A Highly Sensitive 3-Axis Micro Search-Coil Magnetometer enabled by High-Density Through-Silicon-Via Process

We report a highly sensitive 3-axis micro search-coil magnetometer (μSCM) fabricated in one single silicon die and enabled by an in-house developed through-silicon-via (TSV) process. The z-axis μSCM is realized by two planar spiral inductors on both sides of the silicon wafer. The x & y-axis μSCMs are realized inside a silicon wafer by 400 TSVs (an array of 20×20 TSVs with a diameter of 50 μm) for each axis. A conformal polysilicon deposition is utilized to achieve an electrical connection through the etch holes inside the silicon wafer. Although partial filling of TSVs with polysilicon has higher resistance (< 3Ω per TSV) compared to complete filling, the proposed fabrication method is simpler and free of grinding and polishing steps, making it a more cost-effective alternative. The sensitivity (S) of the 3-axis μSCM (S
x
& S
y
= 134 mV/mT, S
z
= 3130 mV/mT at 100Hz) is better than existing μSCMs (13 mV/mT) by more than one order of magnitude.