Open-Source 4 K CMOS Calibration: Integrating IceMOS and Sky130 PDK

We present an open-source calibration methodology for Sky130 CMOS at $\mathbf{4 ~ K}$, focusing on robust initial extraction of threshold voltage (VTH0) and slope factor (n) via the SEKVE parameter-extraction tool. To address measurement noise, a partial Z-score filter is applied to the raw data, reducing extraction errors from above 10% to under 2%. These refined parameters then feed into an iterative BSIM4 calibration using IceMOS. As a result, the final calibrated Sky130 models achieve an accuracy in the strong inversion region with median error percentages of 9.49% for PMOS and just 1.11% for NMOS. Transconductance $g_{m}$ calibration is similarly precise with median errors of 5.95% and 2.46% for PMOS and NMOS, respectively, in the strong inversion region. By separating the SEKV-E and IceMOS steps yet integrating them into a fully open-source flow (including Docker-based ngspice simulations), our approach significantly minimizes manual intervention. The Sky130-compatible IceMOS scripts, Z-score routines, and calibrated device models are publicly available, reinforcing the open-source ecosystem for Cryo-CMOS research.