Two-terminal spin-orbit torque device for ultrafast and high-density memory
Abstract/Contents
- Abstract
- The scaling down of semiconductor devices has been improving the speed of computing, which in turn has been increasing power consumption. A possible solution to limit power consumption is normally-off computing in which on-chip volatile memories are replaced with non-volatile memories. Conventional on-chip memories include dynamic random-access memory (DRAM) and static random-access memory (SRAM) which serve as the main memory and cache memory, respectively. For the replacement of DRAM, spin-transfer torque random access memory (STT-MRAM) appears to be the most promising alternative due to its infinite endurance and relatively fast switching of a few ns. As for the replacement of SRAM, even higher writing speed as fast as < 1 ns is required in order to keep up with the speed of CPU. However, in STT-MRAM, since the initialization of switching relies on random thermal fluctuation, writing in sub-nanosecond regime is stochastic and not practical. Therefore, a high-endurance non-volatile memory with ultrafast writing speed is highly demanded. In fact, such a candidate is also emerging from Spintronics. A relatively new concept, spin-orbit torque effect, is an excitation of torque induced by in-plane current typically in the heavy-metal layer. The spin-orbit torque effect is capable of ultrafast magnetization switching in sub-nanosecond regime as demonstrated in recent papers. MRAM based on spin-orbit torque, SOT-MRAM, is also non-volatile and has an infinite endurance. Thus, SOT-MRAM has a potential to replace SRAM and reduce power consumption. However, all the SOT-MRAM cells studied so far have a three-terminal structure because an in-plane current needs to be applied. This three-terminal structure increases the cell size due to the requirement of two isolated contacts with associated interconnects. Therefore, in this thesis, we designed, fabricated and analyzed the world's first two-terminal SOT-MRAM cell with perpendicular magnetic anisotropy in which in-plane current and out-of-plane current are simultaneously generated upon the application of voltage. Combining the measurement results with analytical models based on extended Landau-Lifshitz-Gilbert equation, we successfully confirmed that the switching is dominantly caused by spin-orbit torque effect rather than conventional spin-transfer torque effect. The switching current and thermal stability factor of the device are measured and compared with conventional STT device. Possible obstacles for mass production of this device is also discussed. This thesis provides a new path for ultrafast and high-density on-chip memory towards normally-off computing.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2017 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Satō, Noriyuki |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering. |
| Primary advisor | Wang, Shan |
| Thesis advisor | Wang, Shan |
| Thesis advisor | Saraswat, Krishna |
| Thesis advisor | Suzuki, Yuri, (Applied physicist) |
| Advisor | Saraswat, Krishna |
| Advisor | Suzuki, Yuri, (Applied physicist) |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Noriyuki Sato. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2017. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2017 by Noriyuki Sato
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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