Silicon Electronics Research Articles

High Sensitivity Hybrid PbS CQD-TMDC Photodetectors up to 2 μm

Recent approaches to develop infrared photodetectors characterized by high sensitivities, broadband spectral coverage, easy integration with silicon electronics and low cost have been based on hybrid structures of transition metal dichalcogenides (TMDCs) and PbS colloidal quantum dots (CQDs). However, to date, such photodetectors have been reported with high sensitivity up to 1.5 $\mu$m. Here we extend the spectral coverage of this technology towards 2 $\mu$m demonstrating for the first time compelling performance with responsivities 1400 A/W at 1.8 $\mu$m with 1V bias and detectivities as high as $10^{12}$ Jones at room temperature. To do this we studied two TMDC materials as a carrier transport layer, tungsten disulfide (WS$_2$) and molybdenum disulfide (MoS$_2$) and demonstrate that WS$_2$ based hybrid photodetectors outperform those of MoS$_2$ due to a more adequate band alignment that favors carrier transfer from the CQDs.

Chemically Tuned p- and n-Type WSe2 Monolayers with High Carrier Mobility for Advanced Electronics.

Monolayers of transition metal dichalcogenides (TMDCs) have attracted a great interest for post-silicon electronics and photonics due to their high carrier mobility, tunable bandgap, and atom-thick 2D structure. With the analogy to conventional silicon electronics, establishing a method to convert TMDC to p- and n-type semiconductors is essential for various device applications, such as complementary metal-oxide-semiconductor (CMOS) circuits and photovoltaics. Here, a successful control of the electrical polarity of monolayer WSe2 is demonstrated by chemical doping. Two different molecules, 4-nitrobenzenediazonium tetrafluoroborate and diethylenetriamine, are utilized to convert ambipolar WSe2 field-effect transistors (FETs) to p- and n-type, respectively. Moreover, the chemically doped WSe2 show increased effective carrier mobilities of 82 and 25 cm2 V-1 s-1 for holes and electrons, respectively, which are much higher than those of the pristine WSe2 . The doping effects are studied by photoluminescence, Raman, X-ray photoelectron spectroscopy, and density functional theory. Chemically tuned WSe2 FETs are integrated into CMOS inverters, exhibiting extremely low power consumption (≈0.17 nW). Furthermore, a p-n junction within single WSe2 grain is realized via spatially controlled chemical doping. The chemical doping method for controlling the transport properties of WSe2 will contribute to the development of TMDC-based advanced electronics.

Metal-Single-Molecule-Semiconductor Junctions Formed by a Radical Reaction Bridging Gold and Silicon Electrodes.

Here we report molecular films terminated with diazonium salts moieties at both ends which enables single-molecule contacts between gold and silicon electrodes at open circuit via a radical reaction. We show that the kinetics of film grafting is crystal-facet dependent, being more favorable on ⟨111⟩ than on ⟨100⟩, a finding that adds control over surface chemistry during the device fabrication. The impact of this spontaneous chemistry in single-molecule electronics is demonstrated using STM-break junction approaches by forming metal-single-molecule-semiconductor junctions between silicon and gold source and drain, electrodes. Au-C and Si-C molecule-electrode contacts result in single-molecule wires that are mechanically stable, with an average lifetime at room temperature of 1.1 s, which is 30-400% higher than that reported for conventional molecular junctions formed between gold electrodes using thiol and amine contact groups. The high stability enabled measuring current-voltage properties during the lifetime of the molecular junction. We show that current rectification, which is intrinsic to metal-semiconductor junctions, can be controlled when a single-molecule bridges the gap in the junction. The system changes from being a current rectifier in the absence of a molecular bridge to an ohmic contact when a single molecule is covalently bonded to both silicon and gold electrodes. This study paves the way for the merging of the fields of single-molecule and silicon electronics.

A wireless body area sensor network based on stretchable passive tags

A body area sensor network (bodyNET) is a collection of networked sensors that can be used to monitor human physiological signals. For its application in next-generation personalized healthcare systems, seamless hybridization of stretchable on-skin sensors and rigid silicon readout circuits is required. Here, we report a bodyNET composed of chip-free and battery-free stretchable on-skin sensor tags that are wirelessly linked to flexible readout circuits attached to textiles. Our design offers a conformal skin-mimicking interface by removing all direct contacts between rigid components and the human body. Therefore, this design addresses the mechanical incompatibility issue between soft on-skin devices and rigid high-performance silicon electronics. Additionally, we introduce an unconventional radiofrequency identification technology where wireless sensors are deliberately detuned to increase the tolerance of strain-induced changes in electronic properties. Finally, we show that our soft bodyNET system can be used to simultaneously and continuously analyse a person’s pulse, breath and body movement. By integrating wireless stretchable on-skin sensor tags and flexible readout circuits attached to textiles using an unconventional radiofrequency identification design, a body area sensor network can be created that can continuously analyse a person’s pulse, breathing and body movement.

Radiation Defects Created in n‐Type 4H‐SiC by Electron Irradiation in the Energy Range of 1–10 MeV

Radiation damage produced in 4H‐SiC n‐epilayers by electrons of different energies is presented. Junction barrier Schottky power SiC diodes are irradiated with 1.05, 2.1, 5, and 10 MeV electrons with doses up to 600 kGy. Radiation defects are characterized by capacitance deep‐level transient spectroscopy and capacitance‐to‐voltage (C–V) measurement. Results, which are compared with previous data obtained on 4.5 MeV electrons, show that the damage structure is very similar for all irradiation energies. Dominating is the generation of simple, thermally unstable defects evidenced by the presence of acceptor levels located at 0.25, 0.38, 0.60, and 0.72 eV below the 4H‐SiC conduction band edge. With increasing energy of electrons, the number of simple defects saturates, and the production of more complex, cluster‐related defects grow. Majority of introduced defects are acceptor centers, which compensate n‐type (nitrogen) doping of the epilayer. The carrier removal rate increases with electron energy and follows well the classical nonionization energy loss (NIEL) scaling for electrons in silicon. The stability of introduced defects and their effect on carrier lifetime reduction are discussed, as well.

A two-qubit gate between phosphorus donor electrons in silicon.

Electron spin qubits formed by atoms in silicon have large (tens of millielectronvolts) orbital energies and weak spin-orbit coupling, giving rise to isolated electron spin ground states with coherence times of seconds1,2. High-fidelity (more than 99.9 per cent) coherent control of such qubits has been demonstrated3, promising an attractive platform for quantum computing. However, inter-qubit coupling-which is essential for realizing large-scale circuits in atom-based qubits-has not yet been achieved. Exchange interactions between electron spins4,5 promise fast (gigahertz) gate operations with two-qubit gates, as recently demonstrated in gate-defined silicon quantum dots6-10. However, creating a tunable exchange interaction between two electrons bound to phosphorus atom qubits has not been possible until now. This is because it is difficult to determine the atomic distance required to turn the exchange interaction on and off while aligning the atomic circuitry for high-fidelity, independent spin readout. Here we report a fast (about 800 picoseconds) [Formula: see text] two-qubit exchange gate between phosphorus donor electron spin qubits in silicon using independent single-shot spin readout with a readoutfidelity of about 94 per cent on a complete set of basis states. By engineering qubit placement on the atomic scale, we provide a route to the realization and efficient characterization of multi-qubit quantum circuits based on donor qubits in silicon.

Ultrafast relaxation dynamics of highly excited hot electrons in silicon

This combined experimental and theoretical investigation reveals that the relaxation of electrons at high excess energy in the conduction band of silicon takes place as two distinctive processes with different time scales, an ultrafast momentum quasiequilibration over the Brillouin zone within 10 fs and a slower energy relaxation of the hot-electron ensembles. The energy relaxation rate is proportional to the electronic density of states over a large range of excess energies. The work generalizes the concept of hot-electron ensembles in semiconductors.

(Invited) Nanostructures and Crystal Defects in Thick GaN and SiC Epitaxial Layers for Power Electronic Switches

The state-of-the-art power switching devices made from SiC and GaN semiconductors contain a high density of crystal defects. Most of these defects are present in starting wafers and some are generated during device processing. There is little conclusive evidence so far on the exact role that the crystal defects paly on device performance, manufacturing yield, and more importantly, long-term field-reliability especially when devices are operating under extreme stressful environments. This paper provides a review of the current state-of-the-art of SiC and GaN power semiconductor material technology, and the potential impact crystal defects may have on high-density power switching electronics. A review of silicon technology development and manufacturing evolution is made to draw a parallel between silicon and wide bandgap (WBG) semiconductor power electronics.

Calculations reveal new insights into heat diffusion in silicon

Monte Carlo calculations based on empirical and ab initio methods show that acoustic phonons, not optical phonons as assumed, receive the majority of energy transferred from hot electrons in silicon.

Boosted Spin Channel Networks for Energy-Efficient Inference

Computational scaling beyond silicon electronics based on Moore’s law requires the adoption of alternate state variables such as electronic spin. Multiple research efforts are underway exploring both Boolean and non-Boolean design space using spin devices in order to make their energy and delay benefits competitive to CMOS. In this paper, we propose spin channel networks (SCN), where the exponential decay property of spin current along the spin channel is exploited to achieve energy-efficient dot product implementation for inference applications. As the use of exponentially decaying spin current for analog computation enforces severe locality constraints, we employ adaptive boosting to design an ensemble of tiny SCNs that work in unison to solve any binary classification task. Such boosted SCNs achieve up to $112\times $ and $14\times $ higher energy efficiency over conventional all-spin-logic-based and 20-nm CMOS designs, respectively.

Spin-orbit Interactions for Singlet-Triplet Qubits in Silicon.

Spin-orbit coupling is relatively weak for electrons in bulk silicon, but enhanced interactions are reported in nanostructures such as the quantum dots used for spin qubits. These interactions have been attributed to various dissimilar interface effects, including disorder or broken crystal symmetries. In this Letter, we use a double-quantum-dot qubit to probe these interactions by comparing the spins of separated singlet-triplet electron pairs. We observe both intravalley and intervalley mechanisms, each dominant for [110] and [100] magnetic field orientations, respectively, that are consistent with a broken crystal symmetry model. We also observe a third spin-flip mechanism caused by tunneling between the quantum dots. This improved understanding is important for qubit uniformity, spin control and decoherence, and two-qubit gates.

(Invited) Self-Powered Wearable and Implantable Electrical> Stimulation Devices for Medical Treatments

Electrical stimulation (ES) is a widely used therapeutic treatment strategy. It showed significantly positive results in treating a variety of diseases, biological disorders, and neurological problems. Today, the emergence of wearable devices is rapidly reshaping the development of medical devices, pushing them from conventional bulky and rigid silicon electronics to flexible and primarily polymer-based systems. Among many types of functions, nanogenerators are developed as a unique device for converting biomechanical energy into electrical pulses. Besides using it directly as a power source, this pulsed electricity can be applied directly as a ES signal for therapeutic treatment. In our recent research, we successfully implemented such an electromechanical system for skin wound healing and vagus nerve stimulation for obesity control. An electrical stimulation bandage was developed by integrating a flexible nanogenerator and a pair of dressing electrodes on a flexible substrate. Rat studies demonstrated rapid closure of a full-thickness rectangular skin wound within 3 days as compared to 12 days of usual contraction-based healing processes in rodents. From in vitro studies, the accelerated skin wound healing was attributed to the electric field-facilitated fibroblast migration, proliferation and transdifferentiation. In another work, an implanted vagus nerve stimulation system was developed. The device comprises a flexible and biocompatible nanogenerator that is attached on the surface of stomach. It generates biphasic electric pulses in responsive to the peristalsis of stomach. The electric signals generated by this device stimulates the vagal afferent fibers to reduce food intake and achieve weight control. This strategy is successfully demonstrated on rat models. Within 100 days, the average body weight is controlled at 350 g, 38% less than the control groups. Both results bring a new concept in electrical therapeutic technology that is battery-free, self-activated and directly responsive to body activities.

Recent Trends and Advances of Silicon-Based Integrated Microwave Photonics

Multitude applications of photonic devices and technologies for the generation and manipulation of arbitrary and random microwave waveforms, at unprecedented processing speeds, have been proposed in the literature over the past three decades. This class of photonic applications for microwave engineering is known as microwave photonics (MWP). The vast capabilities of MWP have allowed the realization of key functionalities which are either highly complex or simply not possible in the microwave domain alone. Recently, this growing field has adopted the integrated photonics technologies to develop microwave photonic systems with enhanced robustness as well as with a significant reduction of size, cost, weight, and power consumption. In particular, silicon photonics technology is of great interest for this aim as it offers outstanding possibilities for integration of highly-complex active and passive photonic devices, permitting monolithic integration of MWP with high-speed silicon electronics. In this article, we present a review of recent work on MWP functions developed on the silicon platform. We particularly focus on newly reported designs for signal modulation, arbitrary waveform generation, filtering, true-time delay, phase shifting, beam steering, and frequency measurement.

Mechanisms of Electron-Induced Single-Event Latchup

In this paper, possible mechanisms by which electrons can induce single-event latchups in electronics are discussed. The energy deposition and the nuclear fragments created by electrons in silicon are analyzed in this context. The cross section enhancement effect in the presence of high-Z materials is discussed. First experimental results of electron-induced latchups are shown in static random access memory devices with low linear energy transfer thresholds. The radiation hardness assurance implications and future work are discussed.

Spin\u2013orbit coupling in silicon for electrons bound to donors

Spin–orbit coupling (SOC) is fundamental to a wide range of phenomena in condensed matter, spanning from a renormalisation of the free-electron g-factor, to the formation of topological insulators, and Majorana Fermions. SOC has also profound implications in spin-based quantum information, where it is known to limit spin lifetimes (T1) in the inversion asymmetric semiconductors such as GaAs. However, for electrons in silicon—and in particular those bound to phosphorus donor qubits—SOC is usually regarded weak, allowing for spin lifetimes of minutes in the bulk. Surprisingly, however, in a nanoelectronic device donor spin lifetimes have only reached values of seconds. Here, we reconcile this difference by demonstrating that electric field induced SOC can dominate spin relaxation of donor-bound electrons. Eliminating this lifetime-limiting effect by careful alignment of an external vector magnetic field in an atomically engineered device, allows us to reach the bulk-limit of spin-relaxation times. Given the unexpected strength of SOC in the technologically relevant silicon platform, we anticipate that our results will stimulate future theoretical and experimental investigation of phenomena that rely on strong magnetoelectric coupling of atomically confined spins.

Двумерная система сильновзаимодействующих электронов в кремниевых (100) структурах

Двумерная система сильновзаимодействующих электронов в кремниевых (100) структурах

Silicon Ablation by Single Ultrashort Laser Pulses of Variable Width in Air and Water

The ablation of silicon by single laser pulses of variable width (0.3–9.5 ps) with a wavelength of 515 nm has been comparatively studied in air and water. A nonmonotonic behavior of ablation thresholds with a minimum at 1.6 ps, which is due to achieving the thermalization time of the electron and ion subsystems in silicon, has been revealed. It has been shown that, with an increase in the pulse width in the considered width range, the efficiency of the ablation of silicon decreases by a factor of 2.5 in air and increases by a factor of 2 in water. This behavior of ablation in air is attributed to a partial transition from phase explosion to surface evaporation, which is suppressed in water.

Design and Test of Irradiation-Related Components in ITER Radial X-Ray Camera

International Thermonuclear Experimental Reactor radial X-ray camera is designed to measure the poloidal profile of the plasma X-ray emission with high spatial and temporal resolutions and will be installed inside equatorial port 12. Due to the harsh environment of neutron and gamma radiations, nuclear radiation hardness of many components has to be considered in design and test, including silicon detector array, electronics, and cabling. As for electronics put in a port cell, a preliminary design of highly integrated preamplifier and program controllable mid-amplifier has been completed, and many tests have been done to investigate the radiation hardness performance of the amplifiers together with detectors. In the Cf-252 neutron test with flux of $\sim 2.23\times 10^{3}\,\,\text {n}\cdot \text {cm}^{-2}\cdot \text {s}^{-1}$ and fluence greater than $1.0\times 10^{10}\,\,\text {n}\cdot \text {cm}^{-2}$ , there was no performance degradation in detector and preamplifier. In the Co-60 gamma test with a dose rate of $0.5\,\,\text {Gy}\cdot \text {min}^{-1}$ and an accumulated dose of 200 Gy, the performance change was not found in preamplifier and mid-amplifier except for some radiation damage to the power module in the board of preamplifier. In the following accelerator neutron test where the neutron flux is $\sim 5\times 10^{7}\,\,\text {n}\cdot \text {cm}^{-2}\cdot \text {s}^{-1}$ and neutron fluence is $2\times 10^{12}\,\,\text {n}\cdot \text {cm}^{-2}$ , the functional problem was not found in preamplifier and cable, while there were occurrences of single-event effect in mid-amplifier. The detector underwent 10% decrease of sensitivity to visible light. In addition, shielding cabinet was designed to provide good protection for electronics inside.

SENSEI: First Direct-Detection Constraints on Sub-GeV Dark Matter from a Surface Run.

The Sub-Electron-Noise Skipper CCD Experimental Instrument (SENSEI) uses the recently developed Skipper-CCD technology to search for electron recoils from the interaction of sub-GeV dark matter particles with electrons in silicon. We report first results from a prototype SENSEI detector, which collected 0.019g day of commissioning data above ground at Fermi National Accelerator Laboratory. These commissioning data are sufficient to set new direct-detection constraints for dark matter particles with masses between ∼500 keV and 4MeV. Moreover, since these data were taken on the surface, they disfavor previously allowed strongly interacting dark matter particles with masses between ∼500 keV and a few hundred MeV. We discuss the implications of these data for several dark matter candidates, including one model proposed to explain the anomalously large 21-cm signal observed by the EDGES Collaboration. SENSEI is the first experiment dedicated to the search for electron recoils from dark matter, and these results demonstrate the power of the Skipper-CCD technology for dark matter searches.

Effect of Temperature on Silicon Carriers Mobilities Using MATLAB

The effect of temperature on the electron and hole mobilities in silicon is studied using MATLAB. A theoretical study has been used for the electrons mobility and holes in silicon. The resulting data allows one to obtain the electron mobility and the hole mobility as a function of doping concentration and continuous temperature range between (200-550 Ko).