Conventional Single-electron Transistor Research Articles

Single electron transistor based on twisted bilayer graphene quantum dots

Electrical properties of twisted bilayer graphene exhibit angle-dependent characteristics, sparking a thriving development in the field of twistronics. However, the application of quantum dots (QDs) made of twisted bilayer graphene in single-electron transistors (SETs) remains largely unexplored so far. We here investigate the electronic properties of twisted bilayer graphene QDs (TBG QDs) within a SET configuration. We compare the performance of conventional and double-gated SET structures and find that the double-gated configuration provides enhanced control over the electronic properties of TBG QDs. We analyze the influence of rotation angles on the charge stability diagrams and observe that the linear and quadratic gate-island coupling strengths generally decrease as the rotation angle decreases. Furthermore, we quantify the effect of QD size on the charge stability diagrams and find that the size of the diamond-shaped regions decreases as the TBG QD size increases. Results presented herein may help pave the way for realization and application of TBG QDs based SET.

Detecting Air Pollutant Molecules Using Tube-Shaped Single Electron Transistor.

An air pollution detector is proposed based on a tube-shaped single-electron transistor (SET) sensor. By monitoring the flow control component of the detector, each air pollutant molecule can be placed at the center of a SET nanopore and is treated as an island of the SET device in the same framework. Electron transport in the SET was incoherent, and the performances of the SET were sensitive at the single molecule level. Employing first-principles calculations, electronic features of an air pollutant molecule within a tube-shaped SET environment were found to be independent of the molecule rotational orientations with respect to axis of symmetry, unlike the electronic features in a conventional SET environment. Charge stability diagrams of the island molecules were demonstrated to be distinct for each molecule, and thus they can serve as electronic fingerprints for detection. Using the same setup, quantification of the air pollutant can be realized at room temperature as well. The results presented herein may help provide guidance for the identification and quantification of various types of air pollutants at the molecular level by treating the molecule as the island of the SET component in the proposed detector.

High-Precision Displacement Sensing of Monolithic Piezoelectric Disk Resonators Using a Single-Electron Transistor

A single-electron transistor (SET) can be used as an extremely sensitive charge detector. Mechanical displacements can be converted into charge, and hence, SETs can become sensitive detectors of mechanical oscillations. For studying small-energy oscillations, an important approach to realize the mechanical resonators is to use piezoelectric materials. Besides coupling to traditional electric circuitry, the strain-generated piezoelectric charge allows for measuring ultrasmall oscillations via SET detection. Here, we explore the usage of SETs to detect the shear-mode oscillations of a 6-mm-diameter quartz disk resonator with a resonance frequency around 9 MHz. We measure the mechanical oscillations using either a conventional DC SET, or use the SET as a homodyne or heterodyne mixer, or finally, as a radio-frequency single-electron transistor (RF-SET). The RF-SET readout is shown to be the most sensitive method, allowing us to measure mechanical displacement amplitudes below 1E-13 m. We conclude that a detection based on a SET offers a potential to reach the sensitivity at the quantum limit of the mechanical vibrations.

Nano-Scale Silicon Quantum Dot-Based Single-Electron Transistors and Their Application to Design of Analog-to-Digital Convertors at Room Temperature

Room-temperature analog-to-digital converters (ADCs) based on nanoscale silicon (Si) quantum dot (QD)-based single-electron transistors (SETs) can be very attractive for high-speed processors embedded in future generation nanosystems. This paper focuses on the design and modeling of advanced single-electron converters suited for operation at room temperature. In contrast to conventional SETs with metallic QD, the use of sub-10-nm Si QD results in stable operation at room temperature, as the observable Coulomb blockade regime covers effectively the higher temperature range. Si QD-based SETs are also fully compatible with advanced CMOS technology and they can be manufactured using routine nanofabrication steps. At first, we present the principles of operation of Si SETs used for room-temperature operation. Possible flash-type ADC architectures are then investigated and the design considerations of possible Coulomb oscillation regimes are addressed. A modified design procedure is then introduced for [Formula: see text]-bit SET-based ADCs, and validated through simulation of a 3-bit ADC with a sampling frequency of 5 GS/s. The ADC core is comprised from a capacitive signal divider followed by three periodic symmetric functions (PSFs). Simulation results demonstrate the stability of output signals at the room-temperature range.

High-Temperature Coulomb Blockade

The Coulomb blockade effect is studied in a single-electron transistor – quantum dot, separated from source and drain areas by tunnel junctions. Peculiarity of the transistor is that it is made on the basis of semiconducting membrane, separated from the suffer. Separating the transistor from the suffer having high dielectric constant leads to the drastic decrease in the quantum dot capacity С and, therefore, to the increase in the Coulomb gap 2 e C/ . This value is important since it determines the upper limit of the transistor working temperature. A direct comparison of the Coulomb gaps before and after separating from the suffer shows that it increases from 40 K (in temperature units) for conventional transistor to 150 K for the «suspended» one. High value of the Coulomb gap has made it possible to observe clear diamond-like structure of condactance dependence on the gate and source-drain voltages, specific for the Coulomb blockade, while typical temperature of this kind of measurements on conventional single-electron transistors is about hundreds of millikelvins. An additional blockade effect, different from the conventional Coulomb blockade is observed. The nature of this effect can be connected with additional mechanical degrees of freedom of the transistor (elastic deformations).

Ultrasonically driven nanomechanical single-electron shuttle

The single-electron transistor is the fastest and most sensitive electrometer available today. Single-electron pumps and turnstiles are also being explored as part of the global effort to redefine the ampere in terms of the fundamental physical constants. However, the possibility of electrons tunnelling coherently through these devices, a phenomenon known as co-tunnelling, imposes a fundamental limit on device performance. It has been predicted that it should be possible to completely suppress co-tunnelling in mechanical versions of the single-electron transistor, which would allow mechanical devices to outperform conventional single-electron transistors in many applications. However, the mechanical devices developed so far are fundamentally limited by unwanted interactions with the electrical mechanisms that are used to excite the devices. Here we show that it is possible to overcome this problem by using ultrasonic waves rather than electrical currents as the excitation mechanism, which we demonstrate at low temperatures. This is a significant step towards the development of high-performance devices.

Chaotic Dirac Billiard in Graphene Quantum Dots

The exceptional electronic properties of graphene, with its charge carriers mimicking relativistic quantum particles and its formidable potential in various applications, have ensured a rapid growth of interest in this new material. We report on electron transport in quantum dot devices carved entirely from graphene. At large sizes (>100 nanometers), they behave as conventional single-electron transistors, exhibiting periodic Coulomb blockade peaks. For quantum dots smaller than 100 nanometers, the peaks become strongly nonperiodic, indicating a major contribution of quantum confinement. Random peak spacing and its statistics are well described by the theory of chaotic neutrino billiards. Short constrictions of only a few nanometers in width remain conductive and reveal a confinement gap of up to 0.5 electron volt, demonstrating the possibility of molecular-scale electronics based on graphene.

Temperature Dependence of Coulomb Oscillations on DNA-Mediated Au Nanoparticle Assembly

We fabricated a single-electron transistor using DNA-assisted assembly of Au nanoparticles. Most devices exhibited clear Coulomb blockade and oscillations. In contrast to conventional single-electron transistors, however, the period of Coulomb oscillations was observed to depend on the temperature. This temperature dependence is probably ascribed to the temperature dependence of gate capacitance.

Low-frequency charge noise in suspended aluminum single-electron transistors

The authors have developed a fabrication method for suspended metallic single-electron transistors (SETs) utilizing a combination of conventional angle evaporation technique and ashing of the underlying organic polymer. The authors’ Al-based suspended devices exhibit clear Coulomb blockade effects typical for conventional SETs. The measured low-frequency charge noise is rather low but still within the range reported for conventional Al devices. We suggest that the noise level can be further reduced by decreasing the effective SET temperature.

3-D Design and Analysis of Functional NEMS-gate MOSFETs and SETs

Nanoelectromechanical system (NEMS)-gate metal- oxide-semiconductor field effect transistor (MOSFET) and single- electron transistor (SET) structures are investigated by combining 3-D design and SPICE simulation. First, the metal gate is simulated by using a 3-D simulator, which enables to design realistic 3-D device structures, and its movement is studied for different design parameters. It is demonstrated that a low stiffness design of the structure is essential for a low-voltage actuation. Results are compared with theoretical numerical simulation and a tunable capacitor model is then embedded in a SPICE simulator and coupled either with a transistor model for MOS-NEMS or with a newly developed SET analytical model for SET-NEMS. It is shown that the use of NEMS membrane can add new functionalities to conventional MOSFET and SET, such as very abrupt switching of the current, which can break theoretical limits of MOSFET, or modulation of Coulomb oscillations governing SET characteristics

Radio-frequency operation of a double-island single-electron transistor

We present results on a double-island single-electron transistor (DISET) operated at radio frequency (rf) for the fast and highly sensitive detection of charge motion in the solid state. Using an intuitive definition for the charge sensitivity, we compare a DISET to a conventional single-electron transistor (SET). We find that a DISET can be more sensitive than a SET for identical, minimum device resistances in the Coulomb blockade regime. This is of particular importance for rf operation, where ideal impedance matching to 50-Ω transmission lines is only possible for a limited range of device resistances. We report a charge sensitivity of 5.6×10−6e∕Hz for a rf-DISET, together with a demonstration of the single-shot detection of small (⩽0.1e) charge signals on microsecond time scales.

Single-shot measurement of the Josephson charge qubit

We demonstrate single-shot readout of quantum states of the Josephson charge qubit. The quantum bits are transformed into and stored as classical bits (charge quanta) in a dynamic memory cell - a superconducting island. The transformation of state |1> (differing form state |0> by an extra Cooper pair) is a result of a controllable quasiparticle tunneling to the island. The charge is then detected by a conventional single-electron transistor, electrostatically decoupled from the qubit. We study relaxation dynamics in the system and obtain the readout efficiency of 87% and 93% for |1> and |0> states, respectively.

Programmable single-electron transistor logic for future low-power intelligent LSI: proposal and room-temperature operation

This paper proposes, for the first time, the concept of programmable logic circuit realized with single-electron transistors (SETs). An SET having nonvolatile memory function is a key element for the programmable SET logic. The writing and erasing operations of the nonvolatile memory function make it possible to tune the phase of Coulomb oscillations. The half-period phase shift induced by the memory function makes the function of SETs complementary to that of the conventional SETs. As a result, SETs having nonvolatile memory function have the functionality of both the conventional (nMOS-like) SETs and the complementary (pMOS-like) SETs. By utilizing this fact, the function of SET circuits can be programmed with great flexibility, on the basis of the information stored by the memory functions. We have successfully fabricated SETs that operate at room temperature and observed the highest room-temperature peak-to-valley current ratio of Coulomb oscillations. The operation of the programmable SET logic is demonstrated using the room-temperature operating SETs. This is the first demonstration of room-temperature SET logic operation. The proposed programmable SET logic provides the potential for low-power, intelligent LSI chips suitable for mobile applications.

Single-electron transistor made of two crossing multiwalled carbon nanotubes and its noise properties

A three-terminal nanotube device was fabricated from two multiwalled nanotubes by pushing one on top of the other using an atomic-force microscope. The lower nanotube, with gold contacts at both ends, acted as the central island of a single-electron transistor while the upper one functioned as a gate electrode. Coulomb blockade oscillations were observed on the nanotube at sub-Kelvin temperatures. The voltage noise of the nanotube single-electron transistor (SET) was gain dependent as in conventional SETs. The charge sensitivity at 10 Hz was 6×10−4 e/Hz.

Coulomb blockade under conditions of inelastic tunneling

It is found that single-electron current oscillations in the drain-gate characteristics of a single-electron transistor fabricated by the step-edge cutoff process, as compared to a conventional single-electron transistor, are damped several times slower and do not change their phase by π as the source-drain voltage increases. This is explained by the strong nonlinearity of the current-voltage characteristics of tunnel junctions, which is caused by the inelastic character of tunneling.

Charge sensitivity of radio frequency single-electron transistor

A theoretical analysis of the charge sensitivity of the radio frequency single-electron transistor (rf-SET) is presented. We use the “orthodox” approach and consider the case when the carrier frequency is much less than I/e where I is the typical current through rf-SET. The optimized noise-limited sensitivity is determined by the temperature T, and at low T it is only 1.4 times worse than the sensitivity of conventional single-electron transistor.

Single-Electron Transistor in Silicon-on-Insulator with Schottky-Contact Tunnel Barriers

We have proposed a novel single-electron transistor (SET) with Schottky tunnel barriers. The proposed SET can be fabricated by employing the standard salicide process and can be merged in the current CMOS VLSI (complementary metal-oxide-semiconductor-very-large-scale integration). We analyzed its characteristics using the Poisson equation and the master equation based on the semi-classical theory. Calculation results show that the proposed SET has good cutoff characteristics similar to those of conventional MOSFETs (metal-oxide-semiconductor-field-effect transistors) while its gate-periodic characteristics are similar to those of conventional SETs.