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Suarez E.,University of Connecticut | Chan P.-Y.,University of Connecticut | Lingalugari M.,University of Connecticut | Ayers J.E.,University of Connecticut | And 2 more authors.
Journal of Electronic Materials | Year: 2013

This paper describes the use of II-VI lattice-matched gate insulators in quantum dot gate three-state and flash nonvolatile memory structures. Using silicon-on-insulator wafers we have fabricated GeO x -cladded Ge quantum dot (QD) floating gate nonvolatile memory field-effect transistor devices using ZnS-Zn0.95Mg0.05S-ZnS tunneling layers. The II-VI heteroepitaxial stack is nearly lattice-matched and is grown using metalorganic chemical vapor deposition on a silicon channel. This stack reduces the interface state density, improving threshold voltage variation, particularly in sub-22-nm devices. Simulations using self-consistent solutions of the Poisson and Schrödinger equations show the transfer of charge to the QD layers in three-state as well as nonvolatile memory cells. © 2013 TMS.

Jain F.C.,University of Connecticut | Miller B.,University of Connecticut | Suarez E.,University of Connecticut | Chan P.-Y.,University of Connecticut | And 5 more authors.
Journal of Electronic Materials | Year: 2011

This paper presents the implementation of a novel InGaAs field-effect transistor (FET), using a ZnSe-ZnS-ZnMgS-ZnS stacked gate insulator, in a spatial wavefunction-switched (SWS) structural configuration. Unlike conventional FETs, SWS devices comprise two or more asymmetric coupled quantum wells (QWs). This feature enables carrier transfer vertically from one quantum well to another or laterally to the wells of adjacent SWS-FET devices by manipulation of the gate voltages (V g). Observation of an extra peak (near both accumulation and inversion regions) in the capacitance-voltage data in an InGaAs-AlInAs two-quantum-well SWS structure is presented as evidence of spatial switching. The peaks are attributed to the appearance of carriers first in the lower well and subsequently their transfer to the upper well as the gate voltage is increased. The electrical characteristics of a fabricated SWS InGaAs FET are also presented along with simulations of capacitance-voltage (C-V) behavior, showing the effect of wavefunction switching between wells. Finally, logic operations involving simultaneous processing of multiple bits in a device, using coded spatial location of carriers in quantum well channels, are also described. © 2011 TMS.

Suarez E.,University of Connecticut | Gogna M.,University of Connecticut | Al-Amoody F.,University of Connecticut | Karmakar S.,University of Connecticut | And 3 more authors.
Journal of Electronic Materials | Year: 2010

This paper presents preliminary data on quantum dot gate nonvolatile memories using nearly lattice-matched ZnS/Zn 0.95Mg 0.05S/ZnS tunnel insulators. The GeO x-cladded Ge and SiO x-cladded Si quantum dots (QDs) are self-assembled site-specifically on the II-VI insulator grown epitaxially over the Si channel (formed between the source and drain region). The pseudo- morphic II-VI stack serves both as a tunnel insulator and a high-κ dielectric. The effect of Mg incorporation in ZnMgS is also investigated. For the control gate insulator, we have used Si 3N 4 and SiO 2 layers grown by plasma- enhanced chemical vapor deposition. © 2010 TMS.

Jain F.C.,University of Connecticut | Chandy J.,University of Connecticut | Miller B.,University of Connecticut | Hasaneen E.-S.,Minia University | Heller E.,RSoft Design Group
International Journal of High Speed Electronics and Systems | Year: 2011

Spatial Wavefunction-Switched (SWS) Field-Effect Transistors (FETs) consist of inversion layers comprising two or more coupled quantum wells (QWs). Carriers can be localized in any of the wells and vertically transferred between them by changing the gate voltage. In addition, carriers can also be laterally transferred between adjacent SWSFET devices by the manipulation of the gate voltages (Vg). This enables processing of two more bits simultaneously by changing the spatial location of the carrier ensemble wavefunction, which in turn determines the state of the device [e.g., electrons in well W2 (01), in W1 (10), in both (11), in neither (00)]. Experimentally, the capacitance-voltage data, having a distinct peak, has been presented in InGaAs-AlInAs two-quantum well structures. The peak(s) are attributed to the appearance of carriers, first in the lower well and subsequently their transfer to the upper well. Use of multiple channels allows for CMOS-like configuration with both transistors having n-channel mobilities. Simulation of an InGaAs SWS inverter computes a gate delay of 0.24ps. A cut-off frequency in excess of 8THz is computed for 12nm channel length InGaAs SWSFETs. Examples, including logic gates and a 3-bit full-adder, are presented to show the reduction of device count when SWS-FETs are employed. © 2011 World Scientific Publishing Company.

Jain F.,University of Connecticut | Karmakar S.,University of Connecticut | Chan P.-Y.,University of Connecticut | Suarez E.,University of Connecticut | And 3 more authors.
Journal of Electronic Materials | Year: 2012

This paper describes fabrication and modeling of quantum dot channel (QDC) field-effect transistors (FETs). A QDC-FET comprises an array of thin-barrier (∼1 nm) cladded Si, Ge, or other quantum dots (3 nm to 4 nm) forming an n-channel on a p-Si layer/substrate between the source and drain regions. Experimental characteristics of fabricated QDC-FETs, consisting of two layers of cladded quantum dot arrays (e.g., SiO x-cladded Si dots and GeO x-cladded Ge dots) serving as the transport channel, are presented. Unlike conventional FETs, QDC-FET structures exhibit step-like I D-V G characteristics and discretely bunched I D-V D characteristics as a function of gate voltage. The transfer characteristics appear to be similar to those of single-electron transistors (SETs). However, QDC-FETs employ transport of many electrons and operate at room temperature. A one-dimensional Tsu-Esaki equation is used to simulate the quantum dot channel and explain the steps in the current-voltage behavior. In particular, the effect of the II-VI barrier layers on Ge dots is modeled. The QDC-FET channel is also modeled as having superlattice-like mini-energy bands whose bandwidth and separation are determined by the dot size, cladding thickness, and barrier height. For a given gate voltage (which determines the carrier concentration), carriers in the inversion channel are transported via mini-energy bands that line up with the Fermi level as the drain voltage V DS is changed, producing step-like multistate electrical characteristics. Formation of the quantum dot channel enables higher-mobility transport on very low-mobility substrates or thin films such as poly-Si. The channel mobility can be further enhanced by partially removing the oxide barrier layer and replacing it with lattice-matched II-VI gate insulator layers. © 2012 TMS.

Chan P.-Y.,University of Connecticut | Suarez E.,University of Connecticut | Gogna M.,University of Connecticut | Miller B.I.,University of Connecticut | And 3 more authors.
Journal of Electronic Materials | Year: 2012

This paper presents an indium gallium arsenide (InGaAs) quantum dot gate field-effect transistor (QDG-FET) that exhibits an intermediate "i" state in addition to the conventional ON and OFF states. The QDG-FET utilized a II-VI gate insulator stack consisting of lattice-matched ZnSe/ZnS/ZnMgS/ZnS/ZnSe for its high-κ and wide-bandgap properties. Germanium oxide (GeO x)-cladded germanium quantum dots were self-assembled over the gate insulator stack, and they allow for the three-state behavior of the device. Electrical characteristics of the fabricated device are also presented. © 2012 TMS.

Agency: GTR | Branch: EPSRC | Program: | Phase: Research Grant | Award Amount: 527.23K | Year: 2012

Historically the optical fibre was perceived to provide unlimited bandwidth, however, the capacity of current communications systems based on single mode optical fibre technology is very close to the limits (within a factor of 2) imposed by the physical transmission properties of single mode fibres. The major challenge facing optical communication systems is to increase the transmission capacity in order to meet the growing demand (40% increase year-on-year) whilst reducing the cost and energy consumption per bit transmitted. If new technologies are not developed to overcome the capacity limitations inherent in single mode fibres and unlock the fibre bandwidth then the growth in the digital services, applications and the economy that these drive is likely to be curtailed. The need for increased capacity in the core and metro areas of the network and within computing data centres is likely to become even more acute as optical access technologies, providing far greater bandwidths directly to the users, take hold and services such as ubiquitous cloud computing are adopted. Multimode optical fibres (MMF) offer the potential to increase the capacity beyond that of current technologies by exploiting the spatial modes of the MMF as additional transmission paths. To fully exploit this available capacity it is necessary to use coherent optical (CO) reception and multiple-input multiple-output (MIMO) digital signal processing techniques analogous to those already used in wireless communication systems such as WiFi. This project aims to develop the technologies and sub-systems required to implement a CO-MIMO system over MMF that exceeds the capacity of current single mode fibre systems and reduces the cost and energy consumption per bit transmitted. To achieve this goal the project addresses the following key engineering challenges necessary to realise a complete system demonstrator. Engineer the channel: The multimode optical fibre MIMO channel, unlike its wireless counterpart, presents the opportunity to engineer the optical channel to optimise its performance for MIMO operation by designing and fabricating new optical fibres, using proven solid core technology, to maximise the MIMO capacity of the fibre. Dynamically control the channel: The transmission characteristic of the multimode optical fibre channel varies with time. We will exploit both the flexible and fast adaptive nature of digital signal processing, and the less energy intensive and slower adaptation of liquid crystal spatial light modulator based optical signal processing to compensate for the channel variation and recover the spatially multiplexed data channels. Employ energy efficient optical amplification: In order to reduce both the energy consumption and cost per bit and to extend the propagation distance into the hundreds of kilometres region it is essential to develop optical fibre amplification technologies that provide amplification to multiple spatial and wavelength channels and thus share the cost. Coherently detect the optical signal to exploit the wavelength and spatial domains: The developed system will combine spatial multiplexing with existing dense wavelength division multiplexing, polarisation multiplexing and multilevel modulation techniques to maximise the capacity. The key to achieving this is the use of coherent optical detection and digital signal processing, which is essential not only to fully exploit the spatial capacity of the MMF channel, but also facilitates the use of existing multiplexing techniques that are difficult to realise in conventional multimode transmission systems. The technologies and systems developed within this project will find applications, ranging from capacity upgrades of existing MMF data networks in data and computer processing centres, through to the installation of new high capacity metro and long haul fibre transmission systems using the MIMO optimised fibres and technologies developed in this project.

Kota S.,RSoft Design Group | Patel J.,RSoft Design Group | Ghillino E.,RSoft Design Group | Richards D.,CUNY - College of Staten Island
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

In this paper, we demonstrate a computer model for simulating a dual-rate burst mode receiver that can readily distinguish bit rates of 1.25Gbit/s and 10.3Gbit/s and demodulate the data bursts with large power variations of above 5dB. To our knowledge, this is the first such model to demodulate data bursts of different bit rates without using any external control signal such as a reset signal or a bit rate select signal. The model is based on a burst-mode bit rate discrimination circuit (B-BDC) and makes use of a unique preamble sequence attached to each burst to separate out the data bursts with different bit rates. Here, the model is implemented using a combination of the optical system simulation suite OptSim™, and the electrical simulation engine SPICE. The reaction time of the burst mode receiver model is about 7ns, which corresponds to less than 8 preamble bits for the bit rate of 1.25Gbps. We believe, having an accurate and robust simulation model for high speed burst mode transmission in GE-PON systems, is indispensable and tremendously speeds up the ongoing research in the area, saving a lot of time and effort involved in carrying out the laboratory experiments, while providing flexibility in the optimization of various system parameters for better performance of the receiver as a whole. Furthermore, we also study the effects of burst specifications like the length of preamble sequence, and other receiver design parameters on the reaction time of the receiver. © 2011 SPIE.

Agency: Department of Defense | Branch: Navy | Program: STTR | Phase: Phase I | Award Amount: 79.69K | Year: 2011

We proposed to perform innovative research towards the developing of a simulation tool consisting of a comprehensive set of models and including modeling techniques that account for the complex interactions between optical network components in WDM LANs, such as those planned for aerospace platforms. To a large extent, the modeling effort will be guided by the ongoing work of the AS-3 WDM LAN working group, with experimental validation to be conducted later in Phase II through a testbed that is applicable to the development activities of the SAE AS-5659 industry standard open architecture. Specifically, Phase I will specify a technique to model optical return loss (ORL) in a system simulation tool, such as OptSim from RSoft Design Group; determine the nature of the complex interactions in WDM LANs resulting from the interplay of optical amplification, ORL, and transients due to amplifier gain dynamics and channel equalization in a multiwavelength network; specify a flexible set of OptSim simulation options and corresponding software configurations that allow the simulation technique to be based on either wavelength-domain simulation (WDS), full waveform (time-domain) simulation, or a combination of WDS and waveform simulation; specify requirements and software modules for a WDM LAN planning tool based on RSoft"s MetroWAND network planning tool; and specify key experiments to validate the modeling techniques during the Phase II effort.

Ghillino E.,RSoft Design Group | Curri V.,Polytechnic University of Turin | Carena A.,Polytechnic University of Turin
International Conference on Transparent Optical Networks | Year: 2011

We evaluate by simulation the maximum reachable distance of ten Nyquist-WDM channels at 240 Gbps based on PM-16QAM in PSCF links. Operating with a channel spacing of only 1.1R S and using Raman amplification, we demonstrate a maximum reachable distance of 3,600 km. Moreover, we make an assessment of the scaling of nonlinear impairments in the case of using hybrid EDFA/Raman amplification. © 2011 IEEE.

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