We demonstrated and analyzed the smooth microwave-driven transition of a superconducting bridge made from Hf into its normal state at bath temperatures below the critical temperature of Hf (Tc ≈ 380 mK). The bridge is integrated on a silicon chip with both the 600-700 GHz double-slot antenna and the 1.5-GHz CPW quarter-wave resonator (Q-factor ~10⁴) made from 100-nm Nb film. The experimental bridge was sized 2.5 um by 2.5 um by 50 nm and tested at temperatures down to 50 mK. Similar to the technique of MKID, we measured the dependence of transmission S21 on microwave power at the bottom of the resonance curve. It was found that the microwave power absorbed in the bridge fits to the model of hot electron gas, P~Te⁶-Tph⁶. The internal NEP down to≈10¯¹⁸ W/√Hz is estimated due to thermal noise at the optimum electron gas temperature, Te ≈ 320 mK. The NEP can be scaled down below ≈10¯¹⁹ W/√Hz via reasonable reduction of the bridge volume. The new detector circuit is suitable for integration within a large imaging array exploiting the FDMreadout.