amplifying a sub femtoamp of current

[joseph2k]

Thanks for the description. Interesting!

I understand we have 1 nV or less at 20 pF. I believe this is possible to
detect provided data acquisition time is longer than life time of the ion.
It is not a problem with Heisenberg, IMHO.

A capacitance of 20 pF is a lot. The signal would increase if C could be
reduced. If this is not possible maybe one could raise the impedance by
means of an inductor to form a tuned circuit at the amplifier input.

I hope someone can give advice on the best choice of 4 Kelvin charge
amplifier. John Larkin suggested a cold jfet. I guess that is a good
suggestion. Some semiconductors do not work at 4K as minority carriers are
not generated thermally as they are at room temp.

Yeow, is that an understatement. All semiconductors not specially designed
to operate below liquid Nitrogen temperatures (about 77K) suffer from
"freeze-out" and do not work at all.

Look at devices called "charge amplifiers" to integrate very small charges
<10uColumbs.

joseph2k

 

[joseph2k]

I am thinking he would be doing dam well to squeek out 100KHz
bandwidth...

Thanks for the reminder, Coulombs number is something like 6.245x10^18;
below picoamperes you are approaching counting basic charge units.

joseph2k

 

[Mike Monett]

Yeow, is that an understatement. All semiconductors not specially
designed to operate below liquid Nitrogen temperatures (about 77K)
suffer from "freeze-out" and do not work at all.

Look at devices called "charge amplifiers" to integrate very small
charges <10uColumbs.

joseph2k

Very interesting, joseph. Here is some more information that might be
useful:

...the lower temperature limit is typically determined by the
ionization energy of the dopants. Dopants usually require some
energy to ionize and produce carriers in the semiconductor. This
energy is usually thermal, and if the temperature is too low, the
dopants will not be sufficiently ionized and there will be
insufficient carriers. The result is a condition called
"freeze-out." For example, Si (dopant ionization energy ~0.05 eV)
freezes out at about 40 K and Ge (ionization energy ~0.01 eV) at
about 20 K. Thus, for example, Ge devices in general operate to
lower temperatures than Si devices.

The various effects described above can be illustrated in a graph
such as the one below (the shape of the curves should not be taken
literally, only as an indication of trends). Ordinarily, the usable
temperature range corresponds roughly to the flat region of each
curve. As can be seen, increasing the doping concentration can
extend both the low and high temperature limits; however, the heavy
doping may not be suitable for a particular device.

On the low-temperature end, there are additional effects that allow
devices to operate below their "freeze-out" temperature. First, if
the semiconductor is doped to a certain concentration, it can attain
degeneracy, a condition in which the dopants require no energy for
ionization. For example, this happens in n-GaAs at a fairly low
doping concentration (~1016 cm-3) that is common in standard
devices. Thus, standard GaAs MESFETs can operate down to the lowest
temperatures, essentially to absolute zero. For Si, degenerate
doping requires a much higher a concentration (~1019 cm-3). On the
other hand, there are effects that prevent operation even before the
device is cooled to the "freeze-out" temperature. For example,
standard Si bipolar transistors cease operating well above the Si
"freeze-out" temperature, as described later.

15) How do temperature capabilities differ between the two main
types of devices: field-effect transistors and bipolar transistors?

Low temperature

Field-effect transistors (FETs): Characteristics of FETs generally
improve with cooling, such as transconductance, leakages, and white
(high-frequency) noise (although Si JFETs degrade below about 100
K); low-frequency noise is less predictable.

The low-temperature limit of field-effect devices depends on the
particular type and material: Si JFETs, are limited by their
freeze-out temperature (about 40 K), but their performance actually
degrades at a higher temperature. Ge JFETs have a similar behavior,
although the relevant temperatures are lower, and under proper
biasing can operate to the lowest cryogenic temperatures. Properly
designed n-channel GaAs JFETs can also operate to the lowest
temperatures, although they are uncommon.

Si MOSFETs, enhancement type, can also operate to the lowest
temperatures because the carriers needed for conduction in the
channel can be ionized by an electric field from the gate. Si
MOSFETs and CMOS circuits are often used at deep cryogenic
temperatures, below the freeze-out of Si.

Various types of heterostructure FETs (HEMTs or MODFETs), usually
based on III-V semiconductors, do not require thermal energy to
ionize the dopants. As a result, they can also be used over the
entire cryogenic temperature range down to the lowest temperatures.

Bipolar transistors: Ordinary Si bipolars (Si BJTs) suffer a rapid
decline in gain with cooling and are unusable below about 100 K.

This in not a result of "freeze-out" but of low emitter-base
injection efficiency. This effect can be avoided by adjusting the
band gaps through "bandgap engineering" as in heterojunction bipolar
transistors (HBTs), such as those based on SiGe. HBTs have
demonstrated operation down to very low cryogenic temperatures and
show increased performance on cooling. On the other hand,
conventional homojunction Ge and GaAs bipolar transistors have also
been reported to operate to very low cryogenic temperatures.

http://www.extremetemperatureelectronics.com/tutorial3.html

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[Mike Monett]

Thanks for the reminder, Coulombs number is something like 6.245x10^18;
below picoamperes you are approaching counting basic charge units.

joseph2k

The Radio Frequency Single Electron Transistor (RF-SET) can go past 100MHz.

Sorry, all my old links have gone bad and I don't have time to google for
more right now.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[Tony Williams]

Very interesting, joseph. Here is some more information that
might be useful:

[huge snip]

http://www.extremetemperatureelectronics.com/tutorial3.html

Interesting post Mike, well worth the read. Thanks for
taking the effort to type it in.

 

[Mike Monett]

Interesting post Mike, well worth the read. Thanks for taking the
effort to type it in.

Tony Williams.

Hi Tony,

Thanks for the nice comment - actually, the credit goes to Randall
Kirschman for gathering and typing the info. All I did was cut and
paste. But people hate to go to a bare link, so I like to post the
relevant info and give a link in case anyone wants to dig some more.

But I will take credit for the nice square justification, however.
That's from my very own personal DOS editor that I wrote and still
use constantly.

Anyone who still uses a DOS editor has run into a problem
transferring information between DOS and Windows. If you edit a file
in DOS, and have another program running in Windows with the same
file loaded, the Windows program may not know the file was updated.

So when you edit the Windows version of the file, you overwrite the
DOS version of the file and lose your information.

This problem plagued me for years, until I found EditPad. The author
must be the smartest Windows programmer I have ever seen. He checks
to see if the file was edited by another program, and automatically
loads the most recent version so you don't lose the info you just
entered. Very slick - and it completely solves the problem. The free
version is available at:

http://www.editpadlite.com/

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[Mike Monett]

joseph2k <[email protected]> wrote:

I am thinking he would be doing dam well to squeek out 100KHz
bandwidth...

The Radio Frequency Single Electron Transistor (RF-SET) can go
past 100MHz.

Sorry, all my old links have gone bad and I don't have time to
google for more right now.

OK, got a minute and searched google for:

rf-set transistor bandwidth

Lots of info if you can get down to -459F. Here's an old one:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NEW HAVEN, Conn.- Scientists at Yale University have developed the
world's most sensitive electrometer, a transistor so sensitive it
can count individual electrons as they pass through a circuit. The
detector could be useful not only in developing and testing
miniaturized electronic devices but also as a highly sensitive light
detector in powerful new microscopes and telescopes.

Made from aluminum, the device is about 1,000 times faster than the
best electrometer on record and 1 million times faster than other
single electron transistors, according to a report by Yale applied
physicist Daniel E. Prober in the May 22 issue of the journal
Science. Working with him on the device were Yale postdoctoral
associate Robert J. Schoelkopf; former graduate student Peter
Wahlgren, now in Gteberg, Sweden; and graduate students Alexay A.
Kozhevnikov and Per Delsing.

"Single electron transistors have been around for about a dozen
years, but our laboratory has developed a new type called a Radio
Frequency Single Electron Transistor (RF-SET) that can measure
charges as small as 15-millionths of an electron. It detects an
extremely large bandwidth," said Prober, an expert in
high-temperature superconductivity as well as electron conduction in
metal films, wires and semiconductors.

The goal of many scientists for the last 10 years has been to
develop more precise frequency measurements and to devise current
voltage standards, said Schoelkopf, who began working on the RF-SET
design while a graduate student at California Institute of
Technology. Without that, researchers cannot study and perfect
extremely miniaturized electronic devices and computer chips at the
level where quantum mechanical effects become important.

Currently, the RF-SET works only at temperatures near absolute zero
Kelvin, or about -459 degrees Fahrenheit, thus requiring a large
refrigerator. The Yale scientists are exploring ways to make the
detector work more effectively at higher temperatures.

On the plus side is the device's high operational speed.
Conventional single electron transistor electrometers have been
limited by slow speeds, typically below frequencies of 1 kilohertz
(1,000 cycles per second), Schoelkopf said. The RF-SET can operate
even at frequencies exceeding 100 megahertz (100 million cycles per
second), where the noise due to background charge motion is
completely negligible. In their report, the Yale researchers
describe how improved versions of this device could even approach
the quantum limit, yielding the best electron detectors possible.

Because the device effectively monitors a wide range of photons -
including X-rays, ultraviolet radiation, light, infrared radiation,
and microwaves - the RF-SET design is "the best by many criteria,
very exciting," Prober said. Among the many potential applications
are far-infrared detectors, being considered by the National
Aeronautic and Space Agency (NASA) for use in astronomy, and
high-resolution electron microscopes that can amplify light for the
study of molecular structure in medicine.

http://www.scienceblog.com/community/older/1998/D/199804120.html

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Schoelkopf et al. improved the sensitivity to 6.3ue/sqrt[Hz] in
1998, so it has to be much better by now:

The Radio-Frequency Single-Electron Transistor (RF-SET): A Fast and
Ultrasen...

Schoelkopf et al.

Science 22 May 1998: 1238-1242
DOI: 10.1126/science.280.5367.1238

Radio-Frequency Single-Electron Transistor as Readout Device for
Qubits: Charge Sensitivity and Backaction

A. Aassime, G. Johansson, G. Wendin, R. J. Schoelkopf, and P.
Delsing

Received 21 November 2000

We study the radio-frequency single-electron transistor (rf-SET) as
a readout device for charge qubits. We measure the charge
sensitivity of an rf-SET to be 6.3ue/sqrt[Hz] and evaluate the
backaction of the rf-SET on a single Cooper-pair box. This allows us
to compare the needed measurement time with the mixing time of the
qubit imposed by the measurement. We find that the mixing time can
be substantially longer than the measurement time, which would allow
readout of the state of the qubit in a single shot measurement.

http://prola.aps.org/abstract/PRL/v86/i15/p3376_1

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[John Perry]

Robert Baer wrote:...

Thanks for the reminder, Coulombs number is something like 6.245x10^18;
below picoamperes you are approaching counting basic charge units.

Hm. It seems to me that he can acquire data at any rate he can achieve
after (or even before) amplification. Whether there's any signal to be
detected is the question you're addressing; correlating a lot of (maybe
unnecessary) data will reveal whether there's any there to be detected, no?

jp

 

[vasile]

Hi
I have a high impedance source at 4 Kelvin generating sub femto-amp of
ac current (10Khz to 1MHz). I have to amplify it to few mVs before
feeding to a DAC.

I think you should start playing with one of these:

http://focus.ti.com/lit/ds/symlink/ddc114.pdf

If you're an optimistic guy, then up to 1KHz bandwith maybe it's
possible.


greetings,
Vasile

Romania
(do you have a map?)