Showing papers on "Biasing published in 2021"

Switching Behavior of a Heterostructure Based on Periodically Doped Graphene Nanoribbon

Abstract: We theoretically propose a switching device that operates at room temperature. The device is an in-plane heterostructure based on a periodically boron-doped (nitrogen-doped) armchair graphene nanoribbon, which has been experimentally fabricated recently. The calculated $I$-$V$ curve shows that for a realistic device with interface width longer than $20$ nm, nonzero electric current occurs only in the region of bias voltage between $\ensuremath{-}0.22$ and $0.28$ V, which is beneficial to low-voltage operation. Furthermore, in this case, the electric current is robust against the change of the potential profile in the interface since the metallic impurity-induced sub-bands with delocalized wave functions contribute to the transmission exclusively. This also suggests the high response speed of the proposed device. We also discuss the temperature dependence, the output impedance, the effect of phonons, and the possible regimes to extend our work, which suggest that our model may have potential room-temperature nanoelectronics applications.

Elimination of Interfacial-Electrochemical-Reaction-Induced Polarization in Perovskite Single Crystals for Ultrasensitive and Stable X-Ray Detector Arrays.

Abstract: Organic-inorganic halide perovskites have exhibited bright prospects in high-sensitivity X-ray detection. However, they generally suffer from the severe field-driven polarization issue that remarkably deteriorates the detection performance. Here, it is demonstrated that the interfacial electrochemical reaction between Au electrodes and halogen in MAPbI3 single crystals (SCs) is the major source of the dark current polarization in the metal-semiconductor-metal (MSM)-structured perovskite X-ray detectors at the initial stage of biasing. By introducing the p- and n-type charge transport layers to isolate the electrodes from contacting the SC surface, the polarization is fully eliminated under a large electric field up to 1000 V cm-1 . Moreover, the resultant lateral p-i-n heterojunction suppresses the dark current of the devices by nearly 3 orders of magnitude as compared to the MSM counterparts and therefore enables a high sensitivity of 5.2 × 106 µC Gy-1air cm-2 and a record low X-ray detection limit down to 0.1 nGyair s-1 . The excellent biasing stability and sensitivity of the devices allow to prepare the linear detector arrays for X-ray imaging applications.

Low-Voltage and Fast-Response SnO 2 Nanotubes/Perovskite Heterostructure Photodetector.

Abstract: One-dimensional metal-oxides (1D-MO) nanostructure has been regarded as one of the most promising candidates for high-performance photodetectors due to their outstanding electronic properties, low-cost and environmental stability However, the current bottlenecks are high energy consumption and relatively low sensitivity Here, Schottky junctions between nanotubes (NTs) and FTO were fabricated by electrospinning SnO2NTs on FTO glass substrate, and the bias voltage of SnO2NTs photodetectors was as low as ∼176 V, which can effectively reduce energy consumption Additionally, for improving the response and recovery speed of SnO2NTs photodetectors, the NTs were covered with organic/inorganic hybrid perovskite SnO2NTs/perovskite heterostructure photodetectors exhibit fast response/recovery speed (∼0075/004 s), and a wide optical response range (∼220-800 nm) At the same time, the bias voltage of heterostructure photodetectors was further reduced to 042 V The outstanding performance is mainly attributed to the formation of type-II heterojunctions between SnO2NTs and perovskite, which can facilitate the separation of photogenerated carriers, as well as Schottky junction between SnO2NTs and FTO, which reduce the bias voltage All the results indicate that the rational design of 1D-MO/perovskite heterostructure is a facile and efficient way to achieve high-performance photodetectors

Performance optimization of thermionic refrigerators based on van der Waals heterostructures

Abstract: In this paper, an irreversible thermionic refrigerator model based on van der Waals heterostructure with various irreversibilities is established by utilizing combination of non-equilibrium thermodynamics and finite time thermodynamics. The basic performance characteristics of the refrigerator are obtained. The effects of key factors, such as bias voltages, Schottky barrier heights and heat leakages, on the performance are studied. Results show that cooling rates and coefficients of performances (COPs) can attain the double maximum with proper modulation of barrier heights and bias voltages. Increasing cross-plane thermal resistance as well as decreasing electrode-reservoir thermal resistance and reservoir-reservoir thermal resistance can enhance the performance of the device. The optimal performance region is the interval between the maximum cooling rate point and the maximum COP point. By modulating the bias voltage, the working state of the device can fall into the optimal performance region. The optimal performance of the refrigerator when using single layer graphene and a few layers graphene as electrode material is also compared.

Broadband Electronically Scanned Reflectarray Antenna With Liquid Crystals

Abstract: In this letter, an electronically beam scanning reflectarray antenna is implemented using nematic liquid crystals (LCs). By loading a tunable phase shifter with a delay line structure in the resonance unit, the phase shift is achieved by tuning the dielectric constant of the LCs with a fixed structure through an external dc bias voltage for each unit. In doing so, dynamically controlling the reflection phase of each independent unit is realized. The experimental results show that the plane reflectarray unit can obtain a phase shift exceeding 360° with good linearity, and the maximum reflection loss is 7 dB. Moreover, a 10 × 10 LC-based planar reflectarray is fabricated and measured, and the bias voltage is loaded by a 100 outputs field-programmable gate array voltage module. In the frequency range of 22.1–26.1 GHz, its 3 dB relative bandwidth is 16.7%, the maximum gain of the main lobe is 20.2 dBi, and the maximum scanning angle is ±45°. The results verify the 2-D scanning functionality and the feasibility of improving the bandwidth of planar reflectarray antenna using LCs.

High performance polarization-sensitive self-powered imaging photodetectors based on a p-Te/n-MoSe2 van der Waals heterojunction with strong interlayer transition.

Abstract: In-plane anisotropic two-dimensional (2D) materials offer great opportunities for developing novel polarization sensitive photodetectors without being in conjunction with filters and polarizers. However, owing to low linear dichroism ratio and insufficient optical absorption of the few layer 2D materials, the comprehensive performance of the present polarization sensitive photodetectors based on 2D materials is still lower than the practical application requirements. In this work, after systematic investigation of the structural, vibrational, and optical anisotropies of layer-structured Te nanosheets, a novel polarization-sensitive self-powered imaging photodetector with high comprehensive performance based on a p-Te/n-MoSe2 van der Waals heterojunction (vdWH) with strong interlayer transition is proposed. Owing to the high rectification ratio (104) of the diode, the device shows excellent photovoltaic characteristics. As examples, the photodetectors exhibited an ultrahigh on/off ratio of 105 at a relatively weak light intensity (4.73 mw cm-2), and the highest responsivity of the device could reach 2106 mA W-1 without any power supply. In particular, benefitting from the excellent dichroism properties of Te nanosheets synthesized in this work, the anisotropic ratio of the photocurrent (Imax/Imin) could reach as high as 16.39 (405 nm, 24.2 mw cm-2). This value obtained under zero bias voltage is much greater than that of present 2D material photodetectors even at a bias voltage. In addition, the highest detectivity is 2.91 × 1013 Jones at a low bias voltage of -0.08 V. This work provides a novel building block for high resolution polarization-sensitive photodetection of weak signals in complex environments.

Defect characterization and charge transport measurements in high-resolution Ni/n-4H-SiC Schottky barrier radiation detectors fabricated on 250 μm epitaxial layers

Abstract: Advances in the growth processes of 4H-SiC epitaxial layers have led to the continued expansion of epilayer thickness, allowing for the detection of more penetrative radioactive particles. We report the fabrication and characterization of high-resolution Schottky barrier radiation detectors on 250 μm thick n-type 4H-SiC epitaxial layers, the highest reported thickness to date. Several 8 × 8 mm2 detectors were fabricated from a diced 100 mm diameter 4H-SiC epitaxial wafer grown on a conductive 4H-SiC substrate with a mean micropipe density of 0.11 cm−2. From the Mott–Schottky plots, the effective doping concentration was found to be in the range (0.95–1.85) × 1014 cm−3, implying that full depletion could be achieved at ∼5.7 kV (0.5 MV/cm at the interface). The current-voltage characteristics demonstrated consistently low leakage current densities of 1–3 nA/cm2 at a reverse bias of −800 V. This resulted in the pulse-height spectra generated using a 241Am alpha source (5486 keV) manifesting an energy resolution of less than 0.5% full width at half maximum (FWHM) for all the detectors at −200 V. The charge collection efficiencies (CCEs) were measured to be 98–99% with no discernable correlation to the energy resolution. A drift-diffusion model fit to the variation of CCE as a function of bias voltage, revealed a minority carrier diffusion length of ∼10 μm. Deep level transient spectroscopy measurements on the best resolution detector revealed that the excellent performance was the result of having ultralow concentrations of the order of 1011 cm−3 lifetime limiting defects—Z1/2 and EH6/7.

Large Tunneling Magnetoresistance in van der Waals Ferromagnet/Semiconductor Heterojunctions.

Abstract: 2D layered chalcogenide semiconductors have been proposed as a promising class of materials for low-dimensional electronic, optoelectronic, and spintronic devices. Here, all-2D van der Waals vertical spin-valve devices, that combine the 2D layered semiconductor InSe as a spacer with the 2D layered ferromagnetic metal Fe3 GeTe2 as spin injection and detection electrodes, are reported. Two distinct transport behaviors are observed: tunneling and metallic, which are assigned to the formation of a pinhole-free tunnel barrier at the Fe3 GeTe2 /InSe interface and pinholes in the InSe spacer layer, respectively. For the tunneling device, a large magnetoresistance (MR) of 41% is obtained under an applied bias current of 0.1 µA at 10 K, which is about three times larger than that of the metallic device. Moreover, the tunneling device exhibits a lower operating bias current but a more sensitive bias current dependence than the metallic device. The MR and spin polarization of both the metallic and tunneling devices decrease with increasing temperature, which can be fitted well by Bloch's law. These findings reveal the critical role of pinholes in the MR of all-2D van der Waals ferromagnet/semiconductor heterojunction devices.

Influence of Light Soaking on Silicon Heterojunction Solar Cells With Various Architectures

Abstract: In this article, we investigate the effect of prolonged light exposure on silicon heterojunction solar cells. We show that, although light exposure systematically improves solar cell efficiency in the case of devices using intrinsic and p-type layers with optimal thickness, this treatment leads to performance degradation for devices with an insufficiently thick (p) layer on the light-incoming side. Our results indicate that this degradation is caused by a diminution of the (i/p)-layer stack hole-selectivity because of light exposure. Degradation is avoided when a sufficiently thick (p) layer is used, or when exposure of the (p) layer to UV light is avoided, as is the case of the rear-junction configuration, commonly used in the industry. Additionally, applying a forward bias current or an infrared light exposure results in an efficiency increase for all investigated solar cells, independently of the (p)-layer thickness, confirming the beneficial influence of recombination on the performance of silicon heterojunction solar cells.

Multi-functional high-efficiency reflective polarization converter based on an ultra-thin graphene metasurface in the THz band.

Abstract: In this study, an ultra-thin reflective metasurface is proposed for polarization conversion in the terahertz band. Each unit cell of metasurface is composed of graphene ribbons lying diagonally on silicon substrate. A reflective metal is also placed at the bottom of the structure. Our polarization converter works as a linear polarization converter (LPC) and linear to circular polarization converter (LTC-PC) by variation of the chemical potential of graphene, which can actively be changed by chemical doping or electrical bias of the graphene. The working bandwidth of LPC changes by adjusting the chemical potential of the graphene. The LPC structure has more than 99% polarization conversion ratio in the frequency range of 0.83-0.92 THz, even by changing the angle of incident wave up to 45°, the results are still acceptable. The LTC-PC has less than 3dB axial ratio (AR) in the frequency range of 0.6-0.67 THz for left-handed circularly polarized (LHCP) waves and 0.72-0.97 THz for right-handed circularly polarized (RHCP) waves. To verify the simulation results, an equivalent circuit model based on the structure performance is proposed. Equivalent circuit model results agree very well with the simulation results. Due to the fabrication feasibility, ultra-thin thickness, incident angle insensitive, and high efficiency, our structure has great potential in state-of-the-art technologies such as imaging, sensing, communication, and other optical applications.

Simultaneous Control of Absorbing Frequency and Amplitude Using Graphene Capacitor and Active Frequency-Selective Surface

Abstract: In this communication, we propose a tunable radar absorber based on the combination of a graphene capacitor with a varactor-loaded active frequency-selective surface (FSS). The absorbing amplitude and frequency can be independently controlled by changing the effective sheet resistance of graphene and the capacitance of the varactor through different bias voltages, respectively. We fabricated the designed absorber and measured its tunable reflectivity. The measured results indicate that the absorber can tune its absorbing frequency ranging from 3.53 to 7.05 GHz under normal incidence when changing bias voltages applied to the varactors from 0.5 to 10 V. By further varying the graphene resistance through the bias voltage, the absorbing amplitude at each absorbing frequency can be dynamically modulated. In addition, it is found that the absorber achieves polarization-insensitive characteristics due to the symmetrical design of the active FSS. The physical mechanism of this absorber is discussed by providing the equivalent transmission-line (TL) model.

Bipolar and Complementary Resistive Switching Characteristics and Neuromorphic System Simulation in a Pt/ZnO/TiN Synaptic Device.

Abstract: In this work, a ZnO-based resistive switching memory device is characterized by using simplified electrical conduction models. The conventional bipolar resistive switching and complementary resistive switching modes are accomplished by tuning the bias voltage condition. The material and chemical information of the device stack including the interfacial layer of TiON is well confirmed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. The device exhibits uniform gradual bipolar resistive switching (BRS) with good endurance and self-compliance characteristics. Moreover, complementary resistive switching (CRS) is achieved by applying the compliance current at negative bias and increasing the voltage at positive bias. The synaptic behaviors such as long-term potentiation and long-term depression are emulated by applying consecutive pulse input to the device. The CRS mode has a higher array size in the cross-point array structure than the BRS mode due to more nonlinear I-V characteristics in the CRS mode. However, we reveal that the BRS mode shows a better pattern recognition rate than the CRS mode due to more uniform conductance update.

Influence of substrate bias and temperature on the crystallization of metallic NbTaTiVZr high-entropy alloy thin films

Abstract: Metallic sputtered high-entropy alloy (HEA) thin films often result in amorphous structures, due to the film growth kinetics and the large atomic size mismatch of the constituent elements. In this paper, single-phase crystalline NbTaTiVZr HEA thin films were achieved by the appropriate choice of both the alloying elements and the synthesis conditions. Regarding the latter, substrate biasing prompts Ar+ ion irradiation during film growth, whereas substrate heating increases the adatom mobility, inducing specific structural modifications. The control of both variables eliminates traditional crystallization strategies, such as adding nitrogen to the gas mixture during film growth or post-thermal annealing of the as-deposited films. Therefore, we have investigated the relationship between the synthesis conditions, the structure, and the mechanical properties of a Nb20Ta26Ti22V16Zr16 HEA thin film, due to its potential application in the field of refractory coating materials. The as-deposited films prepared at 400 °C possessed a body-centered cubic (bcc) phase, and their preferential orientation changed according to the bias voltage value (Vb) chosen. Low energy ion irradiation (Vb ≈ –25 V) resulted in crystallite coarsening and surface roughening. On the other hand, higher negative bias voltages (Vb ≈ –75 V) led to lower growth rates, grain refining, and improved mechanical properties. In addition, the chemical states and composition were determined by X-ray photoelectron spectroscopy (XPS) and the HEA phase formation was predicted using empirical parameters and compared to the results obtained by the Calculation of Phase Diagrams (CALPHAD) approach.

Optimizations of Si PIN diode phase-shifter for controlling MZM quadrature bias point using SOI rib waveguide technology

Abstract: Commercial high-speed silicon (Si) Mach-Zehnder modulator (MZM) required to be active around the quadrature bias point (linear transmission area) with low power consumption, small footprint, and small drive voltage. The bias controlling is done by an optical phase-shifter (PS). However, the accuracy is limited by the drive voltage, laser thermal drift, and fabrication errors. To overcome these problems, we propose in this paper the study and analysis of Si PIN diode PS under forward biasing at 1550 nm wavelength using the standard 220 nm substrate silicon-on-insulator (SOI) rib waveguide technology. Numerical investigations were carried out on the key geometrical parameters, doping concentration, doping locations, operating wavelength, biasing level. Results show that the optimal design can be operated with a lower voltage (Vπ = 1.629 v), lower attenuation (α = 28.985 dB/cm), and short device length with an extremely small voltage-length product VπL = 0.815 vmm. Thus, this PS can be used for designing an efficiency high-speed MZM and to obtain better performances in the optical commutation system.

High-speed and high-power germanium photodetector with a lateral silicon nitride waveguide

Abstract: Up to now, the light coupling schemes of germanium-on-silicon photodetectors (Ge-on-Si PDs) could be divided into three main categories: (1) vertical (or normal-incidence) illumination, which can be from the top or back of the wafer/chip, and waveguide-integrated coupling including (2) butt coupling and (3) evanescent coupling. In evanescent coupling the input waveguide can be positioned on top, at the bottom, or lateral to the absorber. Here, to the best of our knowledge, we propose the first concept of Ge-on-Si PD with double lateral silicon nitride (Si3N4) waveguides, which can serve as a novel waveguide-integrated coupling configuration: double lateral coupling. The Ge-on-Si PD with double lateral Si3N4 waveguides features uniform optical field distribution in the Ge region, which is very beneficial to improving the operation speed for high input power. The proposed Ge-on-Si PD is comprehensively characterized by static and dynamic measurements. The typical internal responsivity is evaluated to be 0.52 A/W at an input power of 25 mW. The equivalent circuit model and theoretical 3 dB opto-electrical (OE) bandwidth investigation of Ge-on-Si PD with lateral coupling are implemented. Based on the small-signal (S21) radio-frequency measurements, under 4 mA photocurrent, a 60 GHz bandwidth operating at −3 V bias voltage is demonstrated. When the photocurrent is up to 12 mA, the 3 dB OE bandwidth still has 36 GHz. With 1 mA photocurrent, the 70, 80, 90, and 100 Gbit/s non-return-to-zero (NRZ) and 100, 120, 140, and 150 Gbit/s four-level pulse amplitude modulation clear openings of eye diagrams are experimentally obtained without utilizing any offline digital signal processing at the receiver side. In order to verify the high-power handling performance in high-speed data transmission, we investigate the eye diagram variations with the increase of photocurrents. The clear open electrical eye diagrams of 60 Gbit/s NRZ under 20 mA photocurrent are also obtained. Overall, the proposed lateral Si3N4 waveguide structure is flexibly extendable to a light coupling configuration of PDs, which makes it very attractive for developing high-performance silicon photonic integrated circuits in the future.

Leakage Current Suppression with Capacitor Voltage Control of Three-level Flying Capacitor Grid-Connected Inverters

Abstract: Leakage current issues are worthy of attention for non-isolated grid-connected systems. This paper introduces the method of eliminating common-mode (CM) voltage and reducing the leakage current based on modulation, and analyzes the correlation between actual effects of the method and the flying capacitor (FC) voltage balance in three-phase three-level FC grid-connected inverter. The proposed carrier-based modulation can balance the FC voltage by changing the transmission sequences of pulses and theoretically achieve zero CM voltage. In order to deal with the low frequency fluctuation and bias voltage of FC caused by asymmetry of actual hardware, the control method is introduced, which controls FC voltage by changing the action times distribution of switches, while still eliminating the CM voltage. Simulation and experimental results are provided to validate that the proposed method can control FC voltage and achieve good performance in suppressions of CM voltage, leakage current and CM EMI noise.

Highly efficient self-powered perovskite photodiode with an electron-blocking hole-transport NiOx layer.

Abstract: Hybrid organic–inorganic perovskite materials provide noteworthy compact systems that could offer ground-breaking architectures for dynamic operations and advanced engineering in high-performance energy-harvesting optoelectronic devices. Here, we demonstrate a highly effective self-powered perovskite-based photodiode with an electron-blocking hole-transport layer (NiOx). A high value of responsivity (R = 360 mA W−1) with good detectivity (D = 2.1 × 1011 Jones) and external quantum efficiency (EQE = 76.5%) is achieved due to the excellent interface quality and suppression of the dark current at zero bias voltage owing to the NiOx layer, providing outcomes one order of magnitude higher than values currently in the literature. Meanwhile, the value of R is progressively increased to 428 mA W−1 with D = 3.6 × 1011 Jones and EQE = 77% at a bias voltage of − 1.0 V. With a diode model, we also attained a high value of the built-in potential with the NiOx layer, which is a direct signature of the improvement of the charge-selecting characteristics of the NiOx layer. We also observed fast rise and decay times of approximately 0.9 and 1.8 ms, respectively, at zero bias voltage. Hence, these astonishing results based on the perovskite active layer together with the charge-selective NiOx layer provide a platform on which to realise high-performance self-powered photodiode as well as energy-harvesting devices in the field of optoelectronics.

High-Performance Flexible Self-Powered Photodetectors Utilizing Spontaneous Electron and Hole Separation in Quasi-2D Halide Perovskites.

Abstract: Although there are recent advances in many areas of quasi-2D halide perovskites, photodetectors based on these materials still cannot achieve satisfactory performance for practical applications where high responsivity, fast response, self-powered nature, and excellent mechanical flexibility are urgently desired. Herein, utilizing one-step spin-coating method, self-assemble quasi-2D perovskite films with graded phase distribution in the order of increasing number of metal halide octahedral layers are successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained and then employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibits impressive performance with the responsivity up to 444 mA W-1 and ultrashort response time down to 52 µs. With a bias voltage of 1.5 V, the device responsivity becomes 3463 mA W-1 with the response speed as fast as 24 µs. Importantly, the device's mechanical flexibility is greatly enhanced since the photocurrent prefers flowing through the metal halide octahedral layers between the top and bottom contact electrodes in the vertical device structure, being more tolerant to film damage. These results evidently indicate the potential of graded quasi-2D perovskite phases for next-generation optoelectronic devices.

High-resolution radiation detection using Ni/SiO2/n-4H-SiC vertical metal-oxide-semiconductor capacitor

Abstract: In this article, we demonstrate the radiation detection performance of vertical metal-oxide-semiconductor (MOS) capacitors fabricated on 20 μm thick n-4H-SiC epitaxial layers with the highest energy resolution ever reported. The 100 nm SiO2 layer was achieved on the Si face of n-4H-SiC epilayers using dry oxidation in air. The Ni/SiO2/n-4H-SiC MOS detectors not only demonstrated an excellent energy resolution of 0.42% ( ΔE/E×100) for 5.48 MeV alpha particles but also caused a lower enhancement in the electronic noise components of the spectrometer compared with that observed for the best high-resolution Schottky barrier detectors. The MOS detectors also exhibited a high charge collection efficiency (CCE) of 96% at the optimized operating bias despite the presence of the oxide layer. A drift-diffusion model applied to the CCE vs gate bias voltage data revealed a minority (hole) carrier diffusion length of 24 μm. Capacitance mode deep level transient spectroscopy (C-DLTS) scans in the temperature range 84–800 K were carried out to identify the resolution limiting electrically active defects. Interestingly, the C-DLTS spectra revealed both positive and negative peaks, indicating the simultaneous presence of electron (majority) and hole (minority) trap centers. It has been inferred that at the steady-state bias for the C-DLTS measurement, the MOS detector operates in the inversion mode at certain device temperatures, causing holes to populate the minority trap centers and, hence, manifests minority carrier peaks as well.

Highly In-Plane Polarization-Sensitive Photodetection in CsPbBr3 Single Crystal.

Abstract: The fully inorganic perovskite lead cesium bromide single crystal (CsPbBr3 SC) is considered as an excellent candidate semiconductor for photodetectors because of its superior humidity resistance, thermal stability, and light stability compared with organic-inorganic hybrid perovskites as well as its photoelectric properties such as large light absorption coefficient and ultralong carrier migration distance. In this Letter, we utilize the inverse temperature solubility of CsPbBr3 in ternary solvents to grow large-sized CsPbBr3 SCs. By the use of the (101) plane, CsPbBr3 SC-based photodetectors are fabricated, which exhibit excellent polarized light response characteristics. The photocurrent relies on the polarization angle in a sinusoidal fashion and shows strong anisotropic optoelectronic properties. The photodetection performance perpendicular to the y axis is significantly higher than that parallel to the y axis, and the dichroic ratio under 405 nm illumination at a bias voltage of 1 V reaches 2.65. The experimental results are consistent with the results of first-principles calculations.

Design and Verification of SFQ Cell Library for Superconducting LSI Digital Circuits

Abstract: We have developed a cell library for superconducting large scale integrated (LSI) digital circuits based on Single Flux Quantum (SFQ) devices. The circuits were designed for a 6-kA/cm2 Nb/AlOx/Nb junction process with 10 mask levels including one ground plane and two Nb wiring layers. The initial design and optimization of the circuit parameters were achieved by means of the optimization functions in a circuit simulator, PSCAN2, to ensure that important circuit parameters, Josephson critical current ( IC ), bias current ( Ibias ), and inductance satisfied minimal margin requirements. Critical margins of IC and Ibias were then further improved manually. To compensate the scattering in the circuit parameters from fabrication by design as much as possible, the critical junction parameters were optimized to further centralize the IC . The library cells were laid out following our design rules determined by systematic experiments on process control monitors (PCM). Basic cells including Josephson transmission lines, splitters, confluence buffers, D flip-flops, T flip-flops, and XOR and NDRO gates were designed, fabricated, and successfully tested at low frequencies. Wide overlaps of the operating regions for the common bias voltages were confirmed.