buried power rails

**Buried Power Rails (BPR)** are **power distribution lines embedded in the front-side silicon substrate below the transistors** — moving VDD and VSS rails from the BEOL metal layers into the chip substrate, freeing up BEOL routing resources and reducing standard cell height. **BPR Integration** - **Trench Formation**: Etch deep trenches into the silicon substrate between active device regions. - **Isolation**: Line the trench with dielectric to isolate the power rail from the substrate. - **Metal Fill**: Fill the trench with a low-resistance metal (W, Ru, or Cu). - **Connection**: Connect BPR to transistor S/D through local interconnects and to BEOL through via connections. **Why It Matters** - **Cell Area**: BPR eliminates power rails from M1, enabling ~15-20% standard cell area reduction. - **IR Drop**: Wider buried rails can reduce power delivery resistance and IR drop. - **Backside PDN**: BPR enables backside power delivery networks (BSPDN) — the future of power distribution. **BPR** is **burying the power lines underground** — embedding power rails in the substrate to free up wiring resources above the transistors.