC
current it should be possible to achieve a higher inductance in a given
space than here. We'd have maybe 1/4th to 1/3rd of the real estate they
had but tens of ohms in DC resistance would be ok. If needed one could
also consider more metal layers. We'd probably have to run it at
13.56MHz. Also at a much lower frequency but there the inductance could
collapse or be whatever it wants to be.

Did anybody ever see this in real life? Experiences? Foundry?

Haven't viewed the document. BUT! Years ago, my partner and I approached
Jim at Linear in order to encorporate MEMs inductors 'under' the SMPS
chips, thereby all the customer need do is to add input cap and output cap
and DONE! So just like a 3 terminal regulator the new family of chips
would appear to the user as the same, but with SMPS chips [and built-in
inductors] the user would have inherently higher efficiency.

My partner had worked out the nasty chemicals to do the high volume
production of the inductor, I provided the electronic expertise and
'patterns'. From memory, we were up into the milliHenries within the
footprint of an SMPS chip and standard package. And with high currents
still above 100uH's

You have to realize the basic material had relative permeability about 1
million and practically zero coercivity, so still had high permeability at
200MHz, [again from memory, over 1000?] pretty incredible when you compare
that performance to the fact that the fe molecule's moment of inertia
ceases permeability around 1-2GHz.

Again, from memory, the permeability of his material at 10-20MHz was
easily in the range of 10,000-40,000.

Now, [again from memory] ANY deposited material was PURE crap compared.
Deposited material had terrible perm and even worse coercivity, which ate
you alive per cycle. Historically, every deposited inductor structure I've
seen was...well, a waste of materials.

He [my partner] had used deposited materials ONLY for filling in a gap,
but NEVER as the main core material, and therein lay his success at the
concept.

Interesting you mention how inductance can collapse at lower frequency. I
once designed a structure that had almost NO inductance at DC, yet
skyrocketed as the frequency went up. Now you're going to get me into
discussing 'startup' problems.

The copper wires were 'deposited and in the original application we were
running current densities through the 'wires' that were incredible.
Comparable to 100A routinely going through a 36Awg wire, that's a decent
comparison. Only when we went to densities on the order of 200A through
36Awg wire did we actually melt our wires. ...our wires were small, on
the order of 25 microns square, but robust.

Also, from memory, I designed RFI/EMI filters for the RJ-45 telco
connectors, built-in common mode chokes something like 80 mil square that
had over 2mH inductance.

If you want, contact me offline, we can go into more detail. And I promise
to quit trying to do this from memory and go get our actual numbers,
models, etc.

Do you need the recipe? I lost contact over the ages here, he is/was older
than me, but his son may know.

 

[RobertMacy]

..snip...
However, there are often inductors in the <1uH range and for high power.
I need the opposite, lots of inductance, low power, must work at
13.56MHz.

Uh,...magnetics are LOW impedance.

You want capacitance, now THAT's high impedance.

 

[Joerg]

Uh,...magnetics are LOW impedance.

You want capacitance, now THAT's high impedance.

?

The inductors on power converter chips are of low inductance because
they must carry large currents. We don't need to, I need as much
inductance as we can reasonably get. So for us the design rules for the
metal layers will probably be the limiting factors.

 

[Joerg]

Folks,

In order to achieve much higher inductance than the usual few
nanohenries on RF chips I am looking at MEMS structures, deposited core
materials and such. It's been done at labs quite a while ago, for
example:

http://www.mems.gatech.edu/msma/pub...s on Silicon Wafers for MEMS Applications.pdf


I am especially curious about the spiral inductor with core in figure 1.
If you need very little in current handling and can exclude any DC
current it should be possible to achieve a higher inductance in a given
space than here. We'd have maybe 1/4th to 1/3rd of the real estate they
had but tens of ohms in DC resistance would be ok. If needed one could
also consider more metal layers. We'd probably have to run it at
13.56MHz. Also at a much lower frequency but there the inductance could
collapse or be whatever it wants to be.

Did anybody ever see this in real life? Experiences? Foundry?

Haven't viewed the document. BUT! Years ago, my partner and I approached
Jim at Linear in order to encorporate MEMs inductors 'under' the SMPS
chips, thereby all the customer need do is to add input cap and output
cap and DONE! So just like a 3 terminal regulator the new family of
chips would appear to the user as the same, but with SMPS chips [and
built-in inductors] the user would have inherently higher efficiency.

We have no space under the chip.

My partner had worked out the nasty chemicals to do the high volume
production of the inductor, I provided the electronic expertise and
'patterns'. From memory, we were up into the milliHenries within the
footprint of an SMPS chip and standard package. And with high currents
still above 100uH's

You have to realize the basic material had relative permeability about 1
million and practically zero coercivity, so still had high permeability
at 200MHz, [again from memory, over 1000?] pretty incredible when you
compare that performance to the fact that the fe molecule's moment of
inertia ceases permeability around 1-2GHz.

Again, from memory, the permeability of his material at 10-20MHz was
easily in the range of 10,000-40,000.

What kind of miracle material was that?

Now, [again from memory] ANY deposited material was PURE crap compared.
Deposited material had terrible perm and even worse coercivity, which
ate you alive per cycle. Historically, every deposited inductor
structure I've seen was...well, a waste of materials.

Can't say that. I and another engineer in this company tried, by
crushing a ferrite core, mixing it with epoxy, and then depositing it.
Not ideal because we used whatever "runny" epoxy happended to be around
but it worked. We can possibly get the real powder but MEMS fabrication
is likely the better option here.

He [my partner] had used deposited materials ONLY for filling in a gap,
but NEVER as the main core material, and therein lay his success at the
concept.

Interesting you mention how inductance can collapse at lower frequency.
I once designed a structure that had almost NO inductance at DC, yet
skyrocketed as the frequency went up. Now you're going to get me into
discussing 'startup' problems.

Ideally it should not collapse because it makes my electronics more
complicated. But we could handle it.

The copper wires were 'deposited and in the original application we were
running current densities through the 'wires' that were incredible.
Comparable to 100A routinely going through a 36Awg wire, that's a decent
comparison. Only when we went to densities on the order of 200A through
36Awg wire did we actually melt our wires. ...our wires were small, on
the order of 25 microns square, but robust.

Also, from memory, I designed RFI/EMI filters for the RJ-45 telco
connectors, built-in common mode chokes something like 80 mil square
that had over 2mH inductance.

If you want, contact me offline, we can go into more detail. And I
promise to quit trying to do this from memory and go get our actual
numbers, models, etc.

Do you need the recipe? I lost contact over the ages here, he is/was
older than me, but his son may know.

I think we are talking about quite different things. My app is not
power, it's signal processing, and a whole lot smaller. For example, the
real estate I have to work with is realistically 0.007" wide and not a
whole lot longer than 0.020", which has to also include the center leg
for the core. The total height can also not be more than roughly 0.007".

We are not 100% sure that we need all this. But there is a realistic
chance and if we do then I want to, as the scouts say, be prepared. At
least have a concept along the lines of "Here is a possible solution and
people have actually done it". That's why I was asking whetehr anyone
has seen something similar to what's shown in figure 1 of the article.

 

[RobertMacy]

Folks,

In order to achieve much higher inductance than the usual few
nanohenries on RF chips I am looking at MEMS structures, deposited core
materials and such. It's been done at labs quite a while ago, for
example:

http://www.mems.gatech.edu/msma/pub...s on Silicon Wafers for MEMS Applications.pdf


I am especially curious about the spiral inductor with core in figure
1.
If you need very little in current handling and can exclude any DC
current it should be possible to achieve a higher inductance in a given
space than here. We'd have maybe 1/4th to 1/3rd of the real estate they
had but tens of ohms in DC resistance would be ok. If needed one could
also consider more metal layers. We'd probably have to run it at
13.56MHz. Also at a much lower frequency but there the inductance could
collapse or be whatever it wants to be.

Did anybody ever see this in real life? Experiences? Foundry?

Haven't viewed the document. BUT! Years ago, my partner and I approached
Jim at Linear in order to encorporate MEMs inductors 'under' the SMPS
chips, thereby all the customer need do is to add input cap and output
cap and DONE! So just like a 3 terminal regulator the new family of
chips would appear to the user as the same, but with SMPS chips [and
built-in inductors] the user would have inherently higher efficiency.

We have no space under the chip.

My partner had worked out the nasty chemicals to do the high volume
production of the inductor, I provided the electronic expertise and
'patterns'. From memory, we were up into the milliHenries within the
footprint of an SMPS chip and standard package. And with high currents
still above 100uH's

You have to realize the basic material had relative permeability about 1
million and practically zero coercivity, so still had high permeability
at 200MHz, [again from memory, over 1000?] pretty incredible when you
compare that performance to the fact that the fe molecule's moment of
inertia ceases permeability around 1-2GHz.

Again, from memory, the permeability of his material at 10-20MHz was
easily in the range of 10,000-40,000.

What kind of miracle material was that?

Now, [again from memory] ANY deposited material was PURE crap compared.
Deposited material had terrible perm and even worse coercivity, which
ate you alive per cycle. Historically, every deposited inductor
structure I've seen was...well, a waste of materials.

Can't say that. I and another engineer in this company tried, by
crushing a ferrite core, mixing it with epoxy, and then depositing it.
Not ideal because we used whatever "runny" epoxy happended to be around
but it worked. We can possibly get the real powder but MEMS fabrication
is likely the better option here.

He [my partner] had used deposited materials ONLY for filling in a gap,
but NEVER as the main core material, and therein lay his success at the
concept.

Interesting you mention how inductance can collapse at lower frequency.
I once designed a structure that had almost NO inductance at DC, yet
skyrocketed as the frequency went up. Now you're going to get me into
discussing 'startup' problems.

Ideally it should not collapse because it makes my electronics more
complicated. But we could handle it.

The copper wires were 'deposited and in the original application we were
running current densities through the 'wires' that were incredible.
Comparable to 100A routinely going through a 36Awg wire, that's a decent
comparison. Only when we went to densities on the order of 200A through
36Awg wire did we actually melt our wires. ...our wires were small, on
the order of 25 microns square, but robust.

Also, from memory, I designed RFI/EMI filters for the RJ-45 telco
connectors, built-in common mode chokes something like 80 mil square
that had over 2mH inductance.

If you want, contact me offline, we can go into more detail. And I
promise to quit trying to do this from memory and go get our actual
numbers, models, etc.

Do you need the recipe? I lost contact over the ages here, he is/was
older than me, but his son may know.

I think we are talking about quite different things. My app is not
power, it's signal processing, and a whole lot smaller. For example, the
real estate I have to work with is realistically 0.007" wide and not a
whole lot longer than 0.020", which has to also include the center leg
for the core. The total height can also not be more than roughly 0.007".

We are not 100% sure that we need all this. But there is a realistic
chance and if we do then I want to, as the scouts say, be prepared. At
least have a concept along the lines of "Here is a possible solution and
people have actually done it". That's why I was asking whetehr anyone
has seen something similar to what's shown in figure 1 of the article.

You should talk to Hasegawa, used to be at Metglas, bought by, bought by,
bought by... He invented the manufacturing technique to make metglas,
amorphic ferromagnetics. I've MEASURED relative permeability at above
1,000,000 on these materials. The stuff's coercivity is nil! Acts like a
magnetic dead short.

Sadly, I just did a search for my work. Apparently it's on several of the
8 HD's that all crashed within a two year period. Yes, including the HDs
that were the BACKUPs for the other HDs !! What's the chance of that? I
have hardcopy somewhere, too, but...

The reason the inductor was placed UNDER the chip was that the inductor
was 40-50 microns thick with bonding pads on top and being metal had
excellent heat transfer characteristics. There is a lot of room in an IC
package. I'm trying to remember the package that was used, but ??

Ok, brush away the cobwebs here: the 'inductor' pattern width was
adjustable in the ranges of 5-10u inuslation, 15-25u copper, 5-10u
insulation, PLUS MATERIAL, so repeat width on the order of 60-100
microns?, that gives what? 3-4 mils? So you can run two strips, down and
back. total length two x 20 mils, or approx 1mm length. You have more
height available than 50 microns so stack several. If you're doing a
common mode choke the pattern becomes: Material, 5-10u, 25u, 5-10u, 25u,
5-10, Material. not very wide. [nothing sacred about the 25u width of
copper, if you can stand the series resistance, make it 10u.] I also
designed this thing to be able to use 'scrap' material from the vendor.
This gave the vender a place to sell quality problems, and gave us a cheap
source, almost raw foundry pricing at weight. For example, manufacturing
would make several years supply for us in around 20 seconds. something
like that. um, 600 fps about 4 inches wide and in 20 seconds you have a
LOT of material. yea, a lot of material.

Depositing permalloy over the top of the 'open' structure was like adding
the I core and GREATLY increases inductance per length, BUT no DC, please.
Or, ONLY use as a common mode choke/transformer.

Tap into the expertise of the HD head designers. They make some cheap,
small magnetics using deposited materials, too. They're might be a bit
closed mouth about what they're capable of.

 

[Joerg]

[...]

I think we are talking about quite different things. My app is not
power, it's signal processing, and a whole lot smaller. For example, the
real estate I have to work with is realistically 0.007" wide and not a
whole lot longer than 0.020", which has to also include the center leg
for the core. The total height can also not be more than roughly 0.007".

We are not 100% sure that we need all this. But there is a realistic
chance and if we do then I want to, as the scouts say, be prepared. At
least have a concept along the lines of "Here is a possible solution and
people have actually done it". That's why I was asking whetehr anyone
has seen something similar to what's shown in figure 1 of the article.

You should talk to Hasegawa, used to be at Metglas, bought by, bought
by, bought by... He invented the manufacturing technique to make
metglas, amorphic ferromagnetics. I've MEASURED relative permeability at
above 1,000,000 on these materials. The stuff's coercivity is nil! Acts
like a magnetic dead short.

A million? Has that been published somewhere?

Sadly, I just did a search for my work. Apparently it's on several of
the 8 HD's that all crashed within a two year period. Yes, including the
HDs that were the BACKUPs for the other HDs !! What's the chance of
that? I have hardcopy somewhere, too, but...

I always back up on DVDs and on flash drives. So far that has never
failed me. Hard drives are a gamble, stuff can age in there.

The reason the inductor was placed UNDER the chip was that the inductor
was 40-50 microns thick with bonding pads on top and being metal had
excellent heat transfer characteristics. There is a lot of room in an IC
package. I'm trying to remember the package that was used, but ??

Ok, brush away the cobwebs here: the 'inductor' pattern width was
adjustable in the ranges of 5-10u inuslation, 15-25u copper, 5-10u
insulation, PLUS MATERIAL, so repeat width on the order of 60-100
microns?, that gives what? 3-4 mils? So you can run two strips, down and
back. total length two x 20 mils, or approx 1mm length. You have more
height available than 50 microns so stack several. If you're doing a
common mode choke the pattern becomes: Material, 5-10u, 25u, 5-10u, 25u,
5-10, Material. not very wide. [nothing sacred about the 25u width of
copper, if you can stand the series resistance, make it 10u.] I also
designed this thing to be able to use 'scrap' material from the vendor.
This gave the vender a place to sell quality problems, and gave us a
cheap source, almost raw foundry pricing at weight. For example,
manufacturing would make several years supply for us in around 20
seconds. something like that. um, 600 fps about 4 inches wide and in 20
seconds you have a LOT of material. yea, a lot of material.

Depositing permalloy over the top of the 'open' structure was like
adding the I core and GREATLY increases inductance per length, BUT no
DC, please. Or, ONLY use as a common mode choke/transformer.

There will not be any DC. There will be a low frequency on it but we can
measure during the zero crossings.

Tap into the expertise of the HD head designers. They make some cheap,
small magnetics using deposited materials, too. They're might be a bit
closed mouth about what they're capable of.

I just wanted to test the waters for now. It'll still be a few months
out. If we end up needing it, and there is a chance that we do, then
I'll have to sit down with our semiconductor guy and possibly in a
conference with some ferrite guys. The material isn't so critical but we
need one that can either be "MEMS'ed" or sputtered or deposited in some
other way.

 

[[email protected]]

A million? Has that been published somewhere?

I have some film made of the stuff, this version:
http://www.metglas.com/assets/pdf/2714a.pdf
....and it's marvelous. Works at LHe, too.

By the way, my colleaques in our institution work on
MEMS inductors, but I don't think they have deposited
magnetic cores. And we're a research organization, so,
even if the cores *were* deposited, I don't think
we can be counted as a "commercial source".

Regards,
Mikko

 

[Joerg]

I have some film made of the stuff, this version:
http://www.metglas.com/assets/pdf/2714a.pdf
...and it's marvelous. Works at LHe, too.

Thanks, Mikko. It looks like the properties begin to fall apart above a
few hundred kHz though. We need to operate at 13.56MHz and that has
purely regulatory reasons. We cannot prevent antenna effects which will
cause the RF to leak out, and this is an internationally recognized ISM
frequency. There is also 6.78MHz but that is not allowed in as many
countries.

By the way, my colleaques in our institution work on
MEMS inductors, but I don't think they have deposited
magnetic cores. And we're a research organization, so,
even if the cores *were* deposited, I don't think
we can be counted as a "commercial source".

Ok, but isn't one of the jobs of your institute to bring this kind of
technology to economic fruition, where it benefits either the people of
the world or at least the country of Finland?

 

[RobertMacy]

A million? Has that been published somewhere?

Don't know but I ran across another guy on the net, irritatingly much more
knowledgeable in modeling using both Jiles-Atherton AND ??, who confirmed
the measurement/comment. He acted less surprised and more like, "Of
course, didn't you know that?"

I always back up on DVDs and on flash drives. So far that has never
failed me. Hard drives are a gamble, stuff can age in there.

Be careful, I've heard that DVD's aluminum foil has problems over time
too. It peels, or worse, corrodes. We have a 'strong' atpmosphere here, so
aluminum 'rusts' and stainless steel appliances turn hazy brown, so I
don't hold much hope for a DVD to survive either.

How about hardcopy? Is that still used?

There will not be any DC. There will be a low frequency on it but we can
measure during the zero crossings.

You may have to force the 'flip' and measure during the transition, but
still possible.

Uh, just remembered. Any ambient magnetic fields to worry about? Fifty
microTeslas may not sound like... And local AC mains or oldtime monitor
fields can get into the milliTesla ranges.

I just wanted to test the waters for now. It'll still be a few months
out. If we end up needing it, and there is a chance that we do, then
I'll have to sit down with our semiconductor guy and possibly in a
conference with some ferrite guys. The material isn't so critical but we
need one that can either be "MEMS'ed" or sputtered or deposited in some
other way.

Sputtered? Then watch out for the structure. You can't believe the idiotic
implementations of some good materials I've seen.
But for basics, and for easily obtainable materials/processes research the
permalloy material, and see if it will work for you. The processes used in
the MEMs approach are NOT compatible with semiconductors - IT WILL KILL
THEM, the product is ok, it's the process that is potent. Has to be done
in a completely different facility, albeit using semiconductor 'like'
processes, still the chemicals devour the chips and gold and aluminum etc.
is ok when finished though. Envision 'peanut allergy'

 

[RobertMacy]

I have some film made of the stuff, this version:
http://www.metglas.com/assets/pdf/2714a.pdf
...and it's marvelous. Works at LHe, too.
By the way, my colleaques in our institution work on
MEMS inductors, but I don't think they have deposited
magnetic cores. And we're a research organization, so,
even if the cores *were* deposited, I don't think
we can be counted as a "commercial source".

Regards,
Mikko

Have you gotten 'razor cut' on it yet? Careful to keep it sealed in bag
with a dessicant, else it will RUST !

You may also note that the material changes characteristics from 'top' to
'bottom' where top is the side that hits the nitrogen cooled roller so is
a bit better.

For MEMS you cannot deposit this material, rather must deposit the 'wires'
instead. Heat, flexing, anything 'ruins' the material. The deposited
magnetic material has much lower perm and much higher coercivity, but does
work in a pinch to fill in a gap.

 

[Joerg]

Don't know but I ran across another guy on the net, irritatingly much
more knowledgeable in modeling using both Jiles-Atherton AND ??, who
confirmed the measurement/comment. He acted less surprised and more
like, "Of course, didn't you know that?"

Mikko just provided a link here in the thread. However, the relative
permeability starts to fall apart rather quickly once you get above the
audio range. A high value only at or near DC isn't very useful in most
inductors.

Be careful, I've heard that DVD's aluminum foil has problems over time
too. It peels, or worse, corrodes. We have a 'strong' atpmosphere here,
so aluminum 'rusts' and stainless steel appliances turn hazy brown, so I
don't hold much hope for a DVD to survive either.

You have to make a new copy once in a while. But it is less risky than a
hard disk which can suddenly grind itself up or die due to external
event such as very close lightning hits.

What surprised me was that my floppy disks from 25 years were still
readable.

How about hardcopy? Is that still used?

Very rarely. I try to minimize paper usage and also the clogging of
shelf and cabinet space. Last weekend I cleaned up some more and, with a
sigh, threw away the large binder with the manual for my ECA224 license.
It's now so old that I'll never use it anymore anyhow. Of course, I
separated out the sheets so they can be recycled cleanly. Can't yet
bring myself to doing that with my old PSpice license because that stuff
is in much nicer cloth-covered binders. But it'll have to be done. Some day.

You may have to force the 'flip' and measure during the transition, but
still possible.

If I have an error because of hysteresis or whatever that may be
tolerable, as long as it is always the same.

Uh, just remembered. Any ambient magnetic fields to worry about? Fifty
microTeslas may not sound like... And local AC mains or oldtime monitor
fields can get into the milliTesla ranges.

Oh, there will be. The inductor should ideally be immune to that. If it
picks up some of it I can ferret out my desired signla via a correlation
method.

Sputtered? Then watch out for the structure. You can't believe the
idiotic implementations of some good materials I've seen.
But for basics, and for easily obtainable materials/processes research
the permalloy material, and see if it will work for you. The processes
used in the MEMs approach are NOT compatible with semiconductors - IT
WILL KILL THEM, the product is ok, it's the process that is potent. Has
to be done in a completely different facility, albeit using
semiconductor 'like' processes, still the chemicals devour the chips and
gold and aluminum etc. is ok when finished though. Envision 'peanut
allergy'

Well, we are doing something similar already but not at liberty to
disclose. You can make things work but yes, have to make sure that
processes aren't killing off each other's results.

 

[RobertMacy]

Thanks, Mikko. It looks like the properties begin to fall apart above a
few hundred kHz though. We need to operate at 13.56MHz and that has
purely regulatory reasons. We cannot prevent antenna effects which will
cause the RF to leak out, and this is an internationally recognized ISM
frequency. There is also 6.78MHz but that is not allowed in as many
countries.

N O O O O ! ! ! !

First, you may NOT want to use this particular alloy since it saturates
around 0.57, they have materials that go to 2T

Second, Those curves and those charts are based on 'old school'
measurements and accepted techniques. They are observations taken using
established techniques, using wires with the material in a 'bulk' form.
Used that way, it's only good application is a high efficiency AC mains
core. When you use it in MEMs, you get down into the molecular
characteristics and believe me that stuff is still a dead magnetic short
out passed 200-400MHz!!

For example, imagine a core that is 2 mils [50 microns] trying to run at
60 Hz, the conductivity is on the order of 1 MS/m so the skin depth is,
look at that! around 2.6 mils, or 65 microns - a great use of the
material. Now try to go higher in frequency and the skin depth eats you
alive. The effective core area drops to nil and of course you have nothing
there!!! See what I mean about old school thinking? Instead imagine the
material used in the micron ranges. NOW the skin depth is better matched
to your requirements.

We're stuck in the fifties here!

 

[[email protected]]

Ok, but isn't one of the jobs of your institute to bring
this kind of technology to economic fruition, where it
benefits either the people of the world or at least the
country of Finland? --
Regards, Joerg http://www.analogconsultants.com/

Yes it is, and we do it. I guess our "commercial
outlet" on MEMS-related stuff is nowadays Murata

www.muratamems.fi

now that they have acquired VTI Technologies. I just
don't know the status of each R&D project in that
direction, as it involves different guys with whom
I merely share the coffee room (the only radius within
which the information really spreads). Some MEMS-related
R&D results end up to companies like Nokia, and those
gadgets may never become publicly available as
individual components.

I know there is work going on related to your needs,
but I'd better just refer to a publicly available source http://www.sciencedaily.com/releases/2013/06/130620071440.htm

Regards,
Mikko

 

[[email protected]]

Have you gotten 'razor cut' on it yet?

Luckily not, there was a warning on the package.

Careful to keep it sealed in bag with a dessicant,
else it will RUST !

Oh, thanks for the alert. There was a warning
on the package about that, too, but I may have
taken it too lightly (it haven't rusted yet).

You may also note that the material changes
characteristics from 'top' to 'bottom' where
top is the side that hits the nitrogen cooled
roller so is a bit better. For MEMS you cannot

I can recognize the texture change across the
strip, but I didn't realize its magnetic properties
change, too. Thanks for the hint.

Regards,
Mikko

 

[RobertMacy]

I can recognize the texture change across the
strip, but I didn't realize its magnetic properties
change, too. Thanks for the hint.

Regards,
Mikko

Perhaps should have said, from TOP to BACKSIDE, the 50 micron distance.

from the shiny surface back to the duller surface.

Not, side to side, or along the strip.

You'll see the perm [huge] and coercivity [near zero] on the shiny side is
incredible, however as you go 'down' into the material it deteriorates a
bit, perm drops a little but the coercivity comes up. probably due to the
'slower' cooling and therefore slight crystallization occurring on the
'backside'

 

[[email protected]]

I can recognize the texture change across the
strip, but I didn't realize its magnetic properties
change, too.
Perhaps should have said, from TOP to BACKSIDE, the 50 micron
distance. from the shiny surface back to the duller surface.
Not, side to side, or along the strip. You'll see the perm
[huge] and coercivity [near zero] on the shiny side is incredible,
however as you go 'down' into the material it deteriorates a bit,
perm drops a little but the coercivity comes up. probably due
to the 'slower' cooling and therefore slight crystallization
occurring on the 'backside'

Oh, I see. My stuff is 16um thick, but I see what you
mean. I have only used it as static shielding material
in LHe, but was intending to make a tape-wound toroid
out of it. Sounds that the stuff has so unusual
characteristics that even making a toroid out of it
would be sooo fifties...

So, if I just splat it over my circuit on PCB,
I should land it shiny side down?

Regards,
Mikko

 

[RobertMacy]

I can recognize the texture change across the
strip, but I didn't realize its magnetic properties
change, too.
Perhaps should have said, from TOP to BACKSIDE, the 50 micron
distance. from the shiny surface back to the duller surface.
Not, side to side, or along the strip. You'll see the perm
[huge] and coercivity [near zero] on the shiny side is incredible,
however as you go 'down' into the material it deteriorates a bit,
perm drops a little but the coercivity comes up. probably due
to the 'slower' cooling and therefore slight crystallization
occurring on the 'backside'

Oh, I see. My stuff is 16um thick, but I see what you
mean. I have only used it as static shielding material
in LHe, but was intending to make a tape-wound toroid
out of it. Sounds that the stuff has so unusual
characteristics that even making a toroid out of it
would be sooo fifties...

So, if I just splat it over my circuit on PCB,
I should land it shiny side down?

Regards,
Mikko

If you're shielding to the outside world, not sure it makes a difference.
For example, I couldn't find much difference between metal thickness A and
two sheets of metal thickness one half A. Unless you separate the sheets
quite a bit. As shielding with the high perm it can 'spot' saturate and
thus have fields punch through, recommend adding a layer of mumetal to
catch remnants.

If you make a toroid out of it [careful, work hardening by bending
'destroys' the goodness, too]; make a 3 winding core, primary, secondary,
and 'control'. Drill a hole through the wrap so you can wind a figure 8
coil to the outsides and through that hole, call it, 'control winding'.
Then locally saturate the core using the control winding with a high
current, low voltage drive. Think like you are mechanically creating a
huge 'air gap' at the saturation region. Just like physically opening and
closing a gap. With the primary and secondary winding on the rest of the
toroid, you end up with a DC-DC transformer [if you do the supporting
electronics right]. Makes for a very interesting little isolated interface.

When I say work harden, I mean it. I had perm go from 1Meg down to 100k
with just flexing less than ten times. However, in the torroid
application, no biggie.

From memory a toroid with its distributed air gap did not have as good a
high frequency performance as different type of structure. The skin effect
eats you alive at every turn [pardon the pun] with this material when it's
used as 'gross' material.

I tried to get both vendors to make 2 micron 'beads' by splattering
directly into the liquid nitrogen, passivate the surface of the spheres,
then 'gently' sintering into larger core material to get high perm, no
coercivity, and nonconductivity, but they were too busy making huge cores
for the power industry to be interested. Even little wires would be better.

Any interest for your firm to do it? Or, somebody out there? we'd make a
fortune! maybe as much as $10k, or even $100k. Boy has out-sourcing
changed MY expectations!

 

[RobertMacy]

The pole pieces of magnetic heads are made of molypermalloy (or at least
they were circa 2005 when IBM sold its disc drive division to Hitachi).
It has a bulk permeability of about 250,000 iirc, and the heads of
course work out to very high frequency.

Cheers

Phil Hobbs

YES! and their dimensions?