International Journal of High Speed Electronics and Systems

Quantum Dot (QD) Optical Modulators can provide high speed modulation in low cost indirect bandgap materials. Si based optical modulators can be realized with the inclusion of self-assembled Ge QDs to provide low cost, high speed CMOS compatible optical devices. In this paper, we present the optical characterization of a novel Ge-QD Si-SiO2 based waveguide for use in as an optical modulator. Optical performance figures of merit are investigated including insertion loss (IL) measurements, and Wavelength dependent loss (WDL). We present a multimode waveguide fabricated with conventional CMOS processing. The waveguide provides 4.43dB/cm loss and individual discrete absorption regimes corresponding to the unique minibands produced by superlattice properties of the self-assembled Ge QDs in the IR regime. Absorption properties of the Ge QDs are demonstrated and verified against the QD superlattice bandgap model. Analysis and simulation is presented to qualitatively compare the QD bandgap energies with the reported optical properties. The QD functionalized structure demonstrates the fundamental optical principles of a QD waveguide, setting the foundation for a active modulation testing of this QD based optical modulator.

We present a cost effective and scalable approach to fabricate solid state thermal neutron detectors. Electrophoretic deposition technique is used to fill deep silicon trenches with ¹⁰B nanoparticles instead of conventional chemical vapor deposition process. Deep silicon trenches with width of 5-6 μm and depth of 60-65 μm were fabricated in a p-type Si (110) wafer using wet chemical etching method instead of DRIE method. These silicon trenches were converted into continuous p-n junction by the standard phosphorus diffusion process. ¹⁰B micro/nano particle suspension in ethyl alcohol was used for electrophoretic deposition of particles in deep trenches and iodine was used to change the zeta potential of the particles. The measured effective boron nanoparticles density inside the trenches was estimated to be 0.7 gm cm^-3. Under the self-biased condition, the fabricated device showed the intrinsic thermal neutron detection efficiency of 20.9% for a 2.5 × 2.5 mm² device area.

In this paper, we propose a structure using four layers of quantum dots on crystalline silicon. The quantum dots site-specifically self-assembled in the p-type material due to the electrostatic attraction. This quantum dot super lattice (QDSL) structure will be constructed using a mixed layer of Germanium (Ge) and Silicon (Si) dots. Atomic Force Microscopy results will show the accurate stack height formed from individual and multi stacked layers. This is the first novel characterization of 4 layers of 2 separate self assemblies. This was also applied to a quantum dot gate field effect transistor (QDG-FET).

This paper presents the design and simulation of static random access memory (SRAM) using Quantum Dot Channel Field-Effect Transistors (QDC-FETs). A QDC-FET consist of two quantum dots (3 nm to 4 nm) forming n-channel between the source and drain Quantum Dot Channel (QDC) on a p-Si substrate regions. The quantum dot channel enables higher-mobility transport on very low-mobility substrates. The structure of a quantum dot channel QDC-FET that has shown four-state characteristics of charge carriers from one channel to other channel of the device. It shows that four states can be obtained in an inverter made of four-state QDC-FETs. The four stats QDC-FETs is suitable for quaternary logic application with less complex and more area efficient than existing quaternary logic circuits. The device with four-state has been modeled using Berkeley Short-channel IGFET Model (BSIM) and Analog Behavioral Model (ABM), the model is suitable for transient analysis at circuit level. This model is optimized for a quaternary inverter logic and used to replace a conventional CMOS SRAM.

Quantum dot channel (QDC) and Quantum dot gate (QDG) field effect transistors (FETs) have been fabricated on crystalline Si using cladded Si and Ge quantum dots. This paper presents fabrication and modeling of quantum dot channel field effect transistors (QDC-FETs) using cladded Ge quantum dots on poly-Si thin films grown on silicon-on-insulator (SOI) substrates. HfAlO₂ high-k dielectric layers are used for the gate dielectric. QDC-FETs exhibit multi-state I-V characteristics which enable two-bit processing, and reduce FET count and power dissipation. QDC-FETs using germanium quantum dots provide higher electron mobility than conventional poly-silicon FETs, and mobility values comparable to conventional FETs using single crystalline silicon.

This paper presents an approach to enhance floating gate quantum dot nonvolatile random access memory (QDNVRAM) cells in terms of higher-speed and lower-voltage Erase not possible with conventional floating gate nonvolatile memories. It is achieved by directly accessing the floating gate layer with a Ge quantum dot access channel via an additional drain (D2) during the Erase and/or Write operation. Quantum mechanical simulations in GeO_x-cladded Ge quantum dot layers functioning as the floating gate as well access channel to facilitate Erase and Write are presented. Experimental data on fabricated long channel nonvolatile random access memory cell with SiO_x-cladded Si dots is presented. Quantum simulations show lower voltage operation for GeO_x-cladded Ge QD floating gate than SiO_x-cladded Si dots. The Erase time is orders of magnitude faster than flash and is comparable to competing NVRAMs.

An inductorless power converter for low-power energy harvesting is presented. The power converter for energy harvesting is employed to maximize power extraction from energy sources. The power converter is based on a capacitive boost converter which is divided into two stages; a number of first-stage in parallel and shared-stage. The first-stage maximizes power extraction from the energy source while the shared-stage operates as a conventional charge pump. For not only low-power energy source but also high-power energy source, the maximum power extraction is targeted by the proposed converter. The extracted power from energy sources enhances by range from 117% to 161% over the conventional design. The output current of the proposed converter with three first-stages is improved by 183% over conventional converter. The peak efficiencies achieved with three and one first-stage are 53.3% and 38.5% for the proposed and the conventional converters, respectively. The peak end-to-end efficiency is enhanced by 198% as compared to the conventional converter. The proposed inductorless power converter has been implemented on a 0.13μm CMOS process.

In this paper, we propose and experimentally demonstrate a mode locked fiber ring laser with the implementation of a photonic crystal fiber (PCF) to generate pulse train at high speed. This fiber ring laser combines rational harmonic mode locking based on a Lithium Niobate Mach-Zehnder modulator and nonlinear polarization rotation from a highly nonlinear PCF. By fine tuning of the modulation frequency and the polarization controllers in the cavity, a 30 GHz pulse train with pulse width 1.9 ps is generated. Without the PCF, the pulse width at 30 GHz from the rational harmonic mode locking is 5.8 ps. We also conduct numerical simulations of the pulse evolution, which shows good agreements of the experimental results.

Chirped superlattices are of interest as buffer layers in metamorphic semiconductor device structures, because they can combine the mismatch accommodating properties of compositionally-graded layers with the dislocation filtering properties of superlattices. Important practical aspects of the chirped superlattice as a buffer layer are the surface strain and surface in-plane lattice constant. In this work two basic types of InGaAs/GaAs chirped superlattice buffers have been studied. In design I (composition modulated), the average composition is varied by modulating the composition of one of the two layers in the superlattice period, but the individual layer thicknesses were fixed. In design II (thickness modulated), the individual layer thicknesses were modulated, but the compositions were fixed. In this paper the surface strain and surface in-plane lattice constant for these chirped superlattices are presented as functions of the top composition and period for each of these basic designs.

We applied the mosaic crystal model to calculate the dynamical x-ray rocking curves for a coherently-strained GaAs/In_0.3Ga_0.7As/GaAs single quantum well grown epitaxially on a GaAs (001) substrate for a number of reflection profiles, including 004, 113, 224, 044 and 444 reflections. We show that it is possible to estimate the threading dislocation density in the quantum well, and therefore detect the pseudomorphic-metamorphic transition, using the widths or normalized intensities of the primary quantum well Bragg peak, or using the widths of the Pendellösung fringes associated with the quantum well structure.

Microwave absorption properties (MAP) of manganese soft spinel ferrite (MnFe2O4) nanoparticles (MSF NPs) mixed with multi-walled carbon nanotubes (MWCNTs) and molded as toroid-shaped pellets were experimentally studied using a coaxial line technique in the frequency range of 2-18 GHz. We used the coaxial line technique because of the smaller sample size, a wider frequency range, and a uniform cross section. The MAP were derived from the measured constitutive parameters, according to the transmission line theory. The results indicate that MWCNTs blended with ferrite nanoparticles represent a promising choice for broadband microwave absorbing materials.

This publication considers the use of a variety of additive manufacturing techniques in the development of wireless modules and sensors. The opportunities and advantages of these manufacturing techniques are explored from an application point of view. We discuss first the origami (4D-printed) structures which take advantage of the ability to alter the shape of the inkjet-printed conductive traces on the paper substrate to produce a reconfigurable behavior. Next, focus is shifted towards the use of additive manufacturing technology to develop skin-like flexible electrical system for wireless sensing applications. We then discuss the development of a fully flexible energy autonomous body area network for autonomous sensing applications, the system is fabricated using 3D and inkjet printing techniques. Finally, an integration of inkjet and 3D printing for the realization of efficient mm-wave 3D interconnects up to 60GHz is discussed.

We propose a scheme to realize all-optical logic operation in quantum-dot semiconductor optical amplifier (QD-SOA) based Mach-Zehnder interferometer (MZI) considering the effects of two-photon absorption (TPA). During propagation of sub-picosecond pulses in QD-SOA, TPA leads to an additional change in carrier recovery dynamics in quantum-dots. We utilize a rate equation model to take into account carrier refill through TPA and nonlinear dynamics including carrier heating and spectral hole burning in the QD-SOA. The simulation results show the TPA induced pumping in the QD-SOA can reduce the pattern effect and increase the output quality of the all-optical logic operation. With TPA, this scheme is suitable for high speed Boolean logic operation at 320 Gb/s.