Ps Delay Research Articles

Anisotropic transport in tellurene FETs

Tellurene, a single layer of tellurium, is a new emerging 2D material and a possible candidate for the post-silicon era. It has anisotropic carrier effective mass in zigzag and armchair directions. Therefore, the study of the anisotropic performance of tellurene FETs is a timely topic. In this work, the authors study the transport mechanism and performance metrics of tellurene n-channel and p-channel transistors using a quantum simulation. Heavy carrier mass in the armchair direction effectively blocks the tunnelling current and the transport is governed by thermionic emission over the potential barrier. On the other hand, lighter carrier mass in the zigzag direction results in a mixed tunnelling and thermionic transport mechanism. The n-channel transistor has an on-state current of 894 μA/μm, a sub-threshold slope of 62 mV/dec, a 9.27 mS/μm transconductance, a 0.129 ps delay, and a 0.046 fJ/μm dynamic power loss. The p-channel metrics are, respectively, 852 μA/μm, 62 mV/dec, 9.24 mS/μm, 0.117 ps, and 0.040 fJ/μm. Both the transistors comply with the International Technology Roadmap for Semiconductors 2026 low operating power device requirements.

A High-Speed Moving Average Integrator in Silicon Photonics for TIA-Less Receivers

A high-speed moving average integrator in silicon photonics is demonstrated. The integrator is monolithically fabricated with an optical receiver front-end operating at 1550 nm. The design consists of an optical splitter, an optical low-loss delay line to implement a 400 ps delay between the two received bit streams, two SiGe photodiodes, and a 200 fF capacitor. The proposed moving average structure can perform four-bit integration at 10 Gbps. The resulting signal at the output of the integrator is the moving average of the received bit streams. The moving average integrator is validated through measurements and simulations at 2.5 and 5 Gbps. The proposed structure facilitates the development of next generation cost-effective and energy-efficient optical transceivers by exploiting optical time delay and moving average operation in silicon photonics. This mitigates the need for multiple clock phase generation and trans-impedance amplification on the electronic chip.

Loss Compensated PCM GeTe-Based Latching Wideband 3-bit Switched True-Time-Delay Phase Shifters for mmWave Phased Arrays

This article reports the first implementation of 3-bit millimeter-wave switched true-time-delay (TTD) phase shifters based on phase-change material (PCM) germanium telluride (GeTe). Two TTD phase shifters are presented. The first phase shifter is designed using four monolithically integrated PCM single-pole triple-throw (SP3T) switches to route the signal through delay lines. The insertion loss variation between various states is minimized by integrating two fixed PCM GeTe elements maintained in the crystalline state, along with the optimized width of the delay lines. The PCM switching cells are latching type, thus, consume no static dc power. The SP3T switches are connected back-to-back in two stages to provide a 3-bit phase shift with 20° precision. The second phase shifter is designed using two back-to-back connected PCM single-pole eight-throw (SP8T) switches. Both phase shifters are designed to operate over an 8 GHz wide frequency band with a center frequency of 30 GHz. The devices are fabricated in-house using an eight-layer microfabrication process. The proposed devices are highly miniaturized with an overall device area of 0.42mm 2 and 1.4mm 2 for the first and second phase shifter, respectively. The first phase shifter exhibit a measured average loss of 4.3 dB with a variation of ±0.3 dB and a return loss better than 20 dB, while the second phase shifter demonstrates low average measured loss of 3.8 dB with only ±0.2 dB loss variation and returns loss better than 17 dB at 30 GHz. Both phase shifters provide 180° linear phase shift with lower than 18 ps delay in the worst case.

Seafloor sediment thickness beneath the VoiLA broad-band ocean-bottom seismometer deployment in the Lesser Antilles from P-to-S delay times

SUMMARYBroad-band ocean-bottom seismometer (OBS) deployments present an opportunity to investigate the seafloor sediment thickness, which is important for constraining sediment deposition, and is also useful for subsequent seismological analyses. The Volatile Recycling in the Lesser Antilles (VoiLA) project deployed 34 OBSs over the island arc, fore- and backarc of the Lesser Antilles subduction zone for 15 months from 2016 to 2017. Using the amplitudes and delay times of P-to-S (Ps) scattered waves from the conversion of teleseismic earthquake Pwaves at the crust–sediment boundary and pre-existing relationships developed for Cascadia, we estimate sediment thickness beneath each OBS. The delay times of the Ps phases vary from 0.20 ± 0.06 to 3.55 ± 0.70 s, generally increasing from north to south. Using a single-sediment and single-crystalline crust earth model in each case, we satisfactorily model the observations of eight OBSs. At these stations we find sediment thicknesses range from 0.43 ± 0.45 to 5.49 ± 3.23 km. To match the observations of nine other OBSs, layered sediment and variable thickness crust is required in the earth model to account for wave interference effects on the observed arrivals. We perform an inversion with a two-layer sediment and a single-layer crystalline crust in these locations finding overall sediment thicknesses of 1.75 km (confidence region: 1.45–2.02 km) to 7.93 km (confidence region: 6.32–11.05 km), generally thinner than the initial estimates based on the pre-existing relationships. We find agreement between our modelled velocity structure and the velocity structure determined from the VoiLA active-source seismic refraction experiment at the three common locations. Using the Ps values and estimates from the VoiLA refraction experiment, we provide an adjusted relationship between delay time and sediment equations for the Lesser Antilles. Our new relationship is ${{H}} = {{1.42}}{{\rm d}}{{{t}}^{ {1.44}}}$ , where H is sediment thickness in kilometres and dt is mean observed Ps delay time in seconds, which may be of use in other subduction zone settings with thick seafloor sediments.

Low-aberration high-speed-compatible optical delay line.

We describe a simple approach to dispersion-free optical delay line design that provides very low aberration over an extended delay range. In this approach, we minimize aberrations by directing non-axial beam displacements along a line of symmetry built into the apparatus. We show improved performance and significant reduction of wavefront aberrations by comparing simulation and experimental results with a similar delay line that lacks this line of symmetry. The new design facilitates transform-limited recovery of spectral resolution in Fourier transform coherent anti-Stokes Raman scattering, and accordingly, we demonstrate 3.5cm-1 spectral resolution with a 10 ps delay scan range.

Multi-Beamforming Provided by Dual-Wavelength True Time Delay PIC and Multicore Fiber

This paper presents a multi-beamformer based on a dual-wavelength photonic integrated circuit (PIC) and multicore fiber (MCF) capable of providing independent delay tuning to two separate beams modulated on different optical carriers. This implementation enables a centralized control of the photonic beamformer, connecting each element of a phase array antenna with a dedicated core of a MCF link and controlling the induced delay (resulting steering angle) by thermo-optically adjusting the heaters of the PIC. The dual-wavelength PIC implements true time delay (TTD) based on optical ring resonators (ORRs). Six different ORR heaters’ configurations are evaluated experimentally, obtaining an induced delay of up to 328 ps at 19 GHz RF. With a measured delay resolution of 4 ps, it is recommended to increase/decrease the delay in small steps (between 10 and 30 ps) in order to keep the switching time in the ms range. Higher delays increments can be induced within longer switching time, e.g. 328 ps requires 1.68 s to stabilize the heaters. The performance demonstration includes the dual-wavelength transmission over 1-km of 7-core MCF and evaluates single-carrier data signals in the K-band centered in 19 GHz RF with up to 4 GHz bandwidth (BW). Operation with OFDM standard WiFi and WiMAX signals is also demonstrated experimentally. A delay of 328 ps can be induced to data signals at 19 GHz RF with up to 3-GHz BW, while 4-GHz BW signals can operate with up to 166 ps delay increment. An almost constant EVM is obtained for each BW below 3 GHz, confirming that changing the beam-steering angle does not affect the quality of the signal.

All-Graphene Nano-Ribbon FET Based Complete FPGA Design

FPGA is among the most successful digital IC. Though initially targeted for prototyping, but received more attention even in small volume production. However, that success is under threat since Silicon is reaching physical limitations. According to ITRS, towards the sub-nanometer regime, various second-order effects affect the functionality and reduces the performance of the device. Research on alternative materials indicates that Graphene is the most attractive candidate, and field-effect transistors using Graphene Nano-Ribbons Field Effect Transistors (GNRFETs) are promising because of their excellent properties. Toward all-Graphene microelectronics, and due to FPGA position in digital design, Graphene-based FPGA needs to be designed, analyzed, and evaluated. This paper explores FPGA design based on GNRFETs. It studies the design and characterization of all parts of a Graphene-based simple FPGA which could be a configurable logic structure for future microelectronics. It covers main parts, by design and characterization of Configurable Logic Block, routing switch, and I/O block, all based on GNRFET. The results as 47 ps delay for output and 23 ps for input proves feasibility, and indicate that proposed C-FPGA designs are much faster than conventional silicon-based counterparts. Power Delay Product of proposed CLB element is 5.3 times lesser than those of silicon counterparts.

CMOS integrated delay chain for X-Ku band applications

A wideband integrated delay chain chip with 5-bit delay control, maximum delay of 120 ps and 3.9 ps delay resolution, designed and fabricated in 0.18 $$\upmu \hbox {m}$$ CMOS technology is presented. Second-order all pass networks (APN) are used as delay structures in this delay circuit. In the design of the two MSB bits of the fabricated chip, a new design approach is used which allows higher group delay to be achieved with fewer number of passive second-order APN circuits. This would in turn reduce insertion loss of the designed delay control chain. Measurement results of the fabricated delay chain show 12.6–20.5 dB insertion loss and less than 3.3 ps RMS delay error over the intended frequency band from 8 to 18 GHz. The fabricated chip occupies an area of $$1.2\times 2.7$$ mm$$^{2}$$ and has no DC power consumption.

Threshold photodissociation dynamics of NO2 studied by time-resolved cold target recoil ion momentum spectroscopy.

We study the near-threshold photodissociation dynamics of NO2 by a kinematically complete femtosecond pump-probe scheme using a cold target recoil ion momentum spectrometer. We excite NO2 to the optically bright Ã2B2 state with a 400 nm pulse and probe the ensuing dynamics via strong field single and double ionization with a 25 fs, 800 nm pulse. The pump spectrum spans the NO(X2Π) + O(3P) dissociation channel threshold, and therefore, following internal conversion, excited NO2 is energetically prepared both "above threshold" (dissociating) and "below threshold" (nondissociating). Experimentally, we can clearly discriminate a weak two-photon pump channel from the dominant single-photon data. In the single ionization channel, we observe NO+ fragments with nonzero momentum at 200 fs delay and an increasing yield of NO+ fragments with near-zero momentum at 3.0 ps delay. For double ionization events, we observe a time-varying Coulombic kinetic energy release between the NO+ and O+ fragments impulsively created from the evolving "hot" neutral ground state. Supported by classical trajectory calculations, we assign the decreasing Coulombic kinetic energy release at longer time delays to the increasing average NO-O distances in the ground electronic state during its large amplitude phase space evolution toward free products. The time-resolved kinetic energy release in the double ionization channel probes the large amplitude ground state evolution from a strongly coupled "inner region" to a loosely coupled "outer region" where one O atom is on average much further away from the NO. Both the time evolution of the kinetic energy release and the NO+ angular distributions support our assignments.

A Reconfigurable DLL-Based Digital-to-Time Converter Using Charge Pump Current Interpolation and Digital Predistortion Linearization

This brief presents a digital-to-time converter (DTC) based on a reconfigurable delay-locked loop that employs dual feedback taps and interpolation at the output of two charge pumps biased with programmable complementary currents from a current digital-to-analog converter (I-DAC) to achieve fine delay tuning. Through selection of the feedback and output delay line taps, the 65-nm CMOS prototype can be configured to achieve different specs, such as a 24.5 ps delay span with a 0.46 ps maximum delay step and 1.33 ps maximum RMS jitter or a span of 244 ps with a 3.30 ps maximum step and 2.63 ps maximum RMS jitter when a 7-bit I-DAC and a 2 GHz input are used. A simple digital predistortion method to compensate for the inherent nonlinearity of the architecture is presented and experimentally shown to improve the worst-case integral nonlinearity from −14.3 LSB (−27.6 ps) to +1.79 LSB (+3.43 ps) for the 244 ps delay span case, and by 67%–88% at all taps for the same loop configuration. Excluding the I-DAC, which would require an estimated 0.2 mW, the DTC consumes 0.665 mW from a 1.25-V supply at 2 GHz and occupies an area of 46 $ {\mu }\text{m}\,\,{\times }$ 28 ${\mu }\text{m}$ .

Discovering Hidden Material Properties of MgCl2 at Atomic Resolution with Structured Temporal Electron Illumination of Picosecond Time Resolution

AbstractA combination of atomic resolution phase contrast electron microscopy and pulsed electron beams reveals pristine properties of MgCl2 at 1.7 Å resolution that were previously masked by air and beam damage. Both the inter‐ and intra‐layer bonding in pristine MgCl2 are weak, which leads to uncommonly large local orientation variations that characterize this Ziegler–Natta catalyst support. By delivering electrons with 1–10 ps pulses and ≈160 ps delay times, phonons induced by the electron irradiation in the material are allowed to dissipate before the subsequent delivery of the next electron packet, thus mitigating phonon accumulations. As a result, the total electron dose can be extended by a factor of 80–100 to study genuine material properties at atomic resolution without causing object alterations, which is more effective than reducing the sample temperature. In conditions of minimal damage, beam currents approach femtoamperes with dose rates around 1 eÅ−2 s−1. Generally, the utilization of pulsed electron beams is introduced herein to access genuine material properties while minimizing beam damage.

Analysis of Hybrid SETMOS T-Gate using Quaternary Multiple Valued (MV) Logic

In future nanometer technology, Single electron devices are promising device element to meet the demand for increasing in density, performance and power dissipation in ultra large scale integration. It appears that CMOS and SETs are rather complementary to each other; it is also true that combining SET and CMOS can provide a new functionality, which is un-mirrored in pure CMOS technology. SET with CMOS hybrid architecture is commonly referred to as SETMOS. It offer coulomb blockade oscillation and quasi periodic negative differential effect which gives an advantage to realize MV logic. Transmission (T)-gate act as universal gate which is implemented by using MV SETMOS. In this paper T-gate is proposed using literal gate of SETMOS device and its application such as single and two variables (multiple) function which act as basic blocks of sequential, logical circuits. Herein, the design functionality of quaternary multiple-valued logic is implemented by using voltage mode SETMOS. Analytical MIB model for SET is calibrated with BSIM 4.6.1 bulk MOSFET at 45 nm. The simulated waveform of circuits is carried out at room temperature in T-spice pro-environment. The proposed circuit with SETMOS device consumes merely 2050 nw of power along with 81 ps delay in comparison to its CMOS counterparts. Several intrinsic parameters (such as propagation delay, switching energy, area and voltage gain) play crucial role in determining the efficiency of the proposed quaternary MV logic T-gate is also investigated.

The Formation Time of Ti-O• and Ti-O•-Ti Radicals at the n-SrTiO3/Aqueous Interface during Photocatalytic Water Oxidation.

The initial step of photocatalytic water oxidation reaction at the metal oxide/aqueous interface involves intermediates formed by trapping photogenerated, valence band holes on different reactive sites of the oxide surface. In SrTiO3, these one-electron intermediates are radicals located in Ti-O• (oxyl) and Ti-O•-Ti (bridge) groups arranged perpendicular and parallel to the surface respectively, and form electronic states in the band gap of SrTiO3. Using an ultrafast sub band gap probe of 400 nm and white light, we excited transitions between these radical states and the conduction band. By measuring the time evolution of surface reflectivity following the pump pulse of 266 nm light, we determined an initial radical formation time of 1.3 ± 0.2 ps, which is identical to the time to populate the surface with titanium oxyl (Ti-O•) radicals. The oxyl was separately observed by a subsurface vibration near 800 cm-1 from Ti-O located in the plane right below Ti-O•. Second, a polarized transition optical dipole allows us to assign the 1.3 ps time constant to the production of both O-site radicals. After a 4.5 ps delay, another distinct surface species forms with a time constant of 36 ± 10 ps with a yet undetermined structure. As would be expected, the radicals' decay, specifically probed by the oxyl's subsurface vibration, parallels that of the photocurrent. Our results led us to propose a nonadiabatic kinetic mechanism for generating radicals of the type Ti-O• and Ti-O•-Ti from valence band holes based on their solvation at aqueous interfaces.

Redefining the Speed Limit of Phase Change Memory Revealed by Time-resolved Steep Threshold-Switching Dynamics of AgInSbTe Devices.

Although phase-change memory (PCM) offers promising features for a ‘universal memory’ owing to high-speed and non-volatility, achieving fast electrical switching remains a key challenge. In this work, a correlation between the rate of applied voltage and the dynamics of threshold-switching is investigated at picosecond-timescale. A distinct characteristic feature of enabling a rapid threshold-switching at a critical voltage known as the threshold voltage as validated by an instantaneous response of steep current rise from an amorphous off to on state is achieved within 250 picoseconds and this is followed by a slower current rise leading to crystallization. Also, we demonstrate that the extraordinary nature of threshold-switching dynamics in AgInSbTe cells is independent to the rate of applied voltage unlike other chalcogenide-based phase change materials exhibiting the voltage dependent transient switching characteristics. Furthermore, numerical solutions of time-dependent conduction process validate the experimental results, which reveal the electronic nature of threshold-switching. These findings of steep threshold-switching of ‘sub-50 ps delay time’, opens up a new way for achieving high-speed non-volatile memory for mainstream computing.

Design of a Sub-Picosecond Jitter with Adjustable-Range CMOS Delay-Locked Loop for High-Speed and Low-Power Applications.

A Delay-Locked Loop (DLL) with a modified charge pump circuit is proposed for generating high-resolution linear delay steps with sub-picosecond jitter performance and adjustable delay range. The small-signal model of the modified charge pump circuit is analyzed to bring forth the relationship between the DLL’s internal control voltage and output time delay. Circuit post-layout simulation shows that a 0.97 ps delay step within a 69 ps delay range with 0.26 ps Root-Mean Square (RMS) jitter performance is achievable using a standard 0.13 µm Complementary Metal-Oxide Semiconductor (CMOS) process. The post-layout simulation results show that the power consumption of the proposed DLL architecture’s circuit is 0.1 mW when the DLL is operated at 2 GHz.

Design and Technology Analysis Bipolar Transistors Based on High Performance Structures AlGaAs / GaAs Structures for Submicron LargeIntegrated Circuits

This paper analyzes performance of bipolar transistors based on AlGaAs/GaAs heterostructures (HBT). Use of heterojunction as emitter junction allows radical improvement of its performance. Numerical simulation of HBT in ring oscillator mode showed that the delay of the BT with 1x2 µm emitter can be reduced to 8 ps at a maximum current of 105 A/cm2. HBT with one and two (emitter and collector) heterojunctions showed 24 ps delay at 9.1 mW and 17 ps at 40 mW.

Strong-field-induced wave packet dynamics in carbon dioxide molecule.

Temporal evolution of electronic and nuclear wave packets created in strong-field excitation of the carbon dioxide molecule is studied employing momentum-resolved ion spectroscopy and channel-selective Fourier analysis. Combining the data obtained with two different pump-probe set-ups, we observed signatures of vibrational dynamics in both, ionic and neutral states of the molecule. We consider far-off-resonance two-photon Raman scattering to be the most likely mechanism of vibrational excitation in the electronic ground state of the neutral CO2. Using the measured phase relation between the time-dependent yields of different fragmentation channels, which is consistent with the proposed mechanism, we suggest an intuitive picture of the underlying vibrational dynamics. For ionic states, we found signatures of both, electronic and vibrational excitations, which involve the ground and the first excited electronic states, depending on the particular final state of the fragmentation. While our results for ionic states are consistent with the recent observations by Erattupuzha et al. [J. Chem. Phys.144, 024306 (2016)], the neutral state contribution was not observed there, which we attribute to a larger bandwidth of the 8 fs pulses we used for this experiment. In a complementary measurement employing longer, 35 fs pulses in a 30 ps delay range, we study the influence of rotational excitation on our observables, and demonstrate how the coherent electronic wave packet created in the ground electronic state of the ion completely decays within 10 ps due to the coupling to rotational motion.

Optimized Finite Difference Method for the Full-Potential XANES Simulations: Application to Molecular Adsorption Geometries in MOFs and Metal-Ligand Intersystem Crossing Transients.

Accurate modeling of the X-ray absorption near-edge spectra (XANES) is required to unravel the local structure of metal sites in complex systems and their structural changes upon chemical or light stimuli. Two relevant examples are reported here concerning the following: (i) the effect of molecular adsorption on 3d metals hosted inside metal-organic frameworks and (ii) light induced dynamics of spin crossover in metal-organic complexes. In both cases, the amount of structural models for simulation can reach a hundred, depending on the number of structural parameters. Thus, the choice of an accurate but computationally demanding finite difference method for the ab initio X-ray absorption simulations severely restricts the range of molecular systems that can be analyzed by personal computers. Employing the FDMNES code [Phys. Rev. B, 2001, 63, 125120] we show that this problem can be handled if a proper diagonalization scheme is applied. Due to the use of dedicated solvers for sparse matrices, the calculation time was reduced by more than 1 order of magnitude compared to the standard Gaussian method, while the amount of required RAM was halved. Ni K-edge XANES simulations performed by the accelerated version of the code allowed analyzing the coordination geometry of CO and NO on the Ni active sites in CPO-27-Ni MOF. The Ni-CO configuration was found to be linear, while Ni-NO was bent by almost 90°. Modeling of the Fe K-edge XANES of photoexcited aqueous [Fe(bpy)3](2+) with a 100 ps delay we identified the Fe-N distance elongation and bipyridine rotation upon transition from the initial low-spin to the final high-spin state. Subsequently, the X-ray absorption spectrum for the intermediate triplet state with expected 100 fs lifetime was theoretically predicted.

Excitation Wavelength Dependence of Excited State Intramolecular Proton Transfer Reaction of 4′-N,N-Diethylamino-3-hydroxyflavone in Room Temperature Ionic Liquids Studied by Optical Kerr Gate Fluorescence Measurement

Excited state intramolecular proton transfer reactions (ESIPT) of 4'-N,N-diethylamino-3-hydroxyflavone (DEAHF) in ionic liquids have been studied by steady-state and time-resolved fluorescence measurements at different excitation wavelengths. Steady-state measurements show the relative yield of the tautomeric form to the normal form of DEAHF decreases as excitation wavelength is increased from 380 to 450 nm. The decrease in yield is significant in ionic liquids that have cations with long alkyl chains. The extent of the decrease is correlated with the number of carbon atoms in the alkyl chains. Time-resolved fluorescence measurements using optical Kerr gate spectroscopy show that ESIPT rate has a strong excitation wavelength dependence. There is a large difference between the spectra at a 200 ps delay from different excitation wavelengths in each ionic liquid. The difference is pronounced in ionic liquids having a long alkyl chain. The equilibrium constant in the electronic excited state obtained at a 200 ps delay and the average reaction rate are also correlated with the alkyl chain length. Considering the results of the steady-state fluorescence and time-resolved measurements, the excitation wavelength dependence of ESIPT is explained by state selective excitation due to the difference of the solvation, and the number of alkyl chain carbon atoms is found to be a good indicator of the effect of inhomogeneity for this reaction.

Femtosecond laser nanomachining initiated by ultraviolet multiphoton ionization

We report on the experimental results of 300 nm features generated on fused silica using a near-infrared (IR) femtosecond laser pulse initiated by an ultraviolet (UV) pulse. With both pulses at a short (~60 fs) delay, the damage threshold of the UV pulse is only 10% of its normal value. Considerable reduction of UV damage threshold is observed when two pulses are at ± 1.3 ps delay. The damage feature size of the combined pulses is similar to that of a single UV pulse. A modified rate equation model with the consideration of defect states is used to help explain these results. This concept can be applied to shorter wavelengths, e.g. XUV and X-ray, with the required fluence below their normal threshold.