Memristor SPICE model and its applications to circuit simulation of memory cell

Bekishev Daniyar & Arman Kapan

Memristor and its characteristics General Memristor Spice Model Memory Cell Simulation

Memristor is a two-terminal electrical component that depends on charge and flux linkage, simply it is a resistor that has a memory. The working principle of memristor is: it has the resistance that always changes depending on the current that has passed previously. But in past years Hewlett-Packard declared that they produced memristor by the help of TiO2/TiO2-x structure[1]. In our paper structures, physical characteristics of the memristors will be explained and one of the most important applications of memristor, which is memory cell, will be further examined and simulations of the memory structure will be done, finally results will be demonstrated.

Physical structure of TiO2 memristor:Figure above shows the construction of the TiO2 memristor. In the TiO2 memristor, a thin undoped titanium dioxide (TiO2) layer with a thin oxygen –deficient doped titanium dioxide (TiO2 - x) layer are clamped between two platinum electrodes. TiO2 is semiconducting material that has high Resistance (Roff) but if the O2 atoms are removed from the material, then empty spaces will act as donor dopants, thus Resistance will be dropped to low values (Ron). When a voltage or current is applied to the device, the width of the TiO2 and TiO2 – x layer varies as a function of the employed voltage or current [3]. As a consequence, the resistance between the two electrodes is adapted. Moreover, it is said to be that the main part of the device is the drifting of the O2 atoms for the applied Electric Field (E) and current (I).

General equation for Memristor:

The figures below represent simulation results for the characteristics of the Memristor:Figure below is the Result of the simulation for the I-V pinched hysteresis loop, where Hysteresis in the circuit is occurred at the time when frequency reached 100KHz.

The figure below shows VI characteristics of the Memristor. Here sinusoidal input voltage is drawn with green, and current I with blue color

Memristor can be used in construction of nonvolatile memory. The memristor give a possibility of using quasi capacitor type of data storage like DRAWs but with long life time. The I-V characteristics of memristor, contain both the current and the integral of current. It means that without any extra circuit, only by cutting the charging current, the voltage of the device decreases to zeros directly. . The characteristic of I-V for memristor makes it possible to create a memory cell. The I-V characteristic is shown in figure below

In figure below a “1” writing pulse is applied which has changes the state of system from 0 to 1. After a pulse for reading operation is applied, its graph is represented in figure 3. Then in response to this pulse the output voltage that is read is interpreted as “1”. This pulse causes the system state to be distorted. The operations repeat, next “0” writing pulse, and after a read pulse is applied again. In this memory the circuit control always performs a read operation before any write operation in order to prevent successive writes of ones or zeros.

And the last figure is the behavior of voltage and memory state in read operation:

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Reference[1] Yakpocic C., 2014, MEMRISTOR DEVICE MODELING AND CIRCUIT DESIGN FOR READ OUT INTEGRATED CIRCUITS, MEMORY ARCHITECTURES, AND NEUROMORPHIC SYSTEMS, from https://etd.ohiolink.edu/!etd.send_file?accession=dayton1398725462&disposition=inline[2] Biolek D., Pershin Y., Di Ventra M., Reliable SPICE Simulations of Memristors, Memcapacitors and Meminductors, from http://arxiv.org/pdf/1307.2717.pdf

Electrical EngineeringIntegrated Circuit Design

NazarbayevUniversity