The effects of Hf content on the radiation hardness of Hf-In-Zn-O thin-film transistors (HIZO TFTs) and HIZO TFTbased circuits are systemically examined. The evaluated circuits, including current-starved ring oscillator, energy harvesting and RF circuits are essential for space electronic systems. It is shown that HIZO TFTs with low Hf concentration have better initial performance while TFTs with high Hf concentration are more stable against radiation. On the other hand, for circuit application, the stable HIZO TFTs are not necessarily preferred for all circuits. The work demonstrates that understanding the device-circuit interactions is necessary for device optimization and circuit reliability improvements for harsh electronic systems.