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RAM recovery

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bbdra

PCHF Member
May 9, 2019
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Hello, I think about one problem and needed to know the opinion of true experts :giggle:

I have read on the internet that RAM needs voltage to keep data, and that, the content will disappear after time, when you disconnect the power supply, you can also rewrite it quite quickly and easily, so the sensitive datata might be unrecoverable.

But I found a study (Remanence in Semiconductor Devices Peter Gutmann IBM T.J.Watson Research Center) from 2001 on the internet, which deals with this issue in more detail and mentions the problem of "hot carriers"

4.2. Hot Carriers
High-energy electrons can cause other problems as
well. A very obvious one is that the device heats up
during operation because of collisions with the atoms in
the lattice, at least one effect of the heating being the
generation of further high-speed electrons. A problem
which is particularly acute in MOSFETs with very
small device dimensions is that of hot carriers which
are accelerated to a high energy due to the large electric
fields which occur as device dimensions are reduced
(hot-carrier effects in newer high-density DRAMs have
become so problematic that the devices contain internal
voltage converters to reduce the external 3.3 or 5V
supply by one or two volts to help combat this problem,
and the most recent ones use a supply voltage of 2.5V
for similar reasons). In extreme cases these hot
electrons can overcome the Si-SiO2 potential barrier
and be accelerated into the gate oxide and stay there as
excess charge [14]. The detrapping time for the
resulting trapped charge can range from nanoseconds to
days [15], although if the charge makes it into the
silicon nitride passivation layer it’s effectively there
permanently (one study estimated a lifetime in excess
of 30 years at 150°C) [16].
This excess charge changes the characteristics of the
device over time, reducing the on-state current in nMOSFETs
and increasing the off-state current in pMOSFETs
[17][18][19]. The change in characteristics
produces a variety of measurable effects, for example
one study found a change of several hundred millivolts
in memory cell signal voltage over a period of a few
minutes [20]. This effect is most marked when a 1 bit
is written after a 0 bit has been repeatedly read or
written from the cell, leading to a drop in the cell
threshold voltage. Writing a 0 over a 1 leads to an
increase in the cell voltage. One way to detect these
voltage shifts is to adjust the settings of the reference
cell in the sense amplifier so that instead of being set to
a median value appropriate for determining whether a
stored value represents a 0 or a 1, it can be used to
obtain a precise measurement of the actual voltage from
the cell.

Hot carriers are generated almost exclusively during switching
transitions [23][24]. The effects of the hot-carrier
stressing can be determined by measuring a variety of
device parameters, including assorted currents,
voltages, and capacitances for the device [25].

Hot-carrier and electromigration effects in the
crypto circuitry could retain an afterimage of
the key long after the original has leaked away
into the substrate.

5. Minimising RAM Data Recoverability
The previous sections have shown a variety of ways in
which stored data can leave traces of its existence
behind. These include the effects of electrical stress on
ionic contaminants and hot-carrier effects (which can
be used to recover overwritten data or data from
memory to which power has been removed), and
electromigration effects (which can be used to
determine, after indefinite time periods, which type of
signal was most commonly carried by a particular part
of a circuit).

5.1. Avoiding Short-term Retention Effects
The best way to avoid short-term retention effects is to
ensure that no memory cell holds a data value for more
than a certain amount of time. Based on the figures
given earlier, a few minutes of storage of a given value
should be treated as an upper bound; storage for any
larger amount of time will cause detectable effects in
the memory cell, although it may take quite a while
longer before these effects really become a problem. In
a series of tests carried out on a sample of SRAM
devices, changes in device threshold voltage,
transconductance, and drain-source current were
observed after 100–500 seconds of stress, leading to a
corresponding change in SRAM access time and
operating voltage [43]. As the SRAM cell in Figure 4
indicates, reads and writes of 0 and 1 bits stress
different access transistors in the cell so that it’s
possible to determine whether a 0 or 1 was stored there
by determining which transistor was stressed the most
(the grey dots in the figure indicate the main stress
locations). The change in cell behaviour can be
determined by recording the cell access time, through
voltage microprobing of the cell’s transistors, or using
some of the other techniques mentioned earlier. Similar
tests have been performed on DRAMs, although in this
case the emphasis was on stress effects on shared
circuitry such as address buffers and sense amplifiers.
While there were quite noticeable effects in all of these
areas the study didn’t examine the effect on individual
storage cells [44].

So if I understood it well, the main problem is the high temperatures of the HW device. According to my considerations, this problem could be overcome by better cooling in the form of cooling pad, fan, or a better airflow.

Is there an expert who understands this issue, and would you please advise me?
 

Pyro

PCHF Member
PCHF Advisor
Jan 12, 2019
515
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I'm a bit confused by what exactly you are asking for.

Adequately cooling ram (as all electronic components) is important, but it is meant for temporary files and running programs to store "active" files that are being used/modified.

If you are looking for a way to make the storage permanent, there is no way to do this with the RAM, it is not designed to store things long term, you would need to buy a storage device (whether that be a SSD or HDD).
 

Bruce

Forum Regular
Moderator
Support Team
Oct 8, 2017
5,375
577
Yeppoon, QLD, Australia.
RAM (random access memory) is volatile, that is, lose the power and you lose the data.
that is what 'memory leakage' is all about, if the RAM isn't refreshed every 5ns (or something like that) the charge in that cell dissipates and the state of the cell (charged or not charged) is lost.

your quoted report doesn't mention what it classes has "high energy", and I'd be surprised if your home PC falls into that category.
it also is referring to SRAM which is CPU cache, DRAM is PC memory.
 

bbdra

PCHF Member
May 9, 2019
85
3
32
your quoted report doesn't mention what it classes has "high energy", and I'd be surprised if your home PC falls into that category.
it also is referring to SRAM which is CPU cache, DRAM is PC memory.
I think they mean all devices containing large printed connections, logical circuits with typical power supply (24V 12V 5V 3,3V) such as desktop computers or notebooks, that contain MOSFETS with high densities like DDR1, DDR2, DDR3 technology that are the successors of the DRAM.

As far as I understand, SRAM and DRAM uses MOSFETs with the difference that modern DDR2, DDR3 or DDR4 have reduced power supply from external 5V-3,3V to 1.8 V or 1.35 V. This corresponds to the previously mentioned: "(hot-carrier effects in newer high-density DRAMs have become so problematic that the devices contain internal voltage converters to reduce the external 3.3 or 5V supply by one or two volts to help combat this problem, and the most recent ones use a supply voltage of 2.5V for similar reasons)"
I think it is precisely because of the high densitiy, so the individual mosfets are not cooled well, high temperatures occurs, and "creates more of the further High-Speed Electons", as they said, which all the heating process probably multiply. For SO-DIMM DDR2 and DDR3 memoryies, the working temperatures are 0-85 ° C, which I believe, because if I touch the chip, it is warm to hot on the surface, I guess 42°C or more. The internal temperatures might be higher, which would correspond to information about the temperatures that are listed on the Internet.

But I am not an expert and I am just guessing, so I will appreciate your help.:unsure:
 

bbdra

PCHF Member
May 9, 2019
85
3
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I wanted to ask if cooling of RAM with a fan or cooling pad prevent the creation of an excessive amounts of other high-speed electrons. and how much it prevents in creation of the trapped excess charges, which can indicate changes in voltage treshold of the cell and serve as information for the recovery of overwritten memory cells.
 

Bruce

Forum Regular
Moderator
Support Team
Oct 8, 2017
5,375
577
Yeppoon, QLD, Australia.
wow - way too deep for this little guy. :whistle:

I don't think that's an area any user will ever need to address.
if such a situation was causing errors, issues, BSoD's or what have you, I'd hope the tech boffins would be all over it.
if from no other angle than a marketing one - "hey get this $500 memory electron fan to reduce high energy collisions" - the nerds and gamer nuts would be knocking down the retail doors!
 

veeg

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bbdra

PCHF Member
May 9, 2019
85
3
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Interesting article about electrons. Depending on what I found out in the remanence in Semiconductor Devices and in an article that posted Veeg, I believe that the temperature plays an important role here.

RAM is no longer hot using a basic cooling pad for $10, but it is not even cold. It is warm, and personally I would not consider such a temperature to be an extreme case, rather as a average working temperature.

If the conductor is not warm, the electrons will not friction and there will be no further heat. In my opinion, RAM cooling should reduce or prevent the creation of excessive charges, what do you think, am I wrong?
 

bbdra

PCHF Member
May 9, 2019
85
3
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Semiconductors are insulators at very low temperatures, but at a suitable temperature, the additional thermal energy allows electrons to jump into the conduction band. Semiconductors can be elements such as Germanium, Zinc, and Silicon, or compounds.

Hot-Electrons​

Hot-electrons occur when a strong electric field is applied across a semiconductor. The electrons obtain energy from the applied electric field, which they dissipate by emitting phonons, exciting other electrons or emitting photons. When an electron's energy exceeds the average thermal energy of the semiconductor, the increase in kinetic energy of the electrons is statistically interpreted as a raising of the electrons' temperature, so they are termed 'hot electrons' . A rough estimate of the threshold electric-field, E threquired to create hot-electrons is given by Ridley [1]

Image78.gif

(4)​

Where E 0 is the energy with zero applied field, and m and t E are the mobility and the energy relaxation time measured at zero field. Typically, E th is about 1kV cm -1 .


This phenomenon is therefore dependent on the semiconductor temperature, am I right?
 

bbdra

PCHF Member
May 9, 2019
85
3
32
RAM modules are fully functional,I just don't know how much the chance is that they will produce Hot Elelectron's / Hot Carrier Effect by normal use, and if at all.

I also wonder what generation RAM is suffering from this problem?
 

bbdra

PCHF Member
May 9, 2019
85
3
32
I don't know if I understood it, but if RAM module remains at low temperatures, it should not occur that the energy of electron exceeds the average thermal energy of the memory dices or conducctor. Isn't there any electro engineer on the forum that could help?
 

Pyro

PCHF Member
PCHF Advisor
Jan 12, 2019
515
89
Ram, like most all other hardware components, are capable of thermal throttling if temperatures are exceeding that of safe operation.

If you're worried your ram will overheat and lose the data being transferred on them or damage the module, make sure you have adequate airflow to the modules.
 

bbdra

PCHF Member
May 9, 2019
85
3
32
Im just asking if there is a risk with any genertion of DDR that electrons overcome the potential barrier
and will be accelerated into the gate oxide and stay there as excess charge at typical workload, and how much this phenomenon would have occurred in these DDR RAM generations in normal situations.
Simply said, would it be possible, for now available RAM, ie DDR2 DDR3 DDR4, to find out in practice and under normal conditions by this phenomenon, what content was in the RAM before it was overwritted?
 

Pyro

PCHF Member
PCHF Advisor
Jan 12, 2019
515
89
Anything is "possible" but I highly doubt this is a common problem since I have never heard of it.

As mentioned before, these components will typically throttle themselves in favor of saving whatever they can before crossing thresholds and barriers.

The only times I have heard of data being recovered off ram was in terms of forensics, but this was when using extremely cold temperatures:
https://ro.ecu.edu.au/cgi/viewcontent.cgi?article=1162&context=adf

If you're looking for a way to make this happen, that is beyond my field of knowledge. :)
 
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