Silicon Electronics Research Articles

Does cosmological evolution select for technology?

If the parameters defining the physics of our universe departed from their present values, the observed rich structure and complexity would not be supported. This article considers whether similar fine-tuning of parameters applies to technology. The anthropic principle is one means of explaining the observed values of the parameters. This principle constrains physical theories to allow for our existence, yet the principle does not apply to the existence of technology. Cosmological natural selection has been proposed as an alternative to anthropic reasoning. Within this framework, fine-tuning results from selection of universes capable of prolific reproduction. It was originally proposed that reproduction occurs through singularities resulting from supernovae, and subsequently argued that life may facilitate the production of the singularities that become offspring universes. Here I argue technology is necessary for production of singularities by living beings, and ask whether the physics of our universe has been selected to simultaneously enable stars, intelligent life, and technology capable of creating progeny. Specific technologies appear implausibly equipped to perform tasks necessary for production of singularities, potentially indicating fine-tuning through cosmological natural selection. These technologies include silicon electronics, superconductors, and the cryogenic infrastructure enabled by the thermodynamic properties of liquid helium. Numerical studies are proposed to determine regions of physical parameter space in which the constraints of stars, life, and technology are simultaneously satisfied. If this overlapping parameter range is small, we should be surprised that physics allows technology to exist alongside us. The tests do not call for new astrophysical or cosmological observations. Only computer simulations of well-understood condensed matter systems are required.

Enhanced Optical Emission from 2D InSe Bent onto Si‐Pillars

AbstractControlling the propagation and intensity of an optical signal is central to several technologies ranging from quantum communication to signal processing. These require a versatile class of functional materials with tailored electronic and optical properties, and compatibility with different platforms for electronics and optoelectronics. Here, the inherent optical anisotropy and mechanical flexibility of atomically thin semiconducting layers are investigated and exploited to induce a controlled enhancement of optical signals. This enhancement is achieved by straining and bending layers of the van der Waals crystal indium selenide (InSe) onto a periodic array of Si‐pillars. This enhancement has strong dependence on the layer thickness and is modelled by first‐principles electronic band structure theory, revealing the role of the symmetry of the atomic orbitals and light polarization dipole selection rules on the optical properties of the bent layers. The effects described in this paper are qualitatively different from those reported in other materials, such as transition metal dichalcogenides, and do not arise from a photonic cavity effect, as demonstrated before for other semiconductors. The findings on InSe offer a route to flexible nano‐photonics compatible with silicon electronics by exploiting the flexibility and anisotropic and wide spectral optical response of a 2D layered material.

Use of Amorphous Silicon (ASi) Electronic Portal Imaging Devices for Other applications for Linear Accelerator Quality Assurance

The success of radiation therapy depends critically on the accuracy of patient alignment in treatment position day after day. Electronic portal imaging devices (EPIDs) are widely used to monitor patient position during daily radiotherapy sessions. To verify other applications for medical linear accelerator quality assurance (linac QA), images of a 10×10 cm² and 18×18 cm² open field were acquired. The EPID was positioned at a fixed detector distance of 150 cm. The wedge profile and wedge factors with high level of accuracy were demonstrated. The profiles acquired using EPID deviated in shape and magnitude by up to 16% from the ion chamber profiles. The use of EPID for linac QA could be simplified by improving the available software analysis tools, thus making it more efficient. The study showed that the EPID aSi500 has the potential to be used as a relative dosimeter, making it a very simple and efficient tool for daily QA. All EPID measurements were performed using the linear accelerator model Varian DMX. The physical characteristics measured in this work suggest that the SLIC-EPID can be an efficient tool for daily QA.

(Invited) Self-Powered Wearable and Implantable Electrical Stimulation Devices for Biomedical Applications

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. This talk will fist introduce the application of flexible nanogenerators as an implantable power source and its biosafety and compatibility. In addition, the pulsed electricity from nanogenerators 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, hair growth, 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. Via a similar design, the electrical pulses were applied to stimulate hair growth. Significantly facilitated hair regeneration results were obtained from Sprague-Dawley rats and nude mice, which was attributed to the improved secretion of vascular endothelial growth factor and keratinocyte growth factor. 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. All the results bring a new concept in electrical therapeutic technology that is battery-free, self-activated and directly responsive to body activities. Keywords: Nanogenerator; Implantable medical devices; Wearable devices; Self-powered systems; Electrical stimulation;

Profile of Paul L. McEuen

In 1965, engineer Gordon Moore predicted that the number of transistors in an integrated circuit would double every two years. This prediction, known as Moore’s Law, has been proven accurate and spurred semiconductor research toward miniaturization. Moore’s Law, however, is starting to plateau. According to Cornell University physicist and National Academy of Sciences member Paul L. McEuen, this plateau presents an opportunity. Over his career, McEuen has worked with silicon devices and studied and fabricated next-generation inorganic and organic materials, such as gallium arsenide and carbon nanotubes. He and others are combining silicon electronics with these novel materials and deploying them in different technological niches. McEuen’s Inaugural Article (1) takes this work a step further by using heterogenous materials in a wireless electronic sensor system that is so small it can barely be seen by the naked eye. Fig. 1. Paul L. McEuen. Image credit: Susan Wiser (photographer). Fig. 2. An OWIC on a fingertip. Image credit: Alejandro Cortese (Cornell University, Ithaca, NY). McEuen grew up in Oklahoma and developed an interest in science and technology from a young age. When he was 13 years old, McEuen experienced an epiphany that would foreshadow his career in science. “I had saved up about $200,” McEuen says, “and bought a telescope to look at stars and planets.” After a few hours, however, he got bored. “Stars and planets don’t do very much,” he adds. So McEuen trained his telescope on a nearby wasp that had settled atop a soda can. “It was stunning,” he recalls. “The wasp looked like an amazing, fantastical machine. I was just blown away. So much complexity in such a small package; that, I think, is when I started to understand that ‘small’ was the way for me.” Now, his Cornell laboratory’s motto, “anything, as long as it’s small,” reflects this early …

Realisation of a quantum current standard at liquid helium temperature with sub-ppm reproducibility

A silicon electron pump operating at the temperature of liquid helium has demonstrated repeatable operation with sub-ppm accuracy. The pump current, approximately 168 pA, is measured by three laboratories, and the measurements agree with the expected current ef within the uncertainties which range from 0.2 ppm to 1.3 ppm. All the measurements are carried out in zero applied magnetic field, and the pump drive signal is a sine wave. The combination of simple operating conditions with high accuracy demonstrates the possibility that an electron pump can operate as a current standard in a National Measurement Institute. We also discuss other practical aspects of using the electron pump as a current standard, such as testing its robustness to changes in the control parameters, and using a rapid tuning procedure to locate the optimal operation point.

Graphitic‐Based Solid‐State Supercapacitors: Enabling Redox Reaction by In Situ Electrochemical Treatment

AbstractThe quest for supercapacitors that can hold both high energy and power density is of increasing significance as the need for green and reliable energy storage devices grows, for both large‐scale and integrated systems. While supercapacitors for integrated technologies require a solid‐state approach, gel‐based electrolytes are generally not as efficient as their aqueous counterparts. Here, we demonstrate a strategy to enhance the performance of quasi‐solid‐state supercapacitors made by graphitized silicon carbide on silicon electrodes and polyvinyl alcohol (PVA)+H2SO4 gel electrolyte. The electrochemical characterization shows an increase of the specific capacitance of the cell up to 3‐fold resulting from a simple agent‐free, in situ, electrochemical treatment leading to functionalization of the graphitic electrodes. The functionalization of the electrodes simultaneously enables redox reactions, without adding any redox agent, and increases the double layer contribution to the overall capacitance. The strategy and insights offered by this work hold great promise for improving quasi‐solid‐state, miniaturized on‐chip energy storage systems, which are compatible with silicon electronics.

System Integration for Plastic Electronics Using Room‐Temperature Ultrasonic Welding

Plastic electronics is attracting increasing attention for both high‐end applications such as flexible organic light‐emitting diode (OLED) displays in mobile phones and low‐cost items such as plastic radio frequency identification (RFID) tags for product labeling and tracking. However, there are numerous technological challenges, not least of which is to develop robust and reliable packaging methods. Unfortunately, most of the established packaging technologies used in conventional silicon electronics are not transferable to plastic electronics due to the high process temperatures involved. The use of room‐temperature ultrasonic welding for the realization of multilayer plastic electronic circuits is explored, identifying two distinct modes of ultrasonic welding that can form combined electrical and mechanical connections between adjacent low‐temperature polymer films with either aluminum or printed silver metallization. Fully functional multilayer wireless charging coils and RFID tags are fabricated to demonstrate the potential of this new system integration approach.

Inductively Coupled Plasma Chemical Vapor Deposition for Silicon‐Based Technology Compatible with Low‐Temperature (≤220 °C) Flexible Substrates

Herein, an inductively coupled plasma chemical vapor deposition (CVD) (ICP‐CVD) technique is adopted for deposition of silicon dioxide and silicon thin films to fabricate metal–oxide–semiconductor (MOS) capacitors and thin film transistors (TFTs). Prior to the fabrication and characterization of the TFTs, C–V measurements and breakdown tests are conducted on MOS capacitors based on silicon dioxide deposited under temperatures as low as 20 °C. The breakdown field of 9 MV cm−1 is validated afterward, which implies the good electrical insulating property for acting as a gate insulator and the feasibility of the TFTs. After going through forming gas and thermal annealing with the highest temperature of 220 °C, the TFTs yield good gate insulating properties, a threshold voltage of 3.7 V, an on/off ratio of 6.4 × 102, field effect mobility of 1.2 cm2 (V s)−1, and a subthreshold slope of 3.9 V dec−1. They show promising electrical properties under such a low‐temperature fabrication process using ICP‐CVD technique compatible for silicon electronics using low‐cost flexible substrates.

Micro-Nano Fabrication of Self-Aligned Silicon Electron Field Emitter Arrays Using Pulsed KrF Laser Irradiation

Self-aligned silicon micro-nano structured electron field emitter arrays were fabricated using pulsed krypton fluoride (KrF) excimer laser crystallization (ELC) of hydrogenated amorphous thin silicon films (a-Si:H) on metal coated backplane samples. We investigate the effect of laser processing parameters on the growth of micro-nano conical structures on the surface of the thin silicon films. Randomly oriented conical structures as high as 1 µm were fabricated using laser pulse frequency of 100 Hz and sample stage scanning speed of 0.25 mm/sec. Best field emission (FE) results were measured from samples with the highest surface features with FE currents in the order of 10−6 A and low turn-on emission threshold of ∼14 V/µm. Light emission from the prototype demonstrators was tested using bespoke driver electronics and planar anodes coated with indium tin-oxide (ITO) and medium voltage FE phosphors, to exemplify their usage for future flat panel display technologies.

Metal/BaTiO3/β-Ga2O3 dielectric heterojunction diode with 5.7 MV/cm breakdown field

Wide and ultrawide bandgap semiconductors can provide excellent performance due to their high energy bandgap, which leads to breakdown electric fields that are more than an order of magnitude higher than conventional silicon electronics. In materials where p-type doping is not available, achieving this high breakdown field in a vertical diode or transistor is very challenging. We propose and demonstrate the use of dielectric heterojunctions that use extreme permittivity materials to achieve a high breakdown field in a unipolar device. We demonstrate the integration of a high permittivity material BaTiO3 with n-type β-Ga2O3 to enable a 5.7 MV/cm average electric field and a 7 MV/cm peak electric field at the device edge while maintaining forward conduction with relatively low on-resistance and voltage loss. The proposed dielectric heterojunction could enable improved design strategies to achieve theoretical device performance limits in wide and ultrawide bandgap semiconductors where bipolar doping is challenging.

Low loss CMOS-compatible silicon nitride photonics utilizing reactive sputtered thin films.

Low temperature deposition of low loss silicon nitride (SiN) thin-films is very attractive as it opens opportunities for realization of multi-layer photonic chips and hybrid integration of optical waveguides with temperature sensitive platforms such as processed CMOS silicon electronics or lithium niobate on insulator. So far, the most common low-temperature deposition technique for SiN is plasma enhanced chemical vapor deposition (PECVD), however such SiN thin-films can suffer from significant losses at C-band wavelengths due to unwanted hydrogen bonds. In this contribution we present a back end of line (< 400°C), low loss SiN platform based on reactive sputtering for telecommunication applications. Waveguide losses of 0.8 dB/cm at 1550 nm and as low as 0.6 dB/cm at 1580 nm have been achieved for moderate confined waveguides which appear to be limited by patterning rather than material. These findings show that reactive sputtered SiN thin-films can have lower optical losses compared to PECVD SiN thin-films, and thus show promise for future hybrid integration platforms for applications such as high Q resonators, optical filters and delay lines for optical signal processing.

A silicon quantum-dot-coupled nuclear spin qubit.

Single nuclear spins in the solid state are a potential future platform for quantum computing1-3, because they possess long coherence times4-6 and offer excellent controllability7. Measurements can be performed via localized electrons, such as those in single atom dopants8,9 or crystal defects10-12. However, establishing long-range interactions between multiple dopants or defects is challenging13,14. Conversely, in lithographically defined quantum dots, tunable interdot electron tunnelling allows direct coupling of electron spin-based qubits in neighbouring dots15-20. Moreover, the compatibility with semiconductor fabrication techniques21 may allow for scaling to large numbers of qubits in the future. Unfortunately, hyperfine interactions are typically too weak to address single nuclei. Here we show that for electrons in silicon metal-oxide-semiconductor quantum dots the hyperfine interaction is sufficient to initialize, read out and control single 29Si nuclear spins. This approach combines the long coherence times of nuclear spins with the flexibility and scalability of quantum dot systems. We demonstrate high-fidelity projective readout and control of the nuclear spin qubit, as well as entanglement between the nuclear and electron spins. Crucially, we find that both the nuclear spin and electron spin retain their coherence while moving the electron between quantum dots. Hence we envision long-range nuclear-nuclear entanglement via electron shuttling3. Our results establish nuclear spins in quantum dots as a powerful new resource for quantum processing.

Ultrathin, High Capacitance Capping Layers for Silicon Electronics with Conductive Interconnects in Flexible, Long‐Lived Bioimplants

AbstractBioimplants that incorporate active electronic components at the tissue interface rely critically on materials that are biocompatible, impermeable to biofluids, and capable of intimate electrical coupling for high‐quality, chronically stable operation in vivo. This study reports a materials strategy that combines silicon nanomembranes, thermally grown layers of SiO2 and ultrathin capping structures in materials with high dielectric constants as the basis for flexible and implantable electronics with high performance capabilities in electrophysiological mapping. Accelerated soak tests at elevated temperatures and results of theoretical modeling indicate that appropriately designed capping layers can effectively limit biofluid penetration and dramatically extend the lifetimes of the underlying electronic materials when immersed in simulated biofluids. Demonstration of these approaches with actively multiplexed, amplified systems that incorporate more than 100 transistors in thin, flexible platforms highlights the key capabilities and the favorable scaling properties. These results offer an effective encapsulation approach for long‐lived bioelectronic systems with broad potential for applications in biomedical research and clinical practice.

Tunable Coupling and Isolation of Single Electrons in Silicon Metal-Oxide-Semiconductor Quantum Dots.

Extremely long coherence times, excellent single-qubit gate fidelities, and two-qubit logic have been demonstrated with silicon metal-oxide-semiconductor spin qubits, making it one of the leading platforms for quantum information processing. Despite this, a long-standing challenge in this system has been the demonstration of tunable tunnel coupling between single electrons. Here we overcome this hurdle with gate-defined quantum dots and show couplings that can be tuned on and off for quantum operations. We use charge sensing to discriminate between the (2,0) and (1,1) charge states of a double quantum dot and show excellent charge sensitivity. We demonstrate tunable coupling up to 13 GHz, obtained by fitting charge polarization lines, and tunable tunnel rates down to <1 Hz, deduced from the random telegraph signal. The demonstration of tunable coupling between single electrons in a silicon metal-oxide-semiconductor device provides significant scope for high-fidelity two-qubit logic toward quantum information processing with standard manufacturing.

Impact of annealing temperature on band-alignment of PLD grown Ga2O3/Si (100) heterointerface

Cost-effective integration with existing silicon CMOS electronics has been one of the primary motivations for most of the emerging non-silicon devices. In this context, β-gallium oxide (Ga2O3) films were deposited on Si (100) substrate using pulsed laser deposition (PLD) technique in this research. After deposition, samples were further annealed at 600 °C and 800 °C under vacuum. X-ray diffractometer (XRD) was employed to observe the crystallinity variation due to the annealing. The crystallinity of samples degrades with annealing at 600 °C and an incremental improvement in crystallinity was again exhibited at 800 °C due to the possible rearrangement of the Ga and O atoms to their optimal sites. Further, x-ray photoelectron spectroscopy (XPS) was used for identification of elements and chemical composition. XPS results were also analyzed to locate the position of Ga 2p and Si 2p core levels and calculate the valance band offset (VBO) at Ga2O3/Si interface. Reflected electron energy loss spectroscopy (REELS) and ultraviolet photoelectron spectroscopy (UPS) were utilized to calculate the bandgap and work function, respectively. Moreover, valance band maxima and Fermi level position of the as-deposited and annealed samples were calculated using UPS. The bandgaps for the as-deposited, annealed samples at 600 °C and 800 °C were estimated to be 4.72 ± 0.05, 4.52 ± 0.05, and 4.48 ± 0.05 eV, respectively. Consequently, the work function of the sample increases with annealing due to increase in the oxygen vacancies and resulting bandgap narrowing. The band offsets (valance band, conduction band) were determined to be (3.35 ± 0.05 eV, 0.26 ± 0.02 eV), (3.55 ± 0.05 eV, 0.15 ± 0.02 eV) and (3.54 ± 0.05 eV, 0.17 ± 0.02 eV) for the as-deposited, annealed samples at 600 °C and 800 °C, respectively. This optimization of band alignment with annealing temperature shall be very useful for controlling the carrier transport at the interface for Ga2O3/Si based devices. Thus, a trade-off is to be performed between VBO and crystallinity of the Ga2O3/Si to operate the devices efficiently and reliably respectively.

InP-on-Si Optically Pumped Microdisk Lasers via Monolithic Growth and Wafer Bonding

On-chip optical light sources are key components in photonic integrated circuits and optical communication. In this paper, we use a novel integration technique called template-assisted selective epitaxy (TASE) to monolithically integrate InP microdisk lasers on silicon. TASE offers several advantages for new device concepts such as lateral doping, dense co-integration of different III–V materials, and in-plane integration with silicon electronics and passive components. Here, we demonstrate room-temperature lasing from InP hexagonal microdisks integrated via TASE. In order to assess and evaluate the viability of TASE, a second InP hexagonal microdisk sample is prepared for comparison using the highly developed and mature direct wafer bonding technique. The lasing performance of the TASE monolithic devices and the bonded microdisk devices is investigated under pulsed optical pumping as a function of temperature and compared. The lasing threshold as well as the light-in light-out curves of our TASE structures compare favorably with the bonded InP hexagonal microdisks. This demonstrates that our TASE approach is a promising technique for the monolithic integration of optical devices on Si.

Numerical simulation of the influence of electron injections on the short-term annealing in pulse-neutron-irradiated p-type Si

The physical reason behind the much more rapid short-term annealing progress in the presence of electrons in P-type silicon irradiated by pulse neutrons is investigated. Continuum equations coupled with defect reactions are used for the numerical simulation on the temporary evolutions of defects at different electron injection ratios. It is indicated that electron injections can significantly accelerate the creations of boron and carbon interstitials, but may have little influence on the creation of the vacancy-oxygen complex. The calculations on the relative concentrations of interstitials and vacancies in different charge states via the electron injection ratio show that more and more interstitials in the doubly positive charge state change into neutral ones, and neutral vacancies are always dominant with an increase in the electron concentration. The thermal diffusion coefficient of neutral interstitials is much larger than the ones of interstitials in other charge states. As a consequence, normal ionization enhanced diffusion for interstitials in the presence of electrons can significantly accelerate the short-term annealing progress in P-type silicon. Ionization enhanced diffusion coefficients for interstitials due to athermal diffusion are further estimated using the Bourgoin mechanism, and results indicate that the diffusion coefficients of positively charged interstitials are improved by several orders of magnitude when compared to their corresponding thermal diffusion coefficients. However, the production of boron and carbon interstitials is only accelerated by about one order of magnitude, which would be ascribed into such large thermal diffusion coefficients of neutral interstitials.

Two-dimensional system of strongly interacting electrons in silicon (100) structures

Studies of various experimental groups that explore the properties of a two-dimensional electron gas in silicon semiconductor systems ((100) Si-MOSFET and (100) SiGe/Si/SiGe quantum wells) in the vicinity of the metal–insulator transition are described and critically analyzed. Results are identified that are common to all research: (i) the effective mass of electrons measured at the Fermi level in the metallic region increases as the electron density decreases and, if extrapolated, tends to diverge; (ii) the behavior of the energy-averaged mass in the metallic region is quite different in the two systems: in Si-MOSFETs, it also exhibits a tendency to diverge, while in the SiGe/Si/SiGe quantum wells it saturates in the limit of low electron densities; (iii) there is a small number (depending on the sample quality) of localized electrons in the metallic phase; (iv) the properties that the electron system exhibits in the insulating phase in the vicinity of the metal–insulator transition are typical of amorphous media with a strong coupling between particles.

Achieving High-Quality Sn-Pb Perovskite Films on Complementary Metal-Oxide-Semiconductor-Compatible Metal/Silicon Substrates for Efficient Imaging Array.

Although Sn-Pb perovskites sensing near-ultraviolet-visible-near-infrared light could be an attractive alternative to silicon in photodiodes and imaging, there have been no clear studies on such devices constructed on metal/silicon substrates, hindering their direct integration with complementary metal-oxide semiconductor (CMOS) and silicon electronics. Typically, high surface roughness and severe pinholes of Sn-rich binary perovskites make it difficult for them to fulfill the requirements of efficient photodiodes and imaging. These issues cause inherently high dark current and poor (dark and photo-) current uniformity. Herein, we propose and demonstrate the room-temperature crystallization in the Sn-rich binary perovskite system to effectively control film crystallization kinetics. With experimental and theoretical studies of the crystallization mechanism, we successfully tune the density and location of nanocrystals in precursor films to achieve compact nanocrystals, which coalesce into high-quality (smooth, dense, and pinhole-free) perovskites with intensified preferred orientation and decreased trap density. The high-quality perovskites reduce dark current and improve (dark and photo-) current uniformity of perovskite photodiodes on CMOS-compatible metal/silicon substrates. Meanwhile, self-powered devices achieve a high responsivity of 0.2 A/W at 940 nm, a large dynamic range of 100 dB, and a fast fall time of 2.27 μs, exceeding those of most silicon-based imaging sensors. Finally, a 6 × 6 pixel integrated photodiode array is successfully demonstrated to realize the imaging application. The work contributes to understanding the fundamentals of the crystallization of Sn-rich binary perovskites and advancing perovskite integration with Si-based electronics.