Through-silicon vias (TSVs) in 3-D ICs are a major source of substrate noise, causing performance degradation of neighboring active devices. To reduce this noise, we propose using a tungsten-filled ground (GND) plug, a TSV-like structure that connects to ground and can extend partially or completely through the substrate. We evaluate the effectiveness of the GND plug in noise isolation based on plug size and placement. We compare the GND plug technique with two other noise mitigation techniques: using a thicker dielectric liner and using a backside ground plane. Our study demonstrates that the GND plug is a superior technology, effective in mitigating TSV-induced substrate noise by an order of magnitude compared to the other two techniques. The GND plug offers a more practical noise isolation approach than using a backside ground plane. GND plug also offers a more compact solution, with 33% less area than a thicker dielectric liner.