V. A. Krupenin

Single-electron transistor with metallic microstrips instead of tunnel junctions

A single-electron transistor (SET) comprising highly resistive Cr thin-film strips (sheet resistance ∼4 kΩ) instead of traditional tunnel barriers is reported. Two such strips (∼1 μm long) connect two Al outer electrodes to an Al island 1 μm in length equipped with a capacitively coupled gate. This transistor with a total asymptotic resistance of 110 kΩ showed a perfect Coulomb blockade and strictly e-periodic reproducible modulation by the gate in wide ranges of bias (V) and gate (Vg) voltages. In the Coulomb-blockade region (|V|⩽ about 0.5 mV), we observed a strong suppression of the transport current, allowing modulation curves V(Vg) with appreciable amplitude to be measured at a fixed bias current value I as low as 100 fA. The background-charge noise of our SET was found to be similar to that of typical Al/AlOx/Al tunnel-junction single-electron transistors, namely δQ≈5×10−4e/Hz at 10 Hz. The electron transport mechanism is discussed.We report on a new type of single-electron transistor (SET) comprising two highly resistive Cr thin-film strips (~ 1um long) connecting a 1 um-long Al island to two Al outer electrodes. These resistors replace small-area oxide tunnel junctions of traditional SETs. Our transistor with a total asymptotic resistance of 110 kOhm showed a very sharp Coulomb blockade and reproducible, deep and strictly e-periodic gate modulation in wide ranges of bias currents I and gate voltages V_g. In the Coulomb blockade region (|V|<0.5 mV), we observed a strong suppression of the cotunneling current allowing appreciable modulation curves V-V_g to be measured at currents I as low as 100 fA. The noise figure of our SET was found to be similar to that of typical Al/AlOx/Al single-electron transistors.

Noise in Al single electron transistors of stacked design

We have fabricated and examined several Al single electron transistors whose small islands were positioned on top of a counterelectrode and hence did not come into contact with a dielectric substrate. The equivalent charge noise figure of all transistors turned out to be surprisingly low, (2.5–7)×10−5e/Hz at f=10 Hz. Although the lowest detected noise originates mostly from fluctuations of background charge, the noise contribution of the tunnel junction conductances was, on occasion, found to be dominant.We have fabricated and examined several Al single electron transistors whose small islands were positioned on top of a counterelectrode and hence did not come into contact with a dielectric substrate. The equivalent charge noise figure of all transistors turned out to be surprisingly low, (2.5–7)×10−5e/Hz at f=10 Hz. Although the lowest detected noise originates mostly from fluctuations of background charge, the noise contribution of the tunnel junction conductances was, on occasion, found to be dominant.

Biosensor based on a silicon nanowire field-effect transistor functionalized by gold nanoparticles for the highly sensitive determination of prostate specific antigen

We have demonstrated label-free and real-time detection of prostate specific antigen (PSA) in human serum using silicon nanowire field effect transistors (NW FETs) with Schottky contacts (Si-Ti). The NW FETs were fabricated from SOI material using high-resolution e-beam lithography, thin film vacuum deposition and reactive-ion etching processes eliminating complicated processes of doping and thermal annealing. This allowed substantial simplifying the transistors manufacturing. A new method for covalent immobilization of half-fragments of antibodies on silicon modified by 3-glycidopropyltrimethoxysilane with thiol groups and 5nm gold nanoparticles (GNPs) was established. NW FETs functionalized by GNPs revealed extremely high pH sensitivity of 70mV/pH and enhanced electrical performance in the detection of antigen due to enhanced surface/volume ratio, favorable orientation of antibody active sites and approaching the source of the electric field close to the transistor surface. Si NWFETs were applied for quantitative detection of PSA in a buffer and human serum diluted 1/100. Response time was about 5-10s, and analysis time per sample was 1min. The limit of PSA detection was of 23fg/mL, concentration range of 23fg/mL-500ng/mL (7 orders of magnitude). The PSA concentrations determined by the NW FETs in serum were compared with well-established ELISA method. The results matched well with the correlation coefficient of 0.97.

Investigation of the offset charge noise in single electron tunneling devices

The offset charge noise in metallic single electron tunneling (SET) devices fabricated on dielectric substrates was experimentally studied. On the basis of stereoscopic measurements of the low-frequency charge noise we show that the substrate makes an essential contribution to the total noise. We have observed that the intensity of the charge noise in SET transistors depends on the biasing dc current but is almost insensitive to temperature variations up to 300 mK. Stability investigations of an SET trap gave storage times of more than 8 h. The performance of such a device is affected by the bias current of a readout electrometer, located nearby, and by background charges.

Aluminium Single Electron Transistors with Islands Isolated from the Substrate

AbstractThe low-frequency noise figures of single-electron transistors(electrometers) of traditional planar and new stacked geometrywere compared. We observed a correlation between the chargenoise and the contact area of the transistor island with adielectric substrate in the set of Al transistors located onthe same chip and having almost similar electric parameters.We have found that the smaller the contact area the lower thenoise level of the transistor. The lowest noise value (δQx=(8±2)×10−6e/

A highly pH-sensitive nanowire field-effect transistor based on silicon on insulator

\sqrt {Hz}

Instability of single-electron memory at low temperatures in Al/AlOx/Al structures

at 10Hz)has been measured in a stacked transistor with an island which wascompletely isolated from a substrate. Our measurements haveunambiguously indicated that the dominant source of thebackground charge fluctuations is associated with a dielectricsubstrate.

Highly Sensitive Electrometers Based on Single Cooper Pair Tunneling

A reliable process has been developed for the fabrication of all-Nb single-electron circuits, based on spin-on glass planarization. The process steps are the in situ growth of Nb/AlOx/Nb sandwich, definition of the patterns of junctions, base electrodes and wiring by use of reactive ion etching and the planarization of a spin-on glass insulation between base electrode and wiring. A single electron transistor made of 0.1 square micrometer area junctions clearly shows the e-periodic Coulomb blockade modulation by a voltage applied to a gate.A reliable process has been developed for the fabrication of all Nb single-electron circuits, based on spin-on glass planarization. The process steps are the in situ growth of Nb/AlOx/Nb sandwich, definition of the patterns of junctions, base electrodes, and wiring by use of reactive ion etching and the planarization of a spin-on glass insulation between base electrode and wiring. A single-electron transistor made of 0.3×0.3 μm2 area junctions clearly shows the e-periodic Coulomb blockade modulation by a voltage applied to a gate.