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Arithmetic Operations within

Memristor-Based Analog Memory

Mika Laiho, Eero Lehtonen

Microelectronics Laboratory, University of Turku

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Key Points

Be able to program the memristor to the

reference resistance using the cyclincally

programming scheme

Computing capability, such as addition,

both on negative and positive analog

conductance, is demonstrated

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Digital Memory verse Analog Memory

Digital memory (1-bit information

depending on ON/OFF state, including

SRAM, DRAM, PCRAM, MRAM, Flash, etc.)

Analog memory (many intermediate states

between ON/OFF states)

Memoristor can be used for both digital

and analog memory

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Memristor

Without programming threshold

Linearly programmed with charge flowing through

the device

AC readout for memory application

Pose high requirements on R/W cycles

With programming threshold

Nonlinear programmed with charge flowingthrough the device

DC readout possible

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Memristor With Programming Threshold

Bipolar reversible and nonvolatile switching of nanoscale TiO2-x devices

J. J. Yang et al., Memristor switching mechanism for metal/oxide/metal nanodevices, Nature Nanotechnology, 2008, 3, 429-433

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Modeling Memristor

The window function

The time derivative of the state variable W

The current through the memristor

and are fitting constants that are used to characterize the ON state

and are the fitting constants used to characterize the net electronic barrier

when the memristor is switched OFF

a, b, p and q are constants depending on the physical properties of the memristor

w is the state variable of the memristor

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Simulated Memristor Characteristics

Device simulation based on SPICE model

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Simulated Memristor Characteristics

Device simulation based on SPICE model

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Memristor Analog Memory/Computing Circuit

VSSR

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Processing as Summation

Monitoring phase Programming phase

gm1 = gm4 + gm5.

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Processing as Invertor

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Processing as Universal Addition

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Conclusions

Memristors could be used as analog

memories and for computing

A two-memristor configuration wasproposed to be used as a memory element

so that addition operations of both positive

and negative numbers could be performed

Further study on performing multiplication

and division is expected

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Limitations

Control circuits for programming the

memristors is too complicated increasing

design complexity Many sequences are required leading to

slow programming

The programming time is unpredictable