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  • FPGA (Field Programmable Gate Array)
FPGAs are silicon chips which uses reprogrammable logic blocks.
Due to the reprogrammable characteristic, FPGA has several advantages compared to ASIC (Application Specified Integrated circuit) chip such as fast time for market entry, high cost and time efficiency. However, FPGA has several problems due to the limitations of SRAM in the switching part.
First, it is hard to scale down SRAM due to the 6-transistors based structure (~120F2). Second, a volatile memory characteristics of SRAM results in large power consumption because power should be provided continuously to save the data.
Furthermore, FPGA needs external non-volatile memory elements to save the data that leads to low density.
To solve the limitations of SRAM, we have been researched an atom switch which has simple 2-terminal structure (~4F2) and non-volatile memory characteristics.
Extremely high-density and low-power FPGA can be realized by replacing the SRAM and external non-volatile memory as atom switch which can operate as the memory and switch simultaneously with low power consumption.
  • 2-terminal switch device
The atom switch so called CBRAM has a MIM structure; TE (top electrode), electrolyte, BE (bottom electrode).
The TE and BE are consist of ionizable metal (Cu, Ag, etc.) and inert metal, respectively.
The electrolyte located between TE and BE is composed of insulating materials.
The CBRAM switching operates as follows; When a positive voltage bias is applied to the TE, ionization of metal atom occurs.
Then, the metal ion migrates to the BE through the electrolyte.
If the metal ion reaches the BE, reduction of metal ion occurs by supplying the electron from BE.
The growth of metal filament to the TE is resulted from the continuous reduction process of metal ions at BE.
After the conductive filament connects TE and BE, CBRAM represents ON state with low resistance state (SET process).
On the other hand, when a negative bias is applied to TE, the connected conductive filament will be rupture by oxidation of metal-filament, and represents OFF state with high resistance state (RESET process).
The programmed ON and OFF states of CBRAM are maintained, resulting in the non-volatile memory characteristics.
Therefore, its possible to realize the high density and low power consumption FPGA by utilizing the structural and electrical characteristics of CBRAM such as simple structure and non-volatile characteristics.
  • Reference
  • B. Attarimashalkoubeh et al., "Effects of Ti buffer layer on retention and electrical characteristics of Cu-based conductive-bridge random access memory (CBRAM)." ECS Solid State Letters 3.10 (2014): P120-P122.