Design and Wafer-Level Fabrication of Wireless Passive LC Pressure Sensors via Micro-Casting Technique for Biomedical Applications

This study introduces a new wafer-level fabrication method for wireless passive LC pressure sensors, intended for pulmonary artery pressure (PAP) monitoring. This approach combines standard MEMS processes with molten-alloy micro-casting, enabling monolithic fabrication of single or dual-layer on-chip spiral inductors and pressure-sensitive capacitors on silicon or glass substrates. The use of Au-Au thermo-compression and anodic bonding creates a vacuum-sealed capacitive cavity and allows for a low-resistance lateral feedthrough from the cavity. Additionally, the metal structures of the inductor and the vertical interconnects to the capacitor are produced in a single micro-casting step, eliminating the need for post-assembly. The sensor demonstrated a frequency shift from 36.47 MHz to 27.63 MHz across a pressure range of 100 kPa to 200 kPa, achieving a high sensitivity of$88.4 \text{kHz} / \text{kPa}$.