Extremely Low-voltage and High-speed Operation Bulk Thyristor-SRAM/DRAM (BT-RAM) Cell with Triple Selective Epitaxy Layers (TEL)

We have successfully developed an alternative SRAM cell for the first time using a bulk thyristor-RAM (BT-RAM) with triple selective epitaxy layers (TEL) for anode, n-base, and cathode. The n-base of the pnp transistor is a key for the thyristor characteristics. We optimized both the thickness and the dopant concentration of the n-base by using an in-situ doped selective epitaxy technique. We obtained high current gain (beta values) for the pnp transistor in a thyristor, and the TEL BT-RAM cell was thus able to read/write at 200 ps at 0.6 V. It also showed good retention characteristics even at 125degC and the possibility of good scalability for a gate length of 45 nm and beyond. The TEL BT-RAM cell is therefore a promising alternative SRAM and DRAM cell for the future generations.