Fabrication and characterization of ZnO thin film piezoelectric sensors on a polyimide membrane is presented in this paper. As a test device a differential pressure liquid flow sensor has been fabricated. We discuss new material combinations for the fabrication of the test devices. The pressure sensor membrane is a thin polyimide sheet bonded to a silicon wafer and the sensing material is sputtered ZnO piezoelectric thin film. The fabricated liquid flow sensor has been tested with a piezoelectric micropump for flow rates from 30 μl h-1 to 300 μl h-1 . Stroke volumes of 1 to 10 nl have been measured. The strain in the sensing layer has been modeled and a transverse piezoelectric coefficient of e31,f= -0.294 C m-2 has been extracted.