Bloch Oscillating Transistor
Bloch oscillating transistor (BOT) is a novel type of low noise amplifier, the operation of which takes advantage of the band structure of a mesoscopic Josephson junction (JJ) in a resistively isolated environment. It is a charge-charge pulse converter where one single quasiparticle triggers a sequence of Cooper pairs, thus yielding a current gain determined by the conversion efficiency.
In general, the BOT can be considered as a complementary component of the SET, in the same fashion as the BJT (bipolar junction transistor) is complementary to the Field Effect Transistor. In other words, BOTs may replace SQUIDs in current read-out applications at large impedance levels on the order of 1 MΩ.
Typical device parameters for a BOT are: collector resistor of 100 kΩ and small 100x100 nm tunnel junctions giving a total device capacitance of 1-2 fF and charging energy of 1 K. Usually, the Josephson junction is made as a SQUID, giving additional tunability of the cricital current and enabling one to find the optimal operation point.
We have measured the current noise spectral density of the Bloch Oscillating Transistor (BOT) as a function of current gain. We find that the equivalent input noise that shows up in the output is less than the shot noise of the normal-insulating-superconductor tunnel junction At the optimal operating point we find a reduced input current noise of 1.0 fA/√Hz) and a corresponding noise temperature of 0.4 K
The current noise was converted to voltage noise in a 100 kΩ load at the collector. The voltage was then measured by two LI-75A low noise preamplifiers and the outputs fed into an HP 89410A vector signal analyzer and cross-correlated. After cross-correlation, the voltage noise of the amplifiers is practically eliminated and we are left with the BOT output noise, the back-action current noise of the LI-75A + any spurious noise source not accounted for.
Related publications
- Noise properties of the Bloch oscillating transistor
R.K. Lindell and P.J. Hakonen
Appl. Phys. Lett. 86, 173507 (2005)
- Bloch oscillating transistor as the readout element for hot electron bolometers
J. Hassel, H. Seppä, J. Delahaye, and P.J. Hakonen
Proc. of SPIE 5498, 818 (2004)
- Bloch oscillating transistor - a new mesoscopic amplifier
J. Delahaye, J. Hassel, R.K. Lindell, M.A. Sillanpää, M.A. Paalanen, H. Seppä, and P.J. Hakonen
Physica E 18,15 (2003)
- Low-noise current amplifier based on mesoscopic Josephson junction
J. Delahaye, J. Hassel, R.K. Lindell, M.A. Sillanpää, M.A. Paalanen, H. Seppä, and P.J. Hakonen
Science 299, 1045 (2003)