MEMs oscillator sensitivity to helium (helium kills iPhones)--make money online

today on Applied Science we're going to

take a look at this interesting and

bizarre failure mode of modern cell

phones if you take a phone and put it in

a plastic bag and then filled the bag up

with helium in about ten minutes the

phone will completely go dead and it

will take three or four days for the

phone to recover sounds completely

ridiculous but Kyle Wiens did a great

blog and video on this on iFixit and

it's totally true and the way that this

was discovered was that someone working

in an MRI facility had a whole bunch of

Apple iPhones die all at the same time

and the first someone thought it might

have been like an electromagnetic pulse

from the machine or something but they

eventually figured out that it was

probably the helium gas being emitted

from the MRI machine and I became pretty

skeptical at this because it is true

that if you put it in a pure 100% helium

environment the phone dies but how much

helium could it really take so in this

video I'm gonna measure exactly how much

helium it takes to kill an iPhone and

also tear down the device inside the

phone that's actually sensitive to

helium and take a look at it under the

electron microscope

so first the surprising result from all

this testing even a two percent helium

environment is enough to disable the

part that is susceptible in these phones

at 2% helium the phone will last about

30 minutes in that environment before

being disabled this is really surprising

and it actually makes the MRI story

start to sound fairly plausible I was

expecting this to be more like half an

atmosphere or three quarters of an

atmospheric helium but as it turns out

somewhere between one and two percent is

the magic point where this thing is as

deadly and 0.2 this is not a swipe

against Apple to their credit in their

user manual they even say that you

shouldn't hang out around boiling

liquefied gases such as helium because

it might affect your phone so they

actually know about the problem and the

chances that you're gonna run into this

are so remote it's it's really not a

problem let's talk about the actual

component that's causing all of these

problems in pretty much all electronics

you need a frequency source called a

clock and traditionally it's delivered

by something that looks like this which

is a quartz crystal inside here there is

a little tiny pea

of quartz with electrodes on it and it's

physically vibrating at a frequency

that's determined by its size and you

can see that this is actually in a metal

can here specifically to keep out

environmental factors that may affect

that piece of quartz over time and and

cause its frequency to shift so one of

the problems with this is that this this

frequency is fairly high it's probably

about 16 or 32 megahertz and that burns

up a lot of power so in battery-operated

electronics it's common to have two

oscillators one at 16 or 32 megahertz

for example and another one at a much

lower clock frequency of just 32

kilohertz so now you have to have two

quartz crystals in your battery-powered

device the problem with having one or

even two quartz crystals in your little

device is that they take up a fair bit

of board space this is not the smallest

quartz crystal available but it's

getting pretty close and it's a bit of a

physical limitation because you just

can't cut the quartz crystal small

enough and still get good frequency

stability and have everything that you

want so there's a modern technology that

replaces the quartz with a much smaller

component in fact you can stack probably

about two or three of these things on

this quartz crystal and what I'm holding

in the tweezers is a MEMS oscillator so

there's no quartz inside this package

there's actually a piece of silicon that

is cut into a tuning fork and and that

is actually oscillating instead of

quartz it's a relatively recent

innovation MEMS oscillators have been

around for a while but the fact that

devices are getting so small phones and

watches for example are making this MEMS

oscillator a better choice than quartz

because it's smaller you might save a

little bit on power as well so you get

better battery life and a smaller device

which is what everyone wants in mobile

electronics the manufacturers know that

the MEMS devices are sensitive to

environmental factors too and so

sometimes they're put into cases that

are made of ceramic with a metal lid and

this is sealed up specifically to keep

environmental stuff out but the problem

is if you want an oscillator that super

super tiny for a wristwatch device for

example

you really can't make this in a metal

lid package you need some other way to

put it together and so the problem is

that by miniaturizing it down so small

it's opened up the susceptibility to

helium and the main reason is that what

this thing is made out of is it's almost

pure silicon will do a teardown on this

and show exactly what's inside here but

the problem is that instead of metal and

ceramic protecting it from the

environment there is no protection it's

just silicon hole the whole device is

actually made from silicon and as it

turns out helium can actually work its

way through the silicon it's not like

there's a crack or a seam or anything in

there the gas is actually going through

the material

it's diffusing through it because it's

such a small molecule getting inside the

device and once the gas is inside there

it causes the oscillator first to rise

in frequency slightly probably because

there's a compensation circuit in there

and then when the concentration gets

high enough it causes the oscillator to

crash to a very low value essentially a

total failure the component in question

is the SI 1532 MEMS oscillator made by a

company called sigh time and you can get

these on digi-key again this isn't a

swipe against side time I think this is

a very weird edge case that probably

isn't worth considering and side time

claims this is the I think smallest

lowest power 32 kilohertz oscillator

that you can get so it's not a cost

optimal

footprint on the board and power I

didn't bother making a circuit board

that would connect up to this footprint

and so to connect up the wiring to these

parts which I knew I wanted to have in

like a sealed container where I could

control the helium atmosphere

I tend a little bit of 40 gauge wire and

just very quickly melt the solder ball

and put the wire in so the whole device

is kind of suspended by its wires and

this works fine for just for connections

or even three here's a look at the test

setup I've got like a gas controlled

manifold here and the blue hose is going

to a vacuum pump that is on the floor

with a valve here then T's into the test

chamber and there's another valve here

and the red hose connects to the source

gas and of course helium is the one

we're talking about

today but I also tried hydrogen which

which had no effect on it and I'll talk

about the results later and then the gas

manifold itself has this pressure gauge

here this thing reads a little strangely

it reads in gauge pressure below

atmospheric so when it reads 101 that's

actually zero absolute because we're at

sea level here strange units but just

kind of go with it at least it's kPa and

then the actual chamber itself is made

from an old vacuum gauge that I took

apart basically to get the pass through

so this is a NW flange I think this is

called and inside here is the wires

holding up the tiny little oscillator

and it's just got a bunch of pin

connection so it's basically just a

sealed chamber with the electrical pass

throughs and this convenient way to open

and close it so the trick with helium

poisoning these things is that they

don't recover very quickly and so if I

test a device I need to quickly get it

out and put a fresh one in so that I'm

always starting with a fresh oscillator

I should point out that throughout these

tests you'll see the draw of the current

draws about 7.5 micro amp which is way

higher than the datasheet spec and most

of the current is actually going into

the frequency counter so if I disconnect

the counter so now the oscillator is

still running it's just not connected to

the frequency counter it drops down to

2.7 micro amp which is still higher than

the datasheet but there's probably other

straight capacitance in here that I

haven't worked away the trick is that

these ultra-low power draws even at 32

kilohertz a straight capacitance ends up

pulling more current than the entire

supply current for the device its health

so when you get down to these crazy low

currents it's kind of tough to chase

away the micro amps and the single

digits like that okay let's talk about

the tests to start off I didn't mix up

air environments with helium like one

way to test this would be to fill up a

container one percent with helium by

pressure and then fill up the remaining

space with air and then do another test

fill out that chamber to two percent

helium by pressure and then fill up the

remainder with air however since the air

is not really playing a part in this at

all it's really only the helium that

matters

we can sort of approach the problem by

just thinking about the partial pressure

of helium so you know think of like a

strainer where the helium is small

enough to go through the strainer but

the air is too big to go through the

strainer it doesn't really matter if the

air is there or not if you have the same

partial pressure of helium so basically

what I want to do is evacuate the

chamber entirely to pure vacuum and then

introduce a small amount of helium to a

pressure that is 1% of an atmosphere

let's say 1 kPa about in the first

experiment I added about 1% of an

atmosphere helium pressure and let that

sit for a while and notice that the

frequency was actually raising very

slightly and I was watching the graph on

the frequency counter and thought it was

kind of leveling off and so initially

what I thought I was going to do is

introduce 1% helium and then go back to

vacuum and watch the frequency return to

normal then go back to 1% helium and try

to characterize sort of the diffusion

constant based on how quickly the

frequency was changing versus how

quickly I was adding and subtracting

this 1% helium

unfortunately it didn't work out that

way because the frequency never returned

there's something going on with the way

the helium diffuses into and out of this

device that I don't fully understand so

it takes a long time for the helium to

diffuse back out even in full vacuum and

this is true in other testing too so for

example in the iFixit blog it only takes

10 minutes in pure helium to disable the

device but it takes days for the thing

to recover and I'm not really sure why

that is and in my testing I saw the same

thing it takes 2 or 3 days to get back

to a functioning oscillator even taking

the power off and putting the power back

on periodically even in vacuum and I'm

not really quite sure why so after

giving up on measuring the diffusion

constant this way I decided maybe just

to try to figure out like the minimum

kill concentration so I went to 2

percent helium thinking that you would

be about the same as 1% but to my

surprise the frequency kept drifting

upward and after about 30 minutes or so

there was a sudden crash where the

frequency started dropping

precipitously and worked its way all the

way down to 3 kilohertz basically a

total failure if the oscillator very

surprising I was expecting this to go

all the way hit a 50% or 60% helium but

it really only took 2% and I think it's

possible that even less would do it

obviously two kills it so somewhere

between 1 and 2% is probably the

unacceptable range for this device

pretty interesting and then also I

tested one atmosphere of helium just to

see and sure enough in just a few

minutes it actually causes the same

failure mode first a frequency rise and

then a sudden crash and if you think

about this wave of helium diffusing

through the silicon inside the device if

the wave is really steep because there's

a lot of helium on the outside of the

device then these this sort of crash

scenario happens more quickly as well so

first the frequency rises kind of do the

same failure point maybe 1 or 2 Hertz

higher than its specified frequency and

then the crash is more abrupt because

this wave of helium is much taller

basically for the lower concentrations

one or two percent the failure is more

gradual because the helium is diffusing

in at the same speed but the the height

of the wave is lower this concept of

diffusion in engineering in general is

sometimes tricky to grasp and so a good

way to think about it is imagine taking

like a frozen pie out of your freezer

and putting it in the oven it doesn't

matter if your oven is a hundred degrees

or a thousand degrees if you take it out

after 5 minutes the center is still

going to be frozen you could have the

hottest oven in the world and it's still

not going to be able to thaw the middle

out through conventional heat exchange

and so the same thing is going on here

the helium is actually diffusing through

the material just like the heat is

diffusing through your frozen pie and

what you can do is change the height of

the wave that is diffusing through the

material but you can't change the speed

at least not by adding more helium to

the equation you can heat the whole

thing up and that might increase the

diffusion constant but the the actual

pressure the thing that you're actually

do

using through the substance doesn't

affect the speed at which it goes

through also its III didn't test

high-temperature diffusion for these

MEMS oscillators it's about 15 degrees C

and all my tests were done at that

temperature let's tear one of these

devices down and see what's inside there

that's so sensitive to helium this is my

setup here I've got a really small

ceramic hot plate under the microscope

and then what I'm going to do is take

one of these devices and put it on the

hot plate and run about 50 or 60 watts

through this little tiny ceramic hot

plate just from the bench supply and

that will allow us to separate the two

dyes that make this device up it has got

an interesting construction there's one

piece of silicon that has the electrical

circuitry on it and that's the more

oblong rectangular shaped piece of

silicon and then there's a smaller

square piece of silicon that has the

MEMS structure in it and the reason that

it's two separate dies is because if you

build a production line to build MEMS

devices it's kind of set up only for

MEMS and if you build a production line

that's only for Simo circuitry then

that's all you get so it's really two

separate dies because they came from

separate production lines I mounted some

of these devices in epoxy and then

sanded them down taking photos

incrementally as I sanded through and

that's actually how I discovered that

there were two separate pieces of

silicon with like an under bonding layer

like a an adhesive or something that's

helping them stay together there's also

a four ball I think solder ball

connecting them together as well the

trouble is this adhesive is incredibly

good and so to get them apart I put them

on the hot plate and then twisted them

with the tweezers to pull the to die

apart which is not so easy since I knew

I was going to do some scanning electron

microscopy on this I also used

conductive epoxy to hold a device down

to the little aluminum stub that goes

into the microscope and then just really

carefully use sandpaper with a

screwdriver

and took off tiny tiny amounts of

material looking at it under the

microscope while it was doing this here

are some images from the electron

microscope these were obtained by

mounting the entire MEMS oscillator in

of epoxy and then grinding from the

bottom into the MEMS device so in theory

you can pull that MEMS die off and mount

it either way and it's actually built as

far as I can tell symmetrically so it

doesn't matter if you grind from the

bottom or the top which is very curious

actually how do you make a MEMS device

that's entirely encased in silicon it's

almost like a bizarre sort of puzzle I

mean it's there's no openings to this

thing there's no seams

there's no lid or anything I mean how do

you make it so let's switch the cartoon

view and we can talk about how this

thing is made it may have been a little

hard to tell in the SEM view but this is

kind of how it looks in schematic form

and the the thing that's actually moving

the tuning fork is this darker object

that I've labeled 3 and it probably

Wiggles in like all the legs are

probably moving in and out at the same

rate but it's possible they did

something tricky in its movement you

know oscillating in a different mode the

actuators are almost certainly

electrostatic so if you put a positive

voltage here in a negative voltage on

the tuning fork it's going to cause this

to be attracted here because opposite

charges attract and you end up with a

total of three leads basically if we

were to boil this down even further it

looks kind of like this and so if you

put your attraction voltage here the

thing moves this way and then when you

release it it'll have a characteristic

wiggle and you can use your other

electrode to sense what's going on in

there okay so we saw that this tuning

fork structure has to be freely moving

in here so imagine these non shaded

parts are permanently fixed but this has

to move it has to be completely open you

know free to move and then maybe the

tuning fork is pinned kind of at a

couple spots like here and here so it's

it's fixed here and here but everything

else has to be free-floating and this

entire thing is encased in silicon how

do they do it

so I found a couple of references that

I'll put links to in the description but

here's the basic idea if you start with

a silicon wafer we can etch a little

piece out of it then you can grow an

oxide layer on it and then you can

deposit silicon onto the oxide and I'm

not exactly sure of the process I think

it's poly silicon but

you can use a patterning system to

basically put silicon down on top of the

oxide then you can put grow oxide or

deposit or grow oxide on top of the

thing that you just deposited and here's

the step that I didn't believe was

possible but apparently it is you can

actually bridge the gap with a new

silicon layer so in my mind if you're

going to deposit silicon it seems like

it would just cover everything but if

you make the gap the right size and you

use the right process you can actually

get a cap of silicon to grow across your

entire device and essentially seal off

the chamber that's in there but then how

do you get the device free I mean it has

to be supported on something we've got

these oxide supports holding the tuning

fork there the trick is that you

purposefully leave some very small vents

in the outside going to the outside of

your entire case here and you use a

hydrofluoric vapor etch process so the

hydrofluoric vapor will etch away all

the oxide but not touch the silicon

itself so you essentially remove the

supports that were holding the tuning

fork in place by letting the HF vapor go

in and then you have to seal off these

little vents and I think as it happens

the vents can be coordinated with your

electrical contacts which you also have

to make through this top layer so that

the the way that you connect

electrically to the tuning fork and the

other electrodes that are inside this

thing are done through these vents

you also need vents in the tuning fork

itself to let the HF gas get through

this entire device so when you look at

the image in the SEM all those weird

little slots and stuff cut in there

might be there for structural reasons

but it's also likely that those slots

are there specifically to let this HF

gas process work pretty pretty cool

actually did not though this was

possible and you end up with a

completely hermetically sealed box after

you close off these vents and I think

the way this is done in the factory is

that you use hydrogen to prevent this

whole thing from getting oxidized and

seal it up with the hydrogen inside it

and then you put it into a really hot

oven in vacuum and the hydrogen actually

diffuses out through the so

lookin at those high temperatures but as

I found out I tested it myself and at

room temperature after one day of one

atmosphere hydrogen

I couldn't detect any shift in frequency

at all so at room temperature the

hydrogen diffusion is so slow that you

know they take millennia or whatever did

to affect it or something but in a hot

oven in vacuum that hydrogen diffuses

out in a timescale that makes

manufacturing these things possible okay

well I hope you found that interesting

see you next time byeTop Search Keyword : online earning, , make money online, earn money online, online earning, online earning sites, make money online free, online money income, earn money online free, money online, best way to earn money online, online income site, money earning websites, best online earning sites, easiest way to earn money online, earn money payment bkash, online money income site