On-chip MEMS platform for in situ thermal characterization of CMOS thin films

Accurate on-chip thermal characterization of thin films is crucial for performance prediction and reliability assurance in CMOS-MEMS devices; however, practical solutions for in situ measurement remain limited. This paper presents a CMOS-MEMS micro thermal property measurement (μTPM) platform capable of simultaneously in situ characterizing the thermal conductivity (λ) and thermal diffusivity (α) of commonly used CMOS thin films, including silicon oxide, polysilicon, and aluminum. The platform incorporated six μTPM devices, each featuring an array of MEMS bridges with lengths optimized to 41.5 μm via computational fluid dynamics (CFD) simulations for improved measurement accuracy, and was fabricated using a standard 0.18 μm CMOS process followed by an in-house developed post-CMOS process. Thermal conductivity was extracted via a steady-state thermal resistance model, while the thermal diffusivity was determined through a frequency-domain phase-lag method based on AC heating. To mitigate signal distortion that limits frequency selection in the phase-lag approach, a phase compensation model was introduced to correct deviations from the ideal semi-infinite thermal wave assumption. Experimental results validate the platform’s capability to accurately characterize thermal properties of key CMOS thin-film materials, with extracted λ values of 1.07–1.21 W·m⁻¹·K⁻¹ (SiO₂), 20.5 W·m⁻¹·K⁻¹ (polysilicon), and 56.5–60.4 W·m⁻¹·K⁻¹ (aluminum) and corresponding α values of 0.91–0.98 mm²·s⁻¹ (SiO₂), 10.8 mm²·s⁻¹ (polysilicon), and 49.7–52.5 mm²·s⁻¹ (aluminum). This work provides a practical, scalable platform for in situ determination of thermal properties, offering a new pathway toward thermal-aware design in CMOS-based microsystems.