We developed a spin transfer torque (STT) model that allows circuit designers to simulate key aspects of spin-transfer torque MRAM (STT-MRAM) such as read and write delays. Our self-contatined, physics-based magnetic tunnel junction (MTJ) SPICE model can reproduce realistic MTJ characteristics based on user-defined input parameters such as the free layer's length, width, and thickness parameters. Using the MTJ SPICE Model, scalability studies of both in-plane and perpendicular MTJs can be performed across different technology nodes with minimal effort.
Block diagram of physics-based STT model
J. Kim, A. Chen, B. Behin-Aein, S. Kumar, J.P. Wang, and C.H. Kim, "A Technology-Agnostic MTJ SPICE Model with User-Defined Dimensions for STT-MRAM Scalability Studies", Custom Integrated Circuits Conference (CICC), Sep. 2015 [LINK TO PAPER] [LINK TO SLIDES]
Switching mechanism |
Device |
Parameter (Default) | Download |
|||||
|---|---|---|---|---|---|---|---|---|
| Dimension | Material | Ms0 | P0 | Alpha | RA | |||
Spin transfer torque (STT) |
In-plane MTJ | 32nm x 96nm x 2.44nm | CoFeB | 1210 | 0.69 | 0.0062 | 5 | STT_model.zip |
| Crystalline perpendicular MTJ | 45nm x 45nm x 0.45nm | FePt | 1210 | 0.62 | 0.03 | 5 | ||
| Interface perpendicular MTJ | 65nm x 65nm x 1.48nm | CoFeB | 1210 | 0.69 | 0.006 | 5 | ||
By using our MTJ compact model, you agree to acknowledge the "UMN MTJ SPICE model, online: http://mtj.umn.edu" in your publications or presentations.
Step1. Download MTJ spice model.
Step2. Extract .zip file. STT model contains three separate zip files for in-plane, crystalline perpendicular and interface perpendicular MTJ.
Step3. Open MTJ_write.sp file (MTJ write example)
Step4. Set MTJ dimensions and material parameters: Ms0, P0, alpha, RA and initial temparature.
(Ms0: saturation magnetization, P0: polarization, both at zero Kelvin temperature.)
Step5. Select anisotropy type using parameter 'MA':
ex) In-plane magnetic anisotropy: MA='0'
Perpendicular magnetic anisotropy: MA='1'
Step6. Select the initial state of free layer using parameter 'ini', and apply voltage with correct polarity.
Magnetization of the fixed layer will be set automatically according to the 'ini' value.
ex) Antiparallel to parallel switching : ini='1' with positive voltage
Parallel to antiparallel switching: ini='0' with negative voltage
Step7. Run SPICE simulation
This work was supported in part by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.