amplifying a sub femtoamp of current

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

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.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:

SPICE Analysis of Crystal Oscillators: Noise-Rejecting Wideband Sampler:

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:

SPICE Analysis of Crystal Oscillators: Noise-Rejecting Wideband Sampler:

[huge snip]

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:

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:

SPICE Analysis of Crystal Oscillators: Noise-Rejecting Wideband Sampler:

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.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:

SPICE Analysis of Crystal Oscillators: Noise-Rejecting Wideband Sampler:

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

I think you should start playing with one of these:

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

greetings, Vasile

Romania (do you have a map?)