4 research outputs found
Dynamical attractors of memristors and their networks
It is shown that the time-averaged dynamics of memristors and their networks
periodically driven by alternating-polarity pulses may converge to fixed-point
attractors. Starting with a general memristive system model, we derive basic
equations describing the fixed-point attractors and investigate attractors in
the dynamics of ideal, threshold-type and second-order memristors, and
memristive networks. A memristor potential function is introduced, and it is
shown that in some cases the attractor identification problem can be mapped to
the problem of potential function minimization. Importantly, the fixed-point
attractors may only exist if the function describing the internal state
dynamics depends on an internal state variable. Our findings may be used to
tune the states of analog memristors, and also be relevant to memristive
synapses subjected to forward- and back-propagating spikes
Exploring the voltage divider approach for accurate memristor state tuning
The maximum exploitation of the favorable properties and the analog nature of memristor technology in future nonvolatile resistive memories, requires accurate multilevel programming. In this direction, we explore the voltage divider (VD) approach for highly controllable multi-state SET memristor tuning. We present the theoretical basis of operation, the main advantages and weaknesses. We finally propose an improved closed-loop VD SET scheme to tackle the variability
effect and achieve <1% tuning precision, on average 3Ă— faster
than another accurate tuning algorithm of the recent literature.Peer ReviewedPostprint (published version
Exploring the voltage divider approach for accurate memristor state tuning
The maximum exploitation of the favorable properties and the analog nature of memristor technology in future nonvolatile resistive memories, requires accurate multilevel programming. In this direction, we explore the voltage divider (VD) approach for highly controllable multi-state SET memristor tuning. We present the theoretical basis of operation, the main advantages and weaknesses. We finally propose an improved closed-loop VD SET scheme to tackle the variability
effect and achieve <1% tuning precision, on average 3Ă— faster
than another accurate tuning algorithm of the recent literature.Peer Reviewe
Memristor-based design solutions for mitigating parametric variations in IoT applications
PhD ThesisRapid advancement of the internet of things (IoT) is predicated by two important factors
of the electronic technology, namely device size and energy-efficiency. With smaller
size comes the problem of process, voltage and temperature (PVT) variations of delays
which are the key operational parameters of devices. Parametric variability is also
an obstacle on the way to allowing devices to work in systems with unpredictable
power sources, such as those powered by energy-harvesters. Designers tackle these
problems holistically by developing new techniques such as asynchronous logic, where
mechanisms such as matching delays are widely used to adapt to delay variations. To
mitigate energy efficiency and power interruption issues the matching delays need to
be ideally retained in a non-volatile storage. Meanwhile, a resistive memory called
memristor becomes a promising component for power-restricted applications owing to
its inherent non-volatility. While providing non-volatility, the use of memristor in delay
matching incurs some power overheads. This creates the first challenge on the way of
introducing memristors into IoT devices for the delay matching.
Another important factor affecting the use of memristors in IoT devices is the
dependence of the memristor value on temperature. For example, a memristance
decoder used in the memristor-based components must be able to correct the read data
without incurring significant overheads on the overall system. This creates the second
challenge for overcoming the temperature effect in memristance decoding process.
In this research, we propose methods for improving PVT tolerance and energy
characteristics of IoT devices from the perspective of above two main challenges:
(i) utilising memristor to enhance the energy efficiency of the delay element (DE), and
(ii) improving the temperature awareness and energy robustness of the memristance
decoder.
For memristor-based delay element (MemDE), we applied a memristor between two
inverters to vary the path resistance, which determines the RC delay. This allows power
saving due to the low number of switching components and the absence of external delay
storage. We also investigate a solution for avoiding the unintended tuning (UT) and a
timing model to estimate the proper pulse width for memristance tuning. The simulation
results based on UMC 180nm technology and VTEAM model show the MemDE can
provide the delay between 0.55ns and 1.44ns which is compatible to the 4-bit multiplexerbased
delay element (MuxDE) in the same technology while consuming thirteen times
less power. The key contribution within (i) is the development of low-power MemDE to
mitigate the timing mismatch caused by PVT variations.
To estimate the temperature effect on memristance, we develop an empirical temperature
model which fits both titanium dioxide and silver chalcogenide memristors. The
temperature experiments are conducted using the latter device, and the results confirm
the validity of the proposed model with the accuracy R-squared >88%. The memristance
decoder is designed to deliver two key advantages. Firstly, the temperature model is
integrated into the VTEAM model to enable the temperature compensation. Secondly, it
supports resolution scalability to match the energy budget. The simulation results of the
2-bit decoder based on UMC 65nm technology show the energy can be varied between
49fJ and 98fJ. This is the second major contribution to address the challenge (ii).
This thesis gives future research directions into an in-depth study of the memristive
electronics as a variation-robust energy-efficient design paradigm and its impact on
developing future IoT applications.sponsored by the Royal Thai Governmen