Juli Blasco

Modeling of the Hysteretic I –V Characteristics of TiO2-based resistive switches using the generalized diode equation

Blasco J, Ghenzi N, Suñé J, Levy P, Miranda E
An equivalent circuit representation for the
conduction characteristics of TiO2-based resistive switches based
on the generalized diode equation is reported. The proposed
model consists of two antiparallel diodes with series and parallel
resistances representing the filamentary current pathway spanning
the oxide layer and the possible parasitic conduction effects.
The model accounts for the pulse-induced hysteretic behavior
exhibited by the I–V characteristic after electroforming. Three
different approaches, each one of them with increased complexity,
are assessed: 1) constant; 2) nanowire-like; and 3) sigmoidal diode
amplitude. In all cases, the logarithmic conductance of the diodes
is modeled using a logistic-type threshold function.

Single-parameter model for the post-breakdown conduction characteristics of HoTiOx-based MIM capacitors

Blasco J, Castán H, García H, Dueñas S, Suñé J, Kemell M, Kukli K, Ritala M, Leskelä M, Miranda E
The post-breakdown conduction characteristics of holmium titanium oxide (HoTiOx)-based metal–
insulator–metal capacitors fabricated by the atomic layer deposition technique on Si substrates were
investigated. Diode-like and power-law models were fitted to the experimental current–voltage (I–V)
curves and the results assessed with the aim of detecting any possible correlation among the model
parameters. It was found that the number of parameters involved can be reduced in both cases and that
for the power-law model a single parameter is solely required to approximate the I–V curves in a wide
current range (from 1011 to 104 A). This property, which has also been observed in a variety of material
systems, was used to simulate the bipolar switching behavior exhibited by the I–V characteristics. The
connection with the physics of electron transport through atom-sized constrictions is discussed.

Modeling of the switching I-V characteristics in ultrathin (5 nm) atomic layer deposited HfO2 films using the logistic hysteron

Blasco J, Jančovič P, Fröhlich K, Suñé J, Miranda E
The current–voltage (I-V) characteristics of Pt/HfO2(5 nm)/TiN resistive switching structures are
modeled using an equivalent electric circuit which consists of two antiparallel diodes in
combination with a single series resistance, the only difference between the diodes being the
threshold functions used to simulate the set and reset events. The switching process is achieved by
means of a mathematical entity called the logistic hysteron, which governs the model parameters.
The authors show that the model is able to capture the shape of the I-V curves both for positive and
negative biases obtained under different current compliance limits for the set process ranging from
0.5 to 10 mA. In order to demonstrate the feasibility of the proposed approach, experimental and
model results for the I-V curves are plotted using alternative representations: linear–linear,
log–linear, and log–log axis. The role played by the series resistance is discussed in terms of the
normalized differential conductance d ln(I)/d ln(V).

Equivalent circuit modeling of the bistable conduction characteristics in electroformed thin dielectric films

Blasco J, Ghenzi N, Suñé J, Levy P, Miranda E
In the last few years a number of models based on simple circuital representations have been proposed to
account for the resistive switching (RS) current–voltage (I–V) characteristics of metal–insulator–metal
(MIM) structures. These devices typically exhibit two well-defined conduction levels after electroforming
often referred to as the low and high resistance states that can be cyclically reached by the application of
bipolar periodic voltage or current. The resulting hysteretic behavior arises from a reversible change of
the electron transmission properties of the insulating film driven by an external stimulus. In this paper,
after an overview of a variety of RS model proposals relying on circuital descriptions and basic analytic
expressions, a model based on the solution of the generalized diode equation is discussed. The model is
simple and flexible and consists of two opposite-biased diodes with series and shunt resistances that represent
the filamentary current pathway spanning the oxide layer as well as the possible parasitic effects.
The model parameters are governed by a mathematical entity called the logistic hysteron that can be
linked to the internal state equation of the so-called memristive systems. For illustrative purposes, the
switching I–V characteristics of TiO2-based MIM structures electroformed with different current compliances
are examined in detail using this approach. Experimental results on bipolar RS by other authors are
also assessed within the same framework.