Click to edit Master title style

A Review ofMTJ Compact Models

Richard DorranceAdvisor: Prof. Dejan Marković

April 15, 2011

Literature Review

STT-MRAM and How it Works

STT = Spin-Torque-Transfer– Use current to flip free layer

between two resistive states

2

Compact Model Requirments

3

50 100 150 200 250 300 350 400140

145

150

155

160

165

170

175

180

185

190

TM

R [

%]

Temperature [K]

Measured

Model

[1] J. D. Harms, et al. (U. Minnesota)

Switching time vs. current fitting. User defined delay for switching. SPICE.

4

[2] A. Nigam, et al. (UVA & Grandis)

Calculate the total transmission probability and density of available states (implemented in SPICE).

Accuracy: ±10% RP, RAP, TMR Physics based… I think…

5

Measured Model

[3] L.-B. Faber, et al. (U. Paris XI)

Model switching probabilities across several parameters. Switching based on user defined threshold and delay. Inaccurate below 10ns pulse widths.

6

Spectre Model

Switching Probabilities

[4] A. Raychowdhury, (Intel)

Uses a linearized LLGE, modified/fitted for thermally activated switching. Crude bias voltage approximation.

Semi- physics, semi-empirical.

7

[5] D. Datta, et al. (Purdue & UCB)

Uses a Non-Equilibrium Green’s Function (NEGF) based quantum transport model. (Physics Based)

8

Voltage Bias

Out of Plain Fields

[6] M. Madec, et al. (ULP)

Traditional LLGE model for precessional switching. Modified Jullière conductance model to include bias

voltage dependencies. Thermally activated switching not considered. VHDL-AMS implementation.

9

Limitations of Current Models

Few model bias voltage dependencies.

No published model incorporates temperature effects.

Empirical models cannot predict behavior.

Most physics models are too cumbersome for compact modeling.

Most models are ill-suited for incorporating statistical variation.

10

References

1. J. D. Harms, et al., “SPICE Macromodel of Spin-Torque-Transfer-Operated Magnetic Tunnel Junctions,” IEEE Transactions on Electron Devices, vol. 57, no. 6, pp. 1425-1430, June 2010.

2. A. Nigam, et al., “Self Consistent Parameterized Physical MTJ Compact Model for STT-RAM,” CAS 2010, vol. 2, pp. 423-426, Oct. 2010.

3. L.-B. Faber, et al., “Dynamic Compact Model of Spin-Transfer Torque Based Magnetic Tunnel Junction (MTJ),” DTIS '09, pp. 130-135, April 2009.

4. A. Raychowdhury, “Model Study of 1T-1STT MTJ” MWSCAS 2010, pp. 5-8, Aug. 2010.

5. D. Datta, et al., “Quantitative Model for TMR and Spin-Transfer Torque in MTJ Devices,” IEDM 2010, pp. 22.8.1-22.8.4, Dec. 2010.

6. M. Madec, et al., “Compact Modeling of Magnetic Tunnel Junction,” NEWCAS-TAISA 2008, pp.229-232, June 2008.

11