Search

We converted Gaussian-distributed voltage noise applied to an electron reservoir into the non-equilibrium free energy of a nanometer-scale dot connected to the reservoir via an energy barrier. Counting statistics of single-electron motion into and out of the dot through the energy barrier allows us to quantitatively analyze the energy transported into the dot as well as changes in the internal energy and effective temperature of the dot in this noise-induced non-equilibrium steady state (NESS). By analyzing the transition rates of electrons moving into and out of the dot, we confirmed that the rectification effect caused by the asymmetry with respect to the direction of electron motion is the origin of the increase in the internal energy of the dot. The information on energy transport in a nanometer-scale dot in the noise-induced NESS obtained in this study with electron counting statistics clarifies the relationship between the non-equilibrium dynamics of a nanodevice and noise applied to it. This study provides us with the means to evaluate device operation using noise as a resource.

We demonstrate charge detection with single-electron resolution at high readout frequency using a silicon field-effect transistor (FET) integrated with double resonant circuits. A FET, whose channel of 10-nm width enables a single electron to be detected at room temperature, is connected to resonant circuits composed of coupled inductors and capacitors, and these double resonant circuits provide two resonance frequencies. When the FET is driven by a carrier signal at the lower resonance frequency, a small signal applied to the FET's gate modulates the resonance condition, resulting in a reflected signal appearing near the higher resonance frequency. Such operation utilizing the double resonant circuits enables charge detection with a single-electron resolution of 3 × 10−3 e/Hz0.5 and a readout frequency of 200 MHz at room temperature. In addition, a variable capacitor used in the double resonant circuits allows charge-sensing characteristics to be controlled in situ.

We performed electron counting statistics to measure the thermoelectric effect in a nanometer-scale silicon dot. To separate the 100-nm-long dot from a silicon nanowire, we used an electrostatically created 30-nm-long energy barrier. By measuring current through a nearby sensor, we observed the random motion of single electrons between the dot and silicon nanowire. The statistics of single-electron motion provides us with information on temperature and voltage at the dot. Under the detailed balance assumption, we determined the temperature difference and the Seebeck voltage between the dot and silicon nanowire. The validity of our analysis was confirmed by observing the energy-barrier height dependence of the Seebeck coefficient. Furthermore, by counting the electrons leaving the dot, a minute output power on the order of sub-zeptowatt from the dot to the silicon nanowire was estimated.

We propose a method for the observation of the electron-initiated impact ionization process in Si, which is potentially capable of detecting individual impact ionization events. This method detects holes generated by the impact ionization with single charge sensitivity. We demonstrate the method at 8 K by detecting the chain of single holes generated for a constant electron-injection current with the injection-energy threshold close to the Si bandgap energy.We propose a method for the observation of the electron-initiated impact ionization process in Si, which is potentially capable of detecting individual impact ionization events. This method detects holes generated by the impact ionization with single charge sensitivity. We demonstrate the method at 8 K by detecting the chain of single holes generated for a constant electron-injection current with the injection-energy threshold close to the Si bandgap energy.

Si-based single-electron tunneling (SET) devices have of late become an important alternative to the metal-based ones, both for ultralarge scale integration (ULSI) electronics and for electrical metrology. We have very recently been designing, fabricating, and measuring SET turnstiles, pumps, and charge-coupled devices using tunable barriers in silicon. Having shown the potential of these devices, we wish to understand the error mechanisms which may manifest themselves, and to predict the level of these errors, in order to decide how feasible these devices will be. In this paper, we devote a substantial amount of analysis to the consideration of the “dynamical” error mechanism. This particular error considers how electrons split up as the barrier is raised, or alternatively how the Coulomb blockade is formed. We then consider a wide variety of other errors, including thermal, frequency, leakage, and heating errors. We show the dependence of the error rate on each of those mechanisms, and predict maxima or...

We observe a quantized current due to single-electron transfer in a small charge-coupled device, which consists of a narrow Si-wire channel with fine gates; the gate is used to form a tunable barrier potential. By modulating two barrier potentials under the fine gates with phase-shifted pulse voltages, quantized numbers of electrons are injected into and extracted from the charge island sandwiched by the two barriers. Current plateaus due to single-electron transfer are clearly observed at 20 K with frequencies up to 100 MHz and a current level of 16 pA.

We propose a simple method to evaluate the triple quantum dots (TQDs) coupled in series with the compact device structure. Compact coupled quantum dots, each with an attached control gate, offer promising applications as quantum computing and single-electron transfer devices. However, device reduction required in practical applications creates a capacitive cross-talk between a control gate and its neighboring dots making it difficult to determine the charge transition boundaries in each dot. To properly evaluate the electron-transfer characteristics of TQDs, a method is proposed whereby the three gate voltages are simultaneously swept. We studied the charge stability diagram of the compact TQDs using Monte Carlo simulations, and confirmed the effectiveness of the method. Compact Si-TQDs were actually fabricated by the use of pattern-dependent oxidation and additional oxidation method for this study. The method was then applied to the stability diagrams obtained from the devices. The nine measurements of t...

An electromechanical resonator is developed in which the dissipation can be dynamically eliminated. The resultant motional dynamics captured by the Van der Pol equation of motion opens up the possibility of a Hopf bifurcation where the mechanical resonance loses stability when the dissipation is eliminated and period-doubling bifurcations when the dissipation becomes negative. In this latter regime, the mechanical spectral response is characterised by multi-stability spanning a bandwidth that is more than an order of magnitude wider than the intrinsic linewidth and it sustains a peak structure that can be tuned by the input used to dynamically manipulate the dissipation.

High-speed and high-accuracy pumping of a single electron is crucial for realizing an accurate current source, which is a promising candidate for a quantum current standard. Here, using a high-accuracy measurement system traceable to primary standards, we evaluate the accuracy of a Si tunable-barrier single-electron pump driven by a single sinusoidal signal. The pump operates at frequencies up to 6.5 GHz, producing a current of more than 1 nA. At 1 GHz, the current plateau with a level of about 160 pA is found to be accurate to better than 0.92 ppm (parts per million), which is a record value for 1-GHz operation. At 2 GHz, the current plateau offset from 1ef (∼320 pA) by 20 ppm is observed. The current quantization accuracy is improved by applying a magnetic field of 14 T, and we observe a current level of 1ef with an accuracy of a few ppm. The presented gigahertz single-electron pumping with a high accuracy is an important step towards a metrological current standard.

Self-diffusion of ion-implanted 30Si in SiO2 formed directly on Si substrates by thermal oxidation was studied as a function of the temperature and SiO2 thickness (200, 300, and 650 nm). The diffusion coefficient increases by about an order of magnitude with decreasing SiO2 thickness from 650 to 200 nm when silicon–nitride capping layers are placed on top of the SiO2, i.e., the distance between the 30Si diffusers and Si/SiO2 interface has a strong influence. Because the stress on SiO2 by nitride estimated for such a change in diffusivity is unrealistically large, Si species, most likely SiO, generated at the Si/SiO2 interface and diffusing into SiO2 must be affecting the self-diffusion of Si in SiO2.

Self-diffusion coefficients of Si in thermally grown SiO2 on a semiconductor-grade silicon wafer have been determined at temperatures between 1150 and 1300 °C under equilibrium conditions using isotope heterostructures (natSiO2/28SiO2). Si self-diffusion was induced by appropriate heat treatments, and the diffusion depth profiles of 30Si isotope from natSiO2 to 28SiO2 layers were determined by secondary ion mass spectrometry (SIMS). The diffusion coefficients found in the present study for 1150–1300 °C are more than two orders of magnitude smaller than the values measured with semiconductor-grade SiO2 in the presence of excess silicon, i.e., in nonequilibrium conditions, and agree very well with previously reported values of Si self-diffusion in fused silica under equilibrium conditions.

Detection of single electrons and single holes is demonstrated at room temperature in Si nanowire transistors using an electron-hole (e–h) system. Photogenerated carriers are stored in a quantum dot electrically formed in a Si wire by a front gate. The stored charges affect the current of the other type of carriers that flow along the bottom of the Si wire. The linear photoresponce of single-charge generation is observed. It is revealed that the recombination occurs by a bimolecular process, suggesting that it is due to the e–h interband transition. These results open up the possibility of developing single-photon devices with this system.

A multipeak negative-differential-resistance device is proposed. The device comprises a single-electron transistor (SET) and a metal–oxide–semiconductor field-effect transistor (MOSFET), and can, in principle, generate an infinite number of current peaks. Operation of the proposed device is verified at 27 K with a SET fabricated by the pattern-dependent oxidation process and a MOSFET on the same silicon-on-insulator wafer. Six current peaks and a peak-to-valley current ratio of 2.1 are obtained, and multiple-valued memory operation is successfully demonstrated.

We have measured the long-term drift and the short-term 1/f noise in the charge offset Q0(t) in two Si-based single-electron tunneling transistors (SETTs). In contrast to metal-based SETTs, these devices show excellent charge stability, drifting by less than 0.01e over weeks. The short-term 1/f noise magnitude is similar to the metal-based devices, demonstrating that different mechanisms are responsible for the short-term noise versus the long-term drift. Finally, we show that, in addition to the excellent stability over time, it may be possible to make the devices more robust with respect to voltage-induced instability as well.

The two-input exclusive-OR (XOR) function was implemented by a multigate single-electron transistor (SET). Two types of multigate SETs operating at 40 K were fabricated on a top silicon layer of an Si-on-insulator wafer by using a special technique called pattern-dependent oxidation. Two small gate electrodes which act as the input gates were formed over the small SET island. The output current of the devices took a high level when a high voltage was applied to either of the two gates with the other gate grounded, while it took a low level when both gates were grounded or fed with a high voltage. It is striking that such an XOR function can be implemented with just one device.

A triple-dot single-electron transistor was fabricated on silicon-on-insulator wafer using pattern-dependent oxidation. A specially designed one-dimensional silicon wire having small constrictions at both ends was converted to a triple-dot single-electron transistor by means of pattern-dependent oxidation. The fabrication of the center dot involved quantum size effects and stress-induced band gap reduction, whereas that of the two side dots involved thickness modulation because of the complex edge structure of two-dimensional silicon. Single-electron turnstile operation was confirmed at 8 K when a 100-mV, 1-MHz square wave was applied. Monte Carlo simulations indicated that such a device with inhomogeneous tunnel and gate capacitances can exhibit single-electron transfer.

We perform feedback (FB) control for suppressing thermal fluctuation in the number of electrons in a silicon single-electron (SE) device composed of a small transistor and capacitor. SEs enter and leave the capacitor via the transistor randomly at thermal equilibrium, which is monitored in real time using a high-charge-sensitivity detector. In order to suppress such random motion or thermal fluctuation of the electrons, SEs are injected and removed using the transistor according to the monitored change in the number of electrons in the capacitor, which is exactly the FB control. As a result, thermal fluctuation in the number of electrons in a SE device is suppressed by 60%, which corresponds to the so-called FB cooling from 300 to 110 K. Moreover, a thermodynamics analysis of this FB cooling reveals that entropy in the capacitor is reduced and the device is at non-equilibrium; i.e., the free energy of the device increases. Since this entropy reduction originates from information about the electrons' motion monitored by the detector, our results by the FB control represent one type of information-to-energy conversion.

We demonstrate a tunnel diode composed of a vertical MoS2/SiO2/Si heterostructure. A MoS2 flake consisting four areas of different thicknesses functions as a gate terminal of a silicon field-effect transistor. A thin gate oxide allows tunneling current to flow between the n-type MoS2 layers and p-type Si channel. The tunneling-current characteristics show multiple negative differential resistance features, which we interpret as an indication of different conduction-band alignments of the MoS2 layers of different thicknesses. The presented tunnel device can be also used as a hybrid-heterostructure device combining the advantages of two-dimensional materials with those of silicon transistors.

The electrical activation of arsenic (As) implanted in Si is investigated with electron spin resonance (ESR), spreading resistance (SR), and secondary ion mass spectroscopy (SIMS). The As ions were implanted with a dose of 1 × 1012 cm−2 and subsequently annealed at various temperatures in the range of 500–1100 °C. The ESR measurements at 10 K show that the density of the As donor electrons for all the annealing temperatures is less than 10% of the As atom concentration measured by SIMS. The SR data indicate that the density of conduction band electrons is several times larger than that of the As donor electrons. These results strongly suggest that most of the As donor electrons are ESR inactive at low temperatures.

Tunability of capacitive coupling in the Si double-quantum-dot system is discussed by changing the number of electrons in quantum dots (QDs), in which the QDs are fabricated using pattern-dependent oxidation (PADOX) of a Si nanowire and multi-fine-gate structure. A single QD formed by PADOX is divided into multiple QDs by additional oxidation through the gap between the fine gates. When the number of electrons occupying the QDs is large, the coupling capacitance increases gradually and almost monotonically with the number of electrons. This phenomenon is attributed to the gradual growth in the effective QD size due to the increase in the number of electrons in the QDs. On the other hand, when the number of electrons changes in the few-electron regime, the coupling capacitance irregularly changes. This irregularity can be observed even up to 40 electrons. This behavior is attributable the rough structure of Si nano-dots made by PADOX. This roughness is thought to induce complicated change in the electron wave function when an electron is added to or subtracted from a QD.

We report high-speed single-hole (SH) transfer using Si tunable-barrier pumps comprising p-type metal-oxide-semiconductor field-effect transistors. A clear SH-transfer-current plateau with the current level of about 160 pA was observed when a clock signal having a frequency of 1 GHz was applied to one of the gates. Temperature dependence measurements of the transfer current reveal that the transfer probability is dominated by non-equilibrium SH escape by thermal hopping from the electrically formed charge island. The lower bound of the relative error rate for the 1-GHz transfer is about 10−3 at a temperature of about 17 K. In addition, we investigate the frequency dependence of the transfer, where we discuss possible sources causing the change in the error rate. These results pave the way for accurate manipulation of SHs and its application to metrological current standards.

Photocurrent polarization properties near the band gap of long‐range ordered Ga0.5In0.5P have been investigated. The linearly polarized PC spectra of the ordered Ga0.5In0.5P show an absorption anisotropy for the [110] and [110] directions together with a large band‐gap reduction. The anistotropy in the PC spectra is due to a crystal‐field splitting at the valence‐band maximum in ordered Ga0.5In0.5P. The PC edge of the [110] polarization is lower at about 10 meV than one of the [110]. The polarization spectra defined by (I110−I110)/(I110+I110), where I110 and I110 are the PC signal intensities measured at the [110] and [110], respectively, show a single broad peak. The maximum polarization reaches about 50% at the energy of the transition between Γ6c and Γ4v, Γ5v. With increased sample temperature, the polarization maximum shifts to the lower energy side according to the change of the Γ6c‐Γ4v,Γ5v transition energy. Even at room temperature, a clear polarization signal was observed.

Spectral blue shift of excitonic transition due to quantum confinement in Si0.84Ge0.16/Si strained‐layer quantum wells, grown by gas‐source Si molecular beam epitaxy, is reported. Intense photoluminescence was observed at elevated temperatures though reduced in intensity due to the thermalization of holes to the Si barriers.

We report the fabrication of lateral gate-all-around InAs nanowire field-effect transistors whose gate overlaps the source and drain electrodes and thus fully encapsulates the nanowire channel. They feature large drive current and transconductance that surpass those of conventional non-gate-overlap devices. The improved device characteristics can be attributed to the elimination of access resistance associated with ungated segments between the gate and source/drain electrodes. Our data also reveal a correlation between the normalized transconductance and the threshold voltage, which points to a beneficial effect of our wet-etching procedure performed prior to the atomic-layer-deposition of the gate dielectric.

Parametric coupling between multiple vibration modes in an electromechanical resonator is demonstrated via a strain inducing piezoelectric pump which enables construction of a mechanical-vibration register. In particular, the coupling between the flexural and torsional vibration modes can exceed their intrinsic dissipation rates enabling operation deep into the strong-coupling regime. The dynamic nature of this parametric coupling also permits temporal manipulation of the mechanical-vibration register enabling both long-lived modes to be rapidly switched off and phonon populations to be coherently exchanged between modes.

We examine the electron mobility and hole mobility at the Si/buried oxide (BOX) interface at which the valley splitting of the electron system is strongly enhanced, and compare the values observed to those at a standard Si/thermal oxide (T-SiO2) interface in the same silicon-on-insulator device. In contrast to the electron mobility, which is lower at the Si/BOX interface, the hole mobility at the Si/BOX interface is found to be slightly higher than that at the Si/T-SiO2 interface.

We demonstrate stochastic resonance (SR), which takes advantage of noise to detect a weak signal, using a field-effect transistor (FET). An FET's structure composed of a nanowire channel enables current characteristics to show strong nonlinearity, which overcomes thermal limitation, and dynamic bistability, both of which boost an effect of SR and silhouette noise from noise. Moreover, the dynamic bistability enables SR effect to be enhanced by adding common noise to multiple FETs. The FET providing such unique characteristics opens the way to use SR for practical applications.

An array of equally spaced oscillations or a comb is created within the bandwidth of the fundamental mode of an electromechanical resonator. This phenomenon utilises 2 continuous-wave (CW) pump excitations that piezoelectrically modulate the tension in the mechanical element and is seeded by a CW harmonic excitation of the first mode i.e., the signal. The resultant comb can be dynamically manipulated via the pumps and signal where the teeth separation can be tuned over 3 orders of magnitude and the comb density can be increased from just 2 teeth to nearly 102.

Low-temperature carrier transport is investigated for indium-doped p-channel transistors and compared with that for boron-doped ones. It is shown that, with a doping concentration of 3 × 1017 cm−3, while hopping conduction via acceptor sites predominates in boron-doped transistors, indium-doped ones exhibit strong carrier localization at 30 K. For temperatures between 100 and 285 K, the transport in indium-doped transistors is dominated by thermally activated valence-band conduction, and its activation energy coincides with the indium ionization energy.

We report on evaluation of transfer accuracy in a single-electron turnstile using silicon nanowire metal-oxide-semiconductor field-effect transistors at 17 K. Single-electron shuttle transfer and single-shot detection of a single electron are used to detect errors of the transfer. Errors for the transfer through an electrostatically formed island are ascribed to thermal processes. We also observed single-electron transfer mediated by a trap level, which exhibits a wide current plateau and a low error rate.

We report a strong Stark effect in electroluminescence (EL) from thin silicon-on-insulator metal-oxide-semiconductor field-effect transistors. The EL peak shows a large Stark shift of up to 50 meV when a gate-induced electric field is applied. Such a large shift is observed because of the strong confinement of carriers by a Si/SiO2 quantum well. Furthermore, we observe a sudden decrease of EL intensity at a specific electric field. This feature is ascribed to electron dissociation from phosphorous atom to subbands in a triangular well at the Si/SiO2 interface by the applied electric field.

A nanofield-effect transistor (nano-FET) is coupled to a massive piezoelectricity based electromechanical resonator integrated with a parametric amplifier. The mechanical parametric amplifier can enhance the resonator’s displacement and the resulting electrical signal is further amplified by the nano-FET. This hybrid amplification scheme yields an increase in the mechanical displacement signal by 70 dB resulting in a force sensitivity of 200 aN Hz−1/2 at 3 K. The mechanical parametric amplifier can also squeeze the displacement noise in one oscillation phase by 5 dB enabling a factor of 4 reduction in the thermomechanical noise force level.

We report the tunneling spectroscopy of thin silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors with tunneling gate oxide. When electrons are injected into a thin SOI well, the gate-tunneling current shows kink structures originating from quantized energy levels in the SOI well. From the theoretical consideration of the energy levels and their density of states, the observed features can be ascribed to electron tunneling into the in-plane fourfold degenerate valley subbands. Furthermore, inhomogeneous peak broadening of the kink structures in the experiment is well explained by the SOI thickness variation.

An electromechanical oscillator embedded with a two dimensional electron gas is capacitively coupled to a silicon field effect transistor (Si-FET). The piezovoltage induced by the mechanical motion modulates the current passing through the Si-FET enabling the electromechanical oscillator’s position to be monitored. When the Si-FET is biased at its optimal point, the motion induced piezovoltage can be amplified resulting in a displacement sensitivity of 6×10−12 mHz−1/2 for a 131 kHz GaAs resonator which is among the highest recorded for an all-electrical room temperature detection scheme.

The authors performed conductance measurements to identify the horizontal position of single boron acceptors in silicon-on-insulator nanoscale field-effect transistors at a temperature of 6 K. The horizontal position, i.e., how far the acceptor is from the source or drain terminal, is qualitatively obtained, and it is shown, on the level of single dopants, that the acceptor near the source significantly affects the subthreshold nature of the transistor.

We observe a lifting of the twofold spin degeneracy of conduction-band electrons in an upper-valley subband with in-plane magnetic field in a SiO2/Si(100)/SiO2 quantum well, which is manifest in a splitting of a feature in the conductivity accompanying the occupation of the upper-valley subband. The splitting increases in proportion to the in-plane magnetic field, allowing the product of the effective g-factor and effective mass g∗m∗ to be obtained. The value remains constant over wide ranges of valley splitting, total electron density, and potential bias.

We demonstrate low temperature operation of an electron-hole bilayer device based on a 40 nm thick layer of silicon in which electrons and holes can be simultaneously induced and contacted independently. The device allows the application of bias between the electrons and holes enhancing controllability over density and confining potential. We confirm that drag measurements are possible with the structure.

Transport dynamics of a few electrons in a quantum dot are investigated in a single-electron ratchet using silicon nanowire metal-oxide-semiconductor field-effect transistors. Time-resolved measurements in a nanosecond regime are carried out to determine the escape times of the first, second, and third electrons from the quantum dot originally containing three electrons. The escape time strongly depends on the number of electrons due to the single-electron charging effect in the quantum dot, which makes it possible to achieve selective ejection of a desired number of electrons.

A common observation in metal-based (specifically, those with AlOx tunnel junctions) single-electron tunneling (SET) devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is to understand the difference between these, and ultimately to overcome the drift in the metal-based devices. A comprehensive set of measurements shows that (1) brief measurements over short periods of time can mask the underlying drift, (2) we have not found any reproducible technique to eliminate the drift, and (3) two-level fluctuators (TLFs) in the metal-based devices are not stable. In contrast, in the Si-based devices the charge offset drifts by less than 0.01e over many days, and the TLFs are stable. We also show charge noise measurements in a SET device over four decades of temperature. We present a model for the charge offset drift based on the observation of nonequilibrium heat evolution in glassy materials, and obtain a numerical estimate in go...

Recent progress of semiconductor technologies requires deep understanding on the device physics in the nanometer scale. Several pioneering researchers studied the nanometer-scale Si structures by the first-principles calculation method and succeeded to predict its significant reduction in the dielectric constant for the structure smaller than 3 nm. Those studies however could not discuss deeper device physics of the field effect transistors (FET) when the structure is used for the FET channel, because their method cannot calculate the charged up structures under the external electric field. We have thus developed a new first-principles method so called the EFED method. Based on this method, we discuss the inversion layer properties of a simple Si nanostructure as the first step.

A circuit utilizing single electrons is demonstrated at room temperature using a silicon-on-insulator metal-oxide-semiconductor field-effect transistor (MOSFET). Individual electrons randomly passing through the nanoscale MOSFET, which are the origin of shot noise, are monitored by an electrometer in real time. This random behavior of single electrons is used as a random number for a stochastic associative memory for image-pattern matching, in which the most preferable pattern is extracted with the largest probability. The use of electron transport in the MOSFET provides high controllability of the randomness as well as fast generation of random numbers. The present result promises single-electron applications using nanoscale MOSFETs.

Nanoampere single-electron pumping is presented at 20K using a single-electron ratchet comprising silicon nanowire metal-oxide-semiconductor field-effect transistors. The ratchet features an asymmetric potential with a pocket that captures single electrons from the source and ejects them to the drain. Directional single-electron transfer is achieved by applying one ac signal with the frequency up to 2.3GHz. We find anomalous shapes of current steps which can be ascribed to nonadiabatic electron capture.

We performed dopant mediated hole transport measurements to identify the depth position of individual boron acceptors and investigate two-acceptor coupling in silicon-on-insulator nanoscale field-effect transistors at a temperature of 6K. The depth position is qualitatively obtained from the analysis of the acceptor-to-gate capacitances. We also observe signatures of a two-acceptor capacitive coupling in the characteristics of the conductance versus the front and back gate voltages.

The authors fabricated nanoscale silicon metal-oxide-semiconductor field-effect transistors (MOSFETs) to detect an infrared (IR) signal at room temperature. The IR signal excites conduction-band electrons in an undoped channel of a MOSFET and some of them are injected through an energy barrier into a storage node (SN) electrically formed by the MOSFET. Small signals, originating from electrons, stored in the SN are detected by an electrometer with a single-electron resolution. Additionally, the MOSFET controls the number and energy of electrons injected into the SN. This enables electrical control of the sensitivity and cutoff wavelengths of IR signals, suggesting the possibility of highly functional IR sensors.

The problem of charge offset drift in single-electron tunneling (SET) devices can preclude their useful application in metrology and integrated devices. We demonstrate that in tunable-barrier Si-based SET transistors there is excellent stability, with a drift that is in general less than 0.01e; these devices exhibit some unwanted sensitivity to external perturbations including temperature excursions. Finally, we show that these devices can be “trained” to minimize their sensitivity to abrupt voltage changes.

Using a device resembling a nano-charge-coupled-device and measuring the Coulomb blockade, we show how the Coulomb blockade degrades with increasing barrier conductance. To explain this behavior, we identify a new parameter, the “barrier capacitance.” This parameter can be used to elucidate information about the energy barrier under a gate with a size of a few tens of nanometers.

A single-electron-based circuit, in which electrons are transferred one by one with a turnstile and subsequently detected with a high-charge-sensitivity electrometer, was fabricated on a silicon-on-insulator substrate. The turnstile, which is operated by opening and closing two metal-oxide-semiconductor field-effect transistors alternately, allows single-electron transfer at room temperature owing to electric-field-assisted shrinkage of the single-electron box. It also achieves fast single-electron transfer (less than 10ns) and extremely long retention (more than 104s). We have applied these features to a multilevel memory and a time-division weighted sum circuit for a digital-to-analog converter.

We have achieved the operation of single-electron tunneling (SET) transistors with gate-induced electrostatic barriers using silicon nanowire metal-oxide-semiconductor field-effect transistor (MOSFET) structures. The conductance of tunnel barriers is tunable by more than three orders of magnitude. By using the flexible control of the tunable barriers, the systematic evolution from a single charge island to double islands was clearly observed. We obtained excellent reproducibility in the gate capacitances: values on the order of 10 aF, with the variation smaller than 1 aF. This flexibility and controllability both demonstrate that the device is highly designable to build a variety of SET devices based on complementary metal-oxide-semiconductor technology.

The ultimate goal of future information processing might be the realization of a circuit in which one bit is represented by a single electron. Such a challenging circuit would comprise elemental devices whose tasks are to drag, transfer, and detect single electrons. In achieving these tasks, the Coulomb blockade, which occurs in tiny conducting materials, plays an important role. This paper describes the current status of research on such single-charge-control devices from the viewpoints of circuit applications.