SPICE Model for Magnetic Tunnel Junctions

Hi Xiaowei

".lib" files are spice model files. ".va" files are verilogA files. You will need to first create a symbol and then use the symbol in Virtuoso Schematic Editor. The symbol will need to have a "model" property to point to the appropriate subckt in the files. The files can then be included in ADE as the model files.

Hope that this helps you.


Best regards
Quek

Hi, Quek

Thanks so much for your reply. I am just a beginner,  trying to understand what your instructions. Sorry for that.

"The symbol will need to have a "model" property to point to the appropriate subckt in the files " not sure what does this mean exactly and how should I do it. I would appreciate it much if you could put it in a way as simple as possible.

Once again thank you so much!

Bless! 

Hi, Quek.

How can I use the two va files, what are their functions: LLGThermRandNum.va and MTJ_res.va  

the LLGThermRandNum.va's content is like this:

// Creator: Xuanyao Fong

// Email: xfong@purdue.edu

// Contributors: Xuanyao Fong

// This block generates random numbers for use with the LLG thermal

// fluctuation calculations

`include "disciplines.vams"

`include "constants.vams"

module ThermRandNumBlk(t1);

output t1;

electrical t1; //External Terminals of the resistor

integer seedVal;

analog begin : res_module

V(t1) <+ $rdist_normal(seedVal, 0.0, 1.0);

end

endmodule

and the MTJ_res.va file is like this:\

// Creator: Harsha Choday

// Email: schoday@purdue.edu

// Contributors: Xuanyao Fong

// This file is a copy of MTJ_QCOM5_res.va with added comment lines

// Resistance model of MTJ with physical params:

// Eb=0.8, delta=0.75, m_fm=0.735, m_ox=0.74, Ms=800, Ku2=30000

// This file and the coefficients for fitting equation generated by MATLAB

`include "disciplines.vams"

`include "constants.vams"

module MTJ_res(t1,t2,MTJ_curr,th,phi,th_hard,phi_hard);

inout t1,t2;

input th,phi,th_hard,phi_hard;

output MTJ_curr;

electrical t1,t2,MTJ_curr,th,phi,th_hard,phi_hard; //External Terminals of the resistor

// Coefficients for fitting Rap

parameter real c1_ap = -6.7524 from (-inf:inf);

parameter real c2_ap = 23.2848 from (-inf:inf);

parameter real c3_ap = -7.56891 from (-inf:inf);

parameter real c4_ap = 24.144 from (-inf:inf);

parameter real c5_p = 1 from (-inf:inf);

// Coefficients for fitting Rp

parameter real c1_p = -5.90497 from (-inf:inf);

parameter real c2_p = 21.5434 from (-inf:inf);

parameter real c3_p = -7.46919 from (-inf:inf);

parameter real c4_p = 25.0243 from (-inf:inf);

parameter real c5_ap = 1 from (-inf:inf);

parameter real Tox = 1.15 from (-inf:inf);

parameter real Area = 3.6298e-15 from (-inf:inf); // 0.25*3.14*2.89*40e-9*40e-9 m2

(* desc="MTJ Resistances", units="Ohm" *) real Gp, Gap, Gmtj, Rmtj, mdp;

analog begin : res_module

real Gp_pre, Gap_pre;

mdp = (sin(V(th))*cos(V(th))*sin(V(th_hard))*cos(V(phi_hard))) + (sin(V(th))*sin(V(phi))*sin(V(th_hard))*sin(V(phi_hard))) + (cos(V(th))*cos(V(th_hard)));

Gp_pre = exp(c1_p*Tox + c2_p)*pow(V(t1,t2),2) + exp(c3_p*Tox + c4_p); // Polynomial gives G/A

Gap_pre = exp(c1_ap*Tox + c2_ap)*pow(V(t1,t2),2) + exp(c3_ap*Tox + c4_ap);

Gp = (pow(Gp_pre,1))*(Area*1e4); // Apply term_pow and multiply area to obtain conductance

Gap = (pow(Gap_pre,1))*(Area*1e4);

Gmtj = Gap + (mdp+1)*0.5*(Gp-Gap);

Rmtj = pow(Gmtj,-1);

I(t1,t2) <+ V(t1,t2)/Rmtj;

V(MTJ_curr) <+ -V(t2,t1)/Rmtj;

end

endmodule

Thanks a lot!!!  

Hi Xiaowei

The snapshot below shows an nmos and in the properties form on the right, we can see a "Model name" field. The actual name of the field is "model". "Model name" is just for display purpose. This field will be netlisted during spectre simulation so that the nmos takes on the model "g45n2svt". This is done through settings in the CDF (component description format). The user will need to include a model file in ADE that describes the contents of "g45n2svt". Otherwise there will be an error during simulation.

You can import the verilogA files and automatically generate their symbols so that the symbols can be placed in a schematic and be connected with other blocks. Here is how you can do it:

a. In library manager, go to "File->New->cellview"
b. Select "verilogA" as the type of cellview
c. Cut and paste the verilogA codes into the text editor
d. Close the editor. There will be a dialog box to ask if a symbol should be generated.
e. Select "Yes".
f. Completed

You can include the following line in the cds.lib file to have an idea of how verilogA files can be used. It is a built-in library of verilogA cells.

DEFINE ahdlLib $CDSHOME/tools/dfII/samples/artist/ahdlLib


Best regards
Quek

Hi, Quek

I don't have cadence on my laptop now. I will try it tomorrow when I get to school.

Just to let you know I appreciate your help more than I can express!

Bless 

Hi, Quek

I tried in library manager file->New->cellview........and then verilogA, but then  it reminds me .....failed. Might it because the cadence in my school doesn't support this function? Cadence in my school is not a full version, I found that several other functions mentioned by others on internet didn't work on the cadence here.

I am thinking of  creating a symbol in Cadence with five terminals( it seems that the MTJ model uses five terminals, attached is the example netlist given on MTJ model). And then use this symbol in the ADE to perform simulation(need to include model file:  LLG.lib &MTJ.lib?).  Will this be possible? how should I do it?

BTW, I did create a symbol with five terminals in the symbol editor, but it fails when I tried to create a netlist of it in the ADE environment. 

Thanks very much for your help!

Xiaowei