Defect‐Engineered ZIF‐8‐Derived Nanoporous Carbon for Ultra‐Stable Flexible Cryogenic Thermistors and Ultra‐Miniature Physiological Sensors

In cryogenic electronics and biomedicine, there is a growing need for flexible temperature sensors operating reliably down to liquid‐nitrogen temperatures while conforming to complex, moving surfaces. However, state‐of‐the‐art metal or ceramic thermistors are rigid and bulky, whereas polymer and hydrogel sensors lose conductivity or drift severely below −150°C, making robust cryogenic sensing extremely challenging. Herein, we design a ZIF‐8‐derived nanoporous carbon as a cryogenic thermistor material by rational defect engineering. By tuning the carbonization temperature, the heteroatom/vacancy defect landscape (N, O, Zn, and carbon vacancies) is programmed to balance percolated graphitic pathways and dense ionized impurity centers, leading to ionized‐impurity‐scattering–dominated transport at deep cryogenic temperatures. The printed carbon thermistors exhibit a wide operating window from 150 to −190°C, a high cryogenic temperature coefficient of resistance (TCR) up to −4.7%/°C, a temperature resolution of 0.05°C, and a response time of 0.58 s. After 100 days of immersion in liquid nitrogen, the TCR drift remains within ±0.2%, evidencing outstanding long‐term cryogenic stability. Benefiting from the printable nature, 0.3 × 0.3 mm 2 micro‐thermistors are integrated into cryopreservation needles and oxygen tubes for real‐time in vivo freeze‐thaw monitoring and contactless sensing, demonstrating the promise of defect‐engineered MOF‐derived carbons for next‐generation flexible cryogenics.