  We demonstrate the design, fabrication, and characterization of wafer-scale,
zero-bias power detectors based on two-dimensional MoS$_2$ field effect
transistors (FETs). The MoS$_2$ FETs are fabricated using a wafer-scale process
on 8 $\mu$m thick polyimide film, which in principle serves as flexible
substrate. The performances of two CVD-MoS$_2$ sheets, grown with different
processes and showing different thicknesses, are analyzed and compared from the
single device fabrication and characterization steps to the circuit level. The
power detector prototypes exploit the nonlinearity of the transistors above the
cut-off frequency of the devices. The proposed detectors are designed employing
a transistor model based on measurement results. The fabricated circuits
operate in Ku-band between 12 and 18 GHz, with a demonstrated voltage
responsivity of 45 V/W at 18 GHz in the case of monolayer MoS2 and 104 V/W at
16 GHz in the case of multilayer MoS$_2$, both achieved without applied DC
bias. They are the best performing power detectors fabricated on flexible
substrate reported to date. The measured dynamic range exceeds 30 dB
outperforming other semiconductor technologies like silicon complementary metal
oxide semiconductor (CMOS) circuits and GaAs Schottky diodes.
