165 research outputs found
Stochastic Memory Devices for Security and Computing
With the widespread use of mobile computing and internet of things, secured communication and chip authentication have become extremely important. Hardware-based security concepts generally provide the best performance in terms of a good standard of security, low power consumption, and large-area density. In these concepts, the stochastic properties of nanoscale devices, such as the physical and geometrical variations of the process, are harnessed for true random number generators (TRNGs) and physical unclonable functions (PUFs). Emerging memory devices, such as resistive-switching memory (RRAM), phase-change memory (PCM), and spin-transfer torque magnetic memory (STT-MRAM), rely on a unique combination of physical mechanisms for transport and switching, thus appear to be an ideal source of entropy for TRNGs and PUFs. An overview of stochastic phenomena in memory devices and their use for developing security and computing primitives is provided. First, a broad classification of methods to generate true random numbers via the stochastic properties of nanoscale devices is presented. Then, practical implementations of stochastic TRNGs, such as hardware security and stochastic computing, are shown. Finally, future challenges to stochastic memory development are discussed
Memory and forgetting processes with the firing neuron model
The aim of this paper is to present a novel algorithm for learning and forgetting within a very simplified, biologically derived model of the neuron, called firing cell (FC). FC includes the properties: (a) delay and decay of postsynaptic potentials, (b) modification of internal weights due to propagation of postsynaptic potentials through the dendrite, (c) modification of properties of the analog weight memory for each input due to a pattern of long-term synaptic potentiation. The FC model could be used in one of the three forms: excitatory, inhibitory, or receptory (ganÂglion cell). The computer simulations showed that FC precisely performs the time integration and coincidence detection for incoming spike trains on all inputs. Any modification of the initial values (internal parameters) or inputs patterns caused the following changes of the interspike intervals time series on the output, even for the 10 s or 20 s real time course simulations. It is the basic evidence that the FC model has chaotic dynamical properties. The second goal is the presentation of various nonlinear methods for analysis of a biological time series. (Folia Morphol 2018; 77, 2: 221–233
Interference of Spread-Spectrum Modulated Disturbances on Digital Communication Channels
In this paper, the effects of random spread spectrum (SS) electromagnetic interference (EMI) on digital communications are addressed. For this purpose, the influence of EMI on a communication channel is described in the framework of information theory in terms of an equivalent channel capacity loss, which is analytically predicted and validated by experimental results. The EMI-induced channel capacity loss for non-modulated and SS-modulated interference generated by a switching-mode DC-DC power converter are then evaluated for different EMI and channel characteristics so that to compare different scenarios of practical interest
Phase Noise Analyses and Measurements in the Hybrid Memristor-CMOS Phase-Locked Loop Design and Devices Beyond Bulk CMOS
Phase-locked loop (PLLs) has been widely used in analog or mixed-signal integrated circuits. Since there is an increasing market for low noise and high speed devices, PLLs are being employed in communications. In this dissertation, we investigated phase noise, tuning range, jitter, and power performances in different architectures of PLL designs. More energy efficient devices such as memristor, graphene, transition metal di-chalcogenide (TMDC) materials and their respective transistors are introduced in the design phase-locked loop.
Subsequently, we modeled phase noise of a CMOS phase-locked loop from the superposition of noises from its building blocks which comprises of a voltage-controlled oscillator, loop filter, frequency divider, phase-frequency detector, and the auxiliary input reference clock. Similarly, a linear time-invariant model that has additive noise sources in frequency domain is used to analyze the phase noise. The modeled phase noise results are further compared with the corresponding phase-locked loop designs in different n-well CMOS processes.
With the scaling of CMOS technology and the increase of the electrical field, the problem of short channel effects (SCE) has become dominant, which causes decay in subthreshold slope (SS) and positive and negative shifts in the threshold voltages of nMOS and pMOS transistors, respectively. Various devices are proposed to continue extending Moore\u27s law and the roadmap in semiconductor industry. We employed tunnel field effect transistor owing to its better performance in terms of SS, leakage current, power consumption etc. Applying an appropriate bias voltage to the gate-source region of TFET causes the valence band to align with the conduction band and injecting the charge carriers. Similarly, under reverse bias, the two bands are misaligned and there is no injection of carriers. We implemented graphene TFET and MoS2 in PLL design and the results show improvements in phase noise, jitter, tuning range, and frequency of operation. In addition, the power consumption is greatly reduced due to the low supply voltage of tunnel field effect transistor
Silicon carbide technology for extreme environments
PhD ThesisWith mankind’s ever increasing curiosity to explore the unknown, including a variety of
hostile environments where we cannot tread, there exists a need for machines to do
work on our behalf. For applications in the most extreme environments and applications
silicon based electronics cannot function, and there is a requirement for circuits and
sensors to be built from wide band gap materials capable of operation in these domains.
This work addresses the initial development of silicon carbide circuits to monitor
conditions and transmit information from such hostile environments. The
characterisation, simulation and implementation of silicon carbide based circuits
utilising proprietary high temperature passives is explored.
Silicon carbide is a wide band gap semiconductor material with highly suitable
properties for high-power, high frequency and high temperature applications. The
bandgap varies depending on polytype, but the most commonly used polytype 4H, has a
value of 3.265 eV at room temperature, which reduces as the thermal ionization of
electrons from the valence band to the conduction band increases, allowing operation in
ambient up to 600°C.
Whilst silicon carbide allows for the growth of a native oxide, the quality has limitations
and therefore junction field effect transistors (JFETs) have been utilised as the switch in
this work. The characteristics of JFET devices are similar to those of early thermionic
valve technology and their use in circuits is well known. In conjunction with JFETs,
Schottky barrier diodes (SBDs) have been used as both varactors and rectifiers.
Simulation models for high temperature components have been created through their
characterisation of their electrical parameters at elevated temperatures.
The JFETs were characterised at temperatures up to 573K, and values for TO V , β , λ ,
IS , RS and junction capacitances were extracted and then used to mathematically
describe the operation of circuits using SPICE. The transconductance of SiC JFETs at
high temperatures has been shown to decrease quadratically indicating a strong
dependence upon carrier mobility in the channel. The channel resistance also decreased
quadratically as a direct result of both electric field and temperature enhanced trap
emission. The JFETs were tested to be operational up to 775K, where they failed due to
delamination of an external passivation layer.
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Schottky diodes were characterised up to 573K, across the temperature range and values
for ideality factor, capacitance, series resistance and forward voltage drop were
extracted to mathematically model the devices. The series resistance of a SiC SBD
exhibited a quadratic relationship with temperature indicating that it is dominated by
optical phonon scattering of charge carriers. The observed deviation from a temperature
independent ideality factor is due to the recombination of carriers in the depletion
region affected by both traps and the formation of an interfacial layer at the SiC/metal
interface.
To compliment the silicon carbide active devices utilised in this work, high temperature
passive devices and packaging/circuit boards were developed. Both HfO2 and AlN
materials were investigated for use as potential high temperature capacitor dielectrics in
metal-insulator-metal (MIM) capacitor structures. The different thicknesses of HfO2
(60nm and 90nm) and 300nm for AlN and the relevance to fabrication techniques are
examined and their effective capacitor behaviour at high temperature explored. The
HfO2 based capacitor structures exhibited high levels of leakage current at temperatures
above 100°C. Along with elevated leakage when subjected to higher electric fields. This
current leakage is due to the thin dielectric and high defect density and essentially turns
the capacitors into high value resistors in the order of MΩ. This renders the devices
unsuitable as capacitors in hostile environments at the scales tested. To address this
issue AlN capacitors with a greater dielectric film thickness were fabricated with
reduced leakage currents in comparison even at an electric field of 50MV/cm at 600K.
The work demonstrated the world’s first high temperature wireless sensor node powered
using energy harvesting technology, capable of operation at 573K. The module
demonstrated the world’s first amplitude modulation (AM) and frequency modulation
(FM) communication techniques at high temperature. It also demonstrated a novel high
temperature self oscillating boost converter cable of boosting voltages from a
thermoelectric generator also operating at this temperature.
The AM oscillator operated at a maximum temperature of 553K and at a frequency of
19.4MHz with a signal amplitude 65dB above background noise. Realised from JFETs
and HfO2 capacitors, modulation of the output signal was achieved by varying the load
resistance by use of a second SiC JFET. By applying a negative signal voltage of
between -2.5 and -3V, a 50% reduction in the signal amplitude and therefore Amplitude
Modulation was achieved by modulating the power within the oscillator through the use
of this secondary JFET. Temperature drift in the characteristics were also observed,
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with a decrease in oscillation frequency of almost 200 kHz when the temperature
changed from 300K to 573K. This decrease is due to the increase in capacitance density
of the HfO2 MIM capacitors and increasing junction capacitances of the JFET used as
the amplifier within the oscillator circuit.
Direct frequency modulation of a SiC Voltage Controlled Oscillator was demonstrated
at a temperature of 573K with a oscillation frequency of 17MHz. Realised from an SiC
JFET, AlN capacitors and a SiC SBD used as a varactor. It was possible to vary the
frequency of oscillations by 100 kHz with an input signal no greater than 1.5V being
applied to the SiC SBD. The effects of temperature drift were more dramatic in
comparison to the AM circuit at 400 kHz over the entire temperature range, a result of
the properties of the AlN film which causes the capacitors to increase in capacitance
density by 10%.
A novel self oscillating boost converter was commissioned using a counter wound
transformer on high temperature ferrite, a SiC JFET and a SiC SBD. Based upon the
operation of a free running blocking oscillator, oscillatory behaviour is a result of the
electric and magnetic variations in the winding of the transformer and the amplification
characteristics of a JFET. It demonstrated the ability to boost an input voltage of 1.3
volts to 3.9 volts at 573K and exhibited an efficiency of 30% at room temperature. The
frequency of operation was highly dependent upon the input voltage due to the
increased current flow through the primary coil portion of the transformer and the
ambient temperature causing an increase in permeability of the ferrite, thus altering the
inductance of both primary and secondary windings. However due its simplicity and its
ability to boost the input voltage by 250% meant it was capable of powering the
transmitters and in conjunction with a Themoelectric Generator so formed the basis for
a self powered high temperature silicon carbide sensor node.
The demonstration of these high temperature circuits provide the initial stages of being
able to produce a high temperature wireless sensor node capable of operation in hostile
environments. Utilising the self oscillating boost converter and a high temperature
Thermoelectric Generator these prototype circuits were showed the ability to harvest
energy from the high temperature ambient and power the silicon carbide circuitry.
Along with appropriate sensor technology it demonstrated the feasibility of being able
to monitor and transmit information from hazardous locations which is currently
unachievable
PUFs based on Coupled Oscillators Static Entropy
We live in a digital era, this led to a shift from traditional industry to a society focused on
information and communication technologies. The amount of shared information is exponen-
tially growing every year. Protecting all this shared information is keeping everyone’s privacy,
is making sure the information is authentic, is keeping everyone safe.
The solution for such problems is cryptography using hardware-based, System on Chip,
SoC solutions such as Random Number Generators, RNGs, and Physical Unclonable Functions,
PUFs. RNGs generate random keys from random processes that occurs inside the system. PUFs
generate fixed random keys using random processes that originated in the fabrication process
of the chip. The objective of this work is to study and compare a static entropy source based
on coupled relaxation oscillators against a state-of-the-art architecture like the static entropy
source based on ring oscillators, in advanced 130nm technology. The characteristic studied
were, area, power consumption, entropy, resistance to temperature, and supply voltage varia-
tions.
Compared to the ring oscillator implementation, the static entropy source designed
showed promising results as a static entropy source, however, it revealed poor results in terms
of area, power consumption, and entropy. Such results mean, the coupled relaxation oscillator
may not be good at generating random numbers, however, it may be good at keeping its state
when under temperature and supply voltage variations.Vivemos numa era digital, o que levou a uma mudança da indústria tradicional para uma
sociedade centrada sobre as tecnologias da informação e da comunicação. A quantidade de
informação partilhada está a crescer exponencialmente todos os anos. Proteger toda esta in-
formação partilhada é manter a privacidade de todos, é garantir que a informação é autêntica,
está a manter todos seguros.
A solução para tais problemas é a criptografia com base em soluções de
hardware,
Sys-
tem on Chip, SoC tais como Geradores de Números Aleatórios, RNGs e Funções FÃsicas Inclo-
náveis, PUFs. Os RNGs geram chaves aleatórias a partir de processos aleatórios que ocorrem
no interior do sistema. Os PUFs geram chaves aleatórias fixas utilizando processos aleatórios
que se originaram no processo de fabrico do chip. O principal objetivo deste trabalho é estudar
e comparar uma fonte estática de entropia baseada em osciladores de relaxação acoplados
contra uma arquitetura de estado de arte como a fonte estática de entropia baseada em osci-
ladores de anel, em tecnologia avançada de 130nm. As caracterÃsticas estudadas foram, a área,
o consumo energia, a entropia, e a resistência à temperatura e variações de tensão de alimen-
tação.
Em comparação com a implementação do oscilador do anel, a fonte estática de entropia
projetada mostrou resultados promissores como fonte estática de entropia, no entanto, reve-
lou maus resultados em termos de área, consumo de energia e entropia. Estes resultados sig-
nificam que o oscilador de relaxação acoplado pode não ser bom a gerar números aleatórios,
no entanto, pode ser bom para manter o seu estado quando sujeito a variações de temperatura
e tensão de alimentação
Integrated RF oscillators and LO signal generation circuits
This thesis deals with fully integrated LC oscillators and local oscillator (LO) signal generation circuits. In communication systems a good-quality LO signal for up- and down-conversion in transmitters is needed. The LO signal needs to span the required frequency range and have good frequency stability and low phase noise. Furthermore, most modern systems require accurate quadrature (IQ) LO signals. This thesis tackles these challenges by presenting a detailed study of LC oscillators, monolithic elements for good-quality LC resonators, and circuits for IQ-signal generation and for frequency conversion, as well as many experimental circuits. Monolithic coils and variable capacitors are essential, and this thesis deals with good structures of these devices and their proper modeling. As experimental test devices, over forty monolithic inductors and thirty varactors have been implemented, measured and modeled. Actively synthesized reactive elements were studied as replacements for these passive devices. At first glance these circuits show promising characteristics, but closer noise and nonlinearity analysis reveals that these circuits suffer from high noise levels and a small dynamic range. Nine circuit implementations with various actively synthesized variable capacitors were done. Quadrature signal generation can be performed with three different methods, and these are analyzed in the thesis. Frequency conversion circuits are used for alleviating coupling problems or to expand the number of frequency bands covered. The thesis includes an analysis of single-sideband mixing, frequency dividers, and frequency multipliers, which are used to perform the four basic arithmetical operations for the frequency tone. Two design cases are presented. The first one is a single-sideband mixing method for the generation of WiMedia UWB LO-signals, and the second one is a frequency conversion unit for a digital period synthesizer. The last part of the thesis presents five research projects. In the first one a temperature-compensated GaAs MESFET VCO was developed. The second one deals with circuit and device development for an experimental-level BiCMOS process. A cable-modem RF tuner IC using a SiGe process was developed in the third project, and a CMOS flip-chip VCO module in the fourth one. Finally, two frequency synthesizers for UWB radios are presented
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