Printed single-chip UHF passive radio frequency identification tags with sensing capability

Two printed single-chip UHF radio frequency identification (RFID) tags compatible with EPC Gen 2 protocol capable of measuring temperature and relative humidity are presented. The UHF RFID chip SL900A, which includes an on-chip temperature sensor, is used on both tags to drive the relative humidity (RH) sensors and the RF communication. These tags have been fabricated on polyimide substrate (Kapton HN) which presents a well known humidity dependence. Printed RH sensors consist of an array of 12 serpentine electrodes fabricated by inkjet printing and an array of 6 screen printed interdigitated electrodes, respectively, to achieve a capacitance of around 35 pF far from the capacitive parasites present in the structure. Both tags are able to provide temperature and relative humidity environmental parameters in digital form answering to the inquiries of a RFID reader in a passive energy mode (without batteries). With very low thermal drifts, below 0.05%RH/°C, a RH range of 30% is covered by both tag with sensitivities of 100 fF/RH% for the inkjetted serpentine structure and 54 fF/RH% for the screen-printed one. Therefore, we propose passive RFID tags with a single silicon chip providing a cost-effective solution to monitor environmental conditions based on printing technologies.