Cryo-compatible CMOS Substrate for On-Chip Magnetic Susceptibility Measurements of 2D Magnet Fe₃GeTe₂

We present a universal cryo-compatible CMOS-based platform for quantum material investigations, engineered for atomic-scale research with a focus on affordability, reproducibility, and ease of integration. This foundry-compatible platform enables high-throughput and standardized studies of materials, including layered van der Waals (vdW) materials and color centers in diamond quantum microchiplets (QMCs). Equipped with on-chip device components such as inductors and transistors, this CMOS device offers an all-in-one solution for probing quantum states at cryogenic temperatures, providing a new standard for scalable and reproducible material studies akin to lab-on-chip devices in biology.

In this work, we demonstrate the platform's capabilities through on-chip magnetic susceptibility measurements of the layered 2D magnet Fe₃GeTe₂ (F3GT). The magnetic susceptibility of F3GT was investigated with an on-chip micro-inductor to create an AC magnetic field, while the magneto-optical Kerr effect (MOKE) was utilized to monitor changes in Kerr rotation. Our results indicate that above the material's Curie temperature (TC ~220 K), the Kerr rotation is negligible, confirming the absence of long-range magnetic order. As temperatures decrease, a distinct peak in Kerr rotation emerges at ~220 K, corresponding to the paramagnetic-to-ferromagnetic transition, with a squared hysteresis loop forming at 188 K. These findings establish a direct measurement of magnetic susceptibility across the transition temperature, offering a clearer understanding of phase transitions in 2D magnets.

The on-chip susceptibility measurements showed a linear dependence on driving voltage bias, and frequency response analysis demonstrated a stable signal up to 250 kHz, constrained only by the bandwidth limit of the photodetector. The device’s compatibility with dry-transfer techniques and its integration of essential components enables the study of 2D magnetic flakes, eliminating previous challenges associated with bulk measurement techniques and complex fabrication requirements. Our CMOS-based system offers a standardized tool with a pathway for automation and high throughput screening for exploring magnetic properties, with promising implications for spintronics and magneto-optoelectronics applications.